1,987 research outputs found
Phase-coherent transport in InN nanowires of various sizes
We investigate phase-coherent transport in InN nanowires of various diameters
and lengths. The nanowires were grown by means of plasma-assisted molecular
beam epitaxy. Information on the phase-coherent transport is gained by
analyzing the characteristic fluctuation pattern in the magneto-conductance.
For a magnetic field oriented parallel to the wire axis we found that the
correlation field mainly depends on the wire cross section, while the
fluctuation amplitude is governed by the wire length. In contrast, if the
magnetic field is oriented perpendicularly, for wires longer than approximately
200 nm the correlation field is limited by the phase coherence length. Further
insight into the orientation dependence of the correlation field is gained by
measuring the conductance fluctuations at various tilt angles of the magnetic
field.Comment: 5 pages, 5 figure
An upper bound for the magnetic force gradient in graphite
Cervenka et al. have recently reported ferromagnetism along graphite steps.
We present Magnetic Force microscopy (MFM) data showing that the signal along
the steps is independent of an external magnetic field. Moreover, by combining
Kelvin Probe Force Microscopy (KPFM) and MFM, we are able to separate the
electrostatic and magnetic interactions along the steps obtaining an upper
bound for the magnetic force gradient of about16 microN/m, a figure six times
lower than the lowest theoretical bound reported by Cervenka et al. Our
experiments suggest absence of MFM signal in graphite at room temperature.Comment: 14 pages, including supplemetary informatio
Interface roughness, valley-orbit coupling and valley manipulation in quantum dots
We present a systematic study of interface roughness and its effect on
coherent dynamical processes in quantum dots. The potential due to a sharp,
flat interface lifts the degeneracy of the lowest energy valleys and yields a
set of valley eigenstates. Interface roughness is characterized by fluctuations
in the location of the interface and in the magnitude of the potential step.
Variations in the position of the interface, which are expected to occur on the
length scale of the lattice constant, reduce the magnitude of the valley-orbit
coupling. Variations in the size of the interface potential step alter the
magnitude of the valley-orbit coupling and induce transitions between different
valley eigenstates in dynamics involving two (or more) dots. Such transitions
can be studied experimentally by manipulating the bias between two dots and can
be detected by charge sensing. However, if the random variable characterizing
the position of the interface is correlated over distances of the order of a
quantum dot, which is unlikely but possible, the phase of the valley-orbit
coupling may be different in adjacent dots. In this case tunneling between like
and opposite valley eigenstates is in effect a random variable and cannot be
controlled. We suggest a resonant tunneling experiment that can identify the
matrix elements for tunneling between like and opposite valley eigenstates.Comment: 18 pages, 6 figure
Effects of environmental factors on development of Pyrenopeziza brassicae (light leaf spot) apothecia on oilseed rape debris
Publication no. P-2001-0221-01R. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2001The development of Pyrenopeziza brassicae (light leaf spot) apothecia was studied on petiole debris from artificially infected oilseed rape leaves incubated at temperatures from 6 to 22 degreesC under different wetness regimes and in 16 h light/8 h dark or continuous darkness. There was no significant difference between light treatments in numbers of apothecia that developed. Mature apothecia developed at temperatures from 5 to 18 degreesC but not at 22 degreesC. The rate of apothecial development decreased as temperature decreased from 18 to 5 degreesC; mature apothecia were first observed after 5 days at 18 degreesC and after 15 days at 6 degreesC. Models were fitted to estimates of the time (days) for 50% of the maximum number of apothecia to develop (t(1); model 1, t(1) = 7.6 + 55.8(0.839)(T)) and the time for 50% of the maximum number of apothecia to decay (t(2); model 2, t(2) = 24.2 + 387(0.730)(T)) at temperatures (T) from 6 to 18 degreesC. An interruption in wetness of the petiole debris for 4 days after 4, 7, or 10 days of wetness delayed the time to observation of the first mature apothecia for approximate to4 days and decreased the number of apothecia produced (by comparison with continuous wetness). A relationship was found between water content of pod debris and electrical resistance measured by a debris-wetness sensor. The differences between values of tl predicted by model 1 and observed values of t(1) were 1 to 9 days. Model 2 did not predict t(2); apothecia decayed more quickly under natural conditions than predicted by model 2.Peer reviewe
Covalent Plasmodium falciparum-selective proteasome inhibitors exhibit a low propensity for generating resistance in vitro and synergize with multiple antimalarial agents
Therapeutics with novel modes of action and a low risk of generating resistance are urgently needed to combat drug-resistant Plasmodium falciparum malaria. Here, we report that the peptide vinyl sulfones WLL-vs (WLL) and WLW-vs (WLW), highly selective covalent inhibitors of the P. falciparum proteasome, potently eliminate genetically diverse parasites, including K13-mutant, artemisinin-resistant lines, and are particularly active against ring-stage parasites. Selection studies reveal that parasites do not readily acquire resistance to WLL or WLW and that mutations in the β2, β5 or β6 subunits of the 20S proteasome core particle or in components of the 19S proteasome regulatory particle yield only <five-fold decreases in parasite susceptibility. This result compares favorably against previously published non-covalent inhibitors of the Plasmodium proteasome that can select for resistant parasites with >hundred-fold decreases in susceptibility. We observed no cross-resistance between WLL and WLW. Moreover, most mutations that conferred a modest loss of parasite susceptibility to one inhibitor significantly increased sensitivity to the other. These inhibitors potently synergized multiple chemically diverse classes of antimalarial agents, implicating a shared disruption of proteostasis in their modes of action. These results underscore the potential of targeting the Plasmodium proteasome with covalent small molecule inhibitors as a means of combating multidrug-resistant malaria
Optically controlled 2D tunnelling in GaAs delta-doped p-n junction
A new type of an optically controlled tunnelling process in a specially designed Esaki diode is investigated. The additional peak appears due to tunnelling of 2D electrons accumulated at ground state of delta doped layers embedded nearby the p-n junction into the valence band of the p⁺-contact. It is found that the voltage position of an additional resonant peak shifts to lower bias voltage with increasing both incident light intensity and temperature. Our experimental data and theoretical simulations show that this shift is a result of an electrical field redistribution in the region of the p-n junction caused by non-equilibrium carriers generated with optic or thermal excitation
Measurement of CP Asymmetries and Branching Fractions in Charmless Two-Body B-Meson Decays to Pions and Kaons
We present improved measurements of CP-violation parameters in the decays
, , and , and of
the branching fractions for and . The
results are obtained with the full data set collected at the
resonance by the BABAR experiment at the PEP-II asymmetric-energy factory
at the SLAC National Accelerator Laboratory, corresponding to
million pairs. We find the CP-violation parameter values and
branching fractions where in each case, the first uncertainties are statistical
and the second are systematic. We observe CP violation with a significance of
6.7 standard deviations for and 6.1 standard deviations for
, including systematic uncertainties. Constraints on the
Unitarity Triangle angle are determined from the isospin relations
among the rates and asymmetries. Considering only the solution
preferred by the Standard Model, we find to be in the range
at the 68% confidence level.Comment: 18 pages, 11 postscript figures, submitted to Phys. Rev.
First Observation of CP Violation in B0->D(*)CP h0 Decays by a Combined Time-Dependent Analysis of BaBar and Belle Data
We report a measurement of the time-dependent CP asymmetry of B0->D(*)CP h0
decays, where the light neutral hadron h0 is a pi0, eta or omega meson, and the
neutral D meson is reconstructed in the CP eigenstates K+ K-, K0S pi0 or K0S
omega. The measurement is performed combining the final data samples collected
at the Y(4S) resonance by the BaBar and Belle experiments at the
asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The
data samples contain ( 471 +/- 3 ) x 10^6 BB pairs recorded by the BaBar
detector and ( 772 +/- 11 ) x 10^6, BB pairs recorded by the Belle detector. We
measure the CP asymmetry parameters -eta_f S = +0.66 +/- 0.10 (stat.) +/- 0.06
(syst.) and C = -0.02 +/- 0.07 (stat.) +/- 0.03 (syst.). These results
correspond to the first observation of CP violation in B0->D(*)CP h0 decays.
The hypothesis of no mixing-induced CP violation is excluded in these decays at
the level of 5.4 standard deviations.Comment: 9 pages, 2 figures, submitted to Physical Review Letter
Measurement of Branching Fractions and Rate Asymmetries in the Rare Decays B -> K(*) l+ l-
In a sample of 471 million BB events collected with the BABAR detector at the
PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is
either e+e- or mu+mu-. We report results on partial branching fractions and
isospin asymmetries in seven bins of di-lepton mass-squared. We further present
CP and lepton-flavor asymmetries for di-lepton masses below and above the J/psi
resonance. We find no evidence for CP or lepton-flavor violation. The partial
branching fractions and isospin asymmetries are consistent with the Standard
Model predictions and with results from other experiments.Comment: 16 pages, 14 figures, accepted by Phys. Rev.
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