5,039 research outputs found
LANDSAT image differencing as an automated land cover change detection technique
Image differencing was investigated as a technique for use with LANDSAT digital data to delineate areas of land cover change in an urban environment. LANDSAT data collected in April 1973 and April 1975 for Austin, Texas, were geometrically corrected and precisely registered to United States Geological Survey 7.5-minute quadrangle maps. At each pixel location reflectance values for the corresponding bands were subtracted to produce four difference images. Areas of major reflectance differences are isolated by thresholding each of the difference images. The resulting images are combined to obtain an image data set to total change. These areas of reflectance differences were found, in general, to correspond to areas of land cover change. Information on areas of land cover change was incorporated into a procedure to mask out all nonchange areas and perform an unsupervised classification only for data in the change areas. This procedure identified three broad categories: (1) areas of high reflectance (construction or extractive), (2) changes in agricultural areas, and (3) areas of confusion between agricultural and other areas
Avionics architecture studies for the entry research vehicle
This report is the culmination of a year-long investigation of the avionics architecture for NASA's Entry Research Vehicle (ERV). The Entry Research Vehicle is conceived to be an unmanned, autonomous spacecraft to be deployed from the Shuttle. It will perform various aerodynamic and propulsive maneuvers in orbit and land at Edwards AFB after a 5 to 10 hour mission. The design and analysis of the vehicle's avionics architecture are detailed here. The architecture consists of a central triply redundant ultra-reliable fault tolerant processor attached to three replicated and distributed MIL-STD-1553 buses for input and output. The reliability analysis is detailed here. The architecture was found to be sufficiently reliable for the ERV mission plan
Changes in Imja Tsho in the Mount Everest Region of Nepal
Imja Tsho, located in the Sagarmatha ( Everest) National Park of Nepal, is one of the most studied and rapidly growing lakes in the Himalayan range. Compared with previous studies, the results of our sonar bathymetric survey conducted in September of 2012 suggest that its maximum depth has increased from 90.5 to 116.3 +/- 5.2 m since 2002, and that its estimated volume has grown from 35.8 +/- 0.7 to 61.7 +/- 3.7 million m(3). Most of the expansion of the lake in recent years has taken place in the glacier terminus-lake interface on the eastern end of the lake, with the glacier receding at about 52 m yr(-1) and the lake expanding in area by 0.04 km(2) yr(-1). A ground penetrating radar survey of the Imja-Lhotse Shar glacier just behind the glacier terminus shows that the ice is over 200 m thick in the center of the glacier. The volume of water that could be released from the lake in the event of a breach in the damming moraine on the western end of the lake has increased to 34.1 +/- 1.08 million m(3) from the 21 million m(3) estimated in 2002.USAID Climate Change Resilient Development (CCRD) projectFulbright FoundationNational Geographic SocietyCenter for Research in Water Resource
Stem cells and fluid flow drive cyst formation in an invertebrate excretory organ.
Cystic kidney diseases (CKDs) affect millions of people worldwide. The defining pathological features are fluid-filled cysts developing from nephric tubules due to defective flow sensing, cell proliferation and differentiation. The underlying molecular mechanisms, however, remain poorly understood, and the derived excretory systems of established invertebrate models (Caenorhabditis elegans and Drosophila melanogaster) are unsuitable to model CKDs. Systematic structure/function comparisons revealed that the combination of ultrafiltration and flow-associated filtrate modification that is central to CKD etiology is remarkably conserved between the planarian excretory system and the vertebrate nephron. Consistently, both RNA-mediated genetic interference (RNAi) of planarian orthologues of human CKD genes and inhibition of tubule flow led to tubular cystogenesis that share many features with vertebrate CKDs, suggesting deep mechanistic conservation. Our results demonstrate a common evolutionary origin of animal excretory systems and establish planarians as a novel and experimentally accessible invertebrate model for the study of human kidney pathologies
HARM: A Numerical Scheme for General Relativistic Magnetohydrodynamics
We describe a conservative, shock-capturing scheme for evolving the equations
of general relativistic magnetohydrodynamics. The fluxes are calculated using
the Harten, Lax, and van Leer scheme. A variant of constrained transport,
proposed earlier by T\'oth, is used to maintain a divergence free magnetic
field. Only the covariant form of the metric in a coordinate basis is required
to specify the geometry. We describe code performance on a full suite of test
problems in both special and general relativity. On smooth flows we show that
it converges at second order. We conclude by showing some results from the
evolution of a magnetized torus near a rotating black hole.Comment: 38 pages, 18 figures, submitted to Ap
A feasibility study of signed consent for the collection of patient identifiable information for a national paediatric clinical audit database
Objectives: To investigate the feasibility of obtaining signed consent
for submission of patient identifiable data to a national clinical
audit database and to identify factors influencing the consent process
and its success.
Design: Feasibility study.
Setting: Seven paediatric intensive care units in England.
Participants: Parents/guardians of patients, or patients aged 12-16
years old, approached consecutively over three months for signed
consent for submission of patient identifiable data to the national
clinical audit database the Paediatric Intensive Care Audit Network
(PICANet).
Main outcome measures: The numbers and proportions of admissions for
which signed consent was given, refused, or not obtained (form not
returned or form partially completed but not signed), by age, sex,
level of deprivation, ethnicity (South Asian or not), paediatric index
of mortality score, length of hospital stay (days in paediatric
intensive care).
Results: One unit did not start and one did not fully implement the
protocol, so analysis excluded these two units. Consent was obtained
for 182 of 422 admissions (43%) (range by unit 9% to 84%). Most
(101/182; 55%) consents were taken by staff nurses. One refusal (0.2%)
was received. Consent rates were significantly better for children who
were more severely ill on admission and for hospital stays of six days
or more, and significantly poorer for children aged 10-14 years. Long
hospital stays and children aged 10-14 years remained significant in a
stepwise regression model of the factors that were significant in the
univariate model.
Conclusion: Systematically obtaining individual signed consent for
sharing patient identifiable information with an externally located
clinical audit database is difficult. Obtaining such consent is
unlikely to be successful unless additional resources are specifically
allocated to training, staff time, and administrative support
Allometric length-weight relationships for benthic prey of aquatic wildlife in coastal marine habitats
We developed models to estimate the soft tissue content of benthic marine invertebrates that are prey for aquatic wildlife. Allometric regression models of tissue wet weight with shell length for 10 species of benthic invertebrates had r2 values ranging from 0.29 for hermit crabs Pagurus longicarpus to 0.98 for green crabs Carcinus maenas. As a class, bivalves had the highest r2 values (0.84) and crustaceans the lowest (0.48). Energy and nutrient content of soft tissue is also presented for the 10 benthic species. The energy content was lowest in crabs, and ranged within 2.20–4.71 kcal g-1 dry weight. Fat content was highly variable (range: 3.5–16.0%), and protein content ranged within 43.1–68.1% and was highest for shrimp Palaemonetes pugio. Comparison between classes of organisms of the amount of soft tissue per unit shell length showed that crustaceans yield five times more soft tissue per unit shell length than bivalves, and four times more than gastropods. The models we present use simple measures, such as the length of shell or wet weight of the entire animal, to quantitatively estimate the amount of available soft tissue in benthic prey that are usually consumed in total (with shell and soft tissue intact) but for which only the soft tissue is used for nutritional gain. This information can be combined with energy and nutrient content data to calculate energy or nutrient based carrying capacities that can help assess available resources for shorebirds, waterfowl and marine mammals
Using Mussel Isotope Ratios to Assess Anthropogenic Nitrogen Inputs to Freshwater Ecosystems
Stable nitrogen isotope ratios (δ15N) of freshwater mussels from a series of lakes and ponds were related to watershed land use characteristics to assess their utility in determining the source of nitrogen inputs to inland water bodies. Nitrogen isotope ratios measured in freshwater mussels from 19 lakes and ponds in Rhode Island, U.S.A., ranged from 4.9–12.6% and were found to significantly correlate with the fraction of residential development in 100 and 200 m buffer zones around the ponds. Mussel δ15N values in 12 of the 19 ponds also showed significant correlation with average dissolved nitrate concentrations, which ranged from 23–327 μg L-1. These observations, in light of previous studies which link elevated δ15N values of nitrogen derived from septic wastewater with those seen in biota, suggest that mussel isotope ratios may reflect nitrogen source in freshwater ecosystems. We followed an iterative approach using multiple regression analysis to assess the relationship between mussel δ15N and the land use categories fraction residential development, fraction feedlot agriculture, fraction row-crop agriculture, and fraction natural vegetation in 100 and 200 m buffer zones and pond watersheds. From this we developed a simple regression model to predict mussel δ15N from the fraction of residential development in the 200 m buffer zone around the pond. Subsequent testing with data from 16 additional sites in the same ecoregion led us to refine the model by incorporating the fraction of natural vegetation. The overall average absolute difference between measured and predicted δ15N values using the two-parameter model was 1.6%. Potential sources of error in the model include differences in the scale and categorization of land-use data used to generate and test the model, differences in physical characteristics, such as retention time and range of residential development, and exclusion of sources of enriched nitrogen such as runoff from feedlot operations or increased nitrogen loading from inefficient or failed septic systems
Cholinergic Modulation of Locomotion and Striatal Dopamine Release Is Mediated by α6α4* Nicotinic Acetylcholine Receptors
Dopamine (DA) release in striatum is governed by firing rates of midbrain DA neurons, striatal cholinergic tone, and nicotinic ACh
receptors (nAChRs) on DA presynaptic terminals. DA neurons selectively express α6* nAChRs, which show high ACh and nicotine
sensitivity. To help identify nAChR subtypes that control DA transmission, we studied transgenic mice expressing hypersensitive α6^(L9’S*)
receptors. α6^(L9’S) mice are hyperactive, travel greater distance, exhibit increased ambulatory behaviors such as walking, turning, and
rearing, and show decreased pausing, hanging, drinking, and grooming. These effects were mediated by α6 α4* pentamers, as α6^(L9’S) mice
lacking α4 subunits displayed essentially normal behavior. In α6^(L9’S) mice, receptor numbers are normal, but loss of α4 subunits leads to
fewer and less sensitive α6* receptors. Gain-of-function nicotine-stimulated DA release from striatal synaptosomes requires α4 subunits,
implicating α6α4β2* nAChRs in α6^(L9’S) mouse behaviors. In brain slices, we applied electrochemical measurements to study
control of DA release by α6^(L9’S) nAChRs. Burst stimulation of DA fibers elicited increased DA release relative to single action potentials
selectively in α6^(L9’S), but not WT or α4KO/ α6^(L9’S), mice. Thus, increased nAChR activity, like decreased activity, leads to enhanced
extracellular DA release during phasic firing. Bursts may directly enhance DA release from α6^(L9’S) presynaptic terminals, as there was no
difference in striatal DA receptor numbers or DA transporter levels or function in vitro. These results implicate α6α4β2* nAChRs in
cholinergic control of DA transmission, and strongly suggest that these receptors are candidate drug targets for disorders involving the
DA system
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