Comparative Studies of Lensing Methods

Predictions of the standard thin lens approximation and a new iterative approach to gravitational lensing are compared with an ``exact'' approach in simple test cases involving one or two lenses. We show that the thin lens and iterative approaches are remarkably accurate in predicting time delays, source positions and image magnifications for a single monopole lens and combinations of two monopole lenses. In the cases studied, the iterative method provided greater accuracy than the thin lens method. We also study the accuracy of a ``2 lens, single lens plane model,'' where two monopole lenses colinear with the observer are modeled by a mass distribution in a single lens plane lying between them. We see that this model can lead to large inaccuracies in physically meaningful situations. A previous version of this paper was published as Phys.Rev.D62, 024025, (2000) with errors in the computation of two lens comparisons. This paper corrects these errors and presents new conclusions which differ from the previous version.Comment: 23 pages, 15 figures, corrected versio

Comparative Studies of Detecting Abusive Language on Twitter

The context-dependent nature of online aggression makes annotating large collections of data extremely difficult. Previously studied datasets in abusive language detection have been insufficient in size to efficiently train deep learning models. Recently, Hate and Abusive Speech on Twitter, a dataset much greater in size and reliability, has been released. However, this dataset has not been comprehensively studied to its potential. In this paper, we conduct the first comparative study of various learning models on Hate and Abusive Speech on Twitter, and discuss the possibility of using additional features and context data for improvements. Experimental results show that bidirectional GRU networks trained on word-level features, with Latent Topic Clustering modules, is the most accurate model scoring 0.805 F1.Comment: ALW2: 2nd Workshop on Abusive Language Online to be held at EMNLP 2018 (Brussels, Belgium), October 31st, 201

Comparative Raman Studies of Sr2RuO4, Sr3Ru2O7 and Sr4Ru3O10

The polarized Raman spectra of layered ruthenates of the Srn+1RunO3n+1 (n=1,2,3) Ruddlesden-Popper series were measured between 10 and 300 K. The phonon spectra of Sr3Ru2O7 and Sr4Ru3O10 confirmed earlier reports for correlated rotations of neighboring RuO6 octahedra within double or triple perovskite blocks. The observed Raman lines of Ag or B1g symmetry were assigned to particular atomic vibrations by considering the Raman modes in simplified structures with only one double or triple RuO6 layer per unit cell and by comparison to the predictions of lattice dynamical calculations for the real Pban and Pbam structures. Along with discrete phonon lines, a continuum scattering, presumably of electronic origin, is present in the zz, xx and xy, but not in the x'y' and zx spectra. Its interference with phonons results in Fano shape for some of the lines in the xx and xy spectra. The temperature dependencies of phonon parameters of Sr3Ru2O7 exhibit no anomaly between 10 and 300 K where no magnetic transition occurs. In contrast, two B1g lines in the spectra of Sr4Ru3O10, corresponding to oxygen vibrations modulating the Ru-O-Ru bond angle, show noticeable hardening with ferromagnetic ordering at 105 K, thus indicating strong spin-phonon interaction.Comment: 9 pages, 12 figure

Comparative Studies on the Butterfly Diversity and Species Richness in Selected Agricultural Fields in Tamil Nadu

Butterflies are valued components of grassland ecosystems both for their aesthetic nature and they provide as pollinators of the ecosystem services. Loss and fragmentation of native habitats, along with other disturbances associated with intensive agriculture can have dramatic effects on butterfly communities. The close link between butterflies and their natural environment make them good candidates for use as ecological indicators. Hence an attempt has been made to study the diversity and pollination tendencies of butterflies between organic crop fields and pesticide sprayed crop fields. The research was set out to establish whether organic and conventional farming systems support different levels of pest and non-pest butterflies. In the present study maximum insect abundance and total number of individuals were recorded in organic fields. The study also proved that organic farming practices can help in the population build-up of natural enemies and pollinators. However there was remarkable difference in Shannon index and Simpson index of diversity between organic and chemical fields. Phytophagous insect populations were very low in number in organic farms. Hence organic farming practices may encourage natural enemies' diversity and may not be favourable for pests

Postgraduate Prospectus 2006-07

Outlines degree and course offerings on Latin American Studies, United States Studies and Comparative American Studies in the Institute for the Study of the Americas

Functional outcome following direct repair or intervertebral fusion for adolescent spondylolysis : a systematic review

A systematic review of the literature was performed to establish whether direct repair of the pars defect or intervertebral fusion achieves better Oswestry Disability Index scores in adolescent spondylolysis or low-grade spondylolisthesis. Nine studies fulfilled the inclusion criteria, reporting a minimum total of 80 direct repairs and 108 fusions because of presumed replication of data between studies. Little statistically or clinically significant difference could be established between the two interventions. The only comparative study showed improved long-term outcome with fusion. Further well-designed prospective comparative studies are required to establish the optimum treatment for this condition