1,525 research outputs found
NVU dynamics. I. Geodesic motion on the constant-potential-energy hypersurface
An algorithm is derived for computer simulation of geodesics on the constant
potential-energy hypersurface of a system of N classical particles. First, a
basic time-reversible geodesic algorithm is derived by discretizing the
geodesic stationarity condition and implementing the constant potential energy
constraint via standard Lagrangian multipliers. The basic NVU algorithm is
tested by single-precision computer simulations of the Lennard-Jones liquid.
Excellent numerical stability is obtained if the force cutoff is smoothed and
the two initial configurations have identical potential energy within machine
precision. Nevertheless, just as for NVE algorithms, stabilizers are needed for
very long runs in order to compensate for the accumulation of numerical errors
that eventually lead to "entropic drift" of the potential energy towards higher
values. A modification of the basic NVU algorithm is introduced that ensures
potential-energy and step-length conservation; center-of-mass drift is also
eliminated. Analytical arguments confirmed by simulations demonstrate that the
modified NVU algorithm is absolutely stable. Finally, simulations show that the
NVU algorithm and the standard leap-frog NVE algorithm have identical radial
distribution functions for the Lennard-Jones liquid
Transcriptional regulation of iron homeostasis of the hemibiotrophic phytopathogen Colletotrichum graminicola
A Class of Parameter Dependent Commuting Matrices
We present a novel class of real symmetric matrices in arbitrary dimension
, linearly dependent on a parameter . The matrix elements satisfy a set
of nontrivial constraints that arise from asking for commutation of pairs of
such matrices for all , and an intuitive sufficiency condition for the
solvability of certain linear equations that arise therefrom. This class of
matrices generically violate the Wigner von Neumann non crossing rule, and is
argued to be intimately connected with finite dimensional Hamiltonians of
quantum integrable systems.Comment: Latex, Added References, Typos correcte
Assessment of the proposed EBMT pediatric criteria for diagnosis and severity grading of sinusoidal obstruction syndrome
An assessment of VMS-rerouting and traffic signal planning with emission objectives in an urban network — A case study for the city of Graz
This paper discusses a case study evaluating the potential impact of ITS traffic management on CO 2 and Black carbon tailpipe emissions. Results are based on extensive microsimulations performed using a calibrated VISSIM model in combination with the AIRE model for calculating the tailpipe emissions from simulated vehicle trajectories. The ITS traffic management options hereby consist of easily implementable actions such as the usage of a variable message sign (VMS) or the setting of fixed time signal plans. Our simulations show that in the current case shifting 5% of vehicles from one route to another one leads to an improvement in terms of emissions only if the VMS is complemented with an adaptation of the signal programs, while the VMS sign or the change of the signal plans alone do not yield benefits. This shows that it is not sufficient to evaluate single actions in a ceteris paribus analysis, but their joint network effects need to be taken into account
Occurrence of Salmonella spp. in flies and foodstuff from pork butcheries in Kampala, Uganda
Food-borne diseases such as salmonellosis are a major cause of human gastroenteritis worldwide, especially in the developing world due to poor sanitary conditions. Flies feed on food and breed in feces and other organic material. As such they are known vectors of Salmonella spp. Given that pork consumption in Uganda is rapidly increasing while good food safety practices remain absent, this study aims to assess the occurrence of Salmonella spp. in pork butcheries as a contribution to improve hygiene.
Seventy-seven pork butcheries out of 179 mapped in a previous survey in Kampala were randomly selected. From June–October 2014, samples of house flies, foodstuff and equipment were collected from all butcheries. Cultural isolation of Salmonella spp. was performed according to ISO 6579:2002.
Among 693 samples, 64 (9%) tested positive for Salmonella enteritidis. Among the positives, 32% were samples of raw pork (25), 25% flies’ midguts (19), less than 9% water (7), tomatoes (6), cabbage (4), onions (2) and one case on roasted pork1, respectively. Positive flies coincided with contaminated foodstuff in 29% of the butcheries. All 154 samples from either butchers’ hands or their equipment were negative for Salmonella spp.
The prevalence of S. enteritidis, especially on raw pork and in flies, illustrates the need for improving food safety in pork butcheries. Further research is required clarifying the gaps; especially the role of flies as microbiological carriers. In this context investigations are ongoing to identify Salmonella serotypes and their antimicrobial drug-resistance situation. However, these findings merit increased attention and can be used to improve knowledge, attitudes and practices amongst butchers.
The research was carried out with the financial support of the Federal Ministry for Economic Cooperation and Development (BMZ), Germany, and the CGIAR Research Program on Agriculture for Nutrition and Health, led by the International Food Policy Research Institute, through the Safe Food, Fair Food project at ILRI. Martin Heilmann got a scholarship from the German Academic Exchange Service (DAAD)
Sublinear-Time Algorithms for Monomer-Dimer Systems on Bounded Degree Graphs
For a graph , let be the partition function of the
monomer-dimer system defined by , where is the
number of matchings of size in . We consider graphs of bounded degree
and develop a sublinear-time algorithm for estimating at an
arbitrary value within additive error with high
probability. The query complexity of our algorithm does not depend on the size
of and is polynomial in , and we also provide a lower bound
quadratic in for this problem. This is the first analysis of a
sublinear-time approximation algorithm for a # P-complete problem. Our
approach is based on the correlation decay of the Gibbs distribution associated
with . We show that our algorithm approximates the probability
for a vertex to be covered by a matching, sampled according to this Gibbs
distribution, in a near-optimal sublinear time. We extend our results to
approximate the average size and the entropy of such a matching within an
additive error with high probability, where again the query complexity is
polynomial in and the lower bound is quadratic in .
Our algorithms are simple to implement and of practical use when dealing with
massive datasets. Our results extend to other systems where the correlation
decay is known to hold as for the independent set problem up to the critical
activity
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Fermionic R-Operator and Integrability of the One-Dimensional Hubbard Model
We propose a new type of the Yang-Baxter equation (YBE) and the decorated
Yang-Baxter equation (DYBE). Those relations for the fermionic R-operator were
introduced recently as a tool to treat the integrability of the fermion models.
Using the YBE and the DYBE for the XX fermion model, we construct the fermionic
R-operator for the one-dimensional (1D) Hubbard model. It gives another proof
of the integrability of the 1D Hubbard model. Furthermore a new approach to the
SO(4) symmetry of the 1D Hubbard model is discussed.Comment: 25 page
Algebraic Bethe ansatz approach for the one-dimensional Hubbard model
We formulate in terms of the quantum inverse scattering method the algebraic
Bethe ansatz solution of the one-dimensional Hubbard model. The method
developed is based on a new set of commutation relations which encodes a hidden
symmetry of 6-vertex type.Comment: appendix additioned with Boltzmann weigths and R-matrix. Version to
be published in J.Phys.A:math.Gen. (1997
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