An iterative algorithm for parametrization of shortest length shift registers over finite rings

The construction of shortest feedback shift registers for a finite sequence S_1,...,S_N is considered over the finite ring Z_{p^r}. A novel algorithm is presented that yields a parametrization of all shortest feedback shift registers for the sequence of numbers S_1,...,S_N, thus solving an open problem in the literature. The algorithm iteratively processes each number, starting with S_1, and constructs at each step a particular type of minimal Gr\"obner basis. The construction involves a simple update rule at each step which leads to computational efficiency. It is shown that the algorithm simultaneously computes a similar parametrization for the reciprocal sequence S_N,...,S_1.Comment: Submitte

Genome wide association mapping of grain arsenic, copper, molybdenum and zinc in rice (Oryza sativa L.) grown at four international field sites

Peer reviewedPublisher PD

Observables, gauge invariance, and the role of the observers in the limit from general relativity to special relativity

Some conceptual issues concerning general invariant theories, with special emphasis on general relativity, are analyzed. The common assertion that observables must be required to be gauge invariant is examined in the light of the role played by a system of observers. Some features of the reduction of the gauge group are discussed, including the fact that in the process of a partial gauge fixing the reduction at the level of the gauge group and the reduction at the level of the variational principle do not commute. Distinctions between the mathematical and the physical concept of gauge symmetry are discussed and illustrated with examples. The limit from general relativity to special relativity is considered as an example of a gauge group reduction that is allowed in some specific physical circumstances. Whether and when the Poincar\'e group must be considered as a residual gauge group will come out as a result of our analysis, that applies, in particular, to asymptotically flat spaces.Comment: 17 page

X-Ray Emission and Optical Polarization of V1432 Aquilae: An Asynchronous Polar

A detailed analysis of X-ray data from ROSAT, ASCA, XMM and RXTE for the asynchronous polar V1432 Aql along with Stokes polarimetry data from SAAO, is presented. Power spectra from long-baseline ROSAT data show a spin period of 12150s along with several system related frequency components. However, the second harmonic of the spin period dominates power spectrum in the XMM data. For the optical circular polarization, the dominant period corresponds to half the spin period. The ROSAT data can be explained as due to accretion onto two hot spots that are not anti-podal. The variations seen in the optical polarization and the ASCA and XMM data suggest the presence of at least three accretion foot prints on the white dwarf surface. Two spectral models, a multi-temperature plasma and a photo-ionized plasma model, are used for spectral study. The RXTE PCA data are used to constrain the white dwarf mass to 1.2$\pm$0.1 M_odot using the multi-temperature plasma model. A strong soft X-ray excess (<0.8 keV) in the XMM MOS data is well modeled by a blackbody component having a temperature of 80-90 eV. The plasma emission lines seen at 6.7 and 7.0 keV are well fitted using the multi-temperature plasma model, however an additional Gaussian is needed for the 6.4 keV line. The multi-temperature plasma model requires a homogeneous absorber fully covering the source and a partial absorber covering 65% of the source. The photo-ionized plasma model, with a range of Fe column densities, gives a slightly better overall fit and fits all emission lines. The presence of a strong blackbody component, a spin period of 12150s, modulation of the 6.4 keV line flux with spin period, and a very hard X-ray component suggest that V1432 Aql is a polar with X-ray spectral properties similar to that of a soft intermediate polar.Comment: 46 pages, including 13 figures and 4 tables, To appear in The Astrophysical Journal, 20 May 2005 issue, vol. 625, Added Report-no and Journal-ref, no change in the text of the pape

Cathode Optimization for an Inert-Substrate-Supported Tubular Solid Oxide Fuel Cell

Inert-substrate-supported tubular solid oxide fuel cells with multi-functional layers were fabricated in this work. The tubular single cells consisted of a porous yttria-stabilized zirconia inert-substrate supporting layer, a Ni anode current collecting layer, a Ni-Ce0.8Sm0.2O1.9 anode electrochemical layer, an yttria-stabilized zirconia/Ce0.8Sm0.2O1.9 bi-layer electrolyte, and a La0.6Sr0.4Co0.2Fe0.8O3−δ cathode. Thickness of the La0.6Sr0.4Co0.2Fe0.8O3−δ cathode layer could be varied from 2.5 to 25.0 μm by controlling the number of dip-coatings in the single cell fabrication process. Electrochemical performance of the tubular single cells was investigated as a function of cathode thickness. Area specific resistance and maximum power density of the single cell were significantly affected by the thickness of the cathode. Increasing the cathode thickness to 15 μm was effective in reducing the sheet resistance of the layer and the area specific resistance of the single cell. Further increasing the cathode thickness induced a higher electrode polarization loss, which originated from insufficient gas diffusion and transport processes. Therefore, the optimum thickness of the La0.6Sr0.4Co0.2Fe0.8O3−δ cathode layer was determined to be 15 μm. At 800°C, the tubular single cell with the optimum cathode thickness displayed the highest observed maximum power density of 559 mWcm−2 under the hydrogen/air operation mode. Additionally, the tubular single cell exhibited good thermal cycling stability between 800 and 25°C for five cycles. These results illustrate the advantages of this system for future applications of the inert-substrate-supported tubular single cells in repeated startup and shut down conditions

Non-cubic layered structure of Ba(1-x)K(x)BiO3 superconductor

Bismuthate superconductor Ba(1-x)K(x)BiO3 (x=0.27-0.49, Tc=25-32K) grown by an electrolysis technique was studied by electron diffraction and high-resolution electron microscopy. The crystalline structure thereof has been found to be non-cubic, of the layered nature, and non-centrosymmetric, with the lattice parameters a ~ ap, c ~ 2ap (ap is a simple cubic perovskite cell parameter) containing an ordered arrangement of barium and potassium. The evidence for the layered nature of the bismuthate superconductor removes the principal crystallographic contradiction between bismuthate and cuprate high-Tc superconductors.Comment: 4 pages, 3 figures, to be published in Physical Review B as a Rapid Communicatio

Disorder Effects in Two-Dimensional d-wave Superconductors

Influence of weak nonmagnetic impurities on the single-particle density of states $\rho(\omega)$ of two-dimensional electron systems with a conical spectrum is studied. We use a nonperturbative approach, based on replica trick with subsequent mapping of the effective action onto a one-dimensional model of interacting fermions, the latter being treated by Abelian and non-Abelian bosonization methods. It is shown that, in a d-wave superconductor, the density of states, averaged over randomness, follows a nontrivial power-law behavior near the Fermi energy: $\rho(\omega) \sim |\omega|^{\alpha}$. The exponent $\alpha>0$ is calculated for several types of disorder. We demonstrate that the property $\rho(0) = 0$ is a direct consequence of a {\it continuous} symmetry of the effective fermionic model, whose breakdown is forbidden in two dimensions. As a counter example, we consider another model with a conical spectrum - a two-dimensional orbital antiferromagnet, where static disorder leads to a finite $\rho(0)$ due to breakdown of a {\it discrete} (particle-hole) symmetry.Comment: 24 pages, 3 figures upon request, RevTe

Spin Gauge Theory of Gravity in Clifford Space: A Realization of Kaluza-Klein Theory in 4-Dimensional Spacetime

A theory in which 4-dimensional spacetime is generalized to a larger space, namely a 16-dimensional Clifford space (C-space) is investigated. Curved Clifford space can provide a realization of Kaluza-Klein theory. A covariant Dirac equation in curved C-space is explored. The generalized Dirac field is assumed to be a polyvector-valued object (a Clifford number) which can be written as a superposition of four independent spinors, each spanning a different left ideal of Clifford algebra. The general transformations of a polyvector can act from the left and/or from the right, and form a large gauge group which may contain the group U(1)xSU(2)xSU(3) of the standard model. The generalized spin connection in C-space has the properties of Yang-Mills gauge fields. It contains the ordinary spin connection related to gravity (with torsion), and extra parts describing additional interactions, including those described by the antisymmetric Kalb-Ramond fields.Comment: 57 pages; References added, section 2 rewritten and expande

Solar-Cycle Characteristics Examined in Separate Hemispheres: Phase, Gnevyshev Gap, and Length of Minimum

Research results from solar-dynamo models show the northern and southern hemispheres may evolve separately throughout the solar cycle. The observed phase lag between the hemispheres provides information regarding the strength of hemispheric coupling. Using hemispheric sunspot-area and sunspot-number data from Cycles 12 - 23, we determine how out of phase the separate hemispheres are during the rising, maximum, and declining period of each solar cycle. Hemispheric phase differences range from 0 - 11, 0 - 14, and 2 - 19 months for the rising, maximum, and declining periods, respectively. The phases appear randomly distributed between zero months (in phase) and half of the rise (or decline) time of the solar cycle. An analysis of the Gnevyshev gap is conducted to determine if the double-peak is caused by the averaging of two hemispheres that are out of phase. We confirm previous findings that the Gnevyshev gap is a phenomenon that occurs in the separate hemispheres and is not due to a superposition of sunspot indices from hemispheres slightly out of phase. Cross hemispheric coupling could be strongest at solar minimum, when there are large quantities of magnetic flux at the Equator. We search for a correlation between the hemispheric phase difference near the end of the solar cycle and the length of solar-cycle minimum, but found none. Because magnetic flux diffusion across the Equator is a mechanism by which the hemispheres couple, we measured the magnetic flux crossing the Equator by examining magnetograms for Solar Cycles 21 - 23. We find, on average, a surplus of northern hemisphere magnetic flux crossing during the mid-declining phase of each solar cycle. However, we find no correlation between magnitude of magnetic flux crossing the Equator, length of solar minima, and phase lag between the hemispheres.Comment: 15 pages, 7 figure

On the injectivity of the circular Radon transform arising in thermoacoustic tomography

The circular Radon transform integrates a function over the set of all spheres with a given set of centers. The problem of injectivity of this transform (as well as inversion formulas, range descriptions, etc.) arises in many fields from approximation theory to integral geometry, to inverse problems for PDEs, and recently to newly developing types of tomography. The article discusses known and provides new results that one can obtain by methods that essentially involve only the finite speed of propagation and domain dependence for the wave equation.Comment: To appear in Inverse Problem