摘要:

Sequences of pictures which show the evolution of two patterns between their continuum and free‐molecule limits are presented. The first sequence examines the flow through an orifice as the orifice Knudsen number is decreased while the pressure ratio across the orifice is kept constant. The second sequence examines the flow about a washer placed at a fixed distance downstream of the orifice as the orifice Knudsen number is decreased. The effects of the first molecular collisions upon the flow pattern are clearly shown in both sequences of pictures. The photographs were obtained by employing the resonance scattering of sodium light by sodium vapor to make the flow visible in a rarefied‐gas‐dynamic wind tunnel.

ISSN:0021-8979    

DOI:10.1063/1.1662538

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Distributions of crystallite sizes and lattice distortions in the direction normal to (110) of the polyethylene crystal are derived from 110 Debye‐Scherrer profiles, by means of a Fourier technique developed by one of the present authors. Samples investigated are linear polyethylene powder, single‐crystal mats grown at 85 °C and 70 °C, and branched polyethylene powder with a different methyl‐group concentration. It is found that in the crystallite size distribution each of the polyethylenes examined has a common peak at about 100, 250, 350, and 450 Å. The presence of branches with lower methyl concentration does not seriously affect the distribution, but at the highest concentration of branches (29 CH3/1000 CH2) peaks at 350 and 450 Å disappear. Lattice distortions in the crystallites of polyethylene cannot be always explained by paracrystalline or strained‐lattice‐type strain alone, but may be generally expressed by a superposition of them.

ISSN:0021-8979    

DOI:10.1063/1.1662539

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A multistep analytical method is described for relating morphology to mechanical properties in crystalline polymers. The analysis is carried out at several microscopic scale levels to permit detailed consideration of morphological structures at each level. As an example, the elastic constants of transcrystalline polyethylene are determined and, upon transformation into complex moduli, the results agree well with the dynamic mechanical measurements of Takayanagi and of Kweiet al.

ISSN:0021-8979    

DOI:10.1063/1.1662540

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Spectroscopic measurements of the vapor flow velocities inside a heat‐pipe oven have been performed as a function of pressure, heater power, and radial position inside the pipe. For this purpose the relative intensity of the collision‐induced satellite lines in laser‐induced resonance fluorescence spectra of the7Li2molecule has been employed. A one‐dimensional flow model is presented which determines the vapor parameters as a function of position along the pipe. It predicts the onset of the sonic flow which has been verified experimentally. A criterion is derived from which the parameters of the vapor can be obtained from the ideal gas relation, neglecting velocity‐dependent terms.

ISSN:0021-8979    

DOI:10.1063/1.1662541

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Measurements of the internal friction in polymers exhibit a spectrum of peaks at low temperatures that are related to the plastic behavior at higher temperatures. This manuscript deals with a particular supramolecular defect that behaves mechanically in a manner consistent with the observations. The defect is a twist disclination consisting of two molecules that cross over one another. The energies of formation and motion for the twist disclination are calculated in terms of the width of the twisted region, the displacement that is produced by the twist, the molecular radius, and the elastic stiffnesses of the molecules. For motion to occur dilatations caused by contour modulations of the molecules must be overcome. This effect yields expressions for the motion activation energy and stress for nonactivated motion. It is shown that molecular bending occurs more readily by elastic deformation than by conformation‐change deformation unless the radius of curvature is less than a critical value (of the order of atomic dimensions).

ISSN:0021-8979    

DOI:10.1063/1.1662542

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Since the high strength of undamaged glass can be further increased by lowering temperature, load‐extension measurements at large strains (up to 13%) were carried out for as‐drawn sodium‐silicate glass fibers at temperatures from −78 to −196 °C. Elastic hysteresis loops were observed when the strain amplitude exceeded 4%. A detailed study of this hysteresis showed that it is indeed the static hysteresis of glass because the magnitude of internal friction, while rather insensitive to strain rate, is obviously amplitude dependent. To interpret the results, a model somewhat analogous to that of pinned dislocation loops used by Granato and Lu¨cke is presented. It is assumed in the model that the number of breaks in the glass network will show an exponential increase with increasing tensile strain and that no breaks will ``heal'' during unloading until the network is again free from applied stress. Torsion pendulumn measurements were also made for the specimens under static tension. The two types of measurements have shown that static tensile strain raises the background in the internal friction vs temperature curve and, at temperatures higher than −150 to ∼ −120 °C, activates the relaxation processes that are superimposed on the background and generally attributed to the migration of alkali ions.

ISSN:0021-8979    

DOI:10.1063/1.1662543

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A perturbation solution is obtained for the propagation of longitudinal shock waves in a one‐dimensional dissipative lattice with a velocity step applied to the first mass. The nonlinear part of the elastic interaction force between neighboring particles is assumed to be of parabolic form. Linear dissipation interaction forces are assumed. Within the range of validity of the solution, the dispersive oscillations at the head of the shock wave are found to grow, remain essentially steady, or diminish with distance, depending on the conflicting effects of nonlinearity of the elastic forces and the dissipative forces.

ISSN:0021-8979    

DOI:10.1063/1.1662544

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The application of the typical metallic refractory compound lanthanum hexaboride as a thin‐film material has been studied. Film properties are estimated by using bulk optical constants derived from a Kramers‐Kronig analysis of the bulk material. Films with thicknesses of 130–2000 Å have been prepared by sputtering and electron‐beam evaporation onto substrates with temperatures between 100 and 1200 °C. The effective optical constants of the films are derived by means of a computer program and used together with the modified Drude theory to give the free‐electron relaxation time. Conductivity measurements give the electron mean free path. The optical and electrical film data are compared with the bulk properties of the material. The observed differences can be explained by the influence of crystal imperfections. The explanation is in qualitative agreement with information from x‐ray diffractometer scans.

ISSN:0021-8979    

DOI:10.1063/1.1662545

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A continuously tunable ultraviolet source around 2535 Å has been obtained by mixing a narrow‐band ruby‐laser beam with a broad‐band dye‐laser beam in a 90° phase‐matched ADP crystal. The 90° phase matching was achieved at convenient temperatures around 23°C. The rates of wavelength change of the mixed light with the 90° phase‐matching temperature and with the phase‐matching angle for fixed temperature were evaluated and found to bed&lgr;M/dTM=1.7 Å/°K andd&lgr;M/d&thgr;M= 24 sin 2&thgr;MÅ deg−1. The spectral bandwidth of the mixed light at half‐intensity was also evaluated and compared with the experimental result of 0.7 Å.

ISSN:0021-8979    

DOI:10.1063/1.1662546

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Laser micromachining of thin metallic films is promising to become an important processing step in the fabrications of electronic circuits. Important applications range from pattern generation of conductive paths to trimming of thin — film resistors. Since the thin films possess vaporization temperatures which generally are much higher than the melting temperature of the underlying dielectric substrate, short — duration pulses such as those available fromQ‐switched and cavity‐dumped lasers must be used. Use of such short pulses minimizes potential thermal damage to the substrate and adjacent areas in the film. To predict the thermal state of the film and substrate, we have developed a theory which takes into account the heat loss due to conduction into the substrate, and the spatial distribution of the irradiating laser beam and its thermal effects in the film. Neglecting thermal gradients across the thickness of the film, we have been able to obtain a closed‐form perturbation solution whose first‐order solution accurately describes the temperature for many film thicknesses and pulse lengths. The second‐order solution which accounts for conduction in a direction transverse to the laser propagation direction may contribute significatnly to the total temperature profile in some cases, particularly for pulse lengths of microsecond duration and longer. The theoretical analysis may be used to estimate the threshold intensity for vaporization of various thin films deposited on dielectric substrates. Estimation of threshold intensity for thin films of bismuth on Mylar and gold on glass is presented. This predicted threshold intensity for vaporization as derived from our first‐ and second‐order solution compares favorably with limited published experimental results.

ISSN:0021-8979    

DOI:10.1063/1.1662547

出版商:AIP    

年代:1973

数据来源: AIP