摘要:

A study of gas separation (cataphoresis) has been made in the positive column of a steady‐state electric discharge, using the binary mixture 2.2% argon‐helium. A glow discharge is initiated in a 0.96‐m‐long tube of 9.5 mm diameter using a high‐voltage stabilized source. The discharge tube employs a brush anode and a brush cathode to obtain uniform discharge and is connected to a bakeable gas handling system. The discharge is scanned spectroscopically from anode to cathode and the emitted spectra of helium (5875) and argon (4152 Å) are monitored. The cataphoresis separation of the constituents is studied with variation of both the gas pressure and the current flowing between the electrodes. It has been found that the ratio of Ar/He increases with increasing distance from anode to cathode. Furthermore, the quality of cataphoresis improves with increasing pressure and current in accordance with theoretical predictions. The effect of the temperature of the walls on the quality of cataphoresis is investigated and found to decrease with increasing temperature in agreement with theory and with Schmeltekopf's experimental study in helium‐neon mixtures.

ISSN:0021-8979    

DOI:10.1063/1.1662716

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Nuclear magnetic resonance (NMR) longitudinal and transverse relaxation rates and repetitive pulse steady‐state magnetizations were measured in porous media containing solutions of NaCl in water. Longitudinal rates show a linear relationship with sample specific surface area, but transverse rates show more complicated behavior. These results are discussed in terms of diffusion and adsorption in the media. Experimental results for steady‐state magnetizations achieved by repetitive pulsing are compared with theoretical calculations presented here. Theoretical expressions are also presented for use in optimizing fast repetitive pulse experiments.

ISSN:0021-8979    

DOI:10.1063/1.1662717

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Room‐temperature values of the thermal‐expansion coefficient, thermal diffusivity, thermal conductivity, density, Young's modulusE, and the temperature coefficient (1/E)dE/dTare presented for two splat‐cooled amorphous alloys of composition (in atomic percent) Pd82Si18and Fe75P15C10. Values ofEwere obtained from the flexural resonant frequencies of cantilever mounted reeds; the thermal properties were derived from internal friction measurements giving the height and location of the thermoelastic ``transverse thermal current'' peak. Compared to crystalline alloys, the amorphous samples are poorer thermal conductors but exhibit a comparable expansion behavior. In view of the small density difference between the amorphous and crystalline states, the most striking difference observed was the lower elastic modulus of the amorphous alloys. The present results supplement a growing body of evidence that materials in the amorphous condition may have a Young's or shear modulus which is typically 20–40% less than the value in the crystalline state.

ISSN:0021-8979    

DOI:10.1063/1.1662718

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A dynamic technique for measuring thermal conductivity in cylindrical geometry is presented. A radially centered heater wire is used. The temperature difference between two different radial positions in the cylindrical specimen is monitored during heating. Measurements are made under vacuum and within a thermal shield to minimize heat losses. Bulk‐specimen temperature rise is restricted to 1/2 °K. For a specified time interval, which is a function of specimen dimensions and thermal properties, the measured temperature difference is constant to within a fraction of 1% and is inversely proportional to the thermal conductivity of the specimen. The thermal diffusivity and heat capacity are not specifically needed to determine the thermal conductivity. Mathematical development of the theory of the technique is presented along with the results of measurements on single‐crystal silicon and aluminum specimens.

ISSN:0021-8979    

DOI:10.1063/1.1662719

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The occurrence of crack propagation in flexible fiber assemblies, specifically woven fabric, is studied. The speed of propagation of a strain wave down a constrained filament is analyzed. Expressions for the strain energy released as the crack propagates and the kinetic energy and shear energy of the retracting material are developed, and the physical significance and relationships between the various forms of energy are studied. The effects of fiber and yarn properties, fabric construction, and coating properties on fabric resistance to crack propagation are analyzed. The analysis developed shows that high‐modulus fibers woven into fabrics with shear stiffness, e.g., long float weaves, can support the greatest applied load without propagating a crack. In the case of coated fabric, a coating with a low modulus at high shear rates applied in a manner whereby it does not penetrate the fabric structure gives the best performance. However, the most promising method for preventing the propagation of crack in coated as well as uncoated fabric is to use fabric with bundles of large yarns woven periodically in both the warp and filling directions.

ISSN:0021-8979    

DOI:10.1063/1.1662720

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The yield of condensed gas released from liquid‐helium‐cooled surfaces under particle bombardment has been measured as a function of surface coverage. The yield has been found to increase at low coverage, then become roughly independent of coverage, and finally to decrease at very high coverage. The observed value of the yield has been found to exceed 104atoms/ion and this value has been explained in terms of a thermal spike model. Where the condensed layer thickness is greater than the range of the incident ions the yield is typically 102−103atoms/ion. This cannot be explained either by thermal spike or conventional sputtering, and it is suggested that ionization of the condensed gas leads to gas release.

ISSN:0021-8979    

DOI:10.1063/1.1662721

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Thin‐film dielectric waveguides with a periodic refractive index, a periodic substrate, or periodic surface are studied. The field is determined from Maxwell's equations using Floquet's theorem. The Brillouin diagram and the interaction regions are investigated. The bandwidth and the attenuation coefficients of the interaction regions are given as a function of the optical wavelength. A number of applications in active and passive integrated optics systems are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662722

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Simultaneous propagation of two otherwise independent modes of a magnetoactive medium has been studied, when the power of the modes is high enough to invoke appreciable nonlinearities. A high‐mobility sample ofn‐InSb is chosen and the transverse intensity profiles for both modes are taken to be Gaussian. Even though the presence of either mode affects the propagation of the other considerably, the nonlinearity‐induced convergence is very different for the two modes. As a result, the ellipticity of the beam is changed drastically. In the helicon limit the focusing of the propagating mode has been predicted in a length ∼ 1 cm at the axial field intensity of 0.3 esu. This focusing is effective only when |&ohgr;−&ohgr;c|> &ngr; and &ohgr;c/&ohgr;<10.

ISSN:0021-8979    

DOI:10.1063/1.1662723

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The absorption coefficient of several rhodamine B solutions excited at 632.8 nm has been measured for temperatures ranging from 200 to 385 °K. The weak monomer absorption coefficient (∼ 10−5times the peak coefficient) at this anti‐Stokes excitation wavelength facilitates a study of the other components of absorption in the dye solution, yielding valuable information on solvent effects and factors affecting the quantum efficiency of fluorescence, such as dimer absorption, impurity content, etc. Whereas at high temperatures (above 30 °C), linear singlet‐singlet monomer absorption is observed to dominate, dimer formation is evident at temperatures below 30 °C, and the impurity absorption appears negligible in either case. From a least‐squares fit of the experimental data with the theoretical dependence of the total (monomer and dimer) absorption upon temperature, the association energy for the dimer is found to be 5.0 kcal/mole. It also seems possible that at temperatures above 50 °C, for solutions with low impurity absorption, quantum efficiencies high enough for radiative cooling of the solution may be attained.

ISSN:0021-8979    

DOI:10.1063/1.1662724

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Expressions are derived for the transient temperature distribution in optically pumped cylindrical laser rods for single‐shot and repetitively pulsed operations. The analysis is performed for both solid and hollow cylindrical laser rods. The solutions are evaluated numerically and temperature histories applicable to a wide range of system parameters are presented graphically. The computations show the dependence of the transient thermal profile on the cooling condition of the rod. The results reveal that in practical situations (cooling factor:A= 2 to 10) the thermal relaxation processes are considerably slower than in the case where a zero thermal impedance (A= ∞) between the rod surface and the cooling fluid is assumed. This explains the discrepancy which existed between the theory and measured decay times of thermal effects in laser rods.

ISSN:0021-8979    

DOI:10.1063/1.1662725

出版商:AIP    

年代:1973

数据来源: AIP