990 research outputs found
Relationships between Veresk Rangeland Vegetation and Environmental Characteristic Using Multivariate Analysis Methods
Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids
Cataloged from PDF version of article.We study the ground-state properties of a two-dimensional spinpolarized fluid of dipolar fermions within the Euler-Lagrange Fermi-hypemetted-chain approximation. Our method is based on the solution of a scattering Schrodinger equation for the "pair amplitude" root g(r), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow-Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree-Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation-dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density-density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings. (C) 2013 Elsevier Inc. All rights reserved
Finite-temperature Screening and the Specific Heat of Doped Graphene Sheets
At low energies, electrons in doped graphene sheets are described by a
massless Dirac fermion Hamiltonian. In this work we present a semi-analytical
expression for the dynamical density-density linear-response function of
noninteracting massless Dirac fermions (the so-called "Lindhard" function) at
finite temperature. This result is crucial to describe finite-temperature
screening of interacting massless Dirac fermions within the Random Phase
Approximation. In particular, we use it to make quantitative predictions for
the specific heat and the compressibility of doped graphene sheets. We find
that, at low temperatures, the specific heat has the usual normal-Fermi-liquid
linear-in-temperature behavior, with a slope that is solely controlled by the
renormalized quasiparticle velocity.Comment: 9 pages, 5 figures, Submitted to J. Phys.
NARX models for simulation of the start-up operation of a single-shaft gas turbine
In this study, nonlinear autoregressive exogenous
(NARX) models of a heavy-duty single-shaft gas turbine (GT) are
developed and validated. The GT is a power plant gas turbine
(General Electric PG 9351FA) located in Italy. The data used for
model development are three time series data sets of two different
maneuvers taken experimentally during the start-up procedure.
The resulting NARX models are applied to three other
experimental data sets and comparisons are made among four
significant outputs of the models and the corresponding measured
data. The results show that NARX models are capable of
satisfactory prediction of the GT behavior and can capture system
dynamics during start-up operation
Density-Functional Theory of Graphene Sheets
We outline a Kohn-Sham-Dirac density-functional-theory (DFT) scheme for
graphene sheets that treats slowly-varying inhomogeneous external potentials
and electron-electron interactions on an equal footing. The theory is able to
account for the the unusual property that the exchange-correlation contribution
to chemical potential increases with carrier density in graphene. Consequences
of this property, and advantages and disadvantages of using the DFT approach to
describe it, are discussed. The approach is illustrated by solving the
Kohn-Sham-Dirac equations self-consistently for a model random potential
describing charged point-like impurities located close to the graphene plane.
The influence of electron-electron interactions on these non-linear screening
calculations is discussed at length, in the light of recent experiments
reporting evidence for the presence of electron-hole puddles in nearly-neutral
graphene sheets.Comment: 11 pages, 9 figures, submitted. High-quality figures can be requested
to the author
Density-functional theory of strongly correlated Fermi gases in elongated harmonic traps
Two-component Fermi gases with tunable repulsive or attractive interactions
inside quasi-one-dimensional (Q1D) harmonic wells may soon become the cleanest
laboratory realizations of strongly correlated Luttiger and Luther-Emery
liquids under confinement. We present a microscopic Kohn-Sham
density-functional theory of these systems, with specific attention to a gas on
the approach to a confinement-induced Feshbach resonance. The theory employs
the one-dimensional Gaudin-Yang model as the reference system and transfers the
appropriate Q1D ground-state correlations to the confined inhomogeneous gas
{\it via} a suitable local-density approximation to the exchange and
correlation energy functional. Quantitative understanding of the role of the
interactions in the bulk shell structure of the axial density profile is
thereby achieved. While repulsive intercomponent interactions depress the
amplitude of the shell structure of the noninteracting gas, attractive
interactions stabilize atomic-density waves through spin pairing. These should
be clearly observable in atomic clouds containing of the order of up to a
hundred atoms.Comment: 13 pages, 9 figures, submitte
The impact of teamwork on an organization’s performance: a cooperative game’s approach
In this article we study the impact of teamwork on the organizations’ performance, considering a cooperative game’s framework. To promote the teamwork culture, performance indexes are considered individually and collectively, respectively, and by comparing the scores that every employee earns individually and collectively, their differences become obvious. In this approach, a cooperative games’ model is used in order to improve the organization’s performance. The proposed model, in addition to evaluating the organization and employee's activities, can implement all payments, including the overtime pay, reward, etc., fairly and along with increasing performance and satisfaction. The cooperative approach creates effective communications between employees and authorities and enhances their motivation for teamwork. Moreover, results can be used for decisions related to employees (such as promotion, transition, firing, and detachment), analysis of training requirements, employees’ development, and research and plan valuation. Our findings show that the collaborative coefficient is a key factor in increasing productivity and improving the efficiency of an organization in the long run. The collaborative coefficient is a new concept in teamwork that has rarely been considered in scientific research.info:eu-repo/semantics/publishedVersio
Ground state properties of a confined simple atom by C fullerene
We numerically study the ground state properties of endohedrally confined
hydrogen (H) or helium (He) atom by a molecule of C. Our study is based
on Diffusion Monte Carlo method. We calculate the effects of centered and small
off-centered H- or He-atom on the ground state properties of the systems and
describe the variation of ground state energies due to the C parameters
and the confined atomic nuclei positions. Finally, we calculate the electron
distributions in plane in a wide range of C parameters.Comment: 23 pages, 9 figures. To appear in J.Phys. B: Atom. Mol. Op
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