690 research outputs found
High Energy Emission Processes in OJ 287 during 2009 Flare
The broadband spectrum of a BL Lac object, OJ 287, from radio to
-rays obtained during a major -ray flare detected by
\emph{Fermi} in 2009 are studied to understand the high energy emission
mechanism during this episode. Using a simple one-zone leptonic model,
incorporating synchrotron and inverse Compton emission processes, we show that
the explanation of high energy emission from X-rays to -rays, by
considering a single emission mechanism, namely, synchrotron self-Compton (SSC)
or external Compton (EC) requires unlikely physical conditions. However, a
combination of both SSC and EC mechanisms can reproduce the observed high
energy spectrum satisfactorily. Using these emission mechanisms we extract the
physical parameters governing the source and its environment. Our study
suggests that the emission region of OJ 287 is surrounded by a warm infrared
(IR) emitting region of . Assuming this region as a spherical
cloud illuminated by an accretion disk, we obtain the location of the emission
region to be . This supports the claim that the -ray
emission from OJ 287 during the 2009 flare arises from a location far away from
the central engine as deduced from millimeter-gamma ray correlation study and
very long baseline array images.Comment: 22 pages, 7 figures, 1 table, accepted for publication in MNRA
Brightest Fermi-LAT Flares of PKS 1222+216: Implications on Emission and Acceleration Processes
We present a high time resolution study of the two brightest -ray
outbursts from a blazar PKS 1222+216 observed by the \textit{Fermi} Large Area
Telescope (LAT) in 2010. The -ray light-curves obtained in four
different energy bands: 0.1--3, 0.1--0.3, 0.3--1 and 1--3 GeV, with time bin of
6 hr, show asymmetric profiles with a similar rise time in all the bands but a
rapid decline during the April flare and a gradual one during the June. The
light-curves during the April flare show days long plateau in 0.1--0.3
GeV emission, erratic variations in 0.3--1 GeV emission, and a daily recurring
feature in 1--3 GeV emission until the rapid rise and decline within a day. The
June flare shows a monotonic rise until the peak, followed by a gradual decline
powered mainly by the multi-peak 0.1--0.3 GeV emission. The peak fluxes during
both the flares are similar except in the 1--3 GeV band in April which is twice
the corresponding flux during the June flare. Hardness ratios during the April
flare indicate spectral hardening in the rising phase followed by softening
during the decay. We attribute this behavior to the development of a shock
associated with an increase in acceleration efficiency followed by its decay
leading to spectral softening. The June flare suggests hardening during the
rise followed by a complicated energy dependent behavior during the decay.
Observed features during the June flare favor multiple emission regions while
the overall flaring episode can be related to jet dynamics.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in Ap
Measurement of the topological surface state optical conductance in bulk-insulating Sn-doped BiSbTeS single crystals
Topological surface states have been extensively observed via optics in thin
films of topological insulators. However, in typical thick single crystals of
these materials, bulk states are dominant and it is difficult for optics to
verify the existence of topological surface states definitively. In this work,
we studied the charge dynamics of the newly formulated bulk-insulating Sn-doped
BiSbTeS crystal by using time-domain terahertz
spectroscopy. This compound shows much better insulating behavior than any
other bulk-insulating topological insulators reported previously. The
transmission can be enhanced an amount which is 5 of the zero-field
transmission by applying magnetic field to 7 T, an effect which we believe is
due to the suppression of topological surface states. This suppression is
essentially independent of the thicknesses of the samples, showing the
two-dimensional nature of the transport. The suppression of surface states in
field allows us to use the crystal slab itself as a reference sample to extract
the surface conductance, mobility, charge density and scattering rate. Our
measurements set the stage for the investigation of phenomena out of the
semi-classical regime, such as the topological magneto-electric effect.Comment: 5 pages, 3 figures, submitted in Augus
Influence of weather parameters on progress of rust disease severity in pea (Pisum sativum L.)
Decision to apply one or more fungicide spray will depend on the risk of rust epidemic in a particular year. Rust epidemic is determined by interaction of three important factors namely, susceptible host, virulent pathogen and the most important i.e. favourable environment for a particular period of time. Therefore, it is necessary to study the correlation between different meteorological parameters and rust severity. Present study revealed that rust dis-ease generally appeared 60 days after sowing and was subsequently increased with a period of time till harvest (4.17 to 64.17 per cent). Disease was observed at a maximum temperature of 16.85 to 24.79áµ’C, 8.09 to 12.27áµ’C minimum temperature, 90.30 to 95.70 percent morning Relative Humidity (RH), 54.80 to 78.40 percent afternoons RH, 0.10 to 5.45mm rainfall and wind velocity of 3.93 to 4.23 km/hr. The correlation between different meteorological parameters and rust severity revealed that per cent disease severity showed highly positive correlation with maxi-mum temperature (r = 0.977), minimum temperature (r = 0.704), rainfall (r = 0.039) and wind velocity(r = 0.093) whereas disease severity show negative correlation with morning(r=-0.925) and afternoon RH (r = -0.926). It was observed that the rust severity is highly influenced by the different weather parameters such as temperature, relative humidity, rainfall and wind velocity. This information will help the researchers in formulating the forecasting model for the rust disease in pea and will also supports farmers in decision making regarding time of occurrence of rust epi-demic and thereby, allow timely scheduling and need based utilization of fungicides accordingly for the management of pea rust
Superconductivity with high upper critical field in Ta-Hf Alloys
High upper-critical field superconducting alloys are required for
superconducting device applications. In this study, we extensively
characterized the structure and superconducting properties of alloys Ta
Hf (x = 0.2, 0.4, 0.5, 0.6 and 0.8). The substitution of Hf (T =
0.12 K, type-I superconductor) with Ta (T = 4.4 K, type-I superconductor)
shows an anomalous enhancement of T with variation of composition.
Interestingly, all compositions exhibited strongly coupled bulk type-II
superconductivity with a high upper critical field. In particular, for
compositions x = 0.2, and 0.4, the upper critical field (H) approached
the Pauli limiting field.Comment: 8 pages, 6 figure
Deforestation analysis using Random Forest and interactive supervised classification approach
The increasing demand for forest resources leads to overexploitation to a greater extent, raising the alarm for the environmental consequences. The excessive use of forest resources results in deforestation, which needs to be addressed for maintaining the natural ecosystem balance. This research focuses on the deforestation analysis of a territory in the Tartar district in Azerbaijan. The changes in the forest area have been analyzed using the high-resolution Azersky satellite datasets for the three alternative years, 2017, 2019, and 2021. Two classification approaches, namely Random Forest (RF) and NDVI- based interactive supervised classification, were implemented for this purpose. The statistical analysis of the results indicates the gradual decrease in the forest area from the year 2017 to the year 2021, which has been evaluated by visual interpretation through the change maps of the forest area. From RF classification results, it has been observed that there has been an overall decrease of 9.5% from 2017 to 2021. Also, the NDVI-based interactive supervised classification approach indicates an overall deforestation rate of 4.79% from 2017 to 2021. This work shows that the forest area in the study region has considerably reduced over the years, and there is a need to closely monitor deforestation in the considered study area
Buffalo Rearing System in Bhadawari Breeding Tract
Bhadawari buffalo is one of the recognized buffalo breeds in India, known for high milk fat content, which may go as high as 14% (Kushwaha et al., 2012). Zachariah (1941) had first described this breed as “Bhadawan” buffalo – the best breed of buffaloes in Uttar Pradesh and found in the districts of Agra and Etah (Central India). Presently Bhadawari Buffaloes are found in the ravines of Yamuna and Chambal rivers spread over in the states of Uttar Pradesh and Madhya Pradesh. These buffaloes have adapted to the harsh conditions of the ravines with undulating topography, thorny and scanty bushes, climatic stress and draught conditions. The buffaloes are of medium size with medium to low milk yield having high fat content. Animals are of copper color, have two white rings on the lower side of the neck and legs are comparatively shorter. Indiscriminate crossbreeding with Murrah buffaloes, for increasing milk production, during the last 3-4 decades has reduced the number of Bhadawari buffaloes in the region. Looking into the need to conserve this gene pool, Indian Council of Agricultural Research has initiated efforts on conservation and improvement of Bhadawari buffaloes at Indian Grassland and Fodder Research Institute, Jhansi (IGFRI) under Network program in the year 2001. The present study was conducted to collect the information regarding existing buffalo rearing practices adopted by the farmers in the Bhadawari breeding tract
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