747 research outputs found
Bilateral Sudden Hearing Loss in Waldenstrom's Macroglobulinemia: MR Appearance
AbstractA 46 year-old man with acquired immunodeficiency syndrome presented with sudden development of vertigo and tinnitus and then simultaneous, bilateral, profound, sudden hearing loss. Magnetic resonance imaging showed bilateral high signal within the cochlea, vestibule, and portions of the semicircular canals on the non-enhanced T1-weighted images, most consistent with recent hemorrhage into the otic labyrinth. Serum analysis and bone-marrow biopsy led to diagnosis of Waldenstrom's macroglobulinemia â a likely cause of the presumed hemorrhage
Comparison of the density-matrix renormalization group method applied to fractional quantum Hall systems in different geometries
We report a systematic study of the fractional quantum Hall effect (FQHE)
using the density-matrix renormalization group (DMRG) method on two different
geometries: the sphere and the cylinder. We provide convergence benchmarks
based on model Hamiltonians known to possess exact zero-energy ground states,
as well as an analysis of the number of sweeps and basis elements that need to
be kept in order to achieve the desired accuracy.The ground state energies of
the Coulomb Hamiltonian at and filling are extracted and
compared with the results obtained by previous DMRG implementations in the
literature. A remarkably rapid convergence in the cylinder geometry is noted
and suggests that this boundary condition is particularly suited for the
application of the DMRG method to the FQHE.Comment: 5 pages, 7 figure
Multicomponent fractional quantum Hall effect in graphene
We report observation of the fractional quantum Hall effect (FQHE) in high
mobility multi-terminal graphene devices, fabricated on a single crystal boron
nitride substrate. We observe an unexpected hierarchy in the emergent FQHE
states that may be explained by strongly interacting composite Fermions with
full SU(4) symmetric underlying degrees of freedom. The FQHE gaps are measured
from temperature dependent transport to be up 10 times larger than in any other
semiconductor system. The remarkable strength and unusual hierarcy of the FQHE
described here provides a unique opportunity to probe correlated behavior in
the presence of expanded quantum degrees of freedom.Comment: 5 pages, 3 figure
Associations Between Left Ventricular Dysfunction and Brain Structure and Function: Findings From the SABRE (Southall and Brent Revisited) Study
Background Subclinical left ventricular (LV) dysfunction has been inconsistently associated with early cognitive impairment, and mechanistic pathways have been poorly considered. We investigated the crossâsectional relationship between LV dysfunction and structural/functional measures of the brain and explored the role of potential mechanisms. Method and Results A total of 1338 individuals (69±6 years) from the Southall and Brent Revisited study underwent echocardiography for systolic (tissue Doppler imaging peak systolic wave) and diastolic (left atrial diameter) assessment. Cognitive function was assessed and total and hippocampal brain volumes were measured by magnetic resonance imaging. Global LV function was assessed by circulating Nâterminal proâbrain natriuretic peptide. The role of potential mechanistic pathways of arterial stiffness, atherosclerosis, microvascular disease, and inflammation were explored. After adjusting for age, sex, and ethnicity, lower systolic function was associated with lower total brain (beta±standard error, 14.9±3.2 cm3; P<0.0001) and hippocampal volumes (0.05±0.02 cm3, P=0.01). Reduced diastolic function was associated with poorer working memory (â0.21±0.07, P=0.004) and fluency scores (â0.18±0.08, P=0.02). Reduced global LV function was associated with smaller hippocampal volume (â0.10±0.03 cm3, P=0.004) and adverse visual memory (â0.076±0.03, P=0.02) and processing speed (0.063±0.02, P=0.006) scores. Separate adjustment for concomitant cardiovascular risk factors attenuated associations with hippocampal volume and fluency only. Further adjustment for the alternative pathways of microvascular disease or arterial stiffness attenuated the relationship between global LV function and visual memory. Conclusions In a communityâbased sample of older people, measures of LV function were associated with structural/functional measures of the brain. These associations were not wholly explained by concomitant risk factors or potential mechanistic pathways
The Density Matrix Renormalization Group for finite Fermi systems
The Density Matrix Renormalization Group (DMRG) was introduced by Steven
White in 1992 as a method for accurately describing the properties of
one-dimensional quantum lattices. The method, as originally introduced, was
based on the iterative inclusion of sites on a real-space lattice. Based on its
enormous success in that domain, it was subsequently proposed that the DMRG
could be modified for use on finite Fermi systems, through the replacement of
real-space lattice sites by an appropriately ordered set of single-particle
levels. Since then, there has been an enormous amount of work on the subject,
ranging from efforts to clarify the optimal means of implementing the algorithm
to extensive applications in a variety of fields. In this article, we review
these recent developments. Following a description of the real-space DMRG
method, we discuss the key steps that were undertaken to modify it for use on
finite Fermi systems and then describe its applications to Quantum Chemistry,
ultrasmall superconducting grains, finite nuclei and two-dimensional electron
systems. We also describe a recent development which permits symmetries to be
taken into account consistently throughout the DMRG algorithm. We close with an
outlook for future applications of the method.Comment: 48 pages, 17 figures Corrections made to equation 19 and table
Environment-mediated structure, surface redox activity and reactivity of ceria nanoparticles
Nanomaterials, with potential application as bio-medicinal agents, exploit the chemical properties of a solid, with the ability to be transported (like a molecule) to a variety of bodily compartments. However, the chemical environment can change significantly the structure and hence properties of a nanomaterial. Accordingly, its surface reactivity is critically dependent upon the nature of the (biological) environment in which it resides. Here, we use Molecular Dynamics (MD) simulation, Density Functional Theory (DFT) and aberration corrected TEM to predict and rationalise differences in structure and hence surface reactivity of ceria nanoparticles in different environments. In particular we calculate reactivity 'fingerprints' for unreduced and reduced ceria nanoparticles immersed in water and in vacuum. Our simulations predict higher activities of ceria nanoparticles, towards oxygen release, when immersed in water because the water quenches the coordinative unsaturation of surface ions. Conversely, in vacuum, surface ions relax into the body of the nanoparticle to relieve coordinative unsaturation, which increases the energy barriers associated with oxygen release. Our simulations also reveal that reduced ceria nanoparticles are more active towards surface oxygen release compared to unreduced nanoceria. In parallel, experiment is used to explore the activities of ceria nanoparticles that have suffered a change in environment. In particular, we compare the ability of ceria nanoparticles, in an aqueous environment, to scavenge superoxide radicals compared to the same batch of nanoparticles, which have first been dried and then rehydrated. The latter show a distinct reduction in activity, which we correlate to a change in the redox chemistry associated with moving between different environments. The reactivity of ceria nanoparticles is therefore not only environment dependent, but is also influenced by the transport pathway or history required to reach the particular environment in which its reactivity is to be exploited. Ă© 2013 The Royal Society of Chemistry
Differential virulence of Candida glabrata glycosylation mutants
The fungus Candida glabrata is an important and increasingly common pathogen of humans, particularly in immunocompromised hosts. Despite this, little is known about the attributes that allow this organism to cause disease or its interaction with the host immune system. However, in common with other fungi, the cell wall of C. glabrata is the initial point of contact between the host and pathogen, and as such, it is likely to play an important role in mediating interactions and hence virulence. Here, we show both through genetic complementation and polysaccharide structural analyses that C. glabrata ANP1, MNN2, and MNN11 encode functional orthologues of the respective Saccharomyces cerevisiae mannosyltransferases. Furthermore, we show that deletion of the C. glabrata Anp1, Mnn2, and Mnn11 mannosyltransferases directly affects the structure of the fungal N-linked mannan, in line with their predicted functions, and this has implications for cell wall integrity and consequently virulence. C. glabrata anp1 and mnn2 mutants showed increased virulence, compared with wild-type (and mnn11) cells. This is in contrast to Candida albicans where inactivation of genes involved in mannan biosynthesis has usually been linked to an attenuation of virulence. In the long term, a better understanding of the attributes that allow C. glabrata to cause disease will provide insights that can be adopted for the development of novel therapeutic and diagnostic approaches
Non-thermal emissions from outer magnetospheric accelerators of middle-aged pulsars
We discuss -ray emissions from the outer gap accelerators of
middle-aged pulsars for part of the series of our studies. A two-dimensional
electrodynamic model is used to solve the distribution of accelerating electric
fields with electron and positron pair creation and radiation processes in the
magnetic meridional plane. We compute the curvature radiation and the
synchrotron radiation by solving the evolution of the Lorentz factor and the
pitch angle. The calculated spectra are compared with observed phase-averaged
spectra. We also use a three-dimensional geometrical model to discuss the pulse
profiles. We argue that the outer gap of middle-aged pulsars occupies the whole
region between the last-open field lines and the critical magnetic field lines,
which are perpendicular to the rotational axis at the light cylinder. We assume
that there is no outer gap accelerator inside the light cylinder between the
rotational axis and the critical magnetic field lines. For the Geminga pulsar,
we demonstrate that the outward curvature radiation dominates in the spectrum
above 10 MeV, while the inward synchrotron radiation dominates below 10 MeV. We
find that the computed spectrum is consistent with the observations in X-ray
through -ray bands. With the pulse morphology of the -ray
emissions, we argue that the inclination angle and the viewing angle for the
Geminga pulsar are and ,
respectively.Comment: 29pages, 11 figure
Small Brain Lesions and Incident Stroke and Mortality: A Cohort Study
Although cerebral lesions â„3mm on imaging are associated with incident stroke, lesions < 3mm are typically ignored
Suppression of Stochastic Domain Wall Pinning Through Control of Gilbert Damping
Finite temperature micromagnetic simulations were used to investigate the magnetisation structure, propagation dynamics and stochastic pinning of domain walls in rare earth-doped Ni80Fe20 nanowires. We first show how the increase of the Gilbert damping, caused by the inclusion rare-earth dopants such as holmium, acts to suppress Walker breakdown phenomena. This allows domain walls to maintain consistent magnetisation structures during propagation. We then employ finite temperature simulations to probe how this affects the stochastic pinning of domain walls at notch-shaped artificial defect sites. Our results indicate that the addition of even a few percent of holmium allows domain walls to pin with consistent and well-defined magnetisation configurations, thus suppressing dynamically-induced stochastic pinning/depinning phenomena. Together, these results demonstrate a powerful, materials science-based solution to the problems of stochastic domain wall pinning in soft ferromagnetic nanowires
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