2,124 research outputs found
Fundamental Limits on Wavelength, Efficiency and Yield of the Charge Separation Triad
In an attempt to optimize a high yield, high efficiency artificial photosynthetic protein we have discovered unique energy and spatial architecture limits which apply to all light-activated photosynthetic systems. We have generated an analytical solution for the time behavior of the core three cofactor charge separation element in photosynthesis, the photosynthetic cofactor triad, and explored the functional consequences of its makeup including its architecture, the reduction potentials of its components, and the absorption energy of the light absorbing primary-donor cofactor. Our primary findings are two: First, that a high efficiency, high yield triad will have an absorption frequency more than twice the reorganization energy of the first electron transfer, and second, that the relative distance of the acceptor and the donor from the primary-donor plays an important role in determining the yields, with the highest efficiency, highest yield architecture having the light absorbing cofactor closest to the acceptor. Surprisingly, despite the increased complexity found in natural solar energy conversion proteins, we find that the construction of this central triad in natural systems matches these predictions. Our analysis thus not only suggests explanations for some aspects of the makeup of natural photosynthetic systems, it also provides specific design criteria necessary to create high efficiency, high yield artificial protein-based triads
Partial Covering Arrays: Algorithms and Asymptotics
A covering array is an array with entries
in , for which every subarray contains each
-tuple of among its rows. Covering arrays find
application in interaction testing, including software and hardware testing,
advanced materials development, and biological systems. A central question is
to determine or bound , the minimum number of rows of
a . The well known bound
is not too far from being
asymptotically optimal. Sensible relaxations of the covering requirement arise
when (1) the set need only be contained among the rows
of at least of the subarrays and (2) the
rows of every subarray need only contain a (large) subset of . In this paper, using probabilistic methods, significant
improvements on the covering array upper bound are established for both
relaxations, and for the conjunction of the two. In each case, a randomized
algorithm constructs such arrays in expected polynomial time
Mechanical Systems with Symmetry, Variational Principles, and Integration Algorithms
This paper studies variational principles for mechanical systems with symmetry and their applications to integration algorithms. We recall some general features of how to reduce variational principles in the presence of a symmetry group along with general features of integration algorithms for mechanical systems. Then we describe some integration algorithms based directly on variational principles using a
discretization technique of Veselov. The general idea for these variational integrators is to directly discretize Hamilton’s principle rather than the equations of motion in a way that preserves the original systems invariants, notably the symplectic form and, via a discrete version of Noether’s theorem, the momentum map. The resulting mechanical integrators are second-order accurate, implicit, symplectic-momentum algorithms. We apply these integrators to the rigid body and the double spherical pendulum to show that the techniques are competitive with existing integrators
Concentration analysis and cocompactness
Loss of compactness that occurs in may significant PDE settings can be
expressed in a well-structured form of profile decomposition for sequences.
Profile decompositions are formulated in relation to a triplet , where
and are Banach spaces, , and is, typically, a
set of surjective isometries on both and . A profile decomposition is a
representation of a bounded sequence in as a sum of elementary
concentrations of the form , , , and a remainder that
vanishes in . A necessary requirement for is, therefore, that any
sequence in that develops no -concentrations has a subsequence
convergent in the norm of . An imbedding with this
property is called -cocompact, a property weaker than, but related to,
compactness. We survey known cocompact imbeddings and their role in profile
decompositions
Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout
The enormous stiffness and low density of graphene make it an ideal material
for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and
electrical readout of monolayer graphene resonators, and test their response to
changes in mass and temperature. The devices show resonances in the MHz range.
The strong dependence of the resonant frequency on applied gate voltage can be
fit to a membrane model, which yields the mass density and built-in strain.
Upon removal and addition of mass, we observe changes in both the density and
the strain, indicating that adsorbates impart tension to the graphene. Upon
cooling, the frequency increases; the shift rate can be used to measure the
unusual negative thermal expansion coefficient of graphene. The quality factor
increases with decreasing temperature, reaching ~10,000 at 5 K. By establishing
many of the basic attributes of monolayer graphene resonators, these studies
lay the groundwork for applications, including high-sensitivity mass detectors
On domain walls in a Ginzburg-Landau non-linear S^2-sigma model
The domain wall solutions of a Ginzburg-Landau non-linear -sigma hybrid
model are unveiled. There are three types of basic topological walls and two
types of degenerate families of composite - one topological, the other
non-topological- walls. The domain wall solutions are identified as the finite
action trajectories (in infinite time) of a related mechanical system that is
Hamilton-Jacobi separable in sphero-conical coordinates. The physical and
mathematical features of these domain walls are thoroughly discussed.Comment: 26 pages, 18 figure
Shocked monazite chronometry: integrating microstructural and in situ isotopic age data for determining precise impact ages
Monazite is a robust geochronometer and occurs in a wide range of rock types. Monazite also records shock deformation from meteorite impact but the effects of impact-related microstructures on the U–Th–Pb systematics remain poorly constrained. We have, therefore, analyzed shock-deformed monazite grains from the central uplift of the Vredefort impact structure, South Africa, and impact melt from the Araguainha impact structure, Brazil, using electron backscatter diffraction, electron microprobe elemental mapping, and secondary ion mass spectrometry (SIMS). Crystallographic orientation mapping of monazite grains from both impact structures reveals a similar combination of crystal-plastic deformation features, including shock twins, planar deformation bands and neoblasts. Shock twins were documented in up to four different orientations within individual monazite grains, occurring as compound and/or type one twins in (001), (100), (10 1 ¯) , {110}, { 212 } , and type two (irrational) twin planes with rational shear directions in [ 0 1 ¯ 1 ¯ ] and [ 1 ¯ 1 ¯ 0 ]. SIMS U–Th–Pb analyses of the plastically deformed parent domains reveal discordant age arrays, where discordance scales with increasing plastic strain. The correlation between discordance and strain is likely a result of the formation of fast diffusion pathways during the shock event. Neoblasts in granular monazite domains are strain-free, having grown during the impact events via consumption of strained parent grains. Neoblastic monazite from the Inlandsee leucogranofels at Vredefort records a 207Pb/206Pb age of 2010 ± 15 Ma (2σ, n = 9), consistent with previous impact age estimates of 2020 Ma. Neoblastic monazite from Araguainha impact melt yield a Concordia age of 259 ± 5 Ma (2σ, n = 7), which is consistent with previous impact age estimates of 255 ± 3 Ma. Our results demonstrate that targeting discrete microstructural domains in shocked monazite, as identified through orientation mapping, for in situ U–Th–Pb analysis can date impact-related deformation. Monazite is, therefore, one of the few high-temperature geochronometers that can be used for accurate and precise dating of meteorite impacts
An evaluation of 9-1-1 calls to assess the effectiveness of dispatch-assisted cardiopulmonary resuscitation (CPR) instructions: design and methodology
<p>Abstract</p> <p>Background</p> <p>Cardiac arrest is the leading cause of mortality in Canada, and the overall survival rate for out-of-hospital cardiac arrest rarely exceeds 5%. Bystander cardiopulmonary resuscitation (CPR) has been shown to increase survival for cardiac arrest victims. However, bystander CPR rates remain low in Canada, rarely exceeding 15%, despite various attempts to improve them. Dispatch-assisted CPR instructions have the potential to improve rates of bystander CPR and many Canadian urban communities now offer instructions to callers reporting a victim in cardiac arrest. Dispatch-assisted CPR instructions are recommended by the International Guidelines on Emergency Cardiovascular Care, but their ability to improve cardiac arrest survival remains unclear.</p> <p>Methods/Design</p> <p>The overall goal of this study is to better understand the factors leading to successful dispatch-assisted CPR instructions and to ultimately save the lives of more cardiac arrest patients. The study will utilize a before-after, prospective cohort design to specifically: 1) Determine the ability of 9-1-1 dispatchers to correctly diagnose cardiac arrest; 2) Quantify the frequency and impact of perceived agonal breathing on cardiac arrest diagnosis; 3) Measure the frequency with which dispatch-assisted CPR instructions can be successfully completed; and 4) Measure the impact of dispatch-assisted CPR instructions on bystander CPR and survival rates.</p> <p>The study will be conducted in 19 urban communities in Ontario, Canada. All 9-1-1 calls occurring in the study communities reporting out-of-hospital cardiac arrest in victims 16 years of age or older for which resuscitation was attempted will be eligible. Information will be obtained from 9-1-1 call recordings, paramedic patient care reports, base hospital records, fire medical records and hospital medical records. Victim, caller and system characteristics will be measured in the study communities before the introduction of dispatch-assisted CPR instructions (before group), during the introduction (run-in phase), and following the introduction (after group).</p> <p>Discussion</p> <p>The study will obtain information essential to the development of clinical trials that will test a variety of educational approaches and delivery methods for telephone cardiopulmonary resuscitation instructions. This will be the first study in the world to clearly quantify the impact of dispatch-assisted CPR instructions on survival to hospital discharge for out-of-hospital cardiac arrest victims.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov NCT00664443</p
Unsupervised Analysis of Classical Biomedical Markers: Robustness and Medical Relevance of Patient Clustering Using Bioinformatics Tools
Motivation: It has been proposed that clustering clinical markers, such as blood test results, can be used to stratify patients. However, the robustness of clusters formed with this approach to data pre-processing and clustering algorithm choices has not been evaluated, nor has clustering reproducibility. Here, we made use of the NHANES survey to compare clusters generated with various combinations of pre-processing and clustering algorithms, and tested their reproducibility in two separate samples. Method: Values of 44 biomarkers and 19 health/life style traits were extracted from the National Health and Nutrition Examination Survey (NHANES). The 1999–2002 survey was used for training, while data from the 2003–2006 survey was tested as a validation set. Twelve combinations of pre-processing and clustering algorithms were applied to the training set. The quality of the resulting clusters was evaluated both by considering their properties and by comparative enrichment analysis. Cluster assignments were projected to the validation set (using an artificial neural network) and enrichment in health/life style traits in the resulting clusters was compared to the clusters generated from the original training set. Results: The clusters obtained with different pre-processing and clustering combinations differed both in terms of cluster quality measures and in terms of reproducibility of enrichment with health/life style properties. Z-score normalization, for example, dramatically improved cluster quality and enrichments, as compared to unprocessed data, regardless of the clustering algorithm used. Clustering diabetes patients revealed a group of patients enriched with retinopathies. This coul
Favorable patient acceptance of ambulatory blood pressure monitoring in a primary care setting in the United States: a cross-sectional survey
BACKGROUND: The use of ambulatory blood pressure monitoring (ABPM) in the diagnosis and management of hypertension in primary care settings in the United States is increasing. Insufficient information is available describing patients' experiences and acceptance of this technology in the United States, where medical insurance coverage of the procedure is often limited. The objective of this study was to describe patient satisfaction with ABPM performed in a primary care office in the United States, using modern ABPM technology. METHODS: Cross-sectional survey performed on consecutive patients referred to the ABPM service of the Family Care Center, University of Iowa Hospitals and Clinics, Iowa City, Iowa from January 2001 to July 2003. Measures of patient satisfaction and acceptance with the device, comfort, and overall session were assessed via a 9-question, Likert-scale response survey. RESULTS: Since its inception two and a half years ago, 245 total ABPM sessions have been conducted in 235 unique patients. Of the 235 eligible respondents, 177 returned completed surveys, yielding a 75% response rate. Three-fourths (75%) of patients believed that undergoing the test was worthwhile considering the time and monetary cost involved, while most (90%) reported they thought the information provided by the test would be helpful to their physician in making treatment decisions. Patients reporting that their physician had clearly explained the benefit of undergoing the testing were more likely to report that they thought the results of the test would be more helpful in making treatment decisions. Few patients (20%) found that wearing the monitor was uncomfortable. CONCLUSIONS: When clinically indicated, clinicians should not hesitate to order ABPM testing for fear of subjecting patients to an uncomfortable test, or an uncovered insurance benefit. When ordering ABPM, they should be sure to educate the patient about the potential benefits of undergoing the testing. Most patients believe the test will provide useful information in making treatment decisions, despite probable lack of insurance coverage, and appear willing to experience some discomfort for the overall gain of the results obtained from undergoing the session
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