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1

My guess is that the foam has some type of sillica in it which may stick to the knife having a detremental effect on its cutting ability possibly cleaning the blades regularly with alcohol could help this but i'm no chemist, hopefully this is helpful


0

Further to your example, although a block of steel with BCC crystal structure may be considered homogeneous and isotropic, industrial processing such as heat treatment, annealing, cold rolling and welding can be used to create anisotropic stress-strain relationships. For example, if a steel rod is heated at one end, it would be considered non-homogenous, ...


2

In short, to my understanding: homogeneous : the property is not a function of position, i.e. it does not depend on $x$, $y$ or $z$. isotropic: the property does not depend on a particular direction. NB: you can have a homogenous property that is not isotropic, i.e. the refractive index of a birefringent material: it is a constant, but this constant has ...


1

I believe that one could rephrase the question as "if the limit of the speed of sound in a medium must be the speed of light in vacuum, what does that mean for the limit on rigidity of an object?" Speed of sound is given by $$c=\sqrt{\frac{E}{\rho}}$$ - it depends on both density and Young's modulus. I would consider "rigidity" to be just the modulus, and ...


2

Long ago I worked at a military base and we had a room size vault. We had quantitative estimates of how long it would take to penetrate the vault under various senarios (techniques that focused on the lock or other parts). The estimates were in the 10-20 hour range, I don't remember exactly. In any case, it is possible to drill through the various forms ...


5

No, it's not possible. The general rule of strength in foams is $\rho^3\propto\sigma^2$ so if you cut the density by a factor of 4, then your strength would be cut by a factor of 8. From a conceptual standpoint slicing a organized shape under a tensile load by a plane perpendicular to the load will show that there are $n$ discrete elements, all under a ...


-3

Yes, infrared light get pass through two polarized films (vertical & horizontal) even those films are 90 degree rotated.


0

A typical particle that can have three states is the hydrogen atom in the ground state (or in general in an ℓ = 0 state), if J = ħ i.e. if the total spin (of the nucleus and of the electron) is ħ. This state has three possible projections of the spin on whatever direction, +ħ, 0, and -ħ. Another typical particle with spin ħ is the deuterium nucleus, s.t. it ...


0

Take any material and three of its energy levels. Three-level systems also go by the name of qutrit. The linked article also links to some research results. The number of states is completely irrelevant for theoretical purposes, it's just like calculating with decimal or binary calculations. As long as you can manipulate and entangle systems across many ...


3

I did some research and it seems that superhydrophobic coating can be used to decrease drag forces to a certain extent because the coating repels the water. It creates an air layer between the surface and the water that causes slip through two-phase flow. This allows the ship to slip past the water.


0

True, stress is a tensor, an as such it changes when you apply a rotation of coordinates. The transformation of a tensor under a coordinate rotation is equivalent to multiply two matrixes: $T'=RT$, where T is the matrix representing the original tensor, T' the one representing the rotated tensor, and R the matrix of rotation. See here for more details


0

You are correct. Homogeneity and isotropy refer to two different things. Homogeneous refers to materials/things that have a uniform composition/structure throughout. This means you cannot easily distinguish one point in a material from another. Anisotropic refers to something which appears different in different directions, as opposed to isotropic which ...


0

I'm not sure I would focus on the the liquid to gas phase change. Sublimation, seems better behaved. I've heard that some alloys do not have well defined melting points. I don't know if something like that occurs in sublimation. But imagine a crystal lattice consisting of two fairly different substances. In this case it seems the material that sublimes at a ...


39

While I agree in principle with David Lynch's answer, I think it's good to take a closer look at the phase diagram (adapted from http://upload.wikimedia.org/wikipedia/commons/4/46/Carbon_basic_phase_diagram.png): I added the arrows to show possible paths you might follow. Red path: diamond would become graphite before melting; the molten carbon becomes ...


26

Carbon, at atmospheric pressure, has no melting point as its triple point is at 10.8 ± 0.2 MPa and 4,600 ± 300 K (~4,330°C or 7,820°F), so it sublimes at about 3,900 K. You can make it liquid at larger pressures, in an inert gas atmosphere. When you cool it, what it becomes depends on the pressure. Below about 10 GPa it will become graphite, above that it ...


0

John's answer is the closest. Actually it does not matter of the optical index. Materials that has micro holes will reflect light randomly with only narrow boundary between the material and air. When there is water to fill up the holes, some of the light reflected into the material, so your eye will see less light reflected from the material.


0

I'm going to follow a paper Phys. Rev. Lett. 101, 055504 that seems to answer this question very concisely. Usual Voight notation: $C_{ijkl} \to C_{mn}$ here, we define Voight and Reuss estimators as defined in Proc. Phys. Soc. A 65 349. For example : $$K^V= \frac{1}{9}\left(C_{11} + C_{22} + C_{33} + 2 (C_{12} + C_{23} + C_{31})\right)$$ and so on for ...



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