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May 7

Volatile solvent in glass bottle with glass stopper?

I suspect that my toluene (for cleaning electronic flux from circuit boards) is evaporating from the plastic bottle. Would a glass bottle with ground glass stopper be better or worse for storing a volatile liquid? 78.149.180.132 (talk) 02:06, 7 May 2019 (UTC)[reply]

see Ground glass joint and Hermetic seal#Glassware sealing. You may need some kind of grease to seal the joint. Graeme Bartlett (talk) 10:53, 7 May 2019 (UTC)[reply]

Per Graeme, the addition of a non-reactive grease would be standard; there's a silicone-based grease which is industry-standard for this. See silicone grease where the article specifically mentions its use in sealing ground-glass joints. This served two purposes: to both seal the joint to prevent leakage AND to lubricate the joint to prevent stickage. --Jayron 32 10:55, 7 May 2019 (UTC)[reply]

No, bottle stoppers aren't greased. Certainly not with silicones.

Yes, toluene will go through the walls of a plastic bottle. Although not as fast as hexane will. It can be such a rate that you can get exposure limit problems in a store cabinet.

If you do store it in glass, the proper type of bottle really ought to be used. There's a plastic shrink wrap over the outside to stop them shattering if you drop them. Also most occupational health people would want you to avoid toluene for something safer. Andy Dingley (talk) 11:02, 7 May 2019 (UTC)[reply]

Well, bottle stoppers can be greased, if you have grease. --Jayron 32 11:33, 7 May 2019 (UTC)[reply]

When I used toluene, long ago, it came in a white metal can. I poured it into a plastic bottle with a long nozzle (it makes it easy to squirt it onto a circuit board without touching it). When done, I poured the remainder of the plastic bottle back into the can. 12.207.168.3 (talk) 13:49, 7 May 2019 (UTC)[reply]

Lately I usually see toluene in glass bottles with plastic screw-caps (bakelite-like, with lining of a softer white plastic) or in metal cans with either metal or various types of plastic caps. SDS says "SUITABLE MATERIAL: metal. stainless steel. carbon steel. aluminium. nickel. polypropylene. glass. tin. MATERIAL TO AVOID: polyethylene." DMacks (talk) 03:52, 8 May 2019 (UTC)[reply]

flying ostritch

The ostrich is the largest bird currently in existence. How big of a wingspan would it need to be able to fly (say even 100 m)? 216.223.104.13 (talk) 17:03, 7 May 2019 (UTC)[reply]

Ostriches are in the ratite family. No matter how wide their wingspan gets, they can never fly because their muscles are not anchored to allow for flight. Assuming you mutate the ostrich to allow the function of flight, the wingspan will have to be huge. Domesticated turkeys cannot fly, but can glide. They are the cutoff point of body weight to wingspan. Domesticated turkeys weigh about 15 to 25 pounds with a wingspan of about 50 to 65 inches. You are looking at about 2.5 to 3.5 inches of wingspan per pound. An ostrich weighs about 250 to 350 pounds. Using the same inch wingspan to pound weight ratio, we get a wingspan of 625 to 875 inches. That is 52 to 73 feet. But, we aren't taking into account the differences in weight distribution, land speed to take off, bone density, or feathers. My point is that they can't fly, no matter the wingspan, but if they could glide short distances (like a domesticated turkey), they would have massive wingspans that would inhibit any movement on the ground. Even if they had tri-fold wings, you are looking at 20 feet per section. How would they walk around? 12.207.168.3 (talk) 17:34, 7 May 2019 (UTC)[reply]

With difficulty. Tigraan^{Click here to contact me} 19:25, 7 May 2019 (UTC)[reply]

Take a look at the skeleton of the ostrich. Compared to flying birds, there's no prominent keelbone, but the hips are bigger. The muscles attached to these are in proportion. Flying birds use the large breast muscles, anchored on this keel, to power their wings. The ostrich has no such large muscles, and nowhere strong enough to attach them. So even if an ostrich was to sprout enormous wings, sufficient to give it a plausible wing loading comparable to other birds (a simple geometrical calculation from other large birds would give one estimate for this), it wouldn't be able to flap them.

Also note that some of the largest flying birds, such as the Andean Condor, are able to flap their wings and take off under their own power, but they largely fly by soaring on updrafts, like sailplanes, not by constantly flapping. The scaling laws for large birds are such that being a very large bird is difficult, even if your wings are nominally large enough.

How big are they? Well a Dalmatian pelican is possibly the largest flappy bird, and that weighs 15kg with a 3m wingspan. An ostrich can weigh six times that, implying a wingspan perhaps 2.5× as broad would be needed - 7.5m, or twenty feet! But as the current non-flying ostrich doesn't have flight muscles, it would need to add those too – implying it would need to be ever bigger. Being a viable bird just gets harder and harder with size, so there is an upper limit on them, about the size of what we currently have. If an ostrich ever did manage to evolve into a flying form, that would probably look more like a pelican, and with less of the ostrich's distinctive (and heavy) powerful legs. Andy Dingley (talk) 17:46, 7 May 2019 (UTC)[reply]

Andy - check out Kori bustard as possibly the largest flying animal.--Phil Holmes (talk) 08:51, 8 May 2019 (UTC)[reply]

The bustards are probably the closest thing to "a flying ostrich" as they're primarily ground-dwelling bipeds, but they haven't entirely lost the ability for flight. They're not great travellers though. Andy Dingley (talk) 09:47, 8 May 2019 (UTC)[reply]

The largest wingspan birds rely on gliding on air currents. See the great albatross for an impressive wingspan up to 3.5 m (11 ft). However, large adult males may weigh only 11 kg (24 lb). So, these gliders need to be very lightweight. If you scaled that up to the 10x weight of an ostrich, the wingspan would be enormous. SinisterLefty (talk) 21:23, 7 May 2019 (UTC)[reply]

Not the pelicans though. Also this is generally considered as soaring rather than gliding. Gliding is what flying squirrels do, and they can only do it for short distances comparable to the size of the tree they jumped from (No-one really knows about pterosaurs, but something similar is regularly hypothesised). Getting any real distance from unpowered flight needs the ability to soar as well, i.e. an exceptionally good glide ratio and also the ability to detect and then make use of natural updrafts. Andy Dingley (talk) 00:05, 8 May 2019 (UTC)[reply]

Thanks, All. This also helps me understand why Pegasus can't really fly. :)

Pennycuick's Newton Rules Biology is one of my favourite science textbooks, for just that reason. Andy Dingley (talk) 00:05, 8 May 2019 (UTC)[reply]

The question of whether Pegasus can fly is also a very serious question in modern philosophy.[1] Andy Dingley (talk) 00:12, 8 May 2019 (UTC)[reply]

Pteranodons were pretty big, with wingspans up to 23 feet according to the article, though it doesn't give their mass. But I thought they were even bigger, like Rodan. Oh well. 67.164.113.165 (talk) 01:28, 8 May 2019 (UTC)[reply]

Actually the article says:

Methods used to estimate the mass of large male Pteranodon specimens (those with wingspans of about 7 meters) have been notoriously unreliable, producing a wide range of estimates from as low as 20 kilograms (44 lb) to as high as 93 kilograms (205 lb). In a review of pterosaur size estimates published in 2010, researchers Mark Witton and Mike Habib demonstrated that the latter, largest estimates are almost certainly incorrect given the total volume of a Pteranodon body, and could only be correct if the animal "was principally comprised of aluminium".[3] Witton and Habib considered the methods used by researchers who obtained smaller mass estimates equally flawed. Most have been produced by scaling modern animals such as bats and birds up to Pteranodon size, despite the fact that pterosaurs have vastly different body proportions and soft tissue anatomy from any living animal.

Nil Einne (talk) 02:50, 8 May 2019 (UTC)[reply]

BTW, according to Argentavis and Pterosaur, some Azhdarchidae in particular Quetzalcoatlus and Hatzegopteryx were even bigger which seems to be supported by their articles, although it sounds like we may be less sure of whether their flight involved some flapping. Nil Einne (talk) 02:59, 8 May 2019 (UTC)[reply]

Quetzalcoatlus has provided enough fossils to allow for some reasonable estimates about size and weight to be made (though there are always uncertainties about that stuff). According to our article (backed by refs), the weights for Q range from 70 kg up to 200-250 kg, nearly twice the size of an ostrich. However, as others have noted, it's not a simple thing to just graft on a set of appropriate wings; the entire animal needs to be redesigned. It seems unlikely that Q flapped much, but it's pretty certain it flew. Matt Deres (talk) 14:11, 8 May 2019 (UTC)[reply]

50 foot wingspan, 1000s of miles of flight range, and a picture showing it about the size of a Cessna -- now that's more like it. Nice! 67.164.113.165 (talk) 08:15, 10 May 2019 (UTC)[reply]

Capacitors

If a capacitor has both capacitance and inductance, is it s transmission line? If not why not?80.2.20.28 (talk) 23:48, 7 May 2019 (UTC)[reply]

Transmission lines are considered, as an implicit part of their definition, to be two-port networks or four-terminal networks; capacitors (even with "real world" internal behaviour) are seen as single-port (or two terminal) networks. You can of course make a two-port network by connecting the two terminals of the capacitor network across both ports.

This isn't about the behaviour of such networks, i.e. their reactance or impedance, it's about their definitions as concepts. Andy Dingley (talk) 00:23, 8 May 2019 (UTC)[reply]

The OP here continues a previous line of questioning [2][3][4].

A capacitor is a discrete electronic component that is manufactured as small as possible. It has lumped characteristics of capacity (desired) and some inconvenient internal inductance and resistance. A transmission line may be any length. It has distributed capacitance, inductance and resistance. A capacitor is not a transmission line. At low frequency an arbitrary length of transmission line can be employed as a capacitor. This was done in an early color TV Decca CTV25 see picture that was delivered with a "spare" roll of coaxial cable on the black case at right. This was the designer's way of providing smoothing capacitance on the high voltage crt anode without investing in a discrete component. DroneB (talk) 11:23, 8 May 2019 (UTC)[reply]

To model a transmission line, you could use a collection of inductors in series and capacitors in parallel. Look in Distributed element model to see this illustrated and described. A correctly matched transmission line will not have a resonance. For your non-ideal capacitor it has inductance and capacitance in series, so it does not look like a transmission line. See LC circuit#Series circuit for a description of this combination. Graeme Bartlett (talk) 12:38, 8 May 2019 (UTC)[reply]

all discrete components are distributed components. All capacitors have inductance.All inductors have capacitance. All resistors have capacitance and inductance.80.2.20.194 (talk) 23:56, 8 May 2019 (UTC)[reply]

SMD capacitors (on the left) with two through-hole capacitors (on the right)

Whether such categorical statements have any useful truth in engineering depends on your operating frequency and you have not yet answered my earlier question. It is unhelpful to dismiss the Lumped element model that is valid whenever

L_{c}\ll \lambda

, where

L_{c}

denotes the circuit's characteristic length, and

\lambda

denotes the circuit's operating wavelength. The discrete SMD capacitors in the picture are correctly idealized as lumped at any frequency they are likely to be used. In contrast, Coaxial cable type RG-58 exhibits capacity of 25pF/ft (82 pF/m) distributed along its length which could be almost any number of wavelengths. DroneB (talk) 08:31, 9 May 2019 (UTC)[reply]