sethoflagos

Let's spill over a bit. Commercial airliners typically cruise at a tad less than 600 mph. Their wings typically take 1/100 second to pass through the air and in that time a slab of air equal to the wing thickness must separate by about 10" and rejoin. We'll leave aside what happens at the blunt end of the leading edge (complicated) and focus on the point where the wing surface is at 45 degrees to the oncoming air. At this point the airstream close to this surface must physically be travelling upwards at the same speed the aircraft is travelling forwards. ie -600 mph. Like any other matter, air at 600 mph will continue travelling at that speed in a straight line unless an external force (and in this case, a substantial one) acts on it. Therefore, one millisecond later the air 'would want' to be about 75 feet above the thickest part of the wing creating a void. In order to stay in contact with the wing surface the air must expand very rapidly, substantially reducing its temperature and pressure. The bulk of the airstream now has 'normal' pressure above it and a partial vacuum below. This provides the large driving force necessary to reverse the direction of the airstream and keep it in contact with the wing surface. Now let's return to Bernouilli. The Bernouilli equation was developed to describe the flow behaviour of water, not gases. If you puncture the base of a water tank, the kinetic energy of the jet is directly proportional to the pressure difference. If you puncture a compressed air vessel, the kinetic energy of the jet is directly proportional to the temperature difference. In the gas case there is also a drop in pressure (giving some sort of apparent validity to the 'Bernouilli Principle') but it is very far from a proportional relationship, and can be highly misleading if Bernouilli is treated as Gospel. Which some of the lay community are prone to do.

Firstly, we can restate this as 'an increase in a fluid's kinetic energy is matched by a decrease in its internal energy'. The internal energy of an ideal gas is purely a function of its temperature. (High altitude air is to all intents and purposes an ideal gas). Therefore in order to create kinetic energy, this must be matched by a corresponding drop in temperature. For 'fast' processes such as the movement of an aircraft wing through a body of air, there is insufficient time for any significant thermal diffusion and therefore the process is very close to one of constant entropy. Under such conditions P = P0 (T/T0)^(1-1/k) where k ~ 1.4 for air So when gas velocity increases therefore temperature decreases therefore pressure decreases. It's an indirect route so not intuitively obvious. Having read the posts above, I suggest you consider: 1) The primary direction of motion of the air over a wing is vertical, not horizontal. The air is accelerated up and down. 2) Pressure is a force, not a form of energy. You can safely disregard any post that tells you otherwise (it's a very common misconception). 3) Eugene Khutoryansky's Youtube videos on thermodynamics are very good. The challenge with this one is in visualising how flow in a pipe can be relevant to your area of interest. It is there but you need to have the right mental image in place. If not, then it probably won't help.

Sometimes emotions run high, don't they?

Try https://www.science.org/content/article/weak-jaw-big-brain

We know from our own example that by shrinking the strong, robust mandibles of our ancestors, we no longer needed such sturdy muscle attachments for them allowing us to shed our supraoccipital crests which in turn allowed us to expand our brain cases. Perhaps the switch from toothed mandibles to beaks allowed a similar shuffling around of soft tissues for modern birds. I found this paper illuminating: https://www.science.org/doi/10.1126/sciadv.abg7099

As regards the K-Pg extinction event, the primary sieve for survival seems to be whether or not a bird posessed teeth. Toothed birds (Enantiornithines & Hesperornithines) which were dominant in the Cretaceous were all wiped out while just a few beaked taxa survived. But this is an interesting read: https://www.smithsonianmag.com/science-nature/why-birds-survived-and-dinosaurs-went-extinct-after-asteroid-hit-earth-180975801 So having both a beak and a more developed brain seem to be linked.

Phoebes are among the tyrant flycatcher family Tyrants are unknown outside the western hemisphere. (I hope @MigL doesn't misread this as another attempt at 'humor'). Hence you're unlikely to be a Brit.

Very hard to say. But take the honeyguides. They have a very complex interaction with humans (including mutual recognition of each others calls), that is thought to have developed over the last 1.9 million years. ie they were coevolving with our H. erectus ancestors. They're neither cuculids nor corvids (more closely related to the woodpeckers), but they are brood parasites. You know tyrant flycatchers and how to spell 'humour'. Canadian? Entirely credible. Or maybe they're just saying '*** off this is our swamp'.

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).