Self-Studying Textbooks

Question: What's the best of way of going through a math textbook for self-learning (and not for  a class)? I ideally want to read material and spend most of time on solving problems in the book. My struggly with reading books myself is that I tend to get bored in the first few chapters when the book introduces basic machinery that's not particularly interesting. How does one get through these parts of the book, and what are some things to keep in mind while self-studying a textbook?
Comment: What textbooks have multiple chapters of uninteresting machinery?
Comment: Suggestions for self-study are apt to depend on the specific book and goals. Saying you "want to read material and spend most of time on solving problems in the book" implies such exercises exist, but advice offered with no more context than that will be overly general.  What level and topics are you interested in?
Answer: Self-learning and book-reading are skills that should be practiced and developed properly. I can't imagine a single answer here getting the job done. If you want to dive into it there's a terrific book called "How to Read a Book: The Classic Guide to Intelligent Reading" (Amazon link for convenience) by Mortimer J. Adler.
It gives a great framework for book-reading and you can generalize it to any kind of self-learning, also, it deals mostly with expository books (Textbooks). It addresses your boredom issue as well.
Every learner should read this book. Especially self-learners.

Self-Studying Textbooks


query only recalled record for approval process

Question: I have a requirement in which I need to query only those record which are recalled, is it possible for using query or through report.
Comment: Can you try `SELECT Id, Status, TargetObject.type, CompletedDate FROM ProcessInstance where status ='Removed'` SOQL
Comment: Please tell me one thing, what is the difference between removed and recalled which word i use in where condition e.g where status='Removed' or where status='Recalled'
Comment: I don't think Recalled will work. Once the record id removed from approval it will change the status to Removed
Comment: how can i access this object through UI, I can't see this object in object manager.
Comment: You wont be able to see this object in object manager as you cannot customise this. Please find the below [article](https://developer.salesforce.com/docs/atlas.en-us.234.0.object_reference.meta/object_reference/sforce_api_objects_processinstance.htm) for the object reference which shows you can use it in query(), retrieve()
Answer: For the records that are recalled you will have status as "Removed" you can use the below SOQL to get the records that are recalled.
<code>SELECT Id, Status, TargetObject.type, CompletedDate FROM ProcessInstance where status ='Removed'
</code>


Is it possible to make token cross chain after its deployment?

Question: Hi i needed to make our ERC20 token crosschain but in process something went wrong and it is deployed on different blockchain with completely different address from other blockchains that is previously deployed. I am not sure if i is possible to do another deployment with same wallet credentials(or is it?), i wanted to see if is it possible to make it cross chain after deployment ? Now i know for moving tokens from one blockchain to another with bridges and atomic swaps but is it the same as being cross chain? If it possible something of above can you tell me in witch direction to start?
Answer: I assume your asking if it's possible to re-deploy the token at the same address being deployed to on other chains.
I think based on what you mention it is not possible, because a contract address is determined based on two factors: The nonce of the sender, and its address. The nonce being how many transactions has been made from the address.
So I assume why the token contract was not created at the same address that you have in other chains is because of nonce inconsistency.
What you can do is to re-deploy the contract with the same nonce from the same address at different blockchains to reproduce the same address. But as I told you, your problem can't be fixed if you missed the nonce that produces the specific address of the token.
You can get the nonce with getTransactionCount  in web3.js
Answer: You can deploy deterministic smart contract to different chain using factory method. In this you can apply same salt to deploy a deterministic smart contract using Factory approach. You can know the contract address before you deploy it. If you want to deploy same contract in same blockchain then you have to destroy the contract but you can deploy in different blockchain (EVM based) the same contract using Factory method and salt. In this case Factory will be the deployer of the contract, you can tweak the smart contract to make your wallet owner of the contract easily.
A simple example code:
//SPDX-License-Identifier: None

pragma solidity ^ 0.8.7;

contract Factory {
    address public owner;
    uint _salt = 1234;

    address public autoCode;
    bool public paid;

    receive() payable external {
        autoCode = address(0);
        unchecked {
            deploy();
        }
        paid = true;
    }

    constructor() {
        owner = msg.sender;
    }

    function deploy() public {
        paid = false;
        if(address(this).balance > 0)
            payable(owner).transfer(address(this).balance);
        autoCode = address(new AutoCode{salt: bytes32(_salt)}());
        require(autoCode == getAddress());
    }

    function getBytecode() public pure returns (bytes memory) {
        bytes memory bytecode = type(AutoCode).creationCode;
        return abi.encodePacked(bytecode);
    }

    function getAddress() public view returns (address){
        bytes32 hash = keccak256(
            abi.encodePacked(bytes1(0xff),
            address(this),
            bytes32(_salt),
            keccak256(getBytecode())));
        return address(uint160(uint256(hash)));
    }
}

contract AutoCode {

    address public owner;

    receive() payable external {
        destroy();
    }

    constructor() {
        owner = msg.sender;
    }

    function destroy() public {
        selfdestruct(payable(owner));
    }

}


What is the name of the image file used for the white tag backgrounds?

Question: Tags are very difficult for me to see on this site because I use reverse-video colors but the tag background image is hard-wired to be white (so I can't see my light text on it).  On other SE sites I've used AdBlock (in Firefox) to block the background image, but that's not working here, nor is pattern-matching the file name from other sites, nor could I deduce it by inspecting the HTML source for a page here.  Can anybody tell me what file name I need to block -- or, if you've got some other implementation here, how I can turn it off so I can read tag names?
Answer: It's not actually an image, it's a CSS gradient. If you want to adjust the style of the site to match your specific requirements I recommend installing the Stylebot extension for Chrome or Stylish for Firefox with which you can click an element on the page and then change its CSS however you want.
Basically you'll want to find .post-tag and then remove or change the background rule used by your browser (for Firefox, it'll be the background: -moz-gradient rule, etc.). Let me know if you need more help.
(Note that there are more rules being applied to the element so if you remove the gradient it'll fall back to background-color, etc.)
Edit
OK, so the first thing you do is click the little S in the bottom left of the browser window to open the Stylish context menu. Then select "write new style -> for ux.stackexchange.com". This will pop open a little dialog. Name it whatever you want (like "Fix tag backgrounds") and then in the code field, put the cursor on the line after the one that starts with @-moz-document and paste:
 .post-tag { background: black !important }

Make sure that after this line, there's a } to end the contents of the field (which you shouldn't need to add; it should already be there).
Then hit preview to see what happens to the page, and save to save it permanently.
You can play around with different colors if you want; CSS accepts a lot of plain english colors; here's a chart (note that if you want to use multiple words, like Pearly Gates, you should surround it in quotes).
Hope that helps!
Comment: Thanks!  I have Stylish but I don't really know CSS (thus far I've pretty much used it to change font sizes and text colors).  Are you fluent enough to be able to give me an example of the style I could plug in to do this?  Thanks!
Comment: @MonicaCellio Done!
Comment: Thanks very much!


Is there any way to check user activation link has been sent

Question: I have created user by profile-2 module with some certain roles,Initially user is in block state,there is one user manager that approved this user and send activation link by email.so how to check activation link already sent or not. if link already sent then need not send again.
For this Is there any module or custom code.
Please help me if anybody knows this.
Answer:
Use Mail Logger  module. It simply logs all outgoing emails into a database table.
You can view the logged emails by going to the Reports -> Outgoing Mail log entries page.
Comment: Thanks for your help but in this module we can clear log.If admin clear log then we miss the values.
Comment: That's why permissions are there. It requires a permission *access mail logger*. Just provide those permissions to users who want to clear the log


my dumb cane's leaves are browning and

Question: I have this dumb cane that I bought 6 months ago from a local store. It did not grow much since then, may be 2 leaves. The existing leaves are also turning brown and are curled up. I also saw something like fungus few weeks ago. So I sprayed some water mixed with baking soda. I water it once a week and it is placed near a window (but not too close). I thought it might be overwatering that's causing browning and inhibiting growth. So I repotted it using store bought potting soil. I washed the roots thoroughly before repotting. What else could I do in order to make it a healthy plant.
Answer: You probably were overwatering it.  You have already done way more than you needed to do.  Just let it get settled in its new pot.   Only water it when the top 1-2" depth of soil is dry.   Never water on a schedule.  Plants will dry out at different times, based on many environmental factors.
Assuming it is winter, you should not next expect it to be growing.  Indoor plants in winter are in a semi-dormant state.  They are still growing, but much much slower.  Since they are growing slower they need much less water.  So it is important to only water when the plant needs water.
I caution making anymore changes.  I also caution you spraying anything on your plant, unless you know what the problem is.  The wrong spray can make things much worse.
The only other advice is to give it a bright window.  They like very bright, but indirect or diffused light.
Answer: What kind of water are you using?  These browning margins and tips are indicative of high salts building up in your soil.
Don't water until your plant/pot/soil feels light when you pick them up. If you are on city water that would be a very good reason the tips are turning brown. The water is full of salts
What do you do for fertilizer?  Another salt source.
You could take your plant into the shower and turn on the cold water.  Soak your plant (s) turn the water off and allow them to drain well.  Don't use saucers for this drenching.
Pick up your plant and its pot and feel the heft of your plant with soaked soil.  You'll be able to tell clearly your plant needs water.  Do not water until that potted plant feels very light.  Just do not water.
Otherwise, your plant looks healthy other than too much water, the soil stays wet too long and the salts will continue to brown the margins and tips.
For better drainage, put some broken pieces of tile beneath the pot and above the saucer.
Comment: I am on city water and I use that to water my plants. I will start using filtered water now, thanks. I used plant food once but I don't know its name. I will update you once I have that info ready.
Comment: I used to buy distilled water from the store in the city to water a few plants. Sounds as if your plant is ready for fertilizer.  Even numbers.  Use half of what the directions, direct.
Comment: what kind of fertilizer would be good for it?
Comment: The best fertilizer I recommend is all purpose, extended release Osmocote 14-14-14 and make sure! you use only half of the recommended directions!  Adding this stuff to your plant's soil (potting soil) will be once maybe twice per year!  At half the directed amounts.  You are a good daddy for your dumb cane!!

my dumb cane's leaves are browning and


Difference between "ignorant" and "uninformed"

Question: What is the difference between ignorant and uninformed? In ordinary usage, is one considered a put down and the other considered a statement of fact? If so, why? Am I ignorant or simply uninformed?
Comment: In southern U.S. dialects, "_ignernt_" (ignorant) is used to mean either unintelligent or stupid, "Well that's just ignert!" "Ignorant" has a stronger derogatory connotation than "uninformed".
Comment: Not an answer as such, but I think it's worth mentioning that the word *ignorant* has a rather different meaning in Scotland and parts of the Caribbean, to that in the rest of the English-speaking world.
Comment: @Mark And that meaning is ... ?
Comment: I'm not sure of a precise definition, but it seems to be something like "arrogantly stupid", as opposed to merely uninformed.
Comment: @MarkBannister. There's a similar usage in Ireland. Here, *ignorant* seems to mean "belligerent" as much as anything else.
Answer: Ignorant means the person in question did not bother to "get informed". Being uninformed can have several causes, not necessarily that of not showing concern.
Comment: *Ignorant* implies a lack of sophistication and education. *Uninformed* doesn't necessarily mean you are uneducated; you just haven't received a particular piece of information yet.
Comment: That's can't be right, because children are ignorant, but it's not a question as to whether they are bothering or not.
Comment: @vy32 That's _exactly_ what it is.
Answer: Well, I hate to disagree with @Milosz, but negativity attaches to both adjectives. Calling someone uninformed is simply a politer way of calling them ignorant.
If you're looking for a more neutral adjective, try unaware.
Comment: Can we get a definitive reference, rather than just some opinions?
Comment: @vy32 Although I understand your frustration, I'm afraid a definitive reference wouldn't be of much help, even if one was to be found. This question seems to be more about individuals' personal opinion rather than any conventions (or lack of those), as illustrated by the equal distribution of votes amongst seemingly contrasting answers.
Comment: As to @Robusto's answer, whilst it is common to say something along the lines of _"I was not wrong, I was uninformed"_ or _"A well-intentioned but uninformed advice"_, paraphrasing those sentences using _ignorant_ would result in a significant difference in connotation.
Comment: As with many such terms, a lot depends on how you say it. Like if you say, "No, wait, Sally, I think you are just uninformed about how to enter data into the new computer system," that would probably be understood as more explanation than criticism. But if you say, "I can't believe somebody could be as ignorant as you! Do you need help dressing yourself?!" that would probably be taken as an insult.
Comment: Disagree.  Context can attach negativity to practically any word, but no negativity at all conventionally attaches to *uninformed* as the word *in and of itself* is used by good writers, any more than negativity conventionally attaches to *forgotten* or *short.*  The word in this sense is not at all like *thankless* or *wicked,* among others, to which negativity does attach even when no specific context is supplied.
Answer: People often contrast "stupid" from "ignorant". "Stupid" means a lack of intelligence, an inability to comprehend information. "Ignorant" means a lack of information.
"Uninformed" means pretty much the same thing as "ignorant". It has a milder tone, but that's about the only difference.
Answer: As can be seen from the form of the word, 'ignorant', strictly speaking, means 'having ignorance,  ignoring the facts, not caring'. However, as is often the case, people use the word loosely to suggest lack of knowledge. It is certainly pejorative. It can also imply lack of social grace, particularly in the expression 'pig ignorant'.
I would say 'uninformed' was designed to be emotionally neutral, a mere statement of fact that someone is not in full possession of the facts. However, the manner of delivery of the word can convey contempt. If a governmental policy etc. is described as uninformed, it implies that not enough trouble has been taken to ascertain the facts.
Comment: @BarryBown: No, you have it backwards.  You are carrying the current connotation of _ignore_ onto _ignorant_.   Actually, the primary sense of _ignorare_ in Latin and _ignorer_ in French (i.e. the earlier senses) is simply _to not know_.   The English sense of _to willfully choose to "not know"_ is more recent.
Comment: @ThePopMachine:  Not only is the English sense of *to willfully choose to "not know"* more recent, it is also seldom attested by good writers, who (as you have observed), know what *ignorare* actually means.  By this I mean no offense to the answerer, who of course is more or less right about the words' colloquial usage in some places.
Comment: @thb Modern dictionaries list the 'not know' sense of 'ignore' as archaic, or simply only list the meaning you say is rarely used by good writers. Online Oxford mentions the original sense in the etymology, but does not list it.


What was on Debbie's list?

Question: In the Ocean's 8 movie, Debbie Ocean (Sandra Bullock) has a list of 15 items. The piece of paper is shown a couple of times in the movie. Once, when Debbie and Lou (Cate Blanchett) are sitting in their den, on a table and Lou tries to snatch the list while Debbie swiftly moves it away. Lou says something to the tune of "you can add him to the list".

 I guess the him in question is Debbie's ex, the guy she is trying to frame for the heist.

The next time we see the list is towards the end of the movie when Debbie scratches off number 14 from the list.

Who's Who

All items preceding the 14th are already crossed out with only the 15th remaining. My guess is these are plays that she may have learnt from Danny or is her heist bucket list of sorts.
UPDATE:
The list seems more likely to be a list of cons. Leaving the 15th item unchecked gives the makers an opportunity to suggest that Debbie is not done yet and there might be a sequel to follow.
Answer: This answer is not complete, as I cannot tell what the items mean, but we can list a few of them at least.

More the merrier

Made in Heaven

Hallellujah Time

Spring Break!

Crack in the Mirror

Poof!

Deviled Eggs

Who's Who?

Cupid's Delight

Now, we are pretty confident that Debbie didn't go on Spring Break after leaving prison. Also playing Who's Who, or listening to Queen's Made in Heaven seems fairly pointless to have in a bucket list.
I would say these are code-names for cons, similar to the first movie.

Made in Heaven is maybe the delicious soup that induces vomiting
Hallellujah Time is the moment when Daphne is on her knees pucking
Spring Break is when Yen and Lou are stealing all the other necklaces
Poof! is the removal of the Toussaint
Deviled Eggs is putting it into a tray to be split in the kitchen.
Who's Who seems to be the final stage of the plan, where the necklace was split between all of them.
Cupid's Delight is probably the framing of the ex.

This is pure conjecture, as I could not find any sources to corroborate any of this.
Answer: Most of the names of the cons reference common idioms and sayings that serve to describe the action in vague terms. Made in Heaven is when they set Daphne up with the skeezy gallerist who sent Debbie to prison. "Match made in Heaven"
Who's who is when they leave the Museum and blend in with the crowd in gowns and the pilfered necklace divided into seven different pieces of jewelry. They blend right into and are indistinguishable from a "who's who" of celebrities and socialites. That one works on two levels!!

What was on Debbie's list?


Which processor architecture is best suited for biginteger arithmetic?

Question: If I were to write assembly code for large integer calculations (e.g. prime factoring, modulo calculations, etc.) with a focus on speed, which architecture would be best suited for this: x86(-64), ARM, PowerPC, MIPS or others?
Comment: Sorry but this question unanswerable in its present form: you're mixing architectures that are at this moment not even targetting the same market segments (mobile vs desktop vs server - so, best suited in what type of computer?).  You could  restate the question as best integer performance per Hertz or per Watt, that might be answerable...
Comment: What language do you plan to use for this ?
Answer: If you work with a small number of variable-size numbers, I think POWER 6 would suit your needs best (although I didn't work with this architecture) since it provides high IPC and very high frequency (up to 5GHz).
It you work with a large number of fixed-size numbers, x86-64 would be the best choice as it has SIMD operations which work on 64-bit numbers, and you can use those operations to speed up long arithmetic operations on multiple numbers. You will likely need an SSE 4.2-capable CPU (Intel Nehalem/Westmere/Sandy Bridge, or the upcoming AMD Bulldozer) since the 64-bit compare instruction PCMPGTQ was only added in SSE 4.2
Also, these GMP benchmark results might be interesting for you
Comment: Yes, but they do not support 64-bit SIMD operations, and using 32-bit SIMD operations is not worth it - simple (non-SIMD) 64-bit ALU operations will deliver better performance
Comment: Power6, Power7 also have SIMD (AltiVec/VMX/VSX)
Answer: IMO nothing beats x86-64, because no one else cares about higher-precision arithmetic
Many RISC architectures like MIPS, DEC Alpha, or RISC-V don't have a flag register so you'll need a separate instruction to get the carry. Therefore they're bad choices and eliminated right away. For example to do a += b in MIPS you need
addu aLow, aLow, bLow     # aLow += bLow
sltu tmp, aLow, bLow      # carry: tmp = (aLow < bLow)
addu aHigh, aHigh, bHigh  # aHigh += bHigh
addu aHigh, aHigh, tmp    # aHigh += carry

With a carry flag you need only 2 instructions: add aLow, bLow; adc aHigh, bHigh
The MIPS designers could have done it better, but they didn't
Higher clock helps as Marco van de Voort said, but those architectures don't have 50%-100% faster clock than the equivalent x86. The remaining things he said are fairly incorrect. It's important to note that arbitrary-precision math isn't trivially parallelized, therefore

Superscalar (more ALUs) doesn't help much because of the dependency chain, which prevents instructions to be run in parallel
Multiple cores and/or multiple sockets are also relatively useless for the same reason.
SIMD also won't generally help‡, because it's meant for processing multiple separate pieces of data and not a single big large integer. You don't have any way to propagate the carry from the lower limb to the next one. See

Is it possible to use SSE and SSE2 to make a 128-bit wide integer?
Is there hardware support for 128bit integers in modern processors?
Is __int128_t arithmetic emulated by GCC, even with SSE?

In short: You really want to calculate the carries in parallel which is very difficult

In the x86 world you already have the carry flag from the beginning. But later Intel introduced the ADX instruction set with the new instructions ADOX, ADCX and MULX for accelerating big integer arithmetic even further. How they helps is explained in Intel's paper New Instructions Supporting Large Integer Arithmetic on Intel Architecture Processors
But it's not only ADX that makes x86 fast. As I mentioned before (‡) SIMD doesn't really help, but nowadays on x86 things may be different. We have very long vectors in x86 (256 bits with AVX2, 512 bits with AVX512 and maybe longer in the future) so if you use various tricks like using a partial-word arithmetic to delay the carry propagation, or arrange the words in strange ways (like llhhllhhllhhllhh) instead of linear like in normal big integer arithmetic (llllllllhhhhhhhh) then SIMD may be faster than scalar operations. For more information you should read

Can long integer routines benefit from SSE?
practical BigNum AVX/SSE possible?
Kogge-Stone Vector Addition

Of course AVX512 will only help if you have very large numbers. Otherwise for a 512-bit number you may have better results with scalar code
No other architectures currently have SIMD registers longer than 128 bits, so even if you can make use of SIMD on them, the cost of calculating the carry would far outweighs the cost of parallel addition. Again this is the reason x86 beats them all
Comment: I think some AArch64 CPUs with SVE (Scalable Vector Extensions) have 256-bit vectors.  (SVE intro: https://community.arm.com/developer/tools-software/hpc/b/hpc-blog/posts/technology-update-the-scalable-vector-extension-sve-for-the-armv8-a-architecture).  I'm not sure how relevant that is, because IDK if SVE has the necessary shuffles to do anything other than pure vertical operations.
Comment: PowerPC has multiple FLAGS registers that I think solves the same problem as ADCX/ADOX.  PowerPC64 should be pretty reasonable for BigInteger stuff on an instruction-count basis, similar to x86-64 unless there are any major gaps I'm not aware of.  ARM64 aka AArch64 may be ok, too; it has 64x64 => high or low half multiply.  (32-bit ARM has some 32x32 => 64-bit 2-output  instructions, but AArch64 only has 32x32=>64 widening or 64x64 -> high half).  But it has integer MAC (multiply-accumulate), unlike x86.  `__int128 * __int128` is fewer instructions than on x86-64: https://godbolt.org/z/K1M_ZA
Comment: But yes, ISAs without FLAGS are definitely at a disadvantage for BigInteger: MIPS, RISC-V, and the obsolete Alpha.  But that's far from universal among RISC ISAs; many RISCs care more about the real world than about RISC purity, e.g. POWER and ARM being the most obvious examples of architectures for which modern high-performance implementations exist.  Of course I think x86-64 is probably still the best bet, but AFAIK it's not fundamentally better than POWER for this, unless x86 `mulx r64` (2 uops) is significantly cheaper than POWER64 `mulld` (64x64=>64) + `mulhdu` (64x64=>high 64).
Comment: The `pmull - Polynomial Multiply Long instructions (PMULL/PMULL2)` from ARM sounds intriguing https://en.wikichip.org/wiki/arm/armv8. I just got an ARM  Cavium ThunderX2 server today with pmull so I'm starting to look into ARM tech.
Comment: @Zboson yeah, the output is quite similar to PPC. I know that they have flags but I didn't know that they also have integer multiply-add


Is this a US military armored vehicle modified for railroad use?

Question: Is the vehicle depicted below some form of US military armored vehicle modified for use on railroads? Is it an MRAP so modified? Is it self-powered or simply able to be towed by a locomotive?
Comment: @ChrisW, it depends on each image search. For instance, this [image search](http://goo.gl/71Q4DW) had 2 pages only of results. I checked them all and none was dated older than the image on pixlr (the date is available either from google or from the post). Pixlr(reputable) had it mentioned also the camera which took the photo "Pentax K100D", and also the users profile has all original photos. One general rule:Google SERP algorithms are extremely smart, and can't be fooled so they will index the first occurrence in the first page. Usually, this is original search and won't be accepted here.
Comment: Please don't answer in comments, use an answer.
Comment: Unanswerable question. A reverse google image linked back to the person who photopgrahed [this](https://www.flickr.com/photos/potjie/3405993963/), he captions it as a Padda, which is **a landmine-protected infantry mobility vehicle that has been in use in South Africa for over 30 years**.
Comment: @georgechalhoub When I use Google image search it returns many copies of the image. How do you use it to find the earliest or original copy of an image?
Answer: Almost certainly not.
Google and Tineye reverse image searches both trace back to this image on Flickr, which describes it as a "Padda" armored patrol vehicle used by the South African railways.  Google image searching on variations of "padda armored vehicle" bring up similar-looking images such as this one.  Perhaps there's mass confusion between a jerry-rigged rail MRAP and the "Padda" (there's precedent: the depicted vehicle has also been misidentified as a rail-adapted version of the Casspir landmine-protected vehicle), but more likely, it's exactly what the Flickr caption says it is.
Comment: Indeed, an earlier commenter found concrete evidence that this specific vehicle is on display at a railway museum in Namibia.


Command prompt in Windows 7

Question: When I open the command prompt, it automatically closes itself after 2-3 seconds. Can anyone help me why Command Prompt in Windows 7 automatically hides after 2-3 seconds?
Answer: You could have a virus running on the system that is closing the command prompt, in order to make it more difficult for you to remove the virus.
Perhaps it is killing processes that are named cmd.exe. I suggest that you make a copy of cmd.exe and call it abcd.exe.  Then run abcd.exe and see if it keeps running.
Comment: +1, I've only seen this behaviour when I've had some virus. Also try to run Regedit and see if it does the same.
Comment: I have seen this virus on XP. Didn't expect to see this one on 7.
Answer: If you are writing a program that executes on the command line, and running it directly from your IDE, not by typing the program name in manually, the command prompt window will close as soon as the program finishes executing. To avoid this, either manually open a command prompt, entering the executable name to run it, or stick a getchar call or equivalent at the end of your program.
Comment: I have just opened the command prompt by writing cmd.exe. When it opens up after 2-3 seconds it automatically close by itself don't know why?
Answer: Are you using Windows 7 build 7000 ? According to this topic, there are known bugs in that build for command prompt and network drives. You can check build version by opening up cmd, see image :

As you see my windows 7 build version is 7601. The lastest version so far. So if your version is before 7601, I suggest you to update to the lastest version.

Command prompt in Windows 7


What is the CFT?

Question: What is the CFT achievement called Crazy Freaking Skills? I have tried all vechiles and none work, I am not sure what the CFT is.
Answer: The CFT is the Crazy Freaking Teleporter.
According to the wiki, you must

Get a best distance of over 800m in the CFT.
Comment: Ok thank you sooooo much Darakath do you know a lot about jet pack if you do I will just ask you next time

What is the CFT?


Splitting table data to pages with numbers

Question: I want to split table data from a database to different pages, everything is good until now, but when I try to to add (?page=) at the end of the url it doesn't work, it's a wordpress page so the url is (www.example.com/page) , when I add for example (?page=) at the end of the url it transfers me to (www.example.com/page/2) but the data are still the same, I limited it to show 4 records in 1 page.
Here's the code to fetch the data from the db, displaying them in a table and limiting them :
            <?php
                $servername = "localhost";
                $username = "root";
                $password = "";
                $dbname = "players";

                $conn = new mysqli($servername, $username, $password, $dbname);

                if ($conn->connect_error) {
                    die("Connection failed: " . $conn->connect_error);
                }

                $start = intval($_GET['start']);
                $limit = 4;

                $sql = "SELECT name, id, connections, first_seen, last_seen FROM players ORDER BY id LIMIT {$start}, {$limit}";
                $result = $conn->query($sql);

                if ($result->num_rows > 0) {
                    while($row = $result->fetch_assoc()) {
                        echo "
".$row["name"]."	".$row["id"]."	".$row["connections"]."	".$row["first_seen"]."	".$row["last_seen"]."
";
                    }
                    echo "
";
                }

                else {
                    echo "0 results";
                }
                $conn->close();
            ?>

Answer: Why don't you use another variable name?
For example: ?pagenum=....
And then on your code you would read that variable:
$start = isset( $_GET['pagenum'] ) ? intval( $_GET['pagenum'] ) : 1;

Comment: Did this helped?


How can I write my answers objectively and in compliance with the site purpose?

Question: Unlike revising an answer to make it objective, what tips can we offer users to answering objectively and in the spirit of the site? I.e., how do we express and assist users in understanding that answers should be scholarly and that any overlap an answer has with their personal beliefs should be incidental (aside from the simple fact that one's religious affiliation might make them somewhat of a reliable resource).
Comment: I was conscious when writing the linked question that in many cases, users are not "aware" of answering from a specific tradition (eg they believe they are just saying what the Bible says, end of story) and may even resent being told that they have a tradition at all. I'd love to find a concise way of talking about objectivity, religious affiliation, background, etc. in a way that makes sense to such users.
Answer: Guidelines and tips for posting answers

Answer from the perspective of an outside observer, such as an archaeologist, historian, or other anthropologist about a denomination, a majority Christian belief, a respected and prominent Christian's statements, or Christian history.
Find at least one relatively credible resource to support your answer before you even write it.

If you heard it last weekend in a sermon, verify it elsewhere first.
If you're attempting to craft an answer that speaks about general Christian belief, just use Wikipedia -- it's democratic knowledge, so it somewhat reliably represents that majority belief.
If you're speaking about a particular denomination's beliefs, find an official resource from that denomination.
If your answer represents a prominent Christian's beliefs, find a quote or citation from that Christian.

Qualify all personal observations, preferences, and other interjections.
State at the top of your answer whose beliefs you're attempting to explain. In doing so, if you find yourself typing, in my opinion, click the discard link.
Offer personal experiences, insights, and analogies only to clarify an official belief, if that official belief is difficult for "outsiders" to understand.
Research other major denominations and be familiar with differences in beliefs. Offer answers from those denominations when able, and answer from your own denomination (if you're a Christian) in a similar fashion.
Comment: I agree with everything here except recommending using Wikipedia.  I know it's usually pretty reliable, but historically, it's been frowned upon a s a source. On the other hand, it's darn hard to find any other source that's close to being as neutral.  I'd play it safe and never answer from a "Christianity teaches" and instead go for the top 3 views. Example: http://christianity.stackexchange.com/questions/12511/how-many-are-there-of-gods-angels/12512#12512
Comment: @DavidStratton Perhaps wikipedia could be an acceptable research starting point. Find a good article, check the references, etc. Could you edit your other suggestion into this answer?
Comment: If you like ... say, >= 75% of what's here, please edit this post rather than submit your own answer. Please add or clarify bullet-points when possible, rather than adding bullets. And, please combine bullet-points and/or remove redundant points when possible. I'd ideally like a single list that easily fits in a single, average, laptop-sized screen to direct answerers to when they get ... excited.
Comment: I'm not so sure if "Catholics Believe" is always the right thing to say.  I asked a priest (who you may know) about participation on this site and he said it's usually better to answer questions by saying "I think" if you've got any doubt.  I don't think people should avoid answer questions just because they're not wholly confident they've got the right answers.
Comment: @PeterTurner Noted. I intended that to be meant a different way than it was interpretable, I think. I'll edit it.
Comment: OK ... I simply removed the last bullet. I think it's redundant and/or implied anyway in the way that I meant it.


Is the two events of an orbiting moon of Jupiter added together to calculate the actual moment?

Question: An observer on earth watching the orbit of a moon around Jupiter.Jupiter is at it's farthest distance from earth roughly 601 million miles which takes light roughly 54 minutes to arrive to earth. When the event of the moon during the observation of the moons orbit passes behind Jupiter the observer views the event happening 54 minutes in the past and the event of the light reappearing at 54 minutes in the past. So does the observer on earth view the whole event 108 minutes in the past for each orbit observed?
Answer: It sounds like you are trying to perform calculations related to Romer's determination of the speed of light.
this link will give you an explanation of what Romer did to calculate the speed of light using the orbit of Io arouhd Jupiter. To answer your question, the earth observer views the event as it happened 54 minutes ago, at that distance. There is no lag caused by any eclipse or like phenomena because the light is not put "on hold" in the case of an eclipse, it is simply blocked. If Jupiter is 54 light-minutes away, then the observer sees events 54 minutes after they happened, and the observer does not view the event 108 minutes after the fact.
Hope this helps.
Comment: Hey Mr Cingoranelli yes I am hoping that perhaps you are interested in the reasoning and constructive discussion concerning the constant.because the dark is instantaneous but the light is not. So each time it reappears it starts a new moment 54 minutes in the past.Kind of like what happens to our moon we do not see the light carrier wave of information in till the reflected light off the moon from the sun returns after the earth blocks the light.that travels from the sun. right? thanks for your interest @rustnorm twitter
Comment: Because dark is the absence of light, dark is not instantaneous. If the travel of light from Jupiter to Earth is stopped, light will still be received from Jupiter for 54 minutes.
Comment: if I had a powerful laser pointed it at the moon after the light is there i shut it off for a 1/4 of a second then turn it back on. There is noway that "roughly"46,000 miles of dark is following light to the moon followed by the light I turned back on see published work at @rustnorm twitter
Comment: I just had another follow up thought light is a carrier wave of present information once it has arrived to be observed and perhaps we a discussing spooky action at a distance aka quantum mechanics. I shall look forward to future interest hopefully lets enjoy the wonderment
Comment: NASA observes a solar flare. 500 seconds later the energy arrives.That means that 8.3 seconds leaves no time for the speed of light to travel with the visaul information. That proves that the speed of visual information is instantaneous, And since dimness is visual information and a light source a billion light years away that is present to be observed dims to dark instantaneously.


Garage door lock broken

Question: The internal side of my garage door lock is broken (first image). Due to this, the cable that pulls the latch is no longer pulling it and hence the garage door cannot be opened (third image). I could not find an exact replacement online or in stores near me for the broken part. What would be the easiest way to have this fixed?
Comment: Just buy a whole new lock, most of them work the same way.
Answer: I would just go and buy a whole new lock.  Trying to repair them by buying pieces, usually cost about the same.
Most garage door locks work the same way, by moving a cable.
Most locks should fit in the same hole as the old lock, even if they look a bit different.
The one I have, has the cable sliding the catches into holes in the track.  Quite sure yours or mine can be replaced with each other.
Comment: The handle mechanism twists to pull on a cable. It doesn't really matter if the other end of the cable is attached to a hinged mechanism like this or a sliding bolt. So long as it pulls the cable, the other end will be actuated. The only twist might be in readjusting the length of the cable if the replacement plate is a different size/has holes in a different place. Shouldn't need to be an _exact_ length, just good enough to cause it to work.
Comment: Bought similar product on Amazon and replaced it. It was an easy install.

Garage Door Lock-Inside Release Handle- Black Plastic Direct Replacement https://smile.amazon.com/dp/B07H3JG6SJ
Answer: Find a metal bracket or piece of steel, drill where the holes are, and either pop-rivet, bolt, or best, weld it onto the existing broken bracket. Might even get away with welding the broken bit back in place, but it looks flimsy to me. Mine was the same - designed so that it would break if someone forced the outside handle trying to gain entry when it was locked. Which actually happened.
With easy access from inside, I also drilled through the runners, so a bolt (or padlock) could be inserted from inside the garage, to stop the door being lifted with a lever - the rollers would just jam.
Answer: Bought similar product on Amazon and replaced it. It was an easy install.
Garage Door Lock-Inside Release Handle- Black Plastic Direct Replacement https://smile.amazon.com/dp/B07H3JG6SJ
Comment: Self-answering a question is great. Answering it by stating that you did what others recommended, then giving your answer the check-mark (accepting it as the "correct" answer) is... tacky. How about giving credit (up votes) to those who provided you with help, then selecting one of the "buy a replacement" answers as the "correct" one, since you probably wouldn't have taken this action without their advice.

Garage door lock broken


Exim - Limit sent mail bounce to the user

Question: Exist some way of to limit sent mail bounce to the user with system filter of Exim MTA?
I need set the header from of the mail bounces in a file, but not know like read it content.
Thanks
Answer: You can create a central filter to filter those bounced messages. With the current exim.pl you can track who is sending emails. There is an option to turn on a limit for how many emails are sent by a particular user. To enable this limit, simply add the number of emails you'd like to allow per day to the /etc/virtual/limit file.
<code>echo 300 > /etc/virtual/limit_username
</code>
where username is the user for who you would like to give the limit to.
Also Refer: http://www.farhad.ca/2006/07/27/how-to-disable-delayed-bounce-back-messages-in-exim/


Battery or alternator issues

Question:
Hey so I just purchased a car put a new battery and alternator on it my kids left the door open for many hours and once I put the cables on the battery it'll crank but once the cables come off, the car cuts off as well sometimes it won't do it immediately after I'll have it running and after about 5 minutes it cuts off too. Does anyone know what could be wrong?
Comment: The battery is just used to start the car. The alternator provides power to all the electrical bits, and charges the battery, when the car is running. If the car dies shortly after starting, then I suspect a bad alternator, or, as @RobertSBarnes said, a loose connection. (I wouldn't expect it to run, then die after minutes, if that were the case, but intermittent electrical connections are funny beasts.) Also, punctuation is your friend! :)
Answer: since the battery and alternator are both new it sounds like you might have a loose battery cable or that it's not making a good connection.  it's also possible that by a fluke you got either a defective battery or alternator.  best to take it to an automotive electrician.

Battery or alternator issues


delta neutral option cost

Question: I am trying to understand how an delta neutral profile is generated. I sell a call for strike of 50$ and the delat of this call is 0.5. I buy 0.5*100 stocks to remain delta neutral. Now when the market moves up buy 2$ the new delta is 0.6 . So I buy 10 more stocks and the market now moves down by 2$ which makes me sell 10 stocks. Every time I buy at 52$ and sell at 50$ since the total portfolio value seems to decrease when the stock moves up and down. How does this work in the BSM model ?
Answer: If you sell a call option, in the language of vol trading you are short gamma and vega, and long theta.
So yes, as the underlying wiggles around, if you keep delta-hedged by trading it you will lose some money. This can alternatively be seen as gamma losses (coming from the second-order move in the underlying, which you have not hedged) or as coming from the hedging strategy.
On the other hand, you are compensated for this by the time decay of the option price, ie. its theta.
By the end of the option lifetime, if realized vol over the period (which is effectively what you pay out to hedge) was higher than the implied vol price you received for the option (which was the premium you received), you probably* lost money, and if it was lower then you made money.
*this isn't exactly true due to vol itself being stochastic... here is a great reference on the topic Wilmott, Ahmad: Which Free Lunch...
EDIT
Responding to comment: The first section of the wikipedia page does a good job answering this... if we re-express BS equation as
\begin{align}
{\frac {\partial V} {\partial t}} + {\frac 1 2} \sigma^2 S^2 {\frac {\partial^2 V} {\partial S^2}} = rV - rS {\frac {\partial V} {\partial S}}
\end{align}
then you see that the term on the right (risk-free growth coming from a portfolio of the option and the short delta hedge) exactly cancels the term on the left which is the gamma plus the theta.
So we can hedge away delta, but we are still exposed to these two.
Comment: According to black scholes if Istart buying the stock when I sell the option , I should not lose any money. What am I not considering here?
Comment: First, BS assumes you hedge in infinitely small quantities without transaction costs after every move in the underlying, which hedges out your delta completely. Second, BS assumes vol is deterministic and known at the beginning. However, we would still get some losses from the gamma component due to GBM's "quadratic variation" (basically bigger infinitesimal jumps), it's just that these losses would exactly cancel out our theta profit. This is expressed by the BS equation's partial differentials

delta neutral option cost


Is it possible to copy and paste iCal events in iPad / iPhone?

Question: Is there any way to copy an event in iCal in iPad or iPhone and paste it to a different day? At times, I want to keep the original calendar entry, but repeat on a different day? I am not looking to use the repeat function, as that forces one to use more predictable repeat.
Comment: Yeah - I wish too. I usually satisfy myself with just copying the main event text & pasting into subsequent days. If I'm home, alt/drag on the Mac is a whole lot easier.
Answer: Aside of using the duplicate and repeat there is no copy/paste function.
You can submit a request for the function at http://www.apple.com/feedback/
Answer: I think maybe Apple's team wish users use the Repeat->Custom function when adding an event to create multiple entries of the same thing.
Yet, I also agree a copy/paste feature is highly lacking there...
Answer: A work-around:  email the event to yourself (or create a new event in a new email to yourself).  Hover the cursor over the event in that email, click the down-arrow that appears, edit the date, and then "Add to Calendar."  You can do this for as many dates as you like.
Comment: Can't email an event on the iPhone (unless I'm missing something).
Answer: I have "CalenGoo" on my iPad -- and there's a drag and copy feature which I find indispensable!!  It syncs with Google Calendar (which was why I got in the first place years ago) -- I think they have an iPhone version too, although I like how it works better on my iPad.  Check it out.
Answer: I was looking for this as well when trying to input my work schedule (I work in shifts). The solution I found is to manipulate the repeat function in the following manner: Add the event, select custom repeat "every month", select the applicable days of the month, and finally set the custom repeat to end on the last day of that particular month. It's a hack, but it works. One does wonder why there is no copy/paste feature though...
Answer: Not as such, but I'm using next workaround for non recurring events
(it looks complicated, but try it out, it works quite fine):

Set the event to be repeated e.g. Every Day
Go to the repeated event on the day you need it and set the Repeat back to None and hit the Done button.
Then change the time or add a note, if needed.
When closing the event, a pop-up message appears telling This is a repeating event and prompting you eighter to Save For Future Events or to Cancel.
Choose Save For Future Events.

Result: you have the event copied.

Now, go back to the original event and turn the Repeat function back to None.

Result: The original event is not recurring any more.
Note: You can use the same trick to Copy recurrent events as well. But then, in step 5, you need to go to the next to last of your wanted recurring events and delete it.
Choose Delete All Future Events.
Comment: This is the most ideal workaround given the limitations of iOS. I'd upvote this, but the original request was for a copy/paste solution that doesn't use the Repeat function. But thankful you offered a usable workaround.
Answer: You can not copy/paste an event but you can repeat an event for N-days in a row by using repeat/custom/1 day till end-date for the repeat.


Could I contact with professor and apply for phd position in Germany in the last semester of master study?

Question: I am in the last semester of my master study in Germany and going to publish my master thesis. However, I still need about two months to graduate. Could I contact with the professor in advance and apply for a phd position? I have some project experiences and I can provide the extended abstract of my thesis. Is there a chance that the professor could give an interview? I have sent my CV, Grades, Motivation Letter, Project Report and Extended Abstract of Thesis several weeks ago, but there is no response. Is it the reason that I have not got my master degree?
Comment: When you say "apply for a PhD position", are you referring to an actual, paid job e.g. as a _Wissenschaftlicher Mitarbeiter_ that the professor is offering (which will include time for you to do your PhD) or are you just searching for a professor who may supervise your PhD?
Comment: Related: https://academia.stackexchange.com/questions/193773/how-long-does-it-usually-take-to-hear-back-for-academic-positions-why-havent-i and https://academia.stackexchange.com/questions/45616/how-to-get-people-to-reply-to-emails-and-what-to-make-of-a-no-response
Answer: Yes, now is the time to begin the process of application, not after you finish, unless you want to see a gap in your education.
Why you haven't got a reply is hard to say. Most likely is that the professor just isn't ready to think about accepting a student at the moment or is too busy to be interrupted.
But, if you want to find a position, don't depend on any one contact. Cast a broad net. And, preferably, apply to those who have indicated they are currently looking for students. It improves your chances.
If your first contact was "blind" and extensive, it is possible it was just trashed for lack of a current position. You can ask, since it has been several weeks, if there is a chance for a position. You might get a reply to such a mail.
Comment: Just to add to this: If you aim to be employed by the university you apply at, going through all the necessary steps (candidate selection, having the work contract made and signed...) can easily take a few months. Even if you cannot sign the contract until you have your degree evereything else can be prepared beforehand, provided that the professor is convinced.
Answer: For the sake of this answer, I assume you are looking for a position as a Wissenschaftlicher Mitarbeiter.
Definitely start applying before you finish your Master's thesis. Professors may or may not have open positions (= funding) for PhD students, and if you apply early and they want you to work with them, they may even try to secure funding to enable that. So I don't think that your currently unfinished Master's degree is the issue here.
In my experience, professors are often busy and have long queues of unread e-mails. If you are cold-emailing someone and do not have prior contact, they might not reply at all. I've seen some professors requiring you to put a specific keyword in your subject line when e-mailing them about the possibility of working with them, to show you have informed yourself about the position and their work (e.g. on their home page). Make sure you do that.
It can also be helpful if you know someone else who is already working in the group you are interested in. They already know the ropes and may be able to set up contact.
If this is someone at your current university, you could make an appointment during their office hours.
In general, try to apply to positions that are already being advertised, but also ask around for new openings. Academic positions may also be published on social media, e.g. Twitter, Slack channels for conferences, etc. Make sure your application shows that you are interested in the specific position and group you are applying to and that you have read some of their current work.
And, like when applying to a job in industry, don't assume that you will get the first and only job you apply to. Send out multiple applications.


What determines your spirit guide?

Question: In Myst IV, what determines your spirit guide? I'm on my second play-through and I got Water again so I was wondering how it can be changed? Just to be clear -- I know what to do after you get your spirit guide and what the spirit guide affects, but I want to find out what choices in the game lead to the protectors giving you a certain spirit guide.
Answer: Explanation based on information from ubi forums and mystlore:
Score is a number between 0 and 3, starting at 1. It determines which spirit guide you'll get and is affected by following events (most of which increase it):
In Tomahna:

Take a photo on the monorail: 0.1
Finish the sound puzzle with Atrus: 0.1
See Yeesha's gecko: 0.1
Watch Yeesha play her flute: 0.1
Contact Atrus with the crystal viewer: 0.1

Using linking books:

Link to both Haven and Spire from Tomahna: 0.125
Link to Tomahna from both Haven and Spire: 0.125
Link to Serenia from Tomahna: 0.125
Link to Tomahna from Serenia: 0.125

Other actions:

Spend time in the game: 0.5 total for 20 hours (0.0004 per minute)
Use the Amulet: 0.5 total for all 101 flashbacks (0.0050 per flashback)
Use the zip feature: -0.5 total for 30 uses (-0.0167 per use)
Use the hint map: -0.5 total for 25 uses (-0.02 per use)

How score is mapped to title, description and spirit guide you get:

Child of Fire: 0 to 1
Drawn by the excitement of new experiences, always seeking adventure over stasis. Sometimes your desire to succeed makes you miss the deeper meaning but you always find the answers you seek when you really want them.

Child of Wind: 1 to 2
Attracted by challenge and diversity. Always moving swiftly to the heart of the matter yet willing to take the time needed to understand it.

Child of Water: 2 to 3
You appreciate the beauty and richness of life around you. You are confident in your ability to succeed but willing to seek help when answers seem elusive.
Comment: So the answer is "play badly"?
Comment: Here is a more detailed summary: https://web.archive.org/web/20120330092817/http://en.mystlore.com/wiki/Spirit_guide ; According to this, the above list is nearly correct, except that you start at 1 and you actually deduct points for using zip and hint map. So to get fire, you need to make at least some use of zip and/or hint.
Answer: I once read in an older guide that your stance towards Yeesha in the beginning of the game dictated what spirit you got. There are, apparently, two "key points" where you'd be able to "change" your spirit guide. It seems that, by default, your spirit is set to water, just like Yeesha's, unless you trigger at least one of the two cutscenes below:

When you reach Catherine's lab, there's an experiment Yeesha's conducting with her mother involving trapped firefly-like things. If you free them and she comes and sees it, she gets angry at you, which would make you get a fire spirit later on.
(seems to override 1) If you listen to Yeesha practicing her instrument (interestingly, an ocarina-like thing she uses to play one of Haven's themes) by the family tree, you'd get a wind spirit guide.

When I played it, I'd always get wind (I always went downstairs to listen to her), but I need to play it again to confirm it.
Answer: If you burn through the game as swift as a blaze, a Fire spirit lives within
If your feet beneath glide along and kick up a breeze, a Wind spirit lives within
If instead, you enjoy the game, stop to rest or view or enjoy, a Water spirit lives within
Honestly, it's the three different styles of play
Fires of Gryffindor [DPS] - You want to get through as quickly as possible. You aren't concerned about the beauty of the worlds or backstory or exploration. You're probably using a Guide Book to tear through
Winds of Ravenclaw [TANK] - You may have watched some of the Amulet Memories, but probably not many. You haven't quite stopped to smell the flowers or appreciate the sounds of the creatures of Serenia. Swift of mind, the puzzles took you no time. A bit of a challenge, but somewhat like chess to checkers.
Waters of Hufflepuff [HEALER] - Time and Tide, slow abide. A true Gamer seeks every corner, destroys every bit of crockery, and enjoys every tidbit a beautifully crafted game world can envision. To those of Water, every sense abounds with delight as the birds come alive, textures are felt, and for a time at least, you Live in the Waters of Serenia, the Winds of Spire, and the Fireswamps of Haven.
Forgive me, I'm tired and I get a touch poetic. I do hope someone reads this and replies. I love Myst and wish I could be part of the community.
Comment: I've not played Myst 4, but are there really DPS/Healer/Tank classes with Harry Potter names? That seems like a big departure for the series...
Comment: Is that answer is a mistake? Did you want to post it under another question?

What determines your spirit guide?


"About" vs. "around"

Question:
Roam about/around
Wander about/around
Turn about/around

Which one is correct? Or are all of them correct? Can about and around be used interchangeably?
Answer: In all these cases, you can use either form and it will be correct. Around is used exclusively in these verbs in the US and Canada (I daresay). About is more common in Britain and maybe Australia and Ireland, but I can't be too sure. However, they can definitely be used interchangeably, although if you wish to "localize" your text for the States specifically, you would naturally go with around.
Answer: "around" and "about" after verbs of movement
1 to walk around a small town - that is a circular movement at the outer edge of the town
2 to walk about the town - that means going to various places without a definite destination. Maybe it is a newcomer who wants to get to know the town. In my view It should be "to walk about in (the) town" and I think "in" was omitted long ago. But I don't know whether mother-tongue speakers would agree.
"around" and "about" indicating position
3 Papers were lying around the table on the floor.
4 Papers were scattered about the room on the floor.
In 3 the papers are lying in a circular line enclosing the table.
In 4 the papers are lying on the floor at various places.
These are only two uses of the two prepositions. But both of them have various uses and in some uses they are overlapping.

“About” vs. “around”


Suspension seat post is loose

Question: Is it ok that a suspension seat post like the one shown below (source: cyclande.com) is actually a bit loose (moves a bit left-right and probably also up-down).

The vendor told that for such seats it's OK, but I'm not totally sure.
Comment: Am I right that this movement has no impact on the reliability/lifetime of the saddle/bike? This slight movement is not a problem, but I don't want to invest a lot of time and money in reparations.
Answer: An up-down movement is perfectly fine – that's what suspension seat posts are designed for!
For the side movement it's a bit more complicated. A suspension seat post is basically two tubes sliding into each other with some suspension mechanism. This requires two things: the tubes need a little clearance to move within each other and they need a mechanism that prevents the tubes from rotating towards each other – let's call it anti-rotation machanism. The latter can be for example something like a bolt sliding in a notch or tubes with a non-circular cross-section.
The bad thing is, those two elements are somewhat conflicting. An effective  anti-rotation mechanism requires the least possible clearance, which may inhibit the original purpose of the suspension seat post, which is to allow for up-down motion of the tubes. Therefore, the manufacturers have to find a trade-off between suspension performance and precision. Such precision is expensive and would quite surely also make the seat post heavier. Especially the products from the lower end of the price range might quite surely sacrifice some of the precision for a more "reliable" suspension performance.
So to answer the question: yes, some side rotation or wiggle (something like +-2-3 degrees) should be quite common.
Comment: Yes, I saw a 2° rotation, unlikely more than this.
I hope this has no significant impact on the lifetime of the seat post / saddle (see my new comment to the question).
Answer: I have used a couple of these seats over the years - the ones I had did have some movement - noticeable when riding. Although not ideal, you do get used to it.  It comes down to cost - it would be more expensive to precision manufacture them with no movement, but at some point people would stop buying, and another point, might as well buy a full suspension bike.
Answer: Yes, it's ok and to be expected. Even expensive dropper posts, which work via the same basic principles as telescoping suspension seatposts, have a bit of side to side movement. For the suspension seatposts, just ensure that the collar at the top of the stationary (outer) portion of the seatpost is firmly hand tight.

Suspension seat post is loose


Yields and prices when consider demand and supply

Question: I know the relationship between price and yield for a simple coupon bond. When the rates go down price goes up. However, when rates go down, I assume bonds are less attractive and as a result the demand for them falls. As demand falls I expect prices to go down as less buyers want them. Aren't there 2 forces pulling prices in different directions then? Please help me understand which force is more important then in this scenario of falling yields for bonds.
Comment: If rates go down, your fixed rate bond, issued before rates declined has a higher coupon. Therefore, demand goes up, until the ytm matches the general market (it declined sufficiently).
Answer: Interest rate changes do not affect the yield of bonds already sold. If the interest rate goes down, bonds with the older interest rates only increase in value because there will always be higher demand for a higher yielding bond than a lower yielding one.
E.X.
You buy a $100 bond with a 1% interest rate
Interest rates fall to 0.5%
Now, to receive the same amount of interest as the bond you currently have, you would need to buy $200 worth of the new bonds.
So the bond you bought would now also be worth $200. Any price under 200 on your bond would be a more preferrable price than buying from the government.
Comment: "So the bond you bought would now also be worth $200." No, not really. It would be worth whatever the current interest rate says about getting $100 at the bond's end date.

Consider your example: as you say, interest rates fall to 0.5%. Let's consider the bond has a remaining time of 1 year. A newly issued bond will give you $5 after one year, additionally to the $100 of principal. Your bond will give you $10 after this year, so you will be able to sell it for (about) $5 more, thus for $105. The buyer will get $100 plus $10 for his $105 → about the same yield as a newly issued bond for $100.
Comment: While you have the general premise correct (bonds values go down as interest rates go up), the bond would not nearly double in price when the rate is cut in half. Most of the bond value is based on the value at redemption.
Answer: Yields are the driving forces, supply and demand will instantly adjust in the market to match any change on yield. The new perceived yield drives the dynamics of supply and demand. Yield is the magnet.
This is very simplified because there are 10 different types of risks that need to be taken into account to pricing bonds.
The bond market is approximately a $50T market. It is extremely efficient in pricing and re-pricing. If there are any inconsistencies, they will be "ARB*" away almost instantly.
*arb: Arbitrage; If an institution holds ABC "AA" bonds that yield 5.25% while its comparable trade at 5.35%, trading desks around the world will dump the 5.25 (everything else equal) until it reaches 5.35 to buy the 5.35 for the same level of risk (AA).
We might say but what about the newly bought 5.35 will the yield drop because of all the new buys. Maybe but guess what will happen? Sellers will step in.
The bond market is in permanent flow toward a perceived point of equilibrium at any moment in time.
But in your question I see a point I haven't addressed here which is the appeal to hold bonds in a falling rate environment.

It can be very profitable to buy bonds at/near the peak of the cycle just before a recession, for example, not only do you receive the coupon, but, you also get capital appreciation if you wanted to sell before maturity and switch to stocks for example.
The real competition to bonds is equities. So in a sense yes, the lower rates are, the more money will flow to stocks. But as you have also seen from the last 20 years, lower yield did NOT translate into higher supply to create falling prices. Because yields rule and prices will gravitate around the perceived yield curve.

All assets compete with each other. If you don't like your bond at 3% because you know NVDA will triple ;-) while fed fund rates are at 0.5, somebody will buy it from you because 3 is better than 0.5. A lot of institutions and corporations have mandates to hold term paper over equities. Demand is always there and they all trade based on the yield curve, whether rates are falling or rising.
Hope this helps


Magnetic moment of electron

Question: Since magnetic moment come from the circulation of charge, what is the origination of the electron's magnetic moment? Because spin of electron is not the classical spin of particle. Can we say that corresponding to every angular momentum there is a magnetic moment and since spin angular momentum is conformed from Stern-Gerlach experiment so there is a magnetic moment.
Comment: Related question by OP: http://physics.stackexchange.com/q/73946/2451
Answer:
Since magnetic moment come from the circulation of charge, what is the origination of the electron's magnetic moment?

It's not true that a magnetic moment always comes from the circulation of charge. An electron's magnetic moment cannot originate entirely from circulation of charge in some internal structure of the electron, because then its g-factor (essentially the ratio of magnetic moment to spin) would then have to equal 1, when in fact it's approximately 2. Similarly, an electron's angular momentum can't come entirely from this type of internal motion, since it would then have to be a whole-number multiple of $\hbar$.
As far as we know, the electron is a pointlike particle without any internal structure such as preons.

Can we say that corresponding to every angular momentum there is a magnetic moment

I don't think so, since photons have spin, but they have no magnetic moment. In general, QED is the theory that predicts $g$ factors, and the $g$ factors are deduced from the more fundamental principles of QED, not just postulated.
Comment: Ben, how the photon does not have magnetic dipole moment? A photon has both [a varying electric and a varying magnetic field component](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Photon_Spin_%2B1.PNG/612px-Photon_Spin_%2B1.PNG). That we can't deflect the photon with an external electric or magnetic field has to do with the frequency of this field components. But both field components exist, aren't they?
Answer: In classical mechanics, a particle with angular momentum $L$ and a charge $q$ will possess a magnetic dipole given by $$ \mu = \frac{q}{2m}L $$ Now, $L$ refers to any type of angular momentum, orbital or rotational.  In quantum mechanics, its the same idea - up to an additional constant $g$.  So, the intrinsic angular momentum of an electron results in an intrinsic magnetic moment.
Also, the Stern-Gerlach experiment detected the magnetic moment of the electron by observing the deflection of silver atoms in an inhomogeneous magnetic field.  The concept of spin can then be introduced to explain the result.
Comment: if spin of electron is not the classical analogy of spin then how we can relate the classical  magnetic moment formula with electron spin magnetic moment to describe the spin angular momentum.
Answer: The magnetic moment of the electron is associated with a kind of circulation of its charge. This follows from the Dirac equation. To develop a wave-equation that is first order in derivatives, just like Maxwell's equations are for electromagnetic waves, Dirac had to introduce a four-component wave function, known as a spinor. The plane wave solution yields four independent possibilities, two of which are associated with positive energy and the other two associated with negative energy. Ignoring the negative energy solutions and using two independent solutions  $\psi_1$ and $\psi_2$ it can be shown (Bjorken and Drell Relativistic Quantum Mechanics (1964) p.36) that the probability current density of the electron wave has the form
$$
j^\mu \sim \frac{1}{2m} \left [ \overline \psi_2 p^\mu \psi_1 - (p^\mu \overline \psi_2 ) \psi_1 \right]- \frac{i}{2m} p_\nu (\overline \psi_2 \sigma^{\mu \nu} \psi_1 )
$$
where $\overline \psi=\psi^\dagger \gamma_0$ with $\gamma_0=\begin{bmatrix} 1 & 0 \\ 0 & -1 \end{bmatrix}$ and $p^\mu = i \hbar \partial/\partial x_\mu$ the four-momentum operator and $\sigma_{\mu \nu}=(i/2)[\gamma_\mu,\gamma_\nu]$ the antisymmetric product of two gamma matrices.
This is all rather complicated, but the key point is that the term in square brackets $[...]$ has the same mathematical form as the probability current density in non-relativistic quantum mechanics, as associated with solutions of the Schrödinger equation. However, the second term involves rotations of the wave components and represents the spin current. It is this spin that is connected with the magnetic moment. The electric current density is just this probability current multiplied by the electron charge, which thus implies the spin gives rise to a charge circulation.
In saying the electron is a point-like particle, we really mean that in high-energy collision experiments one cannot find any internal structure. However, under usual circumstances (like low energy) the electron wave itself will always be spread out in space to some extent and its charge, likewise, will never be completely localised. Thus we can always claim there is some motion of the electron charge that gives rise to a current.
To decide whether or not a quantum field has a magnetic moment, we need to interact it with an electric or magnetic field. If we do this for the Dirac electron in the limit of low energy, the spinor wavefunction $\psi=\begin{bmatrix} \phi \\ \chi \end{bmatrix}$ can be written in terms of two-component column matrices $\phi$ and $\chi$ and the Dirac equation in an electromagnetic field with vector potential $\mathbf A$ and scalar potential $\Phi$ becomes (Bjorken and Drell Relativistic Quantum Mechanics (1964) p.12)
$$
i \hbar \frac{\partial \phi}{\partial t}= \left [ \frac{(\mathbf p - (e/c) \mathbf A)^2}{2m}- \frac{e \hbar}{2 mc} \boldsymbol \sigma \cdot \mathbf B+ e\Phi \right ] \phi
$$
This equation can be derived from two coupled equations associated with the Dirac equation in the limit of weak potentials and low energy, where $\chi \approx \frac{1}{2mc}\boldsymbol \sigma \cdot (\mathbf p - (e/c)\mathbf A) \phi$. The component $\chi$ depends on the vector of Pauli spin matrices $\boldsymbol\sigma$, i.e. has spin. It is this component that leads to the dependence of $\phi$ on the Pauli spin matrices that couple with the magnetic field $\mathbf B= \nabla \times \mathbf A$.
For a weak, uniform magnetic field we can write $\mathbf A = \frac{1}{2}(\mathbf B \times \mathbf r)$ which satisfies $\mathbf B = \nabla \times \mathbf A$ since $\mathbf B$ is a constant. On expanding out the wave equation with no electric potential we get
$$
i \hbar \frac{\partial \phi}{\partial t}= \left [ \frac{\mathbf p^2}{2m}- \frac{e }{2 mc}\left ( \mathbf L + 2 \mathbf S \right ) \cdot \mathbf B \right ] \phi
$$
where $\mathbf L=\mathbf r \times \mathbf p$ is the orbital angular momentum operator and $\mathbf S=\frac{\hbar}{2}\boldsymbol \sigma$ is the electron spin operator with eigenvalues $\pm \frac{1}{2} \hbar$. The term $ \frac{e }{2 mc} (2 \mathbf S \cdot \mathbf B) \rightarrow g \mu_B \mathbf s \cdot \mathbf B$ which expresses the interaction of a magnetic field with a magnetic moment $\mathbf m = g \mu_B \mathbf s$ with $\mu_B= e\hbar /2mc$ the Bohr magneton and the correct $g$ factor of $g=2$. This demonstrates that the combination of the electron charge $e$ and its spin $\mathbf s$ creates a magnetic moment that interacts with a magnetic field $\mathbf B$. Thus the spin combined with a charge looks just like a circulating current.

Magnetic moment of electron


Command line command to read Oracle Database export Success Message In log File

Question: We have several oracle 19c servers with daily exports. I would like to find a way to run a command to read the export log file to find the success message for the day. e.g. I would like to putty into the linux server have a command I can copy and paste that will read the daily export log file and tell me in one command/output that the export was successful or not? or any better ideas to automate reporting that daily exports are successful on 40+ servers?
Comment: Take a look at `ansible`. This is the kind of automation it was designed for.
Answer: Assume that you always start your export log files with 'expdp_' and always end them with '.log'.  Then
<code>egrep -c '(^Job)(?!(successfully))' expdp_*.log
</code>
will give you a listing of the log filenames and the number of times 'Job' but not 'successfully' occured in that file.  Get a zero count and the export was successful, get a non-zero count and the export had a problem.
Answer: I admit that it is not a command line solution but datapump has control tables and these could be analyzed with SQL


Is it possible to grow brain tissue in vitro? Can we make a super-brain this way?

Question: I wonder whether such experiments were conducted? Is it possible to create a "biological super-computer" this way?
Comment: Hi, this is John from the ethics committee at your local university. Please meet me tomorrow at 9 PM at my office so that we can further discuss the details of your oncoming experiment.
Comment: can you specify what you mean by "brain tissue"? it is possible to culture stem cells to neurons. It is possible to create organoids (artificial collection of several tissues).
Comment: More importantly, you currently asking two questions: is it possible to create artificial brain, and is it possible to use such brain as super computer. COnsider asking two separate questions instead
Answer: This is actually not an unheard of idea among neuroscientists and is an aspect of much research.  Brains in general have amazing computational powers and abilities that allow them to circumvent the limitations of computation which is usually based on a Turing Machine. Neurons pursue highly parallel architectures and exhibit cognition or even emotions or do highly sensitive signal processing, which has heretofore been unapproachable with computational methods such as Machine Learning.
As such many researchers are focused on understanding the brain or at least the brain's structure to augment or produce computation.  Here are a couple of examples of neuron arrays flying virtual or real drones....
The ethical issues aren't great concerns because neural cell networks can be encouraged to grow differentiating from easy to grow cell lines like fibroblasts.
Another approach to augmented computing is to interface directly into a living brain. Model brain organoids are a popular topic of interest and could one day be used to interface to other computational systems.  There are of course many devices that try to interface to the brain via electrical fields in the same way EEGs work.
there are connectome projects that are trying to understand the neural connections between cells that are so important to brain development, with the theory that the topology of these networks might enable even computers to perform like brains.
Comment: Moore's Law of computation (which was in no way a law) was an observation of a trend in the fabrication of computor memory). Unless your brain is receiving upgrades from Intel every two years, your statement would seem difficult to understand.
Comment: fixed this in edit


How can I visualize principal bundles?

Question: I'm trying to learn how to think about principal bundles where the fibre is a lie group with local trivialization $ϕ^{-1}_i:π(U_i)→U_i×G$ . For example $ϕ^{-1}_i:π(S^2)→S^2×U(1)$ (if that makes sense) . But I don't know how to think of this (and other products with lie groups like that) geometrically in 3D space. How does $S^2×U(1)$ look like? I know that U(1) rotates things, but I can't visualize a thing that rotates other things. What does it mean if I put U(1) at every point on $S^2$? It get's even worse if I want to think about a connection on a principal bundle which is defined on the tangent space of the lie group. I guess there is a lot of higher dimensional stuff going on, but isn't there an easy 3D example which captures every concept at once?
Comment: There is a unique non-trivial principal $O(1)$-bundle over $S^1$, namely the unique _connected_ double cover of $S^1$. This is easy enough to visualise.
Comment: @ZhenLin What does this have to do with the question...?
Comment: @OP Do you know that $U(1) \cong S^1$ (as Lie groups), where $S^1$ is the circle, aka the complex numbers of modulus $1$?
Comment: @NajibIdrissi It is the easiest non-trivial example of a principal $G$-bundle that can be embedded in $\mathbb{R}^3$.
Answer: There's no doubt you will have to learn to stretch your geometric intuition quite a bit in order to understand principal bundles. The intuition is built up in little steps, each with their own way of visualization, and there might not ever be one big picture in which to visualize everything, except for the very simplest examples.
Regarding principal $U(1)$ bundles, let me start with a few more-or-less obvious things. $U(1)$ is the circle group. Algebraically, $U(1)$ can be represented in a few ways: as unit circle $S^1$ in the complex plane, with the group operation being multiplication of unit complex numbers $z_1,z_2$ producing another unit cmoplex number $z_1 \cdot z_2$; or as angles, i.e. as elements of the quotient group $\mathbb{R}/2\pi \mathbb{Z}$, and the group operation on two angles $\theta_1,\theta_2$ produces an angle $\theta_1+\theta_2$. These two algebraic descriptions are related by the universal covering homomorphism $\mathbb{R}\to S^1$ given by $\theta \mapsto e^{2\pi i \theta}$.
You say you cannot visualize a thing that rotates other things, but perhaps you can visualize that $U(1)$ rotates any oriented round circle $C$: an element of $U(1)$ represented by an angle $\theta$ rotates the circle $C$ through the angle $\theta$.
Here's an example of a principal $U(1)$ bundle you can visualize entirely in $\mathbb{R}^3$: the bi-infinite annulus $\mathbb{R} \times S^1$, with projection map $\mathbb{R} \times S^1 \to \mathbb{R}$ defined by $(x,z) \mapsto x$. It can be embedded into $\mathbb{R}^3$ by the map $(x,z) \mapsto (x,\text{Re}(z),\text{Im(z)}$.
Regarding the principal bundle $U(1) \times S^2$, it cannot be globally embedded into $\mathbb{R}^3$, so you're back to building your intuition up in little steps. In this case, remember that the universal cover of the circle $U(1)=S^1$ is $\mathbb{R}$, and so the universal cover of $U(1) \times S^2$ is $\mathbb{R} \times S^2$. We can think of $\mathbb{R} \times S^2$ as a principal $\mathbb{R}$ bundle over $S^2$, and there is quite a nice embedding $\mathbb{R} \times S^2 \mapsto \mathbb{R}^3$ defined by mapping $(x,p) \in \mathbb{R} \times S^2$ to the scalar multiple $e^x p$. If you fix $p$ and let $x$ vary the image is the "deleted ray" through $p$ based at the origin, but with the base point at the origin deleted.
The final step of visualizing $U(1) \times S^2$ requires you to use your knowledge of quotient topologies: from the universal covering map $\mathbb{R} \to U(1)$ we obtain a universal covering map $\mathbb{R} \times S^2 \to U(1) \times S^2$. You can think of this quotient another way, using the fact that $U(1)$ is the quotient of the interval $[0,2\pi]$ where the points $0$ and $2\pi$ are identified. Thus $U(1) \times S^2$ can be visualized as the quotient of all the points in $\mathbb{R}^3$ between the inner sphere of radius $e^0=1$ and the outer sphere radius $e^{2\pi} \approx 535.49$, then identifying each point $p$ on the inner sphere with the corresponding point $e^{2\pi} p$ on the outer sphere.
Comment: Hi Lee, thx for reply. Do you mean this : http://mathworld.wolfram.com/images/gifs/circbuns.gif  ?
Comment: @JonnyPython: that looks like a different way of viewing things than my answer.

How can I visualize principal bundles?


Bootstrap proof of Gronwall's inequality (exercise 1.26 in Tao)

Question: I am trying to do Exercise 1.26 in Tao's book on nonlinear dispersive equations. I wanted to check if my proof seemed correct/in the spirit of the exercise (proving Gronwall via a bootstrap), since it is more convoluted than I would have thought. I would be interested if there is a more direct (bootstrap) proof. (More detailed questions listed below.) (Also included at the end is a lemma's proof that is needed, but is unrelated to the bootstrap method, so is included at the end.)
Exercise: Use the bootstrap method to give another proof of Gronwall's integral inequality: for $A, B, u \geq 0$ continuous on an interval $[t_1, t_2]$, if
$$
u(t) \leq A + \int_{t_0}^t B(s) u(s)\, ds,
$$
then
$$
u(t) \leq A\exp(\int_0^t B(s)\, ds).
$$
Proof of exercise. The proof is by bootstrap argument. Let $H(t)$ be the statement that
$$
u(t') \leq (1 + 2\epsilon)A\exp(\int_{t_0}^{t'} B(s)\, ds) \hspace{5mm} \forall t' \in [t_0, t]
$$
and $C(t)$ the statement that
$$
u(t') \leq (1 + \epsilon)A\exp(\int_{t_0}^{t'} B(s)\, ds) \hspace{5mm} \forall t' \in [t_0, t].
$$
To complete the bootstrap argument one must show $H(t) \implies C(t)$. We do this as follows:
\begin{align}
u(t) &\leq A + \int_{t_0}^t B(s) u(s)\, ds \\
&\leq A + \int_{t_0}^t B(s)(1 + 2\epsilon)A\exp(\int_{t_0}^s B(\tau)\, d\tau)\, ds \\
&=: F(t).
\end{align}
We want to show that this is less than or equal to $(1 + \epsilon)A\exp(\int_{t_0}^t B(s)\, ds)$, which we call $G(t)$. To do this, we note that:
$$
F(t_0) = A < (1 + \epsilon)A = G(t_0). \tag{1}
$$
Thus we can conclude there is some $\delta > 0$ such that on $[t_0, t_0 + \delta]$, $F(t) < G(t)$. Therefore $H(t) \implies C(t)$, so we have proven the desired result, but only on $t\in [t_0, t_0 + \delta]$. Since we are given so little hypotheses on $u$, I don't see how to conclude that $t_0 + \delta$ can be immediately replaced by $t_1$.
Therefore, we need to do the following. First, we note that the above proof can be repeated on $[t_0 + \delta, t_0 + 2\delta]$ to show that
$$
u(t) \leq A'\exp(\int_{t_0 + \delta}^t B(s)\, ds) \hspace{5mm} \forall t_0 + \delta \leq t \leq t_0 + 2\delta,
$$
where
$$
A' = A + \int_{t_0}^{t_0 + \delta} B(s)u(s)\, ds. \tag{2}
$$
Note that in order to make this $\delta$ uniform one needs in (1) to choose it based on $B$'s maximum, which is finite. Thus the above proof pushes through to show (2). Next, one needs the following lemma:
Lemma. Suppose $t_0 \leq t_1 \leq t_2$, and suppose we have:
$$
u(t) \leq A\exp(\int_{t_0}^t B(s)\, ds) \hspace{5mm} \forall t_0 \leq t \leq t_1 \tag{A}
$$
and
$$
u(t) \leq A'\exp(\int_{t_1}^t B(s)\, ds) \hspace{5mm} \forall t_1 \leq t \leq t_2 \tag{B},
$$
where
$$
A' = A + \int_{t_0}^{t_1} B(s) u(s)\, ds.
$$
Then we have:
$$
u(t) \leq A\exp(\int_{t_0}^t B(s)\, ds) \hspace{5mm} \forall t_0 \leq t \leq t_2. \tag{C}
$$
Essentially, this lemma says that we can "glue" the results above on $[t_0, t_0 + \delta], [t_0 + \delta, t_0 + 2\delta]$ to achieve the desired conslusion on $[t_0, t_0 + 2\delta]$. Since $\delta$ was uniform one can continue until $t_1$ is reached, completing the proof.
Questions: 1) Does the above proof seem correct? What I really want to know is if this seems like the intended "bootstrap method" proof, which is maybe harder to say (and more subjective). For instance, the bootstrap method came in only as one small portion of the argument; I could not immediately conclude the exercise after using the bootstrap method, more work had to be done. Is there a simpler/shorter proof where the bootstrap method is the main ingredient used?
For completeness, here is a proof of the lemma. Note that since (A) implies (C) for $t_0 \leq t \leq t_1$, we only need to show (C) for $t_1 \leq t \leq t_2$. By (B), we have, for all $t_1 \leq t \leq t_2$:
\begin{align}
u(t) &\leq (A + \int_{t_0}^{t_1}B(s)u(s)\, ds)\exp(\int_{t_1}^t B(s)\, ds) \\
&= (A + \int_{t_0}^{t_1}B(s)u(s)\, ds)\exp(\int_{t_0}^t B(s)\, ds)\exp(-\int_{t_0}^{t_1} B(s)\, ds).
\end{align}
The goal is to show that this is less or equal to $A\exp(\int_{t_0}^t B(s)\, ds)$. Therefore it suffices to show that
$$
F(t_1) := A + \int_{t_0}^{t_1}B(s)u(s)\, ds  \leq A\exp(\int_{t_0}^{t_1} B(s)\, ds) =: G(t_1).
$$
To show this, note that $F(t_0) = A = G(t_0)$. Also,
$$
F'(t) = B(t) u(t), \hspace{5mm} G'(t) = AB(t) \exp(\int_{t_0}^t B(s)\, ds).
$$
But we have already, by assumption (A), that $F'(t) \leq G'(t)$ exactly, for all $t_0 \leq t \leq t_1$. Therefore integrating we find $F(t_1) \leq G(t_1)$, which was the desired conclusion.
Answer: I think your proof is correct, but it can be made simpler by first observing that
$$\int_{t_0}^t B(s)e^{\int_{t_0}^sB(s')\,ds'}\,ds=e^{\int_{t_0}^tB(s)\,ds}-1$$
The inequality $F(t)\leq G(t)$ is then equivalent to $e^{\int_{t_0}^{t}B(s)\,ds}\leq 2$, which does not necessarily hold for all $t$. It looks like you fixed this by working on intervals of size $\delta$, but instead you can let $H(t)$ be $u(s)\leq (1+M\epsilon)Ae^{\int_{t_0}^sB(t)\,dt}$ for all $s\in [t_0,t]$ where $M$ is chosen so that $$(M-1)e^{\int_{t_0}^{t_1}B(t)\,dt}\leq M$$


What does a family do for charging and storage of multiple Apple devices?

Question: What does a family with multiple devices do for charging and storage of a growing number of devices.  We now have 4 laptops 5 iPads and 5 iPhones plus several other iPods. Are there any cabinets designed for the home that can charge and house this many?  I am tired of the cords and devices laying all over my house.
Comment: Hi and welcome to the Apple stackexchange. Thank you for providing some information on your problem. Could you also add to your question what sort of laptops you have? MacBook Pro? MacBook Air? etc... This will make it easier for the users to provide you with a specific answer.
Answer: I find the cables die pretty frequently. The kids always get them knotted, or stress them. So, I buy a lot of cheap ones. Something like these. At $4 for 5 I tend to buy 15-20 a time. Takes months to run through them and I don't fret about it. We have a huge stock of the actual little bricks from the many iPhones we've had.
I've also seen a lot of interesting little projects for charging and cable management:

DIY Charging Cell Phone Holder
Desk Phone Charger Holder

The neatest/simplest being:

Neatly Organize USB Cables and Charging Cords on your Desk

Also several items like this on the market:

Bamboo Charging Station

And finally, I'm putting these by the bed so my phone can charge over night:

U-Socket USB Wallplug
Comment: Thanks for doing research on this topic, you got some very interesting stuff here. Is there a special reason why you included the links in a way which makes them unclickable?
Answer: This isn't necessarily Apple-specific (I don't believe there is a mass Apple-friendly charging station), but a cheaper option would be to consolidate all of the cables into one space. For example, you can have a power strip with USB-compatibility in one area of your house and have your family charge their devices there. For example, I have a device like this that suits all of my charging needs.


Is permission needed to use a living famous person as a character in a game?

Question: If I wanted to sell an iphone game in which you play as a famous person, would that require permission from the famous person?
Comment: Yes! Otherwise you will be sued (100% guaranteed :D ) they will claim you are using their names to promote your game.
Comment: Many celebrities register their names or stage-names as **trademarks** to prevent people from using their publicity to sell a product.
Answer: Depends on factors such as whether you're making money (and who for), whether it's a parody, what country's laws apply, etc.
A parody game making money for charity in a country with very strong fair use doctrines is going to be different to an academic venture in a country without a concept of fair use.
We are not lawyers; ask a lawyer.
Answer: Now just as a heads up, we aren't lawyers and you shouldn't take advise from a forum website as legal advise.
Now to answer your question: most likely
It really depends on where you live and which laws govern it for any game. Such that if you live in India, you would need to look at local law.
Being released on iOS, you typically would also need to adhere to US law since Apple is based in the US.
So let's look at one fairly relevant example. In this case they won the lawsuit for using "likeness" without permission. That means that even without using their name, the characters in-game were close enough to their real-life counterparts that EA was forced to fork a lot of money.
Now let's look at a more recent example. In this case Lindsay Lohan is suing in a very similar fashion. Now if I remember correctly, this one never went anywhere. However is goes to illustrate that people being people will get upset when they aren't paid.
Now on the flip side of the matter is publicity. A small-time game may be able to get away with it. "If nobody knows, then nobody will sue me" is unfortunately too common. Although in case a game gets big, suddenly you get noticed, and likely shut down or sued.
Answer: In short, ABSOLUTELY!
It's basically the same as stealing their name and everything they've worked for to say that they like and want to sponsor your game, when they probably don't.
Your best bet is most likely to make a character that looks similar without being an exact replica, then change the first name. This way you have a character that reminds your players of the famous character without actually using the famous person. It's not guaranteed to keep you from being sued but it's a much better option than using the person without permission.


Substitute of Celery in Harira

Question: If Celery isn't available then what other vegetable or green vegetable can I use as a substitute for the making of Harira Soup?
Answer: Celery has a very specific flavour profile.
The closest substitute for a soup would be parsley leaves and stalks.
To get even closer to the flavour, you could add celery salt or vegetable stock powder/cubes.
In my experience, the most dominant flavour by far in soup stock is the celery.
Comment: Watch out on boiling parsley in a soup. Maybe there is a way to do it, like: "don't leave it in too long"; or "don't use a certain part of the plant"; .... or *something*, but I cooked a lot of parsley in a soup once and it was quite bitter. Better to add uncooked chopped parsley at the end as a "finishing touch" -- my humble opinion. Cooking *cilantro* on the other hand, also related to celery, it came out quite tasty.
Answer: I would actually try fennel. It will give you a lot more of the anise flavor, so perhaps don't put so much in it. A bit of fennel and parsley as suggested by Carmi might be a good combination, at least in terms of flavor.

Substitute of Celery in Harira


Can composition be used in unit/integration testing over inheritance

Question: In larger projects, there can often be a group of tests that test the functionality of related classes. These tests often share a lot of setup and preparation functionality.
What happens then is that a base class is defined for these test cases so that they can share there instance fields and common functionality. This leads to problems when a test uses a lot of functionality present in multiple classes.
Would it be possible to use some form of composition for this type of code reuse?
Let me give a concrete example. I have a few classes that can 'write' a list of transactions, defined by the interface 'TransactionWriter'. Concrete implementations are 'FileTransactionWriter' and 'ConsoleTransactionWriter'.
Both of the test classes for these implementations would need to set up transactions with some arbitrary data. This code would be duplicated in both classes if not extracted to a base test class. But can the same goal be achieved with composition?
Answer: The trade-off between inheritance and composition is exactly the same for test code as it is for business code.
Composition requires delegating calls for all functionality that you want to project to your own public interface. That means that composition becomes more cumbersome the larger the functionality that you want to reuse.
Inheritance achieves the reuse with no extra effort, but itself leads to bloated public interfaces because it always reuses everything. Also, many languages only allow you to inherit once.
This means that to reuse one specific it of functionality like writing things, inheritance might be a good solution, but it depends too much on the specifics of our code base to give a general answer.


Seller signed title but buyer completed info

Question: I traded my truck for work to be completed on my house , I signed the title but did not put buyers name or any other info , he filled it in and got it in his name and has not completed the work on my house is legal in Florida for buyer to fill in sellers info and put incorrect sales price
Answer: When you sell a vehicle, you are required to submit a notice of sale, where you provide various bits of information, and you swear under penalty of perjury that the information that you provided is true. Note at the bottom of the form that it states that ownership does not change until purchaser is issued a certificate of title. The owner also fills in the Transfer of Title by Seller section on the title. Also you must remove the license plates.
There seem to be two separate issues here. First, you are legally exposed on the vehicle sale for having falsely sworn to untrue information (you are supposed to fill in the seller sections completely, and read what it says where you signed about swearing to tell the truth). I assume the buyer put down a (substantially) lower sale price, to avoid paying taxes. The buyer would definitely be in hot water over such deliberate tax fraud. You could still be civilly liable for acts involving your truck, until the notice of sale is files.
Second, I suppose you want the truck back since the work wasn't done, but since you didn't go through the formalities of filing proper paperwork so that the title reflects a lien equal to the amount that you are effectively "loaning" the buyer (to be repaid in labor), you can't repossess the vehicle. That doesn't mean that you can't sue the guy for breach of contract, you just have to go through a different legal process. If he did work on the house and the bargain was "do this in exchange for my truck", the court won't order him to return the truck, though it might do that if you pay him money for the work he did. He could be ordered to pay you the amount necessary for you to hire someone else to finish the job – or he could just finish the job (probably cheaper for him).
Comment: I knew better than to do it but he was trying to get his license back after 15 yrs and wanted to have a blow machine put in before going to court for driving on suspended license ,most recent charge and just before that he got a drug charge so he's probably going to jail any way .  I thought he would be a little more appreciative but I guess another lesson learned . Thank you for your reply