3,643 research outputs found
Insulatorâmetal transitions in Pr0.7Ca0.3MnO3 induced by a magnetic field
A magnetic field induced insulator to metal transition has been observed in both polycrystalline and single crystals samples of Pr0.7Ca0.3MnO3. Application of a magnetic field leads to a first-order phase transition from an insulating to a conducting state at low temperatures. The hysteresis associated with this transition allows the resistivity at 4 K to be varied by more than eight orders of magnitude depending on the field history of the sample
Remotely triggered scaffolds for controlled release of pharmaceuticals
Fe3O4-Au hybrid nanoparticles (HNPs) have shown increasing potential for biomedical applications such as image guided stimuli responsive drug delivery. Incorporation of the unique properties of HNPs into thermally responsive scaffolds holds great potential for future biomedical applications. Here we successfully fabricated smart scaffolds based on thermo-responsive poly(N-isopropylacrylamide) (pNiPAM). Nanoparticles providing localized trigger of heating when irradiated with a short laser burst were found to give rise to remote control of bulk polymer shrinkage. Gold-coated iron oxide nanoparticles were synthesized using wet chemical precipitation methods followed by electrochemical coating. After subsequent functionalization of particles with allyl methyl sulfide, mercaptodecane, cysteamine and poly(ethylene glycol) thiol to enhance stability, detailed biological safety was determined using live/dead staining and cell membrane integrity studies through lactate dehydrogenase (LDH) quantification. The PEG coated HNPs did not show significant cytotoxic effect or adverse cellular response on exposure to 7F2 cells (p < 0.05) and were carried forward for scaffold incorporation. The pNiPAM-HNP composite scaffolds were investigated for their potential as thermally triggered systems using a Q-switched Nd:YAG laser. These studies show that incorporation of HNPs resulted in scaffold deformation after very short irradiation times (seconds) due to internal structural heating. Our data highlights the potential of these hybrid-scaffold constructs for exploitation in drug delivery, using methylene blue as a model drug being released during remote structural change of the scaffold
Disorder-induced critical exponents near a ferromagnetic quantum critical point in Mn1âxCrxSi
We report the observation of critical behavior in Mn1âxCrxSi (0â€xâ€1) close to a T = 0 K quantum critical point, consistent with the Belitz-Kirkpatrick-Vojta (BKV) theory of disordered metallic ferromagnets. The critical exponents are in good agreement with the theoretical predictions of the BKV theory in the preasymptotic limit. A non-Fermi liquid-like behavior is seen down to 200 mK in the transport and thermodynamic properties around the critical concentration xC = 0.2. Quantum criticality and self-consistency of the exponents is further confirmed using a scaling analysis of the magnetization and heat capacity data. A recovery to Fermi liquid-like behavior is displayed on moving away from the critical composition, as well as with the application of a magnetic field
Crystal growth and properties of the non-centrosymmetric superconductor, Ru7B3
We describe the crystal growth of high quality single crystals of the
non-centrosymmetric superconductor, Ru7B3 by the floating zone technique, using
an optical furnace equipped with xenon arc lamps. The crystals obtained are
large and suitable for detailed measurements, and have been examined using
x-ray Laue patterns. The superconducting properties of the crystals obtained
have been investigated by magnetisation and resistivity measurements. Crystals
have also been grown starting with enriched 11B isotope, making them suitable
for neutron scattering experiments.Comment: 4 pages, 5 figures. Accepted for publication in Journal of Crystal
Growt
Torque magnetometry study of the spin reorientation transition and temperature-dependent magnetocrystalline anisotropy in NdCo5
We present the results of torque magnetometry and magnetic susceptibility measurements to study in detail the spin reorientation transition (SRT) and magnetic anisotropy in the permanent magnet NdCo5. We further show simulations of the measurements using first-principles calculations based on density-functional theory and the disordered local moment picture of magnetism at finite temperatures. The good agreement between theory and experimental data leads to a detailed description of the physics underpinning the SRT. In particular we are able to resolve the magnetization of, and to reveal a canting between, the Nd and Co sublattices. The torque measurements carried out in the ac and ab planes near the easy direction allow us to estimate the anisotropy constants, K 1, K 2 and K 4 and their temperature dependences. Torque curves, Ï(Îł) recorded by varying the direction of a constant magnetic field in the crystallographic ac plane show a reversal in the polarity as the temperature is changed across the SRT (240 < T < 285 K). Within this domain, Ï(Îł) exhibits unusual features different to those observed above and below the transition. The single crystals of NdCo5 were grown using the optical floating zone technique
Static magnetic moments revealed by muon spin relaxation and thermodynamic measurements in quantum spin ice YbTiO
We present muon spin relaxation (SR) and specific-heat versus
temperature measurements on polycrystalline and single-crystal samples
of the pyrochlore magnet YbTiO. exhibits a sharp peak at a
of 0.21 and 0.26~K for the single-crystal and polycrystalline
samples respectively. For both samples, the magnetic entropy released between
50~mK and 30~K amounts to per Yb. At temperatures below
we observe a steep drop in the asymmetry of the zero-field SR time spectra
at short time scales, as well as a decoupling of the muon spins from the
internal field in longitudinal magnetic fields of ~T for both the
polycrystalline and single-crystal samples. These muon data are indicative of
static magnetic moments. Our results are consistent with the onset of
long-range magnetic order in both forms of YbTiO.Comment: 6 pages, 4 figures, accepted to PR
Tunability of the spin reorientation transitions with pressure in NdCo5
We present pressure-dependent magnetization measurements carried out in the domain of the spin reorientation transitions (SRTs) of a NdCo5 single crystal. The application of a hydrostatic pressure leads to a shift in the SRTs to higher temperatures. This shift is found to be very sensitive to pressure, with the SRT temperatures increasing at a rate of â17 K/GPa. To explain the experimental results, we have also performed first-principles calculations of the SRT temperatures for different applied strains, which corroborate the experimental findings. The calculations attribute the pressure dependence of the SRTs to a faster weakening of the Co contribution to the magnetocrystalline anisotropy with pressure compared to the Nd contribution
Single crystal growth, structure and magnetic properties of Pr2Hf2O7 pyrochlore
Large single crystals of the pyrochlore Pr2Hf2O7 have been successfully grown
by the floating zone technique using an optical furnace equipped with high
power Xenon arc lamps. Structural investigations have been carried out by both
synchrotron X-ray and neutron powder diffraction to establish the
crystallographic structure of the materials produced. The magnetic properties
of the single crystals have been determined for magnetic fields applied along
different crystallographic axes. The results reveal that Pr2Hf2O7 is an
interesting material for further investigations as a frustrated magnet. The
high quality of the crystals produced make them ideal for detailed
investigations, especially those using neutron scattering techniques.Comment: Accepted for publication in J. Phys.: Condens. Matte
Use of a 3-item short-form version of the Barthel Index for use in stroke: systematic review and external validation
Background and PurposeâThere may be a potential to reduce the number of items assessed in the Barthel Index (BI), and shortened versions of the BI have been described. We sought to collate all existing short-form BI (SF-BI) and perform a comparative validation using clinical trial data.
MethodsâWe performed a systematic review across multidisciplinary electronic databases to find all published SF-BI. Our validation used the VISTA (Virtual International Stroke Trials Archive) resource. We describe concurrent validity (agreement of each SF-BI with BI), convergent and divergent validity (agreement of each SF-BI with other outcome measures available in the data set), predictive validity (association of prognostic factors with SF-BI outcomes), and content validity (item correlation and exploratory factor analyses).
ResultsâFrom 3546 titles, we found 8 articles describing 6 differing SF-BI. Using acute trial data (n=8852), internal reliability suggested redundancy in BI (Cronbach α, 0.96). Each SF-BI demonstrated a strong correlation with BI, modified Rankin Scale, National Institutes of Health Stroke Scale (all Ïâ„0.83; P<0.001). Using rehabilitation trial data (n=332), SF-BI demonstrated modest correlation with quality of life measures Stroke Impact Scale and 5 domain EuroQOL (Ïâ„0.50, P<0.001). Prespecified prognostic factors were associated with SF-BI outcomes (all P<0.001). Our factor analysis described a 3 factor structure, and item reduction suggested an optimal 3-item SF-BI comprising bladder control, transfer, and mobility items in keeping with 1 of the 3-item SF-BI previously described in the literature.
ConclusionsâThere is redundancy in the original BI; we have demonstrated internal and external validity of a 3-item SF-BI that should be simple to use
Structure and superconductivity of two different phases of Re3W
Two superconducting phases of Re(3)W have been found with different physical properties. One phase crystallizes in a noncentrosymmetric cubic (alpha-Mn) structure and has a superconducting transition temperature T(c) of 7.8 K. The other phase has a hexagonal centrosymmetric structure and is superconducting with a T(c) of 9.4 K. Switching between the two phases is possible by annealing the sample or remelting it. The properties of both phases of Re(3)W have been characterized by powder neutron diffraction, magnetization, and resistivity measurements. The temperature dependences of the lower and upper critical fields have been measured for both phases. These are used to determine the penetration depths and the coherence lengths for these systems
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