3,830 research outputs found
Non-Equilibrium Modeling of the Fe XVII 3C/3D ratio for an Intense X-ray Free Electron Laser
We present a review of two methods used to model recent LCLS experimental
results for the 3C/3D line intensity ratio of Fe XVII (Bernitt et al. 2012),
the time-dependent collisional-radiative method and the density-matrix
approach. These are described and applied to a two-level atomic system excited
by an X-ray free electron laser. A range of pulse parameters is explored and
the effects on the predicted Fe XVII 3C and 3D line intensity ratio are
calculated. In order to investigate the behavior of the predicted line
intensity ratio, a particular pair of A-values for the 3C and 3D transitions
was chosen (2.22 10 s and 6.02 10
s for the 3C and 3D, respectively), but our conclusions are independent
of the precise values. We also reaffirm the conclusions from Oreshkina et
al.(2014, 2015): the non-linear effects in the density matrix are important and
the reduction in the Fe XVII 3C/3D line intensity ratio is sensitive to the
laser pulse parameters, namely pulse duration, pulse intensity, and laser
bandwidth. It is also shown that for both models the lowering of the 3C/3D line
intensity ratio below the expected time-independent oscillator strength ratio
has a significant contribution due to the emission from the plasma after the
laser pulse has left the plasma volume. Laser intensities above W/cm are required for a reduction in the 3C/3D line intensity
ratio below the expected time independent oscillator strength ratio
Meeting the Changing Need for Herbage Seed Quality Assurance in the 21st Century
Quality assurance is a key element in the herbage seed supply chain. The measurement and management of seed quality is discussed in terms of its four main parameters - genetic, physical, vital, and phytosanitary quality - which provide information on the expected performance of herbage seed when sown in the field. During the past century, seed quality management systems have evolved in response to national and regional differences in economic development, crop characteristics, merit testing, and the demands of international trade. The pace of change in the management of seed quality assurance has intensified in developed countries over the past decade or so, driven mainly by the ability to protect intellectual property, the consolidation of seed companies into larger units, and government policy aimed at deregulating the delivery of quality assurance. In developed countries, this has seen the strong private seed sector taking increasing responsibility for seed quality assurance, both economically and legally, together with the emergence of private seed testing laboratories and in-house certification programs. However, developing countries without a strong private seed sector are better served by the more traditional model in which government takes on the role and responsibility for managing seed quality assurance in the public interest. This paper explores recent trends in seed quality management and their strategic implications for different countries now and in the future with particular reference to herbage seed
Calorimeter Clustering Algorithms: Description and Performance
This note describes the performance of the calorimeter clustering algorithms used for ATLAS, and which provide inputs for particle identification. ATLAS uses two principal algorithms. The first is the ``sliding-window'' algorithm, which clusters calorimeter cells within fixed-size rectangles; results from this are used for electron, photon, and tau lepton identification. The second is the ``topological'' algorithm, which clusters together neighboring cells, as long as the signal in the cells is significant compared to noise. The results of this second algorithm are further used for jet and missing transverse energy reconstruction. This note first summarizes the steps of the calorimeter reconstruction software. A detailed description of the two clustering algorithms is then given. A last section summarizes their performance. The results presented in this note are obtained with the ATLAS athena software releases 12 and 13
Lower entropy bounds and particle number fluctuations in a Fermi sea
We demonstrate, in an elementary manner, that given a partition of the single
particle Hilbert space into orthogonal subspaces, a Fermi sea may be factored
into pairs of entangled modes, similar to a BCS state. We derive expressions
for the entropy and for the particle number fluctuations of a subspace of a
fermi sea, at zero and finite temperatures, and relate these by a lower bound
on the entropy. As an application we investigate analytically and numerically
these quantities for electrons in the lowest Landau level of a quantum Hall
sample.Comment: shorter version, typos fixe
Dirac R-matrix calculations for the electron-impact excitation of neutral tungsten providing noninvasive diagnostics for magnetic confinement fusion
Neutral tungsten is the primary candidate as a wall material in the divertor
region of the International Thermonuclear Experimental Reactor (ITER). The
efficient operation of ITER depends heavily on precise atomic physics
calculations for the determination of reliable erosion diagnostics, helping to
characterise the influx of tungsten impurities into the core plasma. The
following paper presents detailed calculations of the atomic structure of
neutral tungsten using the multiconfigurational Dirac-Fock method, drawing
comparisons with experimental measurements where available, and includes a
critical assessment of existing atomic structure data. We investigate the
electron-impact excitation of neutral tungsten using the Dirac R-matrix method
and, by employing collisional-radiative models, we benchmark our results with
recent Compact Toroidal Hybrid measurements. The resulting comparisons
highlight alternative diagnostic lines to the widely used 400.88nm line.Comment: 10 pages, 6 figure
Measuring the transaction costs of historical shifts to informal drought management institutions in Italy
Published: 29 June 2020Coase shows how costly resources are (re)allocated via costly institutions, and that transaction costs must therefore be positive. However, Coase did not elaborate on transitions between institutions which incur positive transaction costs that are characterized by numerous institutional complementarities; that is, feedback loops that inform the need for, and pathways toward, institutional change. Economic investigations of complementary modes of (re)allocation are rarely undertaken, let alone studies of transitions between modes. However, modes of (re)allocation that achieve similar results at less cost are generally viewed as having production-raising value. This paper measures the costs of transitioning drought management institutions in Italy toward informal, participatory, and consensus-based approaches during several recent drought events. The chosen model is Drought Steering Committees, which offer a substitute for current formal (less flexible) planning approaches, and where lower transaction costs that are associated with the transition are inferred. Our results highlight the relevance of empirical assessments of ‘costly’ transitions based on a historical study of transaction costs, as well as supporting previous works that highlight the value of contextual analysis in economic studies, in order to identify the benefits of institutional investment.Adam Loch, Silvia Santato, C. Dionisio Pérez-Blanco and Jaroslav Mysia
A large-scale R-matrix calculation for electron-impact excitation of the Ne O-like ion
The five J levels within a or ground state complex provide
an excellent testing ground for the comparison of theoretical line ratios with
astrophysically observed values, in addition to providing valuable electron
temperature and density diagnostics. The low temperature nature of the line
ratios ensure that the theoretically derived values are sensitive to the
underlying atomic structure and electron-impact excitation rates. Previous
R-matrix calculations for the Ne O-like ion exhibit large spurious
structure in the cross sections at higher electron energies, which may affect
Maxwellian averaged rates even at low temperatures. Furthermore, there is an
absence of comprehensive excitation data between the excited states that may
provide newer diagnostics to compliment the more established lines discussed in
this paper. To resolve these issues, we present both a small scale 56-level
Breit-Pauli (BP) calculation and a large-scale 554 levels R-matrix Intermediate
Coupling Frame Transformation (ICFT) calculation that extends the scope and
validity of earlier JAJOM calculations both in terms of the atomic structure
and scattering cross sections. Our results provide a comprehensive
electron-impact excitation data set for all transitions to higher shells.
The fundamental atomic data for this O-like ion is subsequently used within a
collisional radiative framework to provide the line ratios across a range of
electron temperatures and densities of interest in astrophysical observations.Comment: 17 pages, 8 figure
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