641 research outputs found
Deployment status of the Las Cumbres Observatory Global Telescope
Our global network of telescopes is designed to provide maximally available optical monitoring of time variable sources, from solar system to extra-galactic objects, and ranging in brightness from about 7-20m. We are providing a distributed network with varied apertures but homogeneous instrumentation: optical imaging, with spectroscopic capabilities. A key component is a single centralized process that accepts (in real time) and schedules TAC approved observing requests across the network; then continuously updates schedules based on status, weather and other availability criteria. Requests range from occasional to continuous monitoring, at slow to high-speed cadences (imaging and fast photometry), and includes rapid response to targets of opportunity. Each node of the network must be fully autonomous, with software agents to control and monitor all functions, to provide auto-recovery as necessary, and to announce their status and capabilities up the control structure. Real-time monitoring or interaction by humans should be infrequent. Equipment is designed to be reliable over long periods to minimize hands-on maintenance, by local or LCOGT staff. Our first 1m deployment was to McDonald Obs. in April 2012. Eight more 1m telescopes are close to deployment to complete the Southern ring, scheduled by end-2012
Structural Transition of Actin Filament in a Cell-Sized Water Droplet with a Phospholipid Membrane
Actin filament, F-actin, is a semiflexible polymer with a negative charge,
and is one of the main constituents on cell membranes. To clarify the effect of
cross-talk between a phospholipid membrane and actin filaments in cells, we
conducted microscopic observations on the structural changes in actin filaments
in a cell-sized (several tens of micrometers in diameter) water droplet coated
with a phospholipid membrane such as phosphatidylserine (PS; negatively-charged
head group) or phosphatidylethanolamine (PE; neutral head group) as a simple
model of a living cell membrane. With PS, actin filaments are distributed
uniformly in the water phase without adsorption onto the membrane surface
between 2 and 6 mM Mg2+, while between 6 and 12 mM Mg2+, actin filaments are
adsorbed onto the inner membrane surface. With PE, actin filaments are
uniformly adsorbed onto the inner membrane surface between 2 and 12 mM Mg2+.
With both PS and PE membranes, at Mg2+ concentrations higher than 12 mM, thick
bundles are formed in the bulk water droplet accompanied by the dissolution of
actin filaments from the membrane surface. The attraction between actin
filaments and membrane is attributable to an increase in the translational
entropy of counterions accompanied by the adsorption of actin filaments onto
the membrane surface. These results suggest that a microscopic water droplet
coated with phospholipid can serve as an easy-to-handle model of cell
membranes
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Molybdenum evidence for expansive sulfidic water masses in ~750Ma oceans
The Ediacaran appearance of large animals, including motile bilaterians, is commonly hypothesized to reflect a physiologically enabling increase in atmospheric and oceanic oxygen abundances (pO2). To date, direct evidence for low oxygen in pre-Ediacaran oceans has focused on chemical signatures in the rock record that reflect conditions in local basins, but this approach is both biased to constrain only shallower basins and statistically limited when we seek to follow the evolution of mean ocean chemical state through time. Because the abundance and isotopic composition of molybdenum (Mo) in organic-rich euxinic sediments can vary in response to changes in global redox conditions, Mo geochemistry provides independent constraints on the global evolution of well-oxygenated environments. Here, we establish a theoretical framework to access global marine Mo cycle in the past from the abundance and isotope composition of ancient seawater. Further, we investigate the ~ 750 Ma Walcott Member of the Chuar Group, Grand Canyon, which accumulated in a rift basin with open connection to the ocean. Iron speciation data from upper Walcott shales indicate that local bottom waters were anoxic and sulfidic, consistent with their high organic content (up to 20 wt.%). Similar facies in Phanerozoic successions contain high concentrations of redox-sensitive metals, but in the Walcott Member, abundances of Mo and U, as well as Mo/TOC (~ 0.5 ppm/wt.%) are low. ÎŽ98Mo values also fall well below modern equivalents (0.99 ± 0.13â° versus ~ 2.35â° today). These signatures are consistent with model predictions where sulfidic waters cover ~ 1â4% of the global seafloor, corresponding to a ~ 20â80 fold increase compared to the modern ocean. Therefore, our results suggest globally expansive sulfidic water masses in mid-Neoproterozoic oceans, bridging a nearly 700 million-year gap in previous Mo data. We propose that anoxic and sulfidic (euxinic) conditions governed Mo cycling in the oceans even as ferruginous subsurface waters re-appeared 800â750 Ma, and we interpret this anoxic ocean state to reflect a markedly lower atmospheric and oceanic O2 level, consistent with the hypothesis that pO2 acted as an evolutionary barrier to the emergence of large motile bilaterian animals prior to the Ediacaran Period.Organismic and Evolutionary Biolog
A prothrombinase-based assay for detection of resistance to activated protein C
In this paper we present a new method for the detection of resistance to activated protein C (APC) that is based on direct measurement of the effect of APC an the cofactor activity of plasma factor Va. The factor V present in a diluted plasma sample was activated with thrombin and its sensitivity towards APC was subsequently determined by incubation with phospholipids and APC; The loss of factor Va cofactor activity was quantified in a prothrombinase system containing purified prothrombin. factor Xa and phospholipid vesicles and using a chromogenic assay for quantitation of thrombin formation. The reaction conditions were optimized in order to distinguish normal, heterozygous and homozygous APC-resistant plasmas. Maximal differences in the response of these plasmas towards ATC were observed when factor Va was inactivated by APC in the absence of protein S and when the: cofactor activity of factor Va was determined at a low factor Xa concentration (0.3 nM).Addition of 0.2 nM APC and 20 mu M phospholipid vesicles to a 1000-fold diluted sample of thrombin-activated normal plasma resulted in loss of mon than 85% of the cofactor activity factor Va within 6 min. Under the same conditions, APC inactivated similar to 60% and similar to 20% of the factor Va present in plasma samples from APC-resistant individuals that were heterozygous or homozygous for the mutation Arg(506)-->Gln in factor V, respectively. Discrimination between the plasma samples from normal and heterozygous and homozygous APC-resistant individuals was facilitated by introduction of the so-called APC-sensitivity ratio (APC-sr). The APC-sr was defined as the ratio of the factor Va cofactor activities determined in thrombin-activated plasma samples after 6 min incubation with or without 0.2 nM APC and was multiplied by as 100 to obtain integers (APC-sr = {factor Va(+APC)/factor Va(-APC)} x 100). Clear differences were observed between the APC-sr of plasmas from normal healthy volunteers (APC-sr: 8-20, n = 33) and from individuals that were heterozygous (APC-sr: 35-50, n = 17) or homozygous APC resistant (APC-sr: 82-88, n = 7). There was no mutual overlap between the APC-sr of normal plasmas and plasmas from heterozygous or homozygous APC resistant individuals (p < 0.0001), In all cases our test gave the same result as the DNA-based assay. Since the test is performed on a highly diluted plasma sample there is no interference by conditions that affect APC resistance tests that are based on clotting time determinations (e.g. coagulation factor deficiencies, oral anticoagulation, heparin treatment. the presence of lupus anticoagulants, pregnancy or the use of oral contraceptives). Furthermore, we show that part of the factor Va assay can be performed on an autoanalyzer which increases the number of plasma samples that can be handled simultaneously
The Palomar Transient Factory: System Overview, Performance and First Results
The Palomar Transient Factory (PTF) is a fully-automated, wide-field survey
aimed at a systematic exploration of the optical transient sky. The transient
survey is performed using a new 8.1 square degree camera installed on the
48-inch Samuel Oschin telescope at Palomar Observatory; colors and light curves
for detected transients are obtained with the automated Palomar 60-inch
telescope. PTF uses eighty percent of the 1.2-m and fifty percent of the 1.5-m
telescope time. With an exposure of 60-s the survey reaches a depth of
approximately 21.3 in g' and 20.6 in R (5 sigma, median seeing). Four major
experiments are planned for the five-year project: 1) a 5-day cadence supernova
search; 2) a rapid transient search with cadences between 90 seconds and 1 day;
3) a search for eclipsing binaries and transiting planets in Orion; and 4) a
3-pi sr deep H-alpha survey. PTF provides automatic, realtime transient
classification and follow up, as well as a database including every source
detected in each frame. This paper summarizes the PTF project, including
several months of on-sky performance tests of the new survey camera, the
observing plans and the data reduction strategy. We conclude by detailing the
first 51 PTF optical transient detections, found in commissioning data.Comment: 12 pages, 11 figures, 3 tables, submitted to PAS
Demography and Viability of a Hunted Population of Polar Bears
We estimated demographic parameters and harvest risks for a population of polar bears (Ursus maritimus) inhabiting Baffin Bay, Canada and Greenland, from 1974 to 1997. Our demographic analysis included a detailed assessment of age- and sex-specific survival and recruitment from 1221 marked polar bears, which used information contained within the standing age distribution of captures and mark-recapture analysis performed with Program MARK. Unharvested (natural) survival rates for females (± 1 SE) from mark-recapture analysis were 0.620 ± 0.095 (cubs), 0.938 ± 0.042 (ages 1â4), 0.953 ± 0.020 (ages 5â20), and 0.919 ± 0.046 (ages 21+). Total (harvested) survival rates for females were reduced to 0.600 ± 0.096 (cubs), 0.901 ± 0.045 (ages 1â4), 0.940 ± 0.021 (ages 5â20), and 0.913 ± 0.047 (ages 21+). Mean litter size was 1.59 ± 0.07 cubs, with a mean reproductive interval of 2.5 ± 0.01 years. By age 5, on average 0.88 ± 0.40 of females were producing litters. We estimated the geometric means (± bootstrapped SDs) for population growth rates at stable age distribution as 1.055 ± 0.011 (unharvested) and 1.019 ± 0.015 (harvested). The model-averaged, mark-recapture estimate of mean abundance (± 1 SE) for years 1994â97 was 2074 ± 266 bears, which included 1017 ± 192 females and 1057 ± 124 males. We incorporated demographic parameters and their error terms into a harvest risk analysis designed to consider demographic, process, and sampling uncertainty in generating likelihoods of persistence (i.e., a stochastic, harvest-explicit population viability analysis). Using our estimated harvest of polar bears in Baffin Bay (88 bears/yr), the probability that the population would decline no more than could be recovered in five years was 0.95, suggesting that the current hunt is sustainable.De 1974 Ă 1997, on a Ă©valuĂ© les paramĂštres dĂ©mographiques dâune population dâours polaires (Ursus maritimus) habitant la baie de Baffin (Canada et Groenland), ainsi que les risques associĂ©s Ă leur prĂ©lĂšvement. Notre analyse dĂ©mographique comprenait un bilan dĂ©taillĂ© de la survie et du recrutement par Ăąge et par sexe, bilan menĂ© sur 1221 ours polaires Ă©tiquetĂ©s et qui faisait appel Ă lâinformation contenue dans les limites de la structure dâĂąge des captures Ă un moment prĂ©cis, ainsi que des analyses de marquage-recapture rĂ©alisĂ©es avec le logiciel MARK. Les taux de survie sans prĂ©lĂšvements (câest-Ă -dire naturels) des femelles (± 1 erreur-type) tirĂ©s de lâanalyse de marquage-recapture Ă©taient les suivants: 0,620 ± 0,095 (oursons), 0,938 ± 0,042 (1â4 ans), 0,953 ± 0,020 (5â20 ans) et 0,919 ± 0,046 (21 ans et plus). Les taux de survie globaux (avec prĂ©lĂšvements) des femelles diminuaient Ă : 0,600 ± 0,096 (oursons), 0,901 ± 0,045 (1â4 ans), 0,940 ± 0,021 (5â20 ans) et 0,913 ± 0,047 (21 ans et plus). La taille moyenne des portĂ©es Ă©tait de 1,59 ± 0,07 ourson avec des intervalles moyens de reproduction de 2,5 ± 0,01 ans. ArrivĂ©es Ă lâĂąge de cinq ans, en moyenne 0,88 ± 0,40 des femelles avaient eu des petits. On a Ă©valuĂ© que les moyennes gĂ©omĂ©triques (± Ă©cart-type bootstrappĂ©) pour les taux de croissance de la population Ă la structure dâĂąge stable Ă©taient de 1,055 ± 0,011 (sans prĂ©lĂšvements) et de 1,019 ± 0,015 (avec prĂ©lĂšvements). La valeur estimĂ©e Ă partir du marquage-recapture, moyennĂ©e par le modĂšle, de lâabondance moyenne (± 1 erreur-type), pour les annĂ©es allant de 1994 Ă 1997 Ă©tait de 2074 ± 266 ours, dont 1017 Ă
} 192 femelles et 1057 ± 124 mĂąles. On a intĂ©grĂ© les paramĂštres dĂ©mographiques et leurs termes dâerreur dans une analyse des risques de prĂ©lĂšvements conçue pour tenir compte des incertitudes dĂ©mographiques, de processus et dâĂ©chantillonnage lors du calcul des probabilitĂ©s de persistance (c.-Ă -d. une analyse stochastique de la viabilitĂ© de la population qui tient compte des prĂ©lĂšvements). En se basant sur nos prĂ©lĂšvements estimĂ©s de lâours polaire dans la baie de Baffin (88 ours/an), la probabilitĂ© que la population ne dĂ©cline pas plus que ce quâelle pourrait rĂ©cupĂ©rer en 5 ans Ă©tait de 0,95, ce qui suggĂšre que la chasse actuelle est durable
Deployment status of the Las Cumbres Observatory Global Telescope
Our global network of telescopes is designed to provide maximally available optical monitoring of time variable sources, from solar system to extra-galactic objects, and ranging in brightness from about 7-20m. We are providing a distributed network with varied apertures but homogeneous instrumentation: optical imaging, with spectroscopic capabilities. A key component is a single centralized process that accepts (in real time) and schedules TAC approved observing requests across the network; then continuously updates schedules based on status, weather and other availability criteria. Requests range from occasional to continuous monitoring, at slow to high-speed cadences (imaging and fast photometry), and includes rapid response to targets of opportunity. Each node of the network must be fully autonomous, with software agents to control and monitor all functions, to provide auto-recovery as necessary, and to announce their status and capabilities up the control structure. Real-time monitoring or interaction by humans should be infrequent. Equipment is designed to be reliable over long periods to minimize hands-on maintenance, by local or LCOGT staff. Our first 1m deployment was to McDonald Obs. in April 2012. Eight more 1m telescopes are close to deployment to complete the Southern ring, scheduled by end-2012
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Energy Harvesting for Structural Health Monitoring Sensor Networks
This report has been developed based on information exchanges at a 2.5-day workshop on energy harvesting for embedded structural health monitoring (SHM) sensing systems that was held June 28-30, 2005, at Los Alamos National Laboratory. The workshop was hosted by the LANL/UCSD Engineering Institute (EI). This Institute is an education- and research-focused collaboration between Los Alamos National Laboratory (LANL) and the University of California, San Diego (UCSD), Jacobs School of Engineering. A Statistical Pattern Recognition paradigm for SHM is first presented and the concept of energy harvesting for embedded sensing systems is addressed with respect to the data acquisition portion of this paradigm. Next, various existing and emerging sensing modalities used for SHM and their respective power requirements are summarized, followed by a discussion of SHM sensor network paradigms, power requirements for these networks and power optimization strategies. Various approaches to energy harvesting and energy storage are discussed and limitations associated with the current technology are addressed. This discussion also addresses current energy harvesting applications and system integration issues. The report concludes by defining some future research directions and possible technology demonstrations that are aimed at transitioning the concept of energy harvesting for embedded SHM sensing systems from laboratory research to field-deployed engineering prototypes
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