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排序方式: 共有704条查询结果,搜索用时 62 毫秒
51.
Sundfeldt M Widmark M Wennerberg A Kärrholm J Johansson CB Carlsson LV 《Journal of materials science. Materials in medicine》2002,13(11):1037-1043
The addition of sodium fluoride to poly (methyl-methacrylate) (PMMA) bone cement may theoretically improve the fixation of joint replacement. This hypothesis was tested in an animal model using nine mature healthy lop-eared rabbits. A femoral prosthesis was inserted in both knees to resurface the patellofemoral articulation. The same acrylic cement, with and without sodium fluoride, was randomised between the two sides for prosthetic fixation. Two screw shaped implants machined from cured rods of either cement were also inserted bilaterally into the proximal tibia. Qualitative and quantitative histomorphometry of the bone tissue response surrounding the cement in the femur and the intact tibial implants revealed similar results regardless of sodium fluoride addition. Six weeks after surgery removal, torque did not significantly differ between the two sides. Our findings indicate that addition of sodium fluoride to PMMA has little effect on implant stability and bone remodeling in rabbits in the short-term. 相似文献
52.
We present an empirical model for the waveguiding properties of directly UV-written planar waveguides in silica-on-silicon. The waveguides are described by a rectangular core step-index profile, in which model parameters are found by comparison of the measured waveguide width and effective index with modal field calculations. The model is used as input for beam propagation method calculations to design UV-written optical components. Subsequent fabrication of such components showed a good agreement with the model predictions. Using the model will reduce the number of iterations and thereby the development time of new optical devices. 相似文献
53.
A whole-field speckle strain sensor is presented. The speckle strain sensor allows the measurement of all three in-plane components of the strain field simultaneously without touching the surface of the sample. The strain fields are extracted from the in-plane motion of defocused laser speckles in a telecentric imaging system. To distinguish the contribution to the speckle motion from surface translation, rotation, and strain, the speckle motion from three lasers with different illumination directions and wavelengths has to be analyzed separately. Simultaneous acquisition of the three individual speckle patterns is achieved by means of splitting the light from the lasers onto separate but synchronized detectors with the aid of dichroic mirrors. The motion of the speckles is calculated with digital speckle photography (speckle correlation), which enables the strain sensor to measure strain fields with noise levels as low as 10 microstrain. 相似文献
54.
Mikael Ciftan Robert G. Brown Edward Saibel 《International Journal of Engineering Science》1983,21(11):1285-1293
A new technique for the detection of microcrack precursors and for the study of the dynamics of crack propagation is proposed. The technique uses laser Raman scattering off of adsorbed surface species to detect microcrack precursors via variations in the Raman spectrum associated with the stresses localized within such precursors. We give extensive theoretical justification and detail several approaches designed to substantiate the plausability of the technique proposed. This technique can become a valuable tool for the detection of microcrack precursors as well as studies of phenomena including adsorption, catalysis. adhesion, wear and the dynamics of stress-corrosion cracking. 相似文献
55.
We present a model for quantitative measurements in binary mixtures of nitrogen and carbon monoxide by the use of dual-broadband rotational coherent anti-Stokes Raman spectroscopy. The model has been compared with experimental rotational coherent anti-Stokes Raman scattering spectra recorded within the temperature range of 294-702 K. Temperatures and concentrations were evaluated by spectral fits using libraries of theoretically calculated spectra. The relative error of the temperature measurements was 1-2%, and the absolute error of the CO concentration measurements was <0.5% for temperatures < or =600 K. For higher temperatures, the gas composition was not chemically stable, and we observed a conversion of CO to CO2. The influence of important spectroscopic parameters such as the anisotropic polarizability and Raman line-broadening coefficients are discussed in terms of concentration measurements. In particular, it is shown that the CO concentration measurement was more accurate if N2-CO and CO-N2 line-broadening coefficients were included in the calculation. The applicability of the model for quantitative flame measurements is demonstrated by measuring CO concentrations in ethylene/air flames. 相似文献
56.
57.
A Review of Statistical Approaches to Level Set Segmentation: Integrating Color,Texture, Motion and Shape 总被引:8,自引:4,他引:8
Daniel Cremers Mikael Rousson Rachid Deriche 《International Journal of Computer Vision》2007,72(2):195-215
Since their introduction as a means of front propagation and their first application to edge-based segmentation in the early
90’s, level set methods have become increasingly popular as a general framework for image segmentation. In this paper, we
present a survey of a specific class of region-based level set segmentation methods and clarify how they can all be derived
from a common statistical framework.
Region-based segmentation schemes aim at partitioning the image domain by progressively fitting statistical models to the
intensity, color, texture or motion in each of a set of regions. In contrast to edge-based schemes such as the classical Snakes,
region-based methods tend to be less sensitive to noise. For typical images, the respective cost functionals tend to have
less local minima which makes them particularly well-suited for local optimization methods such as the level set method.
We detail a general statistical formulation for level set segmentation. Subsequently, we clarify how the integration of various
low level criteria leads to a set of cost functionals. We point out relations between the different segmentation schemes.
In experimental results, we demonstrate how the level set function is driven to partition the image plane into domains of
coherent color, texture, dynamic texture or motion. Moreover, the Bayesian formulation allows to introduce prior shape knowledge
into the level set method. We briefly review a number of advances in this domain. 相似文献
58.
Mikael Svahnberg Tony Gorschek Thi Than Loan Nguyen Mai Nguyen 《Requirements Engineering》2013,18(1):85-103
Software products are usually developed for either a specific customer (bespoke) or a broader market (market-driven). Due to their characteristic, bespoke and market-driven development face different challenges, especially concerning requirements engineering. Many challenges are caused by an inadequate requirements engineering process, and hence there is a need for process improvement frameworks based on empirical research and industry needs. In a previous article we introduced Uni-REPM, a lightweight requirements engineering process assessment framework based on a review of empirically motivated practices in market-driven and bespoke requirements engineering literature. In this article, we validate this framework in academia as well as industry, in order to prepare Uni-REPM for widespread industry use. We conduct two validations; a static validation based on interviews with seven academic experts and a dynamic validation where Uni-REPM is applied in four industrial organisations. Uni-REPM is refined according to the feedback obtained in the validations. The study shows that Uni-REPM is a quick, simple, and cost-effective solution to assess the maturity level of the requirements engineering process of projects. Moreover, the assessment method using checklists is highly usable and applicable in various international development environments. 相似文献
59.
Niall Robert Hamilton James Wood Alexander Galloway Mikael Brian Olsson Robbie Yuxuan Zhang 《Journal of Nuclear Materials》2013,432(1-3):42-51
At the heart of any procedure for modelling and assessing the design or failure of dissimilar material brazed joints there must be a basic understanding of the metallurgy and mechanics of the joint. This paper is about developing this understanding and addressing the issues faced with modelling and predicting failure in real dissimilar material brazed joints and the challenges still to be overcome in many cases. An understanding of the key metallurgical features of such joints in relation to finite element modelling is presented in addition to a study of the mechanics and stress state at an abrupt interface between two materials. A discussion is also presented on why elastic singularities do not exist based on a consideration of the assumption of an abrupt change in material properties and plasticity in the vicinity of the joint. In terms of modelling real dissimilar material brazed joints; there are several barriers to accurately capturing the stress state in the region of the joint and across the brazed layer and these are discussed in relation to a metallurgical study of a real dissimilar material brazed joint. However, this does not preclude using a simplified modelling approach with a representative braze layer in design and failure assessment away from the interface. In addition modelling strategies and techniques for assessing the various failure mechanisms of dissimilar material brazed joints are discussed. The findings from this paper are applicable to dissimilar material brazed joints found in a range of applications; however the references listed are primarily focussed on work in fusion research and development. 相似文献
60.
Specifying OLAP Cubes on XML Data 总被引:6,自引:0,他引:6
Mikael R. Jensen Thomas H. Møller Torben Bach Pedersen 《Journal of Intelligent Information Systems》2001,17(2-3):255-280
On-Line Analytical Processing (OLAP) enables analysts to gain insight about data through fast and interactive access to a variety of possible views on information, organized in a dimensional model. The demand for data integration is rapidly becoming larger as more and more information sources appear in modern enterprises. In the data warehousing approach, selected information is extracted in advance and stored in a repository, yielding good query performance. However, in many situations a logical (rather than physical) integration of data is preferable. Previous web-based data integration efforts have focused almost exclusively on the logical level of data models, creating a need for techniques focused on the conceptual level. Also, previous integration techniques for web-based data have not addressed the special needs of OLAP tools such as handling dimensions with hierarchies. Extensible Markup Language (XML) is fast becoming the new standard for data representation and exchange on the World Wide Web. The rapid emergence of XML data on the web, e.g., business-to-business (B2B) e-commerce, is making it necessary for OLAP and other data analysis tools to handle XML data as well as traditional data formats.Based on a real-world case study, this paper presents an approach to specification of OLAP DBs based on web data. Unlike previous work, this approach takes special OLAP issues such as dimension hierarchies and correct aggregation of data into account. Also, the approach works on the conceptual level, using Unified Modeling Language (UML) as a basis for so-called UML snowflake diagrams that precisely capture the multidimensional structure of the data. An integration architecture that allows the logical integration of XML and relational data sources for use by OLAP tools is also presented. 相似文献