Realistic System Model Research Articles

Probing the Active Site Chemistry of Supported Gold Catalysts with Charged Au25 q Nanoclusters (q = -1, 0, +1)

Charged Aun+/− sites are hypothesized as key reaction centers in gold catalysis, but their charge state and mechanistic roles remain controversial. Two examples include CO2 reduction and CO oxidation. Converting CO2 into value-added products is critical for green-house gas mitigation and renewable fuels discovery, and oxidizing CO in the presence of water is central to the industrially important water gas shift reaction (WGS: CO + H2O → CO2 + H2). Debate surrounds the charge state of Au active sites, and variously charged Aun+/0/− species and/or the catalyst-support have all been proposed as reaction centers for CO oxidation and CO2 reduction. We used differently charged Au25 q clusters (q = −1, 0, +1) to precisely identify the role of active site charges in heterogeneous gold catalysis. Au25 q are unique because they have three stable charge states, their crystal structure has been solved, and their small size (~1nm) allows computational modeling of realistic cluster-adsorbate systems. In this regard, Au25 q can serve as well-defined active sites for probing the chemistry of charged catalyst species. Experimental studies and density functional theory identified a relationship between the active site charge, the stability of adsorbed reactants or products and the reaction rate. We found charge-dependent electrocatalytic activity for CO2 reduction, CO oxidation and O2 reduction reactions in aqueous media. Anionic Au25‾ promoted CO2 reduction by stabilizing CO2 + H+ coadsorption. Cationic Au25 + promoted CO oxidation by stabilizing CO + OH− coadsorption. Finally, stronger product adsorption at Au25 + inhibited O2 reduction. These results provide insight into the role of charged active sites and should help guide future catalyst design.

Quantum biology on the edge of quantum chaos.

We give a new explanation for why some biological systems can stay quantum coherent for a long time at room temperature, one of the fundamental puzzles of quantum biology. We show that systems with the right level of complexity between chaos and regularity can increase their coherence time by orders of magnitude. Systems near Critical Quantum Chaos or Metal-Insulator Transition (MIT) can have long coherence times and coherent transport at the same time. The new theory tested in a realistic light harvesting system model can reproduce the scaling of critical fluctuations reported in recent experiments. Scaling of return probability in the FMO light harvesting complex shows the signs of universal return probability decay observed at critical MIT. The results may open up new possibilities to design low loss energy and information transport systems in this Poised Realm hovering reversibly between quantum coherence and classicality.

Three-level coordination in power system stabilization

This paper presents a new methodology for the synthesis of power system stabilizers (PSSs) and speed governors in order to satisfy some recent objectives and constraints imposed by the evolution of large-scale interconnected power systems. As a consequence of the increasing size of these systems, the frequency of some inter-area modes diminishes so much so that these oscillatory phenomena interact with the dynamics of the speed governors. These low-frequency inter-area modes are also more spread (i.e., they involve a larger number of generators) than the other inter-area modes of the system. This two particularities require several supplementary levels of coordination when tuning the PSSs and the governors of the machines involved in these oscillatory phenomena. To ensure this, the synthesis of the aforementioned regulators is done using a new control model which takes into account the key interactions of the dynamics of the power system. It thus allows the coordination of control actions among several generators as well as between the electrical and mechanical paths. This control framework ensures also an optimal trade-off performance/robustness. Validation simulations have been carried out with the Eurostag software on a realistic large-scale model of the interconnected European power system.

Dynamic Modeling and Control of Interleaved Flyback Module-Integrated Converter for PV Power Applications

For photovoltaic applications, the interleaved flyback module-integrated converters (MICs) (IFMICs) operating in continuous conduction mode (CCM) show the advantages of high power density, low voltage and current stresses, and low electromagnetic interference but demonstrate a difficult control problem compared to the discontinuous conduction mode. This paper concentrates on the control issues and presents detailed modeling, in-depth dynamic analysis, and a two-step controller design approach for IFMIC systems operating in CCM. The proposed modeling approach is based on the fourth-order system considering the dynamics of the output CL filter. This realistic fourth-order system modeling shows the presence of a resonant peak at a certain frequency, which can cause phase loss and constraints of system bandwidth. A decoupled two-step controller design approach is thus proposed to simplify the modeling and control synthesis in the IFMIC development. The decoupled controller consists of a proportional-integral controller (based on the simplified model), followed by a lag term for mitigating the effect of the resonant peak. A 200-W digitally controlled MIC prototype is constructed for evaluation purposes. The simulation and experimental results verify the effectiveness of the proposed modeling and control approaches.

Self Organization of Tilts in Relay Enhanced Networks: A Distributed Solution

Despite years of physical-layer research, the capacity enhancement potential of relays is limited by the additional spectrum required for Base Station (BS)-Relay Station (RS) links. This paper presents a novel distributed solution by exploiting a system level perspective instead. Building on a realistic system model with impromptu RS deployments, we develop an analytical framework for tilt optimization that can dynamically maximize spectral efficiency of both the BS-RS and BS-user links in an online manner. To obtain a distributed self-organizing solution, the large scale system-wide optimization problem is decomposed into local small scale subproblems by applying the design principles of self-organization in biological systems. The local subproblems are non-convex, but having a very small scale, can be solved via standard nonlinear optimization techniques such as sequential quadratic programming. The performance of the developed solution is evaluated through extensive simulations for an LTE-A type system and compared against a number of benchmarks including a centralized solution obtained via brute force, that also gives an upper bound to assess the optimality gap. Results show that the proposed solution can enhance average spectral efficiency by up to 50% compared to fixed tilting, with negligible signaling overheads. The key advantage of the proposed solution is its potential for autonomous and distributed implementation.

Selecting and Utilizing Sequential Residual Generators in FDI Applied to Hybrid Vehicles

In order to obtain a realistic model of a complex system, thousands of possible residual generators need to be used for diagnosis. Based on engineering insights of the system to be monitored, certain algebraic and dynamic properties of the residual generators may be preferred, and therefore, a method for finding sequential residual generators is developed that accounts for these properties of the residual generator candidates. It is shown that only a small fraction of all residual generator candidates fulfill fundamental requirements, and thereby, proves the value of systematic methods. Furthermore, methods are devised for utilization of the residual generators, such as initialization of dynamic residual generators. A proposed method, considering the fault excitation in the residuals using the internal form of the residuals, significantly increases the diagnosis performance. A hybrid electric vehicle is used in a simulation study for demonstration, but the methods used are general in character and provides a basis when designing diagnosis systems for other complex systems.

Numerical analysis of stochastic dispersion of micro-particles in turbulent flows in a realistic model of human nasal/upper airway

Turbulent flow field and particle deposition in a realistic model of human upper airway system including: nasal cavity, nasopharynx, oropharynx, larynx and trachea were analyzed numerically. The Lagrangian approach was used to find the trajectories of micron-size particles for the breathing rates of 30, 45 and 60l/min. The continuous phase flow was evaluated using a RANS (Reynolds Average Navier-Stokes) turbulence model and the effect of turbulent fluctuations on particle trajectories was modeled using a continuous random walk (CRW) stochastic model, which is based on the normalized Langevin equation. The total and regional deposition fractions of micro-particles were evaluated and the effect of turbulent fluctuations on the particle deposition rate was investigated.

Exact fluid lumpability in Markovian process algebra

Quantitative analysis by means of discrete-state stochastic processes is hindered by the well-known phenomenon of state-space explosion, whereby the size of the state space may have an exponential growth with the number of agents of the system under scrutiny. When the stochastic process underlies a Markovian process algebra model, this problem may be alleviated by suitable notions of behavioural equivalence that induce lumping at the underlying continuous-time Markov chain, establishing an exact relation between a potentially much smaller aggregated chain and the original one. For the analysis of massively parallel systems, however, lumping techniques may not be sufficient to yield a computationally tractable problem. Recently, much work has been directed towards forms of fluid techniques that provide a set of ordinary differential equations (ODEs) approximating the expected path of the stochastic process. Unfortunately, even fluid models of realistic systems may be too large for feasible analysis. This paper studies a behavioural relation for process algebra with fluid semantics, called projected label equivalence, which is shown to yield an exactly fluid lumpable model, i.e., an aggregated ODE system which can be related to the original one without any loss of information. Project label equivalence relates sequential components of a process term. In general, for any two sequential components that are related in the fluid sense, nothing can be said about their relationship from the stochastic viewpoint. We define and study a notion of well-posedness which allows us to relate fluid lumpability to the stochastic notion of semi-isomorphism, which is a weaker version of the common notion of isomorphism between the doubly labelled transition systems at the basis of the Markovian interpretation.

Effects of Isometric Scaling on Vertical Jumping Performance

Jump height, defined as vertical displacement in the airborne phase, depends on vertical takeoff velocity. For centuries, researchers have speculated on how jump height is affected by body size and many have adhered to what has come to be known as Borelli’s law, which states that jump height does not depend on body size per se. The underlying assumption is that the amount of work produced per kg body mass during the push-off is independent of size. However, if a big body is isometrically downscaled to a small body, the latter requires higher joint angular velocities to achieve a given takeoff velocity and work production will be more impaired by the force-velocity relationship of muscle. In the present study, the effects of pure isometric scaling on vertical jumping performance were investigated using a biologically realistic model of the human musculoskeletal system. The input of the model, muscle stimulation over time, was optimized using jump height as criterion. It was found that when the human model was miniaturized to the size of a mouse lemur, with a mass of about one-thousandth that of a human, jump height dropped from 40 cm to only 6 cm, mainly because of the force-velocity relationship. In reality, mouse lemurs achieve jump heights of about 33 cm. By implication, the unfavourable effects of the small body size of mouse lemurs on jumping performance must be counteracted by favourable effects of morphological and physiological adaptations. The same holds true for other small jumping animals. The simulations for the first time expose and explain the sheer magnitude of the isolated effects of isometric downscaling on jumping performance, to be counteracted by morphological and physiological adaptations.

The solar system between order and chaos

Poincaré’s fertile error reintroduced the oldest open question in dynamical systems: the problem of stability of orbits in the n-body problem. After Poincaré the problem was studied by Birkhoff, Kolmogorov, Arnold and Moser. Laskar, using the secular system introduced by Lagrange, showed that the orbits of the planets in a realistic model of the solar system are chaotic with a Lyapounov exponent of 1/(5 Myrs).

Opportunistic Channel-Aware Spectrum Access for Cognitive Radio Networks with Interleaved Transmission and Sensing

Opportunistic spectrum access in a cognitive radio network has been a challenge due to the dynamic nature of spectrum availability and possible collisions between the primary user (PU) and the secondary user (SU). To maximize the spectrum utilization, we propose a spectrum access strategy where SU's packets are interleaved with periodic sensing to detect PU's return. Similar to earlier works on distributed opportunistic scheduling (DOS), we formulate the sensing/probing/access process as a maximum rate-of-return problem in the optimal stopping theory framework and show that the optimal channel access strategy is a pure threshold policy. We consider a realistic channel and system model by taking into account channel fading and sensing errors. We jointly optimize the rate threshold and the packet transmission time to maximize the average throughput of SU, while limiting interference to PU. Our numerical results show that significant throughput gains can be achieved with the proposed scheme compared to other well-known schemes. Our work sheds light on designing DOS protocols for cognitive radio with optimal transmission time that takes into account the dynamic nature of PUs.

Identifying the Role of Vascular Adaptation in the Genesis of Isolated Systolic Hypertension

Isolated systolic hypertension (ISH) is a chronic human disease characterized by an increase in mean and pulse pressure. This increase is attributed to structural changes that result in an increase in the arterial modulus of elasticity (E) and wall thickness (h), both of which decrease arterial compliance. The causes of ISH have been difficult to identify in human studies because changes in pulse pressure causes a change in compliance, and a change in compliance causes a change in pulse pressure. We therefore employed a realistic human arterial system model to manipulate these processes independently and identify the role of adaptive processes in the genesis of ISH. First, we employed the classical arterial model developed by Westerhof (1968) to determine regional pulsatile pressures from arterial lengths, radii, h and E, and Laplace's law to determine circumferential wall stresses. Then, we assumed that h increases with mean wall stress, and E decreases with pulsatile wall stress. Reported values of pulse pressure, flow, h and E emerged from this complex interaction of hemodynamics and adaptation. Although increases in mean pressure yielded modest increases in pulse pressure and h, it failed to produce an increase in E. The only way to reproduce increases in pulse pressure, h, as well as E was to decrease the sensitivity of the adaptive response of E to pulsatile wall stress—simulating a failure of mechanotransduction.

DE optimized parallel 2-DOF PID controller for load frequency control of power system with governor dead-band nonlinearity

In this paper, design and performance analysis of Differential Evolution (DE) algorithm based parallel 2-Degree Freedom of Proportional-Integral-Derivative (2-DOF PID) controller for Load Frequency Control (LFC) of interconnected power system is presented. A two area thermal system with governor dead-band nonlinearity is considered for the design and analysis purpose. The design problem is formulated as an optimization problem and DE is employed to search for optimal controller parameters. Conventional and modified objective functions are used for the design purpose. Conventional objective functions employed in the paper are Integral of Time multiplied by Squared Error (ITSE) and Integral of Squared Error (ISE). In order to further increase the performance of the controller, a modified objective function is derived using Integral Time multiply Absolute Error (ITAE), damping ratio of dominant eigenvalues, settling times of frequency and peak overshoots with appropriate weight coefficients. The superiority of the proposed approach has been demonstrated by comparing the results with a recently published technique, i.e. Craziness based Particle Swarm Optimization (CPSO) for the same interconnected power system. Further, sensitivity analysis is performed by varying the system parameters and operating load conditions from their nominal values. It is observed that the proposed controllers are quite robust for a wide range of the system parameters and operating load conditions from their nominal values. Finally, the proposed approach is extended to a more realistic power system model by considering the physical constraints such as time delay, reheat turbine, Generation Rate Constraint (GRC) and governor dead band.

1P138 既知遺伝子調節関係に基づいた細胞分化の力学系モデル(09.発生・分化,ポスター,日本生物物理学会年会第51回(2013年度))

1P138 既知遺伝子調節関係に基づいた細胞分化の力学系モデル(09.発生・分化,ポスター,日本生物物理学会年会第51回(2013年度))

Multi-Coaffiliation Networks and Public Health Applications

Infectious diseases are a global concern. The challenge for public health bodies relies upon optimizing the distribution of scarce or costly control measures to maximize their impact on the outbreak dynamics. Risk identification has focused on schools and child-care centers mainly because they represent dense masses of highly immunologically naive hosts for the pathogens. To advance the design of mitigation strategies, epidemiology researchers have broaden their perspective through the use of computational tools designed to provide decision support for multiple scenarios. To identify at-risk populations, we propose a computational algorithm that recreates a realistic social model of the school system of a selected study place. It is a known fact that childhood diseases are spread through the social contacts that occur in the classrooms while schools are in session. Through synthetic reconstruction, the algorithm generates a synthesized population database. The demographic simulations are created at the level of individuals, households and schools. Then a school to school network is built as a representation of the social model. The algorithm outputs a new graph B′, representing the Multi- Coaffiliation Network (MCN) with number of vertices of order O(S), where S represents the number of schools. The resulting weighted network includes a value associated with each school as a possible intervention location. The riskevaluation of the schools in the network can be derived in a wide range of applications in both research and public policy analysis.

Three-dimensional modelling of the venous system by direct multislice helical computed tomography venography: technique, indications and results

The aim of multislice helical computed tomography venography (CTV) is to provide a precise, global and three-dimensional (3D) anatomical depiction of the venous network of the lower limbs. A multislice and multidetector spiral CT acquisition of the lower limbs with contrast injection of the dorsal foot produces about 1000 slices in 30 seconds. Dedicated volume-rendering software can compute a realistic and interactive 3D model of the venous system in realtime. This new tool furnishes an accurate 3D representation of the whole venous system of the lower limb with a realistic 3D model of the limbs, providing a road map of the varicose networks complementary to the duplex ultrasound (DUS). CTV allows a complete morphological study of the deep veins, including the detection of anatomical variations and proximal venous obstruction, not easily detectable by DUS. In the case of deep vein thrombosis, it has been shown to be a good diagnostic tool, well correlated with sonography. It also demonstrates, in some cases, haemodynamic patterns which are not available by DUS, particularly for perforator veins and congenital vascular malformations. The use of virtual reality techniques enables a complete anatomical study of both deep and superficial veins including a virtual dissection of the limbs. CTV is also a great educational tool to learn anatomy of the venous system and a powerful research tool to improve our knowledge of venous anatomy.

A realistic cellular automata model of bus route system based on open boundary

In this article, a cellular automata model under opening boundary condition is proposed to simulate the characteristics of bus route. Through massive numerical simulations, phase diagram is obtained, which consists of four regions, including uniform region, insufficient capability region, bunching region, and serious congestion region. By studying the characteristics of each phase region and comparing the average speed and utilization, it is found that the position in uniform region or bunching region but near to the border of insufficient capability region is the best. Furthermore, phenomena of inhomogeneous bus stop situations are simulated, and resolution of driving shuttle buses is discussed. Comparing the simulation results with the real-life bus route investigation, some similarities are found.

Increasing pulse wave velocity in a realistic cardiovascular model does not increase pulse pressure with age

The mechanism of the well-documented increase in aortic pulse pressure (PP) with age is disputed. Investigators assuming a classical windkessel model believe that increases in PP arise from decreases in total arterial compliance (C(tot)) and increases in total peripheral resistance (R(tot)) with age. Investigators assuming a more sophisticated pulse transmission model believe PP rises because increases in pulse wave velocity (c(ph)) make the reflected pressure wave arrive earlier, augmenting systolic pressure. It has recently been shown, however, that increases in c(ph) do not have a commensurate effect on the timing of the reflected wave. We therefore used a validated, large-scale, human arterial system model that includes realistic pulse wave transmission to determine whether increases in c(ph) cause increased PP with age. First, we made the realistic arterial system model age dependent by altering cardiac output (CO), R(tot), C(tot), and c(ph) to mimic the reported changes in these parameters from age 30 to 70. Then, c(ph) was theoretically maintained constant, while C(tot), R(tot), and CO were altered. The predicted increase in PP with age was similar to the observed increase in PP. In a complementary approach, C(tot), R(tot), and CO were theoretically maintained constant, and c(ph) was increased. The predicted increase in PP was negligible. We found that increases in c(ph) have a limited effect on the timing of the reflected wave but cause the system to degenerate into a windkessel. Changes in PP can therefore be attributed to a decrease in C(tot).

Reliability, redundancy and risk as performance indicators of structural systems during their life-cycle

Structural reliability, redundancy and risk as performance indicators are expected to change over time due to structural deterioration and time-variant loadings. The objective of this paper is to investigate the effects of (a) the deterioration in structural resistance, (b) the type of system modeling, and (c) the correlations among the failure modes of components on the time-dependent reliability, redundancy and risk of structural systems. A representative three-component system is used to demonstrate a general approach for studying these effects. This approach is then applied to an existing highway bridge in Colorado. The bridge is modeled using different types of systems with the consideration of two extreme correlation cases among the failure modes of the girders. An event-tree model is used to assess the direct, indirect, and total risk associated with the failure of component/system due to corrosion and traffic loads. The results reveal the importance of realistic system modeling and time effects in the quantification of reliability, redundancy and risk.

Toward self-describing and workflow integrated Earth system models: A coupled atmosphere-ocean modeling system application

The complexity of Earth system models and their applications is increasing as a consequence of scientific advances, user demand, and the ongoing development of computing platforms, storage systems and distributed high-resolution observation networks. Multi-component Earth system models need to be redesigned to make interactions among model components and other applications external to the modeling system easier. To that end, the common component interfaces of Earth system models can be redesigned to increase interoperability between models and other applications such as various web services, data portals and science gateways. The models can be made self-describing so that the many configuration, build options and inputs of a simulation can be recorded. In this paper, we present a coupled modeling system that includes the proposed methodology to create self-describing models with common model component interfaces. The designed coupled atmosphere-ocean modeling system is also integrated into a scientific workflow system to simplify routine modeling tasks and relationships between these tasks and to demonstrate the enhanced interoperability between different technologies and components. Later on, the work environment is tested using a realistic Earth system modeling application. As can be seen through this example, a layered design for collecting provenance and metadata has the added benefit of documenting a run in far greater detail than before. In this way, it facilitates exploration and understanding of simulations and leads to possible reproducibility. In addition to designing self-describing Earth system models, the regular modeling tasks are also simplified and automated by using a scientific workflow which provides meaningful abstractions for the model, computing environment and provenance/metadata collection mechanisms. Our aim here is to solve a specific instance of a complex model integration problem by using a framework and scientific workflow approach together. The reader may also note that the methods presented in this paper might be also generalized to other types of Earth system models, leading to improved ease of use and flexibility. The initial results also show that the coupled atmosphere-ocean model, which is controlled by the designed workflow environment, is able to reproduce the Mediterranean Sea surface temperature when it is compared with the used CCSM3 initial and boundary conditions.