Scope of high-frequency time keeping in searches for short-period gamma-ray sources

The online version of the original article can be found at     

Search for 12.6 millisecond periodicity in TeV gamma rays from Cygnus X-3

Cygnus X-3, an X-ray binary with an orbital period 4.8 hr was seen to be emitting γ-rays with the same period at TeV energies by several groups. In addition the Durham group (Chadwicket al. 1985) published their observations on the existence of a pulsar in the Cyg X-3 system, emitting TeV γ-rays with a periodicity of approximately 12.6 ms. We observed this object during 1986 October-November and did not detect any pulsed emission of TeV γ-rays in the range of periods from 12.5850 to 12.5967 ms.     

Assessing changes in the above ground biomass and carbon stocks of Lidder valley,Kashmir Himalaya,India

The changes in the land use and land cover (LULC), above ground biomass (AGB) and the associated above ground carbon (AGC) stocks were assessed in Lidder Valley, Kashmir Himalaya using satellite data (1980–2013), allometric equations and phytosociological data. Change detection analysis of LULC, comprising of eight vegetation and five non-vegetation types, indicated that 6% (74.5 km²) of the dense evergreen forest has degraded. Degraded forest and settlement increased by 20 and 52.8 km², respectively. Normalized difference vegetation index was assessed and correlated with the field-based biomass estimates to arrive at best-fit models for remotely sensed AGB estimates for 2005 and 2013. Total loss of 1.018 Megatons of AGB and 0.5 Megatons of AGC was estimated from the area during 33-year period which would have an adverse effect on the carbon sequestration potential of the area which is already facing the brunt of climate change.     

Mechanization and technical interactions in multi-species Indian fisheries: implications for economic and biological sustainability

Joint capture of multiple species by multiple fleets results in technical and economic interactions between fleets. This paper develops a bioeconomic model that incorporates interrelationships between fleets for a representative fishery in India. The study analyzes the impacts of overcapitalization on bio-economic sustainability. Results show that a continuation of the current fishing intensity would deplete most commercially important species in the near future. However, an optimal effort re-allocation between fleets would increase fishery profits substantially, although some species would remain unsustainable. The study demonstrates how the newly emerging, large bodies of fishery data can be used for management decisions in developing countries.     

Quasi-periodic, global oscillations in sea level pressure on intraseasonal timescales

The sea level pressure (SLP) variability in 30–60 day intraseasonal timescales is investigated using 25 years of reanalysis data addressing two issues. The first concerns the non-zero zonal mean component of SLP near the equator and its meridional connections, and the second concerns the fast eastward propagation (EP) speed of SLP compared to that of zonal wind. It is shown that the entire globe resonates with high amplitude wave activity during some periods which may last for few to several months, followed by lull periods of varying duration. SLP variations in the tropical belt are highly coherent from 25°S to 25°N, uncorrelated with variations in mid latitudes and again significantly correlated but with opposite phase around 60°S and 65°N. Near the equator (8°S–8°N), the zonal mean contributes significantly to the total variance in SLP, and after its removal, SLP shows a dominant zonal wavenumber one structure having a periodicity of 40 days and EP speeds comparable to that of zonal winds in the Indian Ocean. SLP from many of the atmospheric and coupled general circulation models show similar behaviour in the meridional direction although their propagation characteristics in the tropical belt differ widely.     

A copula-based closed-form binary logit choice model for accommodating spatial correlation across observational units

This study focuses on accommodating spatial dependency in data indexed by geographic location. In particular, the emphasis is on accommodating spatial error correlation across observational units in binary discrete choice models. We propose a copula-based approach to spatial dependence modeling based on a spatial logit structure rather than a spatial probit structure. In this approach, the dependence between the logistic error terms of different observational units is directly accommodated using a multivariate logistic distribution based on the Farlie-Gumbel-Morgenstein (FGM) copula. The approach represents a simple and powerful technique that results in a closed-form analytic expression for the joint probability of choice across observational units, and is straightforward to apply using a standard and direct maximum likelihood inference procedure. There is no simulation machinery involved, leading to substantial computation gains relative to current methods to address spatial correlation. The approach is applied to teenagers’ physical activity participation levels, a subject of considerable interest in the public health, transportation, sociology, and adolescence development fields. The results indicate that failing to accommodate heteroscedasticity and spatial correlation can lead to inconsistent and inefficient parameter estimates, as well as incorrect conclusions regarding the elasticity effects of exogenous variables.

Gamma Ray and Hadron generated Čerenkov Photon Spectra at Various Observation Altitudes

We study the propagation of erenkov photons generated by Very HighEnergy -rays and hadrons in the atmosphere. The photon productionheight distributions are estimated from semi-empirical methods andcompared with those derived by standard simulation techniques. Incidentspectra at various observation altitudes are then derived after applyingwavelength dependent corrections due to photon attenuation in theatmosphere during the propagation of photons from the height of productionto the height of observation. These are generated both for -ray and hadron primaries of various energies. The derivedproduction height distributions agree very well with those generated bythe simulation package `CORSIKA' at all energies and for both -ray and proton primaries. The incident photon spectra are found to beboth altitude and primary energy dependent. The peak ofthe incident spectrum shifts towards the shorter wavelength withincreasing altitude of observation for a given primary. Also the peak ofthe photon spectrum shifts towards the shorter wavelength withincreasing energy of the primary at a given altitude. The fraction of the UVcomponent in the incident erenkov spectrum is estimated both for-ray and hadronic primaries at various observation altitudes andenergies. Hadron generated erenkov spectra are marginally richer in UVlight and the difference increases slightly at higher altitudes. The fraction of the UV to the visible light in the erenkov spectrum could be a usefulparameter to separate -rays from cosmic ray background only if onecan measure this fraction very accurately.     

Pulsar Observations and Structure of the Local ISM

Results from new observations of pulsars using the Ooty Radio Telescope(ORT) are used for investigating the structure of the Local InterstellarMedium (LISM) and the nature of the plasma turbulence spectrum in theInterstellar Medium (ISM). The observations show anomalous scintillationtowards several nearby pulsars, and these are modelled in terms oflarge-scale spatial inhomogeneities in the distribution of plasma densityfluctuations in the LISM. A 3-component model, where the Solar neighborhoodis surrounded by a shell of enhanced plasma turbulence, is proposed for theLISM. The inferred scattering structure is strikingly similar to the LocalBubble. The nature of the plasma turbulence spectrum is found to be Kolmogorov-like in the spatial scale range 10⁶ m to 10¹¹ m,and there is evidence for excess power at larger spatial scales.     

Artificial Neural Network Approach for Reconstruction of Event Arrival-Direction in Wide-Angle Atmospheric Cerenkov Detector Arrays: A Feasibility Study

A feasibility study has been carried out to assess the potentialof an Artificial Neural Network (ANN) for determiningthe direction of incidence of an Atmospheric Cerenkov Event(ACE) from the arrival-time information registered by aspaced-array of wide-angle Cerenkov detectors. Theresults obtained so far, using both, simulated and experimental data, indicate that a properly-trained net can yield a degree of accuracy which is comparable with what is achieved through the conventional ²-minimization, wavefront-fitting procedure.     

Energetics of the Kerr-Newman black hole by the penrose process

We have studied in detail the energetics of Kerr-Newman black hole by the Penrose process using charged particles. It turns out that the presence of electromagnetic field offers very favourable conditions for energy extraction by allowing for a region with enlarged negative energy states much beyondr = 2M, and higher negative values for energy. However, when uncharged particles are involved, the efficiency of the process (defined as the gain in energy/input energy) gets reduced by the presence of charge on the black hole in comparison with the maximum efficiency limit of 20.7 per cent for the Kerr black hole. This fact is overwhelmingly compensated when charged particles are involved as there exists virtually no upper bound on the efficiency. A specific example of over 100 per cent efficiency is given.