Integral of Hermite polynomial multiplied by $\exp(-x^2/2)$

Question: What is the value of $\int_{-\infty}^{\infty}e^{-\frac{x^2}{2}}H_n(x)dx$ where $H_n(x)$ is the $n^{\small\mbox{th}}$ Hermite Polynomial (physicist's convention)?
Comment: Do you mean the probablists' Hermite polynomials or the physicists' Hermite polynomials?  See: http://en.wikipedia.org/wiki/Hermite_polynomials#Definition
Answer: For probabilists' Hermite polynomials: The Hermite polynomials are the orthogonal polynomials corresponding to the weight function $w(x) = e^{-x^2/2}$.  This means that $\int_{-\infty}^{\infty} H_n(x)H_m(x)e^{-x^2/2} \, dx = 0$ whenever $n \not= m$ (or equivalently, $\int_{-\infty}^{\infty} H_n(x) P(x) e^{-x^2/2} \, dx = 0$ for any polynomial $P$ of degree less than $n$).  Since $H_0(x) = 1$, it follows that $$\int_{-\infty}^{\infty} H_n(x)e^{-x^2/2} \, dx = \int_{-\infty}^{\infty} H_n(x)H_0(x)e^{-x^2/2} \, dx = 0$$  for all $n > 0$.  The only time this integral is non-zero is when $n = 0$, in which case $$\int_{-\infty}^{\infty} H_0(x)e^{-x^2/2} \, dx = \int_{-\infty}^{\infty} e^{-x^2/2} \, dx = \sqrt{2\pi}.$$
Comment: I guess it depends on [which "Hermite polynomials"](http://en.wikipedia.org/wiki/Hermite_polynomials#Definition) Tarek is asking about.
Comment: I am asking about the physicists' Hermite polynomials.
Comment: Ok, then disregard this and go Mhenni's route.  I mistakenly assumed you were using the probabilists' polynomials because you were using the corresponding weight.
Comment: @Tarek, then you should have edited your question to include the normalization you're working with...
Answer: Notice that, if $n$ is odd , then the integrand is an odd function which implies that the integral equals to $0$. If $n$ is even, then the integral equals to
$$ {2}^{2\,n+\frac{5}{2}}\Gamma  \left( n+ \frac{3}{2} \right),\quad n=0,1,2,\dots. $$
Note this, in the above formula, $n=0$ corresponds to the case $H_{2}(x)$, $n=1$ correspons to the case $H_{4}(x)$ and so on.
One can have instead, the formula which include the case $n=0$
$$ {4}^{n}\sqrt {2}\,\Gamma  \left( n+\frac{1}{2} \right), \quad n=0,1,2,\dots.  $$
Again, in the above formula, $n=0$ corresponds to the case $H_{0}(x)$, $n=1$ corresponds to the case $H_{2}(x)$ and so on.
Comment: How did you calculate this?
Answer: Using the generating funtion $e^{2xt-t^2}=\sum_{n=0}^\infty H_n(x)\frac{t^n}{n!}$ we can obtain two recurrence relations.
Differentiating with respect to $t$ we obtain $H_{n+1}(x)=2xH_n(x)-2nH_{n-1}(x)$ for $n\geq 1$ with $H_0(x)=1$ and $H_1(x)=2x$. Similarly, differentiating with respect to $x$ we obtain $\frac{d}{dx}H_n(x)=2nH_{n-1}(x)$ for $n\geq 1$.
Now, define $I_n=\int_{-\infty}^{\infty}e^{-x^2/2}H_n(x)dx$ then
$$\begin{align}I_{n+1}&=\color{blue}{\int_{-\infty}^{\infty}2xe^{-x^2/2}H_{n}(x)dx}-2nI_{n-1}\\
&=\color{blue}{-2e^{-x^2/2}H_n(x)\Big|_{-\infty}^{\infty}+4nI_{n-1}}-2nI_{n-1}=2nI_{n-1}.
\end{align}$$
where the integral in blue was solved by parts and since that $H_n$ is a polynomial of degree $n$ we have that $\lim_{x\to\pm\infty}e^{-x^2/2}H_n(x)=0$, therefore
$-2e^{-x^2/2}H_n(x)\Big|_{-\infty}^{\infty}=0$.
To finish, since $$I_0=\int_{-\infty}^{\infty}e^{-x^2/2}H_0(x)dx=\int_{-\infty}^{\infty}e^{-x^2/2}dx=\sqrt{2\pi}$$ and $$I_1=\int_{-\infty}^{\infty}e^{-x^2/2}H_1(x)dx=\int_{-\infty}^{\infty}2xe^{-x^2/2}dx=0$$ we conclude that $I_{2n+1}=0$ for all $n\in\mathbb{N}$ and
$$\begin{align}I_{2n}&=2(2n-1)I_{2n-2}\\
&=2^2(2n-1)(2n-3)I_{2n-4}\\
&~~\vdots\\
&=2^n(2n-1)(2n-3)\cdots1\cdot I_0\\
&=2^n\frac{2n(2n-1)(2n-2)(2n-3)\cdots1}{2n(2n-2)\cdots2}I_0\\
&=2^n\frac{(2n)!}{2^nn!}I_0\\
&=\frac{(2n)!}{n!}I_0\\
&=\frac{(2n)!}{n!}\sqrt{2\pi}.\end{align}$$
Answer: Since the weighting function corresponds to the probabilists Hermite polynomials, the substitution
$$
\operatorname{H}_n(x)=2^{\frac{n}{2}}\operatorname{He}_n(\sqrt{2}x)
$$
and the integral becomes
$$
I_n = 2^{\frac{n}{2}}\int_{-\infty}^\infty\operatorname{He}_n(\sqrt{2}x)e^{-\frac{x^2}{2}}dx.
$$
We can use the Hermite multiplication theorem
$$
\operatorname{He}_n(\gamma x)=n!\sum_{k=0}^{\left \lfloor \frac{n}{2} \right \rfloor }\frac{1}{2^kk!(n-2k)!}\gamma^{n-2k}\left(\gamma^2-1\right)^k \operatorname{He}_{n-2k}(x)
$$
with $\gamma=\sqrt{2}$ to obtain
$$
I_n = 2^{\frac{n}{2}}n!\sum_{k=0}^{\left \lfloor \frac{n}{2} \right \rfloor }\frac{1}{2^kk!(n-2k)!}2^{\frac{n}{2}-k}\int_{-\infty}^\infty\operatorname{He}_{n-2k}(\sqrt{2}x)e^{-\frac{x^2}{2}}dx.
$$
The integral is zero whenever $n$ is odd, so we enforce this by setting $n=2s$.  Using orthogonality of the probabilists Hermite polynomials
$$
\int_{-\infty}^\infty \operatorname{He}_n(x)\operatorname{He}_m(x)e^{-\frac{x^2}{2}}dx = n!\sqrt{2\pi}\delta_{n,m}
$$
the desired integral becomes
$$
I_{2s} = \frac{(2s)!}{s!}\sqrt{2\pi}.
$$


Quantum Collapse

Question: When we observe a quantum object does it collapse into a point? Or does it collapse into a smaller wave of area that is out of our range of accuracy? My gut tells me the latter.
Answer: The concept of "collapse" is a misleading one. Objects which are in the dimensional range of quantum mechanics do not "collapse" like pricked deflated balloons.
Observation means any interaction a particle  described by a wavefunction might have. The square of the wavefunction will tell us what the probability is to observe the particle at a specific (x,y,z,t). Elementary particles are considered as point particles and in that sense when they appear at a specific point  they are a point.
One needs a distribution of several interactions to measure the probability distribution for specific reactions. This is what is being done at the LHC in CERN, measuring millions of interactions in order to study the probability distributions and compare them with predictions of theory.
But quantum mechanics describes also complex objects like molecules and crystals and even superconductors. Measurements on these objects follow the probability distributions of the complex interactions but the collective measurements will also reveal the size of atoms or molecules. A single scatter on an atom of a crystal will give a specific (x,y,z,t) point for it but a large statistical accumulation of scatterings will give a size for it which is within our measurement accuracies.
For example these nanotechnology atom arrangements:

There are a large number of photons scattering off the atoms, each sampling the probability distribution that describes them, and they are within our measurement capacity.
Comment: Your misconception lies in thinking of the wave as a physical wave where the energy/mass is spread in space time. The wave nature appears in the probability distribution , the square of the wave function. The wave function is not a space time distribution of the mass/energy of the particle. The particle is whole, a point if elementary, a specific spatial distribution if complex. The misunderstanding comes partly from the old double slit experiments (one hole no interference). There are newer experiments which detect the particle going through a single slit and still the pattern appears,
Comment: You should stop thinking classically when studying quantum mechanical entities. They are entities, sometimes appearing as particles, sometimes as probability waves. The mass spread out is a science fiction type visualizations and leads to mystical thinking. Density is not a quantum mechanical concept.
Comment: Well here is a follow up (to explain my idea a bit more clearly) lets say you did an experiment and you know the 10 m radius circle within which there is atom... your "observation" confirms that the atom is definitely not outside of that circle when you observed it... therefore at that moment in time, when you observed it the likelihood of finding the atom within the space you observed was 1... the atom was obviously where it was... but to the accuracy of a 1 cm radius circle you don't know where it is... so in that accuracy it is still a wave
Comment: See http://en.wikipedia.org/wiki/Double-slit_experiment#With_particle_detectors_at_the_slits .It is the change in the boundary conditions from going from one slit to two slits that changes the wavefunction and therefore the probability distributions. A one cm circle defines a classical boundary. as quantum mechanical behavior appears for particles/atoms at dimensions of order 10^-8cm or so your particle is very well defined within the circle, classically.
Comment: I am having trouble reconciling point like particles... That would imply infinite density... For any non zero energy and therefore infinite gravitational pull for any non zero energy
Comment: The idea of it retaining a fuzzy nature even when observed... Effectively solved this issue... The mass being spread out unless more accurate observations are made
Answer: Indeed, the latter. What you measure is actually not a pure projection operator $|x\rangle \langle x|$ but something more smudged like $M_x = \int dy \, p_y |y\rangle \langle y|$. Further general measurements need not be matrices, they need to be linear operators, the most general physical form of which are completely positive maps.
This means there is some probability that your measurement assigned value $x$ to the position of an object which was actually at a different location. Operators of this form will not in general collapse the wavefunction into a point. But if you are not careful the information you did not collect will be erased by interaction with the environment, which can make your system nearly classical.
Answer: As said by anna v, the "wave function" is not at all a real space-time wave function, it is only a probability amplitude, that is complex numbers which allow us to calculate probabilities.
The problem of "collapse thinking" comes because we often think in the Schrodinger representation, because in this representation, states depend on time.
To avoid this problem of "collapse thinking", a good way is to use the Heisenberg representation. In this representation, states do not depend on time (but operators depend on time).
In fact, in the Heisenberg representation, You can choose a matrix representation for the operators such as the states do no depend on "space", for instance, in the harmonic oscillator, the position operator is an infinite matrix which could be written  : $$X(t) \sim a e^{+ i \omega t} + a^+ e^{- i \omega t}$$, with $a_{i,i+1} = \sqrt{i + 1}$, $a^+_{i + 1,i} = \sqrt{i + 1}$, with $i=0,1.....\infty$
That is, your state $|\Psi>$ is a set of constant complex numbers $\Psi_i$, $i=0,1.....\infty$, relative to some basis (the energy basis).
Your state $|\Psi>$ is a complex (infinite) vector upon which the (infinite) matrix $X(t)$ acts.
From my point of view, a way to understand these $\Psi_i$ is to see them as initial conditions.
Suppose you make a measurement on this state $|\Psi>$, a measurement is an interaction. There is no reason why the initial conditions have to be conserved in this interaction.
To see a classical analogy, when you throw a ball against a wall, the initial conditions before and after the bouncing are not the same.
It  is the same here, staying in the Heisenberg representation, after the measurement, there are  new "initial conditions" $\Psi'_i$.
It is possible, for instance, that only one of the  $\Psi'_i$ will be different of zero, for instance $\Psi'_0 \neq 0$ and $\Psi'_i = 0$ if $i \neq 0$, so you might think of some "collapse", but it is just a special expression that "initial conditions", after the measurement, can take.
Answer: Keep in mind that, depending on which interpretation of quantum mechanics you prefer, wavefunction collapse might not even exist. Some interpretations, such as the Copenhagen interpretation (CI), have it, and some, such as the many-worlds interpretation (MWI) don't. Since all of these interpretations make the same predictions about the outcome of experiments, we can't say empirically which is true, and therefore we can't say empirically how a certain feature of one of them (wavefunction collapse) truly works.
However, within the framework of CI, there are some constraints required for consistency. It's not possible for any measurement of position to be exact. If it were, then the collapsed wavefunction would be a delta function in position space, which corresponds to an infinite sine wave in momentum space. But an infinite sine wave isn't normalizable, so it isn't a physically possible wavefunction.

Quantum Collapse


Building a Data analytics website with PostgreSQL

Question: I need help with someone giving me advice on how do I go about building a data analytics website with data from PostgreSQL. I research on Django framework to help build a data analytics website but there seems to be a lack of information to help me with it. Can someone tell me how do I go about it? I need to build a website which user and filter out the data, Something like Tableau which is customizable.
Answer: Django isn't oriented toward analytics.  Look at R Shiny instead.


Wifi hardware to improvement network

Question: I do not know if the question is well located, but I come to request a recommendation, I am having problems with getting a wireless router that meets my needs, in this case I look for one that can manage broadband through QOS or some method of Administration, but that has capacity for about 20 Devices. Now I have a DLINK Dir 822 and every 50 seconds the connection is dropped, I do not know if it's because of the warm atmosphere of the tropic at this time, but I want a new computer to solve this in my house. regards
Comment: So your core requirements are a) support for 20 devices over WiFi and b) that it can cope with tropical conditions. Anything else? Price? Top Speed? Standards?
Comment: C) bandwith control; Price <= 100? Top =anyone? Standards=most common to get compatibilty?
Answer: I decided to try my luck with a router:
Asus RT-AC51U AC750
And use a pair of access point in the house.
So far, all stable, stable speeds, 0 drops, the router accepts multiple configurations and extensive compatibility .
and Based on Linux.

Wifi hardware to improvement network


Installing a watering system and edging above it: any pros and cons?

Question: Here is the picture that is worth 1000 words Since I am about to install the edging that you see in the backyard (area covered by the runs 1-4) I am considering installing the irrigation pipes in a channel formed by cutting a drain pipe in half along the longitudinal axis and then install the slabs that make the edge on top. The actual shape of the path will be pure rectangular I gave up on the zig-zags you see in the picture Do you see any issues raised by this design? The idea is to be able to reach the pipes easily without digging them out of the ground. This will add support to the slabs as well
Answer: It is not a common solution.
I like the idea that you are flexible, without digging: this is real gardening, not like most irrigation system where you should calculate precisely the amount of water in each pipe, and so you will have trouble if you want to do other experiments, or just a vegetable garden in some corner.
Disadvantages: much more prone to frost, so you should close and remove water on time, and personally I do not like the esthetics. I'm not sure if it will be also a place for animals to hides (snakes, spiders, etc.). I think that in few years the pipes and edging will be below lawn level. And I think there are other disadvantages: in fact your solution is seldom seen.
I would go to the different corners with a line, and from there I would irrigate the lawn, and pass the irrigation system just below soil, hidden by vegetation and bushes (so no real digging). On the other hand, it is your garden, and you have much better idea on what you will plant.
I'm not sure about pipe 5: if you want to irrigate your lawn, I see risk you "water" also your house.
My tip: check out Gardena website and catalogues. They sell expensive stuffs, but so they have good documentation (to get inspirations). And they are much more on DIY (and not as "requires professionals to install", so every few years you may change layout), and they base is to start from a spigot (your other question). Hunter instead has a lot of documentation about professional irrigation systems and designs (and how to do the detailed calculations), probably too complex (and too long to read all docs).
Comment: I m set on the orbit models as their controller seems to work with Google Assistant which is what I use for other things
As far as #5 goes and actually every single line you see is designed to sprinkle the flowerbeds using directional jets limited for that small area with flower beds next to the sprinkler. The central area is grass and I do not plan to water it
THese will be pop up sprinklers
The layout is what is recommended in the Orbit manual on pag 11 and the following https://www.irrigationdepot.ca/boutique/PDF/Guide_Orbit_Installation_AN.pdf
Comment: re:freezing, it will happen anyway unless I dig 4' deep into the ground so I could as well just hide the piles 1in under the slabs (to protect them from accidental digging)
Comment: I don't get the aesthetics comment, what is bothering you? Everything will be hidden. If the path is bothering you that is not related to the irrigation system, I am about to put that one in anyway. I need it ass cutting grass is sending clips into the flower beds and the grass is growing into the flower bedes. The lawn mower will step on that edge with the wheels allowing me to cut near the edge from the lawn size
Comment: freezing: it is about first freezing (you may be more diligent, but usually I wait first freeze to close external water supplies, but in my region first freeze is not so bad, and my setup permit me not to have problems on first freeze). Aesthetics: it is personal (and I'm more used on English style then Italian style of gardening).
Comment: the edging is 6" wide and I am betting on the fact that it it will be half covered by grass and plants, leaving me enough spate to run the mower on it. it will look less intrusive or dominant when it mingles in the landscape. I did not aim for a certain style I just looked for solutions to problems that I had and I followed some general guide lines explained in a few books I browsed about this
I will stop watering way ahead of the first freeze as Toronto is near lake Ontario and it rains well enough in October https://toronto.weatherstats.ca/charts/precipitation-monthly.html


Do Preference Attributes relate to data extension subscribers at all?

Question: I've never found a way where preference management attributes or even profile center attributes come into play when solely using data extensions. How would we utilize, for example, the preference of a subscriber who only wants to receive Plain-Text emails if we use data extensions only?
Answer: You'll have to run an automation that updates the All Subscriber list for the HTML Email column and set it as false to receive only Plain-Text emails. Extract your data from your data extension and import it into All Subscribers
In Automation Studio:
Data Extract > File Transfer > Import
Then map your HTML Email to your Subscriber Key and Email Address.
Comment: Can this process be done the other way as well? Data Extract All Subscribers info > File Transfer and Import into Data Extension?
Comment: No but you query _Subscribers or manually Export.


what if I used sour paint on my walls?

Question: I used sour smelling paint on my walls in my spare bedroom about 2 months ago and the smell is still there even after I used fresh paint and put two more coats of the fresh paint. What should I do.? Is it safe to be in that room.? It isn't as bad as it was but you can still smell it.
Answer: Honestly you might be re-drywalling the whole room.  If you smell sour that is basically mold.  If you can smell it then it must be producing mold in the air which affects your family.  So you have two choices:

Tear down drywall and start over.
Go through a grueling process of using lacquer and paint removal products that are just horrible.  And now you have two more coats on top of it.  This will make your whole house smell and is just and absolute mess.  And the kicker, you could do this and still have smell problems.

Obviously using the paint was really dumb.  My rule is if I have to ask myself if I should use something or not, I don't unless a pro or research says its OK.
Comment: Man, that's a drag.
Comment: @iLikeDirt - yea sucks... Like $15 worth of bad paint will cost maybe 500+.
Answer: You don't need to tear down to the dry wall. Clean your walls with a bleach solution (1 part bleach to 10 parts water). Air dry. Use Kilz primer over the sour paint. It will seal in the odors and the bacteria.Then repaint with new paint. The odor will be gone.

what if I used sour paint on my walls?


Why is the entropy production inside the system zero for a reversible process?

Question: For a reversible process, why is the production of entropy within the system equal to zero?
Answer: See Transport Phenomena by Bird, Stewart, and Lightfoot, Chapter 11, Problem 11.D.1 Equation of change for entropy.  They show that the local rate of entropy generation within a system is expressible as the sum of 3 terms, one proportional to the square of the temperature gradient, the second proportional to the square of the velocity gradient, and the third proportional to the square of the concentration gradient.  In a reversible process, all three of these terms approach zero.
Comment: Chet, do the first two terms roughly relate to temperature disequilibrium (temperature gradient) and pressure or force disequilibrium (velocity gradient)? And does the third term relate to chemical disequilibrium? In my head I have entropy generation as being due to disequilibrium which, in turn, is necessary to drive all real processes. I suppose it may be a little simplistic.
Comment: @Bob D Yes.  They relate to the rate of entropy generation per unit volume from temperature gradients, velocity gradients, and (I guess you found the other part of the development) concentration gradients.  The presence of the various gradients provide the "driving forces" for finite rates of heat-, momentum-, and mass transfer.
Answer: It is not the production of "energy" that is zero in a reversible process but the generation of entropy that's zero.
Entropy is generated in a process as a result of disequilibrium between a system and its surroundings. Examples are pressure disequilibrium and thermal (temperature) disequilibrium. A reversible process is carried out slowly so that the system and surroundings are always in equilibrium.
Hope this helps.
Comment: Hahaha yes my bad, it was a typo. Thanks for your answer!
Comment: Hi Bob.  I think you'll like the analysis in the reference I mentioned in my Answer.  It has filled many of the gaps that had existed in my understanding.
Comment: @ChetMiller Hi Chet. Looked it up on line to see if any free down loads. Not sure I want to shell out a hundred bucks (being a cheap skate!)
Comment: @Bob D During my long engineering career, I used this book more than all my others combined.  It has a wealth of information.


Hedging against FX for bond portfolio

Question: Let's say I've bond is USD with a maturity of 25yrs and yield of 5% and coupon 7%, but I'm located in Europe and wanna hedge the USD risk, How can I use cross currency swap to do this ?
Answer: Aligning your bond's cashflows with the CCS cashflows timing-wise, you would look to pay fixed USD 7% on one leg and on the other leg either

(a) receive fixed EUR (fix-fix CCS), or
(b) receive float EUR, like EURIBOR or ESTR plus a spread (fix-float CCS).

NB: this is a bit simplifying and you should of course also think of the bond notional redemption at maturity + take into consideration notional exchanges at the start/end of the xccy swap as well as nominal resets on itself. It can be a bit more challenging to align all of these in practice, especially if you do not do it on a stand-alone basis for this very bond, but rather a whole book of fixed income products.
Comment: I would even say that this does not require a XCCY swap but a set of simple FX forwards struck at the coupon dates could help as well.
Comment: That is of course correct, but the OP asked specifically how one could use a CCS to hedge.
Comment: Yes, absolutely okay - No worries.
Comment: Thank you for your response, so basically what you mean is that I'll take my coupons in usd and exchange them against another fixed amount in eur I get this part but what I don't get is how to make sure that I'm fully hedged how to determine that rate of exchnage ? and what fixed rates to use in currency swap ?
Comment: Can you clarify your question, please -- i.e., what you mean with "**determining the rate of exchange**"?
Regarding the fixed rates: the USD leg will pay 7% (exactly matching your coupon), and the EUR fixed rate of the xccy swap will be determined by the market (basically the respective yields determined by relative supply/demand for EUR and USD)
Comment: EUR/USD is physical delivery, so the bond holder promises to pay physical USD on the day when the bond pays interest/principal. But if you have to use non-delivery forwards for some EM currency, then the exchange rate gets observed on the day of bond cash flow, and the hedge cash flow is 2 days later.
Answer: If you have not already purchased the USD bond, you would enter into the following cross currency swap:

Purchase the amount of USD (vs EUR) using the dirty price (clean price + accrued interest) required to settle the bond purchase.

Sell USD (vs EUR) for each coupon (in the US typically semi annually using the day count convention for your bond, in your case 7%/2 sa) and the principal at maturity (the maturity will typically have one coupon + the notional amount) to settle on the dates when you would receive them.

Technically the above is not a currency swap as the market would know it since there are interim Sell USD Buy EUR forwards in the periods between the purchase date and the maturity date of the bond.  However, any dealer can price this for you and package it up into a swap.
If you already have the bond and are looking to hedge, just do leg 2 described above. Sell USD forward where the value date is on each of the coupon and maturity dates.
The rates you would use to sell the USD will be determined by the USD and the EUR yield curves on the day you trade.
Answer: If the bond is a US treasury instrument and you can assume that it has no credit risk, then you hedge the cash flows as other answers described - an FX forward for each expected cash flow (bond interest and principal payments), or a cross-currency swap whose USD leg matches the bond, or an asset swap. Note that if you receive fixed EUR, then you have EUR interest rate risk that you probably want to hedge as well.
But if your USD bond has credit risk, then you have 3 risks:

FX rate
USD interest rate
bond issuer's credit risk

Moreover the credit risk has 2 separate pieces: the LGD, the loss if the bond defaults; and credit01/cs01/cr01, the change in your bond's mark to market if the credit spread changes 1 basis point, if you're marking to market the bond (trading book or fair value option of banking book). You can't hedge them all at all, let alone statically. If the bond defaults, then you're stuck with the FX and IR hedge (such as the asset swap) that you no longer need.
One possible dynamic hedging approach is that since you're long the credit now, you buy CDS protection (note that you trade 5Y protection because no one trades 25Y CDS anymore) to flatten the credit01 to a comfortable level; and get less cross-currency swap, weighing the bond's cash flows by its probability of survival. As time passes and credit spread changes, you recalculate your credit01, fx delta, and interest rate risk, and if they are more than you want, then you re-adjust the hedges to flatten your risks to comfortable levels. You will not be flat LGD, and you will have tenor mismatch in your credit01, but hopefully you will be able to unwind everything before the bond gets close to actually defaulting. You can run a monte-carlo simulation with conservative transacton cost assumptions to estimate how much this can cost. Note that your accounting rules may not allow your dynamic hedges to be called hedges.
Comment: Very interesting and nice to see you @DimitriVulis again here. So question, if I am Euro client and buy a US HY bond assuming there is credit risk. I do wish to get US rate risk and the credit risk of the bond. The currency hedge somehow transfer my US rate risk to EUR rate risk as you mentioned above. What I can do about that? In addition, I do want to take the full ride on the credit risk of the bond but wish not get into a situation that the bond default my hedge position is still unwinded. Is there any way of overcoming it?

Hedging against FX for bond portfolio


12v battery banks and amp hours

Question: So I'm new to the battery banks. One bank is (6) cells made of (2) 6v, 12 amp hour sealed lead batteries each. Wired parallel to make a 12v, 144 amp hour bank. Is that correct?
Next I have a smaller bank, that is (2) 12v, 18 amp hour sealed lead batteries, paralled Making a 12v 36 amp hour, is that correct?
If I'm on the right track I'm glad. So my last question is. If break my 2 battery bank down, so they are 18 amp hours. Will it hurt to tie them into the other bank where each cell is 24 amp hours? I know with big differences it is hard on the smaller amp hour batteries, but was hoping it wouldn't be the case here and I could get 180 amp hours if I'm correct. Thanks for any advice. Hope I'm on the right track....
Comment: Please check and edit second and third sentences. They aren't making sense to me.
Comment: Did that help the confusion?
Comment: No. For a start, a battery is made of cells, not vice-versa. Then, if you wire 12 6V 12Ah batteries in parallel you would have a 6V 144Ah bank. 6 of those wouldn't give you a 12V 144Ah bank unless you kept 4 as spares. So I still don't understand.
Comment: Now it confuses me even more. Better draw a diagram of what is in parallel en what is in series. For me a cell is the 2V part of a battery, so your using of the word confuses me. And the second sentence has 12 batteries of 6V 12AH each. If you put those in 6 parallel pairs of 2 you get a 12V, 72 AH combo, not 144 AH. Remember: parallel adds the AH, series adds the V.
Comment: (12) 6v batteries to make, (6) 12v batteries.
Comment: Is your use of ( ) some sort of standard notation that I don't know?
Comment: No just that there are 12 of the 6 volt batteries. That I made into 6 of the 12 volt batteries, Running + to - .
Comment: OK so 2 of your 6V batteries make a 12V battery. And you start with 12 (6V) batteries so you can make 6 12V batteries. Each of these is 12Ah, so you have 12V 72Ah as Wouter says. So where does 144Ah come from?
Comment: I got it figured out.
Answer: I think something's gone wrong with your maths.  If you connect two 6V 12Ah batteries in series, then you'll get a 12V 12Ah battery.  Wire six 12V 12Ah batteries in parallel, and you'll only get a 12V 72Ah battery, not 12V 144Ah.
Answer: Maybe this will help.  When you connect batteries in series the voltage adds the amp hours are equal to the lowest rated one. When you connect them in parallel the current (amp hours) adds the voltage remains the same.  Never put parallel two batteries of different voltage ratings in parallel, or you will see smoke city.
Example:  If you connect two 6 volt batteries in series you will get 12 volts, that can be paralleled with another 12 volt battery but you cannot parallel a 6 volt and a 12 volt battery.
Batteries are made up of cells (2.2 volt batteries).  A 6 volt will have three of these in series and can have many parallel strings each string with three cells in series.  A 12 volt battery is the same but has six cells in series.
If you charge them expect 80% efficiency on a good day.  Simply stated to get 80 Amp Hours charge you need to add about 100 amp hours.
Hopefully this helps.
Gil

12v battery banks and amp hours


SIMBL Agent crashing frequently

Question: I just replaced a MacBook Pro running High Sierra with a new MacBook Pro M1 running Big Sur, and migrated my applications and accounts using Migration Assistant.
I noticed this evening that ReportCrash is using quite a bit of CPU, sometimes as much as 25% in both my regular user account and my admin account. I opened Console and saw that there were lots of Crash Reports from SIMBL Agent -- every 20-30 minutes in my user account and even more frequently in the admin account.
I removed the directories ~/Library/Application Support/SIMBL and /Library/Application Support/SIMBL (they both just contained SafariSource.bundle), but this didn't solve the problem.
Then I checked system.log, and every few seconds it's logging
Aug 29 00:11:05 Barry-Margolins-MacBook com.apple.xpc.launchd[1] (net.culater.SIMBL.Agent[29138]): removing service since it exited with consistent failure - OS_REASON_OBJC | Objective-C garbage collection is no longer supported.
Aug 29 00:11:05 Barry-Margolins-MacBook com.apple.xpc.launchd[1] (net.culater.SIMBL.Agent): Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

I tried killing this launchd service with
sudo launchctl unload /Library/LaunchAgents/net.culater.SIMBL.Agent.plist

and got the error:

/Library/LaunchAgents/net.culater.SIMBL.Agent.plist: Could not find specified service
Unload failed: 113: Could not find specified service

What do I have to do to kill this?
Comment: What are you using SIMBL for? Also have you rebooted?
Comment: I have no idea what I'm using it for, it was probably for something I used many years ago.
Comment: I have a feeling it was for a Mail plugin.
Answer: I removed the file
/Library/LaunchAgents/net.culater.SIMBL.Agent.plist

and rebooted, and this has stopped.

SIMBL Agent crashing frequently


Is there a Minecraft command to retrieve a player inventory?

Question: I'd like to create a Minecraft data pack to let a player see what he dropped/lost upon death (whatever he had in inventory+hotbar+offhand+armor+etc). I got the GUI part but i'm missing how to read a user inventory with a command so i can fill the new GUI with those items. I don't think /testfor is viable since i'd have to test for every single block present in the game and also i'd lose all the tags attached to an item (Edit: i've read that command is available only on BE, this is for JE). I tried to look at the documentation of /replaceitem but it doesn't seem useful either. Thanks in advance.
Comment: Possible duplicate of [How would you copy a player's inventory into a double chest?](https://gaming.stackexchange.com/questions/374406/how-would-you-copy-a-players-inventory-into-a-double-chest)
Comment: Upvote, even though I believe it to be impossible. To my understanding, yes, you would have to test for everything; every item ID, every enchantment type and level, every banner pattern, every leather armour colour code, etc. Some parts could probably be made easier, for example you would only need binary search and therefore 13 commands to check all 12326391 possible leather colours, but you would also have to set whatever you have as a display, so unless that's a scoreboard display (like the sidebar), you would have to have one command per value. Or you transfer the number from the...
Comment: ...scoreboard back into some NBT value. But even if you solve all of this, there's still the problem of item names, which can have up to 35 characters, as far as I know pretty much all of Unicode (1114112 different characters) is allowed, which makes the number of combinations a few novemsexagintillion or more than 600 command blocks even if binary search is somehow possible (which I doubt). And even if you're insane enough to program all of that, there are also shulker boxes, which make the number of possibilities explode once again (to `whatever your previous number was` to the power of 27).
Comment: So your real question becomes: How accurate do you want this display to be? Is just item type enough? Or also damage? Or also leather armour dye? Or...
Comment: I want it to be as accurate as possible, ideally the new GUI being a clone of the player's inventory (without the player being able to take back the items). If that's impossible with commands I'm not fixed on that and i could learn how to program a mod that does that. The data pack was just a convenient way to distribute the new feature to friends who play on my server.
Comment: You said you had the GUI already, what is it? Just a chest standing around that players can look into? Maybe that helps when creating the rest of the command system.
Answer: It seems that this is not possible. Maybe you could do something that detects if the player dies and teleports all the items on the ground or something along those lines. Perhaps using hoppers. You could also make sure that it doesn't teleport other items in the world by doing a radius. Although to my knowledge doing it any other way is impossible. You can use a scoreboard objective to test if the player has died.
Answer: You need a place to store the player data before the player dies.
You can copy the player's inventory to another entity, perhaps an invisible armor stand at 0,0.
/execute as <player selector> run data modify entity <global armorstand selector> Items set from @s Items

Then, once the player is dead and whatnot, you need to copy the inventory from the armor stand to a chest/minecart chest for the player to be able to retrieve the items.
/execute as <chest selector> run data modify entity @s Items set from <global armorstand selector> Items


SharePoint Drop Down Menu

Question: I am trying remove an item from the drop down menu. I recently linked the recycling bin to each of our plants, and now it is showing up in the drop down menu. I checked global navigation and had no luck. Please see the attached pictures for reference.
Answer: For the Current Navigation:
You can click Edit Links   button on the page and click the Delete icon next the navigation link to delete the link you don't need.

Another method, navigate to Site settings > Look and Feel > Navigation, select the link and click Delete.

For the Global Navigation:
I suppose that you are using the Managed Navigation.
Open the "Term Store Management Tool to edit term sets. Uncheck the Show in Global Navigation Menu for the "Recycling Bin …" term.

SharePoint Drop Down Menu


Repair of antique standing lamp light fitting (UK)

Question: I have broken this light fitting off an antique wooden lamp stand. It's a bayonet fitting, which screws onto a brass screw thread. Is this a standard fitting? Does anyone know where I could get one in the UK? Thanks.
Answer: The last time I was in Broken & Quick they still had those light fittings - as I nearly got two to make a couple of desklamps.
Answer: It's not a standard engineering fitting, but they are readily available.
The older ones are usually 1/2" BSB (not BSP British Standard Pipe, but BSB British Standard Brass. This is 26tpi, same as cycle thread, but a different thread form: 55 degree instead of 60.
https://www.tlc-direct.co.uk/Products/BG252.html
Newer studded threads are M10 and M13 metric threads.
You can get adapters to fit a 1/2" on a 3/8" or a 10mm threaded stud
https://www.tlc-direct.co.uk/Products/LY1110.html
This site has lots of bits for more unusual applications.
https://www.lampsandlights.co.uk/lighting-components.php
Answer: The brass screw threads are standard but the rest of the fixture looks unique. You have a few of options: Take the fixture to a lighting store and try to get an exact duplicate or go to a home store and look for something close. Do you want to have the same type/size of bulb? If not, there are quite a few choices. Good luck from the USA.
Comment: If the lamp really is antique, I don't think that fitting is original.  I think it would originally have been Bakelite - which means the OP probably doesn't care about an exact replacement.
Answer: That brass thing looks like a pretty standard hickey. The entire white plastic  assembly above it gets replaced as a unit, that is the lamp socket, and it may have an internal switch as well.
Expect to find a huge variety of replacement sockets, and if the socket type has been annoying you, this is your opportunity to change it.
Don't be surprised if the replacement looks quite different from this unit.  I generally expect to find steel ones that are plated to look brass.


Changing the name of a Portal

Question: I tried to change the name of a Portal. The business which used to be where that location is at is no longer in business and a new business is there. So, I wanted to update the picture and name. When I touched the picture in the game, to 'edit' it provided me with update capabilities but then that's where it became a problem. I tried to use the 'Google' update capability - and that wouldn't refresh the information. Why not? Am I doing it wrong?
Comment: I think we crashed the Pokemon Go servers so much that the Ingress servers broke too.
Comment: @Studoku I think they broke their own servers by releasing Pokemon Go to 26 additional countries
Comment: Possible related answer: http://gaming.stackexchange.com/questions/203995/is-there-a-reason-why-portal-title-edit-submissions-stopped-returning-confirmati
Answer: The Portal name and photo editing functionality doesn't change the Portal name and photo immediately. Your request will be examined by Niantic and if it's a proper request will be implemented. Nowadays this process takes a few months.
A confirmation email will be sent in just a few seconds after pressing the "Send" button on the edit window. If you're not receiving this confirmation there is a possibility that it is being tagged as spam by your email service provider because you're sending too much requests and receiving too much confirmation emails.
Yes, Niantic doesn't provide you with information that the Portal already has a waiting request by you or other agents. You can only find it out by looking at your own request confirmation emails or when you get an answer (positive or negative) from Niantic.
Comment: What's too bad about this - is when the update request is sent to them, there's no 'thank you your change request has been submitted' response from the game. Also, for those that come back to it - there's no place where it says that there's a change pending. So, someone next week could possibly go in and request the exact same change as well.
Answer: I get a lot more portal photo review than portal name review accepted though. Even if the requested change is legitimate, it doesn't mean Niantic is going to accept it.
Be patient and don't expect any fast answers from Niantic.
Portal reviews takes usually 1 month+ before it's accepted or declined.

Changing the name of a Portal


Looking for the right Church

Question: I'm Tom and I am from India (South) and it's been 4 wonderful months here in the US. I came here to do my masters study in computer science. I've been struggling hard to find a right church here. I really miss going to Church. My denomination is from CSI(Church of South India). I'd really appreciate if anyone could suggest me the right denomination I can look onto, coz there are like a dozen denominations here in the US and I am confused. Thanks in advance !!
Comment: Is there a Christian Union at your university, if so, go to their meetings and ask them.      And just pick a church and go there to see what it is like, any church that helps you in your relationship with God, is better then straying at home.
Comment: What is the CSI like? What beliefs does it teach/you believe?
Comment: There's a lot more than a dozen! You might want to edit a link to http://www.csisynod.com/aboutus.php or another page from that site into your question, together with a brief quote and perhaps some explanation from your point of view. You should be able to find one or more of the denominations that merged to form CSI. I would recommend attending some churches in your area on a trial basis.
Comment: Welcome to Christianity.SE. For a quick overview, please take the [Site Tour](http://christianity.stackexchange.com/tour). For moreon what this site is all about, see: [How we are different than other sites](http://meta.christianity.stackexchange.com/q/1808/20394). We can't really recommend a church for you. That's a personal decision. You'll need to canvas the churches in your area, talk to some of the pastors, and see if there are any that work for you.
Comment: Oh you work for the CSI?. Cool
Comment: Why look for the right church ? Let the right church look for you.
Answer: From the CSI website comes the following (from the drop-down menu "About Us"):

The Church of South India is the result of the union of churches of varying traditions Anglican, Methodist, Congregational, Presbyterian, and Reformed. It was inaugurated in September 1947, after protracted negotiation among the churches concerned. Organized into 24 dioceses, each under the spiritual supervision of a bishop, the church as a whole is governed by a synod, which elects a moderator (presiding bishop) every 2 years. Episcopacy is thus combined with Synodical government, and the church explicitly recognizes that Episcopal, Presbyterian, and congregational elements are all necessary for the church's life. The Scriptures are the ultimate standard of faith and practice. The historic creeds are accepted as interpreting the biblical faith, and the sacraments of baptism and the Lord's Supper are recognized as of binding obligation.

Based on this excerpt from CSI's website, I'd say you would be safe in visiting churches with the following words in their names:

Anglican

Methodist

Congregational

Presbyterian

Reformed

From the CSI's statement of faith, as quoted by gracelightcity:

". . . the Scriptures are the ultimate standard of faith and practice. The historic creeds are accepted as interpreting the biblical faith, and the sacraments of baptism and the Lord's Supper are recognized as of binding obligation."

Given the Church of South India's emphasis on the Word of God being
the final word in both faith and practice, I'd stick with churches which have a similar commitment to the Bible.
That you are "struggling to find the right church" is a good sign. I recommend you pick out a church with one of the five key words in it (as listed above) and see if that church has a website to which you can go for further information. Does something you read about a given church resonate strongly within you? If so, visit that church. See if you feel comfortable there. Ask yourself if the church members there make you feel welcomed, accepted, and loved. If so, perhaps the Holy Spirit is indicating that that church is for you. If not, try another church.
In conclusion, the matter of choosing a church to be your home church is very important. Church "shopping" can sometimes be a daunting task, but the criteria for choosing should be pretty much the same for any Christian. More specifically, the church you choose to be your home church should be a place where you are fed spiritually, experience true fellowship in the Holy Spirit, and are "put to work" in a ministry in which your spiritual gift-mix can be used to edify that local assembly of believers and bring glory to God.
I wish you well in the process!
Answer: Well there are not dozens of denominations here in the US, there are thousands. The CSI is interesting in that it blends some Protestant traditions that have classically been opposed to each other here in the US. I will leave out Roman Catholic and Eastern Orthodox from the initial discussion as they are not Protestant as your home church was.
I have visited many different types of churches here and generally like to break them down on a set of spectrums (forgive the simplifications):

Calvinist to Arminian (or Augustinian to Cassian for historical folks, or Reformed to Free Will)
Liturgical to Evangelical (bit of a misnomer as no church isn't evangelical, Evangelical here refers to a more "seeker-friendly" style of worship and soteriology)
Fundamental to Liberal

Liturgical
Liturgical vs Evangelical is the worship style and generally also encapsulates whether the church uses a more sacramental or scholastic/individualistic soteriology. It is also usually a good indication of whether the church is high church or low church (explanation to follow).
A liturgical worship service is focused around the participation in communion and most such churches teach that such participation confers saving grace upon the communicants (ie - it is sacramental). Sacramental also means that they tend to teach that the church is indeed essential to a person's salvation (ie - communal not individualistic soteriology).
Such churches will also tend to be high church meaning that there is a hierarchical order of authority that terminates with a high ranking bishop. There is usually a communion of bishops that together direct the entire communion.
The worship services at a liturgical church tend to include formal vestments for the clergy, traditional music with pianos and organs, and service of communion from a single chalice served by the presbyter/priest/pastor and generally more traditionally beautiful buildings.
Anglican and Lutheran fall into this category with Methodists and Presbyterian often taking up some middle ground. Note that some Anglican and Lutheran communions have moved towards the Evangelical side recently.
Evangelical
Evangelical covers a broad range of stuff, but for the purposes of this post we'll say that it covers the individualistic soteriology and seeker-friendly worship style (although technically there are Evangelical Liturgical Lutherans, whatever I'm not a scholar).
At these churches the worship emphasizes reaching a contemporary audience with contemporary music and a well crafted sermon. This can range from a single acoustic guitar to an entire rock band with flashing lights, stage fog, and skinny jeans. But the main focus is usually the sermon from what is hopefully an engaging pastor.
These churches tend to teach that salvation is mainly a personal relationship stemming from a personal commitment/conversion in which the church simply serves as a place of fellowship. The sacraments don't confer grace so much as they are a reminder.
The governance of such churches is usually centralized at the local level with a looser affiliation with other members of the communion. The church governance is usually more democratic, but a local pastor can also turn into a mini-pope.
Reformed, Baptist, Congregationalists, community churches, and most any mega-church around you will fall into this category.
Calvinist vs Arminian
This is a pretty simple difference. Arminians believe that the free will of man must be exercised for salvation and Calvinists don't. Presbyterians and Reformed will be more hard core Calvinist and Lutherans to a lesser degree. Methodists are more explicitly Arminian and not sure about Anglicans (CS Lewis was certainly not Calvinist). Low churches are usually split on the issue, so you'd have to ask the pastor. Most mega-churches avoid the topic as they see it as something that just brings division.
Fundamental to Liberal
Fundamentalism arose in response to modern skepticism. A fundamental church confesses that you must believe in some basic tenants of the Christian faith to be Christian like the divine inspiration of the Bible, the virgin birth and incarnation, the resurrection of Christ, etc. Liberals generally like to question fundamental doctrines, like criticizing whether the Bible is authentic and questioning whether homosexuality is an acceptable Christian lifestyle. In general there are deep ends on both sides of this pool.
Liberalism tends to be more prominent in high church communions and fundamentalism in low church (There is a ton of detail here, but I can't go into it right now, for instance I believe there is an unhealthy form of ultra fundamentalism that involves calling people heretics when they don't believe in the literal 6 day creation and stuff like that, but that's for another post).
Now if I were you I would skip this whole Protestant mess and just return to the ancient church and become Eastern Orthodox :).
Answer: The Church of South India currently aligns under Anglican Communion [Wikipedia].
It formed in 1947 and is the second largest Christian denomination in Southern India behind Roman Catholic, currently claiming 4 million parishioners, 11,000 ministers, 100 hospitals, 2000 schools, and 130 colleges.
It absorbed Calvinist denominations at some point and maintains a certain degree of dogma suggesting such. However, it's sacraments, liturgy, and hierarchy are Anglican in origin [this is all Wikipedia].
Socially, it's course has become more liberal in the last 10 years, ordaining female ministers and being (perhaps reluctantly) supportive of the LGBTQ community.
An Anglican church seems like your best first choice. But I liked the comment mentioning any church is better than staying at home!

Looking for the right Church


Redirecting to original (unauthenticated page) after spring security openid authentication

Question: I have implemented spring security openid integration using the sample available here:OpenId+Spring Integration
The integration works fine. When I request a protected resource I get redirected to a login page and after authentication I'm automagically redirected to the protected resource.
However, if I am on an unprotected page ( similar to the situation described here: http://forum.springsource.org/showthread.php?95317-Redirect-to-original-page-after-login-success-failure ) and I click on the login button..I get redirected to the homepage after login. I would like to be redirected to the page where I clicked the login button from.
The spring forum thread suggests overriding the buildReturnToUrl method. I have debugged thru it. It always generates a returnToURL of the form:
http://localhost:8080/listocal/j_spring_openid_security_check

There was some behind the scene communication between op and Rob Winch and I'm not sure how op actually overwrote it.
Alternatively, I have tried to create another filter with code like this:
public void doFilter(....) {
...
DefaultSavedRequest savedRequest = new DefaultSavedRequest((HttpServletRequest) request, new PortResolverImpl());

((HttpServletRequest)request).getSession().setAttribute("SPRING_SECURITY_SAVED_REQUEST", savedRequest);

}

If this filter runs before the OpenIDAuthenticationFilter then the savedrequest is removed by RequestCacheAwareFilter ( probably because of this issue: https://jira.springsource.org/browse/SEC-1241)
If this filter runs after OpenIDAuthenticationFilter then I do run into the issue where post parameters get concatenated after each request.
Can someone point out the right way forward on this?
Answer: This question was answered by the spring-security team on the spring forums. See this:
http://forum.springsource.org/showthread.php?128480-Redirecting-to-original-(unauthenticated-page)-after-spring-security-openid-authentic
Comment: Prashant do you have any demo for this?


How do I read strawberry facts?

Question: In Fruit Ninja, to unlock one of the achievements, you have to "Read three strawberry facts".  What does that mean?  Somehow, I got that achievement; how did I do it?
Answer: When you finish games, you get a random fruit fact on the same screen where you get your stats for each round. You must have been given three strawberry related ones at some point in time. The strawberry ones seem to be more rare than others (which might be related to the fact that they are an achievement).
In some versions, there are arrows on the screen that let you change between views (so you can actually see the fruit fact you get at the end of the round).
It will look something like this (this particular shot is from the iOS version):
Comment: I never noticed those arrows that let you change screens before.  Mind mentioning those explicitly (maybe even throw in a screenshot? :P) for the people as unobservant as I am?
Comment: @John Done! (Although the screenshot only accounts for one version)
Comment: You can get the arrows on the iPhone or iPod touch.

How do I read strawberry facts?


Error: `EIGRP is restricted to stub configurations only on this platform`

Question: We just bought some new Cat4507R+E distribution switches.  When we bought the switches, we asked for an Advanced Services K9 image, but our reseller told us they only come with a Universal K9 image.  I didn't know better, so I said OK.
However, when I tried to bring the switches online in production, I had a problem with a huge number of unreachable subnets.   After sweating it for a very long fifteen minutes (while my boss insulted me for not testing the switch), I finally tracked the problem down to eigrp stub connected in the EIGRP process.
I tried remove the "eigrp stub" statement but I couldn't. When I tried, the switch errors out with EIGRP is restricted to stub configurations only on this platform.
I had to roll back to our original distributions and my boss got even hotter about it.
My google searches blame this problem on the ip base license, which only supports EIGRP stub routing.   Our reseller says it will take at least 24 hours and thousands of dollars to get the Advanced Services K9 upgrade.  We didn't budget for the extra expense and we have other business units waiting on the upgrade.  Oh yeah, and my boss isn't happy.
Before we borrow money from another department, is there anything else we can do to get this working now?
Answer: I really don't like how Cisco crippled EIGRP in the ipbase image... at a minimum, you should get some kind of warning that your configuration won't work, but they haven't done that either.
As you discovered, eigrp stub prevents EIGRP from advertising downstream routes from the switches connected to your distribution.
You can trick EIGRP into advertising routes it learned from other rotuers (even as a stub router) by using a stub leak-map...
ip prefix-list p~MATCH_ANY seq 5 permit 0.0.0.0/0 le 32
!
route-map r~MATCH_ANY permit 10
 match ip address prefix-list p~MATCH_ANY
!
router eigrp 100
 no auto-summary
 network 172.16.0.0
 eigrp log-neighbor-warnings
 eigrp log-neighbor-changes
 eigrp stub connected summary static redistributed leak-map r~MATCH_ANY

Technically, you can get away with using eigrp stub leak-map indefinitely, without upgrading your ipbase image.
Comment: We indeed had the same problem and also solved it with the stub leak feature? Works well
Comment: Thanks, above solution is working perfectly for me. however i am in process to upgrade the IOS but this solution made be confident that this was IOS level issue only.
Comment: As today this is still working or was already patched in latest iOS releases? Another question: can I do this trick in the IP Lite IOS version?
Answer: Your 4507 comes with an evaluation license that will let you run enterprise services for 60 days.  You can activate the eval with the "license boot level entservices" command.  Note this requires a reload of the switch.  This will buy you some time while you purchase a permanent license.


Can I make the project files/source code of my comerical Unity game avalible as a DLC or with the game?

Question: Is it legal and/or a good idea to let the players download the source code/project files of a comerical Unity game with the game or as a DLC?
Comment: To clarify: the source code and project files you're talking about are wholly your creations, not work you've licensed from third parties? Then who exactly are you worried might bring a legal case against you for distributing them? You wouldn't need to distribute the engine since it's a free download anyway.
Answer: Before you publish your sourcecode, make sure you actually have all the rights to it. Be careful about any 3rd party assets you downloaded from the Unity marketplace or elsewhere which might end up in your project. You can only publish those with the explicit permission of the creator. This also applies to stuff you got for free.
Is it a good idea?
The game sourcecode will be quite useless for most of your target demographic. Most gamers will either not be able to read the code or won't be interested in it (I would certainly not look at it - that would just be detrimental to my game experience). But there are two small sub-cultures in every game community which will have quite a lot of interest in it:

Powergamers who want to completely understand all the game mechanics. But not all of them will need the sourcecode to do that. A few will buy the source and then create a wiki which describes all the formulas and algorithms.
Modders, because having the sourcecode allows them to change your game in any way they want.

The second demographic is the one you might want to cater to. An active modding community can add huge value to a game.
Just make sure they don't take your base-game and offer it for free to people who haven't bought it. Any OSI-approved open source licenses explicitly allow that, so they might not be the best to protect your business interests. You might want to ask a lawyer specialized in software copyright to draft a license agreement for your sourcecode which makes sure people can use it only for documenting and modding your game.
One downside of having a strong modding community is that any DLC you release later will compete with the content offered by the modding community, so it will only sell well if you can offer a level of quality which goes far beyond what the modders are able to deliver.


Feedback in multistage amplifier

Question: I found this schematic online for an audio amplifier and I noticed the 100k was some sort of feedback system between the base of the first stage and the emitter of the next. How would you describe this feedback mechanism? What is its effect on the gain and bandwidth of the system?
Comment: Are you wanting more detailed information? Or is LvW's broad strokes sufficient? For example, do you want a walk-through covering not only sensitivity issues for DC biasing but also an explanation about gain and frequency response with the why's and wherefore's? Or what?
Answer: Both transistors have local negative feedback - provided by the emitter resistors. This feedback mechanism is effective for both dc (operational point) and for ac (signals).
The 100k resistor fulfills two tasks: (a) It determines the bias point of the first transistor (together with the 10k resistor at the base) and - at the same time - it provides overall negative feedback for additional stabilization of the DC quiescent operational point of the whole circuit. This feedback path is NOT effective for signals due to the 10uF capacitor to ground. Therefore, THIS feedback path has practically no influence on gain and bandwidth (in contrast to to the feedback provided by the emitter resistors.
Comment: The last sentence is correct as long as the signal input has a very small source resistance. Otherweise the 100k path allows a very small signal feedback also.
Answer: Because of the filtering capacitor, this is just DC bias. No effect on the gain and the BW. Without the 10uF cap, the feedback will be current type in parallel. This will reduce the input resistance and the gain. But will extend the BW.
Comment: Signal feedback (without the 10µF cap) depends on the signal source resistance Rs. No feedback for Rs=0.

Feedback in multistage amplifier


Pronunciation of "ikebana" by non-Japanophones

Question: Apart from "very rarely", how is "ikebana" (Japanese flower arrangement) typically pronounced in real life by non-Japanophones? Is it the same as how it's pronounced in Japanese, or has it changed like "karaoke", "kamikaze" and "karate"?
Comment: /ˌiːkəˈbɑːnə/ or  /ˌiːkəˈbænə/ i prefer both as for Japanese I don't know
Comment: Well, the "ik" is going to be pronounced either "ick" or "ike", the "e" may be pronounced (probably as a "short-e") or, especially if the first syllable is "ike", it may not be pronounced at all.  "bana" will be pronounced "bay-nuh", "bah-nuh", or "ban-uh", pretty much independent of how the first part is pronounced.
Answer: You may listen to the Japanese pronunciation for yourself by clicking the speaker icon in the lower-left of the input box.  Non-japanaphones is a very large class of speakers, and likely there are as many unique ways to mispronounce Japanese as there are other languages.  Besides mispronouncing long vowels and the Japanese "r," anglophones tend to substitute their language's stress accent for the Japanese pitch accent.
Comment: Having listened to the Japanese and American pronunciation at that site, I have to say the American mangles the pronunciation. As an American who studied Spanish, I find that pronouncing Japanese wotds as if they were Spanish gives a better rendering (at least of the vowels, if not the stress). Of course, some consonants  (in particular "tsu") are difficult for both Spanish and English speakers to say, as there is no real equivalent phoneme in Spanish or English. And some (e.g. "shu") are easier for AmE speakers than for Spanish native speakers.
Comment: I downvoted because this answer is almost purely about the Japanese pronunciation, and thus off-topic for this site about the English language. The questioner even specifically asks for how the word is "typically pronounced in real life by non-Japanophones," but the only information we get about the pronunciation in English is vague. Also, even if it's not meant in a negative way here, I dislike the use of "mispronunciation" to refer to nativized pronunciations of foreign words.
Comment: I don't even know where to start with the misconceptions in your comment, so I'm just going to thank you for owning the downvote.


Github-like "pull requests" without Github

Question: I work as an analyst for a financial institution, which, due to data sensitivity, will not store any data in the cloud. However, I'm having some success getting my team to use Git for code management. I was wondering whether there was any way to implement Github-like pull requests in our own server. The specific feature I'm interested in is the ability to submit a changeset for comments, without actually having it merged into a given branch. I like the workflow of (1) submit changes, (2) have changes reviewed and commented on, and (3) either accept the commit or reject it. Can this be implemented (even better, can this be easily implemented) on our own servers?
Answer: git request-pull anyone?

Summarizes the changes between two commits to the standard output, and includes the given URL in the generated summary...

This should do the trick...
Comment: You probably approve it by writing a positive email about it, and you merge it using the git merge command, and then you push your merge commit to wherever it needs to be.
Comment: Great, Now how do I approve that PR and merge it upstream?
Answer: You can self host GitHub for a price, personally I think it is very expensive but it is available as an alternative if you just love GitHub.
Personally I went with Gitorious and had great success with it. Self hosting it and integrating the project/repository features with a typical Git Merge Request system, it works great for distributed and non-distributed teams.
Comment: I'm actually just looking for that single feature. Most other features - easy sharing of codebases, following & forking, fancy project stats, newsfeed (ha!) - aren't necessary for our projects.
Comment: Don't use the other features.  You do need a managed server for hosting your git repository anyway.  I actually recommended GitHub for Enterprise over other solutions such as Collabnet.  The most important need you would have is to make sure it ends up in the enterprise SCM (which is likely not github unless your bank is cool)
Answer: There are many alternatives to github.com that include a pull request feature, including several that you can install on your own server, either for a fee or in accordance with a free licence. Free options include Gitorious, Phabricator and Gitlab CE. One option that you would have to pay for is GitHub Enterprise.
See:
https://en.wikipedia.org/wiki/Comparison_of_source_code_hosting_facilities
https://en.wikipedia.org/wiki/Forge_(software)


Google Analytics exclude filter not recognizing multiple patterns

Question: I'm trying to exclude my top-level page and certain section pages from a custom report using the exclude filter. It works for a single pattern (i.e. \news), but when I try multiple patterns separated by pipes as described here (i.e. \news|\blog|\catvideos), none of the patterns are filtered. I would create a filter for each pattern but I need more filters than the maximum allowed by analytics. Is there something wrong with my syntax? Any advice would be appreciated.
Answer: Here's a solution I found. Instead of using the "exact" match setting for the filter pattern, I switched to "regex". The regex string to filter the multiple-pattern string in the example above would be ^\/news$|^\/blog$|^\/catvideos$.
Answer: Select "Matching Regex" instead of "containing" while filtration. And then simply enter the pattern you are entering i.e. (\news|\blog)


Why is Izual a demon again?

Question: At the end of Act IV in Diablo 3, before getting to Diablo, we have to fight a once-again demonic Izual. How did this happen? Didn't we free his soul when we killed him in Diablo 2?
Answer: It's worth remembering that even after defeating Izual in Diablo II, he was never really redeemed - in fact, he took the time to give some extra villainous speeches in spirit form.

Tyrael was a fool to have trusted me! You see, it was I who told Diablo and his brothers about the Soulstones and how to corrupt them. It was I who helped the Prime Evils mastermind their exile to your world. The plan we set in motion so long ago cannot be stopped by any mortal agency. Hell itself is poised to spill forth into your world like a tidal wave of blood and nightmares. You and all your kind...are doomed.

Further, we know that it's extremely difficult to get rid of an angel or demon's spirit just by killing them - Tyrael took a mere twenty years to reform his body after being caught up in the destruction of the Worldstone, while our good friend Diablo and company persistently refuse to stay down.
Though I don't believe it's fully explained how he returned to form - his original fall is mentioned in the Act IV lore books, but I haven't found one detailing his second fall if such a thing exists - it's certainly not outside the realm of possibility that at some point he returned to the Great Evils again, or that Diablo specifically sought him out on his joyride to go smash up the High Heavens.
Answer: The lore in Diablo 3 seems to deliberately leave this as an open question. "Izual's Descent" implies that Izual's body was expected to reform as an angel and return to heaven, but did not:

...Tyrael claimed that [Izual] was slain years ago, but his replacement has never emerged from the chrystal arch.

I'm tempted to say based on Izual's spirit mocking the angels and claiming responsibility for the prime evils' plot to take over Sancturary in Diablo 2, that he did not reappear in heaven because his spirit was no longer angelic, but given that the lore in Diablo 3 seems deliberately vague on this point, it's possible that the story behind Izual's failure to reappear as an angel might be planned for a future expansion.

Why is Izual a demon again?


How do I see the number for an unknown caller who is not in my contact list?

Question: I have an iphone 4 and although I get a notification for a missed call but i cant see the number of the person calling all it shows is missed call from "unknown" i cant find anything on the internet regarding a fix or a setting? please help, if a person calls me and they're not in my contact list i can never call back cause i don't know who called? this is extremely frustrating!
Answer: Whether the caller's number shown or not does not depend on your contact list. It is the information which is provided by the carrier (AND the caller because the caller can disable it and you won't see any number even if the caller is in your contact list).
If you see "unknown" that means the CallerID was not provided. If it's provided then you would see the number of the callers even if they're not in your contact list.


When can I assume a force to be constant?

Question: If I have a force $F(x)$, can I assume it to be constant in any infinitesimal interval such as $Rd\theta$,$ dy \over cos\phi$, $dz$ etc. or can I assume it to only be constant in the interval $[x,x+dx)$? If yes, can you prove it mathematically and if not, which infinitesimal intervals can I assume a force to be constant in & why?
Comment: I think you can only do that, in general, if the element is infinitesimal in *all* dimensions. So $dx\,dy\,dz$ is fine, but $R\,d\theta$ is not.
Comment: @lemon : That looks like an answer, not a comment.
Comment: related: [impulses and delta functions](https://en.wikipedia.org/wiki/Dirac_delta_function)
Comment: @lemon I disagree. If the force is finite, the change across an infinitesimal interval will always be infinitesimal, so the force can be treated as a constant. The triple infinitesimal is just a much smaller infinitesimal
Comment: @AlbertAspect Consider a large $R$ and the force $f(R)=1/R$. The force is far from constant across $R\,d\theta$...
Comment: @lemon That is not what I meant, I am assuming that R is constant. The same can be said about your assumption if the force changes in time. perhaps the question should clarify constant for what purpose
Comment: It is very difficult to discuss general cases. Each specific case may have a different answer. I suggest that you ask about the particular problem situation(s) which is causing difficulty.
Answer: What you want to do is a Taylor Expansion. Assuming that  $F\in C^1(\mathbb{R}^3)$ you have:
$$ F(\mathbf{x})=F(\mathbf{x}_0)+\nabla F(\mathbf{x})|_{\mathbf{x}_0}\cdot(\mathbf{x}-\mathbf{x}_0) + \mathcal{o}(\mathbf{x}-\mathbf{x}_0)$$
So, you can approximate $F$ to be constant only if the first (and higher) order terms are neglectable for your purposes. Here I've showed you a general expansion, but you can write the gradient in any coordinate system (for example spherical) you wish. If it's legitimate to consider only the zeroth order of the expansion usually depends on the explicit form of $F(\mathbf{x})$ and the particular application in which you want to make this approximation.

Let's now consider a one-variable function $F:\mathbb{R}\to\mathbb{R}$, $F\in C^N(\mathbb{R})$. It's then possible to write it using the Taylor theorem:
$$ F(x)=\sum_{k=0}^{N}\frac{d^kF}{dx^k}|_{x_0}\frac{(x-x_0)^k}{k!} +\mathcal{o}((x-x_0)^k)$$
If we put N=1, we get:
$$ F(x)=F(x_0)+\frac{dF}{dx}|_{x_0}\cdot(x-x_0)+\mathcal{o}(x-x_0)$$
That means that you can legitimately consider $F(x)\simeq F(x_0)=\text{constant}$ in the neighborhood of $x_0$ only if the first (and higher) order derivative of $F(x)$ evaluated in $x=x_0$ times $(x-x_0)$ is small enough to be considered neglectable for your purposes.
Here I wrote $F:=F(x)$, but it's exactly the same if $F:=F(\theta)$. Just put $x\mapsto\theta$ (or any other variable you wish) in the above formulas.

Consider now the limit for $\mathbf{x}\to \mathbf{x_0}$, i.e. $\mathbf{x}-\mathbf{x_0}\simeq d\mathbf{x}$. The differential of the function $F(\mathbf{x})$ is its linear increase respect to its variables. It is defined as:
$$dF=\nabla F \cdot d\mathbf{x} =\frac{\partial F}{\partial x}dx+\frac{\partial F}{\partial y}dy+\frac{\partial F}{\partial z}dz$$
So F is not increasing (i.e. $F$ is constant) when moving along a direction only if the partial derivative in the same direction is zero. You can write this in any coordinate system you want. For example in spherical:
$$dF=\frac{\partial F}{\partial r}dr+\frac{1}{r}\frac{\partial F}{\partial \theta}rd\theta+\frac{1}{r\sin\theta}\frac{\partial F}{\partial \phi}r\sin\theta d\phi$$
So just evaluate the partial derivative and see if it's zero. If that's the case, then you can consider the function constant along that direction.
Comment: I only know single variable calculus(Calc I). Is there any way to do this using those basic tools?
Comment: Yes, of course. I edited the answer to add the single variable case. Let me know if now it's more clear.
Comment: This is essentially telling me when/why I can assume $F(x)$ to be constant in the interval $[x_0, x_0+dx]$ and $F(\theta)$ to be constant in the interval $d\theta$, $f(z)$ to be constant in the interval $dz$ etc. but my question was whether I can assume $f(x)$ to be constant in **any** infinitesimal interval such as $d\theta$, $dz$, $dy/cos\phi$ etc., not just $dx$ because I've seen it done in my physics classes but I don't understand $why$ I can do it.
Comment: Well, if you consider $F(\mathbf{x})$ to  be a three-dimensional force (i.e. $F:\mathbb{R}^3\to\mathbb{R}^3$), you need to know multi-variable calculus, otherwise you can't be rigorous. Then the answer is the first one i wrote you. If you're thinking about $F(x)$ as having only a single variable (for example if you consider the line $R\theta$ with $R=constant$) the you can simply use the second answer I wrote.
If you don't know enough math to understand the above formulas, I'm afraid the only thing you can do is evaluate $\frac{F(x+\Delta x)-F(x)}{F(x)}$ and check if is $\ll 1$.
Comment: I edited my answer again, trying to be even more clear and using explicitly infinitesimal quantities. I hope that now you can more easily understand the matter. Let me know.
Comment: I think a good example of what I'm trying to say is http://physics.stackexchange.com/questions/312961/why-can-i-assume-the-force-to-be-constant-in-this-particular-interval
Comment: Ok, but my answer doesn't change: if $\frac{\partial F}{\partial y}=0$ then the force is constant along the $y$ direction. Otherwise it's not.


Simple Question: Speed of Electromagnetic Waves in a Medium

Question: If the speed of an electromagnetic wave in a particular medium is such that $v = c$, the speed of light, does this mean that the permeability $\mu = \mu_0$, i.e. that of a vacuum and the index of refraction is also $n = \frac{c}{v} = 1$? Also $\epsilon = \epsilon_0$?
Comment: when the light moves in vaccum, the value of epsilon is ofcourse equal to epsilon nought.
Answer: As for $\mu$ or $\varepsilon$, not necessarily, this only means that $\sqrt{\frac{\varepsilon\mu}{\varepsilon_0\mu_0}}=1$ at the specific frequency. This is possible, e.g., if  $0<\mu<1$. The above is about phase velocity, although, as far as I understand, your statement is not necessarily true for group velocity either. As for the velocity of the front of the wave, it is always equal to the velocity of light in vacuum, as far as I remember. As for $n$, yes, your statement seems correct (at least if we do not consider losses in the medium).
Comment: *As for the velocity of the front of the wave, it is always equal to the velocity of light in vacuum* I don't think this is right. It sounds like you're talking about the signal velocity: http://en.wikipedia.org/wiki/Signal_velocity The signal velocity is usually equal to the group velocity, which is usually less than c.
Comment: @Ben Crowell: http://en.wikipedia.org/wiki/Front_velocity
Comment: I see, +1. I hadn't been aware of precursor signals.


What benefits does Nessus have over OpenVAS?

Question: Nessus and OpenVAS appear to have fairly similar features. Why would you choose one over the other, besides the benefit of commercial support (which isn't available for Nessus Home Feed users anyways)?
Comment: @Rory mentioned the GUI below, so additionally, pretend that I use the CLI version of each for the sake of argument ;>
Answer: I think that both projects will have their strong and weak points.  At the moment I'd say that Nessus appears to have a wider range of plugins available and arguably a better user interface than the standard OpenVAS client/server implementation.
In addition Nessus seems to have widened their original focus in unauthenticated vulnerability scanning to include authenticated (audit) style checking.  In several scenarios this is likely to produce more accurate results than unauthenticated scanning.  Having looked at these scanners authenticated scanning capabilities, Nessus does seem more advanced here than OpenVAS
EDIT : Just thought I'd add another couple of things I've noticed which could be relevant to people looking to evaluate these two.  If you're looking at Database Scanning (Oracle/SQL Server) Nessus offers credentialed scanning for these, with DB level creds, which will find some vulnerabilities.
That said if you're interested in database vuln scanning NeXpose could be well worth considering, it seems to have good authenticated and unauthenticated database scanning.
Comment: @dre Well I've not done a detailed look at coverage but going on the numbers on their pages http://www.openvas.org/openvas-nvt-feed.html mentions 18000 NVTs, for nessus there's mention of 40000 plugins here http://www.tenablesecurity.com/plugins/index.php?view=all
Comment: We use Nessus, and have gotten a lot of milage out of the audit files. If you actually have configuration guidelines then being able to build your own audit files is a great help.
Comment: I was under the impression that OpenVAS had more plugins than Nessus, and that OpenVAS also included authn checking with SLAD -- http://openvas.org/compendium/security-local-auditing-daemon.html?
Answer: A recent test of Nessus and OpenVAS shows the benefits in using multiple scanners due to the difference in the signatures:
Nessus, OpenVAS and Nexpose VS Metasploitable (blog post by Peter at HackerTarget)
Out of 15 known security holes in the system used for the test, 4 were spotted by all four tested tools (Nessus, OpenVAS, Nexpose and some Nmap scripts); 7 were only spotted by some and 4 were missed completely.
Tenable responded with an article on The Right Way To Configure Nessus For Comparison.
Comment: This article "The Right Way To Configure Nessus For Comparison" is dated Paul Asadoorian August 24, 2012 so that doesn't really qualify as recent.
Answer: Though Nessus comes at a hefty price whereas OpenVAS is free and open-source but Nessus has a larger range of common vulnerabilities and exposures (CVE) coverage. Nessus even has better server-side compatibility. Also, OpenVAS doesn't offer policy management whereas Nessus does.
Answer: From years of Nessus usage (against competitors such as Retina, OpenVAS etc) it is not perfect, but it is still better than the competition for coverage, and ease of translation into real-world results.


Who wrote this poem?

Question:
This is what grief is.
A hole ripped through the very fabric of your being.
The hole eventually heals along the jagged edges that remain. It may even shrink in size.
But that hole will always be there.
A piece of you always missing.
For where there is deep grief, there was great love.
Don't be ashamed of your grief.
Don't judge it.
Don't suppress it.
Don't rush it.
Rather, acknowledge it.
Lean into it.
Listen to it.
Feel it.
Sit with it.
Sit with the pain. And remember the love.
This is where the healing will begin.
Comment: Welcome to the site. You will need to add more information to this question to help get an answer. Where and when did you first see the poem? Take our [tour] and visit the [help] to get some tips on how to ask a question.
Answer: After some research, I think this was probably written by a woman named Monica Bobbitt.
Ms. Bobbit posted the poem to Facebook on September 13, 2020. Like most postings of this poem online (there are many), it is accompanied by this photo of a sculpture called Melancolie, created by the sculptor Albert György. It is strongly implied that the photo inspired the poem.
Ms. Bobbitt does not explicitly indicate that she wrote the poem. She does not indicate that she was quoting the poem from somewhere else either, but frankly most of the postings I found don't do that.
So why do I suspect that she is the original author?

Age of post. I could not find any postings of the poem that are older than Ms. Bobbitt's. The second-oldest post I could find is one week later, and seems to be a copy-paste of Ms. Bobbitt's post (including the paragraph describing the photo) with added text at the start and end.

According to TinEye, the photo has been floating around the internet since at least 2017, but those older posts don't have the poem in them.

It's in her wheelhouse. Ms. Bobbitt, according to both her Facebook profile and her blog (A Goat Rodeo), is a Canadian military widow who writes and lectures about living through grief and loss. Putting these kinds of feelings into words is literally her job.

Similarity to other work. Ms. Bobbitt expressed some sentiments that are quite similar to the given poem in her blog post "50 Things I Learned After I Was Widowed":

Grief demands to be heard, so don't even try to bury it. Until you lean into it, acknowledge it, and process it, you will never heal.

Grief is the price you pay for love. Love is so worth the price.

She also posted a different poem on April 12, 2022, on both Facebook and her blog, that is similar to the given poem in both style and subject matter. And she explicitly signed that poem with her name.

I suppose the next step would be to contact Ms. Bobbitt and ask her directly if she wrote the poem. I'm not going to bother doing that, but let me know if you do.
Answer: Yesterday, January 22, 2024, my family has confirmed through Facebook Messenger with the author directly, that yes indeed, Monica Bobbitt did write the poem about what grief is. We were moved by this poem after the death of my father 3 weeks ago and it summed up exactly what I was feeling. Thank you for all of your own research in pointing us in the right direction.
Comment: Welcome to the site, and sorry for your loss. Would it be possible to share a screenshot of this message (with personal information removed) to verify your claim?

Who wrote this poem?


Page - specific Datepicker config in jcalendar.tpl

Question: How does one add a default value in one of Datepicker fields while adding or editing Relationship? For example, set today's date as a start date at Enabled checkbox check and as the end date if un-checked.  Should it be a custom piece of jQuery code or it's better to alter jcalendar.tpl? If latter, how one defines "Add/Edit Relationship" modal frame has been triggered and not, say, "Add/Edit Membership?" one.
Answer: You can set a datepicker's default value in the setDefaultValues() method of the form.  Here is a snippet of code that sets a date to today if none exists, and to a saved date if it does:
    if (empty($data['thank_you_date'])) {
      $defaultValues['thank_you_date'] = date('Y-m-d');
    } else {
      $defaultValues['thank_you_date'] = $data['thank_you_date'];
    }


Laminar Flow Fountain Shelter?

Question: Say you were stranded on an island with no shelter whatsoever, but for some odd reason you had all the supplies and water necessary to construct a laminar flow water dome as a shelter.
Keep in mind -- you have unlimited fountain creating supplies. You could make the most badass laminar water dome to ever exist.
Would it protect against rain? Wind? UV Light?
Comment: Welcome to Worldbuilding.SE!  We're glad you could join us!  When you have a moment, please [click here](https://worldbuilding.meta.stackexchange.com/questions/6388) to learn more about our culture and take our [tour].  Our [help/on-topic] explains that questions must be specific and answerable, must include context, must include restrictions/requirements, and should include research.  The Q is missing details (nature of laminate water, e.g. thickness, size of area protected, etc) and it is [primarily opinion-based](https://worldbuilding.meta.stackexchange.com/questions/6436#6437). (\*Cont.\*)
Comment: Welcome to the site Kimbo Saki, when you have a few minutes, please take the [tour] and read up in our [help] about how we work: [ask].
Comment: If you think about it, houses today are not impervious to wind, and I would expect laminar water to be less so.  Laminar water is transparent - unless the water is imbued with UV-protecting chemicals, which might ruin the laminar effect.  There's all kinds of possibilities and potential problems here, but you've provided no means of judging a best answer, no limits/restrictions, and have provided no insight into what your own research has revealed ([SE strongly recommends research](https://meta.stackexchange.com/q/244216/395595)).
Comment: What is laminar flow water?  And how is building something badass not you asking us for story ideas?  As for protection... that's personal preference though most houses protect against wind and UV and provide some low-light spaces too.
Comment: Is it even possible to make a hemisphere flow like that? Half-pipe tunnel, sure, but hemispheres would require the intersection of many different vectors of water moving at different speeds. Surely that takes it out if the laminar flow regime and back into regular ol' splashy territory?
Answer: The laminar water flow dome would provide shelter from UV since water is opaque to UV.
And it would provide shelter against wind as long as the wind force was less than the surface tension of the water wall.  Once it exceeds that, then when the wind start to over come the inertia of the water it would blow the wall into particles of water. A similar argument applies to rain, sleet, and hail.
If you can create concentric hemispheres, then their strength with be additive.  With outer shells dissipating some energy of disrupting forces like wind, rain, sleet, and hail.
And, if the wind came from a specific direction, then water walls and jets could be pulsed to sap energy before it reached the shelter.
I would expect the shelter to be the same temperature as the water, and to be humid and maybe misty at times since brownean motion would cause water molecules to collide and knock themselves out of the walls.
Comment: Sounds about right +1. Only thing I'd add is that if you can build and run this, you almost certainly can also add some ventilation system to control airflow inside the dome to manage humidity and some basic heating.
Comment: yes, @nemi,  i forgot about ventilation.  I wonder if one could suffocate under this kind of doorless, windowless shelter.
Answer: My first thought was if you had all the equipment to build such a dome, why not apply it in other ways to provide a more complete survival strategy? But the truth is that it doesn't take much to generate laminar flow.
The ultimate problem with this is that fluid dynamics preclude portal style entries and ventilation. Also, I'm not convinced that we fully understand the impact of UV on things like photosynthesis. To elaborate, about a decade ago I bought my sons some solar powered science experiments for Christmas (no, I'm not a normal Dad, but then I don't have normal sons either). We build them together over the school holidays (remember that the summer break coincides with the Christmas break in antipodean climes) and something very interesting happened. While they were under the Solar-Tuff UV screening covering of our outdoor patio, they wouldn't work. At first I thought we had collectively missed a step in building them, but the moment I took them outside the cover they went wild with activity.
My point being, that if plants at least partially rely on UV for photosynthesis, the dome you intend to create is going to cause some difficulties in crop growth, not to mention the fact that you have no way of making a 'natural door' to your dome, meaning that atmospheric exchange is also going to be problematic.
This is not to say the idea in isolation isn't sound; it's just that when considering new environments, it's not good to consider each element in isolation because the individual parts tend to generate a synergy that isn't evident by summing the parts - you can only observe the whole to understand the actual impact. In this instance, the opacity of water to UV radiation, and the lack of an obvious portal solution for atmospheric exchange in your water dome is still going to make life difficult under your dome from a food and air perspective.
The good news is that your subjects aren't going to die of thirst, unless of course the amount of water needed precludes potable reserves for drinking and cooking. Which of course brings up another small point. Ideally, you'd make your dome out of grey water on grounds that it is the most environmentally sustainable model because you want all the potable water you can get your hands on for drinking and for crops. But, that also means that you want to remove any detergents and the like because they can disrupt the cohesion of water and potentially disrupt the laminar flow of your doem.
All of a sudden, a plastic dome, particularly a recycled plastic dome, may make better sense for your population given the relative short-term biological needs of your population as far as water is concerned.

Laminar Flow Fountain Shelter?


Installing Server with existing data on drives

Question: I have a Windows 7 HTPC which I'm planning on turning into a headless Home server using Ubuntu server as its OS. I'd like to use LVM.
My current set-up is 1x64gb ssd as the boot drive and 2xSATA drives for media storage.
I'd want Ubuntu to create a virtual drive comprising all 3 physical drives.
My problem is that I don't have enough hard drive space to back-up my existing files whilst installing the server.
Is it possible to install the server yet keep hold of my media?
Comment: Which drive is Windows installed on and do you keep your data on separate drives?
Comment: Hi, Windows (and programs) are on drive c (the ssd). Everything else is on the other two drives.
Comment: Then you can just install Linux on the C drive. Then you can raid the 2 disks together, then move everything to a folder on the drive.
Comment: Would my data be safe though through the process? I can't move the excisting files off the drives (I don't have enough spare disk space on any other drives at the moment) and not enough free space on the drives on the potential server to back everything up.
Answer: If you have to ask yourself the question: "Should I back up?" then the answer is a very probable:Yes! So, head over here: What's a good back-up strategy for 1 desktop PC? and read it. (You're user type 4)
If you're unsure about yourself, you're likely to make mistakes, so a backup is needed even more!  Borrow a drive from someone, bribe someone to give you a drive or buy one if needed...  Heck, throw a party and have everyone bring their backup drive and distribute all your files among everyone!
If I was wrong about the back-up, come back here and down-vote my answer.  Don't be the next one in my long list of people I've told to back-up before continuing and then reading a comment a bit later: "You've just made me lose all my |@*$# data!" because they listened to someone else...


Nitrogen-Oxygen Gas Giant

Question: Assuming such a stellar body is even possible, could human or animal life (also assuming they have a way to avoid being pulled toward the planet's core) breathe its outer atmosphere? Would such life be crushed by the atmosphere's pressure?
Comment: Related: [Could air gas giants exist?](https://worldbuilding.stackexchange.com/q/11764/601)
Comment: Let's put it to a test we can introduce our most hardy lifeform on Earth the extremophile which volunteered willingly in the name of science. It will float quite happily at the top of the cloud since it is quite resistant to deadly radiation from space, soon it will be sucked down towards the core due to convection current. As it is pulled nearer to the core the atmospheric pressure and temperature builds up quickly. The pressure easily reached thousands of times higher than Earth's and temperature soars to over 10000℃ more than enough to vaporize anything. May the volunteer rest in peace
Answer: Jupiter's surface gravity is only 2.4 times that of earth. Uranus is only 0.86 of earth. So gravity is no issue as long as you can stay aloft in the atmosphere.
The level at which the atmosphere is too dense for life depends on the biological machinery of the life in question. The density varies from the top to the bottom of the atmosphere. It is reasonable to say that life cannot exist right at the top where the density is very very low and the radiation is very high, or at the bottom in which the pressure is immense.
Depending on the size of your gas giant, all kinds of things are possible and many science fiction stories feature airborne plants and animals living in the atmosphere of suitable gas giants.
The main thing is being able to reliably maintain altitude within some given band.
A simple search on google will turn up articles like this
Answer: May I introduce you to the Ice Giants?  The ice giants are formed of sulfur, oxygen and nitrogen with a relatively small amount of hydrogen and helium (20%) compared to Jupiter and Saturn (90%).

200 K is -73C so life as we know it isn't breathing that atmosphere.
Comment: Extremophiles :p
Answer: Gas giants are no place for life as we know it. Period. Reason being that a gas giant is composed 95% of gas. The core of a gas giant is composed of gas which condensed to liquid/solid form under incredible pressure. At the surface of a gas giant, the pressure would be at horrific levels (earthly life forms would be crushed into less than 50% their earth volume).
Also, since there are no large water bodies on the planet, the heat difference between the day and night sides would be extreme, leading to storms, dunes and vortexes, the magnitude of which reels the brain and makes us shiver in horror. Read about the Giant Red Spot to know what I am talking about here! Forget life. Anything larger than a virus would be torn apart into shreds within seconds.

Nitrogen-Oxygen Gas Giant


Translating grave marker written in Hebrew?

Question: I'm doing the tree and need to know who this man's parents are, anyone know Hebrew?
Comment: Please always include anything written on a grave marker as formatted text rather than only as a picture so that it is available for searching and easily readable on all devices.
Answer: The first line says: "Here lies"
2nd and 3rd lines are:  "Schmuel, son of Zev"
4th line says: "died on the 4th intermediate day of Sukkot 697".
So the 4th line simply gives the date of death in Hebrew. You add 5000 to the 697 to give the Hebrew year 5697. The Hebrew date is the equivalent of Oct 6, 1936, so there is no new information here.
One new piece of information is that Morris' Hebrew name was Schmuel which usually translates to Samuel. The English name "Morris" does not have a Hebrew equivalent.
The other new piece of information is that Morris' father's Hebrew name was Zev, meaning wolf. Sometimes the Yiddish name of a person with the Hebrew name Zev is Volf.