High efficiency thermionic converter studies

The objective is to improve thermionic converter performance by means of reduced interelectrode losses, greater emitter capabilities, and lower collector work functions until the converter performance level is suitable for out-of-core space reactors and radioisotope generators. Electrode screening experiments have identified several promising collector materials. Back emission work function measurements of a ZnO collector in a thermionic diode have given values less than 1.3 eV. Diode tests were conducted over the range of temperatures of interest for space power applications. Enhanced mode converter experiments have included triodes operated in both the surface ionization and plasmatron modes. Pulsed triodes were studied as a function of pulse length, pulse potential, inert gas fill pressure, cesium pressure, spacing, emitter temperature and collector temperature. Current amplifications (i.e., mean output current/mean grid current) of several hundred were observed up to output current densities of one amp/sq cm. These data correspond to an equivalent arc drop less than 0.1 eV

Measurements at low energies of the polarization-transfer coefficient Kyy' for the reaction 3H(p,n)3He at 0 degrees

Measurements of the transverse polarization coefficient Kyy' for the reaction 3H(p,n)3He are reported for outgoing neutron energies of 1.94, 5.21, and 5.81 MeV. This reaction is important both as a source of polarized neutrons for nuclear physics experiments, and as a test of theoretical descriptions of the nuclear four-body system. Comparison is made to previous measurements, confirming the 3H(p,n)3He reaction can be used as a polarized neutron source with the polarization known to an accuracy of approximately 5%. Comparison to R-matrix theory suggests that the sign of the 3F3 phase-shift parameter is incorrect. Changing the sign of this parameter dramatically improves the agreement between theory and experiment.Comment: 12 pages, RevTeX, 5 eps figures, submitted to Phys. Rev.

High efficiency thermionic converter studies

Research in thermionic energy conversion technology is reported. The objectives were to produce converters suitable for use in out of core space reactors, radioisotope generators, and solar satellites. The development of emitter electrodes that operate at low cesium pressure, stable low work function collector electrodes, and more efficient means of space charge neutralization were investigated to improve thermionic converter performance. Potential improvements in collector properties were noted with evaporated thin film barium oxide coatings. Experiments with cesium carbonate suggest this substance may provide optimum combinations of cesium and oxygen for thermionic conversion

Fixed-dose combination therapy for the prevention of cardiovascular disease.

This is the protocol for a review and there is no abstract. The objectives are as follows: To determine the effectiveness of fixed-dose combination therapy on optimising CVD risk factors and reducing CVD fatal and non-fatal events for both primary and secondary prevention of CVD. Details of CVD events and risk factors included are listed in the methods. We will also determine any adverse events associated with taking fixed-dose combination therapy. This will include studies conducted in both developed and developing regions of the world

UCN Upscattering rates in a molecular deuterium crystal

A calculation of ultra-cold neutron (UCN) upscattering rates in molecular deuterium solids has been carried out, taking into account intra-molecular exictations and phonons. The different moelcular species ortho-D2 (with even rotational quantum number J) and para-D2 (with odd J) exhibit significantly different UCN-phonon annihilation cross-sections. Para- to ortho-D2 conversion, furthermore, couples UCN to an energy bath of excited rotational states without mediating phonons. This anomalous upscattering mechanism restricts the UCN lifetime to 4.6 msec in a normal-D2 solid with 33% para content.Comment: 3 pages, one figur

Coal liquefaction process streams characterization and evaluation: Investigation of the forms of sulfur in five Wilsonville resid samples by XAFS and moessbauer spectroscopy

This study demonstrated the feasibility of using XAFS and Moessbauer spectroscopy for the examination of distillation resid materials derived from direct coal liquefaction. The least-squares analysis of the XANES region of the K-shell XAFS spectra was shown to be technique which can be used to determine the sulfur forms in coal liquefaction-derived resid samples. The large amount of pyrrhotite in the resid samples (71 to 99% {plus_minus}10% of the total sulfur) interfered with the precise quantitative analysis of the organic sulfur. However, a spectral subtraction routine was successfully used to provide semi-quantitative results for sulfur species other than the pyrrhotite. Moessbauer spectroscopy, considered a more accurate method than XAFS for the quantitative analysis of inorganic iron-sulfur species (pyrite, pyrrhotite, iron sulfates), was successfully used to speciate these materials in the coal liquefaction resids. Further application of XAFS and Moessbauer spectroscopy as process development tools appears justified by these results

High-Sensitivity Measurement of 3He-4He Isotopic Ratios for Ultracold Neutron Experiments

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of 3He to 4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10e-14 level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of 3He/4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.Comment: 11 pages, 10 figure

Adapting SAM for CDF

The CDF and D0 experiments probe the high-energy frontier and as they do so have accumulated hundreds of Terabytes of data on the way to petabytes of data over the next two years. The experiments have made a commitment to use the developing Grid based on the SAM system to handle these data. The D0 SAM has been extended for use in CDF as common patterns of design emerged to meet the similar requirements of these experiments. The process by which the merger was achieved is explained with particular emphasis on lessons learned concerning the database design patterns plus realization of the use cases.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 4 pages, pdf format, TUAT00