1,481 research outputs found
Investigation of potential driver modules and transmission lines for a high frequency power system on the space station
The feasibility of using Series Resonant Inverter as the driver module for high frequency power system on the Space Station was assessed. The performance of the Series Resonant Inverter that was used in the testing of the single-phase, 2.0-kw resonant AC power system breadboard is summarized. The architecture is descirbed and the driver modules of the 5.0 kw AC power system breadboard are analyzed. An investigation of the various types of transmission lines is continued. Measurements of equivalent series resistor and inductor and equivalent parallel capacitors are presented. In particular, a simplified approach is utilized to describe the optimal transmission line
Investigation of potential driver modules and transmission lines for a high frequency power system on the space station
The objective was to assess the feasibility of using the Series Resonant inverter as the driver module for the high frequency power system on the Space Station. This study evaluates the performance of the Series Resonant driver when it was operated with a dc input voltage and run through a series of tests to determine its start-up performance, response to load changes, load regulation, and efficiency. Also, this study compares the Series Resonant driver to another kind of driver that uses a Power Transistor snubber. An investigation of the various types of transmission lines is initiated. In particular, a simplified approach is utilized to describe the optimal transmission line
Blueprint for the Dissemination of Evidence-Based Practices in Health Care
Proposes strategies for better dissemination of best practices through quality improvement campaigns, including campaigns aligned with adopting organizations' goals, practical implementation tools and guides, and networks to foster learning opportunities
Surgical Treatment of Liver Trauma: Technical Considerations and Case Reports
The incidence of abdominal trauma, and thus that of liver trauma, has been increasing in the past few years. Improvements in the understanding of the anatomy of the liver and improvements in diagnostic techniques have resulted in shorter and better operations with less delay between injury and surgery. Improvements in transportation to adequate hospital facilities and vigorous resuscitative measures have also contributed to lowering the mortality rate for this type of injury. Suggestions are made for the surgical management of liver injuries, together with illustrative case reports
Arthropod abundance and diversity in street trees of south Texas, USA
In urban areas, street trees provide a variety of ecological services, including biodiversity conservation. In this study we examined arthropod diversity on native and non-native street trees sampled during the fall of 2010 and spring of 2011 in McAllen, Texas, one of the most rapidly growing urban areas in the country. Eighty-eight street trees were sampled by removing arthropods from the lower canopy foliage using a hand held vacuum. Arthropods were collected into nylon bags, identified to order, and counted by morphospecies. Overall, street trees supported a significant and diverse population of arthropods: a total of 1,971 arthropods were collected, from which 12 different orders and 102 different morphospecies were identified. We found arthropod abundance was higher on street trees native to the Lower Rio Grande Valley compared to non-native trees, especially for beetles, wasps, bees, ants, and spiders. This difference was particularly striking in spring when trees were flushed with new growth. The significant deficiency of arthropods on non-native trees is indicative of their relatively low value for maintaining entomological fauna. Local land managers who aim to include biodiversity conservation in their efforts thus should enhance the urban forest through the conservation of existing native remnant trees and promoting the use of native tree species in landscaping
Error Control of Iterative Linear Solvers for Integrated Groundwater Models
An open problem that arises when using modern iterative linear solvers, such as the preconditioned conjugate gradient method or Generalized Minimum RESidual (GMRES) method, is how to choose the residual tolerance in the linear solver to be consistent with the tolerance on the solution error. This problem is especially acute for integrated groundwater models, which are implicitly coupled to another model, such as surface water models, and resolve both multiple scales of flow and temporal interaction terms, giving rise to linear systems with variable scaling. This article uses the theory of “forward error bound estimation” to explain the correspondence between the residual error in the preconditioned linear system and the solution error. Using examples of linear systems from models developed by the US Geological Survey and the California State Department of Water Resources, we observe that this error bound guides the choice of a practical measure for controlling the error in linear systems. We implemented a preconditioned GMRES algorithm and benchmarked it against the Successive Over-Relaxation (SOR) method, the most widely known iterative solver for nonsymmetric coefficient matrices. With forward error control, GMRES can easily replace the SOR method in legacy groundwater modeling packages, resulting in the overall simulation speedups as large as 7.74×. This research is expected to broadly impact groundwater modelers through the demonstration of a practical and general approach for setting the residual tolerance in line with the solution error tolerance and presentation of GMRES performance benchmarking results
‘Question Moments’: A Rolling Programme of Question Opportunities in Classroom Science
This article has been made available through the Brunel Open Access Publishing Fund.This naturalistic study integrates specific 'question moments' into lesson plans to
increase pupils' classroom interactions. A range of teaching tools has explored
students' ideas through opportunities to ask and write questions. Their oral and written
outcomes provide data on individual and group misunderstandings. Changes to the
schedule of lessons were introduced to discuss these questions and solve disparities.
Flexible lesson planning over fourteen lessons across a four-week period of highschool
chemistry accommodated students' contributions and increased student
participation, promoted inquiring and individualised teaching, with each teaching
strategy feeding forward into the next
Quasi-chemical Theories of Associated Liquids
It is shown how traditional development of theories of fluids based upon the
concept of physical clustering can be adapted to an alternative local
clustering definition. The alternative definition can preserve a detailed
valence description of the interactions between a solution species and its
near-neighbors, i.e., cooperativity and saturation of coordination for strong
association. These clusters remain finite even for condensed phases. The
simplest theory to which these developments lead is analogous to quasi-chemical
theories of cooperative phenomena. The present quasi-chemical theories require
additional consideration of packing issues because they don't impose lattice
discretizations on the continuous problem. These quasi-chemical theories do not
require pair decomposable interaction potential energy models. Since
calculations may be required only for moderately sized clusters, we suggest
that these quasi-chemical theories could be implemented with computational
tools of current electronic structure theory. This can avoid an intermediate
step of approximate force field generation.Comment: 20 pages, no figures replacement: minor typographical corrections,
four references added, in press Molec. Physics 199
Mirror Symmetry and Other Miracles in Superstring Theory
The dominance of string theory in the research landscape of quantum gravity
physics (despite any direct experimental evidence) can, I think, be justified
in a variety of ways. Here I focus on an argument from mathematical fertility,
broadly similar to Hilary Putnam's 'no miracles argument' that, I argue, many
string theorists in fact espouse. String theory leads to many surprising,
useful, and well-confirmed mathematical 'predictions' - here I focus on mirror
symmetry. These predictions are made on the basis of general physical
principles entering into string theory. The success of the mathematical
predictions are then seen as evidence for framework that generated them. I
attempt to defend this argument, but there are nonetheless some serious
objections to be faced. These objections can only be evaded at a high
(philosophical) price.Comment: For submission to a Foundations of Physics special issue on "Forty
Years Of String Theory: Reflecting On the Foundations" (edited by G. `t
Hooft, E. Verlinde, D. Dieks and S. de Haro)
Adaptive cluster expansion for the inverse Ising problem: convergence, algorithm and tests
We present a procedure to solve the inverse Ising problem, that is to find
the interactions between a set of binary variables from the measure of their
equilibrium correlations. The method consists in constructing and selecting
specific clusters of variables, based on their contributions to the
cross-entropy of the Ising model. Small contributions are discarded to avoid
overfitting and to make the computation tractable. The properties of the
cluster expansion and its performances on synthetic data are studied. To make
the implementation easier we give the pseudo-code of the algorithm.Comment: Paper submitted to Journal of Statistical Physic
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