Turning a Digital Camera into an Absolute 2D Tele‐Colorimeter

We present a simple and effective technique for absolute colorimetric camera characterization, invariant to changes in exposure/aperture and scene irradiance, suitable in a wide range of applications including image‐based reflectance measurements, spectral pre‐filtering and spectral upsampling for rendering, to improve colour accuracy in high dynamic range imaging. Our method requires a limited number of acquisitions, an off‐the‐shelf target and a commonly available projector, used as a controllable light source, other than the reflected radiance to be known. The characterized camera can be effectively used as a 2D tele‐colorimeter, providing the user with an accurate estimate of the distribution of luminance and chromaticity in a scene, without requiring explicit knowledge of the incident lighting power spectra. We validate the approach by comparing our estimated absolute tristimulus values (XYZ data in ) with the measurements of a professional 2D tele‐colorimeter, for a set of scenes with complex geometry, spatially varying reflectance and light sources with very different spectral power distribution.     

模拟嵌入式FRP条增强钢筋混凝土梁抗剪的三维力学模型

嵌入式FRP增强钢筋混凝土梁抗剪是进行结构修复的新技术,由于嵌入式FRP所具有的一些优势,使其成为较好的外贴加固技术,越来越受到重视。嵌入式FRP主要优势在于材料开发、对结构完整性的保护以及相对较快的适用性。由于FRP条复杂的几何尺寸,粘结后的非线性力学性能,混凝土受拉性能的离散性,使得嵌入式FRP条加固的性能十分复杂,一般通过试验来获得其性能。为更好地掌握表面嵌贴FRP带的性能,提出三维力学模型,用于模拟在相似加载过程中,嵌入式FRP条体系对钢筋混凝土梁抗剪强度的贡献。模型很好地解释了试验结果,并在模型中考虑了粘结滑移力和混凝土破坏之间的相互作用以及相邻FRP条之间的相互作用等复杂现象。     

Multistage Switching Architectures for Software Routers

Software routers based on personal computer (PC) architectures are becoming an important alternative to proprietary and expensive network devices. However, software routers suffer from many limitations of the PC architecture, including, among others, limited bus and central processing unit (CPU) bandwidth, high memory access latency, limited scalability in terms of number of network interface cards, and lack of resilience mechanisms. Multistage PC-based architectures can be an interesting alternative since they permit us to i) increase the performance of single- software routers, ii) scale router size, iii) distribute packet-manipulation and control functionality, iv) recover from single-component failures, and v) incrementally upgrade router performance. We propose a specific multistage architecture, exploiting PC-based routers as switching elements, to build a high-speed, large-size, scalable, and reliable software router. A small-scale prototype of the multistage router is currently up and running in our labs, and performance evaluation is under way.     

Flexible joints control: A minimum-time feed-forward technique

The paper proposes a linear programming approach to the feed-forward minimum-time control of flexible joints. Taking into account both input and output constraints, the optimal bang–bang control is computed by discretizing a continuous-time joint model and by solving a sequence of linear programming feasibility problems. The resulting joint motion is a smooth rest-to-rest motion without oscillations. Theoretical analysis is presented and proof of convergence is given. Experimental results illustrate the proposed open-loop technique. Comparisons are made with inversion-based techniques.     

F-substituted hydroxyapatite nanopowders: Thermal stability,sintering behaviour and mechanical properties

Fluorine-substituted hydroxyapatites are considered promising materials for bone scaffolding. In this study a systematic investigation on F-half substituted hydroxyapatite (F-HAp, Ca₁₀(PO₄)₆OHF) obtained by precipitation is reported. Results on composition analysis, thermal behaviour, and sinterability are presented for a comparison with the respective pure hydroxyapatite. Samples were characterised by electron microscopy, induced coupled plasma-atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N₂ adsorption measurements, X-ray diffraction and dilatometry. A semicrystalline F-substituted hydroxyapatite powder made up of needle-like nanoparticles was obtained. Notwithstanding that it was thermally stable up to 1300 °C, it was sintered at relatively low temperatures obtaining a very fine microstructure with a relevant nano-porosity, beneficial in view of cell adhesion and in-growth.Hardness, elastic modulus and toughness of produced samples were investigated by Vickers–Knoop microhardness testing. Significant improvements of the mechanical properties were observed for the F-substituted hydroxyapatite, in comparison with pure hydroxyapatite.     

Biomechanical evaluation of cell-loaded and cell-free hydroxyapatite implants for the reconstruction of segmental bone defects

Porous hydroxyapatite (HA) scaffoldings are currently used in tissue engineering for bone reconstruction. When this osteoconductive biomaterial is combined with osteoprogenitor cells, it acquires osteoinductive features which accelerate and improve bone formation in vivo. The aim of our study was to assess the mechanical properties of HA–bone complexes undergoing indentation tests, and relate stiffness to composition and structure as examined by micro X-ray. To this purpose, 35-mm tibia diaphyseal resections were performed in sheep. Gaps were filled using porous HA cylinders. Implants were loaded with autologous bone marrow stromal cells (BMSC); cell-free cylinders were used as control. After 8 weeks, bone tissue was found within the internal macropores of cell-loaded HA carriers, and in control implants, bone formation was mostly limited to the outer surface. As assessed by indentation testing the stiffness values of bone–HA composites were halfway between those of HA scaffoldings and tibia bone. Cell-loaded implants were stiffer than cell-free ones. In a cell-loaded implant we also analyzed the variation of stiffness along the main axis of the tibia.     

Chemical synthesis and sintering behaviour of highly dispersed W/Cu composite powders

The paper reports the preparation of W/Cu composite powders by a wet process based on the reduction of selected copper precursors in ethylene glycol and in the presence of tungsten powders. Reactions were performed in different conditions of temperature, time and concentration of the copper precursor. Two different Cu compounds, Cu(AcO)₂·H₂O and CuO (coarse or fine) and two W powders (coarse or fine) were used. The reaction yields ranged from 75% to 98%. Dense bodies (up to 97% fractional density) with highly homogeneous microstructure as well as high electrical conductivity (up to 41% IACS) were obtained by sintering W/Cu powders at 1350 °C.