Algebraic and geometric structures in string backgrounds

We give a brief introduction to the study of the algebraic structures -- and their geometrical interpretations -- which arise in the BRST construction of a conformal string background. Starting from the chiral algebra \cA of a string background, we consider a number of elementary but universal operations on the chiral algebra. From these operations we deduce a certain fundamental odd Poisson structure, known as a Gerstenhaber algebra, on the BRST cohomology of \cA. For the 2D string background, the correponding G-algebra can be partially described in term of a geometrical G-algebra of the affine plane \bC^2. This paper will appear in the proceedings of {\it Strings 95}

Electronic Structures of SiC Nanoribbons

Electronic structures of SiC nanoribbons have been studied by spin-polarized density functional calculations. The armchair nanoribbons are nonmagnetic semiconductor, while the zigzag nanoribbons are magnetic metal. The spin polarization in zigzag SiC nanoribbons is originated from the unpaired electrons localized on the ribbon edges. Interestingly, the zigzag nanoribbons narrower than $\sim$4 nm present half-metallic behavior. Without the aid of external field or chemical modification, the metal-free half-metallicity predicted for narrow SiC zigzag nanoribbons opens a facile way for nanomaterial spintronics applications.Comment: 10 pages, 5 figure

The weld seam detection method based on the infocrnet model

Weld seam detection is particularly crucial within industrial systems, as it promptly reflects the quality of product fabrication and performance, ensuring the final metallurgical product’s quality while mitigating potential losses stemming from product quality issues. This paper proposed the InfoFPN Cross Refinement Network (InfoCRNet) for the weld seam detection, achieving an accuracy rate of 98,90% and F1 score of 98,85 %

Classical Scattering in 1+11+1 Dimensional String Theory

We find the general solution to Polchinski's classical scattering equations for $1+1$ dimensional string theory. This allows efficient computation of scattering amplitudes in the standard Liouville $\times$ $c=1$ background. Moreover, the solution leads to a mapping from a large class of time-dependent collective field theory backgrounds to corresponding nonlinear sigma models. Finally, we derive recursion relations between tachyon amplitudes. These may be summarized by an infinite set of nonlinear PDE's for the partition function in an arbitrary time-dependent background.Comment: 15 p

Tunneling Conductance Between Parallel Two Dimensional Electron Systems

We derive and evaluate expressions for the low temperature {\it dc} equilibrium tunneling conductance between parallel two-dimensional electron systems. Our theory is based on a linear-response formalism and on impurity-averaged perturbation theory. The disorder broadening of features in the dependence of tunneling conductance on sheet densities and in-plane magnetic field strengths is influenced both by the finite lifetime of electrons within the wells and by non-momentum-conserving tunneling events. Disorder vertex corrections are important only for weak in-plane magnetic fields and strong interwell impurity-potential correlations. We comment on the basis of our results on the possibility of using tunneling measurements to determine the lifetime of electrons in the quantum wells.Comment: 14 pages, 5 Fig. not included, revtex, IUcm92-00

Effect of feed rate on forming quality of cross wedge rolling of gear shaft teeth

In order to improve the forming quality of cross wedge rolling of gear shaft teeth, this paper adopts the single factor research method and uses DEFORM - 3D software to carry out the finite element simulation of the rolling process with different feed rate dies.The results show that the total feed rate of 2,75 mm is the most appropriate, and the tooth top defect of rolled piece gear can be repaired under this condition. The feed rate in the first stage is more important than that in the other stages, and the suitable range of it is 1,0 mm - 1,2 mm

Enhancement of magnetoresistance in manganite multilayers

Magnanite multilayers have been fabricated using La0.67Ca0.33MnO3 as the ferromagnetic layer and Pr0.7Ca0.3MnO3 and Nd0.5Ca0.5MnO3 as the spacer layers. All the multilayers were grown on LaAlO3 (100) by pulse laser deposition. An enhanced magnetoresistnace (defined (RH- R0)/R0) of more than 98% is observed in these multilayers. Also a low field magnetoresistance of 41% at 5000 Oe is observed in these multilayer films. The enhanced MR is attributed to the induced double exchange in the spacer layer, which is giving rise to more number of conducting carriers. This is compared by replacing the spacer layer with LaMnO3 where Mn exists only in 3+ state and no enhancement is observed in the La0.67Ca0.33MnO3 / LaMnO3 multilayers as double exchange mechanism can not be induced by external magnetic fields.Comment: 13 pages, 5 Figure

Modular input-series-input-parallel output-series DC/DC converter control with fault detection and redundancy

A novel high-power modular input-series-input-parallel output-series connected DC/DC converter for medium-voltage application is proposed. Emphasis has been placed on power sharing control to compensate parameter mismatches and achieve equal power distribution between modules. Converter control is extended to achieve fault-tolerant operation by exploiting modularity to provide redundancy in the event of any failure. The proposed control scheme is validated through application-level simulations and scaled-down experiments to testify the reliability of the proposed control for ensuring power sharing between modules under a range of operating conditions. The results validate the proposed converter and associated control scheme indicating this to be a promising topology for high-power medium-voltage applications

Active power sharing in input-series-input-parallel output-series connected DC/DC converters

A high-capacity DC/DC converter with novel input-series-input-parallel output-series connection and with autonomous power sharing between modules is proposed. The proposed scheme is well suited for large-scale wind farm DC collection networks, as it avoids the charging current issues associated with its AC counterpart, and offers lower losses and reduced size and weight when a medium- or high-frequency transformer is used. Small-signal analysis is used to derive the control structures for the converter input and output stages. The proposed control scheme is validated through simulation and experimentation, including demonstration of autonomous power sharing between modules under several operating conditions