Recent comments in /f/askscience

Intern11 t1_j9vb4jp wrote

Reply to comment by [deleted] in Does the common flu vaccine offer any buffer against H5N1 (Bird Flu)? by Esc_ape_artist

That vaccine will only protect you from the current variant of the bird flu which only passes from birds to animals. If the virus mutates and transforms into one that can pass from person to person we would need to engineer a whole new vaccine which wouldn’t be worked on until we found the dominant strain of the new pandemic.

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darkfred t1_j9v9fa8 wrote

Reply to comment by toalv in It seems like we havent heard anything about carbon nanotubes for almost a decade. is there anything exciting involving those these days? by mintysmellshowntell

Absolutely, i mentioned fiberglass because right now it's essentially the same thing, with the same strength. Even if the carbon fibers get as long as fiberglass it's not a game changer from current practice, cause it will still be an order of magnitude more expensive.

The real game changer would be the technology for weaving the nanotubes into macro scale carbon fiber mesh load struts that were rigid enough to be cast in concrete in place of steel reinforcement or structural beams and don't need to be resin impregnated but mechanically bond directly to the concrete.

This would be huge because the negative thermal expansion coefficient of woven nanotube fiber could be manipulated by casting temperature to prestress the truss and even an entire slab from the inside out and might, despite carbon fibers being much more elastic than steel, completely replace it in some applications.

edit: OTOH, if someone doesn't figure out some elegant solution like this to the problems of carbon fiber's elasticity and thermal expansion coefficient, it's just never going to work with concrete. Steel and concrete are a magical material properties match on every front except for oxidation.

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Puppy-Zwolle t1_j9v992x wrote

Reply to Do all thinking creatures on Earth use neurons? Does an example of non-neuron based biological "intelligence" exist? by Wun_Weg_Wun_Dar__Wun

Neurons are among the oldest cells evolutionarily speaking. If you go beyond small clusters of cells you need a way to get signals across your organism. Short distances? No problem but larger distances or more complex instuctions, or better timed reactions you need 'cable'. Enter the neuron.

So basically neurons developed into 'intelligence' from a 'need' to communicate internally. From this you can evolve stuff like bigger muscles, legs, arms. Brain.

So unless we discover intelligence in plants I'm afraid neurons are the only way to go.

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Coomb t1_j9v6ofp wrote

Reply to comment by treeses in why is sign convention for work different on chemistry and physics? by Melodic-Recipe2618

What I will call the mechanical engineering convention (i.e. work done by a system is positive) since it's certainly the convention that was either exclusively or overwhelmingly used in mechanical engineering when I was taking my classes 10 years ago or so, has an (arguable) pedagogical advantage when introducing enthalpy, which is an extremely commonly used parameter in mechanical engineering and probably in most other forms of engineering.

By definition, H = U + PV. If we assume that the internal energy is the only parameter of the working fluid that is changing, and not other things like its gravitational potential energy or its bulk kinetic energy, the engineering convention equation for the change in energy associated with heat addition and work performed is dU = dQ - dW.

The differential form of the enthalpy is dH = dU + d(PV) = dU + PdV + VdP.

Substitute and you have dH - PdV + VdP = dQ - dW. Make the further assumption of constant pressure and then

dH - PdV = dQ - dW

The pressure work done by the fluid as its enthalpy is increased, and the work done by the system on its surroundings, have the same sign. It makes it more obvious that the PdV component is the amount of enthalpy "lost" by allowing the fluid to expand against external pressure.

The toy problem that is usually used to introduce this is gas in a well insulated cylinder with a piston head held down by weights on the head. What happens when you add heat to the gas? Some of the energy goes into increasing the temperature (and therefore internal energy) - obviously the gas heats up. But just measuring the internal energy of the gas before and after you've added heat to it doesn't accurately tell you how much heat you added. This is of course because some of the heat also goes into raising the weight on the piston against gravity. For people who are mechanically inclined, this is a relatively intuitive physical scenario, and it helps illustrate why enthalpy is a more useful parameter for many engineering problems than internal energy alone.

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