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排序方式: 共有71条查询结果,搜索用时 15 毫秒
1.
2.
The paper presents a wave basin experiment of a direct-driven point-absorber wave energy converter moving in six degrees of freedom. The goal of the work is to study the dynamics and energy absorption of the wave energy converter, and to verify under which conditions numerical models restricted to heave can capture the behaviour of a point-absorber moving in six degrees of freedom. Several regular and irregular long-crested waves and different damping values of the power take-off system have been tested. We collected data in terms of power output, device motion in six degrees of freedom and wave elevation at different points of the wave basin. A single-body numerical model in the frequency domain and a two-body model in the time domain are used in the study. Motion instabilities due to parametric resonance observed during the experiments are discussed and analysis of the buoy motion in terms of the Mathieu instability is also presented. Our results show that the simplified models can reproduce the body dynamics of the studied converter as long as the transverse non-linear instabilities are not excited, which typically is the case in irregular waves. The performance of the more complex time domain model is able to reproduce both the buoy and PTO dynamics, while the simpler frequency domain model can only reproduce the PTO dynamics for specific cases. Finally, we show that the two-body dynamics of the studied wave energy converter affects the power absorption significantly, and that common assumptions in the numerical models, such as stiff mooring line or that the float moves only in heave, may lead to incorrect predictions for certain sea states. 相似文献
3.
Lev Bukovsky Krzysztof Ciesielski 《Proceedings of the American Mathematical Society》2005,133(2):605-611
A topological space is a -space provided that, for every sequence of continuous functions from to , if the series converges pointwise, then it converges pseudo-normally. We show that every regular Lindelöf -space has the Rothberger property. We also construct, under the continuum hypothesis, a -subset of of cardinality continuum.
4.
A new technique for the latent state estimation of a wide class of nonlinear time series models is proposed. In particular, we develop a partially linearized sigma point filter in which random samples of possible state values are generated at the prediction step using an exact moment-matching algorithm and then a linear programming based procedure is used in the update step of the state estimation. The effectiveness of the new filtering procedure is assessed via a simulation example that deals with a highly nonlinear, multivariate time series representing an interest rate process. 相似文献
5.
Abstract Recently, several papers have expressed an interest in applying the Growth Optimal Portfolio (GOP) for pricing derivatives. We show that the existence of a GOP is equivalent to the existence of a strictly positive martingale density. Our approach circumvents two assumptions usually set forth in the literature: 1) infinite expected growth rates are permitted and 2) the market does not need to admit an equivalent martingale measure. In particular, our approach shows that models featuring credit constrained arbitrage may still allow a GOP to exist because this type of arbitrage can be removed by a change of numéraire. However, if the GOP exists the market admits an equivalent martingale measure under some numéraire and hence derivatives can be priced. The structure of martingale densities is used to provide a new characterization of the GOP which emphasizes the relation to other methods of pricing in incomplete markets. The case where GOP denominated asset prices are strict supermartingales is analyzed in the case of pure jump driven uncertainty. 相似文献
6.
7.
We present a general condition, based on the idea of n-generating subgroup sets, which implies that a given character represents a point in the homotopical or homological -invariants of the group G. Let be a finite simplicial graph, the flag complex induced by , and the graph group, or 'right angled Artin group', defined by . We use our result on n-generating subgroup sets to describe the homotopical and homological -invariants of in terms of the topology of subcomplexes of . In particular, this work determines the finiteness properties of kernels of maps from graph groups to abelian groups. This
is the first complete computation of the -invariants for a family of groups whose higher invariants are not determined - either implicitly or explicitly - by
1.
Received: October 18, 1996 相似文献
8.
The gauge-invariant topological charge is defined for, and the inequalities supplying the lower bound on the action of an SO(4) gauged O(5) sigma model in four dimensions are established. The consistency of the solution with finiteness of the action and with topological stability is briefly verified for a particular dynamical example. Against the background of the topologically stable finite energy solitons of SO(d) gauged O(d+1) sigma models in d dimensions already known for d=2 and for d=3, the present example can be viewed as a demonstration by induction for the existence of such solitons in the case of arbitrary k. 相似文献
9.
Jan Krouwer 《Accreditation and quality assurance》2002,7(11):461-467
Hospital laboratories have error rates that are too high and in some cases may be responsible for adverse patient treatment.
This paper introduces reliability growth management (RGM), which is based on learning curve theory, as a method to improve
laboratory error rates. RGM is widely used in the defense and automotive industry to solve problems when resources are limited
and knowledge about the product and/or process is incomplete. An example of RGM, which was used to improve the reliability
of instrument assay systems in the medical diagnostics industry is presented. RGM is a closed-loop process that entails creating
a goal and event model, classifying events with failure review and corrective action system (FRACAS), tracking progress and
predicting completion with Duane analysis. Results achieved by RGM were far better than those obtained by previously used
methods. RGM techniques can be transferred to hospital laboratories to reduce laboratory error rates. The advantages of RGM
compared to other quality initiatives such as ISO 9000 and Six Sigma are discussed.
Received: 3 February 2002 Accepted: 17 July 2002
Acknowledgements The majority of the work of transferring reliability growth management from the defense industry to the medical device industry
was performed by Keith K. McLain, while he was at Ciba Corning Diagnostics. Keith is now at Ortho-Clinical Diagnostics (email:
KMcLain@ocdus.jnj.com).
Presented at the European Conference on Quality in the Spotlight in Medical Laboratories, 7–9 October 2001, Antwerp, Belgium
Abbreviations
RGM Reliability growth management · FRACAS failure review and corrective action system · CAP College of American Pathologists · LIS laboratory information system · HIS hospital information system
Correspondence to Jan Krouwer 相似文献
10.
S.S.M. Tavares J.M. Pardal A.M. Gomes 《Journal of magnetism and magnetic materials》2010,322(17):L29-451
Duplex stainless steels are high strength and corrosion resistant steels extensively used in the chemical and petrochemical industry. The best mechanical properties and corrosion resistance are obtained with a microstructure composed by equal parts of ferrite and austenite and free from tertiary phases. Sigma phase is one of these deleterious tertiary phases. In the present work different amounts of sigma phase were precipitated by heat treatments in a UNS S31803 stainless steel. Some specimens were cold rolled before sigma phase precipitation in order to evaluate the effect of deformation on the magnetic measurements. The amount of sigma phase was precisely determined by microscopy and image analysis for each heat treatment condition. The effects of sigma phase on the steel properties were investigated, confirming the detrimental effects of very small percentages on corrosion resistance and toughness. Two magnetic methods were used to detect sigma phase: magnetization saturation measurements in a Vibrating Sample Magnetometer and ferritoscope testing. Both methods were found to be sensitive to small percentages of sigma phase in the microstructure. 相似文献