554 research outputs found
Magnetic Moment Formation in Graphene Detected by Scattering of Pure Spin Currents
Hydrogen adatoms are shown to generate magnetic moments inside single layer
graphene. Spin transport measurements on graphene spin valves exhibit a dip in
the non-local spin signal as a function of applied magnetic field, which is due
to scattering (relaxation) of pure spin currents by exchange coupling to the
magnetic moments. Furthermore, Hanle spin precession measurements indicate the
presence of an exchange field generated by the magnetic moments. The entire
experiment including spin transport is performed in an ultrahigh vacuum
chamber, and the characteristic signatures of magnetic moment formation appear
only after hydrogen adatoms are introduced. Lattice vacancies also demonstrate
similar behavior indicating that the magnetic moment formation originates from
pz-orbital defects.Comment: accepted to Phys. Rev. Let
Stem Cell Interventions for Bone Healing: Fractures and Osteoporosis
With the ageing population, musculoskeletal conditions are becoming more inherent. Delayed union is defined as a slower than normal fracture healing response, with no healing after 4 to 6 months; however, union is anticipated given sufficient time. In the context of delayed/non-union, fragility fractures in osteoporotic populations carry significant patient morbidity and socioeconomic costs. Multiple mechanisms hinder fracture healing in osteoporotic patients, imbalanced bone remodelling leads to impaired bone microarchitecture due to reduced osteoblast number and activity and as such, callus formation is diminished. Since stem cells can self-renew and differentiate into various tissue lineages, they are becoming very popular in tissue regeneration in musculoskeletal conditions. In this review we discuss the role of stem cells in physiological fracture healing and their potential therapeutic use following a fracture. We explore the potential of stem cells, the release of chemokines and cytokines to reduce fracture risk in osteoporosis
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Measurements of interfacial area concentration in two-phase bubbly flow
Interfacial area concentration is an important parameter in the two-fluid model for two-phase flow analysis, which is defined as the total interface area per unit mixture volume and has the following local time-averaged expression: {bar a}{sup t} = 1/{Delta}T {Sigma}{sub j}(1/{vert_bar}V{sub i} {center_dot} n{sub i}{vert_bar}){sub j}, where j denotes the j-th interface that passes the point of interest in a time interval {Delta}T. V{sub i} and n{sub i} refer to the bubble interface velocity and surface normal vector, respectively. To measure this parameter, the double-sensor probe technique is commonly used. Due to the influences of the bubble lateral motions, however, the measurement results should be interpreted via a certain statistic approach. Recently, to take into account the effects of the probe spacing, Wu and Ishii provided the following new formula to correlate the measurable values to the interfacial area concentration: {bar a}{sub i}{sup t} = 2N{sub b}/{Delta}T ({Delta}{bar t}/{Delta}s) [2 + (1.2{sigma}{sub {Delta}t}/{Delta}{bar t}){sup 2.25}], for D = 1.2 {approximately} 2.8 {Delta}s, where N{sub b} refers to the number of the bubbles that hit the probe front tip during time interval {Delta}T, {Delta}s denotes the distance between the two probe tips, D is the bubble diameter, {Delta}{bar t} represents the measured average time interval for an interface to travel through the two probe tips, and {sigma}{sub {Delta}t} is the standard deviation of {Delta}t. The theoretical accuracy of this formula is within {+-} 5% if the sample size is sufficiently large. The purpose of this study is to evaluate this method experimentally using an image processing method
Precision Electron-Beam Polarimetry using Compton Scattering at 1 GeV
We report on the highest precision yet achieved in the measurement of the
polarization of a low energy, (1 GeV), electron beam, accomplished
using a new polarimeter based on electron-photon scattering, in Hall~C at
Jefferson Lab. A number of technical innovations were necessary, including a
novel method for precise control of the laser polarization in a cavity and a
novel diamond micro-strip detector which was able to capture most of the
spectrum of scattered electrons. The data analysis technique exploited track
finding, the high granularity of the detector and its large acceptance. The
polarization of the A, ~GeV electron beam was measured with a
statistical precision of ~1\% per hour and a systematic uncertainty of
0.59\%. This exceeds the level of precision required by the \qweak experiment,
a measurement of the vector weak charge of the proton. Proposed future
low-energy experiments require polarization uncertainty ~0.4\%, and this
result represents an important demonstration of that possibility. This
measurement is also the first use of diamond detectors for particle tracking in
an experiment.Comment: 9 pages, 7 figures, published in PR
Tunneling Spin Injection into Single Layer Graphene
We achieve tunneling spin injection from Co into single layer graphene (SLG)
using TiO2 seeded MgO barriers. A non-local magnetoresistance ({\Delta}RNL) of
130 {\Omega} is observed at room temperature, which is the largest value
observed in any material. Investigating {\Delta}RNL vs. SLG conductivity from
the transparent to the tunneling contact regimes demonstrates the contrasting
behaviors predicted by the drift-diffusion theory of spin transport.
Furthermore, tunnel barriers reduce the contact-induced spin relaxation and are
therefore important for future investigations of spin relaxation in graphene.Comment: 10 pages, 4 figures. To appear in Physical Review Letter
Development and Validation of a Targeted Next-Generation Sequencing Gene Panel for Children With Neuroinflammation
Importance Neuroinflammatory disorders are a range of severe neurological disorders causing brain and spinal inflammation and are now increasingly recognized in the pediatric population. They are often characterized by marked genotypic and phenotypic heterogeneity, complicating diagnostic work in clinical practice and molecular diagnosis.
Objective To develop and evaluate a next-generation sequencing panel targeting genes causing neuroinflammation or mimicking neuroinflammation.
Design, Setting, and Participants Cohort study in which a total of 257 genes associated with monogenic neuroinflammation and/or cerebral vasculopathy, including monogenic noninflammatory diseases mimicking these entities, were selected. A customized enrichment capture array, the neuroinflammation gene panel (NIP), was created. Targeted high-coverage sequencing was applied to DNA samples taken from eligible patients referred to Great Ormond Street Hospital in London, United Kingdom, between January 1, 2017, and January 30, 2019, because of onset of disease early in life, family history, and/or complex neuroinflammatory phenotypes.
Main Outcomes and Measures The main outcome was the percentage of individuals with definitive molecular diagnoses, variant classification, and clinical phenotyping of patients with pathogenic variants identified using the NIP panel. The NIP panel was initially validated in 16 patients with known genetic diagnoses.
Results The NIP was both sensitive (95%) and specific (100%) for detection of known mutations, including gene deletions, copy number variants, small insertions and deletions, and somatic mosaicism with allele fraction as low as 3%. Prospective testing of 60 patients (30 [50%] male; median [range] age, 9.8 [0.8-20] years) presenting with heterogeneous neuroinflammatory phenotypes revealed at least 1 class 5 (clearly pathogenic) variant in 9 of 60 patients (15%); 18 of 60 patients (30%) had at least 1 class 4 (likely pathogenic) variant. Overall, a definitive molecular diagnosis was established in 12 of 60 patients (20%).
Conclusions and Relevance The NIP was associated with molecular diagnosis in this cohort and complemented routine laboratory and radiological workup of patients with neuroinflammation. Unexpected genotype-phenotype associations in patients with pathogenic variants deviating from the classic phenotype were identified. Obtaining an accurate molecular diagnosis in a timely fashion informed patient management, including successful targeted treatment in some instances and early institution of hematopoietic stem cell transplantation in other
Local density of states and scanning tunneling currents in graphene
We present exact analytical calculations of scanning tunneling currents in
locally disordered graphene using a multimode description of the microscope
tip. Analytical expressions for the local density of states (LDOS) are given
for energies beyond the Dirac cone approximation. We show that the LDOS at the
and sublattices of graphene are out of phase by implying that the
averaged LDOS, as one moves away from the impurity, shows no trace of the
(with the Fermi momentum) Friedel modulation. This means that a
STM experiment lacking atomic resolution at the sublattice level will not be
able of detecting the presence of the Friedel oscillations [this seems to be
the case in the experiments reported in Phys. Rev. Lett. {\bf 101}, 206802
(2008)]. The momentum maps of the LDOS for different types of impurities are
given. In the case of the vacancy, features are seen in these maps. In
all momentum space maps, and features are seen. The
features are different from what is seen around zero momentum. An
interpretation for these features is given. The calculations reported here are
valid for chemical substitution impurities, such as boron and nitrogen atoms,
as well as for vacancies. It is shown that the density of states close to the
impurity is very sensitive to type of disorder: diagonal, non-diagonal, or
vacancies. In the case of weakly coupled (to the carbon atoms) impurities, the
local density of states presents strong resonances at finite energies, which
leads to steps in the scanning tunneling currents and to suppression of the
Fano factor.Comment: 21 pages. Figures 6 and 7 are correctly displayed in this new versio
Spin Relaxation in Single Layer Graphene with Tunable Mobility
Graphene is an attractive material for spintronics due to theoretical
predictions of long spin lifetimes arising from low spin-orbit and hyperfine
couplings. In experiments, however, spin lifetimes in single layer graphene
(SLG) measured via Hanle effects are much shorter than expected theoretically.
Thus, the origin of spin relaxation in SLG is a major issue for graphene
spintronics. Despite extensive theoretical and experimental work addressing
this question, there is still little clarity on the microscopic origin of spin
relaxation. By using organic ligand-bound nanoparticles as charge reservoirs to
tune mobility between 2700 and 12000 cm2/Vs, we successfully isolate the effect
of charged impurity scattering on spin relaxation in SLG. Our results
demonstrate that while charged impurities can greatly affect mobility, the spin
lifetimes are not affected by charged impurity scattering.Comment: 13 pages, 5 figure
Measurement of the Neutron Radius of 208Pb Through Parity-Violation in Electron Scattering
We report the first measurement of the parity-violating asymmetry A_PV in the
elastic scattering of polarized electrons from 208Pb. A_PV is sensitive to the
radius of the neutron distribution (Rn). The result A_PV = 0.656 \pm 0.060
(stat) \pm 0.014 (syst) ppm corresponds to a difference between the radii of
the neutron and proton distributions Rn - Rp = 0.33 +0.16 -0.18 fm and provides
the first electroweak observation of the neutron skin which is expected in a
heavy, neutron-rich nucleus.Comment: 6 pages, 1 figur
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