1,382 research outputs found
Evolution of electromagnetic and Dirac perturbations around a black hole in Horava gravity
The evolution of electromagnetic and Dirac perturbations in the spacetime
geometry of Kehagias-Sfetsos(KS) black hole in the deformed Horava-Lifshitz(HL)
gravity is investigated and the associated quasinormal modes are evaluated
using time domain integration and WKB methods. We find a considerable deviation
in the nature of field evolution in HL theory from that in the Schwarzschild
spacetime and QNMs region extends over a longer time in HL theory before the
power-law tail decay begins. The dependence of the field evolution on the HL
parameter are studied. In the time domain picture we find that the
length of QNM region increases with . But the late time decay of field
follows the same power-law tail behavior as in the case of Schwarzschild black
hole.Comment: The article was fully rewritten, references added, to appear in MPL
First record of rare skate off Gulf of Mannar
On 20th July 2007, one single specimen of
roundel skate was accidentally caught by fish
trawl net operated off Gulf of Mannar at a depth of
70m and landed at Pamban-Therkuvadi. The
specimen was identified as Raja texana, Chandler,
1921, belonging to the family Rajidae. The fish was a
female measuring 360mm in length and weighing
760 g. It is for the first time this species was recorded
from the Gulf of Mannar Sea
Probiotic effects of lactic acid bacteria against Vibrio alginolyticus in Penaeus (Fenneropenaeus) indicus (H. Milne Edwards)
Cell free extracts of four strains of Lactic acid bacteria (LAB) viz. Lactobacillus. acidophilus,
Streptococcus.cremoris, Lactobacillus bulgaricus –56 and Lactobacillus bulgaricus –57 inhibited
growth of Vibrio alginolyticus in nutrient broth. The antagonism of LAB to Vibrio
alginolyticus was further confirmed by streak plating wherein suppression of growth of Vibrio
was obtained.
Juveniles of Penaeus indicus (average weight 0.985 ± 0.1 g) on administering orally a
moist feed base containing 5 × 106 cells·g of the four LAB probionts for a period of four weeks
showed better survival (56 to 72%) when challenged with V. alginolyticus by intra-muscular
injection of 0.1 ml containing 3 × 109 cells·ml. Animals maintained on a diet devoid of bacterial
biomass exhibited 80% mortality
Ecology and biodiversity of open sea cage farm at Mandapam, India
Farming of marine fin and shellfish species is an age old practice across the globe
to augment the seafood demand and to supplement the rich protein food. Fin fish
mariculture in India has been a recent initiative and the Central Marine Fisheries
Research Institute was successful in developing captive breeding and seed
production technique for cobia (Rachycentron canadum) and silver pompano
(Trachinotus blochii). The open sea cages are particularly advantageous for
maintaining the brood stock of potential species for captive breeding. However,
the ecology of the cage farming sites is of paramount importance and should be
conducive for the survival, health and growth of fishes that are farmed. In the present
study, an attempt was made to understand the ecology and biodiversity of the cage
farming area at Mandapam in Gulf of Mannar, south-east coast of India
Fishing methods in coral reef areas of the Gulf of Mannar
Fishing methods being practised in the reef areas
of the Gulf of Mannar for finfishes are trawling,
gillnetting, fishing by hooks and lines and traps. Out of
these, the most important device is trawling by which
the most diverse and the highest quantity of finfishes
are being landed from coral reef areas in this region
Performance Evaluation and Experimental Studies on Metallised Gel Propellants
Metallised gel propellants offer higher specific impulse and volumetric loading, reduced vaporisation loss, spillage and slosh problems and easy storage in comparison to the conventional liquid propellants. Theoretical performance analysis of gel propellant containing Al in unsymmetrical dimethyl hydrazine-dinitrogen tetroxide (UDMH-N/sub 2/O/sub 4} system shows peak Isp (vacuum condition) of 316.7 s and 318.3 s at oxidiser/fuel (O/f) ratios of 1.5 and 1.0, respectively for 30 per cent and 40 per cent UDMH-Al gel propellants, under standard conditions. The effect of other parameters like area ratio and chamber pressure on performance has been brought out in view of mission oriented applications. Aluminium has been found to be a better choice over magnesium in metallised gel propellants. Experimental studies on UDMH gellation using propellant grade (15 micrometer)and pyrotechnic grade (1.5 micrometer)Al in 500g batch level show that gellant(methyl cellulose) concentration could be reduced by 50 percent using pyrotechnic grade Al. The pseudoplastic-thixotropic behaviour, flow rate through die holes, burst pressure tests and bulk density are studied. UDMH -25 to 30 per cent Al gels with both grades of Al are found to be stable, pseudoplastic (shear thinning) and thixotropic (time-dependent shear thinning), but their flow pattern through die holes differ in nature
Natural Rubber Based Fuel Rich Propellant for Ramjet Rocket
Development of fuel rich propellants for air-breathing propulsion is one of the frontier areas of research. This carries less oxidiser than the normal propellants, uses ram air for complete combustion and is heavily metallised. Studies were conducted at VSSC for the development of hydroxyl-terminated natural rubber (HTNR)-based Mg and Mg-Al alloy-filled polyurethane systems. The HTNR prepolymer was modified to make it free of acid functionality so as to avoid reaction with the metals and was then reacted with calculated amount of propylene oxide in the presence of tertiary amine catalyst at room temperature. Various levels of Mg and Mg-Al alloy were used in different compositions and the effect on propellant characteristics was studied. TMP and butane diol were used for higher crosslinking, chain extension, etc and their effects were evaluated. Propellant compositions using 30-35 per cent by weight of Mg/Mg-Al alloy with the modified prepolymer have been developed. They exhibit good processibility and mechanical properties. The feasibility of room temperature curing was attempted. Motors weighing 2 kg with 100 mm OD and 200 mm length were successfully static-tested in the primary mode for performance evaluation
Coral reef fishes of Gulf of Mannar, S.E of India
The coral reef ecosystem supports a wide variely of flora and fauna and Gulf of Mannar is one of its kind, located in the south-east of India. It comprises 21 islands along the 140 km stretch between Tuticorin and Rameswaram
Capillary Filling of Anodized Alumina Nanopore Arrays
The filling behavior of a room temperature solvent,
perfluoromethylcyclohexane, in approximately 20 nm nanoporous alumina membranes
was investigated in situ with small angle x-ray scattering. Adsorption in the
pores was controlled reversibly by varying the chemical potential between the
sample and a liquid reservoir via a thermal offset, T. The system
exhibited a pronounced hysteretic capillary filling transition as liquid was
condensed into the nanopores. These results are compared with Kelvin-Cohan
theory, with a modified Derjaguin approximation, as well as with predictions by
Cole and Saam.Comment: 4 pages, 3 figures, pre-proof
Developmental Studies on Metallised UDMH and Kerosene Gels
The influence of particulate and hydrocolloid gellants and different surfactants on gellation of metallised stable gels of unsymmetrical dimethyl hydrazine (UDMH) and kerosene containing 30 per cent 15 micron Aluminium was studied. Metallised UDMH and kerosene gels were characterised with respect to pseudoplasticity, thixotropy, consistency and yield stress using Contrave's rheometer. The effect of shear rate and temperature on the viscosity of these gels was determined. Thermal stability, hypergolicity tests and flow rate studies were also conducted. Metallised UDMH and kerosene gels are found to be stable, thixotropic and pseudoplastic and easily flowing like a liquid under shear force
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