Molecular System Dynamics for Self-Organization in Heterogeneous Wireless Networks

Summary form only given. We investigate the problem of propagating of data to nodes and scheduling of available nodes in a dynamic data communication network. The goal of scheduling algorithm is to find a request-service scheduling such that the total communication cost is minimized. In the special case in which all requests are of equal priorities and all services have equal performance, the scheduling problem becomes the mapping of the maximum number of requests to the free service-nodes. Scheduling in a communication network entails the efficient search of a mapping from request-nodes to free service-nodes such that circuit blockage in the network are minimized and service-nodes are maximally utilized.

Nowadays, the nano-machining process is used to produce high quality finished surfaces with precise form accuracy. To understand and analyze the chip formation mechanism of nano-machining process on an atomistic scale, since the experimentation is not an easy task, numerical simulation such as molecular dynamic (MD) simulation is a very useful method. In this paper, MD simulation of the nano-metric cutting of single-crystal copper was performed with a single crystal diamond tool. The model was solved with both pair wise Morse potential function and embedded atom method (EAM) potential to simulate the inter-atomic force between the work-piece and a rigid tool. The chip formation mechanism, dislocation generation, tool forces and generated temperature were investigated. Results show that the Morse potential cannot perform an appropriate defect formation and plastic deformation in nano-metric cutting of metals. Also, tool forces in Morse potential are more than the forces in EAM potential. Furthermore, the fluctuations of resultant forces in Morse potential are greater than that of EAM. In addition, using many-body interaction potentials like EAM can lead to substantial changes in surface energies, elastic-plastic properties and atomic displacement, compared with the pair-wise potentials like Morse. Finally, the atomic displacement investigation shows that in EAM potential study, only the atoms in a local region near the cutting process are displaced, but in Morse potential a large portion of atoms has affected during cutting process. Subsequently, the chip temperature in EAM potential is more than that of Morse potential.

In nanometric cutting process, the actual material removal can take place at atomic level, which makes it difficult or impossible to observe the machining phenomena and measure the cutting parameters in experiments. However, it is crucial to investigate the cutting process in nanoscale. In this study, the molecular dynamics (MD) method is employed to model and simulate the process of cutting monocrystalline copper. The two-body Morse potential and the many-body EAM potential are used for the atoms interaction in the workpiece to study the effect of different potential function on the simulation results. It is found that there are no obvious differences in the chip formation between Morse and EAM potential, but the Morse potential results in higher potential energy and more chips generated in the cutting process.

The Study on the Communication Network of Wide Area Measurement System in Electricity Grid

Although the computation of heat flux and thermal conductivity either via Fourier's law or the Green-Kubo relation has become a common task in molecular dynamics simulation, contributions of three-body and larger many-body interactions have always proved problematic to compute. In recent years, due to the success when applying to pressure tensor computation, atomic stress approximation has been widely used to calculate heat flux, where the lammps molecular dynamics package is the most prominent propagator. We demonstrated that the atomic stress approximation, while adequate for obtaining pressure, produces erroneous results in the case of heat flux when applied to systems with many-body interactions, such as angle, torsion, or improper potentials. This also produces incorrect thermal conductivity values. To remedy this deficiency, by starting from a strict formulation of heat flux with many-body interactions, we reworked the atomic stress definition which resulted in only a simple modification. We modified the lammps package accordingly to demonstrate that the new atomic stress approximation produces excellent results close to that of a rigid formulation.

When there are high and low frequency motions in systems with long and short range forces a judicious choice of reference system leads to very large accelerations in molecular dynamic (MD) simulations. Building on our previous work where we have developed reference system methods for systems with high frequency oscillators, disparate masses, or long range forces, we present a double reference system method which leads to acceleration of as much as 20 in systems consisting of 864 molecules with Lennard-Jones (12-6) forces. Much larger savings should be achieved when this method is applied to longer range forces and larger systems.

A critical piece of the Smart Grid (SG) infrastructure is the supporting Communication Networks that facilitate data gathering, monitoring and control of the electric grid. Over the years, electric utilities built robust communication networks for their transmission and distribution systems, but stopped short of the "last mile" connections to the end user. A primary goal of the SG is to expand the communications network throughout and beyond the Distribution Network (DN); thus, enabling a holistic management and control of the electric grid from generation to consumption. For the realization of the Smart Grid goals, two-way communication capabilities must extend beyond the Distribution Network to the end user, allowing two-way data flow, e.g., real-time energy pricing as well as real-time demand data back to the utility operators. Selecting an appropriate communications architecture is the first and most important decision in designing a communications network since it will have lasting effects on the efficiency, reliability and cost of the network. This paper presents and evaluates various communication architectures for deployment of the SG within the DN and to the end users.

The method of constant pressure molecular dynamics (MD), developed by Andersen for monoatomic fluids is extended to the MD, in Cartesian coordinates, of molecular systems with constraints. Andersen’s proof is easily generalized after decoupling internal degrees of freedom from the center-of-mass. Only these last degrees are directly affected by Andersen’s transformation (demon). The Cartesian equations of motion of individual atoms are derived from a generalized Andersen’s Lagrangian. The equations are quite similar to those of the usual MD simulation at constant volume apart from an additional term coupling the molecular center-of-mass and the volume of the sample. The volume appears now as a dynamical variable evolving from the imbalance between imposed external pressure and instantaneous values of the molecular stress tensor. Some numerical aspects are discussed and the technique is briefly illustrated for the case of rigid diatomic molecules.

In this paper we investigate the impact of a Relay Node (RN) placement plan on a heterogeneous wireless network called Hybrid Wireless Network with dedicated delay nodes (HWN*) in terms of system capacity, transmission delay and Quality of Service (QoS). A novel HWN* Heuristic RN Placement (HHRP) algorithm, which considers RN assistance & support for radio resource sharing such as inter-network traffic balancing, TD/CDMA soft handover, routing and user mobility has been implemented. A system level simulation is used to quantify the benefits of HWN* using HHRP algorithm over HWN* with other RN placement plans and multi-hop cellular networks. I. INTRODUCTION A heterogeneous wireless network refers to a wireless net- work that is comprised of wireless nodes with different radio access technologies or equipment with different operating systems. For example, it can be a wireless sensor network including bluetooth based radio access and zigbee 802.15.4 based radio access or a hybrid wireless network including cellular access and 802.11b/g based radio access. Specifi- cally for a hybrid wireless network, the increase of cellular communication intensity results in a reduction in cell size, thus much denser clusters are required resulting in increased infrastructure cost and system complexity. Meanwhile, the bursty nature of communication traffic and path loss results in traffic prediction difficulty. A solution must be found to provide effective resource management, congestion control and routing. The hybrid wireless network which incorporates cellular and MANET interfaced RELAY nodes, provides a practical approach for this. Nevertheless, the dedicated relay infrastructure approach can be also be adapted to the emerging wireless sensor network in order to maintain node connectivity, support sensor data aggregation and optimise power consump- tion.

In this article, uncertainty quantification is applied to molecular dynamics (MD) simulations of concentration driven ionic flow through a silica nanopore. We consider a silica pore model connecting two reservoirs containing a solution of sodium (Na(+)) and chloride (Cl(-)) ions in water. An ad hoc concentration control algorithm is developed to simulate a concentration driven counter flow of ions through the pore, with the ionic flux being the main observable extracted from the MD system. We explore the sensitivity of the system to two physical parameters of the pore, namely, the pore diameter and the gating charge. First we conduct a quantitative analysis of the impact of the pore diameter on the ionic flux, and interpret the results in terms of the interplay between size effects and ion mobility. Second, we analyze the effect of gating charge by treating the charge density over the pore surface as an uncertain parameter in a forward propagation study. Polynomial chaos expansions and Bayesian inference are exploited to isolate the effect of intrinsic noise and quantify the impact of parametric uncertainty on the MD predictions. We highlight the challenges arising from the heterogeneous nature of the system, given the several components involved, and from the substantial effect of the intrinsic thermal noise.

Reverse-osmosis (RO) plays an important role in many natural and industrial processes such as water purification, wastewater treatment, and food and beverage processing. Molecular dynamics (MD) simulation of extremely dilute (ppm concentrations) RO systems are generally impractical due to the high computational cost associated with the large number of particles that must be included in the MD system. These systems are nevertheless of great industrial importance. Here, we propose a new method of MD simulations for reverse-osmosis using molecular replication (MR-RO) for concentrating very dilute solutions in a fraction of the computational time required by ‘direct reverse-osmosis’ (D-RO). In this study, we demonstrate the application of this method to concentrate a dilute LiCl solution ( x LiCl = 1.22 × 10 − 3 ) by these two methods MR-RO and D-RO. We validated the optimised method by comparing a wide range of properties obtained from the ‘rigorous’ D-RO method. In this preliminary study we saw a saving of over an order of magnitude in computational time. Even larger savings are possible by increasing the frequency of replication and compression steps. The proposed method thus opens the possibility of using MD for screening studies of potential RO membranes in extremely dilute solutions.

Semi-supervised anomaly detection in dynamic communication networks

Coordinated Path Following of Multiple UAVs for Time-Critical Missions in the Presence of Time-Varying Communication Topologies

Many studies have shown that Vegas TCP has a better throughput and stability than Reno TCP in homogeneous networks with a single TCP flavor, but performs less well in heterogeneous networks in which two TCP flavors coexist. The progressive behavior of Reno TCP and the conservative behavior of Vegas TCP cause a bias when they are used simultaneously, and thus Vegas TCP fails to obtain a fair share of the bandwidth. This paper examines the origins of this bias and proposes a threshold-based congestion control mechanism designed to alleviate the resulting unfairness problem. The simulation results show that the proposed scheme achieves a higher throughput than the conventional Vegas TCP scheme and preserves the stability of the conventional scheme when used in heterogeneous wired and wireless networks.

An important and modern trend in wireless network is managing and accessing in heterogeneous wireless networks structures effectively. Vertical handover or handoff technology is major and acting vital role in wireless communication, it has key challenging issues in wireless network, while handover gets call drop kind of latency and call quality minimization. So the communication networks needs an efficient and dynamic services and knowledge monitoring management to select network for handover of different network environments (example: WiMAX, WiFi, WLAN, etc.). In this paper we proposed the concepts of knowledgeable monitoring (KM-method), cognitive advisor (CA) and Advanced Handover Optimization (AHO) technique to improve effective network selection for seamless communication, while travels over heterogeneous wireless networks (HWN). KM-method monitoring and manage effective network selection and holding connected mobile nodes inform header files also maintaining re-initiate to next network information (network IP address, user ID, new path, etc.). CAVHO-Cognitive Advisor based Vertical Handover (VSH and V2H) and KM-methods perform and measures velocity and direction of mobility nodes through SRSS sequential Received Strength Signal. Also CA receives the nearest networks details of each another using nearest neighbouring concept with SDT ratio Algorithm. Optimization technique (AHO) performs dynamically balancing the threshold level of speed, load and quality based on Receiving signal strength and user preference. Simulation results of CAVHO Shows it secure and increases the handover probability of access also proposed system reduce delay and improve quality of services and throughput.