2,820 research outputs found
Geometric Phase in Eigenspace Evolution of Invariant and Adiabatic Action Operators
The theory of geometric phase is generalized to a cyclic evolution of the
eigenspace of an invariant operator with -fold degeneracy.
The corresponding geometric phase is interpreted as a holonomy inherited from
the universal connection of a Stiefel U(N)-bundle over a Grassmann manifold.
Most significantly, for an arbitrary initial state, this geometric phase
captures the inherent geometric feature of the state evolution. Moreover, the
geometric phase in the evolution of the eigenspace of an adiabatic action
operator is also addressed, which is elaborated by a pullback U(N)-bundle.
Several intriguing physical examples are illustrated.Comment: Added Refs. and corrected typos; 4 page
High-throughput profiling and analysis of plant responses over time to abiotic stress
Sorghum (Sorghum bicolor (L.) Moench) is a rapidly growing, high-biomass crop prized for abiotic stress tolerance. However, measuring genotype-by-environment (G x E) interactions remains a progress bottleneck. We subjected a panel of 30 genetically diverse sorghum genotypes to a spectrum of nitrogen deprivation and measured responses using high-throughput phenotyping technology followed by ionomic profiling. Responses were quantified using shape (16 measurable outputs), color (hue and intensity), and ionome (18 elements). We measured the speed at which specific genotypes respond to environmental conditions, in terms of both biomass and color changes, and identified individual genotypes that perform most favorably. With this analysis, we present a novel approach to quantifying colorbased stress indicators over time. Additionally, ionomic profiling was conducted as an independent, low-cost, and high-throughput option for characterizing G x E, identifying the elements most affected by either genotype or treatment and suggesting signaling that occurs in response to the environment. This entire dataset and associated scripts are made available through an open-access, user-friendly, web-based interface. In summary, this work provides analysis tools for visualizing and quantifying plant abiotic stress responses over time. These methods can be deployed as a time-efficient method of dissecting the genetic mechanisms used by sorghum to respond to the environment to accelerate crop improvement
Photocarrier lifetime and transport in silicon supersaturated with sulfur
Doping of silicon-on-insulator layers with sulfur to concentrations far above equilibrium by ion implantation and pulsed laser melting can result in large concentration gradients. Photocarriers generated in and near the impurity gradient can separate into different coplanar transport layers, leading to enhanced photocarrier lifetimes in thin silicon-on-insulator films. The depth from which holes escape the heavily doped region places a lower limit on the minority carrier mobility-lifetime product of 10⁻⁸ cm²/V for heavily sulfur dopedsilicon. We conclude that the cross-section for recombination through S impurities at this concentration is significantly reduced relative to isolated impurities.Research at Rensselaer was supported by the Army
Research Office under Contract No. W911NF0910470 and
by the NSF REU program at Rensselaer. Research at Harvard
was supported by US Army ARDEC under Contract
No. W15QKN-07-P-0092. D.R. was supported in part by a
National Defense Science and Engineering Graduate fellowship
Prevalence of filarioid nematodes and trypanosomes in American robins and house sparrows, Chicago USA
AbstractHosts are commonly infected with a suite of parasites, and interactions among these parasites can affect the size, structure, and behavior of host–parasite communities. As an important step to understanding the significance of co-circulating parasites, we describe prevalence of co-circulating hemoparasites in two important avian amplification hosts for West Nile virus (WNV), the American robin (Turdus migratorius) and house sparrow (Passer domesticus), during the 2010–2011 in Chicago, Illinois, USA. Rates of nematode microfilariemia were 1.5% of the robins (n=70) and 4.2% of the house sparrows (n=72) collected during the day and 11.1% of the roosting robins (n=63) and 0% of the house sparrows (n=11) collected at night. Phylogenetic analysis of nucleotide sequences of the 18S rRNA and cytochrome oxidase subunit I (COI) genes from these parasites resolved two clades of filarioid nematodes. Microscopy revealed that 18.0% of American robins (n=133) and 16.9% of house sparrows (n=83) hosted trypanosomes in the blood. Phylogenetic analysis of nucleotide sequences from the 18s rRNA gene revealed that the trypanosomes fall within previously described avian trypanosome clades. These results document hemoparasites in the blood of WNV hosts in a center of endemic WNV transmission, suggesting a potential for direct or indirect interactions with the virus
An automated, high-throughput method for standardizing image color profiles to improve image-based plant phenotyping
High-throughput phenotyping has emerged as a powerful method for studying plant biology. Large image-based datasets are generated and analyzed with automated image analysis pipelines. A major challenge associated with these analyses is variation in image quality that can inadvertently bias results. Images are made up of tuples of data called pixels, which consist of R, G, and B values, arranged in a grid. Many factors, for example image brightness, can influence the quality of the image that is captured. These factors alter the values of the pixels within images and consequently can bias the data and downstream analyses. Here, we provide an automated method to adjust an image-based dataset so that brightness, contrast, and color profile is standardized. The correction method is a collection of linear models that adjusts pixel tuples based on a reference panel of colors. We apply this technique to a set of images taken in a high-throughput imaging facility and successfully detect variance within the image dataset. In this case, variation resulted from temperature-dependent light intensity throughout the experiment. Using this correction method, we were able to standardize images throughout the dataset, and we show that this correction enhanced our ability to accurately quantify morphological measurements within each image. We implement this technique in a high-throughput pipeline available with this paper, and it is also implemented in PlantCV
The Asymmetric Merger of Black Holes
We study event horizons of non-axisymmetric black holes and show how features
found in axisymmetric studies of colliding black holes and of toroidal black
holes are non-generic and how new features emerge. Most of the details of black
hole formation and black hole merger are known only in the axisymmetric case,
in which numerical evolution has successfully produced dynamical space-times.
The work that is presented here uses a new approach to construct the geometry
of the event horizon, not by locating it in a given spacetime, but by direct
construction. In the axisymmetric case, our method produces the familiar
pair-of-pants structure found in previous numerical simulations of black hole
mergers, as well as event horizons that go through a toroidal epoch as
discovered in the collapse of rotating matter. The main purpose of this paper
is to show how new - substantially different - features emerge in the
non-axisymmetric case. In particular, we show how black holes generically go
through a toroidal phase before they become spherical, and how this fits
together with the merger of black holes.Comment: 28 pages, 10 figures, uses REVTEX. Improved quality figures and
additional color images are provided at http://www.phyast.pitt.edu/~shusa/EH
Stromal cell-derived factor and granulocyte-monocyte colony-stimulating factor form a combined neovasculogenic therapy for ischemic cardiomyopathy
ObjectiveIschemic heart failure is an increasingly prevalent global health concern with major morbidity and mortality. Currently, therapies are limited, and novel revascularization methods might have a role. This study examined enhancing endogenous myocardial revascularization by expanding bone marrow-derived endothelial progenitor cells with the marrow stimulant granulocyte-monocyte colony-stimulating factor and recruiting the endothelial progenitor cells with intramyocardial administration of the potent endothelial progenitor cell chemokine stromal cell-derived factor.MethodsIschemic cardiomyopathy was induced in Lewis rats (n = 40) through left anterior descending coronary artery ligation. After 3 weeks, animals were randomized into 4 groups: saline control, granulocyte-monocyte colony-stimulating factor only (GM-CSF only), stromal cell-derived factor only (SDF only), and combined stromal cell-derived factor/granulocyte-monocyte colony-stimulating factor (SDF/GM-CSF) (n = 10 each). After another 3 weeks, hearts were analyzed for endothelial progenitor cell density by endothelial progenitor cell marker colocalization immunohistochemistry, vasculogenesis by von Willebrand immunohistochemistry, ventricular geometry by hematoxylin-and-eosin microscopy, and in vivo myocardial function with an intracavitary pressure-volume conductance microcatheter.ResultsThe saline control, GM-CSF only, and SDF only groups were equivalent. Compared with the saline control group, animals in the SDF/GM-CSF group exhibited increased endothelial progenitor cell density (21.7 ± 3.2 vs 9.6 ± 3.1 CD34+/vascular endothelial growth factor receptor 2–positive cells per high-power field, P = .01). There was enhanced vascularity (44.1 ± 5.5 versus 23.8 ± 2.2 von Willebrand factor-positive vessels per high-power field, P = .007). SDF/GM-CSF group animals experienced less adverse ventricular remodeling, as manifested by less cavitary dilatation (9.8 ± 0.1 mm vs 10.1 ± 0.1 mm [control], P = .04) and increased border-zone wall thickness (1.78 ± 0.19 vs 1.41 ± 0.16 mm [control], P = .03). (SDF/GM-CSF group animals had improved cardiac function compared with animals in the saline control group (maximum pressure: 93.9 ± 3.2 vs 71.7 ± 3.1 mm Hg, P < .001; maximum dP/dt: 3513 ± 303 vs 2602 ± 201 mm Hg/s, P < .05; cardiac output: 21.3 ± 2.7 vs 13.3 ± 1.3 mL/min, P < .01; end-systolic pressure-volume relationship slope: 1.7 ± 0.4 vs 0.5 ± 0.2 mm Hg/μL, P < .01.)ConclusionThis novel revascularization strategy of bone marrow stimulation and intramyocardial delivery of the endothelial progenitor cell chemokine stromal cell-derived factor yielded significantly enhanced myocardial endothelial progenitor cell density, vasculogenesis, geometric preservation, and contractility in a model of ischemic cardiomyopathy
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Design and Initial Results of a Multi-Phase Randomized Trial of Ceftriaxone in Amyotrophic Lateral Sclerosis
Objectives: Ceftriaxone increases expression of the astrocytic glutamate transporter, EAAT2, which might protect from glutamate-mediated excitotoxicity. A trial using a novel three stage nonstop design, incorporating Phases I-III, tested ceftriaxone in ALS. Stage 1 determined the cerebrospinal fluid pharmacokinetics of ceftriaxone in subjects with ALS. Stage 2 evaluated safety and tolerability for 20-weeks. Analysis of the pharmacokinetics, tolerability, and safety was used to determine the ceftriaxone dosage for Stage 3 efficacy testing. Methods: In Stage 1, 66 subjects at ten clinical sites were enrolled and randomized equally into three study groups receiving intravenous placebo, ceftriaxone 2 grams daily or ceftriaxone 4 grams daily divided BID. Participants provided serum and cerebrospinal fluid for pharmacokinetic analysis on study day 7. Participants continued their assigned treatment in Stage 2. The Data and Safety Monitoring Board (DSMB) reviewed the data after the last participants completed 20 weeks on study drug. Results: Stage 1 analysis revealed linear pharmacokinetics, and CSF trough levels for both dosage levels exceeding the pre-specified target trough level of 1 µM (0.55 µg/mL). Tolerability (Stages 1 and 2) results showed that ceftriaxone at dosages up to 4 grams/day was well tolerated at 20 weeks. Biliary adverse events were more common with ceftriaxone but not dose-dependent and improved with ursodeoxycholic (ursodiol) therapy. Conclusions: The goals of Stages 1 and 2 of the ceftriaxone trial were successfully achieved. Based on the pre-specified decision rules, the DSMB recommended the use of ceftriaxone 4 g/d (divided BID) for Stage 3, which recently closed. Trial Registration ClinicalTrials.gov NCT00349622
LitMiner: integration of library services within a bio-informatics application
BACKGROUND: This paper examines how the adoption of a subject-specific library service has changed the way in which its users interact with a digital library. The LitMiner text-analysis application was developed to enable biologists to explore gene relationships in the published literature. The application features a suite of interfaces that enable users to search PubMed as well as local databases, to view document abstracts, to filter terms, to select gene name aliases, and to visualize the co-occurrences of genes in the literature. At each of these stages, LitMiner offers the functionality of a digital library. Documents that are accessible online are identified by an icon. Users can also order documents from their institution's library collection from within the application. In so doing, LitMiner aims to integrate digital library services into the research process of its users. METHODS: Case study RESULTS: This integration of digital library services into the research process of biologists results in increased access to the published literature. CONCLUSION: In order to make better use of their collections, digital libraries should customize their services to suit the research needs of their patrons
Fake news as a floating signifier: hegemony, antagonism and the politics of falsehood
‘Fake news’ has emerged as a global buzzword. While prominent media outlets, such as The New York Times, CNN, and CBS, have used the term to designate misleading information spread through websites, President Donald Trump has recently used the term as a negative designation of these very ‘mainstream media’. In this article, we argue that the concept of ‘fake news’ has become an important component in contemporary political struggles. We showcase how the term is utilised by different positions within the social space as a means of discrediting, attacking and delegitimising political opponents. Excavating three central moments within the construction of ‘fake news’, we argue that the term has increasingly become a ‘floating signifier’: a signifier lodged in-between different hegemonic projects seeking to provide an image of how society is and ought to be structured. By approaching ‘fake news’ from the viewpoint of discourse theory, the paper reframes the current stakes of the debate and contributes with new insights into the function and consequences of ‘fake news’ as a novel political category
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