Induced spawning in sea urchins

The gonad wall of the sea urchin consists of an outer epithelium, the outer surface of which is bathed in the perivisceral fluid, a middle layer of conspicuous bands of smooth muscles and connective tissue and an inner layer of developing gametes with nutritive cells (Vivek Raja, 1980). The release of gametes, in nature is effected by the contraction of the muscular bands which is directly under the stimulatory effect of the radial nerve hormone (Cochran and Engelmann, 1972). The gamete discharge may be induced by acetylcholine, potassium chloride or by electrical stimulation

Thin layer chromatographic separation of lipids in ovary, testis and gut of the sea urchin Salmacis virgulata

Sea urchins accumulate large amounts of lipid in ovary during its reproductive cycle (Giese, 1966 ; Vivek Raja, 1980); Lipids deposited in the developing gonads may be synthesized within the oocytes or transported from the gut. A variety of lipid classes are also found to occur in the ovary, testis, gut, body wall and coelomocytes of the sea urchins (Allen, 1974; Vivek Raja, 1980). The present experiment is designed to separate and identify the different lipid classes present in gut, testis and ovary of the sea urchin Salmacis virgulata employing thin layer chromatographic metho

SDSS J092712.64+294344.0: recoiling black hole or merging galaxies?

We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that from the Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [OIII]4960,5008 we put a 3 sigma limit on the relative acceleration to be less than 32 km s^-1 yr^-1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [OIII]5008 line from the zem = 0.7128 component is extended beyond the spectral point spread function. We infer the linear extent of this line emitting region is ~8 kpc. We also find a tentative evidence for an offset between the centroid of the [OIII]5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299 degrees. This corresponds to the zem = 0.7128 system being at an impact parameter of ~1 kpc with respect to the zem = 0.6972 in the north west direction. Based on our observations we conclude that the binary black hole model is most unlikely. The spatial extent and the sizes are consistent with both black hole recoil and merging scenarios.Comment: accepted for publication in MNRAS Letter

Network approach towards understanding the crazing in glassy amorphous polymers

We have used molecular dynamics to simulate an amorphous glassy polymer with long chains to study deformation mechanism of crazing and associated void statistics. The Van der Waals interactions and the entanglements between chains constituting the polymer play a crucial role in crazing. Thus, we have reconstructed two underlying weighted networks, namely, the Van der Waals network and the Entanglement network from polymer configurations extracted from the molecular dynamics simulation. Subsequently, we have performed graph-theoretic analysis of the two reconstructed networks to reveal the role played by them in crazing of polymers. Our analysis captured various stages of crazing through specific trends in the network measures for Van der Waals networks and entanglement networks. To further corroborate the effectiveness of network analysis in unraveling the underlying physics of crazing in polymers, we have contrasted the trends in network measures for Van der Waals networks and entanglement networks in the light of stress-strain behaviour and voids statistics during deformation. We find that Van der Waals network plays a crucial role in craze initiation and growth. Although, the entanglement network was found to maintain its structure during craze initiation stage, it was found to progressively weaken and undergo dynamic changes during the hardening and failure stages of crazing phenomena. Our work demonstrates the utility of network theory in quantifying the underlying physics of polymer crazing and widens the scope of applications of network science to characterization of deformation mechanisms in diverse polymers.Comment: 19 pages, 8 figures, supplementary information (SI) available from authors upon reques