Theory of collective motion of interacting gas of polyvalent Hg atoms at 3.0, 6.3 and 9.0 particles per nm

Collective dynamics of interacting gaseous mercury at high temperatures and pressures having densities of 3.0, 2.1 and 1.0 g cm⁻³, as determined very recently by the measurement of dynamical structure factor using the inelastic X-ray scattering, have been successfully explained, making use of the recently modified microscopic theory of a simple fluid. It also turns out that in determining the collective dynamics of all the three systems of the mercury vapor, the two body interactions, as prevalent in a weakly interacting system, play a dominant role.     

Evanescent-wave-excited quasi-two-dimensional random lasing

We report on random lasing from a dye-scatterer system directly excited by evanescent modes formed over a dielectric-dielectric interface. The system is quasi-two-dimensional because of the subwavelength exponential decay of the excitation energy. Spectral narrowing by a factor of approximately 13 was obtained under diffusive scattering conditions. The peak intensity exhibited a unique dual-saturation behavior due to the localized nature of the excitation. We observed a reduction of threshold for samples with a higher dye concentration because of a larger excitation-state occupation number within the same interaction volume.     

Spin-lock MRI with amplitude- and phase-modulated adiabatic waveforms: an MR simulation study

INTRODUCTION: Image contrast between tissue types can be generated based on their T1/T2 ratio using spin-lock MRI techniques. An interesting application of such a concept would be to generate contrast in tissue with tissue relaxation times modified using exogenous contrast agents. An amplitude-modulated adiabatic waveform has been shown in the past to perform spin-lock MRI. However, implementation of this waveform may not prove to be efficient and practical in research or a clinical setup due to high radiofrequency power deposition. Recent advancement in software and hardware MR technology allows implementation of amplitude- and phase-modulated adiabatic waveforms on MR systems. The aim of this work was to explore role of adiabatic waveforms in performing rho imaging and demonstrate that amplitude- and phase-modulated waveforms [e.g., hyperbolic secant, B1 independent rotation-4 (BIR-4) waveforms] can be used to distinguish materials that differ in T1/T2 ratio. METHODS AND RESULTS: MR simulation was performed using computer routines implemented in MATLAB environment (Mathworks, Natick, MA). Modified Bloch equations with trapezoidal, hyperbolic secant and BIR-4 waveforms were used to perform MR simulation. Trapezoidal waveforms were only used for comparison to other waveforms. Gadolinium DTPA (Gad-DTPA) (T1/T2 approximately 1) and manganese chloride (MnCl(2)) (T1/T2 approximately 10) were used as examples of contrast agents due to their routine use in clinical and research setups and more importantly because they provide good examples of materials differing in T1/T2 ratios. Results of spin locking using trapezoidal waveform agree very well with the previously published results, thereby validating the computer routines used in this MR simulation. Plots of M(rho) (magnetization vector in rho domain) vs. offset frequency show distinct curves for these materials differing in T1/T2 for the three waveforms. BIR-4 waveform demonstrated a 40% difference in M(rho) ( approximately 150 Hz) for the materials. Rate of spin lock with hyperbolic secant waveform was rapid compared to other waveforms. DISCUSSION: MR simulation using contrast agents Gad-DTPA and MnCl(2) provided a useful way to demonstrate that amplitude- and phase-modulated adiabatic waveforms can be used to perform spin-lock imaging. Future work involves implementation of these waveforms on MR scanners and performing in vivo imaging to generate tissue contrast based on relaxation times ratio.     

Characterization of energy levels in the nucleus170Lu

Configuration assignments are derived for the observed energy levels in the odd-odd deformed nucleus¹⁷⁰Lu₉₉ based on the calculations of the two-particle band head energies for a zero range residual interaction, the beta-feeding characteristics, and the observed features for similar bands in the neighbouring nuclei. In particular, specific assignments are given for theJ ^π =1⁺ levels at 198.4 keV, 349.0 keV and 785.5 keV. The ambiguities with respect to the assignments for theK ^π=3⁻ bands are discussed. A new isomer withJ ^π =7⁺ and half-life of several seconds is predicted around (225±25) keV and experiments are suggested to identify it.     

Light scattering from a fluid in a nonequilibrium steady state: Plane Couette flow

We calculate the Rayleigh-Brillouin light scattering spectrum from a newtonian fluid undergoing a plane Coutte flow using the Landau-Lifshitz method of fluctuating hydrodynamics. Our results for both the Rayleigh and the Brillouin lines differ significantly from all the previous results.     

Level structures in the odd-odd nucleus180Re

Experimental data on energy levels of the odd-odd deformed nucleus¹⁸⁰Re obtained from radioactive-decay and heavy-ion reaction studies are analysed to deduce spin-parity and configuration assignments for the six observed rotational bands based on the selection rules for fast beta transitions, criteria for the relative-energy ordering of the triplet and singlet bandheads, two-particle-plus-rotor model calculations including Coriolis mixing, rotational energy systematics involving staggering features, and considerations of gyromagnetic ratios, signature splittings and rotational band alignments.     

Measurement ofL III subshell photoelectric cross-sections in highZ-elements

L _III subshell photoelectric cross-sections in lead, thorium and uranium at 13·596, 16·896 and 17·781 keV respectively have been determined. The results are found to agree well with theory.