Wikipedia:Reference desk/Archives/Science/2021 February 1

= February 1 =

Stabbing someone in the midst of a heart attack
Hello, Wikipedians I`m just posting this question because I`m curious what would happen if you stabbed someone in the heart while they were in the midst of a heart attack? Thank You — Preceding unsigned comment added by 98.113.197.52 (talk) 00:51, 1 February 2021 (UTC)
 * They would probably die. ←Baseball Bugs What's up, Doc? carrots→ 04:16, 1 February 2021 (UTC)
 * If you have reason to think they are a vampire, the recommendation is to use a wooden stake for best results. --Lambiam 11:48, 1 February 2021 (UTC)
 * There is a famous scene showing an emergency intracardiac injection of epinepherine in the movie Pulp Fiction to keep the person's heart beating, but it was after the person had overdosed on heroin, not during a heart attack. Also, the heart injection was fictional: those injections are usually given in a leg muscle.  See epipen.  I wonder if you may have been remembering that scene. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 08:32, 1 February 2021 (UTC)
 * Are you thinking of pericardial tamponade? It can cause cardiac arrest, which is technically not a Heart attack (disambiguation) but is often colloquially called one. Pericardiocentesis, a treatment for pericardial tamponade, could be rather inadequately described as stabbing someone near the heart. Pericardiocentesis can be lifesaving, but it is ideally administered before the patient goes into cardiac arrest. If you want medical advice, take an advanced first aid course that includes first aid for firearm wounds (being shot in the heart is a common cause of pericardial tamponade). HLHJ (talk) 03:54, 2 February 2021 (UTC)
 * Assuming the blade doesn't directly enter the heart - which would cause instant death - the two would compound each other. A heart attack causes decreased heart oxygenation, while stabbing causes blood loss. Less blood means even less oxygen going to the unharmed parts of the heart. So the answer is, very likely, the person would die. RedPanda25 21:12, 3 February 2021 (UTC)
 * The OP specifically said stabbed "in the heart". ←Baseball Bugs What's up, Doc? carrots→ 23:29, 3 February 2021 (UTC)


 * Did you intend to find an answer from a legal perspective? Like what happens if you kill someone, who was dying within seconds? — Preceding unsigned comment added by Bumptump (talk • contribs) 21:46, 3 February 2021 (UTC)
 * Since the OP has only made the one edit, we may never know. ←Baseball Bugs What's up, Doc? carrots→ 23:30, 3 February 2021 (UTC)

Unlimited bandwith for over-the-air broadcasting
If everyone in my city had a radio they tuned to the same station at once, or a broadcast TV tuned to the same channel, we could all watch/listen simultaneously with no bandwidth or capacity issues (ignoring weather, antenna location, distance from the source, etc.) But if we all tried to make a mobile phone call or use the internet at once, we would have capacity issues. My guess is because of the two-way nature of phones and the internet, and also physical constraints such as the towers and the fiber and cable wiring. But is there a better explanation for this and would it also apply to satellite TV/radio?174.16.121.131 (talk) 00:59, 1 February 2021 (UTC)


 * I do not think that this is correct. In electronics, if you add more resisters in parallel, eventually the total resistance would be reduced to the point that the voltage would not be measurable. In other words, each receiver adds to the load on the transmitter until the transmitter is no longer able to drive the signal through the noise.
 * Another way to look at it is that each receiver also is a transmitter which transmits a signal roughly opposite (but smaller in magnitude) to the primary transmitter and partially cancelling it out. JRSpriggs (talk) 01:48, 1 February 2021 (UTC)

Basically as the signal to noise ratio decreases, the ability to extract information from the stuff coming into the receiver also decreases. If there are 1000 transmitters on a frequency and you're trying to listen to just one of them, the other 999 are "noise". The theoretical limits are established in Shannon's noisy channel coding theorem and modern spread-spectrum modulation schemes (like in current mobile phone systems) are really very good. By comparison, old-school broadcast radio is terrible. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 07:48, 1 February 2021 (UTC)


 * In a radio broadcast, there's a single transmitter sending the same signal to everybody at the same time. When using modile phones, the transmitters have to send a different signal to each separate user, so the total amount of signal is much higher. PiusImpavidus (talk) 08:45, 1 February 2021 (UTC)


 * The term "bandwidth" has two different meanings. In signal processing, "bandwidth" refers to the size of the portion in the frequency spectrum taken up by the signal. It can be related to the maximum rate of information transfer, but is a property of the signal, not coupled to a notion of channel. In networking, "bandwidth" is a property of a channel, directly specified as the maximum rate of information transfer. So the best explanation, I think, is that the set-up conflates these two notions. --Lambiam 11:41, 1 February 2021 (UTC)
 * Yes, modern satellite TV and satellite radio is duplex just like cellular service or the Internet; satellite receivers and the transmitters on the satellite communicate back-and-forth. One reason for this is to encrypt the signals, so free riders can't pick up the broadcasted content. --47.152.93.24 (talk) 18:51, 4 February 2021 (UTC)
 * on the claim satellite TV or radio is duplex. I'm sure they exist, but I've never heard of them, nor any part of the world where they are common. Unencrypted satellite TV is generally just some variety of DVB-S. Encrypted satellite TV is generally just some variety of DVB-S with some form of encryption in the mix. While it is theoretically possible someone would require two-way communication for that, nearly all do not, even the infamous NDS VideoGuard. The smart card does require regular updates, but it doesn't need outward communication for those. (If you take out the smart card for a very long time, it's possible it won't work, in that case some outward communication maybe required either by the STB or end user.) For stuff like Pay-per-view, two way communication can be required but even then only in a limited way. In particular, for PPV purchased from the set top box or similar, there is some need for the box to communicate the purchase decision, but this was traditionally via modem and nowadays often via wired ethernet or Wi-Fi. For PPV purchased over the internet or phone, there's generally no need for the STB to communicate outwards as the provider simply signals the STB a few times and assumes it's received. Nil Einne (talk) 11:45, 5 February 2021 (UTC)
 * I'm no expert, but I do have DirecTV service, and the receiver definitely talks to the satellite. You can access information about receivers through their website/app, regardless of whether the receiver has an Internet connection. Similarly, you can access PPV content, etc. through a receiver with no Internet connection. --47.152.93.24 (talk) 02:42, 6 February 2021 (UTC)
 * I see zero indication from either our article or a general search that DirectTV STBs are able to communicate via satellite. What do you mean by "you can access information"? Of course you can see what PPV content is available on the STB. There's zero need for the STB to communicate outwards for that as I already explained. The provider is simply sending that information all the time. Likewise, the provider knows about your STB, which channels you are subscribed to etc, that's how it works. So you can see that information on the internet. Can you actually purchase PPV content from the STB with no internet or phone line connected? (DirectTV themselves don't think so [//www.att.com/support/article/directv/KM1009938/].) And I don't mean "try to", I mean actually purchase. Plenty of STBs have terrible UIs so it's very probable it would appear you can purchase PPV content until you actually try the final step of purchasing when it may then tell you you need an internet connection. (But don't blame me if it does work and you have to pay.) Note as I already explained, purchasing PPV content via the internet or phone or SMS or whatever is expected. There's zero reason the STB needs to communicate outwards for this. The provider simply signals the STB to provide access (via the satellite).  Can you see information that is exclusive to the STB? For example, if you have a PVR type STB, can you actually see what you recorded even though you set up the recordings through the STB with no internet or phone line connected? (Setting up recordings over the internet, again the provider may keep track of such recordings and can communicate with the STB via satellite to let it know what you want to record without needing an outgoing connection from the STB.)  If you can do either of these or something else where outwards communication is required, how sure are you that the STB really has no access outwards communication via other means? Have you checked the back of the STB to make sure they didn't connect an ethernet line or phone line when setting it up? Note that if you have Wi-Fi internet in the home provided by AT&T and didn't bother to change the default password, there's a reasonable chance AT&T just set up the STB to access this Wi-Fi. Even if you did change the Wi-Fi password, if you're using their router there's a good chance they have remote access for management so perhaps they take your Wi-Fi password and provide it to the STB.  Of course it's possible there's no need for any of this since the STBs come with built in mobile network support in some form, for something so simple even 2G would be enough (some old smart meters use 2G for example, it's one reason 2G is being kept in a number of places) although considering this is AT&T, newer STBs would probably just have 4G if they wanted to do that.  Nil Einne (talk) 05:13, 6 February 2021 (UTC)
 * P.S. See e.g. [//blog.solidsignal.com/tutorials/can-share-satellite-dish-neighbor/]. Why would DirecTV only come after people for possible misuse if the STB has a phone or internet connection ,if the STB could report this via satellite? BTW, it's theoretically possible that AT&T would allow the STB to automatically connect to a neighbour's password protected Wi-Fi that they know about although I find this very unlikely. However more likely it may connect to a non password protected Wi-Fi, perhaps without even asking you. From what I can tell e.g. [//forums.att.com/conversations/directv-dvr-receivers/my-recordings-are-being-recorded-next-door/5defd522bad5f2f6062f3368], it should be clear somewhere on the STB if you are connected to Wi-Fi and you can disable it but as always unless you actually did that you shouldn't assume it's the case. (It is theoretically possible that the connected thing could be misleading if it does know WiFi details of some AP it can see somehow, but I find this very unlikely.)  I didn't find any indication that DirectTV STBs generally have any sort of mobile network connection.  I did find [//www.defender.com/pdf/260145AppNote.pdf] [//itstillworks.com/directv-deca-17350.html] [//www.reddit.com/r/HomeNetworking/comments/bbimc4/will_deca_coax_to_ethernet_adapters_work_if_im/] which suggests that DirectTV was and probably still is using co-ax for ethernet via DECA splitters. So actually rather than just checking the STB for any connection, although I still suspect the UI should be clear about any internet connection but maybe not a phone line one, you probably need to check your router as well and ensure all ethernet cables are something you know about. If your internet comes from AT&T, you might also want to check that your "modem" or whatever if it's different from your router in case it has more than one output.  Nil Einne (talk) 06:00, 6 February 2021 (UTC)

Who predicted an Analemma (position of the sun in the sky) before it got photograph in 1990s?
Wiki page of Analemma didn't mention history of Analemma clearly well. If Albert Einstein predicted Gravitational waves then who predicted Analemma? Rizosome (talk) 06:21, 1 February 2021 (UTC)
 * This article (which is given as a reference in Analemma, so anybody could have found it) mentions Jean Paul Grandjean de Fouchy as the "inventor" of this particular type of representation in 1740. It is based on the concepts of equation of time and mean solar time. --Wrongfilter (talk) 07:31, 1 February 2021 (UTC)
 * Although in principle it could be predicted by someone who knew enough about the Earth's motion around the Sun and orientation in space, it can in fact be observed very simply (by plotting the position of, for example, the shadow of a fixed object on a fixed surface every few days over the course of a year), so it was known about long before before such knowledge was developed. Sundials, an ancient technology, generally take it into account. According to this, the 1st-century BCE Roman architect Vitruvius utilised the concept in his work (in order to know where shadows of buildings would or would not fall) and described its calculation and use in Book 9, Chapter 7 of his work De Architectura Libri Decem, though he didn't claim to have discovered it, and it was likely known to scholars at least several centuries earlier. {The poster formerly known as 87.81.230.195} 90.200.40.9 (talk) 10:07, 1 February 2021 (UTC)
 * As I understand it, Vitruvius' analemma was not identical to the figure that Rizosome asked about. For that figure to become apparent one needs a certain way of reckoning time (at what time of day do you have to take the indivdual exposures that go into the photograph?) – that's why I mentioned mean solar time, which is a concept that Vitruvius did not know about. Nevertheless there is obviously a relation between what Vitruvius did and what de Fauchy did. --Wrongfilter (talk) 10:45, 1 February 2021 (UTC)
 * In any case, the annual north–south swinging of the solar position has been observed and known since antiquity. To observe the much smaller east–west deviations requires sufficiently accurate timekeeping devices, such as the pendulum clock, invented in 1656. By the time of Fouchy (who deserves an article), the biannual east–west movement must also have been detected. No one (as far as we know) can be said to have "predicted" it; the observation preceded the explanation. Fouchy's role is that of an inventor: he invented a graphical method to relate the position of the Sun in the sky (giving the apparent solar time) to the mean solar time. --Lambiam 11:20, 1 February 2021 (UTC)

From here, Analemma is developed by the French astronomer Grandjean de Fouchy. But in Analemma his name is missing. Is 1730 in science vandalism? Rizosome (talk) 15:45, 1 February 2021 (UTC)
 * Sources disagree about the year. Here we read "since 1730", but here we see "1740". Without extensive investigation, it is hard to tell which is wrong. --Lambiam 16:06, 1 February 2021 (UTC)
 * In his 1797 treatise De la mesure du temps par les horloges, scientist and watchmaker Ferdinand Berthoud writes that he knew of three analemmata having been drawn, the first being by Grandjean de Fouchy at the Count of Clermont, and two more he drew himself in 1737. This makes the date 1740 too late. It may be impossible to assign a precise date, because it seems that Fouchy has not published his invention but merely told others, such as Berthoud. Several French sources give an imprecise date, writing "vers 1730" ("around 1730" or "circa 1730"). --Lambiam 11:03, 2 February 2021 (UTC)


 * Lien de courtoisie: fr:Jean-Paul Grandjean de Fouchy. -- ToE 19:36, 1 February 2021 (UTC)

A number of churches in Italy have an analemma inlaid in the floor, and a pinhole in the south wall so that an image of the sun at noon falls thereon. One day in 200x, the sun was partially eclipsed for Italy at noon, and someone put out a call for photographs of the image of the crescent sun on such churches' analemmata. I supposed when I saw this gallery that the analemmata were made in the Renaissance, but perhaps not? —Tamfang (talk) 02:29, 3 February 2021 (UTC)
 * This would have been the solar eclipse of October 3, 2005. It is possible that the traced figure and its significance was discovered independently several times, and it is not strictly impossible that some of these inlaid analemmata stem from the Renaissance. Some clock towers had striking clocks that were accurate enough already then; they would have struck the sexts every day at the same mean solar time. It would be interesting to historians of timekeeping to know the earliest construction dates. --Lambiam 09:32, 3 February 2021 (UTC)
 * Perhaps the solar eclipse of August 11, 1999, which passed as a partial eclipse over Italy around 10:45 UTC = 11:45 CET. (I had the privilege of watching its glorious totality that day from Amasya.) --Lambiam 17:08, 4 February 2021 (UTC)