OC test on transformer

Question: Can any one explain me in detail the magnetizing current and working currents that occur in no load conditions? I know that they are the vertical and horizontal components of no load current.. But how? Explain practically?
Answer: For a transformer, in no-load conditions you might as well forget about the secondary winding and regard the transformer primary as an inductor. I'm presuming here that you are talking about power transformers.
Magentizing current is due to the inductance of the primary winding. This is the dominant current and for a typical medium power transformer such as used in home appliances (before the introduction of switch-mode supplies) 10 henries might be a good value.
At 50Hz the inductive reactance is \$2\pi F L = 3142\Omega\$. This causes a current to flow (from a 220Vac supply) of 70\$mA_{RMS}\$. This is nearly a purely reactive current lagging the voltage supply by nearly 90º.
Losses - there are two main losses - eddy current losses and hysteresis losses. Eddy current losses are due to eddy currents being induced in the silicon-steel laminates: -

If the laminates were a perfect conductor the induced currents would serve only to reduce the inductance of the primary winding i.e. there would be no losses. However, the relatively poor conductivity of the laminate and it's thin width restrict eddy currents and, in effect put a resistor in parallel with the primary inductance.
Aside - Ferrites (at low-medium frequencies) have much higher resistance and have much lower eddy current losses - this is also why they are used at high frequencies.
Hysteresis losses come about because of the shape of the BH curve. As you magnetize the core then demagnetize the core you find that there is wasted energy in reversing the magnetic domains in the laminates. This forms another resistor in parallel with the primary inductance.
Both losses can be lumped together to form one value of resistance representing loss of the unloaded transformer.
Does this help? There's more about transformer losses here

OC test on transformer


Hedging Renminbi with EUR

Question: Hedging Renminbi with EUR. What is the reason why FX traders sometimes go long EUR to hedge shorts in RMB?
Comment: Where did you read that?
Comment: Chats with some traders. I know cny is indexed to usd and other ccys. So I was wondering if there was any relationship between eur and and cny = f (usd,..)
Answer: This is not an answer but I cannot post the comment as it is too long with the link:
Never heard of this. Maybe best to ask the traders you chatted to and post your answer afterwards here.  Simply looking at a chart makes me wonder how this should work.
If a European firm hedges their EURRMB exposure by selling/buying RMB to buy/sell EUR (forward), that is just a normal fx (forward) transaction but not hedging your RMB short position with EUR.

Hedging Renminbi with EUR


Fixed pulse width with 555 Timer

Question: new here.
I have a question regarding sending a PWM signal to a brushless motor ESC using a 555 timer. I'm using an Arduino Uno to control it currently, but I'd like to simplify my setup.
I have an underwater thruster that I only care to run on/off at a constant set speed, and I'm currently accomplishing thus using the Arduino servo library to send a 2ms fixed pulse width @ 50hz (10% duty cycle).
I've seen schematics on other posts here using a 555, an assortment of parts, and a potentiometer to modulate pulse width. Does anyone know how a schematic would look to accomplish what I'm currently doing, but with a 555 timer? Any and all help is greatly appreciated.
Comment: Am I correct in thinking you want to make a 555 oscillator with variable pulse width (duty cycle) controlled by a potentiometer and a frequency of 50Hz? Is the 50Hz critical, or could it vary with the duty cycle? I also presume that the output of the timer drives some sort of power transistor and thence the motor. Have you considered just using the potentiometer to vary the output voltage (or current) of the power device directly and do away with the variable duty cycle. Why are you going from analogue (the potentiometer) to digital (the 555) and back to analogue (the motor)?
Comment: Google 555 servo tester and you'll find plenty of beginner-oriented writeups. All you need is something like 1-2ms pulse width at around 50Hz.
Comment: @PeterJennings my intent is to send a PWM signal to an electronic speed controller for a brushless 3-phase motor. That's the only way those can run off DC. I don't want my setup to include a potentiometer (which is the only thing I've seen with tutorials I've found) since those are used to modulate the pulse width which in turn controls the speed that the ESC is spinning the motor at, and I want the same fixed pulse width that I'm currently getting using the Arduino.
Comment: Additionally, the 50hz freq is critical since that's what ESCs operate at.
Comment: by the way, I'm not convinced removing the microcontroller and keeping the 555 is what I'd call the most simplified version of your circuit – for this job, your microcontroller plus a single decoupling capacitor would do, for a 555-based solution the 555 plus seven or eight (GodJihyo's answer is missing the decoupling cap you'd want on VCC) component solution is necessary, which is way more complex.
Answer: If all you need is a 2 mS pulse every 20 mS you could use the standard 555 astable multivibrator circuit and calculate the timing capacitor and resistor values to do that.

With a 0.1uF capacitor R1 works out to 230880 ohms and R2 is 28860.
The formula for the pulse with is Tpulse / (0.693 * C1)
R2 = 0.002 / (0.693 * 0.1E-6) = 28860
For the total cycle time it's (Tcycle / (0.693 * C1)) - (2 * R2)
R1 = (0.02 / (0.693 * 0.1E-6)) - 57720 = 230880
You can use standard resistors that are close to those values with something like a 10 turn pot in series with each one to trim the values to what you need.
This will give you an output where the 2 mS pulses are negative going, so you will need to invert the output if you want positive going pulses. I have added a transistor inverter on the output of the 555 as a basic example, but you would need to design something that would give you the correct polarity and signal level necessary to drive your ESC.
Circuit in LTspice with inverted output:
Comment: Thank you so much! I'll give it a shot and see what happens.
Comment: @JosephAtilano Please note I have made some edits to my answer regarding the interfacing of the 555 to the ESC.
Comment: Caught that. Thanks!
Answer: There is a problem with the answer posted by GodJihyo.
Q1 probably will be on continuously, never pulsing.  The upper half of the NE555 output stage is a Darlington pair.  This cannot pull up to the positive rail close enough to turn off Q1.  Per the datasheet, the minimum output headroom is 0.9 V, more than enough to keep Q1 on during the high portions of the output cycles.
Separate from that, if you set R1 and R5 to the nearest standard 1% tolerance (E-96) values, the output waveform changes from 90% to 90.08%.
Your current system has a mark/space ratio of 9.  You don't say what kind of adjustment range you want on the output pulse width, and there are several ways to modify the circuit for this.  The most simple is to replace R5 with two resistors in series, one fixed and one variable.  For example, a 24K 5% resistor combined with a 10K pot gives a mark/space ratio adjustment range of from 7.824 to 10.67.  In terms of the percentage change from what you have now, the range is -13% to +18%.
The tradeoff is that the overall frequency no longer is fixed.  The frequency will not change as much as the ON pulse width, varying from -4% to +3%.  There are other circuit options that vary the mark/space ratio while holding the frequency closer to constant.
Comment: In that case, an open-collector NPN gets you the correct output polarity plus logic level conversion in one part.
Comment: LTspice needs to fix their 555 model.. apparently.
I changed it to an NPN, hopefully that's a better example circuit. Obviously the load is going to dictate the interface between the 555 and itself, it could be a mosfet or a logic gate, or whatever.
If you're going to want to vary the on/off ratio without affecting frequency it will need to be more complicated, but the OP did say it was to be fixed so I based my answer on that.
Comment: I don't know what a "brushless motor ESC" is, so my assumption is that your output transistor is driving the motor directly.  Either transistor polarity will work, but a PNP would keep the turn-off transient current surges off of the power rail.
Comment: Electronic Speed Controller. It controls the speed of a motor based on the width of the pulses supplied to it. A 1 mS pulse is the lowest speed, 2 mS is the highest, and the pulse repetition rate is usually 50 Hz. It should just need a logic level signal, the OP said they are currently using an Arduino to generate the pulses. With the 555 circuit they will need to come up with a circuit to match the output level and polarity to what the ESC input takes.

Fixed pulse width with 555 Timer


Should asset prices be always normalized by M2

Question: When economists look at the financial asset prices, do they adjust them by something like M2 in order to judge how valued something is compared to the previous historic periods? It seems like otherwise one is looking at a non-normalized version of the data, no?
Answer:
Should asset prices be always normalized by M2?

No because M2 would not appropriately correct for value in the previous time period.

When economists look at the financial asset prices, do they adjust them by something like M2 in order to judge how valued something is compared to the previous historic periods?

Economists use deflators not M2. Using deflator all dollar values are expressed in the same historical units. For example, if something has value 100 in 2010 and 250 in 2020 and deflator between the two time periods is 2 because price level doubled you can express the 250 in 2010 dollars by calculating 250/2=125 making the two values comparable across history.
Comment: why M2 would not correct appropriately? Is it because not all money supply is flows into financial assets?
Comment: @spacemonkey because m2 doesnt always have an effect since it's not only variable that determines price level. You don't want just use random variables, for example you wouldn't want to use the volume of precipitation per year to adjust the prices. m2 is in this context not completely random, but the relationship is not straightforward. With deflator you will get the most accurate correction.
Comment: 1muflon1, by deflator you mean adjusting for inflation?
Comment: @spacemonkey well it's actually for price level, but inflation is positive change in price level so yes in case there was increase in aggregate prices
Comment: 1muflon1, got it, thanks!


Improving performance of ArcGIS Pro while working on a network?

Question: As many others, I'm working from home at the moment. ArcGIS Pro is running on my local machine with access to remote file servers through a VPN. VPN is at times running quite slow due to everyone working from home and thus every operation in ArcGIS Pro, like adding data, geoprocessing and exporting data, is quite slow. Are there any tricks to speed up ArcGIS Pro on a slow network? E.g. increasing cache size if possible? Using a local scratch gdb? I can't copy files over to a local database cause colleagues also have to be able to work on the same projects and with the same geodatabases.
Comment: File geodatabase isn't safe for multiple writers anyway, so there isn't much to be gained from processing through a VPN.  Copy what you can locally. You certainly don't want the project geodatabase at the long end of a busy, slow chain of network hops.
Answer:
The best option is to leave a computer on physically on the network you're working on, and then Remote Desktop into the computer itself. That way the data isn't actually moving over the internet, which even under more ideal conditions I've found terribly slow.  Rather, just the image of what is on the screen is moving over the internet, which is far less burdensome. The computer physically on the network does all the work, and you just see an image of what is happening.
Another option as Vince says is to copy as much as you can locally.
Finally, we've found ArcMap to be faster than ArcGIS Pro over a VPN,
so you might switch up the software you're using if you can...
Answer: No question the best option is to use remote desktop, but in addition I have found two things that helped in some siutations:

Turn of indexing. Settings -> Options -> Indexing -> Check radio button "Don't create index"
Publish a feature server webservice through Portal then work with the data through the web service. Add data -> Data from Path -> Enter the URL of the feature web service. The problem with this approach is if you have editor tracking turned on, it's not the best for that.


Why did the EMH never take on a name?

Question: In at least two episodes in Voyager's first season, their EMH expressed desires of a 'people' name, as he was striving to be more than than temporary substitute for a flesh-and-blood doctor—yet later on he seems to forget all about it. Is there a reason for this (preferably a better one than shoddy writing)?
Comment: I would say that he came to identify with being called The Doctor. By the time he had time to seriously start looking for a name, all of them sounded hollow beside what his friends had been calling him since he activated.
Comment: It comes up semi-regularly throughout the entire series, including the final episodes.  Are you asking why the writers never had him choose one, or looking for an in-universe reason for his indecision?
Comment: I had hoped for an in-universe explanation, yes.
Comment: I think the Doctor's name on Voyager is Joe Zimmerman. We know his actual name is Joe, endgame. He thinks of himself as son to Dr. Lewis Zimmerman, his creator, saved his life and patched up their Father & Son like relationship. He also looks identical to him save the length/style of hair. Joe Zimmerman in my book.
Comment: Well out of universe, because it is a running gag.
Answer: He does choose a name. Eventually. The Doctor's name is revealed in Endgame part 1, the penultimate episode of the series.

 (The EMH enters with a young lovely on his arm.)
 PARIS: Doc!
 (Paris is going bald.)
 EMH: Mister Paris. Voyager's pilot, medic, and occasional thorn in my side. Where have you been hiding yourself?
 PARIS: I've been busy.
 EMH: New holonovel?
 PARIS: I'll make sure to get your input before I send it off to my publisher. Aren't you going to introduce me to your date?
 EMH: Mister Paris meet Lana, my blushing bride.
 PARIS: You're married?
 LANA: Tomorrow is our two week anniversary.
 PARIS: Well, congratulations. My invitation must have gotten lost in subspace.
 EMH: Oh, you should be flattered. We took a page from your book and eloped.
 LANA: Joe has a real flair for romantic gestures.
 PARIS: Joe?
 EMH: I decided I couldn't get married without a name.
 PARIS: It took you thirty three years to come up with Joe?
 EMH: It was Lana's grandfather's name.

Of course, this is the future timeline that Admiral Janeway comes from, and the events of Endgame may have changed the timeline so that the Doctor doesn't pick a name.
Comment: "preferably a better one than shoddy writing" — guess it was actually shoddy watching, @Nu'Daq!
Answer: The Doctor tried several names, but is not known to have settled on one in the primary timeline.
Out of universe, his name in the early scripts was Zimmerman after Herman Zimmerman.

In several early first-season Star Trek: Voyager scripts and during the pre-production phase, the character of The Doctor was referred to by name as Doc Zimmerman after Herman Zimmerman, since the show's producers had not yet decided to leave him unnamed. (VOY Season 2 DVD trivia text version of "The 37's")

My speculation?  He got used to being The Doctor.  Everyone else did.  There weren't any other doctors on board to get confused with.  His name reminds everyone of his ability and uniqueness, which would stroke his ego just fine.
As generic as being called The Doctor seems, it became more associated with his identity than naming himself after a famous artist or someone else's relative.
Comment: @WolfieInu Who? ;)
Comment: +1 for the ego-stroking bit. Think of it this way: he's not just "a doctor." He is The Doctor.
Answer: The Doctor has chosen names or given names in several episodes. Some names he used only once because they reminded him of painful memories.

http://en.memory-alpha.org/wiki/The_Doctor
Despite not having an official name, The Doctor has used several names on a temporary basis. Below is a list of names he used:
Lord Schweitzer (VOY: "Heroes and Demons")
The first of a number of names chosen by The Doctor in honor of great medical figures of Earth's past. In this case, the name was used in order to interact with Freya and other characters in Harry Kim's holographic recreation of the poem Beowulf; following Freya's "death", The Doctor discontinued using the name, finding the association with her too painful to bear.
Schmullus (VOY: "Lifesigns", "Resolutions")
Given to The Doctor by Denara Pel.
Wolfgang Amadeus Mozart & Vincent van Gogh (VOY: "Before and After")
Adopted in succession by The Doctor sometime around 2378 of an alternate timeline, during a period of interest in great cultural figures of Earth's history.
Kenneth (VOY: "Real Life")
Chosen in order to interact with his holographic family.
Joe (VOY: "Endgame")
Chosen by The Doctor in 2404 of an alternate timeline, in which Voyager returned home 16 years later than it ultimately did. Apparently a permanent selection.
In addition, over the years several crew Voyager crewmembers such as Paris, Harry Kim, Chakotay, and B'Elanna Torres took to simply calling him "Doc." Kim introduced him to a holographic representation of Crell Moset as "Doc." (VOY: "Nothing Human")

Given his attitude of discarding his names everytime he has a painful or sad experience, there is no way of telling whether he will settle on a name.
Answer: I can't recall completely - but I do seem to remember that he had come to identify himself as Doctor and, while he had tried using a name, he realised that having a name was not the same as having an identity or personality and being recognised as a sentient being.

Why did the EMH never take on a name?


Debugging a jnlp application with Eclipse

Question: I can't seem to be able to debug a JNLP application with Eclipse. The problem I'm getting is very similar to that described in this SO question, i.e., javaws appears to be starting the VM twice. The first time it starts fine with the remote debugging options and provided I use the suspend=y option I can even attach the Eclipse debugger to the VM, but as soon as it attaches the VM dies and javaws starts it again without the debugging options.
Here's how I'm launching the app:
javaws -J-Xdebug -J-Xnoagent -J-Djava.compiler=NONE -J-Xrunjdwp:transport=dt_socket,address=8989,server=y,suspend=y http://myserver/launch.jnlp

Since I have suspend=y, whilst it's waiting for a debugger to attach I can use ps -ef | grep java to see the java process with all the correct options running. Indeed, I can connect the Eclipse debugger to it, but as soon as I do that the process terminates and javaws starts a new java process. If I subsequently do another ps I can see a new (different PID) java process now without the debugging options. Attempting to connect to this process from Eclipse just gives "connection refused".
I'm using Java 6 on Mac OS X Lion 10.7.3 if that makes any difference.
The author of the SO question I mentioned above says he solved the problem apparently by accident so the cause of the problem is not apparent (or I'm too stupid to get it).
Any ideas?
Answer: Check if you have more then Java  7 update 67.
If you do I know that oracle has open bug for this.
some how from update 67 and above there is problem with this.
I had the same problem. I roll back to Java 7 update 60 and now its working fine.
I suggesting to remove all Java installation and then install


Why was the reelection rate for the US House of representatives in 2010 the lowest since 1970?

Question: According to OpenSecrets the relection rate dropped from 95% to 85% from 2008 to 2010. The last time the rate was as low as 85% was 1970. What's the reason for the drop in the reelection rate in 2010?
Answer: FiveThirtyEight, a political statistics blog, has this to say on the 2010 election: (Wayback link because the images aren't working in the current version)

Rather than a realigning election, then, 2010 served as more of an aligning election: Congressional districts behaved less independently from one another, and incumbency status mattered less. Instead, they hewed tightly to national trends and the overall partisanship of each district. Most of the House incumbents whose districts had been outliers before (mainly Democrats like Representative Gene Taylor of Mississippi, whose district gave just 31 percent of its vote to Mr. Obama, but also a couple of Republicans like Representative Joseph Cao of Louisiana) were forced into early retirement.

In other words, in the 2008 election, a lot of districts which would normally have elected a Republican elected a Democrat instead, likely because of Obama on the ticket.  In 2010, when those outliers reverted to their natural partisanship, the out-of-place Congressman they elected lost his or her seat despite being the incumbent.
Additionally, the increased partisanship atmosphere led to long-standing Congressmen in opposed districts (a Democrat in a generally Republican district, or vice versa) losing some of the advantage from being an incumbent, letting their district revert to it's "natural" leaning.
Comment: Gene Taylor had his seat not because the 2008 election but since 1989. To the extend that he's representative as FiveThirtyEight claims he is Obama being on the ticket in 2008 isn't a good explanation. It would only explain it if the congressman got his seat the first time in 2008
Comment: @Christian - The stance the article is taking is that things are becoming more and more dominated by national trends and partisanship.   Incumbency mattered less.  So outliers like Taylor (a Democrat in a very Republican district) are getting booted out.  I may have summarized an overly localized an argument out of it, though.
Comment: I think whether or not the election of Obama has something to do with the effect matters a lot, when trying to understand why this happened in 2010.
Comment: @Christian - It does, but there aren't many data points to derive conclusions from. After all, presidential elections are rare things - there's been two since the iPhone kicked off the popular smartphone market (which helped the rise of social media), three since 9/11, six since Taylor was elected. There have been twice as many congressional elections, but voting in off-year ones can be different. All on top of the changing political climate.  That's all a long way to say that Obama being elected definitely had *an* impact on the ticket that year, but the specific amount is hard to quantify.
Comment: @Christian - Beyond that, I'm not sure what else I can add.  Can you clarify what more you're looking for?
Comment: Why did it happen in 2010 and not at another election? What political forces are responsible?


Brakes Pedal on 2004 Pontiac Sunfire Goes to the Floor

Question: Why do my brakes go all the way to the floorboard? I added brake fluid. It's not as bad, but still doing it.
Comment: Welcome to Motor Vehicle Maintenance & Repair!
Answer: While there is probably air in the lines (as Mark stated), the bigger question is why is there air in the lines. You've either lost some fluid somewhere, or all your brakes are worn out and the calipers have all the fluid in them (effectively draining the master cylinder).  If they are anywhere close to being used up (especially at all four corners), you run the risk of having run your master cylinder dry. Check to see how your brake pads look. Even if the brakes do need changing, you'll need to get your brakes bled. If the brakes aren't at issue, you'll need to discover where the leak is at before you drive it anymore.
Answer: Air in system need the bleed the brake lines


Should I use a resistor in series when connecting a pin to logic level high?

Question: I'm trying to design a circuit with MAX8934AETI+. I'm confused about how to connect a pin to logic level high. For example, pin 6 in the picture below is meant to be connected to logic level high to assign the input current limit to 500mA, but does this mean I need to put a resistor in series with it? I do not see anything else in the datasheet about this.
Answer: On your datasheet, the table on page 7 gives the logic thresholds as low max of 0.4 V, high min of 1.3 V. The absolute max ratings allow 0 to 6 V on PEN2. This means it can be connected directly to a VCC of 5 V.
However, resistors are cheap, expose a test point, and allow you ground that point during debug or test if that's a useful thing to do, or easily hand modify a PCB to change the function.  If you've got space and the budget for a resistor, then it doesn't hurt to use one. Use one on every pullup and pull down if you can, you never know when the ability to easily change a 'fixed' pin is going to save you some trouble.
You might wonder why I looked at the absolute max ratings. The idea of pulling inputs up with a resistor being a very good idea dates back to the days of TTL, when the VCC absolute max was 7 V, but the inputs could only tolerate 5.5 V. If the rail spiked to between 5.5 V and 7 V during some fault condition, then ICs with a resistor pullup would survive, those with direct pullups might not.
Answer: For ATE testability, resistors are used, but not necessary for CMOS, otherwise.
However for TTL due to failure modes with reverse Vbe inputs >5.5 V a current limiting 10k resistor can be shared by 10 inputs.
These design rules were set about 50 yrs ago.


Help, Cant get my first LM741 inverter circuit right

Question: Im trying to configure my first (and basic) LM741 op amp inverter.
My Vcc is +5V, my input is a 1.5v DC battery, the positive connected to the inverting input pin 2, and the negative connected to non-inverting input pin 3.
Rf is 473k, Rin is 220k, so looking for a gain of about 2, and therefore looking for an output of about -3v, or thereabouts.
But using my multimeter, +ve lead on output, -ve lead on V-, I measure +2.06V
What am I doing wrong?
Thanks in advance
matthew
Comment: don't use 741, especially not on 5v rail, it needs min +/- 10v to work.
Comment: With a single +5V powere supply, NO op-amp can possibly output a negative voltage.
Comment: Please have a look here: https://electronics.stackexchange.com/questions/304521/reasons-not-to-use-a-741-op-amp
Comment: @TonyM: it still is not single ended, and I would assume he tries 0-5V not -5-5V
Comment: @Neil_UK, the TI datasheet specifies +/-5V min but I take your very valid point :-) But I'd say don't use the 741 because: it's rubbish. And it's been rubbish since about 1980, far superseded ever since. At least use an LM358N, that'll do a 3..32V single-ended supply. No point investing learning time in a dead-end part, OP.
Comment: Quite right - apologies and comment corrected, Neil_UK and @PlasmaHH
Comment: Schematics are generally more useful than a picture of the circuit.
Answer:
What am I doing wrong?

Top of the "reasons for not using the 741" list is the minimum supply voltage being nominally +/- 10V (although it will work down to +/- 5V without any guarantees). Running off a single 5 volt rail is rather a waste of time.
Next on the list is "Input voltage range is typically from -Vs + 2 volt to +Vs - 2 volt" so, even if you ran the 741 from a 20 volt supply, your 1.5 volt input would contravene #2.

looking for an output of about -3v, or thereabouts

7th on the list is "Typical output voltage swing is -Vs + 1 volt to +Vs - 1 volt" - this means the output is restricted to producing voltages that are within 1V above the negative rail and 1 volt below the positive rail so, if you are expecting an output of -3V you are going to be disappointed.
Listen, don't ever think of using this part - get some modern decent op-amps.


How many times can you round a number?

Question: For a typical rounding algorithm, I'm wondering how long the rounding chain goes for when you round up a number. For example, if you have a decimal like 0.4445,  you round the last 5 up, which would round it to 0.4450, which would round it to 0.4500,  which would round it to 0.5000, which would round to 1.0000? Or does the rounding stop after the initial rounding?
Answer: The purpose of rounding is typically to give a number to a certain number of significant digits. This is never done in such a chain as in your example. Let me try to elucidate why:
So we are given a number $0.4445$. Now if we were to round this to three decimal places we would indeed get $0.445$. Rounding the resulting number to two places gives $0.45$. However this does not represent the rounding of the original number, $0.4445$ to two places, for that would be $0.44$.
So rounding successively has no real meaning. An even more obvious example than the one above is that successive rounding of $0.4445$ yields $1$, whereas rounding the number to the ones place initially gives $0$.
Basically, don't ever round successively.
Comment: This doesn't answer the question. The question is about how many iterations it takes for a particular rounding algorithm to terminate.
Comment: @jack right.  Maybe my question isn't clear enough
Comment: My apologies, I didn't gather that from the question, I took it to ask how many times should one round. Sorry about that
Comment: @Growler this looks really accessible: http://www.clivemaxfield.com/diycalculator/popup-m-round.shtml

How many times can you round a number?


Max RAM for Boot Camp?

Question: What is the max amount of RAM that Windows 7 64 bit Boot Camp partition in my late 2011 2.4 i5 MBP 8.1 with OS X Lion can utilize?
Answer: Boot Camp doesn't restrict the amount of RAM available, therefore the maximum is the maximum as delineated by Windows 7 64 bit, 192 GB.
Answer: The Windows 7 64 Bit OS via BootCamp will utilize the available RAM on your Mac which is 16 GB (max).

Max RAM for Boot Camp?


Why use past continuous where there is no obvious interruption

Question: I am studying past simple and past continuous and then encountered an exercise(filling the blank with the words in parentheses in correct tense) as below:

Last night, while I was doing my homework, Angela (call) called. She said she (call) was calling me on her cell phone from her biology classroom at UCLA...

The bold texts are correct answers. I have no problem of the first one, it indicates a longer action was interrupted (by a shorter one). But the second answer uses the past continuous and I couldn't understand it. I could not figure out which usage of past continuous it belongs to. Could anyone help explaining? I learned the 5 usages of past continuous from English Page(http://www.englishpage.com/verbpage/pastcontinuous.html). Thanks for your time and effort!
Comment: @Robusto So in the context Angela just say "I am calling you on my cell phone from my biology classroom" (present continuous), and "I" turn it to past continuous just because "I" describe the whole story in past simple?
Comment: This is just how people talk. In a sentence like "I'm calling about your ad for the apartment" the use of present continuous expresses more immediacy, what the caller is doing *right now*. In the context of a past event, as in your example, present continuous becomes past continuous.
Comment: It's reported speech, so you report what *she* was saying at the time she said it.
Answer:
She said she  was calling me on her cell phone from her biology classroom at UCLA...

This sentence represents reported speech with the reporting verb "say" in the past simple.The original sentence would be

"I am calling you on my cell phone from..."

with the verb in the present continuous am calling, because she is doing that now. With backshifting it becomes was calling in the reported speech.


Why "he knows it" and not "he know it"

Question: Why is it I know it and They know it but He knows it? But then I knew it,  They knew it and He knew it?
Answer: In many languages, and in Indo-European languages in particular, verbs are conjugated according to person and number.  In other words, the ending of the verb changes based on the person of the subject (I, you or he/she).
Examples:
<code>        English   Hungarian  Romanian  Greek

I       know      tudok      știu      ξέρω

you     know      tudsz      știi      ξέρεις

he/she  knows     tud        știe      ξέρει
</code>
In the past, all Indo-Europan languages used to have verb conjugation, including English (see Old English verb conjugation---the ending in the 3rd person contained -þ/ð, the modern day "th", which is similar in pronunciation to s/z).  But as time passed and languages changed, some of them have lost verb conjugation and now indicate the person by prepending a pronoun (I, you or he/she).  One example is Norwegian, where even the copula ("to be") lost conjugation.  In English this process was not complete.  The -s in the third person is a remnant, and the verb "to be" has a different form in all persons.

It is interesting to note that the original English 2nd person singular (thou) was replaced by 2nd person plural (you).  In archaic texts that still use thou, you will find thou knowest, using the -st ending. Thus until fairly recently, English has not just one, but two preserved endings: 2nd person -st and 3rd person -s.

You might find it interesting that some languages conjugate verbs not only according to the person of the subject, but also the person of the object.  In Hungarian (which is not Indo-European), "I know him" is "ismerem" while "I know you" is "ismerlek" (this is different from "tudok" which means "to know a fact").
Answer: You want things to make sense? English is not the language for you, then. All past tense are conjugated the same, regardless of 1st person, 2nd person, etc.
I sang, he sang, they sang. We wrote, you wrote, she wrote...
I'm sorry, we have a strange language. The answer to most of these questions is "historical reasons".
Comment: Yes, and I'd like to know these historical reasons. I mean... it's quite weird. It's so weird that the history must be interesting.
Comment: The history, where known, can be unrewarding. Often one can discover when a change occurred but the reasons why are unknown. However, I share your curiosity.

Why "he knows it" and not "he know it"


Can the 5V and 3.3V power pins be used to power multiple devices?

Question: I am building a device that will be controlled by several digital encoders, all which are hooked up to the device's Raspberry Pi 3 model B. I know this may be a trivial question but bear with me as I have never built a device using a RPi before, but can a single one of the 5V pins be used to power multiple digital encoders, or muxs, or other devices in the system that need 5V power? I was thinking put the 5V pin into a breadboard and be able to plug any device into connected pin holes that need power. The digital encoders require 5V power @ 30ma. And if they can be used to power multiple devices, what is the maximum amperage output of the 5V pins and 3.3V pins? Additionally, can these pins be deactivated while the RPi is on or do they always output a set voltage?
Answer: Yes, the 5V and 3V3 power rails may be used to power multiple devices.
The power rails are not switchable, power is always available while the Pi is powered.
The amount of power available from the 5V and 3V3 rails is determined by the amount of power you can feed in via the microUSB power socket (or via the 5V power rail if you are powering via the expansion header).
Different Pi models have different microUSB polyfuses which limit the current.  You can use the residue of current after that needed to power the Pi and its peripherals.
Early model Pis have a limited amount of 3V3 power because of the chips used, perhaps only 50 mA or so.  Later model Pis have upgraded chips and you may be able to draw 500 mA or so.
The Pi3 has a two amp polyfuse.  Provided you have spare power you should be able to draw up to almost an amp from both the 5V and 3V3 power rails.
Answer: You don't specify which Pi, but for Pi3 You can draw 800mA from 3.3V and 1200mA (possibly more) from 5V, given an adequate power supply (2.5A).
The actual current depends on what else you have connected. If you are drawing lots from USB, the 5V would be correspondingly reduced.
Earlier models has lower capacity.
See Raspberry Pi Power Limitations for more detail.


How are our enzymes able to perform quantum tunnelling?

Question: The hydrogen protons undergo quantum tunnelling in the the sun to fuse into helium, but are only able to do so as they are under immense heat and pressure and the protons and electrons get separated. But our digestive system also makes use of quantum tunnelling to quicken the digestive process, but how do the enzymes free up the electrons when our body temperature is so low?
Answer: The probability of quantum-mechanical tunneling through a barrier depends on the energy involved in the barrier.  For two protons to fuse requires overcoming an energy barrier of many millions of electron-volts.  By contrast, energy barriers to configuration changes in atoms and molecules are typically a few electron-volts or even a fraction of an electron-volt.
Quantum-mechanical tunneling can occur in enzymes at room temperature because the energy barriers are comparable to thermal energies at room temperature, a few milli-electron-volts.
Answer: I don't know much about digestion, so I'm not sure about which biological process you're referring to. That said, the tunneling probability only requires energies which are significant compared to the energy barrier. The sun is trying to fuse nuclei together, and the energy that binds nuclei together is huge. So it takes a lot of energy and very high temperatures. In chemical situations, the energy that binds an electron to an atom or molecule (or the energy that binds atoms together) can be millions of times lower than the energy barrier present in the sun. So it's not necessarily surprising that chemical-energy tunneling processes can occur at room temperature.
Comment: Think of particles as a bunch of marbles in a box. If you shake it harder (higher temperature) it's more likely some of them will end up jumping out of the box. If the box is very large (the sun), you might need to shake it very, very hard; otherwise less vigorous shaking (lower temperatures) might still be able to push marbles out.
Comment: but how does a high temperature increase the chance of tunnelling to occur?
Comment: But still there remains a little probability of tunnelling happening so that it causes fusion, but that kind of release of energy would kill us, so why doesn't it happen?
Comment: @Learn_to_forget the energy released by a single nuclear fusion is not enough to kill you, and at body temperature such an event happens very, very rarely (probably functionally never)


ACF and Gutenberg block, how to use blocks without ?

Question: I'm working with Gutenberg blocks via ACF. It's great compromise between classic / ACF and the Gutenberg. Another great thing is <InnerBlocks />. However, in one block can be used only one <InnerBlocks /> tag, so it's kind of problematic, if I want to have more control over the html structure in my block. So: I have block with two divs (two columns). In each one I want to use Gutenberg blocks. Is there any way to insert specified block directly in my code, like image or group, without inner block?
Answer: No, you can't have multiple InnerBlocks. But you can create a second intermediate block, just like WordPress Core does with the columns and column block.
Comment: Thanks! But can I create a second intermediate block directly inside ACF block?


Any quotient group of $(\mathbb Q,+)$ is torsion

Question: We know that $\mathbb Q/\mathbb Z$ is a torsion group. Can we extend this to every quotient group of $\mathbb Q$? Thanks for hints.
Answer: Any nonzero subgroup of $(\mathbb{Q},+)$ contains an infinite cyclic group.
The quotient of $(\mathbb{Q},+)$ by any infinite cyclic group is torsion.
The quotient group of any torsion group is torsion.
Comment: No, not necessarily.  For example, the subgroup generated by $2/3$ does not contain $\mathbb{Z}$, but it does contain $2\mathbb{Z}$.
Comment: Thanks. You mean every subgroup of Q has Z as an infinite subgroup?
Answer: I want to give a proof which exploits the known structure theory of divisible abelian groups.  In this particular case it is evidently not the shortest proof available, but I hope that the basic technique will be of wider use.
Let $G$ be a divisible abelian group, and consider the exact sequence
$0 \rightarrow G[\operatorname{tors}] \rightarrow G \rightarrow G/G[\operatorname{tors}] \rightarrow 0$.
Now the torsion subgroup of a divisible abelian group is divisible: if $x \in \mathbb{G}[\operatorname{tors}]$ and $n \in \mathbb{Z}^+$, there exists $y \in G$ such that $ny = x$.  But also there exists $m \in \mathbb{Z}^+$ such that $mx = 0$, so $(mn) y = 0$ and $y \in \mathbb{G}[\operatorname{tors}]$.
Since an abelian group is divisible iff it is injective as a $\mathbb{Z}$-module, the first term in the above sequence is injective, so it splits:
$G \cong G[\operatorname{tors}] \times V$,
where $V$ is divisible and torsionfree, hence can be given uniquely the structure of a $\mathbb{Q}$-vector space.  Moreover, if $G \rightarrow H$ is a homomorphism of divisible groups, then after choosing subgroups $V_G$ of $G$ and $V_H$ of $H$ as above, then the natural map $V_G \hookrightarrow G \hookrightarrow H \rightarrow V_H$ is $\mathbb{Q}$-linear.
Now back to the problem: here we have $G = V_G$ is a $\mathbb{Q}$-vector space of dimension one and we are given a surjective map $f: G \rightarrow H$, so the map $\mathbb{Q} \cong V_G \rightarrow V_H$ is surjective and $\mathbb{Q}$-linear.  Therefore it is either injective -- in which case $f$ is injective (in the language of the problem, this corresponds to taking the quotient  by the zero group) or $V_H = 0$, i.e., $H = f(G)$ is a torsion group.
Answer: Let $H$ a non-zero subgroup of $\Bbb Q$ and let $0\neq h=\frac mn\in H$. It is clear that $m=n\cdot h\in H$ and so $m{\Bbb Z}<H$.
Therefore, there's a surjective map ${\Bbb Q}/m{\Bbb Z}\rightarrow{\Bbb Q}/H$, so the latter quotient is torsion because is a quotient of a torsion group.
Comment: Just realized that this is just Jangwei's answer spelled out.......
Answer: I think you are wondering if every nontrivial quotient group of $\mathbb{Q}$ is torsion. In fact, for a nontrivial subgroup $H$ of $\mathbb{Q}$, there is a minimal positive number $h \in H$, then, we have $h\mathbb{Q} \subseteq H$, and $G/H$ is torsion.
I hope I am not mistaken.
Comment: I'm not sure if it's true that there exists such a $h\in H$. Consider the set $H=\lbrace \frac{p}{q}|p\text{ is even and }q\text{ is odd}\rbrace$. $H$ is a subgroup of $\langle \mathbb{Q},+\rangle$ (easy check), but there's no such minimal positive $h\in H$- for any $h_0\in H$, $0<h_0\frac{1}{3}<h_0$ is a smaller element of $H$.
Comment: Suppose $H=\mathbb Z$, if you mean $h\mathbb Q$ as multiplication then it is only true for $h=0$, and $h\mathbb Q=\{0\}$. If you meant addition then there is *no* integer such that $h+q\in\mathbb Z$ for *all* $q\in\mathbb Q$.


What will be the major enol form of methyl acetoacetate?

Question:
I presume the best enol form would have a double bond between the two $\ce{C=O}$ so they're conjugated, but I'm not sure how the resonance would play out.
Answer: The enol forms of beta-diketones and beta -ketoesters are stabilized
by intramolecular hydrogen bonds in its enolic form. Enol structure with greater conjugation is more stable and amajor enol.

update :
In organic chemistry terms, conjugation is used to describe the situation that occurs when π systems (e.g. double bonds) are "linked together".
A conjugated system requires that there is a continuous array of "p" orbitals that can align to produce a π bonding overlap along the whole system.If a position in the chain does not provide a "p" orbital or if geometry prevents the correct alignment, then the conjugation is interrupted (broken) and therefore lost at that point. Due to extra π bonding interactions between the adjacent π systems there is an overall stabilization of the system .This is referred to as the delocalisation energy or the resonance energy or conjugation energy

source:
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch10/ch10-1-1.html
According to MO theory,1,3-butadiene ,comprised of four overlapping p orbitals are mathematically combined to produce four molecular orbitals.As seen in figure , the four π electrons of a conjugated diene occupy the two lowest energy MOs (the bonding MOs).Specifically, the two electrons that occupy ψ1 are delocalized over four carbon atoms. This delocalization accounts for the observed stabilization energy .

source :
Organic chemistry ,David R. Klein.page no.773
ref :Advanced Organic ,Chemistry FIFTH EDITION ,Part A: Structure and Mechanisms FRANCIS A. CAREY
and RICHARD J. SUNDBERG
Comment: @andselisk i have reformatted .Thankyou.
Comment: Ehhm, I see you removed a lot, but it's still not clear 1. what is a quotation and what is your work; 2. what page number(s) were used. Also, the formatting is still lacking proper spacing here and there, plus there is a bunch of links for the images at the end that are not used elsewhere.
Comment: Based on abrupt paragraphs with numerous new lines and wrong Unicode characters (e.g. Eszett in place of beta) the answer looks copy-pasted from a poorly OCRed book (the ref you mentioned?). If you are quoting a third-party source, please use corresponding markup (`> ...`) and do at least minimal corrections to the text to make it more readable/editable; also use proper bibliography referencing with page numbers.


Should I keep "redirect only" methods in my Controller?

Question: Controller:
function indexAction()
{
    if ($condition)
        $this->renumPosition($id);    //LINE #1
}

//Redirect only - function's sole purpose is to call another function
function renumPosition($id)
{
    $this->repository->renumPosition($id);
}

Repository:
function renumPosition($id)
{
    //SQL, DQL, ORM code follows
    ...
}

Question
Should Line #1 (above) be instead
$this->repository->renumPosition($id);

and should the renumPosition within Controller be removed?
The question is .. when do I defer execution directly to my model/repository layer, and when do I call a Controller's function which defers to model/repository layer?
This perhaps is a really subtle question.  Just to note, my intent here is NOT to save an extra function call, but to align myself with a programming philosophy.
For example, I can make an argument that when Controller should be cognizant of an action, I should have a public method in Controller that may make a call to repository.  But then, when it is an internal action, maybe I can call repository directly without making a separate method call in Controller.
Does that make sense?
What my Goal/Concern is
Here is the Legacy code I started with:
Controller:
function indexAction()
{
    if ($condition)
        $this->renumPosition($id);    //LINE #1
}

function renumPosition($id)
{
    //Heavy SQL, DQL, ORM code follows - say 50-70 lines
    ...

    $db->db_function($sql)

    ...

    $db->db_function($moreSql)

    //some more code here that relates to DB transactions
    $db->db_function($moreSql)
}

As the code above was mostly storage related, I moved it all into my Repository class.  I ended up with this in my Controller:
function renumPosition($id)
{
    $this->repository->renumPosition($id);
}

I looked at the above and said to myself -- why do I have a function in my Controller that has a sole purpose of calling another function?  Why have this indirection?  Why have code cluttering my cognitive and screen space when I can totally and completely eliminate it.  And so I did.  I called the repository function directly and removed Controller's "redirection" function entirely.  But then I asked myself -- Did I do the right thing? That's what I am trying to figure out with my question.
Answer: Yes, you did the right thing by removing the function renumPosition from your Controller.
Functions must have a reason to exist and just the fact there was a legitimate function before you started to refactor is not a valid reason to keep the function around after you have refactored its reasons for existence away.
There are two main reasons to create functions:

To reduce code duplication. If a piece of functionality is needed at multiple places in the code, then encapsulating that functionality in a function means that you don't have to duplicate that code all over the place (and find it back if it needs a change or bug fix). When creating functions for this reason, you should also keep the next bullet in mind.
To create an abstraction. If a piece of functionality consists of multiple operations, it can be helpful in understanding that block of code by giving it a name. The most convenient way of giving a block of code a name is by creating a function with that name that contains the code.

In the original code, the renumPosition function in the Controller created an abstraction over the database operations and had a reason for existing due to that.
After you moved the database interaction to the Model, renumPosition in Controller did not provide a useful abstraction anymore and you can hardly argue that the code duplication increases if you replace a function call to function A with a function call to function B.
Comment: Thank you.  However, looking further and working with code, I see that I will have to keep the redirection method in my Controller.  Why:  Because eliminating this one function means I have to call my model directly from my routing class, which breaks MVC a bit.  In my case, Controller prepares the repository and provides some extra data and checks conditions and *delegates* the work to repository.  So I think I'll have to keep that function afterall.  It serves the purpose of not breaking MVC, and initializations of supporting classes and data.
Comment: @Dennis: That is fine. If you have a good reason to keep a function around, even if it is a one-liner, then you should keep the function around.
Answer: I am not entirely sure what are you trying to achieve here. If your reason is code duplication in Controller Actions, you should look into a Service layer that sits between your controller and repository.
From your controller you would call a service function _userService.GetUser(5) and then you can use this function throughout your controller. The GetUser(int id) function would handle anything else that it needs to do, including making a call to repository, mapping the data to view model or whatever other logic you want.
Comment: Thanks.  See my question for added goal/purpose behind it
Comment: You did the right thing - you should aim for controllers to be as lean as possible, and move any other logic elsewhere.
Answer: There are two schools of thought when it comes to where the most logic should be placed in an MVC application: 1) the Controller should be stupid and most of your logic should be in the Model; 2) the Model should be stupid and most of your logic should be in the Controller.
Both ways have their up and down sides.
In the end, it doesn't matter which way you choose as long as you are consistent.
Stupid Controller Method
This method makes your Controller act as a traffic cop for all of your Models.
Your Controller methods would instantiate Models, and then pass control to the Model for further processing. Error states (including validation failures) in the Models would require an error to be raised back to the Controller (and eventually the View). Your application's business logic would then be contained in the Models.
In this method, the Model would also be responsible for this like logging either by creating a Logging Model.
Stupid Model Method
This method basically makes your Model not much more than a data validator and storage mechanism.
Your Controller methods would still instantiate Models, set properties and fields, check for validation failures or other error states, and tell the Model to save it's data to storage. Error states could be immediately sent back to the View. Your application's business logic would be contained in the Controller.
In this method, the Controller would also be responsible for things like logging by creating a Logging Model.


Trying to upgrade Premium Residential Zones to Luxury

Question: In SimCity Buildit I am trying to upgrade my Premium Residential zones to Luxury zones.  Will building a swimming pool do that?
Answer: A swimming pool might help increase the land value of the residential zones. The standard, premium and luxury types of houses are based on the land value. The darker the blue, the higher the land value. Adding more specialisation buildings will help increase the land value.
You can read more on EA's help pages: Building Residential Zones in Simcity Buildit
Answer: Well, in most SimCity games zones will upgrade if you place something for the people in it to use/enjoy/visit. If thats a public tool your talking about you can give it a shot.


pvz2 bugs in worlds?

Question: Right now I'm playing pvz2 and I beat the first 3 worlds but it it says that I haven't beaten them on the bottom of the world.For ancient Egypt it says that 21/25 levels beaten.For pirate seas 24/25 and for wild west 20/25. And when I open the worlds it shoes that I haven't beaten those levels and I have to do them again.HELP!!! Is this some sort of bug or do I have to do them again?
Answer: I've been in a situation like this before.
It was iCloud doing this on my iPad.
Check for any cloud backup applications on your device.
Answer: If you beat the Zomboss on all 3 worlds it sounds like a bug to me. Sorry.

pvz2 bugs in worlds?


Existence of abstract objects for a physicalist

Question: Let's say I'm a physicalist. Usually then, I will think of abstract objects as mental constructs, which are dictated by mental states, which, as a physicalist will say, are manifestations of physical things (e.g. a bunch of elementary particles, which we call the brain, interacting with each other inside my head). Given this, can we say that abstract objects (e.g. numbers, etc) for a physicalist physically exist?
Comment: I think a relevant key word here is [nominalism](http://plato.stanford.edu/entries/physicalism/#12) (j).
Comment: Yes we can. More. They physically exist for everybody even non physicalist. Because qualia is physical. Everything what exists is physical.
Comment: Thus, when we say that 3 is greater than 2, we are saying that the mental construct corresdponding to 3 is greater than the mental construct corresponding to 2 ?
Comment: @MauroALLEGRANZA what you're talking about is the _relation_ between the numbers 2 and 3. Relation between two abstract objects is itself an abstract object, for sure. Hence, it is a mental construct, fundamentally governed by physical entities (from the physicalist's point of view).
Answer: You can say that a neural representation of abstract objects physically exist; that wouldn't be controversial for a physicalist.
You need only postulate, however, that certain computational systems (like our brains) recognize similarities between distinct objects; this seems rather weaker than what one normally means by an object (abstract or otherwise) existing.  For instance, one could theoretically remember every case of an item that was called a "chair" and perform a pairwise comparison between a new object that may be a chair and all of those; and if this new object is as similar to the other chairs as they are to each other, and there is no other label with a set of exemplars that is a better mtach to the object you've got, then you have a chair.  This is a perfectly functional system for naming and recognizing chairs, but what in this description is this "abstract chair"?
So it is not necessary to suppose that abstract objects exist, even if we act as though there is such an abstract object.  Ultimately, a physicalist probably ought to defer to evidence regarding whether abstract objects effectively exist in brains or not (the physical world certainly contains regularities, but one is under no obligation to create an abstraction to instantiate those regularities).
Answer: From Gottlob Frege, Basic Laws of Arithmetic (1893), new english translation by Philip Ebert & Marcus Rossberg, Oxford UP 2013, page xxiv :

We have to think of cognition as an activity that does not create what is cognised, but grasp what is already there.
When I grasp a pencil, many things take place in my body: stimulation of the nerves, changes in the tension and the pressure of muscles, tendons and bones, changes in the circulation of blood. The sum of these processes, however, is not the pencil, nor do they create it. The latter has being independently of these processes. It is essential to grasping that there is something which is grasped; the inner changes alone are not the grasping. Similarly, what we mentally apprehend has being independently of this activity, of the ideas and their changes that are part of or accompany the apprehension; it is neither the sum of these processes nor is it created as part of our mental life.
Comment: Don't you think that using an example with a pencil (a material thing that I can see, touch, etc) is a cheap trick to "show" that abstract objects have some sort of existence outside minds, just as pencils do?
Comment: @user132181 - I stay with your "analogy" : if "mental constructs are dictated by mental states, which, as a physicalist will say, are manifestations of physical things"; thus a mental state corresponding to the number 2 is the manifestation of which thing ?
Comment: It's a manifestation of elementary particles, interacting with each other.
Answer: All we need is a neural representation of criteria to be satisfied. Since those criteria to be satisfied can find themselves to be multiply realizable, or multiply represented, in various nervous systems, or various minds, we as physicalists need not commit ourselves to the mind-independent existence, spatiotemporal or not, of what take the place of abstract objects in our ontic discourse.


New instance with same @@VERSION as existing instances

Question: I have a SQL Server 2008 R2 server with several instances installed. Is there a way to add a new instance and have it be to the same build as the existing (and updated / patched) instances?
Answer: No, unfortunately there is no magic "be like that guy" feature. What you have to do is either:

install RTM and then apply the SP + CU; or
slipstream the same SP + CU into the RTM binaries and install that. These instructions are applicable to both SQL Server 2008 and SQL Server 2008 R2, though the process is a little easier in SQL Server 2012.

The former is easier but could require more downtime.


Can we create Junction object with one master-detail and one lookup field?

Question: Can we create Junction object with one master-detail and one lookup field? What will be its security configuration in case Lookup relationship field is created first?
Comment: For the first question, yes you can. I don't understand the second question. Do you mean when creating the junction object fields, or when creating a junction object record? For the former, what security issues could you have? For the latter, a Master Detail field is always required, so must be set when first creating the record.
Comment: Great question. I also wondered if there are any security implications.
Comment: @PhilW I want to know if the org-wide default will be ControlledByParent or Public Read/Write
Comment: Just set it how you want it for the Lookup. Master Detail children are always Controlled by Parent.
Answer: Answer to your first questions is "Yes" you can have a junction object by using one parent as M-D and another as Lookup.
For second question sharing setting of your child object would be Controlled by parent and it can't be changed to anything else.
Depending on your use case you can expand or restrict sharing setting on child object from "Sharing Setting" option at master detail relationship field.

Allows users with at least Read access to the Master record to create, edit, or delete related Detail records.
Allows users with at least Read/Write access to the Master record to create, edit, or delete related Detail records.

Remember you cant create a child record without linking master object record


same transactions by different miners at same time

Question: i have a private network having 3 nodes, two are mining and one is listener. All three nodes are connected as peers. Now, is there any way where both miners pass same transaction at same time.
Comment: What do you mean by "pass" ?
Comment: @FlorianCastelain i want to send same transaction from two nodes at same time. And both of these nodes are miners
Comment: You can send these transactions, but only one will get through. You should have a look at concensus and mining algorithm to understand how it works.
Answer: Whether your signed transaction comes from a client connected to node1, a client connected to node2, or on the network from node1 to node2, if it is the same hash and binary content, for all practical purposes it is the same transaction. The nodes do not keep duplicates in their transaction pool, so they will just say "yep, seen this one already".
Think about it, in a gossip network like Ethereum, a new transaction may come to your node from multiple peers at different times. This is a natural occurrence.
Now, did you mean "mine" the tx at the same time on 2 different blocks? Well, this is what we call a soft fork, and in practice, a node wins, eventually. You can find literature about it.


Can't find "install" option for Dropbox installation

Question: I have been trying to install Dropbox from the software center but I can't find the "install" option, it only shows the "use this source" option. I also tried to install it via terminal and still failed.
Comment: Did you try to download it from dropbox site and install? https://www.dropbox.com/install?os=lnx
Answer: First you have to enable repository and update from ppa.
dropbox is available from main repository for 14.04. so run following command in terminal to enable main & universe repository:
sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe"

The main component contains applications that are free software, can be freely redistributed and are fully supported by the Ubuntu team. & The universe component is a snapshot of the free, open-source, and Linux world.

Then setup key:
sudo apt-key adv --keyserver pgp.mit.edu --recv-keys 5044912E

Then setup repository:
sudo sh -c 'echo "deb http://linux.dropbox.com/ubuntu/ trusty main" >> /etc/apt/sources.list.d/dropbox.list'

Then update and install:
sudo apt-get update
sudo apt-get install dropbox

After that you can launch it from dash:

I have tested it and worked for me. Hope it helps.

Note: If your Ubuntu version is not trusty then change "release-name" in
    sudo sh -c 'echo "deb http://linux.dropbox.com/ubuntu/ <release-name> main" >> /etc/apt/sources.list.d/dropbox.list' at setting up repository. You can also run $(lsb_release -sc) to find release-name.
Comment: W: Failed to fetch http://linux.dropbox.com/ubuntu/dists//Release.gpg  Unable to connect to linux.dropbox.com:http:

I keep getting this error messages "W: Failed to fetch http://ppa.launchpad.net/tucan/unstable/ubuntu/dists/precise/Release.gpg  Unable to connect to ppa.launchpad.net:http:"
Comment: Did you replace with your release name (e.g., trusty)?
Comment: @amc No,i downloaded it from the dropbox site
Answer: Supposing you are using nautilus as your file manager, open a terminal and write
sudo apt-get install nautilus-dropbox

(or search for that package in the software center)
this shpuld then install dropbox automatically
Answer: From Terminal use the following command,
sudo apt-get install nautilus-dropbox

If you have an no Dropbox indicator in the top panel use the following command,
sudo apt-get install libappindicator1

Once installed restart.


What is meant by Excitation-Autoionization?

Question: I am confused and not sure what Excitation-Autoionization really means. In Dopita & Sutherlend's book 'Astrophysics of the Diffusive Universe' (2003, page 104) is written: 'At sufficiently HIGH electron impact energies, MORE THAN ONE electron of the target nucleus may be excited, leaving the atom in an unstable state, which is stabilized by the radiationless ejection of an electron, possibly followed by a radiative decay of the ionized atom back to its ground state. This process is known as excitation-autoionization.' On the other hand, in the Kaastra et al. (2008; Space Science Reviews, Volume 134, Issue 1-4, pp. 155-190) is written (Section 3.2.5.): 'In principle, if the free electron has INSUFFICIENT energy, there will be no ionisation. However, EVEN IN THAT CASE it is sometimes still possible to ionise, but in a more complicated way. The process is as follows. The collision can bring ONE of the electrons in the outermost shells in a higher quantum level (excitation). In most cases, the ion will return to its ground level by a radiative transition. But in some cases the excited state is unstable, and a radiationless Auger transition can occur. The vacancy that is left behind by the excited electron is being filled by ANOTHER electron from one of the outermost shells, while the excited electron is able to leave the ion.' Each individual explanation seem reasonable to me, but it seems to me that these explanations are different. Am I missing something? I would like to clarify what is meant by Excitation-Autoionization.
Answer: What they mean is that, when you transfer enough energy to an atom to excite more than one electron to an excited state you actually end up with enough net energy to ionize one of the electrons which eventually does happen.
For example let's say you excite $\text{He}$ to the $\text{2s 2s}$ state, since the energy of the atom is now greater than the energy of $\text{He}^+ + e^-$, eventually one of the electrons will get kicked out of the atom without any accompanying photons. This is what's known as autoionization. What this means is that states where multiple electrons are excited are actually not genuine eigenstates but instead meta-stable states.
Comment: Thank You very much. Yes, I think I understand. What confuses me is that in the mentioned paper (Kaastra et al. 2008) they explain the EA (Excitation-Autoionization) process by the fact that one electron is excited, not two. So it seems to me that the first explanation (Dopita & Sutherlend) implies the excitation of two and the other (Kaastra et al.) only one electron. Does this mean that both types of processes can happen and can be called EA processes?


Why this file "ProjectName_TemporaryKey.pfx" gets created in my project?

Question: Why does the file "ProjectName_TemporaryKey.pfx" get created in project?
And what is its use in the project? I have EDM in my project and some forms, etc.
Answer: This is a file used for code signing:

Assembly signing (also called strong-name signing) gives an
  application or component a unique identity that other software can use
  to identify and refer explicitly to it. A strong name consists of its
  simple text name, version number, culture information (if provided),
  plus a public/private key pair. This information is stored in a key
  file; this can be a Personal Information Exchange (PFX) file or a
  certificate from the current user's Windows certificate store

Here is a bit more info.
Comment: Your answer was helpful.
Comment: But when I tried creating new pfx with password. It gives me an error.

    Error 3 Unable to copy file "obj\x86\Debug\Utility 1.0.exe" to "bin\Debug\Utility 1.0.exe". The process cannot access the file 'bin\Debug\Utility 1.0.exe' because it is being used by another process. Eduron.Utilities
Comment: To your surprise, it builds in release mode. Would u be more kind to answer this query of mine. Thanks in advance.
Answer: You must be having click once based deployment.Such click once apps needs to be signed digitally by a certificate.If you dont have a certificate of your own  the publishing system will create one for you. you can also take a look at this.
Comment: Your answer helped a lot to understand what this file is meant for. Expected more precise answer which was being told by @Dimitar Dimitrov in his answer.
Comment: I believe your link is no longer valid: " this"


java applet java.security.AccessControlException: access denied java.net.SocketPermission

Question: I friend of mine gave me a script to run minecraft skins on my site but i keep getting this error and i dont have any clue how to go about this... =(
http://allcitybuilder.com/new/example.html
java.security.AccessControlException: access denied (java.net.SocketPermission www.minecraft.net:80 connect,resolve)
   at java.security.AccessControlContext.checkPermission(Unknown Source)
   at java.security.AccessController.checkPermission(Unknown Source)
   at java.lang.SecurityManager.checkPermission(Unknown Source)
   at java.lang.SecurityManager.checkConnect(Unknown Source)
   at sun.plugin2.applet.Applet2SecurityManager.checkConnect(Unknown Source)
   at sun.net.www.http.HttpClient.openServer(Unknown Source)
   at sun.net.www.http.HttpClient.<init>(Unknown Source)
   at sun.net.www.http.HttpClient.New(Unknown Source)
   at sun.net.www.http.HttpClient.New(Unknown Source)
   at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)
   at sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
   at sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)
   at net.minecraft.skintest.math.Zombie$1.run(Zombie.java:82)

Answer: Normally Applets are only allowed to access the host they came from (in your case allcitybuilder.com). Thus, you either have to put the file to view also to this host (or install a proxy there), or your applet needs additional privileges to have more access.
For the applet to have more access, it needs to be digitally signed, and the user needs to confirm the applet loading.
But there is no way to say "I need only access to minecraft.net" and for the user to grant you only this permission (without manual editing of policy files), so it is an "all or nothing".  Also, if the user refuses, the applet may either run with usual applet permissions (on Sun's Plugin) or not run at all (on IcedTea).
With JNLP you can get a confirmation for the user for individual actions, but this is only for local access, no remote one.
Answer: You must allow the Applet to connect to a resource.
Have a look at the sigend Applet tutorial: http://www-personal.umich.edu/~lsiden/tutorials/signed-applet/signed-applet.html
Answer: Probably the easiest thing would be to copy the resources to your site, making sure you have been granted appropriate rights by the copyright holder.
Alternatively, the site may add a crossdomain.xml file to allow access to code loaded from non-same-origin sites.
It is possibly to sign the code to gain full access to the local machine. However, this requires the user to accept the risk and writing secure code is surprisingly difficult.


What is signal ground

Question: I encountered signal ground symbol while studying 555 IC
Please explain why isn't a simple ground connection used and how does signal ground differ from normal ground. I am a first year undergraduate, kindly explain the most basics.This inverted triangle symbol
Comment: in most electronic circuits, the ground is the reference point where you put the negative probe of your DMM or oscilloscope ...... that is usually the negative terminal of the power supply
Comment: In this case the terms "signal ground" and "normal ground" are synonyms.  Voltage is the difference between two electric potentials p0 and p1--i.e., V=p1-p0. When looking at an electronic circuit schematic diagram, the circuit's designer defines one circuit node as the 'zero electric potential' node, or "ground potential" node, or "circuit ground", or "signal ground", etc.  The electric potential difference (voltage) at the circuit's other nodes is usually measured relative to the circuit's ground potential node.
Comment: Normal ground is where potatoes come from.  and even in elecronics ground has many different meanings. what research have you done?
Comment: I tried to read it on internet but they say too less about it and i couldn't comprehend.
Comment: I understand ground in physics means an extremely gigantic capacitor like earth where any practical amount of charge poured would produce no tangible voltage change for all practical purposes at undergraduate level.
Answer:
Figure 1. Various earth and ground symbols. Source: Ground, earth, chassis.
"Ground" is a reference point in an electrical circuit. It is used as a reference point for voltage measurements. As a result a voltage may be above ground (positive) or below ground (negative). This is very like a surveyor taking a reference point in a certain location and referencing all other points to that datum.
The most common reference is Earth itself. Power systems are usually "earthed" at some point to provide a reference for the system voltages. The earth symbol represents the parallel plates that were buried in the soil to ensure good conductivity. (The plates were connected by wire and early forms of the symbol show the vertical line connecting all the plates. The modern "cleaner" symbol omits the vertical.)
The ground symbols indicate the generic reference point. Even if there is no earth or chassis connection it is common to refer to one point or voltage in the circuit as "ground". In equipment where electrical isolation is provided between sections of the circuit two or more ground symbols may be required to indicate which ground the components are connected to.
I have written further on the topic and given circuit examples in the linked article.
Comment: Thanks a lot !!!
Comment: Don't forget to upvote useful answers and "accept" the best answer if there is one that answers your question.
Comment: Is that your blog ?
Comment: Yes. See my user profile.
Answer: Lets examine this circuit/system, which has a SignalGround of length 13 feet, running from the 100 microvolt Return wire of the Moving Coil vinyl record playback cartridge, thru 5' coax, thru RIAA preamp, thru 3' of coax to the 100 watt Audio Power Amplifier, then thru 5' of Speaker Return wire to the speaker (which has about 100 volts PeakPeak, or 1,000,000X larger than the sensor signal).

simulate this circuit – Schematic created using CircuitLab
Signal Ground runs all the way from the MovingCoil sensor which is left-most 1uH inductor (bottom node of that inductor is the "ground") thru the 5 feet of cable to the J1 JFET, to the RIAA capacitors (C3 and C4), thru the rest of the low-noise RIAA preamplifier transistors, out the COAX CABLE to the 100 watt audio power amplifier, and finally to ONE of the leads to the speaker.
The non-ground wire of the speaker will have substantial signal voltage {100 watts and 8 ohms => ~ 30 volts RMS or 100 volts PeakPeak), and electric fields will couple to EARTH, with those currents needing to find a path back home.
The designer gets to DESIGN all these paths. Its an incremental process of learning. For now, start with viewing a sheet of copper as your ground.
The (charging, or displacement) current thru a capacitor is I = C * dV/dt.
The dV/dT of 100 volts at 60Hz is 100 * (60 * 2 * pi) = 100 * 377 = 37,700 volts per second.
Now we need the "capacitance".
What is the capacitance between you and the earth thru your shoes?
What is the capacitance between two wires? look up the wire-wire capacitance formul (Electric Fields between two wires)
What is the capacitance between a wire and a plate?
After you ask these questions, and you gather up just a few (4? 5?) formulas, you can perform your own analysis of electric-field-induced stray currents. You will begin to think about shielding, and you will be on the way to designing high-fidelity (high signal-noise-ratio) circuits and systems.

What is signal ground


Intall CU to New SP2016 Farm?

Question: when installing a new SP farm, is it recommended to install the CU before or after running the products configuration wizard for the first time ?
Answer: Each time you install a Public Update, you must run the Config Wizard. The order you're asking about does not matter. You can either install RTM and then the PU you need to, then run the Config Wizard, or install RTM, run the Config Wizard, install the PU, run the Config Wizard.
Just don't forget that you must install both the sts-x-none and wssmui patches each month (with an exception of the Feb 2018 patch - only sts-x-none was released and you would use the wssmui patch from Jan 2018).
Comment: Thanks trevor, so no problem on Installing the CUs/PUs, before configuring the server right ?
the questions is because we wanted to install the "App Server with distribuited cache Min role", but it is not available on the original Release
Comment: There is no such role, there is DC + FE and App + Search. But yes, you can install RTM, then say March 2018 PU and finally run the Config Wizard.
Comment: Right ! it is FE + DC , sorry  for the confusion !
Answer: If you want to configure a MinRole Arhitecture, you should install PU before running Configuration Wizard, as long as MinRole is available after 'Feature Pack 1'.

Intall CU to New SP2016 Farm?


ADC Selection Pulsed Measurement

Question: I am planning to measure the voltage of an rgb LED pulsed with an ADC. The pulse is around 20ms long. The pulse is necessary so the self-heating is within reason so it won´t affect the any characteristics.
My Question is now what properties my ADC should have like Sampeling Rate, Bits, etc. so my measurement will be good.
Comment: The first thing you need to do is define what "good" means to you. That will be necessary to define all of the ADC specifications.
Comment: Why are you applying a voltage pulse instead of a current pulse? If you have a good model for Vf=Vt+If*Rs you only need to know Vt for each colour and measure Rs which may have a tolerance of +25%/-10% for good parts from 10%*If to max for calibrated color mixing
Comment: Using a test validation of the Cauer model and tempco, ΔVf/ΔT   of  -2 to -5 mV/'C (?) you choose an error voltage ΔV from the desired ΔT for a pulse of Δt then measure the Vt at 100uA or 0.1% Pmax to know that your assumption of  ΔT~0 is valid.
Comment: What does an "analog to digital converter" have to do with pulsing an LED? How would those two things interact?
Comment: If you want to measure a voltage peak, a voltmeter with peak-hold feature is an ADC with display and range controls.
Answer: Regarding your use of the pulse: good idea. Lets examine how long that pulse should be, if you want to measure the LED properties.
A cubic meter of silicon has 11,400 seconds thermal time constant. This is measured by uniformly heating one face, letting the heat flow out the opposite face, and insulating the other 4 faces.
A cubic 0.1 meter (10cm) is 100X faster, at 114 seconds thermal time constant.
A cubic cm is another 100X faster, at 1.14 seconds thermal time constant.
Notice all these sizes --- meter, 0.1meter, 1cm --- are much larger than the size of the LED junction depths.
A cubic millimeter is another 100X faster, at 0.0114 seconds (11.4 milliSeconds). This may be the size of the LED silicon, but what about the junction depth, right below that bond wire?
A cubic 0.1mm ---- 100 microns in size, or 4 mils, or 0.004 inches --- is another 100X faster, at 0.000114 seconds, or 114 microSeconds.
A cubic 10 microns is size is thermal time constant of 1.14 microSeconds.
The 10 micron size may be about the accurate sampling window, if you wish to avoid thermal heating effects.
Comment: Well, i already tried to create a thermal model with ltspice ( Cauer Type). The self heating is within reason. But i am not sure what sampeling rate etc my adc should have in the range of 20 ms
Comment: @ValentinHuppertz you should consider taking several fast readings and then you will know how many milliseconds might be "too many". In my experience on power MOSFETs suffering from catastrophic thermal runaway, the device can be "dead" between 100 us and 10 ms after applying power.
Comment: @ Andy Some years back I used a grid simulation, in SPICE, to show how an OVER TEMPERATURE detector needs to be within 10 microns of the Power Transistor being protected. And 10 microns is1.14 microSeconds.; the 10 micron size is about the **DEPTH** of the collector junction for bipolars, and perhaps the **WELL** depth for MOSFETS. That 10 micron distance is to PROTECT THE DOPING, to shut off the transistor before the temperature is melting the metal and migrating the doping.

ADC Selection Pulsed Measurement


Hilbert class field whose class number is 1.

Question: How to describe Hilbert class field of an imaginary quadratic field whose class number is 1 ? What happens to unramification at finite places ?
Answer: In general, if $K$ has class number one, then the ring of integers $\mathcal{O}_K$ is a PID, hence an UFD. In this case, $K$ is its own Hilbert class field - see here. Indeed, a number field $K$ with class number $1$ cannot have an abelian unramified extension larger than $K$ itself.


Anyone tried to bond merchandise in Qatar airport?

Question: Has anyone tried bonding hand carried merchandise into Qatar for one day stop over? I've looked in Hamad airport website if they have that service but couldn't find any information . I will be travelling to Qatar with precious stones for a one day stop over, I need to know if I could leave them at customs and pick up when I depart or will I be able to just carry them outside.
Answer: What I know for sure,

The Doha airport has no locker facility for in-transit passengers.
If the stones you have are in the form of some Jewelry and you are wearing it, then you can carry with you outside the airport.
If you can not carry them, book the lounge which provides the locker facility. There are lounges at Doha airport which provides the safe locker services. (Charges may apply extra)
You can also book a good transit hotel room which has locker inside.

Make sure,

You must carry proofs of those stones/Jewelry belongs to you.
-If customs finds those stones, then you should have enough evidence to show that they are not for sale.
Confirm the amount of jewelry or stones you can carry with you. Every country has specific rules when it comes to GOLD and Diamonds.

For more details read this Security and Custom @ Doha Airport
My suggestion,

Carrying highly valuable items during travel is always risky. That too when you are traveling to a unknown country. try to minimize the risk by keeping all paperwork needed and follow the rules and law of that specific country.

Hope this helps.


When can an AggregateException contain more than 1 inner exception?

Question: I have a question regarding the .NET Task Parallel Library's error handling. In which cases will an AggregateException hold more than 1 inner exception? I know this can happen for ex. when calling Task.WaitAll(anArrayOfTasks), and 2 or more tasks are throwing an exception, but are there any other cases (i.e., can it be possible that, if only waiting for 1 task to finish, you get more than 1 inner exceptions)?
Comment: Not related to Parallel Library. Suppose you have a method to delete a list of files, but some are locked. You can use an `AggregateException` to rethrow for the locked files and continue to delete the rest of the files.
Answer: A task can raise an aggregate exception which inherently can contain multiple inner exceptions. This means that you should always consider an aggregate exception with multiple inner exceptions when working with tasks. Even if you're not using Task.WaitAll, the task you're waiting on might internally wait for multiple subtasks. Alternatively, the task your waiting on might return multiple exceptions. You simply can't know as a caller.
Comment: I agree that in the general case, you should assume that you might get a list of exceptions and design your error handling as such, I just want to know if handling a single async task which does not depend on other async tasks will ever create a situation in which more than 1 exception is being passed.
Comment: Might, just might. It's not very likely though. IF the inner task waits for mulitple child tasks. A new AggregateException will be created containing 1 AggregateException containing multiple (possibly aggregate!) inner exceptions. Therefore its always a good practice to call the Flatten method over the AggregateException in order to get all exceptions and handle them as a collection
Comment: How would you pass the errors to the UI in this case? Normally, if performing an operation, you can have two outcomes, either success, or an error. Designing an UI to implicitly handle error lists would seem confusing in my oppinion, and having two cases (one for one error and one for multiple errors) seems to overcomplicate things. I was thinking of always handling at most 1 exception in the UI, and logging all exceptions (and presenting a message to the user to check the error log for ex).
Comment: Thats a valid question. Going Async means that instead of having the luxury of havign linear code where if one branch fails, you can precisely act , you have multiple branches of code that execute at the same time where each one of them can end up in a unsuspected state (exception) and you have to recover from all of them. Exception handling is not as simple as showing a message box. What if your download operation fails in the middle. Is the socket closed? What if 2 async download operations fail? I would suggest you rethink your design based on async principles
Comment: I presented an oversimplified version of what I'm trying to achieve, but still, I will probably treat exceptions on a per-case basis, as exception handling in async scenarios is too complicated to find a silver bullet for it.
Answer: This can happen if you have a "parent" task and one or more "child" tasks that are attached to the parent. What that means is that the parent task will finish only when all of its child tasks finish and the exceptions from child tasks are also propagated to the parent task.
Take, for example, the following code:
var task = Task.Factory.StartNew(
    () =>
    {
        Task.Factory.StartNew(
            () => { throw new Exception("inner"); },
            TaskCreationOptions.AttachedToParent);

        throw new Exception("outer");
    });

If you Wait() on that task, it thows an AggregateException, that looks like this:

AggregateException

Exception: outer
AggregateException

Exception: inner

If you don't like that it can contain AggregateExceptions inside AggregateExceptions, you can use the Flatten() method. There's also another method that can be used for processing of AggregateExceptions: Handle().
Comment: Thanks for the answer, +1 for mentioning the Handle() method, I didn't know about that.