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Search Results: 1 - 10 of 339682 matches for " David J. Arrowsmith "
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The colour of electroplated golds
David J. Arrowsmith
Gold Bulletin , 1986, DOI: 10.1007/BF03214651
Abstract: The origin of the colour of gold and gold alloy electrodeposits is discussed, whether any new colours may be expected, and whether theory may be used to predict the colour of new alloys.
Communication models with distributed transmission rates and buffer sizes
David Arrowsmith,Mario di Bernardo,Francesco Sorrentino
Physics , 2006,
Abstract: The paper is concerned with the interplay between network structure and traffic dynamics in a communications network, from the viewpoint of end-to-end performance of packet transfer. We use a model of network generation that allows the transition from random to scale-free networks. Specifically, we are able to consider three different topologycal types of networks: (a) random; (b) scale-free with \gamma=3; (c) scale free with \gamma=2. We also use an LRD traffic generator in order to reproduce the fractal behavior that is observed in real world data communication. The issue is addressed of how the traffic behavior on the network is influenced by the variable factors of the transmission rates and queue length restrictions at the network vertices. We show that these factors can induce drastic changes in the throughput and delivery time of network performance and are able to counter-balance some undesirable effects due to the topology.
Effects of variations of load distribution on network performance
David Arrowsmith,Mario di Bernardo,Francesco Sorrentino
Computer Science , 2005,
Abstract: This paper is concerned with the characterization of the relationship between topology and traffic dynamics. We use a model of network generation that allows the transition from random to scale free networks. Specifically, we consider three different topological types of network: random, scale-free with \gamma = 3, scale-free with \gamma = 2. By using a novel LRD traffic generator, we observe best performance, in terms of transmission rates and delivered packets, in the case of random networks. We show that, even if scale-free networks are characterized by shorter characteristic-path- length (the lower the exponent, the lower the path-length), they show worst performances in terms of communication. We conjecture this could be explained in terms of changes in the load distribution, defined here as the number of shortest paths going through a given vertex. In fact, that distribu- tion is characterized by (i) a decreasing mean (ii) an increas- ing standard deviation, as the networks becomes scale-free (especially scale-free networks with low exponents). The use of a degree-independent server also discriminates against a scale-free structure. As a result, since the model is un- controlled, most packets will go through the same vertices, favoring the onset of congestion.
A Sources-of-Error Model for Acoustic/Infrasonic Yield Estimation for Above-Ground Single-Point Explosions  [PDF]
Stephen J. Arrowsmith, Rodney W. Whitaker, Jonathan K. Maccarthy, Dale N. Anderson
InfraMatics (InfraMatics) , 2012, DOI: 10.4236/inframatics.2012.11001
Abstract: Acoustic/infrasonic measurements contain physical information enabling an estimate of the yield of a single-point explosion that is on or above ground. A variety of semi-empirical and numerical models have been developed for estimating the yield based on the amplitude of a recorded acoustic signal. This paper utilizes existing semi-empirical models-suitable for timely yield estimation—and develops the mathematical framework to properly account for uncertainties in these models, in addition to measurement uncertainties. The inclusion of calibration parameters into our mathematical model allows for the correction of constant path specific effects that are not captured in existing semi-empirical models. The calibrated model provides a yield estimate and associated error bounds that correctly partitions total error into model error and background noise. Yield estimation with the models is demonstrated with single-point, above ground chemical explosions at Los Alamos National Laboratory (LANL) experimental testing facilities.
Local δ18O and δ2H variability in UK rainfall
M. D. Jones,M. J. Leng,C. Arrowsmith,C. Deuchars
Hydrology and Earth System Sciences Discussions , 2007,
Abstract: Rainfall collected twice weekly from 3 nearby UK stations between November 2004 and October 2006 allows local differences in δ18O and δ2H to be observed. Local gradients in δ18Op appear to be of the same order of magnitude as national trends, suggesting the spatial δ18Op picture is more complicated than the one currently available from sparse GNIP coverage. Comparing data from this study with previous work we find that average δ18Op has changed in the UK over the last 20 years concurrent with an average temperature increase although inter-annual controls on the values remain seasonal temperature and the amount of precipitation in each rain event. Climate-isotope relationships observed from the weekly data do not explain the observed decadal scale shifts.
The complete genome, comparative and functional analysis of Stenotrophomonas maltophilia reveals an organism heavily shielded by drug resistance determinants
Lisa C Crossman, Virginia C Gould, J Maxwell Dow, Georgios S Vernikos, Aki Okazaki, Mohammed Sebaihia, David Saunders, Claire Arrowsmith, Tim Carver, Nicholas Peters, Ellen Adlem, Arnaud Kerhornou, Angela Lord, Lee Murphy, Katharine Seeger, Robert Squares, Simon Rutter, Michael A Quail, Mari-Adele Rajandream, David Harris, Carol Churcher, Stephen D Bentley, Julian Parkhill, Nicholas R Thomson, Matthew B Avison
Genome Biology , 2008, DOI: 10.1186/gb-2008-9-4-r74
Abstract: The genome of the bacteremia-associated isolate S. maltophilia K279a is 4,851,126 bp and of high G+C content. The sequence reveals an organism with a remarkable capacity for drug and heavy metal resistance. In addition to a number of genes conferring resistance to antimicrobial drugs of different classes via alternative mechanisms, nine resistance-nodulation-division (RND)-type putative antimicrobial efflux systems are present. Functional genomic analysis confirms a role in drug resistance for several of the novel RND efflux pumps. S. maltophilia possesses potentially mobile regions of DNA and encodes a number of pili and fimbriae likely to be involved in adhesion and biofilm formation that may also contribute to increased antimicrobial drug resistance.The panoply of antimicrobial drug resistance genes and mobile genetic elements found suggests that the organism can act as a reservoir of antimicrobial drug resistance determinants in a clinical environment, which is an issue of considerable concern.The rise of antimicrobial drug resistance in bacteria is one of the biggest threats to healthcare provision in the developed world. Few new antimicrobial drugs are undergoing clinical trials, and almost none are effective against Gram-negative multi-drug resistant (MDR) pathogens [1]. A return to the pre-antibiotic era is a possibility, and for some infections is the current reality [2].Antimicrobial resistance in historically common pathogens is usually either acquired on a mobile genetic element or results from a mutation [3]. However, some opportunistic pathogens are intrinsically resistant to the actions of a number of antimicrobial classes. These tend to be of environmental origin, and their intrinsic drug resistance determinants either provide resistance to antibiotics produced by competitors, or represent broad-spectrum methods for removing toxic compounds or waste products that, by chance, protect against antimicrobials [3,4]. It is known that established opportuni
Resilience of Natural Gas Networks during Conflicts, Crises and Disruptions
Rui Carvalho, Lubos Buzna, Flavio Bono, Marcelo Masera, David K. Arrowsmith, Dirk Helbing
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0090265
Abstract: Human conflict, geopolitical crises, terrorist attacks, and natural disasters can turn large parts of energy distribution networks offline. Europe's current gas supply network is largely dependent on deliveries from Russia and North Africa, creating vulnerabilities to social and political instabilities. During crises, less delivery may mean greater congestion, as the pipeline network is used in ways it has not been designed for. Given the importance of the security of natural gas supply, we develop a model to handle network congestion on various geographical scales. We offer a resilient response strategy to energy shortages and quantify its effectiveness for a variety of relevant scenarios. In essence, Europe's gas supply can be made robust even to major supply disruptions, if a fair distribution strategy is applied.
The Bogdanov Map: Bifurcations, Mode Locking, and Chaos in a Dissipative System
David K. Arrowsmith,Julyan H. E. Cartwright,Alexis N. Lansbury,Colin M. Place
Physics , 1994, DOI: 10.1142/S021812749300074X
Abstract: We investigate the bifurcations and basins of attraction in the Bogdanov map, a planar quadratic map which is conjugate to the H\'enon area-preserving map in its conservative limit. It undergoes a Hopf bifurcation as dissipation is added, and exhibits the panoply of mode locking, Arnold tongues, and chaos as an invariant circle grows out, finally to be destroyed in the homoclinic tangency of the manifolds of a remote saddle point. The Bogdanov map is the Euler map of a two-dimensional system of ordinary differential equations first considered by Bogdanov and Arnold in their study of the versal unfolding of the double-zero-eigenvalue singularity, and equivalently of a vector field invariant under rotation of the plane by an angle $2\pi$. It is a useful system in which to observe the effect of dissipative perturbations on Hamiltonian structure. In addition, we argue that the Bogdanov map provides a good approximation to the dynamics of the Poincar\'e maps of periodically forced oscillators.
Fair sharing of resources in a supply network with constraints
Rui Carvalho,Lubos Buzna,Wolfram Just,Dirk Helbing,David K. Arrowsmith
Physics , 2011, DOI: 10.1103/PhysRevE.85.046101
Abstract: This paper investigates the effect of network topology on the fair allocation of network resources among a set of agents, an all-important issue for the efficiency of transportation networks all around us. We analyse a generic mechanism that distributes network capacity fairly among existing flow demands. The problem can be solved by semi-analytical methods on a nearest neighbour graph with one source and sink pair, when transport occurs over shortest paths. For this setup, we uncover a broad range of patterns of intersecting shortest paths as a function of the distance between the source and the sink. When the number of intersections is the maximum and the distance between the source and the sink is large, we find that a fair allocation implies a decrease of at least 50% from the maximum throughput. We also find that the histogram of the flow allocations assigned to the agents decays as a power-law with exponent -1. Our semi-analytical framework suggests possible explanations for the well-known reduction of the throughput in fair allocations. It also suggests that the combination of network topology and routing rules can lead to highly uneven (but fair) distributions of resources, a remark of caution to network designers.
Robustness of Trans-European Gas Networks
Rui Carvalho,Lubos Buzna,Flavio Bono,Eugenio Gutierrez,Wolfram Just,David Arrowsmith
Physics , 2009, DOI: 10.1103/PhysRevE.80.016106
Abstract: Here we uncover the load and fault-tolerant backbones of the trans-European gas pipeline network. Combining topological data with information on inter-country flows, we estimate the global load of the network and its tolerance to failures. To do this, we apply two complementary methods generalized from the betweenness centrality and the maximum flow. We find that the gas pipeline network has grown to satisfy a dual-purpose: on one hand, the major pipelines are crossed by a large number of shortest paths thereby increasing the efficiency of the network; on the other hand, a non-operational pipeline causes only a minimal impact on network capacity, implying that the network is error-tolerant. These findings suggest that the trans-European gas pipeline network is robust, i.e., error tolerant to failures of high load links.
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