Jump to content


Senior Members
  • Posts

  • Joined

  • Last visited

  • Days Won


Everything posted by sethoflagos

  1. Not here. Within the circles I move in, beer is the social brew of choice. Only to geordies who ask daft questions. More the chutzpah of those who believe their taste in tea is somehow superior to anybody else's. There is no universal 'perfect cuppa'. Just an individual's preference. The similarity of sugar cellars to salt cellars in many establishments has caused most of us to have conducted unplanned experiments with salty tea.
  2. It does. Been recycling tepid tea that way for years.
  3. It'd need a minute in the microwave otherwise you may as well be drinking bathwater.
  4. Bless their little cotton socks! What do they miss out? The preheating the teapot bit, or the tea cosy to keep the heat in?
  5. There's likely as much arsenic in the water you stew it in. See https://pubmed.ncbi.nlm.nih.gov/25526572/
  6. Personally I take my tea strong, black and well stewed. The more astringent the better within reason. But it seems there are some folks who just can't get enough blandness into their lives. Salting tea sounds to me as doolally as decaf, but whatever floats your ⛵.
  7. Do you imagine that 'billions' is an appropriate counting unit for, say, all the different possible permutations of the up to 40+ billion base pair sequences of DNA? (Try running 4^4^10 through your calculator to get an idea)
  8. Ditto @Bufofrog. Could be something as simple as an unsuitable mattress. At least, that's my experience.
  9. I mentioned it once in passing. It isn't a cornerstone of my argument. While grateful for your advice, I'm at a loss to see how it applies to the optical rectennas under discussion.
  10. On reflection, I'm inclined to think that it's a bit of each. The salinity of the Hadean oceans would no doubt have reflected the mantle Na:K ratio which in turn is reflected in the Na:K estimated ratio of the solar system. So perhaps the similarity in current times isn't as much of a coincidence as I suggested in an earlier post. However, with the onset of plate techtonics in the mid-Archaean, the two following quotes, taken together indicate that both surface waters and their salt inventory are being continually recycled to and from the mantle: I guess the turnover time is at least oto 1 billion years so it's a very slow process and almost certainly not at equilibrium. But it is clear that there is some continuous limited exposure to mantle cation ratios that would act as a negative feedback loop tending to restore primitive values. Which leaves us with having to deal with why continental crust is so markedly different with a near unity Na:K mass ratio. Arguably so, but at constructive plate margins, there is no neighbouring granite for them to migrate to. Rather we have a fractionation process that might be roughly summarised as: 3 Peridotite => 1 Dunite + 2 (Gabbro + Basalt) Dunite is over 90% olivine, offers very limited hospitality to Na (maybe in some residual pyroxene) but as far as I can tell none to K. So most of the Na and all of the K plus the rest of the more volatile components creates a gabbro melt that ascends to fill the gap between the separating plates. At this point I wanted to give some indicative Na:K ratios for oceanic crust gabbro/basalt. Only to find lots of field data showing Na:K ratios up to 50+ for gabbro and 2 for basalt. The common understanding is that basalt is simply rapidly cooled gabbro. Clearly this is somewhat of a simplification. On the face of it, the fractionation process is not the unitary division I've just described, but some multistage fractionation process that preferentially shunts Na into the gabbro levels and K into the basalts. I'd be interested in your views on this. Anyway, it appears that we have the K concentrated in the upper basaltic levels of the oceanic crust, possibly in the form of a feldspathoid such as leucite, the Na evenly spread between the basalt and lower gabbro horizons within clinopyroxenes such as augite, and below the crust mantle boundary a zone of depleted cumulate dunite. At the other end of the conveyor hopefully the picture is a little clearer. As the old oceanic plate is subducted, it eventually reaches a region of high temperature, high pressure which (give or take a little controversy) is where it is converted to a highly metamorphosed rock type called eclogite, mainly comprising pyralspite garnet and a sodium rich clinopyroxene called omphacite. With the K being concentrated in the contact zone of the upper levels of the oceanic crust, and an incompatible mineral assemblage forming beneath it, the path for transport of the vast majority of it into the continental crust appears non-problematic. Na on the other hand has the option of joining with the K to progress upwards, or staying in situ within a compatible mineral assemblage. The nett result seems to be a roughly equal mass diffusion of sodium and potassium into the lower levels of continental crust. I basically have zilch documentary evidence to support the overall picture of this mass balance, but it makes some sort of sense to me and my researches haven't yet thrown up anything that cotradicts it significantly. Hope it helps. I'm not going to lose sleep over that 🙂
  11. Sodium is relatively happy in some mafic minerals, particularly clinopyroxenes. I suspect potassium simply won't fit in that lattice. In a feldspar environment, the alkali metal hole is clearly big enough for potassium and maybe this gives a little more stability to the potassium version under most surface conditions. However relative weathering rates show a high pH and temperature sensitivity so perhaps there are multiple mechanisms at play.
  12. @swansont's reference is dominated by the composition of the earth's mantle. This is indeed the ultimate source of sodium and potassium at the earth's surface, and the sodium:potassium ratio is strikingly similar to the marine ratio. However, I think this is coincidental. Except for odd cases such as a notable ocean bed exposure off the Cape Verde islands, surface waters and upper mantle rocks are not significantly in contact. Rather, there are a number of fractionation processes in the vicinity of the crust-mantle boundary that enrich the alkali metal content and deplete the mafic materials (Mg, Fe predominantly), starting with emplacement of basalt/gabbro at constructive plate margins and culminating with the granitisation of the base of the continental crust at destructive plate margins. Even this is quite a simplification as there are a number of other processes involved most of which are not fully understood, so I tend to take a first order engineering approximation of the mantle injecting granite into the continental crust. It's easier on my head and the overall mass balance still works. The concentration factors of 30 for sodium and 600-ish for potassium reflect their relative preferences for a granitic environment over a peridotite environment.
  13. If this helps, the primary route for transport of sodium and potassium into the earth's crust from the mantle is via emplacement of granitic intrusions which occurs in roughly equal weight proportion. From https://en.wikipedia.org/wiki/Granite Chemical weathering of rock minerals follow the Goldich Dissolution Series This indicates that the potassium rich minerals (orthoclase, muscovite, biotite) are relatively resistant in comparison to sodium rich minerals (sodic plagioclase, some amphiboles and clinopyroxenes). By logical extension, sodium is over-represented in sea water and evaporites, whereas potassium is over-represented in detrital sands and sandstones.
  14. Reckon so. I've seen somewhere that albite (sodium feldspar) weathers at 10 times the rate of orthoclase (potassium feldspar).
  15. Excellent link! Cherry-picking one particularly apt paragraph:
  16. We're pretty much aligned here, and I too am pushing the limits of my understanding of EM field behaviour. I was hoping that @swansont or someone else with expertise in this field would have picked up on my previous post and confirmed or otherwise the mental picture I have of this. But in the absence of such... I think it reasonable to picture the thermal energy of a metallic antenna as being largely contained in the motion of a 'gas' of the unbound electrons. If you can persuade a significant excess of these to move in a coordinated way in a particular direction then that yields an electrical current distinct from the thermal motion. However, I suspect that this requires the incoming radiation to be both directional and/or phase-coordinated. Thermal radiation from the sun satisfies the directionality requirement and I presume the higher frequency part of the spectrum may have sufficient 'kick' to push a few electrons across the junction gap of a diode which might explain the measurable current reported in that scenario. But ambient thermal radiation is omnidirectional and the individual photons are much weaker. Trying to extract energy from this scenario just sounds a little too Maxwell's Demonish for comfort. May be this picture is all wrong, but it at least tends towards consistency with the Kirchoff's Law/2nd Law objections I raised earlier.
  17. I'm getting a picture here of transmitted photons perturbing the EM field of an antenna aligned with the source somewhat analogously to a steady trade wind generating oceanic waves. And just as the energy of oceanic waves can be harvested by an appropriate machine, the waves in the field of the antenna induce an alternating pd across the terminals of the antenna which can in turn be harvested. Is this analogy a useful one?
  18. You're effectively claiming the ability to extract useful work from a system at thermal equilibrium. Not sure there's anywhere to go from here.
  19. Just to emphasise this crucial point, consider the major introgression of 'alien' DNA the ancestors of some of us experienced in the not too distant past. Yet the vast majority of our genome has been swept clean of neanderthal alleles (the so-called neanderthal deserts). This example is far from the picture of small random mutations slowly accumulating over time. And yet the end result is just what Darwin would have predicted. We retained useful alleles, particularly those helpful to climate adaptation and immune responses, and lost those those that didn't sit well with the core sapiens 'team' of genes. It undoubtedly influenced the speed of evolution, but the fundamental principle of evolution by natural selection remained unchallenged. As we're in the Speculations section, I might add that I'm inclined to the view that evolution by natural selection is an inevitable process driven by differential efficiencies in the utilisation of energy flow through a system. The detailed mechanics of genetics then becomes more of a consequential effect than a prime.cause.
  20. He wouldn't be. Just faster than the light heading 'in his direction' was receding from the event horizon.
  21. Does the light need to be travelling in the outward direction? If the infalling observer is falling faster than the wavefronts are receding, he catches up with them doesn't he?
  22. The detailed mechanics of aerial design are way beyond my pay grade, but you seem to be making two distinctions here that I would be wary of: Until it is. Can you say this when the received phonons are indistinguishable from the sea of thermal phonons flooding the lattice of the receiving aerial? Cooling is thermodynamically difficult. I'd be reluctant to use the word in place of "not getting quite as warm as you might otherwise expect". Revisiting Kirchoff's Law briefly, there are some useful bits of information to be had from Electromagnetic Reciprocity. This caught my eye:
  23. The bottom line here is Kirchoff's Law of Thermal Radiation which is often expressed as: If this were not true then there could be spontaneous nett heat flow from a cool body to a hotter one which simply doesn't happen. However, the proviso 'in thermal equilibrium' is key since 'arbitrary bodies' can have widely different emissivities at different wavelengths corresponding to different equilibrium temperatures. This is where the misunderstandings arise. Taking an arbitrary example quote from https://en.wikipedia.org/wiki/Emissivity Here the absorptivity is with reference to thermal equilibrium radiation at the surface temperature of the sun, whereas the emissivity is with reference to local thermal equilibrium in the vicinity of the collectors. The collectors are NOT in thermal equilibrium with the surface of the sun. Without the temperature difference, there would be no loophole to exploit. Okay so far. But note that emission by the antennae is NOT independent of the temperature of the antennae, The receiver does not reradiate incident solar radiation because it is not at the same equilibrium temperature. Therefore there is an asymmetry between absorption and emission that can be exploited. But refer to the relevant paragraph in https://en.wikipedia.org/wiki/Optical_rectenna The proposal neglects to consider the equivalence of absorptivity and emissivity at thermal equilibrium. So it falls foul of Kirchoff's Law, and by logical extension, the 2nd Law of Thermodynamics.
  24. As I understand it, the theorical maximum efficiency from a 2nd Law point of view is 1 minus the temperature ratio of absorber over emitter. This yields something like 85% for solar spectrum conversion. Trying to convert near ambient spectrum IR would yield zilch I suspect as the antenna would be emitting about as much as it absorbed.
  25. Imagine the current generated is used to charge a battery. Losses are generated by the required electrode overpotentials and internal Ohmic resistance of the cell resulting in radiation of waste heat to the environment. An overall picture of the thermodynamics can be found here. Closely related is Thermodynamic bounds on Work Extraction from Photocells and Photosynthesis which connected a lot of loose strings for me at least. Attached. Well worth a read imho. Photocells and Photosyntesis.pdf
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.