Mechanical Engineering

A new theory of exact solutions is presented for the problem of the slow viscous Stokes flow of a plane, doubly connected annular viscous blob driven by surface tension. The formulation reveals the existence of an infinite number of conserved quantities associated with the flow for a certain general class of initial conditions. These conserved quantities are associated with a class of exact solutions. This work is believed to provide the first exact solutions for the evolution of a doubly connected fluid region evolving under Stokes flow with surface tension.

Motivated by the viscous sintering of amorphous materials in the presence of a distribution of rigid platelet inclusions added to increase the strength of the final sintered medium, a simple model for the shrinkage of compressible pores close to a wall in Stokes flow is proposed. The model assumes that the pore remains elliptical/ellipsoidal in shape at all times. The model is expected to be valid provided the pore is not too far from spherical and not too close to the wall. It relies on a separation of the flow into 'inner' and 'outer' problems. The inner problem is to assume that the ellipsoid evolves in a linear ambient flow given by the first two terms in a local expansion of an outer flow produced by the image singularity distribution of a point-sink near a planar no-slip boundary. The focus of the present paper is to test the viability of the model in the planar case. Using a spectral method based on analytic functions and conformal mappings, the results of a full numerical simulation are compared with the predictions of the planar model. The effects of the proximity of the pore to the wall, the anisotropy in the pore shape and its relative orientation to the wall are all examined. It is observed that, as they shrink, pores drift towards the wall becoming elongated in the direction perpendicular to the wall.

This paper presents a combined numerical and analytical investigation into various problems involving two symmetric interacting constant-pressure bubbles evolving in two-dimensional Stokes flow. The bubbles have constant surface tension on their boundaries and are taken to be in an ambient straining flow. First, a novel numerical method based on conformal mappings is presented to compute the free-surface evolution. Then, a special class of time-evolving exact solutions to the problem is derived and used to check the numerical code. These solutions reveal that, for bubbles with shrinking area, a competition between the imposed strain and surface tension can lead to either a slit or a point as the limiting shape. Numerical solutions of fixed-area bubbles are then computed and reveal that when they are forced together by a straining flow, a thin lubrication layer forms. In the absence of surface tension, large-curvature regions develop at the bubble edges and these are smoothed out by capillary effects. Further, motivated by the viscous sintering application, a study of interaction effects on the pure surface-tension-driven shrinkage of circular bubbles is investigated and compared, in an appropriate limit, to a recently derived 'ellipticalpore model'.

New analytical techniques for studying the motion of a point vortex in fluid domains bounded by straight walls having an arbitrary number of gaps are presented. By exploiting explicit formulae for the Kirchhoff-Routh path function in multiply connected circular domains, combined with a novel construction of conformal mappings from such circular domains to multiply connected slit domains, the governing Hamiltonians for the motion of a point vortex in a number of physically interesting fluid regions involving walls with gaps are derived. The vortex trajectories in several illustrative cases are computed. These examples include finding the vortex paths around a chain of islands sitting off an infinite coastline, around islands in an unbounded ocean and around a sequence of islands situated between two headlands.

The classic exact solution due to Lagally Die reibungslose strömung im aussengebiet zweier kreise. Z. Angew. Math. Mech. 9, 299-305.) for streaming flow past two cylindrical aerofoils (or obstacles) is generalized to the case of an arbitrary finite number of cylindrical aerofoils. Given the geometry of the aerofoils, the speed and direction of the oncoming uniform flow and the individual round-aerofoil circulations, the complex potential associated with the flow is found in analytical form in a parametric pre-image region that can be conformally mapped to the fluid region. A complete determination of the flow then follows from knowledge of the conformal mapping between the two regions. In the special case where the aerofoils are all circular, the conformal mapping from the parametric pre-image region to the fluid domain is a Möbius mapping. The solution for the complex potential in such a case can then be used, in combination with the Blasius theorem, to compute the distribution of hydrodynamic forces on the multi-aerofoil configuration.

A numerical algorithm is presented for the computation of the Schottky-Klein prime function on the Schottky double of multiply connected circular domains in the plane. While there exist classical formulae for the Schottky-Klein prime function in the form of infinite products over a Schottky group, such products are not convergent for all choices of multiply connected circular domains. The prime function itself, however, is a well-defined function for any multiply connected circular domain. The present algorithm facilitates the evaluation of this prime function when the planar domains are such that the classical infinite product representation is either not convergent or so slowly convergent as to be impracticable.

The use of visual displays is seen as a supportive tool for solving design problems.Throughout the design process, and particularly in the early stages of the process, designers are exposed to vast collections of visual displays. These are external representations, i.e., pictures, diagrams, or sketches, which provide designers with helpful explicit and non explicit references. Despite the importance of this pictorial
material, only a small number of researches have dealt with the spontaneous use of visual displays as an aid in design problem solving when no instruction to use analogy is given. Furthermore, no studies have been conducted to examine whether visual displays play a more significant role in solving ill-defined or well-defined design problems. The main goal of this work is to empirically research the use of visual displays in these two problem contexts, by studying the design process of groups of designers with different levels of expertise. Findings showed that both experts and
novices profited from the use of visual displays in ill-defined design problem solving, resulting in a significant enhacement of the quality of design solutions. Additional results showed that visual displays did aid experts, but not novices, to improve their performance in solving well-defined design problems. These findings may have Design Aided By Visual Displays: A Cognitive Approach consequences for design education. It is suggested that practicing with a large number
of within-domain visual displays (which belong to the same or very close realm of the problem) and a large collection of between-domain visual sources (which belong to a different or remote realm of the problem) can help designers in general, and novices in particular, to spontaneously retrieve meaningful information, and to enhance their design abilities.

In the symmetric rendezvous search game played on K n (the completely connected graph on n vertices) two players are initially placed at two distinct vertices (called locations). The game is played in discrete steps and at each step each player can either stay where he is or move to a different location. The players share no common labelling of the locations. They wish to minimize the expected number of steps until they first meet. Rendezvous search games of this type were first proposed by Steve Alpern in 1976. They are simple to describe, and have received considerable attention in the popular press as they model problems that are familiar in real life. They are notoriously difficult to analyse. Our solution of the symmetric rendezvous game on K 3 makes this the first interesting game of its type to be solved, and establishes the long-standing conjecture that the Anderson-Weber strategy is optimal.

This paper presents a self-improving reactive control system for autonomous robotic navigation. The navigation module uses a schemabased reactive control system to perform the navigation task. The learning module combines case-based reasoning and reinforcement learning to continuously tune the navigation system through experience. The case-based reasoning component perceives and characterizes the system's environment, retrieves an appropriate case, and uses the recommendations of the case to tune the parameters of the reactive control system. The reinforcement learning component refines the content of the cases based on the current experience. Together, the learning components perform on-line adaptation, resulting in improved performance as the reactive control system tunes itself to the environment, as well as on-line learning, resulting in an improved library of cases that capture environmental regularities necessary to perform on-line adaptation. The system is extensively evaluated through simulation studies using several performance metrics and system configurations.

Case-based reasoning systems have traditionallybeen used to perform high-level reasoning in problem domains that can be adequately described using discrete, symbolic representations. However, many realworld problem domains, such as autonomous robotic navigation, are better characterized using continuous representations. Such problem domains also require continuous performance, such as continuous sensorimotor interaction with the environment, and continuous adaptation and learning during the performance task. We introduce a new method for continuous casebased reasoning, and discuss how it can be applied to the dynamic selection, modification, and acquisition of robot behaviors in autonomous navigation systems. We conclude with a general discussion of case-based reasoning issues addressed by this work.

In a recent paper, Dritschel and McCullough established the existence of completely positive maps of operator algebras that have a unique extension property. In this expository note we give a more explicit rendering of that result geared to operator systems, and discuss consequences.

The project integrates work in natural language processing, machine learning, and the semantic web, bringing together these diverse disciplines in a novel way to address a real problem. The objective is to extract and categorize machine components and subsystems and their associated failures using a novel approach that combines text analysis, unsupervised text clustering, and domain models. Through industrial partnerships, this project will demonstrate effectiveness of the proposed approach with actual industry data.

We establish the existence and uniqueness of finite free resolutions -and their attendant Betti numbers -for graded commuting d-tuples of Hilbert space operators. Our approach is based on the notion of free cover of a (perhaps noncommutative) row contraction. Free covers provide a flexible replacement for minimal dilations that is better suited for higher-dimensional operator theory.

The eigenvalues of a self-adjoint n × n matrix A can be put into a decreasing sequence λ = (λ1, . . . , λn), with repetitions according to multiplicity, and the diagonal of A is a point of R n that bears some relation to λ. The Schur-Horn theorem characterizes that relation in terms of a system of linear inequalities.

Product systems are the classifying structures for semigroups of endomorphisms of B(H), in that two E0-semigroups are cocycle conjugate iff their product systems are isomorphic. Thus it is important to know that every abstract product system is associated with an E0-semigrouop. This was first proved more than fifteen years ago by rather indirect methods. Recently, Skeide has given a more direct proof. In this note we give yet another proof by a very simple construction.

Let X = {λ1, . . . , λN } be a finite set of complex numbers and let A be a normal operator with spectrum X that acts on a separable Hilbert space H. Relative to a fixed orthonormal basis e1, e2, . . . for H, A gives rise to a matrix whose diagonal is a sequence d = (d1, d2, . . . ) with the property that each of its terms dn belongs to the convex hull of X. Not all sequences with that property can arise as the diagonal of a normal operator with spectrum X.

A challenge of design education is the question of how to help designers develop skills in design problem-solving. How can designers be taught to use relevant prior knowledge to solve new design problems? To answer this question we must know more about differences between experts and novices regarding the use of prior knowledge to solve ill defined problems. In design, visual analogy is used as a powerful problem-solving strategy; the evidence, however, is hitherto mostly anecdotal. In this study our objective is to determine empirically whether, and how, the use of visual analogy can improve design problem-solving by both novice and expert designers. Our results indicate that the use of visual analogy improves the quality of design across the board, but is particularly significant in the case of novice designers. These findings lead to conclusions regarding design training and education.

The behavior of steel-concrete composite beams is strongly influenced by the type of shear connection between the steel beam and the concrete slab. For accurate analytical predictions, the structural model must account for the interlayer slip between these two components. In numerous engineering applications ͑e.g., in the fields of structural optimization, structural reliability analysis, and finite element model updating͒, accurate response sensitivity calculations are needed as much as the corresponding response simulation results. This paper focuses on a procedure for response sensitivity analysis of steel-concrete composite structures using displacement-based locking-free frame elements including deformable shear connection with fiber discretization of the cross section. Realistic cyclic uniaxial constitutive laws are adopted for the steel and concrete materials as well as for the shear connection. The finite element response sensitivity analysis is performed according to the direct differentiation method. The concrete and shear connection material models as well as the static condensation procedure at the element level are extended for response sensitivity computations. Two steel-concrete composite structures for which experimental test results are available in the literature are used as realistic testbeds for response and response sensitivity analysis. These benchmark structures consist of a nonsymmetric, two-span continuous beam subjected to monotonic loading and a frame subassemblage under cyclic loading. The new analytical derivations for response sensitivity calculations and their computer implementation are validated through forward finite difference analysis based on the two benchmark examples considered. Selected sensitivity analysis results are shown for validation purposes and for quantifying the effect and relative importance of the various material parameters in regards to the nonlinear monotonic and cyclic response of the testbed structures.

This study examined state and trait anxiety in competitive lifesavers and swimmers. The participants completed the SAS and the CSAI-2d before a training session and the CSAI-2d again before a competition. The competitive lifesavers were found to have lower levels of cognitive and somatic anxiety than competitive swimmers. Both groups were found to have lower levels of self-confidence but higher levels of somatic anxiety before a competition than before regular training sessions. Lifesavers found their levels of somatic anxiety to be more facilitative than the swimmers did. Both groups perceived that higher levels of self-confidence were more facilitative before competition than before training. Differences in the relationship between state and trait anxiety for swimmers and lifesavers were observed. The generally lower levels of cognitive and somatic state anxiety in lifesavers and their interpretation of somatic anxiety during competition would benefit their performance and decision making.

Live bacterial vaccines have great promise both as vaccines against enteric pathogens and as heterologous antigen vectors against diverse diseases. Ideally, room temperature stable dry formulations of live bacterial vaccines will allow oral vaccination without cold-chain storage or injections. Attenuated Salmonella can cross the intestinal wall and deliver replicating antigen plus innate immune activation signals directly to the intestinal immune tissues; however, the ingested bacteria must survive firstly gastric acid and secondly the antimicrobial defences of the small intestine. We found that the way in which cells are grown prior to formulation markedly affects sensitivity to acid and bile. Using a previously published stable storage formulation that maintained over 10% viability after 56 days storage at room temperature, we found dried samples of an attenuated Salmonella serovar Typhimurium vaccine lost acid and bile resistance compared to the same bacteria taken from fresh culture. The stable formulation utilised osmotic pre-conditioning in defined medium plus elevated salt concentration to induce intracellular trehalose accumulation before drying. Dried bacteria grown in rich media without osmotic pre-conditioning showed more resistance to bile, but less stability during storage, suggesting a trade-off between bile resistance and stability. Further optimisation is needed to produce the ultimate room temperature stable oral live bacterial vaccine formulation.

The home advantage is a widely acknowledged sporting phenomenon, especially in association football. Here, we examine the second leg home advantage, an effect that is discussed in the public domain but which has received very little scientific attention. The second leg home advantage effect occurs when on average teams are more likely to win a two-stage knock-out competition when they play at home in the second leg. That is, both teams have a home advantage but this advantage is significantly greater for the team that plays at home second. Examining data from three different European Cup football competitions spanning 51 years, we show that the second leg home advantage is a real phenomenon. The second leg home team has more than a 50% probability to qualify for the next round in the competition even after controlling for extra time
and team ability as possible alternative explanations. The second leg home advantage appears, however, to have decreased significantly over the past decade. Possible reasons for its existence and subsequent decline are presented.

Some probabilistic aspects of the number variance statistic are investigated. Infinite systems of independent Brownian motions and symmetric α-stable processes are used to construct new examples of processes which exhibit both divergent and saturating number variance behaviour. We derive a general expression for the number variance for the spatial particle configurations arising from these systems and this enables us to deduce various limiting distribution results for the fluctuations of the associated counting functions. In particular, knowledge of the number variance allows us to introduce and characterize a novel family of centered, long memory Gaussian processes. We obtain fractional Brownian motion as a weak limit of these constructed processes.

We consider a sequence of random graphs constructed by a hierarchical procedure. The construction replaces existing edges by pairs of edges in series or parallel with probability p and 1−p respectively. We investigate the effective resistance across the graphs, first-passage percolation on the graphs and the Cheeger constants of the graphs as the number of edges tends to infinity. In each case we find a phase transition at p = 1 2 .

A WKB method was recently used to extend rapid distortion theory (RDT) to initially inhomogeneous turbulence strained by irrotational mean flows [S.V. Nazarenko, N. Kevlahan, B. Dubrulle, J. Fluid Mech. 390 (1999) 325]. This theory takes into account the feedback of turbulence on the mean flow, and it was used by Nazarenko et al. to explain the effect of strain reduction caused by turbulence observed by Andreotti et al. In this paper, we develop a similar WKB RDT approach for shear flows. We restrict ourselves to problems where the turbulence is small-scale with respect to the mean flow length-scale and turbulence vorticity is weak compared to the mean shear. We show that the celebrated log-law of the wall exists as an exact analytical solution in our model if the initial turbulence vorticity (debris of the near-wall vortices penetrating into the outer regions) is statistically homogeneous in space and shortly correlated in time. We demonstrate that the main contribution to the shear stress comes from very small turbulent scales which are close to the viscous cut-off and which are elongated in the stream-wise direction (streaks). We also find that anisotropy of the initial turbulent vorticity changes the scaling of the shear stress, but leaves the log-law essentially unchanged.

A 2D numerical investigation is presented of shock wave propagation into a gas whose density is modulated in the transverse direction across the width of a shock tube. These density modulations represent temperature distributions in which low density corresponds to high temperature gas and high density corresponds to low temperature gas. This work is motivated by recent shock-plasma experiments, and mechanisms to explain the experimentally observed shock "splitting" signatures are investigated. It is found that the shock splitting signatures are more pronounced when the shock wave is more strongly curved or bowed. This occurs as the depth of the initial density profile is increased. The gross features of the shock splitting signatures are relatively insensitive to variations in the shape of the initial density profile (into which the shock propagates). Several interesting features of vorticity production and evolution are also indicated.

The orientational order and dynamics in suspensions of self-locomoting slender rods are investigated numerically. In agreement with previous theoretical predictions, nematic suspensions of swimming particles are found to be unstable at long wavelengths as a result of hydrodynamic fluctuations. Nevertheless, a local nematic ordering is shown to persist over short length scales and to have a significant impact on the mean swimming speed. The consequences of the large-scale orientational disorder for particle dispersion are also discussed.

Numerical simulations reveal the formation of singular structures in the polymer stress field of a viscoelastic fluid modeled by the Oldroyd-B equations driven by a simple body force. These singularities emerge exponentially in time at hyperbolic stagnation points in the flow and their algebraic structure depends critically on the Weissenberg number. Beyond a first critical Weissenberg number the stress field approaches a cusp singularity, and beyond a second critical Weissenberg number the stress becomes unbounded exponentially in time. A local approximation to the solution at the hyperbolic point is derived from a simple ansatz, and there is excellent agreement between the local solution and the simulations. Although the stress field becomes unbounded for a sufficiently large Weissenberg number, the resultant forces of stress grow subexponentially. Enforcing finite polymer chain lengths via a FENE-P penalization appears to keep the stress bounded, but a cusp singularity is still approached exponentially in time.

We study the behavior of an elastic loop embedded in a flowing soap film. This deformable loop is wetted into the film and is held fixed at a single point against the oncoming flow. We interpret this system as a two-dimensional flexible body interacting in a two-dimensional flow. This coupled fluid-structure system shows bistability, with both stationary and oscillatory states. In its stationary state, the loop remains essentially motionless and its wake is a von Kármán vortex street. In its oscillatory state, the loop sheds two vortex dipoles, or more complicated vortical structures, within each oscillation period. We find that the oscillation frequency of the loop is linearly proportional to the flow velocity, and that the measured Strouhal numbers can be separated based on wake structure.

The dynamics of slender filaments or fibers suspended in Stokesian fluids are fundamental to understanding many flows arising in physics, biology and engineering. Such filaments can have aspect ratios of length to radius ranging from a few tens to several thousands. Full discretizations of such 3D flows are very costly. Instead, we employ a non-local slender body theory that yields an integral equation, along the filament centerline, relating the force exerted on the body to the filament velocity. This hydrodynamical description takes into account the effect of the filament on the fluid, and is extended to capture the interaction of multiple filaments as mediated by the intervening fluid. We consider filaments that are inextensible and elastic. Replacing the force in the slender body integral equation by an explicit expression that uses Euler-Bernoulli theory to model bending and tensile forces yields an integral expression for the velocity of the filament centerlines, coupled to auxiliary integro-differential equations for the filament tensions. Based on a regularized version of these slender body equations that is asymptotically equivalent to the original formulation, we construct a numerical method which uses a combination of finite differences, implicit time-stepping to avoid severe stability constraints, and special quadrature methods for nearly singular integrals. We present simulations of single flexible filaments, as well as multiple interacting filaments, evolving in a background shear flow. These simulations show shear induced buckling and relaxation of the filaments, leading to the storage and release of elastic energy. These dynamics are responsible for the development of positive first normal stress differences, commonly associated with visco-elastic fluids that are suspensions of microscopic elastic fibers.

Using slender-body hydrodynamics, we study the flow-induced deformation of a high-aspect-ratio elastic filament. For a filament of zero rest curvature rotating in a viscous linear shear flow, our model predicts a bifurcation to shape instabilities due to compression by the flow, in agreement with experimental observations. Further, nonlinear simulations of this shape instability show that in dilute solutions, flexibility of the fibers causes both increased shear thinning as well as significant nonzero first-normalstress differences. These stress differences are positive for small-to-moderate deformations, but negative for large-amplitude flexing of the fibers.

square vessel would also generate antivortices in order to comply with the imposed symmetry. By proper arrangement of the laser ®elds, the vortex patterns in Bose±Einstein condensates con®ned by triangular or square traps could also reveal symmetry-induced antivortices.

A mechanism by which smooth initial conditions evolve towards a topological reconfiguration of fluid interfaces is studied in the context of Darcy's law. In the case of thin fluid layers, nonlinear PDEs for the local thickness are derived from an asymptotic limit of the vortex sheet representation. A particular example considered is the Rayleigh-Taylor instability of stratified fluid layers, where the instability of the system is controlled by a Bond number B. It is proved that, for a range of B and initial data ''subharmonic'' to it, interface pinching must occur in at least infinite time. Numerical simulations suggest that ''pinching'' singularities occur generically when the system is unstable, and in particular immediately above a bifurcation point to instability. Near this bifurcation point an approximate analytical method describing the approach to a finite-time singularity is developed. The method exploits the separation of time scales that exists close to the first instability in a system of finite extent, with a discrete spectrum of modes. In this limit, slowly growing long-wavelength modes entrain faster short-wavelength modes, and thereby, allow the derivation of a nonlinear evolution equation for the amplitudes of the slow modes. The initial-value problem is solved in this slaved dynamics, yielding the time and analytical structure of a singularity that is associated with the motion of zeros in the complex plane, suggesting a general mechanism of singularity formation in this system. The discussion emphasizes the significance of several variational principles, and comparisons are made between the numerical simulations and the approximate theory.

We present a space robotic system capable of capturing a free-flying satellite for the purposes of on-orbit satellite servicing. Currently such operations are carried out either manually or through discrete-event scripted controllers. The manual approach is costly and exposes astronauts to danger, while the scripted approach is tedious and brittle. Consequently, there is substantial interest in performing these operations autonomously, and the work presented here is a step in this direction. To our knowledge, ours is the only satellite-capturing system that relies on vision and cognition to deal with an uncooperative satellite. Our innovative system combines visual perception (object identification, recognition, and tracking) with high-level reasoning in a hybrid deliberative/reactive computational framework. The reasoning module, which encodes a model of the environment, performs deliberation to control the perception pipelineit guides the vision system, validates its performance, and suggests corrections when vision is performing poorly. Furthermore, it advises the behavioral controller to carry out its tasks. Reasoning and related elements, among them intention, context, and memory, are responsible for the robustness and reliability of the overall system. We demonstrate our prototype system controlling a robotic arm that autonomously captures a free-flying satellite in a realistic laboratory setting that faithfully mimics on-orbit conditions.

Triangular B-splines are a new tool for modeling a broad class of objects de ned over arbitrary, non-rectangular domains. They provide an elegant and uni ed representation scheme for all piecewise continuous polynomial surfaces over planar triangulations. To enhance the power of this model, we propose triangular NURBS, the rational generalization of triangular B-splines, with weights as additional degrees of freedom. Fixing the weights to unity reduces triangular NURBS to triangular B-splines. Conventional geometric design with triangular NURBS can be laborious, since the user must manually adjust the many control points and weights. To ameliorate the design process, we d e v elop a new model based on the elegant triangular NURBS geometry and principles of physical dynamics. Our model combines the geometric features of triangular NURBS with the demonstrated conveniences of interaction within a physics-based framework. The dynamic behavior of the model results from the numerical integration of di erential equations of motion that govern the temporal evolution of control points and weights in response to applied forces and constraints. This results in physically meaningful hence highly intuitive s h a p e v ariation. We apply Lagrangian mechanics to formulate the equations of motion of dynamic triangular NURBS and nite element analysis to reduce these equations to e cient n umerical algorithms. We demonstrate several applications, including direct manipulation and interactive sculpting through force-based tools, the tting of unorganized data, and solid rounding with geometric and physical constraints.

We present a learning technique that automatically synthesizes realistic locomotion for the animation of physics-based models of animals. The method is especially suitable for animals with highly flexible, many-degree-of-freedom bodies and a considerable number of internal muscle actuators, such as snakes and fish. The multilevel learning process first performs repeated locomotion trials in search of actuator control functions that produce efficient locomotion, presuming virtually nothing about the form of these functions. Applying a short-time Fourier analysis, the learning process then abstracts control functions that produce effective locomotion into a compact representation which makes explicit the natural quasi-periodicities and coordination of the muscle actions. The artificial animals can finally put into practice the compact, efficient controllers that they have learned. Their locomotion learning abilities enable them to accomplish higher-level tasks specified by the animator while guided by sensory perception of their virtual world; e.g., locomotion to a visible target. We demonstrate physics-based animation of learned locomotion in dynamic models of land snakes, fishes, and even marine mammals that have trained themselves to perform "SeaWorld" stunts.

We present a surveillance system, comprising wide field-of-view (FOV) passive cameras and pan/tilt/zoom (PTZ) active cameras, which automatically captures and labels high-resolution videos of pedestrians as they move through a designated area. A wide-FOV stationary camera can track multiple pedestrians, while any PTZ active camera can capture high-quality videos of a single pedestrian at a time. We propose a multi-camera control strategy that combines information gathered by the wide-FOV cameras with weighted round-robin scheduling to guide the available PTZ cameras, such that each pedestrian is viewed by at least one active camera during their stay in the designated area.

The goals of this paper are two-fold: (i) to present our initial efforts towards the realization of a fully autonomous sensor network of dynamic video cameras capable of providing perceptive coverage of a large public space, and (ii) to further the cause of exploiting visually and behaviorally realistic virtual environments in the development and testing of machine vision systems. In particular, our proposed sensor network employs techniques that enable a collection of active (pan-tilt-zoom) cameras to collaborate in performing various visual surveillance tasks, such as keeping one or more pedestrians within view, with minimal reliance on a human operator. The network features local and global autonomy and lacks any central controller, which entails robustness and scalability. Its functionality is the result of local decision-making capabilities at each camera node and communication between the nodes. We demonstrate our surveillance system in a virtual train station environment populated by autonomous, lifelike virtual pedestrians. Our readily reconfigurable virtual cameras generate synthetic video feeds that emulate those generated by real surveillance cameras monitoring public spaces. This type of research would be difficult in the real world given the costs of deploying and experimenting with an appropriately complex camera network in a large public space the size of a train station.

As an important feature, orientation field describes the global structure of fingerprints. It provides robust discriminatory information other than traditional widely-used minutiae points. However, there are few works explicitly incorporating this information into fingerprint matching stage, partly due to the difficulty of saving the orientation field in the feature template. In this paper, we propose a novel representation for fingerprints which includes both minutiae and model-based orientation field. Then, fingerprint matching can be done by combining the decisions of the matchers based on the global structure (orientation field) and the local cue (minutiae). We have conducted a set of experiments on large-scale databases and made thorough comparisons with the state-of-the-arts. Extensive experimental results show that combining these local and global discriminative information can largely improve the performance. The proposed system is more robust and accurate than conventional minutiae-based methods, and also better than the previous works which implicitly incorporate the orientation information. In this system, the feature template takes less than 420 bytes, and the feature extraction and matching procedures can be done in about 0.30 s. We also show that the global orientation field is beneficial to the alignment of the fingerprints which are either incomplete or poor-qualitied.

Branch prediction is the predominant approach for minimizing the pipeline breaks caused by branch instructions. Traditionally, branch prediction is accomplished in one of two ways, static prediction at compile-time via compiler analysis or dynamic prediction at run-time via special hardware structures. In this paper, we propose a novel technique that aims to combine the strengths of the two approaches -the lower cost of compile-time analysis with the effectiveness of dynamic prediction. Specifically, we propose that the compiler use profile feedback to define a prediction function for each branch and insert a few explicit instructions per branch into the compiled code to compute the prediction function. These instructions are carefully selected to predict the direction of the branch using any information available during run-time. A strength of this approach is that information beyond branch history can be used to make predictions, such as the contents of the architectural registers. To substantiate our proposal, we present an algorithm for selecting the prediction instructions, and demonstrate the performance of the approach against contemporary static and dynamic branch prediction strategies.

Pearling is an interactive technique for extracting the centerline and varying thickness of (hand-drawn) curves in images. It works in realtime, is capable of tracing complex curve networks, and supports gesture-driven interactive editing to trim or extend the selection.

This paper addresses two major challenges new product development teams face in making a product people want. The first challenge is to frame the design situation based on a real need of a customer. The second, less obvious, challenge is to get everyone on the team in agreement about what that framing is - everyone needs to be on the same page about what it is they're doing. Yet these two challenges are not independent, they are intertwined with each other, connected by the concrete research and sharing activities the teams perform. We introduce a framework to help understand the path of a design team along these two dimensions as well as illustrations of the three most common paths observed among graduate multidisciplinary new product development teams as supported by interviews and survey data. These case studies form the basis of four themes and twelve design principles to help teams navigate the new product development process.