Science desk
< January 31	<< Jan \| February \| Mar >>	February 2 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 1

Unregistered SIM cards

Which countries still don't require people to register their prepaid SIM cards? --49.145.78.106 (talk) 04:46, 1 February 2014 (UTC)[reply]

Which countries do? HiLo48 (talk) 07:29, 1 February 2014 (UTC)[reply]

Certainly not in the UK. We bought a 'disposable' SIM card (with cash) to use while we were on vacation there back in December - it cost 50 UK pounds and had 50 pounds worth of pre-paid minutes & texts on it - and the whole process was completely anonymous. SteveBaker (talk) 14:19, 1 February 2014 (UTC)[reply]

@HiLo48: Which countries? Examples: Kenya, Malawi, Zambia, Uganda --49.147.165.12 (talk) 02:31, 3 February 2014 (UTC)[reply]

South Africa https://www.mtn.co.za/support/Pages/Rica.aspx 196.214.78.114 (talk) 10:18, 3 February 2014 (UTC)[reply]

I wonder whether these cards in the UK, Kenya, Malawi and so on are truly anonymous, or whether they require some form of activation like calling the number to be activated from a landline, which would leave a track to follow in case you decide to use the SIM for harassment, prank calls, drug dealing, or other criminal activity. Indeed, although they might be quite convenient for tourists, checking the ID of someone would just require 1 minute, and can avoid problems down the line. OsmanRF34 (talk) 13:00, 3 February 2014 (UTC)[reply]

It is rather unlikely that there is any such requirement for activation with anonymous prepaid systems: you arrive at an airport, and expect immediate activation of your newly purchased card. Even a landline is of little use, because it could be from the lobby of a hotel. And assuming that the telephone infrastructure leaves the sort of trace, and that it is readily accessible, is assuming NSA-like capabilities of third-world countries. It is also a misconception that registering numbers is a direct countermeasure to crime; it is not difficult to get a card that is registered in way way that does not connect it to the user. It seems more likely that the registration process is a way of simplifying traffic analysis where full traffic analysis is still beyond the capability of the authorities. I suspect that in countries with the capability of recording and analysing telephone traffic on an ongoing basis such as the UK and USA, individuals can be tracked far more reliably through analysis of the frequency of specific numbers called, even when they are not from the same phone. —Quondum 16:05, 3 February 2014 (UTC)[reply]

The SIM card I bought at a phone store at London Gatwick airport may well have needed some kind of registration - but that was all done by the guy behind the counter at the store - who didn't ask our names or require any sort of ID. Since we paid with cash - any kind of registration process could only have identified the store and/or it's owner. Of course, the airport is stuffed full of security camera - I'm quite sure that if someone in authority wanted to figure it out, they could have timed when the card was sold to the pictures of my wife and I standing at the store counter - then compared those images to people going through passport control and thereby figured out *exactly* who bought the phone card with that phone number associated with it. The incredible power of this kind of security surveillance is not in one single source of information - but in combining multiple sources - each of which is relatively innocuous.

Note also, that every phone has a unique number built into it - aside from the number on the SIM card and the actual phone number. That number can also be read from the cell tower - so just buying a 'disposable' SIM card isn't enough to ensure that you can't be tied to phone calls. You'd really need to buy a 'disposable' phone too. SteveBaker (talk) 19:23, 3 February 2014 (UTC)[reply]

store meat in vacuum?

A couple of sections up, I was reminded of a novel set in a city on the Moon. Expecting a large influx of refugees, the city slaughters most of its meat animals, to reduce competition for air and water. They can't eat all the meat right away, and haven't enough freezer space for all of it; but, I thought, what if the carcasses are stored outside? Obviously they'll dry out in a hurry (enough of a hurry to kill all bacteria?), but does that make the protein useless? Could it be used later for soup stock, say? —Tamfang (talk) 07:10, 1 February 2014 (UTC)[reply]

Lots of dried meat is eaten around the world see: Dried meat. It's just a case of preparing it properly - usually using salt to kill the bacteria. Richerman (talk) 08:34, 1 February 2014 (UTC)[reply]

The freezing would prevent bacterial problems - so you don't need the salt. Wrapping the meat tightly in plastic would certainly help to delay the onset of freezer burn in much the way that vacuum packing does. But in any case, freezer burn mostly only affects the surface of the meat - so entire cow carcasses would probably be unaffected - especially if the hide is left on it. SteveBaker (talk) 14:15, 1 February 2014 (UTC)[reply]

Note that anything outdoors on the moon will fluctuate between extremely cold and extremely hot, with a "day" lasting a month. The hot phase will do bad things to meat. Looie496 (talk) 16:31, 1 February 2014 (UTC)[reply]

Although some of the craters are in permanent shadow and extremely cold at the bottom [1] Richerman (talk) 17:18, 1 February 2014 (UTC)[reply]

Is sea star wasting syndrome the same thing as starfish wasting disease?

I've created an article for sea star wasting syndrome, which is currently in the news. Some searching revealed an already existing article starfish wasting disease. It looks like these might be about the same thing, but I don't know enough about marine biology to make the call. Are these the same? -- The Anome (talk) 11:19, 1 February 2014 (UTC)[reply]

They're the same thing. I saw a report on this problem on TV a few weeks ago. The terms "sea star" and "starfish" are synonyms. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:53, 1 February 2014 (UTC)[reply]

Thanks. I've added mergefrom/mergeto tags to the articles. -- The Anome (talk) 14:19, 1 February 2014 (UTC)[reply]

Dieting too quickly.

When dieting, it's frequently said that if you eat too little, your body will go into "starvation mode" in which your metabolism becomes more efficient - and it'll actually be harder to lose weight.

My question is for how long do you have to eat too little to produce this effect - and how long does the body take to go back to a normal metabolic rate when you resume eating more?

Some diets claim that skipping even a single meal is too much - where others suggest that you need to take a break from dieting every four to six months in order to avoid this effect!

Is there some scientific evidence for the onset, duration and magnitude of this effect? Is it even true?

SteveBaker (talk) 14:40, 1 February 2014 (UTC)[reply]

This study shows that fasting for 24 hours actually increases metabolic rate. Also check out this blog post which - using thyroid surrogate markers - suggests that going under 25kcal/kg lean BW/day (in combination with an exercise-induced 1300kcal/day deficit!) could decrease metabolic rate. Markr4 (talk) 17:33, 1 February 2014 (UTC)[reply]

Firstly, dieting really means: Latin diaeta, way of living, not food reduction. Simply reducing food intake can also reduce muscle mass as well as fat. The latter is not good. The body is sacrificing itself to make up for the shortfall of real nutrition (starvation mode). Dieting should really be about eating balanced diet where the body feels sated and not hungering for more, with all it needs have been satisfied. The high sugar and fat rich foods (like ice cream) that we like today, were unknown to out ancient ancestors. Modern prepossessed foods are very short on those other stuffs, that stops our bodies hungering for more. The packaging may have little bit printed on the back stating the fibre content etc as the amount recommend as a daily intake but add up the days consumption of all those printed bits and there is a lot missing. So the body is hungering in the hope of some real food to make up for that short full. The Paleolithic diet is odd to try at first, but it doesn't necessitate eating too little. Alas, it is also not a commercially viable wait-loss-plan that can be owned by any company, so it receives no commercial promotion.--Aspro (talk) 18:50, 1 February 2014 (UTC)[reply]

Well, to be fair, a real Paleolithic diet probably involved a lot of fasting, need it or not. :0 Wnt (talk) 03:53, 3 February 2014 (UTC)[reply]

True. In palaeolithic times and up to quite recently (on the evolution time scale) there were seasonal times of want. The homo-sapient has a metabolism to go into a acute starvation mode but that is different from a 'chronic' starvation mode as in modern dieting protocols . For instance, we can store up several months worth of ascorbic acid to see us over the winter. Swedish mothers used to encourage their children to run around naked in the spring sunshine (even though they did not have a notion about vitamin D) but cultural wisdom that got passed down from mother to daughter was proved right. A true palaeolithic diet in this sense, would harken back to the old wisdom of my grandmother's time, which was only eat foods that are in season. Now that one can buy Californian grown lettuces way up in Alaska in January, makes this true natural diet difficult, for as I admit, do like a good salad at any time of the year. So one has to aim for the median. If one is living up in (say) Caribou, Maine, then eating high fat foods (energy rich) during the winter keeps you warm. Yet for a Hispanic living down in the warm south and consuming high fat/sugar takeaways.... this is a recipe for diabetes, obesity and an early death.--Aspro (talk) 22:04, 3 February 2014 (UTC)[reply]

Aspro's claims about "nutrient deficiency" increasing appetite are common, but there isn't actually any evidence for it. It's more likely that foods like ice cream promote overindulgence because they taste nice. Markr4 (talk) 12:20, 3 February 2014 (UTC)[reply]

Yeah! Heroin an Smack make you feel nice to. What is your point? Micronutrient-rich diet's? I say you are allowing yourself to baffled by 'his' science. A good diet contains more. An mixture of protein, carbohydrates, fatty acids etc., as well as micronutiants and vitamins. Also, talk to a cattle farmer. He may mention Mineral lick. The cattle partake in them instinctively (cattle can't read health advice articles). If you have ever looked after livestock – you will see they go for what they need first. Cumulatively, that blows your sided Stephan Guyenet argument out of the water. --Aspro (talk) 21:59, 3 February 2014 (UTC)[reply]

What exactly is your claim? My understanding from your original reply was that: modern diets promote obesity via excessive caloric intake, this excessive intake occurs because the body is still hungry for the nutrients that are missing in junk food (e.g. fibre, protein, omega 3, ...). My dispute with this claim is that modern diets aren't actually lacking in any nutrient. You can still become obese eating a nutrient-rich diet if you just add in the junk food on top, but presumably you're claiming that if one eats a nutrient rich diet, one will not have an appetite for junk food such as ice cream? Please clarify. Markr4 (talk) 12:29, 4 February 2014 (UTC)[reply]

Yes, if one eats a nutrient rich diet, one will not have an appetite for junk food such as ice cream – it has no appeal. To try and eat junk food on top of a nutritious diet and it feels like force feeding and unappetizing. The important word here is Nutrient. Your quote:modern diets aren't actually lacking in any nutrient. Ah, but do they contain enough? E.g., Your automatic transmission may have a little fluid in it but if there is not enough your car what be going anywhere. The noise it makes means it hungers for more transmission fluid, adding more engine oil to the engine does not help this. Breeding the Nutrition Out of Our Food, The American Society for Clinical Nutrition: Origins and evolution of the Western diet: health implications for the 21st century. Nutritional Science seems to be on my side rather than uneducated opinion. Is that sufficient clarification? If not, please post as a separate question as it is getting off topic to the OP's question.--Aspro (talk) 19:52, 4 February 2014 (UTC)[reply]

Macrophages (and glucose, or glycation products)

I'm reading a textbook of mine and came across a claim during a discussion of how the body prevents glycation and cross-linking of proteins, that macrophages "seek out glucose molecules, engulf them, destroy them, and send them to the kidneys for elimination". I have never heard of this function of macrophages and questioned whether it was true, but cannot find any sources supporting this claim. Does anyone know if this actually happens? Bramble claw x 15:47, 1 February 2014 (UTC)[reply]

It's true in a sense but weirdly worded. Glucose is the fuel that macrophages primarily burn, so they do "engulf and destroy" them, but the more commonly used terms would be "uptake" and "metabolize". The products of glucose metabolism are CO2 and water -- the water is indeed sent to the kidneys for elimination, but this is again a weird way of putting it. Looie496 (talk) 16:27, 1 February 2014 (UTC)[reply]

Yeah, I was wondering if that was what they meant, but in that case, all cells that metabolize should have been mentioned. Bramble claw x 17:26, 1 February 2014 (UTC)[reply]

It seems they must have wanted to say "seeks out glycated molecules", otherwise they went to a lot of bother to say macrophages absorb sugar from blood plasma, and there'd be no point of saying anything was sent to the kidneys, unless they meant water. μηδείς (talk) 23:06, 1 February 2014 (UTC)[reply]

Yeah, I think they're looking for advanced glycation end-products with both hands and a flashlight. Wnt (talk) 01:54, 3 February 2014 (UTC)[reply]

Stiffest Material

Wich materiasl has the highest Bending stiffness? I want to ask cause it is realy interresting which material has the most highest stiffness or bending stiffness. cause you can make great things out of it and you have little weight but you dont have to make complaints out of it.Saludacymbals (talk) 17:49, 1 February 2014 (UTC)[reply]

You might want to read articles such as Young's modulus, Stiffness, Graphene and Carbon nanotube. You might not be looking to maximize some specific property, or you might find that many materials exist that surpass your expectations, and that other criteria (other properties and cost) might be significant. —Quondum 19:15, 1 February 2014 (UTC)[reply]

From the basic theory of bending, there are 2 important equations relating materials properties, loading, and geometry. The first important property is the Young's modulus. However, the yield strength is also important as the theory is only valid as long as the stress at all points remains below the yield stress. Which one is more important would depend on the geometry of your beam because, as they depend on factors like the second moment of area and how the load is distributed.

It's also only valid for pure bending (there are more complicated theories that can take more complicated loading into account). The geometry can also affect whether it will buckle before it will fail in bending.

And if you're making an actual object out of something, you also have to take brittleness into account. Many stiff materials are also brittle, which means if you do exceed the maximum load, it will shatter rather than bend in plastic deformation.

Many materials also exhibit anisotropic properties (properties that differ depending on direction). Rope is fairly stiff when pulled in tension but has virtually no bending stiffness because it's made up of fibers all oriented in one direction. So how you turn your raw material into a bar will also affect its bending strength.

The highest Young's modulus known is linear acetylenic carbon. However, all the calculations are theoretical based on quantum mechanics no one has actually been able to make more than a few molecules of it and it's not known how, or even if, it could be made into a bulk material.

Diamond is a distant second and could be used to make really small objects.

If you wanted to make something relatively big, the best choice is probably tungsten carbide. It's usually formed as a powder mixed with a softer metal like cobalt. But its melting point is "only" 2870 C, so casting it into a solid piece is difficult, but possible. Osmium has similar properties but at around US$100/gram (where 1 g is a 3.5 mm cube) it probably isn't very practical. Mr.Z-man 21:12, 1 February 2014 (UTC)[reply]

Yes. The stiffest materials such as diamond carbon nanotube are too exotic for commonly manufactured things and you may be more interested in materials with high strength-to-weight ratio. Consider the usefulness of balsa wood which weighs little but is used to construct a warplane, wind turbine blades or a sea-going raft because its Specific strength (see article) exceeds metals such as aluminium and brass. You may also be interested in Steel which inexpensive, recyclable and is not one but a wide range of different alloys 1 2 3 that can be selected not only for stiffness but also for their strength, hardness, toughness, wear resistance, corrosion resistance, Weldability, Ductility and hardenability. I don't understand what the OP means about complaints but suspect that Cymbal making may be another article of interest. 84.209.89.214 (talk) 21:18, 1 February 2014 (UTC)thanks for your kind information! but i only thought of the bending stiffness from a material in this case.Saludacymbals (talk) 21:43, 2 February 2014 (UTC)[reply]