7,217 research outputs found
Selective Dynamic Nuclear Spin Polarization in Spin-Blocked Double-Dot
We study the mechanism of dynamical nuclear spin polarization by hyperfine
interaction in spin-blocked double quantum dot system. We calculate the
hyperfine transition rates and solve the master equations for the nuclear
spins. Specifically, we incorporate the effects of the nuclear quadrupole
coupling due to the doping-induced local lattice distortion and strain. Our
results show that nuclear quadrupole coupling induced by the 5% indium
substitution can be used to explain the recent experimental observation of
missing arsenic NMR signal in the spin-blocked double dots.Comment: 4 pages, 3 figure
Frequency control of photonic crystal membrane resonators by mono-layer deposition
We study the response of GaAs photonic crystal membrane resonators to thin
film deposition. Slow spectral shifts of the cavity mode of several nanometers
are observed at low temperatures, caused by cryo-gettering of background
molecules. Heating the membrane resets the drift and shielding will prevent
drift altogether. In order to explore the drift as a tool to detect surface
layers, or to intentionally shift the cavity resonance frequency, we studied
the effect of self-assembled monolayers of polypeptide molecules attached to
the membranes. The 2 nm thick monolayers lead to a discrete step in the
resonance frequency and partially passivate the surface.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let
Reduced functional measure of cardiovascular reserve predicts admission to critical care unit following kidney transplantation
Background: There is currently no effective preoperative assessment for patients undergoing kidney transplantation that is
able to identify those at high perioperative risk requiring admission to critical care unit (CCU). We sought to determine if
functional measures of cardiovascular reserve, in particular the anaerobic threshold (VO2AT) could identify these patients.
Methods: Adult patients were assessed within 4 weeks prior to kidney transplantation in a University hospital with a 37-bed
CCU, between April 2010 and June 2012. Cardiopulmonary exercise testing (CPET), echocardiography and arterial
applanation tonometry were performed.
Results: There were 70 participants (age 41.7614.5 years, 60% male, 91.4% living donor kidney recipients, 23.4% were
desensitized). 14 patients (20%) required escalation of care from the ward to CCU following transplantation. Reduced
anaerobic threshold (VO2AT) was the most significant predictor, independently (OR = 0.43; 95% CI 0.27–0.68; p,0.001) and
in the multivariate logistic regression analysis (adjusted OR = 0.26; 95% CI 0.12–0.59; p = 0.001). The area under the receiveroperating-
characteristic curve was 0.93, based on a risk prediction model that incorporated VO2AT, body mass index and
desensitization status. Neither echocardiographic nor measures of aortic compliance were significantly associated with CCU
admission.
Conclusions: To our knowledge, this is the first prospective observational study to demonstrate the usefulness of CPET as a
preoperative risk stratification tool for patients undergoing kidney transplantation. The study suggests that VO2AT has the
potential to predict perioperative morbidity in kidney transplant recipients
Real-space Visualization of Charge Density Wave Induced Local Inversion-Symmetry Breaking in a Skyrmion Magnet
Intertwining charge density wave (CDW) with spin and pairing order parameters
is a major focus of contemporary condensed matter physics. Lattice distortions
and local symmetry breaking resulted from CDWs are crucial for the emergence of
correlated and topological states in quantum materials in general. While the
presence of CDWs can be detected by diffraction or spectroscopic techniques,
atomic visualization of the CDW induced lattice distortions remains limited to
CDW with short wavelengths. In this letter, we realized the imaging of
incommensurate long-wavelength CDWs based on cryogenic four-dimensional
scanning transmission electron microscopy (cryo-4DSTEM). By visualizing the
incommensurate CDW induced lattice modulations in a skyrmion magnet EuAl4, we
discover two out-of-phase intra-unit cell shear modulations that specifically
break the local inversion-symmetry. Our results provide direct evidence for the
intertwined spin and charge orders in EuAl4 and key information about local
symmetry. Furthermore, we establish cryo-4DSTEM as an indispensable approach to
understand CDW induced new quantum states of matter
Panoramic insights into microevolution and macroevolution of a Prevotella copri-containing lineage in primate guts
Prevotella copri and its related taxa are widely detected in mammalian gut microbiomes and have been linked with an enterotype in humans. However, their microevolution and macroevolution among hosts are poorly characterized. In this study, extensively collected marker genes and genomes were analyzed to trace their evolutionary history, host specificity, and biogeographic distribution. Investigations based on marker genes and genomes suggest that a P. copri-containing lineage (PCL) harbors diverse species in higher primates. Firstly, P. copri in the human gut consisted of multiple groups exhibiting high genomic divergence and conspicuous but non-strict biogeographic patterns. Most African strains with high genomic divergence from other strains were phylogenetically located at the root of the species, indicating the co-evolutionary history of P. copri and Homo sapiens. Secondly, although long-term co-evolution between PCL and higher primates was revealed, sporadic signals of co-speciation and extensive host jumping of PCL members were suggested among higher primates. Metagenomic and phylogenetic analyses indicated that P. copri and other PCL species found in domesticated mammals had been recently transmitted from humans. Thirdly, strong evidence was found on the extensively horizontal transfer of genes (e.g., genes encoding carbohydrate-active enzymes) among sympatric P. copri groups and PCL species in the same primate host. Our study provides panoramic insights into the combined effects of vertical and horizontal transmission, as well as potential niche adaptation, on the microevolutionary and macroevolutionary history for an enterotype-representative lineage
A proposal for the measurement of Rashba and Dresselhaus spin-orbit interaction strengths in a single sample
We establish an exact analytical treatment for the determination of the
strengths of the Rashba and Dresselhaus spin-orbit interactions in a single
sample by measuring persistent spin current. A hidden symmetry is exploited in
the Hamiltonian to show that the spin current vanishes when the strength of the
Dresselhaus interaction becomes equal to the strength of the Rashba term. The
results are sustained even in the presence of disorder and thus an experiment
in this regard will be challenging.Comment: 5 pages, 5 figure
Measurement of Rashba and Dresselhaus spin-orbit magnetic fields
Spin-orbit coupling is a manifestation of special relativity. In the
reference frame of a moving electron, electric fields transform into magnetic
fields, which interact with the electron spin and lift the degeneracy of
spin-up and spin-down states. In solid-state systems, the resulting spin-orbit
fields are referred to as Dresselhaus or Rashba fields, depending on whether
the electric fields originate from bulk or structure inversion asymmetry,
respectively. Yet, it remains a challenge to determine the absolute value of
both contributions in a single sample. Here we show that both fields can be
measured by optically monitoring the angular dependence of the electrons' spin
precession on their direction of movement with respect to the crystal lattice.
Furthermore, we demonstrate spin resonance induced by the spin-orbit fields. We
apply our method to GaAs/InGaAs quantum-well electrons, but it can be used
universally to characterise spin-orbit interactions in semiconductors,
facilitating the design of spintronic devices
Spin Electronics and Spin Computation
We review several proposed spintronic devices that can provide new
functionality or improve available functions of electronic devices. In
particular, we discuss a high mobility field effect spin transistor, an
all-metal spin transistor, and our recent proposal of an all-semiconductor spin
transistor and a spin battery. We also address some key issues in
spin-polarized transport, which are relevant to the feasibility and operation
of hybrid semiconductor devices. Finally, we discuss a more radical aspect of
spintronic research--the spin-based quantum computation and quantum information
processing.Comment: 17 pages, 3 figure
Dynamic Localization in Anisotropic Coulomb Systems: Field Induced Crossover of the Exciton Dimension
The effective dimensionality of excitons can be drastically changed by applying an alternating electric field. On the basis of a full three-dimensional description of both coherent and incoherent phenomena in anisotropic structures it is found that appropriate applied oscillating fields change the exciton wave function from anisotropic three dimensional to basically two dimensional. This effective-dimension change is caused by dynamic localization which leads to an increase of the exciton binding energy and of the corresponding oscillator strength
Influence of Static and Dynamic Disorder on the Anisotropy of Emission in the Ring Antenna Subunits of Purple Bacteria Photosynthetic Systems
Using the reduced density matrix formalism the time dependence of the exciton
scattering in light-harvesting ring systems of purple bacteria is calculated.
In contrast to the work of Kumble and Hochstrasser (J. Chem. Phys. 109 (1998)
855) static disorder (fluctuations of the site energies) as well as dynamic
disorder (dissipation) is taken into account. For the description of
dissipation we use Redfield theory in exciton eigenstates without secular
approximation. This is shown to be equivalent to the Markovian limit of Capek's
theory in local states. Circular aggregates with 18 pigments are studied to
model the B850 ring of bacteriochlorophyls within LH2 complexes. It can be
demonstrated that the dissipation is important for the time-dependent
anisotropy of the fluorescence. Smaller values of static disorder are
sufficient to produce the same decay rates in the anisotropy in comparison with
the results by Kumble and Hochstrasser
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