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Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 12/07/2022 14:44:35 »

Eternal student, I hope your family are ok. Covid seems to be very erratic in terms of symptoms and severity of illness, even for the vaccinated. I assume I had it(big assumption) as I did not bother doing an antigen test this time. What led to this assumption is that I got a collection of signs and symptoms very similar to the vaccine (Pfizer) side effects, which I have never got from viral infections before. It was however very mild overall. Wishing a quick recovery for all.

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Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 11/07/2022 13:32:47 »

Eternal student, i'm sure our resident philosopher alancalverd,  has plenty of conundrums and paradoxes to stimulate your analytic skills. Hope he doesn't blacklist me for this suggestion!!

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Physics, Astronomy & Cosmology / Re: Why can't i understand the andromeda paradox?

« on: 08/07/2022 12:43:11 »

Eternal student, all is clear this morning though I don't feel 100% yet. It's simply two participants(halc won't allow observers-he's correct) in different frames disagreeing on the timing of an event. My malfunctioning engineering brain viewed the two frames as being sufficiently similar as to consider them equivalent. A higher speed of one participant would give a greater slope to your green line. The wording in the wiki article(penrose's version) still 'hurts' my brain. Many thanks again.

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Physics, Astronomy & Cosmology / Re: Why can't i understand the andromeda paradox?

« on: 05/07/2022 16:24:22 »

Thank you, eternal student, for your detailed reply. I can follow your reasoning explicitly, however I can't grasp the concept, if that makes any sense. Bottom line: I think I have covid too. I had sudden onset low back pain and brain is not in gear and i'm making mistakes in everything I do. I will return in a few days(hopefully).ps i'm fully "vaxxed" as the conspiracy theorists would call it.

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Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 21/06/2022 18:34:27 »

I don't want to sound overly contentious but I see a dimensional conflict in your integration result: how can area be equal to a linear expression ie 4πr? I am quite familiar with cylindrical and spherical coordinates but I can never remember the expressions and I would have to look them up any time I need them, especially the spherical.

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Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 21/06/2022 14:48:47 »

One small addendum, not directed at previous contributors but more for general readers. I get the impression that a common misunderstanding is that the inverse square law always holds in non-extreme(ie non relativistic) scenarios. This is not so: the inverse square law applies only to point sources(or sources that can be interpreted as point sources), an infinite line source will have a 1/r decrement and an infinite surface source will be constant at all distances. Real world sources of line and surface types will require additional calculations to determine field strength.

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 14/06/2022 19:47:17 »

Pardon me for butting in but the easiest way to understand a black hole is in terms of escape velocity. As gravity gets stronger and stronger the escape velocity increases. When it reaches or exceeds c, the speed of light in vacuo, nothing including light can escape. I realise most of you understand this explicitly, this is for the op, neilep.

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Plant Sciences, Zoology & Evolution / Re: What are your favourite Plant Pictures?

« on: 14/06/2022 11:33:15 »

Datura innoxia, the downy thorn apple. Difficult to grow successfully in my climate(Ireland) due to blight attack. This is my wife's hand near the flower, not mine.

downy thornapple.jpg (52.13 kB . 480x640 - viewed 2346 times)

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General Science / Re: What is the actual Brayton Cycle efficiency?

« on: 09/06/2022 19:40:50 »

Nobody seems to be rushing to help. It's 50 years since I studied this stuff but there is a problem with your efficiency expression: the efficiency will be the net shaft work after the compressor work is subtracted from the turbine work all divided by the heat supplied. Your expression only has temperatures. Now if net shaft work is zero and you are employing a propulsion nozzle after the turbine then it's more complicated. I am in error, of course the net work can be expressed in terms of temperature values; on looking it up in my small tech library I find efficiency= T1-T2+T3-T4/T3-T2.

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Physics, Astronomy & Cosmology / Re: What is the mechanism of Hawking radiation?

« on: 09/06/2022 16:15:41 »

Yes indeed I do enjoy any diversions that lead to improved understanding of any area of maths or science. The cancellation of infinities in quantum theory would be very hard for me to accept as rigorous maths. However I do understand that a theory which is not realistic in simple terms can be very useful if it explains observations and makes predictions that can be verified.

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Chemistry / Re: Help with quoted enthalpy values, please.

« on: 04/06/2022 15:54:20 »

If your reaction produces two products the total delta h will be the sum of the individual delta h of each product multiplied by the molar concentration of each final product. Often delta h values are not easily determined by direct experimental method and are computed by known values associated with the initial reactants. Google the born-haber cycle.

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Chemistry / Re: Help with quoted enthalpy values, please.

« on: 04/06/2022 13:30:02 »

It's 50 years since I studied this stuff and I really should not be hazarding a "guess" especially since physical chemistry was my worst performing subject. The enthalpy is for the formation of the product, 2 moles at 50kj each. You cannot ascribe it to the reactants without going through the full cycle of initial activation energy to produce the reactive species that participate in forming the new molecule. A lot of ionic reactions derive much of their net  negative enthalpy from lattice energy of the formed product.(I shouldn't have said anything-i'm sure I have confused you as much as myself)

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Physics, Astronomy & Cosmology / Re: What is charge?

« on: 31/05/2022 15:08:56 »

Yea, that's pretty much as expected, thank you(s).

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Cells, Microbes & Viruses / Re: Monkeypox: Could it be similar to cowpox, and just a mild variant of smallpox?

« on: 28/05/2022 20:50:24 »

There seems to be an assumption that covid has gone away. It is still spreading and mutating. It's unlikely to return as a variant with increased pathogenicity and/or the ability to evade current vaccines but it is a possibility. It's early days in the evolution of a fast evolving virus.

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Physics, Astronomy & Cosmology / Re: Does The Universe Spin ?

« on: 27/05/2022 14:57:54 »

Spin in relation to what? A spin is usually observed from some static frame of reference. Maybe it is spinning and this causes the observed expansion but there is no way to determine this without said frame of reference which by definition does not exist.

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New Theories / Re: Insulin myths and the science that broke through

« on: 18/05/2022 16:46:36 »

I can't answer your questions, it's 50 years since I studied chem/biochem and I never worked in this field. I am just stating that insulin can cause rapid passage of glucose into cells(not specifying which type) leading to life threatening hypoglycaemia. The point being that insulin is a direct stimulant of glucose transport-if it was just a glucagon antagonist this effect would not happen.

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New Theories / Re: Insulin myths and the science that broke through

« on: 13/05/2022 10:55:08 »

An injection of insulin in a non-diabetic will cause a hypo which can easily be fatal. The effect is immediate, shifting glucose from circulation to cytosol. As I remember this has been used in the past as a "perfect murder" tool since no extraneous substances are found at post mortem. Prior to the use of ect insulin injection was used to trigger prompt convulsions(ghastly concept) but was dropped for the 'safer' electrical procedure.                                       9

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New Theories / YouRe: Insulin myths and the science that broke through

« on: 28/04/2022 18:34:53 »

You state that "insulin does not reduce blood sugar". This is patently false as an injection of insulin can produce a hypoglycaemic crisis which can be fatal. On the subject of adipose deposition insulin will do this only if your calorie intake is greater than your energy requirements. Now if a diabetic omits their insulin they can eat more without weight gain because excess glucose is excreted through the kidneys(causing nephropathy). On the subject of exercise when fasting, muscle stores sufficient glycogen for it's needs until gluconeogenesis gets going in the liver.