Quenching of the Deuteron in Flight

We investigate the Lorentz contraction of a deuteron in flight. Our starting point is the Blankenbecler-Sugar projection of the Bethe-Salpeter equation to a 3-dimensional quasi potential equation, wqhich we apply for the deuteron bound in an harmonic oscillator potential (for an analytical result) and by the Bonn NN potential for a more realistic estimate. We find substantial quenching with increasing external momenta and a significant modification of the high momentum spectrum of the deuteron.Comment: 11 pages, 4 figure

Recent results from the G(0) experiment

We have measured parity violating asymmetries in elastic electron-proton and quasi-elastic electron-deuteron scattering at backward electron angle. These measurements have been done at two momentum transfers : Q(2) = 0.22 and 0.63 (GeV/c)(2). Together with our previous forward angle measurement [1], we can extract strange quark contributions to the electromagnetic form factors of the nucleon, as well as nucleon axial form factor coming from the neutral weak interaction. The results indicate a strange quark magnetic contribution close to zero at these Q(2), and a possible non zero strange quark electric contribution for the high Q(2). The first Q(2) behavior measurement of the nucleon axial form factor in elastic electron scattering shows a good agreement with radiative corrections calculated at Q(2) = 0 and with a dipole form using the axial mass determined in neutrino scattering

Measurement of the Parity-Violating Asymmetry in Inclusive Electroproduction of pi(-) near the Delta(0) Resonance

The parity-violating (PV) asymmetry of inclusive pi(-) production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Delta(0) resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Delta)(-) that characterizes the parity-violating gamma N Delta coupling. Zhu et al. calculated d(Delta)(-) in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(gamma)(-) = -5.2 to + 5.2 ppm. The measurement performed in this work leads to A(gamma)(-) = -0.36 +/- 1.06 +/- 0.37 +/- 0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V-ud/V-us. The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N - Delta axial transition form factors using PV electron scattering

Eta-Helium Quasi-Bound States

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters

G0^0 Electronics and Data Acquisition (Forward-Angle Measurements)

The G$^0$ parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross section was measured for $\vec{e}p$ elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required on the asymmetry, the G$^0$ experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events at a mean rate of 2 MHz per detector with low deadtime and to minimize helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G$^0$ forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section A. It has been written with Latex using \documentclass{elsart}. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment In Press (2007

Peritoneal carcinomatosis from gastric cancer: a multi-institutional study of 159 patients treated by cytoreductive surgery combined with perioperative intraperitoneal chemotherapy

BACKGROUND: Peritoneal carcinomatosis (PC) from gastric cancer has long been regarded a terminal disease with a short median survival. New locoregional therapeutic approaches combining cytoreductive surgery with perioperative intraperitoneal chemotherapy (PIC) have evolved and suggest improved survival. MATERIALS AND METHODS: A retrospective multicentric study was performed in French-speaking centers to evaluate the toxicity and the principal prognostic factors in order to identify the best indications. All patients had cytoreductive surgery and PIC: hyperthermic intraperitoneal chemotherapy (HIPEC) and/or early postoperative intraperitoneal chemotherapy (EPIC). RESULTS: The study included 159 patients from 15 institutions between February 1989 and August 2007. The median follow-up was 20.4 months. HIPEC was the PIC used for 150 procedures. Postoperative mortality and grade 3-4 morbidity rates were 6.5 and 27.8%, respectively. By multivariate analysis, the institution had a significant influence on toxicity. The overall median survival was 9.2 months and 1-, 3-, and 5-year survival rates were 43, 18, and 13%, respectively. The only independent prognostic indicator by multivariate analysis was the completeness of cytoreductive surgery. For patients treated by complete cytoreductive surgery, the median survival was 15 months with a 1-, 3-, and 5-year survival rate of 61, 30, and 23%, respectively. CONCLUSIONS: The therapeutic approach combining cytoreductive surgery with PIC for patients with gastric carcinomatosis may achieve long-term survival in a selected group of patients (limited and resectable PC). The high mortality rate underlines this necessarily strict selection that should be reserved to experienced institutions involved in the management of PC and gastric surgery

Probabilistic chemotherapy in knee and hip replacement infection: the place of linezolid

Prosthetic joint infection (PJI) can occur with a wide range of microorganisms and clinical features. After replacement surgery of prosthetic joint, prescription of probabilistic broad-spectrum antimicrobial therapy is usual, while awaiting microbial culture results. The aim of our study was to describe the antibiotic susceptibility of microorganisms isolated from hip and knee PJI. The data were collected to determine the best alternative to the usual combination of piperacillin-tazobactam (TZP) or cefotaxime (CTX) and vancomycin (VAN). Based on a French prospective, multicenter study, we analyzed microbiological susceptibility to antibiotics of 183 strains isolated from patients with confirmed hip or knee PJI. In vitro susceptibility was evaluated: TZP+VAN, TZP+linezolid (LZD), CTX+VAN, and CTX+LZD. We also analyzed resistance to different antibiotics commonly used as oral alternatives. Among the 183 patients with PJI, 62 (34%) had a total knee prosthesis, and 121 (66%) a hip prosthesis. The main identified bacteria were Staphylococcus aureus (32.2% of isolates), coagulase-negative staphylococci (27.3%), Enterobacteriaceae (14.2%), and Streptococcus (13.7%). Infections were polymicrobial for 28 (15.3%) patients. All combinations were highly effective: CTX+VAN, CTX+LZD, TZP+VAN, and TZP+LZD (93.4%, 94%, 98.4%, and 98.9% of all cases respectively). Use of LZD instead of VAN in combination with a broad-spectrum beta-lactam covers almost all of the bacteria isolated in PJI. This association should be considered in probabilistic chemotherapy, as it is particularly easy to use (oral administration and no vancomycin monitoring)

Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude

We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A$_\perp$, at two Q$^2$ values of \qsquaredaveragedlow (GeV/c)$^2$ and \qsquaredaveragedhighII (GeV/c)$^2$ and a scattering angle of $30^\circ < \theta_e < 40^\circ$. The measured transverse asymmetries are A$_{\perp}$(Q$^2$ = \qsquaredaveragedlow (GeV/c)$^2$) = (\experimentalasymmetry alulowcorr $\pm$ \statisticalerrorlow$_{\rm stat}$ $\pm$ \combinedsyspolerrorlowalucor$_{\rm sys}$) $\times$ 10$^{-6}$ and A$_{\perp}$(Q$^2$ = \qsquaredaveragedhighII (GeV/c)$^2$) = (\experimentalasymme tryaluhighcorr $\pm$ \statisticalerrorhigh$_{\rm stat}$ $\pm$ \combinedsyspolerrorhighalucor$_{\rm sys}$) $\times$ 10$^{-6}$. The first errors denotes the statistical error and the second the systematic uncertainties. A$_\perp$ arises from the imaginary part of the two-photon exchange amplitude and is zero in the one-photon exchange approximation. From comparison with theoretical estimates of A$_\perp$ we conclude that $\pi$N-intermediate states give a substantial contribution to the imaginary part of the two-photon amplitude. The contribution from the ground state proton to the imaginary part of the two-photon exchange can be neglected. There is no obvious reason why this should be different for the real part of the two-photon amplitude, which enters into the radiative corrections for the Rosenbluth separation measurements of the electric form factor of the proton.Comment: 4 figures, submitted to PRL on Oct.

Evidence for Strange Quark Contributions to the Nucleon's Form Factors at Q2Q^2 = 0.108 (GeV/c)2^2

We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of $Q^2$ = \Qsquare (GeV/c)$^2$ and at a forward electron scattering angle of 30$^\circ < \theta_e < 40^\circ$. The measured asymmetry is $A_{LR}(\vec{e}p)$ = (\Aphys $\pm$ \Deltastat$_{stat}$ $\pm$ \Deltasyst$_{syst}$) $\times$ 10$^{-6}$. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A$_0$ = (\Azero $\pm$ \DeltaAzero) $\times$ 10$^{-6}$. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher $Q^2$. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be $G_E^s$ + \FakGMs $G_M^s$ = \GEsGMs $\pm$ \DeltaGEsGMs at $Q^2$ = \Qsquare (GeV/c)$^2$. As in our previous measurement at higher momentum transfer for $G_E^s$ + 0.230 $G_M^s$, we again find the value for $G_E^s$ + \FakGMs $G_M^s$ to be positive, this time at an improved significance level of 2 $\sigma$.Comment: 4 pages, 3 figure

The prognosis of streptococcal prosthetic bone and joint infections depends on surgical management-A multicenter retrospective study

BACKGROUND: The optimal treatment of streptococcal prosthetic joint infections (PJIs) is unclear. METHODS: A cohort of streptococcal PJIs was reviewed retrospectively in seven reference centers for the management of complex bone and joint infections, covering the period January 1, 2010 to December 31, 2012. RESULTS: Seventy patients with monomicrobial infections were included: 47 had infections of total hip arthroplasty and 23 had infections of total knee arthroplasty. The median age was 77 years (interquartile range (IQR) 69-83 years), the median Charlson comorbidity score was 4 (IQR 3-6), and 15.6% (n=11) had diabetes. The most commonly identified streptococcal species were Streptococcus agalactiae and Streptococcus dysgalactiae (38.6% (n=27) and 17.1% (n=12), respectively). Debridement, antibiotics and implant retention (DAIR) was performed after a median time of 7 days (IQR 3-8 days), with polyethylene exchange (PE) in 21% of cases. After a minimum follow-up of 2 years, 27% of patients had relapsed, corresponding to 51.4% of DAIR treatment cases and 0% of one-stage (n=15) or two-stage (n=17) exchange strategy cases. Rifampicin or levofloxacin in combination therapy was not associated with a better outcome (adjusted p= 0.99). S. agalactiae species and DAIR treatment were associated with a higher risk of failure. On multivariate analysis, only DAIR treatment and S. agalactiae were independent factors of relapse. Compared to DAIR without PE, DAIR with PE was only associated with a trend towards a benefit (odds ratio 0.33, 95% confidence interval 0.06-1.96; adjusted p= 0.44). CONCLUSIONS: Streptococcal PJIs managed with DAIR have a poor prognosis and S. agalactiae seems to be an independent factor of treatment failure