Home About us Contact
|
Home About us Contact | ||
|
|
||
Background Medium (background + medium)
Selected AbstractsInfluence of complex formation upon inclusion of Mn(II), Co(II), Ni(II), and Cu(II) in ZnC2O4·2H2OCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2004B. Donkova Abstract The inclusion of 3d-impurities Mn(II), Co(II), Ni(II) and Cu(II) in a crystalline precipitate of ZnC2O4·2H2O is investigated. This study is a part of the systematic one deal with the mechanism of inclusion of 3d-ions in sparingly soluble oxalate systems. The experiments are carried out in bi- end multi-component systems at two different mediums , one with deficiency of oxalate ions, another with excess. The insertion of 3d-ions upon mass crystallization of ZnC2O4·2H2O does not proceed by a simple ionic substitution. The results show that the inserted amount of impurity depends on some physicochemical characteristics of the neutral monooxalato complexes [MnC2O4]o, [CoC2O4]o, [NiC2O4]o and [CuC2O4]o. Good agreement between included impurity and the concentration of its complex in the solution is established. The stability constant of monooxalato complex affects the impurity inclusion. This effect depends on the medium nature. In the deficiency of oxalate ions the factor determining the inclusion is thermodynamic one , stability of monooxalato complexes. In the excess of oxalate ions inserted amount depends on kinetic factor , the formation rate of these complexes. In the term of that the insertion of Mn(II) is definitely different in the two mediums while that of the Ni (II) does not depend on the medium. The copper shows deviation from overall dependence in the two mediums due to the Jahn-Teller distortion. Its double decreasing insertion in the excess of oxalate ions is related with stabilization of [Cu(C2O4)2]2- . The conclusions presume that by varying the background medium and taking in view the ions present in the solution, the amount of inserted impurities can be predicted and controlled. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vertically fractured transversely isotropic media: dimensionality and deconstructionGEOPHYSICAL PROSPECTING, Issue 2 2009Michael A. Schoenberg ABSTRACT A vertically fractured transversely isotropic (VFTI) elastic medium is one in which any number of sets of vertical aligned fractures (each set has its normal lying in the horizontal x1, x2 -plane) pervade the medium and the sets of aligned fractures are the only features of the medium disturbing the axi-symmetry about the x3 -axis implying that in the absence of fractures, the background medium is transversely isotropic (TI). Under the assumptions of long wavelength equivalent medium theory, the compliance matrix of a fractured medium is the sum of the background medium's compliance matrix and a fracture compliance matrix. For sets of parallel rotationally symmetric fractures (on average), the fracture compliance matrix is dependent on 3 parameters , its normal and tangential compliance and its strike direction. When one fracture set is present, the medium is orthorhombic and the analysis is straightforward. When two (non-orthogonal) or more sets are present, the overall medium is in general elastically monoclinic; its compliance tensor components are subject to two equalities yielding an 11 parameter monoclinic medium. Constructing a monoclinic VFTI medium with n embedded vertical fracture sets, requires 5 TI parameters plus 3×n fracture set parameters. A deconstruction of such an 11 parameter monoclinic medium involves using its compliance tensor to find a background transversely isotropic medium and several sets of vertical fractures which, in the long wavelength limit, will behave exactly as the original 11 parameter monoclinic medium. A minimal deconstruction, would be to determine, from the 11 independent components, the transversely isotropic background (5 parameters) and two fracture sets (specified by 2 × 3 = 6 parameters). Two of the background TI medium's compliance matrix components are known immediately by inspection, leaving nine monoclinic components to be used in the minimal deconstruction of the VFTI medium. The use of the properties of a TI medium, which are linear relations on its compliance components, allows the deconstruction to be reduced to solving a pair of non-linear equations on the orientations of two fracture sets. A single root yielding a physically meaningful minimum deconstruction yields a unique minimal representation of the monoclinic medium as a VFTI medium. When no such root exists, deconstruction requires an additional fracture set and uniqueness is lost. The boundary between those monoclinic media that have a unique minimal representation and those that do not is yet to be determined. [source] Electromagnetic fields in a steel-cased boreholeGEOPHYSICAL PROSPECTING, Issue 1 2005Ki Ha Lee ABSTRACT The development of an electromagnetic numerical modelling scheme for a magnetic dipole in an arbitrary casing segment in an inhomogeneous conductivity background has been difficult, due to the very high electrical conductivity and magnetic permeability contrasts between the steel casing and the background medium. To investigate the effect of steel casing efficiently, we have developed an accurate but simple finite-element modelling scheme to simulate electromagnetic fields in a medium of cylindrically symmetric conductivity structures. In order to preserve the cylindrical symmetry in the resulting electromagnetic fields, a horizontal loop current source is used throughout. One of the main advantages of the approach is that the problem is scalar when formulated using the azimuthal electric field, even if the casing is both electrically conductive and magnetically permeable. Field calculations have been made inside the cased borehole as well as in another borehole which is not cased. Careful analyses of the numerical modelling results indicate that the anomaly observed in a cross-borehole configuration is sensitive enough to be used for tomographic imaging. [source] Magnetic jets from swirling discsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006D. Lynden-Bell ABSTRACT A broad swathe of astrophysical phenomena, ranging from tubular planetary nebulae through Herbig,Haro objects, radio galaxy and quasar emissions to gamma-ray bursts and perhaps high-energy cosmic rays, may be driven by magnetically dominated jets emanating from accretion discs. We give a self-contained account of the analytic theory of non-relativistic magnetically dominated jets wound up by a swirling disc and making a magnetic cavity in a background medium of any prescribed pressure, p(z). We solve the time-dependent problem for any specified distribution of magnetic flux P(R, 0) emerging from the disc at z= 0, with any specified disc angular velocity ,d(R). The physics required to do this involves only the freezing of the lines of force to the conducting medium and the principle of minimum energy. In a constant pressure environment, the magnetically dominated cavity is highly collimated and advances along the axis at a constant speed closely related to the maximum circular velocity of the accretion disc. Even within the cavity the field is strongly concentrated towards the axis. The twist in the jet field ,B,,/,|Bz|, is close to and the width of the jet decreases upwards. By contrast, when the background pressure falls off with height with powers approaching z,4, the head of the jet accelerates strongly and the twist of the jet is much smaller. The width increases to give an almost conical magnetic cavity with apex at the source. Such a regime may be responsible for some of the longest strongly collimated jets. When the background pressure falls off faster than z,4, there are no quasi-static configurations of well-twisted fields and the pressure confinement is replaced by a dynamic effective pressure or a relativistic expansion. In the regimes with rapid acceleration, the outgoing and incoming fields linking the twist back to the source are almost anti-parallel so there is a possibility that magnetic reconnections may break up the jet into a series of magnetic ,smoke-rings' travelling out along the axis. [source] | ||||||||||