12,317 research outputs found
Quasi-modal vibration control by means of active control bearings
This paper investigates a design method of an active control bearing system with only velocity feedback. The study provides a new quasi-modal control method for a control system design of an active control bearing system in which feedback coefficients are determined on the basis of a modal analysis. Although the number of sensors and actuators is small, this quasi-modal control method produces a control effect close to an ideal modal control
Magnetic bearings for free-piston Stirling engines
The feasibility and efficacy of applying magnetic bearings to free-piston Stirling-cycle power conversion machinery currently being developed for long-term space missions are assessed. The study was performed for a 50-kWe Reference Stirling Space Power Converter (RSSPC) which currently uses hydrostatic gas bearings to support the reciprocating displacer and power piston assemblies. Active magnetic bearings of the attractive electromagnetic type are feasible for the RSSPC power piston. Magnetic support of the displacer assembly would require unacceptable changes to the design of the current RSSPC. However, magnetic suspension of both displacer and power piston is feasible for a relative-displacer version of the RSSPC. Magnetic suspension of the RSSPC power piston can potentially increase overall efficiency by 0.5 to 1 percent (0.1 to 0.3 efficiency points). Magnetic bearings will also overcome several operational concerns associated with hydrostatic gas bearing systems. These advantages, however, are accompanied by a 5 percent increase in specific mass of the RSSPC
Systems analysis of electricity production from coal using fuel cells
Gasifiers, heat transfer, gas stability, quench, water-gas shift reaction, reforming-methanation, other catalytic reactions, compressors and expanders, acid-gas removal, the fuel cell, and catalytic combustors are described. System pressure drops, efficiency of rotating power equipment, heat exchangers, chemical reactions, steam systems, and the fuel cell subsystems are discussed
The Organic Research Centre - Elm Farm:Bulletin 87
Bulletin 87 with coverage of Avian Influenza H5N1 in Suffolk,commentary on Biofuels, a paper on the organic "transition to sustainable resilience",paper on participatory approach to agronomy trials,update on evolutionary breeding of wheat project,article on formation of new growers alliance in UK
Myosin VIIA is required for aminoglycoside accumulation in cochlear hair cells.
Myosin VIIA is expressed by sensory hair cells and has a primary structure predicting a role in membrane trafficking and turnover, processes that may underlie the susceptibility of hair cells to aminoglycoside antibiotics. [3H]Gentamicin accumulation and the effects of aminoglycosides were therefore examined in cochlear cultures of mice with different missense mutations in the myosin VIIA gene, Myo7a, to see whether myosin VIIA plays a role in aminoglycoside ototoxicity. Hair cells from homozygous mutant Myo7a(sh1) mice, with a mutation in a non-conserved region of the myosin VIIA head, respond rapidly to aminoglycoside treatment and accumulate high levels of gentamicin. Hair cells from homozygous mutant Myo7a(6J) mice, with a mutation at a highly conserved residue close to the ATP binding site of the myosin VIIA head, do not accumulate [3H]gentamicin and are protected from aminoglycoside ototoxicity. Hair cells from heterozygotes of both alleles accumulate [3H]gentamicin and respond to aminoglycosides. Although aminoglycoside uptake is thought to be via apical surface-associated endocytosis, coated pit numbers on the apical membrane of heterozygous and homozygous Myo7a(6J) hair cells are similar. Pulse-chase experiments with cationic ferritin confirm that the apical endocytotic pathway is functional in homozygous Myo7a(6J) hair cells. Transduction currents can be recorded from both heterozygous and homozygous Myo7a(6J) hair cells, suggesting it is unlikely that the drug enters via diffusion through the mechanotransducer channel. The results show that myosin VIIA is required for aminoglycoside accumulation in hair cells. Myosin VIIA may transport a putative aminoglycoside receptor to the hair cell surface, indirectly translocate it to sites of membrane retrieval, or retain it in the endocytotic pathway
Calculation of the nucleon axial charge in lattice QCD
Protons and neutrons have a rich structure in terms of their constituents,
the quarks and gluons. Understanding this structure requires solving Quantum
Chromodynamics (QCD). However QCD is extremely complicated, so we must
numerically solve the equations of QCD using a method known as lattice QCD.
Here we describe a typical lattice QCD calculation by examining our recent
computation of the nucleon axial charge.Comment: Prepared for Scientific Discovery through Advanced Computing (SciDAC
2006), Denver, Colorado, June 25-29 200
Nucleon structure in the chiral regime with domain wall fermions on an improved staggered sea
Moments of unpolarized, helicity, and transversity distributions,
electromagnetic form factors, and generalized form factors of the nucleon are
presented from a preliminary analysis of lattice results using pion masses down
to 359 MeV. The twist two matrix elements are calculated using a mixed action
of domain wall valence quarks and asqtad staggered sea quarks and are
renormalized perturbatively. Several observables are extrapolated to the
physical limit using chiral perturbation theory. Results are compared with
experimental moments of quark distributions and electromagnetic form factors
and phenomenologically determined generalized form factors, and the
implications on the transverse structure and spin content of the nucleon are
discussed.Comment: Talks of J.W. Negele and D.B. Renner at Lattice 200
Non-local quantum correlations and detection processes in QFT
Quantum detection processes in QFT must play a key role in the description of
quantum field correlations, such as the appearance of entanglement, and of
causal effects. We consider the detection in the case of a simple QFT model
with a suitable interaction to exact treatment, consisting of a quantum scalar
field coupled linearly to a classical scalar source. We then evaluate the
response function to the field quanta of two-level point-like quantum model
detectors, and analyze the effects of the approximation adopted in standard
detection theory. We show that the use of the RWA, that characterizes the
Glauber detection model, leads in the detector response to non-local terms
corresponding to an instantaneously spreading of source effects over the whole
space. Other detector models, obtained with non-standard or the no-application
of RWA, give instead local responses to field quanta, apart from source
independent vacuum contribution linked to preexisting correlations of
zero-point field.Comment: 23 page
Phonons and Colossal Thermal Expansion Behavior of Ag3Co(CN)6 and Ag3Fe(CN)6
Recently colossal positive volume thermal expansion has been found in the
framework compounds Ag3Co(CN)6 and Ag3Fe(CN)6. Phonon spectra have been
measured using the inelastic neutron scattering technique as a function of
temperature and pressure. The data has been analyzed using ab-initio
calculations. We find that the bonding is very similar in both compounds. At
ambient pressure modes in the intermediate frequency part of the vibrational
spectra in the Co compound are shifted to slightly higher energies as compared
to the Fe compound. The temperature dependence of the phonon spectra gives
evidence for large explicit anharmonic contribution to the total anharmonicity
for low-energy modes below 5 meV. We found that modes are mainly affected by
the change in the size of unit cell, which in turn changes the bond lengths and
vibrational frequencies. Thermal expansion has been calculated via the volume
dependence of phonon spectra. Our analysis indicates that Ag phonon modes in
the energy range from 2 to 5 meV are strongly anharmonic and major contributors
to thermal expansion in both compounds. The application of pressure hardens the
low-energy part of the phonon spectra involving Ag vibrations and confirms the
highly anharmonic nature of these modes.Comment: 19 pages, 14 figures and one tabl
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