Levelset based fluid topology optimization using the extended finite element method

This study focuses on finding the optimal layout of fluidic devices subjected to incompressible flow at low Reynolds numbers. The proposed approach uses a levelset method to describe the fluid-solid interface geometry. The flow field is modeled by the incompressible Navier?CStokes equations and discretized by the extended finite element method (XFEM). The no-slip condition along the fluid-solid interface is enforced via a stabilized Lagrange multiplier method. Unlike the commonly used porosity approach, the XFEM approach does not rely on a material interpolation scheme, which allows for more flexibility in formulating the design problems. Further, it mitigates shortcomings of the porosity approach, including spurious pressure diffusion through solid material, strong dependency of the accuracy of the boundary enforcement with respect to the model parameters which may affect the optimization results, and poor boundary resolution. Numerical studies verify that the proposed method is able to recover optimization results obtained with the porosity approach. Further, it is demonstrated that the XFEM approach yields physical results for problems that cannot be solved with the porosity approach.     

DATA BASE CATHEDRALS

Data base architects are seemingly obsessed with structure, but they must become more applications-oriented if they want their great structures to stand the test of time. The trend is clear: the role of the data base administrator is drifting away from purely technical concerns toward responsibilities that were once the domain of the applications developer.     

Numerical instabilities in level set topology optimization with the extended finite element method

This paper studies level set topology optimization of structures predicting the structural response by the eXtended Finite Element Method (XFEM). In contrast to Ersatz material approaches, the XFEM represents the geometry in the mechanical model by crisp boundaries. The traditional XFEM approach augments the approximation of the state variable fields with a fixed set of enrichment functions. For complex material layouts with small geometric features, this strategy may result in interpolation errors and non-physical coupling between disconnected material domains. These defects can lead to numerical instabilities in the optimized material layout, similar to checker-board patterns found in density methods. In this paper, a generalized Heaviside enrichment strategy is presented that adapts the set of enrichment functions to the material layout and consistently interpolates the state variable fields, bypassing the limitations of the traditional approach. This XFEM formulation is embedded into a level set topology optimization framework and studied with “material-void” and “material-material” design problems, optimizing the compliance via a mathematical programming method. The numerical results suggest that the generalized formulation of the XFEM resolves numerical instabilities, but regularization techniques are still required to control the optimized geometry. It is observed that constraining the perimeter effectively eliminates the emergence of small geometric features. In contrast, smoothing the level set field does not provide a reliable geometry control but mainly improves the convergence rate of the optimization process.     

Review of A critical psychology: Interpretation of the personal world.

Reviews the book, A critical psychology: Interpretation of the personal world by Edmund V. Sullivan (1984). In this book, the author gives an indication of what an alternative psychology might look like. In doing this he draws on the ideas of a number of European philosophers and social scientists whose work has been generally ignored by North American psychologists. What distinguishes Sullivan's critical psychology from other alternatives to the mainstream is his insistence that the conditions for human action be traced not simply to the intentional activity of individuals but to the social structures of domination in which individual intentions are embedded. These are the structures of ethnicity, gender, and class. What Sullivan criticizes is that "psychologists take structural relationships of power such as capital over labour, men over women, and change them into intrapsychic phenomena." This book is an important contribution to the growing literature on alternatives to mainstream psychology. It is distinguished by its intellectual sophistication and by its marshalling of perspectives that run counter to local cultural traditions. At the very least it is a volume that ought to provoke an expansion of all too narrow disciplinary horizons. Incidentally, the very concept of intellectual "horizon" is one that the author analyses in a particularly constructive way, showing its relevance in the context of psychological research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Drift detection and removal for sequential structure from motion algorithms

In sequential Structure from Motion algorithms for extended image or video sequences, error build up caused by drift poses a problem as feature tracks that normally represent a single scene point will have distinct 3D reconstructions. For the final bundle adjustment to remove this drift, it must be told about these 3D-3D correspondences through a change in the cost function. However, as a bundle adjustment is a nonlinear optimization technique, the drift needs to be removed from the supplied initial solution to allow for convergence of the bundle adjustment to the real global optimum. Before drift can be removed, it has to be detected. This is accomplished through understanding of the long term behavior of drift which leaves 3D reconstructions from short sequences intact. Drift detection boils down to identifying reconstructions of the same scene part that only differ up to a projective transformation. After detection, the drift can be removed from future processed images and an Adapted Bundle Adjustment using correspondences supplied by the drift detection can remove the drift from previous images. Several experiments on real video sequences demonstrate the merit of drift detection and removal.     

Visual Modeling with a Hand-Held Camera

In this paper a complete system to build visual models from camera images is presented. The system can deal with uncalibrated image sequences acquired with a hand-held camera. Based on tracked or matched features the relations between multiple views are computed. From this both the structure of the scene and the motion of the camera are retrieved. The ambiguity on the reconstruction is restricted from projective to metric through self-calibration. A flexible multi-view stereo matching scheme is used to obtain a dense estimation of the surface geometry. From the computed data different types of visual models are constructed. Besides the traditional geometry- and image-based approaches, a combined approach with view-dependent geometry and texture is presented. As an application fusion of real and virtual scenes is also shown.     

"Off-On" Electrochemical Hairpin-DNA-Based Genosensor for Cancer Diagnostics

A simple and robust "off-on" signaling genosensor platform with improved selectivity for single-nucleotide polymorphism (SNP) detection based on the electronic DNA hairpin molecular beacons has been developed. The DNA beacons were immobilized onto gold electrodes in their folded states through the alkanethiol linker at the 3'-end, while the 5'-end was labeled with a methylene blue (MB) redox probe. A typical "on-off" change of the electrochemical signal was observed upon hybridization of the 27-33 nucleotide (nt) long hairpin DNA to the target DNA, in agreement with all the hitherto published data. Truncation of the DNA hairpin beacons down to 20 nts provided improved genosensor selectivity for SNP and allowed switching of the electrochemical genosensor response from the on-off to the off-on mode. Switching was consistent with the variation in the mechanism of the electron transfer reaction between the electrode and the MB redox label, for the folded beacon being characteristic of the electrochemistry of adsorbed species, while for the "open" duplex structure being formally controlled by the diffusion of the redox label within the adsorbate layer. The relative current intensities of both processes were governed by the length of the formed DNA duplex, potential scan rate, and apparent diffusion coefficient of the redox species. The off-on genosensor design used for detection of a cancer biomarker TP53 gene sequence favored discrimination between the healthy and SNP-containing DNA sequences, which was particularly pronounced at short hybridization times.     

Model for Estimating Evaporation and Transpiration from Row Crops

Accurate estimates of crop evapotranspiration ETc, that quantify the total water used by a crop, are needed to optimize irrigation scheduling for horticultural crops and to minimize water degradation. During early growth, accurate assessments of ETc are difficult in vegetable crops because of high soil evaporation due to frequent irrigation. A model to estimate ETc for vegetable crops, using only daily reference evapotranspiration data as an input parameter, was developed. It calculates crop transpiration and soil evaporation based on ground cover and daily radiation intercepted by the canopy. The model uses a two-stage soil evaporation method adapted to conditions of variable reference evapotranspiration. The model was evaluated against data using measurements from two seasons of lettuce crop, two tomato fields in the same season, and one season of broccoli crop production. Using all of the crop data, the root-mean-square error for measured versus modeled daily ETc was 0.72 mm day?1, indicating that the model works well.     

Expressed emotion and patient-relative interaction in families of recent onset schizophrenics.

Examines the interaction patterns of relatives of young, recent onset schizophrenic patients classified as displaying either high or low expressed emotion (EE) by two measures, the original Camberwell interview method and a recently developed brief method. The former was administered during the hospitalization period and the latter was administered approximately 2 months later when the patient was in the community. Family interactions were coded with an observational coding system that permitted sequential patterns to be analyzed as a function of the EE status of the family. No relation between the Camberwell EE rating and interactional behavior was found. However, high EE-critical relatives, defined by the brief EE method, were more negative in direct interactions than low EE relatives or high EE relatives classified as emotionally overinvolved. Sequential analyses indicated that high EE-critical relatives showed extreme negative escalation patterns. Patients' reactions to high EE-critical relatives were characterized by self-justification and negative nonverbal behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)