Wikipedia:Reference desk/Archives/Science/2015 March 30

= March 30 =

What does the ground electrode actually do (in ECG)?
What does the ground electrode (on the right leg) actually do (in ECG)? what is its function as ground? 149.78.243.172 (talk) 01:08, 30 March 2015 (UTC)


 * Essentially, it provides a reference for quantifying the voltages picked up by the other electrodes. Here is a useful article on what the ECG voltages mean. Also see Ground (electricity) for elaboration on ground as a reference voltage. Short Brigade Harvester Boris (talk) 02:00, 30 March 2015 (UTC)


 * Right, the ground electrode serves the same sort of function in measuring voltage as sea level does in measuring altitude -- it provides a zero point to measure from. Looie496 (talk) 14:25, 30 March 2015 (UTC)


 * That's a nice analogy. I reserve the right to plagiarize it shamelessly. Short Brigade Harvester Boris (talk) 02:06, 31 March 2015 (UTC)


 * Well, not really. The Driven right leg circuit does not explain very well, but see the section titled "Driven right-leg circuitry" here: . &mdash;eric 03:32, 31 March 2015 (UTC)


 * That doesn't actually contradict what we wrote, but I understand the confusion. My experience has been that students always have trouble with the concept of voltage, because there seems to be a tremendous compulsion to think of it in absolute terms, even though it is intrinsically a relative measure.  It's the same difficulty that calculus students have in dealing with the constant of integration when calculating antiderivatives. Looie496 (talk) 13:41, 31 March 2015 (UTC)
 * Thank you Sir for your comments. So is it not possible to use the electrodes without this ground? it couldn't give us a certain indicates? (I'm surprised because I always thought the aim of the ground is only to defend on the persons from electrocution...)192.117.186.252 (talk) 02:01, 1 April 2015 (UTC)

DOE radiation worker annual exposure limit


Our spaceflight radiation carcinogenesis article contains this graph which indicates that the DOE radiation worker annual exposure limit is 20 millisievert. The source of the graph is from this JPL which discusses the radiation exposure measured by Mars Science Laboratory both during its trip to Mars and during surface operations.

I have always understood that the NRC used a 50 millisievert annual planned exposure limit for radiation workers, as described by their Standards for Protection Against Radiation, § 20.1201 Occupational dose limits for adults. Does the DOE set lower limits? I couldn't find an equivalent DOE document, but this nukeworker.com page gives a DOE annual dose limits for occupational radiation exposure of radiological workers at the National Labs of 5000 mrem which is equivalent to 50 mSv. Has there been a reduction in this limit? -- ToE 12:05, 30 March 2015 (UTC)


 * As another data point, Lawrence Berkeley National Laboratory publishes a radiation safety guideline that emphasizes two points: "As Low As Reasonably Achievable" exposure, and "control levels below federal dose limits." Their EH&S policy enumerates a complete table listing dosimetry limits for all types of circumstances, and all are below the ultimate limit set by federal regulation.  So, it stands to reason that NASA's contractor (Southwest Research Institute) that made the graph (shown at right) found similar limits in some other unnamed Department of Energy document.  I would consider them to be a reliable source.  The radiation safety department at my local particle accelerator publishes Radiological Safety, and they cite 10 CFR 835 as the authoritative federal law that supersedes local policies.  10 CFR §835.202 enumerates dose limits, and appears to be the source of the 5 rem total effective dose number - but there is extensive context for that value!
 * Ultimately, you're mincing words and so you're bound to encounter some technicalities: what is the limit on exposure? There are many different limits (as this Department of Energy chart from the Low Dose program office illustrates), and a violation of any specific limit would entail different consequences, both with respect to health and safety, and also with respect to administrative policy enforcement.
 * Nimur (talk) 12:26, 30 March 2015 (UTC)


 * Tangentially - people looking to get a casual feel for radiation doses might enjoy this fairly well-referenced XKCD infographic, which IMO does a good job of explaining some of the orders of magnitude involved . SemanticMantis (talk) 14:51, 30 March 2015 (UTC)


 * The Low Dose program office chart that Nimur linked to, gives the "DOE/NRC dose limit for workers" as 5 rem/year, as does DOE's Occupational Radiation Exposure Report (pages 2-1, 2-2). So it is likely that the JPL chart-maker simply made in error. Abecedare (talk) 15:14, 30 March 2015 (UTC)
 * Fair point, but the other resources I linked provided 2 rem as the "Administrative Control Level." "An administrative control level is a numerical dose constraint established at a level below the regulatory limits in order to administratively control and help reduce individual and collective doses."  (Additional references).
 * You can find the very same in many other official Department of Energy reports, like the 2013 Occupational Radiation Exposure Report (which is the latest available).
 * Nimur (talk) 15:23, 30 March 2015 (UTC)
 * Yes, it is very likely that the difference arises from confusion between the DOE regulatory limit (5 rem/year) and DOE Administrative Control Level (2 rem/year), and in some sense the 2 rem/year number is more representative of what DOE monitored workers are practically kept under (Exhibit 3-4 in the DOE report). However I would still have preferred if the chart had not used the word "Limit" so casually, lest we edge up to the  In through the looking glass territory. :) Abecedare (talk) 15:44, 30 March 2015 (UTC)

Thank you all. I was familiar with ALARA, but not with the Administrative Control Level. That explains it. -- ToE 17:28, 30 March 2015 (UTC)

All bureaucracy aside, it is interesting that places like Ramsar, Mazandaran seem hard to associate with cancer, despite background radioactivity over limits. When it comes to spaceflight or Mars colonization, I wonder if it is possible to get a sort of "radiation suntan" i.e. a biological response to low-level radioactivity that compensates for continuous low level exposure. Wnt (talk) 02:09, 31 March 2015 (UTC)
 * Bureaucracy aside! Department of Energy deals with nuclear weapons safety.  Many hard lessons were learned in the first few decades - after people got sick, got hurt, and died!  If you'd like to read an anecdote on this topic, Richard Feynman's short essay Los Alamos From Below talks about how bureaucracy worked during Manhattan project.
 * It was great. The lieutenant takes me to the colonel and repeats my remark. The colonel says, “Just five minutes, “and then he goes to the window and he stops and thinks. That's what they're very good at -- making decisions. I thought it was very remarkable how a problem of whether or not information as to how the bomb works should be in the Oak Ridge plant or not had to be decided and could be decided in five minutes. So I have a great deal of respect for these military guys, because I never can decide anything very important in any length of time at all.
 * With due respect, Wnt, I hope that if you ever have the privilege and responsibility to work with invisible hazardous ionizing radiation, you'll learn to respect a little bit of the bureaucracy, even if you cannot understand it.
 * Along the very same lines: if you should ever find yourself making decisions about safety for manned space flight, let us all hope that your spacecraft passengers can trust that your decision-making procedure has some element of rigor and a healthy, conservative margin! One may jest that NASA is bureaucratic, and one can even argue that the bureaucracy might sometimes actually impede real safety.  (The very same physicist I quoted moments ago did exactly levy that accusation in his "Personal Observations" appendix to the Rogers Commission report!)  But NASA must err on the side of caution, as we have all learned after many tragic spaceflight accidents.  Bureaucratic rules exist because something happened, and the rule-makers wanted to make sure something never happens again.  If you should ever work with high energy materials, operate a spacecraft, or generally be responsible for somebody else's well-being, "something happened" are two words you never want to hear.
 * Nimur (talk) 14:15, 31 March 2015 (UTC)
 * I think you read too much into my phrase. I actually have played with biological research quantities of P32, S35, occasionally tritium, and I know the basics of exposure.  But it's hard to take bureaucracy too seriously when on one hand there is a whole university department tasked, mostly, with giving out these tiny amounts of radioactives (we're talking under a millicurie) in a safe way, and on the other hand, the common destination of much of them is down the sink.  But I always took it much, much more seriously than the Russians, who would typically say something about Chernobyl, laugh, spray some Rad-Con to help get those pesky counts off their thumb, eat a sandwich, go back to pipetting... :)  But I should say that  suggests that there may be real cancer consequences for the mild extra exposures of flight crews, which indeed is less than astronauts have to deal with.  But we don't actually know that's the reason. Wnt (talk) 19:37, 31 March 2015 (UTC)


 * International Congress Series published the proceedings of a 2005 conference on the subject of Ramsar-like places with naturally high-radiation levels. My guesstimate is that we are talking about a potential single-digit percentage increase in the base-cancer rate. So it is not surprising that such an increase (even if the theoretical risk calculations are true) would not have been yet observed at Ramsar, with a population of only 30,000. Dan Fagin's Toms River gives a good journalistic account of how difficult, and frustratingly inconclusive, such epidemiological investigations can be.
 * NASA's Risk of Radiation Carcinogenesis has a short section towards the end on biological countermeasures against radiation during long space-flights, with links to related references.
 * Abecedare (talk) 02:40, 31 March 2015 (UTC)
 * That last reference is interesting. Mostly it goes on about antioxidants as a method, hypothetically, to reduce damage from reactive oxygen species caused by radiation.  But at the end they conclude with contrary data that leaves it up in the air whether antioxidants increase or decrease the risk of cancer.  Honestly I don't believe cells are test tubes and am skeptical of the relevance of a compound's redox properties.  But they also mention the use of amifostine to protect tissue from radiation damage, which has been suggested to affect DNA repair; the biochemical pathways are what interest me most.  For example alpha-2-macroglobulin has been proposed as a natural radioprotective agent by many means including DNA repair.   I'm thinking that if biology has evolved specific proteins or other substances to protect against radiation, then changes in the levels of these substances ought to affect the degree of radiation resistance.  So it would subsequently require only some mechanism of sensation of damage to have a working "radiation suntan" mechanism; but so far as I know that's still only speculation on my part. Wnt (talk) 13:15, 31 March 2015 (UTC)

What is the cause, the IVF or Osborn waves?
I've read many articles and all of them (including Wikipedia on Osborn wave) says that Osborn waves caused by idiopathic ventricular fibrillation, but one of the articles (I think it's the origin of the all sources...) says the opposite. I'm confused. 213.57.29.113 (talk) 20:29, 30 March 2015 (UTC)
 * The Wikipedia article doesn't say they are caused by idiopathic ventricular fibrillation. It says they occur in people with ventricular fibrillation.  Correlation is not causation.  -- Jayron 32 21:30, 30 March 2015 (UTC)
 * What does it mean? How can you see the Osborn waves while having VF (or even idiopathic)? In all of the articles it's written that idiopathic VF (and only IF, as I understand). so What is the meaning of "occur in people with ventricular fibrillation"?. Thanks! 213.57.29.113 (talk) 21:55, 30 March 2015 (UTC)

Viral movement
How do viruses move when they're inside the body? — Preceding unsigned comment added by Joey13952 alternate account (talk • contribs) 20:51, 30 March 2015 (UTC)
 * They are carried by the fluids of the body, the same way other extracellular molecules are. See Virus, especially the life cycle sections.  -- Jayron 32 21:41, 30 March 2015 (UTC)