Wikipedia:Reference desk/Archives/Science/2014 July 27

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July 27

Bubonic Plague

What is the chance of contracting Bubonic plaque from a bite from a rat infected with Bubonic plague? Hypothetically in this scenario infected fleas of the rat didn't bite the person (the normal vector to host transferal for yersinia pestis). --KAVEBEAR (talk) 02:07, 27 July 2014 (UTC)

I hope this isn't actually a request for medical advice. If you or someone you know has been bitten by a rat, please see a doctor!

The CDC has a number of web pages about plague linked from this page. This page about its "Ecology and Transmission" lists three transmission modes: fleas, airborne droplets in the case of pneumonic plague, and "contact with contaminated fluid or tissue". Well, being bitten is a form of contact, so it would depend on whether the rat's mouth and saliva contain the bacteria. This page about its "Symptoms" says that bubonic plague bacteria multiply in the closest lymph node, but "can spread to other parts of the body". So it makes sense that a rat's bite could indeed be infectious. I was not able to find anything directly addressing the question "What is the chance?", though. --50.100.189.160 (talk) 09:38, 27 July 2014 (UTC)

Also, I believe many people have at least a partial immunity to bubonic plague by now, which is why, despite there still being many areas of the planet where people, rats, and fleas all live closely together, it's not the type of pandemic it once was. Of course, if a new strain develops, people may lack any resistance to that, and it could once again become widespread. StuRat (talk) 13:06, 27 July 2014 (UTC)

There are nearly always a few people immune to almost any disease; consider the case of AIDS-resistant sex workers. Why bubonic plague doesn't flare out into Black Death any more is not well understood, but the existence of a few resistant people is probably not a significant part of the explanation. Antibiotics, advances in vermin control, and greater separation of people from animals probably all play a much larger role. It's also possible that the bacterium itself is now different. I recall reading a article which noted that, during plague epidemics, everything involved is sick - the people, the rats, the fleas, and even the bacteria themselves. Matt Deres (talk) 19:01, 27 July 2014 (UTC)

Unlike AIDS, bubonic plague has been around for well over a thousand years, and killed off a substantial portion of many generations, giving human survivors time to develop immunity, assuming it hasn't mutated to prevent this. And, of course, a population develops herd immunity without every individual being immune. StuRat (talk) 19:45, 27 July 2014 (UTC)

Yes, hosts can evolve to become more resistant, but the infectious agents can also evolve to become more or less virulent. A highly fatal disease is likely to become less so in order to maximize its spread and avoid killing off all the hosts. - Nunh-huh 03:46, 30 July 2014 (UTC)

The factor of resistant people becomes apparent when you watch the mortality rates over smaller periods of a century or so - epidemics tend to come in waves, as more non-resistant people fill up the population, only to be culled every few decades. You see that in the plagues of medieval Europe and in other epidemics like cholera. The current situation is something different; modern Western populations are not immune to plague - we've had no real selective pressure for centuries, so we'd be easy pickings for Yersinia. What's changed is our relationship to animals and fleas combined with effective drugs to nip potential plague outbreaks fairly easily. You know who doesn't have those things? - the places that still experience plague outbreaks, like the poorer areas of India. Matt Deres (talk) 03:01, 30 July 2014 (UTC)

Oddly enough, the reverse seems to transmit the disease well - cats and dogs biting infected animals get the disease via the mucous membrane in their mouths ref. I haven't found anything that directly answers your question, but that does point to the disease passing through the mouth. Matt Deres (talk) 18:51, 27 July 2014 (UTC)

I think a bigger reason is that people are more hygienic and don't have fleas as a general rule. Fleas biting people was the transmission route during the black death periods. When the rat die, fleas went to a new host and Europeans didn't particularly care or bathe regularly. Compare that with Japanese culture in the same time period. --DHeyward (talk) 19:48, 27 July 2014 (UTC)

Rats don't bite humans unless they are rabid or need to defend themselves. They are a prey animal. Looie496 (talk) 14:46, 28 July 2014 (UTC)

It only takes once. Doctor to patient: "The good news is, you don't have bubonic plague. The bad news is, you've got rabies. It was nice knowing you." ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:18, 28 July 2014 (UTC)

In spite of the fact that predatory animals such as dogs and cats get the plague and presumably continue to bite humans and other animals at least occasionally, animal bites (well, mammal bites) are not a significant vector of plague transmission. Rather, plague normally is spread among animal populations from prey to predator. So it would seem that the chances of getting plague from the bite of an infected rat are pretty low. It is not impossible; a bite that draws blood could expose you to a risk of septicemic plague. However, while that form of the disease acts very quickly, it is by far the least common of the three major forms of plague. John M Baker (talk) 18:33, 29 July 2014 (UTC)

LAMI

What does a matrix isolation setup look like where the guest species is generated by pulsed laser ablation, and where post-deposition photosynthesis is facilitated? Plasmic Physics (talk) 12:50, 27 July 2014 (UTC)

What does LAMI stand for here? Matrix isolation is an experimental technique in chemistry and physics where a material is trapped within an unreactive matrix. A host matrix is a continuous solid phase in which guest particles (atoms, molecules, ions, etc.) are embedded. Here are various images. 84.209.89.214 (talk) 01:07, 29 July 2014 (UTC)

Laser Ablation Matrix Isolation. Plasmic Physics (talk) 05:53, 30 July 2014 (UTC)

Scientists talking outside of their area of expertise?

Is there are name for those situations where someone with a solid scientific background attempts to speak with authority on a subject matter far outside of their own particular area of knowledge - and ends up talking utter nonsense of the 'not even wrong' variety or perpetuating horrible bunk, yet nonsense which is taken seriously by the public because the person advancing the idea is an otherwise well-respected doctor, or a professor, or whatever?

For example, you might get a theoretical physicist claiming that he has discovered proof that Jesus walked with dinosaurs, or a chemist stating that he has discovered a method of curing cancer with magnets. Things that many people in the real world would dismiss as 'probably hooey', if the source had just been 'some random guy with a website'. --Kurt Shaped Box (talk) 20:39, 27 July 2014 (UTC)

Ultracrepidarian. See also argumentum ad verecundiam and junk science. Tevildo (talk) 21:11, 27 July 2014 (UTC)

Thanks. I could name some examples, but WP:BLP. I'm sure that you can all think of a few though... --Kurt Shaped Box (talk) 21:50, 27 July 2014 (UTC)

Well, since he's dead, we can name Linus Pauling. StuRat (talk) 14:28, 28 July 2014 (UTC)

Indeed, and this leads to the answer to the OP: "the Linus Pauling effect". --Heron (talk) 19:47, 28 July 2014 (UTC)

So, is he the reason for the 'take your vitamin CD - there's something going around' (or 'eat lots of oranges when you have a cold - because you need the vitamin C') thing? --Kurt Shaped Box (talk) 22:32, 28 July 2014 (UTC)

Appeal to authority and Ad hominem are articles referring to related concepts. They describe the error in saying "What this scientist said about the history of Rome sounds a bit strange but he is a highly respected nuclear physicist so he must be right." Dolphin (t) 01:40, 29 July 2014 (UTC)

The other day someone told me that Buzz Aldrin doesn't believe in evolution. They didn't seem to care when I pointed out that his degree was in engineering. Katie R (talk) 15:34, 29 July 2014 (UTC)

I should point out that Aldrin, although a devout Christian, does believe in evolution. See this interview from the Daily Telegraph. "It was not that remarkable, that special, that unusual, that life here on earth evolved gradually, slowly, to where we are today." Tevildo (talk) 16:17, 29 July 2014 (UTC)

Perhaps the other person was thinking of global warming? Aldrin does work as an example here in that he has publicly spoken in favor of climate change denial, but he has no expertise in climatology. See Buzz Aldrin#Climate change. Red Act (talk) 16:42, 29 July 2014 (UTC)

Well I'm actually quite happy with scientists giving an opinion in an area they are not too familiar with. And I take note of their views. After all they are trained in the scientific method. However I would point out that Buzz Aldrin is not a scientist - he is a famous and I think quite intelligent person but he has not had a scientific training so his views count about the same as any other reasonably intelligent Joe Public as far as I'm concerned which I'm afraid is not terribly high compared to the scientists involved in an area of study. Dmcq (talk) 17:01, 29 July 2014 (UTC)

I guess one can debate what counts as a "scientist", but Dr. Aldrin does have a Doctor of Science degree from MIT in astronautics. His doctoral thesis was "Line-of-sight guidance techniques for manned orbital rendezvous." Red Act (talk) 17:24, 29 July 2014 (UTC)

That does count as a training in science even if he isn't a scientist. I guess I really mean scientists as lots of people study like that but it is just something they do on their route to doing something else. One has to admit though that a training in the scientific method is nowhere near a full protection from irrationality - it is just a help in keeping on the straight and narrow. Sometimes I wonder if the best measure of intelligence is the ability to rationalize and delude oneself, scientists need help in keeping that in check. Dmcq (talk) 22:32, 29 July 2014 (UTC)

Yeah - just to bring up a good example, there have been a few cases over the years of scientists loudly proclaiming that they have discovered the one real psychic in the mass of phonies and proved beyond all doubt that physic phenomena exist - and basically been all like 'I am an intellectual and a man of science - it is ABSOLUTELY IMPOSSIBLE that I have been fooled by well-executed magic tricks or rationalized away any results that didn't fit in with what I was hoping to find' (followed by listing all their qualifications and accomplishments in a completely different area) when challenged by sceptics. Good old-fashioned hubris, I guess... --Kurt Shaped Box (talk) 22:57, 29 July 2014 (UTC)

Does Newton's law of cooling apply to a hot car?

An automobile's interior on a sunny day will heat up, but eventually will have a limiting temperature after a few hours. I'm not sure if the law applies here, since the temperature rise is due to external radiation rather than conduction alone, but a graph I've seen has shown that without air conditioning, the rise appears to be of the form A-exp(-at). Is my intuition correct?--Jasper Deng (talk) 20:58, 27 July 2014 (UTC)

Yes -- as a car heats up, it will lose more heat to its surroundings until eventually the rate of cooling will equal the rate of heating. 24.5.122.13 (talk) 01:58, 28 July 2014 (UTC)

That doesn't really answer my question, since there are an infinite number of functions with finite initial condition and a finite limit as t→∞.--Jasper Deng (talk) 03:01, 28 July 2014 (UTC)

To a first approximation, yes. The external heat source (the sun) in not involved n the law of cooling; it is merely a constant power source. In your exponential model, you have assumed that the interior of the car acts as a single thermal mass. However, under some conditions, you might get the system acting according to differential equations of higher order. For example, if the body absorbing the bulk of the solar radiation is a metal object of substantial thermal mass inside the window, the interior of the car would initially warm up very slowly, with temperature gain accelerating as the metal object grew hotter, after which equilibrium would be reached. This would be expected to result in interior temperature rise being the sum of two decaying exponentials with different time constants. Nevertheless, for each heat flow path, Newton's law of cooling would remain fairly accurate. —Quondum 03:14, 28 July 2014 (UTC)

Some complicating factors:

1) The sunlight will not be constant, but will vary as the Earth rotates, clouds move over the car, etc.

2) There are multiple forms of cooling. At a low temperature difference, thermal conduction from the car to air will occur. At higher differences, the air outside the car will start to rise as laminar flow, assuming no wind, setting the car up like a cooling tower, using convection to cool the car faster. Wind has the potential to cool the car even quicker. Then, at high temperature differences, radiation of infrared/heat from the car will become significant.

So, other than in lab conditions, I wouldn't expect to see a smooth graph of interior temps. StuRat (talk) 14:40, 28 July 2014 (UTC)

In my local newspaper, I saw a graph consistent with Newton's law of cooling (but note again my comment about the existence of other such functions)- it was only for the first hour or so, when the change in the sun angle is small enough to be neglected, it would seem.--Jasper Deng (talk) 15:45, 28 July 2014 (UTC)

That seems reasonable. In most physical systems, simplifying assumptions can be made, and the simplified model then remains a reasonably accurate description. If your question is whether a first-order model is a reasonable for the typical parked car, the answer would be yes, mostly. One can argue that in the time span involved the typical car on a typical day can be adequately modelled as a single thermal mass with a constant power source and a cooling function that obeys Newton's law of cooling. Over very short and very long times, or with atypical configurations or nonconstant heat source profiles, the complicating factors become significant. So, in effect, for the typical configuration, your intuition is correct. —Quondum 16:11, 28 July 2014 (UTC)

Newton's law derives from $C{\frac {dT}{dt}}={\frac {T^{*}-T}{R}}$ (for heat capacity C, "external" temperature $T^{*}$ and thermal resistance R). Adding a constant heat input q is equivalent to changing $T^{*}$, which simply means that the equilibrium temperature isn't the same as the surrounding temperature. For a hot car, this is hardly surprising! --Tardis (talk) 07:44, 30 July 2014 (UTC)

Aftermath of the 79 A.D. Mount Vesuvius eruption

This could be an appropriate question for the Humanities desk too, but I decided to ask here.

Following the Eruption of Mount Vesuvius in 79, the deaths of 16,000 people and the loss of several towns and villages to the volcano, I presume that the Roman authorities will have launched an investigation to determine exactly what had happened there - and that learned men of the day would have been sent forth to the area soon afterwards to investigate and tasked with devising plausible explanations for the mechanism of a volcanic eruption. As far as I'm aware, this would have been the first major European volcanic eruption in over a thousand years and at the time, no-one would have the slightest idea about what had just occurred.

Now, I suppose that there would be a lot of people who simply believed that it was punishment from the gods, or somesuch - but I'm curious as to what the scientists of the day concluded about the disaster. Anyone know? Or has this information been lost to history now? --Kurt Shaped Box (talk) 22:26, 27 July 2014 (UTC)

I would have thought the the authorities would have considered it self-evident what happened. The idea that they would see a need for "devising plausible mechanisms" is an attitude that mainly developed after the scientific method became widely adopted during the Renaissance. But if you want the historical facts, you probably do want that other desk. --50.100.189.160 (talk) 22:46, 27 July 2014 (UTC)

Well, self-evident in that 'a mountain exploded and hot stuff came out', I suppose - but even back then, I'd have thought that there would be much in interest in finding out 'why?' for the purposes of then figuring out 'is it possible to know in advance if this is going to happen again, either here or with another mountain upon which lots of people are living?'. --Kurt Shaped Box (talk) 22:52, 27 July 2014 (UTC)

Of course, the classic description of that particular eruption was in the letters of Pliny the Younger, in which he recounted the death of his uncle Pliny the Elder in the Vesuvian eruption. But the Romans were quite familiar with volcanic eruptions, particularly those of Mount Etna. The Romans in general (at least those of a scientific bent) usually attributed volcanoes to the interaction of subterranean fires and winds; see Volcanology#Greco-Roman science. Deor (talk) 23:58, 27 July 2014 (UTC)

As one of only five known Epicurean Wikipedians, I'm almost compelled to challenge the notion that Lucretius was of a "scientific bent". But then it'd just get all rhetorical in here, and leave roughly half of us wondering whether Vesuvius or our own great-great-uncles are anything more than figments, in "truth". That's certainly for the other desk. InedibleHulk (talk) 00:00, 30 July 2014 (UTC)