Medium, material

Ability to handle sticky materials Medium Good Poor... 

Radiation The emission and propagation of energy through space or through a material medium in the form of waves. The term also includes subatomic particles, such as a, P, and cosmic rays and electromagnetic radiation. 

In an elastic material medium a deformation (strain) caused by an external stress induces reactive forces that tend to recall the system to its initial state. When the medium is perturbed at a given time and place the perturbation propagates at a constant speed (or celerity) c that is characteristic of the medium. This propagating strain is called an elastic (or acoustic or mechanical) wave and corresponds to energy transport without matter transport. Under a periodic stress the particles of matter undergo a periodic motion around their equilibrium position and may be considered as harmonic oscillators. 

Since the speed of light in any material medium is less than the speed of light in a vacuum, the numerical value of the refractive index for any liquid is greater than one. 

Figure 5. Fatigue life as a function of sulfur content for a sand-asphalt-sulfur mix. Test temperature 50°F (10°C). Test frequency 60 Hz. Materials medium-coarse sandt and 150/180 pen. asphalt. Asphalt content 6% wt (15),...

A reminder The electric force between two charges depends on the medium between them. The electric force in the presence of a material medium is less than that which operates when only a vacuum is present The ratio of the force in a vacuum to the force in the medium is a characteristic of the medium and is known as its dielectric constant, . 

Then, Maxwell s equations for any arbitrary material medium reduce to the system of Maxwell equations (MEs) for the vacuum (see any standard source, such as Ref. 62,63,64, or 65). In CGS units, MEs are [66] ... 

The oldest and still intensely used biocidal materials release silver ions. Variations in the design of such materials is still the subject of the majority of publications on antimicrobial coatings. The designs cover sparingly soluble silver salts [87], silver nanoparticles [88], silver nanocomposites [89], and elemental silver coatings [32], The release of the silver ions and of other biocides is controlled by the encapsulating matrix, the solubility of the compound, and the material/medium equilibrium constant. 

When passing through a material medium the vibrations are impeded and hence become sensitive to the arrangement of matter in the medium. In many solid structures, especially crystals, a preferred direction of vibration that allows ready transit is selected by the waves. In the process a beam... 

The general statement that connects quantum theory to experimental observations such as optical activity can be put as follows. We subject the material medium to some experimental procedure using a probe light beam, and observe a certain outcome after the probe has passed through the system, for example by analysing the scattered light. If we define the density matrix tot for the combined system of material medium + probe, and characterize the measurement by some operator, then the probability that the specified outcome of the measurement is observed, is given by,... 

In the particular case of optical activity I can describe the experiment by choosing % to be the electric polarization operator P(x, t) for the material medium, while tot refers to the combined system of matter interacting with the polarized light beam. Note that [ tot> P] = 0, where P is the space-inversion operator (see40 and Sect. 4). Then the mean value,... 

Material Media and Their Reaction to External Fields. In a material medium, a charge distribution can induce some charge separations, or dipoles, which help to minimize the total energy. Similarly, an external magnetic field will induce some magnetic dipoles in the medium to counteract this field. To handle these effects, an electric polarization (or electrical dipole moment per unit volume) P and a magnetization (or magnetic dipole moment per unit volume) M are defined. If the medium is linear and isotropic, these two new vectors P and M are proportional to E and to H, respectively ... 

The geometry of the ellipsometric measurement is shown in Fig. 2.13. The anisotropic material medium under study has coordinate z > 0, while the isotropic ambient medium (air) has z < 0 the electromagnetic field components of interest are the tangential components Ex, Ey, Hx, and Hy the plane of incidence is the xz plane. 

In contrast to the mechanisms of conduction and convection, where energy transfer through a material medium is involved, heat may also be transferred through regions where a perfect vacuum exists. The mechanism in this case is electromagnetic radiation. We shall limit our discussion to electromagnetic radiation which is propagated as a result of a temperature difference this is called thermal radiation. 

For further progress it is necessary to specify how E varies with D, or how P depends on Ea. For this purpose, we introduce the constitutive relations D - e(T,V)E or P - ot0(T,V)F0, where e is the dielectric constant and a0 is a modified polarizability. (Conventionally, the polarizability is defined through the relation P - oE, but no confusion is likely to arise through the introduction of this variant.) Note several restrictions inherent in the use of these constitutive relations. First, the material under study is assumed to be isotropic. If this is not the case, e and c 0 become tensors. Second, the material medium must not contain any permanent dipole moments in the preceding constitutive relations P or E vanishes when E0 or D does. Third, we restrict our consideration to so-called linear materials wherein e or a0 do not depend on the electric field phenomena such as ferroelectric or hysteresis effects are thus excluded from further consideration. These three simplifications obviously are not fundamental restrictions but render subsequent manipulations more tractable. Finally, in accord with experimental information available on a wide variety of materials, e and aQ are considered to be functions of temperature and density assuming constant composition, these quantities vary with T and V. 

Note that in (5.6.7) P - 0 and E - D - Ea if the material medium is absent. Therefore the quantity E2/8n may be considered to represent the free energy density arising from the presence of the electric field in vacuum. The term - P E0/2 then represents the Helmholtz free energy density due to the interaction of the system with the medium we write... 

---