摘要:

It is shown that under practical assumptions both ray and wave theories of the prism waveguide coupler can be applied to the whole range of the coupling strength parameter 0⩽h⩽1, and yield identical results. A numerical example is given, which shows the range of validity of the weak coupling approximation.

ISSN:0021-8979    

DOI:10.1063/1.327633

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A jet formation routine has been generated that can be used with (Lagrange) explosive cone‐collapse calculations. It calculates the velocities of jet and slug elements, as well as their mass, formation point, and time. The equations and method of operation are presented here. Experimental jet velocities agree with the model to 10%. Jet deformation calculations required yield strengths up to 24 kbar to yield agreement with experiments on copper jets.

ISSN:0021-8979    

DOI:10.1063/1.327634

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Thermal properties are essentially involved in the acoustic response of a liquid or solid sample to the absorption of chopped light. Recently, the first experimental observation of the photoacoustic effect at first‐order phase transitions has been published. In the present work we calculate the temperature variation in the gas at the surface of a sample and determine its amplitude and phase angle. Therefore we solve the differential equation of conduction of heat for a medium exhibiting a temperature gradient superposed by a temperature oscillation due to absorption of light with sinusoidal varying intensity. In the medium there exist two regions of different thermodynamic phases separated by an interface at transition temperature. The latent heat for phase transition is taken into account via a boundary condition for the heat flow at the interface. We have assumed the optical‐absorption coefficient to be much larger than the thermal‐diffusion coefficient realized in strongly absorbing materials. The application of our calculation to measured data is discussed with respect to the technique used to detect the acoustic signal. With the model, we present here, the experimental results can be described fairly well.

ISSN:0021-8979    

DOI:10.1063/1.327641

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Comparisons between hard‐x‐ray experimental spectra and those obtained from a planar one‐dimensional one‐temperature fluid laser‐produced plasma model show good agreement over several orders of magnitude in x‐ray intensity and for Nd‐laser irradiances varying between 2×1014and 8×1015W/cm2. The key to this agreement is the careful modeling of electron‐energy flux limitation by return‐current‐driven ion‐acoustic turbulence. The hard‐x‐ray temperature agrees with a (I&lgr;2)1/3scaling law.

ISSN:0021-8979    

DOI:10.1063/1.327642

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Stable formation of a multichannel arc is observed in low‐pressure rare‐gas–mercury discharges in a concentric tube where a hot cathode is located in the inner tube and two to six anodes are arranged symmetrically in the space between the inner tube and the outer bulb. The discharge current for each discharge channel is found to be deeply modulated at high frequencies by the anode oscillations which take place in a regular, complex sequence depending on the anode configuration. In a discharge tube with two anodes, anode oscillation occurs alternately, causing discharge transfers between the anodes. With three anodes, the discharge transfers take place in a manner similar to a ring counter, as anode oscillations occur in turn in geometrical order. In the four and five anode configurations, oscillations occur sequentially in time, but not sequentially in the anode configuration. In the case of six anodes, stable formation of a multichannel arc is not observed.

ISSN:0021-8979    

DOI:10.1063/1.327643

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Spherical expansion of the luminous front around a laser‐heated microshell target in 20 Torr of helium is compared with theory in the mass‐dependent region. Microshell targets from 74‐ to 7970‐ng initial mass irradiated with up to 0.13 TW (Terawatt) of 1.06‐&mgr;m light were studied. Effects of the initial mass and changing &ggr; on the front history are discussed. It is concluded that extraction of expansion energy from the front motion is not easily accomplished in this close‐in region.

ISSN:0021-8979    

DOI:10.1063/1.327644

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The paper presents a study of the cutoff frequencies of a class of electromagnetic waves, designated here as intermediate frequency waves, which can propagate in a plasma column enclosed in a conducting cylinder and embedded in a static axial magnetic field. These waves reduce to lower hybrid waves or magnetohydrodynamic TE waves under suitable conditions. The cutoff frequencies of the intermediate frequency modes have been investigated, covering all possible values of &ohgr;pe,&ohgr;ce, anda, where &ohgr;peis the plasma frequency, &ohgr;ceis the electron cyclotron frequency, andais the plasma radius. The study includes all the possible types of modes, namely, circularly symmetricI0mmodes and asymmetricInmmodes withn? 1, eachInmmode being split into two, calledI+nmandI−nmmodes, corresponding to two different polarizations of the field components. The cutoff frequency &ohgr;c 0of anyInmmode withn? 0 is found to be confined to the frequency domain 0 to &ohgr;nm, where &ohgr;nmis the cutoff frequency of the TEnmmode in an empty waveguide. The zero frequency is approached if &ohgr;peoratends to infinity or &ohgr;cetends to zero, the other parameters remaining constant in each case. The frequency &ohgr;c 0tends to &ohgr;nmif &ohgr;ceis sufficiently large for any given set of &ohgr;peanda. The study of intermediate frequency modes reveals that these modes can broadly be divided into the following two categories: (1)I−n1modes withn? 1, and (2) modes other thanI−n1modes. The nature of variation of &ohgr;coith &ohgr;pefor fixed values of &ohgr;ceandaforI−n1modes is, in general, quite different from that for the other modes. Furthermore, &ohgr;c 0tends to &ohgr;ciasatends to zero with &ohgr;peand &ohgr;ceheld fixed in the case ofI−n1modes, while for other modes &ohgr;c 0tends to &ohgr;lhunder the same condition, where &ohgr;ciis the ion cyclotron frequency and &ohgr;lhis the lower hybrid frequency. AnyInmmode withn? 0 is found to reduce to the magnetohydrodynamic TEnmmode at or near the cutoff under the condition: &ohgr;pi≫&ohgr;nm, where &ohgr;piis the ion plasma frequency. Finally, it is shown how the charge density in a bounded magnetoplasma can easily be determined in most experimental situations by using the cutoff frequency characteristic of the dominantI−11mode.

ISSN:0021-8979    

DOI:10.1063/1.327645

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Tests are made of the ability of currently available theory to predict experimental ratios of the electric field to gas density E/N required for the steady‐state operation of low‐current, moderate‐pressure discharges in hydrogen‐helium mixtures. In the experiments the fractional concentration of H2in He was varied from 1% to 4% and the discharge current, i.e., 40±10 &mgr;A, and total gas density, i.e., 1023–1025atoms/m3, were chosen to avoid gas heating and striations. The experimental E/N values for the 4‐mm‐diam tube varied from 6×10−21V m2for 1% H2in He at a gas density of 7×1024m−3to about 4×10−20V m2for 4% H2in He at 1.5×1023m−3. Theoretical steady‐state E/N values versus gas density were calculated using (a) solutions of the Boltzmann equation for He metastable excitation, He ionization, and H2ionization rate coefficients; (b) published theoretical calculations of the effects of a finite Debye length and a finite ion mean free path on the electron loss rate; and (c) models for the ion‐molecule conversion and Penning ionization processes. The differences between theoretical and experimental values ofE/Nare less than 10% for total gas densities above 6×1023m−3, but are 20–30% for a gas density of 1.6×1023m−3. We conclude that except at low gas densities the simple theory gives a good description of low‐current discharges in this gas mixture.

ISSN:0021-8979    

DOI:10.1063/1.327646

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Both experimental and theoretical evidences are presented for polar and nonpolar contributions to liquid‐crystal orientations on surface‐treated substrates. Polar and nonpolar components of substrate surface energies are determined from contact angle measurements using polar liquids. Liquid‐crystal orientations are characterized using orientation angles and anchoring strength coefficients at substrate surfaces, both of which are measured by the magneto‐capacitance method. Numerical calculations give correlations between liquid‐crystal orientation and substrate surface energy components, which are in good agreement with experimental results. These calculated correlations involve the critical surface tension hypothesis as a limited case when polar interfacial interactions are negligible.

ISSN:0021-8979    

DOI:10.1063/1.327602

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

It is proposed that the growth of quartz crystals into fused silica is effected by a mechanism involving the breaking of an Si‐O bond and its association with an OH group, followed by cooperative motion of the nonbridging oxygen and the hydroxyl group which results in the crystallization of a row of several molecules along a crystalline‐amorphous interfacial ledge. This mechanism explains, at least qualitatively, all the results of our earlier experimental study of the dependence of quartz crystal growth upon applied pressure: large negative activation volume; single activation enthalpy below Si‐O bond energy; growth velocity constant in time, proportional to the hydroxyl and chlorine content, decreasing with increasing degree of reduction, and enhanced by nonhydrostatic stresses; lower preexponential for the synthetic than for the natural silica.

ISSN:0021-8979    

DOI:10.1063/1.327647

出版商:AIP    

年代:1980

数据来源: AIP