301 research outputs found
PMD75 Patient Self-Testing of Oral Anticoagulation Therapy by CoaguChek® XS System. Rapid Health Technology Assessment in Slovak Health Care Environment
The Berry phase of dislocations in graphene and valley conserving decoherence
We demonstrate that dislocations in the graphene lattice give rise to
electron Berry phases equivalent to quantized values {0,1/3,-1/3} in units of
the flux quantum, but with an opposite sign for the two valleys. An elementary
scale consideration of a graphene Aharonov-Bohm ring equipped with valley
filters on both terminals, encircling a dislocation, says that in the regime
where the intervalley mean free path is large compared to the intravalley phase
coherence length, such that the valley quantum numbers can be regarded as
conserved on the relevant scale, the coherent valley-polarized currents
sensitive to the topological phases have to traverse the device many times
before both valleys contribute, and this is not possible at intermediate
temperatures where the latter length becomes of order of the device size, thus
leading to an apparent violation of the basic law of linear transport that
magnetoconductance is even in the applied flux. We discuss this discrepancy in
the Feynman path picture of dephasing, when addressing the transition from
quantum to classical dissipative transport. We also investigate this device in
the scattering matrix formalism, accounting for the effects of decoherence by
the Buttiker dephasing voltage probe type model which conserves the valleys,
where the magnetoconductance remains even in the flux, also when different
decoherence times are allowed for the individual, time reversal connected,
valleys.Comment: 14 pages, 7 figures; revised text, added figure, accepted for
publication by PR
Topological Defects Coupling Smectic Modulations to Intra-unit-cell Nematicity in Cuprate
We study the coexisting smectic modulations and intra-unit-cell nematicity in
the pseudogap states of underdoped Bi2Sr2CaCu2O8+{\delta}. By visualizing their
spatial components separately, we identified 2\pi topological defects
throughout the phase-fluctuating smectic states. Imaging the locations of large
numbers of these topological defects simultaneously with the fluctuations in
the intra-unit-cell nematicity revealed strong empirical evidence for a
coupling between them. From these observations, we propose a Ginzburg-Landau
functional describing this coupling and demonstrate how it can explain the
coexistence of the smectic and intra-unit-cell broken symmetries and also
correctly predict their interplay at the atomic scale. This theoretical
perspective can lead to unraveling the complexities of the phase diagram of
cuprate high-critical-temperature superconductors
Commensurate period Charge Density Modulations throughout the Pseudogap Regime
Theories based upon strong real space (r-space) electron electron
interactions have long predicted that unidirectional charge density modulations
(CDM) with four unit cell (4) periodicity should occur in the hole doped
cuprate Mott insulator (MI). Experimentally, however, increasing the hole
density p is reported to cause the conventionally defined wavevector of
the CDM to evolve continuously as if driven primarily by momentum space
(k-space) effects. Here we introduce phase resolved electronic structure
visualization for determination of the cuprate CDM wavevector. Remarkably, this
new technique reveals a virtually doping independent locking of the local CDM
wavevector at throughout the underdoped phase diagram of the
canonical cuprate . These observations have significant
fundamental consequences because they are orthogonal to a k-space (Fermi
surface) based picture of the cuprate CDM but are consistent with strong
coupling r-space based theories. Our findings imply that it is the latter that
provide the intrinsic organizational principle for the cuprate CDM state
Electronic States of Graphene Grain Boundaries
We introduce a model for amorphous grain boundaries in graphene, and find
that stable structures can exist along the boundary that are responsible for
local density of states enhancements both at zero and finite (~0.5 eV)
energies. Such zero energy peaks in particular were identified in STS
measurements [J. \v{C}ervenka, M. I. Katsnelson, and C. F. J. Flipse, Nature
Physics 5, 840 (2009)], but are not present in the simplest pentagon-heptagon
dislocation array model [O. V. Yazyev and S. G. Louie, Physical Review B 81,
195420 (2010)]. We consider the low energy continuum theory of arrays of
dislocations in graphene and show that it predicts localized zero energy
states. Since the continuum theory is based on an idealized lattice scale
physics it is a priori not literally applicable. However, we identify stable
dislocation cores, different from the pentagon-heptagon pairs, that do carry
zero energy states. These might be responsible for the enhanced magnetism seen
experimentally at graphite grain boundaries.Comment: 10 pages, 4 figures, submitted to Physical Review
Stable Isotope Labeling by Essential Nutrients in Cell Culture for Preparation of Labeled Coenzyme A and Its Thioesters
thalamic damage predicts the evolution of primary progressive multiple sclerosis at 5 years
BACKGROUND AND PURPOSE: Reliable markers to monitor PPMS are still needed. We investigated whether conventional and DTI measures of thalamic damage are predictive of long-term disability accumulation in PPMS. MATERIALS AND METHODS: Brain conventional and DTI scans were obtained at baseline and after a mean follow-up of 15 months in 54 patients with PPMS and 8 healthy controls. Patients were reassessed clinically after 5 years. At baseline and follow-up, measures of lesion load, brain atrophy, and NTV were obtained. MD and FA histograms of the NAWM, the whole GM without the thalami, and the thalami were obtained. A multivariate analysis evaluated the predictors of long-term neurologic deterioration. RESULTS: At follow-up, 35 patients showed disability worsening. At baseline, compared with healthy controls, patients with PPMS had lower NTV ( P P = .002) and higher thalamic ( P = .002) and whole GM without the thalami ( P = .005) MD. During follow-up, the change of thalamic FA was higher in PPMS versus healthy controls ( P = .01). Baseline NTV and thalamic DTI quantities differed significantly between patients with PPMS with and without thalamic lesions. Baseline thalamic quantities were significantly correlated with the extent of brain T2 lesions and the severity of NAWM damage. The multivariate model included average NAWM MD (OR = 1.46, P = .005) and FA thalamic change (OR = 0.84, P = .02) as independent predictors of EDSS score deterioration (Nagelkerke R 2 = 0.55). CONCLUSIONS: Short-term accrual of thalamic damage and the severity of NAWM involvement predict the long-term accumulation of disability in PPMS
Visualizing the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator
Superconductivity emerges from the cuprate antiferromagnetic Mott state with
hole doping. The resulting electronic structure is not understood, although
changes in the state of oxygen atoms appear paramount. Hole doping first
destroys the Mott state yielding a weak insulator where electrons localize only
at low temperatures without a full energy gap. At higher doping, the
'pseudogap', a weakly conducting state with an anisotropic energy gap and
intra-unit-cell breaking of 90\degree-rotational (C4v) symmetry appears.
However, a direct visualization of the emergence of these phenomena with
increasing hole density has never been achieved. Here we report atomic-scale
imaging of electronic structure evolution from the weak-insulator through the
emergence of the pseudogap to the superconducting state in Ca2-xNaxCuO2Cl2. The
spectral signature of the pseudogap emerges at lowest doping from a weakly
insulating but C4v-symmetric matrix exhibiting a distinct spectral shape. At
slightly higher hole-density, nanoscale regions exhibiting pseudogap spectra
and 180\degree-rotational (C2v) symmetry form unidirectional clusters within
the C4v-symmetric matrix. Thus, hole-doping proceeds by the appearance of
nanoscale clusters of localized holes within which the broken-symmetry
pseudogap state is stabilized. A fundamentally two-component electronic
structure11 then exists in Ca2-xNaxCuO2Cl2 until the C2v-symmetric clusters
touch at higher doping, and the long-range superconductivity appears.Comment: See the Nature Physics website for the published version available at
http://dx.doi.org/10.1038/Nphys232
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