Image denoise by fourth-order PDE based on the changes of laplacian

Fourth-order partial differential equation (PDE) proposed by You and Kaveh (You-Kaveh fourth-order PDE), which replaces the gradient operator in classical second-order nonlinear diffusion methods with a Laplacian operator, is able to avoid blocky effects often caused by second-order nonlinear PDEs. However, the equation brought forward by You and Kaveh tends to leave the processed images with isolated black and white speckles. Although You and Kaveh use median filters to filter these speckles, median filters can blur the processed images to some extent, which weakens the result of You-Kaveh fourth-order PDE. In this paper, the reason why You-Kaveh fourth-order PDE can leave the processed images with isolated black and white speckles is analyzed, and a new fourth-order PDE based on the changes of Laplacian (LC fourth-order PDE) is proposed and tested. The new fourth-order PDE preserves the advantage of You-Kaveh fourth-order PDE and avoids leaving isolated black and white speckles. Moreover, the new fourth-order PDE keeps the boundary from being blurred and preserves the nuance in the processed images, so, the processed images look very natural.

Neutron quasi-elastic scattering in disordered solids: a Monte Carlo study of metal-hydrogen systems

The dynamic structure factor of neutron quasi-elastic scattering has been calculated by Monte Carlo methods for atoms diffusing on a disordered lattice. The disorder includes not only variation in the distances between neighbouring atomic sites but also variation in the hopping rate associated with each site. The presence of the disorder, particularly the hopping rate disorder, causes changes in the time-dependent intermediate scattering function which translate into a significant increase in the intensity in the wings of the quasi-elastic spectrum as compared with the Lorentzian form. The effect is particularly marked at high values of the momentum transfer and at site occupancies of the order of unity. The MC calculations demonstrate how the degree of disorder may be derived from experimental measurements of the quasi-elastic scattering. The model structure factors are compared with the experimental quasi-elastic spectrum of an amorphous metal-hydrogen alloy.

Exact colorations of graphs and digraphs

A coloration is an exact regular coloration if whenever two vertices are colored the same they have identically colored neighborhoods. For example, if one of the two vertices that are colored the same is connected to three yellow vertices, two white and red, then the other vertex is as well. Exact regular colorations have been discussed informally in the social network literature. However they have been part of the mathematical literature for some time, though in a different format. We explore this concept in terms of social networks and illustrate some important results taken from the mathematical literature. In addition we show how the concept can be extended to ecological and perfect colorations, and discuss how the CATREGE algorithm can be extended to find the maximal exact regular coloration of a graph.

Computational modeling of mold filling and related free-surface flows in shape casting: an overview of the challenges involved

Accurate representation of the coupled effects between turbulent fluid flow with a free surface, heat transfer, solidification, and mold deformation has been shown to be necessary for the realistic prediction of several defects in castings and also for determining the final crystalline structure. A core component of the computational modeling of casting processes involves mold filling, which is the most computationally intensive aspect of casting simulation at the continuum level. Considering the complex geometries involved in shape casting, the evolution of the free surface, gas entrapment, and the entrainment of oxide layers into the casting make this a very challenging task in every respect. Despite well over 30 years of effort in developing algorithms, this is by no means a closed subject. In this article, we will review the full range of computational methods used, from unstructured finite-element (FE) and finite-volume (FV) methods through fully structured and block-structured approaches utilizing the cut-cell family of techniques to capture the geometric complexity inherent in shape casting. This discussion will include the challenges of generating rapid solutions on high-performance parallel cluster technology and how mold filling links in with the full spectrum of physics involved in shape casting. Finally, some indications as to novel techniques emerging now that can address genuinely arbitrarily complex geometries are briefly outlined and their advantages and disadvantages are discussed.

High current density induced damage mechanisms in electronic solder joints: a state-of-the-art review

High current density induced damages such as electromigration in the on-chip interconnection /metallization of Al or Cu has been the subject of intense study over the last 40 years. Recently, because of the increasing trend of miniaturization of the electronic packaging that encloses the chip, electromigration as well as other high current density induced damages are becoming a growing concern for off-chip interconnection where low melting point solder joints are commonly used. Before long, a huge number of publications have been explored on the electromigration issue of solder joints. However, a wide spectrum of findings might confuse electronic companies/designers. Thus, a review of the high current induced damages in solder joints is timely right this moment. We have selected 6 major phenomena to review in this paper. They are (i) electromigration (mass transfer due electron bombardment), (ii) thermomigration (mass transfer due to thermal gradient), (iii) enhanced intermetallic compound growth, (iv) enhanced current crowding, (v) enhanced under bump metallisation dissolution and (vi) high Joule heating and (vii) solder melting. the damage mechanisms under high current stressing in the tiny solder joint, mentioned in the review article, are significant roadblocks to further miniaturization of electronics. Without through understanding of these failure mechanisms by experiments coupled with mathematical modeling work, further miniaturization in electronics will be jeopardized

Implementation of cognitive mapping, spatial representation and wayfinding behaviours of people within evacuation modelling tools

Within the building evacuation context, wayfinding describes the process in which an individual located within an arbitrarily complex enclosure attempts to find a path which leads them to relative safety, usually the exterior of the enclosure. Within most evacuation modelling tools, wayfinding is completely ignored; agents are either assigned the shortest distance path or use a potential field to find the shortest path to the exits. In this paper a novel wayfinding technique that attempts to represent the manner in which people wayfind within structures is introduced and demonstrated through two examples. The first step is to encode the spatial information of the enclosure in terms of a graph. The second step is to apply search algorithms to the graph to find possible routes to the destination and assign a cost to the routes based on their personal route preferences such as "least time" or "least distance" or a combination of criteria. The third step is the route execution and refinement. In this step, the agent moves along the chosen route and reassesses the route at regular intervals and may decide to take an alternative path if the agent determines that an alternate route is more favourable e.g. initial path is highly congested or is blocked due to fire.

Surface-enhanced Raman scattering studies of rhodanines: Evidence for substrate surface-induced dimerization

The surface-enhanced Raman scattering (SERS) spectra of rhodanine adsorbed on silver nanoparticles have been examined using 514.5 and 632.8 nm excitation. There is evidence that, under the experimental conditions used, rhodanine undergoes a nanoparticle surface-induced reaction resulting in the formation of a dimeric species via the active methylene group in a process which is analogous to the Knoevenagel reaction. The experimental observations are supported by DFT calculations at the B3-LYP/cc-pVDZ level. Calculated energies for the interaction of the E and Z isomers of the dimers of rhodanine with silver nanoparticles support a model in which the (intra-molecular hydrogen bonded) E isomer dimer is of lower energy than the Z isomer. A strong band, at 1566 cm(-1), in the SERS spectrum of rhodanine is assigned to the nu(C=C) mode of the dimer species.

Exploration of the student experience of e-learning: beginning to bridge the learning divide

Introduction This proposal aims, through debate within symposium to explore the student experience of e-learning. The team facilitating the discussion will draw upon their experience of an HEA funded pathfinder project, the main aim of which was to collect learner stories about their experience of using technology in their everyday learning activities at the University of Greenwich across a range of programmes, levels, locations and student groups. Method The project design responded to the growing body of student voice literature and then utilised and built upon the JISC-funded studies that focussed on understanding the learner perspectives on the role of technology in learning, namely: • the LEX study which investigated a broad spectrum of technology use by eliciting rich data about learners’ feelings, beliefs and intentions towards e-learning (Creanor et al, 2006); • the LXP studies which explored disciplinary differences in uses of technology by university students through a variety of methodologies (Conole et al, 2006). Results The symposium will be organised as a round table discussion that will be structured into three sections: • Designing an online survey tool, and the results of our survey. • Exploring student stories. • What can learned from the project and taking the findings back to enhance learning. To stimulate discussion each section will start by asking the participants to discuss and debate a particular question, this will be followed by an interactive presentation by the respective member of the project team who will share the findings of the project and invite contributions to the resulting discussion from personal perspectives. The questions are: • What is effective learning within a context of digital technology? • What are the myths and truths about the identity of today's learners? • What practical changes need to happen in order to see real change? Conclusion The final section of the symposium will invite contributions from the participants in order to collate the views and perspectives of all the participants in order to focus the discussion on the following: • The issues that have arisen as a result of the round table debates. • New speculative approaches to enhancing the student experience. • A controversial stand to the future of Higher Education teaching and learning and the role and integration of technology within that education. The symposium will provide an opportunity to explore the predictive value of Student Experience of E-Learning Laboratory (SEEL) project.