A Decision-Process Analysis of Implicit Coscheduling

This paper presents a theoretical framework based on Bayesian decision theory for analyzing recently reported results on implicit coscheduling of parallel applications on clusters of workstations. Using probabilistic modeling, we show that the approach presented can be applied for processes with arbitrary communication mixes. We also note that our approach can be used for deciding the additional spin times in the case of spin-yield.Finally, we present arguments for the use of a different notion of fairness than assumed by prior work.International Conference on Parallel and Distributed Computing</i

Oscillatory behaviour in a lattice prey-predator system

Using Monte Carlo simulations we study a lattice model of a prey-predator system. We show that in the three-dimensional model populations of preys and predators exhibit coherent periodic oscillations but such a behaviour is absent in lower-dimensional models. Finite-size analysis indicate that amplitude of these oscillations is finite even in the thermodynamic limit. In our opinion, this is the first example of a microscopic model with stochastic dynamics which exhibits oscillatory behaviour without any external driving force. We suggest that oscillations in our model are induced by some kind of stochastic resonance.Comment: 7 pages, 10 figures, Phys.Rev.E (Nov. 1999

Spurious diffusion in particle simulations of the Kolmogorov flow

Particle simulations of the Kolmogorov flow are analyzed by the Landau-Lifshitz fluctuating hydrodynamics. It is shown that a spurious diffusion of the center of mass corrupts the statistical properties of the flow. The analytical expression for the corresponding diffusion coefficient is derived.Comment: 10 pages, no figure

Internet Service via Broadband Satellite Networks

The demand for Internet bandwidth has grown rapidly in the past few years. A new generation of broadband satellite constellations promises to provide high speed Internet connectivity to areas not served by optical fiber, cable or other high speed terrestrial connections. However, using satellitelinks to supply high bandwidth has been difficult due to problems with inefficient performance of the Internet's TCP/IP protocol suite over satellite. We describe an architecture for improving the performance of TCP/IP protocols over heterogeneous network environments, especially networks containing satellite links. The end-to-end connection is split into segments, and the protocol on the satellite segment is optimized for the satellite link characteristics. TCP congestion control mechanisms are maintained on each segment, with some coupling between the segments to produce the effect of end-to-end TCP flow control. We have implemented this design and present results showing that using such gateways can improve throughput for individual connections by a large factor over paths containing a satellite link.The research and scientific content in this material has been published in the Proceedings of the SPIE, vol. 3528, February 1999, 169-180.</Center

Lifespan theorem for constrained surface diffusion flows

We consider closed immersed hypersurfaces in $\R^{3}$ and $\R^4$ evolving by a class of constrained surface diffusion flows. Our result, similar to earlier results for the Willmore flow, gives both a positive lower bound on the time for which a smooth solution exists, and a small upper bound on a power of the total curvature during this time. By phrasing the theorem in terms of the concentration of curvature in the initial surface, our result holds for very general initial data and has applications to further development in asymptotic analysis for these flows.Comment: 29 pages. arXiv admin note: substantial text overlap with arXiv:1201.657

Behaviour and passage of European silver eels (Anguilla anguilla) at a small hydropower plant during their downstream migration

Between 2004 and 2007, 116 downstream migrant silver eels (Anguilla anguilla) were monitored at a hydropower plant on the Gave de Pau river in South-West France using radio and PIT telemetry. The objectives of the study were: (i) to determine the environmental conditions when eels arrived and passed the facility; (ii) to determine the rate of eel escapement (passage other than via the turbines); (iii) to describe the behaviour of eels faced with the intake structure and the permeability of the intake trashracks for the different sizes of eel; and (iv) to determine whether surface bypasses originally designed for salmon could be effective for eels. Five types of behaviour of silver eels in the forebay and at the plant intakes were identified. The study showed the key factor influencing both eel behaviour and the route taken through the plant was variation in river discharge. Escapement rate was related to eel length and the spill flow to river flow ratio, which could be described by a logistic regression model. The surface bypasses originally designed for salmon were found to aid downstream eel migration significantly. At velocities < 0.40 m·s−1, no eels, even the largest, for which the racks are a physical barrier, were found impinged on the trashracks

Evolution of Chemistry in the envelope of Hot Corinos (ECHOS). I. Extremely young sulphur chemistry in the isolated Class 0 object B335

Within the project Evolution of Chemistry in the envelope of HOt corinoS (ECHOS), we present a study of sulphur chemistry in the envelope of the Class 0 source B335 through observations in the spectral range 7, 3, and 2 mm. We have modelled observations assuming LTE and LVG approximation. We have also used the code Nautilus to study the time evolution of sulphur species. We have detected 20 sulphur species with a total gas-phase S abundance similar to that found in the envelopes of other Class 0 objects, but with significant differences in the abundances between sulphur carbon chains and sulphur molecules containing oxygen and nitrogen. Our results highlight the nature of B335 as a source especially rich in sulphur carbon chains unlike other Class 0 sources. The low presence or absence of some molecules, such as SO and SO+, suggests a chemistry not particularly influenced by shocks. We, however, detect a large presence of HCS+ that, together with the low rotational temperatures obtained for all the S species (<15 K), reveals the moderate or low density of the envelope of B335. We also find that observations are better reproduced by models with a sulphur depletion factor of 10 with respect to the sulphur cosmic elemental abundance. The comparison between our model and observational results for B335 reveals an age of 10$^4$$<$t$<$10$^5$ yr, which highlights the particularly early evolutionary stage of this source. B335 presents a different chemistry compared to other young protostars that have formed in dense molecular clouds, which could be the result of accretion of surrounding material from the diffuse cloud onto the protostellar envelope of B335. In addition, the analysis of the SO2/C2S, SO/CS, and HCS+/CS ratios within a sample of prestellar cores and Class 0 objects show that they could be used as good chemical evolutionary indicators of the prestellar to protostellar transition

Automated Network Fault Management

Future military communication networks will have a mixture of backbone terrestrial, satellite and wireless terrestrial networks. The speeds of these networks vary and they are very heterogeneous. As networks become faster, it is not enough to do reactive fault management. Our approach combines proactive and reactive fault management . Proactive fault management is implemented by dynamic and adaptive routing. Reactive fault management is implemented by a combination of a neural network and an expert system. The system has been developed for the X.25 protocol. Several fault scenarios were modeled and included in the study: reduced switch capacity, increased packet generation rate of a certain application, disabled switch in the X.25 cloud, disabled links. We also modeled occurrence of alarms including severity of the problem, location of the event and a threshold. To detect and identify faults we use both numerical data associated with the performance objects (attributes) in the MIB as well as SNMP traps (alarms). Simulation experiments have been performed in order to understand the convergence of the algorithms, the training of the neural networks involved and the G2/NeurOn-Line software environment and MIB design

Sharp two-sided heat kernel estimates for critical Schr\"odinger operators on bounded domains

On a smooth bounded domain \Omega \subset R^N we consider the Schr\"odinger operators -\Delta -V, with V being either the critical borderline potential V(x)=(N-2)^2/4 |x|^{-2} or V(x)=(1/4) dist (x,\partial\Omega)^{-2}, under Dirichlet boundary conditions. In this work we obtain sharp two-sided estimates on the corresponding heat kernels. To this end we transform the Scr\"odinger operators into suitable degenerate operators, for which we prove a new parabolic Harnack inequality up to the boundary. To derive the Harnack inequality we have established a serier of new inequalities such as improved Hardy, logarithmic Hardy Sobolev, Hardy-Moser and weighted Poincar\'e. As a byproduct of our technique we are able to answer positively to a conjecture of E.B.Davies.Comment: 40 page

Gas phase Elemental abundances in Molecular cloudS (GEMS) VI. A sulphur journey across star-forming regions: study of thioformaldehyde emission

In the context of the IRAM 30m Large Program GEMS, we present a study of thioformaldehyde in several starless cores located in star-forming filaments of Taurus, Perseus, and Orion. We investigate the influence of the environmental conditions on the abundances of these molecules in the cores, and the effect of time evolution. We have modelled the observed lines of H2CS, HDCS, and D2CS using the radiative transfer code RADEX. We have also used the chemical code Nautilus to model the evolution of these species depending on the characteristics of the starless cores. We derive column densities and abundances for all the cores. We also derive deuterium fractionation ratios, Dfrac, to determine and compare the evolutionary stage between different parts of each star-forming region. Our results indicate that the north region of the B213 filament in Taurus is more evolved than the south, while the north-eastern part of Perseus presents an earlier evolutionary stage than the south-western zone. Model results also show that Dfrac decreases with the cosmic-ray ionisation rate, while it increases with density and with the degree of sulphur depletion. In particular, we only reproduce the observations when the initial sulphur abundance in the starless cores is at least one order of magnitude lower than the solar elemental sulphur abundance. The progressive increase in HDCS/H2CS and D2CS/H2CS with time makes these ratios powerful tools for deriving the chemical evolutionary stage of starless cores. However, they cannot be used to derive the temperature of these regions, since both ratios present a similar evolution at two different temperature ranges (7-11 K and 15-19 K). Regarding chemistry, (deuterated) thioformaldehyde is mainly formed through gas-phase reactions (double-replacement and neutral-neutral displacement reactions), while surface chemistry plays an important role as a destruction mechanism.Comment: 31 pages, 26 figure