Function Of Excitation Frequency Research Articles

Symmetry-Forbidden Resonant Raman Scattering inCu2O

We have observed resonant Raman scattering from the two longitudinal branches of the Raman-forbidden ${F}_{1u}$ modes of ${\mathrm{Cu}}_{2}$O. The agreement between our measured scattering cross section as a function of excitation frequency and a calculated cross section which assumes an intraband Fr\ohlich electron-phonon interaction is good. This represents a quantitative confirmation of the resonant-Raman-scattering theory proposed by Martin.

Mechanical impedance of the femur: A preliminary report

We performed a preliminary study of the feasibility of determining the degree of union of healing femoral neck fractures by measurement of mechanical impedance. Two experiments were performed on an excised female femur. First, impedance and the reactance were determined as a function of excitation frequency. In this experiment, the excised femur vibrated as a rigid mass up to approximately 70 Hz. At higher frequencies, the vibratory mode became complex; numerous resonances and antiresonances were observed. Second, the reactance of the femur was measured at ten excitation frequencies under four conditions: in the intact state, after removal of a small wedge of bone from the antero-superior quadrant of the neck, after removal of the head, and after re-attachment of the head. Large differences in reactance were observed with these changes. This suggests that in vivo measurement of femoral mechanical impedance may allow determination of the degree of union of healing fractures of this bone.

Resonance Raman scattering of the I 2 molecule in solution

Resonance Raman scattering of the I 2 molecule in chloroform solution is reported. Several overtones are observed both stokes and antistokes, making it possible to determine ω e and ω e x e for the ground state from a ΔG 1 2 plot. In contrast to what is observed for I 2 in the gas phase the same general spectrum is obtained whether the exciting frequency is above or below the dissociation limit of the 3Π 0+ state. The spectrum in solution resembles closely the gas phase spectrum excited above the dissociation limit. Using the chloroform spectrum as internal standard, relative intensities of the I 2 Raman lines have been determined as a function of excitation frequencies. The dependence of the intensity on the excitation frequency is strong, the intensity increases by a factor of ⋍2 between 4765 Å and 5145 Å. This behaviour can be understood on the basis of a theory recently advanced by the author.

The use of nuclear spin-echoes to measure hyperfine field distributions in ferromagnets

A general expression for the nuclear magnetic resonance spin-echo signal in a ferromagnet is derived. Spin echoes stimulated from hyperfine field distributions in Co alloys are interpreted in terms of the analysis, and the observed behaviour of spin-echo shape as a function of excitation conditions is shown to be consistent with the predictions. The theoretical expression is used to obtain the conditions under which measurement of the spin-echo amplitude as a function of excitation frequency can be expected to reflect the hyperfine field distribution in a ferromagnet.

Radiation Impedance of a Piston on Cohesive Soil

An experimental investigation was made to determine the mechanical radiation impedance of a rigid piston on the surface of clay soil. The force on and the velocity of the piston were measured to determine both the real and imaginary parts of the radiation impedance as a function of excitation frequency of the piston. Measurements were made for six different combinations of moisture and density of the soil, and results of these measurements are presented in graphical form. In the frequency range 50–200 cps, the load presented to the piston by the soil is essentially the same as would be presented by a mechanical compliance, the value of which varies with both moisture and density of the soil. The value of this compliance was computed for six different combinations of moisture and density. Second-order dependence of compliance on moisture and density was assumed, and coefficients in a second-order equation relating compliance to moisture and density were computed. The three-dimensional surface that represents this equation is presented in graphical form. Errors in the results are discussed.

Third Sound in Liquid Helium Films

The existence of "third sound," a surface wave on thin films of superfluid helium, has been demonstrated experimentally. The velocity and attenuation of the waves have been measured as functions of excitation frequency, film thickness, and temperature. In the main, the results agree with earlier predictions and yield new information about the forces which cause the formation of helium films. Preliminary measurements on third sound in moving films and on surface-tension ripples on bulk liquid helium are also described.