3,544 research outputs found
A Catchment-Based Land Surface Model for GCMs and the Framework for its Evaluation
A new GCM-scale land surface modeling strategy that explicitly accounts for subgrid soil moisture variability and its effects on evaporation and runoff is now being explored. In a break from traditional modeling strategies, the continental surface is disaggregated into a mosaic of hydrological catchments, with boundaries that are not dictated by a regular grid but by topography. Within each catchment, the variability of soil moisture is deduced from TOP-MODEL equations with a special treatment of the unsaturated zone. This paper gives an overview of this new approach and presents the general framework for its off-line evaluation over North-America
Quasiparticle transport equation with collision delay. II. Microscopic Theory
For a system of non-interacting electrons scattered by neutral impurities, we
derive a modified Boltzmann equation that includes quasiparticle and virial
corrections. We start from quasiclassical transport equation for
non-equilibrium Green's functions and apply limit of small scattering rates.
Resulting transport equation for quasiparticles has gradient corrections to
scattering integrals. These gradient corrections are rearranged into a form
characteristic for virial corrections
Robust optical emission polarization in MoS2 monolayers through selective valley excitation
We report polarization resolved photoluminescence from monolayer MoS2, a
two-dimensional, non-centrosymmetric crystal with direct energy gaps at two
different valleys in momentum space. The inherent chiral optical selectivity
allows exciting one of these valleys and close to 90% polarized emission at 4K
is observed with 40% polarization remaining at 300K. The high polarization
degree of the emission remains unchanged in transverse magnetic fields up to 9T
indicating robust, selective valley excitation.Comment: 5 pages, 3 figure
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
In-situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects
Combined in-situ x-ray photoemission spectroscopy, scanning tunnelling
spectroscopy and angle resolved photoemission spectroscopy of molecular beam
epitaxy grown Bi2Te3 on lattice mismatched substrates reveal high quality
stoichiometric thin films with topological surface states without a
contribution from the bulk bands at the Fermi energy. The absence of bulk
states at the Fermi energy is achieved without counter doping. We observe that
the surface morphology and electronic band structure of Bi2Te3 are not affected
by in-vacuo storage and exposure to oxygen, whereas major changes are observed
when exposed to ambient conditions. These films help define a pathway towards
intrinsic topological devices.Comment: 8 pages, 5 figure
Generalized "Quasi-classical" Ground State for an Interacting Two Level System
We treat a system (a molecule or a solid) in which electrons are coupled
linearly to any number and type of harmonic oscillators and which is further
subject to external forces of arbitrary symmetry. With the treatment restricted
to the lowest pair of electronic states, approximate "vibronic"
(vibration-electronic) ground state wave functions are constructed having the
form of simple, closed expressions. The basis of the method is to regard
electronic density operators as classical variables. It extends an earlier
"guessed solution", devised for the dynamical Jahn-Teller effect in cubic
symmetry, to situations having lower (e.g., dihedral) symmetry or without any
symmetry at all. While the proposed solution is expected to be quite close to
the exact one, its formal simplicity allows straightforward calculations of
several interesting quantities, like energies and vibronic reduction (or Ham)
factors. We calculate for dihedral symmetry two different -factors (""
and "") and a -factor. In simplified situations we obtain . The formalism enables quantitative estimates to be made for the dynamical
narrowing of hyperfine lines in the observed ESR spectrum of the dihedral
cyclobutane radical cation.Comment: 28 pages, 4 figure
Developmental nmda receptor dysregulation in the infantile neuronal ceroid lipofuscinosis mouse model
Protein palmitoylation and depalmitoylation alter protein function. This post-translational modification is critical for synaptic transmission and plasticity. Mutation of the depalmitoylating enzyme palmitoyl-protein thioesterase 1 (PPT1) causes infantile neuronal ceroid lipofuscinosis (CLN1), a pediatric neurodegenerative disease. However, the role of protein depalmitoylation in synaptic maturation is unknown. Therefore, we studied synapse development in Ppt1-/- mouse visual cortex. We demonstrate that the developmental N-methyl-D-aspartate receptor (NMDAR) subunit switch from GluN2B to GluN2A is stagnated in Ppt1-/- mice. Correspondingly, Ppt1-/- neurons exhibit immature evoked NMDAR currents and dendritic spine morphology in vivo. Further, dissociated Ppt1-/- cultured neurons show extrasynaptic, diffuse calcium influxes and enhanced vulnerability to NMDA-induced excitotoxicity, reflecting the predominance of GluN2B-containing receptors. Remarkably, Ppt1-/- neurons demonstrate hyperpalmitoylation of GluN2B as well as Fyn kinase, which regulates surface retention of GluN2B. Thus, PPT1 plays a critical role in postsynapse maturation by facilitating the GluN2 subunit switch and proteostasis of palmitoylated proteins
Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3
Terahertz and far-infrared electric and magnetic responses of hexagonal
piezomagnetic YMnO3 single crystals are investigated. Antiferromagnetic
resonance is observed in the spectra of magnetic permeability mu_a [H(omega)
oriented within the hexagonal plane] below the Neel temperature T_N. This
excitation softens from 41 to 32 cm-1 on heating and finally disappears above
T_N. An additional weak and heavily-damped excitation is seen in the spectra of
complex dielectric permittivity epsilon_c within the same frequency range. This
excitation contributes to the dielectric spectra in both antiferromagnetic and
paramagnetic phases. Its oscillator strength significantly increases on heating
towards room temperature thus providing evidence of piezomagnetic or
higher-order couplings to polar phonons. Other heavily-damped dielectric
excitations are detected near 100 cm-1 in the paramagnetic phase in both
epsilon_c and epsilon_a spectra and they exhibit similar temperature behavior.
These excitations appearing in the frequency range of magnon branches well
below polar phonons could remind electromagnons; however, their temperature
dependence is quite different. We have used density functional theory for
calculating phonon dispersion branches in the whole Brillouin zone. A detailed
analysis of these results and of previously published magnon dispersion
branches brought us to the conclusion that the observed absorption bands stem
from phonon-phonon and phonon- paramagnon differential absorption processes.
The latter is enabled by a strong short-range in-plane spin correlations in the
paramagnetic phase.Comment: subm. to PR
A Mathematical Model for Supermarket Order Picking
Order picking consists in retrieving products from storage locations to sat- isfy independent orders from multiple customers. It is generally recognized as one of the most significant activities in a warehouse (Koster et al, 2007). In fact, order picking accounts up to 50% (Frazelle, 2001) or even 80% (Van den Berg, 1999) of the total warehouse operating costs. The critical issue in today’s business environ- ment is to simultaneously reduce the cost and increase the speed of order picking. In this paper, we address the order picking process in one of the Portuguese largest companies in the grocery business. This problem was proposed at the 92nd European Study Group with Industry (ESGI92). In this setting, each operator steers a trolley on the shop floor in order to select items for multiple customers. The objective is to improve their grocery e-commerce and bring it up to the level of the best inter- national practices. In particular, the company wants to improve the routing tasks in order to decrease distances. For this purpose, a mathematical model for a faster open shop picking was developed. In this paper, we describe the problem, our proposed solution as well as some preliminary results and conclusions.info:eu-repo/semantics/publishedVersio
Point symmetries in the Hartree-Fock approach: Symmetry-breaking schemes
We analyze breaking of symmetries that belong to the double point group
D2h(TD) (three mutually perpendicular symmetry axes of the second order,
inversion, and time reversal). Subgroup structure of the D2h(TD) group
indicates that there can be as much as 28 physically different, broken-symmetry
mean-field schemes --- starting with solutions obeying all the symmetries of
the D2h(TD) group, through 26 generic schemes in which only a non-trivial
subgroup of D2h(TD) is conserved, down to solutions that break all of the
D2h(TD) symmetries. Choices of single-particle bases and the corresponding
structures of single-particle hermitian operators are discussed for several
subgroups of D2h(TD).Comment: 10 RevTeX pages, companion paper in nucl-th/991207
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