263 research outputs found
Two Lane Traffic Simulations using Cellular Automata
We examine a simple two lane cellular automaton based upon the single lane CA
introduced by Nagel and Schreckenberg. We point out important parameters
defining the shape of the fundamental diagram. Moreover we investigate the
importance of stochastic elements with respect to real life traffic.Comment: to be published in Physica A, 19 pages, 9 out of 13 postscript
figures, 24kB in format .tar.gz., 33kB in format .tar.gz.uu, for a full
version including all figures see
http://studguppy.tsasa.lanl.gov/research_team/papers
A comparative study of the use of tiger-specific and heterologous microsatellite markers for population genetic studies of the Bengal tiger (Panthera tigris tigris)
Comparison of genetic diversity indices of heterologous and species-specific microsatellite loci within a species may provide a panel of appropriate markers for genetic studies, but few studies have carried out such comparisons. We examined and compared the genetic characteristics of tiger-specific and heterologous loci in eight captive Bengal tigers. The mean polymorphic information content (PIC) value of the tiger-specific microsatellite loci (n = 15) was 0.447, and the number of alleles was from 2 to 4 per locus. In comparison, the heterologous microsatellite loci (n = 15) had a mean PIC value of 0.539, and the number of alleles per locus was three to five. Our findings indicate that the heterologous markers have a higher frequency (n = 11) of polymorphic microsatellite loci and number of alleles per locus compared with tiger-specific loci. We pooled the highly polymorphic (PIC > 0.5) tiger-specific loci (n = 5) and heterologous microsatellite loci (n = 11) except one and noted a higher mean observed heterozygosity and PIC values of 0.668 and 0.575, respectively, compared with the heterologous and tiger-specific loci taken alone. Using a locus selection criterion of PIC > 0.5, we recommend a combined panel of 16 highly polymorphic loci for genetic studies of the wild population of the Bengal tigers and suggest that either a combination of tiger-specific and heterologous microsatellite primers or heterologous primers be used in genetic studies related to the ecology, biology, socio-biology and behavior of Bengal tigers as >13 loci are needed in such studies.Keywords: Bengal tiger, highly polymorphic, tiger-specific, heterologous, microsatellite loci
Macroscopic Dynamics of Multi-Lane Traffic
We present a macroscopic model of mixed multi-lane freeway traffic that can
be easily calibrated to empirical traffic data, as is shown for Dutch highway
data. The model is derived from a gas-kinetic level of description, including
effects of vehicular space requirements and velocity correlations between
successive vehicles. We also give a derivation of the lane-changing rates. The
resulting dynamic velocity equations contain non-local and anisotropic
interaction terms which allow a robust and efficient numerical simulation of
multi-lane traffic. As demonstrated by various examples, this facilitates the
investigation of synchronization patterns among lanes and effects of on-ramps,
off-ramps, lane closures, or accidents.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Large Eddy Simulation of acoustic pulse propagation and turbulent flow interaction in expansion mufflers
A novel hybrid pressure-based compressible solver is developed and validated for low Mach number acoustic flow simulation. The solver is applied to the propagation of an acoustic pulse in a simple expansion muffler, a configuration frequently employed in HVAC and automotive exhaust systems. A set of benchmark results for experimental analysis of the simple expansion muffler both with and without flow are obtained to compare attenuation in forced pulsation for various mean-flow velocities. The experimental results are then used for validation of the proposed pressure-based compressible solver. Compressible, Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation of a muffler with a mean through flow is conducted and results are presented to demonstrate inherent limitations associated with this approach. Consequently, a mixed synthetic inflow boundary condition is developed and validated for compressible Large Eddy Simulation (LES) of channel flow. The mixed synthetic boundary is then employed for LES of a simple expansion muffler to analyse the flow-acoustic and acoustic-pulse interactions inside the expansion muffler. The improvement in the prediction of vortex shedding inside the chamber is highlighted in comparison to the URANS method. Further, the effect of forced pulsation on flow-acoustic is observed in regard to the shift in Strouhal number inside the simple expansion muffler
Modeling and Simulation of Multi-Lane Traffic Flow
A most important aspect in the field of traffic modeling is the simulation of
bottleneck situations. For their realistic description a macroscopic multi-lane
model for uni-directional freeways including acceleration, deceleration,
velocity fluctuations, overtaking and lane-changing maneuvers is systematically
deduced from a gas-kinetic (Boltzmann-like) approach. The resulting equations
contain corrections with respect to previous models. For efficient computer
simulations, a reduced model delineating the coarse-grained temporal behavior
is derived and applied to bottleneck situations.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
A perspective on multinational enterprise’s national identity dilemma
This conceptual paper identifies gaps and contributes to the literature on ‘identity’ dilemmas faced by multinational enterprises operating in a globalised world. Various characteristics and business strategies of multinational enterprises are delineated and analysed through the lens of social identity theory and international business concepts such as market and institutional logic. Our analysis, based on multiple cases, and derived from a variety of industries and countries, associates the identity dilemma to informed business strategy. Our findings suggest that while multinational enterprises face identity dilemmas that they sometimes use to their advantage, it also poses several challenges. Through our conceptualisation, we derive five distinct propositions to shape future research directions
Isolated Splenic Metastasis from Rectal Carcinoma: A Rare Occurrence
The presence of isolated splenic metastasis in rectal carcinoma is uncommon and usually presents as an asymptomatic mass, noted incidentally on imaging. Splenectomy is usually performed with the goal of curing metastatic disease. It is unclear if adjuvant chemotherapy affords any benefit, and the prognosis is unknown. The case of a young woman is reported, in whom an isolated metastatic lesion in the spleen was discovered 9 months after adjuvant chemotherapy for stage III rectal adenocarcinoma. The patient has remained disease-free for nearly 5 years following splenectomy and chemotherapy. To our knowledge, this is the fourth reported case in the English literature of an isolated splenic metastatic lesion from rectal cancer. We discuss the unique presentation, the importance of post-treatment surveillance, and the implementation of multi-modality treatment strategies in this young patient
Hydrogel coated monoliths for enzymatic hydrolysis of penicillin G
The objective of this work was to develop a hydrogel-coated monolith for the entrapment of penicillin G acylase (E. coli, PGA). After screening of different hydrogels, chitosan was chosen as the carrier material for the preparation of monolithic biocatalysts. This protocol leads to active immobilized biocatalysts for the enzymatic hydrolysis of penicillin G (PenG). The monolithic biocatalyst was tested in a monolith loop reactor (MLR) and compared with conventional reactor systems using free PGA, and a commercially available immobilized PGA. The optimal immobilization protocol was found to be 5 g l−1 PGA, 1% chitosan, 1.1% glutaraldehyde and pH 7. Final PGA loading on glass plates was 29 mg ml−1 gel. For 400 cpsi monoliths, the final PGA loading on functionalized monoliths was 36 mg ml−1 gel. The observed volumetric reaction rate in the MLR was 0.79 mol s−1 m−3monolith. Apart from an initial drop in activity due to wash out of PGA at higher ionic strength, no decrease in activity was observed after five subsequent activity test runs. The storage stability of the biocatalysts is at least a month without loss of activity. Although the monolithic biocatalyst as used in the MLR is still outperformed by the current industrial catalyst (immobilized preparation of PGA, 4.5 mol s−1 m−3catalyst), the rate per gel volume is slightly higher for monolithic catalysts. Good activity and improved mechanical strength make the monolithic bioreactor an interesting alternative that deserves further investigation for this application. Although moderate internal diffusion limitations have been observed inside the gel beads and in the gel layer on the monolith channel, this is not the main reason for the large differences in reactor performance that were observed. The pH drop over the reactor as a result of the chosen method for pH control results in a decreased performance of both the MLR and the packed bed reactor compared to the batch system. A different reactor configuration including an optimal pH profile is required to increase the reactor performance. The monolithic stirrer reactor would be an interesting alternative to improve the performance of the monolith-PGA combination
Gas-kinetic derivation of Navier-Stokes-like traffic equations
Macroscopic traffic models have recently been severely criticized to base on
lax analogies only and to have a number of deficiencies. Therefore, this paper
shows how to construct a logically consistent fluid-dynamic traffic model from
basic laws for the acceleration and interaction of vehicles. These
considerations lead to the gas-kinetic traffic equation of Paveri-Fontana. Its
stationary and spatially homogeneous solution implies equilibrium relations for
the `fundamental diagram', the variance-density relation, and other quantities
which are partly difficult to determine empirically.
Paveri-Fontana's traffic equation allows the derivation of macroscopic moment
equations which build a system of non-closed equations. This system can be
closed by the well proved method of Chapman and Enskog which leads to
Euler-like traffic equations in zeroth-order approximation and to
Navier-Stokes-like traffic equations in first-order approximation. The latter
are finally corrected for the finite space requirements of vehicles. It is
shown that the resulting model is able to withstand the above mentioned
criticism.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
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