摘要:

In a tensile stress field, certain polymeric solids deform and develop quasifracture formations. Each such formation is termed a craze. Previous analyses by Knight and Lauterwasser and Kramer have treated a craze by introducing either an assumed or a measured displacement field for the calculation of the stress distribution around the craze profile. In this paper the new phase of oriented polymer molecular bundles within the craze profile has been considered through the use of a linear modulus function for those bundles. Both displacement and stress fields have been calculated. This model developed for studying planar crack has its limitations when it is used for craze investigations. The basic model treatment depends upon classical linear fracture mechanics which is not valid for materials with a zone of craze occurrence. In addition, anisotropic and nonlinear as well as time dependent considerations are difficult to be incorporated into the model analysis.

ISSN:0021-8979    

DOI:10.1063/1.329819

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Brillouin scattering is used to study the elastic behavior of oriented poly(ethylene terephthalate) films. The elastic constantsC11,C13,C33, andC44are determined by measurements of the quasilongitudinal and quasitransverse hypersonic velocities at different angles in the film. The total orientational parameter is calculated for the three draw ratios from the Brillouin hypersonic velocities and are found to be similar to the orientational parameter in the amorphous phase obtained with a different technique.

ISSN:0021-8979    

DOI:10.1063/1.329820

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Raman and Brillouin scattering techniques have been used to study the effect of chain orientation in uniaxially extruded isotactic polypropylene. The orientation parameters ⟨P2⟩ and ⟨P4⟩ are obtained by measuring several Raman scattering intensities associated with the CH2rocking mode at 841 cm−1. Both ⟨P2⟩ and ⟨P4⟩ parameters represent the average of the local orientational distribution of the polypropylene backbone. The Raman scattering result for ⟨P2⟩ is found in good agreement with the previous study using another vibrational band. The high‐frequency elastic constants C11, C33, C44, and C13of extruded isotactic polypropylene are determined by Brillouin scattering. The elastic constants of deformed polymers have been related to the orientation parameters determined by Brillouin scattering. The result obtained for ⟨P2⟩ at high extension using Brillouin scattering is found to be smaller than that of Raman. The result suggests that the pair orientation correlation between segments is important in affecting the hypersonic velocity.

ISSN:0021-8979    

DOI:10.1063/1.329821

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An investigation of the structure of polyacetylene is carried out taking into account intrachain interactions. The distribution of torsional angles along the polymer chain is obtained using a transfer integral method. The most stable configuration at low temperature appears to be the cis‐transoid conformation.

ISSN:0021-8979    

DOI:10.1063/1.328574

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

In this paper we analyze the dynamics of a model electrowetting display (EWD) system, derive the operating parameters, and discuss the device performance. To discuss the problem we generalize the Washburn‐Yarnold treatment for the motion of a liquid slug in a capillary tube. It is shown that EWD’s have both memory and voltage threshold, and thus intrinsic matrix addressability. These properties are intimately related to the frictional surface tension forces developed between the metal and the electrolyte. Finally we present a model voltage‐driving scheme for matrix‐addressable EWD’s.

ISSN:0021-8979    

DOI:10.1063/1.329822

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

We describe the use of a microphone for detection of atomic and molecular beams in a high‐vacuum environment. Two experiments were carried out to demonstrate this detection method. Pulsed beams of argon were detected using a conventional electret microphone where the output of the microphone was displayed directly on an oscilloscope or processed with a boxcar averager to remove the transient oscillations of the microphone diaphragm. Amplitude modulated, continuous beams of atomic argon were also detected using a lock‐in amplifier. The microphone possesses a response to the pressure or momentum flux in the beam that appears to be unique among beam detectors. We use the classical equipartition theorem to calculate the magnitude of the random fluctuations in the output voltage of the microphone that is used to give an expression for the minimum detectable momentum flux in the beam. For a typical microphone we find this to be 3×10−8Pa, (in a 1‐Hz bandwidth), which corresponds to a minimum number density of 1×106cm−3for an effusive argon beam at 300 K.

ISSN:0021-8979    

DOI:10.1063/1.329823

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Laser action from neutral Xe transitions has been achieved in an Ar–Xe mixture at 1 atm and in a He–Xe, He–Ar–Xe mixture at 2.5 atm excited by a UV preionized short discharge (&Dgr;t?50 ns). In the best mixture, He–Ar–Xe (100–60–1), an overall conversion efficiency of 0.2% was obtained with a 10‐mJ output. These nonoptimized results may be improved by decreasing the input energy density and increasing the pressure.

ISSN:0021-8979    

DOI:10.1063/1.329824

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Saturation curves for laser‐induced sodium fluorescence in a propane‐air flame under the cw and the pulsed excitations were measured to examine the contribution of chemical reaction via the excited states of sodium atom to saturated fluorescence. Saturation behavior for the pulsed excitation of ns duration is interpreted by the ordinary two‐level model taking account of spatial and temporal distribution of the laser intensity. The fluorescence intensity under the cw excitation levels off at much lower intensity than the ordinary saturation intensity. Consideration of species distributions in the flame indicates that the hydroxide formation process results in the saturation of the cw fluorescence. From the time‐resolved fluorescence measurement, the rate constant for this molecular formation is estimated to be around 1×107s−1.

ISSN:0021-8979    

DOI:10.1063/1.328538

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An analytical calculation is presented for the effects of finite length on the magnetic levitation of a cylindrical metal shell encircling an alternating‐current filament, which system was treated previously by ignoring end effects. The levitational end corrections are calculated by analyzing the differences in magnetic‐field distribution between the finite‐length and endless geometries. This approach yields a new eigenvalue equation, and expansion of the magnetic‐field corrections in corresponding eigenfunctions leads, after some reduction, to a compact set of equations determining the expansion coefficients. From this formulation, the levitation force is expressed solely in terms of field coefficients for the region bounded by the shell inner surface and end planes. An approximation for these coefficients is then developed from the basic equations, yielding an anlytical formula for the levitational end corrections. The approximation formula is shown to give satisfactory results for representative cases. The exact solution for the magnetic field in the equilibrium configuration is appended.

ISSN:0021-8979    

DOI:10.1063/1.328539

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The recombination reaction NF2+F+M→NF3+M has been investigated theoretically using a RRKM approach. Adequate agreement is found with the available association and decomposition data in low pressures of He or Ar. The recombination in 4 atm of Ne is calculated to be much slower than would be expected from extrapolation of the low‐pressure, three‐body rate constant. In particular, little recombination should occur during a discharge or electron‐beam laser excitation pulse (≲1 &mgr;s), but reformation of NF3should be the dominant loss mechanism for F and NF2. The theoretical techniques used here should be equally applicable to other important recombination processes in laser media.

ISSN:0021-8979    

DOI:10.1063/1.328540

出版商:AIP    

年代:1981

数据来源: AIP