摘要:

Using simultaneous measurements of current, voltage, and radius, the resistance of the restrike channels of thin exploding wires can be determined with good accuracy. Restrikes developing at the exterior or in the interior of exploding thin constantan and copper wires were examined. The wire length was 13 cm for constantan and 13.8 cm for copper, the wire diameter was 0.005 cm and the applied voltage was 1–23 kV. The results show that restrikes developing at the exterior of the wire have higher resistances than the restrikes developing in the interior. The values of the restrike resistance were compared with the relations of Toepler and Rompe and Weizel. The latter relation seems to be better suited for the description of the restrike resistance of thin exploding wires. The conductivity of the restrikes increases with increasing applied voltage and at high voltages the conductivity reaches values of 3×104(&OHgr; m)−1. The conductivity seems to reach its maximum on the ledge observed on the voltage oscillograms and to fall afterwards.

ISSN:0021-8979    

DOI:10.1063/1.1657284

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Experiments were carried out in which cavitating bubbles were produced by impact and by fast‐travelling rods, and filmed by high speed photography. The experiments showed that cavitation is a necessary but not a sufficient condition for dynamic nucleation of the ice phase in the liquid. A temperature dependence was confirmed from nucleation threshold measurements. No attempt was made to confirm or disprove the various mechanisms proposed in the literature to explain freezing induced by cavitation.

ISSN:0021-8979    

DOI:10.1063/1.1657285

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A kinetic model for the four level iodine laser is presented which includes pumping, radiative, and collisional transfer between levels. Numerical results obtained are shown to be in good agreement with available experimental data. The model correctly predicts the influence of pressure level and flash lamp parameters on the laser output and the occurrence of spiked pulses.

ISSN:0021-8979    

DOI:10.1063/1.1657286

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The speed of response of a 6328‐Å helium‐neon laser interferometer has been investigated under various conditions of operation. The laser oscillated in a small number of modes (all TEM00). At low output levels, the bandwidth of the interferometer was proportional to the output power, and except very close to threshold was not unduly affected by variation of the output spectrum. For values of the excitation parameter &eegr; (the ratio of unsaturated line‐center gain‐to‐loss) between 1.0 and 1.25, the bandwidthf0was approximatelyf0≃[(&eegr;−1)/1.7&eegr;](J/2&pgr;),whereJis the fraction of the radiation energy lost per second from the cavity. The observations are interpreted in terms of loss modulation, taking into account the coupling between the intensities in the various modes of oscillation. The results obtained are equally applicable to other examples of loss modulation.

ISSN:0021-8979    

DOI:10.1063/1.1657287

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that high power,Q‐spoiled lasers offer an interesting method for obtaining clean surfaces in vacuum. However, complete removal of oxygen and sulfur contamination from nickel surfaces by laser bombardment at 100 MW/cm2produced irreparable surface damage that is attributed to filamentizing of the laser beam and/or to nonuniform surface reflectivity. On the other hand, application of the technique at 30 MW/cm2successfully removed the (7×7) satellite structure from (111) silicon surfaces without surface damage.

ISSN:0021-8979    

DOI:10.1063/1.1657288

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Formulas are developed for the two‐dimensional magnetic field (and its derivatives of all orders) produced by a long straight conductor of uniform current density. These formulas are independent of whether the field point lies inside or outside the conductor and avoid ambiguities due to multiple values of the complex logarithm. Evaluation of the formulas can be done numerically, with the arbitrary conductor boundary approximated by a polygon, or graphically, or mechanically.

ISSN:0021-8979    

DOI:10.1063/1.1657289

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Torque measurements have been made on single‐crystal dysprosium. The constant K1was determined in the paramagnetic region, and also in the antiferromagnetic region, where the transition to ferromagnetism appeared as a large distortion in the torque curves. From the data in the paramagnetic region the saturation value of K1is predicted as 1.1×108ergs g−1. The constant K4was determined in the ferromagnetic region, and changes in sign were observed at field strengths close to the critical value. The changes in easy direction for magnetization are compared with the behavior of the magnetostriction of dysprosium.

ISSN:0021-8979    

DOI:10.1063/1.1657290

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Nickel ferrites with scaled average grain sizes and lognormal size distributions were prepared by hot‐pressing and subsequent annealing and by conventional firing. Average grain sizes ranged from less than 1 to 10 &mgr;. The dielectric loss, saturation magnetization, bulk density, and linewidth measurements confirmed that almost all samples were good nickel ferrites. Lognormal distributions allow with easy calculations to evaluate for each sample the fraction of grains having diameters below certain values that are critical for the loss mechanism. Orthogonal and parallel pump measurements of threshold fields atXband showed a very regular behavior with average grain sizes: ∥hcritvaried from 80 Oe for 0.9‐&mgr; sample to 8 Oe for a 10‐&mgr; sample with a dependence of the typehcrit≈x¯−2forx¯<2 &mgr;,hcrit≈x¯−0.5forx¯>2 &mgr;. An analysis of the distribution of grains shows that ∥hcritincreases steeply for samples having about 80% or more of the number of grains with sizes less than 3 &mgr;. Regular behaviors of the imaginary part of the permeability (atHdc≈4&pgr;Ms/3) with average sizes are found at 9.23, 12.12, and 19.75 GHz: losses increase with decreasing grain sizes but not as much as threshold fields, with a dependence of the type &mgr;″min≈x¯−0.5. The high‐power figure of meritF*, measured on spheres atXband, increases with decreasing grain size from 0.07 to 0.26, thus encouraging the fine grain approach for microwave device applications.

ISSN:0021-8979    

DOI:10.1063/1.1657291

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Internal friction measurements were carried out on germanium specimens with either edge or screw dislocations. The Kessler peak and logarithmic trend were checked with the edge character specimens. The screw character specimens showed two new peaks and another logarithmic stage, all characterized by low activation energies. A logarithmic dependence of the peak temperature on the dislocation density was also observed. Under certain conditions, regarding the kink distance dependence on dislocation density and on pinning lengths, the results concerning the screw dislocations may be interpreted in terms of smooth kink‐free motion while the edge dislocation phenomena can be explained on the basis of damping mechanisms depending on interactions between either kinks and dragging points or point defects and dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1657292

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Three linear combinations of the six adiabatic third‐order elastic constants in cubic crystals can be determined by use of the ultrasonic second‐harmonic generation technique. The combinations which are obtained are designatedK3[100],K3[110], andK3[111]. In the work reported here, room‐temperature values of theK3's have been measured for strontium titanate single crystals. The reported values are (in units of 1012dyn/cm2):K3[100]=C111=−49.6±4.3K3[110]=14(C111+3C112+12C166=−27.3±3.2K3[111]=19(C111+6C112+12C144+24C166+2C123+16C456=−27.9±2.6.The data have been compared with the theoretical values ofK3for the alkali halide crystals, and it has been observed that the ratio of |C111|/C11for strontium titanate agrees with the corresponding ratio for many of the NaCl type crystals. In order to estimate the six third‐order elastic constants of strontium titanate, it has been assumed that the Cauchy relations extended to third‐order elastic constants hold.

ISSN:0021-8979    

DOI:10.1063/1.1657293

出版商:AIP    

年代:1969

数据来源: AIP