30 research outputs found
Optically excited states in positronium
Optical excitation are reported of the 1 3S-2 3P transition in positronium, and a second excitation from n=2 to higher n states. The experiment used light from two pulsed dye lasers. Changes in the positronium annihilation rate during and after the laser pulse were used to deduce the excited state populations. The n=2 level was found to be saturable and excitable to a substantial fraction of n=2 positronium to higher levels. Preliminary spectroscopic measurements were performed on n=14 and n=15 positronium
Transient x-ray diffraction used to diagnose shock compressed Si crystals on the Nova laser
Transient x-ray diffraction is used to record time-resolved information about the shock compression of materials. This technique has been applied on Nova shock experiments driven using a hohlraum x-ray drive. Data were recorded from the shock release at the free surface of a Si crystal, as well as from Si at an embedded ablator/Si interface. Modeling has been done to simulate the diffraction data incorporating the strained crystal rocking curves and Bragg diffraction efficiencies. Examples of the data and post-processed simulations are presented
GUCY2C Opposes Systemic Genotoxic Tumorigenesis by Regulating AKT-Dependent Intestinal Barrier Integrity
The barrier separating mucosal and systemic compartments comprises epithelial cells, annealed by tight junctions, limiting permeability. GUCY2C recently emerged as an intestinal tumor suppressor coordinating AKT1-dependent crypt-villus homeostasis. Here, the contribution of GUCY2C to barrier integrity opposing colitis and systemic tumorigenesis is defined. Mice deficient in GUCY2C (Gucy2cβ/β) exhibited barrier hyperpermeability associated with reduced junctional proteins. Conversely, activation of GUCY2C in mice reduced barrier permeability associated with increased junctional proteins. Further, silencing GUCY2C exacerbated, while activation reduced, chemical barrier disruption and colitis. Moreover, eliminating GUCY2C amplified, while activation reduced, systemic oxidative DNA damage. This genotoxicity was associated with increased spontaneous and carcinogen-induced systemic tumorigenesis in Gucy2cβ/β mice. GUCY2C regulated barrier integrity by repressing AKT1, associated with increased junction proteins occludin and claudin 4 in mice and Caco2 cells in vitro. Thus, GUCY2C defends the intestinal barrier, opposing colitis and systemic genotoxicity and tumorigenesis. The therapeutic potential of this observation is underscored by the emerging clinical development of oral GUCY2C ligands, which can be used for chemoprophylaxis in inflammatory bowel disease and cancer
Molecular Signatures Reveal Circadian Clocks May Orchestrate the Homeorhetic Response to Lactation
Genes associated with lactation evolved more slowly than other genes in the mammalian genome. Higher conservation of milk and mammary genes suggest that species variation in milk composition is due in part to the environment and that we must look deeper into the genome for regulation of lactation. At the onset of lactation, metabolic changes are coordinated among multiple tissues through the endocrine system to accommodate the increased demand for nutrients and energy while allowing the animal to remain in homeostasis. This process is known as homeorhesis. Homeorhetic adaptation to lactation has been extensively described; however how these adaptations are orchestrated among multiple tissues remains elusive. To develop a clearer picture of how gene expression is coordinated across multiple tissues during the pregnancy to lactation transition, total RNA was isolated from mammary, liver and adipose tissues collected from rat dams (nβ=β5) on day 20 of pregnancy and day 1 of lactation, and gene expression was measured using Affymetrix GeneChips. Two types of gene expression analysis were performed. Genes that were differentially expressed between days within a tissue were identified with linear regression, and univariate regression was used to identify genes commonly up-regulated and down-regulated across all tissues. Gene set enrichment analysis showed genes commonly up regulated among the three tissues enriched gene ontologies primary metabolic processes, macromolecular complex assembly and negative regulation of apoptosis ontologies. Genes enriched in transcription regulator activity showed the common up regulation of 2 core molecular clock genes, ARNTL and CLOCK. Commonly down regulated genes enriched Rhythmic process and included: NR1D1, DBP, BHLHB2, OPN4, and HTR7, which regulate intracellular circadian rhythms. Changes in mammary, liver and adipose transcriptomes at the onset of lactation illustrate the complexity of homeorhetic adaptations and suggest that these changes are coordinated through molecular clocks
Recommended from our members
Livermore Big Trees Park Soil Survey
Lawrence Livermore National Laboratory (LLNL) will sample and analyze soil in the Big Trees Park area in Livermore, California, to determine if the initial level of plutonium (Pu) in a soil sample taken by the U.S. Environmental Protection Agency (EPA) in September 1993 can be confirmed. Nineteen samples will be collected and analyzed: 4 in the area where the initial EPA sample was taken, 2 in the nearby Arroyo Seco, 12 in scattered uncovered soil areas in the park and nearby school, and 1 from the sandbox of a nearby apartment complex. Two quality control (QC) samples (field duplicates of the preceding samples) win also be collected and analyzed. This document briefly describes the purpose behind the sampling, the sampling rationale, and the methodology
Recommended from our members
Method for rapid, high sensitivity tritiated water extraction
We have developed a thermal vacuum desorption process to rapidly extract water from environmental samples for tritium analysis. Thermal vacuum desorption allows for extraction of the moisture from the sample within a few hours in a form and quantity suitable for liquid scintillation counting and allows detection of tritium at the levels of <2 Bq/L of milk, <0.5 Bq/gm of vegetation, and < 0.5 Bq/gin of soil. We developed a prototype unit that can process batches of twenty or more samples within 24 hours. Early data shows that a high percentage of water is extracted reproducibly without enrichment or depletion of the tritium content. The quench coefficient of the extracted water is low allowing for accurate, direct liquid scintillation counting. Excellent comparison has been observed with results using freeze-dry lypholization as the water extraction method
Leaching study of nuclear melt glass: Part I
Ground samples of three nuclear melt glasses from underground nuclear explosions at the Nevada Test Site (NTS) were leached at 25/sup 0/C with natural ground water from NTS. Using our dynamic single-pass flow-through leaching system we monitored the release of radionuclides from the glasses during 420 days of leaching. We continually flowed the ground water over the melt glass at flow rates of 185 ml/day for half of the samples and 34 ml/day for the rest. Leachate solutions were collected continuously, and composite samples, collected on days 1, 2, 3, 6, 11, 32, 38, 70, 120, 230 and 420, were analyzed using low-background Ge(Li) gamma spectrometers. For most of the radionuclides the leach rate decreased smoothly throughout the experiment. Except for /sup 95/Zr, /sup 144/Ce, and /sup 155/Eu, there was no difference between the fast (185 ml/day) and slow (34 ml/day) flow-rate leach rates. The measurable leach rates ranged from a high of 1 x 10/sup -2/ g-glass/m/sup 2/ day for /sup 22/Na (slow flow-rate, day 1 in glass No. 2) to a low of 1 x 6/sup -6/ g-glass/m/sup 2/ day for /sup 54/Mn (slow flow-rate, day 420 in glass No. 2). Most of the leach-rate values were about 5 x 10/sup -4/ g-glass/m/sup 2/ day initially, decreasing to 5 x 10/sup -6/ g-glass/m/sup 2/ day after 420 days of leaching. The leach rates had not leveled off by the end of the experiment and were, in general, continuing to decrease. From the activities in the leachate solutions, we determined the percent of the pre-leach activity leached from the melt glasses during the experiment. Only /sup 124/Sb, in one fast flow-rate channel of glass No. 2, exceeded 3% of the initial activity leached. The majority of the samples released less than 1% of the pre-leach activity for a given radionuclide. The percent activity released from the samples leached at the fast and slow flow rates were nearly equal
Recommended from our members
Environmental report 1994. Volume No. 2
This volume 2 of the Lawrence Livermore National Laboratory`s (LLNL`s) annual Environmental Report 1994 is a detailed data report that provides individual data points, where applicable, along with some summary data and more detailed accounts of sample collection and analytical methods. Six chapters have information on monitoring of air, surface water, groundwater, soil and sediment, vegetation and foodstuffs, and environmental radiation; two other chapters cover compliance sel-monitoring and quality assurance