Electron-hole coupling and the charge density wave transition in TiSe2

Angle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the ( 2 x 2 x 2) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition.     

Reverse α–α´ phase separation in Fe-20Cr-6Al alloy

The reverse α–α′ phase separation in Fe-20Cr-6Al alloys has been monitored by differential scanning calorimetry in as-hot rolled and recrystallized samples previously aged at 435?°C. The splitting in the position of the minima, and the increasing enthalpy change involved, might be explained in terms of dissolution of α′ particles with different compositions and volume fractions. These results are fully consistent with the α–α′ phase separation kinetics determined by atom probe tomography during ageing at 435?°C. The monitoring of activation energy for α′ dissolution indicates that it is faster in as-hot rolled samples. Finally, the activation energy evolution indicates that there is first a dissolution of β′ Fe(AlTi) phase followed by α′ dissolution.     

Correction of B0 susceptibility induced distortion in diffusion-weighted images using large-deformation diffeomorphic metric mapping

Geometric distortion caused by B0 inhomogeneity is one of the most important problems for diffusion-weighted images (DWI) using single-shot, echo planar imaging (SS-EPI). In this study, large-deformation, diffeomorphic metric mapping (LDDMM) algorithm has been tested for the correction of geometric distortion in diffusion tensor images (DTI). Based on data from nine normal subjects, the amount of distortion caused by B0 susceptibility in the 3-T magnet was characterized. The distortion quality was validated by manually placing landmarks in the target and DTI images before and after distortion correction. The distortion was found to be up to 15 mm in the population-averaged map and could be more than 20 mm in individual images. Both qualitative demonstration and quantitative statistical results suggest that the highly elastic geometric distortion caused by spatial inhomogeneity of the B0 field in DTI using SS-EPI can be effectively corrected by LDDMM. This postprocessing method is especially useful for correcting existent DTI data without phase maps.     

Experimental investigation of the two-photon widths of the chi(c0) and the chi(c2) mesons

Using 12.7 fb(-1) of data collected with the CLEO detector at CESR, we observed two-photon production of the cc states chi(c0) and chi(c2) in their decay to pi(+)pi(-)pi(+)pi(-). We measured gamma(gammagamma)(chi(c))xB(chi(c)-->pi(+)pi(-)pi(+)pi(-)) to be 75+/-13(stat)+/-8(syst) eV for the chi(c0) and 6.4+/-1.8(stat)+/-0.8(syst) eV for the chi(c2), implying gamma(gammagamma)(chi(c0)) = 3.76+/-0.65(stat)+/-0.41(syst)+/-1.69(br) keV and gamma(gammagamma)(chi(c2)) = 0.53+/-0.15(stat)+/-0.06(syst)+/-0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of gamma(gammagamma)(chi(c0))/gamma(gammagamma)(chi(c2)), evaluated to be 7.4+/-2.4(stat)+/-0.5(syst)+/-0.9(br), with QCD-based predictions.     

Some effects of signal bandwidth and spectral density on the acoustic-reflex threshold in the elderly

The acoustic-reflex thresholds (ART) for multicomponent tonal complexes of varying bandwidth and spectral density were obtained from 20 normal-hearing (air-conduction thresholds less than or equal to 20 dB HL at 250-8000 Hz) young adults ranging in age from 20-30 years and 20 normal-hearing, old subjects ranging in age from 60-71 years. The results revealed that the ART decreased with spectral density, plateauing after seven components in the young group and after five components in the old group; the decrease in the acoustic-reflex threshold as a result of the increase in spectral density was less in the old than in the young group. The bandwidth effect (when bandwidth was plotted in hertz or octaves) on the acoustic-reflex threshold was present in the young adults, but substantially reduced in the elderly, as evidenced by the statistically significant interaction between subject group and signal bandwidth. The spectral density results are discussed in terms of their theoretic implications for the energy summation capacity and frequency resolution of the auditory system. The bandwidth results are discussed in terms of their theoretic implications for the frequency-resolving power of the auditory system.     

A measurement of the proton structure functions from neutrino-hydrogen and antineutrino-hydrogen charged-current interactions

Within the framework of the quark-parton model, the quark and anti-quark structure functions of the proton have been measured by fitting them to the distributions of the events in the Bjorkeny variable. The data used form the largest sample of neutrino and antineutrino interactions on a pure hydrogen target available, and come from exposures of BEBC to the CERN wide band neutrino and antineutrino beams. It is found that the ratiod _v /u _v of valence quark distributions falls with increasing Bjorkenx. In the context of the quark-parton model the results constrain the isospin composition of the accompanying diquark system. Models involving scattering from diquarks are in disagreement with the data.     

Reaction field model with free volume for the NMR chemical shift of129Xe dissolved in organic solvents

The temperature dependence of the NMR chemical shift of¹²⁹Xe dissolved in liquid alkanes is examined in the context of the reaction field model. An essential feature of the theory is the inclusion of the temperature dependence of the density of thesolvent. The theory of free volume for liquids is incorporated into the reaction field model to account for this temperature dependence. Comparison of the theory with previously reported measurements indicates the sensitivity of the¹²⁹Xe chemical shift to the free volume of liquids. Incorporation of free volume improves the agreement between measurement and theory for branched alkane solvents, and resolves the origin of the 62 ppm intercept in the plot of reaction field as a function of¹²⁹Xe chemical shift for the n-alkanes.