10,215 research outputs found
Exchange-correlation functionals from the strongly-interacting limit of DFT: Applications to model chemical systems
We study model one-dimensional chemical systems (representative of their
three-dimensional counterparts) using the strictly-correlated electrons (SCE)
functional, which, by construction, becomes asymptotically exact in the limit
of infinite coupling strength. The SCE functional has a highly non-local
dependence on the density and is able to capture strong correlation within
Kohn- Sham theory without introducing any symmetry breaking. Chemical systems,
however, are not close enough to the strong-interaction limit so that, while
ionization energies and the stretched H2 molecule are accurately described,
total energies are in general way too low. A correction based on the exact next
leading order in the expansion at infinite coupling strength of the
Hohenberg-Kohn functional largely improves the results.Comment: 9 pages, 6 figures. Submitted to PCCP's Themed Collection on Density
Functional Theory and its Application
Optimized coupling of cold atoms into a fiber using a blue-detuned hollow-beam funnel
We theoretically investigate the process of coupling cold atoms into the core
of a hollow-core photonic-crystal optical fiber using a blue-detuned
Laguerre-Gaussian beam. In contrast to the use of a red-detuned Gaussian beam
to couple the atoms, the blue-detuned hollow-beam can confine cold atoms to the
darkest regions of the beam thereby minimizing shifts in the internal states
and making the guide highly robust to heating effects. This single optical beam
is used as both a funnel and guide to maximize the number of atoms into the
fiber. In the proposed experiment, Rb atoms are loaded into a magneto-optical
trap (MOT) above a vertically-oriented optical fiber. We observe a
gravito-optical trapping effect for atoms with high orbital momentum around the
trap axis, which prevents atoms from coupling to the fiber: these atoms lack
the kinetic energy to escape the potential and are thus trapped in the laser
funnel indefinitely. We find that by reducing the dipolar force to the point at
which the trapping effect just vanishes, it is possible to optimize the
coupling of atoms into the fiber. Our simulations predict that by using a
low-power (2.5 mW) and far-detuned (300 GHz) Laguerre-Gaussian beam with a
20-{\mu}m radius core hollow-fiber it is possible to couple 11% of the atoms
from a MOT 9 mm away from the fiber. When MOT is positioned further away,
coupling efficiencies over 50% can be achieved with larger core fibers.Comment: 11 pages, 12 figures, 1 tabl
Photodissociation of the OD radical at 226 and 243 nm
The photodissociation dynamics of state selected OD radicals has been examined at 243 and 226 nm using velocity map imaging to probe the angleâspeed distributions of theD(2S) and O(3P2) products. Both experiment and complementary first principle calculations demonstrate that photodissociation occurs by promotion of OD from high vibrational levels of the ground Xâ2Î state to the repulsive 1â2ÎŁâ state
Prognostic significance of endogenous adhesion/growth-regulatory lectins in lung cancer
Objective: To determine the expression of endogenous adhesion/growth-regulatory lectins and their binding sites using labeled tissue lectins as well as the binding profile of hyaluronic acid as an approach to define new prognostic markers. Methods: Sections of paraffin-embedded histological material of 481 lungs from lung tumor patients following radical lung excision processed by a routine immunohistochemical method (avidin-biotin labeling, DAB chromogen). Specific antibodies against galectins-1 and - 3 and the heparin-binding lectin were tested. Staining by labeled galectins and hyaluronic acid was similarly visualized by a routine protocol. After semiquantitative assessment of staining, the results were compared with the pT and pN stages and the histological type. Survival was calculated by univariate and multivariate methods. Results: Binding of galectin-1 and its expression tended to increase, whereas the parameters for galectin-3 decreased in advanced pT and pN stages at a statistically significant level. The number of positive cases was considerably smaller among the cases with small cell lung cancer than in the group with non-small-cell lung cancer, among which adenocarcinomas figured prominently with the exception of galectin-1 expression. Kaplan-Meier computations revealed that the survival rate of patients with galectin-3-binding or galectin-1-expressing tumors was significantly poorer than that of the negative cases. In the multivariate calculations of survival lymph node metastases ( p < 0.0001), histological type ( p = 0.003), galectin-3-binding capacity ( p = 0.01), galectin-3 expression ( p = 0.03) and pT status ( p = 0.003) proved to be independent prognostic factors, not correlated with the pN stage. Conclusion: The expression and the capacity to bind the adhesion/growth regulatory galectin-3 is defined as an unfavorable prognostic factor not correlated with the pTN stage. Copyright (C) 2005 S. Karger AG, Basel
Cascade time-scales for energy and helicity in homogeneous isotropic turbulence
We extend the Kolmogorov phenomenology for the scaling of energy spectra in
high-Reynolds number turbulence, to explicitly include the effect of helicity.
There exists a time-scale for helicity transfer in homogeneous,
isotropic turbulence with helicity. We arrive at this timescale using the
phenomenological arguments used by Kraichnan to derive the timescale
for energy transfer (J. Fluid Mech. {\bf 47}, 525--535 (1971)). We show that in
general may not be neglected compared to , even for rather low
relative helicity. We then deduce an inertial range joint cascade of energy and
helicity in which the dynamics are dominated by in the low wavenumbers
with both energy and helicity spectra scaling as ; and by at
larger wavenumbers with spectra scaling as . We demonstrate how,
within this phenomenology, the commonly observed ``bottleneck'' in the energy
spectrum might be explained. We derive a wavenumber which is less than
the Kolmogorov dissipation wavenumber, at which both energy and helicity
cascades terminate due to dissipation effects. Data from direct numerical
simulations are used to check our predictions.Comment: 14 pages, 5 figures, accepted to Physical Review
Cornelius Lanczos's derivation of the usual action integral of classical electrodynamics
The usual action integral of classical electrodynamics is derived starting
from Lanczos's electrodynamics -- a pure field theory in which charged
particles are identified with singularities of the homogeneous Maxwell's
equations interpreted as a generalization of the Cauchy-Riemann regularity
conditions from complex to biquaternion functions of four complex variables. It
is shown that contrary to the usual theory based on the inhomogeneous Maxwell's
equations, in which charged particles are identified with the sources, there is
no divergence in the self-interaction so that the mass is finite, and that the
only approximation made in the derivation are the usual conditions required for
the internal consistency of classical electrodynamics. Moreover, it is found
that the radius of the boundary surface enclosing a singularity interpreted as
an electron is on the same order as that of the hypothetical "bag" confining
the quarks in a hadron, so that Lanczos's electrodynamics is engaging the
reconsideration of many fundamental concepts related to the nature of
elementary particles.Comment: 16 pages. Final version to be published in "Foundations of Physics
The Line-of-Sight Proximity Effect and the Mass of Quasar Host Halos
We show that the Lyman-alpha optical depth statistics in the proximity
regions of quasar spectra depend on the mass of the dark matter halos hosting
the quasars. This is owing to both the overdensity around the quasars and the
associated infall of gas toward them. For a fiducial quasar host halo mass of
(3.0+/-1.6) h^-1 x 10^12 Msun, as inferred by Croom et al. from clustering in
the 2dF QSO Redshift Survey, we show that estimates of the ionizing background
(Gamma^bkg) from proximity effect measurements could be biased high by a factor
of ~2.5 at z=3 owing to neglecting these effects alone. The clustering of
galaxies and other active galactic nuclei around the proximity effect quasars
enhances the local background, but is not expected to skew measurements by more
than a few percent. Assuming the measurements of Gamma^bkg based on the mean
flux decrement in the Ly-alpha forest to be free of bias, we demonstrate how
the proximity effect analysis can be inverted to measure the mass of the dark
matter halos hosting quasars. In ideal conditions, such a measurement could be
made with a precision comparable to the best clustering constraints to date
from a modest sample of only about 100 spectra. We discuss observational
difficulties, including continuum flux estimation, quasar systematic redshift
determination, and quasar variability, which make accurate proximity effect
measurements challenging in practice. These are also likely to contribute to
the discrepancies between existing proximity effect and flux decrement
measurements of Gamma^bkg.Comment: 25 pages, including 14 figures, accepted by Ap
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