14,731 research outputs found
Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT results
There have been discussions in the recent literature regarding the accuracy
of the available electron impact excitation rates (equivalently effective
collision strengths ) for transitions in Be-like ions. In the present
paper we demonstrate, once again, that earlier results for are
indeed overestimated (by up to four orders of magnitude), for over 40\% of
transitions and over a wide range of temperatures. To do this we have performed
two sets of calculations for N~IV, with two different model sizes consisting of
166 and 238 fine-structure energy levels. As in our previous work, for the
determination of atomic structure the GRASP (General-purpose Relativistic
Atomic Structure Package) is adopted and for the scattering calculations (the
standard and parallelised versions of) the Dirac Atomic R-matrix Code ({\sc
darc}) are employed. Calculations for collision strengths and effective
collision strengths have been performed over a wide range of energy (up to
45~Ryd) and temperature (up to 2.010~K), useful for applications in
a variety of plasmas. Corresponding results for energy levels, lifetimes and
A-values for all E1, E2, M1 and M2 transitions among 238 levels of N~IV are
also reported.Comment: This paper with 5 Figs. and 8 Tables will appear in MNRAS (2016
UK Soils: their phosphorus sorption capacity and potential for P removal from sewage effluents in emergent hydrophyte treatment systems
Composite fermions from the algebraic point of view
Composite fermion wavefuctions have been used to describe electrons in a
strong magnetic field. We show that the polynomial part of these wavefunctions
can be obtained by applying a normal ordered product of suitably defined
annihilation and creation operators to an even power of the Vandermonde
determinant, which can been considered as a kind of a non-trivial Fermi sea. In
the case of the harmonic interaction we solve the system exactly in the lowest
Landau level. The solution makes explicit the boson-fermion correspondence
proposed recently.Comment: 11 pages 1 figur
The Ever Changing Circumstellar Nebula Around UW Centauri
We present new images of the reflection nebula surrounding the R Coronae
Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its
appearance significantly. At the estimated distance of UW Cen, this nebula is
approximately 0.6 ly in radius so the nebula cannot have physically altered in
only 8 years. Instead, the morphology of the nebula appears to change as
different parts are illuminated by light from the central star modulated by
shifting thick dust clouds near its surface. These dust clouds form and
dissipate at irregular intervals causing the well-known declines in the R
Coronae Borealis (RCB) stars. In this way, the central star acts like a
lighthouse shining through holes in the dust clouds and lighting up different
portions of the nebula. The existence of this nebula provides clues to the
evolutionary history of RCB stars possibly linking them to the Planetary
Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color
One step multiderivative methods for first order ordinary differential equations
A family of one-step multiderivative methods based on Padé approximants to the exponential function is developed.
The methods are extrapolated and analysed for use in PECE mode.
Error constants and stability intervals are calculated and the combinations compared with well known linear multi-step combinations and combinations using high accuracy Newton-Cotes quadrature formulas as correctors.
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The Oyster River Culvert Analysis Project
Studies have already detected intensification of precipitation events consistent with climate change projections. Communities may have a window of opportunity to prepare, but information sufficiently quantified and localized to support adaptation programs is sparse: published literature is typically characterized by general resilience building or regional vulnerability studies. The Fourth Assessment Report of the IPCC observed that adaptation can no longer be postponed pending the effective elimination of uncertainty. Methods must be developed that manage residual uncertainty, providing community leaders with decision-support information sufficient for implementing infrastructure adaptation programs. This study developed a local-scale and actionable protocol for maintaining historical risk levels for communities facing significant impacts from climate change and population growth. For a coastal watershed, the study assessed the capacity of the present stormwater infrastructure capacity for conveying expected peak flow resulting from climate change and population growth. The project transferred coupled-climate model projections to the culvert system, in a form understandable to planners, resource managers and decision-makers; applied standard civil engineering methods to reverse-engineer culverts to determine existing and required capacities; modeled the potential for LID methods to manage peak flow in lieu of, or combination with, drainage system upsizing; and estimated replacement costs using local and national construction cost data. The mid-21st century, most likely 25-year, 24-hour precipitation is estimated to be 35% greater than the TP-40 precipitation for the SRES A1b trajectory, and 64% greater than the TP-40 value for the SRES A1fi trajectory. 5% of culverts are already undersized for the TP-40 event to which they should have been designed. Under the most likely A1b trajectory, an additional 12% of culverts likely will be undersized, while under the most likely A1fi scenario, an additional 19% likely will be undersized. These conditions place people and property at greater risk than that historically acceptable from the TP-4025-year design storm. This risk level may be maintained by a long-term upgrade program, utilizing existing strategies to manage uncertainty and costs. At the upper-95% confidence limit for the A1fi 25-year event, 65% of culverts are adequately sized, and building the remaining 35%, and planned, culverts to thrice the cross-sectional area specified from TP-40 should provide adequate capacity through this event. Realizable LID methods can mitigate significant impacts from climate change and population growth, however effectiveness is limited for the more pessimistic climate change projections. Results indicate that uncertainty in coupled-climate model projections is not an impediment to adaptation. This study makes a significant contribution toward the generation of reliable and specific estimates of impacts from climate change, in support of programs to adapt civil infrastructures. This study promotes a solution to today\u27s arguably most significant challenge in civil infrastructure adaptation: translating the extensive corpus of adaptation theory and regional-scale impacts analyses into localscale action
Long-term high fat feeding of rats results in increased numbers of circulating microvesicles with pro-inflammatory effects on endothelial cells
Obesity and type 2 diabetes lead to dramatically increased risks of atherosclerosis and CHD. Multiple mechanisms converge to promote atherosclerosis by increasing endothelial oxidative stress and up-regulating expression of pro-inflammatory molecules. Microvesicles (MV) are small ( < 1 μm) circulating particles that transport proteins and genetic material, through which they are able to mediate cell–cell communication and influence gene expression. Since MV are increased in plasma of obese, insulin-resistant and diabetic individuals, who often exhibit chronic vascular inflammation, and long-term feeding of a high-fat diet (HFD) to rats is a well-described model of obesity and insulin resistance, we hypothesised that this may be a useful model to study the impact of MV on endothelial inflammation. The number and cellular origin of MV from HFD-fed obese rats were characterised by flow cytometry. Total MV were significantly increased after feeding HFD compared to feeding chow (P< 0·001), with significantly elevated numbers of MV derived from leucocyte, endothelial and platelet compartments (P< 0·01 for each cell type). MV were isolated from plasma and their ability to induce reactive oxygen species (ROS) formation and vascular cell adhesion molecule (VCAM)-1 expression was measured in primary rat cardiac endothelial cells in vitro. MV from HFD-fed rats induced significant ROS (P< 0·001) and VCAM-1 expression (P= 0·0275), indicative of a pro-inflammatory MV phenotype in this model of obesity. These findings confirm that this is a useful model to further study the mechanisms by which diet can influence MV release and subsequent effects on cardio-metabolic health
Development of a speech autocuer
A wearable, visually based prosthesis for the deaf based upon the proven method for removing lipreading ambiguity known as cued speech was fabricated and tested. Both software and hardware developments are described, including a microcomputer, display, and speech preprocessor
Inspiring minds: How big questions can build students’ epistemic insight and improve attitudes towards STEM
This article examines the impact that an ‘epistemically insightful’ approach to informal science learning can have on students’ attitudes, aspirations and perceptions of STEM subjects. It uses interim findings from a research and outreach project, including sustained Saturday activity programmes for ages14–16 and residential summer schools for ages 15–19, designed to create confident scholars who can engage with difficult philosophical questions raised by current technological advances. The Inspiring Minds project at Canterbury Christ Church University, Kent, UK, delivers informal science learning in schools and informal settings based on an epistemic insight-led approach to STEM outreach and education
A report on SHARP (Spacecraft Health Automated Reasoning Prototype) and the Voyager Neptune encounter
The development and application of the Spacecraft Health Automated Reasoning Prototype (SHARP) for the operations of the telecommunications systems and link analysis functions in Voyager mission operations are presented. An overview is provided of the design and functional description of the SHARP system as it was applied to Voyager. Some of the current problems and motivations for automation in real-time mission operations are discussed, as are the specific solutions that SHARP provides. The application of SHARP to Voyager telecommunications had the goal of being a proof-of-capability demonstration of artificial intelligence as applied to the problem of real-time monitoring functions in planetary mission operations. AS part of achieving this central goal, the SHARP application effort was also required to address the issue of the design of an appropriate software system architecture for a ground-based, highly automated spacecraft monitoring system for mission operations, including methods for: (1) embedding a knowledge-based expert system for fault detection, isolation, and recovery within this architecture; (2) acquiring, managing, and fusing the multiple sources of information used by operations personnel; and (3) providing information-rich displays to human operators who need to exercise the capabilities of the automated system. In this regard, SHARP has provided an excellent example of how advanced artificial intelligence techniques can be smoothly integrated with a variety of conventionally programmed software modules, as well as guidance and solutions for many questions about automation in mission operations
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