Combination Of Simulation Tools Research Articles

Controlling Adaptive Contention Window to Improve Safe Message Received Rate in VANET

The primary goal of Vehicular Ad Hoc Networks (VANETs) is to support the secure transmission of applications via vehicles. Broadcasting is an important form of communication in the VANET network. Since there is no recovery for broadcast frames in the VANET network, the rate of receiving safe messages can become very low, especially in dense network conditions. In this paper, we present a new broadcast coordination mechanism with the aim of adaptive control of CW size to improve the received rate of safety messages. Each vehicle in the VANET can identify current local conditions of the network such as collisions or congestion by analyzing recently successfully sent and received frames. Based on the analysis of the received frame rate at each vehicle, the proposed mechanism controls the CW size and uses the EDCA mechanism to prioritize the important data flows. Using a combination of simulation tools in VANET, we build simulation scenarios in different network conditions to evaluate the received rate of safety messages compared to the default mechanism in the 802.11p standard. Simulation results have demonstrated that the proposed mechanism improves the received rate of safety messages better than the default mechanism in the 802.11p standard in all cases.

Simulation tools for decision support to adaptive forest management in Europe

In forest management there is a tendency towards measuring less and simulating more. In this context the development of reliable, user friendly forest simulators has become economically relevant. The objective of this perspective paper is to highlight the recent trends in forest simulation and to identify the remaining challenges to make forest simulation a reliable tool for forest policy and management. Experiences with forest simulators for various purposes in different geographical contexts illustrate how the important challenges of forest decision support can be addressed through flexible customization for different end-user categories, offering spatially explicit approaches at the landscape scale, and integrating empirical and mechanistic models in hybrid and bayesian simulation approaches. Recent development trends in forest simulation for decision support are mainly related to the ever increasing calculation speed and capacity of computers, facilitating the development of robust tools with comfortable user interface and realistic functions and options. Another trend is the combination of simulation tools with optimization and choice algorithms fading away the difference between simulators and decision support systems. The remaining challenges are basically in the high expectations of stakeholders concerning the ability of simulators to predict a range of outcomes in terms of ecosystem services and sustainability indicators, as well as the quality of their outcome in terms of output credibility to stakeholders. Need for accepted and realistic model validation and verification methods preferably using empirical data is crucial in this matter.

Solid-solution precursor to melting in onion-ring Pd–Pt nanoclusters: a case of second-order-like phase change?

The thermodynamical behaviour of icosahedral, multilayer Pd-Pt clusters is addressed using a combination of simulation tools, mainly parallel tempering Monte Carlo. A preferential swapping trial move is introduced to increase the chance of successfully exchanging Pd and Pt atoms in the cluster. The 2-, 3- and 4-shell, Pd-rich clusters have been studied. We generally find that the clusters melt at a temperature significantly below the bulk melting point at the same corresponding composition. More interestingly, for the smaller clusters melting is initiated by a solid-solution intermediate phase in which the overall icosahedral frame remains, but the Pd and Pt atoms can swap sites. The transition to this solid-solution phase is seen to have a continuous, second-order like character, which is interpreted from the similarity between the present system with the ferromagnetic Ising model on the 3D cubic lattice. As the cluster grows, the onion-ring structure becomes thermodynamically unstable. The 4-layer cluster already exhibits a solid-solution in its core at temperatures as low as 100 K. The bulk behaviour is thus recovered at very small scales.

Temporal and steric analysis of ionic permeation and binding in SERCA via moleculardynamic simulations

The availability of the crystal structure of the sarco(endo)plasmic reticulum calciumATPase (SERCA) has allowed atomic-level molecular dynamic (MD) simulations of thismembrane transport protein to be done. The biomedical and nanotechnologicalimplications of this work are discussed as well as the methods of performing the simulationsand analysis. We have performed nanosecond timescale simulations of SERCA for several ofits known conformations in a lipid/water environment. One simulation containedCa2+ ions, while others without ions were analyzed by techniques such as steric pathwaydetermination. We discuss details of the resulting putative cytoplasmic and lumenalpathways, along with experimental evidence from the literature to support ourconclusions. Finally, we give a brief overview of future research directions, as theypertain to MD simulations and their analysis. The methodology used in this workshows that significant insight into the structure–function relationship of ion-motivetransmembrane pumps can be derived by a combination of simulation tools and analysistechniques including MD trajectories, steric analysis and electrostatic potentials.

Damage evolution and surface defect segregation in low-energy ion-implanted silicon

We have combined computer simulations and atomic-resolution tunneling microscopy to investigate the kinetics of defect migration during annealing of ion implanted Si(111)-7×7. Using atomically-clean and flat surfaces as sinks for bulk point defects introduced by the irradiation, we observe distinct, temperature-dependent surface arrival rates for vacancies and interstitials, and we demonstrate that the distinct kinetics of each type of bulk point defect govern their surface segregation kinetics. A combination of simulation tools provides a detailed description of the processes that underlie the observed temperature-dependence of defect migration.

Defect Diffusion During Annealing of Low-Energy Ion-Implanted Silicon

AbstractWe present a new approach for investigating the kinetics of defect migration during annealing of low-;energy, ion-implanted silicon, employing a combination of computer simulations and atomic-resolution tunneling microscopy. Using atomically-clean Si(111)-7×7 as a sink for bulk point defects created by 5 keV Xe and Ar irradiation, we observe distinct, temperature-;dependent surface arrival rates for vacancies and interstitials. A combination of simulation tools provides a detailed description of the processes that underly the observed temperature-dependence of defect segregation, and the predictions of the simulations agree closely with the experimental observations.

Defect Diffusion During Annealing of Low-Energy Ion-Implanted Silicon

AbstractWe present a new approach for investigating the kinetics of defect migration during annealing of low-energy, ion-implanted silicon, employing a combination of computer simulations and atomic-resolution tunneling microscopy. Using atomically-clean Si(111)-7×7 as a sink for bulk point defects created by 5 keV Xe and Ar irradiation, we observe distinct, temperature-dependent surface arrival rates for vacancies and interstitials. A combination of simulation tools provides a detailed description of the processes that underdy the observed temperature-dependence of defect segregation, and the predictions of the simulations agree closely with the experimental observations.