Coherent single pion production by antineutrino charged current interactions and test of PCAC

The cross section for coherent production of a single π^? meson in charged current antineutrino interactions on neon nuclei has been measured in BEBC to be (175±25) 10^?40 cm²/neon nucleus, averaged over the energy spectrum of the antineutrino wide band beam at the CERN SPS; this corresponds to (0.9±0.1) % of the total charged current \(\bar v_\mu \) cross section. The distributions of kinematical variables are in agreement with theoretical predictions based on the PCAC hypothesis and the meson dominance model; in particular, theQ ² dependence is well described by a propagator containing a massm=(1.35±0.18) GeV. The absolute value of the cross section is also in agreement with the model. This analysis thus provides a test of the PCAC hypothesis in the antineutrino energy range 5–150 GeV.     

Substrate affinities for membrane transport proteins determined by 13C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy

We have devised methods in which cross-polarization magic-angle spinning (CP-MAS) solid-state NMR is exploited to measure rigorous parameters for binding of (13)C-labeled substrates to membrane transport proteins. The methods were applied to two proteins from Escherichia coli: a nucleoside transporter, NupC, and a glucuronide transporter, GusB. A substantial signal for the binding of methyl [1-(13)C]-beta-d-glucuronide to GusB overexpressed in native membranes was achieved with a sample that contained as little as 20 nmol of GusB protein. The data were fitted to yield a K(D) value of 4.17 mM for the labeled ligand and 0.42 mM for an unlabeled ligand, p-nitrophenyl beta-d-glucuronide, which displaced the labeled compound. CP-MAS was also used to measure binding of [1'-(13)C]uridine to overexpressed NupC. The spectrum of NupC-enriched membranes containing [1'-(13)C]uridine exhibited a large peak from substrate bound to undefined sites other than the transport site, which obscured the signal from substrate bound to NupC. In a novel application of a cross-polarization/polarization-inversion (CPPI) NMR experiment, the signal from undefined binding was eliminated by use of appropriate inversion pulse lengths. By use of CPPI in a titration experiment, a K(D) value of 2.6 mM was determined for uridine bound to NupC. These approaches are broadly applicable to quantifying binding of substrates, inhibitors, drugs, and antibiotics to numerous membrane proteins.     

Utilizing Lifetimes to Suppress Random Coil Features in 2D IR Spectra of Peptides

We report that the waiting time delay in 2D IR pulse sequences can be used to suppress signals from structurally disordered regions of amyloid fibrils. At a waiting time delay of 1.0 ps, the random coil vibrational modes of amylin fibrils are no longer detectable, leaving only the sharp excitonic vibrational features of the fibril β-sheets. Isotope labeling with (13)C(18)O reveals that structurally disordered residues decay faster than residues protected from solvent. Since structural disorder is usually accompanied by hydration, we conclude that the shorter lifetimes of random-coil residues is due to solvent exposure. These results indicate that 2D IR pulse sequences can utilize the waiting time to better resolve solvent-protected regions of peptides and that local mode lifetimes should be included in simulations of 2D IR spectra.     

Measurement of the electric form factor of the neutron at Q2 = 0.3-0.8 (GeV/ c) 2 ⋆

The electric form factor of the neutron, G_E,n, has been measured at the Mainz Microtron by recoil polarimetry in the quasielastic D(¯e, e¯n)p reaction. Three data points have been extracted at squared four-momentum transfers Q ² = 0.3, 0.6 and 0.8 (GeV/c)². Corrections for nuclear binding effects have been applied.This revised version was published online in March 2005. In the previous version, the email address of one author was inadvertently assigned to multiple authors.     

Dynamic contrast-enhanced MRI of vascular changes induced by the VEGF-signalling inhibitor ZD4190 in human tumour xenografts

Dynamic contrast-enhanced magnetic resonance imaging (DCEMRI) was used to examine the acute effects of treatment with an inhibitor of vascular endothelial growth factor (VEGF) signaling. ZD4190 is an orally bioavailable inhibitor of VEGF receptor-2 (KDR) tyrosine kinase activity, which elicits broad-spectrum antitumour activity in preclinical models following chronic once-daily dosing. Nude mice, bearing established (0.5-1.0 mL volume) human prostate (PC-3), lung (Calu-6) and breast (MDA-MB-231) tumor xenografts, were dosed with ZD4190 (p.o.) using a 1 day (0 and 22 h) or 7 day (0, 24, 48, 72, 96,120,144, and 166 h) treatment regimen. DCEMRI was employed 2 h after the last dose of ZD4190, using the contrast agent gadopentetate dimeglumine. Dynamic data were fit to a compartmental model to obtain voxelwise K(trans), the transfer constant for gadopentetate into the tumor. K(trans) was averaged over the entire tumor, and a multi-threshold histogram analysis was also employed to account for tumor heterogeneity. Reductions in K(trans) reflect reductions in flow, in endothelial surface area, and/or in vascular permeability. A vascular input function was obtained for each mouse simultaneously with the tumor DCEMRI data. ZD4190 treatment produced a dose-dependent (12.5-100 mg x kg(-1) per dose) reduction in K(trans) in PC-3 prostate tumors. At 100 mg x kg(-1), the largest concentration examined, ZD4190 reduced K(trans) in PC-3 tumors by 31% following 2 doses (1 day treatment regimen; p < 0.001) and by 53% following 8 doses (7 day regimen; p < 0.001). Comparative studies in the three models using a showed similar reductions in K(trans) for the lung and breast tumors using the histogram analysis, although the statistical significance was lost when K(trans) was averaged over the entire tumor. Collectively these studies suggest that DCEMRI using gadopentetate may have potential clinically, for monitoring inhibition of VEGF signaling in solid tumors.     

Driven depinning of strongly disordered media and anisotropic mean-field limits

Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the drive and slip along at least one of the directions transverse to the motion. In the limit of infinite-range elastic and viscous coupling this model has a tricritical point separating a region where the depinning is continuous, in the universality class of elastic depinning, from a region where depinning is hysteretic. Many of the collective transport models discussed in the literature are special cases of the generic model.