5,259 research outputs found
Geometric erogdicity of a bead-spring pair with stochastic Stokes forcing
We consider a simple model for the
uctuating hydrodynamics of a
exible polymer
in dilute solution, demonstrating geometric ergodicity for a pair of particles that interact with each other through a nonlinear spring potential while being advected by a
stochastic Stokes
uid velocity field. This is a generalization of previous models which
have used linear spring forces as well as white-in-time
uid velocity fields.
We follow previous work combining control theoretic arguments, Lyapunov functions, and hypo-elliptic diffusion theory to prove exponential convergence via a Harris
chain argument. To this, we add the possibility of excluding certain "bad" sets in phase
space in which the assumptions are violated but from which the systems leaves with a
controllable probability. This allows for the treatment of singular drifts, such as those
derived from the Lennard-Jones potential, which is an novel feature of this work
A possible observational bias in the estimation of the virial parameter in virialized clumps
The dynamics of massive clumps, the environment where massive stars
originate, is still unclear. Many theories predict that these regions are in a
state of near-virial equilibrium, or near energy equi-partition, while others
predict that clumps are in a sub-virial state. Observationally, the majority of
the massive clumps are in a sub-virial state with a clear anti-correlation
between the virial parameter and the mass of the clumps ,
which suggests that the more massive objects are also the more gravitationally
bound. Although this trend is observed at all scales, from massive clouds down
to star-forming cores, theories do not predict it. In this work we show how,
starting from virialized clumps, an observational bias is introduced in the
specific case where the kinetic and the gravitational energies are estimated in
different volumes within clumps and how it can contribute to the spurious
anti-correlation in these data. As a result, the observed
effective virial parameter , and in some
circumstances it might not be representative of the virial state of the
observed clumps.Comment: A&A letter, accepte
Artemether resistance in vitro is linked to mutations in PfATP6 that also interact with mutations in PfMDR1 in travellers returning with Plasmodium falciparum infections.
BACKGROUND: Monitoring resistance phenotypes for Plasmodium falciparum, using in vitro growth assays, and relating findings to parasite genotype has proved particularly challenging for the study of resistance to artemisinins.
METHODS: Plasmodium falciparum isolates cultured from 28 returning travellers diagnosed with malaria were assessed for sensitivity to artemisinin, artemether, dihydroartemisinin and artesunate and findings related to mutations in pfatp6 and pfmdr1.
RESULTS: Resistance to artemether in vitro was significantly associated with a pfatp6 haplotype encoding two amino acid substitutions (pfatp6 A623E and S769N; (mean IC50 (95% CI) values of 8.2 (5.7 - 10.7) for A623/S769 versus 623E/769 N 13.5 (9.8 - 17.3) nM with a mean increase of 65%; p = 0.012). Increased copy number of pfmdr1 was not itself associated with increased IC50 values for artemether, but when interactions between the pfatp6 haplotype and increased copy number of pfmdr1 were examined together, a highly significant association was noted with IC50 values for artemether (mean IC50 (95% CI) values of 8.7 (5.9 - 11.6) versus 16.3 (10.7 - 21.8) nM with a mean increase of 87%; p = 0.0068). Previously described SNPs in pfmdr1 are also associated with differences in sensitivity to some artemisinins.
CONCLUSIONS: These findings were further explored in molecular modelling experiments that suggest mutations in pfatp6 are unlikely to affect differential binding of artemisinins at their proposed site, whereas there may be differences in such binding associated with mutations in pfmdr1. Implications for a hypothesis that artemisinin resistance may be exacerbated by interactions between PfATP6 and PfMDR1 and for epidemiological studies to monitor emerging resistance are discussed
Floral development and potential pollinators of Syzygium myhendrae (Bedd. ex Brandis) Gamble, a wild endemic tree of the Southern Western Ghats, India
Syzygium myhendrae, is a semi-evergreen, endemic and endangered tree species of the Southern Western Ghats, India which exhibits bi-annual mode of flowering and fruiting behaviour. This research is specifically aimed to observe the sequence of morphological processes occurring during floral development and to identify the potential pollinators from the different floral visitors. These aims are achieved by examining the individual trees of candidate species during their flowering season. Sticky traps, bee bowls, sweep nets and pan traps were used to capture floral visitors at the anthesis stage. Visitation frequency and visitor activity index were calculated to distinguish effective pollinators from visitor insects. The results showed nine stages in flower development starting from flower bud emergence to fruit ripening, which took 6-9 weeks. Nine species of insects were recorded as visitors. Honey bees (Apis cerana, ApisMdorsata and Tetragonula iridipennis), butterflies (Hypolimnas misippus,pachilopta pandiana), wasp species, beetle species, fly species were exclusively visiting the flowers of the candidate species. Among the honey bees, Apis dorsata showed high visitation frequency (0.40±0.01) followed by Apis cerana (0.31±0.02) and Tetragonula iridipennis (052±0.02). As per the visitation frequency, it can be concluded that Apis dorsata was the most frequent and effective pollinator
Magnetic Field Uniformity Across the GF 9-2 YSO, L1082C Dense Core, and GF 9 Filamentary Dark Cloud
The orientation of the magnetic field (B-field) in the filamentary dark cloud
GF 9 was traced from the periphery of the cloud into the L1082C dense core that
contains the low-mass, low-luminosity Class 0 young stellar object (YSO) GF 9-2
(IRAS 20503+6006). This was done using SOFIA HAWC+ dust thermal emission
polarimetry (TEP) at 216 um in combination with Mimir near-infrared background
starlight polarimetry (BSP) conducted at H-band (1.6 um) and K-band (2.2 um).
These observations were augmented with published I-band (0.77 um) BSP and
Planck 850 um TEP to probe B-field orientations with offset from the YSO in a
range spanning 6000 AU to 3 pc. No strong B-field orientation change with
offset was found, indicating remarkable uniformity of the B-field from the
cloud edge to the YSO environs. This finding disagrees with weak-field models
of cloud core and YSO formation. The continuity of inferred B-field
orientations for both TEP and BSP probes is strong evidence that both are
sampling a common B-field that uniformly threads the cloud, core, and YSO
region. Bayesian analysis of Gaia DR2 stars matched to the Mimir BSP stars
finds a distance to GF 9 of 270 +/- 10 pc. No strong wavelength dependence of
B-field orientation angle was found, contrary to previous claims.Comment: 18 pages, 6 figures ApJ, accepte
Environmental deterioration in Lakshadweep and need for conservation of living resources
The Lakshadweep Archipelago is located on the Laccadive - Chagos ridge, believed to be the submarine extension of the Aravalli mountains. The various atolls rise from a depth ranging from 1500 to 4000 m. The Lakshadweep Archipelago consists of 12 atolls, 3 reefs and 5 submerged banks, all of coral formations. The total land area is about 32 sq km. The height of islands vary from 1 to 1.4 m from MSL
Evaluation of brightness temperature from a forward model of ground-based microwave radiometer
Ground-based microwave radiometers are getting great attention in recent years due to their capability to profile the temperature and humidity at high temporal and vertical resolution in the lower troposphere. The process of retrieving these parameters from the measurements of radiometric brightness temperature (TB) includes the inversion algorithm, which uses the background information from a forward model. In the present study, an algorithm development and evaluation of this forward model for a ground-based microwave radiometer, being developed by Society for Applied Microwave Electronics Engineering and Research (SAMEER) of India, is presented. Initially, the analysis of absorption coefficient and weighting function at different frequencies was made to select the channels. Further the range of variation of TB for these selected channels for the year 2011, over the two stations Mumbai and Delhi is discussed. Finally the comparison between forward-model simulated TBs and radiometer measured TBs at Mahabaleshwar (73.66°E and 17.93°N) is done to evaluate the model. There is good agreement between model simulations and radiometer observations, which suggests that these forward model simulations can be used as background for inversion models for retrieving the temperature and humidity profiles
A timeline for massive star-forming regions via combined observation of o-HD and ND
Context: In cold and dense gas prior to the formation of young stellar
objects, heavy molecular species (including CO) are accreted onto dust grains.
Under these conditions H and its deuterated isotopologues become more
abundant, enhancing the deuterium fraction of molecules such as NH that
are formed via ion-neutral reactions. Because this process is extremely
temperature sensitive, the abundance of these species is likely linked to the
evolutionary stage of the source.
Aims: We investigate how the abundances of o-HD and ND vary
with evolution in high-mass clumps.
Methods: We observed with APEX the ground-state transitions of o-HD
near 372 GHz, and ND(3-2) near 231 GHz for three massive clumps in
different evolutionary stages. The sources were selected within the
G351.77-0.51 complex to minimise the variation of initial chemical conditions,
and to remove distance effects. We modelled their dust continuum emission to
estimate their physical properties, and also modelled their spectra under the
assumption of local thermodynamic equilibrium to calculate beam-averaged
abundances.
Results: We find an anticorrelation between the abundance of o-HD and
that of ND, with the former decreasing and the latter increasing with
evolution. With the new observations we are also able to provide a qualitative
upper limit to the age of the youngest clump of about 10 yr, comparable to
its current free-fall time.
Conclusions: We can explain the evolution of the two tracers with simple
considerations on the chemical formation paths, depletion of heavy elements,
and evaporation from the grains. We therefore propose that the joint
observation and the relative abundance of o-HD and ND can act
as an efficient tracer of the evolutionary stages of the star-formation
process
Capture of a live South African cape locust lobster at Vizhinjam
landing centre informed the capture of a new lobster
hitherto unknown to them. Immediately it was
brought to CMFRI Marine Aquarium and kept alive
and was identified to be slipper lobster of Scyllarides
and the species confirmed as Scyllarides elisabethae,
the South African locust lobster
Preliminary report on a reconnaissance survey of the major coastal and marine ecosystems in Gulf of Kutch
The region of Gulf of Kutch was possibly more
an arid zone in the pleistocene, almost approaching
to a desert condition, than what it is at present. The
gulf is believed to be the result of a wide indentation
or subsidence that allowed encroachment of the sea
in the geological past. The whole area is still supposed
to be seismically unstable. The Gulf of Kutch covers
an area of circa 7,350 sq. km with a maximum depth
of 60 m. The tidal range varies from 3.06 to 5.89 m
with an average of 4 m. The intertidal zones are sandy
and muddy or with sandstones of vast expanse and
prolonged exposure
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