摘要:

Results of two‐dimensional calculations on the detonation of slabs of high explosive of finite dimensions are presented graphically. The effect of the side rarefactions from the free surfaces are shown and two methods of amelioration of these effects are demonstrated. In particular it is shown that the inclusion of metal fences suitably angled to the direction of detonation produces a large reduction in the side effects.

ISSN:0021-8979    

DOI:10.1063/1.1659580

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The concept of the thermal diffusivity as a characteristic constant of a heterogeneous material is examined. By considering the derivation of the heat conduction equation, and the concept of the thermal wavelength associated with a particular problem, a general criterion for the homogeneity of a material under transient conditions is obtained. This criterion limits the scale of heterogeneity of the material (expressed as a lattice spacing) to be much smaller than the minimum thermal wavelength associated with the problem. The flash method of measuring the thermal diffusivity is considered in detail. The criterion developed limits the particle size of a particulate phase to be much smaller than the sample thickness for the sample to be considered homogeneous, and for the usual relation between the thermal diffusivity and thermal conductivity to hold.

ISSN:0021-8979    

DOI:10.1063/1.1659581

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements of the heat capacity, thermal expansion, and thermal conductivity on synthetic crystals of undoped and neodymium‐doped fluorapatite are reported. Fitting the low‐temperature specific heat data to a Debye model yields a Debye temperature of 550°K. At 25°C the thermal expansion coefficients are 10.0×10−6°K−1and 9.4×10−6°K−1, respectively, along the [0001] and [101¯0] directions. The thermal‐expansion measurements yield a Debye temperature of 500°K. A typical value of the thermal conductivity is 0.020 W cm−1°K−1at room temperature. The thermal conductivity is only feebly temperature dependent and, similar to the thermal‐expansion coefficient, shows very little crystallographic anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.1659583

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The dynamic yield strengths for several ceramics were measured under shock‐wave compression. The Hugoniot elastic limit (HEL), taken as the amplitude of the observed elastic precursor traveling ahead of the compressional wave, was 154 and 82 kbar for B4C and BeO ceramics, respectively, and ranged from 61 to 134 kbar for several Al2O3ceramics. These values apply to 6‐mm‐thick samples; in some cases there were variations with sample thickness. The offset of the Hugoniot from the isotropic compression curve in the stress‐volume plane indicates a nonzero yield strength above the HEL for Al2O3. This yield strength is somewhat less than the yield strength at the HEL. The compaction of porous ceramics is found to follow a quadratic variation with stress, full compaction being reached at about four times the HEL.

ISSN:0021-8979    

DOI:10.1063/1.1659584

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Complex variable methods are used to make a further exploration of the consequences of a quadratic fit to shock wave data in the velocity plane on the form of the Hugoniot. When complex pressures and compressions are introduced, the Hugoniot has three branch points. One of them is a critical point of multiplicity two and defines the separation between two branches of the Hugoniot. The other two are complex conjugates and their positions depend on a parameter involving the three coefficients of the quadratic fit. Reduced Hugoniots are defined for each material introducing reduced coordinates referred to the pressure and relative compression at the critical point; the form of these curves depends only on the parameter that determines the positions of the conjugate branch points. It is suggested that this parameter might probably be interpreted as a new property of all materials in solid and liquid phases. Polyurethane, cesium, water, and corundum are used as examples to show the agreement with experimental data. Some experiments are needed to test the validity of results at pressures higher than those available in the literature.

ISSN:0021-8979    

DOI:10.1063/1.1659585

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Stimulated emission at 1.663 &mgr; due to a4S3/2→4I9/2transition has been observed from Er3+ions in a crystal of YAlO3. The threshold for pulsed laser action at room temperature was 52 J. Crystalline Stark levels determined from absorption and fluorescence spectra and fluorescence lifetimes of YAlO3:Er3+are reported.

ISSN:0021-8979    

DOI:10.1063/1.1659588

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A CO2laser heterodyne system was successfully used to measure plasma density‐length product (DLP) in the 1013–1014‐cm−2range, with &mgr;sec response. This was done in the extremely adverse environment of the Astron‐controlled fusion experimental area at the Lawrence Radiation Laboratory, Livermore. The results indicate that the system is capable of covering a plasma DLP range of 1012–1016cm−2with 20‐nsec response.

ISSN:0021-8979    

DOI:10.1063/1.1659589

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Nonuniform excitation of tandem‐bisected GaAs lasers produces light pulses whose width is not resolved by presently available photodiodes. We have used an intensity correlation technique involving phase matched second harmonic generation in LiIO3to investigate the output of such a laser. From this measurement we inferred a pulse width of 100 psec.

ISSN:0021-8979    

DOI:10.1063/1.1659590

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The focused output of a ruby laser has been used to drive waves which travel in the same direction as the laser beam. The density gradient produced by expanding high‐pressure air or hydrogen into a vacuum was irradiated by the laser from the vacuum side of the jet. A luminous plasma was observed to propagate up the jet, through the orifice, and into the gas reservoir. Observations of this type have application to the study of comparable waves generated at the surface of a solid. Measurements of the luminous front velocity are reported over the gas density range of 1–7 amagats and laser power range of 100–500 MW. The scaling relations for this front velocity with laser intensity and gas density are derived for many of the interaction models proposed in the literature. Only the gasdynamic model with fluid motions induced during laser heating compares favorably with the data.

ISSN:0021-8979    

DOI:10.1063/1.1659591

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A novel experimental method employing multilayer targets has been developed permitting a more detailed study of laser‐produced plasmas through analysis of the spectrum emitted by a given layer as a function of its location. This method allows us to study the progression of the interaction phenomena into the interior of the target and to examine the plasma expansion phase. It could thus be demonstrated that the plasma produced at different depths within the target has essentially the same characteristic parameters and that the hot plasma region is delimited by very sharp gradients towards the interior of the target. In the expansion phase the importance of recombination phenomena has been well established up to certain limits beyond which our observations are compatible with the notion of freezing of the degree of ionization at closed‐shell electron configurations in carbon and aluminum plasmas. A comparison of our experimental results with simple theoretical models is included.

ISSN:0021-8979    

DOI:10.1063/1.1659592

出版商:AIP    

年代:1971

数据来源: AIP