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File 129131808679.jpg - (61.75KB , 610x416 , bacteria_arsenic.jpg )
1027 No. 1027 hide watch expand quickreply [Reply] [Edit]
Nasa announced it has discovered a bacterium that consumes arsenic and even uses it to construct its genetic material
thoughts?
14 posts and 1 image omitted. Click Reply to view.
>> No. 1042 [Edit]
>>62
If he wanted to only mean one specific Fox viewer he should have said "a certain Fox news viewer." "A fox news viewer" refers to the generic Fox viewer.
>> No. 1043 [Edit]
>>63
I assumed he took a quote from the Fox News website or one of those shows where people submit comments like Bill O'Reilly's, maybe I'm wrong.
>> No. 1044 [Edit]
http://www.newscientist.com/article/mg14419490.800-microbes-have-arsenic-licked.html

>29 October 1994
>> No. 1045 [Edit]
It basically substitutes phosphorous as a building block for organic molecules. So it's not that surprising at all, since both phosphorous and arsenic are within the same period. It basically has the same function as phosphorous in these cells, except that it's much bigger than phosphorous. But that discovery also shows how extraterrestrial life could be radically different than living organisms on Earth.

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971 No. 971 hide watch expand quickreply [Reply] [Edit]
Part 1: Structure of materials

You can imagine materials being composed of atoms with springs attached to one another. A force is needed to pull the atoms apart and compress them closer together. The way these atoms are stuck together determine many properties of the material. Part 1 will deal with atomic structure of materials, including packing, the categories of structures and bond energy (how much energy needed to alter the structure).
15 posts and 6 images omitted. Click Reply to view.
>> No. 987 [Edit]
Part 3: Dislocations and ways to make metals stronger

Part 3(a): What dislocations are

Dislocations are essentially 'imperfections in the crystal structure'. The atoms in a crystal do not always line up perfectly, and there may be some abnormalities such as a missing atom or an extra atom which distorts the pattern of the lattice. Dislocations can travel through the crystal along 'slip planes' using a caterpillar-like motion. Diagrammatically, we use a perpendicular symbol to depict a dislocation. A typical engineering alloy will contain 100,000km worth of dislocations per centimetre cubed.

Dislocations may or may not be wanted in a material, depending on circumstances. Introducing more dislocations into a material tends to set up a 'forest of dislocations' which causes dislocations to get tied up in one another, stopping them (and the slip plane) from moving. This makes a material hard, but at the same time makes it more brittle and inflexible. Hardness might be desirable in a bridge girder which you don't want to wobble, but undesirable for steel used in springs.
>> No. 988 [Edit]
Part 3(b): Intrinsic lattice resistance to dislocations

For a dislocation to move, it needs to break and reform a bond between two atoms. This requires a force, and this resistive force is called the intrinsic lattice resistance, symbol Fi. Dislocations move when the slip planes slide over each other.

In metals, Fi is low because of the non-directional nature of the bonding which means that the atoms don't give a fuck that they're sliding. In contrast, ceramics have a high Fi because bonds between atoms are highly directional, and breaking one bond to move a dislocation implies breaking fifty million other bonds on the slip plane too.
>> No. 989 [Edit]
Part 3(c): Making metals stronger

In this section I will describe some techniques used to increase the overall lattice resistance of metals, and hence stop dislocations from moving. The movement of dislocations is the mechanism by which slip planes move, and on a macroscopic scale is 'bending' which is often undesirable.

Solid solution strengthening: Is basically 'alloying'. Consider this: with water, you can dissolve sugar into it and get a solution of water with sugar molecules interspersed through it. With metals, the same is true: you can 'dissolve' molten zinc into molten copper and receive a 'solution' of both.

How does this inhibit the movement of dislocations? Solid solution strengthening introduces impurity atoms into the crystal lattice. These impurities have different atom size compared other atoms, and so they distort the crystal lattice. Dislocations need more force/energy to move past these distortions. Two main factors are responsible for the increase in intrinsic lattice resistance: difference is atom size and the amount of impurities added. Copper and zinc have fairly similar atom size, so there needs to be a mixture of about 30% Zinc to 70% copper. Carbon and iron have a huge difference in atom size, so only 0.3% of carbon needs to be added to the Iron to get the same effect.

Precipitation hardening: Let us carry our analogy with sugar and water further. If you add lots of sugar to hot water and dissolve it all, you may find out that some of the sugar recrystallises out of the solution when it cools down. The same thing occurs with metal alloys. Some impurity atoms will 'precipitate', forming small particles of impurities inside the matrix of the alloy.

These precipitate particles impede dislocation movement. Dislocations are forced to either go around, or cut through these particles. If they go around the particle, the dislocation tends to leave traces of itself around the particle called 'Orowan loops', which themselves impede dislocation movement and get bigger and bigger with each passing dislocation.

Work hardening: This is basically working the metal to deliberately introduce more dislocations, and create a forest of dislocations to stop dislocation motion. The metal can be hammered, rolled, bent, d
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>> No. 990 [Edit]
Part 4: Fast fracture

Fast fracture is when cracks in a material expand rapidly, causing a catastropic failure of the material, even if its below yield point stress. For a crack to grow, there needs to be sufficient stress on the crack. To calculate this critical stress, we consider the work needed for the crack to grow. The work done by the load needs to be greater than the difference between change in elastic energy and energy absorbed at the crack tip (this crap doesn't make no sense.) Equation:

δW ≥ δUel - Gc.t.δa

Gc is the energy absorbed per unit area of crack, with t(delta)a being the new crack area. Gc is the measure of the materials 'toughness', and is how much energy is needed to propagate a crack. A high Gc means the material is tough and cracks have a hard time getting bigger (e.g copper), a low one implies the opposite (e.g ceramics).

Honestly I don't know what i'm talking about in this section.

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1019 No. 1019 hide watch expand quickreply [Reply] [Edit]
Gravitational Potential Energy: described by the equation

Ep = -G*m1*m1/r Where G is the universal gravitation constant, m1 is mass of planet 1, m2 mass of planet 2, and r the distance between the center of mass between planets. For various reasons, they put a negative sign in front of this equation. But you can't have negative energy! Can you figure out why theres a negative sign?
3 posts and 2 images omitted. Click Reply to view.
>> No. 1023 [Edit]
Would this possibly be a black hole?
>> No. 1024 [Edit]
if the force is being constructed as a vector the negative sign simply indicates its direction.
the direction being down toward the earth.
>> No. 1025 [Edit]
>>6
But this isn't force, but potential energy.

As distance between the two planets increases, the potential energy should increase. But the equation dictates that the potential energy will simply approach zero from the negative side. Whys that?
>> No. 1026 [Edit]
Because it is supposed to be negative.

>This potential energy is more strongly negative than the total potential energy of the system of bodies as such since it also includes the negative gravitational binding energy of each body. The potential energy of the system of bodies as such is the negative of the energy needed to separate the bodies from each other to infinity, while the gravitational binding energy is the energy needed to separate all particles from each other to infinity.

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