Thermal and acoustic effects in optical phase conjugation in Rhodamine 6G solutions with nanosecond pulses

Thermally induced phase conjugation by degenerate four-wave mixing in solutions of Rhodamine 6G in ethanol in the weak absorption region, low-reflectivity regime, and nonosecond time domain is reported. Evidence of oscillatory acoustic modes in the nonlinear medium is presented and existing theories are shown to explain satisfactorily the experimental results.     

X-ray diffraction study of 'side-on fixed' homopolysiloxanes from nematic to smectic C phases

The X-ray patterns for the nematic phase in a series of side-on fixed polysiloxanes show different kinds of diffuse elements which imply complex short range ordering. A systematic structural study of the evolution of the patterns versus two molecular parameters, namely the spacer length and the length of the terminal aliphatic tails, suggests the possible occurrence of a smectic C phase for certain values of these parameters. Taking into account these tendencies, new synthesis led to a nematic-smectic C polymorphism observed for the first time in side-on fixed polysiloxanes.     

Reaction field model with free volume for the NMR chemical shift of129Xe dissolved in organic solvents

The temperature dependence of the NMR chemical shift of¹²⁹Xe dissolved in liquid alkanes is examined in the context of the reaction field model. An essential feature of the theory is the inclusion of the temperature dependence of the density of thesolvent. The theory of free volume for liquids is incorporated into the reaction field model to account for this temperature dependence. Comparison of the theory with previously reported measurements indicates the sensitivity of the¹²⁹Xe chemical shift to the free volume of liquids. Incorporation of free volume improves the agreement between measurement and theory for branched alkane solvents, and resolves the origin of the 62 ppm intercept in the plot of reaction field as a function of¹²⁹Xe chemical shift for the n-alkanes.     

Monte Carlo simulations in the vicinity of the critical point: Vapour-liquid coexistence curve

A generalized Gibbs-ensemble methodology with a fluctuating particle is used to determine the coexistence vapor-liquid densities for a square-well fluid. It is shown that the presence of the fluctuating particle in sub-states of the Markov chain of states supresses considerably density fluctuations which makes it possible to carry out simulations efficiently even for temperatures very close to the critical temperature.     

Monte-Carlo calculations of cloud returns for ground-based and space-based LIDARS

A Monte-Carlo model is described which has been developed for calculation of multiply scattered LIDAR returns. Results are shown for the common problem selected by the MUSCLE (MUltiple SCattering LIDAR Experiments) group for intercomparison, which represents a typical ground-based cloud-sensing scenario. This is contrasted with returns from the same cloud sensed by a space-based LIDAR, where multiple-scattering effects are much greater. The magnitude of multiple-scattering effects is seen to be largely determined by the optical depth across the receiver field of view at the cloud.     

Hyperbolic stefan problem in a curvilinear sector

The problem with unknown boundaries for a first-order semilinear hyperbolic system is studied in the case where the curve of definition of the initial conditions degenerates to a point. An existence and uniqueness theorem for a classical solution of the problem is proved for small t.     

Synthesis of a new class of uridine phosphorylase inhibitors

A new series of potent uridine phosphorylase inhibitors have been prepared from barbituric acid. Among them, 1-[(2-hydroxyethoxy)methyl]-5-)(m--benzyloxy)benzylbarbituric acid ( 37 , BBBA) is the most promising having a K_i value of 1.1 ± 0.2 nM with uridine phosphorylase from human liver. The new inhibitors are easily synthesized and are better inhibitors of human uridine phosphorylase than their uracil counterparts.     

Turbulence modelling of the shear layers in the trailing edge region of a modern rear-loaded airfoil at incidence

After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results.