1,931 research outputs found
Convection and AGN Feedback in Clusters of Galaxies
A number of studies have shown that the convective stability criterion for
the intracluster medium (ICM) is very different from the Schwarzchild criterion
due to the effects of anisotropic thermal conduction and cosmic rays. Building
on these studies, we develop a model of the ICM in which a central active
galactic nucleus (AGN) accretes hot intracluster plasma at the Bondi rate and
produces cosmic rays that cause the ICM to become convectively unstable. The
resulting convection heats the intracluster plasma and regulates its
temperature and density profiles. By adjusting a single parameter in the model
(the size of the cosmic-ray acceleration region), we are able to achieve a good
match to the observed density and temperature profiles in a sample of eight
clusters. Our results suggest that convection is an important process in
cluster cores. An interesting feature of our solutions is that the cooling rate
is more sharply peaked about the cluster center than is the convective heating
rate. As a result, in several of the clusters in our sample, a compact cooling
flow arises in the central region with a size R that is typically a few kpc.
The cooling flow matches onto a Bondi flow at smaller radii. The mass accretion
rate in the Bondi flow is equal to, and controlled by, the rate at which mass
flows in through the cooling flow. Our solutions suggest that the AGN regulates
the mass accretion rate in these clusters by controlling R: if the AGN power
rises above the equilibrium level, R decreases, the mass accretion rate drops,
and the AGN power drops back down to the equilibrium level.Comment: 41 pages, 7 figures, accepted for publication in ApJ. Changes in this
version: extended discussion of Bondi accretion in clusters, better mass
model, new numerical solution
Catalysing the host plant resistance: An insight into phyto-hormone mediated ISR against dry root rot of chickpea
Dry root rot (DRR) of chickpea caused by Rhizoctonia bataticola has become a serious concern to chickpea production. Changing climatic elements like frequent low soil moisture stress and high temperature are among the probable factors increasing DRR incidence in chickpea. Management of the DRR is challenging, owing to its wide host range, lack of resistant sources and uneconomical chemical control measures. Therefore, an alternate resistance management approach against this disease may be achieved by exploitation of host plant resistance through phyto-hormone mediated induced systemic resistance (ISR). The present study aims to identify the role of phyto-hormones in inducing systemic resistance against chickpea DRR. Two Phytohormones Methyl Jasmonic Acid (MeJA) and Salicylic Acid (SA) were used in this study to induce systemic resistance (ISR) against DRR. Of them MeJA was proved to be a robust in playing vital role in inducing resistance against targeted pathogen. The disease severity based on per-cent disease susceptibility index (derived from modified 0-9 rating scale) showed that plants treated with MeJA 50ppm displayed lower degree of DRR severity than the other subtreatments viz., MeJA at 25ppm and 75ppm. Also, the fungal propagule concentrations present in the root tissues sampled at different time points were analogous with theabove findings. A high positive correlation was observed in the results from real-time qPCR based absolute quantification
POLLINATOR DIVERSITY AND FORAGING DYNAMICS ON MONSOON CROP OF CUCURBITS IN A TRADITIONAL LANDSCAPE OF SOUTH INDIAN WEST COAST
Studies on insect pollinator ecology and dynamics are very rarely carried out in traditional Indian agriculture landscapes. Indiscriminate landscape changes in the rural areas and tendencies towards crop monocultures can have significant effects on pollinator habitats and effectiveness. This study was aimed at observing insect pollinators, their visitation frequencies and timings on monsoon cucurbit crops such as Cucumis sativus L., C. pubescens Willd., Momordica charantia L., Trichonsanthes anguina L. and Luffa acutangula L. (Roxb.), in a coastal Karnataka Village.  This study was also aimed at covering the significance of the surrounding landscape elements in sustaining pollinator elements. Bees, such as Apis dorsata, A. cerana and Trigona sp., were major visitors on all cucurbits, except snake gourd which was pollinated mainly by lepidopterans. Insect species were found to partition floral resources of any given crops between them by minimal overlapping in their visitation timings. Natural elements of the landscape around, mainly a village forest and rocky savanna furnished habitats for bees and lepidopterans. Prolifically blooming monsoon herbs on lateritic plateaus, by providing nectar resources for pollinators, presumably play key role in making the case study village well known for monsoon vegetables
Diagnostic Techniques of Soil Borne Plant Diseases: Recent Advances and Next Generation Evolutionary Trends
All about 80000 diseases have been recorded in plants throughout the world, of them majority are associated with soil-borne diseases. Early, speedy and reliable detection of plant pathogens is prerequisite to optimize suitable and accurate management strategy. Traditionally, the most prevalent techniques used to identify plant pathogens relied upon culture-based morphological approaches; these methods were laborious, time-consuming. Molecular detection strategies could solve these limitations with improved accuracy and reliability. The DNA and protein based pathogen detection techniques such as DNA fingerprinting, biochemical assays, isothermal amplification techniques and serology are gaining importance in rapid soil borne pathogen detection due to their high degree of specificity to distinguish closely related organisms at different taxonomic levels. Here, we review the various molecular tools used for detection of several soil borne plant pathogens and its implementation in agriculture
Convection in galaxy-cluster plasmas driven by active galactic nuclei and cosmic-ray buoyancy
Turbulent heating may play an important role in galaxy-cluster plasmas, but
if turbulent heating is to balance radiative cooling in a quasi-steady state,
some mechanism must set the turbulent velocity to the required value. This
paper explores one possible regulating mechanism associated with an active
galactic nucleus at cluster center. A steady-state model for the intracluster
medium is presented in which radiative cooling is balanced by a combination of
turbulent heating and thermal conduction. The turbulence is generated by
convection driven by the buoyancy of cosmic rays produced by a central radio
source. The cosmic-ray luminosity is powered by the accretion of intracluster
plasma onto a central black hole. The model makes the rather extreme assumption
that the cosmic rays and thermal plasma are completely mixed. Although the
intracluster medium is convectively unstable near cluster center in the model
solutions, the specific entropy of the thermal plasma still increases outwards
because of the cosmic-ray modification to the stability criterion. The model
provides a self-consistent calculation of the turbulent velocity as a function
of position, but fails to reproduce the steep central density profiles observed
in clusters. The principal difficulty is that in order for the fully mixed
intracluster medium to become convectively unstable, the cosmic-ray pressure
must become comparable to or greater than the thermal pressure within the
convective region. The large cosmic-ray pressure gradient then provides much of
the support against gravity, reducing the thermal pressure gradient near
cluster center and decreasing the central plasma density gradient. A more
realistic AGN-feedback model of intracluster turbulence in which relativistic
and thermal plasmas are only partially mixed may have greater success.Comment: version 2: minor changes in wordin
Magnetohydrodynamics of the Early Universe and the Evolution of Primordial Magnetic Fields
We show that the decaying magnetohydrodynamic turbulence leads to a more
rapid growth of the correlation length of a primordial magnetic field than that
caused by the expansion of the Universe. As an example, we consider the
magnetic fields created during the electroweak phase transition. The expansion
of the universe alone would yield a correlation length at the present epoch of
1 AU, whereas we find that the correlation length is likely of order 100 AU,
and cannot possibly be longer than AU for non-helical fields. If the
primordial field is strongly helical, the correlation length can be much
larger, but we show that even in this case it cannot exceed 100 pc. All these
estimates make it hard to believe that the observed galactic magnetic fields
can result from the amplification of seed fields generated at the electroweak
phase transition by the standard galactic dynamo.Comment: 15 pages, REVTeX. Added results of numerical simulation, enlarged and
revise
Evolution in the split-peak structure across the Peak Effect region in single crystals of -NbSe
We have explored the presence of a two-peak feature spanning the peak effect
(PE) region in the ac susceptibility data and the magnetization hysteresis
measurements over a wide field-temperature regime in few weakly pinned single
crystals of -NbSe, which display reentrant characteristic in the PE
curve near (0). We believe that the two-peak feature evolves into distinct
second magnetization peak anomaly well separated from the PE with gradual
enhancement in the quenched random pinning.Comment: 9 figure
Finite-Correlation-Time Effects in the Kinematic Dynamo Problem
Most of the theoretical results on the kinematic amplification of small-scale
magnetic fluctuations by turbulence have been confined to the model of
white-noise-like advecting turbulent velocity field. In this work, the
statistics of the passive magnetic field in the diffusion-free regime are
considered for the case when the advecting flow is finite-time correlated. A
new method is developed that allows one to systematically construct the
correlation-time expansion for statistical characteristics of the field. The
expansion is valid provided the velocity correlation time is smaller than the
characteristic growth time of the magnetic fluctuations. This expansion is
carried out up to first order in the general case of a d-dimensional
arbitrarily compressible advecting flow. The growth rates for all moments of
the magnetic field are derived. The effect of the first-order corrections is to
reduce these growth rates. It is shown that introducing a finite correlation
time leads to the loss of the small-scale statistical universality, which was
present in the limit of the delta-correlated velocity field. Namely, the shape
of the velocity time-correlation profile and the large-scale spatial structure
of the flow become important. The latter is a new effect, that implies, in
particular, that the approximation of a locally-linear shear flow does not
fully capture the effect of nonvanishing correlation time. Physical
applications of this theory include the small-scale kinematic dynamo in the
interstellar medium and protogalactic plasmas.Comment: revised; revtex, 23 pages, 1 figure; this is the final version of
this paper as published in Physics of Plasma
Effect of pinning and driving force on the metastability effects in weakly pinned superconductors and the determination of spinodal line pertaining to order-disorder transition
We explore the effect of varying drive on metastability features exhibited by
the vortex matter in single crystals of 2H-NbSe and CeRu with varying
degree of random pinning. An optimal balance between the pinning and driving
force is needed to view the metastability effects in typically weakly pinned
specimen of low temperature superconductors. As one uses samples with larger
pinning in order to differentiate the response of different metastable vortex
states, one encounters a new phenomena, viz., the second magnetization peak
(SMP) anomaly prior to the PE. Interplay between the path dependence in the
critical current density and the non-linearity in the electromagnetic response
determine the metastability effects seen in first and the third harmonic
response of the ac susceptibility across the temperature regions of the SMP and
the PE. The limiting temperature above which metastability effects cease can be
conveniently located in the third harmonic data, and the observed behavior can
be rationalized within the Beans Critical State model. A vortex phase diagram
showing the different vortex phases for a typically weakly pinned specimen has
been constructed via the ac susceptibility data in a crystal of 2H-NbSe
which shows the SMP and the PE anomalies. The phase space of coexisting weaker
and stronger pinned regions has been identified. It can be bifurcated into two
parts, where the order and disorder dominate, respectively. The former part
continuously connects to the reentrant disordered vortex phase pertaining to
the small bundle pinning regime, where the vortices are far apart, interaction
effects are weak and the polycrystalline form of flux line lattice prevails.Comment: Submitted to the Special Volume on Vortex State Studies, Pramana J.
Phy
Development of the Asia pacific consortium on osteoporosis (APCO) framework: Clinical standards of care for the screening, diagnosis, and management of osteoporosis in the Asia-pacific region
Guidelines for doctors managing osteoporosis in the Asia-Pacific region vary widely. We compared 18 guidelines for similarities and differences in five key areas. We then used a structured consensus process to develop clinical standards of care for the diagnosis and management of osteoporosis and for improving the quality of care.Purpose: Minimum clinical standards for assessment and management of osteoporosis are needed in the Asia-Pacific (AP) region to inform clinical practice guidelines (CPGs) and to improve osteoporosis care. We present the framework of these clinical standards and describe its development.Methods: We conducted a structured comparative analysis of existing CPGs in the AP region using a 5IQ model (identification, investigation, information, intervention, integration, and quality). One-hundred data elements were extracted from each guideline. We then employed a four-round Delphi consensus process to structure the framework, identify key components of guidance, and develop clinical care standards.Results: Eighteen guidelines were included. The 5IQ analysis demonstrated marked heterogeneity, notably in guidance on risk factors, the use of biochemical markers, self-care information for patients, indications for osteoporosis treatment, use of fracture risk assessment tools, and protocols for monitoring treatment. There was minimal guidance on long-term management plans or on strategies and systems for clinical quality improvement. Twenty-nine APCO members participated in the Delphi process, resulting in consensus on 16 clinical standards, with levels of attainment defined for those on identification and investigation of fragility fractures, vertebral fracture assessment, and inclusion of quality metrics in guidelines.Conclusion: The 5IQ analysis confirmed previous anecdotal observations of marked heterogeneity of osteoporosis clinical guidelines in the AP region. The Framework provides practical, clear, and feasible recommendations for osteoporosis care and can be adapted for use in other such vastly diverse regions. Implementation of the standards is expected to significantly lessen the global burden of osteoporosis
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