5,481 research outputs found
Order-N Density-Matrix Electronic-Structure Method for General Potentials
A new order-N method for calculating the electronic structure of general
(non-tight-binding) potentials is presented. The method uses a combination of
the ``purification''-based approaches used by Li, Nunes and Vanderbilt, and
Daw, and a representation of the density matrix based on ``travelling basis
orbitals''. The method is applied to several one-dimensional examples,
including the free electron gas, the ``Morse'' bound-state potential, a
discontinuous potential that mimics an interface, and an oscillatory potential
that mimics a semiconductor. The method is found to contain Friedel
oscillations, quantization of charge in bound states, and band gap formation.
Quantitatively accurate agreement with exact results is found in most cases.
Possible advantages with regard to treating electron-electron interactions and
arbitrary boundary conditions are discussed.Comment: 13 pages, REVTEX, 7 postscript figures (not quite perfect
SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Inter-network Chromosphere
On 12 March 1996 we obtained observations of the quiet Sun with the SUMER
instrument. The observa- tions were sequences of 15-20 second exposures of
ultraviolet emission line profiles and of the neighboring continua. These data
contain signatures of the dynamics of the solar chromosphere that are uniquely
useful because of wavelength coverage, moderate signal-to-noise ratios, and
image stability. The dominant observed phenomenon is an oscillatory behavior
that is analogous to the 3 minute oscillations seen in Ca II lines. The
oscillations appear to be coherent over 3-8". At any time they occur over
approx. 50 % of the area studied, and they appear as large perturbations in the
intensities of lines and continua. The oscillations are most clearly seen in
intensity variations in the UV (lambda > 912 A) continua, and they are also
seen in the intensities and velocities of chromospheric lines of C I, N I and O
I. Intensity brightenings are accompanied by blueshifts of typically 5 km
s. Phase differences between continuum and line intensities also
indicate the presence of upward propagating waves. Three minute intensity
oscillations are occasionally seen in second spectra (C II 1335), but never in
third spectra (C III and Si III). Third spectra and He I 584 show oscillations
in velocity that are not simply related to the 3 minute oscillations. The
continuum intensity variations are consistent with recent simulations of
chromospheric dynamics (Carlsson & Stein 1994) while the line observations
indicate that important ingredients are missing at higher layers in the
simulations. The data show that time variations are crucial for our
understanding of the chromosphere itself and for the spectral features formed
there.Comment: 8 pages, 3 figs, AASTeX, Accepted for publication in APJ letter
Collective vibrational states with fast iterative QRPA method
An iterative method we previously proposed to compute nuclear strength
functions is developed to allow it to accurately calculate properties of
individual nuclear states. The approach is based on the
quasi-particle-random-phase approximation (QRPA) and uses an iterative
non-hermitian Arnoldi diagonalization method where the QRPA matrix does not
have to be explicitly calculated and stored. The method gives substantial
advantages over conventional QRPA calculations with regards to the
computational cost. The method is used to calculate excitation energies and
decay rates of the lowest lying 2+ and 3- states in Pb, Sn, Ni and Ca isotopes
using three different Skyrme interactions and a separable gaussian pairing
force.Comment: 10 pages, 11 figure
The Theory of the Interleaving Distance on Multidimensional Persistence Modules
In 2009, Chazal et al. introduced -interleavings of persistence
modules. -interleavings induce a pseudometric on (isomorphism
classes of) persistence modules, the interleaving distance. The definitions of
-interleavings and generalize readily to multidimensional
persistence modules. In this paper, we develop the theory of multidimensional
interleavings, with a view towards applications to topological data analysis.
We present four main results. First, we show that on 1-D persistence modules,
is equal to the bottleneck distance . This result, which first
appeared in an earlier preprint of this paper, has since appeared in several
other places, and is now known as the isometry theorem. Second, we present a
characterization of the -interleaving relation on multidimensional
persistence modules. This expresses transparently the sense in which two
-interleaved modules are algebraically similar. Third, using this
characterization, we show that when we define our persistence modules over a
prime field, satisfies a universality property. This universality result
is the central result of the paper. It says that satisfies a stability
property generalizing one which is known to satisfy, and that in
addition, if is any other pseudometric on multidimensional persistence
modules satisfying the same stability property, then . We also show
that a variant of this universality result holds for , over arbitrary
fields. Finally, we show that restricts to a metric on isomorphism
classes of finitely presented multidimensional persistence modules.Comment: Major revision; exposition improved throughout. To appear in
Foundations of Computational Mathematics. 36 page
Reappraising the Spite Lithium Plateau: Extremely Thin and Marginally Consistent with WMAP
The lithium abundance in 62 halo dwarfs is determined from accurate
equivalent widths reported in the literature and an improved infrared flux
method (IRFM) temperature scale. The Li abundance of 41 plateau stars (those
with Teff > 6000 K) is found to be independent of temperature and metallicity,
with a star-to-star scatter of only 0.06 dex over a broad range of temperatures
(6000 K < Teff < 6800 K) and metallicities (-3.4 < [Fe/H] < -1), thus imposing
stringent constraints on depletion by mixing and production by Galactic
chemical evolution. We find a mean Li plateau abundance of A(Li) = 2.37 dex
(7Li/H = 2.34 X 10^{-10}), which, considering errors of the order of 0.1 dex in
the absolute abundance scale, is just in borderline agreement with the
constraints imposed by the theory of primordial nucleosynthesis and WMAP data
(2.51 < A(Li)[WMAP] < 2.66 dex).Comment: ApJ Letters, in pres
Pain and health-related quality of life in a geographically defined population of men with prostate cancer
In order to provide baseline data on pain and health-related quality of life, to explore factors predicting pain and reduced quality of life, and to find potentially undertreated cases in men with prostate cancer, we undertook a population-based questionnaire study. The questionnaire, which included the EuroQo1 instrument, the Brief Pain Inventory form and 8 specially designed questions, was sent to all men with prostate cancer in the county of Östergötland, Sweden. Of the 1442 men included in the study, 1243 responded to the questionnaire. Altogether 42% had perceived pain during the previous week and 26% stated their quality of life to be 50% or lower on a visual analogue scale. A high rating of health care availability and short time since diagnosis were found to significantly predict lower ratings of pain (P< 0.05). Pain was found to be a significant predictive factor for decreased quality of life together with high age, low rating of health care availability and palliative treatment (P< 0.05). In conclusion, assessment and treatment of pain is essential for a good quality of life in men with prostate cancer. The monitoring of prostate cancer patients should be individualized to fit the demands of the groups with the greatest need for support. © 2001 Cancer Research Campaign http://www.bjcancer.co
Evidence for Shape Co-existence at medium spin in 76Rb
Four previously known rotational bands in 76Rb have been extended to moderate
spins using the Gammasphere and Microball gamma ray and charged particle
detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV.
The properties of two of the negative-parity bands can only readily be
interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model
calculations if they have the same configuration in terms of the number of g9/2
particles, but they result from different nuclear shapes (one near-oblate and
the other near-prolate). These data appear to constitute a unique example of
shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters
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