Advanced Pulsed Plasma Thrusters and Their Application as a Part of Small Spacecraft Propulsion Systems

The paper presents the research results of the effect of a capacitor energy storage device configuration on the specific characteristics of advanced modern propulsion systems based on the ablative pulsed plasma thrusters (APPT). These thrusters are designed to perform specific tasks within the small spacecrafts with the onboard power capacity up to 200 W.     

Landsat satellite imagery of the Qattara Depression area,Egypt

The Qattara Depression lies in the northern part of the Western Desert of Egypt at a distance of some tens of kilometers to the south of the Mediterranean Sea Coast. The depression in question is the largest one in the great Sahara extending across North Africa. It covers an area of some 19,000 km² at ? 60 m level and the absolute level of its lowest point is about ? 134 m. The depression extends for about 300 km in a roughly ENE-WSW direction, while its width is variable reaching to a maximum of about 145 km. Feasibility studies are currently carried out for the Qattara solar-hydro-electric project which aims at generating hydro-electric power by the drop of the Mediterranean Sea water into the depression after passing through a canal/tunnel system. Peak load electric power may be also generated by raising the water to the small hollow of Deir Kirayim, situated at a higher level near the depression, and allowing it to drop to a low level.For the purpose of assessing the regional criteria involved in the implementation of the project and the environmental impact of such implementation, the Qattara Depression and the surrounding area has been studied on a regional scale by the utilization of LANDSAT satellite imagery. The maps produced by the interpretation of the images in question include those of the geological and environmental units, structural lineations, drainage and vegetation cover. Lineation density and drainage density maps are derived by the computation of the structural lineation and drainage maps respectively. A map of groundwater conditions is worked out on the basis of the image interpretation, and the observations previously carried out on the groundwater aquifers in the Qattara Depression and the surrounding area. LANDSAT satellite image interpretation and computation are supported by intensive observations carried out in the field as well as chemical, petrological and mineralogical analyses of the samples collected.The LANDSAT satellite images proved to be of great importance in mapping the Qattara Depression floor which is hardly accessible to classical mapping, and especially in view of the large area which could be covered by imagery mapping in a reasonably short time compatible with the duration of the feasibility study. The special characters of the spaceborne multispectral imagery have been paramount in deciphering the major regional features of the investigated area.The overall synoptic picture of the regional setting of the geological and environmental units, faults, fractures and folds, drainage lines and plant cover in the large area studied has been clarified for the first time. It has been demonstrated that the Qattara Depression is actually constituted of several small depressions. The environmental impact of the project implementation has been visualized especially regarding the possible influence of the saline water on the fresh groundwater sources. The thick salt accumulation in the depression has been found to be of such extension as to increase the salinity of the Mediterranean Sea water stored in the depression following the implementation of the project. The lineation density map has been particularly of great help in the localization of sites subjected to intense crustal deformation, greater slope instability and run off surface water flooding.     

Partial pressures and nature of products. Application to the photolysis of PH3 and NH3 in the atmosphere of Jupiter and Saturn.

The photolysis of mixtures of gases containing NH3 or PH3 presents important differences mainly due to the strength of the X-H bond. On some examples, these differences are evidenced and the consequences for mixtures of gases containing these two compounds are shown: the photolysis of ammonia and ethylene mainly gives ethyl-, butyl- and hexylamine whereas the photolysis of phosphine and ethylene leads to ethyl- and vinylphosphine. When gaseous mixtures of NH3, PH3 and ethylene are photolyzed together, the presence of phosphine dramatically decreases the formation of nitrogen derivatives. The relevance of such lab studies to the atmospheres of Jupiter and Saturn is discussed.     

Development of a gas chromatography compatible Sample Processing System (SPS) for the in-situ analysis of refractory organic matter in martian soil: preliminary results

In the frame of the 2009 Mars Science Laboratory (MSL) mission a new sample preparation system (SPS) compatible with gas chromatography–mass spectrometry (GC–MS) has been developed for the in situ analysis of complex organic molecules in the Martian soil. The goal is to detect, if they exist, some of the key compounds that play an important role in life on Earth including carboxylic acids, amino acids and nucleobases.     

Massive Stars: Input Physics and Stellar Models

We present a general overview of the structure and evolution of massive stars of masses ≥12 M _⊙ during their pre-supernova stages. We think it is worth reviewing this topic owing to the crucial role of massive stars in astrophysics, especially in the evolution of galaxies and the universe. We have performed several test computations with the aim to analyze and discuss many physical uncertainties still encountered in massive-star evolution. In particular, we explore the effects of mass loss, convection, rotation, ¹²C(α,γ)¹⁶O reaction and initial metallicity. We also compare and analyze the similarities and differences among various works and ours. Finally, we present useful comments on the nucleosynthesis from massive stars concerning the s-process and the yields for ²⁶Al and ⁶⁰Fe.     

M-correlated sweeps performance analysis of mean-level CFARprocessors in multiple target environments

This paper is devoted to the detection performance evaluation of the mean-level (ML) constant false-alarm rate (CFAR) detectors processing M-correlated sweeps in the presence of interfering targets. The consecutive pulses are assumed to be fluctuating according to the Swerling I model. Exact expressions are derived for the detection probability of the conventional mean-level detector (MLD) and its modified versions under Rayleigh fluctuating target model. Performance for independent sweeps can be easily obtained by setting the sweep-to-sweep correlation coefficient equal to zero. Results are obtained for both homogeneous and nonhomogeneous background environments. It is shown that for fixed M, the relative improvement over the single sweep case increases as the correlation between sweeps decreases. For the same parameter values, the minimum MLD has the best performance in the presence of extraneous target returns among the reference noise samples     

Nucleosynthesis in massive stars

We discuss three aspects of the nucleosynthesis in massive and intermediate-mass stars during their early evolutionary phases. These are related to the CNO abundances in giant or supergiant stars, to the²⁶Al yield from massive stars via stellar wind, and to the production of the s-process nuclei in massive stars.     

A refined trigonometric shear deformation theory for thermoelastic bending of functionally graded sandwich plates

A refined trigonometric shear deformation theory (RTSDT) taking into account transverse shear deformation effects is presented for the thermoelastic bending analysis of functionally graded sandwich plates. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, the displacement components are expressed by trigonometric series representation through the plate thickness to develop a two-dimensional theory and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The sandwich with homogeneous facesheet and FGM core is considered. Material properties of the present FGM core are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The influences played by the transverse shear deformation, thermal load, plate aspect ratio, and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of functionally graded plates.     

Remote sensing detection of gold related alteration zones in Um Rus area, Central Eastern Desert of Egypt

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Phased Array L-band Synthetic Aperture Radar (PALSAR) images covering the Um Rus area in the Central Eastern Desert of Egypt were evaluated for mapping geologic structure, lithology, and gold-related alteration zones. The study area is covered by Pan-African basement rocks including gabbro and granodiorite intruded into a variable mixture of metavolcanics and metasediments. The first three principal component analyses (PCA1, PCA2, PCA3) in a Red-Green-Blue (RGB) of the visible through shortwave-infrared (VNIR + SWIR) ASTER bands enabled the discrimination between lithological units. The results show that ASTER band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB identifies the lithological units and discriminates the granodiorite very well from the adjacent rock units.The granodiorites are dissected by gold-bearing quartz veins surrounded by alteration zones. The microscopic examination of samples collected from the alteration zones shows sericitic and argillic alteration zones. The Spectral Angle Mapper (SAM) and Spectral Information Divergence (SID) supervised classification methods were applied using the reference spectra of the USGS spectral library. The results show that these classification methods are capable of mapping the alteration zones as indicated by field verification work. The PALSAR image was enhanced for fracture mapping using the second moment co-occurrence filter. Overlying extracted faults and alteration zone classification images show that the N30E and N-S fractures represent potential zones for gold exploration. It is concluded that the proposed methods can be used as a powerful tool for ore deposit exploration.     

Comparing two models of the Earth''s magnetosphere

The existence of a multiplicity of models of the Earth's magnetosphere raises the question: when are two of them equivalent in representing the real magnetosphere? The isomorphism of any two models of the Earth's magnetosphere is defined in terms of magnetic field characteristics. To assess to what degree empirical models are isomorphic with physical ones, two magnetospheres are compared: the magnetosphere of Mead and Fairfield [1975] and the physical magnetosphere proposed by Buneman, [1993]. Parameters realizing the isomorphism are found for the Buneman magnetosphere and the distribution in space of magnetic field characteristics are presented for both models.