897 research outputs found
Payload Positioning System for Gravity Gradient Satellite
Many current satellites rely on active control systems to maintain attitude. Passively controlled gravity gradient satellites cost less and are more reliable, but have difficulty accommodating independently moving payloads such as pointable telescopes. To eliminate these difficulties, use of a counter rotating inertia is proposed to negate payload induced transient instabilities. Counter rotating inertias have been used before with limited success due to residual torque/momentum. In gravity gradient satellites, this is absorbed by the gravity gradient restoring torques. A single axis (of a three axis) demonstration gimbal using a bifilar pendulum with PC controlled servo feedback loop and simulated pointable payload was designed and tested. Results without momentum compensation resulted in large excursions and pointing stability problems. Measured displacements using the counter rotating inertia momentum compensation system were within specified and predicted values
Infinite series solutions of the symmetry equation for the dimensional continuous Toda chain
A sequence of solutions to the equation of symmetry for the continuous Toda
chain in dimensions is represented in explicit form. This fact leads to
the supposition that this equation is completely integrable.Comment: 9 pages, latex, no figure
Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments
The strange properties of the nucleon are investigated within the framework
of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying
the symmetry conserving SU(3) quantization. We present the form factors
, and the electric and magnetic strange form
factors incorporating pion and kaon asymptotics. The results
show a fairly good agreement with the recent experimental data from the SAMPLE
and HAPPEX collaborations. We also present predictions for future measurements
including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed.
Accepted for publication in Phys.Rev.
A Perturbative Calculation of the Electromagnetic Form Factors of the Deuteron
Making use of the effective field theory expansion recently developed by the
authors, we compute the electromagnetic form factors of the deuteron
analytically to next-to-leading order (NLO). The computation is rather simple,
and involves calculating several Feynman diagrams, using dimensional
regularization. The results agree well with data and indicate that the
expansion is converging. They do not suffer from any ambiguities arising from
off-shell versus on-shell amplitudes.Comment: 22 pages, 8 figures. Discussion of effective range theory added,
typos correcte
Evidence for short range orbital order in paramagnetic insulating (Al,V)_2O_3
The local structure of (Al_0.06V_0.94)_2O_3 in the paramagnetic insulating
(PI) and antiferromagnetically ordered insulating (AFI) phase has been
investigated using hard and soft x-ray absorption techniques. It is shown that:
1) on a local scale, the symmetry of the vanadium sites in both the PI and the
AFI phase is the same; and 2) the vanadium 3d - oxygen 2p hybridization, as
gauged by the oxygen 1s absorption edge, is the same for both phases, but
distinctly different from the paramagnetic metallic phase of pure V_2O_3. These
findings can be understood in the context of a recently proposed model which
relates the long range monoclinic distortion of the antiferromagnetically
ordered state to orbital ordering, if orbital short range order in the PI phase
is assumed. The measured anisotropy of the x-ray absorption spectra is
discussed in relation to spin-polarized density functional calculations.Comment: 8 pages, 5 figure
Solution of the Crow-Kimura and Eigen models for alphabets of arbitrary size by Schwinger spin coherent states
To represent the evolution of nucleic acid and protein sequence, we express
the parallel and Eigen models for molecular evolution in terms of a functional
integral representation with an -letter alphabet, lifting the two-state,
purine/pyrimidine assumption often made in quasi-species theory. For arbitrary
and a general mutation scheme, we obtain the solution of this model in
terms of a maximum principle. Euler's theorem for homogeneous functions is used
to derive this `thermodynamic' formulation of evolution. The general result for
the parallel model reduces to known results for the purine/pyrimidine
alphabet and the nucleic acid alphabet for the Kimura 3 ST mutation
scheme. Examples are presented for the and cases. We derive the
maximum principle for the Eigen model for general . The general result for
the Eigen model reduces to a known result for . Examples are presented for
the nucleic acid and the amino acid alphabet. An error catastrophe
phase transition occurs in these models, and the order of the phase transition
changes from second to first order for smooth fitness functions when the
alphabet size is increased beyond two letters to the generic case. As examples,
we analyze the general analytic solution for sharp peak, linear, quadratic, and
quartic fitness functions.Comment: 50 pages, 8 figures, to appear in J. Stat. Phys; some typos fixe
Experimental pulse technique for the study of microbial kinetics in continuous culture
A novel technique was developed for studying the growth kinetics of microorganisms in continuous culture. The method is based on following small perturbations of a chemostat culture by on-line measurement of the dynamic response in oxygen consumption rates. A mathematical model, incorporating microbial kinetics and mass transfer between gas and liquid phases, was applied to interpret the data. Facilitating the use of very small disturbances, the technique is non-disruptive as well as fast and accurate. The technique was used to study the growth kinetics of two cultures, Methylosinus trichosporium OB3b growing on methane, both in the presence and in the absence of copper, and Burkholderia (Pseudomonas) cepacia G4 growing on phenol. Using headspace flushes, gas blocks and liquid substrate pulse experiments, estimates for limiting substrate concentrations, maximum conversion rates Vmax and half saturation constants Ks could rapidly be obtained. For M. trichosporium OB3b it was found that it had a far higher affinity for methane when particulate methane monooxygenase (pMMO) was expressed than when the soluble form (sMMO) was expressed under copper limitation. While for B. cepacia G4 the oxygen consumption pattern during a phenol pulse in the chemostat indicated that phenol was transiently converted to an intermediate (4-hydroxy-2-oxovalerate), so that initially less oxygen was used per mole of phenol.
Strange nucleon form factors in the perturbative chiral quark model
We apply the perturbative chiral quark model at one loop to calculate the
strange form factors of the nucleon. A detailed numerical analysis of the
strange magnetic moments and radii of the nucleon, and also the momentum
dependence of the form factors is presented.Comment: 18 pages, 6 figure
Nucleon-Nucleon Interaction and Isospin Violation
The application of the chiral effective theory to processes with two or more
nucleons is discussed. We gain a qualitative understanding of the gross
features of nuclear physics and quantitative, testable postdictions and
predictions involving photons and pions.Comment: 17 pages, 2 ps figures, uses lamuphys.sty and epsfig.sty; invited
plenary talk at the Chiral Dynamics Workshop, Mainz, Sept 1-5 199
The effects of the composition of microporous layers on the permeability of gas diffusion layers used in polymer electrolyte fuel cells
The effects of the composition of the microporous layer (MPL) on the through-plane permeability of the gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs) have been thoroughly experimentally investigated in this paper. For a given PTFE loading in the MPL, the GDL permeability was found to decrease with increasing carbon loading and this is due to the increase in the thickness of the MPL. For all the investigated carbon loadings of the MPL, the permeability values of the GDLs were found to have common trends for the PTFE loadings ranging from 10 to 50% (by weight): the GDL permeability increases when the PTFE loading in the MPL is increased from 20 to 50%; the GDL permeability decreases when the PTFE loading in the MPL is increased from 10 to 20%; and the GDL permeability is a minimum at 20% PTFE loading present in the MPL. On the other hand, the permeability of the GDL was found to depend on the carbon loading of the MPL in the PTFE range 0–10%. The effects of the MPL composition on the MPL permeability were found to be similar to those on the GDL permeability. However, the permeability values of the MPLs of the same composition, which were supposed to be ideally the same, were found to significantly vary. This was attributed to the MPL penetration into the body of the carbon substrates
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