Initial System Configuration Research Articles

Dynamics of plasma piston composition

The article is devoted to the stratification of plasma formation in the railgun channel. The motion model for a composition of plasma pistons interacting with each other, rails and railgun walls was proposed. It was shown that the maximum impulse that could be transmitted to the throwing body in this system substantially depends on the initial position of the plasma pistons, according to the simulation results. The rational initial system configuration is obtained, at which the maximum value of the momentum transferred to the throwing body is reached. Possible options for obtaining such a configuration and a qualitative model of the stratification of a single plasma formation into several plasma pistons were proposed.

Epidemic outbreaks on two-dimensional quasiperiodic lattices

We present a novel kinetic Monte Carlo technique to study the susceptible-infected-removed model in order to simulate epidemic outbreaks on two quasiperiodic lattices, namely, Penrose and Ammann-Beenker. Our analysis around criticality is performed by investigating the order parameter, which is defined as the probability of growing a spanning cluster formed by removed sites, evolving from an initial system configuration with a single random chosen infective site. This system is studied by means of the cluster size distribution, obtained by the Newman-Ziff algorithm. Additionally, we obtained the mean cluster size, and a cumulant ratio to estimate the epidemic threshold. In spite of the quasiperiodic order moves the transition point, compared to periodic lattices, this is not able to alter the universality class of the model, leading to the same critical exponents. In addition, our technique can be generalized to study epidemic outbreaks in networks and diffusing populations.

All-Atom Molecular Dynamics Simulations of Dimeric Lung Surfactant Protein B in Lipid Multilayers.

Although lung surfactant protein B (SP-B) is an essential protein that plays a crucial role in breathing, the details of its structure and mechanism are not well understood. SP-B forms covalent homodimers, and in this work we use all-atom molecular dynamics simulations to study dimeric SP-B’s structure and its behavior in promoting lipid structural transitions. Four initial system configurations were constructed based on current knowledge of SP-B’s structure and mechanism, and the protein maintained a helicity consistent with experiment in all systems. Several SP-B-induced lipid reorganization behaviors were observed, and regions of the protein particularly important for these activities included SP-B’s “central loop” and “hinge” regions. SP-B dimers with one subunit initially positioned in each of two adjacent bilayers appeared to promote close contact between two bilayers. When both subunits were initially positioned in the same bilayer, SP-B induced the formation of a defect in the bilayer, with water penetrating into the centre of the bilayer. Similarly, dimeric SP-B showed a propensity to interact with preformed interpores in the bilayer. SP-B dimers also promoted bilayer thinning and creasing. This work fleshes out the atomistic details of the dimeric SP-B structures and SP-B/lipid interactions that underlie SP-B’s essential functions.

Determination of the accuracy and reliability of molecular dynamics simulations in estimating the melting point of iron: Roles of interaction potentials and initial system configurations

Molecular dynamics (MD) simulations were carried out to investigate the melting transition of iron with an aim to determine the accuracy and reliability of simulated melting points (MP), computing efficiency, and the role played by initial configurations. Two simulation techniques with equilibrium and non-equilibrium heating, and two well-known potentials: Mendelev (EAM) and Etesami (MEAM) were used to investigate a variety of initial configurations containing perfect crystal solid lattice and solid-liquid (S-L) coexistence regions with a number of S-L interfaces and relative S-L proportions (PC, SLSS-2, SLSS-4, SLSS-2 (20%L) and SLSS-2(80%L)). The simulated magnitude of MPs using the non-equilibrium heating method was found to be ~2020 K, which is about 200 K higher than experimental MP of iron (1811 K). Similar values were obtained for both potentials, PC and SLSS-2 configurations; there was a strong evidence for hysteresis effects as well. Simulations with equilibrium heating technique showed that MPs were found to be identical for the wide range of S-L configurations investigated: Mendelev potential (1769 ± 1 K) and Etesami potential (1811 ± 1 K). Corresponding results from the purely solid PC configurations were found to be much higher (1981 ± 1 K and 1951 ± 1 K respectively). Results on other system properties including pair distribution functions, density, local melting and solidification are also reported. These studies have helped identify optimal simulation parameters, potentials and computational approaches to probe the melting region of iron towards applications to problems of industrial importance.

Creeper: a tool for detecting permission creep in file system access controls

Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources. This is certainly true of file systems whereby information needs to be protected against unintended access. User permissions often evolve over time, and changes are often made in an ad hoc manner and do not follow any rigorous process. This is largely due to the fact that the structure of the implemented permissions are often determined by experts during initial system configuration and documentation is rarely created. Furthermore, permissions are often not audited due to the volume of information, the requirement of expert knowledge, and the time required to perform manual analysis. This paper presents a novel, unsupervised technique whereby a statistical analysis technique is developed and applied to detect instances of permission creep. The system (herein refereed to as Creeper) has initially been developed for Microsoft systems; however, it is easily extensible and can be applied to other access control systems. Experimental analysis has demonstrated good performance and applicability on synthetic file system permissions with an average accuracy of 96%. Empirical analysis is subsequently performed on five real-world systems where an average accuracy of 98% is established.

Hybrid Artificial Intelligence System for the Design of Highly-Automated Production Systems

Abstract The automated design of production systems is a young field of research which has not been widely explored by industry nor research in recent decades. Currently, the effort spent in production system design is increasing significantly in automotive industry due to the number of product variants and product complexity. Intelligent methods can support engineers in repetitive tasks and give them more opportunity to focus on work which requires their core competencies. This paper presents a novel artificial intelligence methodology that automatically generates initial production system configurations based on real industrial scenarios in the automotive field of body-in-white production. The hybrid methodology reacts flexibly against data sets of different content and has been implemented in a software prototype.

Integrated Hybrid Electrochemical and Thermal Metal Hydride Systems for Low-Cost and Efficient High Pressure Hydrogen Compressors

The United States Department of Energy (DOE) has identified three scenarios to transport and delivery hydrogen at large scale [1]. Each of the approaches requires the presence of high pressure hydrogen systems. Currently DOE set its fueling station pressure targets at approximately 875 bar with flow rates up to 100 kg/h [1]. Among the other targets for hydrogen compression systems, DOE identified the uninstalled cost target for the FY 2020 at 275,000 $, the energy requirement at 1.6 kWh/kg, availability equal to 85% and annual maintenance cost equal to 4% of the uninstalled cost[1] [1]. The current mechanical compressors cannot achieve the DOE targets and they have several additional drawbacks working at the specified operating conditions. Valid alternative processes are represented by electrochemical compression (EC) systems and thermal compression systems, exploiting the properties of suitable hydrogen absorption materials. Here, an alternative two-stage hybrid compressor system is proposed, with a first stage (lower pressure) EC, coupled in series with a second stage (higher pressure) metal hydride (MH) thermal compression system. The EC operates at compression ratios on the order of 10-20, reaching pressures of about 100-200 bar. Molecular hydrogen is oxidized at the anode producing protons and electrons. They are driven through the proton exchange membrane and combine with electrons at the cathode to deliver high pressure hydrogen. The outlet pressure is maintained at relatively low values (≤ 100-200 bar) in order to avoid hydrogen back diffusion. The second stage of the system, operating at higher pressures, is comprised of a thermal compression system, based on MH materials. Such compounds absorb hydrogen in an exothermic chemical reaction and release the absorbed hydrogen in the reverse endothermic chemical reaction. Their equilibrium pressure is a direct exponential function of the operating temperature, determined by the Van’t Hoff equation. Therefore, providing high temperature thermal power during the desorption process, the hydrogen pressure can be increased without the use of electricity. The paper presents recent results obtained from the project, funded by the DOE-FCTO, involving Greenway Energy, Savannah River National Laboratory and Sustainable Innovation. A techno-economic model of the hybrid system was developed and adopted to identify the initial baseline system configuration. Several MEA concepts have been examined for the EC, to find the optimized solution to be coupled with the MH system. The baseline system is currently based on Nafion(R) 117 membranes, operating at temperatures of 150 oC and pressures up to 100 bar. Results show suitable voltage and current density values of the EC, reaching adequate technical performance of the EC system and ability to be paired with the MH compressor. Long term tests of the EC system are planned to be run, to assess the performance time degradation of the Nafion(R) membrane at the operating conditions of interest. Specific techno-economic analyses have also been carried out for the MH system, identifying two existing MH material formulations, based on Ti hydrides, as the baseline candidates for the current application. A new finned tube configuration was selected to realize an effective heat exchange between the heat transfer fluid (i.e. water at pressures of 7-7.5 bar) and the MH material. Detailed transport models were developed to simulate the performance of the MH configuration. The adopted solution demonstrated the ability to transfer the heating and cooling (sensible and latent) power required to desorb and absorb hydrogen in the MH system in about 10 minutes for half a cycle. A matching operating point between the EC system and the MH system was also identified to recover the waste heat available from the EC system into the MH system at about 130-150 oC, without any additional external heating power. The system, integrating an electrochemical compressor with a pure thermal compressor, demonstrated the potential to closely approach the DOE 2020 technical targets for high pressure compression.

Free Energy Calculations of Membrane Permeation: Challenges Due to Strong Headgroup-Solute Interactions.

Understanding how different classes of molecules move across biological membranes is a prerequisite to predicting a solute's permeation rate, which is a critical factor in the fields of drug design and pharmacology. We use biased molecular dynamics computer simulations to calculate and compare the free energy profiles of translocation of several small molecules across 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) lipid bilayers as a first step toward determining the most efficient method for free energy calculations. We study the translocation of arginine, a sodium ion, alanine, and a single water molecule using the metadynamics, umbrella sampling, and replica exchange umbrella sampling techniques. Within the fixed lengths of our simulations, we find that all methods produce similar results for charge-neutral permeants, but not for polar or positively charged molecules. We identify the long relaxation time scale of electrostatic interactions between lipid headgroups and the solute to be the principal cause of this difference and show that this slow process can lead to an erroneous dependence of computed free energy profiles on the initial system configuration. We demonstrate the use of committor analysis to validate the proper sampling of the presumed transition state, which in our simulations is achieved only in replica exchange calculations. On the basis of these results we provide some useful guidance to perform and evaluate free energy calculations of membrane permeation.

ABORDAGEM ERGONÔMICA DA MOVIMENTAÇÃO HUMANA, SUA NATUREZA COMPLEXA E ASPECTOS PARA SUA SIMULAÇÃO

No artigo, a movimentação humana, por si só, é apresentada como sendo parte de um sistema ergonômico rico em complexidade. São também incluídos diversos aspectos relevantes envolvidos na movimentação humana, necessários para o desenvolvimento de um modelo computacional. É proposto que esta seja uma modelagem baseada em agentes ergonomicamente situada. Assim, os comportamentos individuais, coletivos e emergentes apresentados na movimentação humana são uma consequência da configuração inicial do sistema, das suas vizinhanças, da auto-organização dos agentes envolvidos e de suas interações locais.

Free Energy Calculation of Membrane Permeation - Simulation Results Suggest Relaxation of Headgroup-Solute Interactions is the Slowest Degree of Freedom

Molecular Dynamics (MD) simulations have been extensively used to investigate membrane-solute interactions. Understanding the interactions associated with solute translocation across lipid bilayers facilitates prediction of passive permeation rates of cell membranes, which is a very important property in the field of drug design and pharmacology. In this work, we use accelerated MD techniques to calculate the free energy of translocation of several small molecules across 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) lipid bilayers as a first step toward understanding the translocation mechanism. We compare the results for the translocation of arginine, a sodium ion, alanine and water as obtained from Metadynamics, Umbrella Sampling and Replica Exchange Umbrella Sampling. Within the fixed length of our simulation, we find that all methods produce comparable results for neutral permeants, but the results differ for polar and positively charged molecules. Using replica exchange umbrella sampling, we identify the difficulty in relaxation of strong electrostatic interactions between lipid headgroups and the solute to be the cause of this difference. Only after extensive equilibration, the artifacts from electrostatic interactions decay, allowing us to calculate the correct free energy profiles of all studied permeants. We show that the true transition state is sampled using replica exchange umbrella sampling. Most importantly, we highlight the large extent to which the results of free energy calculations depend on initial system configurations. Based on our results, we provide some guidance to evaluate the accuracy of free energy profiles that will be helpful to elucidate the mechanism of membrane permeation.

Avoiding dynamic singularities in Cartesian motions of free-floating manipulators

Free-floating manipulators are subject to dynamic singularities that complicate their Cartesian motions and restrict their workspace. In this work, the Cartesian trajectory planning of free-floating manipulators is studied. A methodology is developed in which, for given end-effector trajectories, appropriate initial system configurations are found that result in singularity avoidance during end-effector motion. The method applies to both planar and spatial systems, with and without initial angular momentum, and to any desired end-effector position and attitude trajectories.

Dynamic stepping information process method in mobile bio-sensing computing environments

Recently, the interest toward human longevity free from diseases is being converged as one system frame along with the development of mobile computing environment, diversification of remote medical system and aging society. Such converged system enables implementation of a bioinformatics system created as various supplementary information services by sensing and gathering health conditions and various bio-information of mobile users to set up medical information. The existing bio-information system performs static and identical process without changes after the bio-information process defined at the initial system configuration executes the system. However, such static process indicates ineffective execution in the application of mobile bio-information system performing mobile computing. Especially, an inconvenient duty of having to perform initialization of new definition and execution is accompanied during the process configuration of bio-information system and change of method. This study proposes a dynamic process design and execution method to overcome such ineffective process.

Modeling and Simulating Human Arm Movement Using a 2 Dimensional 3 Segments Coupled Pendulum System

A two dimensional three segments coupled pendulum system that mathematically models human arm configuration was developed along with constructing and solving the equations of motions for this model using the energy (work) based approach of Lagrange. The equations of motion of the model were solved iteratively both as an initial value problem and as a two point boundary value problem. In the initial value problem solutions, both the initial system configuration (segment angles) and initial system velocity (segment angular velocities) were used as inputs, whereas, in the two point boundary value problem solutions initial and final configurations and time were used as inputs to solve for the trajectory of motion. The results suggest that the model solutions are sensitive to small changes in the dynamic forces applied to the system as well as to the initial and boundary conditions used. To overcome the system sensitivity a new approach is suggested.

Video Distribution Techniques Over WiMAX Networks for m-Health Applications

In this paper, we propose a novel approach for video distribution over IEEE 802.16 networks for mobile Healthcare (m-Health) applications. The technique incorporates resource distribution, scheduling, and content-aware video streaming taking advantage of a flexible quality of service functionality offered by IEEE 802.16/WiMAX technology. The proposed technique is thoroughly investigated using network simulator software under various real-life m-Health scenarios, which include streaming video over medium access control layer service connections. It is shown that the technique is fully compatible with the WiMAX standard specification and allows a 9-16% increase in the overall network throughput, which is dependent upon the initial system configuration and the selection of WiMAX user parameters.

Tracking an omnidirectional evader with a differential drive robot

In this paper we consider the surveillance problem of tracking a moving evader by a nonholonomic mobile pursuer. We deal specifically with the situation in which the only constraint on the evader's velocity is a bound on speed (i.e., the evader is able to move omnidirectionally), and the pursuer is a nonholonomic, differential drive system having bounded speed. We formulate our problem as a game. Given the evader's maximum speed, we determine a lower bound for the required pursuer speed to track the evader. This bound allows us to determine at the beginning of the game whether or not the pursuer can follow the evader based on the initial system configuration. We then develop the system model, and obtain optimal motion strategies for both players, which allow us to establish the long term solution for the game. We present an implementation of the system model, and motion strategies, and also present simulation results of the pursuit-evasion game.

Glassiness, rigidity, and jamming of frictionless soft core disks

The jamming of bidisperse soft core disks is considered, using a variety of different protocols to produce the jammed state. In agreement with other works, we find that cooling and compression can lead to a broad range of jamming packing fractions ϕ{J}, depending on cooling rate and initial configuration; the larger the degree of big particle clustering in the initial configuration, the larger will be the value of ϕ{J}. In contrast, we find that shearing disrupts particle clustering, leading to a much narrower range of ϕ{J} as the shear strain rate varies. In the limit of vanishingly small shear strain rate, we find a unique nontrivial value for the jamming density that is independent of the initial system configuration. We conclude that shear driven jamming is a unique and well-defined critical point in the space of shear driven steady states. We clarify the relation between glassy behavior, rigidity, and jamming in such systems and relate our results to recent experiments.

Robust self-stabilizing weight-based clustering algorithm

Ad hoc networks consist of wireless hosts that communicate with each other in the absence of a fixed infrastructure. Such networks cannot rely on centralized and organized network management. The clustering problem consists of partitioning network nodes into non-overlapping groups called clusters. Clusters give a hierarchical organization to the network that facilitates network management and that increases its scalability. In a weight-based clustering algorithm, the clusterheads are selected according to their weight (a node’s parameter). The higher the weight of a node, the more suitable this node is for the role of clusterhead. In ad hoc networks, the amount of bandwidth, memory space or battery power of a node could be used to determine weight values. A self-stabilizing algorithm, regardless of the initial system configuration, converges to legitimate configurations without external intervention. Due to this property, self-stabilizing algorithms tolerate transient faults and they are adaptive to any topology change. In this paper, we present a robust self-stabilizing weight-based clustering algorithm for ad hoc networks. The robustness property guarantees that, starting from an arbitrary configuration, after one asynchronous round, the network is partitioned into clusters. After that, the network stays partitioned during the convergence phase toward a legitimate configuration where the clusters verify the “ad hoc clustering properties”.

Costing RAM design and test analysis model for production facility

The objective of this paper is to provide a model for effective implementation of costing RAM (reliability, availability and maintainability) management in the design and procurement of production facility. This research proposed a two-stem model of costing RAM design and test for production facility. In Step 1, a static model is proposed to find an initial system configuration to meet the required performance based on system RAM and life cycle cost (LCC) and analyze the trade-off relationships between various RAM factors (reliability and maintainability) and LCC. In Step 2, we developed time and failure truncated models for system reliability test and analysis. For computational purposes, we developed computer programs and have shown the sample results. By the sample test run, the proposed model has shown possibilities to provide a good method to analyze system performance evaluation for both design and operational phase. This model can be applied to a wide variety of systems, not only for costing RAM of the production facilities but also for the other kind of equipment.

EVAPRO: economic and financial evaluation of water supply projects

The present paper describes a computer-based system for water supply project appraisal called EVAPRO, standing for EVAluation of water PROjects. The aim of EVAPRO is to facilitate economic and financial assessment of water supply projects under different investment and operating scenarios, and changes to initial system configuration. The software consists of automating the feasibility study of water projects using information about population and water demand forecasts, potential water resources, investment decisions, financial resources and water pricing policy. It embodies a set of tools, including linear programming techniques, numerical methods and financial calculations, and combines operational optimization with financial analysis to assess the feasibility of water supply projects.The software is intended for water production and distribution agencies and aims to assist engineers and decision-makers in water supply project evaluation and feasibility assessment.

Airborne communications node risk reduction strategy

An airborne communications node (ACN) opens up a wide variety of new services for the warfighter. Such a system can provide theater-wide communications and reach-back connectivity to out-of-theater sites through satellite communication links. It could also implement a 'virtual' airborne command and control center (ABCCC) on an unmanned aerial vehicle such as the Global Hawk. To demonstrate some of these capabilities on an unmanned aerial vehicle by the year 2000, L-3 Communications has constructed a system integration lab (SIL) to address the technical issues perceived to be pivotal to a successful ACN implementation. We have developed an open systems approach that is scaleable and fully expandable to include an assortment of candidate communication systems. The initial system configuration includes elements of the Global Hawk integrated communications system, an asynchronous transfer mode (ATM) switch, a communications manager and selected tactical radios. Radio element interface units (REIUs) adapt the personality of each type of radio to the ATM environment and provide the 'plug and play' capability. A multi-level security system allows the hardware to handle data from various sources at different security levels. This paper summarizes our approach to risk reduction and reports on progress to date towards demonstrating the capabilities of an airborne communications node.