Studying the Imaging Characteristics of Ultra Violet Imaging Telescope (UVIT) through Numerical Simulations

Ultra-Violet Imaging Telescope (UVIT) is one of the five payloads aboard the Indian Space Research Organization (ISRO)'s ASTROSAT space mission. The science objectives of UVIT are broad, extending from individual hot stars, star-forming regions to active galactic nuclei. Imaging performance of UVIT would depend on several factors in addition to the optics, e.g. resolution of the detectors, Satellite Drift and Jitter, image frame acquisition rate, sky background, source intensity etc. The use of intensified CMOS-imager based photon counting detectors in UVIT put their own complexity over reconstruction of the images. All these factors could lead to several systematic effects in the reconstructed images. A study has been done through numerical simulations with artificial point sources and archival image of a galaxy from GALEX data archive, to explore the effects of all the above mentioned parameters on the reconstructed images. In particular the issues of angular resolution, photometric accuracy and photometric-nonlinearity associated with the intensified CMOS-imager based photon counting detectors have been investigated. The photon events in image frames are detected by three different centroid algorithms with some energy thresholds. Our results show that in presence of bright sources, reconstructed images from UVIT would suffer from photometric distortion in a complex way and the presence of overlapping photon events could lead to complex patterns near the bright sources. Further the angular resolution, photometric accuracy and distortion would depend on the values of various thresholds chosen to detect photon events.Comment: Submitted to PASP, 16 Pages, 9 figure

Dissociation dynamics of transient anion formed via electron attachment to sulfur dioxide

We report the molecular dynamics of dissociative electron attachment to sulfur dioxide (SO2) by measuring the momentum distribution of fragment anions using the velocity slice imaging technique in the electron energy range of 2–10 eV. The S- channel results from symmetric dissociation which exhibits competition between the stretch mode and bending mode of vibration in the excited parent anion. The asymmetric dissociation of parent anions leads to the production of O- and SO- channels where the corresponding neutral fragments are formed in their ground as well as excited electronic states. We also identify that internal excitation of SO- is responsible for its low yield at higher electron energies

Dynamics of Dissociative Electron Attachment to Aliphatic Thiols

Dissociative electron attachment (DEA) shows functional group-dependent site selectivity in the $H^-$ ion channel. In this context, the thiol functional group has yet to be studied in great detail, although this functional group carries importance in radiation damage studies where the low-energy secondary electrons are known to induce damage through the DEA process. We report detailed measurements of absolute cross-sections and momentum images of various anion fragments formed in the DEA process in simple aliphatic thiols. We also compare the observed dynamics with that reported earlier in hydrogen sulphide, the precursor molecule for this functional group and also with aliphatic alcohols. Our findings show substantial resemblance in the underlying dynamics in these compounds and point to a possible generalisation of these features in the DEA to thiols. We also identify various pathways that contribute to the $S^-$ and $SH^-$ channels

THERMAL DIFFUSION AS A PURIFICATION TOOL

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72201/1/j.1749-6632.1966.tb49745.x.pd

Velocity map imaging for low-energy electron-molecule collisions

The development of an experiment for velocity map imaging (VMI) of fragment ions arising from electron-molecule collisions is discussed. The angular distribution of O− from the dissociative attachment and dipolar dissociation of O2 is measured and compared with the existing data. The details of the technique and its importance to electron-molecule collisions are discussed

Socio-epidemiological factors of medical termination of pregnancy: an overview in a tertiary care institute

Background: The Medical Termination of Pregnancy (MTP) was legalized in India by an Act in 1971. The present study is a data analysis over 5 years to gauge the changing trends in the urban government establishment with respect to various socio economical parameters. The objective of the study was to find out the incidence rate of the MTP in the urban government run hospital. The auxiliary objective was to find out the reason for which the MTP is carried out; the age group availing the facility of the services and the secondary contraception the couple uses after the MTP.Methods: A Five (5) year data of MTP was analyzed by keeping the MTP register of the hospital as a reference. The data is presented in the formal protocol of data presentation.Results: The incidence rate of MTP is 27.93/1000 live births in the institute. The primary reason of MTP is failure of contraception. This fact highlights unmet need of contraception and counselling. The maternal age group of 21-30 yrs is availing MTP services the most. The surgical method is more prevalent than the medical method in practicing the MTP. The permanent method of contraception in the form of Tubal ligation is increasing as a choice of contraception after MTP.Conclusions: The awareness of MTP Act and impact of legalizing the abortion is increasing the society and the increasing number of service rendered through the government establishment underlines the increasing faith in the system. The incidence rate of MTP is 27.93/1000 live births in the institute. The primary reason of MTP is failure of contraception. This fact highlights the huge unmet need of contraception and counselling. The maternal age group of 21-30 yrs is availing MTP services the most. Though there is changing trends for medical method of termination of pregnancy but the surgical method is still favoured. The permanent method of contraception in the form of Tubal ligation is increasing as a choice of contraception after MTP. Still the religious differences are evident in availing the MTP services and needs to be addressed tactfully

Dynamics of the dissociative electron attachment to Ethanol

We report the detailed dynamics of the site selectivity observed in the dissociative electron attachment (DEA) process in ethanol based on the momentum images obtained using the velocity slice imaging technique. The H- dissociation channel shows the site selectivity where the anion signal from the O-H site peaks at 6.5 eV and 8 eV, and that from the C-H site peaks at 9.5 eV. The momentum images also show the two-body dissociation dynamics for the O-H site break-up. This dissociation channel shows a substantial effect of the torsion mode of vibrations on the electron attachment process. In contrast, the C-H site dissociation results from the many-body break-up consistent with the earlier reports of DEA dynamics from organic molecules. We have also found that the OH- channel has a resonance at 9.3eV and is produced with very little kinetic energy. Using the isotope substitution, we show the role of H atom scrambling in the C-O bond dissociation leading to the OH- channel. This channel shows a substantial deviation from the corresponding photodissociation dynamics

Development of endotension after multiple rounds of thrombolysis after endovascular aneurysm repair

Endoleaks, defined as blood flow outside the graft but inside the aneurysm sac, are a common complication after endovascular aneurysm repair. Sometimes however, for reasons not fully understood, expansion of the aneurysm sac can occur with no identifiable endoleak, a phenomenon termed endotension, or a type V endoleak. We describe a case of endotension in a 71-year-old man that developed after recurrent stent graft thrombosis requiring thrombolysis 3 years after the initial endovascular implantation. To our knowledge, this is the first description in the literature of endotension after multiple rounds of thrombolytic treatment

Electron attachment and quantum coherence in molecular hydrogen

Single electron attachment to a molecule may invoke quantum coherence in different angular momentum transfer channels. This has been observed in the 14 eV dissociative electron attachment resonance in molecular hydrogen where a coherent superposition of two negative ion resonant states of opposite parity is created, with the s and p partial waves of the electron contributing to the attachment process. Interference between the two partial wave contributions leads to a forward – backward asymmetry in the angular distribution of the product negative ions. Since these two resonant states dissociate to the same n = 2 state of H and H−, this asymmetry is further modified due to interference between the two paths of the dissociating molecular negative ion along different potential energy curves. This interference manifests as a function of the electron energy as well as isotopic composition. This case is akin to the quantum interference observed in photodissociation by one-photon vs two-photon absorption