Stable splitting scheme for general form of associated plasticity including different scales of space and time

An efficient implementation of the operator split procedure for boundary value solution with plastic flow computation is presented for a general form of associated plasticity model. We start with the general form of phenomenological model of plasticity where the yield criterion is not restricted to a simple (quadratic) form, and the elasticity tensor does not have constant entries. We then turn to the multi-scale model of plasticity which employs the fine scale representation of the plastic deformation along with the homogenization procedure for stress computation. We also visit the plasticity model with rate sensitive plastic response where plastic flow computation is carried out at fine scale in time. We proved herein the sufficient and necessary conditions for the proposed operator split procedure to converge, for any such general form of associated plasticity. Moreover, we presented a systematic manner for constructing the main ingredients for the plastic flow computation and the global Newton’s iteration, such as the consistent elastoplastic tangent.     

Intelligent Programming of CNC Turning Operations using Genetic Algorithm

CAD/CAM systems are nowadays tightly connected to ensure that CAD data can be used for optimal tool path determination and generation of CNC programs for machine tools. The aim of our research is the design of a computer-aided, intelligent and genetic algorithm(GA) based programming system for CNC cutting tools selection, tool sequences planning and optimisation of cutting conditions. The first step is geometrical feature recognition and classification. On the basis of recognised features the module for GA-based determination of technological data determine cutting tools, cutting parameters (according to work piece material and cutting tool material) and detailed tool sequence planning. Material, which will be removed, is split into several cuts, each consisting of a number of basic tool movements. In the next step, GA operations such as reproduction, crossover and mutation are applied. The process of GA-based optimisation runs in cycles in which new generations of individuals are created with increased average fitness of a population. During the evaluation of calculated results (generated NC programmes) several rules and constraints like rapid and cutting tool movement, collision, clamping and minimum machining time, which represent the fitness function, were taken into account. A case study was made for the turning operation of a rotational part. The results show that the GA-based programming has a higher efficiency. The total machining time was reduced by 16%. The demand for a high skilled worker on CAD/CAM systems and CNC machine tools was also reduced. Received: September 2004 / Accepted: September 2005     

Quasiparticle Dynamics from the Bose–Einstein Condensation to the BCS-Like Regions of the Phase Diagram in YBa2Cu3O7?δ

In the underdoped region of the phase diagram, time-resolved opticalexperiments on quasiparticle recombination dynamics show that the state ischaracterized by a temperature independent energy gap E _g which exists at alltemperatures and has a magnitude which appears inversely proportional todoping. Close to optimum doping another, collective gap becomes visiblesimultaneously, which has a BCS-like temperature dependence and closes atT _c.     

Induced phytoextraction/soil washing of lead using biodegradable chelate and permeable barriers

Chelate-induced remediation has been proposed as an effective tool for the extraction of lead (Pb) from contaminated soils by plants. However, side-effects, mainly mobilization and leaching of Pb, raise environmental concerns. Biodegradable, synthetic organic chelate ethylenediaminedisuccinic acid (EDDS), and commonly used ethylenedimanetetraacetic acid (EDTA) were used for induced phytoextraction with a test plant Brassica rapa and in situ washing of soil contaminated with 1350 mg/kg of Pb. Horizontal permeable barriers were placed 20 cm deep in soil columns and tested for their ability to prevent leaching of Pb. The reactive materials in the barriers were nutrient enriched vermiculite, peat or agricultural hydrogel, and apatite. EDTA and EDDS addition increased Pb concentrations in the test plant by 158 and 89 times compared to the control, to 817 and 464 mg/kg, respectively. In EDTA treatments, approximately 25% or more of total initial soil Pb was leached in single cycle of chelate addition. In EDDS treatments, 20% of the initial Pb was leached from columns with no barrier, while barriers with vermiculite or hydrogel and apatite decreased leaching by more than 60 times, to 0.35%. 11.6% of total initial Pb was washed from the soil above the barrier with vermiculite and apatite, where almost all leached Pb was accumulated. Results indicate that use of biodegradable chelate EDDS and permeable barriers may lead to environmentally safe induced Pb phytoextraction and in situ washing of Pb.     

3-D/2-D registration of CT and MR to X-ray images

A crucial part of image-guided therapy is registration of preoperative and intraoperative images, by which the precise position and orientation of the patient's anatomy is determined in three dimensions. This paper presents a novel approach to register three-dimensional (3-D) computed tomography (CT) or magnetic resonance (MR) images to one or more two-dimensional (2-D) X-ray images. The registration is based solely on the information present in 2-D and 3-D images. It does not require fiducial markers, intraoperative X-ray image segmentation, or timely construction of digitally reconstructed radiographs. The originality of the approach is in using normals to bone surfaces, preoperatively defined in 3-D MR or CT data, and gradients of intraoperative X-ray images at locations defined by the X-ray source and 3-D surface points. The registration is concerned with finding the rigid transformation of a CT or MR volume, which provides the best match between surface normals and back projected gradients, considering their amplitudes and orientations. We have thoroughly validated our registration method by using MR, CT, and X-ray images of a cadaveric lumbar spine phantom for which "gold standard" registration was established by means of fiducial markers, and its accuracy assessed by target registration error. Volumes of interest, containing single vertebrae L1-L5, were registered to different pairs of X-ray images from different starting positions, chosen randomly and uniformly around the "gold standard" position. CT/X-ray (MR/ X-ray) registration, which is fast, was successful in more than 91% (82% except for L1) of trials if started from the "gold standard" translated or rotated for less than 6 mm or 17 degrees (3 mm or 8.6 degrees), respectively. Root-mean-square target registration errors were below 0.5 mm for the CT to X-ray registration and below 1.4 mm for MR to X-ray registration.     

Haptic Interaction Stability With Respect to Grasp Force

This paper addresses the contact instability of admittance control of a haptic interface. A high level of rigidity of the grasp of a subject operating the haptic interface will result in unstable behavior of the haptic interaction. Experiments with a system dedicated to measuring grasp force were performed to explore the conditions when grasp force has reached the critical grasp force that destabilizes the haptic interface. The critical grasp force was quantified for various values of virtual environment parameters. The experimental results are compared to simulation results obtained with a model of haptic interaction. To improve stability, two methods were applied: one with virtual coupling, the other with a compensator filter. A model was used to define the structure of the compensator filter and to determine the parameters of the virtual coupling and the compensator filter. Experimental and simulation results confirmed an improvement of stability. Both methods allow higher grasp forces of the human operator, and experiments show that the compensator filter allows higher grasp forces than the virtual coupling.     

Production of aluminium killed steels with high sulphur contents for automotive industry

The influence of aluminium deoxidation and various amounts of injected CaSi on resulphurized steel has been investigated. The type of inclusion formed depends on the aluminium, silicium, calcium and sulphur contents. The chemical composition of the oxide inclusion was in good agreement with the prediction of the thermodynamical equilibrium calculation.     

Tem analyses of the local crystal and domain structures in (Na(1-x)K(x))0.5Bi(0.5)TiO3 perovskite ceramics

The local crystal and domain structures of the ((Na(1-x)K(x))(0.5)Bi(0.5)TiO(3) (NBT-KBT) solid solutions were studied because of their influence on the enhanced electromechanical properties of ceramics. Based on X-ray diffraction, the morphotropic phase boundary (MPB) was determined for the composition x = 0.20, in which the rhombohedral and the tetragonal structures were observed to coexist. However, detailed domain-structure analyses using transmission electron microscopy (TEM), performed on the NBT, KBT, and five NBT-KBT solid-solution compositions, revealed some structural changes at/near the MPB. In the samples on the tetragonal side of the MPB, the grains showed a lamellar domain structure with 90° orientations of the individual domains, separated by straight domain boundaries, i.e., (011)/(101) twin planes. The rhombohedral samples on the other side of the MPB showed a typical square-net pattern with needle-like or lamellar ~71°/109° rhombohedral domains with (001) and/or (110) twin planes separating the individual domains. The domain structure at the MPB showed well-defined lamellar domains. Based on the occurrence of the superstructure reflections in the SAED patterns of various crystallographic zones, on the characteristic splitting of the reflections, and on the domain morphology observations, the crystal structure in/near the boundary region was determined to be a tetragonal structure with an in-phase oxygen octahedral tilt system (probably a(0)a(0)c(+)). It is suggested that the tetragonal polar order is partly induced from the rhombohedral structure at the MPB as a result of mechanical loading during TEM sample preparation.     

Silver nanoparticles on titanate nanobelts via the self-assembly of weak polyelectrolytes: synthesis and photocatalytic properties

A weak-polyelectrolyte multilayer on a surface of titanate nanobelts (Ti-NBs) was utilized as a template for in situ Ag nanoparticle formation in the fabrication of Ag-loaded Ti-NBs nanocomposites. The polyelectrolyte multilayer (PEM) was fabricated using layer-by-layer self-assembly of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on the surface of high-surface-area titanate nanobelts (Ti-NBs) synthesized using a hydrothermal procedure. The concentration of Ag nanoparticles in the PEM was controlled by repeating the ion-loading/reduction cycle. The subsequent annealing of the Ag/Ti-NBs-PEM nanocomposites yielded nanostructured crystalline Ag/Ti-NBs. Transmission electron microscopy (TEM) techniques (HRTEM, SAED) and x-ray powder diffraction (XRD) were employed to evaluate the morphological, structural and growth characteristics of the silver nanocrystallites in the Ag/Ti-NBs nanocomposites. The UV-vis photoactivity of the as-fabricated nanocomposites was monitored by the degradation of the cationic dye methylene blue (MB). An enhanced UV photo-efficiency was observed for the Ag/Ti-NBs nanocomposites compared with pure Ti-NBs. As-fabricated Ag(x)/Ti-NBs nanocomposites also exhibited visible photoactivity assisted by the near-field amplitudes of the localized surface plasmon resonance (LSPR) of the silver nanoparticles in the 1D nanocomposite.     

A protocol for evaluation of similarity measures for rigid registration

The accuracy and robustness of a registration method depend on a number of factors, such as imaging modality, image content and image degrading effects, the class of spatial transformation used for registration, similarity measure, optimization, and numerous implementation details. The complex interdependence of these factors makes the assessment of the influence of a particular factor on registration difficult, although it is often desirable to have some estimate of such influences prior to registration. The similarity measure used to create the cost function is one of the factors that most influences the quality of registration. Traditionally, limited information on the behavior of a similarity measure is obtained either by studying the quality of the final registration or by drawing plots of similarity measure values obtained by translating or rotating one image relative to the "gold standard." In this paper, we present a protocol for a more thorough, optimization-independent, and systematic statistical evaluation of similarity measures. This protocol estimates a similarity measure's capture range, the number, location and extent of local optima, and the accuracy and distinctiveness of the global optimum. To show that the proposed evaluation protocol is viable, we have conducted several experiments with nine similarity measures and real computed tomography and magnetic resonance (MR) images of a spine phantom, MR brain images, and MR and positron emission tomography brain images, for which "gold standard" registrations were available. We have also studied the impact of histogram bin size on the behavior of nine similarity measures. The proposed evaluation protocol is useful for selecting the best similarity measure and corresponding optimization method for a particular application, as well as for studying the influence of sampling, interpolation, histogram bin size, partial image overlap, and image degradation, such as noise, intensity inhomogeneity, and geometrical distortions on the behavior of a similarity measure.