sum of irrational numbers - are there nontrivial examples?

Question: I know that the sum of irrational numbers does not have to be irrational. For example $\sqrt2+\left(-\sqrt2\right)$ is equal to $0$. But what I am wondering is there any example where the sum of two irrational numbers isn't obviously rational like an integer and yet after, say 50 digits after the decimal point it turns out to be rational. Are there any such examples with something non-trivial going on behind the scenes?
Comment: Take any complicated rational $r$ and some irrational $i$. Then $j=r-i$ is irrational and $j+i=r$.
Comment: That is a much harder question!  Nobody knows if $\pi+e$ is rational.
Comment: Relevant: [Sum of irrational radicals is irrational?](http://math.stackexchange.com/questions/479092/sum-of-irrational-radicals-is-irrational) asks if there are nontrivial examples where $\sqrt[n]a + \sqrt[m]b$ is rational; the answer is no.
Comment: My thougts exactly, after I posted this. But I am interested more in the cases like pi+e.
Comment: It's a much harder question to ask such things about _transcendental_ numbers.  (And we don't even know whether $ \ \gamma \ $  or  $ \ \zeta(5) \ $ are irrational...)
Comment: Possibly also interesting: [The sum of irrationals is irrational?](http://math.stackexchange.com/questions/157245/the-sum-of-irrationals-is-irrational)
Comment: Got something from an answer below?
Answer: Choose two irrational numbers $x$ and $y$ randomly, say independently and each according to the Lebesgue measure on $(0,1)$. Then $x+y$ is irrational with full probability. (Proof: For every real number $z$, $P[x+y=z]=0$, hence $P[x+y\in\mathbb Q]=\sum\limits_{z\in\mathbb Q}P[x+y=z]=0$, QED.)
In this sense, the sum of "almost every" pair of irrational numbers is irrational. Note that, to begin with, "almost every" real number is irrational...
Comment: I didn´t understand the proof, but I upvoted the answer as I think it brings something new to the discussion.
Comment: Now, I understand the proof, nice.
Answer: The examples below are not quite what you're asking for (because the results, while not obviously rational, wind up being nice integers), but they may nonetheless be amusing:
$$\sqrt{3 \; + \; 2\sqrt{2}} \; - \; \sqrt{3 \; - \; 2\sqrt{2}} \; = \; 2$$
$$\sqrt[3]{3\sqrt{21} \; + \; 8} \; - \; \sqrt[3]{3\sqrt{21} \; -\; 8} \; = \; 1$$
$$\sqrt[3]{2 \; + \; \sqrt{5}} \; - \; \sqrt[3]{-2 \; + \; \sqrt{5}} \; = \; 1$$
$$\sqrt[3]{10 \; + \; \sqrt{108}} \; - \; \sqrt[3]{-10 \; + \; \sqrt{108}} \; = \; 2$$
$$\sqrt[3]{9 \; + \; 4\sqrt{5}} \; + \; \sqrt[3]{9 \; - \; 4\sqrt{5}} \; = \; 3$$
How can these be verified? In the first example, squaring, then rearranging, then squaring works. In the second example, show that the numerical expression is a solution to $x^3 + 15x - 16 = 0$ and then show that $x=1$ is the only real solution to this cubic equation by observing that $x^3 + 15x - 16 = (x-1)(x^2+x+16).$ The third example winds up being the only real solution to $x^3 + 3x - 4 = (x-1)(x^2 + x + 4),$ the fourth example winds up being the only real solution to $x^3 + 6x - 20 = (x-2)(x^2 + 2x + 10),$ and the fifth example winds up being the only real solution to $x^3 - 3x - 18 = (x-3)(x^2 + 3x + 6).$
Comment: Is it just me, or a single pattern is evident in all those examples?
Comment: @Adam: I suspect there is some type of "preservation of field extension over the rationals under a certain quadratic conjugation operation" that holds for each of these equations, but I don't know enough algebra (or have time now to research the issue) to be more explicit. If you pose this as a question, then I'm sure you'll get several good answers, which I would also be interested in seeing.
Comment: @DaveL.Renfro Note that $$\sqrt{3+2\sqrt 2}=1+\sqrt 2$$ and the second expression is $$\frac12+\frac{\sqrt{21}}2$$ and $$\sqrt[3]{\sqrt{108}+10} =1+\sqrt{3}$$ (found with the help of Wolfram Alpha)
Answer: If $a+b=q$, where $a,b\notin\mathbb{Q}$ and $q\in \mathbb{Q}$, then $a=q-b$, so just choose
a rational number whith sufficiently long period of decimals and you will get what you want.
On the other hand, this is still quite trivial, since here we just sum up $b$ and $q-b$ (in your question, $q=0$).


Can I gather community opinions of a specific information security practice?

Question: Say I want to know "do people on security.SE report bad practices in their corporate information security to corporate IT". Does the question belong to the main site, meta or shouldn't be asked?
Comment: @TildalWave I think questions that have multiple valid answers are ok here (the same way they are ok on pretty much any SE website). We have many such questions, and many are well received. On the other hand, questions that are only opinion based, or really more of a general survey are of course of-topic. I generally wouldn't see a problem with a questions like `Is it proper practice to report security issues in a company to the IT department?`. For me, that would fall under the topics incident response or policies.  Of course, the way OP phrased the question it's just a poll and of-topic.
Comment: Of course, to not get closed as too broad, my example question would need to have more details added in the question body. Still, I wouldn't say it's categorically of-topic. The chat is of course a great suggestion if the OP indeed only wants to start a poll, and doesn't want to know current best practices.
Answer: If I understand you correctly, you want to run a yes/no poll.  Polling questions are off-topic on main sites but are usually acceptable on meta sites if suitably constructed.
This has been discussed on the main SE Meta here.  Essentially, be clear what you are polling for and set a close date.


what is a transceiver reconfiguration controller on FPGA

Question: I have come across this on an (Altera) FPGAs that make use of high speed protocols but don't know what it does.
Comment: all that is good, but what exactly is a transceiver reconfiguration controller. This point has not been mentioned by anyone.
Answer: There are some cases, when the transceiver is used for application, that can work in various modes or speeds. E.g. SDI (http://en.wikipedia.org/wiki/Serial_digital_interface). If You use SD quality video signal, the data rate is 270Mbps, if You connect HD video HD-SDI to the same interface, then the data rate is 1485Mbps. Same for other SDI standards. Now the deserializer does deserialization of the data... From SD-SDI it extracts 27Mhz clock and 10 bits of data. From HD-SDI it extracts 74MHz clock and 20 bits of data. Because of internal PLL clock difference and data bus difference, You need to reconfigure transceiver for proper clock recover, because the clock has to be recovered from the same wire as data.
Answer: A transceiver is a combination of analog and digital blocks. The analog block (the PMA)  can have sub blocks such as clock recovery unit, transmitter PLL, bit serializer and de-serializer and the digital part consist of one of all of the following blocks, data-aligner, phase-compensation and in many cases something like 8b/10b decoder and encoder.
To simplify the whole thing, when you connect 2 devices through high speed serial interface, you need create some kind of control to make sure your data transfers correctly between these devices.
This gets even more complicated when you have multiple lines of data running at multi Gigabits/second.
The transceiver 'aligns' those lines and takes care of the electrical issues between those devices. And at the same time, it makes sure that faulty data is detected and in some case it is fixed before sending it to the higher layer of the communication protocol.
You can create most of the digital parts in HDL, but many modern FPGAs have those implemented in HW already to make it easier for people to use. Both Altera and Xilinx have some wizards to generate a wrapper for the type of serial interface you want to access.
You can find some more in dept information about them on these pages:

Altera Transceiver Overview: Stratix IV and HardCopy IV
Wikipedia - Multi-gigabit transceiver
Xilinx 7 Series FPGA Transceivers Wizard

You can also read this interesting short booklet from Xilinx : High-Speed Serial I/O
Made Simple
Answer: A "transceiver" in this context is a hardware block that converts from a high-speed serial interface (too fast for normal FPGA logic and IO to deal with directly) to an internal parallel interface.
The transceivers on a FPGA are usually highly configurable supporting many different speeds and protocols. In simple systems you can just configure the transceiver statically by passing settings to the transceiver IP block which the synthesis tool then turns into configuration settings in your programming file.
But sometimes you want to change the settings of the transceiver without reprogramming the FPGA. The transceiver reconfiguration controller block gives you an interface to reprogram the transceiver from within your logic system.
Answer: The transceiver reconfiguration controllers are not very will documented. As far as I understand it, the controller has a couple of main purposes. The thing to keep in mind is that the high speed transceivers are very complex mixed signal blocks. They have a very large array of (mostly undocumented, at least publicly) configuration and calibration settings. Some of these are straightforward, like PLL divider settings and line coding settings. Many of these settings are specific to the protocol in use and need to be reloaded if the protocol needs to be changed on the fly. The parameters are usually exposed through a memory interface, so using a small soft core CPU makes sense to load these. However, other settings are a bit more low level. Things like bias voltages and currents for various analog blocks and other internal transceiver components. Things that need to be adjusted over time to compensate for temperature and voltage variations and manufacturing differences between parts to keep the transceiver operating correctly. The firmware on the reconfiguration controller also manages these settings continuously, which is why you need one even if you don't intend to switch high level settings on the fly.


Can you choose to add a template to a druid's animal companion instead of adding a hit die?

Question: One of my fellow players posed a scenario that I can't really find a satisfactory answer to. A level 10 character has the Wild Cohort feat and can have an animal companion as a level 7 druid. Since he can have an animal companion with 7 hit dice, can he choose to add a template instead of adding a hit die to avoid the maximum number of hit die his companion can have?
Comment: Possible duplicate of [Can I 'upgrade' my Animal Companion with the Giant or Advanced Creature templates instead?](http://rpg.stackexchange.com/questions/77022/can-i-upgrade-my-animal-companion-with-the-giant-or-advanced-creature-template)
Comment: @TuggyNE Close, but that one's for PF instead of 3.5e. I almost VtC'd before I caught that detail at the last minute.
Comment: Can you source the version of the feat Wild Cohort that you're using in your game? I'm concerned that it isn't the feat [Wild Cohort](http://archive.wizards.com/default.asp?x=dnd/re/20031118a) with which I'm most familiar as that feat neither measures a wild cohort's value in Hit Dice nor caps the wild cohort's Hit Dice.
Comment: In D&D 3.0e, a druid's animal companion did have a hit die cap.  @SevenSidedDie, are you sure you were correct in adding the dnd-3.5e tag, rather than a 3.0e tag?
Comment: @DanB [Yep.](http://rpg.stackexchange.com/revisions/80585/1)
Comment: I must have misread.
Comment: @SevenSidedDie: I did see that, but as far as I know the distinction is not meaningful in this case; the rules are sufficiently similar that closing as a dupe is the correct way to say "yes, these work the same way".
Comment: @TuggyNE We've had this come up before and it's less tangled to just treat them as separate. The alternative means dealing with errors in VtCs, arguments about degree of rule similarity, and problems when errata or Voice of Designer makes them no longer the same. Easier and cleaner just to let them be independent games with independent questions from the outset.
Answer: The feat Wild Cohort provides no option for the wild cohort to have a template
The benefit of the feat Wild Cohort says, in part, that

You gain an animal cohort.... Provided the DM gives her approval, at 1st level you can choose from a badger, camel, dire rat, dog, riding dog, eagle, hawk, horse (light or heavy), owl, pony, snake (Small or Medium viper), or wolf. Like a druid, you can choose more powerful animals as you increase in level. These alternative animal cohorts work like the alternative animal companions available to a druid, but they are available as cohorts later than they are available as animal companions. When selecting an alternative animal cohort, use the list of alternative animal companions on page 36 of the Player's Handbook, but treat yourself as a druid three levels lower than your character level....

Thus the wild cohort is much like an animal companion that, likewise, is acquired without templates. Further, the wild cohort's number of Hit Dice isn't specified; instead, the creature with the feat Wild Cohort has an ersatz effective druid level, which doesn't translate easily or directly into the wild cohort's Hit Dice or Challenge Rating. Finally, an animal is specified throughout the feat's description; a template that changes the wild cohort into something other than an animal renders the cohort invalid.
...But, hey, it's a game
If everyone agrees that instead of a regular ol' badger that a half-celestial half-dragon badger is somehow acceptable (like, maybe the guy with the feat Wild Cohort is a monk or something), that's great, and no one can stop you. Have fun.
Comment: So said player could not have a wolf with a ghost template, going off RAW.
Comment: @SiamSid  According to RAW, absolutely not. A creature with the feat Wild Cohort can't *via* that feat gain, for example, a [ghost](http://www.d20srd.org/srd/monsters/ghost.htm) [dog](http://www.d20srd.org/srd/monsters/dog.htm).


How prevalent are old x64 processors lacking the cmpxchg16b instruction?

Question: The cmpxchg16b instruction for doing atomic 128 bit memory exchanges is not supported on old versions of the x64 processor but it seems like this has been supported by newer versions of the processor for several years now. How likely am I to encounter a 64-bit machine with an old processor that lacks this instruction?
Comment: Your most important customer certainly have one of those in one of their critical production server thats used only for important tasks run on Christmas Eve, but nowhere else, and absolutely not in the test environment...
Comment: I don't think question this should have been migrated to superuser. It just ensures that fewer people who know the answer will ever see this question.
Answer: You are looking at early AMD 64-bit processors, before Rev F (which is when they moved to DDR2 memory). There is some early stepping D Intel Noconas too that did not support it, I think, but these are rarer.
Answer: I have no data regarding the prevalence of certain types of CPUs, so I can't directly answer your question. However, you can find out whether the CPU supports CMPXCHG16B by checking whether CPUID.01h.ECX.bit13 is 1 (available) or 0 (not available).
Also note that Intel's manuals suggest that for this instruction to be carried out atomically, you need to combine it with the LOCK prefix.
Comment: @PhiS: I'm pretty sure Christopher was talking about the lack of support for the cmpxchg16b. What to do if _that_ is missing
Comment: Yes, I know how to check the cpuid result. The issue is what to do if it is not supported. I would rather not waste time working around a missing instruction if I am never going to see that case in practice.
Comment: @Christopher Barber - CPUID has been supported since late 486 processors, which also implies that every 64-bit capable x86 processor will support CPUID.
Answer: Support in the CPU may not actually be enough as some Core 2 users found out on the launch of Windows 8.1, particularly those having an Intel DP35DP motherboard. I'm not yet sure what in the motherboard could prevent CMPXCHG16B from working. Probably the feature detection bits can be disabled by BIOS. To summarize what Yuhong Bao's blog says on this, there was a processor errata in early Core 2 chips (E0/R0 steppings of the 45nm Core 2) that caused their features to be misreported via CPUID. It was possible to work around this via BIOS/microcode update, as far as I can tell.
Comment: See http://yuhongbao.blogspot.ca/2015/06/why-your-core-2-processor-appear-to-not.html


What is the difference between "to benefit from" and "to profit from"?

Question: I do not understand when it is more accurate to say "to benefit from" than "to profit from". Are they interchangeable or is there precise context to employ one rather than the other?
Comment: There is a similar question: [Difference between "advantage" and "benefit"](https://ell.stackexchange.com/questions/80024/difference-between-advantage-and-benefit)? It is not an exact duplicate.
Comment: Note that this is an exact duplicate of the question at [EL&U](https://english.stackexchange.com/questions/497747/what-is-the-difference-between-to-benefit-from-and-to-profit-from).
Answer: These two phrases are roughly identical, but there are some important nuances.
In this instance, to profit from can have a connotation that someone or something has been exploited.

'Entrepreneurs' profited from the public's general lack of market knowledge, reselling the product they imported directly from China at triple (or more) the cost.

However, this is not always the case. The phrase is also frequently used literally (as in relating to money) and as a synonym of to benefit from.

The company profited from the market surge in the fourth quarter.
We really profited from your experience on that project!

To benefit from is most usually used without this connotation, though it can. It is also more rarely used to reference monetary gains the same way to profit from is.

The homeless people in the city benefited from the city-wide food drive.
"Are you trying to tell me that the stock traders didn't benefit from having insider knowledge?"
Comment: I'm inclined to agree with you, but the dictionary does not seem to bolster your claim that "profit from" is a pejorative.  See for example https://dictionary.cambridge.org/us/dictionary/english/profit-from-sth  *"I profited enormously from working with her."*
Comment: "Sharon profited immensely from all her studying." I fail to see how that is anything but wholesome.
Comment: @Andrew 'Usually' does not mean 'Always', but I will concede that 'usually' may be too strong a term. I will edit the answer to better convey the ways the term can be used.


Determing limits of rotation in a robot workspace

Question: How to determine the limit range of end effector orientation (Roll-Pitch-Yaw) at one specific point(XYZ)?I had derived Forward/Inverse kinematic. I'm making a program for 6DOF articulated robot arm so that the user can know the limit of tool rotation in Global axis(Roll-Pitch-Yaw) at a certain point.
Comment: I'm not familiar with OpenRAVE. I've seen it could be used in python. Could it be used in visual Basic(VB.net) programming?
Answer: The kinematic answer to this question is pretty complex, but I'll answer it in the way in which I would attack this problem. If you're trying to understand the math behind what is going on, this might not be the answer you're looking for:
I don't know if you're familiar with OpenRAVE, but it is a really nice project that has a tool called IKFast. IKFast is a tool that [attempts to] provides automated analytical inverse kinematic solutions to any serial manipulator. OpenRAVE has built many very useful tools around their ability to create analytical solutions, one of which is the ability produce all the possible joint space solutions to a workspace pose. This example shows what I'm talking about.
All you have to do is create a model of your robot that is OpenRAVE friendly and run that example which spits out an array of joint value arrays that correspond to all the possible solutions to the pose. There is a tool that converts ROS's urdf models to openRAVE models in case you're already using ROS.
I realize there is a programming learning curve to learning OpenRAVE but I believe that curve is much easier to overcome than the curve associated with understanding the complexities of analyzing the inverse kinematics of a robot arm manually. Not to mention, when you solve the kinematics of an arm, its only good for that particular arm. But if you learn how to do this using OpenRAVE, you will be able to do it quickly with almost any arm in the future.
Comment: In that example, they use Transform6D ik model, but in your case you'll want Translation3D
Answer: I will explain how to determinate the "normal" three dimensional workspace and then extrapolate to orientation. I hope to be useful.
Let $q$ the position of your robotic arm motors, so its value describe completely the position of your manipulator at each time. First we suppose that the motors of our robot have no limits so, abusing of the notation, we write $q \in \mathcal Q$, i.e., the configuration space and the joint's velocities $ \dot q \in \mathbb R^n$ for all $\mathcal Q$. Now we call $p = [\matrix{x^\top \psi^\top}]^\top$ the column vector with position and the euler's angles. Now, the differential direct kinematics reads
$$
\dot p = J(q) \;\dot q
$$
Where the jacobian $J$ has to parts
$$
J=\pmatrix{J_x \cr J_\psi}
$$
This equation can be readed as "for infinitesimal changes in the joint's positions, give me the infinitesimal changes in the end-effector's positions/orientation". In fact velocity deals with infinitesimal displacement in infinitesimal time.
The limits of the operations space $\Omega \in \mathbb R^3$ of a manipulator are the points where no infinitesimal changes of the joints positions gives infinitesimal changes in space positions. In other words, at these points it is not possible to achieve displacements in, at least, one direction.  This means that it the joint configurations $\bar{q}$ is in the limit of hte workspace if
$$
\mbox{Rank}\;( J_x(\bar{q})) < 3
$$
because there is at least one direction of the three dimensional space $\mathbb R^3$ that is outside the co-domain of the linear mapping given by the matrix $J_x(\bar q)$
The same reasoning can be applied to orientation. We looks for points in $\mathcal Q$ where infinitesimal changes in the joint's positions give no change in some orientation parameter, say an euler angle. The problem of using the previous formula as $\mbox{Rank}\; J_\psi$ is that the matrix $J_\psi$ could have a rank less than 3 because a representations singularity. That can be overrided using another  minimal orientation representation like quaternions, or simply changing the used euler angles in the singular points.
Now if each motor have its limit we write  $q_i \in [q_{i}^0, q_i^1]$. We call $\partial \mathcal Q $ the set of all configurations $q$ for which at least one component is in its limit.  We have that for $ q \in \partial \mathcal Q $ there is at least one $i$ for which $\dot q_i \in \mathbb R^+$ XOR $\dot q_i \in \mathbb R^-$, i.e., for the joint $q_i$, when it is at its upper limit, necessarily $\dot q \le 0$, and, when it is at its lower limit, necessarily $\dot q \ge 0$. For the limits of the workspace $\Omega \subset \mathbb R^3$ we have that the formula $\mbox{Rank}\;J_x < 3$ cannot be used in $\partial \Omega$, because at these points the domain of $J_x$ is not a vector space. At the points  $\bar q \in \partial \mathcal Q$  there is one direction that is forbidden for $\dot {\bar q}$, the mapping of that directions $J_x \dot{\bar q}$ is also a forbidden direction if and only if it is linearly independent of the mapping of all possible velocities $J_x \dot q_j$   in the three-dimensional space, then it is a limit of the workspace. In other words, a forbidden joint velocity maps into a forbidden end-effector displacement if and only if, there is not another allowed infinitesimal joint displacement that maps into a displacement in that direction. The same reasoning can be applied to orientation, taking into account the representations singularities.
So, your software shout do this:

in $\mathcal Q$ just seek for the values of $q$ where $\mbox{Rank}\;J_\psi < 3$ taking into account the representation singularities.
for each point in $\partial \mathcal Q$ you have to identify the forbidden velocity, say $\dot z$ and take its mapping $v = J_\psi \dot z$. Now construct the matrix $J'_\psi$ removing the $i$ column of each joint that lies in its limits. If $v^\top (J'_\psi) =0 $ then the direction is a limit in the orientation. Always taking into account the representations singularities!


What happens if the tokenURI api serves a different metadata?

Question: The way to reference the actual payload of the NFT is a centralized endpoint. When I create the NFT I might provision an API with an endpoint that serves a particular piece of data. What's to stop me (or anyone) to modify the endpoint after the token is sold?
Answer: Nothing.
That's one of the reasons why services such as IPFS are preferred. With IPFS you can't change the contents while keeping the same URL.


The leaves of my aloe plant are growing stacked. Is that okay?

Question: So I have had this aloe plant for three years and she has been doing fairly well, producing plenty of pups (the ones in the pot have grown since I separated 7 from her 4 months ago) but I have noticed that her leaves are growing on top of each other instead of fanning out. Should I be worried or is there something that I can do to help her?
Thanks in advance!
Comment: Does the pot have drainage holes? How close to a window is your plant - trying to establish how much light it gets...
Answer: No, it's growing perfectly.  Believe it or not Aloe vera exist no where naturally in the world.  It is thought that is comes form North Africa.   Today, we have many plant that we call Aloe vera that are not true Aloe vera.  Some growing in spiral and some grow stacked.  Many aloes grow stacked.
Comment: Thank you for your reply! This is my first plant and I want to do right by her.
Answer: The light question by Bamboo above is an important one. If this is in fact Aloe vera, it looks starved for light. Unless it is in front of a south-facing window it's probably not getting enough light for the typical compact growth habit.
Has this plant been fertilized? excessive fertilizer will also cause abnormal growth. Looking at the plant, it appears it may have been fertilized relatively recently. Note short leaves lower on the plant, longer leaves near the top.
So, to address your specific question; your plant is not exhibiting typical Aloe vera growth. To improve the compactness of the plant it needs more light. If you are fertilizing you should cut back until you are able to provide better light.
Comment: I have not fertilized the plant since I have had it. To address the short leaves at the bottom, they are from where I have cut some off. I can try it by a more south facing window, however the only option is facing west and I have a younger aloe plant growing there, otherwise north facing is my only option in my unit.
Comment: As long as you're OK with it, do what you can. It isn't normal growth, but I've seen much, much worse. You've done well by removing the offsets and should continue that . They can get very pot-bound left to their own devices.
Comment: I have moved it to where it will hopefully get more light. Thank you for your help!


Identify this succulent?

Question:
Can you help me identify this plant?
Answer: Moonstones a species of Pachyphtum. Also known as Sugaralmond plant. The meaning of the name Pachyphytum oviferum is thick plant bearing eggs. The stems (20 cm long, 1 cm thick) rise then fall with about 15 leaves. These leaves are 3 to 5 cm long, 1.8 to 3 cm wide and 8 to 17 mm thick.
Leaves are pale blue-green to bluish-purple, looking like a sugared almond confection.[1]
The inflorescence consists of a 30 cm stem bearing scarlet, bell-shaped flowers
Tip:
A good way to tell if your moonstone plant needs watering is to examine the leaves. If they appear plump and feel firm, the plant doesn't need to be watered. If the leaves appear wrinkly or feel soft, it's time to water. Since overwatering is the main cause of most succulent problems, it's better to underwater than to water too frequently.

Identify this succulent?


Earth-sun distance

Question: I understand that the moon - Earth distance is increasing as the friction of tidal action causes energy loss. Does this mechanism happen with the Earth and other planets, is the Earth - Sun distance changing?
Answer: Yes, the Earth is moving away from the Sun in a course of millions of years, so the moving away is about as fast as the Moon's from Earth. However don't worry because as the Sun gets older it also gets hotter so the habitable zone moves together with Earth or so. At the peak of the Sun's red giant phase the Earth is said to be either there where Mars currently is (about 50% farther from the Sun) or there where Jupiter currently is (about 5 times farther). We don't know exactly, there are several models. But we do know that the Earth and the Sun move slowly away of each other, just like the Moon from the Earth (the Moon reportedly moves away at about 1.6 inches a year on average, and with Earth-Sun it is similar). All planets' orbits are moving away from the Sun slowly.

Earth-sun distance


About Acknowledgements part

Question: I had a research stay abroad in an Institute 2 years ago. A short while after leaving institute (about 1 month later) I submitted an article related to my work there to a journal. Recently my article has been accepted to publish.
As I had an email address belongs to hosting server of the institute where I was working there, I want to write that as my email address. Is it right to write email address and the name of institute as the contact address for my article whiles I have left there? In addition,
Comment: Use an email address that will be valid for a long time.
Comment: Or for such case there is appropriate to select "corresponding author" - may not be the first author, but e.g. your supervisor or head of the lab which very probably work long time in an Institute and will do in future.
Answer: This may vary from field to field, but in my experience (chemistry) it is always the case that you list your affiliation as the institution(s) where you performed your work; where appropriate, you can list more than one affiliation. In the case that an author's affiliation has changed since the work was performed, the convention is to add an additional "Currently at" or "Presently at" affiliation - your publisher would be able to give the details of how to do this for your article.
For an example of a publisher's take on this, see this excerpt from the ACS publications author guidelines:

Institution Address: The author affiliation(s) listed should be the institution(s) where the work was conducted. If the present address of an author differs from that at which the work was done, that address should be given in an Author Information note

About Acknowledgements part


Pumpkin carpaccio: correct use of the name

Question: IN my view, carpaccio is thinly sliced beef, nothing else. But now, it seem OK to serve salmon carpaccio, or even, as I recently saw, pumpkin carpaccio. Am I to assume that everything thinly sliced and spreaded on a plate can be called a carpaccio nowadays? Can I expect, say, cheese cake carpaccio soon? Or is that still very liberal pretentious use of the name of a specific dish?
Comment: I'd argue that it needs to not only be thinly sliced, but also raw and served with a light dressing.  And more likely meat or at least a protein.  But if you're trying to be fancy, 'pumpkin capaccio' sounds fancier than 'shaved pumpkin salad'.
Comment: So, it is basically salad? We must fear the day we get a lettuce carpaccio...
Comment: @MarcLuxen The usage you're seeing here seems to be restricted to shaved/thinly-sliced things, not leaves that are already thin and flat. That is, the process of making it is very similar to beef carpaccio, just with a different ingredient instead of beef.
Comment: What if you shave the lettuce?
Answer: "Pumpkin carpaccio" sounds reasonable to me. It's fairly clear what it means: something like carpaccio, but made with pumpkin.
I think as long as people generally understand what's meant by the term, there's not really much point in trying to deem it "correct" or "incorrect". Sure, carpaccio is a fancy foreign food, so this might sound fancy or even pretentious depending on context, but it's still a reasonable thing to say. (And this isn't a new usage; for example here's a melon carpaccio from 2003.)
Of course, this doesn't change what the canonical carpaccio is; that's still going to be meat or fish. But it's fairly typical to combine multiple terms to describe something, even if one of the terms individually definitely wouldn't suggest the right thing.
For example, I'm sure you wouldn't blink an eye at use of the term "tofu hot dogs", even though "hot dog" on its own clearly means meat. The combination of the terms doesn't mean "hot dogs can be made of whatever you want", it means "this thing is like a hot dog, but made with tofu." And if someone tries to say "technically, that's not a hot dog" people will most likely just roll their eyes.
Perhaps some of the issue here is that carpaccio is a foreign word in English, and in Italian the usage is likely a lot more restricted. But in English, people are going to say what it makes sense to them to say, and combining terms like this generally makes sense. (That said, even Italians may be flexible; for example here's a zucchini carpaccio, posted in 2003, that's apparently inspired by the version at a restaurant in Rome.)

As a final note, you said carpaccio means just beef to you. Even the Italian Wikipedia page says it includes meat and fish, not just beef. If you're more picky than Italians about the definition of a traditional food, I think you may be taking it a little too far.
Comment: Does a hot dog contain meat? Really? ;-)


txt file into pandas

Question: I have a txt file where values are randomly separated, sometimes there is a single space, and sometimes there are many. I am importing the file into pandas with pd.read_csv, but I get only one column in my DataFrame.  How can I define the sep parameter to read the values properly?
Answer: Do you only need to differentiate between one or more spaces?
If so, maybe you can make use of a regular expression separator as listed in the pandas docs.
Something like this:
pd.read_csv(... sep='\s+', ...)

Also, consider adding the parameter delim_whitespace as such:
pd.read_csv(..., delim_whitespace=True, ...)

Comment: Thank you. I think I've found some other way. I will try with read_fwf. I think I will be able to cover most of the values with that instead of read_csv

txt file into pandas


Is hierarchial a word?

Question: I've found one reference that says hierarchial is an alternative form of hierarchical, but it's an unreferenced resource.  Some wiseacre wrote a bug fix for my software saying hierarchical was the only spelling of the word and I'd like to prove said wiseacre wrong. So, can someone crack open the Oxford English Dictionary with the tiny print and help me out?
Comment: The online OED does not have _hierarchial_ either as an entry or as an alternative spelling. It does however have _hierarchal_, with no cross-reference between that and _hierarchical_.
Answer: Neither Oxford Dictionaries nor the OED has an entry for hierarchial, but the OED does have entries for hierarchal and hierarchic as well as hierarchical. This, however, is not to say that hierarchial doesn't exist.
Answer: Between "a word" and "not a word" is a no-man's-land where the casualties of past flame wars lie bleeding.
That said, your proposed variant is wobbling on two weak legs, not only is the -ial unusual here at best, but the heir- is generally considered a typo when it happens.
You might be able to show it meets the condition of at least having some use, but it wouldn't be advisable to use.
For that matter, I can find jerarchy, jerarchye, cherarchy, ierarche each mentioned in the OED as having been forms used for hierarchy, but that doesn't make any of them spellings to use in most modern contexts.
Comment: yeah, the most annoying part about the word (whether or not it ever existed in medical terminology) is that it appears to have been removed from government websites probably by some gigantic spell checker in the sky.  It was used, and appears to be copied from US Government sources in our source code hundreds of times, but is no longer found on cms.gov.
Answer: Wiktionary lists hierarchial as an alternative form of hierarchical. (NB spelling)
Google tries to correct to hierarchical, though.
Interestingly, the NIH (which should particularly know the difference between hierarchical and hierarchial) lists their "Office of Acquisition and Logistics Management" Hierarchial Structure. This might be more common in the Sciences and technology.

Hierarchial taxonomy terms should not be unique on different parents.
  You can perform a Hierarchial Run to solve your model for multiple objectives simultaneously. (IBM)
Hierarchial Coassembly of a Cyanine Dye in Poly(vinyl alcohol) Fibrous Films by Electrospinning (ACS Journals)
Hierarchial Task Analysis (book by) Andrew Shepherd
Comment: So, perhaps a medical records program might be more likely to use the spelling "Heirarchial" than something to do with Military or Religious power structures?
Comment: Yes, I would agree with that, although hierarchical would still be more common.
Comment: The fact that it appears only in Wiktionary confirms my opinion that it is the best place to go for misspelled words.

Is hierarchial a word?


What happened to the original Jurassic Park gate prop?

Question: I have always wondered what really happened to the Jurassic Park gate prop, and the "stone" archway.  Does Universal Studios have the "stone" archway for their Jurassic Park ride?
Comment: @Möoz - I presume OP means the actual prop. It's been moved from the original filming location; http://www.kauaisurfclothing.com/jurassic-park-gate-kauai/
Comment: This is a perfectly on-topic question, even if it is asking about a real world prop.
Comment: I'm only going to post a comment since I have no actual clue regarding this gate, but from  former research on large props and even being fortunate to see a few films being filmed (from a distance) near where I've lived, most large props are dismantled and simply trashed or even burned.  The gate wasn't a real gate. It was likely made of molded plastics, plaster and paint.  Often, when shooting is done, large props are destroyed because it's the easiest way to deal with them, rather than paying to dismantle and ship it from Hawaii to Hollywood for storage.
Comment: You mean in real life?
Comment: @Edlothiad Agreed.
Answer: After chasing up a considerable number of people involved in the Hawaii location filming, I managed to touch base with my good friend Rick Carter, the film's Production Designer via email.
His recollection is that he is quite sure that the gate was ...

"...struck and trashed after the filming..."

...and that whatever remained of the gates and materials were obliterated by the elements, notably ...

"...hurricane Iniki [which made landfall] during the end of the production on the island of
  Kauai, Hawaii, which probably damaged them significantly."

It's possible that pieces of the gate could be found nearby the gate site (noting that the poles that are show to tourists aren't actually part of the original since they're nearly a hundred feet ahead of the site where the gate was placed) if one were to look hard enough, but since the gate was likely made out of little more than flimsy sheets of balsawood painted brown for wood and grey for stone, they could literally have gone anywhere.
Comment: @vallismortis - He was the overseas PD so it's unlikely that he'd have had any involvement in the making (or lighting) of the dinosaurs in the set. I'll ask around though.
Comment: This might be a stretch, but could you use your connections to find the answer to this [question about the DNA sequence on the velociraptor](https://scifi.stackexchange.com/q/237365/105798) as well?
Answer: There are several YouTube videos of people going to the location of the Gate filmed in the movie.
7 years ago
4 years ago
This year
The actually Gate was located about 300 feet past these 2 poles. There is nothing left of the gate.
The last 2 give a pretty good description of how to get there if you want to see it yourself.
Comment: If you scroll a little later in the third video, the lady explains that **these aren't the poles that held up the gates, but rather "trail markers", presumably added by locals so that they could show them to tourists**; https://youtu.be/L2wKoHTk1UM?t=423
Answer: Let me answer this in part.
The old gates were constructed out of a haphazardly-welded iron frame, with a mix of concrete, sand and crushed Waialeale volcanic rock used to create the facade (have a look at the helipad prop/Manawaiopuna falls stair case - these are protected original structures, although the pad is in a thousand parts now - these demonstrate the concrete composition as found at the gate location).
I do not know what came of our actual 'wooden' gate prop - I think that was taken away to allow access to the road again after filming, along with the park lettering, but the concrete poles that currently stand on the loop road were absolutely used in the movie to hold and add tension to the 'electric-fence', connected about 12 feet away from the gate and away from the road itself.  These have been repositioned and erected since. The wire was originally looped through holes drilled into the iron framework on both the gate and the poles (you can still where the wires were cut in the concrete posts), with the facade added over the top.
There was a trench that ran along the length of the road up to the gate, holding potted ferns/palms etc. None of this was ever removed from the site outside of locals collecting souvenirs, and some of the plants are still on site, growing naturally in the foot-deep mud on either side of the road.  The trench also still exists and is a great reference to show the road-to-gate filming location - in fact this can also be seen simply using Google earth.  Hurricane Iniki destroyed both the gate prop and the Rex paddock fence, however there is still to this day chunks of concrete with volcanic rock embedded in it lying on the road and through the swamp in that area.
If you look hard enough, you will see that the fence wire was actually reused up at the 'Rex paddock' to stabilise a concrete dam, and the fence iron posts were cut and reused for both the water dam system nearby and the various 4wd gates through the area.  There is still traces of grey paint on some of these. :)
Also… if you look hard enough you will find some of the fence mounts that were concreted to the ground.  They basically look like a circle of concrete around a cut wire in the middle… this wire was used behind the fence to stabilise it and support the whole structure from falling backwards as was the case after Iniki hit the island.
With the final movie coming out shortly, hope this info helps to bring light to some of the secrets that have sat quietly for the last 30 years…. :)
Comment: Hi, welcome to the site. You speak as though you were someone who worked on the film itself. Is that the case, and if so, would you mind clarifying who you are, and what role you played in the making of the film?
Comment: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).


Backing up Master-Master replicated MySQL databases

Question: I have two MySQL 5.5 databases which replicate each other. What's the best way to back these machines up? I would like to prioritise speed/ease of restoration.  Should I add extra slaves to both machines and also replicate there, and then periodically stop those slaves and copy the data somehow? Is a mysqldump enough, or should I be copying the whole data directory somehow?
Comment: If your concern is HA, but the two servers are sitting on the same earthquake fault / tornado plain / hurricane path / etc., it is not very HA.
Answer: This is a Master/Master setup, so I would advise the following

Do not mysqldump from either Master. Both Masters should be used as Active/Passive

Active : Receives all writes
Passive : Replicates from Active (Hot Standby for Failover)

Add an additional slave from each Master

Can be low commodity in CPU since SQL thread processes one command at a time
Should have the same RAM and plenty of Diskspace for Backups

If you do go with additional slaves, you can use either mysqldump or xtrabackup.
Answer:
Master master and write to both nodes? Recipe for disaster!! Avoid doing that.

Now points for answer:

you don't need slaves to both nodes.  As they are in master master, slaving from 1 of them is fine.
if one node is passive, configure backup there.
if writing to both, create slave and setup backup there.
You need logical backup? Use mysqldump.
all innodb? Large db? Use xtrabackup.
Check out how to setup xtrabackup with Holland framework.. physical backup restore will be faster than logical as db grows.
Comment: +1 to this, however, if for some reason your mysql servers are running on Windows then it's only mysqldump for you or maybe mydumper run from a linux server, but not xtrabackup :)


Client unable to authenticate when connecting to WCF service

Question: I have a WCF service hosted in a Windows service. The application is an intranet app, and I have programmatically set the bindings on both the service and the client as:
NetTcpBinding aBinding = new NetTcpBinding(SecurityMode.Transport);
aBinding.Security.Transport.ClientCredentialType = TcpClientCredentialType.Windows;
aBinding.Security.Transport.ProtectionLevel = System.Net.Security.ProtectionLevel.EncryptAndSign;

Both the service and client have endpoints configured with SPNs:
EndpointAddress = new EndpointAddress(uri, EndpointIdentity.CreateSpnIdentity("Service1"));

As far as I know, I have setup the bindings correctly-- and I am usually able to connect to the service just fine. I did however run into a case where on a server running Windows Server 2003 R2, x64, SP2 I get the following exception immediately when the client tries to connect:
INNEREXCEPTION -- Exception Message:
InvalidCredentialException: Either the target name is incorrect or the server has rejected the client credentials.
Stack Trace:
at System.Net.Security.NegoState.ProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Net.Security.NegotiateStream.AuthenticateAsClient(NetworkCredential credential, String targetName, ProtectionLevel requiredProtectionLevel, TokenImpersonationLevel allowedImpersonationLevel)
   at System.ServiceModel.Channels.WindowsStreamSecurityUpgradeProvider.WindowsStreamSecurityUpgradeInitiator.OnInitiateUpgrade(Stream stream, SecurityMessageProperty& remoteSecurity)

I get the exception when I try to connect to the service from another machine in the domain, but if I connect to the service on the same machine running the service it works fine.
The hosting service itself is running as a domain user account-- but I have tried running the service as a Local System and Network Service to no avail. I have checked the Local Security Policies for the server and didn't see anything amiss (i.e. 'Access this computer from the network' includes 'Everyone').
Anyone have an idea of what could resolve this?
I am wondering if I need to do something in Active Directory with respect to the service's SPN? I have read some about using setspn.exe to register or refresh SPNs, but I haven't needed to do this before. Why would this be working with other configurations but not the one above?
Answer: Try and run the service as an account that has local administrator access - if you can't run the service with this much permisison, then I belive you'll need to use setspn.exe as you have alluded to.


Do net returns on mutual funds include expense ratio?

Question: I'm considering an actively managed bond fund (DODIX) versus an similar index fund (VBMFX). Both are high quality intermediate funds. The 10-year return of DODIX (exp ratio 0.43%) is 0.86% higher than VBMFX (exp ratio 0.22%). When financial research companies show 10 year returns (example image below), does the return include the amount deducted from expense ratios? If that is the case, would the yield advantage of DODIX be the entire 0.86%? Or do expense ratios need to be considered resulting in a DODIX yield advantage of 0.65% (0.86% -0.43% + 0.22%)? Thanks
Comment: Can ask this poster. http://money.stackexchange.com/questions/5462/how-to-quantify-differences-in-return-with-low-expense-ratio-vs-high-expense-rati/5478#5478
Comment: In my experience the Dodge & Cox funds are phenomenal. Having said that, I soon as I recommended one (the international fund) to a friend it tanked (along with the rest of the market).
Answer: The published yields include the expense fees.
Be careful when looking at funds to look beyond the historical performance. Read and understand the prospectus and holdings of the fund when you're looking at a new investment.
In this case, the Dodge & Cox fund is looking to provide the highest income possible, including corporate, US agency (SBA, GNMA) and treasury positions. The Vanguard Total Bond attempts to expose you to the entire bond market, which happens to be dominated by US treasury securities. Both are good funds, but have slightly different weaknesses and strengths.
Comment: confirming, so are you saying that when funds post the returns they are after taking the expense ratio into account? E.g., lets say total principal was $100, this grew into $110 end of year, the fund pocketed $1 in expenses. The net return advertised should be $9/$100*100 = 9%. Is that an accurate statement?


Where are the "Connect to Server" settings stored in Mac OS X?

Question: Where are the "Connect to Server" history and favorites stored in OS X?

Hopefully they are in a pList file somewhere as I'd like to sync them between computers using Dropbox.
Answer: They are in ~/Library/Preferences/com.apple.sidebarlists.plist in the favoriteservers dictionary.
Comment: Read via : `defaults read com.apple.sidebarlists favoriteservers`. change `read` to `write` to write, but you have to have a dictionary to write to the plist. If you just want to add one item, you can use `defaults write com.apple.sidebarlists dict-add key, value`
Comment: nice. how can I import / export just that dictionary from the command line?
Answer: I wanted to update this as I was looking and could not find an answer that worked On OS X El Capitan (10.11.5). I started poking around and I found them in a different location.
~/Library/Application Support/com.apple.sharedfilelist/
com.apple.LSSharedFileList.FavoriteServers.sfl

Copy from the old location.
Paste to the new location.
Change the owner (if needed)

Right (CTRL) Click > Get Info > Sharing and Permissions > Unlock > select or add user (making sure it has read/write > Gear > "Make user the owner"
You could also use the terminal with "sudo chown 'username'
'~/Library/Application Support/com.apple.sharedfilelist/com.apple.LSSharedFileList.FavoriteServers.sfl' " making sure to replace 'username' with your actual username.

Relaunch the Finder (might not be required).

In response to the original question, you may be able to put this file in a DropBox folder and run an alias to the Library location. Not sure how it would work with multiple owners and permissions on the file as I don't use dropbox and haven't tested it.


How can I delete soft/motherboard RAID 1 from a different computer?

Question: I have a drive.  It was part of a RAID 1 mirror on a motherboard-based raid controller (nVidia controller on an ASUS A8N-SLI Deluxe), which, if I understand correctly, is considered to be "soft" raid, even though it's independent of the OS.  Both of the SATA controllers on that motherboard are having issues, which means it doesn't recognize that the disk is still in an array.  I've since dismantled that computer and moved the drive to a new one.  I want to repartition the drive, so I booted into gparted and kicked off a resize/move of the larger partition and then growth of the smaller one.  It failed partway through, alerting me that it was having trouble due to the fact that the dmraid driver wasn't loaded and the disk was now a mess (it deleted the first partition and resized the second, but now both appear empty).  It wasn't until then that I realized I was working on the RAID partitions.  I then switched to /dev/sda and found the "real" partitions, at which point I cursed a few times, and then came here.
So my question is this: if I don't care about saving the data at this point, how do I "reset" the disk back to a standard disk, given that it's in a different computer with a completely different SATA controller (now AMD from the ASUS M5A97 LE R2.0 motherboard)?  Can I do this from gparted, or a Gentoo LiveCD (the two live environments I already have discs burned for)? Should I just start the Windows 7 installation at this point, and hope it allows me to wipe it out?
Comment: Well, possibly good news on the data front...a reboot into a fresh gparted environment now shows the new partition size, a fairly full partition, and the partition label on /dev/sda. Still shows the virtual disk though.
Answer: Well that was simple.   Booted Gentoo,  and dmraid -rE did the trick.
Comment: @Karan Whoops, read it on the review and it read weird. Now I see it


ssh login vs ssh authentication

Question: I set up a new system. I have to use ssh XXXX@XXXXXX to login. It wont let me login via telnet . But I didnt set up any keys. So theres nothing to check against. Can someone explain this to me? Also I have another sysstem with ssh and keys, but it asks users for passwords, not pass phrases??
Thanks.
Answer: Telnet is a different protocol from SSH, you cannot use the two interchangeably. Instead of telneting to your host you need to "ssh" using the the ssh command line client or something like PuTTy in windows.
I'm not sure what you mean by "there is nothing to check against", by default SSH allows for both password and keybased auth.
For your other systems you have to make sure you have set up the keys in the correct place. The way it works in breif is:

User mike trys runs ssh firstname.lastname@example.com
The system by default will look in /home/mike/.ssh/id_rsa for the ssh private key.
If the key has a passphrase it will prompt you for it, if not it will just use it.
On the other end hosta will look inside of /home/mike/.ssh/authorized_keys and see if a matching public key to that private key is there, if found it will authenticate you otherwise it will proceed with normal password authentication.

If you try to ssh running as user bob instead of mike, who doesnt have the right key (or doesnt have one at all) then you wont get prompted for a key pass phrase and the remote box will prompt you for a password.
If you want to setup key auth from the start:

ssh-keygen -t rsa (defaults for everything, however you should use a password)
cat /home/username/.ssh/id_rsa.pub (copy output)
Paste the output of the above command into /home/username/.ssh/authorized_keys on remotehost
ssh to the remote host using the user you created the key with to the user where you put the authorized keys file.
Answer: You'll have to make your question clearer to get a better answer, but you don't need a key to login via ssh. You can use the password for the user you're trying to log in as.
If right now your system doesn't let you try to authenticate via a password it may be configured to require public key authentication. Edit the /etc/ssh/sshd_config file on the server and make sure PasswordAuthentication is set to yes.

ssh login vs ssh authentication


Mutually exclusive events are also independent??

Question: Mutually exclusive events are also independent or not ? can some one explain with an example?
Is it compulsory for independent event to be mutually exclusive? what are the relation between both ?
Comment: What was the definition of independent events? $P(A\cap B) =\,?$
Comment: This question is effectively a dupe of http://math.stackexchange.com/questions/941150/what-is-the-difference-between-independent-and-mutually-exclusive-events by the OP, who doesn't seem to have read the answers there :).
Comment: Does this answer your question? [Independent and mutually exclusive](https://math.stackexchange.com/questions/332378/independent-and-mutually-exclusive)
Answer: No, actually if two events are mutually exclusive it is only in a special case that they can be independent. The definitions state that two events $A,B$ are

mutually exclusive iff: $P(A\cap B)=0$, i.e. $A\cap B =\emptyset$,
independent iff: $P(A\cap B)=P(A)P(B)$.

Assume know that $A,B$ are both mutually exclusive and independent. Then combining the above yields $$P(A)P(B)=0$$ which implies that at least one of the $P(A)$ and $P(B)$ has to be zero.

Informal examples: The events $A=$ I will roll a $6$ and $B=$ I will roll a $2$ are mutually exclusive. They cannot occur simultaneously. Similarly the events "rain" and "no rain" etc.
On the other hand the events "rain" and "I will roll a $6$" can occur simultaneously (i.e. the occurrence of the one does not exclude the occurrence of the other) but they are obviously independent, i.e. if you are given the information that it is "raining" or not you cannot in anyway infer whether I will roll a $6$ or not and vice versa.
Answer: Mutually exclusive and independent are almost opposites of each other. If they are mutually exclusive then if one happens the other cannot happen - quite the opposite of being independent. Independence essentially means that if one event happens it has no effect on whether the other event happens. Mutual exclusivity normally arises when considering the outcomes of ONE experiment e.g roll one die. Then "roll is less than 2" and "roll is greater than 4" are mutually exclusive. Independence normally arises when considering the outcomes of more than 1 experiment, e.g roll 2 dice then "roll on die 1 is less than 2" and "roll on die 2 is greater than 4" are independent.


What effect does karma have?

Question: I'm wondering what effects your Karma has in Fallout New Vegas, since they introduced the reputation with different factions?
Answer: Karma is almost non existent in the game. The only use I can see at this point is affecting which companions will follow you. For example, you cannot have Cass as a follower while you remain evil (Technically, you can because of a quest you need her for, but if you talk to her while you have evil karma she will tell you three times to get your act together before she runs off forever).
So long answer short, its strictly for companions as far as I can tell.
Answer: Karma also affects game endings.
http://fallout.wikia.com/wiki/Fallout%3A_New_Vegas_endings
Comment: Can you, please, include more quotes from the link as an example? Probably under the spoiler. I understand, that this is a nice and detailed wiki, etc. etc. but content there may change and having short examples here may benefit the answer. (Still +1 from me).
Answer: in freeside bad ralf and the other guy won't let you shop there and also if your good the king will send you presents a lot and also in bad the thugs in free side won't attack you they run from you
Comment: That's faction/location reputation, not karma

What effect does karma have?


How do I get Vordt's Hammer?

Question: I got the soul of Vordt after killing him, but I read in the wiki that his hammer can be made using it.
But when I try to use it I get 2000 souls but no hammer.
I am new to the souls games. How do I get the hammer?
Comment: Like the answers said you've lost your chance at this weapon into NG+. Honestly, if you really want to use that weapon, I'd just restart on a new character. You can probably get back and defeat that boss fairly quickly now.
Answer: Soul Transposition in Dark Souls 3 is the process of converting a Boss Soul into a Weapon, or Ring. In order to create items you must have the specific Boss Soul, you must have the Transposing Kiln which drops from Curse-Rotted Greatwood, and you must speak with Ludleth of Courland in Firelink Shrine.
Ludlet will convert the souls to items.
Source.
PS: For as far as I know, when a boss soul is consumed to gain souls, you lose the soul, and will be unable to forge it to items. Untill you beat the boss again in NG+ (or new game with an other character ofcourse.)
Comment: You are correct, the boss soul is consumed when you activate it to get souls. Also, the boss soul can usually be transposed into 2 different items, but you can only pick one, so choose wisely.
Answer: Now that you have consumed the soul of Vordt, you cannot get the hammer (until NG+).
To transform a boss soul into a weapon/spell/ring, you have to get the Transposing Kiln from the Curse-Rotted Greatwood (Undead Settlement boss) and give it to Ludleth of Courland (the guy who sits on the throne in Firelink). Once given, you can trade your boss souls with him.
Source : http://darksouls3.wiki.fextralife.com/Soul+Transposition
Comment: he can still get the hammer in ng+

How do I get Vordt's Hammer?


Apache, SSL Client certificate, LDAP authorizations

Question: High there,
Is it possible to mix mod_ssl and mod_auth_ldap so that the authentication is done with the client certificate and authorizations with mod_auth_ldap (Require group)? If so, can you give me some pointer?
Thanks in advance
Comment: you may find this link useful http://comments.gmane.org/gmane.comp.apache.devel/38519
Answer: OK, for those interested, apache requires the presence of an AuthType directive and the validation of the username by some module.
So I have written a very short module that accepts AuthType Any and accepts any username.
The configuration looks like that:
<Location /slaptest>
    Allow from all
    SSLVerifyClient require
    SSLVerifyDepth 1

    SSLUserName SSL_CLIENT_S_DN_CN

    AuthType Any
    AuthAnyAuthoritative on

    AuthLDAPURL "ldaps://vldap-rectech/ou=XXX,ou=YYY,o=ZZZ?cn"
    AuthzLDAPAuthoritative on
    AuthLDAPBindDN "cn=UUU,ou=Users,ou=XXX,ou=YYY,o=ZZZ"
    AuthLDAPBindPassword "******"
    AuthLDAPGroupAttributeIsDN on
    AuthLDAPGroupAttribute member
    AuthLDAPRemoteUserIsDN off
    Require valid-user
    Require ldap-group cn=ADMIN,ou=Groups,ou=XXX,ou=YYY,o=ZZZ
</Location>

Answer: The following has been tested in Apache HTTP Server 2.4.29 against Windows Server 2019 Active Directory:
<VirtualHost _default_:443>
    SSLEngine on
    SSLCertificateFile /etc/ssl/private/tls_server_cert_and_key.pem
    SSLCACertificateFile /etc/ssl/certs/trusted_root_ca_for_client_certs.pem
    SSLVerifyClient require
    # Use the email from the succesfully authenticated client certificate to look up for the AD user.
    SSLUserName SSL_CLIENT_S_DN_Email
    <Location />
        AuthBasicProvider ldap
        # "userPrincipalName" allows to search by the AD user email.
        # "(!(UserAccountControl:1.2.840.113522.214.171.1243:=2))" filters out disabled AD users, so only active AD users are allowed to be authorized.
        AuthLDAPURL "ldap://<ACTIVE_DIRECTORY_IP>:3268/DC=example,DC=org?userPrincipalName?sub?(objectClass=person)(!(UserAccountControl:1.2.840.1135220.127.116.113:=2))"
        AuthLDAPBindDN "CN=apache-bind-user,CN=Users,DC=example,DC=org"
        AuthLDAPBindPassword "<apache-bind-user-password>"
        <RequireAll>
            Require ldap-group CN=Some Group,CN=Users,DC=example,DC=org
        </RequireAll>
    </Location>
</VirtualHost>

PS: I'm not an expert in Apache HTTP Server or Active Directory, so the previous configuration might not be optimal/secure.


How can we protect the vulnerable online?

Question: Recently the company I work for was asked to pitch for creation of a forum targetted at children as part of a website solution.
I think that at least we should reccommend

Human moderation by a trained individual to protect these kids
Code alarm / suspicious analysis into the forum

How has anyone else tackled this and what Ideas do other people have on this?
Answer: It's not an online forum, but they do discuss some of the things they had to deal with to provide a safe environment for children.  Check out the post-mortem of the game team that developed Disney's toontown: http://www.gamasutra.com/view/feature/2027/postmortem_disney_onlines_.php
Comment: +1 - That Disney article is quite a good read!  Thanks for it.
Comment: Read that article, it's very enlightening.
Answer: Think of "online" as being "a crowded place, that contains strangers".  Some of the solutions will be the same, others won't work.
For instance, at a child care business at a mall you can require parents to check children in, and the same parents to check them out.  This type of thinking will sometimes lead to realization that part of security has to be in the parents hands: you can't "confine" children in an online system, so protecting them from going to the rest of the internet has to be their parents job.
But the idea that every child has a responsible adult is probably a very good one.
Answer: Live moderators are probably your best bet. Disney's Toontown actually ran into quite a few privacy/security problems when they missed that kids are often rather clever.
Although I don't know if it's still in there, there used to be a function where you had an "apartment" you could fill with "furniture," SIMS-style, and then display to other players.
So, players intent on subverting the controlled communication would spell out letters in furniture one at a time until a screen name for an uncontrolled chat was communicated. Allegedly, even after that was discovered there was still a system of displaying pictures that worked just as well.
To summarize, you can't cover all the bases. The best you can do is cover the careless and inept, and try to stay heads-up on strange behavior that could indicate somethings up. So if you have to do a "kids forum," I would definitely go with moderators.


SQL Query Visualisation Tool suggestion

Question: I am looking for a tool that gets my SQL query as input and creates a flow diagram.
I need this tool to be database agnostic, meaning, it should be able to create the flow for any query.
Any help is appreciated
Comment: What do you mean by "the flow"? Also, SQL isn't database agnostic, different DB engines have sligthy different syntaxes.
Comment: Are you looking for a visualization of the query, its execution, or its results?
Answer: One possible way is to use SQL Developer and make it do the execution plan. SQL Developer can work with Oracle, MySQL, Microsoft SQL Server, Microsoft Access, Sybase, Teradata and IBM DB2 RDBMS. But for most of them you may not be able to run the execution plan.

SQL Query Visualisation Tool suggestion


Can a coilgun be used to boost a traditionally or non-traditionally chemically powered weapon?

Question: So, I was wondering if for small scale weaponry (150mm guns and smaller) using a coilgun to assist in the acceleration of a traditional chemically accelerated round, either while in the barrel burning the propellant, or after the round has exited the length of barrel required to burn the propellant.
Comment: Could you clarify if 150mm refers to the length of the weapon or the calibre? As 150mm is quite short- the length of an M4, for example is around 800mm in total and the barrel around 350mm. 150mm would in the range of a pistol
Comment: Why do you want to keep the chemical propulsion? Assuming you want to install this weaponary on a spaceship, just go with pure magnetic accelerators, you should have the energy to spare and wouldn't have to carry the propulsion charges.
Comment: Mostly for crafts that do not have the power plant or weight to allow for a purely magnetic accelerator, and 150mm does not refer to length, that would be short.
Answer: It could be used to supplement the speed of a chemically propelled weapon but unless you like the flavor of a hybrid launcher it's probably impractical compared to a strict magnetic or strict chemical system.
The kinetic energy of a projectile is proportional to the square of the velocity. If you have maxed out the energy that you can add to a projectile via a chemical propellant to get a 50% increase in the velocity you'd need to put in more than double the energy. Unless you absolutely need the extra velocity, you're adding an entire extra system that needs to be powered, maintained, and carried for a nebulous benefit.
If modern firearms are any indication getting a minor increase in velocity isn't going to be worth it.
Comment: Something that follows from this: *doubling* the velocity requires the coilgun portion to impart 3x as much energy as the chemical portion. It'd then still have 86% of its velocity if you eliminated the chemical portion, but without chemical exhaust blasting through the coilgun, with ammunition that takes a faction as much space (more room for coilgun power supply), etc. And if it was just increased projectile energy that you were after, that could be achieved by just using a heavier projectile with the same muzzle velocity. You're most likely better off optimizing down to one or the other.
Answer: In principle, you could, however there are going to be a number of practical considerations. For the lengths of the weapon you stated, (~150mm- I'm going to assume this is the total length as opposed to barrel length) you wont have a significant amount of space to fit your coils, and on top of that you are going to need to keep your power source.  Considering that the amount of energy you can impart to the projectile through EM fields is related to the length of the barrel, you would likely not gain any substantial increase in muzzle velocity.
If it did work at all, you would get a small increase in velocity at the expense of a substantially heavier and larger weapon, when you in all likelihood could have achieved the same effect by user 'hotter' ammunition.
Answer: Frictionless barrel + afterburner oomph
https://en.wikipedia.org/wiki/Coilgun#Non-ferromagnetic_projectiles

Though the cost of power switching and other factors can limit
  projectile energy, a notable benefit of some coilgun designs over
  simpler railguns is avoiding an intrinsic velocity limit from
  hypervelocity physical contact and erosion. By having the projectile
  pulled towards or levitated within the center of the coils as it is
  accelerated, no physical friction with the walls of the bore occurs

Physical contact and friction is an issue with chemical firearms too though arguably less than with a railgun.
I could imagine a hybrid setup with a snubnose pistol type chemical firearm.  This accelerates the projectile into the coilgun which accelerates it further.  Acceleration conferred by any firearm is proportional to the barrel length.  The cool thing about a coil gun is that regardless of how fast the bullet is moving when it enters, the coilgun can accelerate it faster.

A superconducting coilgun called a quench gun could be created by
  successively quenching a line of adjacent coaxial superconducting
  coils forming a gun barrel, generating a wave of magnetic field
  gradient traveling at any desired speed.

Good old 1/2mv^2.  The wallop packed will increase as the square of the added velocity.
Of note - a coilgun that worked like an induction brake need only induce a current within the projectile to make it into an electromagnet.  Your bullet does not need to be a magnet itself.
The big question - it is possible to impart spin on a projectile as it travels in a vacuum thru a coil?


How to show total as well as distributed total among categories

Question: There is a total section on my dashboard and below that, a grid with all the list of data. As a total number of items and their total values need to show on top of the grid distributed among categories, I designed something as per the below screenshot, but want to validate that UX-wise it's ok, or is there a better pattern?
Screenshot of total section:

So in the above design, each box contains below details:

Total Profit/Order.
Total Record/Order count.
Title of that box.

I also tried another way to show data in a grid as shown in the below screenshot.
Grid Data screenshot:

How can I improve this so users can get the idea that 1st one is for what value and 2nd one is for what?
Answer: Here's one quick solution for correcting given layout.

1.Primary Title
2.Primary Amount
3.Secondary Amount with title
Hope this helps.
Cheers.


"Could not validate a connection to elasticsearch"

Question: When I install Magento2.4,gettting error like "Could not validate a connection to elasticsearch". I used XAMPP for windows in my localhost. Please help!
Comment: Read this link about setting's file: [network.host: localhost](https://magento.stackexchange.com/questions/320428/magento-2-4-installation-in-searchconfig-php-line-81-could-not-validate-a-conn)
Answer: Prior to installing 2.4, you should've read pre-requisites for it. It requires elasticsearch to be installed. Use this link to install it, also upgrade php version to >=4 if you haven't already. Then you'll be good to go hopefully.


How to understand the difference between transfer and function call using assembly call(g,a,v,in,insize,out,outsize)

Question: I understand that if there is an external function call, it will use all 7 parameters of the call(g,a,v,in,insize,out,outsize). However, I got a question I know low-level transfers like .transfer() will also use the instruction call(g,a,v,in,insize,out,outsize), if wei > 0, I can treat it as transfers, does that make sense? Meanwhile, should there still be 7 parameters for the instruction call?
Answer: CALL can be used for multiple purposes: mainly function calls and variants of sending ethers: transfer payable and call.
To distinguish between function calls and ether transfer, the simplest way is to check if the input data is blank (the 4th item from the stack's top means input length so it's zero). If the CALL is sending ether it has zero input length. Otherwise, the length of the input follows abi encoding (e.g. 4 bytes if calling function without argument)
I used the ethervm.io annotation for the above :
Opcode CALL
Stack : gas | addr | value | argsOffset | argsLength | retOffset | retLength

Value > 0 is not an indicator of transfer because it can be a call to payable function in the external contract (when argsLength > 0).
With argsLength == 0, to distinguished between different variants of sending ethers, you can look at the gas forwarded (the first item from the stack). If it's 0x8fc, it's probably transfer or send. Otherwise it's direct call. Look at this article from solidity docs for the differences between variants for sending ether
Comment: Thanks a lot for your answer! It helped me a lot, thanks!
Comment: Does it answer your question?, if yes please mark it as the answer. Otherwise, you can further comment on what else do you expect from the answer.


When is this localization map injective, if at all?

Question: Let $K$ be a number field and $E$ be an elliptic curve defined over $\mathbb{Q}$. Consider the localization map
$$
E(K)\otimes \mathbb{Q}_p/ \mathbb{Z}_p \rightarrow \bigoplus_{v|p} E(K_v)\otimes \mathbb{Q}_p/ \mathbb{Z}_p.
$$
Can we say when is the above map injective. I am wondering if there is some properties of K that can guarantee injectivity.
Answer: Often it is, but not always. For instance if $K=\mathbb{Q}$ then the map is injective if and only if the rank of $E(\mathbb{Q})$ is at most $1$. This is because the $p$-adic elliptic logarithm of a non-torsion point $P\in E(\mathbb{Q})$ is non-zero.
The corank of the target is equal to $[K:\mathbb{Q}]$ while the rank of the Mordell-Weil group is often much smaller. In some sense we could expect that the map is as injective as it can be. By composing the map with the logarithm map from $E(K_v)\to K_v$, the question  becomes the analogue to the Leopoldt conjecture for units in number fields; it will have to do with the linear independence of the $p$-adic elliptic logarithm maps. So a first guess would be to think that your map is injective when the rank of $E(K)$ is smaller than $[K:\mathbb{Q}]$; but that is not true.
In fact, there is one important difference to the case of units in that the Galois structure of $E(K)$ is not as simple. Suppose the curve $E$ is defined over a subfield $k$ of $K$. For simplicity suppose $k=\mathbb{Q}$. Assume that $K/\mathbb{Q}$ is Galois with finite group $G$. Then the target space $\prod_{v\mid p} E(K_v)\otimes \mathbb{Q}_p$ is isomorphic to a free rank $1$ module over $\mathbb{Q}_p[G]$ by the logarithm map. Now consider the Mordell-Weil group $E(K)\otimes \mathbb{Q}_p$ as a $\mathbb{Q}_p[G]$-module. This could be of $\mathbb{Q}_p$-dimension smaller than $[K:\mathbb{Q}]$, yet your map is not injective because a particular representation $\rho$ appears more often in the Mordell-Weil group than in $\mathbb{Q}_p[G]$, i.e., more often than $\dim(\rho)$. In this situation it would be possible to conjecture the following: Your map is injective if and only if $\dim_{\mathbb{Q}_p}( E(K)\otimes \mathbb{Q}_p)^\rho \leq \dim_{\mathbb{Q}_p}(\rho)$ for all irreducible $\mathbb{Q}_p[G]$-modules $\rho$.
I guess one could make a general conjecture as to when it is injective depending on the field of definition of $E$. Though maybe there are other restrictions. Ultimately an answer to this question will come from transcendence of values of $p$-adic ellitpic logarithms.
Comment: .. and to answer the actual question. A condition on $K$ only will never do. Just take a rank $2$ curve over $\mathbb{Q}$ then the map will be non-injective for all $K$.
Comment: Since you mentioned that this map is as injective as it can be, should one expect that for elliptic curves $E/\mathbb{Q}$ of rank 0 or 1, as one varies over those $K/\mathbb{Q}$ of fixed degree where the rank of $E$ is still $\leq 1$, the kernel stays bounded?
Comment: @deanjana That is a completely different question. Wlog we may also fix the Galois group $G$ of the Galois closure of $K$ and even the representation $\rho$. Then you ask how often is the $\rho$-part of the Mordell-Weil group of dimension larger than $\dim\rho$. Root numbers sometimes force rank growth, but that will never force more than one copy of $\rho$ I believe. I would tend to believe that it is very hard to find growing fine Mordell-Weil groups. So maybe yes, the corank of your kernel stays bounded. I doubt one can prove much about this.


El gamal correctness

Question: I tried to find online for the correctness of El-Gamal, but I couldn't find any good resource that will teach me how to show the correctness of El-Gamal, could any body show me how is it done?
Comment: It is quite easy and straightforward. Could you tell us more about the problem you encountered? Could you try to write down your computation to verify correctness and show us where you stop?
Answer: Say that $y = g^k \pmod p$ is the public key ($g$ a generator of the group and $p$ a prime, $k$ a secret random integer known as the secret key).
To encrypt $M$ one chooses a random $r$ and compute $(c_1, c_2)$ as $c_1 = g^r \pmod p$ and $c_2 = M \cdot y^r \pmod p$.
You should show that the decryption works: $M = c_2 \cdot (c_1)^{-k}$.
$c_2 \cdot (c_1)^{-k} = M \cdot y^r \cdot (g^r)^{-k} = M \cdot g^{kr} \cdot g^{-kr}  = M \pmod p$

El gamal correctness


Transmission vs reflection grating

Question: What are the advantages/disadvantages of a transmission vs a reflection grating? It seems like  a transmission grating would be easiest to use. I'm trying to get a spectrum from Thomson scattered light in a plasma. The broader the spectrum of the scattered light, the hotter the plasma. It's a weak effect, so it's important to keep as much light as possible. It would also be important that the image of light is not distorted (at least not along a chosen axis... obviously one direction will have the light spread).
Comment: I think no-one's answered this yet because it really depends on what you're trying to do with it. Can you make your question more specific?
Answer: Transmission gratings are less sensitive to polarization and alignment, but cannot transmit at higher wavelengths (ie typically ~2000nm).
Answer: Transmission gratings are less effective if they consist of absorptive grooves. Thus, transmission gratings make sense to around $1000$ lines/mm. There are also holographical transmission gratings, where the spatial variation is not seen in amplitude but in phase. Those gratings show - of course - a different behavior in its spectrum, but have higher light throughput/efficiency.
Reflective gratings, on the other hand, reflect all light and modulate only the "not-wanted" light. Thus they have better efficiency and - as said already - maintain the polarization in a better way.

Transmission vs reflection grating


Lower bounds for norms of commutators

Question: For various reasons I became interested in bounds on the norm of commutators of operators. For instance, if $B(H)$ is the algebra of bounded operators on a Hilbert space, one may ask for a lower bound on $||[A,B]||$ in terms of properties of $A$ and $B$. (It is clear that one can not have simple norm estimates since for $A=1$ one has $[A,B]=0$.) One may consider questions like: Is there a subspace $\Omega$ of $B(H)$ such that $||[A,B]||\geq ||A||$ for all $A\in\Omega$ (keeping $B\in B(H)$ fixed)? More generally, I'm also interested in similar questions for the $L^p$-norm $||A||_p=(\operatorname{tr}|A|^p)^{1/p}$. In the literature, one finds a flora of results concerning upper bounds on norms of commutators (however, for the $L^p$-norm, results are sparse). Is anyone familiar with these types of questions, concerning lower bounds? Can someone point out relevant sources?
Comment: Yes, but I didn't say much about lower bounds.
Comment: Did you check out: http://mathoverflow.net/questions/27345/norms-of-commutators
Answer: This doesn't address the full generality of your question but it might at least suggest places to hunt in the literature.
Thinking of $B$ as fixed, you're asking for a lower bound on the norm of $\operatorname{ad}_B(A)$ as $A$ varies in some subspace. If we take $A$ to range over all of $B(H)$ then MathSciNet directs me to

J. G. Stampfli. The norm of a derivation.
Pacific J. Math. Volume 33, Number 3 (1970), 737–747

in which it's proved that $\Vert \operatorname{ad}_B \Vert$ is equal to twice the distance of $B$ from the subspace ${\mathbb C} I$.
One can consider similar problems for norms of inner derivations on other C*-algebras (the von Neumann case seems apparently behaves just like $B(H)$, see L. Zsido, The norm of a derivation in a $W^\ast$-algebra, Proc. Amer. Math. Soc. 38 (1973), 147–150). In the unital case, it seems like a good place to find out what's known is

MR2274022 (2008f:46071)
  R. J. Archbold, D. W. B. Somerset. Measuring noncommutativity in $C^\ast$-algebras. J. Funct. Anal. 242 (2007), no. 1, 247–271.
Comment: Thanks! I will look into these papers and their references. Looks promising!
Answer: The following result is classical: let $\mathbb H$ be a Hilbert space, and let $A,B\in \mathcal B(\mathbb H)$, then
$
[A,B]\not=I.
$
In finite dimension, just take the trace, and if the dimension is infinite, compute $[A,B^N]$.
This indicates that the most interesting questions about commutators are dealing with unbounded operators. The paradigmatic examples are the creation ($A_+$) and annihilation operators
$(A_-)$
$$
A_\pm=D_t\pm i\frac t2,\quad D_t=-i\partial_t.
$$
We have
$
[A_-,A_+]=I,
$
which is a way to express the uncertainty principle.
$A_+$ is injective with an image of codimension 1 (Fredholm index $-1$) whereas
$A_-$ is surjective with a kernel of dimension 1 (Fredholm index $1$). In the Hermite basis,
$A_+$ is a forward weighted shift, $A_-$ its adjoint, a backward weighted shift.
An interesting category of unbounded operators is given by pseudodifferential operators: taking $A=a(x,D)$ with order $m_1$, $B=b(x,D)$ with order $m_2$, the principal symbol of the commutator $[A,B]$ is $\frac 1i\{a,b\} $ where $\{a,b\}=\partial_\xi a\cdot \partial_x b-
\partial_x a\cdot \partial_\xi b
$ is the Poisson bracket:
$$
\underbrace{[a(x,D), b(x,D)]}_{\text{order $m_1+m_2-1$}}\equiv\frac 1i\{a,b\}(x,D)  \mod{\text{operators of order $m_1+m_2-2$.}}
$$

Lower bounds for norms of commutators


Keyboard Pressing Application

Question: Imagine that problem. When you play some games, sometimes happens situations like "press quickly the X key to escape from ropes" or "press quickly the X key to fill the rage gauge", etc.
Of course, that kind of game destroy keyboards, joysticks, mouses, etc.
I would like to know about programs (preferentially free) that, by example, will press the 'x' key in intervals of, by example, 300ms.
Remember that the built in Windows "keyboard repeat rate" doesn't works for games. When you press (and hold) somekey in the game, the key is not repeated as in default Windows Applications.
Thanks!
Answer: AutoPressKey will do it for you I believe.

Keyboard Pressing Application


Origins of meteorites?

Question: I am aware that the vast majority of meteorites come from the asteroid belt (including 4 Vesta), with some from the Moon and Mars. Are there any other locations from which meteorites have originated (the Kuiper belt? Ceres?). Here it mentions that carbonaceous chondrites formed farthest from the Sun. Is that still within the asteroid belt?
Comment: Well there's the ones from Japan, but I'm not sure they count ;-) [Why would a box full of 1cm balls released into LEO be so scary to an engineer supporting the ISS?](https://space.stackexchange.com/q/21891/12102)
Answer: Kuiper belt (and beyond) objects do sometimes come into the inner solar system: we call them "comets".  However comets have a large proportion of volatiles (water etc) and the non-volatile matter tends to be in the form of small dust particles, neither of which form useful meteorites  Ceres is also covered mostly in ice, so even if some was ejected into space and reach the Earth, it wouldn't survive the descent.
An older paper wonders if very old dead comets might be a source of meteorites, but notes that none have been found. A much more recent paper describes a small (100 µm) particle of cometary dust found embedded in another meteorite.  This dust particle would have come from the outer solar system.

Origins of meteorites?


BlackBerry: Are there any examples on how to localize BB apps for right-to-left languages like Arabic, Hebrew?

Question: I want to localize my Blackberry app to use Arabic language which is right-to-left. I am using SDK 4.5 because I want my app to be forward compatible. I read in this article guidelines for rtl localization. However, none of their suggestions worked (FIELD_LEADING, USE_ALL_WIDTH and isLeftToRight). What should I do exactly to make my fields (Labels and ObjectChoiceFields) align correctly to the right of screen? Are there examples?
Answer: These are features of the 6.0 OS, so they won't work on 4.5.  Yes, they really are that far behind.


Vortex Air Intake

Question: Why is a vortex air intake in an engine cause the fuel to burn more efficiently within a vehicle. Why is this more efficient.
Comment: What kind of engine and fuel?
Comment: fuel injection, automobiles
Answer: As best I have been able to tell, vortex air intakes are mostly a scam designed to sell useless car modifications to people, as discussed on this HowStuffWorks article. In case of the inevitable future link rot, I'll paste the article below:

The internal combustion engines in cars and trucks are essentially large air pumps: The action of the pistons sucks in a precise mix of fuel and air, which is then ignited and vented out through the exhaust. The energy of the burning mixture forces the engine to suck in more of the mix, repeating the cycle. And this next piece of fuel-saving quackery plays off misunderstandings about that process.
Engineers pay close attention to airflow into an engine. The amount of turbulence in the flow can affect how fuel and air mix as they enter the combustion chamber, and this can impact an engine's efficiency. The creators behind intake vortex gadgets often claim that their devices alter this airflow in a way that improves fuel-to-air mixing, improving fuel burn and consequently getting more mileage out of each gallon [source: Allen].
The main warning flag with vortex generators is that they're actually based on antiquated engine technology. Automobiles built before engine management computers became commonplace did rely on the shape and length of intake bodies to manipulate fuel and air mixing. But modern vehicles have computers that constantly adjust fuel flow to match airflow: Create a turbulent airflow in the intake (as a vortex generator does), and the car simply adjusts the amount of fuel it injects [source: Tony's Guide to Fuel Saving Gadgets]. The result? The car may actually run worse, since it's compensating for altered airflow by altering the fuel flow. The computer's fuel-flow rate is calibrated at the factory to provide the right amount of fuel for each combination of driving speed and engine load. Alter this, and you're more likely to hurt performance than improve it [source: Allen].

Basically the gist of it is that vortex intakes might have a small effect on extremely old cars (manufactured before the 1970's), but on modern cars they have no effect at all.
Comment: That was good to know.  Thank you ughh..why you chose that name I don't know.  Thank you DD.
Comment: @Jody: "ughh..why you chose that name I don't know." Because I am the greatest trash can on Earth.

Vortex Air Intake


Do puppies "grow into their feet"?

Question: Some puppies seem to have feet to big for their body.  I have often heard that this is an indicator of a dog that will grow to be a larger dog.  Is there any truth to this idea?  Is a the size of a puppies feet in relation to their body, really an indicator of adult size?
Comment: I have no hard evidence to support this, nor do I have a long experience of raising dogs from pups to adults, so I can't answer definitively, but for both of my pups their feet size did seem to correlate to their adult size.
Answer: The surest indication of a pup's eventual size is the size of his same sex parent, if he is purebred.  It's a big guess if he is a mix.
I can say definitively that paw size is not always an indicator of the finished size of the dog.  I have one purebred German shepherd with huge feet, twice as big as the next dog (also purebred German shepherd), and the bigger one is the one with the smaller feet.  People are always asking me if he's going to grow into his feet.  No, he is full grown.  He just comes from a variety of German shepherd that are large boned and therefore have large feet.  He also has a comparitavely big head, just like his parents.

Do puppies "grow into their feet"?


Showing that a space is Hausdorff

Question: Suppose $X$ is compact and Hausdorff and that $f:X \to Y$ is continuous, closed, and surjective. How can I show that $Y$ is Hausdorff?
Comment: Do you know what you need to prove in order to show that? Any ideas or tries?
Comment: Try reading [here.](https://math.stackexchange.com/questions/1093373/question-about-quotient-of-a-compact-hausdorff-space)
Answer: Since $X$ is compact Hausdorff, $X$ it is normal.
Next, since $f$ is closed, the single-element subsets of $Y$ are closed (as $\{y\} = f''\{x\}$ for some $x \in X$.) It follows that for each pair of distinct $y_0, y_1 \in Y$, the sets $X_0 = f^{-1}(y_0)$ and $X_1 = f^{-1}(y_1)$ are disjoint closed subsets of $X$. Noting that $X$ is normal, you can separate $X_0$ and $X_1$ using open-sets with disjoint closures. The remaining bit is to turn the open-sets separating $X_0$ and $X_1$ into open subsets of $Y$ separating $y_0$ and $y_1$.
Comment: "Turning $X_0$ and $X_1$ into open sets.... " seems problematic. Can you finish this, or give a hint?
Comment: Given any separation of $X_0$ and $X_1$, by disjoint open sets, $U_0$ and $U_1$. The image under $f$ (a closed map) of the complement of $U_k$, namely $C_k = f''(X\backslash U_k)$ is a closed subset of Y with $y_{1-k}$ \in C_k$. and $y_k\not\in C_k$. Hence
Comment: .. letting $V_k = Y \backslash C_k$ be the open complement of $C_k$, you have $y_k \in V_k$  and $y_{1-k} \in V_{1-k}$. Moreover, $V_{k} \cap V_{1-k}  = Y \backslash (C_k \cup C_{1-k}) =\emptyset$
Answer: Let $y_1 \neq y_2$ be distinct points of $Y$. By surjectivity we have $x_1 ,x_2 \in X$ such that $f(x_1) = y_1 , f(x_2) = y_2$. In particular, $f[\{x_i\}] = y_i$ for both $i$ and as in $X$ singletons are closed (Hausdorff implies $T_1$) and $f$ is a closed map (first time we use it), we have that both $\{y_i\}$ are closed in $Y$.
Now, define $F_i = f^{-1}[\{y_i\}] \subseteq X$, $i=1,2$. $F_1$ and $F_2$ are disjoint closed (by continuity of $f$) subsets of $X$, which is compact and Hausdorff and thus $T_4$ or normal. So in $X$ we can find open disjoint subsets $U_1, U_2$ such that $F_1 \subseteq U_1$ and $F_2 \subseteq U_2$.
Now define $O_i = Y\setminus f[X\setminus U_i]$ for $i=1,2$.
These sets are open as $f$ is a closed map and complements of open sets are closed and complements of closed sets are open.
For each $i$ $y_i \in O_i$: suppose $y_i \notin O_i$ then by definition $y_i \in f[X\setminus U_i]$ so $y_i = f(p)$ for some $p \in X \setminus U_i$. But by definition $p \in F_i$ as it maps to $y_i$ and so should be in $U_i$ by $F_i \subseteq U_i$, a contradiction with $p \in X \setminus U_i$. This contradiction shows that $y_i \in O_i$.
$O_1 \cap O_2 = \emptyset$. Suppose that $y$ lies in both. Then for some $x \in X$, $f(x) = y$. As $U_1$ and $U_2$ are disjoint, $x$ must lie in $X\setminus U_1$ or in $X \setminus U_2$ (or both); suppose it lies in $X \setminus U_j$ for some $j \in \{1,2\}$. But then $y = f(x) \in f[X\setminus U_j]$ which means $y \notin O_j$, which is our contradiction.
So $O_1$ and $O_2$ are the required disjoint open neighbourhoods of $y_1$ resp. $y_2$.
Sanity check: we used the closedness of $f$ and its Hausdorffness too, (also to get normality from the combination with compactness), and the continuity of $f$ and its surjectivity. The proof would also have worked if $X$ would have been merely $T_4$ (normal and $T_1$) and $f$ the same (continuous closed surjection).
Answer: Let $y_1 \neq y_2$ in Y. Pick $x_1 ,x_2$ such that $f(x_1)=y_1$ and $f(x_2)=y_2$ Claim: there exist neighborhoods U and V of $x_1$ and $x_2$ such that $f(U) \cap f(V)$ is empty. [ This is where continuity is used]. If not, for any neighborhoods U and V there exist points $t_{UV}$, $s_{UV}$ in U and V such that $f(t_{UV})=f(s_{UV})$ Order the pairs (U,V) by $(U,V) \geq (S,T)$ if U is a subset of S and V is a subset of T. We get nets $\{t_{UV}\}$ and $\{t_{UV}\}$ converging to $x_1$ and $x_2$ respectively. Since f is continuous and $f(t_{UV})=f(s_{UV})$ we get $y_1=f(x_1)=f(x_2)=y_2$ which is a contradiction. This proves the claim. Next pick open sets A, B containing $x_1$ and $x_2$ such that their closures are contained in U and V respectively. Now the complements of the images of the closures of A and B are disjoint neighborhoods of $y_1$ and $y_2$.

Showing that a space is Hausdorff


ORA-22905 in parameterized query

Question: I have a function, that splits a CSV-list into a table of numbers.:
create or replace function SYC_SplitIds
(IDList in varchar2)
return SYC_IDNRTABLE pipelined ...
where SYC_IDNRTABLE is declared as:
SYC_IDNRTable as table of spectrum.SYC_IDNR;
and SYC_IDNR is:
type SYC_IDNr as object(IDNr Integer)
The function itself works fine. At least a query like this works OK:
INSERT INTO TEST_TEMP_IDS
    SELECT IDNr AS ID
    FROM Table(SYC_SplitIDs ('1234,5678'));
However if I try the same query with a parameter instead of a fixed string:
INSERT INTO TEST_TEMP_IDS
 SELECT IDNr AS ID
 FROM Table(SYC_SplitIDs (:IDLIST));

where IDLIST is declared as VARCHAR2(32767) and initialized with the same '1234,5678' string as before, I get an, at least for me, strange ORA-22905 error: "cannot access rows from a non nested table item"
I found that I can avoid this error using:
INSERT INTO TEST_TEMP_IDS SELECT IDNr AS ID
  FROM Table(SYC_SplitIDs (CAST(:IDLIST AS VARCHAR(4000)));

but now I'm limitit to max 4000 bytes which is not enough... How to get the full 32767 byte range back?
Answer: INSERT INTO TEST_TEMP_IDS SELECT IDNr AS ID FROM Table(SYC_SplitIDs (CAST(:IDLIST AS VARCHAR(4000)));

but now I've limit it to max 4000 bytes which is not enough... How to get the full 32767 byte range back?
Maybe you can try using "(CAST(:IDLIST AS VARCHAR(MAX)));"
this might solve the purpose.

ORA-22905 in parameterized query