Wikipedia:Reference desk/Archives/Science/2014 May 14

= May 14 =

HCV
If the Hepatitis C virus can survive on dry surfaces for prolonged periods, why is it so rare in developed countries? — Preceding unsigned comment added by 82.40.46.182 (talk) 02:35, 14 May 2014 (UTC)


 * Even if the virus remains viable, it still needs to get into the bloodstream (probably) to cause an infection. (See Hepatitis C.)  Even if there is viable Hep C on a surface, and you poke it with your finger, it's not going to do anything (probably, and this isn't intended as medical advice or a guarantee of safety) unless you happen to have an open wound.  The principle routes of infection are through blood transfusions (in the developing world) and intravenous drug use (shared needles) in the developed world. TenOfAllTrades(talk) 02:44, 14 May 2014 (UTC)


 * I posted a comment about environmental degradation earlier: I've removed it, because I've just looked up the appropriate reference and been quite shocked by just how slowly -- if at all -- the viruses degrade over time. I wonder how long they can stay viable at room temperature? -- The Anome (talk) 13:08, 15 May 2014 (UTC)

Biochem question
How do (some) living organisms produce primary halides? I'm pretty sure that haloperoxidases can't halogenate anything in the primary position, because they follow Markovnikov's rule. The way I see it, such a primary halide would have to be produced by phosphorylation of a primary hydroxyl group, followed by an Sn1 reaction -- is my understanding correct? 24.5.122.13 (talk) 04:57, 14 May 2014 (UTC)
 * Anyone? 24.5.122.13 (talk) 06:36, 15 May 2014 (UTC)

Cannabis and lung cancer
It says over here, 1,

"Cannabis also has been shown to have a synergistic cytotoxic effect on lung cancer cell cultures in vitro with the food additive butylated hydroxyanisole (BHA) and possibly the related compound butylated hydroxytoluene (BHT). The study concluded, "Exposure to marijuana smoke in conjunction with BHA, a common food additive, may promote deleterious health effects in the lung." BHA & BHT are human-made fat preservatives, and are found in many packaged foods including: plastics in boxed cereal, Jello, Slim Jims, and more."

The paragraph seems to be contradicting itself. First it says that it has a synergistic cytotoxic effect on lung cancer cells with the food additive BHA, but then it says that marijuana smoke in conjunction with BHA maybe promote deleterious health effects in the lung, so which is it? ScienceApe (talk) 15:45, 14 May 2014 (UTC)


 * The presumption is that lung cancer cell lines are derived from cells which are present in (normal) lung tissue, and that toxicity in these lung-derived cell lines may suggest a likelihood of toxicity in lung tissue. That is, the idea is that the A549 cells used in the study recapitulate many of the properties of 'normal' lung cells, and so can be used as a model for how lung cells might respond to toxins.
 * Of course, it's a 12-year-old, primary, in vitro only study that found a modest effect in a non-primary cell line and doesn't seem to have been followed up on...so I'm probably going to go ahead and remove that paragraph from our article as giving undue weight to a source that doesn't meet the requirements of WP:MEDRS.   TenOfAllTrades(talk) 16:02, 14 May 2014 (UTC)


 * Um, there is no "which is it". You've just quoted two synonymous passages.  "Synergistic" means "work together".  "Cytotoxic" means "bad for cells".  So, in the first sentence, it says "Marijuana smokes works together with BHA to have a bad effect on the cells of your lungs" and then in the second sentence it says "Marijuana smokes works together with BHA to have a bad effect on the cells of your lungs."  So the two statements are somewhat redundant.  They say the same thing. --- Jayron  32  02:02, 15 May 2014 (UTC)


 * I guess my answer wasn't as clear as I had hoped. I think ScienceApe noticed that the first part of the passage dealt with cytotoxic effects on lung cancer cells, whereas the second part suggested a negative effect on (presumably) non-cancerous lung tissue&mdash;leading to the question, why would a chemical combination that kills lung cancer be seen as bad for healthy lung?  Our text wasn't explicit in noting that the lung cancer cell line was being used as a model to draw conclusions about the (possible) response of healthy cells in an intact lung.  Without that crucial bit of context – the inconvenient fact that many of the things that kill cancer cells also are quite good at killing normal cells – it would be easy to see a cytotoxic effect on lung cancer cells as a good and desirable thing. TenOfAllTrades(talk) 03:04, 15 May 2014 (UTC)


 * The two statements are not synonymous, but how are they (as the OP says) not compatible? —Tamfang (talk) 21:26, 15 May 2014 (UTC)


 * This study has a really unimpressive abstract. We're talking about 0.2 mM BHA * 180 g/mol = 36 mg/l, and 10 mg/l THC ... these are pretty large amounts.  I'm a little unclear on  but it sounds like food items never contain that much BHA, and the body hopefully isn't preserved like a product on the store shelf.  Tested in one cell line that isn't actually a lung - doesn't have the sort of barrier function you expect a lung to have.  It's not a study that proves anything, even at a primary level, about actual smoking. Wnt (talk) 05:42, 15 May 2014 (UTC)


 * Common sense would indicate that inhaling concentrated quantities of smoke, from whatever source, can't be good for you. ←Baseball Bugs What's up, Doc? carrots→ 05:51, 15 May 2014 (UTC)


 * Common sense has its uses, but its weight in peer-reviewed research is limited. —Tamfang (talk) 21:24, 15 May 2014 (UTC)
 * Oddly enough, some doctors used to promote cigarette smoking. As for the above, it's always comforting to learn that the research bears out the obvious. ←Baseball Bugs What's up, Doc? carrots→ 00:23, 16 May 2014 (UTC)
 * Not to quibble, but wouldn't it be more apt to say "A lot of what seems obvious is what has been borne out by overwhelming evidence"? I find that it's a 50/50 over if new research is obvious - and when it is, it's more in a "Looking at it now, yes that was obvious" sense than a "Of course, I said that ten years ago" sense. It's easy to forget how informed we are by a background of research already. (yes, this is terribly off topic, I apologize).Phoenixia1177 (talk) 05:21, 16 May 2014 (UTC)
 * A lot of us were certain that cigarette smoking was bad for you, long before science dared to report their findings. ←Baseball Bugs What's up, Doc? carrots→ 05:28, 16 May 2014 (UTC)
 * Perhaps, in that specific case, I have no idea what you believed, nor why - however, as a general principle, research and obvious does not seem to go hand in hand, at first. Usually, after a set number of years, what is obvious, is the common understanding of what was researched. If this weren't true, then the billions of folks that didn't believe what we believe would have to have been exceptionally stupid if it was, indeed, obvious - that they, many times, believed the opposite would seem to indicate much of what we know is not, actually, obvious at all. (Since I am derailing the thread here, I'm going to stop at this post - :-) )Phoenixia1177 (talk) 05:38, 16 May 2014 (UTC)

How do portable (not window) A/C units work ?
1) Do they have a hot air discharge hose that blows out a window ? That's the only way I can picture them working.  I saw one had an absurdly inefficient option to heat the condensate to get it to evaporate back into the air (hopefully that's the discharge air, not going back into the room).

2) This type of unit seems like it would be a lot easier to use, if I don't have to remove and replace window screens to place it in spring and remove it in autumn. I'm guessing they are less efficient than window A/C units, and you would also need to drain the condensate, if it can't drip out the window and you don't use the heater option to evaporate it.  So, how does the efficiency compare with window A/C units ?

3) Do any just pump the condensate water out another hose, going to a sink or also out the window ? StuRat (talk) 19:19, 14 May 2014 (UTC)


 * Looks like this page: http://homeenergypros.lbl.gov/profiles/blogs/warnings-about-portable-air-conditioners and this page: http://www.sylvane.com/portable-ac-faq.html - answers most of your questions. Justin15w (talk) 19:28, 14 May 2014 (UTC)


 * Thanks, good info, although they seem to disagree on the value of a second (fresh air intake) hose. The first source says this increases efficiency by not sucking cool air out of the room, which is then replaced by hot, moist air being sucked into the house, while the second source points out that the need for an extra fan and the lower efficiency of cooling the coils with hot, moist air may negate that advantage.  The first source seemed to have numbers to back up their claim that 2 hoses are better, so I tend to trust them.


 * Interestingly, the unit I looked at at the store made absolutely no mention of hoses, condensate, etc., and the pic didn't show them, either. So, that probably means a single hose, and no window install kit is included, and you have to empty the condensate bucket regularly or get a puddle on the floor.  I won't be buying that unit, and probably will stick with window A/C.  My window screens are apparently not removable, so I had to cut a hole in them to install my window A/C, which means I can never open the windows again when the A/C unit is out, or be deluged with bugs.   StuRat (talk) 21:49, 14 May 2014 (UTC)


 * You can cut holes through your wall instead, hire a good drill to put holes through a concrete wall. Standard warning be careful there aren't any wires or pipes there. Site the unit outside in the shade and off the ground a bit. The installation instructions should hopefully tell you also to insulate the pipes going through the wall. Dmcq (talk) 12:06, 15 May 2014 (UTC)


 * In fact here is a nice step by step intro showing the sort of thing required and the various tools needed. Dmcq (talk) 12:19, 15 May 2014 (UTC)


 * LOL, I'm trying to minimize to amount of work required and damage to the house, not maximize it. StuRat (talk) 12:40, 15 May 2014 (UTC)


 * Well of course one can always get the manufacturers to do it but it should cost you less than $400 in hire and extra equipment and it would look much better than a great hulking thing on the window. I'm sure you gain on the worth of the house. Dmcq (talk) 13:29, 15 May 2014 (UTC)


 * The laws of thermodynamics demand that the energy that these things consume as electricity plus the energy they remove from the air as they cool it MUST GO SOMEWHERE...and the "somewhere" clearly shouldn't be "back into the room again"! So there has to be some kind of external hose or something.  Using this waste heat to evaporate the condensate seems like a reasonable thing to do - so that may not be that inefficient.  After all, some people use swamp coolers to cool their homes - and evaporating water is a great way to get rid of waste heat if the air in the room isn't too humid to start with. SteveBaker (talk) 20:25, 14 May 2014 (UTC)


 * That's the problem. Unless you live in a desert, hot air comes with high humidity, and dehumidifying is as important of a function for an A/C unit as actual cooling.  Also, I find my A/C units dehumidify first, with very little cooling until they get the room humidity down to a reasonable level. StuRat (talk) 21:13, 14 May 2014 (UTC)


 * Same deal though - if it pulls the water out of the air while dehumidifying it - then evaporates the resulting liquid - then it just humidified the air again!  So even if it pulls some kind of stunt to get rid of the water, it still has to vent someplace outside.  Those darned conservation laws tell you that if you want to go from air with too much energy and too much water to air with less energy and less water - then there is going to be energy and water left over that has to go somewhere.   Doesn't matter how the machine does it - what matters is were the resulting matter and energy winds up.  In a household situation - out of the window or down some drain are really the only sensible options. SteveBaker (talk) 15:05, 15 May 2014 (UTC)


 * I wonder if you could use the temp diff from the coils to the outside air to generate a bit of electricity, to increase overall efficiency a bit. StuRat (talk) 16:23, 15 May 2014 (UTC)


 * You'd be decreasing their efficiency. If you had a really large radiator where the temperature differential was lower the efficiency could be improved. Dmcq (talk) 11:32, 16 May 2014 (UTC)


 * You want to maximize the rate of heat flow between the coils and the outside air. Anything that reduces this rate (such as a thermoelectric converter) reduces the overall efficiency of the cooling system. --Carnildo (talk) 00:18, 17 May 2014 (UTC)


 * Well, under my system where you provide minimal cooling by cycling on and off, wouldn't the heat in the coils be more valuable, once the A/C is switched off, if it could be used to generate electricity ? Yes, this would mean it would take longer before you would want to turn the A/C back on, but let's assume that's OK.  We could also use a larger heat-sink to hold the heat, like an insulated barrel of water.  StuRat (talk) 13:08, 17 May 2014 (UTC)

Static discharge - where is the charge held and how does it get conducted?
Through what route does static discharge from my person to, say, a tap (faucet)? My skin isn't a very good conductor of electricity right? Where about my person is the static charge being built up when the cause is certain items of clothing? Where are these electrons coming from and wouldn't it end up with an increasingly positive charge? --78.148.110.113 (talk) 22:31, 14 May 2014 (UTC)


 * You're right that skin isn't a very good conductor, and neither is air, which allows a charge to build up until large enough to overcome that resistance. If you were holding onto a good conductor, say a grounded steel bar, then the charge wouldn't build up.  For an example of a person holding a large charge, think of the case where a person's hair stands on end, because of the charge: .  StuRat (talk) 22:45, 14 May 2014 (UTC)


 * See Static electricity. According to http://www.sciencemadesimple.com/static.html electrons are lost from your body to the the material (e.g. wool) and so your body becomes positively charged (click on 'Read more' under 'Where Do the Electrons Go?' and then look at 'Triboelectric series'). When you touch a conductor such as a piece of metal and ground yourself then presumably electrons will then move from the ground to your body to replace those that have been lost and neutralise the positive charge. However, I'm sure someone will correct me if I got that bit wrong :) Richerman    (talk) 23:32, 14 May 2014 (UTC)


 * No, that's pretty much it. -- Jayron  32  01:59, 15 May 2014 (UTC)


 * There's a slight subtlety that the conductor you touch must be connected to the ground for you to discharge. My office has doors with a metal handle in an otherwise completely glass door.  You can build up a fairly significant static charge over the day, which you don't notice until you press the button for the lift on the way home. MChesterMC (talk) 08:28, 15 May 2014 (UTC)


 * In that case, if you have more of a charge than the handle, a slight amount of the charge will go into the handle, but since it has nowhere to go from there, once the charge is equalized, the flow will stop. StuRat (talk) 12:42, 15 May 2014 (UTC)