Do all AEAD implementations use symmetric key ciphers in practice?

Question: Everything I've seen so far in modern implementations (the Linux Kernel AEAD API, JVM crypto provider (AES-GCM), RFC 8439, libsodium, etc) seems to imply that only symmetric key block ciphers are used in practice for AEAD.  Are there asymmetric key algorithms that ensure authenticated encryption?
Answer: When people say "AEAD", they have symmetric schemes in mind. But conceptually, authenticated encryption is not restricted to symmetric keys. It is just the case that public key variants have not received much attention both in the literature and in practice. But there are implementations. For example, NaCl has an API for public-key authenticated encryption, based on security notions by Jee Hea An 2001. The construction is based on public-key encryption and MACs. This shows that AE in the asymmetric setting is fundamentally different from simply signing encrypted messages, as explained in the NaCL API docs:

The crypto_box function is not meant to provide non-repudiation. On the contrary: the crypto_box function guarantees repudiability. A receiver can freely modify a boxed message, and therefore cannot convince third parties that this particular message came from the sender. The sender and receiver are nevertheless protected against forgeries by other parties. In the terminology of https://groups.google.com/group/sci.crypt/msg/ec5c18b23b11d82c, crypto_box uses "public-key authenticators" rather than "public-key signatures."
Users who want public verifiability (or receiver-assisted public verifiability) should instead use signatures (or signcryption).

Apparently this API and the formalization in the paper do not include the "additional data" (AD) part of AEAD but I don't think there is a fundamental limitation. AEAD as a single primitive in the symmetric setting became popular only after 2001, so I believe Jee Hea An simply didn't think about "additional data" as a useful feature back in 2001.
I can only speculate but I believe one reason why authenticated public-key encryption has not received much attention is that (even unauthenticated) public-key encryption itself is a rarely used primitive. Public-key encryption is useful in a setting where the sender and the receiver are not online at the same time. The prominent example is e-mail encryption but unfortunately e-mail encryption never took off for various reasons (Johnny Still, Still Can't Encrypt), and protocols for e-mail security such as PGP/GPG and S/MIME conceptually separate confidentiality and authentication and implement them via public-key encryption and digital signatures (and not MACs!). Of course these can be combined ("sign-then-encrypt", "encrypt-then-sign" or "encrypt-and-sign") but the responsibility for doing so correctly is mostly pushed down to the user, and the 2001 paper shows that all of these constructions are insufficient. (One reason why PGP and S/MIME wanted signatures explicitly is that you can still have authentication for public emails, e.g., posts to public mailing lists.)
The success of the idea that we should consider authenticated encryption as single primitive with a single misuse-resistant API whose users do no need to be cryptography experts came only later in the symmetric setting after people screwed up in endless ways with constructions like "encrypt-then-MAC", "MAC-then-encrypt", "encrypt-and-MAC", which are the symmetric counterparts to the modes mentioned above. Note however that the symmetric and asymmetric settings are hard to compare when it comes to authentication, e.g., due to the mentioned subtleties with repudiability and public verifiability. MACs and signatures are very different beasts.
Comment: I felt like this should be the awarded answer due to pointing to a concrete implementation in NaCl that supports public-key authenticated encryption. Thanks for that! That said, it makes sense that _in practice_ there are very few implementations for such because of how public key crypto is used as you pointed out as well as the additional inherent complexity (two keys, etc per @maarten-bodewes) and the pitfalls with EtM, MtE, EaM schemes.
Comment: That is why it is called mutual authentication. Only the parties that have the secret key can test of the authentication. Also, additional data is very useful in networking.
Answer: AEADs are symmetric BY DEFINITION. What's more they are the base point from which we can argue the security of protocol designs.
Asymmetric authenticated encryptions schemes are known as signcrypt schemes, and PGP is probably the best-known example.
Comment: I could be wrong, but RFC 5116 is more about AEAD for network protocols rather than a formal definition/requirement for all AEAD implementations.  Also, and not that Wikipedia is any authority of course, but the [AEAD page](https://en.wikipedia.org/wiki/Authenticated_encryption) mentions symmetric key ciphers, but not as a mandatory scheme, which led me to believe that asymmetric key authenticated encryption was feasible, albeit not common, and likely not as a primitive. In any event, I'm grateful for your answer! Thank you!
Comment: P.S. Thanks for the `signcrypt` pointer - that was helpful.
Answer:
Do all AEAD implementations use symmetric key ciphers in practice?

Yes, but that's more by definition than because of unwillingness it seems.
Please note that you do require two key pairs, one for encryption and one for signing to achieve the confidentiality and message integrity / authenticity that an AEAD scheme offers. That means that any AEAD scheme for asymmetric ciphers needs to be significantly more complex than for the symmetric sense (the paper pointed to by real-or-random shows this complexity as well). Then there is the issue of trusting the public keys which may require an entire PKI. Therefore I think things like asymmetric encryption & signature generation are handled at the protocol level.
For symmetric ciphers it made sense to specify AEAD ciphers as some kind of secure drop: use this and you get authenticity for free, using a single key (mostly). Moreover, with an AEAD cipher such as GCM or one that uses Poly1305 you get a nice speedup compared to HMAC as well. That's a rather different proposition than what is required to perform authenticated encryption using asymmetric primitives.
Comment: That's a good point about the two keys.  As an [implementor](https://github.com/jwtk/jjwt) of the JWT RFC specifications (7515-7519), Encrypt-then-Mac is a supported algorithm per [RFC 7516 Appendix B](https://tools.ietf.org/html/rfc7516#appendix-B), and generated secure-random keys are double their usual length because they had to be split into two distinct keys: one for encryption, the other for hmac. (The alternative/preferred AES-GCM algorithm in those RFCs is obviously simpler and uses a single key, and is faster as you pointed out).


what is personality view?

Question: inner conversation of mind has reduced now.after a period of had stopped during meditation.is it due to Samadhi which achieved?And what is personality view?
Comment: Maybe related: [What are examples of identity-view?](https://buddhism.stackexchange.com/q/5862/254)
Answer: Inner conversation will greatly decrease in the second jhana, I'm happy you have experienced this. Yes, this is a development of Samadhi and you are on the right track. A lack of personality view basically speaking, means that you know deeply within yourself that you are simply body, feeling, mental formation, consciousness and perception. That's all, no matter how hard you look that's all you can find. and that's fine. The more developed Samadhi becomes the more the concept of personality fades. It must fade for Samadhi to arise. Keep in mind that until fully awakened you will still have a concept of personality, you need one to survive, however and any time you can turn inwards and try to look for the self or personality and find nothing, it is a very pleasant and peaceful feeling. In that moment you understand that you are everything and nothing simulatiously and nothing can touch you. The fully awakened arahant would reside continuously in this nothingness of self which would, unless he/she retreated to a forest for the lifetime, would find existing in society quite difficult. This is the final fetter of conceit the Buddha talks about. Furthermore, when one understands how personality and personality traits occur one understands them as impermanent, unsatisfactory and not self. Additionally, this is underscored and affirmed by recollecting past lives and seeing how much of a different person you were depending on different circumstances, this helps you to let go of attachment to the personality traits you have. Everything changes.
Comment: During practice even pain arises, it will goes off by noting .is it due to let go of attachment to the body?Is it non self?
Comment: I can see from another comment that you do vipassana practice. You should be aware that the Buddha did not teach this, it's simply not in the suttas. What is likely happening is that you are remaining mindful of your object and the body is relaxing enough for you to move through the jhanas. The mind settles in second jhana which feels empty and almost non-self, in the third there is very little sense of self. In the fourth personality is essential gone. 'purity of mindfulness due to equanimity'
Comment: If you are experiencing pain in your sitting, try incorporating a hatha yoga routine before sitting. The body must be strong. Letting go of attachment of the body does not cause pain, it causes pleasant feeling and satisfaction.
Answer: Personality view is seen things as internal (five aggregate) and external (five aggregate).
You perceive internal as I,me and myself and external as not me, not mine and not myself.
Comment: During vipassana practice what happened to the mind when personality goes off?
Comment: The way I understand it also gradual. At Sotapanna stage the personality view is eradicated. At Anagami stage personal identification  (attachment and aversion to Rupa) with Rupa is  eliminated. At Arhant stage personal identification (to five aggregate) is eradicated.

what is personality view?


workstation 7 and host-only no connectivity

Question: I have a WinXP 32 host (IBM T400) with VWware workstation 7 (7.0.1 build-227600) and some guest OS (Win xp, NT, etc.)
I can ping from the host to guest OS and vice versa, but... every other "protocols" do not work at all. No http from host to guest, no CIFS, nothing, nothing, nothing.
Windows firewall is turned off, TCP/IP filer is turned off.
i re-installed VMware workstation, then the networking started working again, but, after some reboots... it stopped again.
Connectivity among guest OS... it works FINE.
Can not understand... problems exist just between host and guest. Host-only or NAT... it is the same.
Any suggestion?
Answer: You might want to check to see if the ICS service (in windows services.) on the host is started - turn if off if it is.


How can I convert a laptop into a desktop?

Question: I have an old laptop that I don't really use anymore, but I think would be useful as a desktop. Are there any instructions for taking a laptop motherboard and putting it into a case and converting to a desktop?
Answer: Don't bother taking it apart - just imagine the existing laptop case is your desktop's new slim case.
1) Since you sound like you're comfortable opening it, if you do, clean the fans and cooling tubes/fins with a light bristled, non-static brush. If you don't see the fans and/or heat sink, skip this.
2) The advice about the laptop cooling device is good but can be overkill (and add to noise) if your existing fans are running fine. Especially if you can clean them out.
3) Most laptop already have a VGA out - some recent ones also had DVI out. Since yours is old, it'll probably be VGA. Note that the VGA resolution may not be the latest and greatest (i.e. it could be less than 1080p). Plug your existing monitor's VGA cable into that VGA out display.
4) Reuse your existing AC power adapter
5) Buy/reuse a keyboard, mouse
6) Power on and enjoy !!
Comment: No reason to take it apart.  Putting it into a desktop case would be difficult add no benefit.  Laptop motherboards are non-standard and can not just be screwed into a standard case.  Laptop motherboards also do not come with standard connectors to attach peripherals. You wouldnt be able to attach a new SATA drive or new video card.
Answer: It's not that simple, but possible.
Laptops motherboard isn't standardized like ATX/BTX/ITX mother boards.
Comment: AFAIK ITX is a subset of ATX…
Answer: considering a laptop is way smaller than most desktops? Set the laptop to use an external screen. Close the laptop. plug in screen, monitor ext. done. Optionally hide it someone inconspicuious
Answer: I have my laptop on a desk open, I never use its mouse or keyboard, but it is plugged in to a KVM and I use a external keyboard, mouse and monitor (Can't imagine many people who are on this site who do not have these spare lying around!), I got an USB to 2x PS2 ports off of eBay for £3 (including shipping).
I keep my laptop open because I use dual screen feature.
(I am just kicking myself as to why I spent so much on this laptop, when I should of just got a desktop, I hardly ever take it around with me!)


How can I overcome the causes of anger?

Question: When I get angry with someone, I can usually calm this feeling after some time through meditation practices.
But I'm wondering how can I overcome the causes of this 'anger' in a way that I don't get angry anymore with something?
Comment: In my experience, persistent practice of metta infuses me with loving kindness and reduces my anger. I think meta changes your nature so you don't get angry anymore. It cleanses you from any kind of negative thought. IMHO, metta should be the answer. The best way to practice metta is by chanting a Pali mantra, _sabbe sattā bhavantu sukhitattā._
Answer: Excellent that you are interested in this! You are motivated to attain Arhatship! Permanent uprooting of the poisons is achievement of Theravedin Enlightenment/Arhatship.
I will summarize the pathway in a recursive way that you can not only use for any of the three poisons (anger, greed, delusion)... but you will find will be permanently valuable for the entire path!

1st training: restrain your action by following the Eightfold path. Force yourself to follow Right Speech, Right Action, Right Livelihood no matter what!
2nd training: use anything you would use for the 2nd training, concentration. This can be a contemplation that fixates your attention away from the anger (breathing, brahmavihara, etc.)
3rd training: vipassana. Be clearly nakedly aware of the emotion as a sensation. It will dissolve.

The 3rd training is hard to do without proper advancement in 2nd training.
The 2nd training is hard to do without proper advancement in the 1st training.
The 1st training you must do or else you will sink into a lower form of existence in the next life.
Rmemember that the above method may seem like a lot in words but it's main success is in the lifestyle path you choose (animal-killers or prostitutes are not Right Livelihood and will experience more poisons than others always) and being mindful in the moment (#2 and #3), transforming the emotion. This can be a matter of a split second.
I have not referenced any lengthy suttas in this text but these are all true things said by the Buddha. I would recommend seeing the chapter on the Three Trainings within the free book Mastering the Core Teachings of the Buddha for more info and read the entire book.
Super big secrets.
Answer: how can I overcome the causes of this 'anger' in a way that I don't get angry anymore with something?
You overcome anger by being AWARE of anger.
1.When anger arises note "anger".Remember it's not your anger".It's just anger.By doing this you create detachment from it.Creating distance or space.That is usually enough to give you some gap to talk yourself out of it.
But if it persists and you find yourself struggling.Then..
2.Focus on the anger.
NOTE: Do not focus on angry thoughts,or memories or plans.When i say focus on the anger i mean focus on the physical/sensations of anger.The heat in your body,the sweat on your face,tension around your jaw,the saliva being produced in your mouth,the heat behind your ears.Be aware of your overall physical state when your angry.
Now tell me where is that anger? Show me where it is.Try to find it?So that i can mark that part of your body with a marker.We'll know who the culprit is!Is it that feeling in the back of you neck?Oh it's moved up to your head.Why is it moving around? Now it's gone down your spine.
Why is it you can feel anger so strongly but you can never seem to pinpoint it in one spot.It just moving all the time.Anger looks so big, mean and overwhelming when your not paying attention to it but once you take a closer look it seems to be reduce in size,nothing more than tiny particles swirling around different spots of your body and even then if you pay more attention you'll reduce it to nothing.It's dissolved.
We think anger is solid and permanent but it's not.When anger lurks in the deep waters of our subconscious we have a distorted view of it.It becomes an impulse that we must let out or it becomes unhealthy,it gathers momentum demanding action to be taken.But the anger is not doing this.We are.By our inability to see it clearly(ignorance).when we bring it to the surface of consciousness we see it for what it is.Just sensations arising and falling going it's own way.So the next time anger arises stay with it in this way.But if you can not then by all means practice restraint.
Answer: Like all emotions, anger is a healthy, honest, innate insight into your sense of wellbeing.
You have the right, as a human being, to feel and be angry. A therapist once told me that 'anger is your dignity', or a call from your soul to be have your sense of self valued.
That you are interested in resolving your anger in a way that is compassionate to someone is
endearing. But, denying your right to be angry is limiting your right to feel, live, and love freely.
Your anger, as unreasonable as it might seem, is coming from an honest place and is likely prompting you to change an aspect of your relationship with someone. However, acting aggressively or denying someone's feelings is not 'right action'.
To transform your anger, you may have to change the way you communicate with the 'someone' you mentioned by being more honest and being willing to be vulnerable about painful, troubling feelings. You may also have to change your relationship to your anger and the lens you view anger.
Anger is a sign of a weakened relationship, with someone else or within yourself. If you meditate on the causes of your anger, meditate to strengthen your compassion for the wound causing your anger and conditions you can create, within yourself and within the relationship with someone else. And do so to liberate your all of your strength and your relationship.
Comment: Granted I'm not that knowledgeable, but it seems to me that the only part of this which touches on a Buddhist approach is the reference to meditation and and even that doesn't seem very Buddhist to me. This seems like a conventional Western psychotherapy viewpoint.
Comment: My answer isn't traditionally Buddhist because in my experience the Buddhist teachings on anger haven't been productive. In a forum intended to communicate Buddhist teachings, it would have been best to describe sutras or philosophy innate to Buddhism.  Thanks for the comment.
Answer: Anger result due to ignorance. Ignorance of when we make sense input our perception and views makes us react to our sense input. We see, hear or feel something which we do not like or something turns out to not what we expect, we react with anger.
Hence when you get some sense input jest look at it as feeling. Bee mindful of the feeling it cause and just leave it at that without any reaction knowing that the feeling also will pass away.
If the above does not work you could try doing some loving kindness meditation.

How can I overcome the causes of anger?


Why is there a yellow light on my Wii?

Question: I have an original Wii model that I bought recently. I have never used a Wii before, and in the user manual, it says that the power light should be red when off. However, sometimes it is yellow, and I am worried that this may be a malfunction. What does the yellow light mean?
Answer: Reference to the above question: techforums.nintendo.com/thread/2328
The yellow light indicates that the Wii is off but the WiiConnect24 is on, operating in standby mode. You can turn this light off by going to (Wii Icon) > Settings > WiiConnect24 > WiiConnect24 > Off and select Confirm.
At times, you will also see the Wii's disc slot glow. This means that there is new information received over the internet (messages, new Shop content, forecast alerts, etc.), and can be adjusted, or even turned off, at any time.
Comment: It is recommended to do a system update if you leave your Wii connected.  Very early versions of the firmware will overheat the device because the fan does not turn on when the device retrieves data from the internet.
Comment: It would have been nice, however, if Nintendo had informed us in the _user manuals_ about the yellow light!
Comment: **Because the [Nintendo Wi-Fi Connection service was closed in 2014](http://www.nintendo.com/whatsnew/detail/vyWpoM6CBIe6FjW8NIY7bvzOrgBURhzw), some features of WiiConnect24 will not work.** This does not mean that the Wii can't use the internet, as such functions like the Shop Channel are still active.

Why is there a yellow light on my Wii?


Can I use PWM with hardware audio input?

Question: I know that i cannot use pwm and audio output at the same time, can I use the audio input? I want to move some servos based on an audio trigger signal.
Comment: What do you mean by audio input?  I'm ignorant in this area but was not aware of any audio input support being provided by the hardware PWM peripheral.
Comment: never mind, i thought the pi had a 4 pole jack, so it had a microphone input.
Comment: You can use a USB dongle for audio.  Also note that there are plenty of ways of providing servo suitable PWM on the Pi without using the hardware PWM peripheral.
Answer: There is no audio input on the Pi. You can use a GPIO header sound card (check here for an incomplete short list) for audio input. It is likely that you will not be able to use the PWM onboard if you use the I2S bus for the external audio input.
Comment: You could also use a run-of-the mill USB sound adapter with a mic jack.  *Most* of them should be fine, feel free to ask if you are unsure (but please don't ask "Which one should I buy?", read "Asking for specific purchasing recommendations" on the [off-topic page](http://raspberrypi.stackexchange.com/help/on-topic) first).


I want to become a salesforce developer

Question: I did my Masters in computer science but have no knowledge of any language properly, i want to become a salesforce developer, is it easy because i am network engineer but now i want to start my carrier with salesforce developer...please suggest me
Answer: I would recommend to register yourself on Salesforce Trailhead and spend sometime on developer modules.
URL: https://developer.salesforce.com/trailhead/en
Answer: There are several ways to learn Salesforce.
Use trailhead to learn salesforce : Salesforce Trailhead
Register for upcoming free webinars for quick introduction on Apex, VF and so on. Webinars
Visit Developer blogs to know about Salesforce. Blogs
Answer: Trail heads can be your basic step. Then follow some structured courses specifically based on certification.
Also note that you need to be good in Admin and Dev to become successful in salesforce. Also certification is very crucial and need to take it for success in salesforce.
I recommend you to start with Administrator Certification and then followed by Platform App builder and then Developer certification. Because the initial two certification will give you the basics and then follow your interest by taking the advance certification like Developer mode.
I recommend below sites for your reference

Trail heads - A must for the newbies and starters
Certifiedondemand - paid, but worth for that amount
Udacity - training courses free & paid
Udemy - similar to Udacity
Communities - you can google it to get access to various related communities

I want to become a salesforce developer


Checkbox dirty state

Question: I would like to highlight any changes made to a long list of form checkboxes.
That way the user can review all the changes made (whether checked or unchecked) before saving.
Are there any examples for checkbox dirty states?
I looked at material design and there is no mention there.
Any ideas?
Comment: What does highlighting the changes help the user do? Is it potentially preventing a serious problem, or is it more of an FYI?
Comment: These checkboxes can be used by multiple users during different sessions. The idea is that the user can easily distinguish between changes made during current session and other changes. For example a user might open the form and see 10/20 items have been checked. He can check 5 more. Before saving he wants to easily see which changes are going to take effect
Comment: This might be useful for your case.
[https://uxdesign.cc/new-ux-pattern-meet-the-double-check-8fc3895bebb2](https://uxdesign.cc/new-ux-pattern-meet-the-double-check-8fc3895bebb2)
Answer: You could highlight all changed items in the form in a background colour, such as Yellow. I don't know whether this is good practice, but I have seen this already.
Comment: Sadly I don't, because I saw it in an internal application which I can't publish images of.
Comment: Do you have any example?
Answer: Use a combination of versioning and element styling to highlight the changes. Since the case is, "As a user I want to learn about what's changed by myself and others", you might have a "Show changes since last login" mode that highlights each changed item - could be a background color on the checkbox and label, could be a different color font, could be a dotted line box around the changes - I'd play around and see what looks good. Perhaps the user can hover on the changed items to see who made the change. Perhaps you can include full versioning to see which changes were made each time the form was altered.
Answer: You can use a different styling on newly checked items to differentiate them from previously checked items, such as different background color, borders, or font weight. For example, you can use a background color same as or similar to the background color of the 'Save' button. That way you will be correlating updates to the saving action.

Checkbox dirty state


Why does a web server's public key certificate have to be signed by a certificate authority?

Question: In other words, what would be the security risk of not signing public key certificates by certificate authorites (from a user perspective)? I mean, the data is still encrypted... What could a man in the middle do with a non signed certificate?
Comment: They can generate their own certificate with exactly the same information. How does the user tell the difference?
Comment: @pjc50: by looking at the certificate path. A non-self-signed certificate will have a certificate path. If this path leads to a trusted root then the certificate is trusted, otherwise it isn't. You can of course add additional trusted roots yourself (I've done this for my own CA so I can easily create certificates for local use).
Answer: The purpose of SSL when used with HTTP is not just to encrypt the traffic, but also to authenticate who the owner of the website is, and that someone's been willing to invest time and money into proving the authenticity and ownership of their domain.
It's like purchasing a relationship, not just encryption, and the relationship instils, or assumes, a certain level of trust.
That said, I asked a similar question a few months ago, and the basic answer that came back was "SSL is a bit of a scam"
Comment: Certs are issued for domains. There is nothing preventing you from generating a self signed certificate, it'll just pop up a scary warning (that people won't read) because the browser doesn't trust the issuing CA. The "multiple SSL on One IP" issue has been discussed many times here. Here's a thread with a good answer http://serverfault.com/questions/73162/can-i-run-two-different-secure-sites-using-the-port-443-on-the-same-server
Comment: I thought SSL certificates were issued for IPs, not domains. Why did you need different certificates for domains hosted on the same IP? Furthermore, the Wikipedia page on HTTPS mentions it is possible to get certificates for free... The CA business really sounds like a scam to me.
Comment: Thanks Zypher, you took the words out of my mouth :) And certificates for for domains, not IP's. We have three IP addresses for three servers that serve our heaviest website, and they all have the same certificate loaded.
Answer: Imagine a situation where you are to deliver $1,000,000 to a person named John Smith you have never met or communicated with.  You are told you can meet him in a crowded public location.  When you go to meet him you will need some way to be sure that he is actually the person you are looking for, and not some other random person claiming to be John Smith.  You might ask for some government ID, a business card.  You might ask a person you trust who has actually met the John Smith for help identifying him.
A self-signed certificate uniquely identifies a system, but it doesn't do anything to prove that the system is who it claims to be.  I can easily self-sign a certificate and claim to be serverfault.com, google.com, or yourbank.com.  Certificate Authorities basically act as a third party that is trusted by the client to verify a certificate is actually valid for the name the site claims to own.
Answer: The SSL business is indeed a bit of a scam.  More than a bit, in fact, when you're paying about 20p per byte for some cryptographically-interesting data.  What you're paying for is for whichever CA you use to sign your certificate with one of their private keys after proving to themselves that you are indeed entitled to use the domain/host name that the certificate is for.  As Farseeker says, it's a trust relationship - the CA trusts you (after they've vetted you), the world's web browsers trust the CA (usually), and therefore the worlds web browsers will trust your cert.  And don't get me started about Extended Validation...


question on ていく and てくる?

Question: In the following sentence, 最近、宿題をしてこない生徒が多いです which means "Many students come to school without doing homework." why doesn't this mean "Many students don't come to school or do homework." or even "Many students do homework and don't come to school"?
Comment: Related: https://japanese.stackexchange.com/a/30534/5010
Answer: The negative in the sentence ない is used for the noun 宿題 homework hence the translation "Many students come to school without doing homework." is correct, not the other two.
If you are asking about the difference between "...ていく" and "...てくる", they are usually used as suffixes meaning "to go and do ..." and "to come and do ...". You should see this, this and also this to understand it better.
Comment: "in the sentence ない is used for the noun 宿題 homework" → Can you elaborate more on how 宿題 (or any noun in general) is connected to ない?
Answer: It never means "Many students don't come to school or do homework.", which would be something like 宿題をしなかったり来なかったりする学生が多いです.

"Many students come to school without doing homework"
"Many students do homework and don't come to school"

For these two, there are possible ambiguity, which is usually disambiguated by context and stressing (くる will be considerably weaker if in an idiom). Context always matters, because:

宿題をしてこない学生が多いです
風邪をひいてこない学生が多いです

#3 would be more likely understood as #1, but #4 as "be sick and don't come". Ambiguity in parsing is common in every language, like in a classic example "time flies like an arrow; fruit flies like a banana", where the reader is expected to solve it with common sense.
In writing, a conscientious writer would feel putting a comma (宿題をして、こない) or making it kanji (宿題をして来ない) if they really mean #2, but this is totally optional.

FYI sometimes I think that Vてくる pattern is more appropriate to be translated "one has V-ed by (the time) one gets here", in terms of where the actual focus lies.

question on ていく and てくる?


Old science fiction book about telepathy, telekinesis, pyrokinesis and mental control of insects

Question: I'm looking for a novel that I read 30 years ago (1980-1990s?) about a group of people who worked in pairs of couples as telepath/telekinetics that watched out for humans. In the book, some humans had telepathy, telekinesis, pyrokinesis or communication with insects. The humans usually had only one ability and they were fairly infrequent. The "watchers" had all these abilities and hid amongst the humans. There were a several couples of watchers that lived on Earth and I think the moon & Mars were colonized. It started out with the watchers getting involved as detectives in a murder case. The book ended with something about a voracious group of aliens (Denebs maybe?) that were coming to our system. I remember there was a metaphor of the aliens devastating regions of space like moths.
Answer: Could this be Sentinels From Space by Eric Frank Russell? There's an extensive list of mutant types mentioned in the novel including those who can influence insects. The main antagonists are the "Denebs".

Called before the World Council, Space Captain David Raven is told
  that he must stop a clandestine war being waged against Terra by
  people seeking independence for Mars and Venus. The Council's leader,
  Oswald Heraty, tells him that Humanity is on the verge of interstellar
  flight and that there have been hints of intelligent life "out there":
  Heraty wants Humanity to face any potential dangers as a unified
  society, so he doesn't want Mars and Venus gaining independence. After
  leaving the Council, David goes to see Mr. Conrad, the director of the
  Terran Security Bureau. As true telepaths, Conrad and David speak mind
  to mind. Conrad gives David a list of the twelve known types of
  mutants and notes that the clandestine war is being waged by mutants
  sabotaging Terran infrastructure.
David returns to the home that he shares with his companion, Leina,
  and shortly a team of phony police officers arrives. David switches
  bodies with the hypno and then with hypnotic power convinces the
  others on his team that David has already left. Later David reverses
  the switch and obtains from the shaken hypno the identity of the
  leader of the sabotage effort, a Venusian insectivocal named Arthur
  Kayder. Visiting Kayder, David obtains from Kayder's valet the
  information he wants on the underground base from with the saboteurs
  launch their attacks. He then goes to the spaceport and boards a ship
  bound for Venus.
Comment: Totally *Sentinels from Space*. The moth reference at the end is probably due to the particular nature of the watchers.
Answer: Almost certainly Sentinels From Space.
The reference to moths relates to a form of life after death. Humans are simply the "grubs" of a race made up of force-fields rather than material bodies.

"Now and again one [grub] more daring than the rest might have sneaked from the hiding-place of its own grub-conditioning and peered furtively into the dark and seen a great bright-eyed moth like a nocturnal butterfly beating gloriously through the endless night. And it would cower down, sorely afraid, totally unable to recognise - itself !  - - - As instinctively as a baby moves feet it is not consciously aware of possessing, or a kitten similarly puts forth claws, so did he spread forth huge, fan-shaped fields of force and swoop in the wake of his fellows - - he knew what he had become and what the little white grubs [ie humans] had yet to be. Homo In Excelsis."


Is it possible to melt diamonds into a liquid?

Question: Is it possible to melt diamonds into a liquid? I mean if you heat diamond at open air it will start to burn around 700 degrees Celsius, reacting with oxygen to produce carbon dioxide gas. In the absence of oxygen it will transform into graphite, a more stable form of carbon, long before turning into graphite. My question is, is it possible to melt diamonds into liquid? If so, then, how? If not, then why?
Comment: See this related [question about **liquid carbon**](http://chemistry.stackexchange.com/q/6068/30)… the answers include a phase diagram of carbon, which answers your question
Comment: @CURIE To avoid oxidizing the diamond, it would have to be heated in a vacuum or inert atmosphere, yes. Exposed to oxygen, it would burn completely far before it ever got close to melting. But this is not particularly special, for many substances would react with our atmosphere before melting/boiling.
Comment: "...I mean if you heat diamond at open air it will start to burn around 700 degree celsius, reacting with oxygen to produce carbon dioxide gas....." If it burns reacting with oxygen, producing carbon dioxide, then it mean there is no diamond or diamond liquid, it has all got converted into  carbon dioxide. I don't know whether what I am saying makes sense or not, but that is what I thought when I read this question. There might exist liquid diamond during heating, but it gets converted to carbon dioxide, in a specific time interval.
Answer: Liquid carbon does indeed exist, but perhaps surprisingly, relatively little is known about it. It only exists above around $4000\ \mathrm{K}$ and $100\ \mathrm{atm}$, which are not trivial conditions to sustain and probe. There certainly are many theoretical studies into the properties of liquid carbon, though. You can find a phase diagram for carbon here, though it is likely just a rough guide. The specific bonding properties of carbon atoms in the liquid phase still seems uncertain to some extent because carbon is very versatile and can create very dissimilar structures (easily seen comparing its two most common phases, graphite and diamond). This source suggests that bonding in the liquid varies continuously between linear acetylenic chains, graphite-like and diamond-like structures, depending on the exact conditions.
Edit: Now I realize that obtaining liquid carbon and melting diamonds are two slightly different things. Liquid carbon is trivial to obtain compared to melting a diamond. As you mention, heating diamond at relatively low pressures will cause it to convert into graphite before it could melt. The only way to inhibit that would be to exploit the slight difference in density between graphite and diamond; as diamond is denser, the increased pressure will stabilize it slightly, decreasing the tendency for diamond to revert back to graphite.
You'll need a lot of pressure though! Rigorously speaking, according to the phase diagram above, to obtain liquid carbon directly from melting a diamond would require a pressure of at least $10\ \mathrm{GPa}$, which is about $10^5\ \mathrm{atm}$. To put that into perspective, it's about $1/30$ of the pressure at the centre of the Earth. Amazingly, we actually can reach such absurd pressures in the lab by compressing two diamonds against each other. However, if the conditions required conditions for melting diamond (and sustaining it in molten form) are reached, it would probably compromise the integrity of the instrument and cause catastrophic (possibly explosive) failure, so I don't think anyone will be purposefully melting diamonds any time soon! Other techniques could be used (laser inertial confinement, light-gas guns, etc), but I believe most would only transiently produce liquid diamond.
Answer: Carbon, which makes up diamond, can certainly exist as a liquid and phase transition between the diamond phase and the liquid phase seems to be possible based on this phase diagram. Whether diamonds melting can actually be observed depends on the kinetics though: The phase transition may be too slow to be observed on a human time scale.
Comment: While transformation of diamond into graphite is very slow even in moderately high temp., melting isn't such a kinetically hindered thing. Over 4000 K accelerates things very much and melting happens fast or not at all.


Autoscrolling in ArcGIS Geoprocessing Results window?

Question: When checking the results window for messages while doing a lot of background processing it's rather annoying to scroll to the current message. So i was wondering if there is a trick to directly scroll to the current message line or is there such a feature in newer (>10.2) versions of ArcGIS?
Comment: You ask about "newer versions of ArcGIS" but what version are you using?
Comment: I don't follow what you mean by scrolling to the current message. Can you please post a picture of what it looks like?
Comment: While messages keep popping up in  the Results window its scrollbar stays in the same position and can only be moved to the current message manually. By current message i mean the most recent arcpy.AddMessage of a running script. So when i check on a script that runs for several hours und outputs a lot of (crucial) messages I dont want to scroll to the current message. Sorry for beeing unclear I thought the title is moreless self explanatory..
Answer: When running the script/tool in background mode, the Results window won't scroll to the latest message. This is not implemented in ArcGIS Desktop up to version 10.6, and it most likely won't be available in the upcoming versions.
Your only options are:

To use the foreground processing in ArcMap where the tool dialog window will be auto-scrolled to the latest message.
Use ArcGIS Pro where only background processing is enabled and the log auto-scrolls to the latest message.

Demo from Pro tool (with the messages being printed):
<code>for i in range(15):
    time.sleep(1)
    arcpy.AddMessage(i)
</code>
The recording:
Comment: Foreground processing isn't an option since i use 64 bit background processing (these options are related, aren't they?). So i assume it's play with what you got. But thank you for your elaborate answer!
Comment: @maxwhere, you are right, if you run a tool with 64bit background processing you won't be able to run them in foreground. Keep in mind that you could migrate to Pro at some point.


Beneficiary IRAs and Required Minimum Distributions

Question: If you receive a (non-spousal) Beneficiary-traditional IRA as a beneficiary due to death, is there a way to avoid taking a Required Minimum Distribution until your own retirement age?  Or are you always required to take an RMD regardless of your current age?
Comment: an interesting corollary of a good answer to this question may answer these questions: Can my kids inherit my IRA and not take distributions until **they** turn 70 1/2? Can they leave the unused part of the IRA to their kids on the same condition? Can taxes be thus deferred indefinitely?
Answer: The IRS does not let you defer withdrawals from a traditional IRA inherited from someone other than your spouse until your retirement age.
IRS Pub 590

If you inherit a traditional IRA from
  anyone other than your deceased
  spouse, you cannot treat the inherited
  IRA as your own. This means that you
  cannot make any contributions to the
  IRA. It also means you cannot roll
  over any amounts into or out of the
  inherited IRA. However, you can make a
  trustee-to-trustee transfer as long as
  the IRA into which amounts are being
  moved is set up and maintained in the
  name of the deceased IRA owner for the
  benefit of you as beneficiary.
Like the original owner, you
  generally will not owe tax on the
  assets in the IRA until you receive
  distributions from it. You must begin
  receiving distributions from the IRA
  under the rules for distributions that
  apply to beneficiaries.
...
If the
  beneficiary is an individual, to
  figure the required minimum
  distribution for 2010, divide the
  account balance at the end of 2009 by
  the appropriate life expectancy from
  Table I (Single Life Expectancy) in
  Appendix C
Answer: One note to add to Alex' - The RMD divisor for a beneficiary is decremented by one each year, the table is not consulted each year as an over 70-1/2 account holder (of own account) would. A small, but important, distinction.


Guitar Drummer Pa system

Question: So me and a friend have got a partial band lol.  Its me on guitar and vocals and him on the drums.  My question is how should we set up.  we usually play in my shop metal walls and concrete floors.  I just recently purchased a peavey 4 channel mixer and 2 Yamaha speakers.  We have played like 3 times with it and honestly for us not having any idea about how to place anything it doesnt sound to bad.  I just think it could be better.  Any ideas or suggestions would be greatly appreciated.
Comment: What exactly is the question? Can you be more specific?
Comment: Like our speaker placement? Usually we just kinda throw it up and play.....but should both speakers be way away from us? Is it ok that I sit beside the drummer or is this all just a personal preference?
Comment: What does it sound like to other people?  Are you planning on playing in other venues or just in the shop?
Comment: Well they say it sounds good.  For now no we will stick to the shop we are guna have to get a little better before we try playing for more people than family.
Answer: You must have seen plenty of bands in gig situations, so know how that set up works.
But for rehearsals, it doesn't have to be like that - in fact, it's often detrimental, in the early stages, if it is.
First off, in rehearsals, eye contact is essential, as is being able to hear yourself, and everyone else, clearly.
Drums don't sound so good when played in corners, so put them half-way along a flat wall. P.a. speakers can be far from each other, close to opposite walls, but unlike a gig situation, where they're for the audience, you can angle them round, so they're facing you - whether it's the two, or a bigger band with bass, keys, another guitar, etc. If they feed back, they could be swung away from being directly in line with mics. Or, you could do a rare thing - turn the volume down. Several auditions I've been to (which is a rehearsal set up, or should be), everything's been so loud, I couldn't listen to things clearly. Waste of time!
So, your amp. for now, middle of room, facing drummer, you between it and drummer. Speakers on stands (or chairs/tables for now). But really experimentation is the name of the game - try out different placings, but maybe use this template as a start point. Good luck!
Comment: Turning down the volume is an excellent idea - everything to reduce volume and noise will improve your sound and keep your ears happy and healthy. "Metal walls and concrete floors" may be problematic - try placing some old carpets on the floors and walls if you have too much noise going on.

Guitar Drummer Pa system


What is the best milk fat content for a toddler aged 2?

Question: I've read contradicting claims about whether you can give skim milk for toddlers over 2, or just low-fat.
In fact, my daughter is two and a half and only 12 kg, so our goal would be to gain weight, and she gets a better appetite after skim milk.
Should we give low-fat or skim milk?
Comment: I don't have an answer to your question, but I want to point out that full-fat milk has a content of about 3% fat, while skim milk has about 2%. I would be surprised if it makes much of a difference, really.
Comment: @Ana From skim to whole milk is a 50% calorie jump (~100 vs. ~150 for 1 cup) _via Google/USDA_
Comment: @Erica - that's indeed quite a calorie jump. My bad.
Comment: @Ana As far as I know skim milk has <1% milk and low-fat has about 2%, see here: https://en.wikipedia.org/?title=Fat_content_of_milk
Answer: Dr David Ludwig and Dr Walter Willet published a 2013 opinion column in JAMA Pediatrics that questioned the value of recommending low-fat or skim milk for children. While much of the article is behind a paywall, I did find  a discussion of the opinion column (and it was also discussed on Time).

Ludwig and Willett argued in their paper that children who don't feel
  satiated from a glass of skim milk—which contains 83 calories and no
  fat—may be inclined to eat an extra cookie or two as compared to when
  they drink whole milk, with its 8 grams of fat and 150 calories.

"We just don't see any benefit for focusing on reducing fat," Ludwig
    said. "We think it's a holdover from a paradigm that evolved in the
    late 20th century based on the relatively simplistic idea that fat has
    the most calories per gram and that eliminating fat will reduce weight
    gain."

The explanation for why skim milk is correlated to higher BMI appears to be due to the fat content. The saturated fat found in whole milk contributes to a feeling of fullness; kids who drink skim milk don't get satiated as quickly, and get hungry again more quickly.

You're coming at it from a slightly different perspective from many parents: rather than thinking about cutting down on milk fat to reduce obesity (which evidence suggests doesn't work), you seem to be thinking about using instead encouraging more calorie intake (which, from both your experience and what research seems to indicate, might work). However, from a glance at developmental charts, your daughter is about 25th percentile. That's below average, but not (as far as I can tell) underweight or failing to thrive.
If you're finding that she eats less food with whole or 2% milk because she feels full more quickly, you could also consider switching things up: serve milk partway through the meal, or as a snack between mealtimes. This is more an area of personal preference than science, though. There are fat-soluble vitamins naturally found in milk fat which need to be added back in when the fat is removed, and I personally tend towards a less-processed choice.
Comment: An aside that I found hilarious: while searching for articles on "nutrition milk fat", I turned up a number that were about what to feed your cows to increase the fat in their milk :)
Answer: This could probably be a question from your pediatrician but I could say that we gave our kids whole milk until they were about 2 then switched them to 2%.  Our boys have no problem gaining weight though.  In fact they are a little on the chubby side.  If weight gain is your goal then I would stay with whole milk for a little longer.
Comment: Thanks for your answer, but I would prefer some expert opinion/reference. Some studies show that fat milk results in weight loss and vica versa, so the situation is not that simple. Also, science is changing fast and pediatricians might not be the best at answering such questions (unlike a random person from the net ;).


Is the word "I" a dangling linguistic pointer with no actual referent?

Question: Is the word "I" a dangling linguistic pointer with no actual referent? Otherwise, what exactly is this slippery referent? Could it be possible the phrase "I am" is meaningless due to a lack of an actual referent?
Comment: Good question. Bertrand Russell, after abandoning "sense-data", asserts that the subject is a logical fiction. I can't quote it here because I don't understand it yet. But thanks for bringing it up.
Comment: Do you consider an ear and eye also fictions? As _EAR_ can not hear an ear itself, nor can an _EYE_ see the eye itself (you are thinking of mirror?). The art and power of DENYING something can not be hold by us. Thus your statement of I not existing is definitely wrong. If I would be nothing, it will be NOTHING. As long as it is something (no matter how clear) it is already NEVER nothing. Possibly Trivial?
Answer: I would start answering this by pointing out that, even if it is syntactically meaningless, it would be dangerous to assume it is semantically meaningless.  Wars have been fought over those two words, expressed in many many languages.
In the most basic parts of language, syntax catches up with semantics.  When forming a language, the need for concepts proceeds the creation of the syntax (at least it appears to do so for the early phrases).  Virtually all cultures (if not literally all cultures) support the concept of a Self (which can be exactly as slippery as you worry it is).  This concept proves useful enough that it was given a single-syllable utterance (whether as a word "I" or verb conjugation).
Consider: entire schools of philosophy have arisen to combat the question of "what is the self?" because the "self" is such a useful semantic concept to have in virtually everything we do, and yet it does prove particularly difficult to pin down to a syntactic definition.
Answer: Well, if  utter the word 'I', it's quite clear what it refers to: sequitur. If I utter 'I am', it's also quite clear what I say with my utterance: something that is true iff sequitur exists. On the other hand, if David Kaplan utters 'I am', he says something that is true exactly if David Kaplan exists.  So, no problem here: 'I' is an indexical, whose referent in any context of utterance is simply the speaker of the context. Going intensional one might also say that the intension of 'I' in some context c is simply the constant function that assigns to each possible world (or index more generally) the speaker of c. (The referent of 'I' in c is then what the intension of 'I' in c assigns to the world of the context.)
What might be confusing is the fact that Kaplan's and sequitur's uses of 'I' have something in common, a sort of standing meaning, that does not vary with context. This can't be one of the intensions Kaplan and sequitur express with their uses of 'I', since in your context 'I' does express neither the one nor the other.
Rather, this standing meaning is a rule that tells us how to get from a given context to 'I''s intension in that context. This rule can be represented by a function from contexts to intensions, which can be described as follows: It assigns to any context c the (constant) intension which assigns to any world the speaker of c. Kaplan calls this function the character of 'I'.
So now we have to layers of meaning for 'I': 'I''s contextually invariant character (operating on contexts) and 'I''s intension in a context (operating on worlds). Your confusion arises from trying to treat 'I''s character as it were 'I''s intension in a context. 'I''s intension in a context returns a definite referent for any world as argument (the context's speaker). The character, however, returns intensions which have to be evaluated in worlds.
Answer: Ernst Mach, a physicist and philosopher, was a proponent of the view that
there is no such thing as the self, the "I" and therefore that "I" has, strictly speaking, no referent.
(His theory also gives a explanation in terms of proto-evolutionary psychology of why we ordinarily think there is such a thing as the self.)
He argues this at length in the first chapter of his book The Analysis of Sensations (Die Analyse der Empfindungen, 1886/1905) which expounds his "Elemententheorie" (theory of elements) based on psychological and 'sociobiological' findings of his time.
Here is his memorable conclusion (IMO in a terrible English translation):

The primary fact is not the ego, but the elements (sensations). What was said on p. 21 as to the term " sensation " must be borne in mind. The elements constitute the I. That I have the sensation green signifies that the element green occurs in a given complex of other elements (sensations, memories). When I cease to have the sensation green, when I die, then the elements no longer occur in the ordinary, familiar association. That is all. Only an ideal mental-economical unity, not a real unity, has ceased to exist. The ego is not a definite, unalterable, sharply bounded unity. None of these attributes are important; for all vary even within the sphere of individual life; in fact their alteration is even sought after by the individual. Continuity alone is important. This view accords admirably with the position which Weismann has reached by biological investigations. […] But continuity is only a means of preparing and conserving what is contained in the ego. This content, and not the ego, is the principal thing. This content, however, is not confined to the individual. With the exception of some insignificant and valueless personal memories, it remains presented in others even after the death of the individual. The elements that make up the consciousness of a given individual are firmly connected with one another, but with those of another individual they are only feebly connected, and the connexion is only casually apparent. Contents of consciousness, however, that are of universal significance, break through these limits of the individual, and, attached of course to individuals again, can enjoy a continued existence of an impersonal, superpersonal kind, independently of the personality by means of which they were developed. To contribute to this is the greatest happiness of the artist, the scientist, the inventor, the social reformer.
The ego must be given up ["Das Ich ist unrettbar", lit. "The I cannot be rescued"]. It is partly the perception of this fact, partly the fear of it, that has given rise to the many extravagances of pessimism and optimism, and to numerous religious, ascetic, and philosophical absurdities. In the long run we shall not be able to close our eyes to this simple truth, which is the immediate outcome of psychological analysis. We shall then no longer place so high a value upon the ego, which even during the individual life greatly changes, and which, in sleep or during absorption in some idea, just in our very happiest moments, may be partially or wholly absent.
(The Analysis of Sensations, Ch. 1 slightly amended, emphasis added)

You can read/download the whole book in English translation for free (public domain):

The Analysis of Sensations and the Relation of the Physical to the Psychical (translated by Williams and Waterlow, Open Court, 1914).

More on Ernst Mach:

Ernst Mach, Wikipedia entry
Ernst Mach, SEP entry
Quotes by Mach
Comment: can you not make a similar argument to conclude that there is no referent to the words cloud, pile of dirt, country, solar system?
Comment: @nir: Yes, indeed. But with a proviso. Mach's critical target here is naive realism and folk-ontologies, i.e. entities Mach thought one could explain by evolutionary psychology. "Countries" and "solar system" wouldn't fit, I think. But he also targets more advanced notions retaining features found in folk-ontologies. Here Mach's background motivation is a general dislike of "thing"-like ontologies, which he saw as associated with an outdated mechanistic worldview. (So, in physics he thought of particle ontologies as antiquated and that wave-like models would be the next big thing.)
Comment: This is very similar to Russell's view that the sensation of colour is colour itself. Russell did not arrive at this view until his _Analysis of the Mind_ published in 1921.
Answer: Short Answer... "I" has a referent, albeit not a concrete one.
Longer Answer...
"I" can refer to a variety of things.  For instance, is "I" referring to the same thing in the following statements?

I am upset.
I will kick the ball.

In the first, "I" seems to point to a feeling agent.  In the second, it seems to point to a willing agent, or perhaps even the physical one.
On the other hand, "I" may be a logical fiction, as the hypothetical identity or substance behind the feeling, willing and physical.
However, because it's a logical fiction doesn't mean it has no referent; it's just that its referent is an abstraction.
A lot has been written on this, although much of it is in the Eastern tradition (like Buddhism).  On the more (Western) philosophical front, Bundle Theory may be a good start, and Derek Parfitt has done long treatments of this subject.
As an aside, the case of "I" being a logical fiction is actually a specific case of a more general negation of substance ontology.  That is, Bundle Theorists would point out that there is no identity beyond the perceptions we have of things, we simply give them identity as logical fictions, and the "I" is a particular instance of this, wherein we give an identity to our sensations, thoughts, possessions, etc...


CRL number generation sequence: can I use a time stamp?

Question: RFC 5280 states that the CRL number should monotonically increase. I have seen this common practice of incrementing the CRL number by 1, every time a new CRL is generated. But can I use a Unix (epoch based) time stamp as the CRL number, which is monotonically increasing ?
Comment: advantage of counter: you can be sure to not have missed a CRL in between.
Answer: Using a time stamp is certainly allowed, provided it is truly monotonically increasing. What I want to point out here is that computers have knowledge of the current date and time through their internal clock, which may be subject to drift and therefore to alterations to put it "back in line". Some systems will rely on NTP, a network protocol which is not the most secure protocol ever (in fact, base NTP is completely unauthenticated, thereby active attacker may fool with your clocks to some extent). Other CA, that try to work without relying on an unsecured network protocol, may be subject to heavy drifting over time, thereby requiring an occasional manual reset. Both the drift and the risk of human error may induce the CA into issuing a CRL with a non-monotonic number, which is a problem.
Another point to take into consideration is that "relying parties" (the systems that will read and process your CRL) may convert CRL numbers into relatively small integers, under the (faulty) assumption that "MAX" means "fits in a signed 32-bit integer". Beware of Year 2038! This would not be, technically, your fault (the RFC is clear in that respect), but it would still impact the already flimsy support for revocation.
For these reasons, a CRL counter, that is updated and saved across reboots, seems to be a better idea, from an engineering point of view.


Alien analogues to the vertebrate ear?

Question: How could an auditory organ perceive sound waves with a completely different anatomy from the vertebrate ear (e.g. canal, typanum, bones) at the same effectiveness?
Answer: It looks like stiff antennae or hairs are your best best; the most well-studied invertebrate ear seems to be the Johnston's organ, a multipurpose mechanoreceptor found in the joints of insect anatennae. A larger organism which needed to listen to a wide frequency range might require an array of different-length hairs.
Comment: Oh, a belated welcome to Worldbuilding.
Comment: According to your link, the Johnston's organ only works within one wacelength of the sound source and is used for close-range specialized purposes, not a general sound sense.
Answer: The eardrum and bones are an impedance matching device that conveys the sound in air to the underlying sense organ, the cochlea.
The cochlea works with stiff hairs reacting to pressure waves.  Do you want a different way for that to work? If hearing started underwater, that seems the most natural evolution.
The added parts to make it work efficiently in air could be different.  Could a coclea (primary sensor) be devised to naturally work in air?  That would eliminate the need for the rest of the stuff which basically serves as an adaptor.
Then you'll get different adaptations to allow the primary pressure sensor to work in air.
Another drastic difference would be to consider how a microphone works.  The cochlea mechanically does a frequency spectrum analysis. An eardrum that had a direct high-frequency sampling of its deflection would be utterly different. The nerve signal would get a waveform, which then needs to be processed by the nervous system to notice features (if not doing a spectrum). So more like how the optic nerve takes raw data and finds lines, patters, color space transform etc. The audio nerve would take a waveform either as a single point or a small window of time that the wave moves through, and does the analysis in software. It may be able to use different algorithms than we get by starting from the frequency decomposition.
Another answer (dunc123) mentioned piezoelectric crystals.  That makes me consider that a microphone system as I speculated on above may evolve from an earlier mechanism used for sensing acceleration (like our own otoliths) rather than from something like a lateral-line sense.
Comment: +1 for the high frequency sampling eardrum.  This would operate extremely well with sonar due to the huge variety of analysis that could be performed. Other auditory abilities might be present that we do not understand.
Answer: An auditory organ's job is to detect tiny movements.  If we want something truly alien then we need to think of a different way to detect those movements.  First we should look at how the ears we have work.
The vertebrate ear is a very complicated organ.  Sound waves enter the outer ear and cause the eardrum to vibrate.  This causes some small bones to vibrate which in turn cause a fluid to vibrate.  The vibrating fluid causes some hairs to vibrate.  These are attached to cells which detect the vibrations using mechanoreceptors.  In fact, these are the most sensitive mechanoreceptors in our body.  Most of our mechanoreceptors are in our skin, contributing to our sense of touch.  We often feel sounds with our skin, especially low frequency ones.
Insects and other arthropods detect sound using a chordotonal organ which can be located in all sorts of places within their body.  The basic operation of it is similar to our ear: it uses mechanoreceptors to detect vibrations.
Hearing and touch both use mechanoreceptors to detect the movements we call sound.  However we have another sense that we can use to detect sound.  We can see sound when, for example, we look at the cone of a speaker.  Eyes don't use mechanoreceptors; they use photoreceptors.
Tiny hairs surrounding the alien's eyes would vibrate in response to sound. Different hairs may respond to different frequencies. The eyes would detect the movement and transmit this to the brain.  Their eyes would need to be at least bifocal, allowing them to clearly perceive both the exceptionally close hairs and events occurring in the outside world.  Refocusing of the smaller lens would allow it to focus on different ranges of hairs, providing a band-pass filter for the alien.
Instead of observing the hairs directly vibrating the alien eye may respond to the diffraction patterns caused by light shining through their array of fine hairs. As the hairs move, so the patterns change.
Of course, they wouldn't be able to hear in the dark.  At least, not until they evolved to have ultraviolet bioluminescence in the fine eye hairs. Or behind them in the case of the diffraction detection method. This would prevent the light from interfering with vision in other wavelengths and vice versa.

"Those youngsters today never seem to take their eyebuds out.  My
  brood play their music so loud I can see the whole house vibrating!
  And the amount of glowing eye makeup they wear..."

Taste and smell are harder to use to detect the influence of sound waves.  Some type of symbiotic bacteria living within massively flared nostrils perhaps.  They would emit chemicals in response to high frequency stimulation.  An alien using this method would require exceptionally accurate response to smells and tastes.
On the other hand, deposits of piezoelectric crystals across the alien's body may generate suitable electrical signals to interface directly with their nervous system.
Comment: A *low* frequency has a very long wavelength; on the scale of a room. E.g. 80 Hz (the crossover point for speakers) comes to 4.3 meters.  How does skin feel this mechanically?
Comment: «auditory organ's job is to detect tiny movements.» pressure differences are not movement.  The link to [Johnston's organ](https://en.wikipedia.org/wiki/Johnston%27s_organ) noted by newcomer stellatedHexahedron indicates that air particle movement can be detected within about 1 wavelength from the source, and is a *near field* phenomina.
Answer: Possibly by detecting resonance on a membrane through nerve signals.
Sound is vibrations in the air, and when those waves run into things you get vibrations.
Human skin is sensitive to sound to some extent, especially low frequencies.
If the aliens membrane had a lot of nerves running through it, it could be pretty sensitive to vibrations at higher frequencies. This is similar to the human tympanum, but any structure designed to detect sound vibrations is going to work in a similar way, and so parallel evolution is to be expected.

Alien analogues to the vertebrate ear?


'Doppler redshift' Vs 'Cosmological redshift'

Question: It is not difficult to understand the differences between 'Doppler redshift' and 'Cosmological redshift' conceptually. But how do astronomers distinguish them when doing observations?
Comment: My answer to [this question](http://physics.stackexchange.com/q/154507/23473) probably covers how they remove doppler shift from cosmological shift
Comment: Patrick, is it a duplicate? http://physics.stackexchange.com/questions/113939/differentiating-the-gravitational-redshift-and-the-cosmological-redshift?rq=1
Comment: Not quite. Gravitational redshift is something different to the doppler effect.
Comment: Red shift could also be interpreted as photon frequency damping. https://physics.stackexchange.com/q/412426/97890
Answer: I think there are duplicates of this, but couldn't immediately locate them.
The answer is you cannot tell observationally whether a single redshift measurement is caused by the expansion of the universe or by something moving away rapidly.
However, if one wished to interpret the ensemble of redshifts that we see in a non-expanding universe, then you must place us at the centre of the universe. You would then have to explain why more distant galaxies are moving faster and why at very large distances, the simple Hubble law breaks down (and the microwave background and the primordial elemental abundances and so on).
Comment: Also, you can interpretcosmological redshift as the result of the integrated doppler shifts between infinitely many local frames moving at infinitesimal velocitiy differences.
Answer: Cosmological redshift can be interpreted as the accumulated Doppler redshifts between infinitely many frames of reference, each locally at rest and moving away from us at a certain velocity. So you cannot distinguish the two because they are basically different cases of the same thing.
However, as it says in @Rob Jeffries' answer above:

when looking at many galaxies in the same region of the Universe, and they all show velocities distributed around a certain average velocity away from us, and
when we see that this velocity-distance relation holds true across the sky,

we conclude that this average velocity is the expansion velocity of the Universe at that distance, and the deviations are Doppler shifts due to local proper motion of the individual galaxies.
Comment: what do you mean by accumulated Doppler ? one analyzes redshift from light coming from one particular source. Huge or small is related to the scale of the observation.
Comment: I mean that the light is Doppler-redshifted a little bit when shifting between these frames locally at rest in the expanding Universe. The many infinitesimal Doppler shifts due add up to one greater redshift which is what we measure.
Answer: Although I'm not an expert, I believe the simple answer is:
1) you can not tell them apart in individual cases
and,
2) very simply, statistically you can pick up (apparently - quite clearly and obviously) the big picture.  "Standard candles" can help and, very simply, overall averages set a picture.
I believe this is a dupe question .. Differentiating the gravitational redshift and the cosmological redshift?


Why do we need to provide false labels to the discriminator on purpose to train GANs?

Question: This is the tutorial that I used to learn about GANs. In this tutorial, it taught us to intentionally provide false labels to "fool" the discriminator, but does it make the discriminator actually inaccurate? I don't quite understand his explanation, can anyone help me?
Comment: We want to improve the G so we feed into D fake images and tell they are true in order to calculate a gradient towards real images. Take a look at the second part of [this answer](https://ai.stackexchange.com/questions/24094/what-is-the-right-way-to-train-a-generator-in-a-gan/24147#24147). I created an illustration there.
Answer:
in this tutorial, it taught us to intentionally provide false labels to "fool" the discriminator, does it make discriminator actually inaccurate?

When training GANs, the training steps for the generator and discriminator are separate:

There is a training stage for the discriminator, where it is presented with a mix of generated and real data, all correctly labelled. It is important at this stage to not update the generator (otherwise it will get worse by helping to make the fake data look more fake).

There is a training stage for the generator, where the discriminator is presented with only generated data, all labelled incorrectly as if it were real. It is important at this stage to not update the discriminator.

Typically you will alternate between the two stages frequently, making small updates to discriminator and generator separately. Some GANs use metrics to decide how much of each to do, because you don't want either the generator or discriminator to win outright and stop progress - at least at the start.
So yes there is a stage where you deliberately "fool" the discriminator, because being able to do so is the goal of the generator. However, one key detail of this stage is that the discriminator weights are not updated from that faked data. Instead the gradients from that stage are used only to update and improve the generator.
It may help if you don't think of the false labels as being "fool the discriminator", but instead they are "measure how well the generator is fooling the discriminator".


Exit node of circuit for requesting hidden service descriptor

Question: When we need a hidden service descriptor, we have to build a circuit to access a hidden service directory. Is this circuit a normal circuit, or is the third hop of the circuit an exit node?
Answer: Every aspect of accessing a hidden service takes place within the Tor network. No exit nodes need to be involved.
The process is well explained here: Tor: Hidden Service Protocol

... the client can initiate connection establishment by downloading the descriptor from the distributed hash table.  ...  the client now knows the set of introduction points and the right public key to use. Around this time, the client also creates a circuit to another randomly picked relay and asks it to act as rendezvous point by telling it a one-time secret.  ...  the client sends an introduce message including the address of the rendezvous point and the one-time secret to one of the introduction points  ...  The service creates a circuit to the rendezvous point and sends the one-time secret to it in a rendezvous message...


1 and 2 keys to change tabs in Safari (like in Opera)

Question: In Opera browser 1 and 2 keys can be used to change between tabs. Is it possible to set up this shortcut in Safari? I tried adding a "Show Previous Tab" shortcut in keyboard preferences but is does not allow me to set a shortcut without a modifier key (ctrl/alt/cmd).
Answer: You wouldn't make the shortcut from keyboard preferences. I believe that you would add this shortcut from Automator however I am not on my computer right now so I think that will work but I haven't tested this specific shortcut. If that dosent work then there is always the option of "⌘+`/⌘+Shift+' " to go to the next or previous tab. Hope this helps!
Answer: Not quite what you're asking, but I found SafariTabSwitching extension recently and am very happy with it
https://github.com/rs/SafariTabSwitching
It let's you switch tabs using Cmd-(tab number) like all other browsers.
Comment: This is part of Safari without the need for the extension, but also the extension doesn't precisely replicate the needs of the question which is that one can switch through all tabs using those two keys rather than switching to exactly tab 1 or 2.
Answer: The keyboard shortcuts to switch between tabs in Safari are cmd-shift-{ (previous tab) and cmd-shift-} (next tab).
You can also use cmd-1, cmd-2, etc. to jump to the tab that corresponds with that number, up to 8 (e.g. cmd-5 will jump to the fifth tab from the left, from whichever tab you're currently on). cmd-9 will jump to the right-most tab.


Where do adults make friends outside of work?

Question: Outside of work it seems like some adults have no social life. Can someone tell me where and how adults make friends outside of their work place?
Comment: I asked the same question here https://interpersonal.stackexchange.com/questions/16906/making-brand-new-friends-without-coming-across-as-needy
Comment: @aaron-f : to me, it could be. Or not. As I said, it's very very broad, and neither you nor me would make friends the same way or in the same kind of places. And you may not like my friends too :)) even if you're right/wrong, my original comment stands, I guess. OP really needs to narrow down to something we can answer.
Comment: Hey there! Welcome to the IPS family. This is quite a broad question, we need to know more about the situation in order to answer it completely, otherwise this is likely to get closed. Could you add some details, maybe explain why one would have troubles socializing outside of work? Do you have an example of struggles to make friends in an environment that is not related to work? Feel free to ask if you need help, and have a great time around!
Comment: Hi SomeBloke, and welcome to IPS. As interesting as this question can be, it doesn't really fit the requirements of this stack. It seems **very** broad, and can be *opinion-based*, because it depends on so many factors, including the personality. That's why I'm voting to close this question, and if this happens, it'll give you more time to edit/improve it. Please take the tour (again?) and read some meta posts about good questions. Thanks.
Comment: @OldPadawan when I read the question, rather than asking "how do people make friends?", it sounded to me like the OP is not yet an adult, and wants to know how making friends is different for adults compared to children. Would an answer that suggests that making friends as adults is not all that different to making friends as children, be ok?
Answer: There's lots of different ways. Johanna has mentioned a few already.
I would suggest additionally that when looking for activities, try and pick something that is reflective of:

Your personal interests
The kinds of people you want to meet

In regards to the first: Say you enjoy literature and reading. Join a book club. Do you enjoy the great outdoors? Join a bushwalking club (this is a thing in Australia maybe not elsewhere.) Some activities will lend better for this than others. For example you might join a gym. Some gyms have a particular focus on both fitness and fostering a social environment for it's members.
Regarding the second: Different places will lead you to meeting different kinds of people. Have a think about particular acitivities, the general age group that will be taking part, and decide with that in mind.
Extra Note: I would urge you to try a few different things outside your normal habitual hobbies and hobbies not common in your workplace. It will increase the chances of meeting people different to yourself and from outside any of your standard work circles.
Comment: Answering broad questions is discouraged on IPS, as it leads to broad answers as well. May I ask you to review your answer after OP edits their question to make it less broad?
Comment: It wasn't flagged as broad when I answered it. But your point still stands so yes I will.


Offering a compressed file for download that's around 1.2 GB, should we split it into smaller parts?

Question: The file contains thousands of PDFs and will be posted on a government website. The primary audience is researchers and the media, desktop, not mobile. We plan to indicate the filesize. Given 1.2 gb is pretty big, are there any reasons we should split the file into smaller parts? Asking because I'm just not sure.
Comment: Is it necessary that all files be downloaded together? Or is it just a case where the client is lazy to not create a proper library and dump everything together in a compressed folder? Are you asking about the technical restrictions of downloads?
Answer: I think you should split the file into smaller parts, but not necessarily by file type but how the user consume them.
Lets say your file contains documentation and media files for Java. PDF, Video, Images , and Code file all make up to 1.2 GB. You might wanna provide them as:

Table of Contents
Core Java
Advanced Java
Java books
Java Tutorial Series
Download all - 20 minutes to download based upon 1mbps connection

All the items should be individually downloadable but user should be able to download it as package.
Answer: I occasionally use large datasets for analysis and appreciate being able to download everything in one go. There are, however, a couple of points which helps usability a lot:

Check that pause and resume download works in chrome/safari (it will usually just work on a normal web-server or CDN).
Provide a plain HTML-link to the file without authentication. Allow the user to download using alternative tools such as WGET or Curl easily.
Don´t do cache-busting (Web servers are good at handling static files and won´t mess this up by default).

A few gigabytes is a non-issue for most people in 2019.
Cheers,
Answer: I've worked on .GOV and GDS.
You should start by discovering what the user needs are.
"As a user I need all the thousands of files because of X" as opposed to "as a user I need access to thousands of files I can search and browse as a resource" are very different and will greatly affect your solution.
My gut feeling is 1GB file (zip) of all PDFs is a total no-no.
But do your research.
Comment: I wouldn't class it as an outright no-no; I've encountered situations where I've wanted to download what amounted to several GB of documents. However, in every case where that was a possibility, the documents were stored uncompressed, and I added the ones I wanted to a 'basket', which was then compressed on-the-fly for download.
Comment: Without going into too much detail, we have done the research and there is a use case for providing a compressed file with all the PDFs. But, my gut feeling is similar to yours in terms of the file size, and I'd like some thoughts around what considerations we should take into account.
Comment: then you can have an option to "download all files" but it's very much a secondary option. Your interface should be geared around display a list of PDFs the user can pick and choose from.
Answer: Provide both an all inclusive download and smaller organized sets.
Many users may decide to download the whole thing, but it is not unimaginable that someone may need only a few files from such a large dataset.
For example, what if Alice mentions to Bob that she is looking for statistics on X event. Bob remembers that those figures can be found in a set of 50 PDFs from your download. Without finer grain control, Alice now has to wait for thousands of files to download just to get the 50 she needs.