6,702 research outputs found
Cellular structure of -Brauer algebras
In this paper we consider the -Brauer algebra over a commutative
noetherian domain. We first construct a new basis for -Brauer algebras, and
we then prove that it is a cell basis, and thus these algebras are cellular in
the sense of Graham and Lehrer. In particular, they are shown to be an iterated
inflation of Hecke algebras of type Moreover, when is a field of
arbitrary characteristic, we determine for which parameters the -Brauer
algebras are quasi-heredity. So the general theory of cellular algebras and
quasi-hereditary algebras applies to -Brauer algebras. As a consequence, we
can determine all irreducible representations of -Brauer algebras by linear
algebra methods
Diversity of chemistry and excitation conditions in the high-mass star forming complex W33
The object W33 is a giant molecular cloud that contains star forming regions
at various evolutionary stages from quiescent clumps to developed H II regions.
Since its star forming regions are located at the same distance and the primary
material of the birth clouds is probably similar, we conducted a comparative
chemical study to trace the chemical footprint of the different phases of
evolution. We observed six clumps in W33 with the Atacama Pathfinder Experiment
(APEX) telescope at 280 GHz and the Submillimeter Array (SMA) at 230 GHz. We
detected 27 transitions of 10 different molecules in the APEX data and 52
transitions of 16 different molecules in the SMA data. The chemistry on scales
larger than 0.2 pc, which are traced by the APEX data, becomes more
complex and diverse the more evolved the star forming region is. On smaller
scales traced by the SMA data, the chemical complexity and diversity increase
up to the hot core stage. In the H II region phase, the SMA spectra resemble
the spectra of the protostellar phase. Either these more complex molecules are
destroyed or their emission is not compact enough to be detected with the SMA.
Synthetic spectra modelling of the HCO transitions, as detected with the
APEX telescope, shows that both a warm and a cold component are needed to
obtain a good fit to the emission for all sources except for W33 Main1. The
temperatures and column densities of the two components increase during the
evolution of the star forming regions. The integrated intensity ratios
NH(32)/CS(65) and
NH(32)/HCO(43) show clear trends as a
function of evolutionary stage, luminosity, luminosity-to-mass ratio, and
H peak column density of the clumps and might be usable as chemical
clocks.Comment: 66 pages, 28 figures, 8 tables, accepted for publication at A&
Nephrotoxicity, high frequency ototoxicity, efficacy and serum kinetics of once versus thrice daily dosing of netilmicin in patients with serious infections
The effect of dosing regimen on nephrotoxicity, high frequency ototoxicity, efficacy and serum kinetics was studied in a prospective, randomised clinical study. Therapy was started with total daily doses of 6 mg/kg given once (od) or thrice (tid) daily to 56 and 57 patients, respectively. Subsequent doses were adjusted according to serum levels. No major differences in toxicity or efficacy were noticed between od and tid regimens: clinical failures occurred in two and two patients, four and five patients suffered from a decrease of ≥20 dB at least unilaterally at one frequency between 8 and 18 kHz, six and seven patients had a >25 μmol/L or >25% increase in serum creatinine, respectively. Serum creatinine or creatinine clearance did not change significantly during either therapy. Major differences between the two study groups were limited to pharmacokinetic parameters. Od dosing resulted in higher peak (mean of 21.6 vs 7.2 mg/L) and lower trough levels (0.5 vs 1.4mg/L). Half-lives of netilmicin determined between 1 and 8 h increased significantly during therapy with tid (from a mean of 2.75 to a mean of 3.33 h, P<0.01) but not significantly with od (rise from 2.8 to 3.03 h). Much longer half-lives were determined between 8 and 24 h in the od group (mean of 5.7 h, P<0.01). In conclusion, only minimal differences in toxicity and efficacy were observed. Their clinical relevance appears to be minima
Underscreened Kondo effect in S=1 magnetic quantum dots: Exchange, anisotropy and temperature effects
We present a theoretical analysis of the effects of uniaxial magnetic
anisotropy and contact-induced exchange field on the underscreened Kondo effect
in S=1 magnetic quantum dots coupled to ferromagnetic leads. First, by using
the second-order perturbation theory we show that the coupling to
spin-polarized electrode results in an effective exchange field
and an effective magnetic anisotropy . Second, we confirm these
findings by using the numerical renormalization group method, which is employed
to study the dependence of the quantum dot spectral functions, as well as
quantum dot spin, on various parameters of the system. We show that the
underscreened Kondo effect is generally suppressed due to the presence of
effective exchange field and can be restored by tuning the anisotropy constant,
when . The Kondo effect can also be restored by
sweeping an external magnetic field, and the restoration occurs twice in a
single sweep. From the distance between the restored Kondo resonances one can
extract the information about both the exchange field and the effective
anisotropy. Finally, we calculate the temperature dependence of linear
conductance for the parameters where the Kondo effect is restored and show that
the restored Kondo resonances display a universal scaling of Kondo
effect.Comment: 13 pages, 9 figures (version as accepted for publication in Physical
Review B
Noisy Preprocessing and the Distillation of Private States
We provide a simple security proof for prepare & measure quantum key
distribution protocols employing noisy processing and one-way postprocessing of
the key. This is achieved by showing that the security of such a protocol is
equivalent to that of an associated key distribution protocol in which, instead
of the usual maximally-entangled states, a more general {\em private state} is
distilled. Besides a more general target state, the usual entanglement
distillation tools are employed (in particular, Calderbank-Shor-Steane
(CSS)-like codes), with the crucial difference that noisy processing allows
some phase errors to be left uncorrected without compromising the privacy of
the key.Comment: 4 pages, to appear in Physical Review Letters. Extensively rewritten,
with a more detailed discussion of coherent --> iid reductio
Disorder-Induced Multiple Transition involving Z2 Topological Insulator
Effects of disorder on two-dimensional Z2 topological insulator are studied
numerically by the transfer matrix method. Based on the scaling analysis, the
phase diagram is derived for a model of HgTe quantum well as a function of
disorder strength and magnitude of the energy gap. In the presence of sz
non-conserving spin-orbit coupling, a finite metallic region is found that
partitions the two topologically distinct insulating phases. As disorder
increases, a narrow-gap topologically trivial insulator undergoes a series of
transitions; first to metal, second to topological insulator, third to metal,
and finally back to trivial insulator. We show that this multiple transition is
a consequence of two disorder effects; renormalization of the band gap, and
Anderson localization. The metallic region found in the scaling analysis
corresponds roughly to the region of finite density of states at the Fermi
level evaluated in the self-consistent Born approximation.Comment: 5 pages, 5 figure
Soliton effects in dangling-bond wires on Si(001)
Dangling bond wires on Si(001) are prototypical one dimensional wires, which
are expected to show polaronic and solitonic effects. We present electronic
structure calculations, using the tight binding model, of solitons in
dangling-bond wires, and demonstrate that these defects are stable in
even-length wires, although approximately 0.1 eV higher in energy than a
perfect wire. We also note that in contrast to conjugated polymer systems,
there are two types of soliton and that the type of soliton has strong effects
on the energetics of the bandgap edges, with formation of intra-gap states
between 0.1 eV and 0.2 eV from the band edges. These intra-gap states are
localised on the atoms comprising the soliton.Comment: 6 pages, 3 figures, 3 tables, submitted to Phys. Rev.
Aharonov-Bohm Interferometry with Interacting Quantum Dots: Spin Configurations, Asymmetric Interference Patterns, Bias-Voltage-Induced Aharonov-Bohm Oscillations, and Symmetries of Transport Coefficients
We study electron transport through multiply-connected mesoscopic geometries
containing interacting quantum dots. Our formulation covers both equilibrium
and non-equilibrium physics. We discuss the relation of coherent transport
channels through the quantum dot to flux-sensitive Aharonov-Bohm oscillations
in the total conductance of the device. Contributions to transport in first and
second order in the intrinsic line width of the dot levels are addressed in
detail. We predict an interaction-induced asymmetry in the amplitude of the
interference signal around resonance peaks as a consequence of incoherence
associated with spin-flip processes. This asymmetry can be used to probe the
total spin of the quantum dot. Such a probe requires less stringent
experimental conditions than the Kondo effect, which provides the same
information. We show that first-order contributions can be partially or even
fully coherent. This contrasts with the sequential-tunneling picture, which
describes first-order transport as a sequence of incoherent tunneling
processes. We predict bias-voltage induced Aharonov-Bohm oscillations of
physical quantities which are independent of flux in the linear-response
regime. Going beyond the Onsager relations we analyze the relations between the
space symmetry group of the setup and the flux-dependent non-linear
conductance.Comment: 22 pages, 11 figure
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