18,568 research outputs found
A comparison between detailed and configuration-averaged collisional-radiative codes applied to non-local thermal equilibrium plasma
A collisional-radiative model describing nonlocal-thermodynamic-equilibrium
plasmas is developed. It is based on the HULLAC (Hebrew University Lawrence
Livermore Atomic Code) suite for the transitions rates, in the zero-temperature
radiation field hypothesis. Two variants of the model are presented: the first
one is configuration averaged, while the second one is a detailed level
version. Comparisons are made between them in the case of a carbon plasma; they
show that the configuration-averaged code gives correct results for an
electronic temperature Te=10 eV (or higher) but fails at lower temperatures
such as Te=1 eV. The validity of the configuration-averaged approximation is
discussed: the intuitive criterion requiring that the average
configuration-energy dispersion must be less than the electron thermal energy
turns out to be a necessary but far from sufficient condition. Another
condition based on the resolution of a modified rate-equation system is
proposed. Its efficiency is emphasized in the case of low-temperature plasmas.
Finally, it is shown that near-threshold autoionization cascade processes may
induce a severe failure of the configuration-average formalism.Comment: 9
Theoretical study of resonant x-ray emission spectroscopy of Mn films on Ag
We report a theoretical study on resonant x-ray emission spectra (RXES) in
the whole energy region of the Mn white lines for three prototypical
Mn/Ag(001) systems: (i) a Mn impurity in Ag, (ii) an adsorbed Mn monolayer on
Ag, and (iii) a thick Mn film. The calculated RXES spectra depend strongly on
the excitation energy. At excitation, the spectra of all three systems
are dominated by the elastic peak. For excitation energies around , and
between and , however, most of the spectral weight comes from
inelastic x-ray scattering. The line shape of these inelastic ``satellite''
structures changes considerably between the three considered Mn/Ag systems, a
fact that may be attributed to changes in the bonding nature of the Mn-
orbitals. The system-dependence of the RXES spectrum is thus found to be much
stronger than that of the corresponding absorption spectrum. Our results
suggest that RXES in the Mn region may be used as a sensitive probe
of the local environment of Mn atoms.Comment: 9 pages, 11 figure
Resonant x-ray scattering spectra from multipole orderings: Np M_{4,5} edges in NpO2
We study resonant x-ray scattering (RXS) at Np M_{4,5} edges in the
triple-\textbf{k} multipole ordering phase in NpO_{2}, on the basis of a
localized electron model. We derive an expression for RXS amplitudes to
characterize the spectra under the assumption that a rotational invariance is
preserved in the intermediate state of scattering process. This assumption is
justified by the fact that energies of the crystal electric field and the
intersite interaction is smaller than the energy of multiplet structures. This
expression is found useful to calculate energy profiles with taking account of
the intra-Coulomb and spin-orbit interactions. Assuming the \Gamma_{8}-quartet
ground state, we construct the triple-\textbf{k} ground state, and analyze the
RXS spectra. The energy profiles are calculated in good agreement with the
experiment, providing a sound basis to previous phenomenological analyses.Comment: 10 pages, 7 figure
Relativistic many-body calculations of the Stark-induced amplitude of the 6P1/2 -7P1/2 transition in thallium
Stark-induced amplitudes for the 6P1/2 - 7P1/2 transition in Tl I are
calculated using the relativistic SD approximation in which single and double
excitations of Dirac-Hartree-Fock levels are summed to all orders in
perturbation theory. Our SD values alpha S = 368 a0 3 and beta S= 298 a 0 3 are
in good agreement with the measurements alpha S=377(8) a 0 3$ and beta S =
313(8) a 0 3 by D. DeMille, D. Budker, and E. D. Commins [Phys. Rev. A 50, 4657
(1994)]. Calculations of the Stark shifts in the 6P1/2 - 7P1/2 and 6P1/2 -
7S1/2 transitions are also carried out. The Stark shifts predicted by our
calculations agree with the most accurate measured values within the
experimental uncertainties for both transitions
Mn L edge resonant x-ray scattering in manganites: Influence of the magnetic state
We present an analysis of the dependence of the resonant orbital order and
magnetic scattering spectra on the spin configuration. We consider an arbitrary
spin direction with respect to the local crystal field axis, thus lowering
significantly the local symmetry. To evaluate the atomic scattering in this
case, we generalized the Hannon-Trammel formula and implemented it inside the
framework of atomic multiplet calculations in a crystal field. For an
illustration, we calculate the magnetic and orbital scattering in the CE phase
of \lsmo in the cases when the spins are aligned with the crystal lattice
vector (or equivalently ) and when they are rotated in the
-plane by 45 with respect to this axis. Magnetic spectra differ
for the two cases. For the orbital scattering, we show that for the former
configuration there is a non negligible ()
scattering component, which vanishes in the 45 case, while the () components are similar in the two cases. From the
consideration of two 90 spin canted structures, we conclude there is a
significant dependence of the orbital scattering spectra on the spin
arrangement. Recent experiments detected a sudden decrease of the orbital
scattering intensity upon increasing the temperature above the N\' eel
temperature in \lsmo. We discuss this behavior considering the effect of
different types of misorientations of the spins on the orbital scattering
spectrum.Comment: 8 figures. In the revised version, we added a note, a reference, and
a few minor changes in Figure 1 and the text. Accepted in Physical Review
Recombination in polymer-fullerene bulk heterojunction solar cells
Recombination of photogenerated charge carriers in polymer bulk
heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and
the fill factor (FF). Identifying the mechanism of recombination is, therefore,
fundamentally important for increasing the power conversion efficiency. Light
intensity and temperature dependent current-voltage measurements on polymer BHJ
cells made from a variety of different semiconducting polymers and fullerenes
show that the recombination kinetics are voltage dependent and evolve from
first order recombination at short circuit to bimolecular recombination at open
circuit as a result of increasing the voltage-dependent charge carrier density
in the cell. The "missing 0.3V" inferred from comparison of the band gaps of
the bulk heterojunction materials and the measured open circuit voltage at room
temperature results from the temperature dependence of the quasi-Fermi-levels
in the polymer and fullerene domains - a conclusion based upon the fundamental
statistics of Fermions.Comment: Accepted for publication in Physical Review B.
http://prb.aps.org/accepted/B/6b07cO3aHe71bd1b149e1425e58bf2868cda2384d?ajax=1&height=500&width=50
Genetics and Genetic Testing in Congenital Heart Disease
Congenital heart defects (CHDs) are structural abnormalities of the heart and great vessels that are present from birth. The presence or absence of extra-cardiac anomalies has historically been used to identify patients with possible monogenic, chromosomal, or teratogenic CHD etiologies. These distinctions remain clinically relevant, particularly with regard to management; however, identification of genetic causes in patients with presumably non-syndromic CHD indicates that isolated CHD can also be genetic in origin. In recent years, the field of cardiac genetics has benefited from a growing understanding of the complex molecular mechanisms underpinning heart development, and the extreme genetic heterogeneity of CHD is increasingly appreciated. Progress has been largely supported by improvements in genetic testing technology derived from worldwide efforts to accurately and economically characterize the full breadth of human genomic variation. The last fifteen years in particular have witnessed emergence and refinement of novel cytogenetic and sequencing technologies, which have proven to be enormously effective tools for both diagnosis and identification of novel CHD-causing genes. These advancements have led to an increasing need for cardiac care providers to be well versed in the molecular genetic origins of CHD and to have working knowledge of the benefits and limitations of available testing methods. In this review, we provide a general overview of key morphologic, molecular, and signaling mechanisms relevant to heart development before summarizing overall progress in the molecular genetic analyses of CHDs and current recommendations for clinical application of genetic testing. Particular emphasis is placed on the utility and limitations of chromosomal microarray analyses (CMAs) and on emerging clinical roles for whole exome sequencing (WES) and other next-generation sequencing (NGS) technologies
The Radio Recovery of SN 1970G: The Continuing Radio Evolution of SN 1970G
Using the Very Large Array, we have detected radio emission from the site of
SN 1970G in the Sc galaxy M101. These observations are 31 years after the
supernova event, making SN 1970G the longest monitored radio supernova. With
flux densities of 0.12 +/- 0.020 mJy at 6 cm and 0.16 +/- 0.015 mJy at 20 cm,
the spectral index of -0.24 +/- 0.20 appears to have flattened somewhat when
compared with the previously reported value of -0.56 +/- 0.11, taken in 1990.
The radio emission at 20 cm has decayed since the 1990 observations with a
power-law index of beta_20cm = -0.28 +/- 0.13. We discuss the radio properties
of this source and compare them to those of other Type II radio supernovae.Comment: 11 pages, 1 table and 2 figures; To appear in Astrophysical Journal
Letter
Trends In Australian Fresh Milk Supply Chains
The completion of the dairy industry deregulation process in June 2000 is transforming the fresh milk and fresh milk products supply chains in Australia. This transformation is set in an environment where markets are getting more complex and competitive, consumers more discerning and conscious about food safety and public policy is more focused on environment related issues. Supply chains are becoming more integrated, and innovation in product, process and supply chains is revolutionising the way products are being produced, distributed and marketed (Fearne & David 1999). This paper is based on research which, following supply chain management literature, identifies the success strategies in the dairy industry supply chains in Australia. The enquiry seeks to understand the nature and shape of supply chains and the exchange relationship between supply and value chains. The fieldwork for the research involved semi-structured interviews at middle to senior management level in the retail, processing, production and input market of the dairy industry supply chains. The data was managed and analysed using software NVivo ver. 2.0, which assists in identifying major themes and relationships between concepts in data
A theory of the electric quadrupole contribution to resonant x-ray scattering: Application to multipole ordering phases in Ce_{1-x}La_{x}B_{6}
We study the electric quadrupole (E2) contribution to resonant x-ray
scattering (RXS). Under the assumption that the rotational invariance is
preserved in the Hamiltonian describing the intermediate state of scattering,
we derive a useful expression for the RXS amplitude. One of the advantages the
derived expression possesses is the full information of the energy dependence,
lacking in all the previous studies using the fast collision approximation. The
expression is also helpful to classify the spectra into multipole order
parameters which are brought about. The expression is suitable to investigate
the RXS spectra in the localized f electron systems. We demonstrate the
usefulness of the formula by calculating the RXS spectra at the Ce L_{2,3}
edges in Ce_{1-x}La_{x}B_{6} on the basis of the formula. We obtain the spectra
as a function of energy in agreement with the experiment of
Ce_{0.7}La_{0.3}B_{6}. Analyzing the azimuthal angle dependence, we find the
sixfold symmetry in the \sigma-\sigma' channel and the threefold onein the
\sigma-\pi' channel not only in the antiferrooctupole (AFO) ordering phase but
also in the antiferroquadrupole (AFQ) ordering phase, which behavior depends
strongly on the domain distribution. The sixfold symmetry in the AFQ phase
arises from the simultaneously induced hexadecapole order. Although the AFO
order is plausible for phase IV in Ce_{1-x}La_{x}B_{6}, the possibility of the
AFQ order may not be ruled out on the basis of azimuthal angle dependence
alone.Comment: 12 pages, 6 figure
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