1,640 research outputs found
Competing mechanisms for singlet-triplet transition in artificial molecules
We study the magnetic field induced singlet/triplet transition for two
electrons in vertically coupled quantum dots by exact diagonalization of the
Coulomb interaction. We identify the different mechanisms occurring in the
transition, involving either in-plane correlations or localization in opposite
dots, depending on the field direction. Therefore, both spin and orbital
degrees of freedom can be manipulated by field strength and direction. The
phase diagram of realistic devices is determined.Comment: To appear in Phys. Rev. B - Rapid Comm. - 5 pages, 3 figure
Effects of the field modulation on the Hofstadter's spectrum
We study the effect of spatially modulated magnetic fields on the energy
spectrum of a two-dimensional (2D) Bloch electron. Taking into account four
kinds of modulated fields and using the method of direct diagonalization of the
Hamiltonian matrix, we calculate energy spectra with varying system parameters
(i.e., the kind of the modulation, the relative strength of the modulated field
to the uniform background field, and the period of the modulation) to elucidate
that the energy band structure sensitively depends on such parameters:
Inclusion of spatially modulated fields into a uniform field leads occurrence
of gap opening, gap closing, band crossing, and band broadening, resulting
distinctive energy band structure from the Hofstadter's spectrum. We also
discuss the effect of the field modulation on the symmetries appeared in the
Hofstadter's spectrum in detail.Comment: 7 pages (in two-column), 10 figures (including 2 tables
Left Atrial Size Physiologic Determinants and Clinical Applications
Left atrial (LA) enlargement has been proposed as a barometer of diastolic burden and a predictor of common cardiovascular outcomes such as atrial fibrillation, stroke, congestive heart failure, and cardiovascular death. It has been shown that advancing age alone does not independently contribute to LA enlargement, and the impact of gender on LA volume can largely be accounted for by the differences in body surface area between men and women. Therefore, enlargement of the left atrium reflects remodeling associated with pathophysiologic processes. In this review, we discuss the normal size and phasic function of the left atrium. Further, we outline the clinically important aspects and pitfalls of evaluating LA size, and the methods for assessing LA function using echocardiography. Finally, we review the determinants of LA size and remodeling, and we describe the evidence regarding the prognostic value of LA size. The use of LA volume for risk stratification is an evolving science. More data are required with respect to the natural history of LA remodeling in disease, the degree of LA modifiability with therapy, and whether regression of LA size translates into improved cardiovascular outcomes
Utilizing a biology-driven approach to map the exposome in health and disease:An essential investment to drive the next generation of environmental discovery
BACKGROUND: Recent developments in technologies have offered opportunities to measure the exposome with unprecedented accuracy and scale. However, because most investigations have targeted only a few exposures at a time, it is hypothesized that the majority of the environmental determinants of chronic diseases remain unknown. OBJECTIVES: We describe a functional exposome concept and explain how it can leverage existing bioassays and high-resolution mass spectrometry for exploratory study. We discuss how such an approach can address well-known barriers to interpret exposures and present a vision of next-generation exposomics. DISCUSSION: The exposome is vast. Instead of trying to capture all exposures, we can reduce the complexity by measuring the functional exposome— the totality of the biologically active exposures relevant to disease development—through coupling biochemical receptor-binding assays with affinity purification–mass spectrometry. We claim the idea of capturing exposures with functional biomolecules opens new opportunities to solve critical problems in exposomics, including low-dose detection, unknown annotations, and complex mixtures of exposures. Although novel, biology-based measurement can make use of the existing data processing and bioinformatics pipelines. The functional exposome concept also complements conven-tional targeted and untargeted approaches for understanding exposure-disease relationships. CONCLUSIONS: Although measurement technology has advanced, critical technological, analytical, and inferential barriers impede the detection of many environmental exposures relevant to chronic-disease etiology. Through biology-driven exposomics, it is possible to simultaneously scale up discovery of these causal environmental factors. https://doi.org/10.1289/EHP8327
A vertical diatomic artificial molecule in the intermediate coupling regime in a parallel and perpendicular magnetic field
We present experimental results for the ground state electrochemical
potentials of a few electron semiconductor artificial molecule made by
vertically coupling two quantum dots, in the intermediate coupling regime, in
perpendicular and parallel magnetic fields up to 5 T. We perform a quantitative
analysis based on local-spin density functional theory. The agreement between
theoretical and experimental results is good, and the phase transitions are
well reproduced.Comment: Typeset using Revtex, 13 pages and 8 Postscript figure
SU(3) Predictions for Weak Decays of Doubly Heavy Baryons -- including SU(3) breaking terms
We find expressions for the weak decay amplitudes of baryons containing two b
quarks (or one b and one c quark -- many relationship are the same) in terms of
unknown reduced matrix elements. This project was originally motivated by the
request of the FNAL Run II b Physics Workshop organizers for a guide to
experimentalists in their search for as yet unobserved hadrons. We include an
analysis of linear SU(3) breaking terms in addition to relationships generated
by unbroken SU(3) symmetry, and relate these to expressions in terms of the
complete set of possible reduced matrix elements.Comment: 49 page
Human Embryonic Stem Cell Technology: Large Scale Cell Amplification and Differentiation
Embryonic stem cells (ESC) hold the promise of overcoming many diseases as potential sources of, for example, dopaminergic neural cells for Parkinson’s Disease to pancreatic islets to relieve diabetic patients of their daily insulin injections. While an embryo has the innate capacity to develop fully functional differentiated tissues; biologists are finding that it is much more complex to derive singular, pure populations of primary cells from the highly versatile ESC from this embryonic parent. Thus, a substantial investment in developing the technologies to expand and differentiate these cells is required in the next decade to move this promise into reality. In this review we document the current standard assays for characterising human ESC (hESC), the status of ‘defined’ feeder-free culture conditions for undifferentiated hESC growth, examine the quality controls that will be required to be established for monitoring their growth, review current methods for expansion and differentiation, and speculate on the possible routes of scaling up the differentiation of hESC to therapeutic quantities
IL-21/type I interferon interplay regulates neutrophil-dependent innate immune responses to Staphylococcus aureus
Methicillin-resistant Staphylococcus aureus (MRSA) is a major hospital- and communityacquired pathogen, but the mechanisms underlying host-defense to MRSA remain poorly
understood. Here, we investigated the role of IL-21 in this process. When administered intratracheally into wild-type mice, IL-21 induced granzymes and augmented clearance of pulmonary
MRSA but not when neutrophils were depleted or a granzyme B inhibitor was added.
Correspondingly, IL-21 induced MRSA killing by human peripheral blood neutrophils.
Unexpectedly, however, basal MRSA clearance was also enhanced when IL-21 signaling was
blocked, both in Il21r KO mice and in wild-type mice injected with IL-21R-Fc fusion-protein. This
correlated with increased type I interferon and an IFN-related gene signature, and indeed antiIFNAR1 treatment diminished MRSA clearance in these animals. Moreover, we found that IFNb
induced granzyme B and promoted MRSA clearance in a granzyme B-dependent fashion. These
results reveal an interplay between IL-21 and type I IFN in the innate immune response to MRS
One-loop corrections to omega photoproduction near threshold
One-loop corrections to photoproduction near threshold have been
investigated by using the approximation that all relevant transition amplitudes
are calculated from the tree diagrams of effective Lagrangians. With the
parameters constrained by the data of , , and reactions, it is found that the one-loop effects
due to the intermediate and states can significantly change
the differential cross sections and spin observables. The results from this
exploratory investigation suggest strongly that the coupled-channel effects
should be taken into account in extracting reliable resonance parameters from
the data of vector meson photoproduction in the resonance region.Comment: 19 pages, REVTeX, 14 figures, title changed, revised version to
appear in Phys. Rev.
Site-Selective Passivation of Defects in NiO Solar Photocathodes by Targeted Atomic Deposition
For nanomaterials, surface chemistry can dictate fundamental material properties, including charge-carrier lifetimes, doping levels, and electrical mobilities. In devices, surface defects are usually the key limiting factor for performance, particularly in solar-energy applications. Here, we develop a strategy to uniformly and selectively passivate defect sites in semiconductor nanomaterials using a vapor-phase process termed targeted atomic deposition (TAD). Because defects often consist of atomic vacancies and dangling bonds with heightened reactivity, we observe-for the widely used p-type cathode nickel oxide-that a volatile precursor such as trimethylaluminum can undergo a kinetically limited selective reaction with these sites. The TAD process eliminates all measurable defects in NiO, leading to a nearly 3-fold improvement in the performance of dye-sensitized solar cells. Our results suggest that TAD could be implemented with a range of vapor-phase precursors and be developed into a general strategy to passivate defects in zero-, one-, and two-dimensional nanomaterials
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