Bianchi Type I Magnetized String Cosmological Model in General Relativity

Bianchi Type I magnetized string cosmological model following the techniques used by Letelier and Stachel, is investigated. To get a determinate model, we assume a condition ∊ = λ (geometric string) where ∊ is the rest energy density, λ the string tension density and expansion (θ) is proportional to eigen value σ₁ ¹ of shear tensor (σ _j ⁱ ), which leads to A = ℓ (BC) ⁿ where A, B, C are metric potentials and ℓ and n are constants. The behaviour of the model in presence and absence of magnetic field is discussed. The physical and geometrical aspects of the model are also discussed.     

Magnetoconvection in Rotating Stars

Linear and nonlinear properties of magnetoconvection in rotating inviscid fluid are investigated. A time dependent one dimensional nonlinear Landau-Gonzburg equation is derived and analyzed at a supercritical pitchfork bifurcation corresponding to a region0 < R _m < R ^* _m (R _m =R ^* _m corresponds to Takens-Bogdanov bifurcation point). This revised version was published online in July 2006 with corrections to the Cover Date.     

Tilted Bianchi Type I Cosmological Models for Barotropic Perfect Fluid in General Relativity

In this paper, we have investigated that tilted Bianchi Type I cosmological models for stiff perfect fluid under a supplementary condition A = B ⁿ between metric potentials, is not possible. The tilted solution is also not possible when we assume A = t ^ℓ, B = t ^m , C = t ⁿ ; ℓ, m and n are constants for ε = p. Thus to preserve tilted nature of model, we assume p = γε, 0 ≤ γ ≤ 1 (barotropic equation of state) for the case A = t ^ℓ B = t ^m and C = t ⁿ . The physical and geometrical aspects of the models are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Back-thrusting in Lesser Himalaya: Evidences from magnetic fabric studies in parts of Almora crystalline zone,Kumaun Lesser Himalaya

The present study aims to understand evolution of the Lesser Himalaya, which consists of (meta) sedimentary and crystalline rocks. Field studies, microscopic and rock magnetic investigations have been carried out on the rocks near the South Almora Thrust (SAT) and the North Almora Thrust (NAT), which separates the Almora Crystalline Zone (ACZ) from the Lesser Himalayan sequences (LHS). The results show that along the South Almora Thrust, the deformation is persistent; however, near the NAT deformation pattern is complex and implies overprinting of original shear sense by a younger deformational event. We attribute this overprinting to late stage back-thrusting along NAT, active after the emplacement of ACZ. During this late stage back-thrusting, rocks of the ACZ and LHS were coupled. Back-thrusts originated below the Lesser Himalayan rocks, probably from the Main Boundary Thrust, and propagated across the sedimentary and crystalline rocks. This study provides new results from multiple investigations, and enhances our understanding of the evolution of the ACZ.     

Properties of dust source material and volcanic ash in Iceland

The volcanic origin, primarily basaltic, of most of the surface material in Iceland influences its physical properties and appearance. Size distributions, shape analyses and melting experiments were made for surface material collected in high-erosion dust source areas and fresh volcanic ash deposits to determine whether they differ from one another and from dust from other major dust sources. The major differences found between Icelandic dust and dust from other major dust sources in the world, such as the Sahara, are in the particle shapes, lower density and darker colour. Icelandic dust particles greater than 20 μm retain volcanic morphological properties that are also found in fresh volcanic ash. Dust and fresh volcanic ash particles less than 20 μm are crystalline and blocky in nature, similar to the dust from other global source regions. The finer grained (<20 μm) Icelandic particles will have similar suspension and transport behaviours and be similarly hazardous to health and infrastructure as non-Icelandic dust. The coarser particles (>20 μm) will have different suspension and transport behaviours than other dusts due to the volcanic morphology. Icelandic surface material has between 5% and 30% glassy particles compared to fresh volcanic ash which has more than 50% glassy particles. Glassy particles were observed to melt at a lower temperature than the mineral grains; and, as a result, volcanic ash is found to be more threatening to aircraft engines than the typical dust from Iceland. Icelandic dust was observed to be blocky, or plate-like in the respirable size fraction, suggesting similar health hazards as dust from other regions.     

Inhomogeneous cosmological models with electromagnetic field in general relativity

In this paper inhomogeneous cosmological models with perfect fluid distributions in presence of electromagnetic field is obtained. Various physical and geometrical properties of the model in presence of electromagnetic field are also discussed.     

The two polymorphs of TlPbSbS3 and the structural relations of phases in the system TlSbS2-PbS

Summary The synthetic TlPbSbS₃ represents a rare example of a sulphosalt with statistical distribution of Tl, Pb and Sb in the structure. Within the TlSbS₂-PbS system, TlPbSbS₃ is the end member of the solid solution series with TlSbS₂, but no solubility with PbS is detected. The high temperature-TlPbSbS₃ is orthorhombic and inverts at about 620 K to the low-temperature phase. The low-temperature modification of TlPbSbS₃ was structurally investigated by X-ray powder diffraction and by the Rietveld analysis of the data. The structure is monoclinic, with a = 4.1707(4) Å, b = 4.2856(4) Å, c = 12.157(1) Å, = 105.49(1)°, space group P2₁/c. Like in the high-temperature form, there is a cation disorder over the equivalent positions in the structure. The interatomic distances of (Tl, Ph, Sb) to S are 2.71, 2.72, 2.88, 3.15, 3.29, 3.51 (Å). There is a close similarity between the TlPbSbS₃ polymorphs and the and forms of SnS, as regards the atomic coordinations and the general structure types and the same type of phase transformation is supposed for both cases. The small differences in the structure type and symmetry, between the low temperature forms of SnS and TlPbSbS₃, result probably from stronger metal-metal interactions in the latter. A substitution-derivative relation to SnS type is established owing to the strong structural effect of the lone electron pairs of Tl and Sb. The substitution of Ag for Tl and Bi for Sb in ABCS₃ type compounds diminishes this effect and PbS type structures are produced.

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Die zwei Polymorphen von TlPbSbS₃ und die Strukturellen Beziehungen von Phasen in System TlSbS₂-PbS

Zusammenfassung Die synthetische Phase TlPbSbS₃ ist ein seltenes Beispiel von einem Sulfosalz mit der statistischen Verteilung von TI, Pb und Sb in der Struktur. In der TlSbS2-PbS Phasensystem, ist TlPbSbS₃ das Endmitglied der Mischkristallreihe, die sich im Richtung TlSbS₂ ausstreckt. Weitere Ausdehnung der Mischkristallreihe in der Richtung SbS konnte nicht bewiesen werden. Die Hochtemperatur-TlPbSbS₃ ist rhombisch und wird beim 620 K in die Tieftemperatur Modifikation umgewandelt. Die Tieftemperaturphase ist mit der Röntgenpulverdiffraktion und Rietveld Methode strukturell untersucht worden. Die ist monoklin, mit den Gitterkonstanten: a = 4.1707(4) Å, b = 4.2856(4) Å, c = 12.157(1) Å, = 105.49(1)°, Raumgruppe P2₁/c. Die statistische Verteilung von Kationen ist auch hier vorhanden. Die zwischenatomare Abstande (Tl, Pb, Sb)-S sind: 2.71, 2.72, 2.88, 3.14, 3.28, 3.51 (Å). Es besteht eine enge Verwandschaft zwischen den polymorphen Modifikationen von TlPbSbS₃ und den und Polymorphen von SnS, was die atomare Koordinationen und den generellen Strukturtypus betrifft, wobei ein ähnlicher Mechanismus der Phasenumwandlung für die beiden Fälle vermutet werden könnte. Die Differenzen in der Struktur und Symmetrie zwischen der Tieftemperaturmodifikationen von SnS und TlPbSbS₃ sind wahrscheinlich durch die bedeutende Metall-Metall Wirkungen in der zweiten verursacht. Die Phase TlPbSbS₃ ist ein substitution-derivative von der SnS Struktur, was durch die starke lone-electron-pair Aktivität von Kationen zu erklären ist. Die Ersetzung von Tl durch Ag und Sb durch Bi vermindert diese Aktivität und die entstandenen Strukturen sind in dem Fall dem PbS-Typus verwandt.

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With 3 Figures     

An Overview of Terrestrial Sequestration of Carbon Dioxide: the United States Department of Energy's Fossil Energy R&D Program

Increasing concentrations of CO₂ and other greenhouse gases (GHG) in the Earth's atmosphere have the potential to enhance the natural greenhouse effect, which may result in climatic changes. The main anthropogenic contributors to this increase are fossil fuel combustion, land use conversion, and soil cultivation. It is clear that overcoming the challenge of global climate change will require a combination of approaches, including increased energy efficiency, energy conservation, alternative energy sources, and carbon (C) capture and sequestration. The United States Department of Energy (DOE) is sponsoring the development of new technologies that can provide energy and promote economic prosperity while reducing GHG emissions. One option that can contribute to achieving this goal is the capture and sequestration of CO₂ in geologic formations. An alternative approach is C sequestration in terrestrial ecosystsems through natural processes. Enhancing such natural pools (known as natural sequestration) can make a significant contribution to CO₂ management strategies with the potential to sequester about 290 Tg C/y in U.S. soils. In addition to soils, there is also a large potential for C sequestration in above and belowground biomass in forest ecosystems.A major area of interest to DOE's fossil energy program is reclaimed mined lands, of which there may be 0.63 ×10⁶ ha in the U.S. These areas are essentially devoid of soil C; therefore, they provide an excellent opportunity to sequester C in both soils and vegetation. Measurement of C in these ecosystems requires the development of new technology and protocols that are accurate and economically viable. Field demonstrations are needed to accurately determine C sequestration potential and to demonstrate the ecological and aesthetic benefits in improved soil and water quality, increased biodiversity, and restored ecosystems.The DOE's research program in natural sequestration highlights fundamental and applied studies, such as the development of measurement, monitoring, and verification technologies and protocols and field tests aimed at developing techniques for maximizing the productivity of hitherto infertile soils and degraded ecosystems.