4,787 research outputs found
Lithium and potassium heat pipes for thermionic converters
A prototypic heat pipe system for an out-of-core thermionic reactor was built and tested. The emitter of the concentric thermionic converter consists of the condenser of a tungsten heat pipe utilizing a lithium working fluid. The evaporator section of the emitter heat pipe is radiation heated to simulate the thermal input from the nuclear reactor. The emitter heat pipe thermal transport is matched to the thermionic converter input requirement. The collector heat pipe of niobium, 1% zirconium alloy uses potassium as the working fluid. The thermionic collector is coupled to the heat pipe by a tapered conical joint designed to minimize the temperature drop. The collector heat flux matches the design requirements of the thermionic converter
Stability investigation of thermally induced flow oscillations in cryogenic heat exchangers Final report
Analytic model of thermal flow oscillations in heat exchangers for supercritical fluid
The magnitude and origin of groundwater discharge to Eastern U.S. and Gulf of Mexico coastal waters
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 10,396â10,406, doi:10.1002/2017GL075238.Fresh groundwater discharge to coastal environments contributes to the physical and chemical conditions of coastal waters, but the role of coastal groundwater at regional to continental scales remains poorly defined due to diverse hydrologic conditions and the difficulty of tracking coastal groundwater flow paths through heterogeneous subsurface materials. We use three-dimensional groundwater flow models for the first time to calculate the magnitude and source areas of groundwater discharge from unconfined aquifers to coastal waterbodies along the entire eastern U.S. We find that 27.1 km3/yr (22.8â30.5 km3/yr) of groundwater directly enters eastern U.S. and Gulf of Mexico coastal waters. The contributing recharge areas comprised ~175,000 km2 of U.S. land area, extending several kilometers inland. This result provides new information on the land area that can supply natural and anthropogenic constituents to coastal waters via groundwater discharge, thereby defining the subterranean domain potentially affecting coastal chemical budgets and ecosystem processes.National Science Foundation Grant Number: EPS-1208909;
NASA Carbon Cycle Science Grant Number: NNX14AM37G2018-04-2
Gamma-Ray Spectral States of Galactic Black Hole Candidates
OSSE has observed seven transient black hole candidates: GRO J0422+32,
GX339-4, GRS 1716-249, GRS 1009-45, 4U 1543-47, GRO J1655-40, and GRS 1915+105.
Two gamma-ray spectral states are evident and, based on a limited number of
contemporaneous X-ray and gamma-ray observations, these states appear to be
correlated with X-ray states. The former three objects show hard spectra below
100 keV (photon number indices Gamma < 2) that are exponentially cut off with
folding energy ~100 keV, a spectral form that is consistent with thermal
Comptonization. This "breaking gamma-ray state" is the high-energy extension of
the X-ray low, hard state. In this state, the majority of the luminosity is
above the X-ray band, carried by photons of energy ~100 keV. The latter four
objects exhibit a "power-law gamma-ray state" with a relatively soft spectral
index (Gamma ~ 2.5-3) and no evidence for a spectral break. For GRO J1655-40,
the lower limit on the break energy is 690 keV. GRS 1716-249 exhibits both
spectral states, with the power-law state having significantly lower gamma-ray
luminosity. The power-law gamma-ray state is associated with the presence of a
strong ultrasoft X-ray excess (kT ~ 1 keV), the signature of the X-ray high,
soft (or perhaps very high) state. The physical process responsible for the
unbroken power law is not well understood, although the spectra are consistent
with bulk-motion Comptonization in the convergent accretion flow.Comment: 27 pages, 3 figures, uses aaspp.sty and psfig.st
Operation and performance of the OSSE instrument
The Oriented Scintillation Spectrometer Experiment (OSSE) on the Arthur Holly Compton Gamma Ray Observatory is described. An overview of the operation and control of the instrument is given, together with a discussion of typical observing strategies used with OSSE and basic data types produced by the instrument. Some performance measures for the instrument are presented that were obtained from pre-launch and in-flight data. These include observing statistics, continuum and line sensitivity, and detector effective area and gain stability
Cumulative reproductive costs on current reproduction in a wild polytocous mammal
Funding Information MarieâCurie Fellowship UCLA Rocky Mountain Biological Laboratory Research Fellowship NSF. Grant Numbers: IDBRâ0754247, DEBâ1119660, DBI 0242960, DBI 0731346 Natural Environment Research Council. Grant Number: NE/L50175X/1 National Geographic SocietyPeer reviewedPublisher PD
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