sethoflagos

I wouldn't have minded one, but no. I rarely drink before midnight these days. You're right of course. The 'chicken' and 'egg' calls are no more than an amusing coincidence, and no one here believes otherwise. But there clearly is some interaction going on between the species and that in itself is interesting. I see no harm in other forum members picking up on this. What do you mean by 'conscious'? A correct answer would be Nobel prize material. @chrisjones has already brought up the free will debate, and the superdeterminist faction of physicists would claim that all actions (including thought, conscious or otherwise) are predetermined. I don't personally believe this for a moment, but I've nothing better to offer than an argument from incredulty. Not sure anyone else has.

The cuckoo tales clearly show that many birds are clearly aware of eggs-istential threats, not only to themselves, but also threats to other species, and can refer to these threats (such as raptors) even when there are none around.

The species (I presume it's two different species) wait for the other species to fall silent before making their calls. So they clearly appear to acknowledge each others existence. We've a bright metallic green cuckoo called the Diederik (it's usual call is dee-dee-deederik). A while ago I was watching one perched on an elevated cable being mobbed by a multispecies group of smaller birds. It's primary response (before eventually flying off) was to mimic (very well!) the call of our local kestrel. There's quite a lot going on here. Interesting article. Thanks!

Taking a balcony break this evening, I was greeted once again with a chorus we get at the height of the rains that has intrigued me for years. Here in southern Nigeria, our frogs don't go 'Ribbit...' There's one species that does a similar and insistent 'Chicken... Chicken... Chicken'. And then there's a second that intersperses a deeper pitched almost lugubrious 'Egg... Egg... Egg'. Is there an Aristotelian debate going on here amongst the lower orders?

Living in the tropics, I'm quite keen on lactic acid fermentation to preserve vegetables rather than to buy fresh daily. Fruit flies are therefore the bane of my life. It's fruit fly maggots that you've found, and they're really keen on lactic acid (Reference: https://lsi.ubc.ca/2021/07/02/not-all-acids-are-equally-sour-gordon-lab-research-sheds-light-on-why-fruit-flies-find-lactic-acid-a-delight/) It's a real bind, but this is why you should be thorough with sterilisation of storage vessels and keeping everything airtight. The stinky stuff isn't the fruit fly maggots though. That's Kahm yeast. But the preventives are much the same.

It's already in the wood. Seasoned wood is typically around 12% moisture at equilibrium, but this shifts around a bit according to the ambient temperature and relative humidity. Since wood (especially softwood) is quite porous, there is a continuous exchange of moisture between the wood and its surroundings. (Reference https://en.wikipedia.org/wiki/Wood_drying) If you prevent this exchange with an impermeable plastic film, then your likely to find free water pooling under it from time to time. Puncture the plastic cover on something like a 5mm pitch to allow the wood beneath to breathe.

Yes there is, since both are driven by Milankovitch cycles. However, the relationship is largely indirect and complex in that glaciations and forestation do not respond to individual Milankovitch cycles to the same extent. 'Regardless of CO2' is not a valid constraint as it is a critical contributory factor to both glaciation and forestation, but again, the response curves have different shapes and different lags (delay between cause and effect). So it's once again a complex correlation. Take a look at the Wikipedia page https://en.wikipedia.org/wiki/North_African_climate_cycles. It explains the relationship between glaciation cycles and Sahara greening cycles in not too technical a way for the layperson to understand. I defer to @Ken Fabian's excellent response (+1). ie Less than you might think. We could in principle reverse much of the damage done by the last two centuries of coal burning by backfilling every coal mine ever dug with charcoal produced from sustainable forestry. But that (at best) would be a thousand year project to solve a fifty year crisis. Too little too late.

Would you care to explain this response. I don't see the relevance.

As a resident of one of those 'African countries close to the equator' I've got to ask why you pick this example? Do you see the equatorial belt as being more at threat due to climate change than Europe or the US? I was under the impression that the greatest impacts were likely to be felt in the higher latitudes.

What your proposal seeks to do is increase the contact area between brine and the lower couple of hundred feet of the atmosphere in order for it to approach equilibrium at 100% RH more rapidly. My point is that nature already does this quite effectively. The missing step is getting heat into the system. This is required to both increase the water holding capacity of the airstream and reduce its density sufficiently to allow it to rise. The amount of heat the sun is putting into the ocean to try and do this is measured in Terawatts. And in the cases we have mentioned that isn't enough to overcome the local conditions which are dominated by cold ocean currents. How many TW do you propose adding to this equation? Have you ever heard the phrase 'latent heat of vapourisation'? Have you any idea what it means?

+1 For the full shebang try https://publications.csiro.au/rpr/download?pid=csiro:EP116380&dsid=DS1

Fair point if you were considering say the 100 miles or so unpumped supply of Manchester via Thirlmere aqueduct. But for more continental scale issues, I think it's probably the wrong question. +1 There must come a point where further development of parched lands is simply unsustainable due.

I do get the picture. 1) If there is a significant onshore wind, it is already humid and will cause rain inland. There is no problem to address. 2) You cannot significantly increase the humidity of this wind without increasing its temperature. 3) The evaporation of brine requires even more heat input. 4) I've not even mentioned the astronomical pumping costs. This quote from https://en.wikipedia.org/wiki/Namib gives an idea of the practical realities you are trying to reverse: ie The 'significant onshore wind' and 'rising thermals' simply don't happen. If they did, it wouldn't be a desert.

Both low lying areas subject to offshore cold water currents/upwellings and predominantly dry trade winds? They are deserts for a reason. Could add the Atacama to this list. (Ekman transport can be an important mechanism in these cases) The lower few hundred feet of steady onshore winds are typically in approximate thermal equilibrium with the ocean, aren't they? So where is the energy to come from to evaporate the water? Even if the air is at lower relative humidity (such as a descending Hadley cell), evaporation is going to chill it further. This doesn't sound like a good recipe for creating a rising thermal. More a recipe for fog. If it worked, nature would already be doing it, I think. As it does here in southern Nigeria during the rainy season. But come november the rainbelt will have moved south to Angola, the Hadley cells will shift what little air movement there is to a north-easterly flow, and it will be both cool (for us) and bone dry. Trying to 'make' it rain here at the turn of the year would be an exercise in futility. Everything would be working against you.

When I was at school there were 30.48 centimetres to one foot, so maybe just multiply the result of your calculation by 30.48? Or is the input to your calculation not in millibars either?

Hydrogen-Oxygen combustion in a fuel cell with full heat recovery is currently capable of around 85% thermodynamic efficiency, so we should be looking at a nett electrical output of a smidgen over 200 kJ/mol. Conventional alkaline electrolysis has a thermodynamic efficiency of ~70%, but a lot of work is currently being done on Proton Exchange Membrane (PEM) technology and we should soon be able to achieve 85% on that too bringing the energy cost (electrical) down to about 280 kJ/mol.

+1 Just to complete the circle, in the combustion cycle only a theoretical maximum of 237 kJ/mol of the enthalpy change is thermodynamically available for conversion to eg electricity for electrolysis (this is the meaning of Gibbs free energy).

Other than the top 6 or 7 commonest crustal elements, it's more about the density of the rocks of which they are a minor/trace component. ie less than 1% by weight of the local rock formation and having negligible impact on the bulk density.

Interesting to note that the last 10 positions on that list include all the Group VIII precious metals at typically 1 ppb whereas Thorium and Uranium despite being considerably heavier nuclei have over 3 orders of magnitude greater crustal abundance. This is strong evidence that the dominant factor is not atomic weight but chemical affinity with the crust being heavily depleted in the siderophilic elements (those that have a chemical affinity for a metallic iron phase) relative to the lithophilic elements which are preferentially drawn to a silica rich phase. Almost as if the crust had been washed 99.9% clean of siderophiles by a descending wave of iron heading for the core.

I'm sure you're better acquainted with the current technical definition of 'standard enthalpy of formation' than I am, and all the caveats that go along with it. And yes, if all those caveats are observed then delta H in the forward direction equals minus delta H in the reverse. But don't those caveats require that conditions at start and finish are globally unchanged? In other words, the equality of enthalpies is dependent on there being no overall change in entropy? That was my understanding but then I'm Chem Eng, not a Chemist.

I take your point. But in the reverse reaction you are breaking bonds by electrolysis, so aren't you steering hydrogen to the cathode and oxygen to the anode thereby unmixing them? I think the piper will still need to be paid his due. Similar arguments can I think be made for all implicit irreversibilities in the process (in both directions). However, the constant making and breaking of bonds in an equilibrium mixture of products and reactants (or similar system) has no irreversibilities. So here, the OP's premise must be true. The energy released by the forward reaction is exactly balanced by that consumed in the reverse.

I think @studiot may have made a valid point. As an example consider that your initial mixing of 2 moles of hydrogen with one mole of oxygen increased the entropy of the mixture by about 1.89 R. In the absence of reaction no energy change occurred and hence there is none to recover in the reverse reaction. However, mixing is an irreversible process (in the thermodynamic sense) and unmixing the products of the reverse reaction back into their pure elemental states will require quite a bit of unbudgeted additional work input.

Perhaps @joigus put it more succintly: I draw your attention to the phrase 'We don't know and we don't care!' Only delta V is relevant in context.

It most definitely isn't. Far better to pick example thermodynamic processes whose paths are simple, well defined and relevant. Excellent point. But this result could have been obtained by considering the gradual inflation of a balloon for example. I pick this because in good teaching examples of PV work, it is usually arranged that the pressure exerted by the surroundings on the surface of the system is well defined and equal to the pressure exerted by the system on the surroundings. In the OP's example, this is not the case: P1, P2, and any possible thermodynamic path between them are complete and utter red herrings. I don't think I mentioned Z, did I? Bit strawmannish there, J 😉. Besides which, all the process simulators seem to be running Peng-Robinson these days. But that's for much later in the course, as you say. By 'out of equilibrium' I'm assuming you mean that the system has significant P, T gradients, ie parts of the system are not in thermodynamic equilibrium with other parts never mind the surroundings. Whether or not it's necessary to invoke N-S (thankfully not in most cases), a reasonable approach may be to shrink the system under consideration to a differential volume moving with the local mean fluid velocity. This unit cell can be assumed to be at some localised P, T equilibrium state with no mass interchange with the surrounding cells, and therefore the standard thermodynamic analytic techniques should be applicable to the interactions of the unit cell with its 'external environment' of neighbouring cells. And then the maths starts, using the equation of state to relate the pressure and density terms in the applicable flow and mass continuity equations. Pointless to go into the methodologies as these are highly case dependent. Sometimes you're lucky and end up with a simple ODE. Sometimes not.

Just to be clear, I have a different viewpoint on this. Modelling of expansion/compression processes assuming constant PV^k is just too good a predictor of real machinery performance to be ignored. Both P and V must be quite mappable through these highly dynamic changes of state irrespective of equilibrium considerations. It is unfortunate that thermodynamics and fluid flow are treated in most universities as separate topics since scenarios such as the OP are under the control of not just the thermodynamic equations of state, but also the appropriate form of Navier-Stokes equations. And the particular example of the OP is dominated by the most challenging form of the Navier-Stokes: that for flow of compressible fluids where both inertial and viscous terms are significant in all three spatial dimensions. Little wonder the OP is confused. And if he's doing one of the pure sciences, it's highly unlikely that he'll ever be given the analytic tools that might help him make sense of it. He would learn far more from looking at gas expansion through a porous plug. Same process of turning U to W but so little of that nasty kinetic stuff that it can be cheerfully ignored.