2,980 research outputs found
Electron-phonon scattering in quantum point contacts
We study the negative correction to the quantized value of the
conductance of a quantum point contact due to the backscattering of electrons
by acoustic phonons. The correction shows activated temperature dependence and
also gives rise to a zero-bias anomaly in conductance. Our results are in
qualitative agreement with recent experiments studying the 0.7 feature in the
conductance of quantum point contacts.Comment: 4 pages, no figure
Sensitivity of double resonance alignment magnetometers
We present an experimental study of the intrinsic magnetometric sensitivity
of an optical/rf-frequency double resonance magnetometer in which linearly
polarized laser light is used in the optical pumping and detection processes.
We show that a semi-empirical model of the magnetometer can be used to describe
the magnetic resonance spectra. Then, we present an efficient method to predict
the optimum operating point of the magnetometer, i.e., the light power and rf
Rabi frequency providing maximum magnetometric sensitivity. Finally, we apply
the method to investigate the evolution of the optimum operating point with
temperature. The method is very efficient to determine relaxation rates and
thus allowed us to determine the three collisional disalignment cross sections
for the components of the alignment tensor. Both first and second harmonic
signals from the magnetometer are considered and compared
Electron rescattering at metal nanotips induced by ultrashort laser pulses
We report on the first investigation of plateau and cut-off structures in
photoelectron spectra from nano-scale metal tips interacting with few-cycle
near-infrared laser pulses. These hallmarks of electron rescattering,
well-known from atom-laser interaction in the strong-field regime, appear at
remarkably low laser intensities with nominal Keldysh parameters of the order
of . Quantum and quasi-classical simulations reveal that a large
field enhancement near the tip and the increased backscattering probability at
a solid-state target play a key role. Plateau electrons are by an order of
magnitude more abundant than in comparable atomic spectra, reflecting the high
density of target atoms at the surface. The position of the cut-off serves as
an in-situ probe for the locally enhanced electric field at the tip apex
Trait-Based Comparison of Coral and Sponge Microbiomes
Corals and sponges harbor diverse microbial communities that are integral to the functioning of the host. While the taxonomic diversity of their microbiomes has been well-established for corals and sponges, their functional roles are less well-understood. It is unclear if the similarities of symbiosis in an invertebrate host would result in functionally similar microbiomes, or if differences in host phylogeny and environmentally driven microhabitats within each host would shape functionally distinct communities. Here we addressed this question, using metatranscriptomic and 16S rRNA gene profiling techniques to compare the microbiomes of two host organisms from different phyla. Our results indicate functional similarity in carbon, nitrogen, and sulfur assimilation, and aerobic nitrogen cycling. Additionally, there were few statistical differences in pathway coverage or abundance between the two hosts. For example, we observed higher coverage of phosphonate and siderophore metabolic pathways in the star coral, Montastraea cavernosa, while there was higher coverage of chloroalkane metabolism in the giant barrel sponge, Xestospongia muta. Higher abundance of genes associated with carbon fixation pathways was also observed in M. cavernosa, while in X. muta there was higher abundance of fatty acid metabolic pathways. Metagenomic predictions based on 16S rRNA gene profiling analysis were similar, and there was high correlation between the metatranscriptome and metagenome predictions for both hosts. Our results highlight several metabolic pathways that exhibit functional similarity in these coral and sponge microbiomes despite the taxonomic differences between the two microbiomes, as well as potential specialization of some microbially based metabolism within each host
Experimental study of laser detected magnetic resonance based on atomic alignment
We present an experimental study of the spectra produced by
optical/radio-frequency double resonance in which resonant linearly polarized
laser light is used in the optical pumping and detection processes. We show
that the experimental spectra obtained for cesium are in excellent agreement
with a very general theoretical model developed in our group and we investigate
the limitations of this model. Finally, the results are discussed in view of
their use in the study of relaxation processes in aligned alkali vapors.Comment: 8 pages, 9 figures. Submitted to Phys. Rev. A. Related to
physics/060523
Capacitance of a quantum dot from the channel-anisotropic two-channel Kondo model
We investigate the charge fluctuations of a large quantum dot coupled to a
two-dimensional electron gas via a quantum point contact following the work of
Matveev. We limit our discussion to the case where exactly two channels enter
the dot and we discuss the role of an anisotropy between the transmission
coefficients (for these two channels) at the constriction. Experimentally, a
channel-anisotropy can be introduced applying a relatively weak in-plane
magnetic field to the system when only one ``orbital'' channel is open. The
magnetic field leads to different transmission amplitudes for spin-up and
spin-down electrons.
In a strong magnetic field the anisotropic two-channel limit corresponds to
two (spin-polarized) orbital channels entering the dot.
The physics of the charge fluctuations can be captured using a mapping on the
channel-anisotropic two-channel Kondo model. For the case of weak reflection at
the point contact this has already briefly been stressed by one of us in PRB
{\bf 64}, 161302R (2001). This mapping is also appropriate to discuss the
conductance behavior of a two-contact set-up in strong magnetic field.
Here, we elaborate on this approach and also discuss an alternative solution
using a mapping on a channel-isotropic Kondo model. In addition we consider the
limit of weak transmission.
We show that the Coulomb-staircase behavior of the charge in the dot as a
function of the gate voltage, is already smeared out by a small
channel-anisotropy both in the weak- and strong transmission limits.Comment: 17 pages, 4 figures, 1 Table; Expands cond-mat/0101126; Sec. VI on
2-contact setup added (Final version for PRB
Contribution of thirdhand smoke to overall tobacco smoke exposure in pediatric patients: study protocol.
BackgroundThirdhand smoke (THS) is the persistent residue resulting from secondhand smoke (SHS) that accumulates in dust, objects, and on surfaces in homes where tobacco has been used, and is reemitted into air. Very little is known about the extent to which THS contributes to children's overall tobacco smoke exposure (OTS) levels, defined as their combined THS and SHS exposure. Even less is known about the effect of OTS and THS on children's health. This project will examine how different home smoking behaviors contribute to THS and OTS and if levels of THS are associated with respiratory illnesses in nonsmoking children.MethodsThis project leverages the experimental design from an ongoing pediatric emergency department-based tobacco cessation trial of caregivers who smoke and their children (NIHR01HD083354). At baseline and follow-up, we will collect urine and handwipe samples from children and samples of dust and air from the homes of smokers who smoke indoors, have smoking bans or who have quit smoking. These samples will be analyzed to examine to what extent THS pollution at home contributes to OTS exposure over and above SHS and to what extent THS continues to persist and contribute to OTS in homes of smokers who have quit or have smoking bans. Targeted and nontargeted chemical analyses of home dust samples will explore which types of THS pollutants are present in homes. Electronic medical record review will examine if THS and OTS levels are associated with child respiratory illness. Additionally, a repository of child and environmental samples will be created.DiscussionThe results of this study will be crucial to help close gaps in our understanding of the types, quantity, and clinical effects of OTS, THS exposure, and THS pollutants in a unique sample of tobacco smoke-exposed ill children and their homes. The potential impact of these findings is substantial, as currently the level of risk in OTS attributable to THS is unknown. This research has the potential to change how we protect children from OTS, by recognizing that SHS and THS exposure needs to be addressed separately and jointly as sources of pollution and exposure.Trial registrationClinicalTrials.gov Identifier: NCT02531594 . Date of registration: August 24, 2015
Subtoxic Concentrations of Hepatotoxic Drugs Lead to Kupffer Cell Activation in a Human In Vitro Liver Model
Drug induced liver injury (DILI) is an idiosyncratic adverse drug reaction
leading to severe liver damage. Kupffer cells (KC) sense hepatic tissue
stress/damage and therefore could be a tool for the estimation of consequent
effects associated with DILI. Aim of the present study was to establish a
human in vitro liver model for the investigation of immune-mediated signaling
in the pathogenesis of DILI. Hepatocytes and KC were isolated from human liver
specimens. The isolated KC yield was cells/g liver tissue with a purity of
>80%. KC activation was investigated by the measurement of reactive oxygen
intermediates (ROI, DCF assay) and cell activity (XTT assay). The initial KC
activation levels showed broad donor variability. Additional activation of KC
using supernatants of hepatocytes treated with hepatotoxic drugs increased KC
activity and led to donor-dependent changes in the formation of ROI compared
to KC incubated with supernatants from untreated hepatocytes. Additionally, a
compound- and donor-dependent increase in proinflammatory cytokines or in
anti-inflammatory cytokines was detected. In conclusion, KC related immune
signaling in hepatotoxicity was successfully determined in a newly established
in vitro liver model. KC were able to detect hepatocyte stress/damage and to
transmit a donor- and compound-dependent immune response via cytokine
production
Separability of Two-Party Gaussian States
We investigate the separability properties of quantum two-party Gaussian
states in the framework of the operator formalism for the density operator.
Such states arise as natural generalizations of the entangled state originally
introduced by Einstein, Podolsky, and Rosen. We present explicit forms of
separable and nonseparable Gaussian states.Comment: Brief Report submitted to Physical Review A, 4 pages, 1 figur
Electron-, Mu-, and Tau-Number Conservation in a Supernova Core
We study if the neutrino mixing parameters suggested by the atmospheric
neutrino anomaly imply chemical equilibrium between mu- and tau-flavored
leptons in a supernova (SN) core. The initial flavor-conversion rate would
indeed be fast if the nu_mu-nu_tau-mixing angle were not suppressed by
second-order refractive effects. The neutrino diffusion coefficients are
different for nu_mu, anti-nu_mu, nu_tau and anti-nu_tau so that neutrino
transport will create a net mu and tau lepton number density. This will
typically lead to a situation where the usual first-order refractive effects
dominate, further suppressing the rate of flavor conversion. Altogether,
neutrino refraction has the nontrivial consequence of guaranteeing the separate
conservation of e, mu, and tau lepton number in a SN core on the infall and
cooling time scales, even when neutrino mixing angles are large.Comment: Slightly expanded version with improved presentation, no changes of
substanc
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