Why can our bodies bleed?
Why does the aorta spray blood when atmospheric pressure is higher than blood pressure?
An acquaintance recently posted an image to FB from his recent trip to the JFK Historic Site asking for an explanation of a visible artifact he states was not visible to the naked eye but was visible through the EVF of his camera and in the final image.    The artifact is a series of bright, nearly-vertical bars and a longer, almost horizontal bar superimposed over the lower part of the door frame and the radiator.  I found a very similar artifact in another image of the same room from a blogger which isn't as compressed:    In both cases the artifact seems to be a vertically inverted image of the post and rail outside the saturated window.  From looking at other images of the room available online I know there is spherical glass ornament topping the table lamp whose shape is visible at the left of the photo.  One response to the OP's question is as follows:     RK: It is lens flare. So, even on an iPhone, the camera lens is made   up of multiple lenses. Each designed to focus the image and make sure   it isn't distorted. Remember a lens bends light.  Sometimes, based on   angle and intensity of the incoming light, some stray light bounces   back and forth while traveling through the various elements that make   up what we think of as a camera lens (some of mine have 16 elements   inside a single lens.) Even the best glass is capable of reflecting   some light instead of passing it through the lens elements to the   sensor.  This is what you are seeing. The railing is overexposed, and   some stray light is bouncing around a bit inside the lens.   My response:     DJ: I don't think it's lens flare or ghosting. Those usually form an   image of starbursts, rings, or circles in a row across the image or in   the shape of the aperture; or a veiling glare or haze. This is forming   an image of the light outside minus objects in its path. It is more   likely a direct reflection/projection off a mirror or the glass in a   picture frame elsewhere in the room onto the opposite wall and the   radiator. There are two other clues which seem to confirm this. First,   the image has a gradiated appearance, it is less distinct in the   relatively bright area on the door frame and brighter in the   relatively darker areas behind and on the radiator. You would expect   lens flare to be more evenly specular. Second, the image representing   the light from below the horizontal rail changes angle on the   different faces of the door frame. Unlike a projection, lens flare is   an image created within the lens, the physical shape of the objects it   superimposes do not change its shape.      OP: If that were the case, would I have been able to see said   reflection in the room without the camera? There was no image I could   see with the naked eye. I notice the image in my phone before I took   the pic and did a double, triple and quadruple take before I took it   so I'm sure.      DJ: It would have been visible at the moment the image was taken, but   it may not have appeared nearly as bright and distinct because your   eyes were accommodating for the bright light coming in the window. The   projection could have easily been obscured by you or anyone around you   changing position or moving through the path of the projected   reflection. Also, it's been caught by other people... (see Image 2)   Notice that, in the linked example, the projection is again distorted   by the surface it falls on.   Anyone else want to chime in with an explanation? how to prove that this positive sequence converges to 1 I have a positive infinite sequence $a_n$ and I know that $a_n$$a_{n+1}$ converges to 1 and also $a_n$$a_{n+2}$ converges to 1.  Why does it mean that $a_n$ also converges to 1? How can I prove it?  Thanks. I consider the co-finite topology on $\mathbb{R}$ that is $$\{G\subset \mathbb{R}, card(\mathbb{R}\setminus G)&lt;+\infty\}\cup \{\emptyset\}$$  What are the convergent sequences in this space .  thank you I have two laptops: Dell xps M1210 and Dell vostro 1400. On MS windows the output volume is so loud that I just need to set volume to around 20% to listen music and watch videos. I use Bose TriPort In-Ear Headphones most of the times. On ubuntu, even if I set 100% volume on the multimedia player, on the desktop volume manager as well, and also on the ncurses GUI of alsa mixer, I get very low volume output. Sometimes while playing some vidoes the volume is so low that I barely hear any words. I have struggled for two years since I started to use ubuntu to solve this mystery. The same sound card which gives excellent sound on MS windows fails miserably on GNU/Linux. Few weeks back I bought an Asus 100PX EEE PC. To my surprise even it also has the same issue. I have tried many versions of ubuntu and also I have done manual compiles of alsa modules without any success. I have asked and read about it in every possible forums and howto's. Nothing has helped me to address the issue. How should I approach obvious proofs like these    I have been trying but couldn't find an elegant way to work these. Any help is highly appreciated ! Especially looking for a nice proof/hint for first problem Applications Don't Show Up in Spotlight Spotlight has stopped showing any results for my Applications. I've tried reindexing and removing the index so it rebuilds it. No change. I've tried adding Applications to the Privacy tab and removing it, no change.  I tried repairing disk permissions and redoing the above, no change. I've tried removing everything from the index except Applications and then I just get nothing for any search at all (except dictionary entries).  I tried adding a symlink in my homedir to Applications and reindexing, but no change.  Any ideas on what to do?  I'm running Snow Leopard.  This is driving me crazy!  Update: I've noticed that when I start a reindex with sudo mdutil -E / and then immediately do a Spotlight search for an app that the app shows up temporarily until Spotlight gets disabled due to active indexing.  After the indexing is done, the app entries go away. So I was reading this:  and while the answers for the first question are good, nobody gave much attention to the second one. In fact, people only said that it can be proved without giving any proof or any.  So, if I have a Lagrangian and ADD an arbitrary function of $\dot{q}$, $q$ and $t$ in such a way that the equations of motion are the same, does this extra function MUST be a total time derivative?   EDIT Ok, I changed my question a little bit:  Question: If I have a function that obeys the Euler-Lagrange equation off-shell, this implies that my function is a time derivative? (This was used in Qmechanic's answer of this other question: , equation 14.)  Also, why people only talk about things that change the Lagrangian only by a total derivative? If this is not always the case that keeps the equation of motion the same, so why is it so important? And why in the two questions I posted about the same statement on Landau&amp;Lifshitz's mechanics book only consider this kind of change in the Lagrangian? Show that  the  alternating  group  $A_4$  of all even permutations of $S_4$ does not contain a  subgroup of order $6$.   For me am thinking to write all elements of $A_4$ and trying to find every cyclic subgroup generated by each element of $A_4$, then I have to check whether there exist such a subgroup or not! This is a long procedure for me, I ask if there is a short way to do this. Why is 4 not an instance of Number? Is it correct to sometimes capitalize words mid-sentence in computer user interfaces? Is it possible to use a spell scroll with a spell that requires a bonus action to cast? The DMG contains spell scrolls (on page 200), with the following rule:     If the spell is on your class's spell list, you can use an action to read the scroll and cast its spell without having to provide any of the spell's components.   This is all well and good for spells with a casting time of 1 action (which admittedly is most of them), but for spells with a bonus action casting time, how is it supposed to work?  Does it require:   Both an action and a bonus action?  Just an action? Just a bonus action? Something else I haven't thought of?   In case it needs saying, I'm not interested in speculation here - only RAW-based answers or explicit statements of developer intent should apply. Storage disk format to use to be utilised by all OS Is it time to be rid of automatic down votes on certain closed questions? Right now,  carry automatic downvotes.  The  for this was largely to enforce specific quality bans in part because people were not down voting questions. Now that question down votes are free on questions and it seems to be pretty commonplace for question quality bans to trigger, even without the automatic votes from closure, and we have completely revamped the closure system. Is it time to reevaluate whether or not these automatic votes are still a good idea?  What benefits do the automatic votes provide and have they effectively run their course? Why is my mesh inversed when Imported to Unity? So I modeled this sword and all the parts were separate meshes. I used a mirror modifier when I was modeling and then I applied the modifier when I was done to make the parts into solid meshes. Put a UV map on everything and it all looked good in Blender.  Then I put it into Unity and I got what you see in the picture. Part of the sword is inversed. Oddly, the inversed part actually maintains the proper silhouette. It maintains the correct shape, but then is shaded like the front half is missing.  Does anyone have an idea of what's going on and how to fix it?  Thanks, James I'm new to the world of Apple, I bought a new Macbook Pro, mid-2020, Intel i7, 16GB RAM. I'm a developer, I run apps like VS Code, Sublime Text, Slack, Chrome (Multiple Windows), I play videos/songs in the background. I have been keeping a track of the energy consumption on my Mac, and it only runs for 4 hours. I have reset my SMC after I upgraded to Big Sur. Is 4 hours normal? or should I go to the service center? Update on 3 Feb 2021: I submitted my Mac to the Apple service center they said they conducted a few tests and the conclusion was that the battery is fine (I don't know what type of test they did). So I guess I'll be using it on AC Update on 12 Feb 2021: Took it to the service center, they didn't find any issues so I started using Safari for work and my battery has improved by 1 hour on Average. Why won't my villagers breed I have created the following structure. The intention is to create fairly compact houses for villager breeding.   This is a section of the houses.   I have 2 of these structures, which would resolve to 28 doors and 4 other types of houses meaning I have 32 houses in total. healed healed 3 villager zombies and locked them inside a small house. One of them sometimes shows hearts, but they won't breed.   I am playing vanilla Minecraft 1.8. The doors are spruce.  What is wrong with these houses? Is there something wrong with spruce doors or half slab roofs? I'm not the most experienced person when it comes to commands. I worked out how to do stuff like when holding x you have y effect. I wanted to think of something that gave other people an effect when hit. Here is what I came up with but I got stuck when it said it couldn't execute the command.  /scoreboard objective add nokill dummy  /scoreboard objective add poi dummy  /scoreboard players set [player] nokill 1  /scoreboard players add @a poi 1 {SelectedItem:{id:minecraft:diamond_sword,display:{Name:{Poison sword}}}}  /execute @a[score_poi_min=1] ~ ~ ~ /effect @p[score_nokill_max=1,r=5] {HurtTime:1} minecraft:poison 10 1 I am a UI designer and developer and have been designing websites for aound 10 years. I want to get into user experience design. I know how to do a design, but I am lagging the terminologies and the technical things in the user experience field.   So how do I go about getting the skills and mindset necessary for being a User Experience Designer? Why can't a domain's root be a CNAME? I've just read  which essentially says that when I set up DNS for example.com, the root record can't be a CNAME, it has to be an A record.  My question is, why?   I'm sure the clever people who designed DNS didn't make arbitary restrictions for no reason, but I don't see what we gain by requring root domains to be A records. I would love to just point my example.com domain to someserver.somewebhost.example and forget about it, but I can't.  Please enlighten me, billpg. I was just awarded +100 reputation on all of my Stack Exchange accounts.  What is this bonus for? It simply says "Association Bonus" on my reputation overview.  Also:   What privileges does the association bonus grant users? Can I lose the association bonus? Does it make my reputation 101 everywhere? Can I earn the association bonus on sites I haven't joined yet? Does it matter which site I earn the 200 reputation on? Will I get an association bonus every time my reputation on a site crosses 200 points? Does the association bonus allow me to answer protected questions? Does the association bonus count towards the reputation cap? Can I get the association bonus if I only have a profile on one site? What else is there to know about the association bonus?