248 research outputs found
Metal hydride hydrogen compressors: A review
AbstractMetal hydride (MH) thermal sorption compression is an efficient and reliable method allowing a conversion of energy from heat into a compressed hydrogen gas. The most important component of such a thermal engine – the metal hydride material itself – should possess several material features in order to achieve an efficient performance in the hydrogen compression. Apart from the hydrogen storage characteristics important for every solid H storage material (e.g. gravimetric and volumetric efficiency of H storage, hydrogen sorption kinetics and effective thermal conductivity), the thermodynamics of the metal–hydrogen systems is of primary importance resulting in a temperature dependence of the absorption/desorption pressures). Several specific features should be optimised to govern the performance of the MH-compressors including synchronisation of the pressure plateaus for multi-stage compressors, reduction of slope of the isotherms and hysteresis, increase of cycling stability and life time, together with challenges in system design associated with volume expansion of the metal matrix during the hydrogenation.The present review summarises numerous papers and patent literature dealing with MH hydrogen compression technology. The review considers (a) fundamental aspects of materials development with a focus on structure and phase equilibria in the metal–hydrogen systems suitable for the hydrogen compression; and (b) applied aspects, including their consideration from the applied thermodynamic viewpoint, system design features and performances of the metal hydride compressors and major applications
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Benefits of rapid solidification processing of modified LaNi{sub 5} alloys by high pressure gas atomization for battery applications
A high pressure gas atomization approach to rapid solidification has been employed to investigate simplified processing of Sn modified LaNi{sub 5} powders that can be used for advanced Ni/metal hydride (Ni/MH) batteries. The current industrial practice involves casting large ingots followed by annealing and grinding and utilizes a complex and costly alloy design. This investigation is an attempt to produce powders for battery cathode fabrication that can be used in an as-atomized condition without annealing or grinding. Both Ar and He atomization gas were tried to investigate rapid solidification effects. Sn alloy additions were tested to promote subambient pressure absorption/desorption of hydrogen at ambient temperature. The resulting fine, spherical powders were subject to microstructural analysis, hydrogen gas cycling, and annealing experiments to evaluate suitability for Ni/MH battery applications. The results demonstrate that a brief anneal is required to homogenize the as-solidified microstructure of both Ar and He atomized powders and to achieve a suitable hydrogen absorption behavior. The Sn addition also appears to suppress cracking during hydrogen gas phase cycling in particles smaller than about 25 {micro}m. These results suggest that direct powder processing of a LaNi{sub 5{minus}x}Sn{sub x} alloy has potential application in rechargeable Ni/MH batteries
A Current Mode Detector Array for Gamma-Ray Asymmetry Measurements
We have built a CsI(Tl) gamma-ray detector array for the NPDGamma experiment
to search for a small parity-violating directional asymmetry in the angular
distribution of 2.2 MeV gamma-rays from the capture of polarized cold neutrons
by protons with a sensitivity of several ppb. The weak pion-nucleon coupling
constant can be determined from this asymmetry. The small size of the asymmetry
requires a high cold neutron flux, control of systematic errors at the ppb
level, and the use of current mode gamma-ray detection with vacuum photo diodes
and low-noise solid-state preamplifiers. The average detector photoelectron
yield was determined to be 1300 photoelectrons per MeV. The RMS width seen in
the measurement is therefore dominated by the fluctuations in the number of
gamma rays absorbed in the detector (counting statistics) rather than the
intrinsic detector noise. The detectors were tested for noise performance,
sensitivity to magnetic fields, pedestal stability and cosmic background. False
asymmetries due to gain changes and electronic pickup in the detector system
were measured to be consistent with zero to an accuracy of in a few
hours. We report on the design, operating criteria, and the results of
measurements performed to test the detector array.Comment: 33 pages, 20 figures, 2 table
Precision Measurement of PArity Violation in Polarized Cold Neutron Capture on the Proton: the NPDGamma Experiment
The NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE) is
dedicated to measure with high precision the parity violating asymmetry in the
emission after capture of spin polarized cold neutrons in
para-hydrogen. The measurement will determine unambiguously the weak
pion-nucleon-nucleon () coupling constant {\it f}Comment: Proceedings of the PANIC'05 Conference, Santa Fe, NM, USA, October
24-28, 2005, 3 pages, 2 figure
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Transpacific Transport of Ozone Pollution and the Effect of Recent Asian Emission Increases on Air Quality in North America: An Integrated Analysis Using Satellite, Aircraft, Ozonesonde, and Surface Observations
We use an ensemble of aircraft, satellite, sonde, and surface observations for April–May 2006 (NASA/INTEX-B aircraft campaign) to better understand the mechanisms for transpacific ozone pollution and its implications for North American air quality. The observations are interpreted with a global 3-D chemical transport model (GEOS-Chem). OMI NO2 satellite observations constrain Asian anthropogenic NOx emissions and indicate a factor of 2 increase from 2000 to 2006 in China. Satellite observations of CO from AIRS and TES indicate two major events of Asian transpacific pollution during INTEX-B. Correlation between TES CO and ozone observations shows evidence for transpacific ozone pollution. The semi-permanent Pacific High and Aleutian Low cause splitting of transpacific pollution plumes over the Northeast Pacific. The northern branch circulates around the Aleutian Low and has little impact on North America. The southern branch circulates around the Pacific High and some of that air impacts western North America. Both aircraft measurements and model results show sustained ozone production driven by peroxyacetylnitrate (PAN) decomposition in the southern branch, roughly doubling the transpacific influence from ozone produced in the Asian boundary layer. Model simulation of ozone observations at Mt. Bachelor Observatory in Oregon (2.7 km altitude) indicates a mean Asian ozone pollution contribution of 9±3 ppbv to the mean observed concentration of 54 ppbv, reflecting mostly an enhancement in background ozone rather than episodic Asian plumes. Asian pollution enhanced surface ozone concentrations by 5–7 ppbv over western North America in spring 2006. The 2000–2006 rise in Asian anthropogenic emissions increased this influence by 1–2 ppbv.Earth and Planetary SciencesEngineering and Applied Science
Influência de práticas culturais e da resistência genética na intensidade do cancro da haste e produção de soja no Cerrado
Os efeitos de práticas culturais e resistência genética na intensidade ao cancro-da-haste da soja (Diaporthe phaseolorum f.sp. meridionalis - Dpm) foram examinados na safra 1995-96 em áreas de produção comercial, que haviam sido severamente atacadas na safra anterior (1994-95). Um experimento investigou os efeitos de cultivo mínimo (MT) e do plantio direto (NT) no desenvolvimento da doença e produtividade das cultivares FT-Cristalina e FT-Seriema. Em outro experimento, semeado em plantio direto, estudou-se o efeito da densidade de plantas (8, 15, 21 e 36 plantas/m) no desenvolvimento da doença e produtividade das cvs. FT-Cristalina (suscetivel), FT- 101 (moderadamente resistente) e FT-104 (resistente). Incidência e severidade da doença foram menores em NT do que em MT. A produtividade aumentou no sistema NT (23% para ‘FT-Cristalina’ e 14% para ‘FT-Seriema’), comparada com as produtividades em MT. As curvas de progresso da doença foram melhor descritas pelos mo- delos de Gompertz e logístico. A severidade do cancro aumentou pro- porcionalmente ao aumento das densidades de plantio nas cvs. suscetível e moderadamente resistente. No final do ciclo, 100% das plantas da cv. FT-Cristalina estavam infetadas por Dpm, em todas as densidades de plantio. Níveis intermediários de doença foram observa- dos na cv. FT-101, enquanto apenas níveis muito baixos de doença ocorreram na cv. FT-104. Estabeleceu-se uma correlação negativa entre severidade de cancro-da-haste e produção. Algumas das práticas estudadas demonstraram potential para aplicação direta no controle da doença, e poderiam ser combinadas considerando-se seus efeitos aditivos.Field experiments were conducted in the 1995-96 soybean (Glycine max) growing season to evaluate the effects of cultural practices and host genetic resistance on the intensity of soybean stem canker, caused by Diaporthe phaseolorum f.sp. meridionalis (Dpm). Experiments were conducted in a commercial field severely infected in the previous (1994-95) season. In one study, minimum tillage (MT) and no-tillage (NT) cropping systems were investigated for their effects on disease development and on plant yields in cvs. FT- Cristalina (susceptible) and FT-Seriema (moderately resistant). Another study evaluated the effects of plant densities (8, 15, 21 and 36 plants/m) on disease development in cvs. FT-Cristalina, FT-101 (moderately resistant) and FT-104 (resistant). Disease incidence and severity were consistently lower in NT than in MT, and plant yields were increased by 23% and 14% in the NT system for the susceptible and moderately resistant cultivars, respectively, compared to the yields in the MT system. The Gompertz and Logistic models described well the disease progress curves in all situations. For both susceptible and moderately resistant cultivars, disease severity increased proportionately to the increase in plant densities. At the end of the season, 100% of the plants of cv. FT-Cristalina were infected by Dpm, at all plant densities. Disease levels on cv. FT-101 were intermediate while only very low disease levels were recorded on cv. FT-104. There was a consistent negative correlation between stem canker severity and yield. Some practices demonstrated potential for direct application in disease control, and could be combined considering their additive effects
Cryogenic characterization of the Planck sorption cooler system flight model
This paper is part of the Prelaunch status LFI papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-0221
Two continuous closed-cycle hydrogen Joule-Thomson (J-T) sorption coolers
have been fabricated and assembled by the Jet Propulsion Laboratory (JPL) for
the European Space Agency (ESA) Planck mission. Each refrigerator has been
designed to provide a total of ~ 1W of cooling power at two instrument
interfaces: they directly cool the Planck Low Frequency Instrument (LFI) around
20K while providing a pre-cooling stage for a 4 K J-T mechanical refrigerator
for the High Frequency Instrument (HFI). After sub-system level validation at
JPL, the cryocoolers have been delivered to ESA in 2005. In this paper we
present the results of the cryogenic qualification and test campaigns of the
Nominal Unit on the flight model spacecraft performed at the CSL (Centre
Spatial de Liege) facilities in 2008. Test results in terms of input power,
cooling power, temperature, and temperature fluctuations over the flight
allowable ranges for these interfaces are reported and analyzed with respect to
mission requirements.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Journal of Instrumentation. IOP Publishing Ltd is
not responsible for any errors or omissions in this version of the manuscript
or any version derived from it. The definitive publisher authenticated
version is available online at 10.1088/1748-0221/4/12/T1201
Survey of nucleon electromagnetic form factors
A dressed-quark core contribution to nucleon electromagnetic form factors is
calculated. It is defined by the solution of a Poincare' covariant Faddeev
equation in which dressed-quarks provide the elementary degree of freedom and
correlations between them are expressed via diquarks. The nucleon-photon vertex
involves a single parameter; i.e., a diquark charge radius. It is argued to be
commensurate with the pion's charge radius. A comprehensive analysis and
explanation of the form factors is built upon this foundation. A particular
feature of the study is a separation of form factor contributions into those
from different diagram types and correlation sectors, and subsequently a
flavour separation for each of these. Amongst the extensive body of results
that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of
axial-vector quark-quark correlations; and for both the neutron and proton the
ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice
Ab initio Quantum and ab initio Molecular Dynamics of the Dissociative Adsorption of Hydrogen on Pd(100)
The dissociative adsorption of hydrogen on Pd(100) has been studied by ab
initio quantum dynamics and ab initio molecular dynamics calculations. Treating
all hydrogen degrees of freedom as dynamical coordinates implies a high
dimensionality and requires statistical averages over thousands of
trajectories. An efficient and accurate treatment of such extensive statistics
is achieved in two steps: In a first step we evaluate the ab initio potential
energy surface (PES) and determine an analytical representation. Then, in an
independent second step dynamical calculations are performed on the analytical
representation of the PES. Thus the dissociation dynamics is investigated
without any crucial assumption except for the Born-Oppenheimer approximation
which is anyhow employed when density-functional theory calculations are
performed. The ab initio molecular dynamics is compared to detailed quantum
dynamical calculations on exactly the same ab initio PES. The occurence of
quantum oscillations in the sticking probability as a function of kinetic
energy is addressed. They turn out to be very sensitive to the symmetry of the
initial conditions. At low kinetic energies sticking is dominated by the
steering effect which is illustrated using classical trajectories. The steering
effects depends on the kinetic energy, but not on the mass of the molecules.
Zero-point effects lead to strong differences between quantum and classical
calculations of the sticking probability. The dependence of the sticking
probability on the angle of incidence is analysed; it is found to be in good
agreement with experimental data. The results show that the determination of
the potential energy surface combined with high-dimensional dynamical
calculations, in which all relevant degrees of freedon are taken into account,
leads to a detailed understanding of the dissociation dynamics of hydrogen at a
transition metal surface.Comment: 15 pages, 9 figures, subm. to Phys. Rev.
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