Objective Model for the Fluctuating Pressure-Strain-Rate Correlations

Representation theorems for isotropic functions are used to construct a closure model for the fluctuating pressure-strain-rate correlation tensor. In contrast to alternative proposals in the literature, the present model does not include a dependence on the vorticity in inertial frames or on the intrinsic spin tensor in noninertial frames because it is shown that this dependence violates objectivity which has been previously suggested to be an essential property of a turbulence closure. The proposed model is calibrated using data from homogeneous shear flows in inertial frames and is tested against data from a variety of turbulent shear flow, in both fixed and rotating frames, with generally very encouraging results. In particular, the results conclusively demonstrate that the absence of dependence on vorticity and intrinsic spin in the model for the pressure-strain-rate correlations does not adversely impact its ability to accurately predict the effects of system rotation on the turbulence.     

A GIS-based methodology for identifying pedestrians’ crossing patterns

A pedestrian trip is a spatiotemporal process going through different states and related to different decisions made at certain times and locations on the urban network. The analysis of pedestrian trips in terms of crossing patterns is a complex task, which is often further limited by a lack of appropriate and detailed data. The objective of this research is the development and testing of appropriate indicators of pedestrian crossing behavior along urban trips, and a methodology for collecting and processing the data required for the analysis of this behavior. First, a comprehensive set of indicators for the assessment of pedestrian behavior in urban areas is proposed (i.e. average trip length, number, type and location of crossings). Then, a GIS tool is developed for the storage and integration of information on pedestrian trips, and the crossings made during the trips, with other geographical information (e.g. road network function and geometry, traffic control and pedestrian facilities). The proposed approach is then tested at network level on a sample of pedestrian trips collected by a field survey. The results suggest specific patterns of pedestrian crossing behavior, such as the tendency to cross at the beginning of the trip and the tendency to cross at mid-block locations when signalized junctions are not available. The results are further discussed in terms of urban planning and management implications. It is concluded that the proposed approach is very efficient for the analysis of pedestrian crossing behavior in urban areas.     

Collaborative recommender systems: Combining effectiveness and efficiency

Recommender systems base their operation on past user ratings over a collection of items, for instance, books, CDs, etc. Collaborative filtering (CF) is a successful recommendation technique that confronts the “information overload” problem. Memory-based algorithms recommend according to the preferences of nearest neighbors, and model-based algorithms recommend by first developing a model of user ratings. In this paper, we bring to surface factors that affect CF process in order to identify existing false beliefs. In terms of accuracy, by being able to view the “big picture”, we propose new approaches that substantially improve the performance of CF algorithms. For instance, we obtain more than 40% increase in precision in comparison to widely-used CF algorithms. In terms of efficiency, we propose a model-based approach based on latent semantic indexing (LSI), that reduces execution times at least 50% than the classic CF algorithms.     

Hough Pyramid Matching: Speeded-Up Geometry Re-ranking for Large Scale Image Retrieval

Exploiting local feature shape has made geometry indexing possible, but at a high cost of index space, while a sequential spatial verification and re-ranking stage is still indispensable for large scale image retrieval. In this work we investigate an accelerated approach for the latter problem. We develop a simple spatial matching model inspired by Hough voting in the transformation space, where votes arise from single feature correspondences. Using a histogram pyramid, we effectively compute pair-wise affinities of correspondences without ever enumerating all pairs. Our Hough pyramid matching algorithm is linear in the number of correspondences and allows for multiple matching surfaces or non-rigid objects under one-to-one mapping. We achieve re-ranking one order of magnitude more images at the same query time with superior performance compared to state of the art methods, while requiring the same index space. We show that soft assignment is compatible with this matching scheme, preserving one-to-one mapping and further increasing performance.     

Cyclic loading for materials with a vanishing elastic region

Within a plastic internal variables formalism of rate independent plasticity, a recently developed constitutive law for plastic material response under stress reversals is shown to apply to materials with a vanishing elastic region. The concept of the bounding surface introduced earlier, replaces the vanished yield and loading surfaces in defining loading-unloading criteria. Good comparison of the model with experimental data is obtained.     

A Si 1.8 GHz RLC filter with tunable center frequency and qualityfactor

A second-order active bandpass filter using integrated inductors was implemented in Si bipolar technology. The filter uses special techniques to make the quality factor and the center frequency tunable. For a nominal center frequency of 1.8 GHz and a quality factor of 35, the filter has 1 dB compression dynamic range of 40 dB, and draws 8.7 mA from a 2.8 V supply     

Constitutive Modeling of Inherently Anisotropic Sand Behavior

A plasticity constitutive framework for modeling inherently anisotropic sand behavior is presented within a modified form of critical state soil mechanics. A second-order symmetric fabric tensor, Fij, describes the material inherent anisotropy, and a scalar-valued anisotropic state variable A is properly defined in terms of a joint invariant of Fij and the stress tensor. The location of the critical state line in the plane of void ratio and effective mean normal stress is not fixed but depends on A, rendering the soil dilatancy also a function of A. In addition, the plastic modulus is made a function of A. The incorporation of these two modifications in terms of A in an existing stress-ratio bounding surface model, achieves the successful simulation of both the contractive and dilative responses of sand over a wide range of variations in stress and density as shown by experimental data. Of particular significance are the results which exhibit the drastic effect of different principal stress orientations in reference to the material axes of anisotropy.     

Access to specific declarative knowledge by expert systems: The impact of logic programming

As part of the operation of an Expert System, a deductive component accesses a database of facts to help simulate the behavior of a human expert in a particular problem domain. The nature of this access is examined, and four access strategies are identified. Features of each of these strategies are addressed within the framework of a logic-based deductive component and the relational model of data.     

Instantaneous frequency based spectral analysis of nuclear magnetic resonance spectroscopy data

Nuclear magnetic resonance spectroscopy signals are modelled as a sum of decaying complex exponentials in noise. The spectral analysis of these signals allowing for their decomposition and the estimation of the parameters of the components is crucial to the study of biochemical samples. This paper presents a novel Gabor filterbank/notch filtering instantaneous frequency (IF) estimator, that enables the extraction of weaker and shorter lived exponentials. This new approach is an iterative procedure where a Gabor filterbank is first employed to obtain a reliable estimate of the IF of the strongest component present. The estimated strongest component is then notch filtered, which un-masks weaker components, and the procedure repeated. The performance of this method was evaluated using an artificial signal and compared to the short time Fourier transform, reassigned STFT, and the original Gabor filterbank approach. The results clearly demonstrate its superiority in uncovering weaker signals and resolving components that are very close to one another in frequency. Furthermore, the new method is shown to be more robust than the ITCMP technique at low signal to noise ratios.