摘要:

The present theoretical analysis permits simple, rigorous calculation of the equilibrium properties of state of a ferroelectric possessing a first‐order phase transition. The positive critical field in BaTiO3is approximately 9×105V/m. Experimental observation of the critical point should result in a better value for the temperature dependence of the fifth‐order thermodynamic coefficient &zgr;.

ISSN:0021-8979    

DOI:10.1063/1.1658151

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The stability against low‐frequency, electrostatic, flute‐like oscillations of a tenuous, hot, plane layer of charged particles embedded in a uniform and constant magnetic field is considered. It is shown that finite Larmor radius effects do not modify essentially the diocotron modes. It is also shown that a layer of particles whose guiding centers are located on a thin (with respect to the thickness of the layer) sheet around the midplane of the layer, is unstable: more precisely it has, for long (with respect to the thickness of the layer) waves, the same dispersion relation which holds for the diocotron modes. This strongly supports the conclusion that the diocotron instability of a charged, tenuous, plane layer is essentially independent from its kinetic structure.

ISSN:0021-8979    

DOI:10.1063/1.1658152

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The storage of protons and3He ions in a circular storage‐ring ion trap with background gas collision‐limited loss time constants up to 8 min long under ultrahigh‐vacuum conditions is described. Storage‐ring traps were derived from the linear quadrupole rf mass filter by shaping the electrodes into circular and racetrack configurations. Operation of the traps with a trapping rf frequency &OHgr; large compared to the secular ion oscillation frequency &ohgr; inhibited ion loss due to nonlinearities in the trapping fields. Long‐term ion storage in such traps may prove useful for radio‐frequency ion spectroscopic purposes.

ISSN:0021-8979    

DOI:10.1063/1.1658153

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Electret theory is briefly summarized and discussed. The electret strength as usually measured is shown to depend on the measuring method, the electret thickness, and the storage conditions. This is caused by charge leakage and sparking. The maximum charge density as a function of electret thickness is calculated; the thicker the electret the lower the maximum charge density. Our electrets are thin (5 &mgr;m) polymer membranes, provided with evaporated gold electrodes. They do not have to be stored in a short‐circuited condition.

ISSN:0021-8979    

DOI:10.1063/1.1658154

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Wave decay on glass surfaces at high temperatures is treated assuming glass to behave as a Newtonian viscous fluid in the high‐temperature region. To meet with different kinds of irregularities and various production techniques, two‐dimensional and axisymmetric waves with several boundary conditions are analyzed, each yielding the amplitude ratio at any instant in terms of the physical constants. Crude experiments are performed and found to agree fairly well with the theoretical results.

ISSN:0021-8979    

DOI:10.1063/1.1658155

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A rudimentary capillary‐type viscometer for measuring viscosities between 103and 1010poise at high pressures is described. Measurements are reported on petroleum ether to 57 kbar where the viscosity is approximately 1010poise and on a 1:1 mixture ofn‐pentane‐isopentane to 54 kbar where the viscosity is approximately 106poise. Measurement precision of the technique is a few percent, but uncertainty in absolute determination at maximum pressure is only within a factor of two. Viscous stresses are shown to decay exponentially with time even at the highest pressures, and no effects of residual stress are observed.

ISSN:0021-8979    

DOI:10.1063/1.1658156

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

To study the anharmonic properties of Al at low temperatures, the pressure derivatives of the elastic constants have been measured from 77° to 300°K. The isothermal elastic constants are obtained as a function of pressure by a self‐consistent analysis of the ultrasonic data. The most probable values for the pressure derivatives are calculated from the results of six measurements of different combinations of the elastic constants. The pressure derivatives are found to be almost constant below &THgr;D/3 and increasing for higher temperatures. Using the quasiharmonic approximation, the Gru¨neisen constant &ggr; is calculated from our results and found to be about 15% higher than the thermal &ggr; in the temperature range studied. We have calculated the elastic &ggr; forT≪&THgr;Dfrom the extrapolated values of the pressure derivatives. It turns out to be 2.51, a value in excellent agreement with the low‐temperature lattice thermal &ggr;. The equation of state in the Murnaghan form and in a series expansion of the volume change in terms of pressure is discussed for Al. A good agreement can be obtained between the ultrasonic and the static and shock compression results if the latter data are analyzed according to the Murnaghan equation of state.

ISSN:0021-8979    

DOI:10.1063/1.1658157

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The feasibility of laser‐machining quartz crystal resonators for frequency and inter‐resonator coupling adjustment has been demonstrated. The inter‐resonator coupling has been adjusted by altering the geometry of the electrode array. The frequency has been adjusted by vaporizing material to form an array of holes on the electrode surface. The results indicate that extremely fine adjustments of inter‐resonator coupling and resonator frequency can be achieved. Frequency adjustments greater than one part in 108have been demonstrated. No degradation of the crystal unit electrical parameters could be detected as a result of the machining process. Furthermore, laser trimming lends itself to automated processing without the need for elaborate vacuum equipment as is presently required with some adjustment techniques. Laser trimming also appears to be ideally suited for adjustment of high‐frequency resonators where fine tolerances are required.

ISSN:0021-8979    

DOI:10.1063/1.1658158

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A number of high‐melting‐point rare‐earth compounds have been examined for superconductivity. In this work LaC2, LuC2, and YGa2were found to be superconductors, but Y3C, LaGa2, La5Sn3, and Y5Sn3did not exhibit superconductivity in tests down to 1.4 K.

ISSN:0021-8979    

DOI:10.1063/1.1658159

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The avalanche breakdown of reverse biasedp‐njunctions in GaP is investigated. Electrical studies comprise measurements of I‐V characteristics, breakdown field, and electrical noise as functions of temperature. The high‐temperature light emission from microplasmas consists of a broad emission band with a maximum, near 1.7–1.8 eV, but otherwise with no structure. Its shape is analyzed in detail and discussed in view of theoretical models. The quantum efficiency of this band is independent of the lattice temperature. Neither the spectral shape nor the quantum efficiency of the emission band appear to be related to details of the energy‐band structure. At low temperatures, additional emission lines caused by minority carrier recombination outside the breakdown region are observed.

ISSN:0021-8979    

DOI:10.1063/1.1658160

出版商:AIP    

年代:1969

数据来源: AIP