91 research outputs found
Numerical studies of confined states in rotated bilayers of graphene
Rotated graphene multilayers form a new class of graphene related systems
with electronic properties that drastically depend on the rotation angles. It
has been shown that bilayers behave like two isolated graphene planes for large
rotation angles. For smaller angles, states in the Dirac cones belonging to the
two layers interact resulting in the appearance of two van Hove singularities.
States become localised as the rotation angle decreases and the two van Hove
singularities merge into one peak at the Dirac energy. Here we go further and
consider bilayers with very small rotation angles. In this case, well defined
regions of AA stacking exist in the bilayer supercell and we show that states
are confined in these regions for energies in the [-\gamma_t, +\gamma_t] range
with \gamma_t the interplane mean interaction. As a consequence, the local
densities of states show discrete peaks for energies different from the Dirac
energy.Comment: 8 page
Cleaning graphene : a first quantum/classical molecular dynamics approach
Graphene outstanding properties created a huge interest in the condensed
matter community and unprecedented fundings at the international scale in the
hope of application developments. Recently, there have been several reports of
incomplete removal of the polymer resists used to transfer as-grown graphene
from one substrate to another, resulting in altered graphene transport
properties. Finding a large-scale solution to clean graphene from adsorbed
residues is highly desirable and one promising possibility would be to use
hydrogen plasmas. In this spirit, we couple here quantum and classical
molecular dynamics simulations to explore the kinetic energy ranges required by
atomic hydrogen to selectively etch a simple residue, a CH3 group, without
irreversibly damaging the graphene. For incident energies in the 2-15 eV range,
the CH3 radical can be etched by forming a volatile CH4 compound which leaves
the surface, either in the CH4 form or breaking into CH3+H fragments, without
further defect formation. At this energy, adsorption of H atoms on graphene is
possible and further annealing will be required to recover pristine graphene.Comment: 9 figures, 27 page
Sentinel lymph node biopsy and morbidity outcomes in early cervical cancer: Results of a multicentre randomised trial (SENTICOL-2).
Pelvic lymph node dissection has been the standard of care for patients with early cervical cancer. Sentinel node (SN) mapping is safe and feasible and may increase the detection of metastatic disease, but benefits of omitting pelvic lymph node dissection in terms of decreased morbidity have not been demonstrated.
In an open-label study, patients with early cervical carcinoma (FIGO 2009 stage IA2 to IIA1) were randomly assigned to SN resection alone (SN arm) or SN and pelvic lymph node dissection (SN + PLND arm). SN resection was followed by radical surgery of the tumour (radical hysterectomy or radical trachelectomy). The primary end-point was morbidity related to the lymph node dissection; 3-year recurrence-free survival was a secondary end-point.
A total of 206 patients were eligible and randomly assigned to the SN arm (105 patients) or SN + PLND arm (101 patients). Most patients had stage IB1 lesion (87.4%). No false-negative case was observed in SN + PLND arm. Lymphatic morbidity was significantly lower in the SN arm (31.4%) than in the SN + PLND arm (51.5%; p = 0.0046), as was the rate of postoperative neurological symptoms (7.8% vs. 20.6%, p = 0.01, respectively). However, there was no significant difference in the proportion of patients with significant lymphoedema between the two groups. During the 6-month postoperative period, the difference in morbidity decreased over time. The 3-year recurrence-free survival was not significantly different (92.0% in SN arm and 94.4% in SN + PLND arm).
SN resection alone is associated with early decreased lymphatic morbidity when compared with SN + PLND in early cervical cancer
Electron transport via local polarons at interface atoms
Electronic transport is profoundly modified in the presence of strong electron-vibration coupling. We show that in certain situations, the electron flow takes place only when vibrations are excited. By controlling the segregation of boron in semiconducting Si(111)-3√×3√R30° surfaces, we create a type of adatom with a dangling-bond state that is electronically decoupled from any other electronic state. However, probing this state with scanning tunnelling microscopy at 5 K yields high currents. These findings are rationalized by ab-initio calculations that show the formation of a local polaron in the transport process
Weakly Trapped, Charged, and Free Excitons in Single-Layer MoS2 in the Presence of Defects, Strain, and Charged Impurities
Few- and single-layer MoS2 host substantial densities of defects. They are thought to influence the doping level, the crystal structure, and the binding of electron-hole pairs. We disentangle the concomitant spectroscopic expression of all three effects and identify to what extent they are intrinsic to the material or extrinsic to it, i.e., related to its local environment. We do so by using different sources of MoS2 - a natural one and one prepared at high pressure and high temperature - and different substrates bringing varying amounts of charged impurities and by separating the contributions of internal strain and doping in Raman spectra. Photoluminescence unveils various optically active excitonic complexes. We discover a defect-bound state having a low binding energy of 20 meV that does not appear sensitive to strain and doping, unlike charged excitons. Conversely, the defect does not significantly dope or strain MoS2. Scanning tunneling microscopy and density functional theory simulations point to substitutional atoms, presumably individual nitrogen atoms at the sulfur site. Our work shows the way to a systematic understanding of the effect of external and internal fields on the optical properties of two-dimensional materials
Development of a blood-based molecular biomarker test for identification of schizophrenia before disease onset
Recent research efforts have progressively shifted towards preventative psychiatry and prognostic identification of individuals before disease onset. We describe the development of a serum biomarker test for the identification of individuals at risk of developing schizophrenia based on multiplex immunoassay profiling analysis of 957 serum samples. First, we conducted a meta-analysis of five independent cohorts of 127 first-onset drug-naive schizophrenia patients and 204 controls. Using least absolute shrinkage and selection operator regression, we identified an optimal panel of 26 biomarkers that best discriminated patients and controls. Next, we successfully validated this biomarker panel using two independent validation cohorts of 93 patients and 88 controls, which yielded an area under the curve (AUC) of 0.97 (0.95-1.00) for schizophrenia detection. Finally, we tested its predictive performance for identifying patients before onset of psychosis using two cohorts of 445 pre-onset or at-risk individuals. The predictive performance achieved by the panel was excellent for identifying USA military personnel (AUC: 0.90 (0.86-0.95)) and help-seeking prodromal individuals (AUC: 0.82 (0.71-0.93)) who developed schizophrenia up to 2 years after baseline sampling. The performance increased further using the latter cohort following the incorporation of CAARMS (Comprehensive Assessment of At-Risk Mental State) positive subscale symptom scores into the model (AUC: 0.90 (0.82-0.98)). The current findings may represent the first successful step towards a test that could address the clinical need for early intervention in psychiatry. Further developments of a combined molecular/symptom-based test will aid clinicians in the identification of vulnerable patients early in the disease process, allowing more effective therapeutic intervention before overt disease onset
Symmetry Breaking in Few Layer Graphene Films
Recently, it was demonstrated that the quasiparticle dynamics, the
layer-dependent charge and potential, and the c-axis screening coefficient
could be extracted from measurements of the spectral function of few layer
graphene films grown epitaxially on SiC using angle-resolved photoemission
spectroscopy (ARPES). In this article we review these findings, and present
detailed methodology for extracting such parameters from ARPES. We also present
detailed arguments against the possibility of an energy gap at the Dirac
crossing ED.Comment: 23 pages, 13 figures, Conference Proceedings of DPG Meeting Mar 2007
Regensburg Submitted to New Journal of Physic
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation
WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m−2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described
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