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  • Articles  (161)
  • Natural Sciences in General  (101)
  • Geosciences  (39)
  • Geography  (18)
  • Technology  (10)
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  • Articles  (161)
Journal
  • 11
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 252 (1974), S. 581-582 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A standard antibody-binding curve was obtained as follows: 4.5 ng (5,000 c.p.m.) of 3H-D8-THC (specific activity 465 mCimMol?1more than 98 %pure,New England Nuclear Corp.) was incubated for 2 h at 4 C with increasing dilutions of anti-serum (0.3 ml). The latter were made up with phosphate-buffered ...
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Environmental geology 15 (1990), S. 111-118 
    ISSN: 1432-0495
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Three hydrographic surveys were carried out in Deep Bay, which is located in the eastern part of Pearl estuary between Shenzhen, the most successful special economic zone of PRC, and Hong Kong. Data on current, size distributions of bottom sediment, suspended solids, and some water quality parameters were obtained. This information is of value for mathematical modeling of tidal circulation and sediment transport in the bay, and also useful in the planning of further development in this area. The sedimentation rate in Deep Bay was estimated by two different approaches, viz. comparison of historical navigation maps and210Pb dating. Information obtained from the maps indicated that average sedimentation rate between 1898 and 1949 was about 8 mm/yr, while a 15 mm/yr figure was obtained from the210Pb dating for recent years.
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  • 13
    ISSN: 1572-9893
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography
    Notes: Abstract Measurement of photosynthetic pigments as ground truth for remotely sensed spectra of boreal communities was tested. Chlorophyll and carotenoid concentrations and ratios were obtained from needles of spruce trees which were healthy as well as those undergoing forest decline (Waldsterben) in Vermont (USA) and Baden-Württemberg (FR Germany). In needles of trees exhibiting forest decline symptoms, chlorophyll pigment concentrations were lower, chlorophyll b levels decreased relative to chlorophyll a, total chlorophyll (a + b) was less relative to total carotenoid, and percent of reflectance in the visible range was higher. Pigment and reflectance data differentiated between needles from healthy and declining sites. These results were compared to remotely sensed spectral data obtained by aircraft and satelitee. As a result of these initial comparisons, it appears that using photosynthetic pigments as ground truth for remotely sensed spectral data may be of value in developing techniques for differentiating undamaged and damaged tree canopies on a large spatial scale. Finally, similar pigment and reflectance properties characterized healthy and declining communities in both Vermont and Baden-Württemberg.
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  • 14
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 18 (1982), S. 1297-1311 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Two new finite elements are developed for the Mindlin theory plate bending problem. The formulation is based on the modified Hellinger-Reissner principle with independent transverse shear strains. Numerical examples indicate that, with properly assumed transverse shear strains, these new elements designated as PLAT8 and PLAT8H do not exhibit locking effect even for very thin plates.
    Additional Material: 4 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 879-893 
    ISSN: 1069-8299
    Keywords: derogatory eigenproblems ; Jordan blocks ; Jordan chains ; Segre characteristic ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The major obstacle to determination of the Jordan chains for a highly degenerated eigenproblem is that the triangular combinations of the principal vectors in a Jordan chain are also principal vectors and the linear combinations of the eigenvectors of all Jordan blocks associated with the same eigenvalue are also eigenvectors. These indeterminate constants will hide the Jordan block structure and make the analysis very difficult. We propose an extended matrix method to find the Jordan chains and eliminate the indeterminate constants so that the Jordan block structure can be computed sequentially. An example with the Segre characteristic [(321)11] is given. © 1998 John Wiley & Sons, Ltd.
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  • 16
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 28 (1989), S. 1567-1576 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the Part I companion paper, various PCG (preconditioned conjugate gradient) strategies for solving the first order time dependent problem Mu̇ + Ku = f were compared. In all cases M was assumed to be the consistent ‘mass’ matrix arising out of conventional finite element semi-discretization of the partial differential equation, and not its lumped approximation. In the present paper, similar PCG strategies are applied to the second order time dependent problem Mü + Cu̇ + Ku = f. Again consistent M and C can be retained. Various global and element level preconditioners are compared and optimized.
    Additional Material: 11 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 28 (1989), S. 1557-1566 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The performances of some PCG (preconditioned conjugate gradient) algorithms are evaluated in the solution of first order time dependent parabolic partial differential equations, such as the heat conduction equation, which have been spatially discretized using finite elements. ‘Consistent mass’ discretizations are preferred by the authors to ‘lumped mass’ ones and various preconditioners are then compared - diagonal, incomplete Choleski and EBE (‘element-by-element’). Recommendations are made and implications for parallel computation outlined.
    Additional Material: 7 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 1253-1273 
    ISSN: 0029-5981
    Keywords: finite element method ; continuum modelling ; traffic equilibrium ; user-optimal pattern ; fixed demand ; variable demand ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, we consider a city with a highly compact Central Business District (CBD), and the commuters’ destinations from the CBD are dispersed over the whole city. The street network is approximated as a continuum and commuters’ movements in the city are measured by the flow intensity, and the local travel cost depends on the location and the traffic flow intensity. We extend the continuum user equilibrium problem to deal with the case of variable demand, in which the traffic demand from any destination in the city to the CBD is assumed to be a function of both the destination location and the total travel cost to the CBD. An equivalent mathematical model is formulated and proved to satisfy the user equilibrium conditions, which is then solved by a finite element solution algorithm. Numerical examples are given to illustrate the effectiveness of the proposed method. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 9 (1985), S. 1-14 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A computational procedure is developed for solving the problem of a circular hydraulic fracture propagating under the action of frac-0fluid being pumped in at a central wellbore. The crack is modelled as continuous distributions of ring dislocations and the resulting elasticity singular integral equation is solved numerically. The fluid flow equations are approximated by local and global interpolation finite difference schemes. The coupling between elasticity and fluid flow is handled numerically, by, two different algorithms: one iterates on crack tip velocity whereas the other varies the time step size until it agrees with the chosen increment in crack length. Sample results are given; it is found that the velocity algorithm is computationally more, efficient and more stable. The model allows detailed tracing of pressure distribution and fluid flow in the fracture, even under complex conditions of cyclic injection and fluid rheology. It may serve as a stand-alone model of (horizontal) hydrafracs-especially at shallow depths-or it may be used as a reference frame to test the various numerical formulation/algorithms required for the ongoing development of a fully 3-D hydrafrac simulator.
    Additional Material: 4 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 403-430 
    ISSN: 0363-9061
    Keywords: swelling ; chemo-poroelasticity ; borehole stability ; osmosis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Water-absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystal dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay-rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non-equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico-chemical equilibrium persists. Using a finite-element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.
    Additional Material: 9 Ill.
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