Wikipedia:Reference desk/Archives/Science/2013 April 4

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< April 3 << Mar | April | May >> April 5 >
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.

April 4[edit]

Alcohol and truth[edit]

Does alcohol make people tell the truth about their thoughts as it lowers inhibitions or does it have a tendency to just make people talk about anything that could be random? Clover345 (talk) 00:22, 4 April 2013 (UTC)

It lowers inhibitions, but some may be inhibited about telling the truth, while others are inhibited about lying. The latter group might make up "tall stories" when drunk. StuRat (talk) 00:31, 4 April 2013 (UTC)
How do you mean? Surely, if you're inhibited about lieing, you would tell the truth. Clover345 (talk) 00:45, 4 April 2013 (UTC)
Yes, when sober, but, when drunk, such people are prone to exaggerate. StuRat (talk) 00:42, 4 April 2013 (UTC)
That's interesting. So do you think its related to personality, so an honest person would always tell the truth when drunk or could they also say things they did not mean for example? Clover345 (talk) 00:45, 4 April 2013 (UTC)
In vino veritas Bus stop (talk) 00:49, 4 April 2013 (UTC)
Hard to say. Some people also seem to get angry when drunk, while others have fun. StuRat (talk) 00:50, 4 April 2013 (UTC)
Just a note, I recall from Roman mythology, in some variants, Bacchus (god of wine/intoxication) is also known as the "God of Truth" because wine "turns off peoples' filters". From a pharmacological view, alcohol acts on the nucleus accumbens causing dopamine to be released. (Which we all know causes pleasure, etc. This of course isn't all there is to alcohol, but this mainly relates to your question.) So with that, you're feeling a lot of pleasure and don't mind telling somebody something revealing. (If you've ever noticed, sometimes when you're happy you feel the need to tell people things you may not usually tell them.) Everybody of course has a different reaction, so that may not necessarily be true. I'd say yes, it definitely does for some people. If you're interested in getting into a deeper pharmacological perspective, just ask; I'd be more than happy to. ChaseAm (talk) 00:58, 4 April 2013 (UTC)


Dr Suzanne Higgs, a researcher at the school of psychology at the University of Birmingham, once said:

"We know alcohol has a disinhibitory effect. We found that when people drank in a particular context, such as in the same room, they developed a tolerance over time and the disinhibitory effect of alcohol went away. When we exposed them to alcohol in a different environment, they were less inhibited again."[1] --Guy Macon (talk) 08:10, 4 April 2013 (UTC)

This is sort of irrelevant, but I'm suspicious that drunkenness could predate alcohol. Alcohol of course readily induces the state, but what if it in fact existed as its own psychological entity and could be induced in prehistoric times by, say, frenzied but sober rites of dancing and chanting? I suspect these things primarily because I've always been quite susceptible to contact high from people drinking, even when I was a child and had never tasted the stuff. Wnt (talk) 19:46, 8 April 2013 (UTC)


Does pyrethrum really drive away all insects? Or are there insect species that are unaffected by it? How long does this effect typically last? (talk) 06:42, 4 April 2013 (UTC)

I wonder how it manages to achieve fertilization if it repels insects. Sorry, no answer but I'm questioning the ability of the plant to repel insects. Richard Avery (talk) 06:56, 4 April 2013 (UTC)
I meant the extract, not the plant itself -- maybe I should have said pyrethrin. (talk) 07:17, 4 April 2013 (UTC)
First drive away is an euphemism. Pyrethrin kills the insects. an article from 1963 {{doi:10.1002/jsfa.2740140908}} that there are pyrethrum-resistant strain of the granary weevil --Stone (talk) 12:46, 4 April 2013 (UTC)
Pyrethrins are repellent ([2] [3] [4] which is presumably what you mean by 'drive away' but no it is unlikely that all insect species will be repelled. I've also wondered about how they achieve pollination before - presumably some insects have coevolved with them and aren't repelled (or might even be attracted). SmartSE (talk) 16:03, 4 April 2013 (UTC)
Your logical mistake was assuming that the incecticidal agent is present in all parts of the plant at all times. The active inceticidal agents, pyrethrins, are mostly concentrated in the hull of the seeds of the senescent plant, long after fertilization, and serves primarily to protect the maturing and mature seed from getting eaten. The concentration of pyrethrins in other parts of the plant and at other stages of its life cyle are, presumably, low enough not to poison or repel potential pollinating insects. Or there simply may be no pyrethrins in the plant at all except in mature seeds. Dominus Vobisdu (talk) 19:34, 4 April 2013 (UTC)
So, does anyone know the answer? (talk) 00:45, 5 April 2013 (UTC)
Yes. --Guy Macon (talk) 08:29, 5 April 2013 (UTC)
Thanks for that intro Guy Macon. Yes, people do know the answer (now). Pyrethrum need to be cross pollinated and so need a vector to effect this. So Pyrethrum obviously don’t repel all things that flit through the air, otherwise the would not be able to propergate. Some of the Diptera and Coleoptera have resistance to this toxin and so are the main pollination vectors. These are lesser pest to the farmer, so Pyrethrum's have a benefit. Synthetic form of this natural insecticide together with the synthetic form of nicotine however, have a chlorine atom addition, which makes them less biodegradable and more toxic. Which, is what all the fuss is about with these new neo-nicotinoids and bee-hive decimation. Bees know how to keep away from toxic worts but these synthetic insecticide are now everywhere – the bees can't avoid coming into contact with them.Aspro (talk) 21:59, 5 April 2013 (UTC)
Thanks, Aspro! Just one minor clarification needed -- what are Diptera, and what exactly are "main pollination vectors"? I'm trying to temporarily set up a small "complete no-fly zone" from which all of the most common flying insects in my area (Central California) will keep away, Diptera and pollination vectors included. (Note that I didn't say anything about killing insects -- I don't care one way or the other if they live or die, just as long as they keep well away from the sprayed area.) So I'm more after the repellent effect than the lethal effect. (talk) 01:43, 6 April 2013 (UTC)
Oh, I guess I read the comment wrong -- I read "some of the Diptera and Coleoptera have resistance to this toxin and so are the main pollination vectors" as "some of the Diptera and Coleoptera have resistance to this toxin and so do the main pollination vectors". In that case, forget the part about the pollination vectors (now that I read it right, I see you meant the pyrethrin-resistant Diptera/Coleoptera). My only remaining question, then, would be: What common species of Diptera and Coleoptera are resistant to pyrethrin? (talk) 04:36, 6 April 2013 (UTC)
This is about to scroll off the page so just a quick comment. In areas where tobacco and pyrthium grow naturally, there are many 'local' Diptera and Coleoptera that have evolved resistance. Going by current knowledge and understanding I think it is too difficult to isolate any particular or common Diptera and Coleoptera as being especially resistant. Therefore, for more information, I suggest you search google scholar. Pyrethroid and neonictinoids are based on natural organic insecticides but are synthetics versions, having chorine atom additions and so are more toxic (effective) and persistent. I'm not personally against insecticides per se. Pour water into a bucket of cigaret ends or pyrethrum foliage and soak, and the juices are a effective biodegradable insecticide for one's own vegetable patch. Note: even though this is safer than synthetics, both nicotine and pyrthium is toxic to humans too. So, stay upwind when spraying and be sensible when handling the liquor. A Polytunnel is a cheap way off maintaining a 'fly-free zone'. In Central California, a misting unit of some sort, may be also required in a polytunnel to keep the temperature blow 98 deg F. Above this temp. a most cultivators get stressed out too much. Aspro (talk) 20:40, 7 April 2013 (UTC)

From the wiki article:Pyrethrins are neurotoxins that attack the nervous systems of all insects. so it is not a repellent.--Stone (talk) 08:40, 7 April 2013 (UTC)

What questions did the greek philosophers ask about light[edit]

the questions that they asked are not always much help as there theory was wrong, however try looking up Alhazen! his theory was correct.
This question was asked by Moon568 (talk · contribs · deleted contribs · logs · edit filter log · block user · block log) in a deleted mainspace article. I add it here on their behalf.--Shirt58 (talk) 10:06, 4 April 2013 (UTC)

Not sure, but Alhazen was not Greek, he was an Arabicized Persian. The widely-held Greek theory of light at the time was the emission theory which held that the source of light was from inside the eyes: your eyes produced light which reflected back into them and allowed you to see. Alhazen's Book of Optics proposed that the source of light had to be outside of the light. This "intromission theory" was not his unique insight, Aristotle and Galen also proposed it about 1400 years before Alhazen, but it did not gain widespread acceptance until Alhazen's experimental methods gave it some backing. --Jayron32 12:24, 4 April 2013 (UTC)
But did they really believe in it? Or is it such a case of wrongly attributed belief, like saying that at the Middle ages humans believed in a flat-Earth, when that was not the case? Isn't it evident that the emission theory could not explain why things get dark at night when the sun is not shining? And how can it be that this sentence is right at all? (from the same article) "Winer et al. (2002) have found recent evidence that as many as 50% of American college students believe in emission theory." OsmanRF34 (talk) 16:36, 4 April 2013 (UTC)
I didn't write that paper. Winer et al. did. Ask them. --Jayron32 21:05, 4 April 2013 (UTC)
I think they (the students and ancient Greeks) understood that objects are illuminated by the sun. What they didn't understand is what it means for an object to be illuminated. Light is obviously related to vision, but the exact relationship is far from obvious. -- BenRG 06:58, 7 April 2013 (UTC)

Flood prediction in the USA[edit]

Guessing that the answer is "no", but I could have overlooked something. Is there any entity that produces reputable flood/river levels forecasts in the USA, besides the National Weather Service? Going to showed me river forecasts almost a week in advance for upstream cities like Cincinnati and St Louis, but they don't do predictions as far in advance for Cairo, Illinois, which is what I'm trying to research. I've looked on Google for other sites, but nothing seemed to be what I needed. Nyttend (talk) 14:43, 4 April 2013 (UTC)

Typically that's a function of the state government, I believe. In California where I live, it is done by the Department of Water Resources -- this is their web site. Looie496 (talk) 15:02, 4 April 2013 (UTC)
The U.S. Geological Survey has a major research role in floods and watersheds. [5]. Shadowjams (talk) 15:41, 4 April 2013 (UTC)
The Army Corp of Engineers is the agency that takes care of water level management for the Missisipi River (amoung other things), so they likely have water level predictions for the entire basin. I don't know if those predictions are publically availible, though. -- (talk) 16:10, 4 April 2013 (UTC)
Gee. Why the army? That seems weird/ HiLo48 (talk) 03:17, 5 April 2013 (UTC)
Hmm, now that you mention it, I'm curious too. One of those things I never spent much time thinking about. --Trovatore (talk) 03:21, 5 April 2013 (UTC)
United States Army Corps of Engineers#Water resources explains it a bit. The ACoE's responsibility for managing the Mississippi Basin dates to 1824, when at the time the Mississippi and its tributaries (esp. the Ohio and the Missouri) were major parts of the U.S. transportation infrastructure, and thus managing that transportation was seen as a key part of the U.S.'s national defense strategy. Remember that control of the Mississippi was key to several U.S. wars during the 19th century; the Battle of New Orleans was primarily a last-ditch effort by the British to gain control of the Mississippi during the War of 1812, while control of the Mississippi was a primary objective of the American Civil War, the key Vicksburg Campaign was basically the straw that broke the back of the South during the war. The Mississippi was also a vital transportation link in maintaining a military presence in the various Indian Wars of the 19th century. Given the key military importance of those waterways, it is understandable that the Army was given the mandate to manage them at that time. Governmental inertia being what it is, even though the Mississippi system is no longer has much in the way of military importance, no one has taken the mandate to manage it away from the ACoE, so they just keep on doing so. --Jayron32 04:52, 5 April 2013 (UTC)
Not just the Mississippi. The Corps is involved in or manages most U.S. water resources, harbors, dams, reservoirs, etc. See United States Army Corps of Engineers#Water resources. Rmhermen (talk) 14:50, 5 April 2013 (UTC)
Well, we're both correct. The ACoE has responsibilities outside of the Mississippi System, but the vast bulk of their bailiwick in water management has to do with the Mississippi and its tributaries itself. That system is massive; 40% of the land area of the U.S. is drained by the Mississippi, and that 40% accounts for most of the flowing water in the U.S. as a whole. So, it is accurate to say that the ACoE is responsible for "most" water resources, and it's main responsibility is the Mississippi; much of the U.S. water resources is the Mississippi. The ACoE also manages other water resources around the country, but most of what they do ends up flowing past New Orleans. --Jayron32 17:18, 5 April 2013 (UTC)
Drift Collection Vessels Unload After Day on the Harbor.jpg
Bigger than that. Around here they handle the Soo Locks and the Great Lakes Waterway channels. In New York Harbor they handle drifting hazard collection among other things. The Saint Lawrence system, Hudson, Charles, Columbia, both Colorados, Los Angeles, I am having trouble finding any major waterway system the USACE is not involved in. Their headquarters locations map show nowhere in the U.S. not part of a USACE district.[6] Rmhermen (talk) 18:21, 5 April 2013 (UTC)
Well, there you go. --Jayron32 20:32, 5 April 2013 (UTC)
The link I posted above provides up to the hour river/stream/creek levels, plus historic data.... etc. Shadowjams (talk) 21:29, 4 April 2013 (UTC)

FEMA s sfha floodplain maps. (talk) 02:04, 5 April 2013 (UTC)

I had always believed the United States Army Corps of Engineers handled all the enormous water-management projects in our country; but on a recent visit to Lake Berryessa, I stopped into the information kiosk and learned all about the history of that site - it is managed by the United States Bureau of Land Reclamation, a totally distinct agency of the United States Department of the Interior. And of course, our other great regional water project is managed by a municipal government; and the infamous California Aqueduct is managed by a state government. Surely if you investigate the responsible authority for water management in your own region, you will find similar delegation of responsibility amongst multiple local, regional, and national agencies. Nimur (talk) 21:11, 8 April 2013 (UTC)

Gradient of a scalar field[edit]

give complete description gradient of a scalar field. — Preceding unsigned comment added by Titunsam (talkcontribs) 17:22, 4 April 2013 (UTC)

Sorry, we don't do homework problems. If this is not a homework problem, please explain why you are asking. Looie496 (talk) 17:33, 4 April 2013 (UTC)
Agree ChaseAm (talk) 17:52, 4 April 2013 (UTC)
The Gradient article has a good description of the gradient of a scalar field. Red Act (talk) 23:21, 4 April 2013 (UTC)

why can't normal cells tackle cancer cells[edit]

a person with cancer will, at most times, have less number of cancer cells than normal cells in his body. Why can't so many normal cells convince or tackle (rather than fight) cancer cells (which are of course none other than the uncontrolled-normal-cells)? anand, chennai — Preceding unsigned comment added by (talk) 17:59, 4 April 2013 (UTC)

That's actually a very interesting question. During metastatis numerous cancerous cells are released from the [malignant] tumor. A majority of these are killed off by the immune system, but some survive, attach to the blood vessel lining, replicate again and cause even more tumors. Is that what you were looking for? If you would like to me to expand on that, I'd love to ChaseAm (talk) 18:10, 4 April 2013 (UTC)
yep, that is the current #1 question. the current theory is that the body is continually tossing out mutant cells which are being killed off by the immune system just like invading foreign cells; this includes many cells which would be cancerous if they survived. so a big field of study is how do the cancer cells which escape this process manage to do so, and how can we help the immune system? [7] for instance. another somewhat related questions; without ample blood supply, a tumor (or any other body part) will die, or at least fail to grow. a successful tumor, cancerous or not, must therefore commandeer the body to grow a network of blood vessels ito it; and we can see where tumors often fail to do so naturally, and are slow growing, or not at all. so, question#2, how does a tumor convince the body to supply it with blood, and what can we do about that? Gzuckier (talk) 20:14, 4 April 2013 (UTC)
One approach to that is to prescribe thalidamide. This is the horrible medication which caused children to be born without arms and legs in the 1950's. It did so by preventing the fetuses from developing new blood vessels in those limb buds. This can also be put to use against tumors, but we'd better make darned sure no pregnant women ever take it. See Thalidamide#Cancer_treatment. StuRat (talk) 08:12, 5 April 2013 (UTC)
Thalidamine is not about how the immune system interacts (ignoring or destroying) with cancer cells. It works like many other cancer medications, destroying cells that grow too fast or blocking growth of new cells. The question is not how to treat cancer, but how do cancer cells manage to deceive or defeat the immune system. OsmanRF34 (talk) 13:53, 6 April 2013 (UTC)
The short version is that cancer cells are slightly damaged regular cells, which replicate out of control. The body still sees them as your cells, not recognizing the damage they're doing. There is some research into ways to "tag" cancer cells so your immune system will kill them, but it's got a long ways to go. — The Hand That Feeds You:Bite 20:07, 7 April 2013 (UTC)
Why kill the cancer cells is also what i ask. When cancer cells are converted to normal cells (rather than being killed by our own immune system or some drugs), the surplus normal cells are automatically removed through apoptosis. This would be relatively easier than when cancer cells are forced to apoptosis. When drugs can be discovered to check cell division in cancer cells, drugs can also be discovered to repair the abnormal cells - anandh, chennai
I should point out tumor antigen and spontaneous remission. My recollection is that melanoma is a cancer particularly prone to immune "miracles" when hope is nearly lost. There is a particularly well known animal model with Sinclair miniature pigs, which frequently develop melanoma but also frequently recover. What strikes me as peculiar about the research in this area is that it seems like more effort has been put into finding just the perfect self antigen to try to get the body to attack because it is mostly present in tumors than simply finding some adjuvant that could be injected willy-nilly into tumors to enhance their immunogenicity. Wnt (talk) 19:41, 8 April 2013 (UTC)

pathophysiology of atherosclerosis[edit]

I've spent ages looking at various different sources trying to figure out the pathophysiology of atherosclerosis. Would I be right in thinking that endothelial wall injury (due to hypertension, shearing forces etc.) is the means by which LDL gets into the vessel walls? And is the presence of LDL what causes macrophages to migrate into the vessel walls? I'm really only looking for a brief overview of the pathology behind atherosclerosis, I'm a med student cramming for exams with 101 other things still to learn! Thanks to anyone who can help! RichYPE (talk) 20:20, 4 April 2013 (UTC)

It doesn't answer your question about how LDL gets in, but can we presume that you've looked at the Pathophysiology section of our atherosclerosis article, which contains a lot of relevant information? Looie496 (talk) 20:41, 4 April 2013 (UTC)
I applaud your honesty but I must warn you that wikipedia is a really bad place to look for that kind of information. There is no consensus on the "root cause" of atherosclerosis. Some medical info you can trust wikipedia for; some you cannot. For a question like that you would be better off simply looking for a recent review article via pubmed or checking Uptodate or Emedicine, which i assume you can easily access through your med school library. One of the weaknesses of wikipedia is the lack of synthesis, which generally requires enough expertise to have digested and put perspective to the medical literature. Editors with high school levels of medical knowledge will dig in and fight to keep an article from being updated from the medical literature. See wp:Randy in Boise; it's a real phenomenon. alteripse (talk) 02:27, 5 April 2013 (UTC)
Our medical articles are actually an area of strength. Not all of them are good -- the atherosclerosis article certainly isn't well organized -- but many of them are pretty good. WikiProject Medicine is one of our more robust WikiProjects, and there are a number of editors with expertise who keep an eye on things and prevent articles from deteriorating. Looie496 (talk) 02:50, 5 April 2013 (UTC)
I have used wikipedia for quick facts. It's good for something like "what is the name of the gene involved in achondroplasia" or "what drug is methimazole". Its overviews of broad topics are poorer. Our medical student doesnt realize he/she already knows more about his question than 99.999% of wikipedians who answer ref desk questions. alteripse (talk) 11:11, 5 April 2013 (UTC)
I'm sure there aren't as many as a hundred thousand editors answering questions on the ref desk, so I suspect that the percentage will be either 100% or much lower. We do have a few medical experts here, but perhaps no experts in pathophysiology of atherosclerosis. (You all know much more about it than I do!) Dbfirs 14:34, 5 April 2013 (UTC)
I wasnt sure about total editors who have responded to ref desk questions of all types in last 10 years. I was guessing at least 1000 but maybe that is a gross overestimate. I have to say i have not seen anyone else answering with broad medical expertise that would exceed that of a medical student, though many of the answers to simpler questions are perfectly accurate. alteripse (talk) 20:39, 5 April 2013 (UTC)
Yes, I agree that 1000 would be closer than 100,000. I think we have a dentist, but I don't know of any highly qualified medical experts — there are a few editors who seem to have some medical knowledge. I agree that the probability of having someone with more specialist knowledge on that topic than the OP is small. Such specialists are probably too busy to edit here regularly. Dbfirs 08:32, 6 April 2013 (UTC)
The answers to the low T question above are appalling. Whle nearly every comment has at least a single partially true assertion, most of the truthful assertions are either not relevant to the question asked or used to make an inaccurate point, or accompanied by false assertions offered with as much confidence. The simple answer to the question is simply "yes, much of it" but explaining the answer and explaining why nearly all of the offered answers are either wrong or irrelevant would take an hour. alteripse (talk) 15:42, 6 April 2013 (UTC)
Well, if you're not going to explain then you're in no position to complain if others do so sloppily. Feel free, of course, to let me know where you think I went wrong there. Meanwhile, the science of root causes can be tricky. For example [8] offers "a" root cause of atherosclerosis, but that turns out to be a laundry list of factors all of which may somehow be involved at an early stage. That is the way of biology - things move in feedback loops, many factors coming together and adding up, which can make it hard to point at one thing with certainty. Nonetheless -- [9] offers a discussion which pretty strongly favors the OP's assertion and, more importantly, suggests a possible way to actually modify the response to lipid-induced damage to make it less problematic. Wnt (talk) 19:59, 8 April 2013 (UTC)

Why is there a current uk shortage of Isosorbide mononitrate heart medication tablets?[edit]

The Pharmacist said it was due to lack of raw materials. Why is this and is it likely to be long term or global problem. — Preceding unsigned comment added by (talk) 20:46, 4 April 2013 (UTC)

It seems the factory which supplies the UK with generic isosorbide mononitrate has temporarily closed (I can't find out what factory or why) - ref. So various prescribing bodies are recommending pharmacists dispense the branded equivalent (e.g.), and the NHS will reimburse this. It may be that the loss of the factory's output isn't being made up by supply of the branded isosorbide mononitrate product. -- Finlay McWalterTalk 22:36, 4 April 2013 (UTC)
This says it's Teva's factory in South Wales (but I can't find any Teva UK plants in Wales, just four in England). It says "stock levels are expected to recover May/June". -- Finlay McWalterTalk 22:42, 4 April 2013 (UTC)
Euticals' plant in Wales closed abruptly after a chemical spill of isosorbide dinitrate. The nitrovasodilators used as medicine are high explosives. That's not a problem for patients, only a tiny amount of chemicals are in each pill. But when you are manufacturing the substances, the amounts involved are much greater and therefore the risk of explosion very high. The plant is being decontaminated. 00:41, 5 April 2013 (UTC)

what are the capacitors for[edit]

hello, in this circuit, what are the capacitors for, specifically the 100µF one between +Vcc and ground (upper center) and the 10µF one between the two resistors (lower center of the schematic)? Asmrulz (talk) 23:54, 4 April 2013 (UTC)

The 100 uF capacitor was presumably intended by the author to bypass any signal or signal harmonic voltage on the power rail. Such signals come from later amplification stages due to finite (non-zero) power supply impedance. Signal or signal harmonics on power rails from later stages by getting into earlier stages constitute feedback, and thus may cause incorrect gain, poor frequency response, distortion, and can if bad enough result in oscillation (such oscillation known as "motorboating" due to the typical sound).
However, showing such a capacitor value in this circuit is meaningless as the later stages and power supply are not shown. 100 uF may well be not required, or may well be insufficient, depending on what later stages and what power supply is actually used.
If the circuit is to be powered by a dedicated battery, as the battery becomes flat and its impedance increases, local feedback will occur via the bias resistor network (the two 47 K resistors). This will upset gain and distortion. The author may have intended the 100 uF capcitor to stop this problem - however 100 uF is insufficient for this purpose.
The 10 UF capacitor in series with the negative feedback shunt R1 is there to reduce the DC gain to unity. Without this the op-amp input offset voltage will be amplified, producing an undesirable and temperature dependent shift in volatge on the op-amp output pin (pin 6). This capacitor will cause a low frequency drop in response, -3 dB at 16 Hz. It is not desirable to amplify very low frequencies (ie below 30 to 50 Hz depending on circumstances), as they cannot be heard and just cause useless pumping of loudspeaker cones.
Keit (talk) 00:25, 5 April 2013 (UTC)
Thank you! I think I got it now, too. The AC "sees" R1+Zc+R2, but the DC sees R1+R2+infinity Asmrulz (talk) 01:08, 5 April 2013 (UTC)
Yep. But more significantly, the AC negative feedback ratio is R1/(R1 + R2) ie 1:23 but the DC feedback is ~infinity/(~infinity+R2), ie 1:1. Keit (talk) 02:25, 5 April 2013 (UTC)