摘要:

The application or removal of a magnetic field of order 5 T to some Gd compounds at low temperatures results in 10–20 K adiabatic temperature changes or the isothermal expulsion or absorption of heat. In particular, the heat absorbed by 1 liter of appropriate magnetic material at 2 K is several hundred J. A rotating device is decribed which will allow cycle times of much less than 1 sec, resulting in approximately 1‐kW refrigeration capacity for each liter of paramagnetic Gd compound. This heat could be expelled with better than 80&percent; of Carnot efficiency into a helium refrigerator operating at 10–14 K.

ISSN:0021-8979    

DOI:10.1063/1.325010

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Changes induced in the orientation of the axes of crystallites in thin films of polyvinylidene fluoride by the application of 6×107V/m at 100 °C for 1/2 h have been observed. The changes were observed by measuring the intensity of x rays diffracted from the film as a function of the orientation of the film relative to the diffracting x‐ray beam. A simple model calculation shows that the results are consistent with the assumption that the changes are induced by the interaction of the applied electric field with the dipole moments of the polyvinylidene fluoride molecules. The model uses the fact that the orthorhombic symmetry of the unit cell results from a small distortion of a hexagonal primitive lattice, the distortion being a 1&percent; decrease in the separation between molecules in the direction of the dipole moments. This model is consistent with the assumption that polyvinylidene fluoride is ferroelectric.

ISSN:0021-8979    

DOI:10.1063/1.325011

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Two‐dimensional images of 1–5‐keV ion beams incident on solid surfaces have been obtained by a method similar to that used in a scanning electron microscope. This easily applied technique produces visual real‐time images, whose size correlates well with beam‐current profile measurements; actual photographs of two such images obtained for different width ion beams are presented. Various target materials have been examined, but only insulators were found effective in producing ion‐beam images by this method. Some mechanisms that may relate to the interaction of ion and electron beams on surfaces are discussed. Those processes that seem to be basic to understanding the surface interactions responsible for this imaging effect are enhanced surface conductivity and charge neutralization. The technique itself has direct application to ion‐beam alignment and diagnostics. The use of coincident ion and electron beams presents a new technique that is potentially useful for the investigation of surface interactions.

ISSN:0021-8979    

DOI:10.1063/1.325012

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The thermal efficiency of the solid‐state engine (SSE) based on the shape‐recovery phenomenon accompanied by the martensite‐parent‐phase (M→P) transformation has been evaluated. Particular application is made for the memory components made with the Nitinol alloys. The result is expressed in terms of the hot and cold reservoir temperatures (TandT0), the latent heat of the M→P transformation, &Dgr;H, the fraction of the M→P transformation, &agr;, and a coefficient &bgr; that depends on the geometry and type of the deformation of the memory component. The relationship between the efficiencies of the SS and the Carnot engines is discussed. The factor &agr; is expressed in terms ofTc, the critical temperature under an applied load, the degree of prestraining of the component, and the volume change involved in the M→P transformation. It is seen that the maximum of the thermal efficiency approaches that of the Carnot engine at anx=T−T0value that depends onT0, &Dgr;H, and &agr;. ChoosingT0=297 K and a Nitinol alloy with &Dgr;H=2 cal/g, the maximum efficiency, about 20&percent;, occurs atx=75 K. Moreover, for a steady‐state heat‐mechanical energy conversion, the critical temperature of the memory component is found in terms of theTandT0temperatures. The engine efficiency in terms of the energy loss due to friction and the heat‐transfer coefficient is analyzed and estimated to be about 16&percent;. It is seen that higher thermal efficiency can be obtained if a Nitinol alloy with a largerHvalue than given above can be found.

ISSN:0021-8979    

DOI:10.1063/1.325013

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Molybdenum sulfide films have been deposited by reactive sputtering of molybdenum in a hydrogen sulfide/argon atmosphere and by sputtering of molybdenum disulfide in pure argon atmosphere at substrate temperatures between room temperature and 480 °C. The structure and composition of the films have been determined as a function of hydrogen sulfide partial pressure and substrate temperature by transmission electron microscopy (TEM) and Rutherford ion backscattering, respectively. The experiments showed that at hydrogen sulfide partial pressures above 2×10−4Torr, MoSxfilms had a rhombohedral structure with 0<x<2.2. The dependence of the film thickness on the hydrogen sulfide partial pressure has been studied. The dependence of the composition on the substrate temperature is interpreted by a different dependence of the sticking coefficient of the components on the temperature.

ISSN:0021-8979    

DOI:10.1063/1.325014

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A scanning laser beam was used to melt and normalize the surface layer of sensitized 304 stainless steel. Subsequent Strauss tests indicated a complete resistance to intergranular corrosion. Mechanical testing at strains less than 15&percent; also showed laser surface melting to indefinitely extend specimen life in a stress corrosion environment. At strains greater than 15&percent;, the laser‐scanned protective layer was breached by cracks. A maximum critical laser‐scanning velocity compatible with normalization of the surface layer is calculated. Similarly, a minimum critical laser‐scanning velocity required to avoid resensitization is determined. The stress distribution in a 304 stainless‐steel specimen with a laser‐melted and self‐quenched surface layer is estimated and shown to be compatible with the observed appearance of martensite in the melted surface layer.

ISSN:0021-8979    

DOI:10.1063/1.325015

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The high spectral intensity of pulsed dye lasers makes possible the saturation of atomic and molecular optical transitions. Because of the low‐intensity wings of the laser beam intensity distribution, the excited volume is only partially saturated. A mathematical procedure is described which yields a formal ’’saturated volume’’ which can experimentally be determined by measuring the degree of saturation using neutral optical filters in the path of the exciting laser beam. In this way, absolute transition probabilities and particle densities can independently be measured, and a mutual test on accuracy is possible. Preliminary results on CH and C2produced in a low‐pressure C3H8/air flame are presented.

ISSN:0021-8979    

DOI:10.1063/1.325016

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The average excitation level of anharmonic molecules in cw beams is determined as well as the distribution of excited states. The deactivation process consists of relaxation, diffusion, and convection. For low excitation levels, a closed solution can be obtained for constant cross section. For higher excitation levels, the variation of the cross section has to be considered and numerical results are presented.

ISSN:0021-8979    

DOI:10.1063/1.325017

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A comprehensive and unique set of measurements of the complex‐dielectric constant of sea ice, performed at several frequencies in the range 0.1–7.5 GHz, is described. In addition, a brief survey of previously published results is given and a set of dielectric models describing the complex‐dielectric behavior of sea ice, over the frequency range 0.1–40 GHz, is discussed.

ISSN:0021-8979    

DOI:10.1063/1.325018

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The problem of a confined plasma created by laser interaction with a thin metallic layer is investigated for the case of time‐dependent confinement boundaries. The self‐regulating ablative (SRA) model is applied to obtain the time dependence of plasma pressure, temperature, and density. Krokhin’s time‐independent boundary solutions are obtained as special cases.

ISSN:0021-8979    

DOI:10.1063/1.325019

出版商:AIP    

年代:1978

数据来源: AIP