CyberWalk : a web-based distributed virtual walkthrough environment

A distributed virtual walkthrough environment allows users connected to the geometry server to walk through a specific place of interest, without having to travel physically. This place of interest may be a virtual museum, virtual library or virtual university. There are two basic approaches to distribute the virtual environment from the geometry server to the clients, complete replication and on-demand transmission. Although the on-demand transmission approach saves waiting time and optimizes network usage, many technical issues need to be addressed in order for the system to be interactive. CyberWalk is a web-based distributed virtual walkthrough system developed based on the on-demand transmission approach. It achieves the necessary performance with a multiresolution caching mechanism. First, it reduces the model transmission and rendering times by employing a progressive multiresolution modeling technique. Second, it reduces the Internet response time by providing a caching and prefetching mechanism. Third, it allows a client to continue to operate, at least partially, when the Internet is disconnected. The caching mechanism of CyberWalk tries to maintain at least a minimum resolution of the object models in order to provide at least a coarse view of the objects to the viewer. All these features allow CyberWalk to provide sufficient interactivity to the user for virtual walkthrough over the Internet environment. In this paper, we demonstrate the design and implementation of CyberWalk. We investigate the effectiveness of the multiresolution caching mechanism of CyberWalk in supporting virtual walkthrough applications in the Internet environment through numerous experiments, both on the simulation system and on the prototype system

Recent development in multimedia e-learning technologies

Multimedia and networking technologies have significantly impacted on our daily activities, particularly in terms of how we learn. Nowadays, classroom teaching no longer simply relies on chalk and blackboard as the prime medium for course dissemination. E-learning technologies have made it possible to provide a virtual classroom environment on the Web through supporting teacher-student and student-student communications, course material distribution as well as online student assessments. They provide students with more control over their learning schedule and pace. On top of this, multimedia technologies further offer students different forms of media to match their learning styles, leading to enhancements of their learning effectiveness. This extended introduction discusses the latest e-learning specific multimedia technologies, their research challenges and future trends from both pedagogical and technological perspectives. We also summarize the papers included in this special issue

Note on a sigma model connection with instanton dynamics

It is well known that the instanton approach to QCD generates an effective term which looks like a three flavor determinant of quark bilinears. This has the right behavior to explain the unusual mass and mixing of the $\eta(958)$ meson, as is often simply illustrated with the aid of a linear SU(3) sigma model. It is less well known that the instanton analysis generates another term which has the same transformation property but does not have a simple interpretation in terms of this usual linear sigma model. Here we point out that this term has an interpretation in a generalized linear sigma model containing two chiral nonets. The second chiral nonet is taken to correspond to mesons having two quarks and two antiquarks in their makeup. The generalized model seems to be useful for learning about the spectrum of low lying scalar mesons which have been emerging in the last few years. The physics of the new term is shown to be related to the properties of an "excited" $\eta'$ state present in the generalized model and for which there are some experimental candidates.Comment: reference added, minor typos correcte

Spin relaxation in (110) and (001) InAs/GaSb superlattices

We report an enhancement of the electron spin relaxation time (T1) in a (110) InAs/GaSb superlattice by more than an order of magnitude (25 times) relative to the corresponding (001) structure. The spin dynamics were measured using polarization sensitive pump probe techniques and a mid-infrared, subpicosecond PPLN OPO. Longer T1 times in (110) superlattices are attributed to the suppression of the native interface asymmetry and bulk inversion asymmetry contributions to the precessional D'yakonov Perel spin relaxation process. Calculations using a nonperturbative 14-band nanostructure model give good agreement with experiment and indicate that possible structural inversion asymmetry contributions to T1 associated with compositional mixing at the superlattice interfaces may limit the observed spin lifetime in (110) superlattices. Our findings have implications for potential spintronics applications using InAs/GaSb heterostructures.Comment: 4 pages, 2 figure

Image-Guided Ablative Therapies for Lung Tumors

While the gold standard for early stage lung cancers is still surgical resection, many patients have comorbidities or suboptimal lung function making surgery unfavorable. At the same time, more and more small lung nodules are being incidentally discovered on computer tomography (CT), leading to the discovery of pre-malignant or very early stage lung cancers without regional spread, which could probably be eradicated without anatomical surgical resection. Various ablative energies and technologies are available on the market, including radiofrequency ablation, microwave ablation, cryoablation, and less commonly laser ablation and irreversible electroporation. For each technology, the mechanism of action, advantages, limitations, potential complications and evidence-based outcomes will be reviewed. Traditionally, these ablative therapies were done under CT guidance with percutaneous insertion of ablative probes. Recently, bronchoscopic ablation under ultrasound, CT, or electromagnetic navigation bronchoscopy guidance is gaining popularity due to improved navigation precision, reduced pleural-based complications, and providing a true “wound-less” option

Species composition, diversity and biomass estimation in coastal and marine protected areas of Terengganu, Peninsular Malaysia

We investigated and compared the tree species composition and diversity of different forest types in Setiu Wetlands and on the three major islands of Terengganu. A total of 24 plots of 25 m × 25 m with four plots in each study site were established, viz. Melaleuca swamp forest in Kampung Fikri, freshwater swamp forest in Kampung Gong Batu, mangrove forest in UMT Setiu research station, and the islands, namely Pulau Bidong, Pulau Redang, and Pulau Perhentian. We calculated the basal area, stand density, Importance Value Index, species diversity, and above-ground biomass in the designated study areas. We assessed 139 tree species from 96 genera and 50 families based on a total of 2608 tree samples of 5 cm DBH and above. The freshwater swamp forest harbored the highest number of species with 20 species in Setiu Wetlands, and among the islands, Pulau Redang had the highest with 56 species. Melaleuca cajuputi was the most dominant species in the Melaleuca swamp forest, while Alstonia spatulata and Rhizophora apiculata are expected in the freshwater swamp and mangrove forest, respectively. Pulau Bidong, Pulau Redang, and Pulau Perhentian are mostly represented by Licania splendens, Shorea glauca, and Vatica sp., respectively. All the dominant species but Licania splendens contributed to the highest amount of above-ground biomass. Our current study indicated that different forest types vary in composition and structure, which may contribute to their unique ecological roles within their specific environment

Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry

In semiconductor heterostructures, bulk and structural inversion asymmetry and spin-orbit coupling induce a k-dependent spin splitting of valence and conduction subbands, which can be viewed as being caused by momentum-dependent crystal magnetic fields. This paper studies the influence of these effective magnetic fields on the intersubband spin dynamics in an asymmetric n-type GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin plasmons using linear response theory. The so-called D'yakonov-Perel' decoherence mechanism is inactive for collective intersubband excitations, i.e., crystal magnetic fields do not lead to decoherence of spin plasmons. Instead, we predict that the main signature of bulk and structural inversion asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting of the spin plasmon dispersion. The importance of many-body effects is pointed out, and conditions for experimental observation with inelastic light scattering are discussed.Comment: 8 pages, 6 figure

The role of point-like topological excitations at criticality: from vortices to global monopoles

We determine the detailed thermodynamic behavior of vortices in the O(2) scalar model in 2D and of global monopoles in the O(3) model in 3D. We construct new numerical techniques, based on cluster decomposition algorithms, to analyze the point defect configurations. We find that these criteria produce results for the Kosterlitz-Thouless temperature in agreement with a topological transition between a polarizable insulator and a conductor, at which free topological charges appear in the system. For global monopoles we find no pair unbinding transition. Instead a transition to a dense state where pairs are no longer distinguishable occurs at T<Tc, without leading to long range disorder. We produce both extensive numerical evidence of this behavior as well as a semi-analytic treatment of the partition function for defects. General expectations for N=D>3 are drawn, based on the observed behavior.Comment: 14 pages, REVTEX, 13 eps figure

Impact of n-methyl-2-pyrrolidone in monoethanolamine solution to the co2 absorption in packed column: analysis via mathematical modeling

This work investigates the reason behind the change of CO2 absorption behaviour exhibited by monoethanolamine (MEA) solution via mathematical modeling analysis when physical absorbent, i.e. n-methyl-2-pyrrolidone (NMP), was added into the solution. The mathematical modeling included the heat model using time resolved numerical method. Based on the results, it was found that lower CO2 removal performance with the addition of NMP into MEA solution at pressure of 0.1 MPa was mainly due to the lower temperature rise along the column, which resulted in lower reaction rate. However, at 3 and 5 MPa pressure conditions, the high physical absorption capability contributed by the presence of NMP in MEA hybrid solution enhanced the CO2 absorption performance of MEA hybrid solution significantly. As such, temperature rise of solution was identified as the dominating factor affecting the performance of the hybrid solvent. The reaction rate of MEA was not affected by the addition of physical solvent. This finding shed crucial insight on the behaviour MEA-NMP hybrid solution which can be applied during scale-up of the process