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91.
92.
Spectral Measurement of the Film-Substrate Index Difference in Proton-Exchanged LiNbO(3) Waveguides 总被引:1,自引:0,他引:1
El Hadi K Rastogi V Shenoy MR Thyagarajan K De Micheli M Ostrowsky DB 《Applied optics》1998,37(27):6463-6467
We report the spectral characterization of proton-exchanged lithium niobate (PE:LiNbO(3)) waveguides in terms of the variation of the refractive-index difference between the waveguiding layer and the substrate. The dispersion of the extraordinary refractive-index increase (deltan(e)) is measured from 405 to 1319 nm with several light sources. Two types of proton-exchanged waveguide, prepared under different conditions, are studied. These measurements should be of use in the optimization of PE:LiNbO(3) waveguides for nonlinear optical applications, particularly in second-harmonic generation in the blue-green wavelength region. 相似文献
93.
A solid state bonding technique under hot pressing was used for joining alumina with thin metal sheets of Ni, Cu and Fe. The microstructure and microchemistry of the ceramic–metal interface and of the fracture interface were examined using scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), in order to identify the adhesion mechanisms and the nature of strength limiting flaws. Interaction between the selected metals and alumina can be physical or physico-chemical in nature: very low amounts of interfacial compounds were formed, depending on the processing conditions and on the presence of oxygen in the system. Fracture and toughness tests indicated that high ceramic–metal interface strengths (up to 177 MPa) were achieved under the adopted processing conditions and that strength and toughness were directly related. Moreover, an increase in hardening in the metal interlayer at a distance of 2–3 m from the interface was observed in the samples with high strength values. The mechanical behaviour was related to several factors that strongly depend on the bonding conditions: plastic deformation of the metal, metal creep, metal intrusion and diffusion into alumina, and chemical reactions at the interface. © 1998 Chapman & Hall 相似文献
94.
Mainella G de Bernardis P De Petris M Mandiello A Perciballi M Romeo G 《Applied optics》1996,35(13):2246-2252
The Millimetre and Infrared Testa Grigia Observatory 2.6-m Cassegrain telescope has been designed to allow high-sensitivity observations in the millimeter spectral range. For this purpose, in order to reduce unwanted contributions from local foregrounds, we adopted a sky-chopping technique, by wobbling the telescope subreflector. We describe the design and performance of the wobbling system, which can endure external forced two and three fields square-wave modulation and includes features such as high frequency, high amplitude, high duty cycle, low microphonics, and high stability. 相似文献
95.
Gregory Gutin Eun Jung Kim Matthias Mnich Anders Yeo 《Journal of Computer and System Sciences》2010,76(8):872-878
We study ordinal embedding relaxations in the realm of parameterized complexity. We prove the existence of a quadratic kernel for the Betweenness problem parameterized above its tight lower bound, which is stated as follows. For a set V of variables and set C of constraints “vi is between vj and vk”, decide whether there is a bijection from V to the set {1,…,|V|} satisfying at least |C|/3+κ of the constraints in C. Our result solves an open problem attributed to Benny Chor in Niedermeier's monograph “Invitation to Fixed-Parameter Algorithms”. The betweenness problem is of interest in molecular biology. An approach developed in this paper can be used to determine parameterized complexity of a number of other optimization problems on permutations parameterized above or below tight bounds. 相似文献
96.
Hans De Sterck Killian Miller Geoffrey Sanders 《Computing and Visualization in Science》2011,14(2):51-65
Recently, it was shown how the convergence of a class of multigrid methods for computing the stationary distribution of sparse,
irreducible Markov chains can be accelerated by the addition of an outer iteration based on iterant recombination. The acceleration
was performed by selecting a linear combination of previous fine-level iterates with probability constraints to minimize the
two-norm of the residual using a quadratic programming method. In this paper we investigate the alternative of minimizing
the one-norm of the residual. This gives rise to a nonlinear convex program which must be solved at each acceleration step.
To solve this minimization problem we propose to use a deep-cuts ellipsoid method for nonlinear convex programs. The main
purpose of this paper is to investigate whether an iterant recombination approach can be obtained in this way that is competitive
in terms of execution time and robustness. We derive formulas for subgradients of the one-norm objective function and the
constraint functions, and show how an initial ellipsoid can be constructed that is guaranteed to contain the exact solution
and give conditions for its existence. We also investigate using the ellipsoid method to minimize the two-norm. Numerical
tests show that the one-norm and two-norm acceleration procedures yield a similar reduction in the number of multigrid cycles.
The tests also indicate that one-norm ellipsoid acceleration is competitive with two-norm quadratic programming acceleration
in terms of running time with improved robustness. 相似文献
97.
Sascha Kuhn August Burr Michael Kübler Matthias Deckert Christoph Bleesen 《Microsystem Technologies》2010,16(10):1787-1801
The injection molding of micro-structures is a promising mass-production method for a broad range of materials. However, the
replication quality of these structures depends significantly on the heat flow during the filling stage. In this paper, the
filling and heat transfer of v-groove and random structures below 5 μm is investigated with the help of an AFM (atomic force
microscope) and thermo couples. A numerical model is developed to predict the filling of surface structures during the filling
and packing stage. The model implies the use of simple fully developed flow models taking the power-law material model into
account. This permits investigation into which ways several processing parameters affect the polymer flow in the surface structures.
The mold wall temperature, which has significant effects on the polymer flow, is varied by using a variothermal mold temperature
control system to validate the model proposed. 相似文献
98.
I. Werbrouck M. Antrop V. Van Eetvelde C. Stal Ph. De Maeyer M. Bats J. Bourgeois M. Court-Picon Ph. Crombé J. De Reu Ph. De Smedt P.A. Finke M. Van Meirvenne J. Verniers A. Zwertvaegher 《Expert systems with applications》2011,38(7):8178-8185
This paper discusses the generation of a high precision DEM (Digital Elevation Model) based on high density airborne LiDAR (Light Detection and Ranging) data for an interdisciplinary landscape archaeological study concerning the settlement history and environment in Sandy Flanders, a region to the north of Ghent (Belgium). The objective was to create a detailed topographical surface free of artificial features and topographical artefacts, in the form of a DEM, visualizing the natural and current topography through the implementation of true ground points only. The semi-automatical removal of these features and artefacts was based on topographical vector data, visual interpretations and slope analysis. Ultimately two DEM’s were constructed (1) a TIN (Triangulated Irregular Network) model, whereby the inherent large file format restricts the usability to large scale and (2) a grid model which can be used for small-, medium- and large-scale applications. Both datasets were used as an image that is interpreted using ancillary data from historical sources. Its usefulness is illustrated in a case of field pattern and microfield topography. Starting from this DEM, the approach of this landscape historical study is mainly retrogressive, i.e. starting from the landscape structures and elements that are still present in the contemporary landscape and moving into the past. 相似文献
99.
The representer theorem for kernel methods states that the solution of the associated variational problem can be expressed
as the linear combination of a finite number of kernel functions. However, for non-smooth loss functions, the analytic characterization
of the coefficients poses nontrivial problems. Standard approaches resort to constrained optimization reformulations which,
in general, lack a closed-form solution. Herein, by a proper change of variable, it is shown that, for any convex loss function,
the coefficients satisfy a system of algebraic equations in a fixed-point form, which may be directly obtained from the primal
formulation. The algebraic characterization is specialized to regression and classification methods and the fixed-point equations
are explicitly characterized for many loss functions of practical interest. The consequences of the main result are then investigated
along two directions. First, the existence of an unconstrained smooth reformulation of the original non-smooth problem is
proven. Second, in the context of SURE (Stein’s Unbiased Risk Estimation), a general formula for the degrees of freedom of
kernel regression methods is derived. 相似文献
100.
An important question for the upcoming Semantic Web is how to best combine open world ontology languages, such as the OWL-based ones, with closed world rule-based languages. One of the most mature proposals for this combination is known as hybrid MKNF knowledge bases (Motik and Rosati, 2010 [52]), and it is based on an adaptation of the Stable Model Semantics to knowledge bases consisting of ontology axioms and rules. In this paper we propose a well-founded semantics for nondisjunctive hybrid MKNF knowledge bases that promises to provide better efficiency of reasoning, and that is compatible with both the OWL-based semantics and the traditional Well-Founded Semantics for logic programs. Moreover, our proposal allows for the detection of inconsistencies, possibly occurring in tightly integrated ontology axioms and rules, with only little additional effort. We also identify tractable fragments of the resulting language. 相似文献