588 research outputs found
Kinematics of dense gas in the L1495 filament
We study the kinematics of the dense gas of starless and protostellar cores
traced by the N2D+(2-1), N2H+(1-0), DCO+(2-1), and H13CO+(1-0) transitions
along the L1495 filament and the kinematic links between the cores and the
surrounding molecular cloud.
We measure velocity dispersions, local and total velocity gradients and
estimate the specific angular momenta of 13 dense cores in the four transitions
using the on-the-fly observations with the IRAM 30 m antenna. To study a
possible connection to the filament gas, we use the fit results of the
C18O(1-0) survey performed by Hacar et al. (2013).
All cores show similar properties along the 10 pc-long filament. N2D+(2-1)
shows the most centrally concentrated structure, followed by N2H+(1-0) and
DCO+(2-1), which show similar spatial extent, and H13CO+(1-0). The non-thermal
contribution to the velocity dispersion increases from higher to lower density
tracers. The change of magnitude and direction of the total velocity gradients
depending on the tracer used indicates that internal motions change at
different depths within the cloud. N2D+ and N2H+ show smaller gradients than
the lower density tracers DCO+ and H13CO+, implying a loss of specific angular
momentum at small scales. At the level of cloud-core transition, the core's
external envelope traced by DCO+ and H13CO+ is spinning up, consistent with
conservation of angular momentum during core contraction. C18O traces the more
extended cloud material whose kinematics is not affected by the presence of
dense cores. The decrease in specific angular momentum towards the centres of
the cores shows the importance of local magnetic fields to the small scale
dynamics of the cores. The random distributions of angles between the total
velocity gradient and large scale magnetic field suggests that the magnetic
fields may become important only in the high density gas within dense cores.Comment: Accepted for publication in A&A. The abstract is shortene
Observations on tuna fishery at Ratnagiri-Malwan area, north-west coast of India
Ratnagiri and Malwan, on the coast of Maharashtra
State, support a good tuna fishery which is of considerable
importance to the local fishermen. Except for
the preliminary note by Ranade (1961), no scientific
information is available on the tuna fishery of this coast.
With a view to enhance our knowledge on the fishery
and biology of tunas from this area, a survey was conducted
by the Central Marine Fishereis Research Institute
during September to December, 1979. The present
account deals with the relevant information collected
during the period of survey and thereafter
Sequence-specific recognition of DNA by the C-terminal domain of nucleoid-associated protein H-NS
The molecular determinants necessary and sufficient for recognition of its specific DNA target are contained in the C-terminal domain (H-NSctd) of nucleoid-associated protein H-NS. H-NSctd protects from DNaseI cleavage a few short DNA segments of the H-NS-sensitive hns promoter whose sequences closely match the recently identified H-NS consensus motif (tCG(t/a)T(a/t)AATT) and, alone or fused to the protein oligomerization domain of phage λ CI repressor, inhibits transcription from the hns promoter in vitro and in vivo. The importance of H-NS oligomerization is indicated by the fact that with an extended hns promoter construct (400 bp), which allows protein oligomerization, DNA binding and transcriptional repression are highly and almost equally efficient with native H-NS and H-NSctd::λCI and much less effective with the monomeric H-NSctd. With a shorter (110 bp) construct, which does not sustain extensive protein oligomerization, transcriptional repression is less effective, but native H-NS, H-NSctd::λCI, and monomeric H-NSctd have comparable activity on this construct. The specific H-NS-DNA interaction was investigated by NMR spectroscopy using monomeric H-NSctd and short DNA duplexes encompassing the H-NS target sequence of hns (TCCTTACATT)with the best fit (8 of 10 residues) to the H-NS-binding motif. H-NSctd binds specifically and with high affinity to the chosen duplexes via an overall electropositive surface involving four residues (Thr109, Arg113, Thr114, and Ala116) belonging to the same protein loop and Glu101. The DNA target is recognized by virtue of its sequence and of a TpA step that confers a structural irregularity to the B-DNA duplex
Shark predation on migrating adult american eels (Anguilla rostrata) in the Gulf of St. Lawrence.
In an attempt to document the migratory pathways and the environmental conditions encountered by American eels during their oceanic migration to the Sargasso Sea, we tagged eight silver eels with miniature satellite pop-up tags during their migration from the St. Lawrence River in Québec, Canada. Surprisingly, of the seven tags that successfully transmitted archived data, six were ingested by warm-gutted predators, as observed by a sudden increase in water temperature. Gut temperatures were in the range of 20 to 25°C-too cold for marine mammals but within the range of endothermic fish. In order to identify the eel predators, we compared their vertical migratory behavior with those of satellite-tagged porbeagle shark and bluefin tuna, the only endothermic fishes occurring non-marginally in the Gulf of St. Lawrence. We accurately distinguished between tuna and shark by using the behavioral criteria generated by comparing the diving behavior of these two species with those of our unknown predators. Depth profile characteristics of most eel predators more closely resembled those of sharks than those of tuna. During the first days following tagging, all eels remained in surface waters and did not exhibit diel vertical migrations. Three eels were eaten at this time. Two eels exhibited inverse diel vertical migrations (at surface during the day) during several days prior to predation. Four eels were eaten during daytime, whereas the two night-predation events occurred at full moon. Although tagging itself may contribute to increasing the eel's susceptibility to predation, we discuss evidence suggesting that predation of silver-stage American eels by porbeagle sharks may represent a significant source of mortality inside the Gulf of St. Lawrence and raises the possibility that eels may represent a reliable, predictable food resource for porbeagle sharks
Is copyright blind to the visual?
This article argues that, with respect to the copyright protection of works of visual art, the general uneasiness that has always pervaded the relationship between copyright law and concepts of creativity produces three anomalous results. One of these is that copyright lacks much in the way of a central concept of 'visual art' and, to the extent that it embraces any concept of the 'visual', it is rooted in the rhetorical discourse of the Renaissance. This means that copyright is poorly equipped to deal with modern developments in the visual arts. Secondly, the pervasive effect of rhetorical discourse appears to have made it particularly difficult for copyright law to strike a meaningful balance between protecting creativity and permitting its use in further creative works. Thirdly, just when rhetorical discourse might have been useful in identifying the significance and materiality of the unique one-off work of visual art, copyright law chooses to ignore its implications
Tuna fisheries in India: Recent trends
Tuna is one of the least exploited resources of the Indian seas accounting for 0.98 % of the total marine
fish catch of India at the 1978 level. On the other hand tuna resources have been exploited by countries such as Japan, Korea and Taiwan from the Indian Ocean. Relevant portions of the recommendations of the 'Symposium on scombroid fishes' held at Mandapam camp. The authorities involved with the planning of the Indian Ocean Expedition give due consideration to gathering and collating the information which should be useful in aiding the development of high seas fisheries for scombroid fishes in the Indian Ocean. In the context of these developments and the need for efficient utilisation of the resources of the Exclusive Economic Zone, a brief account on the trend in the tuna fisheries in the country is presented here
Bacterial porin disrupts mitochondrial membrane potential and sensitizes host cells to apoptosis
The bacterial PorB porin, an ATP-binding beta-barrel protein of pathogenic Neisseria gonorrhoeae, triggers host cell apoptosis by an unknown mechanism. PorB is targeted to and imported by host cell mitochondria, causing the breakdown of the mitochondrial membrane potential (delta psi m). Here, we show that PorB induces the condensation of the mitochondrial matrix and the loss of cristae structures, sensitizing cells to the induction of apoptosis via signaling pathways activated by BH3-only proteins. PorB is imported into mitochondria through the general translocase TOM but, unexpectedly, is not recognized by the SAM sorting machinery, usually required for the assembly of beta-barrel proteins in the mitochondrial outer membrane. PorB integrates into the mitochondrial inner membrane, leading to the breakdown of delta psi m. The PorB channel is regulated by nucleotides and an isogenic PorB mutant defective in ATP-binding failed to induce delta psi m loss and apoptosis, demonstrating that dissipation of delta psi m is a requirement for cell death caused by neisserial infection
The spine of the swan: A Herschel study of the DR21 ridge and filaments in Cygnus X
In order to characterise the cloud structures responsible for the formation
of high-mass stars, we present Herschel observations of the DR21 environment.
Maps of the column density and dust temperature unveil the structure of the
DR21 ridge and several connected filaments. The ridge has column densities
larger than 1e23/cm^2 over a region of 2.3 pc^2. It shows substructured column
density profiles and branching into two major filaments in the north. The
masses in the studied filaments range between 130 and 1400 Msun whereas the
mass in the ridge is 15000 Msun. The accretion of these filaments onto the DR21
ridge, suggested by a previous molecular line study, could provide a continuous
mass inflow to the ridge. In contrast to the striations seen in e.g., the
Taurus region, these filaments are gravitationally unstable and form cores and
protostars. These cores formed in the filaments potentially fall into the
ridge. Both inflow and collisions of cores could be important to drive the
observed high-mass star formation. The evolutionary gradient of star formation
running from DR21 in the south to the northern branching is traced by
decreasing dust temperature. This evolution and the ridge structure can be
explained by two main filamentary components of the ridge that merged first in
the south.Comment: 8 pages, 5 figures, accepted for publication as a Letter in Astronomy
and Astrophysic
Interstellar MHD Turbulence and Star Formation
This chapter reviews the nature of turbulence in the Galactic interstellar
medium (ISM) and its connections to the star formation (SF) process. The ISM is
turbulent, magnetized, self-gravitating, and is subject to heating and cooling
processes that control its thermodynamic behavior. The turbulence in the warm
and hot ionized components of the ISM appears to be trans- or subsonic, and
thus to behave nearly incompressibly. However, the neutral warm and cold
components are highly compressible, as a consequence of both thermal
instability in the atomic gas and of moderately-to-strongly supersonic motions
in the roughly isothermal cold atomic and molecular components. Within this
context, we discuss: i) the production and statistical distribution of
turbulent density fluctuations in both isothermal and polytropic media; ii) the
nature of the clumps produced by thermal instability, noting that, contrary to
classical ideas, they in general accrete mass from their environment; iii) the
density-magnetic field correlation (or lack thereof) in turbulent density
fluctuations, as a consequence of the superposition of the different wave modes
in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio
(MFR) in density fluctuations as they are built up by dynamic compressions; v)
the formation of cold, dense clouds aided by thermal instability; vi) the
expectation that star-forming molecular clouds are likely to be undergoing
global gravitational contraction, rather than being near equilibrium, and vii)
the regulation of the star formation rate (SFR) in such gravitationally
contracting clouds by stellar feedback which, rather than keeping the clouds
from collapsing, evaporates and diperses them while they collapse.Comment: 43 pages. Invited chapter for the book "Magnetic Fields in Diffuse
Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as
per referee's recommendation
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