金属注射成形烧结工艺的试验与数值模拟

采用粘塑性理论建立烧结过程的本构模型,以316L不锈钢粉末注射成形产品为例,设计出烧结过程中重力作用下弯曲梁试验和膨胀计中的自由烧结试验,分别用于标定本构模型中的粘度模量和烧结应力.通过用户子程序,在有限元求解器Abaqus(r)上实现数值模拟,预测产品在烧结过程中的收缩和变形.考虑了重力、摩擦以及注射阶段粉末与粘结剂的偏析效应对于烧结工艺的影响,数值模拟结果与试验结果一致.     

Endocardial Boundary E timation and Tracking in Echocardiographic Images using Deformable Template and Markov Random Fields

We present a new approach to shape-based segmentation and tracking of deformable anatomical structures in medical images, and validate this approach by detecting and tracking the endocardial contour in an echocardiographic image sequence. To this end, some global prior shape knowledge of the endocardial boundary is captured by a prototype template with a set of predefined global and local deformations to take into account its inherent natural variability over time. In this deformable model-based Bayesian segmentation, the data likelihood model relies on an accurate statistical modelling of the grey level distribution of each class present in the ultrasound image. The parameters of this distribution mixture are given by a preliminary iterative estimation step. This estimation scheme relies on a Markov Random Field prior model, and takes into account the imaging process as well as the distribution shape of each class present in the image. Then the detection and the tracking problem is stated in a Bayesian framework, where it ends up as a cost function minimisation problem for each image of the sequence. In our application, this energy optimisation problem is efficiently solved by a genetic algorithm combined with a steepest ascent procedure. This technique has been successfully applied on synthetic images, and on a real echocardiographic image sequence.     

An octree-based proxy for collision detection in large-scale particle systems

Particle systems are important building block for simulating vivid and detail-rich effects in virtual world.One of the most difficult aspects of particle systems has been detecting collisions between particles and mesh surface.Due to the huge computation,a variety of proxy-based approaches have been proposed recently to perform visually correct simulation.However,all either limit the complexity of the scene,fail to guarantee non-penetration,or are too slow for real-time use with many particles.In this paper,we propose a new octree-based proxy for colliding particles with meshes on the GPU.Our approach works by subdividing the scene mesh with an octree in which each leaf node associates with a representative normal corresponding to the normals of the triangles that intersect the node.We present a view-visible method,which is suitable for both closed and non-closed models,to label the empty leaf nodes adjacent to nonempty ones with appropriate back/front property,allowing particles to collide with both sides of the scene mesh.We show how collisions can be performed robustly on this proxy structure in place of the original mesh,and describe an extension that allows for fast traversal of the octree structure on the GPU.The experiments show that the proposed method is fast enough for real-time performance with millions of particles interacting with complex scenes.     

Trifluoperazine increases fatty acid turnover in phospholipids in cultured human fibroblasts

A 24-hr pretreatment of cultured human fibroblasts with trifluoperazine induced a marked increase in incorporation of saturated (stearic, palmitic) and unsaturated (oleic, arachidonic) fatty acids into phospholipids (1.5- to 2-fold for 5.10⁻⁵ M trifluoperazine). Concomitantly, incorporation into cholesteryl esters was strongly inhibited (20% of control for 5.10⁻⁵ M trifluoperazine). The drug did not change the phospholipid composition of treated cells. The effect of trifluoperazine on oleic acid incorporation into phospholipids was time-dependent and reached a maximum after a six-hr preincubation with the drug. Trifluoperazine also induced an increase in the rate of chase of oleic acid from the different phospholipid classes. In vitro preincubation of cell-free extracts with trifluoperazine resulted in activation of phospholipid acyltransferases, whereas cholesterol acyltransferase activity was decreased. The rapid effect of trifluoperazine together with its effect on a cell-free system suggests a direct action of this amphiphilic drug on the acyltransferase activities, probably by modification of the structural organization of cellular membranes.     

Robust Black-Box Modeling of Piezoelectric Actuators for Vibration Drilling Control

In this paper, we study a new modeling approach which is experimentally validated on piezoelectric actuators, in order to derive black-box pseudolinear models for the vibration drilling control. A common way is to use physical based approaches. However, sometimes, complex phenomena occur in the system due to atypical changes of the process behavior, output noise or some hard non-linearities. Therefore, identification methods to achieve the modeling task are adopted. The micro-displacements of the piezoelectric systems generate atypical data named observation outliers in the output signal, involving large errors named innovation outliers in the predicted output signal. Since the normal distribution of these estimation errors is disturbed, and present heavy tails, we choose here as model of contaminated distribution the gross error model (GEM) approach. In order to deal with the innovation outliers, we extend the noise interval range of the scaling factor, tuning the robust Huber’s ρ-function chosen. We propose from this function, a parameterized robust estimation criterion (PREC) and we give the asymptotic covariance matrix of the M-estimator for the Output Error (OE) model structure. A new decisional tool for the models quality, named L ₁-contribution function is proposed. Experimental results are presented and discussed.     

Manifold-ranking based retrieval using k-regular nearest neighbor graph

Manifold-ranking is a powerful method in semi-supervised learning, and its performance heavily depends on the quality of the constructed graph. In this paper, we propose a novel graph structure named k-regular nearest neighbor (k-RNN) graph as well as its constructing algorithm, and apply the new graph structure in the framework of manifold-ranking based retrieval. We show that the manifold-ranking algorithm based on our proposed graph structure performs better than that of the existing graph structures such as k-nearest neighbor (k-NN) graph and connected graph in image retrieval, 2D data clustering as well as 3D model retrieval. In addition, the automatic sample reweighting and graph updating algorithms are presented for the relevance feedback of our algorithm. Experiments demonstrate that the proposed algorithm outperforms the state-of-the-art algorithms.     

Real-time knot-tying simulation

The real-time simulation of rope, and knot tying in particular, raises difficult issues in contact detection and management. Some practical knots can only be achieved by complicated crossings of the rope, yielding multiple simultaneous contacts, especially when the rope is pulled tight. This paper describes a graphical simulator that allows a user to grasp and smoothly manipulate a virtual rope and to tie arbitrary knots, including knots around other objects, in real time. A first component of the simulator computes the global configuration of the rope based on user interactions. Another component of the simulator precisely detects self-collisions in the rope as well as collisions with other objects. Finally, a third component manages collisions to prevent penetration, while making the rope slide with some friction along itself and other objects, so that knots can be pulled tight in a realistic manner. An additional module uses recent results from knot theory to identify, also in real time, which topological knots have been tied. This work was motivated by surgical suturing, but simulation in other domains, such as sailing and rock climbing, could also benefit from it.     

盘磨机低浓磨浆过程强度表征的有效性及应用

本课题采用理论分析方法研究了现有低浓磨浆强度对于不含挡坝等距直齿磨盘低浓磨浆过程的强度表征效果。结果表明,单个磨齿交错区域的净法向力（f_n^net）及切向力（f_t^net）是目前唯一具有实际意义的有效低浓磨浆强度,其不仅适用于不含挡坝等距直齿磨盘低浓磨浆过程的表征,并可扩展至含挡坝磨盘及弧形齿磨盘。而具有实际意义的比边缘负荷（SEL_C及SEL_T）的应用具有一定的局限性,仅适用于恒定参数磨盘低浓磨浆过程的强度表征。实际上,低浓磨浆强度的合理建立、选择及应用不仅反映对磨浆机理的认知,且直接影响低浓磨浆过程的优化控制、齿型参数设计及选择。     

Centrifugal partition chromatography followed by HPLC for the isolation of cis-ε-viniferin,a resveratrol dimer newly extracted from a red Algerian wine

Grapes and related products are considered the major dietary sources of stilbenes. Among these compounds, trans-resveratrol is one of the most important in terms of biological activity, since it has been reported to prevent or to slow the progression of a wide variety of illnesses. We report for the first time the isolation and structure elucidation of cis-ε-viniferin, a biologically active resveratrol dihydrodimer from a red Algerian wine. The Merlot wine was fractionated by column chromatography followed by centrifugal partition chromatography (CPC) and then by reverse-phase semi-preparative HPLC. The structure of cis-ε-viniferin was elucidated by means of 1H NMR and 2D correlations. Cis-ε-viniferin concentrations were determined in wine samples originating from North Africa, most of which are commercially available in France. Stilbene quantification was based on an HPLC method with diode array detection. Unlike trans-ε-viniferin, cis-ε-viniferin was present in almost all wine samples studied and the concentrations ranged from 0.10 to 1.12 mg/l.     

Benefiting from the unique properties of lanthanide ions

The recent upsurge of interest in contrast agents for magnetic resonance imaging, of luminescent chemosensors for medical diagnostic, and lately, for optical imaging of cells has generated an impressive momentum for the coordination and supramolecular chemistry of trivalent lanthanide ions. We shortly review the synthetic methods allowing the introduction of these spherical ions with fascinating optical and magnetic properties into elaborate mono- and polymetallic edifices. We then illustrate these methods by selected examples describing the use of (i) a coronand to produce luminescent liquid crystals, (ii) derivatized calixarenes for 4f-5f element separation, (iii) podates for the production of nanoparticles with high relaxivity and for sensitizing the near-infrared (NIR) emission, and (iv) self-assembly processes for producing functional bimetallic edifices.