Electron-probe investigation of some intergrowths in iron-titanium minerals from Rosetta black sands     

Essam E. El-Hinnawi 《Contributions to Mineralogy and Petrology》1969,21(4):332-337

The nature of exsolution of ilmenite in titanomagnetite and of the alteration of ilmenite in Rosetta black sands was investigated by the electron micro-probe analyzer. The mode of formation of such micro-intergrowths has been explained and mainly attributed to oxidation processes.

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Zusammenfassung Die Entmischungen von Ilmenit und Titanomagnetit und die Umwandlungen von Ilmenit des Schwarz-Sandes aus Rosetta wurden mit Hilfe der Elektronen-Mikrosonde qualitativ untersucht. Die Art von solchen Verwachsungen und deren Entwicklungsablauf wurden diskutiert.

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Theory of radio occultation by Saturn's rings     

Essam A. Marouf  G.Leonard Tyler  Von R. Eshleman 《Icarus》1982,49(2):161-193

The radio occultation technique is developed here as a new method for the study of the physical properties of planetary ring systems. Particular reference is made to geometrical and system characteristics of the Voyager dual-wavelength (13 and 3.6 cm) experiment at Saturn. The rings are studied based on the perturbations they introduce in the spectrum of coherent sinusoidal radio signals transmitted through the rings from a spacecraft in the vicinity of the planet to Earth. Two separate signal components are identified in a perturbed spectrum: a sinusoidal component that remains coherent with the incident signal but is reduced in intensity and possibly changed in phase, and a Doppler-broadened incoherent component whose spectral shape and strength are determined by the occultation geometry and the radial variation of the near-forward radar cross section of illuminated ringlets. Both components are derived in terms of the physical ring properties starting from a conventional radar formulation of the problem of single scattering on ensembles of discrete scatterers, which is then generalized to include near-forward multiple scattering. The latter is accomplished through special solutions of the equation of transfer for particles that are larger than the wavelength. When the occultation geometry is optimized, contributions of an individual ringlet to a perturbed spectrum can be identified with radial resolution on the order of a few kilometers for the coherent component and a few hundred kilometers for the incoherent one, thus permitting high-resolution reconstruction of the radial profile of the optical depth, as well as reconstruction of the radar cross section of resolved ringlets. Simultaneous estimates of the optical depth and radar cross section of a ringlet at 3.6 cm-gl allow separation of its aerial density and particle size, if the particles are of known material and form a narrow size distibution with radii greater than several tens of centimeters. This separation is also achieved for radii ?10 cm from differential effects on the coherent signal parameters at 3.6- and 13-cm wavelengths. For the more general case of a broad size distribution modeled by a power law, the absence of differential effects on the coherent signal binds the minimum size to be ?10 cm. In this case, the radius inferred from an estimate of the radar cross section represents an equivalent radius, which is strongly controlled by the maximum size of the distribution provided that the power index is in the range 3 to 4. On the other hand, detection of differential coherent signal extinction determines an upper bound on the maximum size and a lower bound on the power index, assuming water-ice particles. These bounds, together with an inferred equivalent size, constrain the size distribution at both its small and large ends.  相似文献   

Electrical structure of the tectonically active Kalabsha Fault, Aswan, Egypt     

Mahmoud Mekkawi  Pierre-Andr Schnegg  Tarek Arafa-Hamed  Essam Elathy 《Earth and Planetary Science Letters》2005,240(3-4):764-773

In this work, we use the magnetotelluric (MT) method to detect geoelectrical conductivity anomalies in the Earth's crust and link them to local seismic activity. This application affords the unusual opportunity to study the percolation of water from a lake into a fault system and its effect on the induced seismicity. MT measurements were carried out in the period range 0.0046–420 s at nine sites along a 15 km-long North–South profile crossing the Kalabsha Fault, on the western bank of Lake Aswan. Data were analysed by 2D simultaneous inversion of both polarisations. The resulting model is compared with the local seismicity map and reveals the conductive signature of the fault, as well as geological and tectonic stresses prevailing in the Aswan area. Our MT investigations show the following features:

The measured MT strike aligns with the seismic epicentre axis corresponding to the Kalabsha Fault.

While crossing the Fault, enhanced conductivity is found down to depths of 5 km on a 1–2 km profile segment.

At mid-crustal depths (20 km), a very high conductive body is found to coincide with the main seismic cluster in the Aswan area.

These observations indicate that seismic activity and high electrical conductivity are related. The link between them is the presence of crustal fluids which are presumably the cause of the high conductivity observed. Their presence is also required to trigger the observed seismicity. In addition, we explain the lower conductivity of the local upper crust in terms of stress-modulated rock porosity. We believe that these results are of general significance, as they could explain the mid-crustal seismicity of tectonically active zones.  相似文献   

Discussion on some FFT problems to determine the geoid     

Essam Ghanem LI Jiancheng 《地球空间信息科学学报》2000,3(2):53-57

1　ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｔｈｅｍｉｄ＿1 980ｓ,ｔｈｅｆａｓｔＦｏｕｒｉｅｒｔｒａｎｓｆｏｒｍａｔｉｏｎ(ＦＦＴ)ｂｅｇａｎｔｏｆｉｎｄｗｉｄｅｓｐｒｅａｄｕｓｅｉｎｇｅｏｉｄｄｅｔｅｒ ｍｉｎａｔｉｏｎｂｅｃａｕｓｅｏｆｉｔｓｅｆｆｉｃｉｅｎｔｅｖａｌｕａｔｉｏｎｏｆｃｏｎ ｖｏｌｕｔｉｏｎｉｎｔｅｇｒａｌｓ,ｗｈｅｎｃｏｍｐａｒｅｄｔｏｃｌａｓｓｉｃａｌｎｕ ｍｅｒｉｃａｌｉｎｔｅｇｒａｔｉｏｎ .Ｆｏｒｍａｎｙｙｅａｒｓ,ｔｈｅｐｌａｎａｒ,2＿ＤＦＦＴｈａｄｂｅｅｎｕｓｅｄ (Ｓｃｈｗａｒｚ ,1 …  相似文献   

Photometric study of three ultrashort-period contact binaries     

L. Liu  A. Essam  M. A. El-Sadek  X. Xiong

《Astrophysics and Space Science》2018,363(1):15

We carried out high-precision photometric observations of three eclipsing ultrashort-period contact binaries (USPCBs). Theoretical models were fitted to the light curves by means of the Wilson-Devinney code. The solutions suggest that the three targets have evolved to a contact phase. The photometric results are as follows: (a) 1SWASP?J030749.87?365201.7, \(q=0.439\pm0.003\), \(f=0.0\pm3.6\%\); (b) 1SWASP?J213252.93?441822.6, \(q=0.560\pm0.003\), \(f=14.2\pm1.9\%\); (c) 1SWASP?J200059.78+054408.9, \(q=0.436\pm0.008\), \(f=58.4\pm1.8\%\). The light curves show O’Connell effects, which can be modeled by the assumed cool spots. The cool spots models are strongly supported by the night-to-night variations in the \(I\)-band light curves of 1SWASP?J030749.87?365201.7. For a comparative study, we collected the whole set of 28 well-studied USPCBs with \(P < 0.24\) day. Thus, we found that most of them (17 of 28) are in shallow contact (i.e. fill-out factors \(f<20\%\)). Only four USPCBs have deep fill-out factors (i.e. \(f>50\%\)). Generally, contact binaries with deep fill-out factors are going to merge, but it is believed that USPCBs have just evolved to a contact phase. Hence, the deep USPCB 1SWASP?J200059.78+054408.9 seems to be a contradiction, making it very interesting. Particularly, 1SWASP?J030749.87?365201.7 is a zero contact binary in thermal equilibrium, implying that it should be a turn-off sample as predicted by the thermal relaxation oscillation (TRO) theory.  相似文献   

Time-fractional Burgers equation for dust acoustic waves in a two different temperatures dusty plasma     

S. A. El-Wakil  Essam M. Abulwafa  E. K. El-Shewy  Abeer A. Mahmoud 《Astrophysics and Space Science》2013,346(2):383-393

The reductive perturbation method has been used to derive the Burgers equation for dust acoustic shock waves in unmagnetized plasma having electrons, singly charged ions, hot and cold dust species with Boltzmann distributions for electrons and ions in the presence of the cold (hot) dust viscosity coefficients. The time-fractional Burgers equation is formulated using Euler-Lagrange variational technique and is solved using the variational-iteration method. The effect of time fractional parameter on the behavior of the shock waves in the dusty plasma has been investigated.  相似文献   

Discussion on some FFT problems to determine the geoid     

Essam Ghanem  Li Jiancheng 《地球空间信息科学学报》2013,16(2):53-57

The aim of this investigation is to study some FFT problems related to the application of FFT to gravity field convolution integrals. And the others, such as the effect of spectral leakage, edge effects, cyclic convolution and effect of padding, are also discussed. A numerical test for these problems is made. A large area of Western China selected for the test is located between 30°N～36°N and 96°E～102°E and includes 1 858 gravity observations on land. The results show that the removal of the bias in the residual gravity anomalies is important to avoid spectral leakage. One hundred percent zero padding is highly recommended for further research of the geoid to remove cyclic convolution errors and edge effects. 1-D FFT is recommended for precise local geoid determination because it does not use kernel approximation.  相似文献   

Photometric and spectroscopic analysis of YY CrB     

A. Essam  S.M. Saad  M.I. Nouh  A. Dumitrescu  M.M. El-Khateeb  A. Haroon 《New Astronomy》2010,15(2):227-233

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Diffraction theory modeling of near-forward radio wave scattering from particle clusters     

Fraser S. Thomson  Essam A. Marouf 《Icarus》2009,204(1):290-302

We investigate the use of diffraction theory as an alternative to solving the full electromagnetic problem of near-forward scattering by a collection of dielectric spheres of arbitrary spacing and orientation. We define an amplitude screen, which is constructed by projecting the shadows of a cluster of spheres onto a plane perpendicular to the wave vector of the incident radio wave. The far-field (Fraunhofer) diffraction pattern of the amplitude screen is then computed and compared with the Mie-theoretic result. We show that for EM scattering from a cluster of electrically large spheres—both singly-sized and belonging to a size distribution—there is excellent agreement between the exact Mie solution and its diffraction theory approximation when near-forward scattering is the angular range of interest. This excellent agreement holds over a broad range of particle separation and orientation configurations relative to the incidence direction. It is also achieved at a much reduced computational cost compared with an exact solution of the electromagnetic interaction problem. Fortified by these results, the authors have applied diffraction theory to the analysis of Cassini radio occultation data, thereby detecting fine-scale structure in Saturn’s rings [Thomson, F.S., Marouf, E.A., Tyler, G.L., French, R.G., Rappoport, N.J., 2007. Periodic microstructure in Saturn’s rings A and B. Geophys. Res. Lett. 34, L24203].  相似文献   

Seismicity and major geologic structures of Tiran and Sanafir islands and their surroundings in the Red Sea     

Hamdy A. Aboulela  Essam Aboud  Rashad A. Bantan 《Environmental Earth Sciences》2017,76(23):793

Tiran and Sanafir islands and their surrounding areas are very important due to their location within the Red Sea, which is in a triple junction among the African and Arabian plates and the Sinai Peninsula microplate. Consequently, this area should be studied from a geological point of view, particularly because there is a plan to construct King Salman’s bridge connecting Egypt and Saudi Arabia. Freely available potential field data, such as magnetic and gravity data, were integrated with seismological data from nearby seismic stations to understand the regional structure and seismic activity in the area. Potential field data were analysed using edge detection techniques (Tilt DeRivative and horizontal gradient) for qualitative interpretation and 2D inversion modelling for quantitative interpretation. Seismological data were analysed geostatistically to identify many epicentre locations and estimate the focal depths. The results of the potential field data analysis indicate that Tiran and Sanafir islands are located along a subsurface geological edge trending NW, parallel to the Red Sea. A similarity in potential field anomalies between both islands and the southern Sinai Peninsula indicates that these islands were separated from the Sinai Peninsula during the formation of the Gulf of Aqaba via Dead Sea Transform fault. The analysis of the seismic data indicates that a specific motion characterizes each focal depth solution. The seismic events are related to main structural trends NW–SE and NE–SW.  相似文献