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Search Results: 1 - 10 of 401596 matches for " J. V. Dawson "
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Status of the Double Chooz Experiment
J. V. Dawson
Physics , 2009,
Abstract: The Double Chooz experiment is the first of the next wave of reactor experiments searching for a non-vanishing value of the mixing angle theta_13. The experimental concept and detector design are presented, and the most pertinent backgrounds are discussed. Operation of the far detector is expected to begin by the end of 2009. Installation of the near detector will occur in 2010. Double Chooz has the capacity to measure sin^2(2theta_13) to 3 sigma if sin^2(2theta_13) >0.05 or exclude sin^2 (2theta_13) down to 0.03 at 90% for Delta m_31^2 = 2.5 x 10^-3 eV^2 with three years of data with both near and far detectors.
Organic Liquid TPCs for Neutrino Physics
J. V. Dawson,D. Kryn
Physics , 2014, DOI: 10.1088/1748-0221/9/07/P07002
Abstract: We present a new concept for anti-neutrino detection, an organic liquid TPC with a volume of the order of m$^3$ and an energy resolution of the order of 1% at 3 MeV and a sub-cm spatial resolution.
Insights into the In Vivo Regulation of Glutamate Dehydrogenase from the Foot Muscle of an Estivating Land Snail
Ryan A. V. Bell,Neal J. Dawson,Kenneth B. Storey
Enzyme Research , 2012, DOI: 10.1155/2012/317314
Abstract: Land snails, Otala lactea, survive in seasonally hot and dry environments by entering a state of aerobic torpor called estivation. During estivation, snails must prevent excessive dehydration and reorganize metabolic fuel use so as to endure prolonged periods without food. Glutamate dehydrogenase (GDH) was hypothesized to play a key role during estivation as it shuttles amino acid carbon skeletons into the Krebs cycle for energy production and is very important to urea biosynthesis (a key molecule used for water retention). Analysis of purified foot muscle GDH from control and estivating conditions revealed that estivated GDH was approximately 3-fold more active in catalyzing glutamate deamination as compared to control. This kinetic difference appears to be regulated by reversible protein phosphorylation, as indicated by ProQ Diamond phosphoprotein staining and incubations that stimulate endogenous protein kinases and phosphatases. The increased activity of the high-phosphate form of GDH seen in the estivating land snail foot muscle correlates well with the increased use of amino acids for energy and increased synthesis of urea for water retention during prolonged estivation. 1. Introduction Glutamate dehydrogenase (GDH; E.C. 1.4.1.3) is an important enzyme that contributes to a diverse set of metabolic processes. GDH catalyzes the following reversible reaction within the mitochondrial matrix: Through oxidative deamination, GDH gates the entry of numerous amino acid carbon skeletons into the Krebs cycle for increased energy production or gluconeogenic output. Furthermore, GDH-derived ammonium ions provide the primary source of nitrogen for the synthesis of urea via the urea cycle. In the reverse direction, GDH acts to synthesize L-glutamate for use in protein synthesis or, alternatively, transamination reactions. Given the importance of GDH in both carbohydrate and nitrogen metabolism, it was hypothesized to be a critical enzyme in animals that experience drastic alterations to cellular biochemistry in response to harsh environmental conditions. Animals that live in seasonally hot and dry environments usually require some mechanism to survive periodic droughts and the scarcity of food that typically follows. One such mechanism is estivation, which is a state of aerobic torpor that is employed by a range of organisms including amphibians, reptiles, small mammals, and land snails [1]. Estivation entails major behavioral, physiological, and biochemical adaptations that allow for prolonged survival under harsh conditions. Particularly important for this
Purification and Properties of White Muscle Lactate Dehydrogenase from the Anoxia-Tolerant Turtle, the Red-Eared Slider, Trachemys scripta elegans
Neal J. Dawson,Ryan A. V. Bell,Kenneth B. Storey
Enzyme Research , 2013, DOI: 10.1155/2013/784973
Abstract:
Purification and Properties of White Muscle Lactate Dehydrogenase from the Anoxia-Tolerant Turtle, the Red-Eared Slider, Trachemys scripta elegans
Neal J. Dawson,Ryan A. V. Bell,Kenneth B. Storey
Enzyme Research , 2013, DOI: 10.1155/2013/784973
Abstract: Lactate dehydrogenase (LDH; E.C. 1.1.1.27) is a crucial enzyme involved in energy metabolism in muscle, facilitating the production of ATP via glycolysis during oxygen deprivation by recycling NAD+. The present study investigated purified LDH from the muscle of 20?h anoxic and normoxic T. s. elegans, and LDH from anoxic muscle showed a significantly lower (47%) for L-lactate and a higher value than the normoxic form. Several lines of evidence indicated that LDH was converted to a low phosphate form under anoxia: (a) stimulation of endogenously present protein phosphatases decreased the of L-lactate of control LDH to anoxic levels, whereas (b) stimulation of kinases increased the of L-lactate of anoxic LDH to normoxic levels, and (c) dot blot analysis shows significantly less serine (78%) and threonine (58%) phosphorylation in anoxic muscle LDH as compared to normoxic LDH. The physiological consequence of anoxia-induced LDH dephosphorylation appears to be an increase in LDH activity to promote the reduction of pyruvate in muscle tissue, converting the glycolytic end product to lactate to maintain a prolonged glycolytic flux under energy-stressed anoxic conditions. 1. Introduction Lactate dehydrogenase (LDH; E.C. 1.1.1.27) is a critical enzyme involved in anaerobic metabolism. LDH catalyzes the following reversible reaction: In this capacity, LDH favors the pyruvate reducing direction in skeletal muscle tissue, converting the glycolytic end product to lactate and regenerating the NAD+ pools to maintain a prolonged glycolytic flux [1]. This process is especially critical to those organisms that enter periodically into hypoxic/anoxic environments, where maintaining NAD+/NADH balance is essential for ATP production. Under low oxygen insult, organisms often rely solely on the glycolytic pathway to produce ATP. The greatly reduced production of ATP via glycolysis, as compared to that of oxidative phosphorylation, results in difficult challenges for anoxia-tolerant organisms to overcome. Several of these organisms employ alternate anaerobic pathways to increase ATP yield and/or depress their metabolic rate to survive the low oxygen stress [2]. Furthermore, these organisms typically need to safeguard against the accumulation of acidic glycolytic end products such as lactate, which disrupts cellular homeostasis throughout prolonged exposure to anoxia [2]. Freshwater turtles, Trachemys scripta elegans, have demonstrated a remarkable ability to survive submerged in cold water for 4-5 months during the winter to escape freezing air temperatures. While submerged,
Density of mechanisms within the flexibility window of zeolites
V. Kapko,C. Dawson,I. Rivin,M. M. J. Treacy
Physics , 2011, DOI: 10.1103/PhysRevLett.107.164304
Abstract: By treating idealized zeolite frameworks as periodic mechanical trusses, we show that the number of flexible folding mechanisms in zeolite frameworks is strongly peaked at the minimum density end of their flexibility window. 25 of the 197 known zeolite frameworks exhibit an extensive flexibility, where the number of unique mechanisms increases linearly with the volume when long wavelength mechanisms are included. Extensively flexible frameworks therefore have a maximum in configurational entropy, as large crystals, at their lowest density. Most real zeolites do not exhibit extensive flexibility, suggesting that surface and edge mechanisms are important, likely during the nucleation and growth stage. The prevalence of flexibility in real zeolites suggests that, in addition to low framework energy, it is an important criterion when searching large databases of hypothetical zeolites for potentially useful realizable structures.
An Investigation on Cooling of CZT Co-Planar Grid Detectors
J. V. Dawson,C. Montag,C. Reeve,J. R. Wilson,K. Zuber
Physics , 2008, DOI: 10.1016/j.nima.2008.11.013
Abstract: The effect of moderate cooling on CdZnTe semiconductor detectors has been studied for the COBRA experiment. Improvements in energy resolution and low energy threshold were observed and quantified as a function of temperature. Leakage currents are found to contribute typically $\sim$5 keV to the widths of photopeaks.
Going Coastal: Shared Evolutionary History between Coastal British Columbia and Southeast Alaska Wolves (Canis lupus)
Byron V. Weckworth,Natalie G. Dawson,Sandra L. Talbot,Melanie J. Flamme,Joseph A. Cook
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0019582
Abstract: Many coastal species occupying the temperate rainforests of the Pacific Northwest in North America comprise endemic populations genetically and ecologically distinct from interior continental conspecifics. Morphological variation previously identified among wolf populations resulted in recognition of multiple subspecies of wolves in the Pacific Northwest. Recently, separate genetic studies have identified diverged populations of wolves in coastal British Columbia and coastal Southeast Alaska, providing support for hypotheses of distinct coastal subspecies. These two regions are geographically and ecologically contiguous, however, there is no comprehensive analysis across all wolf populations in this coastal rainforest.
Stable Suppression of Lactate Dehydrogenase Activity during Anoxia in the Foot Muscle of Littorina littorea and the Potential Role of Acetylation as a Novel Posttranslational Regulatory Mechanism
Ali Shahriari,Neal J. Dawson,Ryan A. V. Bell,Kenneth B. Storey
Enzyme Research , 2013, DOI: 10.1155/2013/461374
Abstract: The intertidal marine snail, Littorina littorea, has evolved to withstand extended bouts of oxygen deprivation brought about by changing tides or other potentially harmful environmental conditions. Survival is dependent on a strong suppression of its metabolic rate and a drastic reorganization of its cellular biochemistry in order to maintain energy balance under fixed fuel reserves. Lactate dehydrogenase (LDH) is a crucial enzyme of anaerobic metabolism as it is typically responsible for the regeneration of NAD+, which allows for the continued functioning of glycolysis in the absence of oxygen. This study compared the kinetic and structural characteristics of the D-lactate specific LDH (E.C. 1.1.1.28) from foot muscle of aerobic control versus 24?h anoxia-exposed L. littorea. Anoxic LDH displayed a near 50% decrease in (pyruvate-reducing direction) as compared to control LDH. These kinetic differences suggest that there may be a stable modification and regulation of LDH during anoxia, and indeed, subsequent dot-blot analyses identified anoxic LDH as being significantly less acetylated than the corresponding control enzyme. Therefore, acetylation may be the regulatory mechanism that is responsible for the suppression of LDH activity during anoxia, which could allow for the production of alternative glycolytic end products that in turn would increase the ATP yield under fixed fuel reserves. 1. Introduction Lactate dehydrogenase catalyzes the reversible conversion of pyruvate to lactate, with the concomitant oxidation of NADH to NAD+. Under anaerobic conditions, LDH becomes an important enzyme due to its ability to regenerate NAD+ and allows for continued carbon flow through the glycolytic pathway to support anaerobic ATP synthesis [1]. This process can be especially important in those organisms that are exposed to hypoxic or anoxic conditions for extended periods of time and require energy balance to be maintained solely through the functioning of glycolysis. Littorina littorea are marine molluscs that are native to the intertidal zones of the Atlantic coast of Europe (from Scandinavia to Spain) and have been introduced to the east coast of North America as well as several other locations around the world. Changing tides frequently expose these gill-breathing snails to prolonged oxygen deprivation at low tide [2]. Moreover, environmental conditions, such as high salinity, predation, or water pollutants can cause the snails to shut their shell openings, which over an extended period of time can also generate an anoxic exposure [3, 4]. In order to survive
Interpenetrating plasma shells: near-equipartition magnetic field generation and non-thermal particle acceleration
L. O. Silva,R. A. Fonseca,J. Tonge,J. M. Dawson,W. B. Mori,M. V. Medvedev
Physics , 2003, DOI: 10.1086/379156
Abstract: We present the first three-dimensional fully kinetic electromagnetic relativistic particle-in-cell simulations of the collision of two interpenetrating plasma shells. The highly accurate plasma-kinetic "particle-in-cell" (with the total of $10^8$ particles) parallel code OSIRIS has been used. Our simulations show: (i) the generation of long-lived near-equipartition (electro)magnetic fields, (ii) non-thermal particle acceleration, and (iii) short-scale to long-scale magnetic field evolution, in the collision region. Our results provide new insights into the magnetic field generation and particle acceleration in relativistic and sub-relativistic colliding streams of particles, which are present in gamma-ray bursters, supernova remnants, relativistic jets, pulsar winds, etc..
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