$J/\psi$ gluonic dissociation revisited: I. Fugacity,flux and formation time effects

We revisit the standard treatment due to Xu et al. of suppression due to gluonic bombardment in an equilibrating quark-gluon plasma. Effects arising from gluon fugacity, relative g- flux, and meson formation time are explicitly incorporated in the formulation of the gluon number density, velocity-weighted cross section, and the survival probability. Our new formulae are applied to a numerical study of the pattern of suppression in the central rapidity region at RHIC/LHC energies. The temperature and transverse momentum dependence of our graphs have noticeable differences from those of Xu et al.Received: 27 February 2004, Revised: 3 June 2004, Published online: 6 August 2004     

Structure, stability, and quantum conductivity of small diameter silicon nanowires

Structures and energetics of various types of silicon nanowires have been investigated using both quantum and classical molecular dynamics simulations to determine the most stable forms. The tetrahedral type nanowires have been found to be the most stable and, surprisingly, the polycrystalline forms of nanowires, while having the smallest surface to bulk ratio, are found to be the least stable. We also show that the cagelike nanowires have greater thermal stability than the tetrahedral nanowires. Furthermore, their electrical conducting properties are found to be better than those of tetrahedral nanowires, suggesting useful molecular electronic applications.     

$J/\psi$ gluonic dissociation revisited: II. Hydrodynamic expansion effects

We explicitly take into account the effect of the hydrodynamic expansion profile on the gluonic break-up of the 's produced in an equilibrating parton plasma. Attention is paid to the space-time inhomogeneities as well as Lorentz frames while deriving new expressions for the gluon number density n_g, the average dissociation rate , and the survival probability of , S. A novel type of partial wave interference mechanism is found to operate in the formula of . A non-relativistic longitudinal expansion from the small length of the initial cylinder is found to push the S(p_T) graph above the no flow case considered by us earlier [9]. However, the relativistic flow corresponding to the large length of the initial cylinder pushes the curve of S(p_T) downwards at LHC but upwards at RHIC. This mutually different effect on S(p_T) may be attributed to the different initial temperatures generated at LHC and RHIC. Received: 16 March 2005, Published online: 27 September 2005 PACS: 12.38.Mh     

New fluorescent probes reveal that flippase-mediated flip-flop of phosphatidylinositol across the endoplasmic reticulum membrane does not depend on the stereochemistry of the lipid

Glycerophospholipid flip-flop across biogenic membranes such as the endoplasmic reticulum (ER) is a fundamental feature of membrane biogenesis. Flip-flop requires the activity of specific membrane proteins called flippases. These proteins have yet to be identified in biogenic membranes and the molecular basis of their action is unknown. It is generally believed that flippase-facilitated glycerophospholipid flip-flop across the ER is governed by the stereochemistry of the glycerolipid, but this important issue has not been resolved. Here we investigate whether the ER flippase stereochemically recognizes the glycerophospholipids that it transports. To address this question we selected phosphatidylinositol (PI), a biologically important molecule with chiral centres in both its myo-inositol headgroup and its glycerol-lipid tail. The flip-flop of PI across the ER has not been previously reported. We synthesized fluorescence-labeled forms of all four diastereoisomers of PI and evaluated their flipping in rat liver ER vesicles, as well as in flippase-containing proteoliposomes reconstituted from a detergent extract of ER. Our results show that the flippase is able to translocate all four PI isomers and that both glycerol isomers of PI flip-flop across the ER membrane at rates similar to that measured for fluorescence-labeled phosphatidylcholine. Our data have important implications for recent hypotheses concerning the evolution of distinct homochiral glycerophospholipid membranes during the speciation of archaea and bacteria/eukarya from a common cellular ancestor.     

Two-body B meson decays to eta and eta('): observation of B --> eta K*

In a sample of 19 x 10(6) produced B mesons, we have observed the decays B-->eta K(*) and improved our previous measurements of B-->eta'K. The branching fractions we measure for these decay modes are B(B+-->eta K(*+)) = (26.4(+9.6)(-8.2)+/-3.3)x10(-6), B(B(0)-->eta K(*0)) = (13.8(+5.5)(-4.6)+/-1.6)x10(-6), B(B(+)-->eta'K(+) = (80(+10)(-9)+/-7)x10(-6), and B(B(0)-->eta'K0) = (89(+18)(-16)+/-9)x10(-6). We have searched with comparable sensitivity for related decays and report upper limits for these branching fractions.     

Characteristic wave fronts in magnetohydrodynamics

The influence of magnetic field on the process of steepening or flattening of the characteristic wave fronts in a plane and cylindrically symmetric motion of an ideal plasma is investigated. This aspect of the problem has not been considered until now. Remarkable differences between plane, cylindrical diverging, and cylindrical converging waves are discovered. For instance, when the adiabatic index γ is 2, the magnetic field does not affect the behaviour of plane waves, but does affect cylindrical waves. As the field strength increases, the time t_c taken for the shock formation varies monotonically for plane waves, while for cylindrical waves, in some situations t_c exhibits a unique minimum for diverging waves and a unique maximum for converging waves. For cylindrical converging waves, a shock formation takes place if and only if, γ and the field strength are restricted to certain finite intervals. Moreover, t_c is bounded in all cases except for cylindrical diverging waves. The discontinuity in the velocity gradient at the wave front is shown to satisfy a Bernoulli-type equation. The discussion of the solutions of such equations reported in the literature is shown to be incomplete, and three general theorems are established.     

Radioimmunoassay for individual lactate dehydrogenase isoenzymes 1 and 2

Radioimmunoassays (RIA) for the determination of the individual lactate dehydrogenase (LDH) isoenzymes, LDH-1 and LDH-2 have been developed. LDH-1 can be measured in the range of 5–100 ng and LDH-2 in the range of 5–80 ng, if there is no significant cross reactivity. Immunization of several rabbits with LDH-1 and LDH-2 isoenzymes reveals that some animals do not produce antisera to LDH-2 while those injected with LDH-1 generated antiserum in each case. The results of the binding studies suggest that a 50% binding that is recommended for RIA can be achieved with a titer value of 12000 dilution of the antisera. Cross reactivity studies indicate that LDH-1 cross reacts with the antisera to LDH-2 if its concentration is higher than 30 ng/ml of the RIA mixture while LDH-2 cross reacts with the antisera to LDH-1 only if its concentration exceeds 80 ng/ml.     

Dispersion relations and lattice thermal expansion of dysprosium

The lattice dynamics, second and third order elastic constants and the lattice thermal expansion of dysprosium have been calculated using Keating's approach. The ten third order elastic constants are calculated using four anharmonic parameters. The present model reproduces the measured pressure derivatives of the second order elastic constants of dysprosium well. The low and high temperature limits γ?_I and γ?_H of the lattice thermal expansion are evaluated and the agreement between the calculated γ?_H and that obtained from the thermal expansion and specific heat data is satisfactory.     

Evidence for the production of new particles in cosmic ray experiments deep underground

In the cosmic ray experiments deep underground in the Kolar Gold Mines, a special class of events has been observed, at present 6 in number, characterised by several, (in general 3), charged particles arising from a vertex, either in air or in the thin material of the detectors, with large opening angles; the vertex is at a distance of around 70–100 cms from the rock wall. The most plausible interpretation of these events is that they are due to the decay of new, massive and long-lived particles produced in neutrino collisions inside rock, or through hitherto unknown processes.     

Effect of local strain on the reactivity of carbon nanotubes

The heats of addition of H atom and Me^· radical to carbon atoms of a capped (10,10)-nanotube were calculated by the molecular dynamics (MD) method with Brenner"s potential. According to calculations, the reaction heats linearly depend on the pyramidalization angle, which is a quantitative measure of the local curvature and strain in the planar carbon sheet in the vicinity of the reaction center. Depending on the pyramidalization angle (0—20°), the change in the reaction energy can reach 1 eV. Comparison of the results obtained for a model reaction CH₃ ^· + H^· CH₄ using the ab initio approach and MD simulations with Brenner"s potential shows that this potential can be used in studies of the effect of pyramidalization of the carbon center on its reactivity.