Distributed VR-based simulation for manufacturing

VR-based simulation has been applied to a wide range of industrial applications. The rapid development of networking and Internetworked 3D graphics techniques has already begun to foster the distributed VR-based simulation system. The WWW as the delivery mechanism has made the VR-based simulator widely available and affordable. In this paper, we propose a cost-effective approach to create distributed VR-based simulation systems for manufacturing applications. Using this approach, three VRML manufacturing simulators machining, process flow, factory layout, are described in detail. The current challenges of a distributed VR-based simulator are also discussed

Assessing restoration potential of a critically endangered vegetation type following alien acacia removal

The Fynbos vegetation of the Cape Lowlands is ecologically distinct from mountain Fynbos within the Cape Region of South Africa, but has been highly impacted by agriculture and urban development, while alien plants have invaded most of the remaining natural habitats. Cape Flats Sand Fynbos is a critically endangered lowland vegetation type containing many endemic and threatened species. 100 ha of this vegetation type which was invaded by alien Acacia saligna was cleared in 2012. The standard clearing methods utilised in Lowland Fynbos have resulted in poor native vegetation recovery. Therefore this study aimed to test novel passive (burning) and active (seed sowing) treatments on recovery of native vegetation. After two years all treatments resulted in different recovery trajectories, and modelling treatment responses showed these trajectories to be maintained in the long-term. The passive clearing without burning treatment resulted in herbaceous vegetation dominating, while the active treatment resulted in higher cover, species richness and density of non-sprouting shrubs. A follow-up sowing treatment involving seed pre-treated with smoke and heat improved shrub species richness and seedling density of certain species, especially Thamnochortus punctatus, a dominant structural component species. Therefore an active treatment involving sowing pre-treated seeds after clearing and burning results in best Fynbos recovery compared to either of the passive treatments tested. These restoration methods should be adaptable to other lowland vegetation types within the Fynbos region as well as other Mediterranean climate regions

Active seed sowing can overcome constraints to passive restoration of a critically endangered vegetation type

Invasive alien plants negatively impact ecosystems, but recovery of native vegetation may fail following standard methods of alien species removal alone. Alternative management actions may thus be required. Cape Flats Sand Fynbos is a critically endangered vegetation type in the Cape Floristic Region of South Africa which is threatened by Acacia saligna invasion, but standard clearing methods have failed to restore native vegetation structure. A restoration study was performed comparing passive treatments i.e. clearing without burning (stack-block) versus clearing and burning (burn-block), as well as active intervention by sowing seeds of native species, either initially after burning or a year later, in which seeds were either not pre-treated or pre-treated with smoke and heat exposure before sowing. After two years all treatments resulted in different recovery trajectories, although none resembled the reference condition. Clearing without burning facilitated recovery in less degraded areas with higher initial native shrub cover, but otherwise resulted in limited vegetation recovery. Limited recovery facilitated secondary invasion by herbaceous weeds. Active seed sowing resulted in the highest recovery of native shrub cover and diversity. These findings suggest that passive restoration is constrained by seed limitation, due to the lack of recovery of vegetation components under passive clearing treatment. Active sowing was able to partially overcome this constraint through improved recovery of total shrub cover. However, non-sprouting shrub cover was higher while resprouting shrubs and species of Restionaceae were lower compared to the reference condition. Pre-treatment of seeds before sowing improved establishment of some species. Active treatment involving sowing pre-treated seeds after clearing and burning therefore resulted in best fynbos recovery compared to either of the passive treatments tested. A decision tree has been developed based on these findings in order to guide best protocol for managers

Using simulation to understand the structure and properties of hydrated amorphous calcium carbonate

We report results from studies using four different protocols to prepare hydrated amorphous calcium carbonate, ranging from random initial structures to melting hydrated mineral structures. All protocols give good agreement with experimental X-ray structure factors. However, the thermodynamic properties, ion coordination environments, and distribution of water for the structures produced by the protocols show statistically significant variation depending on the protocols used. We discuss the diffusivity of water through the various structures and its relation to experiments. We show that one protocol (based on melting ikaite) gives a structure where the water is mobile, due to the presence of porosity in the amorphous structure. We conclude that our models of hydrated amorphous calcium carbonate do give a range of behaviour that resembles that observed experimentally, although the variation is less marked in the simulations than in experiments

E-manufacturing in networked virtual environments

E-manufacturing is a new generation of product development solution allows manufacturers all over the world to speed up and slim down everything from design to manufacturing. It has been employed in a wide range of manufacturing activities. Networked Virtual Environments (Net-VEs) have already begun to foster an insightful, intuitive and interactive system that allows effective communication among multiple users. After exploring the architecture and features of Net-VEs, a cost-effective approach to create an e-manufacturing system in Net-VEs is proposed in this paper. The World Wide Web (WWW) as the delivery mechanism has made such system widely available and affordable. We also evaluate an e-manufacting system in Net-VEs by comparison with a traditional product development approach

Supersymmetry with R-Parity Breaking: Contact Interactions and Resonance Formation in Leptonic Processes at LEP2

In supersymmetric theories with R-parity breaking, trilinear couplings of two leptons to scalar sleptons are possible. In electron-positron collisions such interactions would manifest themselves through contact terms in Bhabha scattering and in annihilation to mu or tau pair Interpreting the high x, high Q2 DIS HERA events as charm squark production with squark masses of order 200 GeV, the formation of tau sneutrinos with a mass in the range close to the LEP2 energy or even in reach, is an exciting speculation which can be investigated in the coming LEP2 runs with energies close to 200 GeV.Comment: 13 pages, LaTex file with 3 figures, uses axodraw.sty (included). References updated / limits from rare B decays on Yukawa couplings updated, favoring tau-sneutrinos over mu-sneutrinos/ numerical results unchange

Macroscopic quantum superpositions in highly-excited strongly-interacting many-body systems

We demonstrate a break-down in the macroscopic (classical-like) dynamics of wave-packets in complex microscopic and mesoscopic collisions. This break-down manifests itself in coherent superpositions of the rotating clockwise and anticlockwise wave-packets in the regime of strongly overlapping many-body resonances of the highly-excited intermediate complex. These superpositions involve $\sim 10^4$ many-body configurations so that their internal interactive complexity dramatically exceeds all of those previously discussed and experimentally realized. The interference fringes persist over a time-interval much longer than the energy relaxation-redistribution time due to the anomalously slow phase randomization (dephasing). Experimental verification of the effect is proposed.Comment: Title changed, few changes in the abstract and in the main body of the paper, and changes in the font size in the figure. Uses revTex4, 4 pages, 1 ps figur

Vibrations of a chain of Xe atoms in a groove of carbon nanotube bundle

We present a lattice dynamics study of the vibrations of a linear chain of Xe adsorbates in groove positions of a bundle of carbon nanotubes. The characteristic phonon frequencies are calculated and the adsorbate polarization vectors discussed. Comparison of the present results with the ones previously published shows that the adsorbate vibrations cannot be treated as completely decoupled from the vibrations of carbon nanotubes and that a significant hybridization between the adsorbate and the tube modes occurs for phonons of large wavelengths.Comment: 3 PS figure