303 research outputs found
Global fixed point proof of time-dependent density-functional theory
We reformulate and generalize the uniqueness and existence proofs of
time-dependent density-functional theory. The central idea is to restate the
fundamental one-to-one correspondence between densities and potentials as a
global fixed point question for potentials on a given time-interval. We show
that the unique fixed point, i.e. the unique potential generating a given
density, is reached as the limiting point of an iterative procedure. The
one-to-one correspondence between densities and potentials is a straightforward
result provided that the response function of the divergence of the internal
forces is bounded. The existence, i.e. the v-representability of a density, can
be proven as well provided that the operator norms of the response functions of
the members of the iterative sequence of potentials have an upper bound. The
densities under consideration have second time-derivatives that are required to
satisfy a condition slightly weaker than being square-integrable. This approach
avoids the usual restrictions of Taylor-expandability in time of the uniqueness
theorem by Runge and Gross [Phys.Rev.Lett.52, 997 (1984)] and of the existence
theorem by van Leeuwen [Phys.Rev.Lett. 82, 3863 (1999)]. Owing to its
generality, the proof not only answers basic questions in density-functional
theory but also has potential implications in other fields of physics.Comment: 4 pages, 1 figur
Fleming's bound for the decay of mixed states
Fleming's inequality is generalized to the decay function of mixed states. We
show that for any symmetric hamiltonian and for any density operator
on a finite dimensional Hilbert space with the orthogonal projection onto
the range of there holds the estimate \Tr(\Pi \rme^{-\rmi ht}\rho
\rme^{\rmi ht}) \geq\cos^{2}((\Delta h)_{\rho}t) for all real with
We show that equality either holds for all
or it does not hold for a single with All the density operators saturating the bound for
all i.e. the mixed intelligent states, are determined.Comment: 12 page
A scenario of planet erosion by coronal radiation
Context: According to theory, high-energy emission from the coronae of cool
stars can severely erode the atmospheres of orbiting planets. No observational
tests of the long term effects of erosion have yet been made. Aims: To analyze
the current distribution of planetary mass with X-ray irradiation of the
atmospheres in order to make an observational assessment of the effects of
erosion by coronal radiation. Methods: We study a large sample of
planet-hosting stars with XMM-Newton, Chandra and ROSAT; make a careful
identification of X-ray counterparts; and fit their spectra to make accurately
measurements of the stellar X-ray flux. Results: The distribution of the
planetary masses with X-ray flux suggests that erosion has taken place: most
surviving massive planets, (M_p sin i >1.5 M_J), have been exposed to lower
accumulated irradiation. Heavy erosion during the initial stages of stellar
evolution is followed by a phase of much weaker erosion. A line dividing these
two phases could be present, showing a strong dependence on planet mass.
Although a larger sample will be required to establish a well-defined erosion
line, the distribution found is very suggestive. Conclusions: The distribution
of planetary mass with X-ray flux is consistent with a scenario in which planet
atmospheres have suffered the effects of erosion by coronal X-ray and EUV
emission. The erosion line is an observational constraint to models of
atmospheric erosion.Comment: A&A 511, L8 (2010). 4 pages, 3 figures, 1 online table (included).
Language edited; corrected a wrong unit conversion (g/s -> M_J/Gyr);
corrected values in column 12 of Table 1 (slightly underestimated in first
version), and Figure 2 updated accordingl
On the existence of effective potentials in time-dependent density functional theory
We investigate the existence and properties of effective potentials in
time-dependent density functional theory. We outline conditions for a general
solution of the corresponding Sturm-Liouville boundary value problems. We
define the set of potentials and v-representable densities, give a proof of
existence of the effective potentials under certain restrictions, and show the
set of v-representable densities to be independent of the interaction.Comment: 13 page
Gargalos competitivos da cadeia produtiva da carne bovina brasileira.
bitstream/item/216760/1/Boletim-CiCarne-21.pdfBoletim Cicarne
Density-potential mappings in quantum dynamics
In a recent letter [Europhys. Lett. 95, 13001 (2011)] the question of whether
the density of a time-dependent quantum system determines its external
potential was reformulated as a fixed point problem. This idea was used to
generalize the existence and uniqueness theorems underlying time-dependent
density functional theory. In this work we extend this proof to allow for more
general norms and provide a numerical implementation of the fixed-point
iteration scheme. We focus on the one-dimensional case as it allows for a more
in-depth analysis using singular Sturm-Liouville theory and at the same time
provides an easy visualization of the numerical applications in space and time.
We give an explicit relation between the boundary conditions on the density and
the convergence properties of the fixed-point procedure via the spectral
properties of the associated Sturm-Liouville operator. We show precisely under
which conditions discrete and continuous spectra arise and give explicit
examples. These conditions are then used to show that in the most physically
relevant cases the fixed point procedure converges. This is further
demonstrated with an example.Comment: 20 pages, 8 figures, 3 table
Estimation of the XUV radiation onto close planets and their evaporation
Context: The current distribution of planet mass vs. incident stellar X-ray
flux supports the idea that photoevaporation of the atmosphere may take place
in close-in planets. Integrated effects have to be accounted for. A proper
calculation of the mass loss rate due to photoevaporation requires to estimate
the total irradiation from the whole XUV range. Aims: The purpose of this paper
is to extend the analysis of the photoevaporation in planetary atmospheres from
the accessible X-rays to the mostly unobserved EUV range by using the coronal
models of stars to calculate the EUV contribution to the stellar spectra. The
mass evolution of planets can be traced assuming that thermal losses dominate
the mass loss of their atmospheres. Methods: We determine coronal models for 82
stars with exoplanets that have X-ray observations available. Then a synthetic
spectrum is produced for the whole XUV range (~1-912 {\AA}). The determination
of the EUV stellar flux, calibrated with real EUV data, allows us to calculate
the accumulated effects of the XUV irradiation on the planet atmosphere with
time, as well as the mass evolution for planets with known density. Results: We
calibrate for the first time a relation of the EUV luminosity with stellar age
valid for late-type stars. In a sample of 109 exoplanets, few planets with
masses larger than ~1.5 Mj receive high XUV flux, suggesting that intense
photoevaporation takes place in a short period of time, as previously found in
X-rays. The scenario is also consistent with the observed distribution of
planet masses with density. The accumulated effects of photoevaporation over
time indicate that HD 209458b may have lost 0.2 Mj since an age of 20 Myr.
Conclusions: Coronal radiation produces rapid photoevaporation of the
atmospheres of planets close to young late-type stars. More complex models are
needed to explain fully the observations.Comment: Accepted by A&A. 10 pages, 8 figures, 7 Tables (2 online). Additional
online material includes 7 pages, 6 figures and 6 tables, all include
Evaluation of Xpert® MTB/RIF and ustar easyNAT™ TB IAD for diagnosis of tuberculous lymphadenitis of children in Tanzania : a prospective descriptive study
Fine needle aspiration biopsy has become a standard approach for diagnosis of peripheral tuberculous lymphadenitis. The aim of this study was to compare the performance of Xpert MTB/RIF and Ustar EasyNAT TB IAD nucleic acid amplification assays, against acid-fast bacilli microscopy, cytology and mycobacterial culture for the diagnosis of TB lymphadenitis in children from a TB-endemic setting in Tanzania.; Children of 8 weeks to 16 years of age, suspected of having TB lymphadenitis, were recruited at a district hospital in Tanzania. Fine needle aspirates of lymph nodes were analysed using acid-fast bacilli microscopy, liquid TB culture, cytology, Xpert MTB/RIF and EasyNAT. Latent class analysis and comparison against a composite reference standard comprising "culture and/or cytology" was done, to assess the performance of Xpert MTB/RIF and EasyNAT for the diagnosis of TB lymphadenitis.; Seventy-nine children were recruited; 4 were excluded from analysis. Against a composite reference standard of culture and/or cytology, Xpert MTB/RIF and EasyNAT had a sensitivity and specificity of 58 % and 93 %; and 19 % and 100 % respectively. Relative to latent class definitions, cytology had a sensitivity of 100 % and specificity of 94.7 %.; Combining clinical assessment, cytology and Xpert MTB/RIF may allow for a rapid and accurate diagnosis of childhood TB lymphadenitis. Larger diagnostic evaluation studies are recommended to validate these findings and on Xpert MTB/RIF to assess its use as a solitary initial test for TB lymphadenitis in children
Self-Concept, Individual Characteristics and Counterfeit Consumption: Evidence from an Emerging Market
The study draws on a sample of over 350 consumers from 10 department stores in an emerging market where counterfeit products are available in abundance and there is a huge demand for such goods. The findings reveal that interdependent and independent self traits significantly affect individual characteristics, that is, susceptibility to normative influence, readiness to take social risk, and status acquisition (SA), which in turn influences counterfeit purchase intention. It was discovered that such individual characteristics play a mediating effect on the self‐concept—purchase intention relationship and that high degrees of interdependent self traits positively affect consumers' purchase intention. The study adds to the theory of reasoned action (TRA) by incorporating SA variables into the TRA framework and discovers their significant influence on purchase intention. Some novel insights surrounding counterfeit consumption in an emerging economy context are presented and several implications are extracted to help practitioners appeal to such individual characteristics for combating counterfeit consumption
Transiting exoplanets from the CoRoT space mission IX. CoRoT-6b: a transiting `hot Jupiter' planet in an 8.9d orbit around a low-metallicity star
The CoRoT satellite exoplanetary team announces its sixth transiting planet
in this paper. We describe and discuss the satellite observations as well as
the complementary ground-based observations - photometric and spectroscopic -
carried out to assess the planetary nature of the object and determine its
specific physical parameters. The discovery reported here is a `hot Jupiter'
planet in an 8.9d orbit, 18 stellar radii, or 0.08 AU, away from its primary
star, which is a solar-type star (F9V) with an estimated age of 3.0 Gyr. The
planet mass is close to 3 times that of Jupiter. The star has a metallicity of
0.2 dex lower than the Sun, and a relatively high Li abundance. While
thelightcurveindicatesamuchhigherlevelof activity than, e.g., the Sun, there is
no sign of activity spectroscopically in e.g., the [Ca ] H&K lines
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