FUNDAMENTO DEL POLARIMETRO PDF

Asteraceae: Astereae. Ethnobotany, anatomy and physicochemical characterization of essential oil of Baccharis obovata Hook. Baccharis obovata Hook. Los informantes indicaron que la planta es utilizada en forma consensuada para el tratamiento de alopecia, caspa, diversas dermatitis, y cefaleas. The objectives were to investigate its ethnobotany and shoot anatomy, as well as to characterize physically and chemically its essential oil. Rural informant-interviews were conducted in two Mapuche communities of Northwestern Patagonia, Argentina.

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This article briefly describes the fundamentals of mass and density as well as methods to determine them and their metrological background. To find out what mass is requires knowledge of how atoms, out of which matter is composed, acquire mass. Atoms have a tiny nucleus and an electron shell some , times larger in diameter than the nucleus itself.

These consist of quarks and gluons, which are considered elementary particles Figure 1. Figure 1: The proton left and neutron right contain up quarks u and down quarks d and are held together by gluons the zigzag lines. Source: commons. The mass of elementary particles can be attributed to their degree of interaction with the Higgs field, which is postulated to fill all of space. Particles which do not interact with the Higgs field acquire no mass and move at the speed of light, like the photon for example.

However, only a small percentage of the mass of the atomic nucleus can be attributed to the Higgs mechanism. The majority of its mass comes from the binding energy of the strong nuclear force. It says that energy E and mass m are essentially the same thing. Figure 2: Left: A stick and a rubber ring of equal mass are placed in each pan of a beam balance; the beam is exactly horizontal.

Right: By stretching one rubber ring over the stick energy gets stored in this rubber ring. Therefore, its mass and weight increase and the balance shows a weight difference.

While this effect is much too small to be observable with real balances the principle holds. To see how this relates to the question of where the majority of the mass of the atomic nucleus comes from, see Figure 2. In this illustrative example, a stick and a rubber ring are placed into each pan of a beam balance.

The sticks and the rubber rings are selected to have exactly the same mass and therefore the same weight. This causes the beam of the balance to be exactly horizontal.

If one of the rubber rings is stretched over the stick and this is placed into one pan while in the other pan the stick and the rubber ring remain separate the balance is at least in principle no longer exactly horizontal. Therefore, the mass of the stretched rubber ring is increased and the balance shows a difference in weight, at least in principle. Mass is determined using a balance. Balances utilize the gravitational force exerted by the planet earth on the specimen.

Balances measure a force, and this force is e. The force as measured by the balance is called weight. As long as such measurements are not carried out in a vacuum chamber, they determine the weight in air of the specimen.

This can be corrected for if it is required. Figure 3: Replica of the original kilogram prototype. Source: en.

Modern electronic balances function in a more elaborate way but the fundamentals are the same. For traceable mass determinations, suitable mass units and calibration weights traceable to an international mass standard are required. The current international mass standard is the original kilogram prototype located in Paris, France.

It is a cylinder made of platinum-iridium alloy Figure 3. However, there were issues with the long-term stability of the mass value of the original kilogram prototype.

Therefore, for decades researchers have been working to find a better mass standard which relies on basic physical properties only. These efforts seem to have been successful and it is expected that the original kilogram prototype will be replaced by a new mass standard at the 26th General Conference on Weights and Measures in November Density, i.

As mentioned above, Newton used density as one of the defining properties of mass. The density of a specimen is determined by combining the measurements of mass and volume. For the measurement of mass, see above. Volume measurement can be broken down into length measurements, for which the meter units apply.

The meter is defined as the distance in vacuum a ray of light crosses in slightly more than one third of a nanosecond, so the speed of light and time are the defining properties of a meter. Accurately determining the volume of a solid material is a tedious procedure. Typically a pycnometer of known volume is applied with the specimen placed inside. The volume of the specimen is determined from the volume of liquid or gas it replaces in the pycnometer. Mass and volume determinations are normally carried out in separate steps and the density is computed from the two results.

Figure 4: A bare U-tube in front and the complete oscillating U-tube density sensor in the back. The U-tube is filled with the sample and electronically put into oscillation at its natural frequencies. The density of the sample is derived from these values. To determine the density of liquids the following methods are used:. For a detailed explanation of the technology used by oscillating density meters, see here. The article describes the fundamentals of mass and density.

It starts with an explanation of how the property mass comes about at the level of the atomic nucleus. Then methods to determine mass and density and their metrological background are described. Finally an outlook is given on how the metrological basis of these measurements will change in the near future. Usamos links no nosso site. Eles fazem isso rastreando quais sites os visitantes acessam. Coletamos e combinamos dados sobre nossos visitantes e seu comportamento em nosso site.

What is mass? The mass of elementary particles The mass of elementary particles can be attributed to their degree of interaction with the Higgs field, which is postulated to fill all of space.

The mass of the atomic nucleus Figure 2: Left: A stick and a rubber ring of equal mass are placed in each pan of a beam balance; the beam is exactly horizontal. How the different effects contribute to the mass of the atomic nucleus The mass of the atomic nucleus therefore originates from the following effects: The strong nuclear force within the nucleus: Due to the net positive charge of its constituents a huge electrostatic force strives to blow up the nucleus. The strong nuclear force within the nucleus acts against the electrostatic force and keeps the nucleus bound.

Therefore, the strong nuclear force comprises enormous amounts of binding energy, making a large contribution to the mass of the nucleus. This kinetic energy results in a corresponding increase in mass and would cause the nucleus to explode were it not counteracted by the strong nuclear force. This increases the binding energy of the strong nuclear force and its mass contribution.

The Higgs mechanism: As described above. In fact, this mechanism contributes to the mass of the nucleus least. How is mass determined? Converting weight into mass Figure 3: Replica of the original kilogram prototype. Using the balance in Figure 2, the weight of a specimen can be converted into mass as follows: The weight of the specimen in one pan is balanced by calibration weights of known mass in the other pan, so that the beam becomes horizontal.

Now the mass of the specimen agrees with the mass of the calibration weights, apart from the small air buoyancy effects which are normally ignored. In this way the mass of the specimen is determined. What is density? How is density measured? Density measurement of solids Accurately determining the volume of a solid material is a tedious procedure. Density measurement of liquids Figure 4: A bare U-tube in front and the complete oscillating U-tube density sensor in the back.

To determine the density of liquids the following methods are used: Hydrostatic balance or hydrometer: a body of known volume is immersed into the sample and its weight loss due to buoyancy is determined.

Buoyancy is proportional to density and can easily be converted into the latter. To achieve highly accurate measurements it is essential to accurately control and compensate for temperature, surface tension effects, etc.

Pycnometer: a bottle pycnometer of known volume is filled with the sample liquid. The weight difference between the filled and the empty pycnometer is determined. From that and the known pycnometer volume the density is calculated. Oscillating U-tube density meter: Due to their speed and accuracy these are the most frequently applied instruments for density measurements.

The amount of sample required is much lower than for the above two methods. It is filled with the sample and set into oscillation at its natural frequencies by electronic means. Figure 4 shows an example of an oscillating U-tube density sensor. Conclusion The article describes the fundamentals of mass and density.

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