摘要:

An analysis of the normal acceleration sensitivity of contoured AT‐ and SC‐cut quartz crystal resonators rigidly supported along rectangular edges is performed. The variational principle with all natural conditions for anisotropic static flexure is used in the calculation of the flexural biasing state. However, in this work the biasing shearing stresses with quadratic variation across the thickness of the plate are obtainedaposteriorifrom the flexural solution in the conventional manner. The accompanying quadratically varying biasing shearing strains, which are very important in this work, are obtained from the constitutive equations along with all other quadratically varying strains resulting from the anisotropy. The calculated biasing deformation fields are employed in an existing perturbation equation along with the mode shapes of the contoured resonators to calculate the normal acceleration sensitivities. It is shown that the normal acceleration sensitivity vanishes for many cases and is less than a few parts in 1013for all cases considered.

ISSN:0021-8979    

DOI:10.1063/1.345206

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An optical heterodyne technique has been used to make new measurements of the ultrasonic properties of aqueous solutions of biomolecules, dimethyl sulfoxide, and 1,4‐butanediol. A LiNbO3transducer provided acoustic excitation from 0.2 to 1.5 GHz. Acoustic velocity and attenuation were measured using angularly resolved detection of Bragg‐scattered light from the liquid sample. A thermodynamic theory based on the heat of mixing was used to explain the concentration dependence of the liquid mixture properties. This paper contributes new data at high frequencies, a calculation of measurement sensitivity for this technique, and a complete treatment of a little known thermodynamic theory that describes these results.

ISSN:0021-8979    

DOI:10.1063/1.345207

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Mason’s nonlinearity constantsD[W. P. Mason, inPhysicalAcoustics, edited by W. P. Mason (Academic, New York, 1965), Vol. IIIB, Chap. VI] in GaAs at 298 K have been estimated from second‐ and third‐order elastic constants along the [100], [110], and [111] directions for longitudinal and shear waves. These values are further used to estimate the frequency dependence of the ultrasonic attenuation in the range 40–640 MHz and are found to be in good agreement when compared with experimental values available in the literature. Previously, it was established that phonon‐phonon interactions produce a drag on moving dislocations in a solid. In the present work, the drag coefficients for edge and screw dislocations along the [100] and [110] directions in single‐crystal GaAs have been estimated from the evaluated nonlinearity constantDvalues at 298 K. We have also estimated the values of Breazeale’s nonlinearity parameters &bgr; [M. A. Breazeale and J. Philip, inPhysicalAcoustics, edited by W. P. Mason and R. N. Thurston (Academic, New York, 1984), Vol. XVII, Chap. I] along the [100], [110], and [111] directions and found them to be consistent for the three principal orientations, compared with the results for other samples. It is pertinent to note that the mode Gru¨neisen number &ggr; jiinvolved in the estimation of Mason’s nonlinearity constantDis deceptively similar to Breazeale’s nonlinearity parameter &bgr;. The nonlinearity constantDis evaluated from knowledge of the Gru¨neisen number &ggr; jifor various modes and directions, whereas Breazeale’s nonlinearity parameter &bgr; is the negative ratio of coefficients of nonlinear term to the linear term of the (dissipationless) nonlinear wave equation for pure mode directions. BothDand &bgr;, in general, are temperature dependent.

ISSN:0021-8979    

DOI:10.1063/1.345208

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

For a one‐dimensional liquid or solid slab that undergoes freezing or melting, we solve for the cooling or heating strategy that, subject to certain constraints and approximations, minimizes entropy production and hence maximizes potentially available work. The key constraint is that the freezing or melting process must be completed in a given fixed time. This constraint can correspond, for example, to a fixed production rate in an industrial process. The validity of this optimal strategy and its practical significance are discussed.

ISSN:0021-8979    

DOI:10.1063/1.345209

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have determined densities of negative hydrogen ions in a discharge by a laser detachment technique. We measured the electron density, the electron temperature, and the positive ion density using a Langmuir probe. We also performed extraction measurements. Combination of H−density measurements and extraction measurements yields information about the H−drift velocity. It was found that the velocity scaled with the square root of the electron temperature. All measurements were done as a function of discharge voltage, discharge current, and gas pressure. The densities are compatible with a semiquantitative model in which H−is produced by dissociative attachment of plasma electrons to vibrationally excited molecules and destroyed by wall collisions at very low pressure and collisions with H atoms, positive ions and/or hot thermal electrons at higher pressure.

ISSN:0021-8979    

DOI:10.1063/1.345210

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper we present experimental results obtained for a rf discharge in SF6and for SF6with Ar and/or N2. The data for power dependence of some emission lines usually used in actinometry are acquired and their applicability and excitation kinetics discussed. We also present the spatial (time averaged) variations of some emission lines. From such data the spatial dependence of the high‐energy tail of the electron energy distribution function may be obtained.

ISSN:0021-8979    

DOI:10.1063/1.345211

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Combined theoretical and experimental studies have been accomplished in order to elucidate the features of positive columns in oxygen glow discharges. The Langmuir probe technique was utilized to measure the plasma parameters such as electron temperature and electric field. A tandem mass spectrometer was used to measure relative concentrations of charged particles. These experimental results were found to be in good agreement with the present theoretical calculations based on a slightly ionized stationary plasma model.

ISSN:0021-8979    

DOI:10.1063/1.345288

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A one‐dimensional numerical model has been developed to describe a cylindrical high‐pressure mercury plasma sustained by microwave energy within a cavity applicator by solving Maxwell’s equations together with the energy balance equation. The mercury line radiation has been taken into account for the energy balance by solving the radiation transfer equation for all significant wavelengths. An experimental microwave circuit for the frequency range of 2–4 GHz (Sband) has been designed to guarantee stable discharge operation. Coupling efficiencies >99% into the microwave cavity can always be achieved with proper adjustments. Variation of discharge parameters leads to different types of temperature distributions including profiles with a local minimum in the axis. The temperature distributions predicted by the model are in good agreement with results from spectroscopic experiments.

ISSN:0021-8979    

DOI:10.1063/1.346088

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A study of the application of high‐order TM0m0modes of a cylindrical cavity to the measurement of the density of a magnetized plasma column is presented. It is shown theoretically that judiciously chosen high‐order modes have the potential advantages of both a wide operational range of densities, and a wide range for which a simple perturbation theory is valid. Furthermore, an experiment is described which shows that the TM060mode can be excited with a sufficiently highQvalue to allow accurate determination of the resonant frequencies, and hence plasma density. Favorable comparison between densities in the range 1010–1012cm−3measured by means of the resonant cavity technique and microwave interferometry is presented.

ISSN:0021-8979    

DOI:10.1063/1.345290

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Electrical characteristics of parallel‐plate rf discharges were measured with the goal of obtaining quantitative information of the properties of the discharges, in particular the electrode sheaths. Measurements of the impedance characteristics at variable electrode spacing suggest a transition of the power deposition process from volume to electrode dominated at about 1 Torr in argon. By changing the secondary electrode emission coefficient of the electrodes, it could be shown that the power into electrons emitted from the electrodes is small compared to the total power input. Adding the attachers CF4, C2F6, and SF6caused a large increase of the discharge impedance in the high‐pressure (volume power deposition) regime and shifted the transition to the electrode‐dominated power deposition regime to lower pressures. The impedance behavior versus pressure was modeled with a simple equivalent electrical circuit from which the characteristics of the electrode sheaths and their influence on the electrical characteristics could be derived. The time‐averaged sheath thickness was measured optically and compared with the results using the equivalent circuit. The sheath thickness, decreasing on addition of the attaching gases CF4and SF6, is quite different for these two added gases, which have about the same ionization, but very different attachment cross sections. In contrast, the impedance with added CF4is only slightly less than with SF6, indicating an average electron energy of at least 5 eV where the attachment rates of the two gases become similar. Using variable electrode spacing, the peak electric field was measured both in the electrode sheaths and in the discharge volume. For argon with 23% added SF6, at 1 Torr pressure, the field in the sheath reached 569 and 27 V/cm in the volume; at 0.15 Torr the fields were 300 V/cm in the sheath and below the measurement accuracy in the volume.

ISSN:0021-8979    

DOI:10.1063/1.345291

出版商:AIP    

年代:1990

数据来源: AIP