摘要:

Craters produced by projectile impact in granular materials were studied for a wide range of energies and projectile types. Crater sizes were shown to depend on projectile size and shape and on the particle size of the target material. The volume of the impact crater was related to the kinetic energy of the projectile and to the measurable cohesive strength of the target material. Excellent agreement was found between the experimental results and a hydrodynamic theory of cratering slightly modified from earlier studies.

ISSN:0021-8979    

DOI:10.1063/1.1709288

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Using moire´ fringe pattern techniques, elastic strains were measured in small gold nuclei (10–40 A in radius) prepared by evaporation in ultrahigh vacuum (10−8Torr) onto MoS2substrates. The variation of the elastic strain with the radius and angle of misalignment of the nuclei was found to be consistent with the theories of van der Merwe, Cabrera, and Jesser and Kuhlmann‐Wilsdorf.

ISSN:0021-8979    

DOI:10.1063/1.1709289

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A study of low‐angle subgrain boundaries in tellurium crystals was carried out using electron microscopical techniques. The existence of symmetric tilt boundaries could be proved by the examination of the electron diffraction patterns and the determination of the Burgers vectors forming the boundaries. The motion of the individual dislocations of a boundary at elevated temperatures was investigated and the effect of irradiation with fission fragments studied.

ISSN:0021-8979    

DOI:10.1063/1.1709290

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Scattering and frequency shifting of light reflected from Rayleigh waves in isotropic solids have been observed. The amplitude of the scattered light is correlated with acoustic surface‐wave amplitude. Diffraction patterns are pictured and surface‐wave velocities are calculated based on scattering angles.

ISSN:0021-8979    

DOI:10.1063/1.1709291

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Analytical expressions are developed for obtaining the form that would correspond to the switching‐current pulse of a ferroelectric, if the transit time were non‐negligible. In such a case, two important factors controlling the switching would be: (a) the share of surface area switched by direct nucleation of domains, and (b) the transit velocity of domains walls through the crystal. An experimental switching transient can be characterized by two adimensional data: the expression (im·tm)/(2Ps) and the ratio (change of polarization before the maximum of the current pulse)/(change of polarization after such a maximum). Using these two data as coordinates, a switching pulse can be represented by a point on anx−yplane. From our analytical expressions, a network is plotted on thex−yplane, relating directly the shape of a current pulse to the factors controlling the switching, according to our theory. The method is illustrated using several oscillograms of switching pulses appearing in the literature.

ISSN:0021-8979    

DOI:10.1063/1.1709292

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements of the photoelastic tensor components and figures of merit of several materials selected for possible application in acoustic light modulators and scanners are presented. The most important results are that GaP is superior to fused quartz by nearly two orders of magnitude for modulation and scanning of visible light of wavelength longer than 0.58 &mgr;, and that GaAs is similarly superior at wave‐lengths longer than about 1 &mgr;.

ISSN:0021-8979    

DOI:10.1063/1.1709293

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A theoretical and experimental study was made of the rectification of microwave energy by a thin piezo‐electric disk placed in a ∼3‐GHz reentrant cavity. Using a one‐dimensional approximation, an equivalent circuit consisting of a frequency‐dependent voltage source in series with a capacitance was derived for the rectified output. The voltage is the sum of a coherent part, proportional to the nonlinear coefficients of the constitutive relations and to the Maxwell—Faraday stress, and a thermal part, proportional (for quartz) to the coefficient of thermal expansion. The risetime for the coherent voltage at an overtone acoustic resonance frequency was about 1 &mgr;sec, while that for the thermal heating was of the order of milliseconds. The rectified voltage is proportional to the microwave power and is typically mV/W when polished X‐cut disks are excited at acoustic resonance frequencies and one to two orders of magnitude smaller at other frequencies. No acoustic resonance was observed for C‐cut zinc oxide, and a nearly frequency‐independent value of 20 mV/W was measured.

ISSN:0021-8979    

DOI:10.1063/1.1709294

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Statistical properties of the output fluctuations of a photon detector measuring the intensity of radiation at a given frequency emitted by a dispersive blackbody are investigated using Langevin's technique. The variance‐to‐mean ratio of the accumulated counts, and the power spectral density of the count rate are obtained in terms of properties of the emitting medium. The possibility and limitations of obtaining information about the emitter by measuring these quantities are discussed. It is found in particular that the temperature of the emitting medium can be determined in principle by observing the intensity fluctuations of the radiation at a single frequency. The photon fluctuations in a microwave cavity are also discussed in the framework of the present formalism and compared to previous work.

ISSN:0021-8979    

DOI:10.1063/1.1709295

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A study of the crystallographic orientation of the single‐crystal grains of large (8.5‐cm‐diam) polycrystals of CdS and of thin films of CdS has been made. Chemical and sputter‐etching observations, x‐ray crystallographic techniques, and piezoelectric polarity measurements have been used to classify the growth habits of the thin films as a whole and of the individual grains of the bulk crystals.Three types of grains have been identified in the bulk CdS polycrystals. These are type I:caxis normal to a Cd‐rich growth face; type II:caxis greater than 15° from the normal to an S‐rich growth face; and inverted type II:caxis greater than 15° from the normal to a Cd‐rich growth face. Type I and inverted type II grains exhibit negative compression piezovoltages, while type II grains are positive. Type I grains are identical to the type I single crystals previously discussed by Reynolds, and type II grains are similar to the 14° misoriented type II single crystals of Reynolds.Similar results were obtained from the evaporated CdS thin films which could be classified as type I and type II, with the normal to the type II films about 20° off thecaxis, indicating a close parallelism between the processes occurring in evaporated thin films and in bulk crystal growth. Sputtered CdS films were always type I. It is suggested that the variable efficiencies that have been observed in piezoelectric thin‐film transducers with similar crystallographic orientations are related to orientation inversions in the films.

ISSN:0021-8979    

DOI:10.1063/1.1709297

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The internal electric field distribution has been measured in photoconducting CdS single crystals using the linear electro‐optic effect. The experimental results show a nearly homogeneous field distribution in the crystals for applied fields below the threshold for acoustoelectric oscillations, while a high‐field region was created near the anode for fields above the threshold field. The reproducibility from sample to sample was rather poor. The linear electro‐optic constant was calculated from the experimental results: (r′113−r′333)=2.7×10−12m/V at the optical wavelength 6328 Å.

ISSN:0021-8979    

DOI:10.1063/1.1709298

出版商:AIP    

年代:1967

数据来源: AIP