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Search Results: 1 - 10 of 23577 matches for " Paul Bryans "
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The EUV emission from sun-grazing comets
Paul Bryans,W Dean Pesnell
Physics , 2012, DOI: 10.1088/0004-637X/760/1/18
Abstract: The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) has observed two sun-grazing comets as they passed through the solar atmosphere. Both passages resulted in a measurable enhancement of Extreme Ultraviolet (EUV) radiance in several of the AIA bandpasses. We explain this EUV emission by considering the evolution of the cometary atmosphere as it interacts with the ambient solar atmosphere. Molecules in the comet rapidly sublimate as it approaches the Sun. They are then photodissociated by the solar radiation field to create atomic species. Subsequent ionization of these atoms produces a higher abundance of ions than normally present in the corona and results in EUV emission in the wavelength ranges of the AIA telescope passbands.
Multiple Component Outflows in an Active Region Observed with the EUV Imaging Spectrometer on Hinode
Paul Bryans,Peter R Young,George A Doschek
Physics , 2010, DOI: 10.1088/0004-637X/715/2/1012
Abstract: We have used the Extreme Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft to observe large areas of outflow near an active region. These outflows are seen to persist for at least 6 days. The emission line profiles suggest that the outflow region is composed of multiple outflowing components, Doppler-shifted with respect to each other. We have modeled this scenario by imposing a double-Gaussian fit to the line profiles. These fits represent the profile markedly better than a single Gaussian fit for Fe XII and XIII emission lines. For the fastest outflowing components, we find velocities as high as 200 km/s. However, there remains a correlation between the fitted line velocities and widths, suggesting that the outflows are not fully resolved by the double-Gaussian fit and that the outflow may be comprised of further components.
Observed Variability of the Solar Mg II h Spectral Line
Donald Schmit,Paul Bryans,Bart De Pontieu,Scott McIntosh,Jorrit Leenaarts,Mats Carlsson
Physics , 2015, DOI: 10.1088/0004-637X/811/2/127
Abstract: The Mg II h&k doublet are two of the primary spectral lines observed by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These lines are tracers of the magnetic and thermal environment that spans from the photosphere to the upper chromosphere. We use a double gaussian model to fit the Mg II h profile for a full-Sun mosaic dataset taken 24-Aug-2014. We use the ensemble of high-quality profile fits to conduct a statistical study on the variability of the line profile as it relates the magnetic structure, dynamics, and center-to-limb viewing angle. The average internetwork profile contains a deeply reversed core and is weakly asymmetric at h2. In the internetwork, we find a strong correlation between h3 wavelength and profile asymmetry as well h1 width and h2 width. The average reversal depth of the h3 core is inversely related to the magnetic field. Plage and sunspots exhibit many profiles which do not contain a reversal. These profiles also occur infrequently in the internetwork. We see indications of magnetically aligned structures in plage and network in statistics associated with the line core, but these structures are not clear or extended in the internetwork. The center-to-limb variations are compared with predictions of semi-empirical model atmospheres. We measure a pronounced limb darkening in the line core which is not predicted by the model. The aim of this work is to provide a comprehensive measurement baseline and preliminary analysis on the observed structure and formation of the Mg II profiles observed by IRIS.
Proceedings Second Workshop on Formal Aspects of Virtual Organisations
Jeremy Bryans,John Fitzgerald
Computer Science , 2010, DOI: 10.4204/EPTCS.16
Abstract: FAVO2009 was the second workshop on Formal Aspects of Virtual Organisations. The purpose of the FAVO workshops is to encourage an active community of researchers and practitioners using formal methods in the research and development of Virtual Organisations.
Proceedings Third Workshop on Formal Aspects of Virtual Organisations
Jeremy Bryans,John Fitzgerald
Computer Science , 2012, DOI: 10.4204/EPTCS.83
Abstract: This volume contains the proceedings of the 3rd International Workshop on Formal Aspects of Virtual Organisations (FAVO 2011). The workshop was held in Sao Paulo, Brazil on October 18th, 2011 as a satellite event to the 12th IFIP Working Conference on Virtual Enterprises (PRO-VE'11). The FAVO workshop aims to provide a forum for researchers interested in the application of formal techniques in the design and analysis of Virtual Organisations.
Quantum factorization of 56153 with only 4 qubits
Nikesh S. Dattani,Nathaniel Bryans
Computer Science , 2014,
Abstract: The largest number factored on a quantum device reported until now was 143. That quantum computation, which used only 4 qubits at 300K, actually also factored much larger numbers such as 3599, 11663, and 56153, without the awareness of the authors of that work. Furthermore, unlike the implementations of Shor's algorithm performed thus far, these 4-qubit factorizations do not need to use prior knowledge of the answer. However, because they only use 4 qubits, these factorizations can also be performed trivially on classical computers. We discover a class of numbers for which the power of quantum information actually comes into play. We then demonstrate a 3-qubit factorization of 175, which would be the first quantum factorization of a triprime.
Stochastic Model Checking for Multimedia
Jeremy Bryans,Howard Bowman,John Derrick
Computer Science , 2000,
Abstract: Modern distributed systems include a class of applications in which non-functional requirements are important. In particular, these applications include multimedia facilities where real time constraints are crucial to their correct functioning. In order to specify such systems it is necessary to describe that events occur at times given by probability distributions and stochastic automata have emerged as a useful technique by which such systems can be specified and verified. However, stochastic descriptions are very general, in particular they allow the use of general probability distribution functions, and therefore their verification can be complex. In the last few years, model checking has emerged as a useful verification tool for large systems. In this paper we describe two model checking algorithms for stochastic automata. These algorithms consider how properties written in a simple probabilistic real-time logic can be checked against a given stochastic automaton.
Physical Activity in Adolescents following Treatment for Cancer: Influencing Factors
Marilyn Wright,Angie Bryans,Kaylin Gray,Leah Skinner,Amanda Verhoeve
Leukemia Research and Treatment , 2013, DOI: 10.1155/2013/592395
Abstract: The purpose of this study was to examine physical activity levels and influencing individual and environmental factors in a group of adolescent survivors of cancer and a comparison group. Methods. The study was conducted using a “mixed methods” design. Quantitative data was collected from 48 adolescent survivors of cancer and 48 comparison adolescents using the Godin Leisure-Time Exercise Questionnaire, the Fatigue Scale—Adolescents, and the Amherst Health and Activity Study—Student Survey. Qualitative data was collected in individual semistructured interviews. Results. Reported leisure-time physical activity total scores were not significantly different between groups. Physical activity levels were positively correlated with adult social support factors in the group of adolescent survivors of cancer, but not in the comparison group. Time was the primary barrier to physical activity in both groups. Fatigue scores were higher for the comparison but were not associated with physical activity levels in either group. The qualitative data further supported these findings. Conclusions. Barriers to physical activity were common between adolescent survivors of cancer and a comparative group. Increased knowledge of the motivators and barriers to physical activity may help health care providers and families provide more effective health promotion strategies to adolescent survivors of pediatric cancer. 1. Introduction The probability of survival into adulthood for children treated for cancer has increased from 30% to nearly 80% in the past 30 years [1]. Rates as high as 90% have been achieved for survivors of acute lymphoblastic leukemia [2]. However, this increase in long-term survival comes with a high risk of long-term morbidity and premature mortality from chronic diseases associated with the late effects of cancer treatments. These can include obesity, decreased bone density, poor exercise capacity, reduced muscle strength and extensibility, balance problems, fatigue, sleep problems, osteoporosis, diabetes, cardiovascular disease, pulmonary complications, and psychosocial problems [3–6]. Two-thirds of survivors of childhood cancer experience at least one late effect of cancer treatment, and as many as one-quarter experience a late effect serious enough to limit function or become life threatening [3]. Participation in regular physical activity has been found to have several benefits in adult and pediatric oncology populations including amelioration of many of the noted late effects and reduced risk of some cancers [6–8]. Population levels of participation in
The Power of Nondeterminism in Self-Assembly
Nathaniel Bryans,Ehsan Chiniforooshan,David Doty,Lila Kari,Shinnosuke Seki
Computer Science , 2010,
Abstract: We investigate the role of nondeterminism in Winfree's abstract Tile Assembly Model (aTAM), which was conceived to model artificial molecular self-assembling systems constructed from DNA. Of particular practical importance is to find tile systems that minimize resources such as the number of distinct tile types, each of which corresponds to a set of DNA strands that must be custom-synthesized in actual molecular implementations of the aTAM. We seek to identify to what extent the use of nondeterminism in tile systems affects the resources required by such molecular shape-building algorithms. We first show a "molecular computability theoretic" result: there is an infinite shape S that is uniquely assembled by a tile system but not by any deterministic tile system. We then show an analogous phenomenon in the finitary "molecular complexity theoretic" case: there is a finite shape S that is uniquely assembled by a tile system with c tile types, but every deterministic tile system that uniquely assembles S has more than c tile types. In fact we extend the technique to derive a stronger (classical complexity theoretic) result, showing that the problem of finding the minimum number of tile types that uniquely assemble a given finite shape is Sigma-P-2-complete. In contrast, the problem of finding the minimum number of deterministic tile types that uniquely assemble a shape was shown to be NP-complete by Adleman, Cheng, Goel, Huang, Kempe, Moisset de Espan\'es, and Rothemund (Combinatorial Optimization Problems in Self-Assembly, STOC 2002). The conclusion is that nondeterminism confers extra power to assemble a shape from a small tile system, but unless the polynomial hierarchy collapses, it is computationally more difficult to exploit this power by finding the size of the smallest tile system, compared to finding the size of the smallest deterministic tile system.
ProvAbs: model, policy, and tooling for abstracting PROV graphs
Paolo Missier,Jeremy Bryans,Carl Gamble,Vasa Curcin,Roxana Danger
Computer Science , 2014,
Abstract: Provenance metadata can be valuable in data sharing settings, where it can be used to help data consumers form judgements regarding the reliability of the data produced by third parties. However, some parts of provenance may be sensitive, requiring access control, or they may need to be simplified for the intended audience. Both these issues can be addressed by a single mechanism for creating abstractions over provenance, coupled with a policy model to drive the abstraction. Such mechanism, which we refer to as abstraction by grouping, simultaneously achieves partial disclosure of provenance, and facilitates its consumption. In this paper we introduce a formal foundation for this type of abstraction, grounded in the W3C PROV model; describe the associated policy model; and briefly present its implementation, the Provabs tool for interactive experimentation with policies and abstractions.
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