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November 4

Potentiometer and Zener diode are interchangeable in eletrical circuits?

I discovered that both are somewhat voltage regulators. So those two are interchangeable? Rizosome (talk) 02:09, 4 November 2021 (UTC)[reply]

Rather obviously not. They perform comletely different functions. They are both somewhat resistive and somewhat mettalic too.--Shantavira|^{feed me} 09:04, 4 November 2021 (UTC)[reply]

It requires a very firm grasp to rotate a Zener diode by 90º, and the resulting change in resistance may be permanent. --Amble (talk) 14:00, 4 November 2021 (UTC)[reply]

I discovered that lettuce and poison ivy are both leafy plants. So those two are interchangeable? --Jayron 32 15:41, 4 November 2021 (UTC)[reply]

Goats eat them both, so in a sense I guess? I've done some tests making salads with them, but I will have to leave it to others to do fuller experimentation as I have no interest in pursuing it further. I guess you could say [puts on sunglasses] I've scratched my itch. DMacks (talk) 15:46, 4 November 2021 (UTC)[reply]

Zener diode is so thin in nature why does it need very firm grasp to rotate 90º? Rizosome (talk) 02:12, 5 November 2021 (UTC)[reply]

I'm fairly sure that Amble was pointing out potentiometers are generally used as variable resistors and after connection to a circuit their resistance is generally adjusted by rotation. Trying to rotate a zener diode when it's connected to a circuit is difficult and will likely destroy the diode if successful or at least disconnect it from the circuit. (Although it's true there are potentiometers which are adjusted via sliding and trying to rotate one will likely be equally destructive.) Nil Einne (talk) 07:36, 5 November 2021 (UTC)[reply]

Ok, I understand potentiometer and Zener diode very well now. Rizosome (talk) 04:04, 6 November 2021 (UTC)[reply]

So you have obtained a very firm grasp of the subject matter. --Lambiam 10:15, 6 November 2021 (UTC)[reply]

Was stealth technology for US airplanes based upon on previous technology?

Something I was discussing in the bar tonight. Someone was talking about the Roswell crash and how a bunch of new technology for the US air force came from that.

Apparently the stealth material for fuselage of the planes as used by the USAF just appeared out of nowhere, not based on any previous research? Is that right? And the Russians/Soviets were trying to replicate it and failed until a US stealth bomber was shot down in the Bosnian war and the FSB took samples of the wreckage back to Moscow to be reverse engineered?

Not trying to conspiritard. Just looking for more info. I find it interesting. 146.200.107.70 (talk) 02:24, 4 November 2021 (UTC)[reply]

The idea of radiation-absorbent material predates the alleged 1947 Roswell incident. Those pesky Nazis were doing research in World War II. German submarine U-480 had a special rubber coating to try to defeat sonar. Reimar Horten, one of the designers of the Horten Ho 229 flying wing, claimed he intended to add radar-absorbent material to its surface. Clarityfiend (talk) 03:47, 4 November 2021 (UTC)[reply]

See also the history section in the Stealth technology article. -- 107.15.157.44 (talk) 04:56, 4 November 2021 (UTC)[reply]

It's a blindingly obvious development after radar was invented. No need to involve extraterrestrials. Now if you were to suggest a certain ex-POTUS obtained alien mind-bending technology to use on his endless rallies ... Clarityfiend (talk) 05:36, 4 November 2021 (UTC)[reply]

Stealth: The Secret Race to Invent an Invisible Airplane by Peter Westwick says in the first chapter, Roots of the Revolution, that during WWII, the Germans, British and US all experimented with radar absorbent or reflective coatings, called Schornsteinfeger ("Chimney sweep"), Salisbury Screen and Halpern Anti-Radiation Paint (HARP) respectively. Early work on reducing an aircraft's radar signature by modifying its shape were unsuccessful, mostly because the science behind how radio waves bounce off an object did not begin to be understood until Ohio State University applied computers to the problem in the early 1960s. Air forces worked around the problem with chaff, decoys and electronic countermeasures, and it wasn't until Vietnam and the 1973 Yom Kippur War showed that a better approach was needed. Alansplodge (talk) 12:56, 5 November 2021 (UTC)[reply]

In my list of radar countermeasures, I forgot nap-of-the-earth intrusion, which is flying underneath radar beams. This is the option that the RAF went for, even with their enormous Avro Vulcan bombers. Low flying military training is a whole lot cheaper than spending a gazillion dollars on a totally new technology. Alansplodge (talk) 12:36, 6 November 2021 (UTC)[reply]

B cell

"BCRs allow the B cell to bind to a specific antigen, against which it will initiate an antibody response." This is before somatic hypermutation happens. My question is how can BCRs recognize the "specific" foreign antigen if this is the first time ever they encounter it? 156.142.197.92 (talk) 22:26, 4 November 2021 (UTC)[reply]

If a BCR binds to some antigen (after negative selection in the development phase), it means the antigen is foreign (except when something goes awry, as in autoimmune diseases). It does not need to recognize it. --Lambiam 12:43, 5 November 2021 (UTC)[reply]

user:Lambiam Let's say there is already memory B cell for that specific antigen. If a BCR gets to it before a memory B cell does then the whole immune response (with hypermutation) seems redundant. Am I missing something? 2601:444:4100:F709:392C:B1D8:B5D7:362B (talk) 19:32, 5 November 2021 (UTC)[reply]

Without a parent cell with a BCR recognizing the antigen as foreign, the memory B cell reacting to the antigen would never have come into existence. Also, while memory B cells are often long-lived, they do not persist forever. After a long period, not enough may be left to mount a forceful immune response; it is then a good thing that the first line of defence is still there. --Lambiam 20:24, 5 November 2021 (UTC)[reply]

Oh, and the memory B cells, when encountering the antigen, quickly trigger a strong response. In comparison, the first line fires up slowly. --Lambiam 20:27, 5 November 2021 (UTC)[reply]

user:Lambiam Alright, let me get this straight. Assuming this is the second time the body is encountering a specific antigen, memory B cell would most likely get to the antigen way before a BCR would? Therefore, hypermutation does not happen twice for the same antigen. Am I correct? 2601:444:4100:F709:392C:B1D8:B5D7:362B (talk) 23:03, 5 November 2021 (UTC)[reply]

In an infection, there are usually many foreign elements with a specific given antigen. It is not very likely that the memory B cells recognizing it will get rid of all these antigenic elements before some B cells also encounter one and recognize the antigen. These B cells will do whatever they would have done without the presence of the antigen-specific memory B cells. --Lambiam 00:04, 6 November 2021 (UTC)[reply]

A B-cell usually needs an additional signal from a helper T-cell for its activation. Since T-cell are already selected not be autoreactive (in thymus), it follows that autoreactive B-cells are not activated. Ruslik_Zero 20:31, 5 November 2021 (UTC)[reply]