1,563 research outputs found
Continuum states from time-dependent density functional theory
Linear response time-dependent density functional theory is used to study
low-lying electronic continuum states of targets that can bind an extra
electron. Exact formulas to extract scattering amplitudes from the
susceptibility are derived in one dimension. A single-pole approximation for
scattering phase shifts in three dimensions is shown to be more accurate than
static exchange for singlet electron-He scattering.Comment: 5 pages, 2 figures, J. Chem. Phys. accepte
Complex-valued Time Series Modeling for Improved Activation Detection in fMRI Studies
A complex-valued data-based model with th order autoregressive errors and general real/imaginary error covariance structure is proposed as an alternative to the commonly used magnitude-only data-based autoregressive model for fMRI time series. Likelihood-ratio-test-based activation statistics are derived for both models and compared for experimental and simulated data. For a dataset from a right-hand finger-tapping experiment, the activation map obtained using complex-valued modeling more clearly identifies the primary activation region (left functional central sulcus) than the magnitude-only model. Such improved accuracy in mapping the left functional central sulcus has important implications in neurosurgical planning for tumor and epilepsy patients. Additionally, we develop magnitude and phase detrending procedures for complex-valued time series and examine the effect of spatial smoothing. These methods improve the power of complex-valued data-based activation statistics. Our results advocate for the use of the complex-valued data and the modeling of its dependence structures as a more efficient and reliable tool in fMRI experiments over the current practice of using only magnitude-valued datasets
Exploring non-adiabatic approximations to the exchange-correlation functional of TDDFT
A decomposition of the exact exchange-correlation potential of time-dependent density functional theory into an interaction component and a kinetic component offers a new starting point for non-adiabatic approximations. The components are expressed in terms of the exchange-correlation hole and the difference between the one-body density matrix of the interacting and Kohn-Sham systems, which must be approximated in terms of quantities accessible from the Kohn-Sham evolution. We explore several preliminary approximations, evaluate their fulfillment of known exact conditions, and test their performance on simple model systems for which available exact solutions indicate the significance of going beyond the adiabatic approximation.Fil: Fuks, Johanna Ildemar. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; ArgentinaFil: Lacombe, Lionel. University of New York; Estados UnidosFil: Nielsen, Søren E. B.. Max Planck Institute for the Structure and Dynamics of Matter; Alemania. Center for Free-Electron Laser Science; AlemaniaFil: Maitra, Neepa T.. University of New York; Estados Unido
Modeling of Congestion: A Tool for Urban Traffic Management in Developing Countries
In order to formulate rational traffic management measures for urban roads, it is essential to understand
the effect of different types of vehicle on congestion. The effect of different types of vehicle on
congestion has been captured on the basis of marginal congestion. Using congestion models, the marginal
congestions have been estimated for different road widths, traffic compositions and on-street parking
levels. The peak hour vehicular composition and volume level vary for different roads in an urban area.
Therefore, for assessing the operating conditions for different roads based on a comparable quantitative
measure, the marginal congestion caused per Passenger Car Unit (PCU) of mixed traffic stream has been
estimated and denominated ‘Marginal Congestion Index (MCI)’. The use of MCI for prioritization of
management actions for different urban roads is discussed. It is shown that a congestion model explicitly
accounts for the effects of traffic composition and volume level. Therefore, the effect of different types of
vehicles on congestion at all traffic volumes could be estimated using congestion models. Altogether,
modeling of congestion is established as a tool for formulating rational traffic management measures for
urban roads in developing countries
Oscillator strengths and excited-state couplings for double excitations in time-dependent density functional theory
Although useful to extract excitation energies of states of double-excitation
character in time-dependent density functional theory that are missing in the
adiabatic approximation, the frequency-dependent kernel derived earlier [J.
Chem. Phys. {\bf 120}, 5932 (2004)] was not designed to yield oscillator
strengths. These are required to fully determine linear absorption spectra and
they also impact excited-to-excited-state couplings that appear in dynamics
simulations and other quadratic response properties. Here we derive a modified
non-adiabatic kernel that yields both accurate excitation energies and
oscillator strengths for these states. We demonstrate its performance on a
model two-electron system, the Be atom, and on excited-state transition dipoles
in the LiH molecule at stretched bond-lengths, in all cases producing
significant improvements over the traditional approximations
Modeling Traffic Impact of Flyover at an Urban Intersection Under Mixed Traffic Environment
In order to ease transportation problems, many urban authorities in India have taken up initiative for
construction of flyovers at major intersections. However, in most of the cases a comprehensive planning
approach has not been adopted, either due to lack of fund or ignorance about the planning perspective of
such proposals. The locations for flyovers have been decided based on present day operating conditions
and the traffic impacts of such flyovers at adjacent intersections have not been analysed. In the present
paper, the traffic impact of a flyover along with its adjacent intersection has been analysed, using a
simulation model developed for mixed traffic operations and poor lane discipline prevailing in India.
Through the case study presented in the paper, it has been demonstrated that an ill planned flyover only
shifts the location of the problem without bringing any benefit to traffic. The potential use of simulation
model for analyzing traffic impacts has been shown; and the need for such analysis for the planning of
flyovers has been highlighted
Charge order and phase segregation in overdoped bilayer manganites
There have been recent reports of charge ordering around in the
bilayer manganites. At , there appears to be a coexistence region of
layered A-type antiferromagnetc and charge order. There are also reports of
orbital order in this region without any Jahn-Teller effect. Based on physical
grounds, this region is investigated from a model that incorporates the two
orbitals at each Mn site and a near-neighbour Coulomb repulsion. It is
shown that there indeed is both charge and orbital order close to the
half-doped region coincident with a layered magnetic structure. Although the
orbital order is known to drive the magnetic order, the layered magnetic
structure is also favoured in this system by the lack of coherent transport
across the planes and the reduced dimensionality of the lattice. The
anisotropic hopping across the orbitals and the underlying layered
structure largely determine the orbital arrangements in this region, while the
charge order is primarily due to the long range interactions.Comment: 6 pages, 6 figure
Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State
Using Suzaku and the Rossi X-ray Timing Explorer, we have conducted a series
of four simultaneous observations of the galactic black hole candidate Cyg X-1
in what were historically faint and spectrally hard low states. Additionally,
all of these observations occurred near superior conjunction with our line of
sight to the X-ray source passing through the dense phases of the focused wind
from the mass donating secondary. One of our observations was also simultaneous
with observations by the Chandra-High Energy Transmission Grating. These latter
spectra are crucial for revealing the ionized absorption due to the secondary's
focused wind. Such absorption is present and must be accounted for in all four
spectra. These simultaneous data give an unprecedented view of the 0.8-300 keV
spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet
models of black hole hard states. Three models fit the spectra well: coronae
with thermal or mixed thermal/non-thermal electron populations, and jets. All
three models require a soft component that we fit with a low temperature disk
spectrum with an inner radius of only a few tens of GM/c^2. All three models
also agree that the known spectral break at 10\,keV is not solely due to the
presence of reflection, but each gives a different underlying explanation for
the augmentation of this break. Thus whereas all three models require that
there is a relativistically broadened Fe line, the strength and inner radius of
such a line is dependent upon the specific model, {thus making premature
line-based estimates of the black hole spin in the Cyg X-1 system. We look at
the relativistic line in detail, accounting for the narrow Fe emission and
ionized absorption detected by HETG. Although the specific relativistic
parameters of the line are continuum-dependent, none of the broad line fits
allow for an inner disk radius that is >40 GM/c^2.Comment: 22 pages, 16 figures. Uses emulateapj style. Final three tables
inserted as a figure to avoid issues with astro-ph's version of latex
mangling the use of lscape. To be published in the Astrophysical Journal,
January, 201
Refusing to Endorse. A must Explanation for Pejoratives.
In her analysis of pejoratives, Eva Picardi rejects a too sharp separation between descriptive and expressive content. I reconstruct some of her arguments, endorsing Eva’s criticism of Williamson’s analysis of Dummett and developing a suggestion by Manuel Garcia Carpintero on a speech act analysis of pejoratives. Eva’s main concern is accounting for our instinctive refusal to endorse an assertion containing pejoratives because it suggests a picture of reality we do not share. Her stance might be further developed claiming that uses of pejoratives not only suggest, but also promote a wrong picture of reality. Our refusal to endorse implies rejecting not only a wrong picture of reality but also a call for participation to what that
picture promotes
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