112 research outputs found
Thermally induced instability of a doubly quantized vortex in a Bose-Einstein condensate
We study the instability of a doubly quantized vortex topologically imprinted
on Na condensate, as reported in recent experiment [Phys. Rev. Lett.
\textbf{93}, 160406 (2004)]. We have performed numerical simulations using
three-dimensional Gross-Pitaevskii equation with classical thermal noise.
Splitting of a doubly quantized vortex turns out to be a process that is very
sensitive to the presence of thermal atoms. We observe that even ve ry small
thermal fluctuations, corresponding to 10 to 15% of thermal atoms, ca use the
decay of doubly quantized vortex into two singly quantized vortices in tens of
milliseconds. As in the experiment, the lifetime of doubly quantized vortex i s
a monotonic function of the interaction strength.Comment: 4 pages, 5 figure
Growth conditions, structure, and superconductivity of pure and metal-doped FeTe1-xSex single crystals
Superconducting single crystals of pure FeTe1 xSex and FeTe0.65Se0.35 doped
with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd
into Fe ions site have been grown applying Bridgman's method. It has been found
that the sharpness of transition to the superconducting state in FeTe1 xSex is
evidently inversely correlated with crystallographic quality of the crystals.
Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in
FeTe0.65Se0.35 crystals. The remaining examined ions do not incorporate into
the crystal structure. Nevertheless, they form inclusions together with
selenium, tellurium and/or iron, what changes the chemical composition of host
matrix and therefore influences Tc value. Small disorder introduced into
magnetic sublattice, by partial replacement of Fe ions by slight amount of
nonmagnetic ions of Cu (~ 1.5 at%) or by magnetic ions of Ni (~ 2 at%) and Co
(~5 at%) with spin value different than that of Fe ion, completely suppresses
superconductivity in FeTe1 xSex system. This indicates that even if
superconductivity is observed in the system containing magnetic ions it can not
survive when the disorder in magnetic ions sublattice is introduced, most
likely because of magnetic scattering of Cooper pairs.Comment: 18 pages, 12 figures, 3 table
Microstructural magnetic phases in superconducting FeTe0.65Se0.35
In this paper, we address a number of outstanding issues concerning the
nature and the role of magnetic inhomogenities in the iron chalcogenide system
FeTe1-xSex and their correlation with superconductivity in this system. We
report morphology of superconducting single crystals of FeTe0.65Se0.35 studied
with transmission electron microscopy, high angle annular dark field scanning
transmission electron microscopy and their magnetic and superconducting
properties characterized with magnetization, specific heat and magnetic
resonance spectroscopy. Our data demonstrate a presence of nanometre scale
hexagonal regions coexisting with tetragonal host lattice, a chemical disorder
demonstrating non homogeneous distribution of host atoms in the crystal
lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From
magnetic data and ferromagnetic resonance temperature dependence, we attribute
magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry
nanometre scale regions with structure of Fe7Se8 type. Our results suggest that
nonhomogeneous distribution of host atoms might be an intrinsic feature of
superconducting Fe-Te-Se chalcogenides and we find a surprising correlation
indicating that faster grown crystal of inferior crystallographic properties is
a better superconductor.Comment: 16 pages, 8 figures, 2 table
Phonon promoted charge density wave in topological kagome metal ScVSn
Charge density wave (CDW) orders in vanadium-based kagome metals have
recently received tremendous attention due to their unique properties and
intricate interplay with exotic correlated phenomena, topological and
symmetry-breaking states. However, the origin of the CDW order remains a topic
of debate. The discovery of ScVSn, a vanadium-based bilayer kagome
metal exhibiting an in-plane x 30
CDW order with time-reversal symmetry breaking, provides a novel platform to
explore the underlying mechanism behind the unconventional CDW. Here, we
combine high-resolution angle-resolved photoemission spectroscopy, Raman
scattering measurements and density functional theory to investigate the
electronic structures and phonon modes of ScVSn and their evolution
with temperature. We identify topologically nontrivial Dirac surface states and
multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with
one VHS near the K point exhibiting nesting wave vectors in proximity to the
x 30 CDW wave vector. Additionally,
Raman measurements indicate a strong intrinsic electron-phonon coupling in
ScVSn, as evidenced by the presence of a two-phonon mode and a
large frequency amplitude mode. Our findings highlight the fundamental role of
lattice degrees of freedom in promoting the CDW in ScVSn and
provide important insights into the fascinating correlation phenomena observed
in kagome metals
Morphological Identification and Single-Cell Genomics of Marine Diplonemids
Recent global surveys of marine biodiversity have revealed that a group of organisms known as âmarine diplonemidsâ constitutes one of the most abundant and diverse planktonic lineages 1. Though discovered over a decade ago 2, 3, their potential importance was unrecognized, and our knowledge remains restricted to a single gene amplified from environmental DNA, the 18S rRNA gene (small subunit SSU). Here, we use single-cell genomics (SCG) and microscopy to characterize ten marine diplonemids, isolated from a range of depths in the eastern North Pacific Ocean. Phylogenetic analysis confirms that the isolates reflect the entire range of marine diplonemid diversity, and comparisons to environmental SSU surveys show that sequences from the isolates range from rare to superabundant, including the single most common marine diplonemid known. SCG generated a total of âŒ915 Mbp of assembled sequence across all ten cells and âŒ4,000 protein-coding genes with homologs in the Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology database, distributed across categories expected for heterotrophic protists. Models of highly conserved genes indicate a high density of non-canonical introns, lacking conventional GT-AG splice sites. Mapping metagenomic datasets 4 to SCG assemblies reveals virtually no overlap, suggesting that nuclear genomic diversity is too great for representative SCG data to provide meaningful phylogenetic context to metagenomic datasets. This work provides an entry point to the future identification, isolation, and cultivation of these elusive yet ecologically important cells. The high density of nonconventional introns, however, also portends difficulty in generating accurate gene models and highlights the need for the establishment of stable cultures and transcriptomic analyses. © 2016 Elsevier Lt
Glutathione and glutamate in schizophrenia: a 7T MRS study
In schizophrenia, abnormal neural metabolite concentrations may arise from cortical damage following neuroinflammatory processes implicated in acute episodes. Inflammation is associated with increased glutamate, whereas the antioxidant glutathione may protect against inflammation-induced oxidative stress. We hypothesized that patients with stable schizophrenia would exhibit a reduction in glutathione, glutamate and/or glutamine in the cerebral cortex, consistent with a postinflammatory response, and that this reduction would be most marked in patients with residual schizophrenia an early stage with positive psychotic symptoms has progressed to a late stage characterised by long-term negative symptoms and impairments. We recruited 28 patients with stable schizophrenia and 45 healthy participants matched for age, gender and parental socio-economic status. We measured glutathione, glutamate and glutamine concentrations in the anterior cingulate cortex (ACC), left insula, and visual cortex using 7T proton Magnetic Resonance Spectroscopy (MRS). Glutathione and glutamate were significantly correlated in all three voxels. Glutamine concentrations across the three voxels were significantly correlated with each other. Principal Components Analysis (PCA) produced three clear components: an ACC glutathione-glutamate component; an insula-visual glutathione-glutamate component; and a glutamine component. Patients with stable schizophrenia had significantly lower scores on the ACC glutathione-glutamate component, an effect almost entirely leveraged by the sub-group of patients with residual schizophrenia. All three metabolite concentration values in the ACC were significantly reduced in this group. These findings are consistent with the hypothesis that excito-toxicity during the acute phase of illness leads to reduced glutathione and glutamate in the residual phase of the illness
Improving the clinical assessment of consciousness with advances in electrophysiological and neuroimaging techniques
In clinical neurology, a comprehensive understanding of consciousness has been regarded as an abstract concept - best left to philosophers. However, times are changing and the need to clinically assess consciousness is increasingly becoming a real-world, practical challenge. Current methods for evaluating altered levels of consciousness are highly reliant on either behavioural measures or anatomical imaging. While these methods have some utility, estimates of misdiagnosis are worrisome (as high as 43%) - clearly this is a major clinical problem. The solution must involve objective, physiologically based measures that do not rely on behaviour. This paper reviews recent advances in physiologically based measures that enable better evaluation of consciousness states (coma, vegetative state, minimally conscious state, and locked in syndrome). Based on the evidence to-date, electroencephalographic and neuroimaging based assessments of consciousness provide valuable information for evaluation of residual function, formation of differential diagnoses, and estimation of prognosis
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