The Rayleigh–Brillouin spectrum of hydrogen at high densities

1978 ◽  
Vol 56 (9) ◽  
pp. 1168-1174 ◽  
Author(s):  
A. D. May ◽  
M. Hubert ◽  
V. Ghaem-Maghami
Keyword(s):  
Relaxation Time ◽  
Theoretical Calculations ◽  
Hydrodynamic Theory ◽  
Normal Hydrogen ◽  
Brillouin Spectrum

The Rayleigh–Brillouin spectrum of light scattered from hydrogen at high densities is reported. The observations are compared with translational hydrodynamic theory and ultrasonic experiments. The range of densities includes the relaxation region and we find evidence for multiple relaxation. A mean relaxation time for normal hydrogen at 24 °C of (1.41 ± 0.06) × 10−8 s is found, in agreement with theoretical calculations.

BULK NANOSTRUCTURED MATERIALS OBTAINED BY SHOCK WAVES COMPACTION OF ULTRAFINE TITANIUM AND ALUMINUM

2012 ◽  
Vol 05 ◽  
pp. 391-399
Author(s):  
NIKOLOZ M. CHIKHRADZE ◽  
CONSTANTIN POLITIS ◽  
MIKHEIL CHIKHRADZE ◽  
GEORGE ONIASHVILI
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Theoretical Calculations ◽  
Steel Tube ◽  
Hydrodynamic Theory ◽  
Full Density ◽  
Experimental Investigations ◽  
Disperse Powder ◽  
Explosive Compaction ◽  
Structural Investigations

Theoretical and experimental Investigations of shock wave consolidation processes of Ti - Al nano sized and ultra-disperse powder compositions are discussed. For theoretical calculations of the shock wave loaded materials were used the hydrodynamic theory and experimental adiabatic of Ti and Al . The normal and tangential stresses in the cylindrical steel tube (containers of Ti - Al reaction mixtures) were estimated using the partial solutions of elasticity theory. The mixtures of ultra-disperse Ti and nano sized (≤ 50nm) Al powder compositions were consolidated to full or near-full density by explosive-compaction technology. The ammonium nitride based industrial explosives were used for generation of shock waves. To form ultra-fine grained bulk TiAl intermetallics with different compositions, ultra-disperse Ti particles were mixed with nano-crystalline Al . Each reaction mixture was placed in a sealed container and explosively compacted using a normal and cylindrical detonation set-up. Explosive compaction experiments were performed in range of pressure impulse (5-20) GPa. X-ray diffraction (XRD), structural investigations (SEM) and micro-hardness measurements were used to characterize the intermetallics phase composition and mechanical properties. The results of analysis revealing the effects of the compacting conditions and precursor particles sizes, affecting the consolidation and the properties of this new ultra high performance alloys are discussed.

The Rayleigh–Brillouin spectrum of compressed H2; a test of translational hydrodynamics

1977 ◽  
Vol 55 (1) ◽  
pp. 23-26 ◽  
Author(s):  
M. Hubert ◽  
A. D. May
Keyword(s):  
Reasonable Agreement ◽  
Hydrodynamic Theory ◽  
Rotational States ◽  
Energy And Momentum ◽  
Brillouin Spectrum

This paper reports on a comparison between the observed Rayleigh–Brillouin spectra of compressed hydrogen and those computed according to the translational hydrodynamic theory of Desai and Kapral. Reasonable agreement is found in the range of densities from 19 to 61 amagat units. It is suggested that small residual discrepancies may be due to the neglect of part of the coupling between the energy and momentum fluctuations arising from relaxation of the rotational states, i.e. due to the neglect of the 1ν1 terms.

POPULATION RELAXATION TIME OF OPTICAL PHONONS IN GaAs-AlAs MULTIPLE QUANTUM WELL STRUCTURES

1993 ◽  
Vol 07 (13n14) ◽  
pp. 887-893 ◽  
Author(s):  
K.T. TSEN ◽  
C. CHIA ◽  
J. WEST ◽  
H. MORKOC
Keyword(s):  
Relaxation Time ◽  
Quantum Well ◽  
Theoretical Calculations ◽  
Multiple Quantum Well ◽  
Relaxation Times ◽  
Experimental Results ◽  
Multiple Quantum ◽  
Optical Phonons ◽  
Quantum Well Structures ◽  
Population Relaxation

Population relaxation time of confined as well as interface optical phonons in a series of GaAs-AlAs multiple quantum well structures has been measured by picosecond time-resolved Raman spectroscopy. Our experimental results have shown that (1) within the experimental accuracy, the population relaxation time of confined optical phonons in GaAs-AlAs multiple quantum well structures is independent of GaAs well-width and is given by 6±1 ps at T=10 K; (2) the population relaxation times of both GaAs -like and AlAs -like interface optical phonons increase as GaAs well-width increases from 20 Å to 100 Å. These experimental results are compared with theoretical calculations recently carried out by Gupta and Ridley (Ref. 3).

An Analysis of Stress Relaxation in Elastico-Viscous Fluid Lubrication of Journal Bearings

1978 ◽  
Vol 100 (2) ◽  
pp. 287-294 ◽  
Author(s):  
A. Harnoy
Keyword(s):  
Relaxation Time ◽  
Stress Relaxation ◽  
Load Capacity ◽  
Experimental Studies ◽  
Relaxation Effect ◽  
Journal Bearings ◽  
Friction Torque ◽  
Hydrodynamic Theory ◽  
Lubrication Film ◽  
Bearing Load

The hydrodynamic theory of lubrication in journal bearings is extended to elastico-viscous lubricants. The stress relaxation effect upon flow, pressure distribution, friction, and bearing load capacity is considered. This analysis deals with the case of a small relaxation time compared with the transit time required for the lubricant to pass through the bearing. A lubricant model is assumed with a constant relaxation time and without any cross stresses. It is found that the bearing load capacity of an elastic liquid lubrication film is higher than that of a Newtonian one, while the friction torque remains unchanged. Existing experimental studies have shown considerable improvement in journal bearing performance with elastico-viscous lubricants. This analysis suggests stress relaxation to be one of the factors giving rise to this improvement.

Magnetic and Quadrupole Relaxation in Aqueous BeF2-Solutions

1980 ◽  
Vol 35 (4) ◽  
pp. 447-452
Author(s):  
H. Jena ◽  
W. Kreische ◽  
H. U. Maar ◽  
H. Niedrig ◽  
K. Reuter ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Ground State ◽  
Magnetic Relaxation ◽  
Theoretical Calculations ◽  
Excited Level ◽  
Quadrupole Relaxation ◽  
Distribution Method ◽  
Wide Range ◽  
Time Differential ◽  
State Spin

Abstract In aqueous BeF2-solutions of different concentrations and therefore different viscosities the magnetic relaxation time T1 was measured as a function of the viscosity over a wide range by pulsed NMR-technique. For small viscosities a linear dependence of T1 on the viscosity was observed as predicted by theoretical calculations. Since the ground state spin of 19F is I = 1/2, the quadrupole moment vanishes. For observing quadrupole relaxation of the F-nuclei, one has to use an excited level. With the time differential perturbed angular distribution method (TDPAD) we observed the quadrupole relaxation time TRel of 19F in aqueous BeF2-solutions.

Rayleigh–Brillouin Scattering in Compressed H2, D2, and HD. II

1972 ◽  
Vol 50 (12) ◽  
pp. 1227-1229 ◽  
Author(s):  
E. H. Hara ◽  
A. D. May
Keyword(s):  
Thermal Conduction ◽  
Brillouin Scattering ◽  
Hydrodynamic Theory ◽  
Brillouin Spectrum

The observations presented by Hara et al. for the Brillouin spectrum of H2, D2, and HD are compared with the thermo-hydrodynamic theory of Bhatia and Tong. It is noted that although this theory is qualitatively correct it fails to describe accurately the spectrum at low to medium densities. It is suggested that the introduction of a relaxing thermal conduction might account for the discrepancy observed.

The Rayleigh – Brillouin Spectrum of Normal and Parahydrogen: A Test of Model Solutions of the Wang–Chang Uhlenbeck Equation

1975 ◽  
Vol 53 (4) ◽  
pp. 343-350 ◽  
Author(s):  
M. Hubert ◽  
A. D. May
Keyword(s):  
Relaxation Time ◽  
High Resolution ◽  
Degrees Of Freedom ◽  
Room Temperature ◽  
Good Description ◽  
Molecular Gas ◽  
Model Calculations ◽  
Single Relaxation Time ◽  
Brillouin Spectrum ◽  
Internal Degrees Of Freedom

This paper reports the observation at high resolution of the Rayleigh–Brillouin spectrum of normal and parahydrogen at room temperature. The spectra are compared with a number of kinetic model calculations based on the Wang–Chang Uhlenbeck equation. It is concluded that n-H2 behaves effectively as a system characterized by a single relaxation time for the internal degrees of freedom and that the S6 model of Tenti et al. gives a very good description of the Rayleigh–Brillouin spectrum of a molecular gas at low and medium densities. At higher densities the models fail because the Wang–Chang Uhlenbeck equation is no longer valid.

XUV Absorption Spectra of Carbon Ions

1988 ◽  
Vol 102 ◽  
pp. 71-73
Author(s):  
E. Jannitti ◽  
P. Nicolosi ◽  
G. Tondello
Keyword(s):  
Absorption Spectra ◽  
Cross Section ◽  
Theoretical Calculations ◽  
Photoionization Cross Section ◽  
Carbon Ions

AbstractThe photoabsorption spectra of the carbon ions have been obtained by using two laser-produced plasmas. The photoionization cross-section of the CV has been absolutely measured and the value at threshold, σ=(4.7±0.5) × 10−19cm2, as well as its behaviour at higher energies agrees quite well with the theoretical calculations.

Relative Intensities in ED Patterns From Thin Gold Films

1972 ◽  
Vol 30 ◽  
pp. 636-637
Author(s):  
R. H. Morriss ◽  
J. D. C. Peng ◽  
C. D. Melvin
Keyword(s):  
Theoretical Calculations ◽  
Diffraction Theory ◽  
Gold Films ◽  
Reasonable Accuracy ◽  
Experimental Conditions ◽  
Crystal Perfection ◽  
Heavy Atoms ◽  
Fine Focus ◽  
Convergent Beam ◽  
Beam Diffraction

Although dynamical diffraction theory was modified for electrons by Bethe in 1928, relatively few calculations have been carried out because of computational difficulties. Even fewer attempts have been made to correlate experimental data with theoretical calculations. The experimental conditions are indeed stringent - not only is a knowledge of crystal perfection, morphology, and orientation necessary, but other factors such as specimen contamination are important and must be carefully controlled. The experimental method of fine-focus convergent-beam electron diffraction has been successfully applied by Goodman and Lehmpfuhl to single crystals of MgO containing light atoms and more recently by Lynch to single crystalline (111) gold films which contain heavy atoms. In both experiments intensity distributions were calculated using the multislice method of n-beam diffraction theory. In order to obtain reasonable accuracy Lynch found it necessary to include 139 beams in the calculations for gold with all but 43 corresponding to beams out of the [111] zone.

Sign in / Sign up

Export Citation Format

Share Document