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Saturday, 24 January 2015

Equilibrium Conditions

equlibirum


Statics deals with forces groups that are in equilibrium, that is, for the affected system in that it does not move, it is static. A fulfillment of the conditions of equilibrium always says that the body or the system is at a resting position.

A planar body is in equilibrium if the following conditions are met:

Fr = 0 And  Ma = 0

This means that the total resultant of all the forces and the resultant moment with respect to an arbitrary point A must be zero.
One can relate these conditions to Cartesian coordinates.
This gives three equilibrium conditions:

Sum of the forces in the x-direction is zero: FRx = ΣH = 0

Sum of the forces in the y-direction is zero: Fry = ΣV = 0

Sum of the moments about a point is zero: MA = ΣMAi = 0

These conditions apply to all directions of force. The moment equilibrium must be met for each point of the system.

As the equilibrium conditions are applied, shall be demonstrated by an example.

At a statically determinate mounted circular disk of radius r, the bearing forces are to be determined by the equilibrium conditions. The disc is loaded by its own weight G, a moment M0 and a force F.

From the sum Horizonatlkrfte follows: FRx = AH + F = 0 (1)

From the sum Vertikalkrfte follows: Fry = AV - BV - G = 0 (2)

Of the sum of the moments follows: MS = AV • r - F • r - M0 = 0 (3)

From (1) follows: AH = -F
From (3) follows: AV = F + M0 / r (4)
From (2) and (4) the following: BV = AV - G = F + M0 / r - G

The Discovery of Superconductivity

supercocductivity


That was year 1911, when the Dutch physicist Heike Kamerlingh Onnes discovered superconductivity. He realized that if mercury is cooled to below 4.2 degrees Kelvin, or about minus 269 degrees the resistance of the metal became exactly zero. This means that the current flowing in the cooled metal does not meet any "obstacle" and flows freely without giving rise to decrease of voltage or heating.

We can think of the current as a river of electrons moving in to the conductor; in their motion these particles are partially obstructed by the atoms of the metal itself that, in this way, subtract part of the energy of the electrons dissipating it as heat.

After the discovery of the Dutch physicist, who for this took the Nobel prize in 1913, the phenomenon of superconductivity has been observed in many other metals, each with its own critical temperature, namely at below which the metal becomes superconducting, and with the its critical magnetic field; in fact, not only the temperature affects the superconducting state of the metal but also a particularly intense magnetic field which, being able to penetrate inside the superconductor, alters the state of the superconducting metal and brings it back to the normal conductor.

This theory is known as the BCS, the initials of the three scientists Bardeen, Cooper and Schrieffer who have formulated in 1957 and for which they were awarded the Nobel Prize in 1972.

The Cell theory

cell

The cell is the smallest unit of life, capable of metabolic and reproduction to create or use energy to perform their tasks functions. This is named after Robert Hooke, in 1665, observing thin slices of cork, called "small cells" for the hexagonal spaces he saw in them (Alexander et al 1992;. Smith, 1995; Galvan and Bojorques, 2002; Velasquez , 2005).

Cell theory

Matthias Jacob Schleiden and Theodor Schwann, were the first researchers to generalize and interpret observations on the cell. With the evidence gathered by various researchers, the findings of Shcleiden in plant cells and Schwann their own research published in 1839, in which he proposed the idea that all living organisms are formed from the same type of elementary structure the cell. Made with which was formally established the cell theory.

The cell theory can be summarized in the following statements:

All organisms are composed of one or more cells.

The cell is the fundamental unit of structure and purpose of organisms.

The new stem cells for cell reproduction of cells that already exist 

Properties of Carbon

carbon


relative atomic mass : 12.0107 g / mol
Rank : 6
Melting point : 3652 ° C
Boiling point : 4827 ° C
Oxidation numbers : 4, 2, -4
Density : 2.26 g / cm³
Electronegativity (Pauling) : 2.5
Electron configuration : (He) 2s2 2p2

Physical Properties of carbon:

Natural carbon is a mixture of the carbon isotope 12C (98.89%), 13C (1.11%), 14C (only in trace amounts). 14C is often used as a radioactive indicator in biology for the investigation of metabolic processes. Carbon can come out in two modifications. For one, as hexagonal and electrically conductive graphite and secondly as cubic crystalline diamond.

Chemical properties of carbon:

Carbon is a very unreactive element. It reacts at room temperature only with fluorine. At higher temperatures, however, forms of compounds having a plurality of elements. Of particular importance of the carbon is in organic chemistry, as it is able to form single, double and triple bonds with itself. Thus, it can form carbon chains and rings.

Carbohydrates

Carbohydrates

Carbohydrates are the most important nutrients in human body and are known as energy supplier. Chemically, they are composed of individual sugar molecules and are therefore often referred to as sugar.

Carbohydrates with little sugar molecules are also called "short-chain carbohydrates". If there are more than ten sugar molecules are multiple sugar, as contained in bread, for example, Multiple sugars are also referred to as "long-chain carbohydrates", as they consist of a chain of more sugar molecules.
The carbohydrates are broken down in the body to the smallest unit of sugar (glucose sugar molecule) required by each cell as an energy supplier.

The advantage of carbohydrates compared to other energy sources  is that they can be quickly dismantled and recycled. The liver stores as a central storage organ about one-third and the muscles around two-thirds of the absorbed energy.

The brain cells need glucose to work at full speed. People who do endurance sports or work hard physically, have an increased need for carbohydrates.