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March 6

Plastic sheet pickup truck bed cover vs rigid?

I always wondered what city/highway mpg you'd get with a light rigid cab top to tailgate end hypotenuse wedge (hollow wedge not solid, only thick enough to minimize drag) vs a few pieces of flappy plastic glued on in the same shape maybe with a few rods to keep the shape (the thinnest plastic that wouldn't tear). If your aero shield is flapping in the wind how bad is that? Are all the energy savings of the shape being wasted on the flapping and tugging or only some of it and how much? Rigid aerodynamic shields obviously work so how rigid do they have to be before energy stops being wasted in flappiness or the chemical bonds being stretched by the vacuum and turbulence futile-y trying to tear something? Sagittarian Milky Way (talk) 04:05, 6 March 2023 (UTC)[reply]

Do Tonneau Covers Really Save Gas? Alansplodge (talk) 11:01, 6 March 2023 (UTC)[reply]

That's a horizontal cover not a full four-sided wedge or pyramid, or even a frustum ending at the stern flap in a vertical position. The largest increase in length and presumably aerodynamics would be an inclined plane coming from the roof till at least the top of the vertical stern flap and continuing on the same angle till it meets the horizontal continuation of the bottom of the bed in a horizontal line segment as wide as the width of the rearmost lip, I've never seen a tail wedge or tail pyramid but they're already hard to park even without anything behind the stern hinge, and rearward visibility would be bad) Sagittarian Milky Way (talk) 14:17, 6 March 2023 (UTC)[reply]

Short answer, probably no-one knows because no-one has ever wanted to make one. Perhaps you should make friends with someone with access to Computational fluid dynamics computer modelling (any Formula 1 team headquarters in your vicinity?) or other Automotive aerodynamics tools and get them to run a simulation. Or you could make one to fit your truck and perform comparative runs. {The poster formerly known as 87.81.230.195} 51.198.55.125 (talk) 20:12, 6 March 2023 (UTC)[reply]

For the Streamlining that the OP wonders about, this reference desk cannot evaluate aerodynamic drag values for varying vehicle designs and materials. Such values are found by tests in a Wind tunnel that is ideally large enough for the test vehicle (since not all aerodynamic phenomenae are scaleable to models), is equipped with means to study the wake pattern behind the vehicle and should include a rolling road surface to avoid unrepresentative friction under the vehicle. Wunibald Kamm investigated the drag coefficient obtainable in practical vehicles for which an ideal elongated "teardrop" tail would be impractical and arrived at the famed Kammback compromise that is to truncate the vehicle tail at the point where the cross section area is 50% of the maximum cross-section. This result continues to have widespread usage in car design. Philvoids (talk) 21:24, 6 March 2023 (UTC)[reply]

Heavy chain development mechanism reference

The section V(D)J recombination#Heavy chain does not cite any sources, and I was hoping to find some reference explaining the process at a similar level (I am an engineer, not a biologist). Specifically, how are each of the V, D, and J genes combined, and what is the end result of the recombination? RNA transcript? mRNA? I'd appreciate any help finding an article or book that doesn't get too deep into the molecular biology terminology! Trikekus (:3) 20:15, 6 March 2023 (UTC)[reply]

In a publication in Nature, "Somatic generation of antibody diversity", Susumu Tonegawa wrote in 1983: "The mechanism of V–J or V–D–J joining is not known and the main possibilities will be discussed in more detail below." I do not know if the precise mechanism has since been unraveled, but it operates directly on the DNA, changing the genome of a cell, and in the "main possibilities" discussed by Tonegawa it involves putative specific DNA-binding proteins (DNA polymerase, DNA ligase, ...). --Lambiam 11:05, 7 March 2023 (UTC)[reply]

unraveled ... :)

Thank you for your reply! In this book it seemed like some mechanism had been figured out, but I'm not sure I understand it. I think it's saying that V(D)J recombination results in a new chromosome present in the B cell, so I wonder how that will create an antibody protein eventually. Trikekus (:3) 19:31, 7 March 2023 (UTC)[reply]

"Somatic hypermutation and class switch recombination: After going through V(D)J recombination, B cells subsequently undergo two genetic modifications, SHM and CSR. The purpose of these alterations, mostly in the germinal center, is to increase the affinity and alter the biological properties of immunoglobulin but with a specificity for the antigen." from this 2020 review: V(D)J recombination, somatic hypermutation and class switch recombination of immunoglobulins: mechanism and regulation Modocc (talk) 20:08, 7 March 2023 (UTC)[reply]

The genome of a eukaryotic cell, in this case a B cell, is recorded in the collection of its chromosomes. V(D)J recombination operates on the genes of one chromosome at a time, so the change in the B cell's genome is a change in one of its chromosomes. Proteins are encoded in the genes of the genome and biosynthesized by translating the genes into a sequence of amino acids. The modified genes of the B cell encode antibody proteins. Different modifications give rise to different antibodies. --Lambiam 22:00, 7 March 2023 (UTC)[reply]