19,454 research outputs found
Estimation of ungauged Bahr el Jebel flows based on upstream water levels and large scale spatial rainfall data
The study derives Bahr el Jebel flow data at Mongalla, combining upstream flow from Lake Albert and torrential runoff derived from the Collaborative Historical African Rainfall Model (CHARM) rainfall data in the catchment between Lake Albert and Mongalla using GIS techniques. The results provide an updated rating curve for Lake Albert outflows and currently unavailable flow data at Mongalla, the entry to the Sudd swamp, with a high level of confidence for the period after 1983; data which are essential for detailed hydrological assessments of the swamp system with its significant importance for the economies and lives of people in the area
Methods for measuring the citations and productivity of scientists across time and discipline
Publication statistics are ubiquitous in the ratings of scientific
achievement, with citation counts and paper tallies factoring into an
individual's consideration for postdoctoral positions, junior faculty, tenure,
and even visa status for international scientists. Citation statistics are
designed to quantify individual career achievement, both at the level of a
single publication, and over an individual's entire career. While some academic
careers are defined by a few significant papers (possibly out of many), other
academic careers are defined by the cumulative contribution made by the
author's publications to the body of science. Several metrics have been
formulated to quantify an individual's publication career, yet none of these
metrics account for the dependence of citation counts and journal size on time.
In this paper, we normalize publication metrics across both time and discipline
in order to achieve a universal framework for analyzing and comparing
scientific achievement. We study the publication careers of individual authors
over the 50-year period 1958-2008 within six high-impact journals: CELL, the
New England Journal of Medicine (NEJM), Nature, the Proceedings of the National
Academy of Science (PNAS), Physical Review Letters (PRL), and Science. In
comparing the achievement of authors within each journal, we uncover
quantifiable statistical regularity in the probability density function (pdf)
of scientific achievement across both time and discipline. The universal
distribution of career success within these arenas for publication raises the
possibility that a fundamental driving force underlying scientific achievement
is the competitive nature of scientific advancement.Comment: 25 pages in 1 Column Preprint format, 7 Figures, 4 Tables. Version
II: changes made in response to referee comments. Note: change in definition
of "Paper shares.
(3+1)-Dimensional Hydrodynamic Expansion with a Critical Point from Realistic Initial Conditions
We investigate a (3+1)-dimensional hydrodynamic expansion of the hot and
dense system created in head-on collisions of Pb+Pb/Au+Au at beam energies from
GeV. An equation of state that incorporates a critical end point (CEP)
in line with the lattice data is used. The necessary initial conditions for the
hydrodynamic evolution are taken from a microscopic transport approach (UrQMD).
We compare the properties of the initial state and the full hydrodynamical
calculation with an isentropic expansion employing an initial state from a
simple overlap model. We find that the specific entropy () from both
initial conditions is very similar and only depends on the underlying equation
of state. Using the chiral (hadronic) equation of state we investigate the
expansion paths for both initial conditions. Defining a critical area around
the critical point, we show at what beam energies one can expect to have a
sizable fraction of the system close to the critical point. Finally, we
emphasise the importance of the equation of state of strongly interacting
matter, in the (experimental) search for the CEP.Comment: 8 pages, 8 figure
Does Function Follow Organizational Form? Evidence From the Lending Practices of Large and Small Banks
Theories based on incomplete contracting suggest that small organizations may do better than large organizations in activities that require the processing of soft information. We explore this idea in the context of bank lending to small firms, an activity that is typically thought of as relying heavily on soft information. We find that large banks are less willing than small banks to lend to informationally 'difficult' credits, such as firms that do not keep formal financial records. Moreover, controlling for the endogeneity of bank-firm matching, large banks lend at a greater distance, interact more impersonally with their borrowers, have shorter and less exclusive relationships, and do not alleviate credit constraints as effectively. All of this is consistent with small banks being better able to collect and act on soft information than large banks.
Does Function Follow Organzizational Form? Evidence From the Lending Practices of Large and Small Banks
Theories based on incomplete contracting suggest that small organizations may do better than large organizations in activities that require the processing of soft information. We explore this idea in the context of bank lending to small firms, an activity that is typically thought of as relying heavily on soft information. We find that large banks are less willing than small banks to lend to informationally “difficult†credits, such as firms that do not keep formal financial records. Moreover, controlling for the endogeneity of bank-firm matching, large banks lend at a greater distance, interact more impersonally with their borrowers, have shorter and less exclusive relationships, and do not alleviate credit constraints as effectively. All of this is consistent with small banks being better able to collect and act on soft information than large banks. The opinions in this paper do not necessarily reflect those of the Federal Reserve Board or its staff. This work has been supported by the National Science Foundation (Rajan, Stein), and the George J. Stigler Center for Study of the State and Economy (Rajan). Thanks also to seminar participants at Yale, the Federal Reserve Bank of New York, Tulane, Babson, the University of Illinois, the Federal Reserve Bank of Chicago Bank Structure Conference, the NBER and the Western Finance Association meetings, as well as to Abhijit Banerjee, Michael Kremer, David Scharfstein, Andrei Shleifer, Greg Udell, Christopher Udry and James Weston for helpful comments and suggestions.
Energy Dependence of High Moments for Net-proton Distributions
High moments of multiplicity distributions of conserved quantities are
predicted to be sensitive to critical fluctuations. To understand the effect of
the complicated non-critical physics backgrounds on the proposed observable, we
have studied various moments of net-proton distributions with AMPT, Hijing,
Therminator and UrQMD models, in which no QCD critical point physics is
implemented. It is found that the centrality evolution of various moments of
net-proton distributions can be uniformly described by a superposition of
emission sources. In addition, in the absence of critical phenomena, some
moment products of net-proton distribution, related to the baryon number
susceptibilities ratio in Lattice QCD calculation, are predicted to be constant
as a function of the collision centrality. We argue that a non-monotonic
dependence of the moment products as a function collision centrality and the
beam energy may be used to locate the QCD critical point.Comment: SQM2009 Proceeding, 6 pages, 5 figure
Semi-Empirical Model for Nano-Scale Device Simulations
We present a new semi-empirical model for calculating electron transport in
atomic-scale devices. The model is an extension of the Extended H\"uckel method
with a self-consistent Hartree potential. This potential models the effect of
an external bias and corresponding charge re-arrangements in the device. It is
also possible to include the effect of external gate potentials and continuum
dielectric regions in the device. The model is used to study the electron
transport through an organic molecule between gold surfaces, and it is
demonstrated that the results are in closer agreement with experiments than ab
initio approaches provide. In another example, we study the transition from
tunneling to thermionic emission in a transistor structure based on graphene
nanoribbons.Comment: 8 pages, 8 figures. Submitted to PR
Characterization of Megatrypanum trypanosomes from European Cervidae
Megatrypanum trypanosomes have been isolated from a number of different European Cervidae, but on the basis of morphology it has not been possible to define the species to which these isolates belong. We isolated Trypanosoma (Megatrypanum) theileri from 10 cattle, and Megatrypanum trypanosomes from 11 fallow deer (Cervus dama), 9 red deer (Cervus elaphus), and 4 roe deer (Capreolus capreolus) by blood culture on a biphasic medium (NNN agar slopes). Trypanosomes were propagated in Schneider's Drosophila medium and characterized by isoenzyme analysis and molecular karyotyping. Isocitrate dehydrogenase and phosphoglucomutase were visualized after starch gel electrophoresis of trypanosome lysates. By cluster analysis of this data all isolates from deer were clearly separated from the T. (M.) theileri isolates from cattle. Isolates from roe deer were different not only from T. (M.) theileri but also from the other deer isolates. Isolates from fallow deer and red deer were grouped together. Thus, there are probably at least two different species of Megatrypanum trypanosomes in the three Cervidae. One parasitizing roe deer, the other, apparently less host specific species, infecting red deer and fallow deer. Separation of the chromosomes of Megatrypanum trypanosomes by pulsed-field gradient gel electrophoresis (PFGE) showed that each isolate contained a large number (> 18) of chromosomes ranging in size from 300 to > 2200 kb. The molecular karyotypes were similar for all isolates, although no isolate was identical to anothe
Learning associations between clinical information and motion-based descriptors using a large scale MR-derived cardiac motion atlas
The availability of large scale databases containing imaging and non-imaging
data, such as the UK Biobank, represents an opportunity to improve our
understanding of healthy and diseased bodily function. Cardiac motion atlases
provide a space of reference in which the motion fields of a cohort of subjects
can be directly compared. In this work, a cardiac motion atlas is built from
cine MR data from the UK Biobank (~ 6000 subjects). Two automated quality
control strategies are proposed to reject subjects with insufficient image
quality. Based on the atlas, three dimensionality reduction algorithms are
evaluated to learn data-driven cardiac motion descriptors, and statistical
methods used to study the association between these descriptors and non-imaging
data. Results show a positive correlation between the atlas motion descriptors
and body fat percentage, basal metabolic rate, hypertension, smoking status and
alcohol intake frequency. The proposed method outperforms the ability to
identify changes in cardiac function due to these known cardiovascular risk
factors compared to ejection fraction, the most commonly used descriptor of
cardiac function. In conclusion, this work represents a framework for further
investigation of the factors influencing cardiac health.Comment: 2018 International Workshop on Statistical Atlases and Computational
Modeling of the Hear
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