4,756 research outputs found
Importance of second-order piezoelectric effects in zincblende semiconductors
We show that the piezoelectric effect that describes the emergence of an
electric field in response to a crystal deformation in III-V semiconductors
such as GaAs and InAs has strong contributions from second-order effects that
have been neglected so far. We calculate the second-order piezoelectric tensors
using density functional theory and obtain the piezoelectric field for
[111]-oriented InGaAs quantum wells of realistic dimensions and
concentration . We find that the linear and the quadratic piezoelectric
coefficients have the opposite effect on the field, and for large strains the
quadratic terms even dominate. Thus, the piezoelectric field turns out to be a
rare example of a physical quantity for which the first- and second-order
contributions are of comparable magnitude.Comment: 4 pages, 3 figures, Submitted to Phys. Rev. Let
Solution of the local field equations for self-generated glasses
We present a self-consistent local approach to self generated glassiness
which is based on the concept of the dynamical mean field theory to many body
systems. Using a replica approach to self generated glassiness, we map the
problem onto an effective local problem which can be solved exactly. Applying
the approach to the Brazovskii-model, relevant to a large class of systems with
frustrated micro-phase separation, we are able to solve the self-consistent
local theory without using additional approximations. We demonstrate that a
glassy state found earlier in this model is generic and does not arise from the
use of perturbative approximations. In addition we demonstrate that the glassy
state depends strongly on the strength of the frustrated phase separation in
that model.Comment: 11 pages, 3 figure
Coordination chemistry of amide-functionalised tetraazamacrocycles: structural, relaxometric and cytotoxicity studies
Three different tetraazamacrocyclic ligands containing four amide substituents that feature groups (namely allyl, styryl and propargyl groups) suitable for polymerisation have been synthesised. Gadolinium(III) complexes of these three ligands have been prepared as potential monomers for the synthesis of polymeric MRI contrast agents. To assess the potential of these monomers as MRI contrast agents, their relaxation enhancement properties and cytotoxicity have been determined. A europium(III) complex of one of these ligands (with propargyl substituents) is also presented together with its PARACEST properties. In addition, to gain further insight into the coordination chemistry of the tetra-propargyl substituted ligand, the corresponding zinc(II) and cadmium(II) complexes have been prepared. The X-ray crystal structures of the tetra-propargyl ligand and its corresponding gadolinium(III), zinc(II) and cadmium(II) complexes are also presented
Controls on Stable Water Isotopes in Monsoonal Precipitation Across the Bay of Bengal: Atmosphere and Surface Analysis
Stable hydrogen isotopes in monsoonal precipitation (ÎŽDp) at three sites (Port Blair, Barisal
and Darjeeling) reveal the factors governing ÎŽDp variations over a south-north gradient across the Bay of
Bengal. We found that the ÎŽDp at each site continuously decreases from May to September and these trends
become more pronounced from south to north. The decreasing trends of downstream ÎŽDp closely follow the
decreasing trends of upstream stable hydrogen isotopes in water vapor (ÎŽDv), which indicates that upstream
ÎŽDv properties shape initial spatiotemporal patterns of the downstream ÎŽDp (âshaping effectâ). Additionally,
our results demonstrate that, during moisture transport, upstream vertical air motions (convection and
downward motion) and topographic relief magnify the amplitude of the decreasing trends of downstream
ÎŽD (âmagnifying effectâ). Our findings imply that upstream ÎŽD properties and relevant atmospheric and pv
topographical conditions along the moisture transport pathway need to be considered collectively to better interpret paleoclimate records
Mechanisms of neurodegeneration in a preclinical autosomal dominant retinitis pigmentosa knock-in model with a RhoD190N mutation
D190N, a missense mutation in rhodopsin, causes photoreceptor degeneration in patients with autosomal dominant retinitis pigmentosa (adRP). Two competing hypotheses have been developed to explain why D190N rod photoreceptors degenerate: (a) defective rhodopsin trafficking prevents proteins from correctly exiting the endoplasmic reticulum, leading to their accumulation, with deleterious effects or (b) elevated mutant rhodopsin expression and unabated signaling causes excitotoxicity. A knock-in D190N mouse model was engineered to delineate the mechanism of pathogenesis. Wild type (wt) and mutant rhodopsin appeared correctly localized in rod outer segments of D190N heterozygotes. Moreover, the rhodopsin glycosylation state in the mutants appeared similar to that in wt mice. Thus, it seems plausible that the injurious effect of the heterozygous mutation is not related to mistrafficking of the protein, but rather from constitutive rhodopsin activity and a greater propensity for chromophore isomerization even in the absence of light.We greatly appreciate the assistance of the members of the Bernard & Shirlee Brown Glaucoma laboratory, especially to Chun-Wei Hsu for technical support. SHT is a Burroughs-Wellcome Program in Biomedical Sciences Fellow, and is also supported by the Charles E. Culpeper-Partnership for Cures 07-CS3, Crowley Research Fund, Schneeweiss Stem Cell Fund, New York State N09G-302, Foundation Fighting Blindness [TA-NMT-0116-0692- COLU] (Owings Mills, MD), TS080017 from US Department of Defense, NIH Grants [P30EY019007, R01EY018213, R01EY024698, R01EY026682, R21AG050437], Research to Prevent Blindness (New York, NY), and Joel Hoffmann Scholarship. CSL is the Homer McK. Rees Scholar. JSP is a BEST2016 awardee (BEST/ 2016/030, Conselleria de EducaciĂłn, InvestigaciĂłn, Cultura y Deporte; Generalitat Valenciana) and his research is supported by a Prometeo Grant (PROMETEO/2016/094; Conselleria de EducaciĂłn, InvestigaciĂłn, Cultura y Deporte; Generalitat Valenciana) and by internal funds from Universidad CatĂłlica de Valencia San Vicente MĂĄrtir (2018-128-001). VBM is supported by NIH Grants K08EY020530, R01EY016822, The Doris Duke Charitable Foundation Grant #2013103, and Research to Prevent Blindness (New York, NY); GV is supported by NIH Grants [F30EYE027986 and T32GM007337].Author manuscriptMedicin
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
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