6,063 research outputs found
Unsteady Diffuser Vane Pressure and Impeller Wake Measurements in a Centrifugal Pump
Unsteady surface pressure measurements on a vaned diffuser of a centrifugal pump, and wake measurement of the flow exiting a centrifugal impeller into a vaneless diffuser are presented. Frequency spectra and ensemble averages are given for the unsteady measurements. Two different impellers were used, the pump impeller of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine) and a two-dimensional impeller. The magnitude of the unsteady total pressure measured in the stationary frame at the impeller exit was found to be of the same order of magnitude as the total pressure rise across the pump. The magnitude of the unsteady diffuser vane pressures was observed to be significantly different on suction and pressure side of the vane, attaining its largest value on the suction side near the leading edge while decreasing along the vane
Comment on piNN Coupling from High Precision np Charge Exchange at 162 MeV
In this updated and expanded version of our delayed Comment we show that the
np backward cross section, as presented by the Uppsala group, is seriously
flawed (more than 25 sd.). The main reason is the incorrect normalization of
the data. We show also that their extrapolation method, used to determine the
charged piNN coupling constant, is a factor of about 10 less accurate than
claimed by Ericson et al. The large extrapolation error makes the determination
of the coupling constant by the Uppsala group totally uninteresting.Comment: 5 pages, latex2e with a4wide.sty. This is an updated and extended
version of the Comment published in Phys. Rev. Letters 81, 5253 (1998
An updated analysis of NN elastic scattering data to 1.6 GeV
An energy-dependent and set of single-energy partial-wave analyses of
elastic scattering data have been completed. The fit to 1.6~GeV has been
supplemented with a low-energy analysis to 400 MeV. Using the low-energy fit,
we study the sensitivity of our analysis to the choice of coupling
constant. We also comment on the possibility of fitting data alone. These
results are compared with those found in the recent Nijmegen analyses. (Figures
may be obtained from the authors upon request.)Comment: 17 pages of text, VPI-CAPS-7/
Rotordynamic Forces on Centrifugal Pump Impellers
The asymmetric flow around an impeller in a volute exerts a force upon the impeller. To study the rotordynamic force on an impeller which is vibrating around its machine axis of rotation, the impeller, mounted on a dynamometer, is made to whirl in a circular orbit within the volute. The measured force is expressed as the sum of a steady radial force and an unsteady force due to the eccentric motion of the impeller. These forces were measured in separate tests on a centrifugal pump with radically increased shroud clearance, a two-dimensional impeller, and an impeller with an inducer, the impeller of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Enginer). In each case, a destabilizing force was observed over a region of positive whirl
Where are the missing members of the baryon antidecuplet?
We analyze what consequences has the observation of exotic pentaquark baryons
on the location of the non-exotic baryons belonging to the antidecuplet. We
suggest that there must be a new nucleon state at 1650-1690 MeV and a new Sigma
baryon at 1760-1810 MeV.Comment: 5 pages, 1 figure. Missing reference adde
Geodynamic and metabolic cycles in the Hadean
International audienceHigh-degree melting of hot dry Hadean mantle at ocean ridges and plumes resulted in a crust about 30km thick, overlain in places by extensive and thick mafic volcanic plateaus. Continental crust, by contrast, was relatively thin and mostly submarine. At constructive and destructive plate boundaries, and above the many mantle plumes, acidic hydrothermal springs at ~400°C contributed Fe and other transition elements as well as P and H2 to the deep ocean made acidulous by dissolved CO2 and minor HCl derived from volcanoes. Away from ocean ridges, submarine hydrothermal fluids were cool (=100°C), alkaline (pH ~10), highly reduced and also H2-rich. Reaction of solvents in this fluid with those in ocean water was catalyzed in a hydrothermal mound, a natural self-restoring flow reactor and fractionation column made up of carbonates and freshly precipitated Fe-Ni sulfide and greenrust pores and bubbles, developed above the alkaline spring. Acetate and the amino acetate glycine were the main products, much of which was eluted to the ocean. Other organic byproducts were retained, concentrated and reacted within the compartments. These compartments comprising the natural hydrothermal reactor consisted partly of greigite (Fe5NiS8). It was from reactions between organic modules confined within these inorganic compartments that the first prokaryotic organism evolved. These acetogenic precursors to the Bacteria diversified and migrated down the mound and into the ocean floor to inaugurate the "deep biosphere". Once there the Bacteria, and the recently differentiated Archaea, were protected from cataclysmic heating events caused by large bolide impacts. Geodynamic forces led to the eventual obduction of the deep biosphere into the photic zone where, initially protected by a thin veneer of sediment, the use of solar energy was mastered and photosynthesis emerged. The further evolution to oxygenic photosynthesis was effected as catalytic [CaMn4+] bearing molecules that otherwise would have been interred in the mineral ranciéite in the shallow marine manganiferous sediments, were sequestered and invaginated within the cyanobacterial precursor where, energized by light, they could oxidize water with greater efficiency. Thus, chemical sediments were required both for the emergence of chemosynthesis and of oxygenic photosynthesis, the two innovations that did most to change the nature of our planet
Model dependence of single-energy fits to pion photoproduction data
Model dependence of multipole analysis has been explored through
energy-dependent and single-energy fits to pion photoproduction data. The MAID
energy-dependent solution has been used as input for an event generator
producing realistic pseudo data. These were fitted using the SAID
parametrization approach to determine single-energy and energy-dependent
solutions over a range of lab photon energies from 200 to 1200 MeV. The
resulting solutions were found to be consistent with the input amplitudes from
MAID. Fits with a -squared per datum of unity or less were generally
achieved. We discuss energy regions where consistent results are expected, and
explore the sensitivity of fits to the number of included single- and
double-polarization observables. The influence of Watson's theorem is examined
in detail.Comment: 12 pages, 8 figure
Baryon Resonance Analysis from SAID
We discuss the analysis of data from piN elastic scattering and single pion
photo- and electroproduction. The main focus is a study of low-lying
non-strange baryon resonances. Here we concentrate on some difficulties
associated with resonance identification, in particular the Roper and higher
P11 states.Comment: 4 pages, 6 figures; Nstar2009 Conf Proceedings; small revisio
Search for anisotropic effects of hcp solid helium on optical lines of cesium impurities
The anisotropic effect of a hcp 4He solid matrix on cesium atoms has been
proposed as a tool to reveal the parity violating anapole moment of its
nucleus. It should also result in splitting the D2 optical excitation line in a
way depending on the light polarization. An experimental investigation has been
set up using oriented hcp helium crystals in which cesium metal grains are
embedded. Atoms are created by laser sputtering from this grains. Optical
absorption spectra of the D2 line have been recorded in the temperature range
of 1.0 to 1.4 K at liquid/solid coexistence pressure by monitoring the
fluorescence on the D2 line at 950 nm. No significant effect of the light
polarization has been found, suggesting a statistically isotropic disordered
solid environment for the cesium atoms.Comment: The original publication will be available at
http://www.springerlink.co
SIT4 protein phosphatase is required for the normal accumulation of SWI4, CLN1, CLN2, and HCS26 RNAs during late G1
In Saccharomyces cerevisiae, the RNA levels of the G1 cyclins CLN1, CLN2, and HCS26 increase dramatically during the late G1 phase of the cell cycle. The SIT4 gene, which encodes a serine/threonine protein phosphatase, is required for the normal accumulation of CLN1, CLN2, and HCS26 RNAs during late G1. This requirement for SIT4 in normal G1 cyclin RNA accumulation is at least partly via SWI4. Strains containing mutations in SIT4 are sensitive to the loss of either CLN2 or CLN3 function. At the nonpermissive temperature, temperature-sensitive sit4 strains are blocked for both bud emergence and DNA synthesis. Heterologous expression of CLN2 in the absence of SIT4 function results in DNA synthesis, but most of the cells are still blocked for bud emergence. Therefore, SIT4 is required for at least two late G1 or G1/S functions: the normal accumulation of G1 cyclin RNAs (which is required for DNA synthesis) and some additional function that is required for bud emergence or cell cycle progression through late G1 or G1/S
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