In WHO official website ", it doesn't mention that wearing mask an effective measure to protect people.   I don't understand why wearing mask is not good way to prevent infection of COVID-19.  Is it just because masks are out of stock?
Information about (simple) mask wearing (concerning covid19) is a complete mystery to me. On several official places it is not recommended for a person without symptoms to wear a mask. For example:    (time 0:20)  or here:    However no explanation is given - which makes me wonder (and even angry). I think everybody should wear a mask because:   Many persons feel ashamed wearing it, even those with symptoms. If everybody wears it, they do not feel ashamed and wear it. As far as I know, one is (wrt covid19) contagious before developing symptoms. So if everybody wears the mask also these people do.   The two above points act as a collective protection.   Simple mask certainly will lower "getting / spreading illness" probability. Of course the "holes" (in a simple mask) are too big to prevent completely virus to enter (or get out when coughing), but it lowers probability! Even if it lowers the transmission probability by e.g. 5%, it might be a lot. As a hypothetical example: it might reduce R0 from 1.02 to 0.97 and so stop the virus spread so fast.   The videos are full of self-contradiction. In the same video    time 0:50 the lady says I should wear a mask if I am in contact with an infected person... why if it is inefficient?  Question: What are reasons for not recommending wearing a mask?
Is there a reason the British omit the article when they "go to hospital"? Why do British speakers omit the article in constructions like "go to hospital" or "go on holiday"? Pretty much all American speakers would rephrase those as "go to the hospital" and "go on a holiday", I think. Is there any good reason, or forgotten sense behind those words that might explain why the articles are ommitted?  Are there other common constructions other than those two that the British use that drop the article?  EDIT: I just realized per Kosmonaut's comment that Americans do much the same thing with a few nouns, so this isn't all that special.   Do grammaticists designate nouns that can have their article dropped with anything, i.e. do they have anything in common? How can I identify what application is using a given file? How can I make sure that my on-screen colors are consistent? What medium should be used for long term, high volume, data storage (archival)? Performing deep learning land cover classification using R? I am really new to Deep Learning and, unfortunately, I can't find example codes on land cover classification other than  where the author wrote a script in R for a large dataset.   The main reason that I am asking is because recently I found a few papers on Remote Sensing Image classification using Deep Learning and I was wondering if there were any R examples on that subject.  So, is there a code example, preferably a step-by-step, which I can use?  I found several git repos like  that can do Deep Learning classification with R, BUTT, I am still looking for a simple multi-spectral image segmentation method. An example of that can be found at  and I also found a similar question in  for which the answer is "use something else other than R if you can".  If I find anything that works today I will be posting a working answer. Undo a particular commit in Git that's been pushed to remote repos Is the Higgs boson an elementary particle? If so, why does it decay? The  is an excitation of the Higgs field and is very massive and short lived. It also interacts with the Higgs field and thus is able to experience mass.   Why does it decay if it is supposed to be an elementary particle according to the standard model? Why does an argument similiar to 0.999...=1 show 999...=-1? Why exactly can't a single resistor be used for many parallel LEDs? Why can't you use a single resistor for a number of LEDs in parallel instead of one each? Creating Indexes on DB with Hibernate @Index Annotation Splitting string into pair of characters in Ruby Can a massless rope accelerate? Is there a way to connect my MacBook Pro to two external monitors (either VGA or HDMI; no Thunderbolt) in such a way that the Mac screen serves as a third monitor?  What hardware do I need? How to run ubuntu/xubuntu in a complete non-gui mode Dependency is not satisfiable: libtiff4 when trying to install Lightworks on Ubuntu 14.04 I was trying to install Lightworks 11.5.1 (amd64) on Ubuntu 14.04(amd64) but there's a notice: Dependency is not satisfiable: libtiff4. Is there anyway to solve this dependency issue?  Thanks in advance. What is the best way to return an error from a function when I'm already returning a value? (I was requested to edit the question to explain why it is different that a proposed duplicate question. This seems counterproductive to do here, inside the question it self, but that is what I have been asked by the site and moderators. There is no way for me to vote against their votes. So, here I go: Please stop voting this as a duplicate so quickly, which will eventually lead to this question being closed off. Yes, the other question linked to asks the same math, but any newcomer to the problem who was exposed to it via physics, as I was, will prefer this question instead of the one that is purely mathematically. I beg the moderators to not be pedantic on this one. This question spills into physics, which is why I did the cross post to the physics forum as well.)  How does the sum of the series “1 + 2 + 3 + 4 + 5 + 6…” to infinity = “-1/12”, in the context of physics?  I heard Lawrence Krauss say this once during a debate with Hamza Tzortzis (). I found a transcript of another debate between Krauss and William Lane Craig which has the same sum. Here is the paragraph in full:     Let’s go to some of the things Dr. Craig talked about. In fact, the   existence of infinity, which he talked about which is   self-contradictory, is not self-contradictory at all. Mathematicians   know precisely how to deal with infinity; so do physicists. We rely on   infinities. In fact, there’s a field of mathematics called “Complex   Variables” which is the basis of much of modern physics, from   electro-magnetism to quantum mechanics and beyond, where in fact we   learn to deal with infinity; without the infinities we couldn’t do the   physics. We know how to sum infinite series because we can do complex   analysis. Mathematicians have taught us how. It’s strange and very   unappetizing, and in fact you can sum things that look ridiculous. For   example, if you sum the series, “1 + 2 + 3 + 4 + 5 + 6…” to infinity,   what’s the answer? “-1/12.” You don’t like it? Too bad! The   mathematics is consistent if we assign that. The world is the way it   is whether we like it or not.   -- Lawrence Krauss, debating William Lane Craig, March 30, 2011  Source:   CROSS POST: I'm not sure if I should post this in mathematics or physics, so I posted it in both. Cross post:   EDIT: I did not mean to begin a debate on why Krauss said this. I only wished to understand this interesting math. He was likely trying to showcase Craig's lack of understanding of mathematics or logic or physics or something. Whatever his purpose can be determined from the context of the full script that I linked to above. Anyone who is interested, please do. Please do not judge him out of context. Since I have watched one of these debates, I understand the context and do not hold the lack of a full breakdown as being ignorant. Keep in mind the debate I heard this in was different from the debate above. I have recently installed a custom ROM and cannot find the Play Store. It seems like all apps that belong to Google are missing.  How can I install the Google Apps Package (Play Store, ...) on my Android device? Find all subgroups of $\mathbb{Z}\times\mathbb{Z}$. Find all subgroups of $\mathbb{Z}\times\mathbb{Z}$.   I can find all the infinite subgroups of the form $n\mathbb{Z}\times m\mathbb{Z}$, where $n,m$ run over $\mathbb{Z}$. But I don't know how to write out all the finite subgroups in a uniform expression.  Any suggestions? Thanks in advance. VirtualBox Toolbar is hidden! How to show it? I accidentally hide the main Toolbar from my VirtualBox Manager UI? In my ubuntu 12.04 .   Can anyone let me know the detail steps to display the Toolbar again? I search the whole blogs but can't figure it out!