4,546 research outputs found
Comparison of two methods for describing the strain profiles in quantum dots
The electronic structure of interfaces between lattice-mismatched
semiconductor is sensitive to the strain. We compare two approaches for
calculating such inhomogeneous strain -- continuum elasticity (CE, treated as a
finite difference problem) and atomistic elasticity (AE). While for small
strain the two methods must agree, for the large strains that exist between
lattice-mismatched III-V semiconductors (e.g. 7% for InAs/GaAs outside the
linearity regime of CE) there are discrepancies. We compare the strain profile
obtained by both approaches (including the approximation of the correct C_2
symmetry by the C_4 symmetry in the CE method), when applied to C_2-symmetric
InAs pyramidal dots capped by GaAs.Comment: To appear in J. Appl. Physic
Theoretical interpretation of the experimental electronic structure of lens shaped, self-assembled InAs/GaAs quantum dots
We adopt an atomistic pseudopotential description of the electronic structure
of self-assembled, lens shaped InAs quantum dots within the ``linear
combination of bulk bands'' method. We present a detailed comparison with
experiment, including quantites such as the single particle electron and hole
energy level spacings, the excitonic band gap, the electron-electron, hole-hole
and electron hole Coulomb energies and the optical polarization anisotropy. We
find a generally good agreement, which is improved even further for a dot
composition where some Ga has diffused into the dots.Comment: 16 pages, 5 figures. Submitted to Physical Review
Reintegrating Biology through the Nexus of Energy, Information, and Matter
Information, energy, and matter are fundamental properties of all levels of biological organization, and life emerges from the continuous flux of matter, energy, and information. This perspective piece defines and explains each of the three pillars of this nexus. We propose that a quantitative characterization of the complex interconversions between matter, energy, and information that compose this nexus will help us derive biological insights that connect phenomena across different levels of biological organization. We articulate examples from multiple biological scales that highlight how this nexus approach leads to a more complete understanding of the biological system. Metrics of energy, information, and matter can provide a common currency that helps link phenomena across levels of biological organization. The propagation of energy and information through levels of biological organization can result in emergent properties and system-wide changes that impact other hierarchical levels. Deeper consideration of measured imbalances in energy, information, and matter can help researchers identify key factors that influence system function at one scale, highlighting avenues to link phenomena across levels of biological organization and develop predictive models of biological systems
A pseudopotential study of electron-hole excitations in colloidal, free-standing InAs quantum dots
Excitonic spectra are calculated for free-standing, surface passivated InAs
quantum dots using atomic pseudopotentials for the single-particle states and
screened Coulomb interactions for the two-body terms. We present an analysis of
the single particle states involved in each excitation in terms of their
angular momenta and Bloch-wave parentage. We find that (i) in agreement with
other pseudopotential studies of CdSe and InP quantum dots, but in contrast to
k.p calculations, dot states wavefunction exhibit strong odd-even angular
momentum envelope function mixing (e.g. with ) and large
valence-conduction coupling. (ii) While the pseudopotential approach produced
very good agreement with experiment for free-standing, colloidal CdSe and InP
dots, and for self-assembled (GaAs-embedded) InAs dots, here the predicted
spectrum does {\em not} agree well with the measured (ensemble average over dot
sizes) spectra. (1) Our calculated excitonic gap is larger than the PL measure
one, and (2) while the spacing between the lowest excitons is reproduced, the
spacings between higher excitons is not fit well. Discrepancy (1) could result
from surface states emission. As for (2), agreement is improved when account is
taken of the finite size distribution in the experimental data. (iii) We find
that the single particle gap scales as (not ), that the
screened (unscreened) electron-hole Coulomb interaction scales as
(), and that the eccitonic gap sclaes as . These scaling
laws are different from those expected from simple models.Comment: 12 postscript figure
MEPicides: Potent antimalarial prodrugs targeting isoprenoid biosynthesis
AbstractThe emergence of Plasmodium falciparum resistant to frontline therapeutics has prompted efforts to identify and validate agents with novel mechanisms of action. MEPicides represent a new class of antimalarials that inhibit enzymes of the methylerythritol phosphate (MEP) pathway of isoprenoid biosynthesis, including the clinically validated target, deoxyxylulose phosphate reductoisomerase (Dxr). Here we describe RCB-185, a lipophilic prodrug with nanomolar activity against asexual parasites. Growth of P. falciparum treated with RCB-185 was rescued by isoprenoid precursor supplementation, and treatment substantially reduced metabolite levels downstream of the Dxr enzyme. In addition, parasites that produced higher levels of the Dxr substrate were resistant to RCB-185. Notably, environmental isolates resistant to current therapies remained sensitive to RCB-185, the compound effectively treated sexually-committed parasites, and was both safe and efficacious in malaria-infected mice. Collectively, our data demonstrate that RCB-185 potently and selectively inhibits Dxr in P. falciparum, and represents a promising lead compound for further drug development.</jats:p
Coulomb Distortion Effects for (e,e'p) Reactions at High Electron Energy
We report a significant improvement of an approximate method of including
electron Coulomb distortion in electron induced reactions at momentum transfers
greater than the inverse of the size of the target nucleus. In particular, we
have found a new parametrization for the elastic electron scattering phase
shifts that works well at all electron energies greater than 300 . As an
illustration, we apply the improved approximation to the reaction
from medium and heavy nuclei. We use a relativistic ``single particle'' model
for as as applied to and to recently measured data
at CEBAF on to investigate Coulomb distortion effects while
examining the physics of the reaction.Comment: 14 pages, 3 figures, PRC submitte
Impulsivity is Associated with Increased Metabolism in the Fronto-Insular Network in Parkinson’s Disease
Front. Behav. Neurosci. 9:317. doi: 10.3389/fnbeh.2015.00317 Various neuroimaging studies demonstrated that the fronto-insular network is implicated in impulsive behavior. We compared glucose metabolism (as a proxy measure of neural activity) among 24 patients with Parkinson’s disease (PD) who presented with low or high levels of impulsivity based on the Barratt Impulsiveness Scale 11 (BIS) scores. Subjects underwent 18-fluorodeoxyglucose positron emission tomography (FDG-PET) and the voxel-wise group difference of FDG-metabolism was analyzed in Statistical Parametric Mapping (SPM8). Subsequently, we performed a partial correlation analysis between the FDG-metabolism and BIS scores, controlling for covariates (i.e., age, sex, severity of disease and levodopa equivalent daily doses). Voxel-wise group comparison revealed higher FDG-metabolism in the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), and right insula in patients with higher impulsivity scores. Moreover, there was a positive correlation between the FDG-metabolism and BIS scores. Our findings provide evidence that high impulsivity is associated with increased FDG-metabolis
Coulomb Charging Effects in an Open Quantum Dot
Low-temperature transport properties of a lateral quantum dot formed by
overlaying finger gates in a clean one-dimensional channel are investigated.
Continuous and periodic oscillations superimposed upon ballistic conductance
steps are observed, when the conductance G of the dot changes within a wide
range 0<G<6e^2/h. Calculations of the electrostatics confirm that the measured
periodic conductance oscillations correspond to successive change of the total
charge of the dot by . By modelling the transport it is shown that the
progression of the Coulomb oscillations into the region G>2e^2/h may be due to
suppression of inter-1D-subband scattering. Fully transmitted subbands
contribute to coherent background of conductance, while sequential tunneling
via weakly transmitted subbands leads to Coulomb charging of the dot.Comment: 12 pages, RevTeX, 15 eps figures included, submitted to Phys. Rev.
Experimental Evidence for Coulomb Charging Effects in an Open Quantum Dot at Zero Magnetic Field
We have measured the low-temperature transport properties of an open quantum
dot formed in a clean one-dimensional channel. For the first time, at zero
magnetic field, continuous and periodic oscillations superimposed upon
ballistic conductance steps are observed when the conductance through the dot
exceeds . We ascribe the observed conductance oscillations to
evidence for Coulomb charging effects in an open dot. This is supported by the
evolution of the oscillating features for as a function of both
temperature and barrier transparency. Our results strongly suggest that at zero
magnetic field, current theoretical and experimental understanding of Coulomb
charging effects overlooks charging in the presence of fully transmitted 1D
channels.Comment: To appear in Phys. Rev. Lett. 81 (Oct 19 issue
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