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  • 1
    Electronic Resource
    Electronic Resource
    THE POTENTIAL OF BIOMASS FUELS IN THE CONTEXT OF GLOBAL CLIMATE CHANGE: Focus on Transportation Fuels1 (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Environment and Resources 25 (2000), S. 199-244 
    Details
    ISSN: 1056-3466
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract An ultimate limit on the extent that biomass fuels can be used to displace fossil transportation fuels, and their associated emissions of CO2, will be the land area available to produce the fuels and the efficiencies by which solar radiation can be converted to useable fuels. Currently, the Brazil cane-ethanol system captures 33% of the primary energy content in harvested cane in the form of ethanol. The US corn-ethanol system captures 54% of the primary energy of harvested corn kernels in the form of ethanol. If ethanol is used to substitute for gasoline, avoided fossil fuel CO2 emissions would equal those of the substituted amount minus fossil emissions incurred in producing the cane- or corn-ethanol. In this case, avoided emissions are estimated to be 29% of harvested cane and 14% of harvested corn primary energy. Unless these efficiencies are substantially improved, the displacement of CO2 emissions from transportation fuels in the United States is unlikely to reach 10% using domestic biofuels. Candidate technologies for improving these efficiencies include fermentation of cellulosic biomass and conversion of biomass into electricity, hydrogen, or alcohols for use in electric drive-train vehicles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.energy.25.1.199
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  • 2
    Electronic Resource
    Electronic Resource
    Laminar flow in twisted ducts (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2669-2681 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fully developed flow of an incompressible Newtonian fluid through a duct in which the orientation of the cross section is twisted about an axis parallel to an imposed pressure gradient is analyzed here with the aid of the penalty/Galerkin/finite element method. When the axis of twist is located within the duct, flow approaches limits at low and high torsion, the spatial frequency τ by which the duct is twisted. For small torsion, flow is nearly rectilinear and solutions approach previous asymptotic results for an elliptical cross section. For large torsion, flow exhibits an internal layer structure: a rotating circular-cylinder core with a nearly parabolic axial velocity profile, an internal layer of thickness τ−1 along the perimeter of the largest circular cylinder that can be inscribed in the duct, and nearly quiescent flow outside of the circular cylinder. The maximum rate of swirl in the core of a square duct is found to be at moderate torsion. The primary effect of inertia is an increase in pressure with distance from the axis, due to centrifugal acceleration. When the duct is offset from the axis of twist, inertia leads to one, two, or three primary vortices without apparent bifurcation of steady states, although stability of steady flows is lost beyond detected Hopf points.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858730
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  • 3
    Electronic Resource
    Electronic Resource
    Viscous flow through a rotating square channel (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2968-2979 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fully developed flow of an incompressible Newtonian fluid driven by a pressure gradient through a square channel that rotates about an axis perpendicular to the channel roof is analyzed here with the aid of the penalty/Galerkin/finite element method. Coriolis force throws fast-moving fluid in the channel core in the direction of the cross product of the mean fluid velocity with the channel's angular velocity. Two vortex cells form when convective inertial force is weak. Asymptotic limits of rectilinear flow and geostrophic plug flow are approached when viscous force or Coriolis force dominates, respectively. A flow structure with an ageostrophic, virtually inviscid core is uncovered when Coriolis and convective inertial forces are both strong. This ageostrophic two-vortex structure becomes unstable when the strength of convective inertial force increases past a critical value. The two-vortex family of solutions metamorphoses into a family of four-vortex solutions at an imperfect bifurcation composed of a pair of turning points.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865136
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  • 4
    Electronic Resource
    Electronic Resource
    Disturbed film flow on a vertical plate (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 990-997 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flow of incompressible Newtonian liquid films is governed by the Navier–Stokes system with shear-free, balanced-normal-stress, and kinematic boundary conditions at the free surface. This system is solved here for the evolution of finite-amplitude two-dimensional disturbances to otherwise steady flow down a vertical plate by means of a finite element method adapted for free boundary problems. When flow is specified to be spatially periodic, fully developed steady flows that ensue approach time-periodic states, i.e., waves, the finite amplitude of which depends upon their wavelength. The family of time-periodic states connects to the steady, fully developed flow at a Hopf bifurcation that lies at a critical disturbance length, in agreement with the Orr–Sommerfeld analysis. Initial disturbances to flow down a plate of finite length grow as they propagate downward. In all cases studied here, however, steady flow is eventually approached.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866286
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  • 5
    Electronic Resource
    Electronic Resource
    Accounting for the missing carbon-sink with the CO2-fertilization effect (1996)
    Springer
    Climatic change 33 (1996), S. 31-62 
    Details
    ISSN: 1573-1480
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A terrestrial-biosphere carbon-sink has been included in global carbon-cycle models in order to reproduce past atmospheric CO2, 13C and 14C concentrations. The sink is of large enough magnitude that its effect on projections of future CO2 levels should not be ignored. However, the cause and mechanism of this sink are not well understood, contributing to uncertainty of projections. The estimated magnitude of the biospheric sink is examined with the aid of a global carbon-cycle model. For CO2 emissions scenarios, model estimates are made of the resulting atmospheric CO2 concentration. Next, the response of this model to CO2-emission impulses is broken down to give the fractions of the impulse which reside in the atmosphere, oceans, and terrestrial biosphere - all as a perturbation to background atmospheric CO2 concentration time-profiles that correspond to different emission scenarios. For a biospheric sink driven by the CO2-fertilization effect, we find that the biospheric fraction reaches a maximum of roughly 30% about 50 years after the impulse, which is of the same size as the oceanic fraction at that time. The dependence of these results on emission scenario and the year of the impulse are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140512
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  • 6
    Electronic Resource
    Electronic Resource
    COMPARISON OF PALEOTEMPERATURE RECONSTRUCTIONS AS EVIDENCE FOR THE PALEO-ANALOG HYPOTHESIS (1997)
    Springer
    Climatic change 35 (1997), S. 123-131 
    Details
    ISSN: 1573-1480
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract There is an apparent inconsistency between the estimated low accuracy reported by Kheshgi and Lapenis (1996; hereinafter KL) for the reconstructed zonal-mean annual paleotemperatures for the mid-Holocene, and the high agreement reported by Shabalova and Können (1995; hereinafter SK) between the normalized temperature anomalies of these reconstructed paleotemperatures and those reconstructed for earlier epochs. The reasons for this inconsistency could be: (i) overestimation by KL of the reconstruction errors by more than a factor of two, (ii) significant smoothing of the paleodata resulting in a reduction in the number of independent pieces of information represented by the zonal-mean temperatures, or (iii) bias of the paleotemperature reconstruction by prior knowledge of the expected patterns of climate change. Because it is unlikely that the errors involved in producing the reconstructed mid-Holocene temperatures have been overestimated by more than a factor of two, one or both of the other reasons is the likely explanation for the inconsistency. If this holds true, then support for the paleo-analog hypothesis provided by the mid-Holocene paleotemperature reconstruction is severely weakened.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005348309505
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  • 7
    Electronic Resource
    Electronic Resource
    Does recent global warming suggest an enhanced greenhouse effect? (1993)
    Springer
    Climatic change 23 (1993), S. 121-139 
    Details
    ISSN: 1573-1480
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Considerable controversy has been generated by the observation that the Earth's climate has warmed over the last century. Public policy decisions hinge on the question of whether this trend is natural climate variability or the result of the increase in atmospheric concentrations of greenhouse gases. The strength of the enhanced greenhouse effect depends, in large part, on the uncertain value of climate sensitivity. In this paper climate sensitivity is estimated from the global temperature record by assuming models for greenhouse forcing, climate response to forcing, and climate variability. We find optimal estimates of climate sensitivity are remarkably insensitive to assumptions, at least for forcing excluding the effect of aerosols, and these values are considerably less than most predictions arising from General Circulation Models (GCM's). It is, however, the statistical significance of these estimates that is sensitive to assumptions about climate variability. Assuming climate variability with a time scale of a decade or less, climate sensitivity is estimated to be significantly greater than zero, but also significantly lower than that predicted by GCM's. Climate variability with a century time scale is consistent with both the recent temperature record and the pre-instrumental record for the last millenium; if this type of variability is assumed, the estimate of climate sensitivity has a confidence band wide enough to encompass both zero and typical values obtained by GCM's. With century time-scale variability it will be several decades before confident estimates can be made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01097333
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  • 8
    Electronic Resource
    Electronic Resource
    An accurate one-dimensional model for nonadiabatic annular reactors (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1265-1269 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370819
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  • 9
    Electronic Resource
    Electronic Resource
    Profile equations for film flows at moderate Reynolds numbers (1989)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 1719-1727 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An approximate equation for the evolution of finite-amplitude, long disturbances to Newtonian liquid films is found to be accurate over a wide range of Reynolds numbers. A long-wave expansion leads to a film profile equation asymptotically correct when wave number and Reynolds number are small. Solutions of the film profile equation are compared to exact and other approximate solutions of the Navier-Stokes system. An alternative form of the film profile equation results in remarkably accurate solutions, when Reynolds numbers are moderate, in the cases of standing or monotonically decaying waves in horizonatal films, rising film flow, final acceleration of a moving film, and film flow emerging from a slot coater.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690351017
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  • 10
    Electronic Resource
    Electronic Resource
    Variable penalty method for finite element analysis of incompressible flow (1985)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 5 (1985), S. 785-803 
    Details
    ISSN: 0271-2091
    Keywords: Variable Penalty Method ; Penalty Finite Element Analysis ; Rotating Flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new scheme is applied for increasing the accuracy of the penalty finite element method for incompressible flow by systematically varying from element to element the sign and magnitude of the penalty parameter λ, which enters through ∇.v + p/λ = 0, an approximation to the incompressibility constraint. Not only is the error in this approximation reduced beyond that achievable with a constant λ, but also digital truncation error is lowered when it is aggravated by large variations in element size, a critical problem when the discretization must resolve thin boundary layers. The magnitude of the penalty parameter can be chosen smaller than when λ is constant, which also reduces digital truncation error; hence a shorter word-length computer is more likely to succeed. Error estimates of the method are reviewed. Boundary conditions which circumvent the hazards of aphysical pressure modes are catalogued for the finite element basis set chosen here. In order to compare performance, the variable penalty method is pitted against the conventional penalty method with constant λ in several Stokes flow case studies.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650050903
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