The influence of the jet opening angle on the appearance of relativistic jets

We reinvestigate the problem of the appearance of relativistic jets when geometrical opening is taken into account. We propose a new criterion to define apparent velocities and Doppler factors, which we think being determined by the brightest zone of the jet. We numerically compute the apparent velocity and the Doppler factor of a non homokinetic jet using different velocity profiles. We argue that if the motion is relativistic, the high superluminal velocities beta_{app} ~ gamma, expected in the case of an homokinetic jet, are only possible for geometrical collimation smaller than the relativistic beaming angle 1/gamma. This is relatively independent of the jet velocity profile. For jet collimation angles larger than 1/gamma, the apparent image of the jet will always be dominated by parts of the jet traveling directly towards the observer at lorentz factors < gamma resulting in maximal apparent velocities smaller than gamma}. Furthermore, getting rid of the homokinetic hypothesis yields a complex relation between the observing angle and the Doppler factor, resulting in important consequences for the numerical computation of AGN population and unification scheme model.Comment: Accepted in MNRAS, 12 pages and 9 Figure

Unstable topography of biphasic surfactant monolayers

We study the conformation of a heterogeneous surfactant monolayer at a fluid-fluid interface, near a boundary between two lateral regions of differing elastic properties. The monolayer attains a conformation of shallow, steep `mesas' with a height difference of up to 10 nm. If the monolayer is progressively compressed (e.g. in a Langmuir trough), the profile develops overhangs and finally becomes unstable at a surface tension of about K(delta c_0)^2, where (delta c_0) is the difference in spontaneous curvature and K a bending stiffness. We discuss the relevance of this instability to recently observed folding behavior in lung surfactant monolayers, and to the absence of domain structures in films separating oil and water in emulsions.Comment: 7 pages, 7 figures, LaTex using epl.cls, accepted for Europhys Let

Influence of temperature on the preservation of fish -Winter School on Impact of Climate Change on Indian Marine Fisheries held at CMFRI, Cochin 18.1.2008 to 7.2.2008

Live fish muscle is relaxed and elastic. Immediately after death rigor mortis sets in, then the whole body becomes inflexible and rigid. The onset of rigor depends upon the temperature, particularly on the difference of temperatures between that of water and storage. If the difference is great, shorter is the time from death to rigor. Fish being the most perishable of human foods, they start spoiling the moment they are taken out of water and die. Temperature being a very important factor accelerating the process of spoilage, in a tropical country like India the ambient temperatures are very conductive for causing quick spoilage in fish. The spoilage reactions commencing on the death of the fish proceed at a very rapid pace. The rate of spoilage of fish at 2.5°C is twice as fast as that at –1.1°C. At 5.5°C, it is twice and at 11°C it is four times as fast as that at 0°C. The spoilage cannot be stopped completely. The best that can be done is to slow it down by means of some refrigeration technique, the simplest of which is addition of ice

Storage and Search in Dynamic Peer-to-Peer Networks

We study robust and efficient distributed algorithms for searching, storing, and maintaining data in dynamic Peer-to-Peer (P2P) networks. P2P networks are highly dynamic networks that experience heavy node churn (i.e., nodes join and leave the network continuously over time). Our goal is to guarantee, despite high node churn rate, that a large number of nodes in the network can store, retrieve, and maintain a large number of data items. Our main contributions are fast randomized distributed algorithms that guarantee the above with high probability (whp) even under high adversarial churn: 1. A randomized distributed search algorithm that (whp) guarantees that searches from as many as $n - o(n)$ nodes ($n$ is the stable network size) succeed in ${O}(\log n)$-rounds despite ${O}(n/\log^{1+\delta} n)$ churn, for any small constant $\delta > 0$, per round. We assume that the churn is controlled by an oblivious adversary (that has complete knowledge and control of what nodes join and leave and at what time, but is oblivious to the random choices made by the algorithm). 2. A storage and maintenance algorithm that guarantees (whp) data items can be efficiently stored (with only $\Theta(\log{n})$ copies of each data item) and maintained in a dynamic P2P network with churn rate up to ${O}(n/\log^{1+\delta} n)$ per round. Our search algorithm together with our storage and maintenance algorithm guarantees that as many as $n - o(n)$ nodes can efficiently store, maintain, and search even under ${O}(n/\log^{1+\delta} n)$ churn per round. Our algorithms require only polylogarithmic in $n$ bits to be processed and sent (per round) by each node. To the best of our knowledge, our algorithms are the first-known, fully-distributed storage and search algorithms that provably work under highly dynamic settings (i.e., high churn rates per step).Comment: to appear at SPAA 201

Discovery Of A Molecular Outflow in the Haro 6-10 Star-Forming Region

We present high sensitivity 12CO and 13CO (1-0) molecular line maps covering the full extent of the parsec scale Haro~6-10 Herbig-Haro (HH) flow. We report the discovery of a molecular CO outflow along the axis of parsec-scale HH flow. Previous molecular studies missed the identification of the outflow probably due to their smaller mapping area and the confusing spectral features present towards the object. Our detailed molecular line study of the full 1.6 pc extent of the optical flow shows evidence for both blueshifted and redshifted gas set in motion by Haro~6-10 activity. The molecular outflow is centered at Haro~6-10, with redshifted gas being clumpy and directed towards the northeast, while blueshifted gas is in the southwest direction. The molecular gas terminates well within the cloud, short of the most distant HH objects of the optical flow. Contamination from an unrelated cloud along the same line of sight prevents a thorough study of the blueshifted outflow lobe and the mass distribution at the lowest velocities in both lobes. The cloud core in which Haro~6-10 is embedded is filamentary and flattened in the east-west direction. The total cloud mass is calculated from 13CO(1-0) to be ~200Msun. The lower limit of the mass associated with the outflow is ~0.25Msun.Comment: ApJ Accepted; 9 pages, 8 figures. For high resolution ps file use: http://www.astro.umass.edu/~irena/haro.p

Appraisal of the Quality of Ground Waters in the Arid Zone of Rajasthan and Kutch

A survey and analyses of waters of arid zones of Western Rajasthan and Kutch have been presented. The data on physico-chemical characteristics of about 2000 ground water samples indicate that according to International Standards of drinking water as devised by WHO, 9 per cent waters in Rajasthan and 19 per cent in Kutch conform to permissible limits (TDS &lt; 500 mg/l) and are suitable for drinking. Considering 2000 mg/l TDS, as maximum permissible level, 46 per cent of available waters in Western Rajasthan and 71 per cent in Kutch are potable. 38 and 57 per cent of waters have electrical conductivity less than 2250 micromhos/cm in Rajasthan and Kutch respectively. Salinity and toxicological studies of brackish waters and their remedial measures are also discussed. A tentative correlation between prevailing water-borne diseases, kidney diseases and fluorosis and dissolved solids in waters of Western Rajasthan has also been shown. The waters have been classified into various suitability classes depending upon their composition

Modeling Presenilin-Dependent Familial Alzheimer's Disease: Emphasis on Presenilin Substrate-Mediated Signaling and Synaptic Function

Mutations in PSEN genes, which encode presenilin proteins, cause familial early-onset Alzheimer's disease (AD). Transgenic mouse models based on coexpression of familial AD-associated presenilin and amyloid precursor protein variants successfully mimic characteristic pathological features of AD, including plaque formation, synaptic dysfunction, and loss of memory. Presenilins function as the catalytic subunit of γ-secretase, the enzyme that catalyzes intramembraneous proteolysis of amyloid precursor protein to release β-amyloid peptides. Familial AD-associated mutations in presenilins alter the site of γ-secretase cleavage in a manner that increases the generation of longer and highly fibrillogenic β-amyloid peptides. In addition to amyloid precursor protein, γ-secretase catalyzes intramembrane proteolysis of many other substrates known to be important for synaptic function. This paper focuses on how various animal models have enabled us to elucidate the physiological importance of diverse γ-secretase substrates, including amyloid precursor protein and discusses their roles in the context of cellular signaling and synaptic function

DTI Atlas Building and Statistical Analysis

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