Occlusion Culling Algorithms: A Comprehensive Survey

In this paper, occlusion culling techniques that appeared in the last decade are reviewed. Occlusion culling techniques are responsible for reducing the polygons rendered by the graphics hardware with the target of achieving real-time rendering. The various techniques are discussed in detail and a synopsis table with their main characteristics is given.     

An algorithmic method for the selection of multivariable process control structures

In process systems, the selection of suitable sets of manipulated and controlled variables and the design of their interconnection, known as the control structure selection problem, is an important structural optimisation problem. The operating performance of a plant depends on the control structure selected as well as the characteristics of the disturbances acting on the plant. The economic penalty associated with the variability of main process variables close to active constraints is used in this work in order to develop a quantitative measure for the ranking of alternative control structures. Based on this measure, a general methodology is presented for the generation of promising control structures where general centralised, linear time invariant, output feedback controllers are used to form the closed loop system. The special case of optimal static output feedback controllers is further investigated in this paper. Furthermore, the problem of selecting proper weights in forming quadratic integral performance indices in designing optimal multivariable controllers is addressed. The validity and usefulness of the method is demonstrated through a number of case studies.     

Relaxation of extrinsic and intrinsic stresses in germanium substrates with silicon films

Si films were deposited on Ge substrates at 400°C by two different Physical Vapor Deposition techniques: (A) ion beam sputtering and (B) magnetron sputtering. The intrinsic stresses in the as-deposited films were measured to be compressive and much greater in samples (A), about −1500 to −2000 MPa than in samples (B), about −300 to −500 MPa. The substrates were subsequently exposed to thermal treatments for varying times at 800°C. In the lower stressed (B) samples, the films had relaxed and reduced the overall curvature of the structure whereas in the high stresses (A) samples, an irreversible large increase in the substrate curvature was found to occur. This indicated that plastic deformation in the Ge substrates itself had occurred.     

Gas/particle partitioning of seven volatile polycyclic aromatic hydrocarbons in a heavy traffic urban area

Air samples (vapor- and particle-phase) were taken for 19 sampling events during the period from December 1997 to July 1998 in an urban site in the center of Athens. The urban site is densely populated and characterized by heavy traffic circulation and elevated concentrations of VOCs, NO(x), CO and smoke. Seven volatile polycyclic aromatic hydrocarbons (PAHs) were determined in samples. The temperature dependence of gas-phase atmospheric concentration of PAHs, C(g), was investigated using diagrams of natural logarithm of partial pressures (lnP) vs. reciprocal mid-point temperatures. For the six of seven volatile PAHs, the temperature dependence of lnP was statistically significant (at least at the 90% confidence level) and the temperature accounted for 21-67% of the variability in gas-phase concentrations. The gas-phase concentration C(g) of the very volatile PAHs was affected more significantly by changes in temperature, but the variation of the less-volatile PAHs fluoranthene and pyrene C(g), was better explained by changes in temperature. The temperature dependence of gas/particle partitioning constant K(P) was also examined. Regressions of log(K(P))(-1) vs. T(-1) for fluorene, fluoranthene and pyrene were classified into two different temperature ranges. The gas/particle partitioning of PAHs was studied by correlating the partition constant to the sub-cooled liquid saturation vapor pressure (P(L)(o)). The Junge adsorption model underestimated the particle fraction of volatile PAHs probably due to the presence of non-exchangeable fraction. Slopes (m(r)) of the regressions logK(P) vs. logP(L)(o) were different from the value -1 as Pankow's theory predicts. The short distance between the sampling point and the emission sources is also estimated to be a factor that causes deviations from the theoretical value. Evidence that atmospheric conditions favorable for secondary aerosol formation coincide with higher value of m(r), was provided by limited sampling events. An interrelation was found to exist between the m(r) values, allowing the prediction of the gas/particle partitioning of a series of seven PAHs by the measurement of a single PAH partitioning.     

Transmission and radiation in a slab waveguide coupled to a whispering-gallery resonator: volume-integral-equation analysis

The excitation of a whispering gallery resonator by a surface wave guided in a dielectric slab is analyzed with a rigorous volume-integral-equation approach. The analysis is based on the Green's function concept and the application of the entire-domain Galerkin technique through expansion of the electric field in the resonator in terms of cylindrical wave functions. The algorithm developed yields highly accurate results for the transmission and reflection coefficients in the waveguide. The radiated far field is computed, and the effect of the excitation of a whispering gallery mode on the radiation pattern is studied.     

Effect of vitamin E supplementation on neutrophil function, milk composition and plasmin activity in dairy cows in a commercial herd

Fifty-six Holstein dairy cows from a commercial dairy herd in the Northern part of Greece were used to determine the effect of vitamin E supplementation on immune parameters, milk composition and milk quality. Cows were assigned to one of two experimental groups: control (no vitamin E supplementation) and vitamin E supplementation. Supplementation of vitamin E started 4 weeks prior to and continued up to 12 weeks after parturition. Supplementation included daily oral administration of vitamin E at 3000 i.u./cow prepartum and was reduced to 1000 i.u./cow post partum. Blood samples were collected weekly for 8 weeks starting 4 weeks before parturition, neutrophils were isolated and the following parameters were determined in neutrophils activated by phorbol myristate acetate: total cell-associated and membrane-bound urokinase plasminogen activator (u-PA) activity and superoxide production. Milk samples were collected weekly and fat, protein, lactose, somatic cell count (SCC), plasmin and plasminogen-derived activity were determined. Activated neutrophils isolated from cows that received supplemental vitamin E had higher (P<0.01) total and membrane-bound u-PA activities during the first 3 weeks after parturition and higher (P<0.01) superoxide production during week 1 prepartum and week 1 post partum compared with the corresponding values of activated neutrophils isolated from control cows. Vitamin E supplementation had no effect (P=0.28) on plasminogen-derived activity in milk. Milk obtained from cows that received supplemental vitamin E had SCC lower by 25% (P<0.05) and plasmin lower by 30% (P<0.01) than corresponding values in milk obtained from control cows. The reduction in plasmin as a result of vitamin E supplementation is very beneficial to the dairy industry because plasmin reduces the cheese-yielding capacity of milk, affects the coagulating properties of milk and its overall ability to withstand processing during cheesemaking. In conclusion, vitamin E supplementation had positive effects on the function of bovine neutrophils and milk quality in a commercial dairy herd.     

Design and Analysis of an Efficient Communication Strategy for Hierarchical and Highly Changing Ad-hoc Mobile Networks

In this work we introduce two practical and interesting models of ad-hoc mobile networks: (a) hierarchical ad-hoc networks, comprised of dense subnetworks of mobile users interconnected by a very fast yet limited backbone infrastructure, (b) highly changing ad-hoc networks, where the deployment area changes in a highly dynamic way and is unknown to the protocol. In such networks, we study the problem of basic communication, i.e., sending messages from a sender node to a receiver node. For highly changing networks, we investigate an efficient communication protocol exploiting the coordinated motion of a small part of an ad-hoc mobile network (the runners support) to achieve fast communication. This protocol instead of using a fixed sized support for the whole duration of the protocol, employs a support of some initial (small) size which adapts (given some time which can be made fast enough) to the actual levels of traffic and the (unknown and possibly rapidly changing) network area, by changing its size in order to converge to an optimal size, thus satisfying certain Quality of Service criteria. Using random walks theory, we show that such an adaptive approach is, for this class of ad-hoc mobile networks, significantly more efficient than a simple non-adaptive implementation of the basic runners support idea, introduced in [9,10]. For hierarchical ad-hoc networks, we establish communication by using a runners support in each lower level of the hierarchy (i.e., in each dense subnetwork), while the fast backbone provides interconnections at the upper level (i.e., between the various subnetworks). We analyze the time efficiency of this hierarchical approach. This analysis indicates that the hierarchical implementation of the support approach significantly outperforms a simple implementation of it in hierarchical ad-hoc networks. Finally, we discuss a possible combination of the two approaches above (the hierarchical and the adaptive ones) that can be useful in ad-hoc networks that are both hierarchical and highly changing. Indeed, in such cases the hierarchical nature of these networks further supports the possibility of adaptation.     

On the improvement of anthropometry and pose estimation from a single uncalibrated image

Recently, we developed a technique that allows semi-automatic estimation of anthropometry and pose from a single image. However, estimation was limited to a class of images for which an adequate number of human body segments were almost parallel to the image plane. In this paper, we present a generalization of that estimation algorithm that exploits pairwise geometric relationships of body segments to allow estimation from a broader class of images. In addition, we refine our search space by constructing a fully populated discrete hyper-ellipsoid of stick human body models in order to capture the variance of the statistical anthropometric information. As a result, a better initial estimate can be computed by our algorithm and thus the number of iterations needed during minimization are reduced tenfold. We present our results over a variety of images to demonstrate the broad coverage of our algorithm.Published online: 1 September 2003     

Sub-glassy relaxation modes in PMMA and PMMA + SiO<Subscript>2</Subscript> hosts of non-polar perylene derivatives

The dielectric response of poly(methyl methacrylate) (PMMA) in solid solutions of perylene derivative laser dyes in PMMA and PMMA + SiO₂ has been studied by means of the thermally stimulated depolarization currents (TSDC) technique, with the aim to isolate molecular and phase interactions in the dye blends. The changes in characteristics of the β-relaxation mode of PMMA are interpreted with respect to the dissimilar local environments of the polar carboxy-methyl pendant groups of PMMA. An important "chemical" effect on the β relaxation mechanism recorded in the organic-inorganic composites, is the formation of hydrogen bonds between the acidic pore surfaces of SiO₂ and the acetate side-groups. Several "physical" effects produced by the chromophores and the geometrical confinement, like the modification of the monomer-to-polymer conversion rates, the polymer's free volume and the extent of the PMMA-SiO₂ interaction, are discussed.     

Incrementally updating a hybrid rule base based on empirical data

Abstract: Neurules are a kind of hybrid rules that combine a symbolic (production rules) and a connectionist (adaline unit) representation. One way that the neurules can be produced is from training examples/patterns, extracted from empirical data. However, in certain application fields not all of the training examples are available a priori. A number of them become available over time. In those cases, updating the neurule base is necessary. In this paper, methods for updating a hybrid rule base, consisting of neurules, to reflect the availability of new training examples are presented. They can be considered as a type of incremental learning method that retains the entire induced hypothesis and all past training examples. The methods are efficient, since they require the least possible retraining effort and the number of neurules produced is kept as small as possible. Experimental results that prove the above argument are presented.