Why does adding an emitter resistor to a common emitter amp reduce its gain?

Question: According to the Wikipedia page for common emitter amplifiers,  the addition of an emitter resistor decreased the gain of the circuit. However, to me it appears that if the resistor was omitted, then V_out would be approximately equal to the ground mode (when the transistor is conducting). But when the resistor is present, V_out would be equal to the drop across the resistor. Why then does the resistor reduce the gain? Please note I am very new to transistor circuits, and to electronics in general.
Comment: Maybe the whole problem is confusion around what is meant by "gain?" Often people think of beta as gain. At a given operating point, beta does not change, and external components don't affect beta, or at least not directly (maybe by shifting the operating point). Once you understand that in a common emitter amplifier, the gain is Vout/Vin, with Vout being taken at the collector, and Vin being at the base, then it may make more sense.
Comment: Do you understand the emitter follower or common collector circuit. If not, study it then re-ask your question.
Comment: The gain of a common emitter amplifier is approximately -Rc/Re where Rc is the collector resistor and Re is the emitter resistor. So the smaller Re is, the higher the gain. The larger Re is, the smaller the gain. For a given Rc. Now, if you don't see why the gain is approximately -Rc/Re, then just read about the common emitter amplifier to understand that.
Comment: Have a look at https://www.khanacademy.org/science/in-in-class-12th-physics-india/in-in-semiconductors/in-in-transistor-as-a-device/v/transistor-voltage-amplifier-class-12-india-physics-khan-academy (Hindi accent) and https://en.wikipedia.org/wiki/Common_emitter
Comment: I am really surprised: The second link as given above (wikipedia) contains the following statement: Emitter degeneration with RE would not be identical with negative feedback because it would not influence bandwidth and output resistance. Unbelievable!!
Answer: Gain is the output voltage change divided by the input voltage change.
In the small signal hybrid pi model the collector current changes proportional to the change in base voltage (relative to the emitter) so there is a voltage change at the collector proportional to the load resistance (parallel with ro).

If you add an emitter resistor, the base-emitter voltage does not change as much so the current change is less and therefore the gain is reduced. That is because the emitter current change causes the emitter voltage to change in the same direction as the change in base voltage, partially counteracting the effect.
Answer: It's useful to think of a transistor operating in three modes, cut off, linear, and saturated.
When cut off, the collector current is zero. When saturated, the base current is high, and VCE is small. These are the two modes when using a transistor as a switch. You appear to be thinking of the saturated mode in your question.
Wikipedia is talking about the linear, or amplifying mode, where the collector current is beta times the base current, and VCE is a few volts.
Answer: In a common-emitter amplifier, think of the transistor as a variable resistor controlled by the base current (\$i_b\$):

simulate this circuit – Schematic created using CircuitLab
The output voltage (and thus the voltage gain) is determined by the voltage across the variable resistor (i.e. \$V_{ce}\$).
Now put a resistor between the low-end of the variable resistor and the GND:

simulate this circuit
For the same VCC, the voltage across the variable resistor drops due to the increased total resistance. So the output voltage (determined by the voltage across the variable resistor) drops and so does the gain.
Answer:
The emitter resistor causes negative feedback. This can be shown using a block diagram based on the classical formulas for describing the input-output relations. It is a well-known fact that negative feedback reduces the gain factor. This is - in most cases (opamp) - a desired result of negative feedback.
Note that the output current Ic is determined by the input voltage Vbe via the transconductance gm=d(Ic)/d(Vbe).
(In the block diagram I have used the commonly used simplification Ic=Ie; all voltages and currents are small-signal quantities and not DC values).
The gain formula shows how the resistor RE reduces the gain. More than that, you can see that the simplification Vout/Vin=RC/RE (as mentioned in one answer) is applicable for RE>>1/gm only.
Comment 1: Because the signal output voltage across the collector resistor RC is referenced to common ground - and NOT to the supply voltage - there is a sign inversion between input and output voltages which is not contained in the block diagram (the block RC should habe a negative sign).
Comment 2: It is easy to explain in words how feedback reduces gain. An increase of the input voltage Vb (at the base node) causes an increase in Ie which in turn also increases the voltage across RE. Hence, the emitter voltage Ve goes up and reduces Vbe (if compared with Ve=fixed at ground for RE=0). Hence, the Vbe increase is smaller than the input signal (Vb) increase - and the Ic increase is remarkably smaller if compared with the case RE=0.
(I like to add, that the block diagram and the corresponding explanation of the feedback effect proove again that the BJT is a voltage-controlled device Ic=f[exp(Vbe/Vt)] .)
Answer: Consider the following circuit.

simulate this circuit – Schematic created using CircuitLab
In this circuit Q1, R1, R2, RC, RE, Cin and Cout represent real components.
re represents the intrinsic impedance of Q1. \$ re \approx \dfrac{25}{I_C} \$ ohms if \$ I_C \$ is in mA at room temperature.
The usual design procedure is to pick a quiescent \$ I_C \$ and choose RC such that \$ V_C \$ is half Vdc at this current to maximise voltage swing at the output.
Now if we assume \$ h_{fe} \$ is large Then \$ I_C \approx I_E \$  So the gain is \$ \dfrac{RC}{RE + re} \approx \dfrac{RC}{RE} \$ if re is small relative RE.
I usually play with RC and RE to get nice standard values.  Since we know the quiescent \$ I_E \$ we know \$ V_E \$ and we want \$ V_B \$ to be approximately 0.6V higher than this.  knowing \$ I_B = \dfrac{I_C}{h_{fe}} \$ we can choose R1 and R2, The current in R1 should be large compared with \$ I_B \$ so it does not vary. I usually go with ten times \$ I_B \$ with maximum \$ h_{fe} \$ as a rule of thumb.
Finally we can choose Cin and Cout to have a low impedance at the minimum frequency of interest.
Comment: Warren Hill....In your drawing I see the classical transistor symbol and - in addition - an external quantity re (which is nothing else than the inverse of gm). But gm is the TRANCCONDUCTANCE gm= d(Ic)/d(Vbe) which constitutes the INTERNAL connection (conversion) between input voltage and output current of the BJT. For my opinion, it is not correct to use the traditional symbol for a BJT and - in addition - an external resistance re.
Comment: HI @LvW but re is re = d(Vbe)/d(Ie)
Comment: More than that, we can MODEL the role of gm=1/re using a resistor symbol in an small-signal EQUIVALENT circuit diagram - however, it must not be called "intrinsic impedance" because it is neither an impedance nor a resistance. And we must not use it in "classical" circuit diagram which contains real elements - and not differential (dynamic) quantities. In your drawing, a DC curent would cause a voltage drop across re which is not the case.
Comment: G36...it is a differential quantity called transconductance - if you define it as d(Vbe)/d(Ie) or d(Vbe)/d(Ic). It does not matter. Such a quantity must not appear in a circuit diagram. It is one of the basic rules of circuit diagrams to clearly discriminate between (a) diagrams containing real parts ands (b) equivalent small signal diagrams (without DC relevance).


Reconfiguring DNS without losing Gmail

Question: I have a domain name registered with Google through their G Suite service which utilizes enom, and a server on Digital Ocean. I went ahead and accessed the Google admin panel and then the enom domain services through that. I added the Digital Ocean DNS addresses. The domain now points to server's IP. But at the same time I no longer am receiving any emails to my Gmail account. Is there anything I need to be doing with the enom host records so that I can keep receiving email to that account whilst still using custom DNS addresses?
Comment: You would need to show us a screenshot of current DNS including the MX record before we could even hint and what might be the solution.
Comment: By DNS do you mean Digital oceans Nameservers? If yes, then you need to add Google MX Records in Digital Oceans control panel.
Comment: A domain is controlled by nameservers. Nameservers provider provides the A CNAME AAAA MX TXT and other type of DNS records to who ever queries, on internet. One of the easiest way is that you let us know the domain here, and we will check and help you.
Answer: There could be a couple problems:
Messed up MX records
You need to make sure that your mail records (MX) point to Gmail.   Google has a help document with instructions.
CNAME apex record
It is a problem if you are trying to use a CNAME record at the apex.   If you use a CNAME record for the "no sub-domain" record, email breaks (regardless of email host).   You have to use an A record at the apex or the MX records are ignored.  See Why can't a CNAME record be used at the apex (aka root) of a domain?
Some DNS hosts allow "alias" records to get around this limitation.   They act as proxy records.   You specify a host name (like a CNAME record), but the DNS server looks up the IP address periodically and serves the record as an A record with the IP address.   I don't know if Digital Ocean offers this functionality, but other DNS hosts such as Amazon Route 53 do.

Reconfiguring DNS without losing Gmail


Using a Thermoelectric Cooler

Question: I have recently stumbled across thermoelectric coolers, it is my understanding that when they are powered one side will get colder and the other side will get hotter. Also that the more power supplied will mean increased cooling on one side and increased heating on the other side of the device. However I was wondering how efficient the thermoelectric cooler would be at cooling something like a chip if a heat sink or fan was not used to cool the hot side. I am referring to thermoelectric coolers which are 40mm by 40mm in size.
Answer: Aside from being a potential trip hazard, Peltier devices are very inefficient. They pump some heat from one side to the other, and introduce a relatively large heat source (from the inefficiency).
So if you don't have an effective (big, or forced convection from a fan, or liquid cooled) heat sink on the hotter side, you may end up making both sides hotter, just one a bit hotter than the other.
Comment: @user3623295 Yes, but I'm not sure you'll see a net gain (lower temperature) compared to simply putting the CPU cooler directly on the CPU. The cooler now has to deal with all the heat generated by the Peltier plus all the heat from the CPU so it will run a lot hotter. If that difference exceeds the difference the Peltier can achieve you'll be worse off.
Comment: Yup, a heat pump... but you gotta give the heat a place to go.
Comment: So just adding something like a CPU cooler to the hot side should be enough to keep the cool side cool?
Comment: No I was not intending to cool a CPU with, but I get what you are saying

Using a Thermoelectric Cooler


Why do I suddenly get unkown error when try to log in through Civimobile?

Question: I used to be able to log in into my Joomla based CiviCRM with Civimobile, but last week I logged out on Android, and can't log back in. It finds the site, I think, but when typing in credentials it says "unknown error".
It might be some permission related problem but don't know where check and change these for Civimobile.
Turned off firewall, reinstalled both the app and the extension, didn't help.
I need help here I think.
Answer: The solution was to click "logout from mobile" under my contact summary page/mobile tab;-)
It recreated the API that started working.
Answer: Can you check resource URL in civicrm settings php? It might be because the civicrm path is not set correctly
Comment: Not sure what to look for in civicrm.settings.php. Extention path in civi admin is  [civicrm.files]/ext/ which is actually, https://mysite.com/media/civicrm/ext. (thats where civimobile is)This path I cant find in civicrm.settings.php, but all other extensions seem to be working.
Comment: I would/could use QR code login too, but QR code never appear anymore on my admin page. It used to appear before.
Comment: Sorry i meant resource url in UI
Comment: You mean in the app? I used mysite.com, but maybe I need to add /administrator or something? mysite.com is a basic joomla website with no Civicrm content on the frontpage only on backend. So the question is what is does a civicrm website url should look like, I guess. So weird that it did work before:-O, Now I don't remember if I put in another url or not.


How do I extract attachments from a pdf file?

Question: I have a big number pdf documents with xml files attached to them. I would like to extract those attached xml files and read them. How can I do this programatically using .net?
Comment: Great question, it is very help full but , can i extract the attachments from pdf file using javascript or jquery
Answer: iTextSharp is also quite capable of extracting attachments... Though you might have to use the low level objects to do so.
There are two ways to embed files in a PDF:

In a File Annotation
At the document level "EmbeddedFiles".

Once you have a file specification dictionary from either source, the file itself will be a stream within the dictionary labeled "EF" (embedded file).
So to list all the files at the document level, one would write code (in Java) as such:
Map<String, byte[]> files = new HashMap<String,byte[]>();

PdfReader reader = new PdfReader(pdfPath);
PdfDictionary root = reader.getCatalog();
PdfDictionary names = root.getAsDict(PdfName.NAMES); // may be null
PdfDictionary embeddedFilesDict = names.getAsDict(PdfName.EMBEDDEDFILES); //may be null
PdfArray embeddedFiles = embeddedFilesDict.getAsArray(PdfName.NAMES); // may be null

int len = embeddedFiles.size();
for (int i = 0; i < len; i += 2) {
  PdfString name = embeddedFiles.getAsString(i); // should always be present
  PdfDictionary fileSpec = embeddedFiles.getAsDict(i+1); // ditto

  PdfDictionary streams = fileSpec.getAsDict(PdfName.EF);
  PRStream stream = null;

  if (streams.contains(PdfName.UF))
    stream = (PRStream)streams.getAsStream(PdfName.UF);
  else
    stream = (PRStream)streams.getAsStream(PdfName.F); // Default stream for backwards compatibility

  if (stream != null) {
    files.put( name.toUnicodeString(), PdfReader.getStreamBytes((PRStream)stream));
  }
}

Comment: I'm not so sure of this solution, at least as of the time of my comment. `EF` cannot be accessed directly as a `PdfStream`. Rather it should be accessed as a dictionary, then accessing one of the streams within that as seen in the solution at the end of my comment. Also note the use of `PdfReader.getStreamBytes(PRStream)` (all credit for this to @Robert Lane). A simple call of `getBytes()` on the returned stream will return null. Please see the following solution. `PdfReader.getStreamBytes((PRStream) fileSpec.getAsDict(PdfName.EF).getAsStream(PdfName.F))` [or `PdfName.UF`].
Comment: thanks for the suggestion. I will try this out. +1 for the code sample.
Comment: I have trouble with this line PdfArray embeddedFiles = names.getAsDictionary(PdfName.EMBEDDEDFILES); The compiler says that it cannot convert a PdfDictionary to PdfArray
Comment: Oops.  That's what happens when you write code in a browser.  It should be calling `getAsArray()`.
Comment: Also, the first item of every pair is a `PdfString`, not a `PdfName` which is used to indicate a type of pairing in a `PdfDictionary`. I'm just being thorough because posts on iText are few and far between and I'm hoping to help whomever pops through from having to go through my same troubles haha
Answer: This is an old question, nonetheless I think my alternative solution (using PDF Clown) may be of some interest as it's way much cleaner (and more complete, as it iterates both at document and page level) than the code fragments previously proposed:
using org.pdfclown.bytes;
using org.pdfclown.documents;
using org.pdfclown.documents.files;
using org.pdfclown.documents.interaction.annotations;
using org.pdfclown.objects;

using System;
using System.Collections.Generic;

void ExtractAttachments(string pdfPath)
{
  Dictionary<string, byte[]> attachments = new Dictionary<string, byte[]>();

  using(org.pdfclown.files.File file = new org.pdfclown.files.File(pdfPath))
  {
    Document document = file.Document;

    // 1. Embedded files (document level).
    foreach(KeyValuePair<PdfString,FileSpecification> entry in document.Names.EmbeddedFiles)
    {EvaluateDataFile(attachments, entry.Value);}

    // 2. File attachments (page level).
    foreach(Page page in document.Pages)
    {
      foreach(Annotation annotation in page.Annotations)
      {
        if(annotation is FileAttachment)
        {EvaluateDataFile(attachments, ((FileAttachment)annotation).DataFile);}
      }
    }
  }
}

void EvaluateDataFile(Dictionary<string, byte[]> attachments, FileSpecification dataFile)
{
  if(dataFile is FullFileSpecification)
  {
    EmbeddedFile embeddedFile = ((FullFileSpecification)dataFile).EmbeddedFile;
    if(embeddedFile != null)
    {attachments[dataFile.Path] = embeddedFile.Data.ToByteArray();}
  }
}

Note that you don't have to bother with null pointer exceptions as PDF Clown provides all the necessary abstraction and automation to ensure smooth model traversal.
PDF Clown is an LGPL 3 library, implemented both in Java and .NET platforms (I'm its lead developer): if you want to get it a try, I suggest you to check out its SVN repository on sourceforge.net as it keeps evolving.
Comment: Thanks for adding your solution. It is very usefull!
Comment: even that is a very old querstion and answer this helped me today very much, thank u
Answer: Look for ABCpdf-Library, very easy and fast in my opinion.
Answer: What I got working is slightly different then anything else I have seen online.
So, just in case, I thought I would post this here to help someone else. I had to go through many different iterations to figure out - the hard way - what I needed to get it to work.
I am merging two PDFs into a third PDF, where one of the first two PDFs may have file attachments that need to be carried over into the third PDF. I am working completely in streams with ASP.NET, C# 4.0, ITextSharp 188.8.131.52.
        // Extract Files from Submit PDF
        Dictionary<string, byte[]> files = new Dictionary<string, byte[]>();

        PdfDictionary names;
        PdfDictionary embeddedFiles;
        PdfArray fileSpecs;
        int eFLength = 0;

        names = writeReader.Catalog.GetAsDict(PdfName.NAMES); // may be null, writeReader is the PdfReader for a PDF input stream
        if (names != null)
        {
            embeddedFiles = names.GetAsDict(PdfName.EMBEDDEDFILES); //may be null
            if (embeddedFiles != null)
            {
                fileSpecs = embeddedFiles.GetAsArray(PdfName.NAMES); //may be null
                if (fileSpecs != null)
                {
                    eFLength = fileSpecs.Size;

                    for (int i = 0; i < eFLength; i++)
                    {
                        i++; //objects are in pairs and only want odd objects (1,3,5...)
                        PdfDictionary fileSpec = fileSpecs.GetAsDict(i); // may be null
                        if (fileSpec != null)
                        {
                            PdfDictionary refs = fileSpec.GetAsDict(PdfName.EF);
                            foreach (PdfName key in refs.Keys)
                            {
                                PRStream stream = (PRStream)PdfReader.GetPdfObject(refs.GetAsIndirectObject(key));

                                if (stream != null)
                                {
                                    files.Add(fileSpec.GetAsString(key).ToString(), PdfReader.GetStreamBytes(stream));
                                }
                            }
                        }
                    }
                }
            }
        }

Comment: This solution worked for me! Mark Storer's solution is incorrect, at least as of the time of this posting. `EF` cannot be accessed directly as a `PdfStream`. That much I knew. However, when attempting to access the data using `fileSpec.getAsDict(PdfName.EF).getAsStream(PdfName.F).getBytes()`, all I would get is `null`. The key to your solution, at least for me, was `PdfReader.getStreamBytes(PRStream)`, which yielded `PdfReader.getStreamBytes(fileSpec.getAsDict(PdfName.EF).getAsStream(PdfName.F))`, something I never would have guessed myself by experimenting.
Answer: You may try Aspose.Pdf.Kit for .NET. The PdfExtractor class allows you to extract attachments with the help of two methods: ExtractAttachment and GetAttachment. Please see an example of attachment extraction.
Disclosure: I work as developer evangelist at Aspose.


How does "detection risk" work after update 13?

Question: Before, we established that visibility is discrete. With update 13, however, there is now a number called "detection risk". What does this number mean? How does a lower value affect my visibility?
Answer: It appears that the "detection risk" is the level that the detection meter starts at the moment a guard or camera spots you. So if you have a detection risk of 75, the highest, you will be detected very shortly after a guard or camera spots you.
In this screenshot, my detection risk is 35. The screenshot was taken on the same frame that the camera first noticed me (taken as a clip from a video):

In order to successfully stealth, you're going to want that number to be reasonably low. Around 20 is usually good for me. The lower the better, though.
Comment: Also, interesting note from Update 13: Cameras *will* notice you in casing mode. Full stop. Whether or not they detect you depends on your detection risk, and how long you stay in their view.


Reconstruct the wave-function from one-body reduced density matrix?

Question: Given a many body wave-function for a Fermion system, we can calculate the one-body reduced density matrix straightforwardly. Now suppose we know the one-body reduced density matrix, is there a way to obtain the corresponding wave-function exactly?
Comment: Due Hohenberg-Kohn theorem there is a bijective mapping between the diagonal of the reduced density matrix (just density) and the many body wave function. So one has to "just" solve the inverse problem of finding the external potential which produces the density and then solve the many-body schrödinger equation for that external potential. In practice of course this is never done like that.
Comment: Hi Mikael, thanks for your answer.  I know there is the Gilbert's Theorem which basically states the similar thing for the one body reduced density matrix as Hohenberg-Kohn theorem. I want to know if there is a "practical" way to reconstruct the wave-function approximately if not exactly. One approximate way I can think of is to construct a single Slater determinant from the natural orbitals (the Eigenstate of one body reduced density matrix) with large occupancy. I think the question is how to determinate the coefficients if we expand the wave-function in the complete basis.
Comment: You need more information. Having just the one-body reduced density matrices won't uniquely reconstruct the state. You can surely construct "a" state - see for instance http://www.mathematik.uni-muenchen.de/~lerdos/WS12/MQM/many.pdf page 57.
Comment: @MikaelKuisma Doesn't the Hohenberg-Kohn theorem require that the state is a ground state of a very special Hamiltonian -- one which is uniquely fixed except for a one-particle potential (which only couples to the one-particle density), such as in the case of interacting electrons in an external potential?
Comment: @Martin Thanks very much for pointing out the reference. The proof of theorem 10.2 shows a procedure to reconstruct the state given the one-body reduced density matrix. I have two questions about it. First the author doesn't say whether the way to reconstruct the state is unique or not. Second, the constructed state is a mixed state of single Slater determinant in general. If we know the one body reduced density matrix state is from a pure state, is there a approach to reconstruct the pure state, is it unique?
Comment: @NorbertSchuch yes, under those circumsances only, I forgot to mention.
Answer: No, in the typical case this is not possible.
Given that the fermions are interacting their combined state will be entangled (or in the language of quantum chemistry, they are correlated). This means that the reduced density matrix for a single electronic coordinate will be a mixed density matrix. Or in other words: The one-body density matrix is a classical probability distribution over a set of (not uniquely defined) wave-functions. Such a set is not reducible to a single wave-function with probability 1.


Tax rebate on Home loan on mother's property

Question: I have got a home loan from SBI on my mother's property. she is co-signee on the the loan. Can I use EMI paid for my tax saving.
Comment: Welcome to Money.SE! Please add a country tag to this question. And to your profile, if you'd like. We have members from all over the world, and you'll get a decent answer once the tag is added.
Comment: @JoeTaxpayer This is most likely a question about India with SBI denoting State Bank of India.  I would expect Dheer to provide an answer soon.
Answer: If the property was already built and paid for; post this you have taken a "Loan against Property", you will not be able to claim any tax rebate.
If you mean that the land was on your Mother's name and you have taken a loan to build the house, you can claim rebate if you have completed the construction.


How long did Saphira stay in her egg from the day it was laid by her mother?

Question: How long did Saphira stay in her egg from the day it was laid by her mother?
Comment: see the edit I just made to my answer, should be in time for your deadline
Answer: A little bit over 100 years
Saphira was born shortly before the Fall of the Dragon Riders

Was Saphira's egg laid immediately before/during the Fall, or did it happen a significant amount of time before that?
Christopher Paolini: It was laid fairly close to the Fall.
Twitter, May 31 2022

The Fall of the Dragon Riders ended one hundred years before Eragon found Saphira's egg.
So Saphira spent a bit over 100 years in the egg. Perhaps something like 105 years.


Who has the ability to physically manipulate a repeater's controls?

Question: I know that repeaters on VHF and UHF are primarily automatic, but there will be times when they will fail, or something is not working. The repeater may not respond to the remote control. In these situations, someone will have to climb the top of a building or go up to the top of a mountain and tinker with it. Who can do this?
Answer: The owner of the repeater is typically in control of who has physical access. Often the owner will permit the trustee of the station license (in the US) to have access in order to carry out their lawful responsibilities although the owner and trustee may be one in the same.
When a club maintains a repeater, there is often a technical committee that is charged with keeping the repeater in good working order.
Also consider that in the US, from a legal perspective, the control point of the repeater may be remotely located from the repeater even if the repeater is normally automatically controlled.
Comment: Can you clarify that last paragraph? I'm having trouble parsing it.
Comment: @PeteNU9W The FCC defines a control point as "the location at which the control operator function is performed". Automatic control is defined as "the use of devices and procedures for control of a station when it is transmitting so that compliance with the FCC Rules is achieved without the control operator being present at a control point". Notice neither of these say where the transmitter or repeater is physically located.


What is the difference between words "notability" and "significance"?

Question: I've seen somewhere that "notable" is related to a person or a concrete thing, while "significant" is related to a sign or a symbol. Is it correct?
Comment: Hello, Clarity. How do example sentences provided by online dictionaries support or oppose this claim?
Comment: Hello, Edwin. I was using this https://wikidiff.com/notable/significant dictionary.
Answer: Welcome to ELU Clarity. It's always good to include the research you have done when asking a question, for example, if you consulted any dictionaries what did you find? Also you have asked about slightly different words, in your question title you have asked about notability (the quality of being notable), and significance (the importance of something). But in your question you have asked about notable and significant. This answer focuses
on notable and significant. With that said...
This type of question is best answered by consulting a dictionary, reading the definitions for the words you are interested in comparing, and then analysing for differences in meaning.
Let us look at notable first:

Important and deserving attention, because of being very good or
  interesting. - Cambridge dictionary
Deserving to be noticed or to receive attention; important. - Oxford Dictionary

As you can tell from the above two definitions, if something is notable it is deserving of attention, and Cambridge further say this object is interesting or very good. While Oxford state that the object is important. I guess it goes without saying that if an object is deserving of attention it is interesting (because there is of course something that makes it different from those objects that are not deserving of attention).
But the key with notable is that some object is noteworthy, i.e. deserving of attention.
Now let's look at significant:

Large or important enough to have an effect or to be noticed. -
  Oxford Dictionary
Important or noticeable. - Cambridge Dictionary

You might find it interesting to note that all four definitions include the word important. Something that is noticeable or significant is important for the way in which it stands out against other similar objects of consideration.
From experience of usage I would say that the key distinction between the two words is best highlighted in the Oxford definition for significant. Notice the use of the word Large.
If something is significant it is noteworthy or interesting in some way that is not just important, but very important.
So notable and significant you can see from the definitions are very similar, and any object that one of these words can be used on, the other can also. But significant tends to convey a slightly stronger sense of importance than notable.
So...

"notable" is related to a person or a concrete thing, while
  "significant" is related to a sign or a symbol. Is it correct?

The answer to the above question is no, both words can be used on ideas, symbols, or concrete things, although significant is usually used in relation to ideas more often, it can refer to concrete things still.
e.g.

She looked at him across the table and gave him a significant smile.
   - Cambridge Dictionary

While notable is most definitely used for both ideas and concrete things very frequently.
e.g.
"Her performance was notable".
"He was a notable activist of the Civil Rights Movement" etc.
Comment: There are different senses for 'significant'  (a 'significant smile' is often taken to be one with a hidden [from outsiders] meaning). The stats sense is unique. But the subsense under the 'important' sense  'having or likely to have _a major effect_' needs bringing out more than by 'If something is significant it is noteworthy or interesting in some way that is not just important, but very important'; some things considered very important at the time just fizzle out.


GParted live graphical mode not working

Question: I want to run GParted live 188.8.131.52 on a laptop with both an integrated and discrete graphic card.
I managed to start GParted using the "vga=normal" boot option, but X refuses to start either if select the default configuration or if I run "Forcevideo" selecting either the "vesa" or "nv" options.
In any case the screen shows "Debian GNU/Linux 10 debian tty1" from which I'm not able to run any command.
Does anyone know how to solve the problem?
Answer:
disable the discrete graphics via BIOS or unplug the card from the motherboard(if not embedded obviously) and give it a go
try with an older release, 0.25, 0.27 but this time i686 version (if you already tried with the amd64 or vice versa)
add "gl-debug" as a boot parameter and try starting the X interface manually, save the error and compare with different releases, post it back here
must it be gparted live? this one has also gparted and many more: http://www.system-rescue-cd.org

GParted live graphical mode not working


O-Ring Selection for a round rectangle groove

Question: I'm designing a water proof case for a power bank to be used in an occasional underwater condition. The input and out put port components already have a gasket or sealing ring. Now to close the case I am planning to mill a metal with all walls and floor and then screw the top along with and O-ring. I haven't used an O-Ring before and wanted to know how to select an O-ring for a rounded rectangle groove (Does the circumference being equal to the grove length , enough). Is there any handbook for the same?
Comment: I believe you're overthinking this. Unless that power bank is meant to supply a space shuttle.
Answer: With any O-ring seal, static or dynamic, the key parameter is "O-ring Squeeze" which is defined as the percentage reduction in cross sectional area when compressed from the free state. Since the o-ring acts like a spring, this squeeze is directly related to the sealing force. The greater the squeeze, the greater the sealing force, and the greater resistance to leakage...at least in general.
As with most things, more is not always better, too much squeeze can result in a poor joint since it can cause excess stress in the mating parts, excess friction (in the case of a dynamic seal), and O ring damage since there's a greater risk of the o-ring getting pinched between the two mating surfaces.
In designing O-ring seals in stainless steel with good surface finish, I would try to stick to < 15% squeeze for dynamic seals and 15%-30% for static seals using a standard NBR O-ring from Parker, but it really depends on the type of O-Ring, the materials involved and all of the other specifics of the application.
In your case, you'll want to use an O-ring that has a circumference close to the mean perimeter of your groove. You can, of course buy custom O-rings, but those can be expensive.
There's a lot that goes into the design of a good O-ring joint. The best resource I've found is the Parker O-ring Handbook.
Comment: You could also use "quadro seal" rings that have cross sectional profile that has four lobes instead of a round circular profile. This would seat better in a groove that has square sides . Go to the McMaster-Carr website to see these for yourself.
Comment: "Quadro" or "Quattro" or "Quad" ring seals are all the same thing, depending on the manufacturer or distributor (and who owns which trademark). Almost all o-ring grooves have a rectangular cross section, so the groove shape isn't the reason you'd pick this design. The twin-lip design resists rolling, and the second seal surface improves your odds if the seal gets nicked or the surface isn't perfect. An o-ring will work quite well in its place in most applications. I second the Parker O-ring Handbook. (I was a hydraulic seal engineer.)


"Plug an Ethernet cable into this computer"? With no connections are available

Question: I restarted my Windows 7 laptop 2 times and nothing happened. I have no internet at all. I chose to troubleshoot it and it told me "Plug an Ethernet cable into this computer" I have no idea what that means... It says something like "A. Ethernet cable looks like a telephone cable but with larger connections on the ends. Plug this cable into the opening on the back or side of the computer. Make sure the other end of the cable is plugged into the router. If that does not help, try using a different cable." Can someone explain to me what to do exactly in a less complex way? I'm not a computer genius so I don't really know what to do. It also said "No connections are available" even though all the phones and iPads in the house are working perfectly fine. There is also an update for Windows 10 but I did not update it yet.
Comment: I don't know if it can get less complex than that...  Possibly call someone to help you locally.
Comment: It sounds like your wireless is disabled or not working correctly, so it's defaulted back to other available network connections, in this case an ethernet connection. What model laptop is it? It may be as simple as hitting a button to re-enable wireless.
Answer: These are some suggestions for restoring your wireless connection in Windows 7.

If you are using a router, push the reset button on the router to toggle it off, then wait 10 seconds and push the reset button on the router again to toggle it back on.
Try uninstalling the wireless driver and reinstalling the driver and reboot your computer.
Use the  built-in Windows System File Checker tool to repair missing or corrupted system files.

Ethernet is a family of computer networking technologies for local area (LAN) and larger networks. An ethernet cable looks like a telephone cable, but the connector is wider. A telephone cable has 4 pins, but an ethernet cable has 8.
If your laptop has an ethernet port, then plug in an ethernet cable to make a wired connection from your modem or router to your laptop. The ethernet cable connector will make a soft clicking noise when the plastic spring engages in the ethernet port, indicating that the ethernet cable is firmly plugged in to the ethernet socket as it should be to have a proper electrical connection.
Ethernet cables come in different colors and lengths. These two pictures show what an ethernet cable looks like.
Answer: There are several things that could be wrong:

Your computer has an issue with the connection. You can see your adapters by search for Network Adapters in the Windows search box. At least one Ethernet adapter should show as enabled.
You were running on WiFi and accidentally turned it off. See if you have WiFi on the machine  and can turn it back on.
The Cable has an issue. Are both ends plugged in? Is it damaged in anyway? You should green lights on the places where the cable plugs in.
The router and or modems (the boxes where the internet comes in form the road and goes to your machines may have an issue.) A simple unplug, wait 20 seconds and re plug can help this situation.


How to get blockchain length

Question: I send rpc calls to a node through tezos-client and I would like to know the length, or the height, of the blockchain so I can see if it is synced and, if not, how much time is remaining. How do I do that?
Answer: tezos-client rpc get /chains/main/blocks/head. Look for the value of the level key under the header key in the outputted json.
The output data is quite big, so you can use this:
tezos-client rpc get /chains/main/blocks/head | grep level | head -1
Comment: Since all output of the RPC is JSON, you should look into using `jq` rather than grep/head. Far more powerful for command-line filtering.
Answer: You can also call tezos-client get timestamp repeatedly: it will give you the timestamp of the most recently received block. You'll get an idea on where you're at and how long you have left to synchronize. If you want to synchronize the full state of the blockchain, this might take a long time. Look into snapshots to get into sync faster. You can find snapshots here.

How to get blockchain length


Dog with open wound on leg and no vet available

Question: I found this dog in a graveyard, probably waiting to die, with a huge open wound on its backside 2 days ago. I've been feeding it, helping it regain its strength but I'm concerned, the wound may get infected. What should I do? I live in a small town. We don't have vets that tend to canines here. How do I tend to the wound without hurting the dog or getting bitten myself?
Comment: Thete seems to be a black spot in the center of the wound. Is it more like a scab (dried blood) or is the soft tissue turning black?
Comment: None. It's an open wound and i dont know how deep since I haven't been able to examine the wound properly at all. It took a lot of work just to even take that photo because the dog wouldn't move from it's resting place. That black spot isn't actually a spot but more like a hole.
Answer: The wound is clearly very infected and it's only natural the dog turns it away from you. Please don't try to touch it, it may provoke a (defensive) attack.
You also have to realize that the dog may not survive. If the tissue inside the wound dies off (called a necrosis), it cannot heal and must be surgically removed. It might already be too late to avoid a sepsis due to bacteria from the infection spreading through the whole body.
To fight the infection and relieve the pain, I suggest you go to a pharmacy and ask specifically for one of these drugs:

carprofen (Novox or Rimadyl)
deracoxib (Deramaxx)
firocoxib (Previcox)
meloxicam (Metacam)

All of them are anti-inflammatory drugs and listed as safe for dogs by WebMD. Using human medication like ibuprofen or aspirin can lead to kidney failure in pets.
The pharmacists may ask why you need those (at least they should if they do their job right). Show them the pictures you've taken and let them estimate the proper dosage of the pills.
Give the dog the proper dosage twice a day (or according to what the pharmacist and packaging say) and always together with food. The stomach should not be empty when taking the pills. If the dog doesn't like the pills, coat them in something tasty like cream cheese or a soft sausage. Continue the treatment for as long as the packaging says it's safe.
Comment: Thanks alot. I must add though, the dog keeps on licking at the wound. Doesn't dog saliva have healing properties? It's been 3 days and the dog stood up and moved around for the first time today on it's own. Thats when i became certain of the wound. Incase if the dog does somehow allows me to tend to it's wound, what should i do? Clear the area with a spray bottle and apply an ointment of some kind along with the oral medication that you've advised?
Comment: @HamidSabir I wouldn't touch the wound if I were you. The risk of being bitten is too high (especially if you try to flush it with a desinfactant, which hurts). The benefit is probably low because the bacteria are in the tissue, not on top and you're not properly trained to tend such a wound. The dog should be able to keep dirt out. Just take care it isn't infected with maggots as well.
Comment: I don't think dog spit has healing properties, but the act of licking promotes blood flow to the wound. Which aids healing


Were the Korrealis Prince and Korrealis Sovereign speeders Bind on Pickup or Bind on Equip?

Question: Were the Korrealis Prince and Sovereign speeders BoP or BoE?  I ask because, my character having been poor at the time they were discontinued, I'm interested in buying them from someone now.  I've managed to get one of the two non-faction-specific Korrealis speeders, and have seen the other one listed on the GTN, so they were obviously BoE.  I haven't seen the faction-specific speeders listed though, and couldn't find any info about how they bind; hence, my question.
Answer: The issue with Korrealis and Prince is they were PVP speeders. They required Rank 65 Valor to purchase and use them (I grinded up my PVP all of March for that). Despite them saying the requirements and binding would be removed on Korrealis Speeders, the PVP were exempt from that.
They didn't clarify (though, apparently some posts said only "some" Korrealis speeders would do this despite all being removed) very well so many users had bought up several. In fact, I still have 3 rotting in my bank that are for friends that I have never been able to give them (Similarly, one of them had gotten me a Prince in return).
Because they were PVP and had Valor requires, they were BoP. I've heard mixed things from staff including that it could be a bug (Since what sense does it make it only make half of them tradeable?) or that it was intentional. I was told to make a suggestion thread, but it kind of just blew up...
Comment: That makes more sense.  Hmm, hopefully we can convince BioWare to at least let all the extra ones be sold.
Answer: Both Korrealis Prince and Sovereign speeders are BoP:

Prince
Sovereign
Comment: Hmm, Torhead says this same.  Looks to be the answer, unless it was one of those situations where they made it BoE for everyone who already had them so they could sell them off.  Anyways, thanks!


expectation of log of expectation by Monte Carlo

Question: When considering the approximation by Monte Carlo of an expectation of the form$$\mathfrak{I}=\mathbb{E}^X[\log\{\mathbb{E}^{Y|X}[h(X,Y)|X]\}]$$using a resolution of the form$$\hat{\mathfrak{I}}=\frac{1}{N}\sum_{n=1}^N\log\left\{\frac{1}{M}\sum_ {m=1}^M h(x_n,y_{nm})\right\}$$(when the $x_n$'s are generated from the correct marginal on $X$ and the $y_{nm}$'s from the proper conditional of $Y$ given $X=x_n$) produces a convergent but biased estimator. I wonder if there is a genuine way to produce an unbiased estimator in this case, other than using the trick of McLeish (see equation (1) on page 2).
Comment: I don;t see the connection between McLeish's article which is really dealing with Bayesian methods and Markov Chain Monte Carlo and your problem.
Comment: [Nested sampling](https://arxiv.org/abs/1612.00951) is considering this problem but uses plug-in estimators that result in a biased estimator.
Answer: The methods presented in this work (https://people.maths.ox.ac.uk/gilesm/files/SLOAN80-056.pdf) concern Multi-Level Monte Carlo (MLMC) methods for expectations of this form. MLMC is typically not designed to provide unbiased estimators per se, but can usually be modified to do so using the trick of McLeish.
Broadly, if you are interested in
$$\mathfrak{I}=\mathbb{E}^X \left[ g \left\{\mathbb{E}^{Y|X}[h(X,Y)|X] \right\} \right]$$
then the standard trick is to write
$$\hat{\mathfrak{I}}_{\ell_1, \ell_2} = \frac{1}{N_{\ell_1}} \sum_{i = 1}^{N_{\ell_1}} g \left( \frac{1}{N_{\ell_2}} \sum_{j = 1}^{N_{\ell_2}} h \left(X^i, Y^{i, j} \right) \right)$$
where $N_{\ell_1}, N_{\ell_2}$ are two sequences of positive integers increasing to infinity. One can then form a sort of double-telescoping sum representation of
$$\lim_{\min \left(N_{\ell_1}, N_{\ell_2} \right) \to \infty} \hat{\mathfrak{I}}_{\ell_1, \ell_2}  = \mathfrak{I}$$
and the debiasing trick of McLeish applies. The work of Crisan et al. (https://arxiv.org/abs/1702.03057) is also relevant here.


capacitor discharge direction

Question: This is probably a dumb question, but I am sort of confused. What direction does a cap discharge when a system is turned off? For example, decoupling caps that go to ground. When I shut a system down, does the current flow to ground or does it flow in the reverse direction toward the supply (since it is now 0). Would putting a resistor in series to ground have any effect?
Comment: When you turn the power supply off, the system voltage begins to decay towards ground.  The charge stored in the capacitors goes towards the rest of the system (that is, to where the power supply is connected) and, essentially, keeps the system running for a very short time longer.  But as the supply voltage decays, so does the voltage on the capacitors.
Comment: Same as battery
Answer:
For example, decoupling caps that go to ground.

Caps block DC, so V+ will want to return to ground through the circuit, as usual, taking the easiest path. Decoupling caps are not usually the issue. It is the bulk caps that act like batteries when the power is disconnected.

When I shut a system down, does the current flow to ground

Current only flows toward lower voltages. If voltage is trapped in the circuit, either because the switch physically disconnected V+, or because the power cord was physically disconnected, the device will continue trying to work, consuming the remaining power. Caps will eventually dissipate their charge if there's nowhere for it to go.

or does it flow in the reverse direction toward the supply (since it is now 0).

If a transformers input is switched, but the output is not, the V+ terminal may be the shortest path back to 0V. However, a rectifier between transformer and circuit negates that, leaving GND the only path back.

Would putting a resistor in series to ground have any effect?

A resistor in parallel is called a "bleeder" and is common when the circuit may inadvertently retain unwanted/dangerous voltages. They are basically "soft" shorts, in case the circuit's GND gets disconnected. The drawback of a bleeder is that it dissipates power whether the circuit is operating or being bled.
Answer: When Capacitor discharges current always flows in opposite direction. Current does not flow through the capacitor only chrages the plates (known as virtual current).
vtingole
Comment: "Current does not flow through the capacitor" -- It sure does!

capacitor discharge direction


ER Diagram | Group, Post, User relationship

Question: I need to design an ER diagram, but I am confused in a section, more specifically how to relate the post with the groups, because I need that post contains the information of in which group I publish and that user I publish it, I have two diagrams one where the relation of post, group and user are direct, and other where the post is related by means of the table generated of the relation many to many between group and user. My question is which of these two is more recommended.
Diagram A

Diagram B
Answer: the bridge table group_user between User and group is the right idea, when there is a many to many relationship
But users should be connected directly to posts like in the first image, because only pone user can have written the post-
Conclusion make a new mixed version


show quick look preview in a view

Question: I am trying to show the preview of a file in a View instead of in a panel. All examples I found are about QLPreviewPanel. :(
Thanks in advance for your help.
Comment: The Quick Look programming guide mentions a function [QLThumbnailImageCreate](http://developer.apple.com/library/mac/documentation/userexperience/Reference/QLThumbnailRequest_Ref/Reference/reference.html#//apple_ref/c/func/QLThumbnailImageCreate) which can give you a `CGImageRef` to a thumbnail image for a URL that you specify. Have you looked into that?
Comment: Yes but it only works for the thumnail, not the preview.
Comment: Added a new bit of information to my answer.
Answer: It seems like Apple really wants you to use the QLPreviewPanel; the only possibility I see is "scraping" the preview, by setting the panel to layer-backed and getting the contents of the correct sublayer. Something like this (although I haven't gotten it to work):
[[[QLPreviewPanel sharedPreviewPanel] contentView] setWantsLayer:YES];
[[QLPreviewPanel sharedPreviewPanel] makeKeyAndOrderFront:nil];
NSLog(@"layer: %@", [[[QLPreviewPanel sharedPreviewPanel] contentView] layer]);
// I believe there are two sublayers
id QLcontents = [[[[[[QLPreviewPanel sharedPreviewPanel] contentView] layer] sublayers] objectAtIndex:0] contents];
NSLog(@"contents: %@", QLcontents);
[myView layer].contents = QLcontents;
[myView layer] setNeedsDisplay];

Not a final solution by any means (this doesn't work as is) but maybe it'll point you in a useful direction.
UPDATE: Just stumbled across a category on NSImage,  written by a fellow named Matt Gemmell, which uses QLThumbnailImageCreate. Look for "NSImage+QuickLook" on his source code page. He seems to imply that the QuickLook Panel actually uses QLThumbnailImageCreate. I think that function may be the best way to go. The category might make your life a little easier.
Answer: I've made some headway with this.  The sublayers' contents were nil.  But the old-fashioned subviews work:
[[[QLPreviewPanel sharedPreviewPanel] contentView] setWantsLayer:YES];
[[QLPreviewPanel sharedPreviewPanel] makeKeyAndOrderFront:nil];
NSArray* subviews = [[[QLPreviewPanel sharedPreviewPanel] contentView] subviews] ;
for (id subview in subviews) {
    // The first view is the one we want, which is an unsubclassed NSView.
    // The second is a QLPreviewTitleBarView.  However, instead of relying
    // on that order, we check for the class.
    if ([subview isMemberOfClass:[NSView class]]) {
        NSLog(@"frame of subview: %@", NSStringFromRect([subview frame])) ;
        // The following statement will *remove* the desired subview from
        // the QLPreviewPane and place it into myWindow instead.
        [[myWindow contentView] addSubview:subview];
        break ;
    }
}

It even seems to update myWindow when I send -reloadData to the QLPreviewPane.  I'm feeling slimy.  Not sure what to do next, though.  One problem is to deal with the arbitrary size of the subview.  One of the reasons why I don't like QLPreviewPane is that there is no control over the window size; it gets a view from the generator at some arbitrary size and splats it on the screen.  I guess I could put it into a scroll view.  Another issue is how to deal with the QLPreviewPanel which is still on the screen.  Maybe set its frame origin to off-screen  But I need to go work on another task right now.  Any further ideas would be appreciated.
Later.  I think this approach is going to be to problematic.  First, I tried to get rid of the QLPreviewPane window by sending it a setFrameOrigin:NSMakePoint(10000, 10000).  Result: [QL] Assertion failure ([event window] == window) - Wrong window in event.  Then I tried to omit the call to -makeKeyAndOrderFront: and instead skip up to -reloadData.  Result: [QL] QLError(): -[QLPreviewPanel reloadData] called while the panel has no controller - Fix this or this will raise soon.  See comments in QLPreviewPanel.h for -acceptsPreviewPanelControl:/-beginPreviewPanelControl:/-endPreviewPanelControl:.
The second error is understandable, however it indicates that the QLPreviewPanel will not try to find its data source, as it does, until it is made key or ordered front.  The first assertion, however, indicates that, besides not providing a proper API to get the preview data directly, maybe Apple has laid some traps for the casual hacker like me.
If I come back to this, next time I'll try the more serious hack proposed by Ken Apeslagh.
Answer: Starting in OS X 10.7, there is a public API for this: QLPreviewView.h, which is part of the QuickLookUI framework (which is part of the Quartz framework). There doesn't seem to be documentation on it, but the header file provides some basic info.
Comment: I was getting lost trying to find the f***ing QuickLookUI.framework to include so it recognizes the QLPreviewView class, thanks for pointing me to include the Quartz.framework.

show quick look preview in a view


Logic Design simple door security system with using MUX

Question: I draw the cicuit without using any MUX. But my project says I need to use 4x1 MUXs
and I couldn't find where to use 4x1 MUXs. I tried put MUX of each output but this was very pointless, no need to use 4x1 MUX for the X output. So how do I need to design the circuit using 4x1 MUXs.
Answer: Remember that the combinational logic circuit gives you a 2 bit output, making 4 possible combinations that you have (no card/valid code 1 and 2/invalid code). A 4x1 multiplexer chooses an output from 4 inputs based on a selector input - that is, 2 bits. Ideally you would want to attach the A and B outputs to the MUX inputs - then based on your spec, choose when the output should be on. Then from here, you choose which of the 4 inputs is connected high, and which are grounded.
For e.g., if you want to sound the alarm, then you must make the output 1 for the alarm signal (that is, 0 and 0 for A and B). For that MUX, make the topmost(conventionally) input high, and ground the rest. Then you use 2 other MUX (or maybe 1?) for the doors 1 and 2. Here is an example of the alarm multiplexer, as it only needs to be on for 00 as AB:

EDIT: Here is a crude solution for the multiplex output for your question, using 3 MUXes. See if you can understand how they all work.
Comment: As I understand the task, the alarm should also be ON when wrong keypads are pressed, but valid card is present. For instance if person holds wrong kepayd for door 1 (000) but still uses corect card for door 1 (AB = 11), the alarm should be ON, and door 1 OFF
Comment: Doesn't it say "valid CODE for door 1", implying both the card and correct code have to be in? Only then it will either display 11 or 01 as AB right?
Comment: Well, that obscured me too. But it says in the beginning: "A person may open a particular door if he or she has a card containing the corresponding code AND enters an authorization keypad code".   So I read it as card code and keypad code are two different things, and there are separate cards for door 1 and cards for door 2. So AB are only outputs for the card reader.
Comment: Ah, I see there are 2 different codes now. I thought the 000 etc were unique to each card, but apparently each card has its own code. I think there may need to be additional steps to this now. I do still think the approach of using a MUX for each output is the right way, although there needs to be additional circuitry to output the right 2 bits when the correct card and keycode is inserted.
Comment: I think you approach is correct. I actually used it and it took me 11 MUXes to implement full logic. I think it can be made easier.


Is palmistry a part of astrology?

Question: How can one judge our Graha-dosha by reading only hasth-rekha?
I think from kundli it can be done but how from hastha-rekha? Probably our groha changes in every ten years but does also hasth-rekha changes?
Comment: Why it can't be done? Even from our face or other parts of our body an adept astrologer can predict a lot of things. Its part of samudra sastra.
Comment: Also in our natal chart the grahas are fixed, however in the transit chart they change...and if u are a good observer then u can even notice subtle changes in ur palm lines which evolved with time..
Comment: No they can change even after ur body stops growing..You have to be a keen observer.
Comment: Sorry i completely forgot that i am supposed to give u the book names. Do u want them in Eng or Beng? anyways, here are few books in Bengali . They are of preliminary nature but by studying them u can learn the subject.
Samudrik Vigyan, Samudrik Rekha Vichar (Raman Krishna Chattopadhya), Hath Dekha Sikkha (Paresh Das Burman). [Publisher-Tara library] ... Sachitra Hasta Rekha Vichar o Vigyan. (Sri Surendra Nath Bhattacharya Jyotis Shastri author)
Comment: Also u need the change the title to something else. Scientific speculation is off-topic here.
Comment: I read a book on palmistry by Chiero but that does not inspire me. Can you suggest me some Bengali book or astrology?
Comment: Ok i will definitely do that Let me collect some book names.
Comment: I guess it changes during our grown up times but not that much after our middle age
Comment: Another question: Can you suggest me some apps or online sites where I can make kusthi/kundli using only date and time of birth. Thanks.
Comment: Yes there are many such sites. This one is good: http://astrobix.com/horoscope/birthchart/
Comment: You are welcome. BTW u can easily get them in College Street book shops.
Answer: If you take your palm print every year. You can easily see after 10-15 years that it changes! There is no doubt about it.
Palmistry is part of astrology. In ancient India, Palmistry was known as "Samudrika Shastra".
World's most famous palmist Cheiro learned palmistry from an Indian Brahmin from Maharastra. He mentioned that in his biography.
Ref: Language of the hand by Cheiro
https://www.amazon.in/Cheiros-Language-Hand-Cheiro-ebook/dp/B07C38PKKM/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=1559207417&sr=8-3
By the way, most of the horoscope analysis is done based on the position of planets at the time of native's birth. Your horoscope is basically the snapshot of the sky when you were born. That is why they ask for three info: date of birth, time of birth and place of birth. This snapshot varies depending on time and place. So it is the analysis of fixed planetary positions during your birth that predicts your entire life! Only the transit (or gochara) analysis takes into account of changing planetary positions with time.
Comment: @Pandya What sources are needed? Can you elaborate Pandya? The OP edited after citation notice. Is that enough? Let the rest of the users also know what is missing in the answer so that they will know when to flag for removal or edit properly.
Comment: You should cite some sources.

Is palmistry a part of astrology?


How Do I Get The NBT Data a Specific Block?

Question: I want to get the NBT data of a block as a string e.g. The NBT data of a chest. I know that this is possible as I had to do it a year or so ago for a key to a house I had built.
Comment: Do you want to get the NBT data and store it as a string somehow, or just see it in chat?
Answer: You can use the /blockdata command to see tile entity data. Providing no input will show the current state of that data. For instance, stand on top of a chest and run the following:
/blockdata ~ ~-1 ~ {}

Answer: This way isn't very efficient, but it's how I have always done it (and I don't know another way):

Look at the chest, hold ctrl, and press your pick block button (configurable in options). This should give you a chest item with identical NBT data.
Place a command block down anywhere that doesn't have armor stands adjacent to it (including diagonally)
Run the command using the command block:
/summon ArmorStand ~ ~ ~ {ShowArms:1}

Then put the chest item in the hand of the armor stand, then run this command in the command block:
/entitydata @e[type=ArmorStand,c=1] {}

You can then go to the output of the command block, look for the Items tag and copy the text within the following '['. Alternatively, you can copy the whole output, paste it in a text editor, press ctrl + F, and search for the tag.

An example of what I would copy is:
Items:[0:{Slot:0b,id:"minecraft:sandstone",Count:1b,Damage:0s}

Answer: Just in case, as of ItemsAdder 3.4.1-r4, the following command should return entity data, including NBT, of an item currently being held by a player Player1:
/data get entity @p[name=Player1] SelectedItem

If it does not output anything in-game, you might want to try it on the server console.

Related: How can I see the entity data of an existing item?


Touchpad behaving erratically

Question: Symptoms: Cant move pointer up and down, only side to side. When moving side to side it jumps around erratically. When using USB mouse the pointer jiggles from side to side. The touchpad can detect movement 1cm to 5cm above it, moving in the air without touching it.
This occurs on a dying laptop on which things cease functioning all the time for no real reason, but its annoying because of the pointer twitching and moving side to side if it detects my arms while typing. Is this repairable or is it possible to turn the touchpad off to make it stop twitching the pointer?
Answer: On the right side of your taskbar, open up the hidden icons. You should see something that looks like a touchpad. Right-click on it and select Pointing Device Properties.

This will open a window called Mouse Properties. There are multiple tabs like Buttons and Pointers, but the one you're after is Device Settings, where you then click on the Settings button below the device list.
After that, look for "SmartSense" and click on the options.
SmartSense is a feature that tries to prevent accidentally moving the mouse while typing, and I believe it will work in this case.

After that, turn it on. Slide it around and see what fits you best.

Do tell if this helps!
Comment: I couldnt find SmartSense in settings but I instead checked the box to disable it when a USB mouse is in use, since I dont use the touchpad anyway. Is it normal for a trackpad to detect movement an inch above it without touching it?
Comment: I'm not sure - perhaps you're touching it very lightly? Either way, sounds like you have a very perceptive mouse pad!
Comment: SmartSense is an ASUS application
Comment: @MathManiac No definately not, I can see a good inch of space between my finger and the trackpad. For clarity, It is not above on the X axis, but vertically above it.

Touchpad behaving erratically


Java Generic confusion on wild card

Question: I am learning generic and got struck at some point.here is my class
public class MyValidator{

    private Class providerClass;

    public MyValidator(Container container){
       setProviderClass(container.getInstanc(ValidationProvider.class),"my.providerClass");
   }

    public void setProviderClass(Class<? extends ValidationProvider> providerClass)
    {
        this.providerClass = providerClass;
    }

}

Signature of container is
 <T> T getInstance(Class<T> type, String name)
Gets an instance of the given dependency which was declared in ContainerBuilder.

Container is an inbuild DI mechanism of the platform i am using, but when i call the setter method from inside my constructor i am getting following exception in Eclipse

The method setProviderClass(Class) in the type MyValidator is not applicable for the arguments (ValidationProvider)

I know i am not following the contract properly but not sure how to do this.My intentions are to set the class at run time and it should accept all those implimentation who impliments ValidationProvider which is an interface.
Answer: getInstance(Class type, String name) return T not Class -> an instance of ValidationProvider not a class object.
That's what the exception message says: you need a Class object but you're passing a ValidationProvider object.

Java Generic confusion on wild card


What kind of plastic is used for good camera bodies?

Question: My Canon DSLR camera bodies are made with glass filled plastic over aluminum skeleton.  What is glass filled plastic? It doesn't have the same cheap feeling as common plastic items. I've seen knife handls made with glass-filled nylon,  and it is very hard.  Is it like fiberglass, or microbeads? I imagine it uses that with some kind of thermoplastic as opposed to resin, but does anyone know what kind of plastic?
Answer: It's probably a glass filled polycarbonate.  Composite materials like this get the benefit of the two different types of materials used to make it  - it benefits from the polymer matrix as well as from the glass.  According to the bottom link the glass improves impact, moisture, and chemical resistance of the polycarbonate.

Google Patents Patent 4,247,600 - Metallized plastic camera housing and method
Material Category Search Polycarbonate, 30% Glass Filled
Google Books Industrial Plastics: Theory and Applications Thermoplastics
Comment: Your bottom link is in reference to the polycarbonate in mini CD-R discs that some early digital cameras used to store photos, and not to the material int he bodies themselves.
Comment: @MichaelClark - Although there was a photo and caption of a CD-R, if you read the text above the photo, you'll see other industrial uses - I included that reference because it described why you add glass to the polycarbonate.  Here is a separate reference that may more directly address you question.  http://books.google.com/books?id=g7NvF2jWcp8C&pg=PA200&lpg=PA200&dq=polycarbonate+glass+filled+camera+body&source=bl&ots=Kga7WZ4uKZ&sig=g2b2oTx2OJo1HMezyt_IAhSVmsg&hl=en&sa=X&ei=ciCFVLCDAYaqyATt4YHIBg&ved=0CB8Q6AEwAA#v=onepage&q=polycarbonate%20glass%20filled%20camera%20body&f=false
Answer: Current Canon bodies are made of anything from glass filled polycarbonate, to the same kind of engineering grade plastic that the light boxes of all current DSLRs, including the flagship models such as the Canon 1D X and the Nikon D4 are made of, to magnesium alloy.
Canon pioneered the use of glass filled polycarbonate materials in cameras way back in the film era. The first use of the material was for the lens barrel and some of the other non-optical components of the 50mm f/1.8 lens that was the standard lens for the Canon AE-1. Not long after that Canon and others started using the material for body panels and the like, with an aluminum skeleton and an all metal light box. Today the metal light box has been replaced by more rugged composites made by combining one or several different engineering grade plastics, such as Nylon 6-6 or Ultra-high-molecular-weight polyethylene, with other materials.
Comment: Very interesting. I wonder what camera and lenses were bade from before? SLR came around well into the plastic era. I recall medium format lenses being metal, and any medium or large format camera is a box easily made of any material including wood.  I use UHMW_PE for glides in woodworking, btw. It feels like wax.


Multiple objects/parts are selected in object mode

Question: As noted in the title, when I switch into Object mode, several separate objects are highlighted as one. Is there any way to make them separate?
Answer: You have joined all of those parts into a single object, as can be seen in the outliner where it shows only one object is selected.  You need to go back into edit mode and separate the objects if you wish to have them become separate parts.
In edit mode, select one part, perhaps by island select; (shortcut L) box select; or other means and separate them. (shortcut P and select Selection.)


Can you do an AND on Google Scholar alerts?

Question: In Google Scholar, you can create an alert, such as "neural networks", which will inform you any time there is an article related to "neural networks". However, suppose I am interested in neural networks applied to robot navigation. Is there a way to create an alert that will only inform you when both "neural networks" and "robot navigation" appear in the paper? Essentially, I want to do a logical AND on the search terms.
Answer: Yes, all of the typical operators apply.
AND is implicit so your alert query could be "neural networks" "robot navigation"
Answer: You could create an alert for neural networks + robotics this way google will search all the results that have both words, and again if you are more interested in the robotics part you use a quotation mark like neural networks + "robotics" which brings all the results that absolutely have robotics in them.


Designing a 6x64 Decoder

Question: I am making a 64x32 bit SRAM, I need to use a 6x64 decoder as the Row address decoder. My question, is it possible to design a 6x64 Decoder using  3x8 Decoders?
Comment: Anything is possible, please make your question more specific.
Answer: Feed the same three lower address bits to eight 3x8 decoders, whose outputs (8x8 = 64 bits) are your row select  lines. Use the upper three address bits as the inputs for a single 3x8 decoder, whose outputs select one of the 8 decoders at a time by controlling the enable input.
An alternative is to use one 3x8 decoder for the upper three address bits, another for the lower three bits. You'd then take one of the eight outputs from each of the two decoders, and AND them together. There would be 64 such combinations, so you'd have 64 AND gates, each mapping to an unique address.
Answer: Yes, very much. You can cascade decoders to produce any depth of decoding you want, providing you can tolerate the overall propagation delay.
You don't say if you're using discrete logic ICs such as 74LVC138 or using 3-to-8 decoder macros/etc in something like a CPLD/FPGA or in theory.
As well the 3-bit encoded bus, a 74LVC138 contains three enable inputs: two active low, one active high. You can put a first 74LVC138 on encoded bus bits E[5:3] and that will give you eight enables that each enables one of eight second-level decoders hanging off of E[2:0]. That uses nine 74LVC138s.
A true 3-to-8 decoder may not have an enable input. You can then sacrifice one of its three inputs to make an enable and use it as a 2-to-4 decoder. If its input bit 2 of 2:0 is used as a decoder 'high to enable', the lower 4 of the decoder's 8 outputs cannot be used because they will be active when this bit2/'enable' is low and that's being used as disabled. Use the decoder's higher 4 outputs. Now it's just using these 2-to-4 decoders to make to a tree where a decoder on E[5:4] produces enables for decoders on E[3:2] which produce enables for decoders on E[1:0], similar to the 74LVC138 example above.

Designing a 6x64 Decoder


Is there a rule of thumb for distinguishing male and female names in Chinese?

Question: I often get tripped up when reading names of Chinese people, and trying to work out if they are male or female. Is there a good rule of thumb to follow to determine which is which?
Comment: Real answer is no. As a native speaker, my suggestion is never depend people's gender on their name.
Comment: Still, I think in most cases you can guess correctly with >95% accuracy?
Comment: @OlleLinge But you cannot risk that 5%...
Comment: I added that comment because @AntiGameZ comment made it sound that it's not possible, but I don't think the OP was after an answer that was 100% certain. Saying that it's not possible is simply wrong in my opinion, it's often very clear with a high accuracy, although obviously not 100%.
Comment: Parents give girl a sound-like-girl name.
Answer: In a previous post "How do we choose the correct characters for a westerner name?", I listed some characters that I think are popular in names nowadays. Remember, characters don't express the gender, so there are only some "rough clues" to guess the gender of the person.
One example would be "芳", which means "fragrance,good smell".It's very common to be seen in a woman's name as in 梅艳芳(a last female singer from HongKong) and 谢杏芳(a famous female badminton player). However, I few cases, it appears in a man's name. I.e. 单田芳(a famous Pingshu performer. Note: here 单 pronounces shàn as a family name)
I agree with point 1 in 景洛弘's answer, that meanings could be a clue, but I don't agree with point 2, because in chinese, many characters share the same sound.
Counterexamples to point 2:
ye. There is a famous actor 刘烨(liu2 ye4).
li. li could be "力(li4)", which means "strength". There was a famous linguist 王力(wang2 li4).li could also be "莉(li4)",and "茉莉" means "jasmine". There is a famous actress 牛莉(niu2 li4).
hong. Hong could be "宏(hong2)", which means "huge". There is a famous comedian 黄宏(huang2 hong2). Hong could also be "虹(hong2)", which means "rainbow". There is a famous actress 陶虹(tao2 hong2).
Answer: In my experience, it mostly depends on two things:

What's the meaning of the characters? Flowers, plants, beautiful things in general are used for women's name. If the radical of one of the characters is 女, that will give you another clue. While characters with a meaning related to strength and power (and possibly wealth) are usually for men.
How does the name sound? Names that sound "light" or delicate (yi, ye, li, ling, etc.) are often for women, while rough sounds are more commonly used for men (mou, zhang, hong, etc).
Answer: There is a computer library ('Wudi gender guesser') to predict the gender of a Chinese name, based on statistics of the use of individual Kanji caracters in Male/Female given names. This approach accounts for both for the meaning and the sound.
There is an online version here
http://namesorts.com/2014/03/27/chinese-name-gender-guesser-api/
Answer: Sadly there are no such rules since customs varies from parts of China to other parts. And in different times, there were different trends.
So there are no strict rules to follow. There are just patterns which loosely apply but with many exceptions.
For example, 红(red) is thought to be more common in female names when it is the last character of a name. But in the early years of the PRC, there were many male whose name contains the character.
Another example is that I have a classmate in high school whose name is 王男, 王(wang) is surname, 男 is given name and it literally means man/male. But she is a girl. She said that because the name is given by his grand father and he wanted a boy.
Answer: I don't believe there is a rule of thumb on this. Some characters used as names can be misleading, even for native speakers of Chinese. For example, I've met women named 帥 (meaning handsome, though it can also mean commander) and 虎 (tiger), both of which Chinese people would assume were male names due to their masculine connotations.
Still there are some names that are commonly given to male and female babies, e.g.
Common male names: 偉, 磊, 軍, 傑.
Common female names: 芳, 秀英, 琳娜, 靜, 麗, 秀蘭.


What is the difference between a Tautology and a pleonasm?

Question: What is the difference between these two words? They seem to mean the same thing.
Comment: [Wikipedia](https://en.wikipedia.org/wiki/Tautology_(language)) says "Tautology and pleonasm are not consistently differentiated in literature."
Comment: My math teacher asks me to determine whether the equation 5 - 1 = 4 is true. I add 1 to each side of the equation, so on the next line I write 5 = 5. That line is a tautology (because it is clearly always true) but not a pleonasm (because it is necessary to complete the proof).
Answer: A pleonasm relates to a specific word or phrase where there is redundancy (a "true fact"), whereas a tautology relates more to a logical argument or assertion being made, where it is self-evidently true (or unable to be falsified by logic), such as "I was definitely the oldest person at the meeting because everyone there was born later than me.", or "For the purpose of paying fees, the year is divided into four quarterly payments.".
Comment: A good answer is expected to have supporting references, linked and attributed; answers lacking references come over as, and may merely be, opinion (with no guarantee of being correct or comprehensive). // I don't think there is a consensus that these are the only definitions in use.
Comment: I think the "tautology" mentioned here refers to tautology in the mathematical logic sense, and not in the linguistics sense (although the examples don't match the explanation given). In the linguistics sense, tautology means to repeat the same meaning twice using different words/phrases (e.g. "they arrived one after another in succession" - "one after another" and "in succession" have the same meaning but are phrased differently).

Also, whether rightly or not, people use the two terms interchangeably.
Answer: A Pleonasm uses a descriptor or modifier to express a quality that is necessarily inherent to the word described or modified. Examples: Round circle, falling rain, foreign immigrants, two-wheeled bicycle, reflective mirror, stingy miser, brave heroes, clever genius, close proximity.
A Tautology is a repetition of synonyms to describe or modify a word. He quickly and speedily went away. A tiny little dog. A great big man. Tautology is often used for dramatic effect.
Comment: Some references would be helpful. Have a look at the Wikipedia pages, or try some other trustworthy reference work.
Answer: The two terms are closely related in meaning, but they are applied to different things. Only a complete sentence/proposition/statement can be said to be a tautology, while pleonasm can be applied to something  that does not amount to a complete sentence/proposition/statement. For example,

This circle is round.

is a tautology, because it is true solely in virtue of the meanings of the words that it contains. On the other hand, the expression

round circle

is a pleonasm, because the meaning of the adjective round is already contained in the meaning of the noun, circle that it qualifies, but it is not a tautology, because, by itself, it does not amount to a complete sentence; in fact it would be meaningless to ask whether it is a tautology.
This is how tautology is used in the terminology of logic; as has already been observed in a comment, outside logic, the two terms are used more loosely, and often interchangeably.


Is the "One Country, Two Systems" approach a viable option for Taiwan?

Question: Why would Taiwan avoid this arrangement? Obviously, Taiwan would like to preserve its democracy, but at some point Taipei will have to reckon with the economic realities of the region and relative American decline. Could Beijing ever formulate a version of "One Country, Two Systems" that would work or are the downsides too great for Taiwan?
Comment: Yeah, well, Hong Kong is a shining example of why Taiwan has to see the light.   That's definitely two very separate systems, with an independent judiciary guaranteed all the way to 2047.  They even hold elections too.
Comment: To me "but at some point Taipei will have to reckon with the economic realities of the region" sounds like "[We are the Borg. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own.. Your culture will adapt to service us. Resistance is futile.](https://tropedia.fandom.com/wiki/Resistance_Is_Futile)" Unless you can support the "have to reckon with the economic realities" premise and address  Taiwan's [New Southbound Policy](https://en.wikipedia.org/wiki/New_Southbound_Policy) Are you able to add something to support this premise?
Comment: It's surely an option, but probably not the preferred one at the moment. What do you want to know more about specifically here?  We cannot look into the future, but we can tell you about advantages and disadvantages of different possibilities.
Comment: You already assume a lot. Almost like you already know the answer and only need a confirmation. Better to ask more open ended. Maybe the US and others are still very much able to defend Taiwan from China. Maybe Taiwan thinks that they can manage with the level of protection. Or Taiwan sees other options that you didn't include above and that they like more. It may only be one of many options and currently not the best one.
Comment: @Trilarion I guess I'm just looking for some concrete reasons for why the Taiwanese would refuse the One Country, Two Systems approach considering the increasing inability of the United States to defend Taiwan from the China. Eventually, Taipei will have to come to grips with Chinese regional hegemony.
Comment: I'm not saying you can't, just that it would help your question, or perhaps a new one seeing as how the excessive down-voting and presence of two answer will make it difficult to get anything more done here.
Answer: There don't seem to be takers in Taiwan for this slogan/approach anymore. Quoting Wikipedia:

In January 2019, Xi Jinping, General Secretary of the Chinese Communist Party (CCP), had announced an open letter to Taiwan proposing a "one country, two systems" formula for eventual unification. President Tsai Ing-wen responded to Xi in a January 2019 speech by stating that Taiwan rejected "one country, two systems" and that because Beijing equated the 1992 Consensus with "one country, two systems", Taiwan rejected the 1992 Consensus as well. Tsai expressed her solidarity with Hong Kong protesters, remarking that Taiwan's democracy was hard-earned and had to be guarded and renewed. Pledging that as long as she was Taiwan's president, she would never accept "one country, two systems", Tsai cited what she considered to be the constant and rapid deterioration of Hong Kong's democracy over the course of 20 years. Following the landslide defeat of the KMT in the 2020 Taiwanese presidential election, KMT chairman Johnny Chiang rejected the "one country, two systems" as a feasible model for Taiwan. In 2021 the KMT platform under newly elected chairman Eric Chu also continued to include the 1992 consensus while rejecting "one country, two systems".

Neither the DPP nor the KMT seem to like that phrase anymore. And the Wikipedia article on the "1992 consensus" suggests that latter term has become contested as well, in terms of what it means/meant. The general public in Taiwan nowadays seems to see it as meaning two countries:

When asked
which version of the Consensus a citizen would like to support, most (75.1%) [of Taiwanese polled] endorsed the view
that PRC and ROC are two different countries. Ironically, this might be the exact statement (cross-Strait as country-to-country relations) that founders of the Consensus tried to prevent in the first
place.
Answer: No. "One country, two systems" was a political slogan in China intended for Hong Kong. Everybody agrees it doesn't work.
Comment: @aengel The system clearly did not work for Hong Kong (or rather, did not work in a way agreeable to the citizens of HK, it seems like the Chinese government is thrilled with the results...), why do you think the citizens of Taiwan would have faith in it?
Comment: I would delve a bit more into the literature if I were you. There is a lot of discussion regarding the application of "One Country, Two Systems" beyond Hong Kong and Macau. Many people do believe this is a viable option for Taiwan, especially in Chinese academic circles.
Comment: @DenisNardin I don't think the citizens of Taiwan would have faith in the system. However, at some point Taipei is going to have have to grapple with Chinese regional (if not global) hegemony. China has clearly made it known that Taiwan will eventually come under their rule ("We make no promise to renounce the use of force and reserve the option of taking all necessary means" - Xi Jinping). How will Taiwan deal with that? It will eventually lose an economic/ military conflict and there's doubts about American willingness to defend Taiwan even now.


What are the standings requirements (if any) to anchor a POS in low sec?

Question: I'm looking to anchor a POS in a low security system in EVE, but I can't seem to find a conclusive answer to the question above.  Some guides seem to indicate that standings aren't required to anchor in low security space while other guides seem to indicate that I can only anchor in systems with a security level of (0.10 * (Faction Standing)).  I'm not really sure which guides are right and which are not.
Answer: From the Incursion patch notes: "You can now anchor a POS in a 0.4 system without faction standing."
Incursion Patch Notes, Build 221279
So you do not need standing to anchor in low or null.
Comment: Thanks!  I must have spent at least an hour googling, but I never came across those patch notes.
Answer: You can anchor freely in null sec (0.0) space, low sec has standing requirements.
Between 0.1 and 0.7, you require a faction standing of 10*sec, specifically from EveOnline Wiki

Anchoring a POS in Empire space requires faction with the region's controller, calculated by the formula 10 x system security level. Example: You are trying to anchor a POS in an Amarr Empire controlled system with a security level of 0.5. You must take 10 x 0.5 to calculate the standing you will need with the Amarr Empire to anchor a POS, in this case it would be 5.0. This standing is required from your corporation to faction that holds sovereignity and are updated at downtime. It's value is an average of corporation members standings to faction.
Comment: Thanks.  Unfortunately, I've seen that wiki entry, but then I've also come across other resources that claim that, as of one of the more recent updates, they removed the standings to anchor.  I was hoping somebody here may have first hand experience and be able to say definitively whether or not standings are needed in low sec.
Comment: Oh I can't say then. Last time I played standings were certainly needed, since you had to "fuel" them with documents.


Practical hard 3-sat instances

Question: The $3-SAT$ problem is known to be NP-complete problem. Which means that (as far as I understand), unless $P \neq NP$, for every algorithm $A$ which decides $3-SAT$, $A$ runs in super polynomial time (I know that this is not well defined). A stronger assumption is the "Strong Exponential Time Hypothesis " which states that every algorithm has to run in worst case exponential time.
Does that mean, for example, that every algorithm $A$ (here I refer to a "real" or practical implementation, such as Glucoses, DPLL, Z3, etc.), has an instance of size, say 200, which $A$ will not be able to solve in a reasonable time? I see many sat solvers solving formulas with millions of variables in very short time; and I am aware of subsets of $3-SAT$ which are easy, such as Horn clauses, or a random instance with a known density - but it seems that these solvers work amazingly fast without any assumptions on the input.
I have searched for Sat benchmarks, or instances which should be hard, but when running them on a modern sat solver, it doesn't seem to be a problem.
It is known that complexity assumptions (or claims) are about the asymptotic behavior, my question is: do we know for which $n_0$ these assumptions "kick in" in the case of $3-SAT$? Can we generate, or at least be confident of the existence of a relatively small formula ($< 200$), such that every algorithm requires $\sim2^{200}$ operations?
Answer:
do we know for which $n_0$ these assumptions "kick in" in the case of $3-SAT$? Can we generate, or at least be confident of the existence of a relatively small formula ($< 200$), such that every algorithm requires $\sim2^{200}$ operations?

$3-SAT$ is known to be solvable in time $O(1.321^n)$. Therefore, there is no instance that would force a $\Omega(2^n)$ run time. SETH does not hold for $k-SAT$ for any bounded $k$; it is only expected to hold for general Satsifiability (with no limit on clause size). We don't really know what asymptotic runtime to expect for $k$-SAT for any $k$ (other than something exponential).
Also, for any $SAT$ formula, there is an algorithm solving it in $O(n)$ time. You could never hope to find a single example hard for all algorithms.
One way to generate hard SAT instances is to reduce from Integer Factorization.
Comment: @АлексейУваров I am thinking of an algorithm that contains a hardcoded solution to the particular SAT formula and just outputs it (after checking that the input is equal to the preprogrammed formula). The point is that you can never hope to construct a single example formula that is hard to solve for all algorithms.
Comment: Thanks. I didn't expect for a single instance which will be hard on all algorithms, but given an algorithm, how can I find its hard instances. The question came since every modern SAT solver that I tried seemed to work very fast (obviously, I can only try a tiny fraction of the space), so I am trying to understand where the "exponential barrier" in practice. About int factorization - it is not known this problem is NPC, so why would that way makes hard instances?
Comment: Hi! Could you please explain why is it true that for any SAT formula there is an algorithm that finds it easy? Or at least could you point me to some literature on this? Thank you.

Practical hard 3-sat instances


What do terms half-rate and quarter-rate mean for DRAM memory controllers?

Question: DDR3 Memory controller are often presented as being half rate or quarter rate, but what does this mean? e.g if I have a DDR3 SDRAM that is x16, what does the half or quarter rate imply in that case and why do we need to create such memory controllers?
Answer: From Altera's Using High-Performance DDR, DDR2, and DDR3 SDRAM With SOPC Builder:

Full- or half-rate SDRAM high-performance controllers have the
following definitions:

Full-rate controllers present data to the local interface at twice the width of the actual SDRAM interface at the full SDRAM clock rate.
Half-rate controllers present data to the local interface at four times the width of the actual SDRAM interface at half the SDRAM clock
rate.

Implementing the SDRAM high-performance controllers in half-rate mode
gives the highest possible SDRAM clock frequency while allowing the
more complex core logic to operate at half this frequency.

Basically, half-rate (and by extension, quarter-rate) application interfaces allow the SDRAM clock to be faster relative to your internal system clock. This improves both bandwidth and latency.