Ab Initio Study of Hybrid b-bar-gb Mesons

Hybrid b-bar-gb molecules in which the heavy b-bar-b pair is bound together by the excited gluon field g are studied using the Born-Oppenheimer expansion and numerical simulations. The consistency of results from the two approaches reveals a simple and compelling physical picture for heavy hybrid states.Comment: 4 pages, 3 figures, uses REVTeX and epsf, final published versio

One-Loop Self Energy and Renormalization of the Speed of Light for some Anisotropic Improved Quark Actions

One-loop corrections to the fermion rest mass M_1, wave function renormalization Z_2 and speed of light renormalization C_0 are presented for lattice actions that combine improved glue with clover or D234 quark actions and keep the temporal and spatial lattice spacings, a_t and a_s, distinct. We explore a range of values for the anisotropy parameter \chi = a_s/a_t and treat both massive and massless fermions.Comment: 45 LaTeX pages with 4 postscript figure

Unquenched Charmonium with NRQCD - Lattice 2000

We present results from a series of NRQCD simulations of the charmonium system, both in the quenched approximation and with n_f = 2 dynamical quarks. The spectra show evidence for quenching effects of ~10% in the S- and P-hyperfine splittings. We compare this with other systematic effects. Improving the NRQCD evolution equation altered the S-hyperfine by as much as 20 MeV, and we estimate radiative corrections may be as large as 40%.Comment: Lattice 2000 (Heavy Quark Physics

Impact of catalyst layer morphology on the operation of high temperature PEM fuel cells

Electrochemical impedance spectroscopy (EIS) is a well-established method to analyze a polymer electrolyte membrane fuel cell (PEMFC). However, without further data processing, the impedance spectrum yields only qualitative insight into the mechanism and individual contribution of transport, kinetics, and ohmic losses to the overall fuel cell limitations. The distribution of relaxation times (DRT) method allows quantifying each of these polarization losses and evaluates their contribution to a given electrocatalyst\u27s depreciated performances. We coupled this method with a detailed morphology study to investigate the impact of the 3D-structure on the processes occurring inside a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). We tested a platinum catalyst (Pt/C), a platinum-cobalt alloy catalyst (Pt$_{3}$Co/C), and a platinum group metal-free iron-nitrogen-carbon (Fe–N–C) catalyst. We found that the hampered mass transport in the latter is mainly responsible for its low performance in the MEA (along with its decreased intrinsic performances for the ORR reaction). The better performance of the alloy catalyst can be explained by both improved mass transport and a lower ORR resistance. Furthermore, single-cell tests show that the catalyst layer morphology influences the distribution of phosphoric acid during conditioning

Charmonium Spectrum from Quenched Anisotropic Lattice QCD

We present a detailed study of the charmonium spectrum using anisotropic lattice QCD. We first derive a tree-level improved clover quark action on the anisotropic lattice for arbitrary quark mass. The heavy quark mass dependences of the improvement coefficients, i.e. the ratio of the hopping parameters $\zeta=K_t/K_s$ and the clover coefficients $c_{s,t}$, are examined at the tree level. We then compute the charmonium spectrum in the quenched approximation employing $\xi = a_s/a_t = 3$ anisotropic lattices. Simulations are made with the standard anisotropic gauge action and the anisotropic clover quark action at four lattice spacings in the range $a_s$=0.07-0.2 fm. The clover coefficients $c_{s,t}$ are estimated from tree-level tadpole improvement. On the other hand, for the ratio of the hopping parameters $\zeta$, we adopt both the tree-level tadpole-improved value and a non-perturbative one. We calculate the spectrum of S- and P-states and their excitations. The results largely depend on the scale input even in the continuum limit, showing a quenching effect. When the lattice spacing is determined from the $1P-1S$ splitting, the deviation from the experimental value is estimated to be $\sim$30% for the S-state hyperfine splitting and $\sim$20% for the P-state fine structure. Our results are consistent with previous results at $\xi = 2$ obtained by Chen when the lattice spacing is determined from the Sommer scale $r_0$. We also address the problem with the hyperfine splitting that different choices of the clover coefficients lead to disagreeing results in the continuum limit.Comment: 43 pages, 49 eps figures, revtex; minor changes, version to appear in Physical Review

Percutaneous Aspiration Embolectomy in the Treatment of Acute Arterial Embolic Infrainguinal Vascular Occlusion

Background: Since its introduction, percutaneous aspiration embolectomy (PAE) has become a well-known, widely accepted and frequently applied technique for the treatment of acute arterial embolic infrainguinal vascular occlusion in lower limb ischemia. Purpose: To evaluate the technical and clinical success of sole percutaneous aspiration embolectomy (PAE) for the treatment of acute arterial embolic infrainguinal vascular occlusion. Material and Methods: During a period of 7 years, 50 patients (24 fermale, 48%) with a mean age of 73 (range 53–95) years were identified in whom 54 cases of PAE were performed for the treatment of arterial embolic infrainguinal vascular occlusion. Primary technical success was defined as residual stenosis of <50% in diameter after sole PAE, secondary technical success was defined as residual stenosis of <50% in diameter after PAE and additional percutaneous transluminal angioplasty (PTA) and/or stenting. Clinical outcome parameters (e.g. need for further intervention and/or amputation) were evaluated for the 30-day postinterventional period. Results: The primary technical success rate was 85% (46 of 54 cases). The secondary technical success rate was 96% (52 of 54 cases). Clinical outcome data were achievable in 50 of the 54 cases (93%). In 43 of the 50 patients (86%) there was no need for further intervention within the 30-day postinterventional period. In summary, during this 30-day postinterventional period after PAE amputation was carried out or death occurred in 5 of 50 patients (10%). Conclusion: Minimally invasive PAE is an effective and safe technique for the treatment of acute arterial embolic infrainguinal vascular occlusion

Comparison Studies of Finite Momentum Correlators on Anisotropic and Isotropic Lattices

We study hadronic two- and three-point correlators relevant for heavy to light pseudoscalar meson semi-leptonic decays, using Symanzik improved glue, D234 light quark and NRQCD heavy quark actions. Detailed comparisons are made between simulations on anisotropic and isotropic lattices involving finite momentum hadrons. We find evidence that having an anisotropy helps in extracting better signals at higher momenta. Initial results for the form factors f_+(q^2) and f_0(q^2) are presented with tree-level matching of the lattice heavy-light currents.Comment: 43 pages with 50 postscript figure

Heavy-light spectrum and decay constant from NRQCD with two flavors of dynamical quarks

We report on a study of B mesons on N_f = 2 full QCD configurations using an RG-improved gauge action, NRQCD heavy quark action and tadpole-improved clover light quark action. Results on the heavy-light spectrum and the decay constants from 16^3x32 lattices at a^{-1} ~ 1.5 GeV are presented, and compared with quenched results obtained with the same action combination at matching lattice spacings.Comment: 3 pages, LaTeX, 2 PS figures, talk presented at LATTICE`99 (heavy quarks

Screening of human gene promoter activities using transfected-cell arrays

Promoters are the best characterized transcriptional regulatory sequences in complex genomes because of their predictable location immediately upstream of transcription start sites. Despite a substantial body of literature describing transcriptional promoters, the identification of true start sites for all human transcripts is far from complete. The same is true of the key structural and functional elements responsible for promoter action in different cell types. In order to identify elements responsible for promoter activity, we applied transfected-cell array technology to functionally evaluate promoters for genes involved in inflammatory bowel disease. Seventy-four promoters were examined by reverse transfection of a promoter-fluorescent reporter constructs into a human embryonic kidney cell line (HEK293T). Sixteen (21.6%) promoters were found to be active in HEK293 T cells. Correlations between promoter activity and endogenous transcript level were calculated, and 75% of active promoters were found to be associated with transcriptional activity of their gene counterparts. These results provide experimental evidence of promoter activity, which may aid in understanding the regulation of gene expression. Moreover, this is the first large-scale functional study of regulatory sequences to use a high-throughput transfected-cell array technique

Meandering particle bunches and a link between averages of time series of particle counts and higher-order moments

Time-averaged spatially resolved measurements are used in many fields of physics to determine spatial distributions of a physical quantity. Although one could think that time averaging suppresses all information on time variation, there are some situations in which a link can be established between time averaging and time variability. In this paper, we consider a simple system composed of a particle bunch that moves in space without deforming, and a detector placed at a point in space. The detector continuously counts the number of particles in its neighborhood. Upon sampling, the detector signal gives rise to a time series with, in general, nonvanishing variance. Time series obtained by placing the detector at different locations can then be used to obtain a time-average distribution of the number of particles by computing the time average of all the time series. We show that there is a close relationship between this average profile and higher-order statistics of the time series, including the variance and skewness. We also show a simple procedure by which individual time series can be used to determine features of the shape of the particle bunch