10,360 research outputs found
Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence
We present a method for monitoring crystal orientations in chemically polished and unpassivated multicrystalline silicon wafers based on band-to-band photoluminescence imaging. The photoluminescence intensity from such wafers is dominated by surface recombination, which is crystal orientation dependent. We demonstrate that a strong correlation exists between the surface energy of different grain orientations, which are modelled based on first principles, and their corresponding photoluminescence intensity. This method may be useful in monitoring mixes of crystal orientations in multicrystalline or so-called “cast monocrystalline” wafers.H. C. Sio acknowledges scholarship support from
BT Imaging and the Australian Solar Institute, and the
Centre for Advanced Microscopy at ANU for SEM access.
This work has been supported by the Australian Research
Council
Orbital and interlayer Skyrmions crystals in bilayer graphene
A graphene bilayer in a transverse magnetic field has a set of Landau levels
with energies where
is the effective cyclotron frequency and
All Landau levels but N=0 are four times degenerate counting spin and valley
degrees of freedom. The Landau level N=0 has an extra degeneracy due to the
fact that orbitals and both have zero kinetic energies. At integer
filling factors, Coulomb interactions produce a set of broken-symmetry states
with partial or full alignement in space of the valley and orbital pseudospins.
These quantum Hall pseudo-ferromagnetic states support topological charged
excitations in the form of orbital and valley Skyrmions. Away from integer
fillings, these topological excitations can condense to form a rich variety of
Skyrme crystals with interesting properties. We study in this paper different
crystal phases that occur when an electric field is applied between the layers.
We show that orbital Skyrmions, in analogy with spin Skyrmions, have a texture
of electrical dipoles that can be controlled by an in-plane electric field.
Moreover, the modulation of electronic density in the crystalline phases are
experimentally accessible through a measurement of their local density of
statesComment: 18 pages with 13 figure
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
Meron ground states of quantum Hall droplets
We argue that topological meron excitations, which are in a strong coupling
phase (bound in pairs) in infinite quantum Hall ferromagnets, become deconfined
in finite size quantum Hall systems. Although effectively for larger systems
meron energy grows with the size of the system, when gyromagnetic ratio is
small meron becomes the lowest lying state of a quantum Hall droplet. This
comes as a consequence of the many-body correlations built in the meron
construction that minimize the interaction energy. We demonstrate this by using
mean field ansatzes for meron wave function. The ansatzes will enable us to
consider much larger system sizes than in the previous work [A. Petkovic and
M.V. Milovanovic, PRL 98, 066808 (2007)], where fractionalization into merons
was introduced.Comment: 6 pages, 6 figure
Coordinate shift in the semiclassical Boltzmann equation and the anomalous Hall effect
We propose a gauge invariant expression for the side jump associated with
scattering between particular Bloch states. Our expression for the side jump
follows from the Born series expansion for the scattering T-matrix in powers of
the strength of the scattering potential. Given our gauge invariant side jump
expression, it is possible to construct a semiclassical Boltzmann theory of the
anomalous Hall effect which expresses all previously identified contributions
in terms of gauge invariant quantities and does not refer explicitly to
off-diagonal terms in the density-matrix response.Comment: 6 pages, 1 fugure. submitted to PR
Pulmonary vasospasm in systemic sclerosis: noninvasive techniques for detection
In a subgroup of patients with systemic sclerosis (SSc), vasospasm affecting the pulmonary circulation may contribute to worsening respiratory symptoms, including dyspnea. Noninvasive assessment of pulmonary blood flow (PBF), utilizing inert-gas rebreathing (IGR) and dual-energy computed-tomography pulmonary angiography (DE-CTPA), may be useful for identifying pulmonary vasospasm. Thirty-one participants (22 SSc patients and 9 healthy volunteers) underwent PBF assessment with IGR and DE-CTPA at baseline and after provocation with a cold-air inhalation challenge (CACh). Before the study investigations, participants were assigned to subgroups: group A included SSc patients who reported increased breathlessness after exposure to cold air (n = 11), group B included SSc patients without cold-air sensitivity (n = 11), and group C patients included the healthy volunteers. Median change in PBF from baseline was compared between groups A, B, and C after CACh. Compared with groups B and C, in group A there was a significant decline in median PBF from baseline at 10 minutes (−10%; range: −52.2% to 4.0%; P < 0.01), 20 minutes (−17.4%; −27.9% to 0.0%; P < 0.01), and 30 minutes (−8.5%; −34.4% to 2.0%; P < 0.01) after CACh. There was no significant difference in median PBF change between groups B or C at any time point and no change in pulmonary perfusion on DE-CTPA. Reduction in pulmonary blood flow following CACh suggests that pulmonary vasospasm may be present in a subgroup of patients with SSc and may contribute to worsening dyspnea on exposure to cold
Tolerance to oxidative stress is associated with both oxidative stress response and inherent growth in a fungal wheat pathogen
Reactive oxygen species (ROS) are toxic byproducts of aerobic respiration that are also important in mediating a diversity of cellular functions. ROS form an important component of plant defenses to inhibit microbial pathogens during pathogen-plant interactions. Tolerance to oxidative stress is likely to make a significant contribution to the viability and pathogenicity of plant pathogens, but the complex network of oxidative stress responses hinders identification of the genes contributing to this trait. Here, we employed a forward genetic approach to investigate the genetic architecture of oxidative stress tolerance in the fungal wheat pathogen Zymoseptoria tritici. We used quantitative trait locus (QTL) mapping of growth and melanization under axenic conditions in two cross populations to identify genomic regions associated with tolerance to oxidative stress. We found that QTLs associated with growth under oxidative stress as well as inherent growth can affect oxidative stress tolerance, and we identified two uncharacterized genes in our QTL associated with this trait. Our data suggest that melanization does not affect tolerance to oxidative stress, which differs from what was found for animal pathogens. This study provides a whole-genome perspective on the genetic basis of oxidative stress tolerance in a plant pathogen
Skyrmion pseudoSkyrmion Transition in Bilayer Quantum Hall States at
Bilayer quantum Hall states at have been demonstrated to possess a
distinguished state with interlayer phase coherence. The state has both
excitations of Skyrmion with spin and pseudoSkyrmion with pseudospin. We show
that Skyrmion pseudoSkyrmion transition arises in the state
by changing imbalance between electron densities in both layers; PseudoSkyrmion
is realized at balance point, while Skyrmion is realized at large imbalance.
The transition can be seen by observing the dependence of activation energies
on magnetic field parallel to the layers.Comment: 12 pages, no figure
High-cadence spectroscopy of M-dwarfs – II. Searching for stellar pulsations with HARPS
Stellar oscillations appear all across the Hertzsprung–Russell diagram. Recent theoretical studies support their existence also in the atmosphere of M dwarfs. These studies predict for them short periodicities ranging from 20 min to 3 h. Our Cool Tiny Beats (CTB) programme aims at finding these oscillations for the very first time. With this goal, CTB explores the short time domain of M dwarfs using radial velocity data from the High Accuracy Radial velocity Planet Searcher (HARPS)-European Southern Observatory and HARPS-N high-precision spectrographs. Here we present the results for the two most long-term stable targets observed to date with CTB, GJ 588 and GJ 699 (i.e. Barnard's star). In the first part of this work we detail the correction of several instrumental effects. These corrections are especially relevant when searching for subnight signals. Results show no significant signals in the range where M dwarfs pulsations were predicted. However, we estimate that stellar pulsations with amplitudes larger than ∼0.5 m s−1 can be detected with a 90 per cent completeness with our observations. This result, along with the excess of power regions detected in the periodograms, opens the possibility of non-resolved very low amplitude pulsation signals. Next generation more precise instrumentation would be required to detect such oscillations. However, the possibility of detecting pulsating M-dwarf stars with larger amplitudes is feasible due to the short size of the analysed sample. This motivates the need for completeness of the CTB survey
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