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General Science / What happens when a superconductor is utilised in a circuit?

« on: 21/11/2023 21:58:00 »

Imagine a simple circuit of a battery, a switch, a lamp and a piece of superconducting wire in a loop. What happens when the switch is closed is the question and is a little more complex than it initially appears. Since any piece of wire has both inductance and resistance it therefore has a time constant, l/r which defines the time it takes for the current to rise to ~63% of the value v/r, where v is the applied voltage.  In the case of the superconducting wire this time constant will be infinite and hence no current will flow! This scenario will also involve a potential across the piece of superconducting wire which is obviously impossible. Ok, you say maybe we cannot model a superconductor as having a time constant but we can look at limits: as the resistance is artificially lowered the time constant will be valid and each time it is lowered the time constant will increase until we approach zero resistance where the current will flow but at such a slow rate that it appears to be non-conducting. In this situation I am just looking at the piece of superconducting wire in isolation. There has to be some error in this analysis but I can't find it.

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Just Chat! / What is the origin of the derogatory term "crank"?

« on: 19/11/2023 09:59:23 »

As we well know science is bedevilled with cranks. To me, a crank is a mechanism for converting reciprocating motion to rotary motion. I am just curious how it came to be used for describing some of the nutjobs that inhabit the fringes of science.

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Just Chat! / Everone in hibernation?

« on: 10/11/2023 18:33:17 »

Very quiet around here lately, has hibernation taken hold? Only our esteemed colleague Hamdani seems to be active. I normally start my hibernation around the start of November under a pile of cosy dry leaves expecting to surface in early March. Come to think of it, i'm late starting this year. 

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Just Chat! / What is the purpose of "question of the week"?

« on: 10/11/2023 14:39:15 »

I am not sure about this subforum. Is it open to normal replies or does it have some other function? I have been posting replies but I am not sure if this is the correct protocol.

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Technology / Why is my sattellite receiver behaving oddly?

« on: 29/10/2023 13:33:35 »

I am not a fan of the gogglebox but I occasionally watch a documentary or news channels. For the sake of the boss and our two daughters when they visit I do have a satellite system. Recently some channels have disappeared and when this happens I do a re-scan but it did not work this time and I ended up with only ~90 of the ~300 free to view channels. I am looking at the astra 28.2e, 2e, 2f, 2g with a bargain basement receiver, 4ife 410. I tried every possible setting open to adjustment including several lnb local oscillator settings, each time producing slightly different but inadequate results. I was beginning to think the dish had slipped alignment and was preparing to visit the roof when I noticed a scan setting that I had never used, namely "blind scan". On selecting blind scan I saw a process I had never seen before which consisted of a preliminary scan of all the transponders before the channel scan and bingo! all my missing channels returned. Previously I have selected a scan of "all channels" or "fta"(free to air). I'm confused.

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Just Chat! / Why do parts of a closed thread disappear?

« on: 24/10/2023 09:23:12 »

This morning I noticed Kryptid had euthanized some rubbish and I tried to say thanks via the drop down box. As soon as I had logged on, most of the final page disappeared and this is not the first time this has happened. Oh well, I'll just have to say it here, THANK YOU Kryptid.

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Just Chat! / Why are some threads locked?

« on: 05/10/2023 13:43:14 »

I have noticed that threads which involve a discussion that has been raised on another forum get locked. Don't get me wrong on this, I am not disputing forum rules nor do I have a problem with this, I am just curious as to the criteria for this rule.

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Just Chat! / Anyone going to the party congress?

« on: 01/10/2023 16:16:10 »

I thought Alan might be interested in attending the conservative party congress? Maybe BC too? ( they will probably never talk to me again!!)

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Physiology & Medicine / Is EBV the cause of all so called autoimmune disorders?

« on: 20/09/2023 15:33:50 »

The Epstein Barr virus, EBV, is a commonly acquired pathogen most notable for causing glandular fever, also called mononucleosis. It is also strongly correlated with the development of at least three cancers. It is large dna virus of the herpes group and like other herpes viruses once infection occurs it remains in one's body, generally in a latent form but capable of recrudescence. Much evidence now links prior infection with EBV to the subsequent development of MS and less evidence suggests it may be the causative agent of several other illnesses commonly referred to as autoimmune in nature. This virus invades b lymphocytes and immortalises them thus preventing the normal process whereby anti-self reacting b cells are eliminated by apoptosis. It is beginning to look like this one virus is responsible for an enormous burden of chronic diseases. Whaddya think?   Mods: I thought I already posed this question but could not find it-feel free to delete if so. Also, any idea why I can't do paragraphs? my cursor will not drop down. 

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Just Chat! / Is the universe real?

« on: 06/09/2023 12:01:57 »

Recently I learned, through a conversation with Halc, that quantum theory says that one of the following statements must be false: (A) there can be no retrocausality and (B) counterfactual definiteness exists. The idea that either of these is false seems incomprehensible to me, on an INTUITIVE level. So what's going on here? I don't buy into these "simulation" ideas which in my opinion are just science fiction gone crazy. This will probably be too philosophical for Alancalverd though he is welcome to reply: Buddhism states that reality is an illusion- is it that too far off the mark? PS as I stated in another post I will be incommunicado for ~9days( sectioned under the mental health acts----no! only joking).

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Just Chat! / I'm due to be crowned!

« on: 03/09/2023 21:20:35 »

Looks like my coronation will occur soon. You are all invited to the subsequent bash, as soon as the formalities are completed.

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Just Chat! / How can excessive consumerism be tackled?

« on: 03/08/2023 17:10:58 »

I don't think that many would disagree with me that excessive consumerism is something that needs to be tackled to for us to have a more sustainable future. One particular difficulty I see is the gender disparity: I will wear an item of clothing until it is threadbare or no longer performs it's function while the "boss"( Alancalverd vernacular ) is constantly acquiring new apparel, many such items only getting a handful of uses. How can this need for repeated wardrobe updates, driven by the fashion industry, be tackled?

13

Technology / Any power engineers around to help me with a pole slip query?

« on: 31/07/2023 09:57:38 »

About 15years ago I was running a 1000kva diesel powered alternator at 60% load, in parallel with the grid, when the excitation failed. Not much happened other than the current shot up but not to dangerous levels and the pf went into a lead. The conventional wisdom is that such a scenario can lead to pole slip( ie desynchronisation ) with potentially severe consequences for the rotating diodes or worse to the coupler and/or the crankshaft. This was a brushless four pole salient pole 1500rpm lv machine. My question is this: with the massive damper fitted to all similar alternators that I have seen would the alternator not default to asynchronous operation wherein the damper would be analogous to a squirrel cage rotor, in the case of excitation failure? 

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Physics, Astronomy & Cosmology / Will there be an e field outside two concentric spheres differentially driven?

« on: 26/07/2023 15:14:46 »

A simple setup: two concentric metallic spheres with an internal oscillator powering both, at 180 degrees difference. Will a time varying e field be detected externally to these spheres? Without doing the maths I expect the e field to be restricted to the gap between these spheres.  PS I notice the degree symbol now produces a question mark.

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Physiology & Medicine / Is "neurodiverse" medicalisation of human nature?

« on: 22/07/2023 12:38:11 »

The term neurodiverse is in common use lately. I believe it is the latest attempt to define all aspects of human nature as pathologies. Personally I am very distractible and tick a lot but not all of the boxes for adhd. However, we are all different with various quirks, talents and defects and if this trend continues we will all be classed in some way less that the ideal( but non-existent ) human creature. 

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Just Chat! / I'm too slow

« on: 21/07/2023 20:56:36 »

 just noticed Kryptid closing down a nonsense thread. I logged on to express my thanks but by that time most of page six had disappeared. So I say it here: thank you Kryptid and as I have said previously, I really admire your patience with that onslaught of gibberish.

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Physics, Astronomy & Cosmology / Is this a violation of com?

« on: 21/07/2023 19:12:47 »

An acquaintance on another forum has suggested a possible violation of the conservation of momentum. I am sceptical but don't feel competent to analyse the scenario rigorously. The setup is quite simple: two half wave dipoles are physically separated by a quarter wavelength spacing and fed with two signals with 90degree phase difference, at the resonant frequency. The argument is as follows: the electrostatic field from A arriving at B will be in phase and cause repulsion while the field from B arriving at A will cause attraction in the same direction as the repulsion occurring at B and hence a net force in one direction without reaction. Any thoughts? 

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Just Chat! / Strange ads or am i misinterpreting?

« on: 18/07/2023 21:22:44 »

I ignore all ads and delete where possible but this evening ~9pm I took notice. An ad for two 12guage shotgun cartridges appeared which I clicked on out of curiosity but came back "can't be displayed" or something similar. I don't think ammunition ads are appropriate. I don't own a gun and never have so it's not one of these ads that follow one based on previous search history. It seems to have disappeared now.

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Just Chat! / Where is Colin2b?

« on: 03/07/2023 13:37:28 »

Recently Zer0 enquired about the short absence of BC and magically he reappeared. I have not seen a post from Colin2b recently and I miss his contributions.

20

The Environment / Is the jet stream the ultimate arbiter of local weather?

« on: 30/06/2023 11:30:47 »

Currently in Ireland and I assume in the UK the weather is miserably wet sabotaging my gardening efforts. The perceived wisdom is that the latitude of the jet stream is the determinant of whether we have cyclonic or anticyclonic conditions. Is the jet stream the ultimate arbiter or is it subject to some other phenomena?