Light vector meson and heavy baryon strong interaction

We calculate the coupling constants between the light vector mesons and heavy baryons within the framework of the light-cone QCD sum rule in the leading order of heavy quark effective theory. Most resulting sum rules are stable with the variations of the Borel parameter and the continuum threshold. The extracted couplings will be useful in the study of the possible heavy baryon molecular states

A novel design method of variable geometry turbine nozzles for high expansion ratios

International audienceIn variable nozzle geometry turbines (VNT), opening of the nozzles is used to control turbine mass flow and expansion ratio, allowing more turbine power to be generated over wider operating conditions. In turbocharged vehicles, the nozzles are 'closed' to provide high boosts for engine and vehicle acceleration and for engine braking assistance. At the both conditions, high nozzle expansion ratios are created , and shockwaves may generate from the nozzles. These shocks reduce turbine efficiency and they can cause high cycle fatigue (HCF) damage to the downstream rotor blades. Design of high expansion ratio radial nozzles is difficult for VNT because transonic flows are very sensitive to small geometry changes, and the large semi-vaneless space created by the nozzles makes the design a tricky business. Shock minimised nozzle designs are therefore often achieved by auto-optimisation technique. While design targets may be achieved, this technique does not offer sufficient insights into how the optimal flow field has been derived, so the same optimisation procedure has to be applied to every new design. In this paper, a new design method that overcomes this problem is proposed. The method first uses a conformal mapping to transfer a radial nozzle from the r-θ plane into the x-y plane. Mapped nozzle displays amplification of supersonic acceleration and diffusion. This is explained by the curvature changes brought about by the mapping, and a link between the shock strength and the flatness of the suction surface of the mapped nozzle is found. The amplification and the link can be utilised to design nozzles with reduced shock loss in the x-y plane first and then mapped back to the r-θ plane. Two nozzles for 6:1 expansion ratio were designed in this way and CFD results show a significant reduction of nozzle loss. The nozzles were also checked for fully open condition and no performance penalty was found

Molecular epidemiological study of clinical Acinetobacter baumannii isolates: phenotype switching of antibiotic resistance

BackgroundThe presence of clinical Acinetobacter baumannii (A. baumannii) isolates with differing antibiotic resistance phenotypes in the same patient causes difficulties and confusion in treatment. This phenomenon may be caused by reasons such as cross-infection from neighboring patients that switches to different A. baumannii strain, natural mutation of A. baumannii, inducing of different antibiotic resistance genes expression or acquisition of genes conferring resistance from another source. To elucidate this question, clinical A. baumannii strains, isolated from the same individual patients, showed antibiotic resistance phenotypes switching during the same hospitalization period, were attentively collected for further analysis. Molecular approaches for phylogenetic analysis, including pulsed field gel electrophoresis, multilocus sequence typing, and short tandem repeat analysis, were employed for the chronological studies.FindingsOur results showed that antibiotic resistance phenotype switching could have occurred as a result through both cross-infection and natural mutation roots. Our results also suggest that rapid phenotype switching between paired isolates could occur during one single course of antibiotic treatment.ConclusionsThough cross infection caused antibiotic resistance phenotype switching does occur, natural mutation of A. baumannii isolates is particularly cautious for antibiotic treatment

Risk factor analysis for extended-spectrum β-lactamase-producing Enterobacter cloacae bloodstream infections in central Taiwan

BackgroundEnterobacter cloacae (E.cloacae) bloodstream infection (EcBSI) is an important cause of morbidity and mortality, with an increasing incidence in our hospital. We wanted to elucidate the risk factors of mortality among patients with ESBL-positive EcBSI in central Taiwan.MethodsWe ordered the clinical and microbiological data of cases with diagnosis of EcBSI, and analyzed the isolates by using antibiotyping, detection of ESBL, detection of class 1 integron and genomic fingerprinting by pulsed-field gel electrophoresis (PFGE).ResultsSeventy episodes of EcBSI from 70 patients (56 hospital-acquired infections) were enrolled. Significant differences were found between ESBL-positive and ESBL-negative isolates with regard to risk factors, including the diseases severity (p = 0.03), category of health care-associated infection (p = 0.04), prior use of antibiotics (p = 0.023), and prior use of a ventilator (p = 0.037). A significant difference in mortality between two groups (p = 0.004) was determined using the chi-square test, and a trend in mortality between two groups (p = 0.006, OR = 4.750, 95% C.I.=1.573-14.344) was determined using univariate logistic regression analysis. The predominant clone in ESBL-positive strains was associated with a higher mortality rate but not with the presence of the integron.ConclusionsThe study disclosed four types of clinical characteristics to obtain ESBL-positive EcBSI, and there was a trend in mortality too. We suggested the need to review antibiotic prescription practices, and the possible need to consider ESBL-positive strains in empirical treatment of bloodstream infection

Constructing minimal telescopers for rational functions in three discrete variables

We present a new algorithm for constructing minimal telescopers for rational functions in three discrete variables. This is the first discrete reduction-based algorithm that goes beyond the bivariate case. The termination of the algorithm is guaranteed by a known existence criterion of telescopers. Our approach has the important feature that it avoids the potentially costly computation of certificates. Computational experiments are also provided so as to illustrate the efficiency of our approach