Charge carrier density collapse in La_0.67Ca_0.33MnO_3 and La_0.67Sr_0.33MnO_3 epitaxial thin films

We measured the temperature dependence of the linear high field Hall resistivity of La_0.67Ca_0.33MnO_3 (T_C=232K) and La_0.67Sr_0.33MnO_3 (T_C=345K) thin films in the temperature range from 4K up to 360K in magnetic fields up to 20T. At low temperatures we find a charge carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature T_C a dramatic drop in the number of current carriers $n$ down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data due to a non saturated magnetic state will lead a more pronounced charge carrier density collapse.Comment: 5 pages, 5 EPS figures, submitted to Eur. Phys. J.

Extensive infrared spectroscopic study of CuO: signatures of strong spin-phonon interaction and structural distortion

Optical properties of single-crystal monoclinic CuO in the range 70 - 6000 \cm were studied at temperatures from 7 to 300 K. Normal reflection spectra were obtained from the (001) and (010) crystal faces thus giving for the first time separate data for the $A_{u}$ and $B_{u}$ phonon modes excited in the purely transverse way (TO modes). Mode parameters, including polarizations of the $B_{u}$ modes not determined by the crystal symmetry, were extracted by the dispersion analysis of reflectivity curves as a function of temperature. Spectra of all the components of the optical conductivity tensor were obtained using the Kramers-Kronig method recently extended to the case of the low-symmetry crystals. The number of strong phonon modes is in agreement with the factor-group analysis for the crystal structure, currently accepted for the CuO. However, several "extra" modes of minor intensity are detected. Comparison of frequencies of "extra" modes with the available phonon dispersion curves points to possible "diagonal" doubling of the unit cell \{{\bf a}, {\bf b}, {\bf c}\} $\to$ \{{\bf a}+{\bf c}, {\bf b}, {\bf a}-{\bf c}\} and formation of the superlattice. The previously reported softening of the $A^{3}_{u}$ mode ($\sim$ 400 \cm) with cooling at $T_{N}$ is found to be $\sim$ 10 % for the TO mode. The mode is very broad at high temperatures and strongly narrows in the AFM phase. We attribute this effect to strong resonance coupling of this mode to optical or acoustic bi-magnons and reconstruction of the magnetic excitations spectrum at the N\'eel point. A significant anisotropy of $\epsilon^{\infty}$ is observed: it was found to be 5.9 along the {\bf b}-axis, 6.2 along the {[}101{]} chains and 7.8 the {[}10$\bar{1}${]} chains. The "transverse" effective charge is value is about 2 electrons.Comment: 23 pages, 14 figures, REVTeX, submitted to PR

Microcoil High-Resolution Magic Angle Spinning NMR Spectroscopy

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Infrared studies of a La_(0.67)Ca_(0.33)MnO_3 single crystal: Optical magnetoconductivity in a half-metallic ferromagnet

The infrared reflectivity of a La_(0.67)Ca_(0.33)MnO_3 single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers (20–9000cm^(-1)). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000cm-1 in the ferromagnetic state below the Curie temperature T_C=307K. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near T_C

Infrared Studies of a La_{0.67}Ca_{0.33}MnO_3 Single Crystal: Optical Magnetoconductivity in a Half-Metallic Ferromagnet

The infrared reflectivity of a $\rm La_{0.67}Ca_{0.33}MnO_3$ single crystal is studied over a broad range of temperatures (78-340 K), magnetic fields (0-16 T), and wavenumbers (20-9000 cm$^{-1}$). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000 cm$^{-1}$ in the ferromagnetic state below the Curie temperature $T_C=307 K$. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near $T_C$.Comment: 4 pages, 4 figures, Latex, PostScript; The 7th Joint MMM-Intermag Conference,San Francisco, January 6-9, 1998; The Int. Conf. on Strongly Correlated Electron Systems, Paris, July 15-18,199

Vaccination with Fendrix of prior nonresponding patients with HIV has a high success rate

Background: Patients with HIV have a poor serological conversion rate with the standard vaccination strategy against hepatitis B virus (HBV) of around 50%. Vaccination with Fendrix confers much better results in these patients. In this study, we tested the effect of revaccination with Fendrix in prior nonresponding patients with HIV and aimed to determine which factors are associated with seroconversion. Methods: Eight Dutch HIV treatment centers participated in this retrospective study. Patients infected with HIV-1 and nonresponding to prior course of vaccination against HBV (anti-HBs <10 IU/ml) and who had Fendrix as a second, third or fourth effort to achieve seroconversion were eligible for inclusion. Primary outcome was the proportion of patients with seroconversion after revaccination with Fendrix. Univariate binary logistic regression analyses were used to determine which factors could be used as predictors for seroconversions. Results: We included 100 patients with HIV. The mean age was 47.3 (11.0) years and 86% were men. Revaccination with Fendrix showed a seroconversion rate of 81% (95% confidence interval 72–88%). Median nadir CD4þ cell count was 300 (20–1040) cells/ ml and median CD4þ cell count at the time at starting vaccination with Fendrix was 605 (210–1190) cells/ml. Regression analyses showed no significant factor associated with seroconversion. Conclusions: Revaccination with Fendrix of patients prior nonresponding to other hepatitis B vaccination strategies has a high success rate. Eighty-one percentage responded with seroconversion, irrespective of CD4þ cell count

A systematic review and meta-analysis of the effect of cognitive interventions to prevent intrusive memories using the trauma film paradigm

There is an unmet need for effective early interventions that can relieve initial trauma symptoms and reduce symptoms of posttraumatic stress disorder (PTSD). We evaluated the efficacy of cognitive interventions compared to control in reducing intrusion frequency and PTSD symptoms in healthy individuals using the trauma film paradigm, in which participants view a film with aversive content as an experimental analogue of trauma exposure. A systematic literature search identified 41 experiments of different cognitive interventions targeting intrusions. In the meta-analysis, the pooled effect size of 52 comparisons comparing cognitive interventions to no-intervention controls on intrusions was moderate (g = −0.46, 95% CI [–0.61 to −0.32], p < .001). The pooled effect size of 16 comparisons on PTSD symptoms was also moderate (g = −0.31, 95% CI [–0.46 to −0.17], p < .001). Both visuospatial interference and imagery rescripting tasks were associated with significantly fewer intrusions than controls, whereas verbal interference and meta-cognitive processing tasks showed nonsignificant effect sizes. Interventions administered after viewing the trauma film showed significantly fewer intrusions than controls, whereas interventions administered during film viewing did not. No experiments had low risk of bias (ROB), 37 experiments had some concerns of ROB, while the remaining four experiments had high ROB. To the best of our knowledge, this is the first meta-analysis investigating the efficacy of cognitive interventions targeting intrusions in non-clinical samples. Results seem to be in favour of visuospatial interference tasks rather than verbal tasks. More research is needed to develop an evidence base on the efficacy of various cognitive interventions and test their clinical translation to reduce intrusive memories of real trauma

Magnetic field induced polarization effects in intrinsically granular superconductors

Based on the previously suggested model of nanoscale dislocations induced Josephson junctions and their arrays, we study the magnetic field induced electric polarization effects in intrinsically granular superconductors. In addition to a new phenomenon of chemomagnetoelectricity, the model predicts also a few other interesting effects, including charge analogues of Meissner paramagnetism (at low fields) and "fishtail" anomaly (at high fields). The conditions under which these effects can be experimentally measured in non-stoichiometric high-T_c superconductors are discussed.Comment: 10 pages (REVTEX), 5 EPS figures; revised version accepted for publication in JET

LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources

We present LOFAR Low Band observations of the Bootes and 3C295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam−1, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17 to 52 deg 2. From the observations we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and VLA 74 MHz differential source counts, scaling with a spectral index of −0.7. We find that a spectral index scaling of −0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens towards lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α<−1.1 ) radio sources, that could be associated with massive high redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz and 1.4 GHz for sources in the Booötes field. We cross-correlate these radio sources with optical and infrared catalogues and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7≲z≲2.5 range

Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array

When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to detect these pulses. In this work we propose an efficient trigger implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research Section