Statistics of first-passage times in disordered systems using backward master equations and their exact renormalization rules

We consider the non-equilibrium dynamics of disordered systems as defined by a master equation involving transition rates between configurations (detailed balance is not assumed). To compute the important dynamical time scales in finite-size systems without simulating the actual time evolution which can be extremely slow, we propose to focus on first-passage times that satisfy 'backward master equations'. Upon the iterative elimination of configurations, we obtain the exact renormalization rules that can be followed numerically. To test this approach, we study the statistics of some first-passage times for two disordered models : (i) for the random walk in a two-dimensional self-affine random potential of Hurst exponent $H$, we focus on the first exit time from a square of size $L \times L$ if one starts at the square center. (ii) for the dynamics of the ferromagnetic Sherrington-Kirkpatrick model of $N$ spins, we consider the first passage time $t_f$ to zero-magnetization when starting from a fully magnetized configuration. Besides the expected linear growth of the averaged barrier $\bar{\ln t_{f}} \sim N$, we find that the rescaled distribution of the barrier $(\ln t_{f})$ decays as $e^{- u^{\eta}}$ for large $u$ with a tail exponent of order $\eta \simeq 1.72$. This value can be simply interpreted in terms of rare events if the sample-to-sample fluctuation exponent for the barrier is $\psi_{width}=1/3$.Comment: 8 pages, 4 figure

Superconducting Magnetization above the Irreversibility Line in Tl2Ba2CuO6

Piezolever torque magnetometry has been used to measure the magnetization of superconducting Tl2Ba2CuO6. Three crystals with different levels of oxygen overdoping were investigated in magnetic fields up to 10 Tesla. In all cases, the magnetization above the irreversibility line was found to depart from the behaviour M ~ ln(Hc2/H) of a simple London-like vortex liquid. In particular, for a strongly overdoped (Tc = 15K) crystal, the remnant superconducting order above the irreversibility line is characterized by a linear diamagnetic response (M ~ H) that persists well above Tc and also up to the highest field employed.Comment: RevTeX, 11 pages, 7 encapsulated PostScript figures, submitted to Physical Review

The feasibility of integrating alcohol risk-reduction counseling into existing VCT services in Kenya

This pretest-posttest separate-sample study with intervention and comparison groups documented the abilities and willingness of trained voluntary counseling and testing (VCT) service providers to integrate alcohol screening and risk reduction counseling into their routine service delivery. Pre-test (n=1073) and post-test data (n=1058) were collected from different clients exiting from 25 VCT centers. A 12-month intervention that required all VCT providers from the intervention groups to screen all VCT clients for their alcohol use and offer them brief risk reduction alcoholrelated counseling was implemented. At post-test, the intervention group clients (n=456) had better study outcomes than the comparison group clients (n=602). Intervention clients were more likely to report that their VCT service provider had: asked them about their alcohol use (83% vs. 41%:

Summary: Working Group on QCD and Strong Interactions

In this summary of the considerations of the QCD working group at Snowmass 2001, the roles of quantum chromodynamics in the Standard Model and in the search for new physics are reviewed, with empahsis on frontier areas in the field. We discuss the importance of, and prospects for, precision QCD in perturbative and lattice calculations. We describe new ideas in the analysis of parton distribution functions and jet structure, and review progress in small-$x$ and in polarization.Comment: Snowmass 2001. Revtex4, 34 pages, 4 figures, revised to include additional references on jets and lattice QC

Improving nitrogen use efficiency through overexpression of alanine aminotransferase in rice, wheat, and barley

Nitrogen is an essential nutrient for plants, but crop plants are inefficient in the acquisition and utilization of applied nitrogen. This often results in producers over applying nitrogen fertilizers, which can negatively impact the environment. The development of crop plants with more efficient nitrogen usage is, therefore, an important research goal in achieving greater agricultural sustainability. We utilized genetically modified rice lines overexpressing a barley alanine aminotransferase (HvAlaAT) to help characterize pathways which lead to more efficient use of nitrogen. Under the control of a stress-inducible promoter OsAnt1, OsAnt1:HvAlaAT lines have increased above-ground biomass with little change to both nitrate and ammonium uptake rates. Based on metabolic profiles, carbon metabolites, particularly those involved in glycolysis and the tricarboxylic acid (TCA) cycle, were significantly altered in roots of OsAnt1:HvAlaAT lines, suggesting higher metabolic turnover. Moreover, transcriptomic data revealed that genes involved in glycolysis and TCA cycle were upregulated. These observations suggest that higher activity of these two processes could result in higher energy production, driving higher nitrogen assimilation, consequently increasing biomass production. Other potential mechanisms contributing to a nitrogen-use efficient phenotype include involvements of phytohormonal responses and an alteration in secondary metabolism. We also conducted basic growth studies to evaluate the effect of the OsAnt1:HvAlaAT transgene in barley and wheat, which the transgenic crop plants increased seed production under controlled environmental conditions. This study provides comprehensive profiling of genetic and metabolic responses to the over-expression of AlaAT and unravels several components and pathways which contribute to its nitrogen-use efficient phenotype

Bacterial expression and secretion of various single-chain Fv genes encoding proteins specific for a Salmonella serotype B O-antigen.

Active single-chain Fv molecules encoded by synthetic genes have been expressed and secreted to the periplasm of Escherichia coli using the ompA secretory signal. Four different constructs were developed to investigate the effects of peptide linker design and VL-VH orientation on expression, secretion, and binding to a Salmonella O-polysaccharide antigen. Peptide linker sequences derived from the elbow regions of the Fab molecule were used alone or in combination with the flexible (GGGGS)2 sequence. VL and VH domain order in the single chain molecules had a profound effect on the level of secretion but hardly influenced total expression levels, which were approximately 50 mg/liter, chiefly in the form of inclusion bodies. With VL in the NH2-terminal position, the amount of secreted product obtained was 2.4 mg/liter, but when VH occupied this position the yield was less than 5% of this value. Enzyme immunoassays of the four products showed domain order and linker sequence affected antigen binding by less than an order of magnitude. Attempts to express active Fv from dicistronic DNA were unsuccessful, but active Fv was obtained from single-chain Fv by enzymic cleavage at a site in the elbow linker peptide. The thermodynamic binding parameters of intact and cleaved single-chain Fvs determined by titration microcalorimetry were similar to those of bacterially produced Fab and mouse IgG

B and D Meson Decay Constants in Lattice QCD

We have calculated the decay constants of B and $D$ mesons with lattice QCD. We use an $O(a)$ improved action that takes light quark actions as a starting point, tuned so that it can be directly applied at the physical masses of the $b$ and $c$ quarks. Our results are f_B = 164 \err{+14}{-11} \pm 8 MeV, f_{B_s} = 185 \err{+13}{-8} \pm 9 MeV, f_D = 194 \err{+14}{-10} \pm 10 MeV, and f_{D_s} = 213 \err{+14}{-11} \pm 11 MeV in the quenched approximation. The first error in each case is statistical, and the second is from perturbation theory. We show that discretization errors are under control in our approach, and smaller than our statistical errors. The effects of the quenched approximation may raise our quenched result by up to 10%.Comment: 21 pages, 6 figure

Hidden Non-Abelian Gauge Symmetries in Doped Planar Antiferromagnets

We investigate the possibility of hidden non-Abelian Local Phase symmetries in large-U doped planar Hubbard antiferromagnets, believed to simulate the physics of two-dimensional (magnetic) superconductors. We present a spin-charge separation ansatz, appropriate to incorporate holon spin flip, which allows for such a hidden local gauge symmetry to emerge in the effective action. The group is of the form $SU(2)\otimes U_S(1) \otimes U_E(1)$, where SU(2) is a local non-Abelian group associated with the spin degrees of freedom, U_E(1) is that of ordinary electromagnetism, associated with the electric charge of the holes, and U_S(1) is a `statistical' Abelian gauge group pertaining to the fractional statistics of holes on the spatial plane. In a certain regime of the parameters of the model, namely strong U_S(1) and weak SU(2), there is the possibility of dynamical formation of a holon condensate. This leads to a dynamical breaking of $SU(2) \to U(1)$. The resulting Abelian effective theory is closely related to an earlier model proposed as the continuum limit of large-spin planar doped antiferromagnets, which lead to an unconventional scenario for two-dimensional parity-invariant superconductivity.Comment: 32 pages LATEX, one figure. (More details given in the passage from the Hubbard model to the long wavelength lattice gauge theory; one figure added; no changes in the conclusions.