Jian J. Zhang

Self quotient image for face recognition

The reliability of facial recognition techniques is often affected by the variation of illumination, such as shadows and illumination direction changes. In this paper, we present a novel framework, called the self-quotient image, for the elimination of the lighting effect in the image. Although this method has a similar invariant form to the quotient image by Shashua etc. (2001), it does not need the alignment and bootstrap images. Our method combines the image processing technique of edge-preserved filtering with the Retinex applications of by Jobson, et al., (1997) and Gross and Brajovie (2003). We have analyzed this algorithm with a 3D imaging model and formulated the conditions where illumination-invariant and -variant properties can be realized, respectively. A fast anisotropic filter is also presented. The experiment results show that our method is effective in removing the effect of illumination for robust face recognition.

Numerical analysis of elastic-plastic rotating disks with arbitrary variable thickness and density

Abstract A unified numerical method is developed in this article for the analysis of deformations and stresses in elastic–plastic rotating disks with arbitrary cross-sections of continuously variable thickness and arbitrarily variable density made of nonlinear strain-hardening materials. The method is based on a polynomial stress–plastic strain relation, deformation theory in plasticity and Von Mises’ yield condition. The governing equation is derived from the basic equations of the rotating disks and solved using the Runge–Kutta algorithm. The proposed method is applied to calculate the deformations and stresses in various rotating disks. These disks include solid disks with constant thickness and constant density, annular disks with constant thickness and constant density, nonlinearly variable thickness and nonlinearly variable density, linearly tapered thickness and linearly variable density, and a combined section of continuously variable thickness and constant density. The computed results are compared to those obtained from the finite element method and the existing approaches. A very good agreement is found between this research and the finite element analysis. Due to the simplicity, effectiveness and efficiency of the proposed method, it is especially suitable for the analysis of various rotating disks.

On the friction and wear behaviour of human tooth enamel and dentin

The differences in the friction and wear behaviour of different human tooth structures against titanium have been investigated using a reciprocating apparatus containing an artificial saliva solution. The effects of enamel, enamel rod orientation, and dentin were of particular interest. A normal load of 20 N, reciprocating amplitude of 500 μm, and frequency of 2 Hz were used. Tests lasting up to 5000 cycles were conducted. The micro-indentation hardness of worn teeth specimens was measured. The enamel layer exhibits relatively low friction and good wear resistance. The number of cycles of low friction coefficient, prior to transition to a higher value, depends on enamel thickness and enamel rod orientation. Wear mechanisms differ between layers in the tooth structure.

Elastic-plastic stresses in a rotating solid disk

Abstract A polynomial stress-strain relation is proposed for rotating disks with non-linear strain hardening materials. The basic equation of the disks with constant thickness and constant density under plane stress is derived from the deformation theory of plasticity, Von Mises’ yield criterion and the proposed stress-strain relation. A computing method for such rotating solid disks is developed and the approximate analytical solution is obtained. The validity of the solution is demonstrated by comparing the analytical calculation results with the finite element ones and very good agreement is found. The proposed solution is much more efficient and eassier to use than the FE approach

Bystander Responses to a Violent Incident in an Immersive Virtual Environment

Under what conditions will a bystander intervene to try to stop a violent attack by one person on another? It is generally believed that the greater the size of the crowd of bystanders, the less the chance that any of them will intervene. A complementary model is that social identity is critical as an explanatory variable. For example, when the bystander shares common social identity with the victim the probability of intervention is enhanced, other things being equal. However, it is generally not possible to study such hypotheses experimentally for practical and ethical reasons. Here we show that an experiment that depicts a violent incident at life-size in immersive virtual reality lends support to the social identity explanation. 40 male supporters of Arsenal Football Club in England were recruited for a two-factor between-groups experiment: the victim was either an Arsenal supporter or not (in-group/out-group), and looked towards the participant for help or not during the confrontation. The response variables were the numbers of verbal and physical interventions by the participant during the violent argument. The number of physical interventions had a significantly greater mean in the in-group condition compared to the out-group. The more that participants perceived that the Victim was looking to them for help the greater the number of interventions in the in-group but not in the out-group. These results are supported by standard statistical analysis of variance, with more detailed findings obtained by a symbolic regression procedure based on genetic programming. Verbal interventions made during their experience, and analysis of post-experiment interview data suggest that in-group members were more prone to confrontational intervention compared to the out-group who were more prone to make statements to try to diffuse the situation.

Fast Surface Modelling Using a 6th Order PDE

Although the control‐point based parametric approach is used most widely in free‐form surface modelling, complementary techniques co‐exist to meet various specialised requirements. The partial differential equation (PDE) based modelling approach is especially suitable for satisfying surface boundary constraints. They are also effective for the generation of families of free‐form surfaces, which share a common base and differ in their secondary features. In this paper, we present a fast surface modelling method using a sixth order PDE. This PDE provides enough degrees of freedom not only to accommodate tangent, but also curvature boundary conditions and offers more shape control parameters to serve as user controls for the manipulation of surface shapes. In order to achieve real‐time performance, we have constructed a surface function and developed a high‐precision approximate solution to the 6th order PDE. Unlike some existing PDE‐based techniques, this resolution method can satisfy the boundary conditions exactly, and is able to create free‐form surfaces as fast and almost as accurately as the closed‐form (analytical) solutions. Due to the fact that it has sufficient degrees of freedom to accommodate the continuity of 3‐sided and 4‐sided surface patches at their boundaries, this method is able to model complex surfaces consisting of multiple patches. Compared with existing PDE‐based modelling methods, this method is both fast and can solve a larger class of surface modelling problems.

Technical Section: PDE blending surfaces with C2 continuity

In this paper, we propose to use a general sixth-order partial differential equation (PDE) to solve the problem of C^2 continuous surface blending. Good accuracy and high efficiency are obtained by constructing a compound solution function, which is able to both satisfy the boundary conditions exactly and minimise the error of the PDE. This method can cope with much more complex surface-blending problems than other published analytical PDE methods. Comparison with the existing methods indicates that our method is capable of generating blending surfaces almost as fast and accurately as the closed-form method and it is more efficient and accurate than other extant PDE-based methods.

Curve skeleton skinning for human and creature characters

The skeleton driven skinning technique is still the most popular method for animating deformable human and creature characters. Albeit an industry de facto due to its computational performance and intuitiveness, it suffers from problems like collapsing elbow and candy wrapper joint. To remedy these problems, one needs to formulate the non‐linear relationship between the skeleton and the skin shape of a character properly, which however proves mathematically very challenging. Placing additional joints where the skin bends increases the sampling rate and is an ad hoc way of approximating this non‐linear relationship. In this paper, we propose a method that is able to accommodate the inherent non‐linear relationships between the movement of the skeleton and the skin shape. We use the so‐called curve skeletons along with the joint‐based skeletons to animate the skin shape. Since the deformation follows the tangent of the curve skeleton and also due to higher sampling rates received from the curve points, collapsing skin and other undesirable skin deformation problems are avoided. The curve skeleton retains the advantages of the current skeleton driven skinning. It is easy to use and allows full control over the animation process. As a further enhancement, it is also fairly simple to build realistic muscle and fat bulge effect. A practical implementation in the form of a Maya plug‐in is created to demonstrate the viability of the technique. Copyright

PDE based surface representation—vase design

Abstract The aesthetic features of some free form surfaces, such as vases, despite being adjunct, can prove tedious and time consuming to create by the conventional surface models, such as NURBS. In this paper, we propose a new method that is able to rapidly generate complex free form surfaces, such as vases together with their accessory features using the fourth order partial differential equations (PDEs) with three vector-valued shape parameters. Vases of different shapes can be easily produced by altering the shape parameters, force functions and boundary conditions of the proposed PDE. As computational performance is of paramount significance for interactive computer graphics applications, an analytical solution to the PDE has been derived. The effects of the shape parameters, boundary conditions and force functions on the final surface shape have also been studied.

Surface representation using second, fourth and mixed order partial differential equations

Partial differential equations (PDEs) are powerful tools for the generation of free-form surfaces. In this paper, techniques of surface representation using PDEs of different orders are investigated. In order to investigate the real-time performance and capacity of surface generation based on the PDE method, the forms of three types of partial differential equations are put forward, which are the second, mixed and fourth order PDEs. The closed form solutions of these PDEs are derived. The advantages and disadvantages of each of them are discussed. A number of examples are given to demonstrate the use and effectiveness of the techniques.