Wikipedia:Reference desk/Archives/Science/2016 February 13

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February 13

under what conditions will a Grignard or sodium hydroxide polymerize an epoxide

Nucleophiles like Grignards and organolithium reagents open up the epoxy ring, and so do alkoxides. But when the epoxy ring opens, a new alkoxide is generated, which can then open another epoxy ring ... I'm aware epoxides are used as plastics but apparently this is done under conditions of "curing" and isn't as simple as adding base. Which makes me wonder -- what prevents the newly-formed alkoxy species (especially in aprotic solvent) from attacking another epoxide, which then will create a new alkoxy species to attack yet another epoxide? For example, if my intent is to react ethylene oxide with n-butyllithium, what's to prevent polyethylene glycol polymerization as a side reaction? Yanping Nora Soong (talk) 02:20, 13 February 2016 (UTC)

Anionic polymerization of epoxides to make -CH2CH2O- polyether chains (with various substituents in place of the various H) is well known. One can consider concentration, reactant-ratio, competing nucleophilicity, and counterion effects. DMacks (talk) 22:04, 13 February 2016 (UTC)

Are PUFAs in cooking oils harmful?

Is the consumption of too much PUFAs harmful for health? The Wikipedia article polyunsaturated fat has no mention of any negative health effects. But I found some references, none of them reputed journals, which say too much PUFA is harmful. According to this article, PUFAs can cause free radical damage, excessive skin pigmentation, can damage pancreas cells, can impair protein digestion, can cause live damage. --IEditEncyclopedia (talk) 03:08, 13 February 2016 (UTC)

Too much of anything is harmful for health. The source you cite is only the tiniest step up from NaturalNews -- notice the author's list of recommended health books is a a head-spinning catalogue of woo. Shock Brigade Harvester Boris (talk) 03:19, 13 February 2016 (UTC)

There are 14 reviews and meta-analyses of the effects of PUFA on human health published in mainstream journals, some of which are free to read online. None of them find any dangers to PUFA consumption, even in babies. Now as Boris said, the poison is in the dose. Eat enough of anything and you'll probably get sick. And I'll note that the author of that article you linked got all of his information from the Weston A. Price Foundation, which is well known to advocate dietary advice that is completely divorced from science. Someguy1221 (talk) 05:43, 13 February 2016 (UTC)

cabin pressure for private jets

In airliners the cabin pressure is slightly lower than the normal ground pressure for cost saving reason. This causes a barely noticeable discomfort for passenger.

Is the same thing done for private jets? In this case, the passengers are presumably rich enough for pay for the comfort of 100% ground pressure.

The same question also applies for the humidity as well. [Airliner]] cabin air are pretty dry due to, again, cost-cutting measures. What about private jets? Johnson&Johnson&Son (talk) 06:18, 13 February 2016 (UTC)

According to [1], cabin pressure on private jets can be kept much closer to sea level than is typically done on commercial jets. However, maintaining standard atmospheric pressure is not always possible, as cabin pressure is fundamentally limited by the power output of the plane's engines. Someguy1221 (talk) 06:58, 13 February 2016 (UTC)

I didn't realize that maintaining the cabin pressure, whether for airliner or ultra comfy private jets, took that much engine power. I thought that aircraft cabins were pressure vessel so maintaining a particular pressure (that's within design limits) is "free" in the energy sense? Johnson&Johnson&Son (talk) 07:08, 13 February 2016 (UTC)

(I realise it's not "free" in the financial sense since stronger pressure vessel => more weight => more lift required => larger wings and/or bigger engines => higher costs.) Johnson&Johnson&Son (talk) 07:10, 13 February 2016 (UTC)

maintaining standard atmospheric pressure is not always possible, as cabin pressure is fundamentally limited by the power output of the plane's engines. ' absolute bollocks in context. The power to pressurise the cabin is small compared with the power output of the engines. Greglocock (talk) 11:36, 13 February 2016 (UTC)

If you're an expert, provide a better context or a better source. Someguy1221 (talk) 22:34, 13 February 2016 (UTC)

Actually, let me clarify this myself, given that it was given in poor context. The cabin pressure is fundamentally limited by the electrical power outputted by the planes engines, and the efficiency of the cabin pressurization system, and the air-tightness of the cabin, and the ability of the fuselage to withstand the stress of pressure differentials. Someguy1221 (talk) 08:50, 14 February 2016 (UTC)

The cabin is pressurized using bleed air from the engines, that means the same engines that push air backwards to go forward are quite literally shoving air into the cabin as well (via A/C packs to cool it down, compressing air makes it *hot*), not merely generating electricity for some electrical pump. 85.212.111.153 (talk) 08:00, 16 February 2016 (UTC)

(edit conflict) Stress is a big part of it - reducing pressure relaxes stress on the fuselage. See Cabin pressurization. Our article on bleed air (the air pumped out of the engines to power other systems) says that running cabin pressurization from the engines reduced their efficiency (although it doesn't say how much) but that many modern aircraft use electric pumps instead (which of course still need to get their power from the engine, but apparently this air is easier treat (i.e. to get to the right temperature and pressure). Smurrayinchester 11:46, 13 February 2016 (UTC)

Why not have a look at some promotional literature for several common types of small jet?

The Gulfstream 650ER is arguably the best that money can buy, (unless you're a serious super-billionaire who can afford a private Boeing). "At a cruise altitude of 45,000 feet/13,716 meters, a G650ER cabin is pressurized to an altitude of 4,060 feet/1,237 meters. That cabin altitude is almost two times lower than commercial airlines and significantly better than any non-Gulfstream aircraft in the large-cabin class." Forbes Magazine believes the sale price of this aircraft to be around $65,000,000, although as a general rule, if you want to get an accurate figure, you'd have to fly to the sales office, presumably in a credible aircraft.

Somewhere down the line is the Cessna Citation CJ4. "The CJ4 features separate temperature-control zones for the cockpit and cabin, and digitally managed pressurization that maintains a sea-level cabin up to an altitude of 21,067 feet."

A very nice, slightly more affordable aircraft is the Learjet 75. "The aircraft’s pressurization system provides a sea-level cabin up to 25,700 feet (7,833 m) and a maximum 8,000-foot (2,438-m) cabin altitude at 51,000 feet (15,545 m)."

The KingAir is not a "jet," but is a turboprop and uses Jet-A; pilots of the KingAir can log turbine time. Textron includes this helpful documentary, Transitioning from Piston to Jet on their sales page. The KingAir cabin pressurization controls are a little different than the more expensive jets: this article from Flying magazine explains: "One reason is that with five psi maximum cabin pressure, the cabin altitude is near 12,500 feet when flying at 30,000 feet. That's legal, but not comfortable for every pilot."

About the smallest pressurized cabin you can buy is a Mooney. An M20R is decidedly not a jet, but it will set you back a bit more than half a million dollars, brand new. I found a very nice 1969 Mustang for sale on Trade-A-Plane - N7727M, $135,000 - that has a pressurization switch and an automatic isobaric valve to keep your plane from exploding if you try to pressurize above 5psig (roughly 7,500 cabin pressure altitude at the aircraft's service ceiling). It is incredible what a little money can buy.

Nimur (talk) 16:38, 13 February 2016 (UTC)

Gulfstream's marketing appears to be outdated or misleading. The Boeing 787 Dreamliner is capable of 6,000 feet/1,830 m at 43,000 feet/13,006 m (service ceiling) [2] [3] [4]. I'm not sure what it would be at 45,000 feet but it's not likely to be almost two times 1,237 m. The 787 is definitely a commercial airline now and the ref didn't say anything about most. The Airbus A350 XWB is similar [5] although there are fewer in commercial service at the moment. Interesting enough, Cabin pressurisation suggestions the median pressurisation of both the 747 and A380 is actually below the 6000 feet level that Boeing claims is sufficient (as higher gives diminishing returns), although that probably means a fair few were higher at least for the A380. Some sources like [6] claim 5,000 feet for the A380, but that is contradicted by the study and I can't find any advertising from Airbus about it which suggests to me it's probably wrong. One interesting thing that the source does mention is the SyberJet SJ30 which is supposed to have a sea level cabin to 41,000 feet/12497m, although I'm not sure how easy it is to buy one (well unless you trust that they will deliver the new ones). I guess you could become friends with Morgan Freeman [7] [8] [9]. BTW some of those sources and [10] do discuss how passenger comfort is complicated and you shouldn't just focus on pressurisation. (The sources also discuss pressurisation levels for various airplanes but you may want to check this info, per earlier.) Nil Einne (talk) 19:35, 13 February 2016 (UTC)

Indeed, fair points all around, Nil Einne. One hopes that the buyers of expensive jet aircraft will do a little independent research with multiple sources, and fact-check all the advertisement claims. It is very true that new airliners like the Boeing 787 and the Airbus A380 do provide higher cabin pressurization; this was a major marketing advantage for these new aircrafts. Here are some details: Boeing 787 from the ground up, and the 787 No-Bleed System Architecture, both articles from Boeing's corporate communications magazine. Here's an article from airline Lufthansa: Cabin Air Circulation. I can't emphasize enough that the 787 is only a few hundred million dollars more expensive than the G650-series; so it's bound to have a few enhanced systems. My point, really, is to express that aircraft passenger comfort systems have an incredible range from the very low-end to very high-end. In principle, nothing prevents you from operating an A380 or a 787 or similar large passenger airliner as a private jet; well, it helps if you're some kind of Amir. A handful of the most extravagant movie stars and business-people might fall onto that price-point, too. Most ordinary billionaires would find a smaller jet suitable for their needs, and a lot cheaper to operate. I suspect Gulfstream isn't expecting its clientele to be comparing their aircraft against performance specifications of a wide-body superjumbo. Nimur (talk) 22:08, 13 February 2016 (UTC)

If you think the discomfort from the change in air pressure is "barely noticeable", try sitting near a screaming baby when its ears are popping due to the pressure change. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:22, 13 February 2016 (UTC)

On that topic - there is a great deal of misinformation regarding the required use of a safety restraint or seatbelt for a child when flying on a "private jet" - rather, when the child is a passenger on a flight conducted under Part 91 (or Part 135). Subsequent to one particularly severe fatal accident in 2009, FAA has clarified their seat belt guidance. This is a frequently-asked question in general aviation discussions. 14 C.F.R. §91.107 was amended in 2014; this is a good reminder to always check a current copy of the FARs, especially if you are going to be operating a private jet with small babies on board. Small children under two, like sport parachutists, are among the very few individuals who are especially called out as special exceptions to the normal rules for safety restraint; these individuals aren't impervious to accident, but federal regulations are a little bit more lenient regarding what safety equipment they require.

If the small babies are also sport parachutists, they may use the floor of the aircraft as a seat. In such a case, the operator of the aircraft would be wise to consult an aviation attorney for a professional opinion clarifying the applicable rules, among other reasons.

Nimur (talk) 17:59, 13 February 2016 (UTC)

It's not my fault that you can only afford shitty economy seats.Johnson&Johnson&Son (talk) 02:07, 14 February 2016 (UTC)

Heavens. Please review this flow chart. ericg ✈ 00:49, 17 February 2016 (UTC)

See also the thread Can an airliner provide ground level cabin pressure, temperature, humidity etc? on Aviation SE. – b_jonas 16:26, 15 February 2016 (UTC)

Dissolving Low-density polyethylene

So I have a project. I am making a tea infuser out of polyethylene (LDPE to be exact). I’ve made the overall shape, and now I want to give it a matte finish. The model is too complex to be sanded efficiently, so I am looking for an alternative way I could make it less glossy. I think it might be possible apply some chemicals that will dissolve the top glossy layer of plastic and thus make it matte. Unfortunately I have no Idea what those chemicals might be. So I am stuck with 2 questions:

Firstly I would like to know if you think it is even possible to give a matte finish to a polyethylene part by rubbing/dipping it into some chemicals? What chemicals could that be? Maybe a strong acids or even paint thinner(possibly heated)?

The second question is if my tea infuser would still be foodsafe after I apply said chemicals? If I understand correctly, to dissolve polyethylene I have to subject it to a chemical reaction. Does this mean I will end up having a part made of something other than pure LDPE? Can all the leftover chemicals be washed off after I got the desired finish? 46.138.235.28 (talk) 11:32, 13 February 2016 (UTC)

LDPE is pretty tough, and most solvents won't have an effect on it. That said, my experience (with vapour smoothing 3D printed parts, which means PLA and ABS) is that using solvents makes plastic look glossier, not matte. Rough sanding makes things go cloudy because it's a very random process - some parts get rubbed by the grains, some don't, so there isn't a flat surface to reflect light. Using solvents dissolves the surface evenly (and makes it flow a bit) so you get a glassy finish. Smurrayinchester 11:59, 13 February 2016 (UTC)

Another way to think of how that works (and a kind of spherical cow idealization) is to imagine a surface that's already perfectly flat and smooth with tiny little cube-shaped bumps on it. Let's mentally divide the surface into a grid that's the same size as the little cubical 'bumps'. (If you ever played Minecraft, you should have a mental model for what I'm saying.) If a chemical that dissolves the surface is applied, then the grid cells that are already flat will get dissolved away at the exact same rate everywhere - so the surface will stay flat. But a grid cell containing a bump will be dissolved away simultaneously on all five exposed faces of the cube. So the material in that cell is removed five times faster than for the already smoothed cells...and that results in bumps flattening out much faster than the general surface is eaten away. The net result is that the surface ends up smoother.

Now suppose that there cube-shaped holes in the material. The base of the hole only get lowered slightly - but the four adjacent grid cells get attacked from above and the side - so they dissolve away faster than the surrounding area - and that abrupt hole gets smoothed out laterally...and again, the surface ends up smoother.

So where the surface is initially smooth, it stays smooth - but where there are abrupt changes in surface shape, a uniform erosion process will tend to make them flatter.

A uniform erosion process clearly doesn't make the surface rougher - so rapidly heating the surface until it flows would have much the same effect. You need some source of randomness - which is what sanding or sand blasting does. I wonder if, in your case, applying an active chemical, mixed into a paste with some inert material (like sand) would produce the desired degree of randomness? SteveBaker (talk) 17:03, 13 February 2016 (UTC)

A tea infuser is placed in a cup of boiling water. Water boils at 100 °C. LDPE withstands temperatures of 80 °C continuously and 95 °C for a short time. Making a tea infuser out of LDPE is courting disaster. AllBestFaith (talk) 18:16, 13 February 2016 (UTC)

Indeed, I would avoid putting LDPE in contact with boiling water. Although I can find a few sources that say LDPE withstands boiling water, WP:OR - it will rapidly deform and/or melt when exposed to even these moderate temperatures near 100°C. Here is a source, Sterling Plastics of Minnesota, that cites several standard metrics, including a Heat deflection temperature of 120°F - much lower than boiling water or even warm tea. The plastic will melt at just above the boiling point of water. However, the thing about plastics is that their quality and material properties vary widely - you can't be "very very" certain that your material is guaranteed not to melt at 212°F - or even 180°F. This Material Safety Data Sheet for ExxonMobil's formulation of LDPE resin, hosted by SUNY Stony Brook, says it's insoluble in water and not particularly toxic... but I still wouldn't want to drink tea that "might" have some melted LDPE residue in it. The key takeaway is that you can't be sure exactly what goop your plastic sample contains, and you can't be sure what is going to dissolve in your hot water. Nimur (talk) 18:34, 13 February 2016 (UTC)

If the solvent dissolves the LDPE, then the LDPE dissolves the solvent. So only use a solvent you feel comfortable drinking with your tea. I didn't get to the bottom of the question of what plasticizers are there already and what effect they have - [11] makes LDPE sound like a safe alternative, but [12] says that estrogenic activity can be detected when LDPE is "stressed". I suspect melting, dissolving, and near-destroying over boiling water count as stress. Wnt (talk) 20:34, 13 February 2016 (UTC)

Two careers ago I was developing manufacturing processes for bonding or glueing plastics. There are a variety of solvents available and they are almost without exception stupid things to drink. I recommend sand blasting with sugar. Greglocock (talk) 20:59, 13 February 2016 (UTC)

Though I doubted as much, it occurs to me that there are environmentally friendly options like supercritical CO2 - looking this up, I find some articles like [13] that seem to suggest it dissolves LDPE, though almost without exception they're locked behind paywalls in obscure journals; this is one of those topics that We're Just Not Allow To Know About. But of course, it's essentially impossible for a hobbyist project to use CO2 for this anyway, so the grapes were sour anyway. Wnt (talk) 13:42, 14 February 2016 (UTC)

Damaging effects of gravitational waves

It seemed to me, though I don't really know anything about the subject, that if gravitational waves actually stretch space itself, then even intense waves would not cause any damage to physical objects as they passed through. However, at [14], it says that sufficiently strong waves would "rip you apart". Is that actually correct? 81.132.196.131 (talk) 20:34, 13 February 2016 (UTC)

Spaghettification, due to a non-homogeneous gravitational field near a black hole, may be relevant. StuRat (talk) 20:41, 13 February 2016 (UTC)

If the frequency of the wave is low, then your physical size will be preserved by the same forces that usually preserve it (electromagnetism and electron degeneracy pressure), but if the frequency and amplitude are high enough that they can't react in time, then you will rip/squish instead. Analogy: a boat can survive an ocean wave of any amplitude if the frequency is low enough (because any ocean height is equivalent to any other for floating purposes), but higher frequencies will damage it. -- BenRG (talk) 22:47, 13 February 2016 (UTC)

Its a big theme in Star Trek: Enterprise (season 3) and Star Trek: Enterprise (season 4) but, as many ideas in scifi are, real physicians would discribe this as preposterous imagination contradicting the laws of their science. Additionally you could aproach such an imagination from logic. If that was real, why isnt the hole universe already ripped apart into dust, given these waves would be frequent, atleast in astronomic timescale, by all these waves that must have already occured in the past? --Kharon (talk) 07:29, 14 February 2016 (UTC)

Nutrients needed by cuttings in water, specifically Geraniums

pink and red American Begonias

I've been growing |BegoniaGeraniums from cuttings for a few years. Last year I took some leggy cuttings, from a red and pink plants, rooted them in water, and potted them in the early spring. They look just like the plant to the left, although that is not of my plants nor my upload.

This year I decided to trim the longest stems from the potting that looks like the one at right, and to root them in a clear vase. Given the temperature is 6F right now, I have taken my plants out of the window. These cuttings are doing well, about 6-8 inches long, with 2-3 inch roots. But I don't want to pot them until mid-April. when it will be warm enough for them to stay out all night.

My question is, other than three (smaller-than-peppercorn) balls of NPK fertilizer, do I need to add any other nutrients? Thanks. μηδείς (talk) 20:53, 13 February 2016 (UTC)

Just wondering, how do you deal with the water going bad ? I would think you would need to frequently toss out the smelly water and replace it (hopefully with rainwater or melted snow or at least tap water that's been left out long enough to lose the chlorine compounds). But then that means you would lose the fertilizer every time you replace the water. StuRat (talk) 21:03, 13 February 2016 (UTC)

My wife does a large amount of growing plants like this, and her recommendation is to simply pot them on into compost, but keep the plants indoors until it's safe to put them out.--Phil Holmes (talk) 10:35, 14 February 2016 (UTC)

Why are do you call them American begonias when they are pelargoniums? Richard Avery (talk) 13:44, 14 February 2016 (UTC)

• Thanks, all. Answering the above, first, I have almost no sense of smell, due to nasal-polyp surgery, so I just don't worry about the smell. (I do pour out the water and refresh it when it gets low, but I have only had to do this twice since I took the cuttings at Thanksgiving--the second time the day I posted this question) It's my apartment, and, well....

Second, I don't want to pot them in soil yet, because I am keeping them under the desk lamp next to my computer. They aren't blooming yet, but they are very luxuriant, and they will go in a much larger pot when I do plant them, at which point they'll probably go to a friend or relative with more space than I, as a gift.

Third, [Ack--I said Begonia, meaning Geranium--I do the same with Hydrangea] I call them "Geraniums", because that is the US common name for the plants I pictured above. That's what my mom called them when I helped her plant a bed of them in 1973. I have never heard anyone ever call them Pelargonia, and only became aware of this in the last two years, since I first looked up the Pelargonium × hortorum article. μηδείς (talk) 01:22, 15 February 2016 (UTC)

• I am still interested in the original question. If I don't intend to pot my cuttings for 6-8 weeks from now, is there anything I should add besides NKP to the water in which they have rooted? Thanks. μηδείς (talk) 01:40, 16 February 2016 (UTC)

@Medeis: No, they are fine, don't add anything. Recall that something like 95% percent of their dry weight comes from CO2 in the air. And so ~99.99% of their wet weight is not even NPK, let alone any other trace nutrients. Plants get very little relative mass from soil nutrients, and you mostly likely didn't need to add anything, though the fertilizer probably won't hurt. I might have considered putting in a bit of rooting hormone at the start, but since you have roots already there's no need for that. FYI a fun trick for propagating from cuttings in water: any species of willow will root easily, and exude the goodies (auxin, salycylic acid, etc) into the water as it does so, so most plants will root better in water if you start them along with a pencil-sized willow branch, and you can start other things that would not be possible without some hormonal assistance. SemanticMantis (talk) 05:32, 16 February 2016 (UTC)

Thanks, The main issue is that this is the first time I have rooted a cutting that I did not mean to pot or plant it immediately once the roots were sufficient. I have been pretty successful with either rooting the shoots of, or germinating seeds from the wild, but oddly enough, never heard of the willow trick, even though we used auxin in high school, and I have a jar of rootone (of course). I'll have to go get some willow withies ASAP. μηδείς (talk) 21:58, 16 February 2016 (UTC)

PDF Beiträge zur Araneologie (Beitr. Araneol.), vol. 2: Fossil spiders in Dominican amber?

Is there a PDF of Jörg Wunderlich's book Beiträge zur Araneologie (Beitr. Araneol.), vol. 2: Fossil spiders in Dominican amber? If so how can I download it? Very short question, so sorry, but it would be greatly appreciated if you could. Thanks, Megaraptor12345 (talk) 22:21, 13 February 2016 (UTC)

I don't remember seeing it, although I might have; I'd have to use a search engine. Maybe you could try yourself? Search engines use something called a "web spider", something you seem to have an interest it. Try https://duckduckgo.com GangofOne (talk) 23:03, 13 February 2016 (UTC)

Thanks guys, I found it. Megaraptor12345 (talk) 10:28, 14 February 2016 (UTC)

What about respecting the copyright and buying the book? --Scicurious (talk) 00:49, 14 February 2016 (UTC)