2,367 research outputs found
Possible magnetic-field-induced voltage and thermopower in diluted magnetic semiconductors
In diluted magnetic semiconductors, the carrier concentration and the
magnetization of local moments are strongly coupled, since the magnetic
interaction is mediated by the carriers. It is predicted that this coupling
leads to an electric polarization due to an applied magnetic-field gradient and
to the appearance of a magnetic-field-dependent voltage. An expression for this
voltage is derived within Landau theory and its magnitude is estimated for
(Ga,Mn)As. Furthermore, a large contribution to the thermopower based on the
same mechanism is predicted. The role of fluctuations is also discussed. These
predictions hold both if the magnetization is uniform and if it shows
stripe-like modulations, which are possible at lower temperatures.Comment: 6 pages revtex, 5 figure
The deformation and elastic anisotropy of a new gyroid-based honeycomb made by laser sintering
© 2020 The Author(s) The stiffness, anisotropy and structural deformation of three gyroid-based lattices was investigated, with particular focus on a newly proposed honeycomb gyroid. This honeycomb is based on a modified triply periodic minimal surface (TPMS) equation with reduced periodicity. Using the numerical homogenisation method, the anisotropy of the gyroid lattice types was found to differ greatly, as was the dependence of this anisotropy on the volume fraction. From compression testing of laser sintered polyamide PA2200 specimens, the honeycomb gyroid was found to possess extremely high anisotropy, with Emax*/Emin*, the ratio of the highest to the lowest direction-dependent modulus, ∼250 at low volume fraction. The stiffness and anisotropy of the honeycomb gyroid are compared to equivalent results from the square honeycomb, the closest analogue in the set of conventional honeycomb types. The honeycomb gyroid lattice exhibited novel deformation and post-yield stiffening under in-plane loading; it underwent reorientation into a second, stiffer geometry following plastic bending and contact of its cell walls. The unique deformation behaviour and extremely high anisotropy of the honeycomb gyroid provide strong motivation for further investigations into this new family of reduced periodicity TPMS-based honeycombs
Temperature dependent correlations in covalent insulators
Motivated by the peculiar behavior of FeSi and FeSb2 we study the effect of
local electronic correlations on magnetic, transport and optical properties in
a specific type of band insulator, namely a covalent insulator. Investigating a
minimum model of covalent insulator within a single-site dynamical mean-field
approximation we are able to obtain the crossover from low temperature
non-magnetic insulator to high-temperature paramagnetic metal with parameters
realistic for FeSi and FeSb2 systems. Our results show that the behavior of
FeSi does not imply microscopic description in terms of Kondo insulator
(periodic Anderson model) as can be often found in the literature, but in fact
reflects generic properties of a broader class of materials.Comment: 4 pages, 4 figure
Magnetic superlattice and finite-energy Dirac points in graphene
We study the band structure of graphene's Dirac-Weyl quasi-particles in a one-dimensional magnetic superlattice formed by a periodic sequence of alternating magnetic barriers. The spectrum and the nature of the states strongly depend on the conserved longitudinal momentum and on the barrier width. At the center of the superlattice Brillouin zone we find new Dirac points at finite energies where the dispersion is highly anisotropic, in contrast to the dispersion close to the neutrality point which remains isotropic. This finding suggests the possibility of collimating Dirac-Weyl quasi-particles by tuning the doping
Theoretical Analysis of Electronic and Magnetic Properties of NaVO: Crucial Role of the Orbital Degrees of Freedom
Using realistic low-energy model with parameters derived from the
first-principles electronic structure calculation, we address the origin of the
quasi-one-dimensional behavior in orthorhombic NaVO, consisting of the
double chains of edge-sharing VO octahedra. We argue that the geometrical
aspect alone does not explain the experimentally observed anisotropy of
electronic and magnetic properties of NaVO. Instead, we attribute the
unique behavior of NaVO to one particular type of the orbital ordering,
which respects the orthorhombic symmetry. This orbital ordering acts to
divide all states into two types: the `localized' ones, which are
antisymmetric with respect to the mirror reflection , and
the symmetric `delocalized' ones. Thus, NaVO can be classified as the
double exchange system. The directional orientation of symmetric orbitals,
which form the metallic band, appears to be sufficient to explain both
quasi-one-dimensional character of interatomic magnetic interactions and the
anisotropy of electrical resistivity.Comment: 16 pages, 4 figure
Number distributions for fermions and fermionized bosons in periodic potentials
We compute the spatial population statistics for one-dimensional fermi-gases
and for bose-gases with hard core repulsions in periodic potentials. We show
how the statistics depend on the atomic density in the ground state of the
system, and we present calculations for the dynamical turn-on of the potential.Comment: 8 pages, 4 figures, submitted to Phys. Rev.
Theory of Diamagnetism in the Pseudogap Phase: Implications from the Self energy of Angle Resolved Photoemission
In this paper we apply the emerging- consensus understanding of the fermionic
self energy deduced from angle resolved photoemisssion spectroscopy (ARPES)
experiments to deduce the implications for orbital diamagnetism in the
underdoped cuprates. Many theories using many different starting points have
arrived at a broadened BCS-like form for the normal state self energy
associated with a d-wave excitation gap, as is compatible with ARPES data.
Establishing compatibility with the f-sum rules, we show how this self energy,
along with the constraint that there is no Meissner effect in the normal phase
are sufficient to deduce the orbital susceptibility. We conclude, moreover,
that diamagnetism is large for a d-wave pseudogap. Our results should apply
rather widely to many theories of the pseudogap, independent of the microscopic
details.Comment: 15 pages, 8 figure
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Topology Optimization for Additive Manufacturing
This paper gives an overview of the issues and opportunities for the application of
topology optimization methods for additive manufacturing (AM). The main analysis issues
discussed are: how to achieve the maximum geometric resolution to allow the fine features easily
manufacturable by AM to be represented in the optimization model; the manufacturing
constraints to be considered, and the workflow modifications required to handle the geometric
complexity in the post optimization stages. The main manufacturing issues discussed are the
potential for realizing intermediate density regions, in the case of the solid isotropic material
with penalization (SIMP) approach, the use of small scale lattice structures, the use of multiple
material AM processes, and an approach to including support structure requirement as a
manufacturing constraint.Mechanical Engineerin
Evolution of reciprical teaching and learning: medical students and simulated patients training in partnership
Training simulated patients effectively is vital for the success of the patient volunteer programme in the Graduate School of Medicine at the University of Wollongong. Globally, simulated patients play an essential role in contemporary medical education. Yet, there is a significant gap in the research literature regarding their training and the impact of their feedback on student learning. In 2010, our 2nd and 3rd year medical students replicated realistic interview situations as part of our simulated patient training. This intervention allowed patient volunteers to give feedback but also to receive feedback on their feedback giving skills from students. During these interactions, a strong sense of reciprocal teaching and learning between the incumbent simulated patients and the participating students emerged. Based on these observations, we conducted focus group interviews with both parties. Participants reported an enriched educational experience and better understanding of each other\u27s role in the teaching relationship. Volunteers commented that the approach has given them a better comprehension of the expectations placed upon them by students. Students appreciated the opportunity to support volunteers in what they see as a vital aspect of their medical training
Can analyses of electronic patient records be independently and externally validated? The effect of statins on the mortality of patients with ischaemic heart disease: a cohort study with nested case-control analysis
Objective To conduct a fully independent and external validation of a research study based on one electronic health record database, using a different electronic database sampling the same population.
Design Using the Clinical Practice Research Datalink (CPRD), we replicated a published investigation into the effects of statins in patients with ischaemic heart disease (IHD) by a different research team using QResearch. We replicated the original methods and analysed all-cause mortality using: (1) a cohort analysis and (2) a case-control analysis nested within the full cohort.
Setting Electronic health record databases containing longitudinal patient consultation data from large numbers of general practices distributed throughout the UK.
Participants CPRD data for 34 925 patients with IHD from 224 general practices, compared to previously published results from QResearch for 13 029 patients from 89 general practices. The study period was from January 1996 to December 2003.
Results We successfully replicated the methods of the original study very closely. In a cohort analysis, risk of death was lower by 55% for patients on statins, compared with 53% for QResearch (adjusted HR 0.45, 95% CI 0.40 to 0.50; vs 0.47, 95% CI 0.41 to 0.53). In case-control analyses, patients on statins had a 31% lower odds of death, compared with 39% for QResearch (adjusted OR 0.69, 95% CI 0.63 to 0.75; vs OR 0.61, 95% CI 0.52 to 0.72). Results were also close for individual statins.
Conclusions Database differences in population characteristics and in data definitions, recording, quality and completeness had a minimal impact on key statistical outputs. The results uphold the validity of research using CPRD and QResearch by providing independent evidence that both datasets produce very similar estimates of treatment effect, leading to the same clinical and policy decisions. Together with other non-independent replication studies, there is a nascent body of evidence for wider validity
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