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排序方式: 共有148条查询结果,搜索用时 187 毫秒
1.
This paper examines the non-linear dynamic behaviour of a flexible shaft. The shaft is mounted on two journal bearings and the axial load is supported by a defective hydrodynamic thrust bearing at one end. The defect is a levelness defect of the rotor. The thrust bearing behaviour must be considered to be non-linear because of the effects of the defect. The shaft is modelled with typical beam finite elements including effects such as the gyroscopic effects. A modal technique is used to reduce the number of degrees of freedom. Results show that the thrust bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non-linear analysis. 相似文献
2.
JOSEF MÁLEK JINDŘICH NEČAS K. R. RAJAGOPAL 《Archive for Rational Mechanics and Analysis》2002,165(3):243-269
To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity
of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments.
While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small,
special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place.
Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are
global in time, for a large class of physically meaningful viscosity-pressure relationships.
(Accepted May 1, 2002) Published online November 15, 2002
Communicated by S. S. ANTMAN 相似文献
3.
4.
Enhancing the enzymatic hydrolysis of cellulosic materials using simultaneous ball milling 总被引:1,自引:0,他引:1
Mais Ursula Esteghlalian Ali R. Saddler John N. Mansfield Shawn D. 《Applied biochemistry and biotechnology》2002,98(1-9):815-832
One of the limiting factors restricting the effective and efficient bioconversion of softwood-derived lignocellulosic residues
is the recalcitrance of the substrate following pretreatment. Consequently, the ensuing enzymatic process requires relatively
high enzyme loadings to produce monomeric carbohydrates that are readily fermentable by ethanologenic microorganisms. In an
attempt to circumvent the need for larger enzyme loadings, a simultaneous physical and enzymatic hydrolysis treatment was
evaluated. A ball-mill reactor was used as the digestion vessel, and the extent and rate of hydrolysis were monitored. Concurrently,
enzyme adsorption profiles and the rate of conversion during the course of hydrolysis were monitored. α-Cellulose, employed
as a model substrate, and SO2-impregnated steam-exploded Douglas-fir wood chips were assessed as the cellulosic substrates. The softwood-derived substrate
was further posttreated with water and hot alkaline hydrogen peroxide to remove >90% of the original lignin. Experiments at
different reaction conditions were evaluated, including substrate concentration, enzyme loading, reaction volumes, and number
of ball beads employed during mechanical milling. It was apparent that the best conditions for the enzymatic hydrolysis of
α-cellulose were attained using a higher number of beads, while the presence of air-liquid interface did not seem to affect
the rate of saccharification. Similarly, when employing the lignocellulosic substrate, up to 100% hydrolysis could be achieved
with a minimum enzyme loading (10 filter paper units/g of cellulose), at lower substrate concentrations and with a greater
number of reaction beads during milling. It was apparent that the combined strategy of simultaneous ball milling and enzymatic
hydrolysis could improve the rate of saccharification and/or reduce the enzyme loading required to attain total hydrolysis
of the carbohydrate moieties. 相似文献
5.
Based on the law of error propagation, a general expression is derived to study theoretically the hydrodynamically limited precision associated with each single element of fluid in a concentration profile in flow injection analysis. Convolution of the injection and residence time distribution functions is used to obtain response functions for a homogeneously stirred mixing chamber and for a straight capillary tube. The effects of stochastic variations on overall precision by sample introduction, pumping and timing are elucidated and compared with experimental findings. Resulting practical implications for the use of these two dispersing elements are outlined. 相似文献
6.
In this paper we study symmetry reductions and exact solutions of the shallow water wave (SWW) equation $$u_{xxxt} + \alpha u_x u_{xt} + \beta u_t u_{xx} - u_{xt} - u_{xx} = 0,$$ whereα andβ are arbitrary, nonzero, constants, which is derivable using the so-called Boussinesq approximation. Two special cases of this equation, or the equivalent nonlocal equation obtained by settingu x =U, have been discussed in the literature. The caseα=2β was discussed by Ablowitz, Kaup, Newell and Segur (Stud. Appl. Math.,53 (1974), 249), who showed that this case was solvable by inverse scattering through a second-order linear problem. This case and the caseα=β were studied by Hirota and Satsuma (J. Phys. Soc. Japan,40 (1976), 611) using Hirota's bi-linear technique. Further, the caseα=β is solvable by inverse scattering through a third-order linear problem. In this paper, a catalogue of symmetry reductions is obtained using the classical Lie method and the nonclassical method due to Bluman and Cole (J. Math. Mech,18 (1969), 1025). The classical Lie method yields symmetry reductions of (1) expressible in terms of the first, third and fifth Painlevé transcendents and Weierstrass elliptic functions. The nonclassical method yields a plethora of exact solutions of (1) withα=β which possess a rich variety of qualitative behaviours. These solutions all like a two-soliton solution fort < 0 but differ radically fort > 0 and may be viewed as a nonlinear superposition of two solitons, one travelling to the left with arbitrary speed and the other to the right with equal and opposite speed. These families of solutions have important implications with regard to the numerical analysis of SWW and suggests that solving (1) numerically could pose some fundamental difficulties. In particular, one would not be able to distinguish the solutions in an initial-value problem since an exponentially small change in the initial conditions can result in completely different qualitative behaviours. We compare the two-soliton solutions obtained using the nonclassical method to those obtained using the singular manifold method and Hirota's bi-linear method. Further, we show that there is an analogous nonlinear superposition of solutions for two (2+1)dimensional generalisations of the SWW Equation (1) withα=β. This yields solutions expressible as the sum of two solutions of the Korteweg-de Vries equation. 相似文献
7.
8.
Strachan JD Adler H Alling P Ancher C Anderson H Anderson JL Ashcroft D Barnes CW Barnes G Batha S Bell MG Bell R Bitter M Blanchard W Bretz NL Budny R Bush CE Camp R Caorlin M Cauffman S Chang Z Cheng CZ Collins J Coward G Darrow DS DeLooper J Duong H Dudek L Durst R Efthimion PC Ernst D Fisher R Fonck RJ Fredrickson E Fromm N Fu GY Furth HP Gentile C Gorelenkov N Grek B Grisham LR Hammett G Hanson GR Hawryluk RJ Heidbrink W Herrmann HW Hill KW Hosea J Hsuan H Janos A Jassby DL Jobes FC 《Physical review letters》1994,72(22):3526-3529
9.
10.
Wong KL Bitter M Hammett GW Heidbrink W Hendel H Kaita R Scott S Strachan JD Tait G Bell MG Budny R Bush C Chan A Coonrod J Efthimion PC England AC Eubank HP Fredrickson E Furth HP Goldston RJ Grek B Grisham L Hawryluk RJ Hill KW Johnson D Kamperschroer J Kugel H Ma C Mansfield D Manos D McCune DC McGuire K Medley SS Mueller D Nieschmidt E Owens DK Paré VK Park H Ramsey A Rasmussen D Roquemore AL Schivell J Sesnic S Taylor G Williams MD Zarnstorff MC 《Physical review letters》1985,55(23):2587-2590