Cosmic Rays from Cosmic Strings with Condensates

We re-visit the production of cosmic rays by cusps on cosmic strings. If a scalar field (``Higgs'') has a linear interaction with the string world-sheet, such as would occur if there is a bosonic condensate on the string, cusps on string loops emit narrow beams of very high energy Higgses which then decay to give a flux of ultra high energy cosmic rays. The ultra-high energy flux and the gamma to proton ratio agree with observations if the string scale is $\sim 10^{13}$ GeV. The diffuse gamma ray and proton fluxes are well below current bounds. Strings that are {\it lighter} and have linear interactions with scalars produce an excess of direct and diffuse cosmic rays and are ruled out by observations, while heavier strings ($\sim 10^{15}$ GeV) are constrained by their gravitational signatures. This leaves a narrow window of parameter space for the existence of cosmic strings with bosonic condensates.Comment: 9 pages, 5 figures; revised reference

Evaluation of the factors affecting visual prognosis in patients with traumatic cataract

Background: Ocular trauma is a major cause of visual impairment throughout the world, although little is known about the factors that affect the visual outcome in traumatic cataract in developing countries. The objective of the study was to find out the associated ocular injuries and the factors affecting final visual outcome of patients with traumatic cataract.Methods: This prospective-hospital based study was conducted on 50 patients of traumatic cataract in the department of ophthalmology government medical college, Ernakulam, from January 2009 to December 2011. Patients were managed with lens extraction and intraocular lens implantation. Regular follow up of patients was done and best corrected visual acuity (BCVA) and post-operative complications were assessed at the end of six months.Results: Our study showed that majority (64%) of patients were in the age group of 20 years) (p=0.03). There was no significant difference in final visual outcome of traumatic cataracts caused by penetrating or blunt trauma (p=0.73). Corneal tear was most common associated ocular damage followed by uveitis, lens matter in anterior chamber.Conclusions: Age of the patient affects final visual outcome after surgical treatment of traumatic cataract but type of trauma (blunt/penetrating) had no significant effect on final visual outcome. Corneal tear was most common associated ocular damage

Are HI Supershells the Remnants of Gamma-Ray Bursts?

Gamma-Ray Bursts (GRBs) are thought to originate at cosmological distances from the most powerful explosions in the Universe. If GRBs are not beamed then the distribution of their number as a function of Gamma-ray flux implies that they occur once per (0.3-40) million years per bright galaxy and that they deposit >10^{53} ergs into their surrounding interstellar medium. The blast wave generated by a GRB explosion would be washed out by interstellar turbulence only after tens of millions of years when it finally slows down to a velocity of 10 km/s. This rather long lifetime implies that there could be up to several tens of active GRB remnants in each galaxy at any given time. For many years, radio observations have revealed the enigmatic presence of expanding neutral-hydrogen (HI) supershells of kpc radius in the Milky Way and in other nearby galaxies. The properties of some supershells cannot be easily explained in terms of conventional sources such as stellar winds or supernova explosions. However, the inferred energy and frequency of the explosions required to produce most of the observed supershells agree with the above GRB parameters. More careful observations and analysis might reveal which fraction of these supershells are GRB remnants. We show that if this link is established, the data on HI supershells can be used to constrain the energy output, the rate per galaxy, the beaming factor, and the environment of GRB sources in the Universe.Comment: 8 pages, final version, ApJ Letters, in pres

Intestinal obstruction in pregnancy: three case reports

The occurrence of intestinal obstruction is uncommon in pregnancy and so it is rarely considered as a cause for acute abdominal pain. It is also a life threatening condition to the mother if proper medical intervention is delayed. In this review we present three cases of intestinal obstruction during pregnancy and puerperium. The incidence in our tertiary care center over a period of last 5 years is 1 in 3196 deliveries. These cases were diagnosed preoperatively with x-ray and sonogram. Laparotomy with definitive surgical treatment was performed. The first patient had large bowel obstruction due to sigmoid volvulus, the second patient had a stricture in ileum leading to small bowel obstruction, and the third patient had ileocecal intussusception. There were no maternal deaths but one patient had fetal loss

Switchable lasing in coupled multimode microcavities

We propose the new concept of a switchable multimode microlaser. As a generic, realistic model of a multimode microresonator a system of two coupled defects in a two-dimensional photonic crystal is considered. We demonstrate theoretically that lasing of the cavity into one selected resonator mode can be caused by injecting an appropriate optical pulse at the onset of laser action (injection seeding). Temporal mode-to-mode switching by re-seeding the cavity after a short cool-down period is demonstrated by direct numerical solution. A qualitative analytical explanation of the mode switching in terms of the laser bistability is presented.Comment: Accepted for publication in Physical Review Letters. Published, somewhat shortened versio

Complete integrability versus symmetry

The purpose of this article is to show that on an open and dense set, complete integrability implies the existence of symmetry

Coexistence of excited states in confined Ising systems

Using the density-matrix renormalization-group method we study the two-dimensional Ising model in strip geometry. This renormalization scheme enables us to consider the system up to the size 300 x infinity and study the influence of the bulk magnetic field on the system at full range of temperature. We have found out the crossover in the behavior of the correlation length on the line of coexistence of the excited states. A detailed study of scaling of this line is performed. Our numerical results support and specify previous conclusions by Abraham, Parry, and Upton based on the related bubble model.Comment: 4 Pages RevTeX and 4 PostScript figures included; the paper has been rewritten without including new result

Stability of Naked Singularity arising in gravitational collapse of Type I matter fields

Considering gravitational collapse of Type I matter fields, we prove that, given an arbitrary $C^{2}$- mass function $\textit{M}(r,v)$ and a $C^{1}$- function $h(r,v)$ (through the corresponding $C^{1}$- metric function $\nu(t,r)$), there exist infinitely many choices of energy distribution function $b(r)$ such that the `true' initial data ($\textit{M},h(r,v)$) leads the collapse to the formation of naked singularity. We further prove that the occurrence of such a naked singularity is stable with respect to small changes in the initial data. We remark that though the initial data leading to both black hole and naked singularity form a "big" subset of the true initial data set, their occurrence is not generic. The terms `stability' and `genericity' are appropriately defined following the theory of dynamical systems. The particular case of radial pressure $p_{r}(r)$ has been illustrated in details to get clear picture of how naked singularity is formed and how, it is stable with respect to initial data.Comment: 16 pages, no figure, Latex, submitted to Praman