According to "continuationists" what explains the 1900 year hiatus?

Question: Do "continuationists" (who believe that the signs and wonders of Acts 2 never ceased) explain the apparent 1900 year hiatus as divine sovereignty dispensing early rain then and latter rain now or as 1900 years of a lack of faith and/or understanding?
Answer: I'm a Continualist.    Continualism is the just the assumption that the supernatural gifts never disappeared from the Church in the way that Cessionists describe (People who claim that the gifts "died out with the original apostles").    Many traditional Christians like Orthodox and Catholics are defacto unofficial continualists by virtue of their official theology (they believe in saints through history have done various miracles and possessed other supernatural gifts of healing, prophesy etc.).
There are different opinions on the Pentecostal revival:
A) Some see it as being a legitimate work of the Holy Spirit.   (This is some of the reason why the Catholic Charismatic movement took place during the time of Vatican II of the 1960s where Ecumenicism between Protestants was also under way.   Catholics began attending Full Gospel churches and brought Pentecostalism back with them in their Churches.    This made the bishops nervous but was ultimately accepted by the Church hierarchy as something that was beneficial to the Church, but they started their own movement within Catholicism so Catholics would not adopt other Protestant beliefs that were at odds with official dogma and the Magisterium).
B) Others like many Eastern Orthodox will interpret it as being a kind of delusion.   There is a Russian Orthodox term known as Prelest (Spiritual Delusion) that describes when demons grant supernatural gifts to people to feed their pride and so that they may lead themselves and others into heresy and eventual destruction.  That sort of opinion is common among Eastern Orthodox. A monk who convert to Orthodoxy (from Buddhism) named Seraphim Rose wrote a number of anti-Charismatic books and pamphlets.   There however are a number of converts to Orthodoxy who come from Pentecostal and Charismatic churches.  Some of these people have even become clergy, writers and pundits in the Orthodox Church.   Anyway some of these formerly Charismatic Orthodox,believe the movement to be positve, but also flawed or incomplete (Their background set the stage for them to seek Orthodoxy where they claim to have found "The Fullness of the Faith").
C) Personally I believe the Pentecostal revival is something that is both Spiritual (Of God and at times Satan), but also "Socially Constructed".    By Socially Constructed, I mean the assumption that "spiritual gifts disappeared until 1900" is a reality that was originally created by believing in the assumptions of Cessionism (That I believe are historically and Biblically wrong).    So in other words, it was not that the Gifts totally disappeared, but that Protestants have made an interpretation of history in that direction (By ignoring and disregarding the Church History, and hagiographies of Ancient and Medieval times etc.)
Comment: Okay, so I understand you to not be describing a "new outpouring" but rather "a lack of faith/understanding". If you would that that is the general view of "continuationists" (which I think is more of an uncapitalized designation) then I'll accept that as an answer.
Answer: It may be that the polemic of the early 20th-century Pentecostals led them to make more of the supposed hiatus than there actually was, since history shows us that there was no 1900-year hiatus. While some Church Fathers might have denied the perpetuity of the Gifts, at least part of this was a reaction to the excesses of Montanism. On the other hand, other Church Fathers mentioned the entire panoply of NT charismata.
Irenaeus, 2nd century: "Others have foreknowledge of things to come: they see visions, and utter prophetic expressions. Others still, heal the sick by laying their hands of them, and they are made whole."  (Source: Philip Schaff, Irenaeus Against Heresies Ante-Nicene: 100-325, Vol. 2 of The History of the Christian Church, Grand Rapids: Eerdmans, 1973, p. 531)
Novatian, 3rd century: "This is He who places the prophets in the Church, instructs teachers, directs tongues, gives powers and healings, does wonderful works, offers discrimination of spirits, affords powers of government, suggest counsels, and orders and arranges whatever other gifts, there are of charismata; and thus makes the Lord's church everywhere, and in all, perfected, and completed."  (Source: Philip Schaff, "Treatise Concerning the Trinity, XXIX," Ante-Nicene: 100-325, vol. 2 of The History of the Christian Church, Grand Rapids: Eerdmans, 1973, p. 641)
Of course, Augustine's move away from apparent cessationism in the 5th century is well documented.
The question of the seeming relative paucity of supernatural manifestations has, I think, many answers, among which are probably:

Lack of faith
Lack of teaching and models
Gradual move away in general from lay involvement in ministry
Coldness, which was John Wesley's explanation
Reaction by the Reformers against spurious folk Catholic miracles, etc.
Answer: There are many eschatological systems. The one to which I subscribe (a historicist position) interprets the letters to the seven churches in Revelation as a schema for the church age. Select Individual believers and churches were faithful throughout history, but the church at large lurches between different spritual weaknesses and fads in each age. The sixth age, corresponding to the church of Philadelphia, was the age of the Reformation and extensive foreign missions, from roughly 1450 to 1950. Its faithfulness was accompanied by (or accomplished by) a fresh outpouring of God's spirit. This difference between the church ages accounts for the relative paucity or plenitude of spiritual gifts. They never ceased, but they did vary greatly in how commonly they were expressed in the church.

7 "To the angel of the church in Philadelphia write:
These are the words of him who is holy and true, who holds the key of
  David. What he opens no one can shut, and what he shuts no one can
  open. 8 I know your deeds. See, I have placed before you an open door
  that no one can shut. I know that you have little strength, yet you
  have kept my word and have not denied my name. 9 I will make those who
  are of the synagogue of Satan, who claim to be Jews though they are
  not, but are liars—I will make them come and fall down at your feet
  and acknowledge that I have loved you. 10 Since you have kept my
  command to endure patiently, I will also keep you from the hour of
  trial that is going to come on the whole world to test the inhabitants
  of the earth.
11 I am coming soon. Hold on to what you have, so that no one will
  take your crown. 12 The one who is victorious I will make a pillar in
  the temple of my God. Never again will they leave it. I will write on
  them the name of my God and the name of the city of my God, the new
  Jerusalem, which is coming down out of heaven from my God; and I will
  also write on them my new name. 13 Whoever has ears, let them hear
  what the Spirit says to the churches.

If this position is correct, then the current age is the church of Laodicea, the lukewarm church. True expressions of the gifts will greatly diminish in frequency, provoking prideful people to either counterfeit them in order to avoid admitting their true spiritual condition or deny that they ever happened in the past.
I do not exempt myself. When I was younger, I suffered many nightmares, falsely attributing them to God and believing them to be prophetic. When I searched my own heart through prayer and the light of scripture and rejected this "gift", I was delivered from the nightmares (and a measure of my pride). Years later I was able to enjoy some supernatural fruit of the spirit, but never so much as my proud imagination once thought I possessed, and certainly not prophecies that I could use to command or manipulate other people with for my own elevation. Thus I do not deny the gifts, but neither do I deny the temptation to succumb to unhealthy, possibly demonic influences. We want power, plain and simple. God wants humility.


Are you allowed to ask follow-up questions or duplicate questions if there were no satisfactory answers?

Question: Are things like follow-up questions or duplicate questions if there were no satisfactory answers, permissible on this site?
Answer: No. If its your own question, a bounty is the right way, assuming you have the reputation. If you want to add more helpful, relevant details, go ahead (Thats to say, don't edit to bump. Edit to include more relevant information).
If its a related tangential question, sufficiently distinct to warrant its own question, you can refer back to the old one, but if you're trying to get attention by re-asking, no, thats not the best way to do it
Comment: @JoshZmijewski A good (tactical) edit can often be in the form of re-writing the title. The more descriptive unique words that flow together and describe your problem, the better. Helps to guarantee that the ideal person sees it.
Comment: Okay, thank you for clarifying the rules.
Comment: If it's another user's question, a bounty can help as well.


How do you restrict specific content types per user role

Question: I'm trying to restrict specific content types per user role so that some users can only edit certain content. I've tried configuring content access module but can't seem to restrict content types.
Comment: Check with the drupal default permissions /admin/people/permissions. For each content type and based on role, you can set permissions to create,edit or delete a content.
Answer: You can set the permissions for each content type and role with Drupals default permissions.
Go to /admin/people/permissions there is a section called Node where you can set the individual permissions for each content type:

Create new content
Edit own content
Edit any content
Delete own content
Delete any content

Keep in mind that the permission Bypass content access control overrides the access restrictions of the individual content types. So if a role has this permission, the user can view, edit and delete all content.
Answer: You do it by using Rules module:

Add a rule when user view nodes
Select content type where you want to view content for specific user role
In action add component or action to redirection i.e 301 user or show message Access denied


App to take notes and save sources

Question: I'm working on a research project and ideally, looking for something that would allow me to type notes and save / easily pull up the webpages where the information was obtained from. I don't want to manually put links in the text to avoid clutter. Is there an app for Mac that can do this seamlessly? Thank you!
Comment: Browser bookmarks usually offer a comment field for notes, so that would be the simplest match. Sorry, but your description is a bit vague.
Comment: Thank you for the suggestion. I am looking for something that connects to note taking. Say, an app where I could write "The Empire State Building is located in New York" and be easily able to access a website that supports this fact by hovering over or clicking on part of this text or something like that.
Answer: I believe that both Microsoft OneNote and Evernote offers features that meet your criteria.
Another serious tool for this kind of thing is DEVONthink. I haven't personally used it, but I found the following article to be very persuasive.
https://medium.com/@YRousse/quitting-evernote-adopting-devonthink-608472d9f455
Good luck!
Answer: I would try Evernote.
Evernote has a webclipper that you can use on chrome. It let's you clip articles by taking a screenshot - annotating it, extracting simple text, or bookmark. It saves the link source.
On the app itself(web, mac, mobile) you can highlight text, edit, link to other notes you create or clip. There are so many features that I think would benefit your research.
Here is a list of all their features.
Answer: I would suggest you use the Note app that comes with the system software. This app appears in your dock. I leave it open whenever I'm on my iMac. If I need to make a note I click the app in the dock and it brings up my current note page. I can quickly type my note there. If I highlight a word in the app and then right click, it will do internet searches on that word if you wish. This app can also store everything on iCloud so available on iPhone and iPad if desired.
Answer: Quiver
is great for this, my go-to  note app

App to take notes and save sources


Is it possible to get a specific .onion domain or a domain containing a certain string?

Question: I am trying to create an Onion Service however in the configuration guide it appears that Tor generates a random .onion url for each service so I was wondering if there was a way to get a particular .onion url or one containing a specific string or set of words.
Comment: also worth to look at https://security.stackexchange.com/q/29772/64549
Answer: There are ways to get custom .onion addresses that begin with particular strings.  I have most recently found Scallion to be the easiest to use.  Scallion is an open-source project on Github that has been around for awhile and has full instructions for use in the readme.
https://github.com/lachesis/scallion
After you have generated your vanity hostname and private key, you'll replace the files hostname and private_key in the /var/lib/tor/hidden_service/ folder of your server and restart the service.  If you did it correctly, your hidden service will be accessible over your vanity onion address.


2003 Honda Civic LX won't start

Question: My car will not start and when I do turn the key forward to a certain point the 5 pin main relay starts clicking rapidly and the automatic transmission shift lever solenoid goes crazy with the plunger going in/out rapidly also the dash lights start flickering. There isn't any power to anything else and when I tried turning the headlights on it start making a weird buzzing noise without the lights coming on. So far I've replaced the main relays and ignition switch with no results.
Answer: Have you checked the battery? properly charged and the connections and terminals? I would start there.
Then, check all the earths or grounds between engine / body, engine / battery and body / battery as the next step. Then you are probably into looking at the feeds from the battery to the major components and controls.
Comment: yes, i replaced the battery, checked the connections and terminals after cleaning them with no results
Comment: Is there some event that happened with this vehicle lately? Like floating around in Houston?
Comment: What is the voltage measured over the battery terminals at the moment of all of this craziness?
Comment: @MaSlo as it is nearly a year ago, you would think the OP has either solved it or dumped it ...

2003 Honda Civic LX won't start


Do 親切な (taisetsuna?) really exists?

Question: From a basic Japanese book I'm reading, I found that word in a vocabulary table. Now I'm having problems finding that word using Google, jisho.org, etc. I can find 大切な (taisetsuna) and that kanji sequence Is what I get if I type the romaji in Windows or Linux, but I don't see the other word as an option.
Answer: The word in the title of your question is not 大切{たいせつ}, it is 親切{しんせつ}.
If you look 親切 up in jisho.org, you should discover that: 親切 on jisho.org
Comment: Then what is wrong is the romaji for the word in the vocabulary table of my book. It says TAISETSU-NA when they should said SHINSETSU-NA. As the meaning of the word 親切 at jisho.org matches the one of the book. Only the romaji differs. How do you put the furigana above your kanji?
Comment: You put it in curly braces after the kanji, like this: {しんせつ}
Comment: @HatoruHansou I assume it's a misprint.  (Even good books probably have one or two mistakes here or there.)
Comment: Now I'm sure it is.

Do 親切な (taisetsuna?) really exists?


In what ways did the Insular Indic languages morphologically diverge from Maharashthri Prakrit?

Question: Maharashtri Prakrit is the antecedent southern zone language to all insular Indic languages. What are some characteristics, morphologically speaking, which differentiate these insular languages from their continental counterparts?
Comment: Is the descendance of Singhala from Marashtri Prakrit established now? My rather old knowledge is that Singhala is so mixed up that its regional descend from the Indian subcontinent cannot be determined.
Answer: Sinhala has borrowed lot of words and terms from Tamil,which is a member of Dravidian language division.That peculiarity you observed is mainly due to the above reason.
But Sinhala still maintains a rich vocabulary full of Sanskrit and Magadhi.
Comment: The question asks about morphological features: are they the same, or are they different?


First item in Global Navigation is always current site

Question: I am trying change the order of the Global Navigation in SharePoint 2010. I notice that the current site is the fixed even though in Navigation under "Global Navigation", there is nothing. I am trying to add a new item, the root site, and have that be first.
Answer: If i'm not wrong, the default SharePoint navigation use 2 levels menu. It means that if you would like to use root site as a start point, you will have the same menu as in parent site. if this is true for you, you can simply activate publishing features. After activation you can find out that the Look and Feel section contains Navigation option. If you click on this link you will be redirected to the page where you can customize navigation. Also you can set navigation inheritance from parent site.
Comment: I have publishing feature enabled but my problem is that in my subsite the first menu item is the current site and whatever link I add in Global Navigation, the current site is always first. I would like to change that order but am unable under Navigation because the current site link does not appear.
Comment: I updated my answer. As can you see I use display the same navigation items as the parent site option in subsite. Does it solve your problem or I miss something?
Comment: Thanks, but I can't inherit the navigation, because my subsite's navigation is diferent on purpose. I just want the order to appear as `Home | subsite`, per your example. All I have been able to do is `subsite | Home | OtherLink`
Comment: In this case you should configure navigation by hand. In the **Global Navigation** section choose **Display the navigation items below the current site**, then in the **Navigation Editing and Sorting** section you should choose **Global Navigation folder** in the right size of the page and use **Add Heading** button. If you have a lot of sites that should be customized, you can use PowerShell or create your own feature.


Has there been research done regarding processing speech then building a "speaker profile" based off the processed speech?

Question: Has there been research done regarding processing speech then building a "speaker profile" based off the processed speech? Things like matching the voice with a speaker profile and matching speech patterns and wordage for the speaker profile would be examples of building the profile. Basically, building a model of an individual based solely off speech. Any examples of this being implemented would be greatly appreciated.
Comment: NNs are pretty powerful for this problem. Check this: https://deepmind.com/blog/wavenet-generative-model-raw-audio/ and the implementation here: https://github.com/ibab/tensorflow-wavenet
Answer: Yes, there is. A quick search found this:
Multimodal Speaker Identification Based on Text and Speech (2008).
In the abstract, they write

This paper proposes a novel method for speaker identification based on both speech utterances and their transcribed text. The transcribed text of each speaker's utterance is processed by the probabilistic latent semantic indexing (PLSI) that offers a powerful means to model each speaker's vocabulary employing a number of hidden topics, which are closely related to his/her identity, function, or expertise. Melfrequency cepstral coefficients (MFCCs) are extracted from each speech frame and their dynamic range is quantized to a number of predefined bins in order to compute MFCC local histograms for each speech utterance, which is time-aligned with the transcribed text. Two identity scores are independently computed by the PLSI applied to the text and the nearest neighbor classifier applied to the local MFCC histograms. It is demonstrated that a convex combination of the two scores is more accurate than the individual scores on speaker identification experiments conducted on broadcast news of the RT-03 MDE Training Data Text and Annotations corpus distributed by the Linguistic Data Consortium.

Under figure 2, they write

Identification rate versus Probe ID when 44 speakers are employed. Average identification rates for (a) PLSI: 69%; (b) MFCCs: 66%; (c) Both: 67%.

In section 4, they write

To demonstrate the proposed multimodal speaker identification algorithm, experiments are conducted on broadcast news (BN) collected within the DARPA Efficient, Affordable, Reusable Speech-to-Text (EARS) Program in Metadata Extraction (MDE).

If you need more papers related, you could use a tool like https://the.iris.ai/ to find related papers.
Answer: Speaker identification is quite widely researched domain. Modern approach would be to map speaker information to i-vector, a real-valued vector of 200-400 components that characterizes speaker fully. i-vectors allow very precise speaker identification and verification.
For more information you can check i-vector tutorial
Also you can check state of the art in the results of NIST i-vector challenge
For implementation, you can check the following speaker recognition experiment from Kaldi.
For best accuracy i-vectors are extracted with DNN UBMs, watch out that GMM UBMs are less accurate.
For more in-depth information about speaker recognition methods and algorithms check this textbook.
Answer: Deepmind recently created a voice synthesiser along those lines.
It seems to be incredibly slow, but it might be possible to create a dumped down version of it.
Apparently the task is called parametric TTS (text to speech). This overview might give you some leads.


What are the reasons for this radial piston engine shut down procedure?

Question: In a radial piston engine, before the engine is shut down the rpm is brought to a considerable high power setting of approximately 1950 rpm. This is to burn the unburnt carbon in the spark plugs. Are there other reasons for this specific power setting to be selected before the engine shuts down?
Comment: What engine are you talking about?  Your statement indicates this is a general procedure with radials, but it's news to me.  I've operated an R-985, and you kill it from idle or just above idle, like any other engine. 1950 rpm is around cruise rpm for a 985.
Answer: No Sir, radials do not get run at 1950 RPM before shutdown. That is a higher power setting than a good runup. But it is true that the idle RPM is brought up to around 1000 RPM for a while and the purpose is not to burn the plugs clean -although it couldn't hurt- but to scavenge oil that has pooled in the engine case during idle operation and return it to the oil tank. These engines have a dry sump system where the oil is stored in a reservoir and distributed to the case for lubrication of engine parts, then sucked up by scavenge lines and returned to the oil reservoir. You don't want excess oil sitting in the engine case after shutdown since it can seep into the lower cylinders and cause a hydraulic lock on startup. Source: I operated R-985, R-1340, R-1820, R-1830, R-2600 and R2800's.
Answer: It could also be to remove lead deposits from the spark plugs. Some avgas has an agent added to remove lead deposits, this only works above a certain temperature which is achieved above a certain RPM. We had to do a similar procedure in the Cessna 152.

As you will know, Avgas 100LL contains a compound known as Tetra Ethyl
Lead (TEL) which acts as an octane booster for the fuel. This results
in a fuel which is commonly known as a 100 Octane lean mixture and 130
rich mixture Performance Number fuel.
In practice it is even better than this, with ratings more like 106
lean mixture & 130 rich mixture which are far in excess of the
comparable 85 - 87 octane of road fuels. To achieve this a lot of TEL
is used - around 5 times the quantity that was used in the old Leaded
automotive fuels.
This increase in octane allows aviation engines to produce more power
through increased compression ratios or alternatively by increasing
the inlet pressure by using a turbo or a supercharger. The problem
with using Leaded fuels is that they will always burn with more
deposits than unleaded fuels.
The Tetra Ethyl Lead used for octane boost in the fuel naturally
degrades to form Lead Oxide when it is burned. In reality it is this
oxide which gives the octane boost. The problem is that Lead Oxide is
a solid up to about 900 deg C which is well within the wall
temperatures inside a piston engine.
In order to prevent these deposits from forming, a Lead scavenging
compound is added to Avgas 100LL - this compound is Ethylene
Dibromide. This scavenger is designed to react with the Lead oxide to
form Lead Bromide which is more volatile - becoming a gas at around
200 - 250 oC. This is a low enough temperature to ensure that the Lead
is removed from the engine as a gas end it subsequently goes back to
the solid phase as the exhaust gas cools in the atmosphere.
As a point of interest the pale brown / ash coloured staining that is
often seen leading from the exhausts of high powered engines, such as
those found on the warbirds, is in fact Lead Bromide.
To enable this reaction between the Lead Oxide and the scavenger to
work, there needs to be a relatively high combustion temperature.....

Read more at this link.


Jumping from Drupal 5 to 7

Question: I still have a few sites running on Drupal 5, and I'd rather upgrade directly to 7 when it comes out. I figure it's probably not going to be a supported upgrade path, but still, has anyone tried this (with the betas or RCs), and what should I look out for?
Answer: AFAIK, you cannot upgrade from 5 to 7 in one step. You will have to upgrade to the latest version of D6 first and then upgrade to D7.
With every major version of Drupal, the API changes and contributed modules come and go. That makes upgrading a more difficult task than simply replacing files and running update.php. You will sometimes have to choose which contributed modules you're going to upgrade to, and if you have custom code (modules and/or themes) you will have to adapt it. If you're upgrading from 5 to 7, you need go through that process twice.
Depending on your site and the amount of content and settings you have stored in your database, it may be easier for you to build your D7 site from scratch and then import your existing content using Migrate module.
Of course, regardless of the method you choose: backup, backup, backup before you do anything.
Comment: I'd just add that despite the [#D7CX pledge](http://cyrve.com/d7cx) you might find that you have to wait a while (or help out yourself) after the D7 release before all the modules you're interested in are ready for D7. Also, coming from D5 you might find that some modules aren't being ported to D7.
Comment: Some of the modules I use weren't even ported to D6 in any usable way if at all (project.module I'm looking at you). Otherwise I would have bumped to D6 a while ago.
Answer:
AFAIK, you cannot upgrade from 5 to 7
  in one step. You will have to upgrade
  to the latest version of D6 first and
  then upgrade to D7.

The man who says "It can't be done" is often interrupted by the man who says, "I JUST DID IT" :) To wit:
Nathan Haug: "Direct Drupal 5 to Drupal 7 Migration in 24hrs"
Comment: The TL;DR of the article is "start over and then migrate content". Not exactly a proper upgrade path, although it'll probably be how I do things in the end.

Jumping from Drupal 5 to 7


call graphs for solidity smart contracts

Question: Do we have some open source tools where we can get call graphs for solidity smart contracts execution ? For ex: Suppose Function A in contract C calls some other function B so the graph should contain an edge from A-> B with the parameters that passed from A to B.
Also is there a way to get access  the exact parameter values that are passed between function calls during smart contract execution in a remix browser or truffle ?
Comment: What kind of graphs are you looking for?
Comment: i want to make graphs showing which functions calls or can call other functions by doing a analysis of the smart contracts...
Answer: There's a tool by ConsenSys called surya.
It has option ftrace to create a text represtation of the calls to a function. An example from their readme file:
surya ftrace APMRegistry::_newRepo all MyContract.sol


Parameterized External Content Types?

Question: Suppose I have multiple instances of some line of business app in my environment. Is there a way to create a single External Content Type that can be parametrized and reused? If I have 5 instances, is it necessary to create 5 external lists and 5 external content types, or can the lists indicate which data source should be used?
Comment: can you give an example (in business terms) of how these content types would be parameterized?
Comment: Can I have a single Extenal Content Type called 'customer' when the California customers are in a db on one server and the New York customers are in another? Can the target of a ECT be parameterized as long as the schema is identical?
Comment: oh, I get it - same schema, different database connections.  That's a great question. I would probably just create the separate ECTs, but I'd be interested to hear if there is a solution out there.
Answer: I think the best approach in this case would be to do the CRUD routing at the web-service/stored procedure level.
Alternatively you could write the models in Visual Studio and build logic into the CRUD methods to determine where the record should end up.
Depends where you feel more comfortable placing your business logic, if this is going to be common practice then I would say webservice.

Parameterized External Content Types?


Use of cryptographic hash for computing previous block hashes in blockchains

Question: Why is the previous block hash computed using a cryptographic hash function instead of a regular hash function in Bitcoin and other blockchains?
What cryptographic hash properties (pre-image resistance, second pre-image resistance and collision resistance) are needed and why?
Answer: Collision resistance and pre-image resistance, both first and second, are important for Bitcoin. This answer may not apply to all blockchain instances.
Collision resistance is important for the property of distibuted consensus.

In bitcoin mining, the inputs for the function are all of the most recent, not-yet-confirmed transactions (along with some additional inputs relating to the timestamp and a reference to the previous block).

Think about what would happen if there were more than one input that could hash to the same value.
Preimage resistance is important to the mining process, and by extension to the strength of the consensus which is mined into the blockchain.
Each bitcoin block contains a nonce. The job of miners is to find a nonce value such that the resulting hash of the block contains a certain number of leading zeros. The number of zeroes corresponds to the difficulty of mining the blockchain. Without pre-image resistance, and depending upon the difficulty of finding a pre-image, it could be possible for miners to find a nonce value with less difficulty than by exhaustively enumerating the nonce field. If it were very easy to mine the blockchain, in particular if one group had a significant advantage in doing so, then they could launch an attack in which they control the majority of the hashing power of the bitcoin network. .
Finally, second pre-image resistance is necessary for the same reason as collision resistance. If a second input could be found which matched one of the block hash values then there would be uncertainty about the canonical state of the blockchain.
Comment: **Mining** heavily relies on preimage resistance. It essentially *consists* of finding an input of a certain form whose hash has a specific property. This could be sped up using a preimage attack on the hash function.


Relationship between SOV word order and osV prefixes

Question: I've been reading about the Native American language isolate Washo, and looking at the Universals Archive. If an ergative language is SOV, the object and subject affixes will be prefixes and the main or only alternative order will be OSV. But why is the prefix order osV rather than soV? If the subject and object prefixes are reductions of independent pronouns (and in Washo, they seem to be), one would anticipate soV from SOV.
Comment: Please give genetic information about Washo in your question.  Please also say what sources you have consulted on the language and where your data comes from.  Do you have reason to believe that the osv morphology developed at a stage in the language when the word order was SOV?  It could correspond to an earlier stage (e.g. SVO, with leftward movement of object pronouns).  Note that in general, pronouns and DPs needn't occupy the same positions, as many languages with clitic pronouns demonstrate.
Comment: @Aaron - Washo is a Native American language, an isolate in the Hokan group - and yes, I know that not the original meaning of "isolate". My knowledge of Washo comes from Jacobsen's *Beginning Washo* and the Washo Project website (some people don't have access to JSTOR). I was using Washo as an example of an SOV language with osV prefix order.
Comment: Just out of curiosity: how important is word order in Washo? Does it have any grammatical meaning like in English?
Comment: In what phrase would such agreement prefixes be generated? vP? IP? Could it be a case of strong agreement features necessitating the raising of the object to specIP? This would predict an OSV surface order. Of course, this would require some rule allowing the subject to raise to specCP to obtain the observed SOV surface order.
Answer: You make a number of assertions that appear to be unfounded/misguided:

The only possible alternative to an Ergative SOV language is OSV.

This is a highly unlikely assertion considering that OSV, OVS, and VOS languages together are attested in <5% of the world's languages.
Also, the idea that Ergative/Nominative distinctions would be tied to constituent order is at the very least, confusing.

So what you've asserted about the language is that:

The verb is marked using prefixes (head-marking), and;
These prefixes convey the role of the arguments to be Ergative/Absolutive.
The clause constituent order would be either SOV or OSV.
The affixes are reductions of grammatical pronouns which were, at some point in the past, realised by full lexical items.

From this, I would draw the conclusions:

The verb is so marked because the Subject argument is always obligatory (or a pro-drop, which you have not specified), whereas the Object argument is not always present, as in the case of single-argument predicates.
If word order was important, then in this case, the fact that the verb is final would mean that the arguments of the verb would appear to its left. This means that the Subject would be said after the Object, resulting in the o-s-V construction.
As for the language now becomeing SOV, I have no explanation (as well as very little familiarity with the language itself). However, I will say that the "unmarked" order in the world's languages (where word order is significant) appears to be one where the Subject precedes the Object: English (SVO), French (SOV), Irish (VSO).

This is probably, again, for pragmatic reasons; the Subject is the most salient argument in the predicate, it needs to be expressed, whereas the Object, and sometimes even the process, can be inferred from context.
Comment: I don't fully understand why you say the subject would be said after the object.
Comment: Yeah, I clearly check this often enough. Sorry, let me clarify: I've assumed the assertions that the OP posted are correct.


Animation deforms in Unity

Question: I've imported a character into Unity for a college project and for some bizarre reason, the legs of my character 'squash upwards' when his idle animation plays, either in-game or in the preview window. If I load my character up in Blender though, the animation is perfectly fine. Nothing deforms incorrectly. I'm not sure what the problem is or how I could fix it. I've also tried exporting it as an FBX file, but the animations flicker or the character completely disappears when they play.
Answer: Select bones. CTRL+A (apply transformation), play animation on Blender. It will deform. This is the same result you see in Unity. Delete your animation. Correct and regenerate (re animate) your bones. Now, if you export, unity will see them correctly.
You ALWAYS need to ZERO (freeze), CTRL A (apply transformations) To anything you do in rigging before start animation.
Comment: Okay, thanks. It's something I'll need to bare in mind for the future. What's odd though is that if I solo the idle animation in Blender, save and copy it over to Unity, the animation plays fine. It's only when I have my idle and jump animations that it does it. Thankfully the idle animation isn't that difficult to do, so I'll give it a go.

Animation deforms in Unity


Store movies/tv shows from iTunes on external drive

Question: I'd like to store only movies and tv shows on my external drive. I don't mind keeping my music on my built-in drive. Is there a way to set iTunes so that it only looks for the videos rather than all media?
Answer: Use TuneSpan. Here's an article I wrote about it.


Ogr Python API: set null values in feature

Question: Im trying to convert OGR geodata from one driver to another, like the command line tool ogr2ogr do, but using the python API.
My problem is, that the NULL values in the input data are converted as "None" string in the output data.
The Ogr SetField method:
output_feature.SetField('linetype',None)

does not set the attribute 'linetype' =  None (or null) in the output feature, as expected, but "None" as string.
I tested this with PostgreSQL and GeoJson driver, but probably affected all drivers.
Complete code sample from here:
outDriver = ogr.GetDriverByName("GeoJson")
outDataSource = outDriver.CreateDataSource('test.geojson')
outLayer = outDataSource.CreateLayer("test_layer")

# Add an name field
idField = ogr.FieldDefn("name", ogr.OFTString)
outLayer.CreateField(idField)

point = ogr.Geometry(ogr.wkbPoint)
point.AddPoint(1198054.34, 648493.09)

# Create the feature and set values
featureDefn = outLayer.GetLayerDefn()

#feature 1
feature_1 = ogr.Feature(featureDefn)
feature_1.SetGeometry(point)
feature_1.SetField("name", 'name_1')
outLayer.CreateFeature(feature_1)

#feature 2, name attribute should be NULL but is saved as "None" (string)
feature_2 = ogr.Feature(featureDefn)
feature_2.SetGeometry(point)
feature_2.SetField("name", None)
outLayer.CreateFeature(feature_2)

# Close DataSource
outDataSource.Destroy()

Comment: I suppose that for setting field to null you should use  OGRFeature::UnsetField.
Answer: I had the same issue. My solution was to test if the value is None before using the SetField() method. This avoids going back and forth to set and unset the value.
        field_value = in_feature.GetField(self.fields_name[x])
        if not field_value == None :
            out_feature.SetField(self.fields_name[x], in_feature.GetField(self.fields_name[x]))


Can I upgrade to newer groupsets despite my frame not supporting internal cable routing?

Question: I was given a 5 year old bike with alloy frame with an old Sora groupset and I'm planning to upgrade to the newer Shimano 105 r7000 groupset. Apart from my Shimano R500 wheelset(which I know only supports up to 10 speed) do I need to change anything else? Also my frame does not have internal cable routing, will that be a problem? TIA.
Comment: Speaking of your wheelset, the Shimano HG700 and HG800 cassettes will fit on the 10s freehub. I have on of these on a 10s hub. The issue is that they are 11-34 only, and the jumps between cogs are fairly large. This may be an irritant in a group ride when you're trying to find your optimal cadence at the group's speed. It may be less of an annoyance solo. It will definitely give you a very low low gear, but it will require the mid cage rear derailleur.
Answer: Internal cable routing is not a requirement, as long as you have functional cable stops on your the frame, you should be able to cable up a newer cable group set without issue. In fact it should be easier than internal able routing, which can be quite fiddly to get the cabling to pass through restrictions.
The primary advantage of internal routing is aesthetics, followed by straighter cable lines and less maintenance (because of protection). The latter two are possible, but are not a guarantee with internally routed cables as it largely depends on the design of the frame, and some of the recent internal routing schemes are clearly prioritizing electronic shifting over internal cables.
A good example of the importance of implementation, is my winter road/summer gravel bike, which has decent internal cabling lines and for the most part is well sealed against the external environment, except for one weak spot which allowed water to dribble into the rear shift housing and pool inside the internal tubing by the bottom bracket. The pooling also brought fine grit and eventually cause  shifting to deteriorate substantially. It took me a while to track down the problem as this small area was hard to access and I only determined the issue after replacing all the internal tubing (as a last ditch effort).
With externally routed cabling I would have been able to track down and fix much easier, as it is easy to access all points.  If you ride in poor conditions, and you don't have full length external cabling, there are also ways to better seal external routed shift cables (e.g., Shimano's cable end cap seals) making external routing more robust to poor conditions.
That just leaves aesthetics as the primary benefit of internal cable routing, and maybe straighter cable lines, but recent frame design seems to be negating this positive.


Can I exceed the rated voltage of a motor if I limit its current?

Question: I have a mini motor that's rated at 3 volts. Does this mean that the 3 is the number of volts that will produce the desired amperage for the motor? Could I technically make it work by plugging it into a 10,000 volt circuit and add resistance until it's at the same amperage as it would be for 3 volts?
Comment: If the load torque increases, the motor current increases, and the motor voltage will decrease due to additional voltage drop across the resistor
Comment: If you put a resistor between your 10000V supply and your 3V motor, you're no longer feeding 10000V to the motor.
Comment: Remember that motor current draw can go from almost infinite (when stalled) to BELOW ZERO (when outside force is applied, the motor will become generator). No constant resistor can have same voltage drop at currents ranging from infinity to zero.
Comment: @Agent_L: the stall current is finite and equal to the voltage applied divided by the winding resistance. Almost infinite is really stretching it.
Comment: @user42875 yeah, it is stretching - but winding resistance is extremely small compared to regular operating conditions.
Answer: No, motors don't work that way.
Generally speaking, the voltage that you apply to a motor determines the speed at which it runs, but the current that it draws depends on the mechanical load (torque) that it is driving.
If you applied 10,000 V to a 3-V motor, even through a resistor, it would try to spin far too fast, probably destroying itself.
Comment: Depends on what it is driving. If the load is something like a fan or propeller which has increasing drag with speed then rpm (and motor voltage) will stabilize at the same point it would have done on fixed voltage at the same current. Without a load the motor will speed up until it reaches the speed and voltage that produces the same no-load current - probably way too high so the motor will over-speed and destroy itself.
Comment: But isn't it the number amps that the motor cares about? I thought that there wouldn't be a difference if I plugged it into a 3V circuit with 10 Ohms of resistance compared to a 10,000V circuit with ~33333V Ohms of resistance, since the number of amps would be the same.
Comment: @Justsomeguy: For motors, the amount of amps it draws depends on the amount of volts you supply to it.. motors don't work like other things. If there's not enough amps the motor will simply stall (stop spinning, though the stopping may be momentary so you may see it as stuttering instead of actually stopping). So what may happen is that the motor will try to spin too fast, stall, try to spin too fast, stall completely and stop and at that point you've basically connected your + and - terminals to a length of copper wire (the motor coil) and whatever is limiting the current will fry
Answer: Although in theory that works, it is not practical ... at all.
Let's say your load is 10 Ohms (Making this simple) and it is rated for 10V. This would yield a current of 1A. So let's say I have 10,000V available and want 1A to run through my load, I would add let's say a 10,000 Ohm resistor in series which yields approximately 1A.
Even though this work, now let's talk about power.
$$P = I \cdot V = I^2R$$
For the 10 Ohm resistor, we would dissipate \$P = 1^2 \cdot 10 = 10 \;watts\$. Where in the 10,000 Ohm resistor we would dissipate \$P = 1^2 \cdot 10,000 = 10,000 \;watts\$.
Of course this is not desirable because our power transfer is terrible. We would like maximum power delivered to our load. Therefore we often use a transformer to step down the voltage to an appropriate level.
Of course motors are not resistors (Real and imaginary loads), but the demonstration works for this question. Motors are built with coils, behaving like an inductive load and can't be treated exactly like a resistor. Either way, it is best to deliver maximum power to your load or else you will be wasting valuable energy in your 10,000 Ohm resistor.
Hope that helps, please comment if you have further questions.
Comment: Please don't assume I downvoted your answer, I would not do such a thing. Especially when I do not disagree with your answer.
Comment: This is actually a rather poor answer. Rather than talking about "maximum power", you should be talking about efficiency. The problem is not that the load is not getting enough power (Pout is too low), but rather that you're wasting a lot of input power in the process (Pin is too high). And besides, motors and resistors are very different, but not in the way you describe -- it has a lot to do with back-EMF and very little to do with inductance.
Comment: OK, I apologize and withdraw the comment.
Comment: I am aware that we are interested in efficiency, that is why I mentioned a lot of energy would be wasted in the 10k resistor. I mention the inductance property purely for a basic answer, and just indicating that the motor cannot be treated like a resistor.
Answer: Short answer: not in practice. Long answer:
Effects of voltage and current
Voltage and current ratings generally protect against independent failure mechanisms, in most cases respectively insulation breakdown (especially for semiconductors), and damage due to excessive Joule heating.
Understanding motors
Some components are more flexible than others around their voltage and current rating, up to what is called "absolute maximum" ratings. DC motors are of that kind. Increase the voltage and the power of the motor will increase (meaning, either more speed for a given torque, or more torque for a given speed) - that is, assuming the motor can draw the current it needs. This means that the current is only limited by limiting the voltage across the motor (this is also true for other devices, it can be seen on current limiting power supplies).
You could run a 3V motor at probably 12V with a giant heatsink to make sure the heat gets away faster than it heats up the wires (otherwise they'll melt); however you cannot run such a motor at 10,000V because 1) the insulation will break, increasing drastically the current drawn by the motor 2) whether the insulation broke or not, the current will be so high the wires will melt. Note that depending on the shaft alignment and the bearings, too high a voltage may generate too much vibration and destroy the motor before the heat melts the coil.
Limiting via power resistor
Now, you suggest adding a device to drop the voltage from 10000V to 3V. That would make the motor happy: as long as it gets 3V across it, it will draw current up to its stall current and hopefully it has been designed to cope with that current. However, you are dropping 9997V. If any current is drawn through the device that drops that voltage, this is power that has to be dissipated somehow. 9997*I, even if I is as low as 50mA is 500W... To put that into perspective, 5W aluminium clad resistors are about as big as a finger. Note that power resistors will only drop a fixed voltage at a given current: change the mechanical load on the motor and the voltage across the motor will change, this will lead to unstability... Assuming a 200k resistor for a design current of 50mA, +/-15uA will have a +/-3V effect on the motor! Not to mention that 500W are wasted for 0.15W used.
Limiting via buck converter
You would need a converter with a better efficiency, like buck DC DC converters. Theoretically, they do not drop the voltage themselves, but switch between full voltage and no voltage to achieve the required voltage in average (in this case, the motor inductance filters the current, which filters the voltage via the motor resistance). However, this means switching ON 0.03% of the time - the motor inductance will give you how long full voltage can be applied for before the current is too high, and that will not be long. Therefore 0.03% of that time will be very short, chances are no converters will be able to. The vibrations of the motor due to the high current ripple would probably ruin the motor and its load anyway.
Footnotes
Whether a power resistor or a switching converter is considered, both will have to have 10,000V insulation, which means your product will be huge to respect the creepage distances and insulators thicknesses.
Unless you mean 10,000VAC from the supply grid to 3VDC? In that case, you will have to use a step down transformer and then a rectifier, but I genuinely hope that you know what you are doing.
Answer: Depends on what your goal is. If you want relatively constant speed with varying loads, then a constant voltage source (or even slightly negative series resistance) is best. The motor will be happy unless you load the shaft too heavily, provided you give it no more than the rated voltage. Too heavy a load and it will overheat.
If you want a constant torque with varying loads, then a constant current source is best. The motor will be happy unless you load the shaft too lightly, provided you give it no more than the rated run current. Too light a load and the RPM will wind up and it could damage itself (the motor voltage will exceed the rated voltage under those conditions). A large series resistor behaves more like a constant current source. A >10K source resistance source is easily simulated electronically without the very high voltage and insane resistor.
In reference to your original question, in neither case are you actually exceeding the rated voltage at the motor terminals (the only thing the motor cares about).
Comment: What is negative series resistance?
Comment: @ScottSeidman Output voltage goes up *slightly* as current draw increases, so it behaves like an ideal voltage source in series with negative value resistor. Not a physical negative resistor, of course. The total resistance in the loop should be positive for stability.
Comment: @SpehroPefhany: Motors behave interestingly when the loop resistance goes negative. >:*3  If the net loop resistance is exactly zero, applying a certain amount of torque will cause the motor to produce equal and opposite torque, thus remaining where it is.  If it's slightly positive, the motor will produce opposing torque that's not quite sufficient to prevent it from moving.  If it's negative, the motor will produce opposing torque which makes it turn in the direction opposite the applied torque, which can be fun as long as the motor is always free to move.
Answer: Motors can be damaged by exceeding any of the following maxima:

Mechanical force on components thereof (may cause instant failure)
Amount of magnetic flux (may cause instant failure)
Rotational speed, vibration, etc. (may greatly accelerate wear, or in some cases generate forces resulting in instant failure)
Amount of heat generation in the windings (intermittent operation may allow motor to tolerate more power (heat/second) than sustained)
Amount of heat generated in the bearings (intermittent operation may allow motor to tolerate power (heat/second) than sustained).

It may be possible for a "3-volt" motor to be operated safely at higher voltages under some conditions if those conditions reduce the stress factor which was limited operation to 3 volts and do not raise any other stress factor enough to cause trouble.  What's important is not keeping the motor voltage below the rating, but ensuring that all of the other stress factors stay within their corresponding limits.
Comment: Insulation breakdown is another possibility
Answer: A motor, electrically speaking, is somewhat like an inductor (ignoring any motor loading effects). Inductors resist any change in current so when you apply a voltage to the inductor (read motor), the current will initially be zero but rise exponentially (see http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indtra.html). This results in the full 10,000 volts (assuming you could apply this instantaneously) being applied across the motor windings for a short period of time regardless of what resistor value you use. The high voltage would likely breakdown the winding insulation and result in short circuits across the motor windings.
Practically speaking, a circuit using 10,000 V and a resistor to drive a 3 V motor would be hugely inefficient. The motor current will depend on how much the motor is being loaded. In other words if you selected a resistor that would give 3 V across the motor at no motor load, then added some mechanical load, the voltage across the motor would drop because its trying to draw more current. This would slow the motor down and it would try to draw more current reducing the voltage further and eventually stalling the motor at much less than its rated torque.


Very few research groups: continue doing PhD in this area?

Question: For a PhD in computer science or informatics, are there good reasons not to choose an area of research in which very few (3 or 4) known (small- to middle-sized) research groups work in the world?
Comment: I guess it might help to specify some more details..
Comment: Well. I think it is better to do my a PhD in an "active research area". But how is this determined? Basically by the amount of related literature. However, my supervisor advised me to check how many research groups (and dedicated conferences) are actively working in my research area. Actually there are only few research groups, but several professional ones.
Answer:
are there good reasons not to choose an area of research in which very few people work worldwide?

There might be.

a research clique might be at work: sometimes, often unintentionally, you can observe a bunch of researchers starting to push some topic and ending up absorbed in their own little world proposing extensions of extensions of extensions and not noticing that they became irrelevant. Usually because something is wrong with the problem they work on. But sometimes such a niche might be actually very healthy, except the topic did not caught up more popularity in the relevant mainstream community.
something might be wrong with the problem they tackle: sometimes a group of absorbed (as above) researchers looses connection with reality and pushes towards solving a problem which does not exist anymore because somebody else solved it just by the way along a route to some other problem and everybody else recognized.
something might be wrong with the method the small group applies to the problem they tackle: sometimes the problem is good (see below), but the bunch tries to hopelessly push a method which simply does not yield anything. Often this is accompanied with use of a highly specialized terminology so that it is difficult to see that the method they use and the problem they tackle is in fact very much related to something else what yields more healthy research in the relevant mainstream community.

More generally, don't worry about the size of the field. What matters is whether the problem at the core of the niche is real and sound. Real means that solving it can have an impact on the society at large. You need to believe in your cause. For the sake of this blob, let sound mean that you see a solid way to articulate it and get a grip on it, most preferably including a method to measure progress. If you have the two, you are set even if the community tackling the problem is relatively small. All the rest is up to your capabilities and the difficulty level of the problem.
Trust your judgement.
Answer: One key thing is that there might be no open position for your to continue your line of research, if you wish to.
But here it is an important question, whether there are growing, or are in decline. And, more importantly, if you like and believe in this field.
Otherwise importance of the problem they are solving lies on a different axis than number of groups. Not every important topic is popular (and vice versa).


Is this possible to show the custom userprofile property in user info list without populating values to the property?

Question: I have created two custom userprofile property  , I marked it as replicable to show that property in user info list. My custom property is showing in user information list after when that property have values and profile sync. I am not sure  whether this is default. Is this possible to show the properties in user information list without populating the values?
Answer: Try to manually run the profile synchronization jobs by running the stsadm sync command:
stsadm –o sync

If the information is not synced, try using the following stsadm sync command which will only delete the sync info using PowerShell, then start SharePoint Full Synchronization job again:
stsadm –o sync –listolddatabases <x number of days>
stsadm –o sync –deleteolddatabases <x number of days>

The first command will list Content Databases that have not been synchronized since n days.
The second command will delete the records corresponding to those databases. It doesn't delete databases/end user data.


What is better in Vue, v-if or v-show?

Question: I'm working in a project with Vue 2. I need to know in which case the performance is better: when using v-if or v-show?
I have a long list and each item's list has a form hidden that I need show and hide to click a button that has each item list.
What is better: a toggle class of v-show or add and remove the form with v-if?
Comment: https://vuejs.org/v2/guide/conditional.html#v-if-vs-v-show
Comment: v-if : for conditional rendering ;
v-show : for conditional display/toggle
Answer: tl;dr
Assuming the question is strictly about performance:

v-show: expensive initial load, cheap toggling,
v-if: cheap initial load, expensive toggling.

Evan You provided a more in depth answer at VueJS Forum

v-show always compiles and renders everything - it simply adds the "display: none" style to the element. It has a higher initial load cost, but toggling is very cheap.
Incomparison, v-if is truely conditional: it is lazy, so if its initial condition is false, it won't even do anything. This can be good for initial load time. When the condition is true, v-if will then compile and render its content. Toggling a v-if block actually tearsdown everything inside it, e.g. Components inside v-if are acually destroyed and re-created when toggled, so toggling a huge v-if block can be more expensive than v-show.
Comment: The link is broken.
Answer: Short answer:
Use v-if if the condition won't change that often.
Use v-show if you want to toggle the condition more often.
Note: v-show does not remove the element from the DOM if your condition is false. So people can see it when they inspect your page.
Answer: Adding that usage of 'v-if' can have unexpected consequences, since it connects and disconnects elements from the DOM instead of modifying the elements' display.
For example, if you use it on a form and end up toggling that form off using v-if, you will receive this browser console warning:
    "Form submission canceled because the form is not connected"

If you use 'v-show', you won't encounter this problem.
Answer: v-show just only toggles display property of CSS(either "none" or "block").
When we use v-show the HTML DOM will be on the page only(with the "display" property).
But where as if we use v-if it removes the entire DOM from the page or recreates the entire DOM based on the condition.
Check this example.

If Check

Show Check
 //try to set "ok" by true and false and inspect HTML

Answer: I find a blog that can explain carefully your question:
https://learnvue.co/tutorials/v-if-vs-v-show.
As my experience:

use v-show: if you need to toggle something frequently.
use v-if: the conditional does not change that frequently during the runtime.

Note: a form should use v-show if you don't want to make any breaks.
Answer: V-show
It will load/render all the element in the DOM at once and if the value is false v-show="false" then it will set the element's display to "none"
V-if
It will not load/render the element until the condition is met and renders element as condition is met
Answer: v-if:          add or remove your element.

v-show:          change visible css attibute.

if toggle often, v-show is better. otherwise, we use v-if(since css cost initial load time).
Comment: Your answer does not add anything new to the question, because info you have provided already exists in other answers.

What is better in Vue, v-if or v-show?


Drawing tangent vectors to the Bloch sphere with qutip

Question: I need to plot drawings of qubit dynamics on the Bloch sphere. I know QuTip allows to do such drawings but I specifically need to represent evolution velocities on the Bloch sphere so I need to draw tangent vectors. Is there a way I can do it with QuTip? More generally it would be good to be able to draw affine vectors with QuTip. Do you know of any way I can do it? If this cannot be done with QuTip do you know of any other software that allows me to do it?
Comment: so you are essentially asking how to draw tangent vectors on a sphere? It's fairly easy with Mathematica, see e.g. [this answer](https://mathematica.stackexchange.com/a/9522/27539). [This answer](https://mathematica.stackexchange.com/a/125986/27539) also gives a way to draw the Bloch sphere with MMA.
Comment: Thanks you very much. I am doing in Mathematica right now. But I was also interested to know if there is a way to do it remaining in the qutip environment.
Answer: First of all, qutip is not a visualisation library, even though it does provide some visualisation functionalities, mostly leveraging matplotlib.
However, because qutip does provide handy functionalities to plot Bloch spheres and points on it, it does make sense to ask how one can tweak such functionalities to for example add tangent vectors to the bloch sphere.
Reading the relevant doc page, this functionality does not seem to have been implemented.
However, having a look at the relevant source code, it does not seem particularly difficult to add manually additional vectors to the Bloch sphere.
In particular, at least in the current version of qutip, the vectors are added via the method plot_vectors, which creates the arrows using an Arrow3D object.
One can add any other vector to the sphere by simply adding new Arrow3D objects to the underlying matplotlib axes object.
Here is an example of how to do this:
import matplotlib.pyplot as plt
%matplotlib inline
import qutip
b = qutip.Bloch()
b.render(b.fig, b.axes)
new_arrow = qutip.bloch.Arrow3D(xs=[1, 1], ys=[0, .5], zs=[0, .5],
                    mutation_scale=b.vector_mutation,
                    lw=b.vector_width, arrowstyle=b.vector_style, color='blue')
b.axes.add_artist(new_arrow)

which gives

note that we need to call explicitly b.render instead of b.show because we need the axes object to be created but the plot to not be drawn before we add the new arrow.
Just change the coordinates given to the parameters xs, ys, zs to decide what vectors to draw.
As a final more or less unrelated note, you might also be interested in the drawing library plotly, which allows to build very nice 3d plots (see e.g. these examples).
Comment: You might want to add (as parameter to the `Arrow` object) a `zorder=6` if the arrow is in-between the 2 half spheres or `zorder=8` if it is in front.


2007 bmw 318i on red temp gauge within 5 minutes of starting

Question: On start up is fine but within 5 minutes on red temp gauge, have checked oil water coolant doesn't appear to have any leaks
Comment: Any codes? Could be a faulty sensor or damage to wiring - get it checked - overheating can cause expensive damage.
Answer: When the temp gauge goes up into the red, lift the hood and look, and touch gently: is the motor hot?
If the motor isn't overheating, then the temperature gauge, wiring, or coolant sensor is faulty.
If, on the other hand, the motor is indeed overheating, then the thermostat has failed closed, or the waterpump has failed, or the waterpump drive belt has failed, or one of the coolant hoses or radiator has failed internally and is obstructing the flow of coolant.
@Solar Mike is quite correct: excessive heat can quickly  and seriously damage the motor.


What are the strengths of the Hierarchical Temporal Memory model compared to competing models?

Question: What are the strengths of the Hierarchical Temporal Memory model compared to competing models such as 'traditional' Neural Networks as used in deep learning? And for those strengths are there other available models that aren't as bogged down by patents?
Answer: IMO, the greatest "strength" of HTM is that it is modeled after the human neocortex, which is the most intelligent thing we know of.
But to understand the importance of this simple idea one must contrast it with the most familiar form of AI - Neural Networks (NNs).
Traditional Neural Network AI has been under development for a long time and has many more people working on it than HTM. NNs are capable of performing a bewildering number of tasks, and the list of its accomplishments grows with every passing day.
However, NNs are not thinking. They perform their magic only after being trained on (typically) massive amounts of training data. Training a NN is essentially an advanced form of curve-fitting. If your training data encompasses closely enough what it encounters in new data then it will likely perform very well. However, if it encounters something new (which is sometimes difficult to know beforehand) then it can fail abysmally, and often in a way that humans would never fail.
One example I heard about was on a NN trained on millions of images that could briefly describe what was in new images it had never seen before. It performed fabulously - something like 95-97% accuracy. However, when it was shown an image of a baby holding a toothbrush, it said, "A boy holding a baseball bat." This is not a human-like error. Humans know the difference between a boy and a baby, and a bat and a toothbrush. This is just an example, but it reveals a fundamental problem of NNs - they are not thinking. Useful? Yes. Thinking? No.
Back to HTM. HTM is new and currently has only a handful of researchers working on it. It is "better" than NNs in only a small number of cases - it has a long way to go.
So if by "strengths" you're thinking about what tasks can currently be done better with HTM than with NNs, then most people should still chose NNs.
However, if by "strengths" you're thinking about what has the best chance of achieving general intelligence someday, then I would say hands-down it is HTM.
Answer: HTM is a credible theory about how the brain works, and how brain-like systems could be constructed in software. It includes:

SDR (Sparse Distributed Representation), a means for representing just about any kind of sensory, intermediate or motor data, innately noise resistant and suited to recognising patterns
TM (Temporal Memory), which can recognise SDRs in the context of other preceding SDRs, to learn new patterns "on the job" with no separate training phase
SM (Sequence Memory), which can learn, remember and replay arbitrarily long sequences of SDRs.

ANNs are mature, commercially valuable pattern recognisers made possible by the confluence of vast amounts of computing power, data and commercial opportunity.
HTM is immature and just a fascinating toy, for now. But HTM might just put us on the path to the Holy Grail, true artificial general intelligence, and ANNs will never do that.
Comment: Hi. I've never heard of "sequence memory" in the context of TM. Are you sure you're using the appropriate term here? Can you cite a paper that describes the sequence memory?
Comment: @nbro: I'm glad you asked: https://numenta.com/neuroscience-research/research-publications/papers/continuous-online-sequence-learning-with-an-unsupervised-neural-network-model/. ;-)
Comment: But isn't sequence memory the same thing as temporal memory? Maybe you meant spatial pooler as opposed to one of these two?
Comment: @nbro: Related but distinct is my take. But it is hard to find reliable, consistent, authoritative definitions for these terms.


How error scales with numerical precision in molecular dynamics?

Question: In terms of time-step, numerical error in molecular dynamics scales with square, i.e. $error  \approx dt^2$. But how it look for numerical precision ? E.g. how much bigger will be numerical error when I use half precision, instead single and single instead double ?
Comment: The method is Verlet? Which variant, velocity, leapfrog, something else? Did you de-singularize the potential? Is the step size small enough to have a sufficient sampling density during a collision or fly-by? Why would you prefer single or half precision? Is double precision readily available?
Comment: Which variant, velocity, leapfrog, something else - Leapfrog with BAOAB integration scheme.  "Why would you prefer single or half precision" - speed.

Nevertheless, more general answer would be preferable.
Comment: Before you consider speed can you answer how many significant figures you actually need to do the science you want to do?
Answer: In general in a correctly implemented fixed-step ODE solver method you have 3 sources for numerical errors:

the theoretical method truncation error,
the floating point error from evaluating the ODE function and composing the method step and
the error from accumulating the single updates of size $O(h)$ to the integration result of size $O(1)$.

So the total error in each step is something like
$$
C_1h^{p+1}+C_2\mu_{eval}h+C_2\mu_{acc}
$$
where $\mu_{eval}$ is the machine constant for the number type used for evaluation and $\mu_{acc}$ the one for the number type used in the accumulation of the steps. The global error, in a first approach, results from multiplying with $N=T/h$, giving
$$
C_1h^pT+C_2\mu_{eval}T+C_2\frac{\mu_{acc}T}{h}
$$
So ideally (in an academic situation where variables and derivatives have a scale close to $1$) you would like to have $h^p\ge\mu_{eval}\ge\frac{\mu_{acc}}{h}$. For $p=2$ using single precision in evaluation, $\mu_{eval}=10^{-8}$, and double precision for the accumulation, $\mu_{acc}=10^{-15}$, this would give errors according to the second order of the method down to $h=10^{-4}$. Another variant to achieve increased precision in the accumulation without a different data type is Kahan or compensated summation.
Comment: GPU version started out with the SPDP model, see [here](https://ambermd.org/intel/midpoint.htm): "In addition to the traditional full double precision implementation used in the PMEMD CPU code the Amber 18 midpoint also introduces a mixed precision model, first pioneered with the Amber GPU implementation, termed SPDP. This precision model uses single precision for each particle-particle interaction but sums the resulting forces into double precision accumulators." Because DP is slow on consumer GPUs, an alternative SPFP model was developed replacing DP with 64-bit fixed-point (FP) formats.
Comment: An alternative to IEEE-754 double-precision (`binary64`) accumulation seems to be Q24.40 fixed-point accumulation as used by the GPU version of AMBER: Scott Le Grand, Andreas W. Götz, Ross C. Walker, "SPFP: Speed without compromise—A mixed precision model for GPU accelerated molecular dynamics simulations", *Computer Physics Communications* 184 (2013) 374–380
Comment: Thanks for your answer Lutz, especially that you considered accumulation and evaluation in different precision.

@njuffa Isn't AMBER using double for evaluation and single for accumulation ?


Is anyone restricted to use metro ui in websites?

Question: I found metro User Interface will suit my website's look. I would like a tiled Dashboard with grouped items like Windows 8 start menu and button style and text style identical to metro user interface. So can I do it or am I restricted use the design in my website?
Answer: you can design your website that will run in a web browser.  There are many web browsers that people use, and on many operating systems.  People will view your website in the manner that suits them, not you.
If they use a windows 8 metro app browser to view your website, your design can be proper metro style.  Otherwise it will be a windows 8 style web design in a different setting.
You may want to make an app where you can dictate the environment


mdadm RAID5 with bad sectors and bad blocks

Question: I have a 4 disk RAID5 setup with mdadm in Ubuntu 16.04.
sdb : good
sdc : 8 bad sectors according to SMART, 8 pending, 4 reported errors
sdd : bad blocks present according to mdadm --examine
sde : good
I was naive and assumed the system would notify me of a disk failure.  Since the last update according to "mdadm --examine /dev/sdd" was November, I know that's when it was removed from the RAID.  For 7 months, I've been unwittingly running in degraded mode.  Until this past weekend, when it marked sdc as faulty and my RAID became inactive due to insufficient disks.
SMART (smartctl --xall) says all the disks passed but reports 8 uncorrectable sectors on sdc and 4 uncorrectable errors.  So the disks are reasonably healthy.
The event count was obviously way off on sdd, but only 63 off on sdc.  So I forced an assembly with three disks, and all my data is accessible.  I am sure there are some corrupted files but it is not a huge concern for this data.
I then added the 4th disk back with "mdadm /dev/md0 -a /dev/sdd" and it started to restore but ran into the bad sectors on sdc which it could not reallocate (I assume because it is degraded?) and mdadm marked it as faulty again, and I'm back to where I started.
I found some good instructions on how to keep disks with bad blocks in an array here.
https://stephane.lesimple.fr/blog/how-to-securely-keep-a-hard-drive-with-bad-blocks-in-a-raid-array/
However, I made another mistake. Since I wasn't sure I was going to stick with Linux, the array is formatted with NTFS in case I wanted to run Windows instead.  This means none of the fs commands like fsck or debugfs work.
chkdsk might be able to help, but I'd need to install Windows, and I don't want to go through that pain unless I am sure it will work. I am hoping there is a way to do this with existing Linux utilities.
I have the sectors from kern.log, but strangely it lists 10 sectors with "read error not correctable" messages, which is more than the 8 that SMART reports. If I can convert these sectors to logical blocks, then I could potentially zero them out with dd.
I've already backed up anything critical, so I can just buy new drives, but seems wasteful to toss 4TB drives for a handful of bad sectors.  I am not even sure what is wrong with sdd since it has no bad sectors.
Note: When the RAID was trying to restore after adding the 4th disk, there are hundreds of "failed command: READ FPDMA QUEUED" messages in the kern.log
Googling this suggests I could have a bad SATA cable or power supply.  I have had my fair share of PSU's fail on me, but this would be the first time it causes hard drive failure if that is the case.
Comment: `ddrescue` to healthy drive
Comment: Thanks. I guess I could just try imaging sdc to sdd and if it works great, then I only need to buy one new drive.
Answer: ddrescue did successfully copy from the drive with bad sectors to the one that was disabled from the array back in November, however, only after I replaced my power supply.
In /var/log/kern.log I saw hundreds of failed WRITE FDMA QUEUE commands, so pulled the PSU from a newer machine and after the transplant, ddrescue worked fine.  Took about 10 hours for the 4TB disks. It reported 15 errors totalling 80kb.
Once it finished, sdd looked just like sdc as you'd expect, so I assembled the array with sdb sdd and sde, then I added sdd and let it restore, which it completed without error.  In fact, SMART no longer reports any bad sectors on sdd.  I assume this is because writing to those sectors caused the sectors to be reallocated by the disk.
So all is well, just need to order a new PSU.


Can I get cards randomly?

Question: I recently started playing Sky Force (the new version, on Android) and got my first card, (#1 +1 hangar). After that, I managed to get two more cards, but both were #1.
I think I obtained all three cards in level 1, in both the normal and hard modes.
Does the first level only drop card #1, or does it drop other cards as well? Do all levels drop random cards, without taking normal/hard mode into account?
Answer:
does it drop other cards as well?

Yes the drops are completely Random. What happened to you is a complete coincidence.

Do all levels drop random cards, without taking normal/hard mode into account?

All levels drop random cards, regardless of difficulty or timing.
The hanger card is one of the best card if you play a lot.
Answer: I also got 3 copies of each of the first 2 cards (and even a couple extras) before anything else. As I started moving up in ages, it seemed that when I would go back to lower ages, I would feel as though I was getting less cards per play-thru. I would often get cards that I would lose on dying (again and again), but after mastering the stage, and unlocking the next, I don't get the cards now that I can win and keep them. I now have 3 copies of each card 1-9, plus 17. I have one of each other card besides 19 and 24. I feel that you get more cards if you play the highest level available to you, or the next hardest on your max difficulty available.

Can I get cards randomly?


What does the expression 'Prepayment' mean in hotel booking terms?

Question: I've made a booking for a weekend in Holland online via ebookers. When I completed the transaction and looked at the final receipt, it said "prepayment required" ... does that mean I need to pay at the desk at the end of my stay or does it mean I've paid already when I made the booking online and won't be charged when I leave ?
Comment: @pnuts: That's less weird than it sounds. You generally provide your creditcard details up front, but you usually are not charged right then. There are exceptions though.
Answer: From ebookers.com:

For all products apart from certain hotels full payment is required at the time of booking in order secure your reservation.
For hotel rates that do not require prepayment, your credit or debit card typically would be charged at check-out.

From the above, it clearly means that you have fully paid for the hotel already, and you will not have to pay anything at checkout time, unless you have ordered room service or anything else that requires payment.
Comment: That seems clear enough- "at the time of booking". Some places (Agoda?) charge your credit card well before you check in, but perhaps well after you book the place if you've booked well in advance.
Answer: The term Prepayment covers any payment made prior to arriving at the hotel.  From ebookers.com terms it seems that their prepayment is done at the time of booking.  Others such as Agoda have a variable policies as to when they will bill your credit card, sometimes at booking, sometimes at a set date prior to your arrival (like a week before or two weeks before, etc).
Paying when you check into the hotel would not be considered prepayment.


Movie about a house haunted by a teenage girl who possesses the daughter

Question: I believe it's only the mom and the daughter who move to a new house. The house is haunted by a teenage girl who died there and now she wants to possess the daughter. The ghost ends up succeeding, but the mom figures it out though when she asks her "daughter" where she came up with her name and the ghost can't answer her or doesn't answer correctly.
Comment: If you could, please visit https://scifi.stackexchange.com/tags/story-identification/info and see if you can edit answers to those prompts into your question to help us help you.
Answer: It's Secrets in the Walls (2010)
In IMDB:

How does the movie end? Now believing that Greta has possessed
  Lizzie's body, Rachel pretends not to know and invites "Lizzie" to go
  house-hunting with her. On the way, she stops at the house to pick up
  a trunk. Greta/Lizzie is apprehensive about going in the house, but
  she eventually agrees to help Rachel carry it out to the car. Once
  inside, Rachel asks Greta/Lizzie whether she remembers why she was
  named Lizzie. When Greta/Lizzie can't answer, Rachel confronts her,
  and they begin to struggle. In the fight, Greta/Lizzie falls down the
  staircase, and the necklace is knocked off her neck, allowing Lizzie's
  spirit to re-enter her body. When she comes to, Lizzie answers the
  question. "You named me Elizabeth because she was strong," Mother and
  daughter hug. Some days later, as Rachel, Lizzie, and Molly are moving
  out of the house and the realtor is showing it to a new family, Rachel
  attempts to warn the family that the house is haunted but the husband
  says that they don't believe in ghosts. "You should," Rachel replies.
  In the final scene, as the prospective buyers enter the house, telling
  the realtor that they have two teenage daughters, Greta can be seen
  looking out of an upstairs window.
Comment: Good catch! Out of curiosity, how did you find it?
Comment: I watch, some time ago, this tv film. I remembered the film's young protagonist (Kay Panabaker. She is Danielle Panabaker's sister. Danielle Panabaker is Killer Frost in The Flash (TV Series))


Is it okay for a girl child to have her fathers first name instead of the last/family name?

Question: My mother said it is sunnah that a girl child should have her fathers first name instead of last.
She said it is a sunnah to have the first name.
Is it written anywhere that it is sunnah? If so could you please describe it more. Thankyou.
Answer: Surnames, as we know them, weren't really a thing for Arabs during the time of the prophet. Rather, they were identified using a patronym e.g. "Muhammad ibn Abdullah" (Muhammad, son of Abdullah) or "Fatimah bint Muhammad" (Fatimah, daughter of Muhammad). This sort of naming was already a long-established cultural practice rather than any sort of sunnah introduced by the prophet.
So it is definitely the case that the prophet and those who followed him did name themselves after their father's first name, but for the most part that's just because the first name was also the only name. The fact that this practice was continued by the prophet indicates that it is permissible, but doesn't necessarily suggest any sort of obligation or that it has any sort of blessing attached to it. It is simply how things were done at the time.
The only actual Islamic requirement in this issue that I know of is expressed in the Qur'an:

…ادعوهم لآبائهم هو أقسط عند الله
Call them by [the names of] their fathers; it is more just in the sight of Allah…
 — Al-'Ahzab 5

This requirement refers quite particularly to adopted sons and speaks against the common practice of the time to name an adoptee after the adopted father rather than their original birth father. Even if you generalize it to refer to all children, it really only specifies that they need to be identified as children of their birth father, not necessarily that their name needs to explicitly reflect that, and especially not that it needs to be on a first-name basis.


A boy didn't read every book

Question: In my opinion, "A boy didn't read every book"is ambiguous, it can express"a boy didn't read any book" or "Not every book were read by the boy".Am I right?
Comment: Closely related to an EL&U question: [Understanding the purported ambiguity in "Every boy didn't run"](https://english.stackexchange.com/questions/479640/understanding-the-purported-ambiguity-in-every-boy-didn-t-run)
Answer: "He didn't read every book", in almost any context, means he read some of the books but not all of them. For the other meaning you would say "He didn't read any books." or "He didn't read a single book."
Compare:

He lost every game (=he didn't win any games)
  He didn't win every game (=he lost some games)
Answer: You're right, it's ambiguous.
It's not a form of speech that would normally be used, but it became somewhat popularized in the book and TV series A Game of Thrones.
In the story, one of the characters, Jaqen H'ghar, is known to express ideas in an odd way, using a form of speech called the third person indefinite.
Here are some lines are from the Fandom Game of Thrones wiki:

"Help was not promised, lovely girl. Only death."
  "A man has a thirst. A boy can make a friend."
  "A man teaches a girl."
  "A man thanks a girl."
  "A girl has no name."

The problem with using this form of speech is that, as you point out, the inferred meaning can be ambiguous.

A boy didn't read every book.

At a literal level (in the context of how the speaker is using the phrasing), the meaning is explicit. It's a simple fact that a particular boy didn't read every book—but other details are not provided.
If you assume it to have a different meaning, then you are making assumptions that aren't expressed in the exact wording. But communication doesn't often operate at a literal level, and we do make assumptions based on context.
So, it's broader meaning is unclear:

Were all the books read by someone else? (Perhaps a girl read every book.)
Did the boy read some of the books? (Perhaps a boy only read two books.)

If somebody were to say the phrase in question to me, I would immediately reply with, "What do you mean?"
When things are referred to in this manner, many of the normal assumptions we make about what's being expressed can no longer be made. This is partly because people don't normally speak in this way, so we're not used to knowing how to correctly interpret what's being said.

A boy didn't read every book


google map problem today

Question: Where are the other options? I cannot see them on Google Maps. I used to be able to see a "route options" or "avoid tolls" button but now seems to have disappeared this morning.

Screenshot (click image to enlarge)
Comment: Could it be because you've chosen cycling as an option? Do you see the same effect when you choose driving / public transport?
Answer: I think this not an Google Map Issue. This is Expected Scenario.
If in your current Selected Route any tolls are there then only it will show those options, In your current routes ferries are there. So, you are getting that in your route options.
Answer: I believe that this is because you have the cycling option chosen.  When I start a bike route, I only have the option to avoid ferries.  When I switch it back to a driving route, the options that you are expecting to see return for me.

google map problem today


Whats the difference between Unix, Linux and Ubuntu?

Question: What is Unix, Linux, Ubuntu?
Are they the same thing or different versions or completely different stuff?
This has always made me confused, any explanation would be great.
Answer: Unix was and is (mostly) proprietary. So some people got their collective noggin together in the 1980s and put together something that reproduced Unix functionality without copying its source code, which would have been illegal [insert longer version about Richard Stallman and Linus Torvalds here].
One of the first GNU/Linux distributions was Debian. Ubuntu was created by people that had been involved with Debian and Ubuntu is officially proud of its Debian roots. It's all ultimately GNU/Linux but Ubuntu is a flavor. In the same way that you can have different dialects of English. The source is open so anyone can create their own version of it.
However, Debian is not really useable for mere mortals such as myself and that is where something like Ubuntu comes in. Indeed, I understand that it is specifically the strategy of Canonical, the company behind Ubuntu, to target the non-geek user. Which is why most new GNU/Linux users come to Ubuntu or Mint (which is based on Ubuntu) first.
Comment: I recommend adding the Linux timeline from here: http://futurist.se/gldt/ as a reference for historic knowledge.
Comment: I would add that Ubuntu and Debian are, namely, distros, which means that they use Linux and a collection of core Linux software to provide a GUI/server software with a terminal, shell, etc... Linux on its own won't do much to serve HTTP requests or even manage packages like `apt`.
Answer: This is from Wikipedia: Linux. Cheating I know....

The Unix operating system was conceived and implemented in 1969 at
  AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis
  Ritchie, Douglas McIlroy, and Joe Ossanna. It was first released in
  1971 and was initially entirely written in assembly language, a common
  practice at the time. Later, in a key pioneering approach in 1973,
  Unix was re-written in the programming language C by Dennis Ritchie
  (with exceptions to the kernel and I/O). The availability of an
  operating system written in a high-level language allowed easier
  portability to different computer platforms. With a legal glitch
  forcing AT&T to license the operating system's source code to anyone
  who asked,[22] Unix quickly grew and became widely adopted by academic
  institutions and businesses. In 1984, AT&T divested itself of Bell
  Labs. Free of the legal glitch requiring free licensing, Bell Labs
  began selling Unix as a proprietary product.
Linux is a Unix-like computer operating system assembled under the
  model of free and open source software development and distribution.
  The defining component of Linux is the Linux kernel, an operating
  system kernel first released 5 October 1991 by Linus Torvalds. Linux
  was originally developed as a free operating system for Intel
  x86-based personal computers. It has since been ported to more
  computer hardware platforms than any other operating system. It is a
  leading operating system on servers and other big iron systems such as
  mainframe computers and supercomputers:more than 90% of today's 500
  fastest supercomputers run some variant of Linux,including the 10
  fastest. Linux also runs on embedded systems (devices where the
  operating system is typically built into the firmware and highly
  tailored to the system) such as mobile phones, tablet computers,
  network routers, televisions and video game consoles; the Android
  system in wide use on mobile devices is built on the Linux kernel.
Ubuntu is a computer operating system based on the Debian Linux
  distribution and distributed as free and open source software, using
  its own desktop environment. It is named after the Southern African
  philosophy of ubuntu ("humanity towards others"). As of 2012,
  according to online surveys, Ubuntu is the most popular Linux
  distribution on desktop/laptop personal computers, and most Ubuntu
  coverage focuses on its use in that market.
Ubuntu is sponsored by the UK-based company Canonical Ltd., owned by
  South African entrepreneur Mark Shuttleworth. Canonical generates
  revenue by selling technical support and services related to Ubuntu,
  while the operating system itself is entirely free of charge.
Answer: (I had added the overview-poster to the related question half-jokingliy; But here, it is actually helpful in relation to the other answers:)
There is also a somewhat more detailed poster that I vaguely remember, but for a quick summary, that should be enough:

(Click image to enlarge)
Image from Wikimedia commons: Unix history-simple
(For the details (all), see GNU/Linux Distribution Timeline 12.10 - but that "somewhat more detailed poster" I vaguely remember was somewhere in between...)
Answer: From:-Comparison between Linux And Unix Operating System

Many a times we get confused with Unix and Linux also threat them as
  synonyms but that is not true. UNIX is copyrighted name only few of
  the companies are allowed it i.e. IBM AIX and Sun Solaris and HP-UX.
  This quote from Official Linux kernel README file confuses most.
Linux is a Unix clone written from scratch by Linus Torvalds with
  assistance from a loosely-knit team of hackers across the Net. It aims
  towards POSIX compliance.
In this article I am trying to describe the various differences between Unix and Linux under the following headings.

History
Usage
Cost
GUI
Security
Future OS

History
UNIX was created in the 1960s by the AT&T Bell Labs (Ken Thompson and
  Dennis Ritchie) and first commercially UNIX OS became available in
  1970. First release of Unix was having a command line interpreter and some small utility programs with future extension for the multitasking
  and UNIX evolved from there.
In 1991, Linus Torvalds began working on a UNIX like OS known as
  Minix. The Minix source code was freely available under GNU GPL and he
  successfully modified this code for use on x86 PC systems. By
  September 1991, Torvalds has successfully completed the first Linux
  kernel designed for PCs. This kernel included various system utilities
  and libraries from the GNU project to create a usable operating system
  based completely on open source code.
Usage The UNIX operating system is used in internet servers, workstations & PCs. Backbone of the majority of finance infastructure
  and many 24x365 high availability solutions.
Linux can be installed on a wide variety of computer hardware, ranging
  from mobile phones, tablet computers and video game consoles, to
  mainframes and supercomputers.
Cost Linux is Free (as it is opensource, except the case where you need a supported version i.e. RHEL). You can download it from the
  Internet or redistribute it under GNU licenses. You will see the best
  community support for Linux. Most UNIX like operating systems are not
  free (but this is changing fast, for example OpenSolaris UNIX).
  However, some Linux distributions such as Redhat / Novell provides
  additional Linux support, consultancy, bug fixing, and training for
  additional fees.
GUI Any modern system discussion can not be completed untill unless we discuss about graphical interface. Linux typically provides
  KDE and Gnome, but there are many alternatives such as LXDE, Xfce,
  Unity, Mate, twm, ect. where as Unix most distributions now ship with
  Gnome (initial GUI used to be called CDE i.e. Common Desktop
  Environment).
Comment: Please don't reproduce content from other sites without clearly marking it as a quote.
Comment: "Linux is a Unix clone written from scratch .." , clone and again written from scratch? what we need to understand from 'clone' here?