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  • 1
    Electronic Resource
    Electronic Resource
    Response of maize (Zea mays) to Azotobacter inoculation under fertilized and unfertilized conditions (1987)
    Springer
    Biology and fertility of soils 4 (1987), S. 73-77 
    Details
    ISSN: 1432-0789
    Keywords: Maize seed inoculation ; Azotobacter spp. ; N and P fertilizer ; N2 fixation ; Growth hormones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Inoculated seeds of maize (Zea mays) with 11 Azotobacter strains, sown in the fields receiving no fertilizer and fertilizers (N and P at the rate of 125 and 40 kg ha−1 respectively) increased the grain yield by 19.63% and 15.89% respectively over the corresponding control. The effect was greater in unfertilized than in fertilized soil. The increase in yield due to fertilizers was 21.2% without inoculation and 37.09% with inoculation. The correlations between total yield, and N, P and K uptake were highly significant and comparable among themselves. This indicated that increase in yield due to inoculation was not due to N2 fixation but that some other mechanisms like production of growth hormones by this bacterium may be responsible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280354
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic fields of direct currents in horizontally stratified conductors (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3731-3732 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new proof is given of the result that, for direct current flow (from a constant current source) in a horizontally stratified conductor, the magnetic field outside the conductor is independent of its electrical conductivity. The original proof is based on symmetry considerations and the application of Ampére's law to a contrived current circuit linking the horizontally stratified conductor. The new proof, however, does not rely on the use of any contrived current circuits, but is based on a rigorous analysis of the boundary value problem for the direct current flow in the horizontally stratified conductor. The mathematical techniques employed in this proof would be useful for future calculations in electromagnetism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342607
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic field of a direct current in a cylindrical-shaped conductor imbedded in a resistive half-space beneath a conductive surface layer (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4587-4593 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New applications of Fourier series and integral equation methods have yielded results of significance for electrical prospecting. This paper presents the first model calculation in three dimensions of the magnetic field due to a direct current flow in a conductor imbedded in a half-space beneath a conductive surface layer. The conductor is in the shape of a cylinder of semi-infinite length, and the current flow is from a point source in the surface layer. The vertical component of the magnetic field is given here by a Fourier series integral over a function which satisfies a Cauchy singular integral equation. For the two special cases, namely, an outcropping cylinder with no surface layer and a nearly invisible (in the sense of negligible conductivity contrast with its surrounding) cylinder, this integral equation can be solved exactly to yield closed-form expressions for the vertical component of the magnetic field. The exact solution in the first special case is based on a new generalization of the Hankel integral transform (published separately), and it extends the class of exactly solvable singular integral equations. This exact solution has also yielded as useful byproducts two new standard integrals involving Bessel functions. The integral equation approach used here, in contrast to the well-established surface integral equation approach, is suitable for numerical calculations, and typical magnetic field profiles are presented. The magnetic field results given here would be valuable for interpretation in electrical prospecting (based on the measurement of magnetic fields of direct currents), and the mathematical techniques used here would be useful for future calculations in electromagnetism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343812
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  • 4
    Electronic Resource
    Electronic Resource
    Fabrication, characterization, and theoretical analysis of high-Tc Y-Ba-Cu-O superconducting films prepared by a chemical sol gel method (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1580-1590 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of Y1Ba2Cu3O7−x have been produced on MgO substrates by a chemical sol gel method. X-ray diffraction data indicate that the annealed films have the characteristic orthorhombic structure with lattice constants which are nearly the same as the values reported for the bulk specimen of Y1Ba2Cu3O7−x. Auger electron spectroscopy depth profiling measurements indicate that the films are uniform in thickness and composition. Measurements of electrical resistance of films 1–4.7 μm in thickness have been carried out between 12 and 300 K using a standard four-probe geometry. The films are superconducting with an onset temperature around 95 K and a full transition temperature as high as 79.5 K, and a critical current density of 2700 A/cm2 at 20 K. A theoretical analysis of the critical current density in Y1Ba2Cu3O7−x as a function of temperature has been made in order to determine the characteristics of the junctions between the superconducting grains. Theoretical models which describe the dependence of the critical current density on temperature have been presented and agreement has been found between these models and experimental values for sol gel films. The critical transport current has a temperature dependence which is characteristic of superconductor-normal metal-superconductor (S-N-S) type junctions. The magnitude of the resistance and thickness of the junctions has been determined from the theoretical models. Information regarding calculation of the oxygen content in Y1Ba2Cu3O7−x films is also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349521
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  • 5
    Electronic Resource
    Electronic Resource
    Mathieu integral transforms (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 669-675 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Orthogonality and completeness relations are presented for the quasiorthogonal (i.e., orthogonal with respect to a discontinuous weight function) eigenfunctions of a singular (in the sense of Sturm–Liouville theory) boundary-value problem involving the two-dimensional Helmholtz equation in elliptic–cylinder coordinates. These relations yield as special cases integral transforms whose kernels are products of periodic Mathieu functions and modified Mathieu functions of integral order. The new transforms are analogs of the Weber–Orr transform and of a recently published [J. Math. Phys. 30, 41 (1989)] generalized Hankel transform, and would be applicable to boundary-value problems with elliptical geometries. The proof of the orthogonality and completeness relations is surprisingly simple and is based on a novel application of the Sokhotski–Plemelj equations of distribution theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529409
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  • 6
    Electronic Resource
    Electronic Resource
    Steady currents in composite conductors, eigenfunction expansions, and exactly solvable linear integral equations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 3297-3311 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A novel connection is uncovered between the simple physics of steady current flow in a composite conductor and the theory of integral equations. With a judicious choice of eigenfunction expansions, exploitation of the physical continuity of current flow across a chosen interface in a composite conductor is shown to yield an infinite class of integral equations with exact closed-form solutions. The mathematical derivation of this class is based on the elementary (but also new) notion of formally equating two different eigenfunction expansions of a given arbitrary function. The new class contains as special cases the celebrated Abel integral equation of classical mechanics and the Kramers–Kronig relations of electromagnetic scattering. But it also contains new integral equations (with exact solutions), some with the Cauchy-singularity 1/(x−y) in their kernels, and a new summation equation. These new equations are in themselves intriguing and their exact solutions do not appear to be derivable by the known methods for solving integral equations. An application of the new class of integral equations is given in the context of a particular composite conductor, which consists of a semi-infinite strip imbedded in an otherwise homogeneous whole space conductor (containing a uniform current flow parallel to the strip).The coefficient in the eigenfunction expansion of the potential in the strip satisfies a one-dimensional singular integral equation with a Cauchy-singularity. This singularity is regularized by the application of an integral equation and its exact solution from the new class, resulting in an integral equation with a smooth kernel. This equation together with the eigenfunction expansion provides an elegant representation for the potential in the strip. (The only known exact solutions are for the cases of elliptic-cylinder and ellipsoid geometries in two and three dimensions, respectively.) The new class of integral equations yields the first examples of singular kernels which possess a bilinear expansion in terms of two different complete sets of eigenfunctions, with only the diagonal terms (i.e., those terms in which the summation indices or integration variables are equal) in the expansion being nonzero. Such an expansion for square-integrable kernels (as opposed to singular kernels) is well known in the Hilbert–Schmidt theory of Hermitian operators and in Schmidt's extension to the non-Hermitian case, and it forms the basis for a method of solving Fredholm integral equations. None of these theories, however, yields the bilinear expansions for the singular kernels of our new class.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529492
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  • 7
    Electronic Resource
    Electronic Resource
    A new generalization of the Hankel integral transform (1989)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 41-44 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A study of the eigenfunction expansions associated with the Bessel equation defined on an unbounded composite region has yielded a new generalization of the Hankel integral transform. This generalization contains as a special case an integral transform that is the Neumann (in the sense of boundary value problem) counterpart of the (Dirichlet-type) Weber–Orr transform and which itself is new. It also contains as special cases certain curious integral representations of the Dirac δ function. These representations are in fact the orthogonality conditions for the quasiorthogonal (i.e., orthogonal with respect to a discontinuous weight function) kernels of the new integral transforms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528586
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of cylinder length on transition to doubly periodic Taylor–Couette flow (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 607-609 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Reynolds number for transition from singly to doubly periodic Taylor–Couette flow is studied experimentally and found to vary inversely with the aspect ratio Γ of the fluid column. This transition Reynolds number is also dependent on the number m of azimuthal waves. For a given m, the type of modulating state, which results after this transition, is not affected by Γ, nor does the transition Reynolds number differ for the different types of modulating states which can occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866360
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  • 9
    Electronic Resource
    Electronic Resource
    Coherent structures in a turbulent boundary layer. Part 1: Generation of "artificial'' bursts (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 2124-2139 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In an effort to better understand the physics and structure of coherent events in a turbulent boundary layer, an attempt is made to produce "artificial'' bursts. These are generated in a turbulent boundary layer developed on a flat plate towed in an 18 m water channel and thus with negligible freestream turbulence. The burstlike events are produced by either withdrawing near-wall fluid from two minute holes separated in the spanwise direction or by pitching a miniature delta wing that is flush-mounted to the wall. Either of these two actions generates a hairpinlike vortex and low-speed streak that resemble naturally occurring structures. The resulting sequence of events that occur at a given location can be uniquely controlled, thus allowing detailed examination via phase-locked measurements and flow visualization. In this paper, the proof of concept of artificial burst generation is established by comparing the artificial events with natural, random bursts using flow visualization and hot-film signals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865600
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  • 10
    Electronic Resource
    Electronic Resource
    Petrography and palaeomagnetism of the basalts, southwest Harrat Rabat, Saudi Arabia (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 99 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A total of 151 oriented samples were drilled out of 14 basaltic flows southwest of Harrat Rahat (22.1°N, 39.3°E). Ar39/Ar40 age determinations for these flows range between 3.3 ± 0.17 and 3.73 ± 0.16 Ma. Microscopic observations of 56 thin, and polished sections indicate a secondary crystallization of very fine grained magnetite and iddingsite at the boundaries and along microfractures in the olivine crystals. These single to multi-domain crystals produce a strong secondary magnetization unstable against alternating field demagnetization. The mean direction of these magnetic overprints is: D= 345.4, I= 28.0, α95 = 16.4, k= 32.3, n= 4 (sites) yielding a mean palaeopole at: 285.5°E, 74.4°N, A95 = 14.1, K= 34.5, N= 4. The stable remanent magnetization of all the samples is of reverse polarity and has a mean direction: D= 168.7, I= 38.8, α95 = 3.7, k= 114.5, n= 14, yielding a mean palaeomagnetic pole position at: 310.4°E, 80.0°N, A95 = 3.9, K= 102.6, N= 14. These data, together with other data for the Arabian plate were used to construct a preliminary apparent pole wander path (APWP) for Arabia during the Tertiary. The APWPs for Africa and Arabia during the Tertiary were constructed. Comparison of the Arabic and African APWPs indicate high mobility during the Miocene to Holocene, but the APWPs are in agreement with each other after proper reconstruction of Arabia to Africa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb02051.x
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