How secure is messaging to smart contracts?

Question: If I sent a message via http to a smart contract, how secure is that? If I cannot use TLS, then could someone listen at he port and then intercept the message and then divert the message to an unknown blockchain?
Comment: Can you give the exact scenario where you are worried about ssl? What are you trying to do?
Answer: All the data in the blockchain is public and anyone with a copy of it can read transactions sent to a contract and do anything they want to do with it.

It depends where are your keys stored:

keys are stored in the client side (ie metamask, hardware wallet): transactions are signed and cannot be modified without tampering with the signature.
keys are stored in the server (ie inside a client like geth or parity): you have to secure the communication between your ui and the server, for example with SSL certificates or an SSH tunnel.
Comment: Yes but the issue to me was the HTTP messaging between the contract and the UI; and if someone could interfere with that.
Comment: @TrevorOakley I've added updated my answer with a few notes about that when you have to secure the communication.
Answer: What I would do is create a dapp to interact with the contract,and put that dapp in a safe server with https or a VPN on. This way data from dapp to the contract would be safe. But I guess if between you in the dapp is compromised (let's say with a malware or keylogger) then it won't
Comment: This sounds like we are not using blockchains anymore but a secure server and a normal app. If we require just one server to be used then we have the same issues with a centralised server service.
Comment: If you connect with X method directly to the blockchain, you'll still have this issue.
Comment: My way secure the request from dapp to the blockchain but not from user to the dapp. Using like metamask or myetherwallet on a compromised device would be in any case bad.
Answer: You need to either find a node that accepts SSL or run a local node and setup ngnix with SSL, as described here:
How To SSL Ethereum Geth Node?
Comment: What if someone just uses another node? Can we really require a user to use just one node? I thought that was not possible as all the nodes would run the contract at the same time.
Comment: Ok so how it works is - when you submit a transaction to ethereum, it goes to one node and executes there, and from there it goes to a bunch of other nodes and executes there to make sure the result is the same. You can control the connection between your app and the first note (if you host that node) but you can't control the communication between the nodes (and you don't need to). If you can't force your app to connect to your own node where you can setup reverse proxy with ssl, then it connects to regular nodes over its rcp protocol which doesn't support ssl.
Comment: That is interesting about connecting to one node only.


What does 12 bit resolution mean?

Question: I'm looking at this inclinometer and in the features it says "12 bit resolution." I'm looking for a resolution of up to a 1/10th of a degree but don't understand what the 12 bit resolution means.
Answer: With 12-bit resolution, $2^{12}= 4096$ different numbers can be represented, this means that the measuring range of a given sensor gets split into 4096 pieces.
As an example, if your sensor can measure from 0V to 409.6V (just for nicer math), then with 12-bit resolution, you can resolve the measured value in increments of 0.1V.
Comment: Resolution and accuracy are two different things. Resolution refers to the increment in which the readings are available, i.e. in this case 360°/4096 = 0.09° approx., and accuracy refers to whether the readings are accurate compared to the true value that is being measured. For example, you might be measuring an angle of 10°, and the sensor might report anything between 9.8° and 10.2°.
Comment: As Mohanachz has noted, he's dealing with 0.1 degrees, which would require 3600 "pieces" for which 4096 will cover. The math gets long, stretched out decimal points, but if rounding is acceptable, he's good to go! Unfortunately, the specifications don't match. The device lists 0.2° at 25°C and 0.6° over the entire operating range of temperature. Marketing?
Comment: @am304 you're right, thank you for the suggestion, I'll edit it. I considered it while writing, but thought it would still get the point across what 12 bit resolution means
Comment: You have 12 bit correct but an inclinometer does not measure voltage.
Comment: @paparazzo I used it as example for 12-bit resolution, not referring to OP's specific sensor
Answer: In computers a lot of stuff is measured in bits.  A bit is binary base 2.     $2^{12}= 4096$
That unit measures +- 90 for a total of 180 for a resolution of about 1/23 of a degree.

What does 12 bit resolution mean?


Exchanging fiat tether on SDEX

Question: We have fiat tether tokens that we issued, each token is backed up by an equivalent amount on our bank account, currently we are able to switch between one tether into another using our own exchange for example, You can send USD(T) and get an equivalent amount in UGX(T), so calculate the exchange rate and send an equivalent to the recipient wallet, what I would like to happen is to be able to do this using the SDEX where by you can send buy orders and sell orders and do the conversion automatically. The problem I have been having is that with SDEX you have to set the buy price or sell price yet I would have wanted to get the current market price(Forex) eg the current price of USD->UGX not by the orders set. I tried looking at Kelp but seems too complicated, Any suggestions?
Answer: Happy to answer any questions you have around Kelp (developer of Kelp here). Have you taken a look at the Kelp walkthroughs such as How To Make a Market for a Stablecoin?

Exchanging fiat tether on SDEX


Erasing 1 byte of external Flash memory (winbond)

Question: i'm trying to use an external flash memory Winbond 25q64jvsiq for my Arduino Nano based project for audio recording purposes, to have extra memory for recording 1 byte audio samples, since Arduino nano SRAM memory is too small (8kb), to store at least 1 second of 8 kHz 8 bit samples audio. I'm trying to understand the basics of  bytes storing in my external memory. I'm using SPIMemory library for that, and i can't find a function to erase 1 byte, there is only sectorErase() function. So i wonder is it even possible to erase a single byte of external memory?
Here is a part of code where i try to rewrite (erase one byte and write a new one) a next byte when the button pressed, but when it erase a sector it erases not the one byte but all bytes behind it, and i want to manipulate it more accurate, and erase only one byte:
<code>if(!digitalRead(5)){      //button pressed
     if(e<3){
      e++;
      flash.eraseSector(count);    //erasing a byte
      flash.writeByte(count,e,NOERRCHK); // write a new value
      }  else {
        e=0;
        flash.eraseSector(count);
        flash.writeByte(count,e,NOERRCHK);
        }
     }
</code>
Answer: For a flash chip, no it's not possible to erase a single byte.
The closest you can do is to read an entire sector into memory, erase that sector, modify your in-memory copy, then write the sector back.
You would be better using an SPI SRAM or PSRAM chip instead of a flash chip.


auto-Writing/auto-Inputting application for a lousy routine web-based submitions?

Question: I've started learning python for a week, as always love to learn as much languages as I can ; as python is one of the easiest languages, but still there's lots of things teachers won't tell.
Interacting with web pages is an obvious example; registration in forums and other websites gives a headache, so building a simple python application that just can READ LABELS, and input INFORMATION such as First Name, Last Name, Sex, and Address in their TEXT BOXES, then Submit the page at the end would be fantastic.
Another silly thing, but I MUST know, is how to contact a website first.
If you can provide me with any tips, or help, I appreciate your contribution.
Answer: For a simply contacting the website, consider the requests or twill libraries.  For screen-scraping, BeautifulSoup is your friend.
If third-party libraries really aren't an option, though, you'll need to delve into the htmllib, httplib, urllib, and urllib2 Python modules.


What is the "sine wave" substyle of ITF taekwondo and how did it originate?

Question: Many ITF-based taekwondo practitioners come to notice a difference between different ITF-based organizations with some groups teaching a direct, forceful style and others teaching a more timed, flowing style often referred to as a "sine wave" style.  What are the defining characteristics of this "sine wave" approach to ITF hyungs/tuls and how did this style originate?
Answer: By reading the The Encyclopedia of Taekwon-do written by General Choi Hong Hi, the founder of Taekwon-do, one would find out that the sine-wave is a main characteristic of Taekwon-do and is part of the "Theory of power" that characterizes the style.
The sine-wave emphasizes relaxation on the upward motion and the contraction and explosion on the downward(final) motion. This allows you to put the weight of your body into the technique.
You can read more about the theory of power here: http://www.saskgtf.com/theory.html
Also the differences you see between ITF sine-waves in different practitioners is because the sine-wave has evolved over time and not all teachers will teach it the same way on each move.
Comment: Early versions of the Encyclopedia (like the copy I bought in the late '90s) didn't mention sine wave or describe anything even vaguely resembling it.  Sine wave was only added to ITF TKD in the mid 80s (from memory), so instructors who trained before its introduction often stuck to what they knew - either passively or because they actively disagreed with the sine wave "theory" and supposed benefits.
Answer: The "sine wave" terminology is used, in my experience, to refer to a more bouncing method of footwork in forms. A linear, non-size-wave execution of kata, such as this performance from Shotokan, values direct movement, crisp end positions, and minimal up-and-down movement between stances. In contrast, this "sine-wavey" performance from ITF TKD exemplifies the up-and-down, more fluid method that the term refers to. Notice the exaggerated way that the practitioner settles into each step, and the alternating slow-fast cadence of each movement. This is dissimilar from the rather even pace that the Shotokan stylist uses.
I am not familiar with the origin of this style, except to note that preferences regarding the look and feel of kata performance naturally change over time and with different personalities in charge. But the salient differences seem to be:

More fluid movement rather than crisp, paused stances
Up-and-down movement during steps instead of maintaining a constant vertical position
Rhythmic slow/fast cadence instead of steady
Settling into each stance rather than stepping into it plainly
Comment: Pro tip:I should point out that I got much higher points for Patterns at national and international level when emulating the Shotokan style.
Answer: I started training Taekwon-Do in 1986 in South Australia under Rhee Taekwon-Do (CC Rhee the father of Australian Taekwon-do) and a pupil of Gen Choi.
In those days we did not do a sine wave, power was generated through speed and the use of the large muscles groups.  On my return to the UK, I was taught the sine wave in the ITF style - thus I deduce that the sine wave must have been introduced by the mid 1980's.  I do not know if Rhee TKD (Aus) now incorporates the sine wave.  Interestingly the TAGB does not use the sine wave and stays with the more traditional practices which it used when they split from the ITF.
Answer: Sine wave is the movement of all OFFICIAL ITF schools.
Also, Sine wave looks something like the expansion and contraction in Bak Mei, except that the knee spring replaces the contraction and expansion of the spine and abdomen.
I think it does add power to a strike.
See Bak Mei strategy below:
https://www.youtube.com/watch?v=tojJBiXRKrI


Add Aviation to migration targets for off-topic questions

Question: Would it make sense to add Aviation.SE to the available migration targets for off-topic questions?
Comment: Are there many that should be migrated? I read Aviation.SE quite often and I don't recall seeing any questions migrated from here to there.
Answer: One of the key criteria for default migration paths is the level of migration occurring.

There's no "right" level for establishing a migration path, but tens or hundreds of migrations with a single digit rejection rate seems safe. Single digit migrations in the last 90 days and/or rejection rates that can order a drink without ID are signs that the path will be a waste of time to establish.

A 10K user can see the TSE migration stats, which show no out-migrations in the last 90 days except to Expats, which is established. A more comprehensive SEDE query for questions successfully migrated away turns up only five sites with five or more migrated questions since the dawn of TSE:
<code>
 Site        Count  Latest Migration
 Expatriates   117  2016-05-04 23:41:43
 Outdoors       22  2015-08-09 22:36:13
 Money           9  2014-06-18 13:34:29
 Aviation        5  2015-07-07 15:30:28
 SuperUser       5  2014-01-08 19:43:14
</code>
Since Aviation has seen only five questions from TSE, and the last was ten months ago, I doubt the powers that be will approve it as a direct migration path. Such things are fraught; many users suggest migrations that are inappropriate for the proposed destination but also not inappropriate for the origin.
If you do perceive a lot of questions that would be better-answered at Aviation, then we should step up our efforts to flag them and have moderators move them, and then we can make the case for community migration when the stats are more convincing that such a thing would be beneficial to both communities.
Comment: Aviation SE has graduated and is no longer in public beta...
Comment: @MikeFoxtrot Thanks, good to know.
Comment: This seems to indicate in general, we should do more migration (manual) flagging, and less just closing as offtopic.
Answer: It makes a few tons of sense to me, but I think this can be added by SE staff only, not by admins. So can the admins please chat with the staff to do so if it's approved?


Self signed SSL in Windows

Question: I installed a self-signed SSL in a Windows server. What should I do on the client so that they can establish a secure connection without any warning messages?
Answer: It depends on what client application is generating the warnings.  Is it a web browser?  If so, which browser?
For Internet Explorer, add the certificate (just the public key) to the user or computer's Trusted Root certificate store.  The exact instructions for doing this vary somewhat depending on what Windows version the client is running.
Firefox doesn't use the Windows certificate store though, so you'd have to add it to Firefox's own store.  In 3.6, that can be found in Tools - Options - Advanced - Encryption.  Click the View Certificates button, and add it to the Authorities or Servers list.
I'm not sure about Chrome, Opera, or Safari.

Self signed SSL in Windows


can a plasterboard ceiling hold a 4 kg projector

Question: i want to mount a 4 kg projector in a plasterboard ceiling but can't find the joint so it will have to go in the plasterboard, i wanted to know if it will hold and what kind of things i'll need.
also if it will hold a 100" projector screen that is about 12 kg
really need help with this.
Answer: While I hate mounting things in ceilings without reaching joists (or other framing members), some modern toggle type anchors can hold loads of over 100 kg each in 1/2 inch drywall per anchor (many jurisdictions require 5/8 or thicker drywall in ceilings).

The load on ceiling mounted items is tensile and the use of several mounting anchors should give you lots of room. This link shows the load ratings of one brand of toggle anchors. Brand to brand ratings may vary slightly.
I strongly prefer the rotating bar type toggles over the old spring-wing types. They allow installation and removal without losing the interior component, and the load seems to be better spread over the drywall surface.
While two or more toggle anchors are theoretically more than enough for a 12 kg screen, the ratings are for static tensile use. If the screen is being moved up and down, either mechanically or by hand, that is a dynamic load that multiplies the strain on the fitting.
There still should be enough room for normal use, but understand that someone pulling down with their whole weight on a screen is more than any such mounting bracket can sustain.
Finally, things falling from the ceiling can do serious harm. Make sure that the projector, and especially the screen, do not pose a risk to humans (we can live with broken ceilings and devices).

Images and links are illustrative only, not an endorsement of goods or sources


Selling a used car with unknown miles, bill of sale and title question

Question: I'm a private individual selling to a business (a wrecking service) in the state of Alabama.  My car is dead, doesn't start, the business agreed to buy it off me knowing all of this.  However, since the vehicle is dead, I can not give accurate mileage on bill of sale and title when selling.  Now I do know the approximate mileage from when the vehicle was last in use which is within 1000 miles error.  Should I explicitly write in the bill of sale the approximate mileage or should I write mileage unknown or is there another suggestion that fulfills my legal requirement?
Answer: As a first step, locate and read all the documents you will be signing. I've never lived in Alabama, but in other states, I've had to sign the title, a separate mileage statement, and a bill of sale. At least one of these included a place to check a box indicating that

The mileage written was correct
The odometer was not operating correctly, or
the odometer was beyond it's mechanical limits

(The last item mainly applies to older cars that could only indicate up to 99,999 mi and then would turn back to 00,000 mi.)
If any of these, such as the bill of sale, is free form (that is, you write it yourself without using a form), I would just make sure you don't write anything that contradicts what is on one of the other documents.
If the entire car is not working, then in newer vehicles with an electronic display of the mileage, the odometer isn't working either.


Why is incorruptibility of saints' relics used as proof of their sanctity?

Question: Why is the notion of incorruptibility advanced by some Catholics and some Orthodox when determining the corruptibility or incorruptibility of a saint's relics has never been a part of the beatification or canonization process?
Comment: Can you please explain in a bit more detail what you mean by this part of your question: *when this has never been a consideration of the sanctified nature of the mortal remains?*  (PS: That looks like a Navy dinner dress jacket with cumberbund in your picture. Is it? :-) )
Comment: @KorvinStarmast I think I've understood what he meant. See my edit.
Comment: @Geremia Provided that your edit captured his meaning, thanks. Much clearer.
Comment: Note that incorruptibility is not really a criterion for beatification or canonization, at least not in the Catholic Church. (I can't speak for the Orthodox.) Rather, the important criteria are (1) evidence of heroic virtue in the person's life and (2) a verifiable miracle (one each for beatification and canonization) that can only be explained by the intercession of that person. (Since intercession is practically always on behalf of someone else, the incorruptibility of the saint's body would not qualify; it is, in any case, too easy to confuse with good embalming.)
Comment: Because it shows them as true followers of the one who defeated death and the grave.
Answer: The short answer is no.
Not every saint is expected to have an incorruptible corpse. Although incorruptibility is recognized as supernatural, it is no longer counted as a miracle in the recognition of a saint (The Incorruptibles).
Embalmed bodies were not recognized as incorruptibles. For example, although the body of Pope John XXIII remained in a remarkably intact state after its exhumation, Church officials remarked that the body had been embalmed (Christianity Today) and additionally there was a lack of oxygen in his sealed triple coffin.
Incorruptibility is seen as distinct from the good preservation of a body, or from mummification. Incorruptible bodies are often said to have the odour of sanctity, exuding a sweet or floral, pleasant aroma.
Incorruptibility is not reserved to the Catholic Church alone. There are a number of Orthodox Saints who have incorrupt bodies.
Nowadays the Catholic Church is striving to better understand why some Saints are preserved from corruption, thus seeing if the preservation is indeed miraculous or not. "These saints are in a class by themselves. Even though incorruptibility does not automatically confer sainthood upon the subject, it is still properly appreciated by the Church as a supernatural occurrences. The Church thus seeks the help of scientists and other professional to understand this question in a more modern light!
The lack of formal explanations on this subject seems to stem from the fact that this is an area of expertise for the scientific (professional) community and not the Church to investigate.

"Over the last 15 years, however, a new view of the Incorruptibles has begun to emerge. At the Vatican's request, Italian pathologists, chemists, and radiologists have been poring over the bodies of the ancient men and women interred in church reliquaries. Charged with gleaning new information about the lives of the saints and assisting in the conservation of sacred remains, they have also brought science to the altars of Europe's cathedrals. Already, they have examined more than two dozen saints and beati, shedding light on the mystery of their preservation. While some saints were clearly mummified by their devout followers, others were protected from decay by environmental conditions, raising new questions about incorruptibility. "What is a miracle?" asks Ezio Fulcheri, a pathologist at the University of Genoa and one of the leading researchers on the Incorruptibles. "It's something unexplainable, a special event that may occur in different ways." The causes may seem mysterious "but don't exclude [rare] natural processes that are different from the normal course of things." - The Incorruptible.

Nota Bene: This is my answer to this question.
Answer: Within the Orthodox Church, there is no formal, centralized process for determining whether or not an individual should be included in the list of the saints.  A good description of what is "required" is on the Orthodox Church in America website:

While the glorification of a saint may be initiated because of
  miracles, it is not an absolute necessity for canonization. The Roman
  Catholic Church requires three verified miracles in order to recognize
  someone as a saint; the Orthodox Church does not require this. There
  are some saints, including Saint Nicodemos of the Holy Mountain (July
  14) and Saint Innocent of Moscow (commemorated March 31), who have not
  performed any miracles, as far as we know. What is required is a
  virtuous life of obvious holiness. And a saint's writings and
  preaching must be "fully Orthodox," in agreement with the pure faith
  that we have received from Christ and the Apostles and taught by the
  Fathers and the Ecumenical Councils.
Can the Church "make" a saint? The answer is no. Only God can do that.
  We glorify those whom God Himself has glorified, seeing in their lives
  true love for God and their neighbors. The Church merely recognizes
  that such a person has cooperated with God's grace to the extent that
  his or her holiness is beyond doubt.

Incorruptibility of relics, if it occurs, is usually incidental to and not some precursor to beatification in the Orthodox Church.  Saints are usually venerated by local faithful long before their relics are discovered to be incorrupt or the case for beatification comes before any episcopal synod.
A good example of the process is what is happening in Dallas now with Archbishop Dmitri Royster.  People began venerating him almost as soon as he died, in 2011.  His body was discovered to be incorrupt this year, as it was being moved from a cemetery to the Cathedral of St. Seraphim.  As one witness stated:

We all know that an incorrupt body alone is not a reason for
  glorification.  Having known Vladika for 11 years and seeing the
  fruits of his life in the Lord, I am personally convinced that he is a
  saint. I believe that there are many more people all over the country
  who share that conviction.


How to tell whether a lens has an autofocus motor or not?

Question: I have to buy a lens and I have a Nikon d7000.  I want to know which lenses have AF motors and which do not, as the D7000 has an AF motor built into the body. How do I tell whether a lens has a motor or not?
Comment: Be aware that the D7000's in-body motor doesn't mean that it requires lenses without one. **It will work with both types.**
Comment: possible duplicate of [What type of lens will auto-focus on Nikon bodies without a focus motor?](http://photo.stackexchange.com/questions/5742/what-type-of-lens-will-auto-focus-on-nikon-bodies-without-a-focus-motor)
Comment: I totally agree with the answer and I would recommend even to take a lense with built-in motor (AF-S) because they are quieter and you can benefits from the manual focus overriding. The body AF motor is just there for compatibility with previous generation lenses (AF & AF-D) which is a must have for the more advanced bodies (like serie 7xxx)
Answer: This question is only relevant if you have a camera without a built-in AF motor in the camera, like the D3300. In this case, you would need an AF-S lens that has a motor in the lens itself.
In your case, the D7000 does have a built-in AF motor. This means any AF lens, whether or not it has a motor in the lens itself, will autofocus.
Answer: Why is it important whether it has motor or not? The important question is: will it have autofocus on your camera body.
There is a large lens compatibility table on nikonians.org.
Look for the D7000 line, and make sure you scroll below to see the actual descriptions in "NOTES", especially of "NO!" (with exclamation mark) and "NO" (without exclamation mark).
In general, choose an auto-focus lens, do not use a "F3AF" (little chance :-)) , and you will have autofocus. "AF" lenses will not have 3D matrix exposure mode, and you will only have VR if you use a D or G type VR lens.
Now, if you really want to know whether there is a built-in motor in the lens, you can check it on the Nikon site, or at Ken Rockwell's site. Both show compatibility data, too, the latter also shows data for non-Nikkor lenses.
Answer: The easy answer is that it has an autofocus motor if the lens specification says so!
For Nikon lenses, this is easy: All AF-S and AF-P lenses which have super-sonic and stepping motors, respectively. All other ones in the current lineup do not have an internal focus motor.
For third party lenses, you have to look more carefully at the naming and specifications:

Sigma designates their lenses with super-sonic as HSM but they have ones with standard motors too. Those have no designation in the name but the full specification will say so.
Tokina does not include the type of focus motor whether there is one in the name, so you have to look at the specifications directly.
Tamron is not entirely consistent. Some lenses with motors have no hint in their names while some are labeled PZD or USD, the latter is the ultra-sonic variant.
Samyang and Zeiss also make Nikon F-mount lenses but none has a focus motor until now.

In case you are not familiar with Neocamera, you can easily search for this using our Lens Search. Simply select your mount and then you can choose between Lens Standard or Lens Super Sonic for the Focus Motor option. Conversely, choose Body if you want to find lenses without motors.
Answer: Current Nikon lenses designated as AF-S have a focus motor in them.  (So do older telephoto/supertelephoto lenses designated as AF-I, but these are relatively rare and do not exist in the current lens lineup).
On a D7000, you'll know if the lens has a focus motor or not by how quiet/fast the autofocusing is. AF-S means the lens has a "Silent Wave" motor, which makes it nearly silent and can speed up AF performance.
See also:

Nikon USA's FAQ: "What do all of the abbreviations in Nikon lens names mean?"
What do all those cryptic number and letter codes in a lens name mean?


How to calculate values for decoupling capacitors

Question: For decoupling we just use a capacitor like 1 uF bulk and 0.1 uF ceramic caps at each power pin. But how are these values calculated? How many caps do we need to use in parallel? Can anyone explain it with examples from a datasheet or similar? It seems odd, but I can't get clarity on it.
Comment: Although calculating in some instances could be important, generally speaking it's not really worthwhile.  You just follow the general rules of thumb, and sprinkle these around in the manners mentioned below.  Why?  Because these caps are very inexpensive - Much cheaper to have 10-20% more caps than 'really necessary' compared to the cost of having some spurious crazy problems with a board design which then needs debug and redesign.  That ends up costing MORE in schedule delays and engineers time than a few hundred thousand fractional-penny devices.
Comment: One paradigm is for the decoupling capacitors to provide a low impedance path from power to ground at frequencies from when the power supply is ineffective up to whatever the IC needs.  §12.12 of *High-Speed Signal Propagation* has an example.
Comment: Which explanation do you or not understand? Impedance or time response or frequency attenuation of ESR + Xc & SRF with a  transient load spectrum or switched equivalent impedance.  It helps to know what you already know.
Comment: *Generally*, the datasheet for the component tells you what values to use for decoupling capacitors. Look at that first, and follow its instructions.
Answer: Basically you want something close enough to the pin that at the edge rates in play the bounce is not too bad, and then something further away with (possibly) enough ESR to damp everything to keep the far higher ESL of the supply wiring from screwing things up.
ESL is the critical thing, not in the first instance capacitance and that is almost wholly driven by package geometry.
Generally that means an 0603 or 0402 close to the package pin, and value does not really matter all that much, so as 100nF is readily available, cheap, and every assembly house has a MONSTER reel of them on the feeder, that is what you use, 10n/100n/1u, it mostly don't really matter.
Numbers of caps are driven by the desire to minimise the loop areas (Loop area rises inductance), and frankly we all mostly over do it (sometimes hugely) because the things cost basically nothing, and the time wasted if you need another one and don't have a place to put it is NOT free.
For really extreme boards PDN simulation is a thing, basically using electromagnetics field solvers to optimise cap placement for lowest noise, but unless you are doing something like a server motherboard it is so expensive that just shotgunning a few extra decoupling caps around is cheaper and easier.
One common trap (That you even see on datasheets and app notes!) is something like a couple of values in parallel and only a decade apart, often the resulting resonant impedance peak will be most unwelcome.
Spice some stuff with reasonable parasitics including reasonable trace inductances, ESR and ESL and you will discover wonders, it is an exercise that is totally worth the time.
Comment: @ThePhoton Or go a long way apart and pick a big part that has sufficient ESR! Low ESR is NOT always the way to go, sometimes the fact that a jellybean electrolytic has an ohm or so of ESR is just what you need. If you are going less then a decade apart, why bother? Interestingly you can buy MLCCs with specified levels of ESR, for exactly the damping they provide.
Comment: If you want to avoid resonance between parallel capacitors you want to keep the values closer together not further apart. The recommendation from Murata is no more than a decade apart, for example.
Comment: There are reverse geometry caps for really low ESL (0204, 0306, 0508 for example). Very useful with really fast switching devices.
Comment: @PeterSmith The problem with those is that 1.) they tend to be single-source components (expensive and hard to get) and 2.) the mounting structure on the board will trump their benefit. It's usually better to go with 2 pieces of the regular kind of cap, which is much cheaper and performs the same if not better. Some measurements are demonstrated in Lee Ritchey's _Right the First Time_ book.
Answer: tl; dr: it's not just about the cap values, but their parasitics too.
The data-driven technical answer is, you model it if you have access to the very expensive power integrity software that takes into account the entire physical design and all its parasitics, including those of the capacitors. You optimize the design to achieve the desired target power impedance, while minimizing all the loop areas for the bypassed devices. The software is hundreds of thousands of dollars, and driving it to an accurate result is many months of work. For a complex, high-volume, aggressive-schedule project it could be worth it.
For the rest of us, you follow some time-honored rules of thumb, taking into account some knowledge of capacitor behavior and mis-behavior (like anti-resonance and bias effect.)
A couple of those 'rules of thumb':
Small caps work best for high frequency because their parasitics are smaller. They're most effective when the board layout keeps the inductance to a minimum. That's why they're placed close to pins.
0.1uF has proven to offer a good balance between parasitics and capacity for frequencies of interest at the board level. Some designers will mix 0.1uF with larger and smaller values to achieve a wider frequency response, but this must be done with care to avoid anti-resonance. This can be modeled using SPICE or one of its free alternatives (e.g., LTSpice) using models provided by the manufacturer.
This brings up another 'rule of thumb': When mixing values, use 5 - 10x spacing to avoid anti-resonance. This is why they chose 0.1 + 1uF: they're far enough away from each other that their resonance peaks don't interact (much, anyway.)
Quick-and-dirty, you can use the KEMET K-SIM tool to simulate combined cap values and how their resonances interact. Try it here: https://ksim3.kemet.com/capacitor-simulation
That all said, here's a good Murata guide to that stuff. https://www.murata.com/~/media/webrenewal/support/library/catalog/products/emc/emifil/c39e.ashx
Comment: I thought the point of these in circuit designs was to be parasitic. You substitute in active power from a supply for when the reactive power supplied from the capacitor is too low.
Comment: That doesn't make sense. The point of decoupling is to reduce the impedance of the supply, shunting the large dI/dt switching noise locally at the device. This not only reduces loop area, but makes the caps more effective. The supply inductance outside of the shunted loops then can be helpful instead of harmful. The fact that the caps themselves (as well as their connection to the board) have parasitics is why we bother with mixing values at all.
Answer:
how these values are calculated?

Question: How do we calculate how big a shovel should be?
Answer:\$\text{ }\text{ }\$ We don't; pretty much all shovel makers make the same size because, through years of experience in making, selling and using shovels and, the freedom of information transfer, a size equivalent to a capacitance of 100 nF is about right.
Of course, shovels come with variations in size and some folk will use 10 nF capacitors on each IC supply rail but, the reason may be purely what stock item they have or, it may be driven by the 10 nF circuit generating higher frequencies (and higher frequency supply currents) and therefore, better capacitors with higher self-resonant frequencies are a sensible choice. 10 nF has a higher self-resonance than 100 nF all other things being equal.

How many caps we need use in parallel?

Well, I think you've answered that when you said "0.1uF ceramic caps at each power pin".
Comment: I like this analogy; we use 0.1uF not because someone calculated that value to be the "right" amount, but because it's a good round number that's close enough most of the time.
Answer: Murata - Application Manual for Power Supply Noise Suppression and Decoupling for Digital ICs
https://www.murata.com/~/media/webrenewal/support/library/catalog/products/emc/emifil/c39e.ashx
This is 85 page application manual provides information about the theory and practice of decoupling. The decoupling devices are characterized by a practical measure called insertion loss. The insertion loss of various bypass capacitor values is shown under specified test conditions.
Answer: If you want to know the specific minimum capacitance and maximum ESL and ESR you need or can get away with, you need to take into account the component requirements PCB layout and geometry of the traces. And since placing capacitors changes the PCB layout and traces it can become a recursive problem. In other words, no simple pen and paper calculations here. This is simulation territory.
More generally though, what you need to know is the IC's edge speed, voltage tolerances, transient current requirements, and approximately the trace inductance leading to the IC.
You want the total capacitance high enough so that the voltage tolerances don't spike or dip beyond IC tolerances at the low frequencies, but you want the inductance low enough so that the high frequency currents don't have to take long return paths around the board which produces noise and EMI. This means you need to look at the capacitor impedance curves and target the appropriate impedance at the key frequencies of operation to make sure the inductance is low enough. Placing capacitors in parallel properly increases capacitance and reduces the overall parasitic inductance which helps the high charge demand low frequency currents and inductance sensitive high frequency currents.
Placing multiple capacitors different values can make things worse because each capacitor is capacitance with a parasitic inductance and when they are different they can resonate with each other to produce noise peaks which makes things worse if your IC operating frequencies falls on those peaks.


Multinomial logit, standard and robust errors

Question: I'm computing a multinomial logit model with Biogeme. Looking at the final results, it seems that some variables are not statistically significant when standard errors are considered. However, with robust standard errors, they are all significant. Does anyone know if it make sense in this kind of model consider only the robust standard errors? I don't know if in multinomial logit, as it is different from a linear regression, the use of robust standard errors leads to a different interpretation.
Sorry for this silly question
Answer: When a model is nonlinear in parameters (like your multinomial logit),
the MLE of the parameter vector is both biased and inconsistent if the errors are heteroskedastic, unless you modify the likelihood function to correctly take into account the precise form of heteroskedasticity. This is very different from the linear case. Similarly, the MLE of the asymptotic covariance matrix of the parameters will also be inconsistent. The terms "correctly" and "precise" are key, since it is hard to know exactly what sort of heteroskedasticity you have going on. To make things worse, the bias is also in an unknown direction.
I don't know about Biogeme, but other stats packages have commands that allow you to parameterize the heteroskedasticity.


Volume change in positive deviation from Raoult's Law

Question: Let us take a mixture of ethanol and acetone as an example. When ethanol is mixed with acetone, the hydrogen bonding between ethanol molecules gets disturbed as actone molecules get in between the ethanol molecules. This results in $\Delta_\text{mix} H\gt0 $ as heat must be supplied to make the solution from its constituents (as attraction is less) but I am not sure about $\Delta_\text{mix} V$. This page says it is greater than zero because volume expands on mixing. But I think it should be less than zero because the observed vapour pressure is more than that predicted on the basis of theoretical calculations, so a greater amount of solution will be present in the form of vapour, hence volume of solution will be less (than the sum of the volumes of its constituents). Where am I wrong?
Comment: An intuitive explanation can be found on the page you referenced. The lessened attraction between the constituents effectively means that the average "intermolecular distance" would be greater after mixing than it was before, hence the increased volume. The vapor pressures before and after mixing are not directly relevant here.
Comment: I agree with the increased intermolecular distance, but more vapour pressure means more amount of vapour over solution. As total amount of solution + vapour is constant, this means less solution, hence less volume of solution, so there are two conflicting processes which one dominates?
Comment: @drake01 By the volume change is meant the total volume after mixing, at the same temperature versus sum of volumes of the same amount of liquids before mixing. It should be obvious that evaporation changes the volume,  as the there is less of liquids.
Answer: I'm a little late to the party here, but wanted to chime in.
The link you posted isn't working anymore, but you appear to be making too many assumptions about the system being measured.  Nothing about the measurement of the volume change implies there is necessarily an open space above the liquid for vapor to form.  Imagine an open beaker of ethanol with a small disk floating on top so that no molecules can escape upwards, but it can move up and down with the change in liquid level.  This would also keep the pressure of the liquid constant (although it doesn't really matter since the liquid is essentially incompressible) .
If you were able to inject a certain amount of acetone into this beaker without opening it to the atmosphere for very long, the resulting volume of liquid in the beaker would be greater than the sum of its parts. Hopefully it makes sense that if there is no space for liquid to form, the positive volume change of mixing can show itself.
As far as the idea that more vapor would form to decrease the volume of liquid, realize that evaporation is a time-dependent process, so likely the mixed liquid would reach an effective equilibrium state where it's volume change could be observed before the extra liquid has time to evaporate.  It is true that it would evaporate faster if the effective vapor pressure (technically "fugacity" or "chemical potential") were higher, as the driving force for mass transfer would be greater, but this is also very dependent on the way the system is specified.  Technically if you left the container open in a large room forever, it would all evaporate in either case.
Answer:
but I am not sure about $\Delta_{mix}V$. [...] I think it should be less than zero because the observed vapour pressure is more than that predicted on the basis of theoretical calculations

$\Delta_{mix}V$ refers to the change in the volume of the liquid with mixing, compared to the pure components. The vapour plays no role in this computation. Note also that the lower vapour pressure relative to the pure components means that the free energy of the liquid mixture is lower than the arithmetic average over the free energies of the pure components. This can certainly be interpreted as being due to stronger association between the components in the mixture than in the average of the pure liquids, but does not necessarily imply a specific direction of change (positive or negative) in volume.


I sent 1 IOTA to Bitfinex, transaction is confirmed but money aren't store on my wallet on Bitfinex

Question: It was like that :
1. I wanted to send IOTA to Bitxinex  so  i take adres from my wallet on Bitfinex (according to the instructions) adres is IRFHCFRYIYQYH9T9JNWMT9WUAULEAPWFUJYUPASVVLLPWVONLMVFFUZKODQGDBYGXIFOPKWFXQUEHRKJWHRDX9JKUY
2. After a dozen or so hours - transaction is confirmed by Tangle
(look at https://thetangle.org/transaction/AGMQDQZRRYSFQDC9TNIUPJMPKEQQAVG9YPULYTAGTWCFLOCGY9JMLEE9JBT9IHCMBDRLVAGMRETWZ9999)
3. After an hour (as you can see in Tangle explorer https://thetangle.org/transaction/W9ETYRKVWHDMVBIMHJOHNNHXUW9VYQRSIDBVIQOQJTKHQ9JDQZJ9QJTEPKLXRKFCPPBEJIWYEBKO99999) someone or something executes another transaction as a result my 1 IOTA is taken from the address.
4. In account logs (Bitfinex) there is no trace of these operations, and the account balance is zero.
I can't understand what happened? Did I make a mistake?
and why Tangle and Bitfinex tell a different story of transactions on adres=IRFHCFRYIYQYH9T9JNWMT9WUAULEAPWFUJYUPASVVLLPWVONLMVFFUZKODQGDBYGXIFOPKWFXQUEHRKJWHRDX9JKUY.
https://thetangle.org/address/IRFHCFRYIYQYH9T9JNWMT9WUAULEAPWFUJYUPASVVLLPWVONLMVFFUZKODQGDBYGXIFOPKWFXQUEHRKJW
Comment: I'm voting to close this question as off-topic because this Question is not about Iota it is about Bitfinex.
Comment: It is not like that. The IOTA Foundation cooperates with the Bitfinex stock exchange, so it also partially prompts for its activities. Bitfinex has been holding my money for more than a dozen hours and I can not use it - and they don't respond to the request services (ticets). who should I ask for help and advice if  not to the IOTA community ???
Answer: This is basic practice on Bitfinex. They collect all the iota centralized and keep track of your iota in a Database. This process may take some time. So be patient.
This is not Bitfinex support and if you have questions on Bitfinex use their support please.


"Incremental" hypergeometric distribution?

Question: Box contains $5$ yellow and $3$ red balls. $4$ balls are drawn without replacement. Let $X$ be the number of yellow balls appearing in the first two draws, and let $Y$ be the number of yellow balls appearing in total. Give the joint probability distribution of $X$ and $Y$.
Answer: We want to find, for all relevant $x$ and $y$, the probability that $X=x$ and $Y=y$. Call this number $f_{X,Y}(x,y)$, or, for simplicity, $f(x,y)$.
There are not many possible values of $x$ and $y$, so we can find $f(x,y)$ for each combination.  (Alternately, we can find a general formula for $f(x,y)$. For these small numbers, that is probably not worthwhile.)
We show how to find $f(0,y)$ for all possible values of $y$. The probability that $X=0$ (no yellow on the first two trials) is $\frac{3}{8}\cdot\frac{2}{7}$.
Given that there were no yellow on the first two trials, the probability that $Y=0$ is $0$, since there must be at least $1$ yellow in the next two trials. Thus $f(0,0)=0$.
Suppose there were no yellow on the first two. Then the probability of $1$ yellow overall is $\frac{1}{6}+\frac{5}{6}\cdot\frac{1}{5}=\frac{2}{6}$. Thus $f(0,1)=\frac{3}{8}\cdot\frac{2}{7}\cdot\frac{2}{6}$. This can, if we wish, be simplified. Now we have found $f(0,1)$.
Suppose there were no yellow on the first two trials. Then the probability of $2$ yellow in the next two trials is $\frac{5}{6}\frac{4}{5}=\frac{4}{6}$. Thus $f(0,2)=\frac{3}{8}\cdot\frac{2}{7}\cdot\frac{4}{6}$.
We may want to note that $f(0,3)=f(0,4)=0$.
Now you can do the same sort of calculations for $f(1,y)$ and $f(2,y)$.
Added: We develop a formula. There are $\binom{8}{2}\binom{4}{2}$ equally likely ways to choose $2$ balls and then $2$ mre. There are all equally likely. (Think of the balls as having invisible ID numbers.) This will be the denominator in all our probabilities.
For the numerator, we find the number of ways to have $x$ yellow in the first two, and $y$ yellow overall, so $y-x$ in the next two.
The $x$ yellow can be chosen in $\binom{5}{x}$ ways. The accompanying $2-x$ red can be chosen in $\binom{3}{2-x}$ ways.  Now the $y-x$ yellow can be chosen from the $5-x$ remaining yellows in $\binom{5-x}{y-x}$ ways. And the $2-(y-x)$ red can be chosen from the $3-(2-x)$ remaining reds in $\binom{3-(2-x)}{2-(y-x)}$ ways. That gives a total of
$$ \binom{5}{x}\binom{3}{2-x}\binom{5-x}{y-x}  \binom{3-(2-x)}{2-(y-x)}      .$$
 (In the formula, we use the convention that $\binom{a}{b}=0$ if $a\lt b$.)
Comment: I'd rather want to see a derivation of a general formula.
Comment: I will add one, about $10$ minutes.
Comment: For the denominator, shouldn't it be $\binom{8}{2}\binom{6}{2}$


Why did part of my mesh suddenly turn purple in sculp mode? (Face sets)

Question: I was just sculpting a rock object in object mode, when all of a sudden, parts of it just turned purple.  I don't think I pressed anything I shouldn't have.  I don't know if this is normal of not, but does anyone know how to fix this?
Answer: In Sculpt mode, Face Sets allows you to create separate areas, a little bit like the Mask except you can create as many face sets as you want and you won't have to mask and unmask to switch from a face set to another, when you'll sculpt on a face set it will only affect this face set until you release the left click and click on another face set.
To paint your face sets you need to press left click. Release and left click again to create a new face set, Ctrl and left click on a face set to extend it, Shift left click to smooth the boundaries. In the Face Sets menu > Init Face Sets you can choose another way to create face sets (for example By UV Seams):

Once you've painted, choose your sculpt brush and enable the Face Sets options:

It looks like once you've painted your face sets you can't enable Dyntopo without deleting the face sets, Dyntopo creates new geometry so it makes sense.
Now sculpt:
Answer: never mind, I figured it out.  I had accidantally enabled "face sets"  whatever that is.  But anyway, I got it back to normal now
Answer: How To Remove Face Sets
To remove/reset all Face Sets, you can navigate to the top left corner of your viewport and click the Face Sets button.
From here, click Face Set From Visible to reset the entire mesh back to the default grey.

Alternatively, you can go to the top left corner and click on Viewport Overlays. Then at the very bottom, toggle off Face Set visibility.


Is the consciousness currently in oneself the same as the consciousness that used to be or in the future will be in oneself?

Question: People seem to believe that one's consciousness is a "different" consciousness than that of others, but the "same" consciousness as the one that has been in one's body in the past and the one that will be in one's body in the future. How likely is this to be true? I have almost no knowledge about neuroscience, so please refrain from using much neuroscience jargon if feasible, even if it's at the cost of not giving a thorough explanation. A simple "yes," "no," or "we have no idea" answer would suffice if need be.
Comment: I'm voting to close this question as off-topic because it's a philosophical question.
Comment: @ChristianHummeluhr I answered the question including a more neuroscientific approach to make it less philosophical oriented. I also edited my answer since yesterday (definition and reference added).
Comment: Neuroscience has very little firm to say on any aspect of consciousness, particularly on a very "advanced" topic such as this.  Perhaps this would get more productive attention on philosophy.SE.
Answer: Short answer
Consciousness is different between individuals and can change over time.
Background
Nelkin (1997) provides the following definition of consciousness:

When philosophers and psychologists think about consciousness, they generally focus on one or more of three features: phenomenality (how experiences feel), intentionality (that experiences are "of" something, that experiences mean something), and introspectibility (our awareness of phenomenality and intentionality of experiences).

Although I am not an expert on the matter I think this definition answers your question. You say People seem to believe that one's consciousness is a "different" consciousness than that of others, but the "same" consciousness as the one that has been in one's body in the past and the one that will be in one's body in the future. Because the phenomenality changes over time, because past experience change the way sensations feel (new versus familiar sensations are very different) your statement that consciousness is constant is invalid.
The intentionality and most notably the introspectibility makes consciousness a very personal thing, meaning that your statement ...one's consciousness is a "different" consciousness than that of other is valid.

As a neuroscientist I can tackle the two statements posed on more familiar ground to me. I dare to say that consciousness is not a stable entity, because in the end, sensations, perceptions and awareness of the world are all in your head and generated by neurons. Because psychoneuropharmaca or brain damage can lead to temporary and permanent altered states of consciousness, respectively, the statement that ...the "same" consciousness as the one that has been in one's body in the past and the one that will be in one's body in the future is simply invalid.
From a similar neuroscientific vantage point one's brain is obviously different and physically separate from another person's brain, so we quite frankly are not sharing a consciousness. Consciousness is therefore a personal thing, the more since one can suffer brain damage without another even noticing it, hence one's consciousness is a "different" consciousness than that of others must be true.
Reference
Nelkin N, Philosophy of Science 1993
Comment: +1 Great answer to a very difficult question.
Comment: I know brain damage changes personalities and memories, but why would you think it changes consciousness? Is the concept of having "the same" consciousness even meaningful?
Comment: I edited the answer.
Comment: Though I upvoted this answer, I'm conflicted. On one hand it is a good answer with which I subjectively agree, but on the other hand, it is primarily subjective. I can't give a scientific reason for why I agree, nor can I evaluate the answer scientifically. The answer's credibility ultimately rests on @AliceD being a trained neuroscientist willing to take a firm personal position, not on the answer's semantic contents. While this is probably the best possible answer, it suggests to me that the question is, in fact, philosophical, not cognitive.
Answer: After reading Consciousness article from wikipedia, my answer is no.
Consciousness is the quality or state of awareness, or, of being aware of an external object or something within oneself.

First to deny consciousness exists seems so absurd for undeniably thoughts do exist and over time our awareness grows or falls our thougts change, so by stated definition our consciousness changes over time.
I think that if consciousness was the same in all people individuality and free will wouldn't exist. We are conscious that means we can take control and effect our lives.
I've learned from vedas that we can divide our concious self to thoughts, emotions and focus. We can control our focus because we have free will to do so, and our focus is used to focus our thoughts to whatever we want.
Carl Gustav Jung coined a term "collective unconscious" it is proposed to be a part of the unconscious mind. Jung distinguished the collective unconscious from the personal unconscious, in that the personal unconscious is a personal reservoir of experience unique to each individual, while the collective unconscious collects and organizes those personal experiences in a similar way with each member of a particular species.
Comment: @ Devidenko I think you misunderstand what consciousness it. Consciousness is more than just awareness; robots are aware of their surroundings but aren't typically considered conscious. I also don't understand what you mean when you say, "I think that if consciousness was the same in all people individuality and free will wouldn't exist." That's not a complete sentence.
Comment: On what information specifically are you basing these assertions?  Answers are much more helpful when they have specific information, not just blanket statements.
Comment: I have edited the answer. @Krysta
Comment: Yes, but the crucial difference is that machines are not aware of themselves, as opposed to humans.


2000 mustang 3.8l v6 smog pump issues

Question: I have a 2000 mustangs v6 3.8l The smog pump is not working (I think its an electrical problem) but that's outside of the point. I live in Oklahoma and we have no emission stuff (Amen!!!) so can I just delete the codes it popping up? unless it will make the engine run worse, why should I fix it unless the electrical problems will cause more damage (the service light for the smog pump stuff has been on for over 2-3 years) so I don't think it will. based on FORscan, it gave me two pcm codes p1000, P0411 and obdII P411.
Answer: You may want to think about getting it fixed vs. ignoring it. In this case, the problem is more than likely in the solenoid which directs air from the pump to the cat. Depending on the exact malfunction, you could be seeing decreased fuel mileage and also damaging your catalytic convertor. There are some reasonable tests which were written up on OBD-Codes.com which might help you do your own diagnosis of the issue:

If you have access to a scan tool, with KOEO (Key on engine off) command the AIR pump on. It should activate. If it doesn't, remove and inspect the AIR pump relay for discoloration/melting due to heat. Repair as necessary.
With the ignition on (engine off) check for battery voltage at the switched battery feed to the relay and the relay control circuit. If either of these isn't present, inspect circuit for blown fuse or open/short in the wiring. Repair cause of short and retest. If they are both present, jumper the battery feed to AIR pump feed circuit using a fused jumper. The pump should activate. If not, check for power and ground present at the AIR pump when jumpered. If there is no voltage/ground present at pump repair open in wiring harness. If voltage and ground is present, but pump still does not run, suspect a bad AIR pump. If after jumpering the AIR pump feed circuit the pump activates then the problem is likely the AIR pump relay. Replace and retest.
If the scan tool activates the AIR pump, with KOER (Key on engine running) activate the AIR pump solenoid valve on and see if there is vacuum to the cutoff valve. It should have vacuum present to open the valve. If there is no vacuum present, check the AIR pump's vacuum solenoid valve for vacuum supply from the manifold. If there is vacuum present then the vacuum solenoid is likely bad. Replace it. If there is no vacuum present at the supply to the vacuum solenoid, check for a plugged or damaged vacuum line or plugged vacuum port. But if there is vacuum present at the cut-off valve, shut the engine off and using a vacuum pump, apply vacuum to the cut-off valve and see if it holds a vacuum and that air flows through it when vacuum is applied. If it doesn't hold vacuum or the valve doesn't flow when vacuum is applied, replace the cut-off valve. If the cut-off valve works properly, inspect the check valve for obstruction or to see if it's missing. Replace as necessary.
Check the steel line to the exhaust catalyst as well as the exhaust ports for damage or holes that could give a false reading.

P1000 is a generic Ford code which simply states all of the on board tests have not completed. This is basically a throw away code, so until you get the P0411 fixed, the P1000 code will continue to pop.
In either case, you are going to continue to have the check engine light illuminated whether you fix the smug pump issue or just pull the wiring.
Answer: I'd be tempted to leave it disconnected but then I drive a Volkswagen TDI so emissions is somewhat of a sore subject.
Leaving it disconnected shouldn't do any damage to your car.

2000 mustang 3.8l v6 smog pump issues


How does amazon get away without verifying emails?

Question: I was playing around with Amazon's Check out process today and I noticed something odd. Amazon does not make you activate your account or verify your email address. I only had to enter my email twice during the registration process. They never sent me an activation email. Is this becoming standard? I can understand the reasoning that if you entered someone else's email address during registration the person who actually owns the email address could change the password on the account. It just seems really odd. Can someone explain how they get away with this?
Answer: Email activation doesn't stop automated registration and it's generally a nuisance for the user.
Amazon is in the business of making it as easy as possible for you to register and drill down through their checkout structure so you pay them. An email activation system is just a speed bump with no worthwhile purpose. What does Amazon care if you didn't provide a real email address if you gave real credit card information?
On the other hand, a message board website might want you to verify your email to inconvenience the average spammer. But even then, check out utilities like http://10minutemail.com/10MinuteMail/index.html that makes "bogus" email verification effortless.
Comment: You make some good points, but no anti-spam/bot system is perfect. The idea is just to make it difficult enough that spammers will move on to easier targets. For smaller sites, email verification may be just enough to do that. And most legitimate users are happy to verify their email address. I mean, what do you think will turn off users more? Having to verify your email once on sign-up, or having to wade through spam messages every time you visit the site?
Comment: `Email activation doesn't stop automated registration` It's called [defense in depth](http://en.wikipedia.org/wiki/Defence_in_depth), and it's been a part of security systems since long before humans had words for either "security" or "systems". Actually, strictly speaking, it's been around since [before there were humans](http://en.wikipedia.org/wiki/Hedgehog_defence). You're a bit behind the times on that. Most attackers go for low-hanging fruit. Remove the small trees, most of your problems are solved. Unless you're being attacked by a giraffe.
Comment: In other words, if you take only one thing from my comment above, let it be that spammers are giraffes, and your website [is a hedgehog](http://en.wikipedia.org/wiki/Hedgehog).
Answer: What do you mean how do they get away with that?
The just don't do it...
There's no getting away with anything, as there's nothing that says they have to.
They don't save any information other than email, name, and wish list, so there really isn't that much that someone could get away with if the email address wasn't the registrants...
Comment: A person could fill their drives with garbage. Or eat up their processor cycles; it takes more effort to save something to a database and satisfy constraints than it does to spam a site with random text. Granted, any good firewall or banning system should cut that kind of DoS off at the knees even for an enormous botnet, but still. Of course, for an enormous botnet, there are bigger problems.


Setting the value of a lookupfield(sharepoint dropdown formfield) in sharepoint 2010 list forms

Question: How can i set the value of sharepoint form field dropdown box(lookupfield) in sharepoint list form when the form gets saved (using jquery)
note: the lookupfield (dropdown formfield renders as input if it contains values more than 20)
Answer: I just implemented such a solution a couple of weeks ago
Here is a very good post that will explain all.
Answer: So I have a field called "Data Classification":
var dataClsField = $('select[title="Data Classification"]');

I was trying to set this field with the value of another dropdown called "DataClass" that I got using this code:
var clsFieldValue = $('select[id*="DataClass"] option:selected').val();

For some crazy reason, I had to do both of these options to get my first field to set right:
dataClsField.find('option[value="'+clsFieldValue+'"]').prop('selected', true);
dataClsField.val(clsFieldValue.val());

Note: This was with 2 dropdowns with less than 20 items in each.  I believe the only difference, jQuery-wise, when it goes over that, is that "select" becomes "input" on your selector.


multi-step game, would the contract stop for a while for another transaction to come

Question: To make my question specific, what I want to develop is a multi-step game. And the thing I want to realize is, let's say now we have the game taking players A & B included, and both A & B have the freedom to send transactions to the game contract. In some certain round A may send a valid transaction to the contract can make him win, but is there some method we can develop to hold the contract for a while not yielding the final result (A wins) to see whether or not there is another valid transaction coming from another player (B)?
Answer: Nothing can occur in the contract unless a transaction triggers the action.  To my knowledge there is no conditionally delayed transaction.  Someone would need to pay the gas for a delayed transaction.
Player A could initiate a game completion transaction after the wait period had passed.  The transaction would check to verify enough time had passed before allowing the game completion.  This puts the onus on the player who thinks he or she has won to complete the game, which I assume the winner would want to do.
Comment: is there already something like waiting-cost gas?
Comment: Contracts can't have a pool of gas to be used by callers.  They can own some gas.  There are some interesting ideas in this discussion: https://forum.ethereum.org/discussion/2401/can-a-contract-pay-its-own-gas-fees.  Perhapse the contract can reimburse the caller for spent gas.


Getting started with OpenCV 2.4 and MinGW on Windows 7

Question: How do I install OpenCV 2.4 and compile my code with MinGW?
Comment: Wow, 11 downvotes and 30 upvotes. I think this is a 'too broad question' versus 'this helped me a lot'.
Answer: 1. Installing OpenCV 2.4.3
First, get OpenCV 2.4.3 from sourceforge.net. Its a self-file-extracting so just double click the file to start installation. Install it in a directory, say C:\.

Wait until all files get extracted. It will create a new
directory C:\opencv which contains OpenCV header files, libraries, code samples, etc.
Now you need to add C:\opencv\build\x86\mingw\bin directory to your system PATH. This directory contains OpenCV DLLs which is required for running your code.
Open Control Panel → System → Advanced system settings → Advanced Tab → Environment variables...
You will see a window like shown below:

On the System Variables section,
select Path (1), click Edit... (2), add C:\opencv\build\x86\mingw\bin (3) then click Ok.
This will completes the OpenCV 2.4.3 installation on your computer.

2. Installing MinGW compiler suite
I highly recommend you to use gcc (GNU Compiler Collection) for compiling your code. gcc is the compiler suite widely available in Linux systems and MinGW is the native port for Windows.
Download the MinGW installer from Sourceforge.net and double click to start installation. Just follow the wizard and select the directory to be installed, say C:\MinGW.

Select "C Compiler" and "C++ Compiler" to be installed.

The installer will download some packages from the internet so you have to wait for a while. After the installation finished, add C:\MinGW\bin to your system path using the steps described before.

To test if your MinGW installation is success, open a command-line box and type: gcc. If everything is ok, it will display this message:
gcc: fatal error: no input files
compilation terminated

This completes the MinGW installation, now is the time to write your "Hello, World!" program.

3. Write a sample code
Open your text editor and type the code below and save the file to loadimg.cpp.
#include "opencv2/highgui/highgui.hpp"
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv)
{
  Mat im = imread(argc == 2 ? argv[1] : "lena.jpg", 1);
  if (im.empty())
  {
    cout << "Cannot open image!" << endl;
    return -1;
  }

  imshow("image", im);
  waitKey(0);

  return 0;
}

Put lena.jpg or any image you like in the same directory with the file above. Open a command-line box and compile the code above by typing:
g++ -I"C:\opencv\build\include" -L"C:\opencv\build\x86\mingw\lib" loadimg.cpp -lopencv_core243 -lopencv_highgui243 -o loadimg

If it compiles successfully, it will create an executable named loadimg.exe.
Type:
loadimg

To execute the program. Result:

4. Where to go from here?
Now that your OpenCV environment is ready, what's next?

Go to the samples dir → C:\opencv\samples\cpp.
Read and compile some code.
Write your own code.
Comment: I followed your instructions and got loadimg.exe to build but it crashes straight away when I try to execute it -- exception code=c0000005 and faulting module=libstdc++-6.dll. Running on gdb in eclipse shows a seg fault in libstdc++ . Any ideas as to why this might be?
Comment: Apparently, mingw binaries are no longer included. Check http://grauonline.de/wordpress/?page_id=449 for a description on how to compile OpenCV.
Comment: @user1317084 - Nope.. I moved developement to linux for other reasons. But I believe that you can solve this by getting the latest version from the repo and building it from source..
Comment: If your program CRASHES with a 0000005 error, you should compile the library by yourself, USE NENAD BULATOVIC ANSWER wich is below, after that it should WORK JUST FINE
Comment: Looks like this is a known bug http://answers.opencv.org/question/172/segfault-in-opencv-242-and-mingw-on-winxp/?answer=175#post-id-175
Comment: @volting I face the similar kinda issue.. Have u solved it? Any solution for this?
Comment: @volting check this post: http://stackoverflow.com/questions/17393311/openvc-2-4-5-eclipse-cdt-juno-mingw-error-0xc0000005/17402441#17402441
Comment: @user1317084 http://stackoverflow.com/questions/17393311/openvc-2-4-5-eclipse-cdt-juno-mingw-error-0xc0000005/17402441#17402441
Answer: The instructions in @bsdnoobz answer are indeed helpful, but didn't get OpenCV to work on my system.
Apparently I needed to compile the library myself in order to get it to work, and not count on the pre-built binaries (which caused my programs to crash, probably due to incompatibility with my system).
I did get it to work, and wrote a comprehensive guide for compiling and installing OpenCV, and configuring Netbeans to work with it.
For completeness, it is also provided below.

When I first started using OpenCV, I encountered two major difficulties:

Getting my programs NOT to crash immediately.
Making Netbeans play nice, and especially getting timehe debugger to work.

I read many tutorials and "how-to" articles, but none was really comprehensive
and thorough. Eventually I succeeded in setting up the environment; and after a
while of using this (great) library, I decided to write this small tutorial,
which will hopefully help others.
The are three parts to this tutorial:

Compiling and installing OpenCV.
Configuring Netbeans.
An example program.

The environment I use is:
Windows 7, OpenCV 2.4.0, Netbeans 7 and MinGW 3.20 (with compiler gcc 4.6.2).
Assumptions:
You already have MinGW and Netbeans installed on your system.
Compiling and installing OpenCV
When downloading OpenCV, the archive actually already contains pre-built
binaries (compiled libraries and DLL's) in the 'build' folder. At first, I
tried using those binaries, assuming somebody had already done the job of
compiling for me. That didn't work.
Eventually I figured I have to compile the entire library on my own system in
order for it to work properly.
Luckily, the compilation process is rather easy, thanks to CMake.  CMake
(stands for Cross-platform Make) is a tool which generates makefiles specific
to your compiler and platform. We will use CMake in order to configure our
building and compilation settings, generate a 'makefile', and then compile the
library.
The steps are:

Download CMake and install it (in the installation wizard choose to add
CMake to the system PATH).
Download the 'release' version of OpenCV.
Extract the archive to a directory of your choice. I will be using
c:/opencv/.
Launch CMake GUI.

Browse for the source directory c:/opencv/.
Choose where to build the binaries. I chose c:/opencv/release.

Click 'Configure'. In the screen that opens choose the generator
according to your compiler. In our case it's 'MinGW Makefiles'.

Wait for everything to load, afterwards you will see this screen:

Change the settings if you want, or leave the defaults. When you're
done, press 'Configure' again. You should see 'Configuration done' at
the log window, and the red background should disappear from all the
cells.

At this point CMake is ready to generate the makefile with which we will
compile OpenCV with our compiler. Click 'Generate' and wait for the
makefile to be generated. When the process is finished you should see
'Generating done'. From this point we will no longer need CMake.

Open MinGW shell (The following steps can also be done from Windows' command
prompt).

Enter the directory c:/opencv/release/.
Type mingw32-make and press enter. This should start the compilation
process.

When the compilation is done OpenCV's binaries are ready to be used.
For convenience, we should add the directory C:/opencv/release/bin
to the system PATH. This will make sure our programs can find the
needed DLL's to run.

Configuring Netbeans
Netbeans should be told where to find the header files and the compiled
libraries (which were created in the previous section).
The header files are needed for two reasons: for compilation and for code
completion. The compiled libraries are needed for the linking stage.
Note: In order for debugging to work, the OpenCV DLL's should be available,
which is why we added the directory which contains them to the system PATH
(previous section, step 5.4).
First, you should verify that Netbeans is configured correctly to work with
MinGW. Please see the screenshot below and verify your settings are correct
(considering paths changes according to your own installation). Also note
that the make command should be from msys and not from Cygwin.

Next, for each new project you create in Netbeans, you should define the
include path (the directory which contains the header files), the libraries
path and the specific libraries you intend to use.  Right-click the project
name in the 'projects' pane, and choose 'properties'.  Add the include path
(modify the path according to your own installation):

Add the libraries path:

Add the specific libraries you intend to use. These libraries will be
dynamically linked to your program in the linking stage. Usually you will need
the core library plus any other libraries according to the specific needs of
your program.

That's it, you are now ready to use OpenCV!
Summary
Here are the general steps you need to complete in order to install OpenCV and
use it with Netbeans:

Compile OpenCV with your compiler.
Add the directory which contains the DLL's to your system PATH (in our case:
c:/opencv/release/bin).
Add the directory which contains the header files to your project's include
path (in our case: c:/opencv/build/include).
Add the directory which contains the compiled libraries to you project's
libraries path (in our case: c:/opencv/release/lib).
Add the specific libraries you need to be linked with your project (for
example: libopencv_core240.dll.a).

Example - "Hello World" with OpenCV
Here is a small example program which draws the text "Hello World : )" on a GUI
window. You can use it to check that your installation works correctly. After
compiling and running the program, you should see the following window:

#include "opencv2/opencv.hpp"
#include "opencv2/highgui/highgui.hpp"

using namespace cv;

int main(int argc, char** argv) {
    //create a gui window:
    namedWindow("Output",1);

    //initialize a 120X350 matrix of black pixels:
    Mat output = Mat::zeros( 120, 350, CV_8UC3 );

    //write text on the matrix:
    putText(output,
            "Hello World :)",
            cvPoint(15,70),
            FONT_HERSHEY_PLAIN,
            3,
            cvScalar(0,255,0),
            4);

    //display the image:
    imshow("Output", output);

    //wait for the user to press any key:
    waitKey(0);

    return 0;
}

Comment: This proved really helpful coz i never wanted to use visual studio for compiling opencv . I feel comfortable with Eclipse cdt and did not wanted to fill my hard disk with not so important visual studio . +1
Comment: @RahulVerma You are right, I also had to compile binaries for myself. Described here http://stackoverflow.com/questions/17393311/openvc-2-4-5-eclipse-cdt-juno-mingw-error-0xc0000005/17402441#17402441
Comment: I get a __403 Forbidden__ when accessing the links in your post. Maybe editing your answer and adding the tutorial _into_ it, would be a better idea?
Answer: This isn't working for me. I spent few days following every single tutorial I found on net and finally i compiled my own binaries. Everyting is described here: OpenVC 2.4.5, eclipse CDT Juno, MinGW error 0xc0000005
After many trials and errors I decided to follow this tutorial and to compile my own binaries as it seems that too many people are complaining that precompiled binaries are NOT working for them. Eclipse CDT Juno was already installed.
My procedure was as follows:

Download and install MinGW and add to the system PATH with
c:/mingw/bin
Download cmake from http://www.cmake.org and install it
Download OpenCV2.4.5 Windows version
Install/unzip Opencv to C:\OpenCV245PC\ (README,index.rst and CMakeLists.txt are there with all subfolders)
Run CMake GUI tool, then
Choose C:\OpenCV245PC\ as source
Choose the destination, C:\OpenCV245MinGW\x86  where to build the binaries
Press Configure button, choose MinGW Makefiles as the generator. There are some red highlights in the window, choose options as you need.
Press the Configure button again. Configuring is now done.
Press the Generate button.
Exit the program when the generating is done.
Exit the Cmake program.
Run the command line mode (cmd.exe) and go to the destination
 directory C:\OpenCV245MinGW\x86
Type "mingw32-make". You will see a progress of building
 binaries. If the command is not found, you must make sure that the
 system PATH is added with c:/mingw/bin. The build continues
 according the chosen options to a completion.
In Windows system PATH (My Computer > Right button click >
 Properties > Advanced > Environment Variables > Path) add the
 destination's bin directory, C:\OpenCV245MinGW\x86\bin
RESTART COMPUTER
Go to the Eclipse CDT IDE, create a C++ program using the sample OpenCV code (You can use code from top of this topic).
Go to Project > Properties > C/C++ Build > Settings > GCC C++ Compiler > Includes, and add
the source OpenCV folder "C:\OpenCV245PC\build\include"
Go to Project > Properties > C/C++ Build > Settings > MinGW C++ Linker > Libraries, and add to the Libraries (-l) ONE BY ONE (this could vary from project to project, you can add all of them if you like or some of them just the ones that you need for your project): opencv_calib3d245 opencv_contrib245 opencv_core245 opencv_features2d245 opencv_flann245 opencv_gpu245 opencv_highgui245 opencv_imgproc245 opencv_legacy245 opencv_ml245 opencv_nonfree245 opencv_objdetect245 opencv_photo245 opencv_stitching245 opencv_video245 opencv_videostab245
Add the built OpenCV library folder,  "C:\OpenCV245MinGW\x86\lib" to Library search path (-L).

You can use this code to test your setup:
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/opencv.hpp>
#include <iostream>

using namespace std;
using namespace cv;

int main()
{

Mat img = imread("c:/lenna.png", CV_LOAD_IMAGE_COLOR);

namedWindow("MyWindow", CV_WINDOW_AUTOSIZE);
imshow("MyWindow", img);

waitKey(0);
return 0;
}

Don't forget to put image to the C:/ (or wherever you might find suitable, just be sure that eclipse have read acess.
Comment: My Bad, step 14, i received this error twice in Win7 64bits, using AVG and Windows Security Essentials, i dont remember exactly wich file was throwing the error, but it was about 32% of compilation proccess, using CMake 2.8, after disabling both antivirus it finished with no errors
Comment: While executing mingw32-make on step 15 you received an error "ACCESS IS DENIED"? disable any antivirus or other software that might be locking files
Comment: Where did you get that I had "ACCESS IS DENIED" on step 15? I never had such problem (multiple installations on different computers) with procedure I described above, and I never disabled Antivirus. Also, I think you speak about step 14 not 15.
Comment: I am also using Win7 64bits and AVG but not using Windows Security Essentials. On the other hand, AVG on several occasions blocked my OpenCV C++ compiled programs, the ones that were intensely writing image frames on disk - so, yes, Antivirus software could definitely interfere...
Answer: If you installed opencv 2.4.2 then you need to change the -lopencv_core240 to -lopencv_core242
I made the same mistake.
Answer: On Windows 64bits it´s works:

Download opencv-3.0 (beta), MinGW (command line tool);
Add above respective bin folder to PATH var;
Create an folder "release" (could be any name) into ;
Into created folder, open prompt terminal and exec the below commands;
Copy and Past this command
cmake -G "MinGW Makefiles" -D CMAKE_CXX_COMPILER=mingw32-g++.exe -D WITH_IPP=OFF MAKE_MAKE_PROGRAM=mingw32-make.exe ..\
Execute this command mingw32-make
Execute this command mingw32-make install

DONE
Answer: I used the instructions in this step-by-step and it worked.
http://nenadbulatovic.blogspot.co.il/2013/07/configuring-opencv-245-eclipse-cdt-juno.html
Answer: As pointed out by @Nenad Bulatovic one has to be careful while adding libraries(19th step). one should not add any trailing spaces while adding each library line by line. otherwise mingw goes haywire.


Short story about an astronaut who discovers an injured alien

Question: I am trying to find a book of short science fiction stories that contains a short story about an astronaut crew that land on a moon or planet and one astronaut on an EVA (spacewalk) on the surface discovers a crew of three aliens next to a crashed ship. One of them injured. He sends them back to his ship sacrificing his spot aboard for them. I believe the story is called "The Samaritan".
Comment: Oh my god! I have been search for this for over 2 and a half decades! I first read the short story in an anthology of american literature when I was in grade school in Jamaica! Been searching for it ever since. Thank you! This is so divine
Comment: If you know the title, look it up on [ISFDB](http://www.isfdb.org/). There are 15 results for fiction titles containing `Samaritan`.
Comment: That is correct. The book I am looking for was an American literature book and it also had: Survivor, by Walter F. Moudy
Expendable, by Philip Dick
Answer: It sounds like The Samaritan by Richard Harper. The short story originally appeared in the Feb. 1963 issue of Boys' Life, but has appeared in several subsequent anthologies. A bibiography is available on isfdb.


Translation from the English Apex Predator?

Question: I am doing a project for a logo that intends to use the Latin translation for the term "Apex Predator". From the various web sites if have visited it appears that "Apicem Rapax" is one possible translation. Would like to ask if you can confirm this or provide a more appropriate translation.
Comment: That literally means 'a rapacious man [is doing something to] the summit'. :p
Comment: Does the person who asked this question work for 5.11 tactical? I made a purchase several months ago that came with a patch of a saber tooth tiger skeleton that's says "apicem rapax" underneath..
Answer: My suggestion is praedator summus.
The word summus means "highest", "top", "peak", "last", "supreme", "most important", and similar things.
See Lewis and Short (superus III.C) for details.
An apex predator is the last one in a food chain and at the top of the ecological structure.
I find summus to be a good description of this situation, and it also parallels the literal meaning of "apex" (basic meaning: summus = "highest").
While apex is a Latin noun, I find it more natural to use an adjective than a noun here.
Answer: Apex is a noun, and Latin cannot, unlike English, use nouns as adjectives. I don't know if there was a set phrase for this term, though I doubt it.
Praedator is where we get the word 'predator' from, and like the English, it can mean "hunter."
Apex is a metaphorical word for "top," so I'd suggest something like:
Praedator primus
Primus means "first," but it's often used to mean "best" or "top" or even "greatest," with emphasis on primacy. The chief centurion, for example, of a Roman legion was the primus pilus.


Telescopes to avoid as a beginner?

Question: I've heard people talk about "department store scopes" or "trash scopes". How do I know what to avoid in a beginner scope? How can I know that I'm not getting something we will be more frustrated with than excited about?
Answer: Avoid small refractors and reflectors on skinny tripod mounts. Don't buy from a discount or department store. Don't buy from eBay, CraigsList, or Amazon.
Here are a few web pages with good information on beginner's telescopes:
http://www.gaherty.ca/tme/TME0702_Buying_a_Telescope.pdf
http://www.scopereviews.com/begin.html
http://observers.org/beginner/j.r.f.beginner.html
For more advanced information, read Phil Harrington's Star Ware, 4th edition (Wiley).
You'll get the greatest value for your money with a Newtonian reflector on a Dobsonian mount, such as these:
http://www.telescope.com/Telescopes/Dobsonian-Telescopes/pc/1/12.uts
http://www.skywatchertelescope.net/swtinc/product.php?class1=1&class2=106
Buy from a store which specializes in telescopes and astronomy, either locally or online; don't buy from department stores, discount stores or eBay as mostly what they sell is junk. Find your local astronomy club and try out different telescopes at one of their star parties:
http://www.skyandtelescope.com/community/organizations
I strongly recommend that beginners steer clear of astrophotography until they have learned their way around the sky. Astrophotography is by far the most expensive and difficult area of amateur astronomy.
Many people who buy telescopes have no idea how to find interesting things to observe. A good introduction to finding things is NightWatch by Terence Dickinson (Firefly). A more advanced book is Star Watch by Phil Harrington (Wiley).
Comment: +1 But you should probably mention if you're self referencing your own material (your first link).
Comment: I disagree about astrophotography. Many fun things can be done easily and simply. Star trails, lunar eclipses, moon pics in general, time lapse, aurora. The idea is to have fun, not get published in Sky and Telescope.
Comment: Unfortunately, that's not what most beginners have in mind. They almost always are thinking of prime focus imaging of deep sky objects, which is about the toughest kind of astrophotography there is.
Answer: If you want to start, you may skip scopes for a while and focus on binoculars. This will allow you to get to see a little more than with naked eye, and learn your way around the sky.
Comment: tripods are also useful for showing things to people (e.g. kids) who don't know their way around the sky or might have a hard time holding even moderately strong binoculars steady due to the weight.
Comment: Is it possible to get stabilised binoculars or something? I found when using a pair of binoculars to look at craters on the moon, it required me to touch the binoculars as little as possible, as even my heart beat jogged the binoculars which prevented my eyes from focusing perfectly.
Comment: @Jonathan I have a tripod mount for my binoculars - depending on what model and brand binoculars you buy, tripod mounts are readily available.
Comment: If you can't keep a steady hand with the binocular it means that the multiplication factor is too high. You can find mounts, but as a beginner you don't need high magnification. You need instead to learn your way around the sky, and be able to spot features (like nebulas or prominent galaxies) that are hard to see with the naked eye, but are invaluable for a more advanced initial exploration. @jonathan
Answer: @Bradc asked the question as to what scopes to avoid.  The first thing to RUN from is ANY scope that states a large "X" or multiplication factor!  This is a very good clue that it won't provide useful or enjoyable viewing.  It will be small in diameter, the mount will be flimsy.  You will be looking as if by a straw!  Pointing it will be difficult, it will not track very well.  The sell cheap!  They are in hobby store windows, and on their shelves. They will only have cheap eyepieces, that are made to be easily made with poor optics and will create distortion.  The main lens is full of the chromatic aberrations, or IOW lots of colors that aren't really there.  Find someone or some group.  See what they are using to really see!  They will talk to you and show you what can be seen.  You can learn what to look for and what the costs can be expected to be.
Answer: Assuming by 'beginner scope' means 'cheap', Cheap Astronomy promotes exactly what it says on the tin, and their page on telescopes is clear about what you can and can't expect do with a cheap telescope, in terms of astrophotography etc.
The Cheap Astronomy podcasts are all excellent but definitely listen to episode 10, 'Your First Cheap Telescope'.

Telescopes to avoid as a beginner?


What are the pros and cons of different types of shifter cables?

Question:
What are the pros and cons of regular and slick gear/shifter cables? I just want easy gear changing. I have shimano gears if that helps. I know the difference between them, but I want to know some pros and cons.
What are the pros and cons the stainless steel or galvanised metal cables? I leave it in the shed at night, and when I am not using so it doesn't really get wet all the time. When I ride it often gets wet or muddy. I rarely clean the bike, so it often stays muddy.
Comment: In general, its more about the setup of the cables rather than the cables themselves (assuming they're the right type of cable - for example, never use shifter housing for brake cables) - you need clean cuts on the cable housing and proper routing as well as proper derailleur setup.
Comment: What about rust? Presumably that's the worst enemy? Would you expect e.g. stainless cable to have a longer life span than galvanised cable?
Answer: Regular cables:
Pros:

inexpensive
easy to find

cons:

generally lower quality than slick ones
much of the time they are not pre-stretched, so they have to wear in.
heavier

Slick cables:
Pros:

initially slightly faster shifting
generally come pre-stretched
lighter

cons:

(a big one) once the coating wears off, the shifting becomes A LOT worse, and the cables need to be changed. This is fairly common if the housing isn't cut right or there is bend when entering/exiting a housing stop.
very expensive
installation is harder as the cables are more fragile
adjustment is more finicky

Stainless Steel Cables:

don't rust
slightly slicker

Galvanized:

Cheaper
more bendy


Is a MySQL procedure thread safe?

Question: I am developing some websites that need to interact with a database. I will not bring here a complicated example. My question actually comes down to: Is a MySQL procedure thread safe? If one client on my site triggers a procedure, can I assume it is atomic, or could it interfere with another request from another user?
Answer: Depends on if you're using SQL transactions. Its possible, without the appropriate use of transactions and the actual serialization level, that a procedure can expose some data in a write call, for instance, that is visible to other queries / procedures before the complete procedure has completed.
in short: a given procedure will only be atomic if you use the appropriate transaction level
Comment: which transaction level will helpful for a atomic procedure?
Answer: The database will handle concurrency for you. This is normally done via transactions - any set of statements within a transaction is considered atomic and isolated from other processes. In some databases, a stored procedure will be in an implicit transaction (so you don't need to declare one) - read the documentation for your RDBMS.
Sometimes this will mean that records are locked while another process tries to use them.
You will need to write your application so it can detect such occurrences and retry.
Answer: It really depends on how your server is configured to use transactions. There are tradeoff to consider depending on how your data is used and whether or not dirty, non-repeatable, or phantom reads are acceptable for your application.
Answer: Yes.
It's the DB's job to ensure thread safety among its worker threads, and it's your job to ensure thread safety among your application threads. Since there's a separation between the DB server, and your application, you don't need to worry about thread safety in this case. MySQL's data locking mechanisms will prevent you from corrupting the data in the DB due to simultaneous access from multiple threads in your own app.
Thread safety is more about modifying data in-memory, that is also shared among multiple threads within your app. Since the DB server is its own, separate application, it basically protects you from the scenario you've outlined above.
Comment: Is a local variable in mysql stored procedure thread safe? how about is I use a connection pool with mysql?

Is a MySQL procedure thread safe?


generating 10-100 ns pulses with 20 Hz frequency

Question: For my internship, I was asked to design an LED driver circuit with <100 ns pulse width and <20 Hz frequency for driving an IR LED. It will be used for testing some photodiodes.  Therefore, I am trying to find a pulse generator circuit with very low duty cycle however I could not find any. There are many pulse generator circuits with ns pulse width but all of them has very high frequency. The closest thing I found is a retriggerable monostable multivibrator IC and it looks a little complex(http://www.ti.com/lit/ds/symlink/sn54ls123.pdf). How can I find examples of such circuits? What should I look for?
Comment: Here's an idea to get you started: http://www.linear.com/solutions/1324. One approach, like this one, is to use an arbitrary length pulse, such as one generated by a microcontroller having flexible and even adjustable inter-pulse timing, to trigger a one-shot short-pulse generator.
Comment: ha, @scanny, only an order of magnitude better than necessary!
Comment: @scanny  That looks like a good answwer to me.  Why not post it as such?
Comment: Reminds me of laser jamming/blinding circuits used to defeat police speed measurements...
Answer: When you're a programmer, every problem can be solved with a microcontroller...
Perhaps overkill, but an ATtiny4/5/9/10 (SOT23-6) running at 12 MHz can be programmed to pulse any of its three (four) I/O pins for as low as 83.3 ns at any time interval from 166 ns to over 5 seconds.
Comment: Some ATtiny's even have an internal 64MHz PLL enabling them of 32MHz "PWM" output (16ns pulse)...
Answer: There is a possible solution using delay lines. 10-TAP, TTL-INTERFACED
FIXED DELAY LINE from data delay devices, inc http://www.datadelay.com/datasheets/ddu7c.pdf The part DDU7C-100 has 10 taps with a delay of 10 ns per tap. You connect a square wave signal with < 20 Hz to the input of the delay line. To get a pulse with a length of 20 ns, you connect two taps with a delay of 20 ns between them to the inputs of an a AND gate, the first tap directly, the second tap inverted by a fast inverter. You can vary the pulse length by using different taps.
There are also programmable pulse generators: http://www.datadelay.com/datasheets/3d7608.pdf. A pulse length between 10 ns and 100 ns may be selected with a resolution of 0.25, 0.5 or 1 ns. The pulse width is programmed using a parallel interface with 8 or 12 bit.
Answer: The SN74LS123 is very simple to use, but it is to slow for your problem. You want pulses from 10 ns to 100 ns, but the typical minimum pulse width of a SN74LS123 is 116 ns. As far as I know, all other TTL multivibrators are to slow (minimum puls width) for your problem. Sorry, but I can't recommend another monostable multivibrator for your problem.