The flattening of the X-ray spectrum of sco X-1 at energies beyond 40 keV

The measurements of the hard X-ray spectrum of Sco X-1 in the energy interval 20–150 keV in three balloon flights from Hyderabad, India are reported. These results show conclusively that the spectrum of Sco X-1 is very flat in the energy interval 40–150 keV and the measured fluxes beyond 60 keV are several orders of magnitude higher than those expected on the basis of an extrapolation of bremsstrahlung spectrum from a thin hot plasma at a temperature corresponding tokT=5 keV, which is applicable for Sco X-1 for energies <40 keV. The results are compared with those of other investigators of hard X-rays from Sco X-1, and the implication of the results is briefly discussed.     

Time-dependentH-,X- andY-functions for an anisotropically-scattering atmosphere

We have considered a homogeneous atmosphere scattering anisotropically with Dirac -function type time-dependent incidence. We used the method of integral operator developed by Ambartsumian and the theory ofN-solutions developed by Busbridge to find the correspondingH-function (in semi-infinite atmosphere) andX- andY-functions (in finite atmosphere).     

The spectrum of diffuse cosmic X-rays in the 20–125 keV range

Diffuse cosmic X-rays in the energy range 20–125 keV were measured in four balloon flights from Hyderabad, India during 1968–70 using almost identical X-ray telescopes mounted on oriented platforms. The results from these flights show that the spectrum of the diffuse cosmic X-rays can be represented by the form dN/dE=29E ^–2.1±0.3 photons/(cm² sr s keV) in 20–125 keV interval after corrections for photoelectric absorption and Compton scattering effects in the atmosphere. The best fit spectrum of all published results in the energy interval 20–200 keV can be represented by the form dN/dE=36E ^–2.1±0.1 photons/(cm² sr s keV) after similar corrections are effected, and there is no need for a change of spectral index in this energy interval. The intensity at 20 keV obtained from the above spectrum agrees well with that given by the spectral form dN/dE=10E ^–1.7±0.1 photons/(cm² sr s keV) in the energy interval 1–20 keV in several rocket experiments. Therefore it is concluded that if there is a break in the spectrum, it occurs between 10 and 20 keV with a change of spectral index by about 0.5, or the index is continuously changing from 1.7±0.1 to 2.1±0.1 in 10–20 keV interval. The implications of the results are briefly discussed.     

Effect of PDOP on performance of Kalman Filters for GNSS-based space vehicle position estimation

GPS Solutions - A theoretical performance analysis of Kalman Filters for Global Navigation Satellite System GNSS-based space vehicle position estimation in varying Position Dilution of Precision...     

Variation of γ-Ray and Particle Fluxes At the Sea Level During the Total Solar Eclipse of 24 October, 1995

A Total Solar Eclipse (TSE) was observed from Diamond Harbour (lat. 22.2°N, long 88.2°E) on 24 October 1995. The variation of -ray intensity was measured in the energy range of 0.3–3.0 MeV for different time spans throughout the period of the eclipse. A CR-39 detector was used to look at the change in the fluxes of neutral and charged particles. The maximum drop ( 25%) in the intensity of -ray was observed in the range 2.5–3 MeV during TSE. The CR-39 results showed the appearance of a good number of tracks and a small variation of proton and neutron flux of 10% which was not significant statistically. Low energy -ray fluxes at sea level originate from the secondary electron-photon components of cosmic rays in the atmosphere; its modulation by TSE is interpreted as follows. The cooling of the atmosphere in the path of the umbra induces a reduction of the height of the main production layer of the nuclear component, as a result of which, fewer µ^± mesons (from the decay of the^± mesons) decay to e^±. This leads to a small reduction in the flux of electron-photon component at sea level which originates from this branch; the main branch of e - component from ⁰ decay remains nearly unaffected. As the total mass of air remains the same, little or no change in the slow proton or the neutron flux at sea level is expected. These are consistent with the present observations. For a better understanding, further studies of this new phenomenon during future TSE are suggested.     

Accretion of holographic dark energy: dependency only upon horizon radius of expanding universe

In this paper we deal with accretion of dark energy in the holographic dark energy model for a general non-rotating static spherically symmetric black hole. The mass of the black hole increases or decreases depending on the nature of the holographic dark energy (quintessence or phantom) as well as on some integration parameters. It is to be illustrated that the enhancement or reduction of mass of a black hole is independent of the mass or size of the black hole itself. Rather it depends only upon the radius of the event horizon of the universe. Finally, the generalized second law of thermodynamics has been studied on the event horizon to be assured that the law holds even if when the black hole mass is decreasing though it is engrossing some mass.     

Kinematics of horizontal simple shear zones of concentric arcs (Taylor–Couette flow) with incompressible Newtonian rheology

We present preliminary kinematic analyses of Taylor–Couette flow. We consider deformation of a Newtonian incompressible ductile material inside rotating horizontal listric (concentric circular) boundaries. The velocity profile is curved indicating non-uniform shear strain but leads to the same shear sense. Each material point on progressive shear keeps increasing shear strain linearly with time. A curve of no movement, the ‘neutral curve’, may exist inside the shear zone. Irregular geometries of initially regular markers and their individual non-matching strain paths indicate inhomogeneous deformaion in such Taylor–Couette flow.     

Application of Continuous Wavelet Transform in?Examining Soil Spatial Variation: A?Review

An adequate understanding of soil spatial variation as a function of space and scale is necessary in ecological modeling, environmental prediction, precision agriculture, soil quality assessment and natural resources management. Soil spatial variation can be partitioned into frequencies (scale) and positions (location) by the wavelet transform. This review focuses mainly on different applications of the continuous wavelet transform (CWT) for the identification of the scale and location dependence of soil attributes. We discussed both wavelet spectra and wavelet coherence in our analysis of soil spatial variation. Global wavelet spectra, being the sum of wavelet spectra over all spatial locations at a scale, can be used to examine the dominant scale of variation. Furthermore, some variations at a particular scale persist over all locations (termed global features), whereas others are present at only a few locations (localized features). Wavelet spectra can be used to identify both localized and global features. The combination of localized and global features provides a complete picture of the scale-location information of different processes in the field and may provide better guidance in designing efficient management practices. Wavelet coherency partitions the total correlation between two variables into correlations at different scales and locations, while also revealing the scale- and location-specific relationship between those two variables. This relationship may be helpful in developing predictive links between one property and another.     

Universe bounded by apparent horizon: an irreversible thermodynamic prescription

In this work, we study universe bounded by apparent horizon as an irreversible thermodynamical system. Using the non equilibrium thermodynamical technique, the modified entropy variation on the apparent horizon has been evaluated in general. Two dark energy models are presented and results are analyzed.