1,925 research outputs found
Density Functional Theory of Multicomponent Quantum Dots
Quantum dots with conduction electrons or holes originating from several
bands are considered. We assume the particles are confined in a harmonic
potential and assume the electrons (or holes) belonging to different bands to
be different types of fermions with isotropic effective masses. The density
functional method with the local density approximation is used. The increased
number of internal (Kohn-Sham) states leads to a generalisation of Hund's first
rule at high densities. At low densitites the formation of Wigner molecules is
favored by the increased internal freedom.Comment: 11 pages, 5 figure
Cracks Cleave Crystals
The problem of finding what direction cracks should move is not completely
solved. A commonly accepted way to predict crack directions is by computing the
density of elastic potential energy stored well away from the crack tip, and
finding a direction of crack motion to maximize the consumption of this energy.
I provide here a specific case where this rule fails. The example is of a crack
in a crystal. It fractures along a crystal plane, rather than in the direction
normally predicted to release the most energy. Thus, a correct equation of
motion for brittle cracks must take into account both energy flows that are
described in conventional continuum theories and details of the environment
near the tip that are not.Comment: 6 page
Product recognition in store shelves as a sub-graph isomorphism problem
The arrangement of products in store shelves is carefully planned to maximize
sales and keep customers happy. However, verifying compliance of real shelves
to the ideal layout is a costly task routinely performed by the store
personnel. In this paper, we propose a computer vision pipeline to recognize
products on shelves and verify compliance to the planned layout. We deploy
local invariant features together with a novel formulation of the product
recognition problem as a sub-graph isomorphism between the items appearing in
the given image and the ideal layout. This allows for auto-localizing the given
image within the aisle or store and improving recognition dramatically.Comment: Slightly extended version of the paper accepted at ICIAP 2017. More
information @project_page -->
http://vision.disi.unibo.it/index.php?option=com_content&view=article&id=111&catid=7
Intrinsic anomalous Hall effect in nickel: An GGA+U study
The electronic structure and intrinsic anomalous Hall conductivity of nickel
have been calculated based on the generalized gradient approximation (GGA) plus
on-site Coulomb interaction (GGA+U) scheme. It is found that the intrinsic
anomalous Hall conductivity () obtained from the GGA+U
calculations with eV and eV, is in nearly perfect agreement
with that measured recently at low temperatures while, in contrast, the
from the GGA calculations is about 100% larger than the
measured one. This indicates that, as for the other spin-orbit interaction
(SOI)-induced phenomena in 3 itinerant magnets such as the orbital magnetic
magnetization and magnetocrystalline anisotropy, the on-site electron-electron
correlation, though moderate only, should be taken into account properly in
order to get the correct anomalous Hall conductivity. The intrinsic
and the number of valence electrons () have also been
calculated as a function of the Fermi energy (). A sign change is
predicted at eV (), and this explain qualitatively
why the theoretical and experimental values for Fe and Co are
positive. It is also predicted that fcc NiCo(Fe,Cu) alloys with
being small, would also have the negative with the
magnitude being in the range of cm. The most
pronounced effect of including the on-site Coulomb interaction is that all the
-dominant bands are lowered in energy relative to the by about 0.3 eV,
and consequently, the small minority spin X hole pocket disappears. The
presence of the small X hole pocket in the GGA calculations is attributed
to be responsible for the large discrepancy in the between
theory and experiment.Comment: 7 pages, 3 figures; Accepted for publication in Physical Review
Necessary and sufficient condition for longitudinal magnetoresistance
Since the Lorentz force is perpendicular to the magnetic field, it should not
affect the motion of a charge along the field. This argument seems to imply
absence of longitudinal magnetoresistance (LMR) which is, however, observed in
many materials and reproduced by standard semiclassical transport theory
applied to particular metals. We derive a necessary and sufficient condition on
the shape of the Fermi surface for non-zero LMR. Although an anisotropic
spectrum is a pre-requisite for LMR, not all types of anisotropy can give rise
to the effect: a spectrum should not be separable in any sense. More precisely,
the combination , where is the radial
component of the momentum in a cylindrical system with the z-axis along the
magnetic field and ) is the radial (tangential) component
of the velocity, should depend on the momentum along the field. For some
lattice types, this condition is satisfied already at the level of
nearest-neighbor hopping; for others, the required non-separabality occurs only
if next-to-nearest-neighbor hopping is taken into account.Comment: 7 pages, 2 figure
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Decision‐Making About Reproductive Choices Among Individuals At‐Risk for Huntington's Disease
We explored how individuals at‐risk for HD who have or have not been tested make reproductive decisions and what factors are involved. We interviewed 21 individuals (8 with and 4 without the mutation, and 9 un‐tested) in‐depth for 2 hours each. At‐risk individuals faced a difficult series of dilemmas of whether to: get pregnant and deliver, have fetal testing, have pre‐implantation genetic diagnosis, adopt, or have no children. These individuals weighed competing desires and concerns: their own desires vs. those of spouses vs. broader moral concerns (e.g., to end the disease; and/or follow dictates against abortion) vs. perceptions of the interests of current or future offspring. Quandaries arose of how much and to whom to feel responsible. Some changed their perspectives over time (e.g., first “gambling,” then being more cautious). These data have critical implications for genetic counselors and other health care workers and future research, particularly as more genetic tests become available
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