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Search Results: 1 - 10 of 352989 matches for " D. P. Watts "
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The Crystal Ball programme at MAMI
Watts D.P.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20123701027
Abstract: This contribution will outline the physics programme exploiting the intense energy tagged polarised real photon beam at MAMI-C. The coupling of an intense photon beam and close to complete detector acceptance offers unique opportunities for precision measurements to challenge our understanding of the structure of the nucleon and the nucleus as well as the underlying theory of Quantum Chromo Dynamics (QCD). The experimental facility and the physics programme will be outlined and selected recent preliminary analyses will be presented.
Dibaryons at COSY
M. Bashkanov,H. Clement,D. P. Watts
Physics , 2015, DOI: 10.1007/s10751-015-1190-4
Abstract: Experiments at the Juelich Cooler Synchrotron (COSY) have now found compelling evidence for a new resonant state in the two-baryon system with mass 2380 MeV and a width of 70 MeV. The structure, containing six valence quarks, constitutes a so-called dibaryon, either a hexaquark or a hadronic molecule. The present knowledge about the dibaryon as well as other implications and possible future experiments are discussed.
Universal behavior in a generalized model of contagion
P. S. Dodds,D. J. Watts
Quantitative Biology , 2004, DOI: 10.1103/PhysRevLett.92.218701
Abstract: Models of contagion arise broadly both in the biological and social sciences, with applications ranging from the transmission of infectious diseases to the diffusion of innovations and the spread of cultural fads. In this Letter, we introduce a general model of contagion which, by explicitly incorporating memory of past exposures to, for example, an infectious agent, rumor, or new product, includes the main features of existing contagion models and interpolates between them. We obtain exact solutions for a simple version of the model, finding that under general conditions only three classes of collective dynamics exist, two of which correspond to familiar epidemic threshold and critical mass dynamics, while the third is a distinct intermediate case. We find that for a given length of memory, the class into which a particular system falls is determined by two parameters, each of which ought to be measurable empirically. Our model suggests novel measures for assessing the susceptibility of a population to large contagion events, and also a possible strategy for inhibiting or facilitating them.
Measurement of polarisation transfer in hyperon photoproduction at MAMI
T. C. Jude,D. I. Glazier,D. P. Watts
Physics , 2008, DOI: 10.1142/S0217751X09044188
Abstract: The photoproduction of K+ mesons is an important challenge to recent QCD based chiral perturbation theories in the strange quark sector and is an important constraint on the nucleon excitation spectrum. We present preliminary data from a new high precision measurement using the Crystal Ball detector. The measurement pioneers a new technique for tagging strangeness using detailed cluster analysis in segmented calorimeters which has potential wider application at present and future hadron physics facilities.
The Papua New Guinea tsunami of 17 July 1998: anatomy of a catastrophic event
D. R. Tappin,P. Watts,S. T. Grilli
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2008,
Abstract: The Papua New Guinea (PNG) tsunami of July 1998 was a seminal event because it demonstrated that relatively small and relatively deepwater Submarine Mass Failures (SMFs) can cause devastating local tsunamis that strike without warning. There is a comprehensive data set that proves this event was caused by a submarine slump. Yet, the source of the tsunami has remained controversial. This controversy is attributed to several causes. Before the PNG event, it was questionable as to whether SMFs could cause devastating tsunamis. As a result, only limited modelling of SMFs as tsunami sources had been undertaken, and these excluded slumps. The results of these models were that SMFs in general were not considered to be a potential source of catastrophic tsunamis. To effectively model a SMF requires fairly detailed geological data, and these too had been lacking. In addition, qualitative data, such as evidence from survivors, tended to be disregarded in assessing alternative tsunami sources. The use of marine geological data to identify areas of recent submarine failure was not widely applied. The disastrous loss of life caused by the PNG tsunami resulted in a major investigation into the area offshore of the devastated coastline, with five marine expeditions taking place. This was the first time that a focussed, large-scale, international programme of marine surveying had taken place so soon after a major tsunami. It was also the first time that such a comprehensive data set became the basis for tsunami simulations. The use of marine mapping subsequently led to a larger involvement of marine geologists in the study of tsunamis, expanding the knowledge base of those studying the threat from SMF hazards. This paper provides an overview of the PNG tsunami and its impact on tsunami science. It presents revised interpretations of the slump architecture based on new seabed relief images and, using these, the most comprehensive tsunami simulation of the PNG event to date. Simulation results explain the measured runups to a high degree. The PNG tsunami has made a major impact on tsunami science. It is one of the most studied SMF tsunamis, yet it remains the only one known of its type: a slump.
Identity and Search in Social Networks
D. J. Watts,P. S. Dodds,M. E. J. Newman
Physics , 2002, DOI: 10.1126/science.1070120
Abstract: Social networks have the surprising property of being "searchable": Ordinary people are capable of directing messages through their network of acquaintances to reach a specific but distant target person in only a few steps. We present a model that offers an explanation of social network searchability in terms of recognizable personal identities: sets of characteristics measured along a number of social dimensions. Our model defines a class of searchable networks and a method for searching them that may be applicable to many network search problems, including the location of data files in peer-to-peer networks, pages on the World Wide Web, and information in distributed databases.
Planar Bragg Grating Sensors—Fabrication and Applications: A Review
I. J. G. Sparrow,P. G. R. Smith,G. D. Emmerson,S. P. Watts,C. Riziotis
Journal of Sensors , 2009, DOI: 10.1155/2009/607647
Abstract: We discuss the background and technology of planar Bragg grating sensors, reviewing their development and describing the latest developments. The physical operating principles are discussed, relating device operation to user requirements. Recent performance of such devices includes a planar Bragg grating sensor design which allows refractive index resolution of 1.9×10?6 RIU and temperature resolution of 0.03°C. This sensor design is incorporated into industrialised applications allowing the sensor to be used for real time sensing in intrinsically safe, high-pressure pipelines, or for insertion probe applications such as fermentation. Initial data demonstrating the ability to identify solvents and monitor long term industrial processes is presented. A brief review of the technology used to fabricate the sensors is given along with examples of the flexibility afforded by the technique.
A Monte Carlo Method for Analyzing Mixed-Lattice Substitution Experiment Using MCNP
G.B. Wilkin,B.P. Bromley,D.G. Watts
AECL Nuclear Review , 2012, DOI: http:dx.doi.org/10.12943/anr.2012.00016
Abstract: Critical experiments involving a small region of test fuel substituted into a reference lattice have traditionally been analyzedusing diffusion codes to extract lattice physics parameters of the test fuel such as the critical buckling and the associated bias in the calculation of keff . A method that was first developed in 2006 uses a version of MCNP that was modified to allow the analyst to selectively change fission neutron production in various parts of the model. This paper describes the modification made to MCNP, demonstrates how the substitution experiment analysis is done through several examples using data from the ZED-2 critical facility, and finally, quantifies the expected uncertainties in the method.
Cloud retrievals from satellite data using optimal estimation: evaluation and application to ATSR
C. A. Poulsen,P. D. Watts,G. E. Thomas,A. M. Sayer
Atmospheric Measurement Techniques Discussions , 2011, DOI: 10.5194/amtd-4-2389-2011
Abstract: Clouds play an important role in balancing the Earth's radiation budget. Clouds reflect sunlight which cools the Earth, and also trap infrared radiation in the same manner as greenhouse gases. Changes in cloud cover and cloud properties over time can have important consequences for climate. The Intergovernmental Panel for Climate Change (IPCC) has identified current gaps in the understanding of clouds and related climate feedback processes as a leading cause of uncertainty in forecasting climate change. In this paper we present an algorithm that uses optimal estimation to retrieve cloud parameters from satellite multi-spectral imager data, in particular the Along-Track Scanning Radiometers ATSR-2 and AATSR. The cloud parameters retrieved are the cloud top pressure, cloud optical depth, cloud effective radius, cloud fraction and cloud phase. Importantly, the technique also provides estimated errors along with the retrieved values and quantifies the consistency between retrieval representation of cloud and satellite radiances. This should enable the effective use of the products for comparison with climate models or for exploitation via data assimilation. The technique is evaluated by performing retrieval simulations for a variety of simulated single layer and multi-layer conditions. Examples of applying the algorithm to ATSR-2 flight data are presented and the sensitivity of the retrievals assessed. This algorithm has been applied to both ATSR-2 and AATSR visible and infrared measurements in the context of the GRAPE (Global Retrieval and cloud Product Evaluation) project to produce a 14 year consistent record for climate research (Sayer et al., 2010).
Specific Heat of Ce(1-x)La(x)RhIn(5) in Zero and Applied Magnetic Field: A Very Rich Phase Diagram
J. S. Kim,J. Alwood,D. Mixson,P. Watts,G. R. Stewart
Physics , 2002, DOI: 10.1103/PhysRevB.66.134418
Abstract: Specific heat and magnetization results as a function of field on single- and poly-crystalline samples of Ce(1-x)La(x)RhIn(5) show 1.) a specific heat gamma of about 100 mJ/moleK^2 (in agreement with recent dHvA results of Alvers et al.); 2.) upturns at low temperatures in C/T and chi that fit a power law behavior (<=> Griffiths phase non-Fermi liquid behavior); 3.) a field induced anomaly in C/T as well as M vs H behavior in good agreement with the recent Griffiths phase theory of Castro Neto and Jones, where M~H at low field, M ~ H^lambda above a crossover field, C/T ~ T^(-1+lambda) at low field, and C/T ~ (H^(2+lambda/2)/T^(3-lambda/2))*exp(-mu(eff)H/T) above the same crossover field as determined in the magnetization and where lambda is independently determined from the temperature dependence of chi at low temperatures, chi ~ T^(-1+lambda) and low fields.
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