摘要:

Data are given on the resistivities and thermoelectric powers of the alloys Cu&sngbnd;Pd, Ag&sngbnd;Pd, Au&sngbnd;Pd, Cu&sngbnd;Pt, Ag&sngbnd;Pt, Au&sngbnd;Pt, Cu&sngbnd;Mn, Ag&sngbnd;Mn, and Au&sngbnd;Mn from −195°C to +500°C for the resistivities and to +650°C for the thermoelectric powers. The resistivities of the alloys containing Pd and Pt obey the Matthiessen rule well whereas those with Mn do not. The resistivity of the alloys with more than about 8 atomic % Mn deviate from linearity at the lower temperatures, the temperature of deviation increasing with Mn content. The thermoelectric powers of the Pt and Pd alloys are negative relative to the pure solvents and are reasonably constant relative to the solvents at high temperatures. The thermoelectric powers of the Mn alloys become positive relative to the solvents above certain temperatures (25°C for Cu&sngbnd;Mn, −170°C for Ag&sngbnd;Mn, and 150–250°C for Au&sngbnd;Mn). A brief discussion of the data in relation to theory is given.

ISSN:0021-8979    

DOI:10.1063/1.1722342

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The present work deals with Hall effect and specific conductivity measurements in the case of a nonuniform current density field (that is, when the specimen is not a parallelepiped but has irregularly waved surfaces). It is then impossible to measure separatelyRH(Hall coefficient) and &sgr; (conductivity); it is possible, however, to get their product, the Hall mobility of the carriers. These conclusions are important when dealing with thin films, where the actual geometry of the surface is completely unknown. The preceding remarks are used to interpret the results of some experiments on Au films evaporated on mica. An almost constant mobility is foundversusmean thickness, but its magnitude is about ¼ the bulk mobility. This behavior raises some question about the structure of thin films, and some connection seems to hold between the experiments here described and the results of the measurements of the optical constants of metals.

ISSN:0021-8979    

DOI:10.1063/1.1722343

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Diffuse x‐ray scattering from a single crystal of Cu3Au was observed atT/Tc≅0.995 where the long‐range order parameterSequals 0.85. By annealing at low temperatures, nearly perfect order was obtained. A difference curve yields the diffuse scattering attributable to short‐range order coexisting with the long‐range order state ofS=0.85. Analysis of the diffuse intensity in absolute units gives values of the first three short‐range order coefficients. The first coefficient is found to be close to the perfect order value: &agr;1=0.33. Within experimental error the observed coefficients fit both the Cowley theory and a random long‐range order model equally well.

ISSN:0021-8979    

DOI:10.1063/1.1722344

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Theoretical calculations suggest that the duration (10−11sec) and smallest dimension (20 atom diameters) of thermal spikes in metals undergoing irradiation may be too small to permit the thermal nucleation and growth of crystals of a second phase even though the average ``temperature'' of the spike may be above the melting point. Experiments have been performed which show that even the very energetic fission thermal spikes are too rapid and small to permit the nucleation and growth of a second phase in uranium metal containing 2 atomic % chromium. It is suggested that the terms ``heated'' and ``melted'' are not strictly appropriate to thermal spikes. Rather the region of a thermal spike should be regarded as a highly disturbed zone in which atomic interchange can occur, but which quickly returns to the structure and orientation of the surrounding crystal with a distribution of interstitials and vacancies which may then interact with each other or with other defects possibly present in the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1722345

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Ferrimagnetic resonance has been investigated in several polycrystalline ferrites located in wave guide over a temperature range from 25°C to the Curie point of each ferrite. The ferrimagnetic resonance line width and the apparent gyromagnetic ratio of two types of ferrites were found to change with increasing temperature. The theories of Wangsness and Kittel have been utilized in interpreting the observed effects. The foregoing effects were shown to influence the temperature behavior of the microwave properties of ferrites away from resonance.

ISSN:0021-8979    

DOI:10.1063/1.1722346

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The resolution of the field emission electron microscope is expressed as a function of the ratio of its magnificationMto the time‐of‐flight &tgr; of an electron from emission tip to screen. It is shown that small protrusions on the surface of the tip can provide areas for whichMis much greater than that computed for a perfectly smooth tip. Resolution of the order of 3 A is possible on these protrusions, so that some of their atomic detail should be observable.

ISSN:0021-8979    

DOI:10.1063/1.1722347

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The intensely bright doublets sometimes observed in field emission microscopes vary in size, shape, intensity, and resolution. It is proposed that these doublets are owing to simple small molecules adsorbed on tungsten protrusions or ridges on the tungsten tip covered with a chemisorbed layer of residual gas. The variation in the doublets is ascribed to variation in the size and shape of the protrusions as predicted by a theory developed by D. J. Rose.

ISSN:0021-8979    

DOI:10.1063/1.1722348

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The vortex produced by a weak shock passing over a 5° vertical wedge has been studied experimentally and theoretically. The theory applies to any vortex in isentropic flow which has a certain rotational symmetry, and which expands uniformly in time (pseudo‐stationary flow), without consideration of how the vortex was formed. By fitting essentially one parameter of the theory to the interferometrically observed density, good agreement is obtained over the region of the vortex, except at the very center. The rate of growth of the vortex as a function of free‐stream Mach number has been found in agreement with that predicted by [N. Rott (private communication)] on the basis of another theory. The photographs show a well‐developed spiral slip stream winding off the corner which contains small secondary eddies whose average angular spacing, measured from the vortex center, appears to be roughly independent of shock strength and time.

ISSN:0021-8979    

DOI:10.1063/1.1722349

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The effect of the free surface on the pressure distribution on the upper side of a shallow‐running hydrofoil is considered from a general point of view. Previous theoretical and experimental work is reviewed in order to compare the range of flow variables for which each treatment of the surface proximity problem is valid. A qualitative theoretical expression for the pressure is developed. This result shows the relative importance of the pertinent parameters, and it is shown to agree qualitatively with previous experiments as well as with new pressure measurements made in the free surface water tunnel. The foregoing considerations reinforce the view generally held in the past, that the principles of potential theory when properly applied to hydrofoils, even at shallow submergences, may be expected to lead to valid and useful results.

ISSN:0021-8979    

DOI:10.1063/1.1722350

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A unified treatment is presented of thermoelasticity by application and further developments of the methods of irreversible thermodynamics. The concept of generalized free energy introduced in a previous publication plays the role of a ``thermoelastic potential'' and is used along with a new definition of the dissipation function in terms of the time derivative of an entropy displacement. The general laws of thermoelasticity are formulated in a variational form along with a minimum entropy production principle. This leads to equations of the Lagrangian type, and the concept of thermal force is introduced by means of a virtual work definition. Heat conduction problems can then be formulated by the methods of matrix algebra and mechanics. This also leads to the very general property that the entropy density obeys a diffusion‐type law. General solutions of the equations of thermoelasticity are also given using the Papkovitch‐Boussinesq potentials. Examples are presented and it is shown how the generalized coordinate method may be used to calculate the thermoelastic internal damping of elastic bodies.

ISSN:0021-8979    

DOI:10.1063/1.1722351

出版商:AIP    

年代:1956

数据来源: AIP