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Meyer, M.

Publications and source records attributed to Meyer, M..

31 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Comprehensive geoneutrino analysis with Borexino

This paper presents a comprehensive geoneutrino measurement using the Borexino detector, located at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The analysis is the result of 3262.74 days of data between December 2007 and April 2019. The paper describes improved analysis techniques and optimized data selection, which includes enlarged fiducial volume and sophisticated cosmogenic veto. The reported exposure of ( 1.29 ± 0.05 ) × 10 32 protons × year represents an increase by a factor of two over a previous Borexino analysis reported in 2015. By observing 52.6 - 8.6 + 9.4 ( stat ) - 2.1 + 2.7 ( sys ) geoneutrinos (68% interval) from U 238 and Th 232 , a geoneutrino signal of 47.0 - 7.7 + 8.4 ( stat ) - 1.9 + 2.4 ( sys ) TNU with - 17.2 + 18.3 % total precision was obtained. This result assumes the same Th/U mass ratio as found in chondritic CI meteorites but compatible results were found when contributions from U 238 and Th 232 were both fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a geoneutrino signal from the mantle is excluded at a 99.0% C.L. when exploiting detailed knowledge of the local crust near the experimental site. Measured mantle signal of 21.2 - 9.0 + 9.5 ( stat ) - 0.9 + 1.1 ( sys ) TNU corresponds to the production of a radiogenic heat of 24.6 - 10.4 + 11.1 TW (68% interval) from U 238 and Th 232 in the mantle. Assuming 18% contribution of K 40 in the mantle and 8.1 - 1.4 + 1.9 TW of total radiogenic heat of the lithosphere, the Borexino estimate of the total radiogenic heat of the Earth is 38.2 - 12.7 + 13.6 TW , which corresponds to the convective Urey ratio of 0.78 - 0.28 + 0.41 . These values are compatible with different geological predictions, however there is a ~ 2.4 σ tension with those Earth models which predict the lowest concentration of heat-producing elements in the mantle. In addition, by constraining the number of expected reactor antineutrino events, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW is excluded at 95% C.L. Particular attention is given to the description of all analysis details which should be of interest for the next generation of geoneutrino measurements using liquid scintillator detectors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

The Monte Carlo simulation of the Borexino detector

Borexino is a 300 ton sub-MeV liquid scintillator solar neutrino detector which has been running at the Laboratori Nazionali del Gran Sasso (Italy) since 2007. Thanks to its unprecedented radio-purity, it was able to measure the flux of 7 Be, 8 B, pp, and pep solar neutrinos and to detect geo-neutrinos. A reliable simulation of the detector is an invaluable tool for all Borexino physics analyses. The simulation accounts for the energy loss of particles in all the detector components, the generation of the scintillation photons, their propagation within the liquid scintillator volume, and a detailed simulation of the electronics chain. A novel efficient method for simulating the external background which survives the Borexino passive shield was developed. This technique allows to reliably predict the effect of the contamination in the peripheral construction materials. The techniques developed to simulate the Borexino detector and their level of refinement are of possible interest to the neutrino and dark matter communities, especially for current and future large-volume liquid scintillator experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Identifying TeV Source Candidates among Fermi -LAT Unclassified Blazars

Blazars, in particular the subclass of high synchrotron peaked active galactic nuclei are among the main targets for the present generation of Imaging Atmospheric Cerenkov Telescopes (IACTs), and they will remain of great importance for very high-energy γ-ray science in the era of the Cerenkov Telescope Array (CTA). Observations by IACTs, which have relatively small fields of view (~few degrees), are limited by viewing conditions; therefore, it is important to select the most promising targets to increase the number of detections. The aim of this paper is to search for unclassified blazars among known γ-ray sources from the Fermi Large Area Telescope (LAT) third source catalog that are likely detectable with IACTs or CTA. We use an artificial neural network algorithm and updated analysis of Fermi-LAT data. We found 80 γ-ray source candidates, and for the highest-confidence candidates, we calculate their potential detectability with IACTs and CTA based on an extrapolation of their energy spectra. Follow-up observations of our source candidates could significantly increase the current TeV source population sample and ultimately confirm the efficiency of our algorithm to select TeV sources.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2013

A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

Mars↗
NASA NTRS1999

Calbindin-D(28k) controls [Ca(2+)](i) and insulin release. Evidence obtained from calbindin-d(28k) knockout mice and beta cell lines

The role of the calcium-binding protein, calbindin-D(28k) in potassium/depolarization-stimulated increases in the cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and insulin release was investigated in pancreatic islets from calbindin-D(28k) nullmutant mice (knockouts; KO) or wild type mice and beta cell lines stably transfected and overexpressing calbindin. Using single islets from KO mice and stimulation with 45 mM KCl, the peak of [Ca(2+)](i) was 3.5-fold greater in islets from KO mice compared with wild type islets (p < 0.01) and [Ca(2+)](i) remained higher during the plateau phase. In addition to the increase in [Ca(2+)](i) in response to KCl there was also a significant increase in insulin release in islets isolated from KO mice. Evidence for modulation by calbindin of [Ca(2+)](i) and insulin release was also noted using beta cell lines. Rat calbindin was stably expressed in betaTC-3 and betaHC-13 cells. In response to depolarizing concentrations of K(+), insulin release was decreased by 45-47% in calbindin expressing betaTC cells and was decreased by 70-80% in calbindin expressing betaHC cells compared with insulin release from vector transfected betaTC or betaHC cells (p < 0.01). In addition, the K(+)-stimulated intracellular calcium peak was markedly inhibited in calbindin expressing betaHC cells compared with vector transfected cells (225 nM versus 1,100 nM, respectively). Buffering of the depolarization-induced rise in [Ca(2+)](i) was also observed in calbindin expressing betaTC cells. In summary, our findings, using both isolated islets from calbindin-D(28k) KO mice and beta cell lines, establish a role for calbindin in the modulation of depolarization-stimulated insulin release and suggest that calbindin can control the rate of insulin release via regulation of [Ca(2+)](i).

Non-NASA Center↗
NASA NTRS1995

A preliminary comparison of two perennially ice-covered lakes in Antarctica: Analogs of past martian lacustrine environments

Perennially ice-covered lakes in the Antarctic have been suggested as analogs to lakes which may have existed on the surface of Mars 3.5 billion years ago. During the 1991-1992 austral summer, a joint Russian/American research effort was directed at studies of ice-covered lakes in the Bunger Hills Oasis, Antarctica (66 deg S, 100 deg E). The primary objective of the expedition was to investigate this ice-free area for features analogous to ancient martian environments that may have been capable of supporting life and to compare the ice-covered lakes of the Bunger Hills with those in the McMurdo Dry Valleys of southern Victoria Land (77 deg S, 166 deg E) as part of the continuing studies of Antarctic-Mars analogs.

Andersen, D. T.↗
NASA NTRS1992

Engine system assessment study using Martian propellants

A feasibility study was performed that identified and characterized promising chemical propulsion system designs that utilize two or more of the propellant combinations: LOX/H2, LOX/CH4 and LOX/CO. The engine systems examined focused on the usage of common subsystem/component hardware where feasible. From the evaluation baseline employed, tripropellant MTV LOX cooled and bipropellant LEV and MEV engine systems are identified.

Pelaccio, D.↗
NASA NTRS1991

Effects of 10 days 6 degrees head-down tilt on the responses to fluid loading and lower body negative pressure

In an international collaborative project six normal male subjects were studied before, during and after 10 days 6 degrees HDT. Fluid intake was controlled at 40 ml/(kgbw day). Urine volume and body weight were determined daily. Fluid loading and LBNP were performed in all three phases of the study. Body weight diminished by 2.6% because of fluid loss. Blood volume diminished by 13%. The responses to fluid loading were similar in the three phases of the study. Sixty minutes after end of infusion only 5.5% of the infused saline remained in the intravascular compartment. Excess interstitial fluid was eliminated in the next 24 hs but a negative balance was recorded also in the following day. The compliance of the lower limbs expressed as the rate of limb volume change/unit LBNP change was increased at the end of the HDT phase and during the post HDT phase. The set point of intravascular volume was defended, as shown by the response to FL. HDT increased the compliance of the lower limbs.

Non-NASA Center↗
NASA NTRS1977

A field evaluation of small-scale forest resource aerial photography

An earlier study under somewhat clinical laboratory conditions has suggested the possibility of using smaller scales of forest photography without serious information loss. The present paper subjects this idea to a rigorous field test by a number of experienced user-cooperators. Various combinations of summer black-and-white infrared and color infrared aerial photography at scales of 1:15,840, 1:24,000, 1:31,680, and 1:80,000 were taken over forested portions of Minnesota. Major conclusions are that 1:15,840 is the preferred working photo scale, and that instead of 1:15,840 a scale of 1:20,000 is considered an acceptable substitute.

Marshall, J.↗