Interaction of D-string with F-string: A Path-Integral Formalism

A path integral formalism is developed to study the interaction of an arbitrary curved Dirichlet (D-) string with elementary excitations of the fundumental (F-) string in bosonic string theory. Up to the next to leading order in the derivative expansion, we construct the properly renormalized vertex operator, which generalizes the one previously obtained for a D-particle moving along a curved trajectory. Using this vertex, an attempt is further made to quantize the D-string coordinates and to compute the quantum amplitude for scattering between elementary excitations of the D- and F-strings. By studying the dependence on the Liouville mode for the D-string, it is found that the vertex in our approximation consists of an infinite tower of local vertex operators which are conformally invariant on their respective mass-shell. This analysis indicates that, unlike the D-particle case, an off-shell extension of the interaction vertex would be necessary to compute the full amplitude and that the realization of symmetry can be quite non-trivial when the dual extended objects are simultaneously present. Possible future directions are suggested.Comment: 23 pages, latex, no figure

The application of electrolytic manganese as a substitute ferro alloy

INDIA has got vast deposits of high grade and I low grade manganese ores which are among the most important minerals of the country. High grade ores, which are mined anuually to the extent of more than a million tons , are generally exported or utilised for the production of standard grade ferromanganese. Investigations have been undertaken in N.M.L. and other places in India to upgrade these low grade manganese ores by different methods of beneficiation' and to utilise them for producing standard grade ferromanganese. National Metallurgical Laboratory has also developed a method to produce electrolytic mang-anese from low grade ores.2 4 Electromanganese is now being produced at the rate of 50 kg per day in one cell in the pilot plant set up in the laboratory. This manganese is being utilised for producing nickel-free stainless steel which has already been developed in N.M.L. and also for other experimental purposes, in addition to a portion of the same being supplied to defence and other industries

Offset fields in perpendicularly magnetized tunnel junctions

We study the offset fields affecting the free layer of perpendicularly magnetized tunnel junctions. In extended films, the free layer offset field results from interlayer exchange coupling with the reference layer through the MgO tunnel oxide. The free layer offset field is thus accompanied with a shift of the free layer and reference layer ferromagnetic resonance frequencies. The shifts depend on the mutual orientation of the two magnetizations. The offset field decreases with the resistance area product of the tunnel oxide. Patterning the tunnel junction into an STT-MRAM disk-shaped cell changes substantially the offset field, as the reduction of the lateral dimension comes with the generation of stray fields by the reference and the hard layer. The experimental offset field compares best with the spatial average of the sum of these stray fields, thereby providing guidelines for the offset field engineering.Comment: Special issue of J. Phys. D: Appl. Phys (2019) on STT-MRA

Equity in Engineering Education: The Experiences of Non-Traditional Students in Introductory Engineering Courses with Peer Learning Support

This paper seeks to examine one aspect of the pilot research study entitled, “Engagement in Engineering Pathways: An Initiative to Retain Non-Traditional Students in Engineering” funded by the National Science Foundation Improving Undergraduate STEM Education grant program (Award No. 1712008). This three-year study examines the effect of the use of Peer-Led Team Learning (PLTL) on students’ academic performance, STEM experiences, and persistence in engineering programs [2]. The data collected is from May 2018- May 2020. The present study population is undergraduate engineering students at a multi-campus, federally designated Hispanic-serving, public, two-year college in the southeastern U.S. This paper will specifically address the effects of the PLTL on the student’s STEM experiences

A Resource Based Stage-Structured Fishery Model With Selective Harvesting of Mature Species

In this paper we have considered a model in which revenue is generated from fishing and the growth of the fish depends upon the plankton which in turn follows a logistic law of growth. Here the fish population has two stages, a juvenile stage and a mature stage and we consider the harvesting of the mature fish species. Stability and permanence of the system are discussed. Maximum sustainable yield, maximum economic yield and optimal sustainable yield are obtained and different tax policies are discussed to achieve the reference points