What is the difference between linearizability and serializability?

Question: What is the difference between linearizability and serializability (in the context of Java)? Can you please explain the difference between these with an example or provide a good reference?
Comment: I can't recommend Herlihy's "Art of Multiprocessor Programming" highly enough.  It's challenging, but it addresses this issue head-on, it's seminal stuff, and it is accompanied by a set of good PPT slides and great Java example code, unusual for a book of this theoretical depth.
Answer: The central distinction between the two is that serializability is a global property; a property of an entire history of operations/transactions.  Linearizability is a local property; a property of a single operation/transaction.  Another distinction is that linearizability includes a notion of real-time, which serializability does not:  the linearization point of an operation must lie between its invocation and response times.  (See Tim Harris: Transactional Memory, 2ed.  See Herlihy's slides from The Art of Multiprocessor Programming, the section on Linearizability, which are available here, for some examples and proofs.
Both properties are aimed at the same goal: sequential consistency.  From Herlihy's paper:

Much work on databases and distributed systems uses serializability as the basic correctness condition for concurrent computations. In this model, a transaction is a thread of control that applies a finite sequence of primitive operations to a set of objects shared with other transactions. A history is serializable if it is equivalent to one in which transactions appear to execute sequentially, i.e., without interleaving. A (partial) precedence order can be defined on non-overlapping pairs of transactions in the obvious way. A history is strictly serializable if the transactions' order in the sequential history is compatible with their precedence order...
...Linearizability can be viewed as a special case of strict serializability where transactions are restricted to consist of a single operation applied to a single object. Nevertheless, this single-operation restriction has far-reaching practical and formal consequences, giving linearizable computations a different flavor from their serializable counterparts. An immediate practical consequence is that concurrency control mechanisms appropriate for serializability are typically inappropriate for linearizability because they introduce unnecessary overhead and place unnecessary restrictions on concurrency.

References:

Harris, Tim, James Larus, and Ravi Rajwar:  Transactional Memory, 2ed.  Synthesis Lectures on Computer Architecture.  Morgn & Claypool, 2010.  ISBN 9781608452354.  URL: http://www.morganclaypool.com/doi/abs/10.2200/S00272ED1V01Y201006CAC011?journalCode=cac

Herlihy, Maurice and Jeanette Wing: Linearizability: A Correctness Condition for Concurrent Objects.  ACM Trans. Prog. Lang. and Sys.  Vol. 12, No. 3, July 1990, Pages 463-492. URL
http://www.cs.brown.edu/~mph/HerlihyW90/p463-herlihy.pdf

Papadimitriou, Christos:  The Serializability of Concurrent Database Updates.  Journal of the ACM Vol 26. No 4. October 1979, pp 631-653. URL http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-210.pdf

Herlihy, Maurice and Nir Shavit: The Art of Multiprocessor Programming.  Elsevier, 2008.  ISBN 978-0-12-370591-4.  URL: http://www.elsevier.com/wps/find/bookdescription.cws_home/714091/description#description PPT slides on linearizability are here: http://pub.ist.ac.at/courses/ppc10/slides/Linearizability.pptx

Attiya, Hagit and Jennifer Welch: Sequential Consistency versus Linearizability. ACM Transactions on Computer Systems Vol. 12, No. 2, May 1994, Pages 91-122. URL http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.133.4969&rep=rep1&type=pdf

More Details:
If you really care about this, read the paper that introduced the definitions.  For linearizability, that's Linearizability: A Correctness Condition for Concurrent Objects, Herlihy and Wing.  It's dense, but worth the attention.  Note that in the software transactional memory community, it's an open question whether linearizability is the right goal / property to aim for.
Serializability is about the outcome of a collection of operations/the "system" being expressible as a specific ordering ("as if execution took place in a specific order...") of all the operations.  Linearizability is a property of a single subset of operations in the system... an operation/set of operations are linearizable if they appear to the other operations as if they occurred at a specific instant in (logical) time with respect to the others.  The canonical paper here is Papadimitriou, The Serializability of Concurrent Database Updates.
Think "atomic operation" when you're thinking about "linearizable."  A (set of) operations are linearizable when they (appear to) occur atomically with respect to other parts of the system.  A common formulation is "provide the illusion that each operation takes effect instantaneously between its invocation and response."  The formulation of linearizability is due to Herlihy, which emphasizes that this is a local property, vs. other kinds of sequential consistency properties like "serializability" which are global.
Comment: Thanks a ton Anderson for the wonderful explanation and for the resource links. I am getting a hang of linearizability from those slides.
Comment: @iJeeves: My pleasure.  We now teach a class on concurrency using Herlihy's book (and some of those slides), and it's a great experience.
Comment: These slides are now blocked by a login page.
Comment: Very helpful answer.
Answer: There's a great explanation by Peter Bailis here:

Linearizability versus Serializability

"In plain English, under linearizability, writes should appear to be instantaneous. Imprecisely, once a write completes, all later reads (where "later" is defined by wall-clock start time) should return the value of that write or the value of a later write. Once a read returns a particular value, all later reads should return that value or the value of a later write."
"Serializability is a guarantee about transactions, or groups of one or more operations over one or more objects. It guarantees that the execution of a set of transactions (usually containing read and write operations) over multiple items is equivalent to some serial execution (total ordering) of the transactions."
Answer: See @andersoj's answer for a clear description of the difference between serializability and linearizability.
This is only indirectly relevant to Java concurrent programming.  In general, a concurrent Java program does not need to have either a serializable or linearizable history.  In the cases that do, serializability is generally sufficient for a program (Java or otherwise) for "correctness", though particular problems could require the stronger linearizability property.  But either way, it is the problem that determines the correctness requirements, not Java.
Comment: Agreed, +1.  Java is interesting here in that there's so much discussion and emphasis on the Java Memory Model, etc... but the question here has to do with formal understandings that have to be mapped to processor, language, and specific app req'ts.  (Which most people don't think about most of the time.)
Answer: Check Wikipedia's explanation:
http://en.wikipedia.org/wiki/Linearizability#Linearizability_versus_serializability
It can also be a bit confusing because we also use the term serialize to refer to converting a class into data stream for storage or network transmission.
Comment: Answers consisting largely of links are discouraged on SO, please see: http://msmvps.com/blogs/jon_skeet/archive/2009/02/17/answering-technical-questions-helpfully.aspx and http://meta.stackexchange.com/questions/8231/are-answers-that-just-contain-links-elsewhere-really-good-answers and http://meta.stackexchange.com/questions/7656/how-do-i-write-a-good-answer-to-a-question
Answer: A good way to understand this is to look at this problem from a database standpoint. (I know you ask for a context of java, sorry)
Assuming, you are a database. You accepts multiple transactions operating on the same object concurrently but you only have one single disk arm.
When you received multiple transactions at the same time, you will have to re-order those operations within transactions in some way so you poor disk arm can handle them one-by-one.
Serializable
you have the ability re-arrange those transactions to make it looks like they happens sequentially (one by one).
As you can imagine, it's not always possible if you accept arbitrary transactions (e.g. one bad transaction last 10 years).
So naturally, you enforce some restrictions or conflict prevention mechanisms then you can say "I'm serializable! :)" .
Linearizable
Not only do you need to do what serialization needs you to do. You also take a good look at those transactions. And try very hard to re-arrange those transactions in a sequential fashion without breaking the semantic order of transactions. As you might have noticed, semantic order is the key.
Basically, in order to claim that you are linearizable, you will have to assume/find a linearization point for every transactions and then order them according to the linearization point.
Therefore, it's uncommon for a versatile RDMS database to say Hey I'm linearizable!.
But, it's not uncommon if you are a Key-Value database.
e.g. As a KV database, you can say "I am linearizable!" if you can ensure a read will always get the latest possible write.
(assuming the moment of sending response for the read operation is the linearization point)
This sounds trivial, but will be a major challenge if you are a distributed KV database.
Also note that serializability doesn't require you to give the same guarantee.
Answer: Imagine you have your distributed system running on 3 machines (3 replicas). We simply want to write and read value of key "A".
Linearizable
In this model, our system will work like this - As soon as write(A) is done, we can read the latest value from any of the three replicas. Meaning, once an action (write/read) is done, its impact is visible to all future actions across the whole system (Like an atomic operation).
Here, the order of operation doesn't matter. So, in reality, we want to do write and read, but the system can do read and write and its fine and will still be Linearizable. Paxos/Raft algorithms provide this for a transaction for majority nodes.
Serializable
In this model, all the replicas (machines) will process actions/events in same order. So, if one of the replica does write(A) and read(A), other replicas will do in same order.
Here, it's possible to get stale data from other replicas. Let's say - replica_1 does write(A). Read(A) from replica_1 will return latest value, but if we read from replica_2, we may get old value. The only guarantee is whenever (no time limit) replica_2 will process in same order - write and then read. Zookeeper provides this.
This is a good blog to learn more about this -
http://www.bailis.org/blog/linearizability-versus-serializability/
Let me know if my understanding is incorrect. Happy to learn and grow !


Is the vinegar and baking soda experiment safe for children?

Question: To be more specific, could the carbon dioxide fumes produced in the reaction be harmful to a small child? I don't have a strong background in chemistry, and I was prompted to ask this question when it was suggested by a friend that a mixture of 2 cups of vinegar and baking soda is commonly used to euthanize rodents. I'm aware rodents are more sensitive than humans, but I was concerned that a small child could inadvertantly breathe enough fumes to cause harm. I think it would be a great experiment to introduce children to chemistry if not unsafe. Thanks for any advice or guidance.
Answer: A basic safety rule in chemistry is "don't breathe fumes". Maximum waft a sample of evolved gas to the nose with your hand. Given a controlled environment, adequate size vessels and small quantities and adequate ventilation, it could be a good introduction to chemistry. However - start in the way you should continue - safety glasses, safe operating procedures etc.. BTW, red cabbage makes a good indicator for this.
Answer: I did this experiment with my kids (2yo & 5yo) outside for this reason. We also tied a balloon around the outside of the bottle to keep it isolated and to watch the balloon grow. But to reassure you, one would need to be in an isolated chamber with concentrated CO2 for harmful effects to occur. Remember that CO2 is already present in our bodies and in the air we breathe too, so concentration is everything.
Comment: Unfortunately this anecdote doesn't add much to the present answer and is more suitable as a comment.
Answer: It's pretty safe. The primary source of damage to people from CO2 is asphyxiation. That means you don't get enough oxygen quickly enough. Its danger is similar to helium. You need ridiculously high concentrations of CO2 for it to be harmful and you need prolonged exposure.
You probably drink carbonated drinks. Do you worry about them killing you when your nose gets close to the cup?
I think the much bigger danger is these chemicals getting in people's eyes. Even then, it wouldn't be super dangerous.
Eye glasses are important, though. Lab coat is not really necessary for safety, but it could preserve clothing.
There was already an answer but I thought this might be helpful.
Depending on the quantities of baking soda and vinegar used, it may be perfectly safe to do it indoors, even. In terms of CO2 at least.


Vapour pressure and volume of container

Question: Assume that a liquid is in equilibrium with its vapour in a container which can change volume. If we increase volume LE Chatelier principle states that pressure should increase but final pressure cant be equal to the initial pressure so final pressure will be less than initial pressure?
Comment: Volume Increases => Pressure Increases. Le Chatilier's Principle does not say this. In fact it should be the opposite to this(even that is incorrect). Please elaborate your question.
Comment: The question is ambiguous.  Is the increase in volume carried out under isothermal conditions, adiabatic conditions, or some other conditions?
Answer: Assuming you have a closed container to begin with, and you increase the volume via some mechanism to have more number of particles in the liquid, then you effectively are reducing the vapor pressure. Because the particles that were in the vapor phase have been forced to come down to the liquid.
Comment: so why textbooks refer that vapour pressure depends only in temperature?
Comment: You said that this is a closed container. If this container's lid was acting like a piston or something and that was what you used to change the volume, naturally the gas molecules would be compressed (but they don't want to get compressed - so they escape into the solution - because the interface between the liquid and the gas molecules would compose of strong intermolecular forces to drag those molecules back into the liquid).
Answer: From what I gather, it seems you are asking confirmation for the question you have posed, which is "Is the final pressure of a system, when its pressure is decreased, less than the pressure of the initial system?". If this is not the case, then your question is unclear.
Let's get the assumptions clear.

Le Chatelier's principle states that a system, when one of it's properties is changed, will act in such a way as to counteract this change.
The volume of a hypothetical system ($A_{(l)}⇆A_{(g)}$ for simplicity) is increased.

Increasing the volume of the system does not change the volume of the system in liquid state. It does, however, confer a decrease in the pressure of the gas, per Boyle's Law ($P \varpropto \frac{1}{V}$, given constant temperature). Le Chatelier's principle predicts that our hypothetical system counteracts this change by increasing the pressure of the gas to a final pressure. But this final pressure, as you have correctly claimed, is less than the initial pressure. As much as the system would like to return to the initial pressure, it cannot, because the ratio of gas particles to liquid particles must remain constant.
A decrease in the general pressure of the gas must also mean a decrease in the vapour pressure of the system. An increase in volume means that less gas particles per unit area are pushing on the surface of the liquid, which means that it is easier for liquid particles to escape into the gaseous phase. As the system stabilizes into equilibrium, the final vapour pressure would be lower than the initial vapour pressure.
Comment: "because the ratio of gas particles to liquid particles must remain constant." Where do you get this statement from?
Answer: Reading again some basic thermodynamics and the useful comments/answers already provided, I came up with my own answer.
Vapor pressure is only function of temperature. There is a dynamic equilibrium between the liquid and the vapor:
$$A \, (\mathrm{l}) \longleftrightarrow A \, (\mathrm{g}) $$
with equilibrium constant $K = p_\mathrm{vapor}$.
Lets suppose that the volume of the container is increased. Momentarily, the vapor pressure is decreased, ($T$ and $n$ remain constant, $p = \frac{nrT}{V}$).
Pressure must increase according to the Le Chatelier's principle, which means that some molecules from liquid phase must pass to the gas phase. At the new equilibrium, the vapor pressure obtains again the value it had before the volume increase (is only function of the temperature).
Answer: In the example you have cited, and assuming that the temperature is constant, an increase in volume would potentially decrease the vapour pressure and the system reacts by increasing the number of molecules in the vapour phase by decreasing the number of molecules in the liquid phase until the vapour pressure returns back to its original magnitude.
At a given temperature there is a dynamic equilibrium between the rate at which molecules in the liquid phase move into the vapour phase and the rate at which molecules in the vapour phase move into the liquid phase.
If the density of vapour molecules is reduced when the volume of the system is increased the dynamic equilibrium no longer exists as the rate at which molecules in the liquid phase moving into the vapour phase is greater than the rate at which molecules in the vapour phase moving into the liquid phase.  This continues until both rates are the same and the vapour pressure becomes the same as it was before.

Vapour pressure and volume of container


Where did my reputation go?

Question: I just recently earned a reputation of 2 by editing a user question. I had 159 reputation before. After the edit, I had 161 reputation. Now I see I have 160 reputation. The edit that I made was re edited by someone else. Is that the reason my points vanished?
Comment: Did you downvote an answer? Or are you looking at your rep on meta rather than the main site? meta only syncs every so often.
Comment: @RobertLongson Well, just a moment ago, i down voted an an irrelevant and irrational answer in which a guy was using vulgar and harsh words against coding. Now his answer is completely removed.and I again got my reputation back. So is this the whole story?
Answer: You still have 161 reputation on SO. Meta shows 160, but then, it doesn't sync too often.
So relax, your reputation didn't go anywhere. It is where it is supposed to be, in your SO account.
Comment: Well I believe i just got my point back. I lost point due to a down vote to an answer and then the answer was deleted, giving me my point back.
Comment: Good to know. This effectively means you must continue downvoting answers that are irrelevant or low-quality.
Comment: That is our responsibility
Answer: If you downvote an answer it will cost you 1 rep. If that answer is subsequently deleted you'll get that rep back again.

Where did my reputation go?


how to get all the connected addresess from Metamask?

Question: I'm trying to get all the connected addresses from metamask to my dApp. I know I CAN'T get any non-connected address to my dapp, but now that I've connected 3 of them, when I do provider.listAccounts() it just returns 1
Answer: As per the Metamask Documentation :
The eth_request_requestAccounts rpc returns :

Returns a Promise that resolves to an array of a single Ethereum
address string.

If I'm not wrong, the address returned is the user selected address, not to be confused with a list of connected addresses.
This is a design choice of Metamask to secure users.


iPod won't mount when plugged in

Question: I have a windows formatted iPod with disk access enabled.  Occasionally, my USB connection flakes out.  This used to happen more often when I connected via USB hub, so I no longer do this.  However, when this happens, I can't seem to mount my iPod -- to get it to show up in iTunes or even in the Finder.  Typically, this happens when I am on my Mac, although I'm pretty sure I've had this same problem on Windows.
I've tried:

Rebooting my iPod
Unplugging and plugging back in my iPod
Rebooting my computer

None of these things work.  Fortunately, I eventually figured out that if I plug it in to the other OS, than the problem reverts.  In other words, if the problem happened while connected to my Mac, if I then plug my iPod in to Windows, things get better.  Likewise, if the problem happened while connected to Windows, if I then connect to my Mac it gets better.
This seems odd, and not a general solution for typical people who don't have multiple PC's with differing OS's.  Is there a better way to fix it?
Details:

160 GB
version 1.1.2 PC
Answer: I would recommend re-installing iTunes on both systems. If that doesn't fix it, you can try enabling detection actions such as opening the folder to browse the device when windows recognizes it as a device. You can do this to just see if your OS is even recognizing the fact that your iPod is connected.
Another thing to try, is to use another USB-iPod cable. Your cable might be defective.
Answer: You could also try restoring the ipod to its factory settings.  Refreshing the firmware might solve the  problem since it seems like it's independent of the two operating systems.
Comment: I use the iPod as an external storage drive.  Would refreshing the firmware would case me to lose this data?
Comment: Unfortunately yes.  It will reset the ipod to the same state you got it in.

iPod won't mount when plugged in


Can I avoid to synchronize videos with Google Photos, I want only pictures to be synced

Question: I use Google Photos to synchronize pictures from my smartphone with the cloud. I do not want to synchronize the videos. Is this possible?
Comment: Your question is off-topic here, phone related questions can be asked on their respective stack exchange site (android, windowsphone, ask different).
Answer: In the official Google Photos app, you can't disable backup of videos per se, but you can exclude folders having videos from being backed up. That can be done like this:

In the "Device Storage" view (accessible from the swipe-in sidebar), look for the "cloud" icon to the right of the folder name.
If the Cloud icon is blue with an up arrow on it, backup of that folder is enabled. Tap on the icon to disable backup for that folder.
The Cloud icon should now become white with a slash through it. Congratulations! Backup of a folder has been disabled successfully.
It might happen that your videos are intermixed with your photos, especially if they have been shot on your camera. Move the videos to a separate folder using a file manager app, usually "Videos", and disable backup for that folder from the "Device Storage" view.

This will disable Google Auto-Backup for the selected folders only, leaving the rest unaffected.
Click on image to enlarge
Image Credits @ mobilesiri.com

Source
Comment: Thank you for the answer. Point 4 is the case when using a ZTE Axon 7. Seems as if I have to tell the camera to save the videos elsewhere. Moving with the filemanager is too late, once they are taken, they are automatically uploaded.


Prevent attaching to Notes & Attachments while adding to Quote PDFs

Question: I have a trigger that will save the Quote as PDF in Quote PDFs section (QuoteDocument object) whenever the status is updated to Accepted. The problem is, it also attaches to Notes & Attachments section. Is there a way to suppress attaching to Notes & Attachments?
Answer: No. The system is designed to show it in both places.
Comment: This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - [From Review](/review/low-quality-posts/88213)
Comment: It does provide an answer. While @DavidSchach might elaborate more on the background of the two related lists, this is an answer (and, I believe, a correct one).
Comment: @VigneshwaranG Please tell me how else to answer a Yes/No question. It's not appropriate to ask for a workaround as it is about suppressing something, not finding a way to do something. So please support your assertion that it does not provide the answer the OP is looking for.


Viber Ubuntu 14.04 second launch problem

Question: I've installed Viber with .deb file from viber site. Than i've started it and entered the code. Everything was fine, viber was working well. But then i've switched it off and tried to turn on again. And nothing happened at all. There was no viber in processes, and there was no error message. Viber in the second time just silently didn't start. Do anybody know the way to fix it?
Thank, u)
Answer: I had similar problem on Ubuntu 16.04 but I guess there's no difference. I found solution on Viber support web site https://support.viber.com/customer/en/portal/articles/1506350-opening-ports-for-viber-desktop#.V_1UOrX9-Ak
I had to open following ports for both TCP and UDP: 5242, 4244, 5243, 80, 443. After that everything working fine


Cache aligning data structures

Question: I want to align data structures in my application to cache lines. Here is a simple scenario :
typedef struct container {
  int a;
  int b;
} cont __attribute__((aligned(64));

int main() {
  cont *a;
  a = malloc( sizeof(cont) * 10);
  printf("%p", a);
  return 0;
}

In this case I thought that the starting address of the array will be cache aligned i.e. start at 64 byte boundary. But the address that is printed is 0x9dd008 which is not aligned to 64 byte boundary. Am I missing something in this implementation?
Comment: If you still have any questions, please let me know.  I would be happy to answer.
Answer: You're allocating from the heap, and the address returned is determined by malloc().  Since the code is already compiled, the compiler can't enforce the requested address alignment.
If you try allocating cont on the stack you should see the correct alignment.
Answer: You should use posix_memalign() to allocate memory with a specific memory alignment. In C11 you also have the opportunity to use aligned_alloc() that will provide the same functionality as posix_memalign() in other platforms (beside POSIX) as well.

Cache aligning data structures


In animal crossing new horizons, do old villagers that move out remember you when you meet them again?

Question: I had Chrissy move out, and I ended up seeing her again. When I met her, she had no clue who I was, even if she said she will never forget me. Is that just what villagers say when they leave as well?
Answer: In most situations, villagers do not retain any memory of their time on your island. If you encounter them at your campsite (either randomly or by using an amiibo/card scan) or on a mystery tour island, they will not speak of any previous time on your island. They are a new 'instance' of that villager.
However, there is one exception to this. When a villager moves away from your island, they can move to one of your friend's islands. Whether your friend invites them from a campsite visit, or they automatically move in to a vacant lot on their island, they will remember that they were previous residents on your island. If you visit your friend's island and have a conversation with them, they will typically ask if you remember them from their time on your island. I've had this occur personally, and there are instances of this online (e.g. https://amp.reddit.com/r/AnimalCrossing/comments/gwujv9/villagers_moving_into_friends_island_without/)
Answer: You kind of answered this in your own question. you even experienced it. A villager that moves out is effectively deleted from the game (unless they move into a friend's island). Any phrases you gave them, furniture, clothes, etc. are all gone.
Any time you meet the islander again is a "brand new" character. This also applies to bottles washed up on the beach.
Answer: Probably more because it would be very hard to program and kinda weird if you considered the lore, any villager on the island is your villager ONLY on your island. So my Chrissy on my island is basically a completely different character that looks the same, acts the same but the memories created on your island are proper and only to your island.
When you meet Chrissy again, its another person altogether. Maybe Tom Nook is cloning the villagers and animal crossing as a whole is just Tom Nook creating clones and making sure they work in society and when they suddenly feel the urge to leave the island its Tom Nook throwing them into the normal society as spies. I'M ONTO YOU TOM NOOK.


Cantor's Diagonal Argument

Question: Why Cantor's Diagonal Argument to prove that real number set is not countable, cannot be applied to natural numbers? Indeed, if we cancel the "0." in the proof, the list contains all natural numbers, and the argument can be applied to this set.
Comment: For "why can't we", questions, you should at least do an effort to show the execution of the programme you propose. If you try to even vaguely formulate this you will see where you run into trouble. For one thing, the infinite sequence of digits one might hope to be produced does not match the format required for a natural number.
Comment: After we cross out the "0." the list contains infinite-digit "natural" numbers.
Comment: Because there is no way to apply it. Exactly how are you going to try to use the argument?
Comment: What do you mean by "cancel the $0$"?
Comment: @user1: The list is composed of elements of the set one is trying to prove non-countable; in the proposed proof these would be natural numbers. These are not infinite. A first problem however is that number $i$ on the list need not have an $i$-th digit.
Answer: The list contains all natural numbers, but also quite a few more.
Natural numbers are terminating strings of digits, that is they are of finite length. Cantors diagonal argument enumerates all strings of digits, especially non-terminating ones.  And yes, the set of those is uncountable, whereas the set of terminating strings is in indeed countable.
Comment: I would suggest you be more careful with the wording in your last two sentences.  A subset of the rationals where each member is a non-terminating string is countable (a subset of a countable set is countable).  Thus it is not sufficiently the termination (or non-termination) aspect which characterizes countability.
Comment: The important aspect is that real numbers canot be described with finite strings.
Answer: How about this slightly different (but equivalent) form of the proof?  I assume that you already agree that the natural numbers $\mathbb{N}$ are countable, and your question is with the real numbers $\mathbb{R}$.
Theorem: Let $S$ be any countable set of real numbers.  Then there exists a real number $x$ that is not in $S$.
Proof: Cantor's Diagonal argument.  Note that in this version, the proof is no longer by contradiction, you just construct an $x$ not in $S$.
Corollary: The real numbers $\mathbb{R}$ are uncountable.
Proof: The set $\mathbb{R}$ contains every real number as a member by definition.  By the contrapositive  of our Theorem, $\mathbb{R}$ cannot be countable.
Note that this formulation will not work for $\mathbb{N}$ because $\mathbb{N}$ is countable and contains all natural numbers, and thus would be an instant counterexample for the hypothesis of the natural number version of our Theorem.
Comment: @Bob, I appreciate the comments.  But the Cantor diagonal argument is not wrong, and your example is at best not relevant.  Note in my version of the proof, if you wanted to do the natural number version, it is irrelevant that there is *some* countable set of naturals that does not contain all the naturals.  What matters is that there is also a countable set of naturals that contains *all* the naturals, namely $\mathbb{N}$, and no, the diagonal argument cannot construct a missing natural on $\mathbb{N}$, because there are no missing naturals in $\mathbb{N}$ by definition!
Comment: I think Cantor's proof is wrong, because he defines a number that doesn't exist.Consider the following argument:define S={n\in\matchal{N} and n\in[1,10]}which is obviously countable, and write these number in a column without repetition, and let us call r_n the number in the n-th position.Define the natural number\in[1,10],that belongs to S and so it is in the column,with the property r_n=r_{n-1}. We reach to an absurd because this number cannot stay in any position. But the absurd is because the number with such property does not exist, not because u cannot write in a column the numbers in S.
Comment: by the way I'm not a mathematician. I'm just trying to understand the logic of the proof.
Answer: Cantor's diagonal argument is one of contradiction.  You start with the assumption that your set is countable and then show that the assumption isn't consistent with the conclusion you draw from it, where the conclusion is that you produce a number from your set but isn't on your countable list.  Then you show that for any
If you wanted to do Cantor's diagonal argument, you'd start by assuming the Natural numbers are countable, then try to create a contradiction by producing a number that isn't on the countable list.
Suppose the natural numbers are countable, and we list them then perform Cantor's diagonal technique, producing a string of digits $x$.  $x$ either has an infinite number of non-zero digits or $x$ has a finite number of non-zero digits.
If $x$ has a finite number of non-zero digits, then $x$ is on the list (and it's a Natural number), so there no contradiction.  If $x$ has an infinite number of non-zero digits, then $x$ isn't a Natural number (and it isn't on the list), so there is no contradiction.
Either way, we can't find a contradiction by using Cantor's diagonal argument on the assumption that the Natural numbers are countable, so we can't conclude from that argument that the Natural numbers are uncountable.
The most important part here is to notice that any natural number must have a finite number of non-zero digits.
Answer: Make a list of natural numbers, put into separate rows, as in setup for the Cantor's argument. Applying the diagonal argument extract a new number different from each row. The main, or even maybe the only, reason why this does not disprove countability of natural numbers is that this new constructed number is not necessarily a natural number. True, you have found a new number not among your list, but it is not necessarily a new addition to natural numbers.
Here is an analogy:
Theorem: The set of sheep is uncountable.
Proof: Make a list of sheep, possibly countable, then there is a cow that is none of the sheep in your list. So, your list could not possibly have exhausted all the sheep!
What is wrong with this proof? (Unless you believe there are uncountably many sheep! :))

Cantor's Diagonal Argument


Looking for a CiviCRM SAAS environment

Question: Are there any Civicrm SAAS providers? I don't want to maintain a CiviCRM installation, just be a user. I currently host a client's installation and no longer have capacity to maintain it. Would prefer to pay for someone else to maintain and just allow client to input data, edit data and send mailings.
Comment: Maybe SPARK may be the way to go for the limited needs this organization has, but would need someone to move the data over from CiviHosting to SPARK. Any suggestions on migration? We are willing to pay for the move.
Comment: Talk to @bgm on the spark channel at https://chat.civicrm.org
Comment: I think data migration is not supported by Spark, as it is intended to be just a hosted service with no paid custom support. There are many CiviCRM providers who offer hosting (https://civicrm.org/partners-contributors?custom_181=All&country_id=All&custom_157=Hosting&cms=All). Coop Symbiotic does a lot of bulk low cost hosting. My JMA Consulting are also getting into this.
Answer: If your client's needs are fairly simple then Spark may suit them.
There is a listing of hosting providers here which represents a wide range of options:

Some offer a hosting environment with CiviCRM installed and you manage the rest.
Others provide a predefined set of extensions/configurations which may or may not suit.
Others only provide hosting as part of a package of other services.
Avoid anyone offering an 'enhanced' (lock-in) version.

You may need to contact a few to understand what is really on offer and what suits you.
Answer: I have direct experience of just two, as a volunteer for a small charity, and only for a short time: Spark and CiviHosting. They are distinct offerings: the former is more expensive but easier for a non-techie to cope with during the set-up phase, the latter is less expensive but harder for a non-techie to cope with during the set-up phase. The former imposes more constraints (e.g., in terms of selection of extensions), the latter imposes fewer constraints. I would heartily recommend both for their general helpfulness and speedy responses.

Looking for a CiviCRM SAAS environment


Is it possible to create an optical medium where sound can travel faster than light?

Question: The speed of light decreases with increase in the density of the optical medium whereas the speed of sound increases with increase in the density of the medium.
So is there any possibility to construct a material where sound travels faster than Light.
Comment: Well, if I just think of opaque iron block, that's the medium. But I guess you meant something transparent and really useful as an optical medium.
Answer: It isn't possible to construct a material where the speed of sound is greater than the speed of light in a vacuum, i.e. $c$. That's because the interatomic forces that propagate the vibrations that make up the sound can themselves only propagate at the speed of light. Having said this you can get surprisingly close - in a neutron star the speed of sound can get pretty close to the speed of light.
But I'm guessing that you are specifically interested in comparing the speed of sound to the speed of light in the material, not the speed of light in a vacuum. In this case you need to appreciate that light propagating through a dielectric in not light. The interaction of the light with the dielectric causes the wavefunction of the light to mix with the wavefunction of the electrons in the dielectric to produce a quasiparticle called a polariton. So your question is really can the speed of sound be greater than the speed of a polariton?
And in principle the answer is yes it can. I don't know of any hard data comparing the speed of sound and light, but light can be brought to a complete halt in a Bose-Einstein condensate. Assuming these systems can propagate sound waves (which seems likely) this means that the speed of sound must be greater than the speed of light.
But be cautious about attaching any great physical significance to this. Remember that we are really comparing the speed of sound to the speed of polaritons, and there isn't any special significance to the speed that polaritons propagate.
Comment: @AnanyoBhattacharya: yes, though as I say this isn't any big deal. Nothing is actually travelling faster than light.
Comment: Thank you for the answer ,so it is possible to do so at low temperatures near the absolute zero in BEC right!
Answer: I read an article about a group of scientist that where able to slow down the speed of light to around 40 mph, by producing a monochromatic light source then directing this light source through a dense arrangement of extremely cold Sodium atoms.
I would suggest looking up a Bose-Einstein condensate, which is a condition when matter is cooled to near absolute zero.
So there is conditions in which light can be slower than the speed of sound  but i'm not certain about through that same medium.


Export Vertex Normals into Obj File

Question: I would like to export the from Blender calculated vertex normals into an .obj file. I realized that the amount of vertices in the .obj file does not equal the amount of normals (there are more vertices than vn). I expected that there is a vertex normal for each vertex so there should be the same amount of each.
I guess Blender doesn't export the vertex normals but the face normals and hence there are less normals than vertices.
Did anyone else experience the same problem and solved it somehow? Is there a way to get the vertex normals into the obj file?
Answer: Did you check the "Write Normals" option in the export dialog?
The tooltip for that says: "Export one normal per vertex and per face, to represent flat faces and sharp edges"
To test it I edited the vertex normals of a cube with the blend4web add-on and reimported it and the altered normals were preserved on re-import. So with the checkbox checked it should do it the way you want.
EDIT: I looked in the file and I think see what you mean. Let me investigate.
EDIT2: So it seems the vertex normals are only written once, when they are needed (no duplicates) and in the "f-group" they are then referenced. Each face points to its vertex indices and (via the number after the second slash /) to the belonging vertex normal indices (f v//vn - the middle can also have an index for texture coordinate --> f v/vt/vn). So multiple vertices may be  associated with the same vertex normal index if they share the same value.
https://en.wikipedia.org/wiki/Wavefront_.obj_file
So in order to have a dictionary (vertex index - vertex normal) you would need to go through the faces (the f-group) and follow the reference for each vertex normal, discarding all vertex indices you already have sampled.
EDIT3: Answering your comment below :)
There are sometimes more 'vn's than 'v's, because there are actually more vertices. One entry in the "v group" doesn't really represent a vertex but a set of unique vertex coordinates.
If you e.g. look at the corner vertex of a cube that is hard-shaded, this one vertex is actually 3 vertices! These 3 share the same coordinates and thus only get one 'v', but they have different normals - one for each face the three-fold corner vertex is part of.
They still can only be moved together - a ripped vertex (meaning two or more unconnected vertices in one place) is represented by having more 'v' entries with the same coordinates. For unripped vertices that are part of a hard edge Blender doesn't show the real count in the scene stats, but if you import it e.g. in Unity the vertex count suddenly is much more.
It looks like that this is just the way that the obj format is designed - not unique identities but just pointers to values. You could of course rewrite the exporter to force duplicates, but it would be difficult to be consistent, because of what I described above. It think would result in all hard edges beeing split. Anyway I think it would be more complicated than just reading out the obj file with some loops and stuff. The information is there, it is just represented differently than we would assume at first glance.
EDIT4: To correct myself above - when reading out the obj it's not really possible to discard any vertices if you want to preserve all info. The combination of v, vn and use in an f is what makes them unique, right? So really you can just walk through the faces and fetch the values. Or gather unique v-vn pairs but lose info about their faces.
Comment: I updated my answer, because what I wrote was too long for a comment!
Comment: Thank you for your investigation! ;)
That's what I also figured now that blender does not generate duplicates and just refers to the same vertex normal several times.
But maybe there is still a way to force blender to also generate the duplicates since it would make things a lot easier than searching in the texture coordinates for the references.

What I also realized at the moment is that for some reason in my obj file there are sometimes even MORE vertex normals given than vertices which does not make any sense to me at all!
Comment: What are the cases that it has less 'vn' than 'v'?
Answer: I modified the default OBJ export script to fix this issue. You can download it from GitHub at Wehrdo/blender-obj-export. After enabling the script and disabling the default exporter, simply check "Write All Normals" on the export options.
The default behavior of reusing vertex normal entries caused issues when trying to do mesh morphing (with SceneKit's SCNMorpher), because multiple exports didn't have a one-to-one correspondence between vertex normals.

Export Vertex Normals into Obj File


why is humid air an example of liquid gas solution instead of gas gas solution?

Question: In my textbook, humid air is given as an example to liquid in gas solution. But isn't humidity the amount of water vapour (gas) and therefore should be gas in gas solution?
Comment: A solution is a single phase by definition. So as soon as there is liquid water (droplets) in air, it is not a solution.
Comment: A asking B why C has written something wrong will not provide the answer unless B knows the history or context of such writing.
Comment: Would be nice if you post the identity of the source textbook.
Answer: Humid air is just a mixture of gases. It is not a solution (neither of a gas nor of a liquid) in the sense that a solvent (air) is needed to dissolve a solute (water).  In this sense, water vapour is not dissolved in air; it is just another gas that is mixed with the other gases in the air.
The idea of air "holding" water or being "saturated" with water is misleading. 100 % relative humidity does not correspond to a solubility limit of water in air. It just corresponds to the equilibrium vapour pressure of water at the given temperature.
The equilibrium concentration of water in the atmosphere depends on temperature. It is almost independent of the amount of air (or other gases) that is present and therefore it is almost independent of the total ambient pressure. A vacuum has approximately the same equilibrium concentration of water vapour as the same volume filled with air. At $10\ \mathrm{^\circ C}$, it is about $9.4\ \mathrm{g/m^3}$, at $20\ \mathrm{^\circ C}$, it is about $17.3\ \mathrm{g/m^3}$, and at $30\ \mathrm{^\circ C}$, it is about $30.4\ \mathrm{g/m^3}$.
Answer: Note that not always the water will be in gaseous state (in form of water vapor) in humid air. The moisture we speak of in humid air may be in gaseous state (as water vapor) or liquid state (miniscule water droplets). The former will be considered a homogenous mixture and latter a heterogenous mixture. In case of extremely humid air, the moisture will mostly be in liquid form (as water droplets) and that's when you will consider humid air as liquid-in-gas colloidal system. In less humid air, the moisture will most likely be water vapor rather than water droplets.
You can see my previous answer or this physics.SE question for more information.
Comment: "In case of extremely humid air, the moisture will mostly be in liquid form (as water droplets) and that's when you will consider humid air as liquid-in-gas solution" As you say it yourself, this is a heterogenous mixture and therefore not a solution.
Comment: @Snijderfrey it is a colloidal solution and not true solution. I have edited my answer just to be clear.


Can a battery be used as a ground to protect yourself from static electricty?

Question: There are bracelets for protection from static electricity, but you have to touch it to ground to discharge. Can we use a battery (like watch batteries) on this bracelet?
Comment: I'm concerned about these bracelets. The only static protection bracelets I'm aware of require a ground connection at all times. Do you have a reference to the bracelets you're talking about?
Comment: What function do you think the battery would  perform?
Comment: What bracelet is this about?
Comment: @StarCat search for "grounding bracelet" on Amazon.
Comment: A "bracelet" to me is something that is worn and has no wired connection to anything. A "wrist strap" or "grounding strap" _does_ have a connection to ground, usually through a high value resistor, for the purpose of controlling static but without endangering the wearer. The term "bracelet" probably got introduced through a language translation misunderstanding.
Answer: A battery might technically be used to dump some of the static charge into, but only as much as into a simple similarly sized chunk of metal, or indeed the bracelet itself. That is, the mechanism that makes a battery a battery is not involved, as that works by charges moving from one terminal to another, without affecting the static charge of the entire thing.
In any case, none of it will completely discharge you i.e. bring your body to earth voltage, it can only "dillute" the static charge by spreading it out. If the bracelet/battery even are at a lower potential than your body to begin with, that is. And comparing the size of a big blob of meat and water to that of a bracelet or battery, the effect of these things is rather minimal at all. Basically, lacking further details, those bracelets are a scam if advertised the way you describe (assuming that "touching them to ground to discharge" means doing so intermittently instead of having it constantly connected).
Answer: If neither of the battery's terminals are "earthed", then all you are doing when your statically-charged-ten-thousand-volt-different-from-earth-potential finger touches the battery is raise/lower the battery's potential to also be 10000V different from earth. Inductance and capacitance notwithstanding, no charge will leave your body and end up in the battery somehow.
The battery will be capacitively and inductively coupled to earth also, but ignoring those two aspects, the principle is sound: How can charge flow onto something completely isolated from everything else? Kirchhoff's Current Law tells you that if charge flows into the battery, the same amount of charge must flow out somewhere else. If the battery is "floating", there's nowhere for charge to leave, and therefore no way for charge on your body to enter it in the first place.
The battery will simply have 10000V potential (relative to earth) now too.
Whatever thing you touch to discharge your body must provide a route to earth, for charge to leave your body via that thing, meaning that the only way for the battery to be such a route is if one of its terminals is connected to earth too.
Comment: How about using an empty rechargable battery?
Answer: The electricity charges on your body have the potential to reference the Earth. This is because you are in touch with the earth.
To discharge the electricity in your body, you need to connect your body to an object with the same potential as the Earth. We don't know how much potential a battery has relative to the ground, unless you connect it to the ground.
Generally, we need storage that can store charges from another place with the same reference potential, just like two conductive spheres are isolated from the Earth but they have different potentials to the same Earth.
About the battery you cited, you need to ensure that the battery has a reference same as the electrostatic source. Only in this situation can you use the battery. You need to ensure the reference is alive during and/or after discharging.
Comment: What do you mean by "You need to ensure the reference is alive during and/or after discharging"? A ground reference, by definition, is not powered.
Comment: A battery does nothing for discharging electrostatic charge.  You can still get zapped when you touch a car - and it certainly has a battery.  You would have to ground the battery - at which point you don't need the battery.


Kuberenetes Deployment Controller - Multilpe Vs Single?

Question: I have a deployment specification that says launch 3 pods with nginx containers... Kubernetes creates an deployment object (spec + status). I learnt that deployment controller keeps track of this object and brings status to a desired state of 3 pods ... but couldn't find whether we get one deployment controller created for each deployment object or is there one deployment controller that monitors all deployment object ? Same applies to replication controller too? I know answering one would answer the other one...
Answer: Deployment controller internally uses replication controller which creates replicaset. Deployment controller and replication controller are part of kubernetes controller manager . You generally have more than one controller manager in a cluster for high availability. So for example if you have 3 controller managers then there are 3 deployment and replication controller internally. But at a time one of the controller manager is selected as leader and is active. So even though there are 3 deployment controller and 3 replication controller only one of those are active at a time.
Comment: Thank you Arghya. I got answer to my question...  basically I was trying to know if there will be an instance of a deployment manager created for each deployment manifest in a cluster......  For ex. if there are 5 deployments ( just assume ) will there be 5 deployment managers created.. but from the response you gave, I understood it is not and I get what you are saying.  .....Thank you so much for responding.


How to stop the find command after second match?

Question: How to make find command, that will show only first two matches and then end, something similiar to How to stop the find command after first match? just version for two records.
Comment: I think nothing is wrong with this question to get down-vote (at least in my opinion), if no, please leave comment where it's wrong question.
Comment: In particular nothing wrong without an explanatory comment.
Answer: Replace 1 to 2 in your linked answer.
find . ... -print | head -n 2

Note that this does assume that the filenames are sane, i.e. they do not contain newlines.  Therefore it is not the most appropriate for a scripted solution.  (See Why is looping over find's output bad practice? for more details.)  It's still by far the most suitable approach for quick interactive use.
Also note that on a system with a great many files, this will be faster than a -exec sh -c 'echo "$1"; echo "$2"' _ {} + approach, because the find process will receive SIGPIPE when it tries to write more filenames after head has completed, and then find will end.
Not to mention that the -exec command may print a LOT more than 2 results if there are sufficiently many results.  For example, find / -exec sh -c 'echo "$1"; echo "$2"' _ {} + will not exit for a very long time, and will print two files out of every ARG_MAX results rather than two files total.
Comment: Several ways.  `find [...] | head -n2 | tail -n1`; `find [...] | sed -n '2p'`; `find [...] | awk 'NR==2 { print }'`, amongst myriad others.
Comment: And is there any option, to pick only second reasult from this query?
Answer: Using find with invoking sh:
find . -type f -exec sh -c 'echo "$1" "$2"; done' _ {} +

This will expand all files since of using + terminator of -exec then we are just printing first and second arguments which are first and second files find found.

Or use as following which where you can specify after how many files found (maybe not 2 files, 100 files! then at above you should specify all 100 files!) exit the command (actually shell send exit command and cause find exit its running process).
find -type f -exec sh -c '
    for file; do echo "$file"; c=$((c+1)); [ $c = 2 ] && exit; done' _ {} +

Comment: Note that if there are HUGE numbers of results (in excess of ARG_MAX for the system), this command may also operate on another file besides the one intended.


Which is more stable? CF2 (singlet) or CF2 (triplet)

Question: Generally, we know that triplet carbene is more stable than singlet. But in my book, it is written that singlet difluorocarbene is more stable than triplet difluorocarbene.
What's the reason for it?
Comment: [Wikipedia article](https://en.wikipedia.org/wiki/Difluorocarbene) provides some explanation for the same. If it helps...
Comment: you might be interested in this related question and answer https://chemistry.stackexchange.com/questions/50277/how-does-spin-flipping-of-triplet-carbenes-occur
Answer: So generally singlet is less stable as triplet has half-filled orbitals which leads to stability.
However whenever a group that can give  electrons by back donation (examples being lone pair carriers like $\ce{-OH},$ $\ce{-NH2},$ etc. are attached, they stabilise the singlet by back donation of their lone pair into the vacant orbital of the singlet carbene.
This is similar to back bonding in $\ce{BF3}.$
Comment: i think you can add back bonding?
Answer: Singlet carbene has a vacant p orbital. Whereas triplet carbene doesn't. Same with the case of singlet and triplet difluorocarbene. Due to the availability of vacant orbital back bond is established between F and C singlet, hence more stable.


How does a fuse work?

Question: Ok- lets say a wall socket is providing 300V, at 200A. If I plug a device into that wall outlet, and this device has a 13A fuse, will the fuse blow, since the amperage being delivered is over the threshold of the fuse? And, from what I have read, why does a fuse even exist in the first place- if a device was to short out, or fail, then why should it use anymore current than it was already using? I just cannot wrap my head around this concept, and have tried googling this, and tried using all these different analogies, but electricity in general just baffles me.
Comment: Fuse is used for overcurrent protection.The fuse melts to save the circuit from catching fire when excess current flows through the circuit.When the fuse melts ,it disconnects the circuit and prevents the flow of current.
Answer: In short, a fuse is nothing more than a controlled failure.
If too high current flows into a circuit, a too large power is generated, $$P=I^2R$$Components and wires all have a limit of how much energy they can absorb before melting or burning. If you let it go wild, you will not know which component or wire that will fail first. Maybe an expensive one, a hard-to-replace one, or maybe one that risks causing a fire.
So, to avoid any such random failure that could be catastrophic because we have no clue of where or how severe it would be, then we instead add one component with a lower durability than all other components, parts and wires. And then we make that weakest component of a material that melts rather than burns with flames and we incapsulate it to keep it controlled when it fails. Maybe we even place it on an accessible place so we can easily replace it when failure does happen.
That weakest component is the fuse. It is simply a component chosen to be sacrificed, so that all others will survive.
Answer: Amps are a measure of current or electrical flow.  The wall socket just sitting there will have connectors that are often at a different potential.  Let's go with your scenario that they differ by 300V.
But since they're not connected, there is no current flow.  The current before plugging anything in is exactly 0 amps.  The 200A you mention does not mean that the socket is always delivering any particular current.  It could be a design limit of a particular socket (a maximum rating). But 200A would be incredibly high for a home circuit.
When you connect an appliance to the socket, it (normally) completes a circuit and allows electricity to flow.  But the design of the device determines how much flows.  You can plug in a night light and it will draw only a few milliamps.  You can plug in a hair dryer and cause more than 10 amps to flow.  So just plugging in a device or using it properly doesn't cause the fuse to blow.
Overcurrent causes heating in wires, connectors, and other electrical components and is a fire risk.  A short in a device allows more current to flow, and will heat components in the circuit (that includes wiring inside the walls).  The correct fuse is designed to heat and fail quickly when limits are exceeded.  When the fuse opens, it should stop all electrical flow, preventing fire or additional damage from continued heating.
Answer: The important expressions here are $I=V/R$, which relates the current ($I$) to the voltage ($V$) across a resistance ($R$), and $P=IV$ which relates the power ($P$) dissipated in the resistor to the current flowing through it and the voltage across it.
The wall outlet provides a fixed voltage. When a device is operating normally, it provides a fixed resistance, which in turn results in a reasonable power dissipated in the device.  But if there is a short, then R goes really low, causing the current $I$ to shoot up (since $V$ is held constant).  Thus, $P$ will also shoot up in the regions where there is still some residual resistance (e.g. the wires), causing a lot of extra heat to be generated.  Since this extra heat can cause fires, people use fuses, which are little resistors designed to burn up/melt relatively easily. The fuse melts before anything else does, breaking the circuit and shutting down the current.
If your wall socket is rated to 300 V and 200 A, that means it can withstand 60 kW of power before it burns up.  That's much higher than will normally be flowing through it.  Your fuse is rated to a much lower power because you want the fuse to be the limiting factor in your circuit. If anything melts/burns, you want it to be the fuse.
Answer: No, the fuse on the device won't blow!
The reason the appliances have fuse is to protect their circuitry, or if they are electronic appliances like TV or computer, protect their sensitive electronic systems. Sometimes because of a surge or intermittent fluctuation in the plug power coming from the electric company the appliance fuse would trip, or burn, preventing damage. But if you connect an appliance with lower amps rating than the circuit it plugs to it's ok.
I would use only as much amps as it can, not any more!

How does a fuse work?


How much of a difference will a splitter / diffuser would be on a FWD car?

Question: Out of curiosity, if you can get your hands on a properly engineered splitter, what kind of handling difference would I see?
Any recommendations for a splitter that's not just for show? Any effects on fuel economy?
Answer: tl;dr: You will almost certainly notice no effect at all other than the loss of fuel economy due to the increased weight.
It is very unlikely that a splitter or diffuser will have any measurable benefit unless you are driving a car that is:

Very low to the ground over a ...
Very smooth surface at a ...
Very high speed.

Needless to say, the street is not a good place when considered under any of those criteria.
As a practical example, let us consider the efforts of the good folks at Grassroots Motorsports.  In working on their Le Grand Mk 18, they felt that it was worth their time to install a diffuser (the caboose to a splitter's engine on the aerodynamic train).  This is because their car is super low:

and because the car is "A purpose-made race car built in the 1970s for SCCA's D Sports Racing category."
All that said, a perfect splitter will increase overall downforce if combined with the rest of a properly engineered aerodynamics package.  It will also reduce your top speed and decrease your fuel economy because of the primal law of the universe: there ain't no such thing as a free lunch.
Answer: A splitter is designed to force air around the car instead of allowing it to go under the car. This will affect high speed driving, but won't do much (if anything) for you at highway speeds. The splitters you see on cars on the road are there primarily for looks, not for function. If you are racing your car on the track, you might see some difference, where you'd actually see down for (or reduction of under vehicle pressure) added stability while going fast. This won't improve handling per se, but will improve control of the vehicle at these higher speeds.
Answer: A splitter is really part of a ground effects system, here air is forced under the floor of the car and accelerated out of the back via a rear diffuser. The increased airflow velocity under the car creates a low pressure area which creates down-force.
However for this to be effective it needs to work as an integrated system. The floor needs to be flat and ride height, roll stiffness and rake angle will have a significant effect on how it works. It can also be disrupted by other aerodynamic effects for example if turbulent flow from the tyres gets under the floor it won't work properly.
The airflow out of the back of the diffuser can also potentially interact with the rear wing, if present, and with airflow over the top and sides of the car.
Unless you have a very good idea of what is going on just bolting on an aerodynamic part in isolation won't tend to produce predictable results.
So unless the whole vehicle has been properly analysed in a wind tunnel or good CFD system there is no way to know whether it will work or not. Indeed the compromised in suspension setup needed to make ground effects work may end up making handling significantly worse under normal driving conditions.
Ultimately the only real way to be sure that aerodynamic parts are working is to test them on a track with an experienced driver who can give consistent feedback and allow systematic adjustments to the overall car setup to be made.
Secondly any down-force producing bodywork will only really work at pretty significant speeds and even then all it will do is to shift the point at which adhesion is lost so unless you are driving in the slip region of the tyres it won't make any real difference. Equally unless aerodynamic forces are properly balanced they won't necessarily improve handling.
Answer: In addition to the other answers, the "splitter" fitted on most road cars is mainly down to the designer and the "look" but they can also be designed to increase the flow of cooling air to the brakes, which can be very handy to prevent overheating and brake fade or even total loss.


How do I get an invitation to enter Kosovo?

Question: As a Turkish citizen, I have the right to stay in Kosovo 90 days without a visa. But how do  I enter the Kosovo at first? What documents do I need besides passport?
Answer: When Kosovo grants Turkish citizens visa-free entry for short stays, it is a sign that they don't plan to subject most entering Turks to greater scrutiny than what can reasonably be done on the fly at the border checkpoint.
This has to mean that they don't routinely demand extensive paperwork such as letters of invitation -- if they did, there would be a visa requirement so they had a chance to get a good look at it in peace and quiet.
So unless you arouse more suspicion in the border guard than most other Turks do, what you will need is just your passport, and convincing answers to standard questions: What is the purpose of your trip? Where will you stay? When and how will you leave Kosovo again? Be prepared to document your accommodation bookings, tickets for the journey back home, and that you have enough money for your expenses during the trip.
(if you think you do look suspicious, arm yourself with as much documentation as you can lay your hand on, and hope for the best).
Comment: @CatwithaFez: You'll never be able to get a guarantee that such-and-such is sufficient documentation to be admitted; ultimately it will always be up to the whims and gut feeling of the border guard. What you need to do is be convincing, not to satisfy formal criteria. If you have concrete plans for only two days out of a month's stay, I _expect_ that you'll need a pretty good story explaining why you've done so little planning -- but I don't know how good is good enough.
Comment: A Turkish Citizen is granted visa free entry into Kosovo for up to 90 days. If you wish to stay longer, you will need to apply for a Stay and Work Permit at the Foreigner Registration Office.


How to prevent output voltage spikes

Question: My vaping device operates in two modes, variable temperature control (VT) and variable wattage (WT). The unit first sends out a ~1 second 30 watt/7.74 volt surge to the coil to see which mode it should use(according to the coil you installed). This spike is actually a design flaw in the firmware, it should happen in a fraction of a second and basically unnoticed, a return or refund is not an option anymore. An updated firmware does not do this.
What this spike does is scorches the coil and the ejuice and then hurts your mouth, throat and lungs.
 My question is: I personally need a maximum of 7.0 watts/3.74 volts so could I not just install a resistor, diode, voltage regulator... (close to 7.0/3.74v range) between the control board and coil connections to prevent or absorb this 30w/7.75v spike?
Comment: A flyback diode will prevent a coil (inductor) from spiking, and damaging circuitry.
Comment: If I understood correctly this is actually something you bought? Isn't updating the firmware an option?
Answer: A current limiter is probably the most straightforward way to do this. Check out this answer: https://electronics.stackexchange.com/a/229893/106823
NB that transistor should be AFTER the load coil. Also pay attention to transistor base voltage versus current, you have a lot more current than the 20mA LED circuit. You're probably looking at 0.7V, not 0.6V.
You can also implement this with a mosfet as well but a transistor may be easier to pull off.

How to prevent output voltage spikes


Roof screws need replacing

Question: My roof screws need replacing because of rust, do I do it myself or get someone and pay them ? And how much will it cost ? It's a 4 bedroom obviously tin roof.
Comment: Price/cost is specifically off-topic as it will vary widely in different markets, over time or even in one market form different bidders.
Answer: The first question to be asked whether the whole roof needs replacing - if the screws have rusted out, what condition are the roofing sheets in? Exposed-fastener sheet-steel roofing is NOT a long-term roof like concealed fastener standing-seam. It's an inexpensive, short-life-span roof. (If it was actually tin, you'd strip it off, take it to a scrapper, and put on just about any roof you'd like with the proceeds.)
As for whether you hire it done or do it yourself, that's mostly up to you, your ability to work safely and/or equip yourself to work safely, and your willingness to pay to not be bothered, or take the time to save money. Don't scrimp on safety - falling off a roof can be fatal or very, very expensive in both money and future incapacity. If you hire someone else, make sure that they are actually insured for the work.
I have cleaned up (caulked and re-torqued, as some screws were leaking post-install and it was simpler to do them all that to try and sort exactly which ones) an exposed fastener roof of about 16 squares (1600 square feet) as a DIY job. I dropped a chunk of change on climbing gear (harness, static line, locking carabiner, rescue ascender) at the outset, and I think I replaced my failing cordless drill with a brand-spanking new one as well. It wasn't bad, but I'm not you, either. Ultimately, what you choose to do is your choice.
Answer: Y
our problem is one most people experience unless the roof was installed with the new type of screws. It is not unusual to have to replace them every 10 years or sooner. you can do the job your self if you feel safe doing it. Tin roofs are very slippery unless you are wearing the proper shoes. Always carry a claw hammer with you in case you begin to slide. Should this happen to you, you take the claw hammer and drive the claw into the roof and hold on, it will save you from falling. Anyway you can do the job your self just your building supply company which screws they recommend.
Comment: I've always suspected "safety equipment" means something different in the outback.

Roof screws need replacing


My laptop toshiba satellite p75-A7100 pad right-click is working as a left-click?

Question: My laptop Toshiba satellite p75-A7100 pad right-click is working as a left-click in Ubuntu after updating to 18.04 Ubuntu? I've seen other answers but they are not working for me!
Comment: What other answers have you tried? Please edit your question to provide more information
Comment: In order to increase that chances that somebody gives a good answer to your question, the first thing to do is ask a question; you should edit your post and actually include a question. You should also clarify the context: who gives that error message? When does it give that error message? What are you doing in order to make that error message appear? Is the error message unexpected? If so, what were you expecting to happen?
Answer: Open settings, click on Devices and open the Mouse & Touchpad tab.
You will get a window similar to the one above.
Change the Primary Button to Left.
Comment: Thanks for your kind reply but it is already left  clicked. :)


Do beadboard ceiling panels always run the same direction as porch decking below it, if so, why?

Question: I am finishing a wraparound porch. I've decided to use beadboard plywood panels instead of vinyl, aluminum, or wood tongue and groove planks on the ceiling. I understand why planks would need to run perpendicular to the ceiling joists, but with the boards and my measurements I think it would be simpler for the boards to be installed lengthwise with the joists. Doing that would make the lines in the ceiling run opposite of the deck. Is this just a personal preference? Or some other reason I am not thinking of?
Comment: I edited the question slightly to be more clear that I'm talking about the direction of the ceiling boards.
Answer: Lumber has more strength in the direction of the grain than perpendicular to it. Therefore boards are installed so that they span from joist to joist in the direction of the grain.
Whether a floor board has a dominant strength axis depends entirely on its composition. And whether this matters to you depends on your load calculations and the joist spacing. Check the specs and installation guide for your particular bead board.
Some boards, like OSB, have a major and a minor strength axis. This provides more strength in one direction, which is economically exploited when laying over joists.
For instance, in OSB the strands in the outer layers are aligned parallel to the board's major strength axis, and strands in the inner layers are aligned perpendicular to the major strength axis. The perpendicular axis is also called the minor axis.
With plywood there is an odd number of layers, and adjacent layers have perpendicular grains. There will be one more layer with grains in the direction of the major axis.
Answer: To answer your specific question, ceilings usually follow decking because that's the way we've always done it.
I kid: decking usually runs wide (fewer cuts, tradition), and ceiling boards usually run wide because the underlying framing is usually perpendicular to the house. I think we've come to expect this symmetry.
In your case, the strength of the sheet goods (long axis versus short axis) isn't relevant, as it's just holding itself up. So do whatever you want. It might look really cool and it might look odd to anyone that notices. (I sincerely doubt that many people would actually notice...)
This is just my opinion, but the one tiny detail I'd do is to mirror whatever the treatment is in the corners. If your decking is mitered, then miter the ceiling, etc.
Comment: Thanks  @Aloysius that is what I was looking for, to determine if there was more than just an aesthetic reason.


Clash of Clans restart that can't be fixed

Question: I have been playing EO clash for a while. When I tried to go back the main game, it says "DOWNLOADING EO CLASH UPDATE". I've tried waiting to download the update, but it keeps restarting the game. How do I fix this?
Answer:
Check you are connected to the internet
Restart your device
Leave it on downloading it for a bit, forget about it and come back later
Restart your internet connection
Wait until the next update and contact the support for the game
Reinstall the game itself

Go through each step until it fixes, If it still has not then sorry, but I have no more ideas.
Answer: You need to download the latest update from your app store.
There was an issue in a past update which was preventing the forced update. Manually downloading the new version from the app store will fix it. 100%.


Mixing PEX A and PEX B?

Question: I want to run 1" trunk and 1/2" branches to fixtures, and would prefer to use PEX A mainly for its flexibility. Unfortunately my local stores only carry PEX A in 1/2 and 3/4 sizes. Would it be okay to mix 1" PEX B branching to 1/2" PEX A? I was also not sure if I would go with crimps or expansion, but based on what materials are available to me, I'm thinking it would be best to go the route of 1" PEX B with crimps versus downsizing to 3/4 inch pex A.
Answer: As long as the fittings at the transition points are compatible with both types of PEX, go for it
Plumbing codes generally permit the materials they allow to be mixed freely provided suitable transitions are provided where materials change.  So, you can simply use a fitting that's compatible with both PEX-a and PEX-b at the transition points.

Mixing PEX A and PEX B?


Podcast App Double Speed Missing?

Question: Apple, in their infinite wisdom, has changed the Podcast app (again).  Am I going crazy, or has double speed been removed?
Comment: Found it!  I quick tap of the album art reveals the scrub bar and the double speed.   Grrr, Apple!
Answer: It's still there!
Between the podcast artwork and the progress bar, tap the 1x icon to change the speed. On iPhone 4S and below, tap on the artwork to bring it up.

Podcast App Double Speed Missing?


Using HTML links within translatable string

Question: What harm could happen if I didn't use the wp_kses function when using HTML links within translatable string?
I know what this function do but what I don't understand is why and when should I implement this function? Specially with translatable strings.
Answer: It basically depends on who is doing the translation and how trusted can he be as if you will not filter things out the translator can add JS code, still cookies and whatever.
In most of the places translation is done you will have in any case  a call to esc_html or esc_attr which will mitigate the problem, but obviously if you need an actual link, you can not use those functions. The use of wp_kses just makes sure there are no surprises in the translation.
For example, there is nothing that prevent a translator from translating __('Hi there) into Hi there . translations are never verified to not include such type of things when they are submitted by translators, and while the example is easy to catch, it might be possible to do more complex things that are harder to spot.
Comment: Thanks for your answer.. and this is axactly what I need to know.. what kind of surprise that could happen.. I need a before and after example if it is possible please
Comment: there could be a JS in the translation
Comment: Please be patient and consider I am a beginner.. I need a low low level discussion... how the translator would add those harmful codes? And what do you mean by the translator ? A person or translation tools like poedit
Comment: I mean the person doing the translation, and there is nothing comlex he will just add that JS code the same way he uses poedit to translate all strings
Comment: Ahaaa..so when he translate he may inject codes with the translation itself so when loading the theme/plugin the code runs and do staff.isn't it?
Comment: yes, exactly...


How can I make a 2x2 piston door that is flush with both the inside and outside walls with no visible redstone?

Question: I've been trying to figure out how to create a 2x2 piston door that is flush with the wall on both sides and has no visible redstone (from either side of the door at any point). This would preferably be activated with a button toggle from either side and work ideally in vanilla Minecraft 1.7.10. I have not managed to figure this out myself so I thought I would ask here. My assumption is it would need to have the pistons be powered from below but I'm unsure how to go about it.
Comment: So you mean you have a 1 block thick wall that is visible on both sides (not a tunnel) and want no circuit relevant blocks to be seen? Then the only possible space for the circuit is below the floor and you need all kinds of crazy redstone, including two double-piston-extenders side-by-side which both also act as single extenders which get an additional block delivered to them/taken away. This is kind of on the edge of what a question here is for, you're mainly meant to ask about problems you encounter while doing projects yourself. I won't vote to close, because there might also be an easy...
Comment: ... solution and because I have an idea that I want to post once I have access to Minecraft again in ~2 weeks. I'll write an answer then.
Answer: Sound's like you're asking about a hipster door, seen in this video by Reversed Gravity. The idea of these is that everything is flush with a 1 wide wall, where all the restone is beneath the floor. This design is showcased as 1-wide, but it can be expanded infinitely due to its tileable nature
As far as I can tell, this is the most recent and compact design, but feel free to correct me.
Edit:
As per Fabian's request, here's a screenshot with a slightly modified design so it's 1.15 compatible:

Two things to note:

The red arrows on the blocks are a tweak from a texture pack, they are observers with the arrows telling you which direction they should be facing. The same with the sticky pistons
The observer facing down on the bottom left has a piece of redstone dust on it, this is a modification of the original design because of a change that stopped powered blocks from updating observers
Comment: @FabianRöling updated with screenshot
Comment: A screenshot would help. That video might disappear any moment and web.archive.org doesn't deal very well with YouTube, so archiving it is also likely not possible (also, copyright).
Comment: This is good but if possible I was hoping for one compatible with 1.7.10 as that's the version I play the most
Comment: Ah, sorry that version isn't quite my expertise
Answer:
This …

is a 2×2 door
is flush with a 1 wide wall and the floor
has no visible redstone (if the floor and walls are actually opaque, the glass is just here for demonstration)
can be activated by either one of four pressure plates (and can very easily be extended to any other input)
works in Minecraft 1.7.10, 20w18a, 1.15.2 and probably even 1.0
has a 0 tick opening phase and a 0 tick closing phase, both starting instantly when the input turns on/off

The only issue is that you are very limited in the selection of blocks for the door. Only actual doors work properly. Alternatively, you could also use fence gates on the lower two blocks and air on the upper two, but then the door does not protect e.g. against skeletons shooting at you through it.
Also, I wouldn't really call this a "piston door", but that's just a minor detail. ;)


What is the benefit of playing in all keys on piano

Question: I have heard long ago that to learn a song in all keys was beneficial and would make one a better pianist. Is this true or not? I have never heard the reasons for this.  If beneficial I plan to pick a song and do it. However, it will take time, much time so I want to be sure I am learning to do something that in the end will make me a better pianist.
Comment: For instance, accompanying singers requires a *lot* of transposing. Gerald Moore claimed that during the typical recital, he would play more pieces transposed than in the original key.
Answer: It's about having full mastery of the instrument.  You don't climb a mountain because you need to be on the other side of it NOW.  You climb it because it's there, and because the skills learned will make the next climb easier.
Answer: Taking your time to learn a piece in different keys will give you an opportunity to practice your proficiency playing in each of those keys. Do you find that you have a problem playing in certain keys? If so, this could be a useful exercise.
Another skill that you may (or may not) find useful - depending on the settings on which you play - is the ability to transpose a song 'on the fly'. For this skill, taking your time to learn a piece in different keys will (as before) help your proficiency playing in each of those keys, but that's not enough - you need to also practice taking a piece you know in one key, and then playing it in new key unprepared.
Of course if neither of those sound like skills you need to learn, you might find your time is better spent doing something else. (As Tim alludes to, the second one may only be as useful as knowing how to use the transpose button on your keyboard!)
Answer: On an acoustic piano, it's a great skill to have, being able to play proficiently in all keys. Playing with others will make this easy to understand. Just being able to play a particular song in one key is quite restricting when the singer asks for it in a different key.
Having said that, I occasionally play with a keyboardist who has an electronic piano, and he happily uses the transpose button to play everything in C on his instrument. He's a nice player, but I can't help thinking how his playing would be even better not merely using those same old notes. In fact, I sometimes use the transpose when the band's played 3 numbers all in A - so I can use a different set of notes to stave off possible boredom!
Answer: If you ever play in a band or accompany a soloist, you may have to change keys to fit the soloist. Especially if the soloist didn't get much sleep the night before.
Practicing a piece in various keys allows you to concentrate on how a pattern feel (or look or sound) in different keys without having to learn many different pieces. Not that learning other pieces isn't useful too.


Is there a way to select the formula above the first empty cell and paste downwards till the last full cell?

Question: In this formula:
With Intersect(wsDAO.UsedRange, wsDAO.Columns("R"))
            .AutoFilter 1, "<>Same"
            With Intersect(.Offset(2).EntireRow, .Parent.Range("B:O"))
                .Copy wsDAR.Cells(Rows.Count, "B").End(xlUp).Offset(1)
                .EntireRow.Delete
            End With
            .AutoFilter
        End With

It allows me to take cells from wsDAO in column R, with any other word but the word "Same" puts a copy over to another page 'wsDAR' and deletes the original.
What I'd like to do, and I'm not sure where to start, but what I was thinking is using this part of the script:
lastrow = wsDAO.Range("A" & Rows.Count).End(xlUp).Row

With Intersect(.Offset(2).EntireRow, .Parent.Range("B"))
     .Copy wsDAO.Cells(Rows.Count, "B").End(xlUp).Offset(1)
End With

And use it where in I have a cell in the formula above and copy it down till the last row with data in it.
I just don't know where to start, I figured if I copied the data from another cell but that wouldn't work because of the '.Copy' would override anything saved.
Can someone help me with this? I know I'm a few lines from solving my issues, but I can't seem to wrap my head around it.
Any help would be apprecaited.
Answer: From your sample file, you want to copy the formula in I1 to any empty cell in column I. The following code line should do this:
lastrow = wsDAO.Cells(Rows.Count, "I").End(xlUp).Row

wsDAO.Range("I1:I" & lastrow).SpecialCells(xlCellTypeBlanks).FormulaR1C1 _
    = wsDAO.Cells(1, "I").FormulaR1C1

Comment: Can you clarify what you want to copy and where. A sample file or layout would be helpful at this stage.
Comment: That would just copy the cell downwards, and not change the value of the formula. Already thought of that :)


What happened to the census records kept in the Atrium Libertatis?

Question: According to Wikipedia's article on Atrium Libertatis, the building was demolished and succeeded by another building complex. It doesn't mention explicitly whether or not the census records were moved to the successor building or if they got destroyed along with the Atrium Libertatis.
Comment: Odds are they were written on papyrus -- most Roman records were, as vellum or parchment cost 10x to 100x as much.  Unfortunately, papyrus has a half a half-life of a century or so in a moist climate like Rome (and Alexandria, be it noted) even if they are not destroyed by fire or war. Papyrus documents need have been recopied many times or stored under desert (not merely arid) conditions to survive. Medieval monks saved a lot of what survived to the 800s, but it seems unlikely they would have touched the census records. More likely they  just rotted away even before the Western Empire did.
Answer: As no better answers (like one which has some information on the census records specifically) have been posted, I'll turn my comment into an answer:
The odds are very strong that those records, like most Roman documents, were written on papyrus and rotted away or were burned in ancient times.
Most Roman records were written on papyrus, as it was cheap (imported from Egypt) and vellum or parchment cost substantially more. (The Wikipedia page for papyrus suggests that costs may have been comparable, but that seems at odds with both other sources and the rather complicated process of making vellum from animal skin.) Certainly we have few original documents from Classical times, and some at least would be expected if many had been written on vellum.
In a moist climate like Rome's (or Alexandria's, be it noted) papyrus has a half a half-life of a century or less, being destroyed by mold and insects even if they were not destroyed by fire or war. An ancient library of papyrus scrolls would have been a firetrap, being comprised of (a) large amounts of (b) flammable materials which is (c) rolled so that air can easily get to the flames. (May I impose on you here to complain about Peter Jackson having Gandalf searching the Minas Tirith library piled high with documents having a big open flame?) The Wikipedia page, for example, notes that papyrus documents more than 200 years old were considered remarkable.
To survive to modern times, papyrus documents need have been recopied every century or so or stored under desert conditions to survive. Putting them in a library did not preserve them unless they were regularly recopied -- an expensive process!  Consequently, just about all the surviving Classical papyri were found in the Egyptian deserts.
It seems unlikely that Imperial Rome would spend the money needed to recopy centuries-old census records every hundred years or so and the subsequent Ostrogothic kingdom was even less likely. Note also that the ancient center of Rome -- which is where records were kept -- was subject to regular flooding and was abandoned by the end of antiquity and covered with silt.
Carolingian monks saved a lot of what survived to the 800s by copying it to more durable vellum and parchment, but again it seems unlikely they would have touched the census records even if they found copies of them.
The census records most likely rotted away even before the Western Empire did.


How to know which Windows Process has started / stopped which service

Question: For example, want to know that sample.exe creates MyDriverService and runs Start / Stop to run myDriver.sys
I tried using Process Monitor, API Monitor but there was only information from Services.exe
Answer: It's easy just on computer main screen at my computer logo click right click, then in menu select manage, you will see one new open window with computer information.
In left side menu in last you will find services and applications, click on it then click services you will find their all your computer running and stop services.
Other way you can only see the running services by right clicking on computer screen down window bar then open start task manger, one pop up window will open there will be information of your computer running application running process and many other useful information's
Hope you will find it helpful


How to copy plugins between two eclipses

Question: I have two eclipse directories, both are Galileo. One has plugin A installed, the another has plugin B. Now I want to have just one eclipse, is it save to just copy the plugins directory from one of the eclipses to the other?
Comment: seanf gave the best answer. AFAIK just copying plugins into directories is not a good approach. Consider making his answer the correct.
Answer: I'm not sure when it was introduced, but in Eclipse 3.7 you can install plug-ins from another Eclipse installation via the GUI: File->Import->Install->From Existing Installation.  You can also transfer the list of update sites.  See https://stackoverflow.com/a/10494974/14379
Comment: Didn't work for me until I run the new Eclipse as administrator (on Win10). List was empty until then.
Answer: Yes, but I would recommend using a "shared dropins directory" to avoid the copy altogether.
Modify tour eclipse.ini for both installation:
-Dorg.eclipse.equinox.p2.reconciler.dropins.directory=/<myPath>/mySharedDropins

Sadly, when you originally install a plugin, you cannot install it directly in the shared dropins, so at least one copy is still necessary there.
Answer: Yes, it is safe. This is one way (not the preferred one) to install new plugins.
Comment: Ok, so it works. Nice. I guess I can just zip my plugins folder for backup and copy it back to restore it.
Answer: You can also install one plugin from another using p2. You add the other installed Eclipse as an update site, and you can select the installed plug-in (after unchecking the categorization).
For update site you the following path: /path/to/eclipse/p2/org.eclipse.equinox.p2.engine/profileRegistry/SDKProfile.profile
Answer: An alternative to modifying the .ini file is using Link Files in your Dropins folders. The link files are simply text files with the extension .link. They contain a single (I think, never tried with multiple) line of text of the form:
path=<full path to an external folder>

The folder you reference should have two sub-folders: plugins and features, where you install your plugins. You can install multiple plugins in a single location. You can drop multiple link files, which means, you can maintain sets of plugins and drop them into different Eclipse installations (which is more flexible than using a shared dropins).
More information:

More details on link files (though seriously prehistoric article).
Read about links files in P2 (not very informative).


Chuck replacement - corded BOSCH PSB500 re

Question: I've got a corded Bosch PSB 500 re and want to replace the existing chuck with a keyless one, please can anyone advise me as to which one I need to buy. It would be very easy for me to buy the wrong one!!
Cheers in advance
Comment: Take the existing one off and that will show you the fitting / thread for the replacement.
Comment: I took the liberty of editing your title since you want to replace the chuck itself, not the chuck key.
Answer: Dismount the current chuck, measure the diameter and thread count of the shaft, order something based on that; if it doesn't fit return it for credit and try another.
It may be worth taking the old chuck to your local hardware store and trying various sizes of English and Metric bolts as one way to be sure what size is needed. They may also have gauges which can be used to check this. That would greatly increase your odds of getting the right part in the first attempt.
Note that there may be an alternative approach: rubber grips used to be available which could be stretched over a keyed chuck to permit keyless operation. One of my old drills has this adaptation; it works fine, as long as I'm a bit careful to keep my hand clear of the still-exposed chuck teeth.


How do I download podcasts and put them on in WMP format, so I can transfer them to my non-ipod mp3 player?

Question: I have a Sansa Disk MP3 Player. Is there a way to get the files from iTunes onto Windows Media Player?
Comment: What exact brand and model is your mp3 player?
Answer: Your question title and question content asks for different things. The title asks on how to "download from the internet and then move to WMP and from there to the MP3 player", and the body of the question asks "How do I move my files from itunes to WMP". To an apple user they might seem the same, but they are not.
You don't need Windows Media Player to act as a man-in-the-middle, you can plug the MP3 player in your computer via USB, access it as a normal folder and drag the MP3 files to the music folder, and they will play as normal audio files.
You seem to come from the Apple world, so keep in mind that features such as keeping track of episodes heard, or resuming playback to where you previously stopped in an episode, are not guaranteed to work in a generic MP3 player.
As to how can you get the files from iTunes, I recommend you either use a feed / rss reader to subscribe to the podcast feed, or download the mp3 files directly from the original website.