High-frequency driven capillary flows speed up the gas-liquid phase transition in zero-gravity conditions

Under weightlessness conditions, the phase transition of fluids is driven only by slow capillary flows. We investigate the effect of high-frequency vibrations to reproduce some features of gravity effects and show that such vibrations can greatly modify the phase transition kinetics. The investigation is performed in H2 near its critical point (critical temperature 33 K) where critical slowing down enables the phase transition process to be carefully studied. Gravity effects are compensated in a strong magnetic field gradient.     

All-fiber high-sensitivity pressure sensor with SiO2 diaphragm

The design and fabrication of a miniature fiber Fabry-Perot pressure sensor with a diameter of 125 microm are presented. The essential element in the process is a thin SiO2 diaphragm that is fusion spliced at the hollow end of an optical fiber. Good repeatability and high sensitivity of the sensor are achieved by on-line tuning of the diaphragm thickness during the sensor fabrication process. Various sensor prototypes were fabricated, demonstrating pressure ranges of from 0 to 40 kPa to 0 to 1 MPa. The maximum achieved sensitivity was 1.1 rad/40 kPa at 1550 nm, and a pressure resolution of 300 Pa was demonstrated in practice. The presented design and fabrication technique offers a means of simple and low-cost disposable pressure sensor production.     

Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.     

Plume motion and large-scale circulation in a cylindrical Rayleigh-Bénard cell

We used the time correlation of shadowgraph images to determine the angle Theta of the horizontal component of the plume velocity above (below) the center of the bottom (top) plate of a cylindrical Rayleigh-Bénard cell of aspect ratio Gamma identical with D/L=1 (D is the diameter and L approximately 87 mm is the height) in the Rayleigh-number range 7 x 10(7)相似文献   

Self-organized Monte Carlo localization of critical point via linear filtering

Self-organized Monte Carlo simulations are suggested. Their essence is artificial dynamics consisting of the well-known single-spin-flip Metropolis algorithm supplemented by biased random walk in temperature space. The action of walker is driven by feedback utilizing the linear filtering recursion based on the instantaneous estimates of Binder cumulants. The simulation for 2d Ising model demonstrates that the mean temperature typical for the steady noncanonical equilibrium regime properly approximates the true critical temperature. The estimates of the critical Binder cumulants and critical exponents are also discussed.     

An enantioselective access to 1-alkyl-1,2,3,4-tetrahydroisoquinolines. Application to a new synthesis of (-)-argemonine

Potassium ferricyanide oxidation of salt 1 gave isoquinolinone 7 whose treatment with Grignard reagents resulted in a high-yield formation of substituted isoquinolinium salts 5. The selectivity of the reduction of these salts to give derivatives 6 has been studied. Particularly good selectivities (82-84%) were observed when R is a benzylic group. On the basis of these results, a practical and enantioselective synthesis of the natural alkaloid (-)-argemonine is presented.     

Modified z-gradient filtering as a mean to obtain phased deuterium autocorrelation 2D NMR spectra in oriented solvents

We describe a modified z-gradient filter scheme specifically designed to obtain pure absorption mode deuterium 2D NMR spectra recorded in oriented solvents. The proposed technique is investigated by analysing the evolution of the density operator for a spin I=1. The method is applied to the recently designed Q-COSY and Q-resolved 2D experiments to simplify the analysis of chiral molecules dissolved in weakly orienting chiral liquid crystals. The efficiency of this z-gradient filtering technique is illustrated using the perdeuterated 1-butanol, a prochiral molecule of average Cs symmetry, dissolved in an organic solution of poly-gamma-benzyl-L-glutamate (PBLG). The experimental results as well as the advantages of the new experiments compared with the previous ones are described and discussed.     

Synthesis of 4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide ring systems on sugar templates via carbanion-mediated sulfonamide intramolecular cyclization reactions (CSIC protocols) of glyco-alpha-sulfonamidonitriles

The carbanion-mediated sulfonate intramolecular cyclizations (CSIC protocols) of glyco-alpha-sulfonamidonitriles derived from readily available monosaccharides have been extensively investigated using potassium carbonate, cesium carbonate, n-BuLi, and LDA as bases. As a result, a series of enantiomerically pure spiro(4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide) derivatives have been prepared efficiently and isolated in good yield. The synthesis of these new bicyclic systems is key to accessing a novel range of aza analogues of TSAO nucleosides (ATSAOs).     

Non-Newtonian behavior in simple fluids

Using nonequilibrium molecular dynamics simulations, we study the non-Newtonian rheology of a microscopic sample of simple fluid. The calculations were performed using a configurational thermostat which unlike previous nonequilibrium molecular dynamics or nonequilibrium Brownian dynamics methods does not exert any additional constraint on the flow profile. Our findings are in agreement with experimental results on concentrated "hard sphere"-like colloidal suspensions. We observe: (i) a shear thickening regime under steady shear; (ii) a strain thickening regime under oscillatory shear at low frequencies; and (iii) shear-induced ordering under oscillatory shear at higher frequencies. These results significantly differ from previous simulation results which showed systematically a strong ordering for all frequencies. They also indicate that shear thickening can occur even in the absence of a solvent.