Interaction within the ionosphere in the presence of geomagnetic field

Field intensities within the ionospheric medium during nonlinear transient processes due to interactions among different modes of propagation have been derived taking into consideration the influence of geomagnetic field. The expression for angular distribution of power during wave propagation has also been evaluated.     

The complex, variable near-infrared extinction towards the Nuclear Bulge

Using deep J -, H - and K _S-band observations, we have studied the near-infrared extinction of the Nuclear Bulge, and find significant, complex variations on small physical scales. We have applied a new variable near-infrared colour excess (V-NICE) method to measure the extinction; this method allows for variation in both the extinction law parameter α and the degree of absolute extinction on very small physical scales. We see significant variation in both these parameters on scales of 5 arcsec. In our observed fields, representing a random sample of sight lines to the Nuclear Bulge, we measure α to be  2.64 ± 0.52  , compared to the canonical 'universal' value of 2. Our measured levels of     are similar to previously measured results     ; however, the steeper extinction law results in higher values for   A_J (4.5 ≤ A_J ≤ 10  ) and   A_H (1.5 ≤ A_H ≤ 6.5  ). Only when the extinction law is allowed to vary on the smallest scales can we recover self-consistent measures of the absolute extinction at each wavelength, allowing accurate reddening corrections for field star photometry in the Nuclear Bulge. The steeper extinction law slope also suggests that previous conversions of near-infrared extinction to   A_V   may need to be reconsidered. Finally, we find that the measured values of extinction are significantly dependent on the filter transmission functions of the instrument used to obtain the data. This effect must be taken into account when combining or comparing data from different instruments.     

Disaster prevention,disaster preparedness and local community resilience within the context of disaster risk management in Cameroon

This paper presents a simulation of three components of near-field ground shaking recorded during the main shock at three stations of the September 16, 1978, Tabas (M _w = 7.4), Iran, earthquake, close to the causative fault. A hybrid method composed of a discrete wavenumber method developed by Bouchon (Bouchon in Bull Seismol Soc Am 71:959–971, 1981; Cotton and Coutant in Geophys J Int 128:676–688, 1997) and a stochastic finite-fault modeling based on a dynamic corner frequency proposed by Motazedian and Atkinson (Bull Seismol Soc Am 95:995–1010, 2005), modified by Assatourians and Atkinson (Bull Seismol Soc Am 97:935–1949, 2007), is used for generating the seismograms at low (0.1–1.0 Hz) and high frequencies (1.0–20.0 Hz), respectively. The results are validated by comparing the simulated peak acceleration, peak velocity, peak displacement, Arias intensity, the integral of velocity squared, Fourier spectrum and acceleration response spectrum on a frequency-by-frequency basis, the shape of the normalized integrals of acceleration and velocity squared, and the cross-correlation with the observed time-series data. Each characteristic is compared on a scale from 0 to 10, with 10 being perfect agreement. Also, the results are validated by comparing the simulated ground motions with the modified Mercalli intensity observations reported by reconnaissance teams and showed reasonable agreement. The results of the present study imply that the damage distribution pattern of the 1978 Tabas earthquake can be explained by the source directivity effect.     

Gradient coupling within the terrestrial ionospheric plasma

The gradient coupling within the ionospheric plasma in the presence of local variation of atmospheric heating and other modifications during high power radio wave propagation has been studied. The appropriate form of coupled equations for the modified situation is obtained. The electromagnetic and acoustic modes of wave propagation have been separated and solved, by the WKB method. Field quantities may be used to explore different properties of the medium under the modified condition.     

Artificial modification of ionosphericE-layer by high power radio transmitters

Some anomalous TV receptions in India on band I have been interpreted as being propagated viaF-layer artificially modified by high power broadcast transmitters. In this paper, the possibility of VHF communication by artificially modifiedE-layer is discussed. The presented theoretical analysis shows that high-power broadcast trasmitters can produce substantial changes in temperature and ionisation in theE-layer. The rate of energy transfer from the wave to the medium particles has also been computed. Model calculations are made for a transmitter located near Calcutta. The possibility of the extra-ionisation producing field-aligned structures to support VHF communication is discussed.     

The Effects of Solar Eclipse of August 1, 2008 on Earth’s Atmospheric Parameters

Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.     

Geologic weathering and its implications on the age of the sphinx

The Great Sphinx of Giza is considered by Egyptologists to have been excavated by the Pharaoh Kephren nearly 4500 years ago. Schoch and West (1991) have suggested that the Sphinx is much older, based primarily upon the rounded profile of the strata of the Sphinx thorax and the deep channels present in the walls surrounding the Sphinx ditch. These features, according to them, are due to “precipitation-induced weathering” formed when the Sahara still experienced a humid climate at least 7000 years ago. In this article we show how weathering in an arid environment can produce the rounded profile given the gradual change in lithology of the alternating hard and soft limestone strata. We show further that the channels are actually the pre-Pliocene karst features formed by underground water and exposed due to the excavation of the Sphinx ditch. We propose therefore that, for now, the Sphinx may still be regarded as of pharaonic origin. © 1995 John Wiley & Sons, Inc.     

Dense matter in strong gravitational field of neutron star

Mass, radius and moment of inertia are direct probes of compositions and Equation of State (EoS) of dense matter in neutron star interior. These are computed for novel phases of dense matter involving hyperons and antikaon condensate and their observable consequences are discussed in this article. Furthermore, the relationship between moment of inertia and quadrupole moment is also explored.