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Sample records for mechanics modeling based

  1. Quantum Mechanics Based Multiscale Modeling of Materials

    NASA Astrophysics Data System (ADS)

    Lu, Gang

    2013-03-01

    We present two quantum mechanics based multiscale approaches that can simulate extended defects in metals accurately and efficiently. The first approach (QCDFT) can treat multimillion atoms effectively via density functional theory (DFT). The method is an extension of the original quasicontinuum approach with DFT as its sole energetic formulation. The second method (QM/MM) has to do with quantum mechanics/molecular mechanics coupling based on the constrained density functional theory, which provides an exact framework for a self-consistent quantum mechanical embedding. Several important materials problems will be addressed using the multiscale modeling approaches, including hydrogen-assisted cracking in Al, magnetism-controlled dislocation properties in Fe and Si pipe diffusion along Al dislocation core. We acknowledge the support from the Office of Navel Research and the Army Research Office.

  2. Mechanics model for actin-based motility

    NASA Astrophysics Data System (ADS)

    Lin, Yuan

    2009-02-01

    We present here a mechanics model for the force generation by actin polymerization. The possible adhesions between the actin filaments and the load surface, as well as the nucleation and capping of filament tips, are included in this model on top of the well-known elastic Brownian ratchet formulation. A closed form solution is provided from which the force-velocity relationship, summarizing the mechanics of polymerization, can be drawn. Model predictions on the velocity of moving beads driven by actin polymerization are consistent with experiment observations. This model also seems capable of explaining the enhanced actin-based motility of Listeria monocytogenes and beads by the presence of Vasodilator-stimulated phosphoprotein, as observed in recent experiments.

  3. [Model based study of myocardial stimulation mechanisms].

    PubMed

    Weiss, I; Urbaszek, A; Schaldach, M

    1997-01-01

    The present study investigated the mechanisms of electrical stimulation of a myocardial fibre with the aim of developing improved minimally invasive stimulation methods. Using a dynamic myocyte model, the ionic currents crossing the voltage-dependent channels of the membrane are computed. To trigger an action potential, the membrane must first be depolarized to the threshold potential, when further depolarization continues spontaneously through the avalanche-like opening of the sodium channels. For the development of an action potential, not merely the amount of charge injected into the cell during the stimulus is of importance, but an above-threshold magnitude of the stimulation current is also required. The smallest energy required is achieved when the stimulus duration is chosen to be equal to the chronaxie. A second aspect of the study concerned the far-field stimulation of a muscle fibre, achieved by generating a potential gradient along the fibre. First, using a continuous fibre model, the fibre activating function is computed. In a more detailed study, the discrete segmental structure of the fibre determined by the gap junctions is taken into account, and the impact of these junctions on the activating function analysed. By optimizing the electrode configuration, an appropriate activating function results which guarantees successful stimulation when its maximum is above than threshold potential. The most important finding is that the myocardium can be stimulated by floating electrodes, thus opening up new possibilities for a less invasive electro-stimulation of the heart. PMID:9172726

  4. Mechanism-based Modeling of Long-term Degradation

    NASA Technical Reports Server (NTRS)

    McManus, H. L.; Foch, B. J.; Cunningham, R. A.

    1998-01-01

    The use of composites in high temperature, long lifetime applications requires a basic understanding of composite degradation mechanisms, advances in analytical capabilities, and accurate accelerated and scaled tests. To advance all of these goals, models are proposed based on a variety of fundamental material mechanisms. Thermal, oxygen, and moisture diffusion, chemical reactions, composite micromechanics; modified laminated plate theory, and future mechanics based damage models are used. All models attempt to stay as simple and fundamental as possible. All are coupled, so that interactions between various effects are modeled implicitly. Ongoing efforts at MIT are reviewed here, with some reference to other work, but no attempt is made to do a comprehensive review. Mechanism based models are yielding understanding of the mechanisms behind observed degradation phenomena, are helping to design accelerated tests, and are the first steps towards a predictive capability.

  5. Requirements for energy based constitutive modeling in tire mechanics

    NASA Astrophysics Data System (ADS)

    Luchini, John R.; Peters, Jim M.; Mars, Will V.

    1995-08-01

    The history, requirements, and theoretical basis of a new energy based constitutive model for (rubber) material elasticity, hysteresis, and failure are presented. Energy based elasticity is handled by many constitutive models, both in one dimension and in three dimensions. Conversion of mechanical energy to heat can be modeled with viscoelasticity or as structural hysteresis. We are seeking unification of elasticity, hysteresis, and failure mechanisms such as fatigue and wear. An energy state characterization for failure criteria of (rubber) materials may provide this unification and also help explain the interaction of temperature effects with failure mechanisms which are described as creation of growth of internal crack surface. Improved structural modeling of tires with FEM should result from such a unified constitutive theory. The theory will also guide experimental work and should enable better interpretation of the results of computational stress analyses.

  6. Requirements for energy based constitutive modeling in tire mechanics

    NASA Technical Reports Server (NTRS)

    Luchini, John R.; Peters, Jim M.; Mars, Will V.

    1995-01-01

    The history, requirements, and theoretical basis of a new energy based constitutive model for (rubber) material elasticity, hysteresis, and failure are presented. Energy based elasticity is handled by many constitutive models, both in one dimension and in three dimensions. Conversion of mechanical energy to heat can be modeled with viscoelasticity or as structural hysteresis. We are seeking unification of elasticity, hysteresis, and failure mechanisms such as fatigue and wear. An energy state characterization for failure criteria of (rubber) materials may provide this unification and also help explain the interaction of temperature effects with failure mechanisms which are described as creation of growth of internal crack surface. Improved structural modeling of tires with FEM should result from such a unified constitutive theory. The theory will also guide experimental work and should enable better interpretation of the results of computational stress analyses.

  7. A dependency-based modelling mechanism for problem solving

    NASA Technical Reports Server (NTRS)

    London, P.

    1978-01-01

    The paper develops a technique of dependency net modeling which relies on an explicit representation of justifications for beliefs held by the problem solver. Using these justifications, the modeling mechanism is able to determine the relevant lines of inference to pursue during problem solving. Three particular problem-solving difficulties which may be handled by the dependency-based technique are discussed: (1) subgoal violation detection, (2) description binding, and (3) maintaining a consistent world model.

  8. Image-Based Predictive Modeling of Heart Mechanics.

    PubMed

    Wang, V Y; Nielsen, P M F; Nash, M P

    2015-01-01

    Personalized biophysical modeling of the heart is a useful approach for noninvasively analyzing and predicting in vivo cardiac mechanics. Three main developments support this style of analysis: state-of-the-art cardiac imaging technologies, modern computational infrastructure, and advanced mathematical modeling techniques. In vivo measurements of cardiac structure and function can be integrated using sophisticated computational methods to investigate mechanisms of myocardial function and dysfunction, and can aid in clinical diagnosis and developing personalized treatment. In this article, we review the state-of-the-art in cardiac imaging modalities, model-based interpretation of 3D images of cardiac structure and function, and recent advances in modeling that allow personalized predictions of heart mechanics. We discuss how using such image-based modeling frameworks can increase the understanding of the fundamental biophysics behind cardiac mechanics, and assist with diagnosis, surgical guidance, and treatment planning. Addressing the challenges in this field will require a coordinated effort from both the clinical-imaging and modeling communities. We also discuss future directions that can be taken to bridge the gap between basic science and clinical translation. PMID:26643023

  9. Time dependent mechanical modeling for polymers based on network theory

    NASA Astrophysics Data System (ADS)

    Billon, Noëlle

    2016-05-01

    Despite of a lot of attempts during recent years, complex mechanical behaviour of polymers remains incompletely modelled, making industrial design of structures under complex, cyclic and hard loadings not totally reliable. The non linear and dissipative viscoelastic, viscoplastic behaviour of those materials impose to take into account non linear and combined effects of mechanical and thermal phenomena. In this view, a visco-hyperelastic, viscoplastic model, based on network description of the material has recently been developed and designed in a complete thermodynamic frame in order to take into account those main thermo-mechanical couplings. Also, a way to account for coupled effects of strain-rate and temperature was suggested. First experimental validations conducted in the 1D limit on amorphous rubbery like PMMA in isothermal conditions led to pretty goods results. In this paper a more complete formalism is presented and validated in the case of a semi crystalline polymer, a PA66 and a PET (either amorphous or semi crystalline) are used. Protocol for identification of constitutive parameters is described. It is concluded that this new approach should be the route to accurately model thermo-mechanical behaviour of polymers using a reduced number of parameters of some physicl meaning.

  10. A mechanism-based approach to modeling ductile fracture.

    SciTech Connect

    Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III; McFadden, Sam X.

    2004-01-01

    Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential

  11. THE FUTURE OF COMPUTER-BASED TOXICITY PREDICTION: MECHANISM-BASED MODELS VS. INFORMATION MINING APPROACHES

    EPA Science Inventory


    The Future of Computer-Based Toxicity Prediction:
    Mechanism-Based Models vs. Information Mining Approaches

    When we speak of computer-based toxicity prediction, we are generally referring to a broad array of approaches which rely primarily upon chemical structure ...

  12. Dynamic mechanical characterization and modelling of polypropylene based organoclay nanocomposite

    NASA Astrophysics Data System (ADS)

    Wang, Kui; Matadi Boumbimba, Rodrigue; Bahlouli, Nadia; Ahzi, Said; Muller, René

    2015-09-01

    In order to investigate the dynamic behaviour of polypropylene based organoclay nanocomposite, the polypropylene matrix and a master batch of polypropylene modified anhydrid maleic were mixed by means of melt mixing technique. The experimental characterization was performed by using split Hopkinson pressure bars (SHPB), at different strain rates and temperatures. A significant increase of the yield stress of nanocomposite was shown with the present of organoclay, comparing to neat PP. A three-phase approach based on the micromechanical formulation of the cooperative model is proposed to model the yield behaviour of the polymer nanocomposite. Our proposed approach accounts for strain rate and temperature effects as well as the organoclay exfoliation effect. The predictions of models for the nanocomposite yield behaviour showed a good agreement with experimental data.

  13. A stereo model based upon mechanisms of human binocular vision

    NASA Technical Reports Server (NTRS)

    Griswold, N. C.; Yeh, C. P.

    1986-01-01

    A model for stereo vision, which is based on the human-binocular vision system, is proposed. Data collected from studies of neurophysiology of the human binocular system are discussed. An algorithm for the implementation of this stereo vision model is derived. The algorithm is tested on computer-generated and real scene images. Examples of a computer-generated image and a grey-level image are presented. It is noted that the proposed method is computationally efficient for depth perception, and the results indicate accuracies that are noise tolerant.

  14. Simulating tissue mechanics with agent-based models: concepts, perspectives and some novel results

    NASA Astrophysics Data System (ADS)

    Van Liedekerke, P.; Palm, M. M.; Jagiella, N.; Drasdo, D.

    2015-12-01

    In this paper we present an overview of agent-based models that are used to simulate mechanical and physiological phenomena in cells and tissues, and we discuss underlying concepts, limitations, and future perspectives of these models. As the interest in cell and tissue mechanics increase, agent-based models are becoming more common the modeling community. We overview the physical aspects, complexity, shortcomings, and capabilities of the major agent-based model categories: lattice-based models (cellular automata, lattice gas cellular automata, cellular Potts models), off-lattice models (center-based models, deformable cell models, vertex models), and hybrid discrete-continuum models. In this way, we hope to assist future researchers in choosing a model for the phenomenon they want to model and understand. The article also contains some novel results.

  15. Promoting Evidence-Based Practice: Models and Mechanisms from Cross-Sector Review

    ERIC Educational Resources Information Center

    Nutley, Sandra; Walter, Isabel; Davies, Huw T. O.

    2009-01-01

    This article draws on both a cross-sector literature review of mechanisms to promote evidence-based practice and a specific review of ways of improving research use in social care. At the heart of the article is a discussion of three models of evidence-based practice: the research-based practitioner model, the embedded research model, and the…

  16. Mechanism-Based QSAR Modeling of Skin Sensitization.

    PubMed

    Dearden, J C; Hewitt, M; Roberts, D W; Enoch, S J; Rowe, P H; Przybylak, K R; Vaughan-Williams, G D; Smith, M L; Pillai, G G; Katritzky, A R

    2015-10-19

    Many chemicals can induce skin sensitization, and there is a pressing need for non-animal methods to give a quantitative indication of potency. Using two large published data sets of skin sensitizers, we have allocated each sensitizing chemical to one of 10 mechanistic categories and then developed good QSAR models for the seven categories that have a sufficient number of chemicals to allow modeling. Both internal and external validation checks showed that each model had good predictivity. PMID:26382665

  17. Bioinspired model of mechanical energy harvesting based on flexoelectric membranes.

    PubMed

    Rey, Alejandro D; Servio, P; Herrera-Valencia, E E

    2013-02-01

    Membrane flexoelectricity is an electromechanical coupling process that describes membrane electrical polarization due to bending and membrane bending under electric fields. In this paper we propose, formulate, and characterize a mechanical energy harvesting system consisting of a deformable soft flexoelectric thin membrane subjected to harmonic forcing from contacting bulk fluids. The key elements of the energy harvester are formulated and characterized, including (i) the mechanical-to-electrical energy conversion efficiency, (ii) the electromechanical shape equation connecting fluid forces with membrane curvature and electric displacement, and (iii) the electric power generation and efficiency. The energy conversion efficiency is cast as the ratio of flexoelectric coupling to the product of electric and bending elasticity. The device is described by a second-order curvature dynamics coupled to the electric displacement equation and as such results in mechanical power absorption with a resonant peak whose amplitude decreases with bending viscosity. The electric power generation is proportional to the conversion factor and the power efficiency decreases with frequency. Under high bending viscosity, the power efficiency increases with the conversion factor and under low viscosities it decreases with the conversion factor. The theoretical results presented contribute to the ongoing experimental efforts to develop mechanical energy harvesting from fluid flow energy through solid-fluid interactions and electromechanical transduction. PMID:23496533

  18. The Estimation and Control of the Electroslag Remelting Melt Rate by Mechanism-Based Modeling

    NASA Astrophysics Data System (ADS)

    Li, Wanzhou; Wang, Weiyu; Hu, Yuechen; Chen, Yixing

    2012-04-01

    The process control of industrial electroslag remelting production is addressed in this work. This article proposes a mechanism-based model using electrode displacement to estimate the melt rate, designs the remelting process control system, and uses practical application data to verify the validity of the model. The soft measurement of the melt rate based on mechanism modeling is proved to be an economical and reliable solution to the online melt rate estimation and control for large industrial electroslag remelting furnaces.

  19. Finite element based micro-mechanics modeling of textile composites

    NASA Technical Reports Server (NTRS)

    Glaessgen, E. H.; Griffin, O. H., Jr.

    1995-01-01

    Textile composites have the advantage over laminated composites of a significantly greater damage tolerance and resistance to delamination. Currently, a disadvantage of textile composites is the inability to examine the details of the internal response of these materials under load. Traditional approaches to the study fo textile based composite materials neglect many of the geometric details that affect the performance of the material. The present three dimensional analysis, based on the representative volume element (RVE) of a plain weave, allows prediction of the internal details of displacement, strain, stress, and failure quantities. Through this analysis, the effect of geometric and material parameters on the aforementioned quantities are studied.

  20. VISUALIZATION-BASED ANALYSIS FOR A MIXED-INHIBITION BINARY PBPK MODEL: DETERMINATION OF INHIBITION MECHANISM

    EPA Science Inventory

    A physiologically-based pharmacokinetic (PBPK) model incorporating mixed enzyme inhibition was used to determine mechanism of the metabolic interactions occurring during simultaneous inhalation exposures to the organic solvents chloroform and trichloroethylene (TCE).

    V...

  1. A True-Stress Creep Model Based on Deformation Mechanisms for Polycrystalline Materials

    NASA Astrophysics Data System (ADS)

    Wu, Xijia; Williams, Steve; Gong, Diguang

    2012-11-01

    A true-stress creep model has been developed based on well-recognized deformation mechanisms, i.e., dislocation glide, dislocation climb, and grain boundary sliding. The model provides a physics-based description of the entire creep deformation process with regards to the strain-time history (primary, secondary, and tertiary creep), rupture strain and lifetime, which finds good agreement with experimental observations for Waspaloy. A deformation-mechanism map is constructed for Waspaloy, and a creep failure criterion is defined by the dominant deformation mechanisms leading to intergranular/transgranular fracture. Thus, the model is a self-consistent tool for creep life prediction.

  2. Model-based advice for mechanical ventilation: From research (INVENT) to product (Beacon Caresystem).

    PubMed

    Rees, Stephen E; Karbing, Dan S

    2015-01-01

    This paper describes the structure and functionality of a physiological model-based system for providing advice on the settings of mechanical ventilation. Use of the system is presented with examples of patients on support and control modes of mechanical ventilation. PMID:26737495

  3. Modeling the mechanics of graphene-based polymer composite film measured by the bulge test

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Jun; Sun, You-yi; Li, Dian-sen; Cao, Yang; Wang, Zuo; Ma, Jing; Zhao, Gui-Zhe

    2015-10-01

    Graphene-based polymer composite films have wide-ranging potential applications, such as in sensors, electromagnetic shielding, absorbing materials, corrosion resistance and so on. In addition, the practical applications of graphene-based polymer composite films are closely related to their mechanical properties. However, the mechanical properties of graphene-based polymer composite films are difficult to characterize with tensile tests. In this paper, the bugle test was used to investigate the mechanical properties of graphene-based polymer composite films. The experimental results show that the Young’s modulus of polymer composite films increases non-linearly with an increase in the doping content of graphene, and viscoelastic deformation is induced under cyclic loading conditions. Moreover, in order to describe their mechanical behavior, an ‘Arruda-Boyce’ finite-strain constitutive model (modified BPA model), based on the strain amplification hypothesis, and a traditional ‘Arruda-Boyce’ model was proposed, which incorporated many of the features of previous theories. The numerical treatment of the modified BPA model associated with finite element analysis is also discussed. This new model is shown to be able to predict the experimentally observed mechanical behavior of graphene based polymer composite films measured by the bugle test effectively.

  4. Shape memory behavior of epoxy-based model materials: Tailoring approaches and thermo-mechanical modeling

    NASA Astrophysics Data System (ADS)

    Pandini, Stefano; Avanzini, Andrea; Battini, Davide; Berardi, Mario; Baldi, Francesco; Bignotti, Fabio

    2016-05-01

    A series of structurally related epoxy resins were prepared as model systems for the investigation of the shape memory response, with the aim to assess the possibility of tailoring their thermo-mechanical response and conveniently describing their strain evolution under triggering stimuli with a simple thermoviscoelastic model. The resins formulation was varied in order to obtain systems with controlled glass transition temperature and crosslink density. The shape memory response was investigated by means of properly designed thermo-mechanical cycles, which allowed to measure both the ability to fully recover the applied strain and to exert a stress on a confining medium. The results were also compared with the predictions obtained by finite element simulations of the thermo-mechanical cycle by the employ of a model whose parameters were implemented from classical DMA analysis.

  5. The mechanical properties of a cell-based numerical model of epithelium.

    PubMed

    Merzouki, Aziza; Malaspinas, Orestis; Chopard, Bastien

    2016-05-25

    In this work we use a computational cell-based model to study the influence of the mechanical properties of cells on the mechanics of epithelial tissues. We analyze the effect of the model parameters on the elasticity and the mechanical response of tissues subjected to stress loading application. We compare our numerical results with experimental measurements of epithelial cell monolayer mechanics. Unlike previous studies, we have been able to estimate in physical units the parameter values that match the experimental results. A key observation is that the model parameters must vary with the tissue strain. In particular, it was found that, while the perimeter contractility and the area elasticity of cells remain constant at lower strains (<20%), they must increase to respond to larger strains (>20%). However, above a threshold of 50% extension, the cells stop counteracting the tissue strain and reduce both their perimeter contractility and area elasticity. PMID:27139927

  6. Clearance mechanism assignment and total clearance prediction in human based upon in silico models.

    PubMed

    Lombardo, Franco; Obach, R Scott; Varma, Manthena V; Stringer, Rowan; Berellini, Giuliano

    2014-05-22

    We introduce a two-tier model based on an exhaustive data set, where discriminant models based on principal component analysis (PCA) and partial least squares (PLS) are used separately and in conjunction, and we show that PCA is highly discriminant approaching 95% accuracy in the assignment of the primary clearance mechanism. Furthermore, the PLS model achieved a quantitative predictive performance comparable to methods based on scaling of animal data while not requiring the use of either in vivo or in vitro data, thus sparing the use of animal. This is likely the highest performance that can be expected from a computational approach, and further improvements may be difficult to reach. We further offer the medicinal scientist a PCA model to guide in vitro and/or in vivo studies to help limit the use of resources via very rapid computations. PMID:24773013

  7. Model-Based Fatigue Prognosis of Fiber-Reinforced Laminates Exhibiting Concurrent Damage Mechanisms

    NASA Technical Reports Server (NTRS)

    Corbetta, M.; Sbarufatti, C.; Saxena, A.; Giglio, M.; Goebel, K.

    2016-01-01

    Prognostics of large composite structures is a topic of increasing interest in the field of structural health monitoring for aerospace, civil, and mechanical systems. Along with recent advancements in real-time structural health data acquisition and processing for damage detection and characterization, model-based stochastic methods for life prediction are showing promising results in the literature. Among various model-based approaches, particle-filtering algorithms are particularly capable in coping with uncertainties associated with the process. These include uncertainties about information on the damage extent and the inherent uncertainties of the damage propagation process. Some efforts have shown successful applications of particle filtering-based frameworks for predicting the matrix crack evolution and structural stiffness degradation caused by repetitive fatigue loads. Effects of other damage modes such as delamination, however, are not incorporated in these works. It is well established that delamination and matrix cracks not only co-exist in most laminate structures during the fatigue degradation process but also affect each other's progression. Furthermore, delamination significantly alters the stress-state in the laminates and accelerates the material degradation leading to catastrophic failure. Therefore, the work presented herein proposes a particle filtering-based framework for predicting a structure's remaining useful life with consideration of multiple co-existing damage-mechanisms. The framework uses an energy-based model from the composite modeling literature. The multiple damage-mode model has been shown to suitably estimate the energy release rate of cross-ply laminates as affected by matrix cracks and delamination modes. The model is also able to estimate the reduction in stiffness of the damaged laminate. This information is then used in the algorithms for life prediction capabilities. First, a brief summary of the energy-based damage model

  8. A numerical study of the left ventricle using structure-based bio-mechanical model

    NASA Astrophysics Data System (ADS)

    Zhu, Yunfei; Luo, Xiaoyu; Feng, Yaoqi

    A numerical study of the left ventricle using structure-based bio-mechanical model In space environment, microgravity and radiation can have deleterious effects on the cardiovascular system of the astronauts. The work in this paper is part of an ongoing effort to use mathematical models to provide a better understanding of the impact of long-duration spaceflight on the heart and blood vessels. In this study, we develop a computational left ventricle model before and after myocardium infarction based on cardiovascular mechanical theory. The anatomically realistic model has a rule-based fibre structure and a orthotropic structure-based constitutive model. The differences of deformations in the left ventricle before and after infarction are compared in details. In particular, the effects of fiber direction and fiber dispersion are examined. The disarray of both the fiber and sheet orientation is characterized by a dispersion parameter. The left ventricle volume is calculated from the MRI images and used for the optimization of the parameters of the myocardium. We provide the numerical framework for further study on effects of spaceflight on the cardiovascular system.

  9. Surrogate-based modeling and dimension reduction techniques for multi-scale mechanics problems

    NASA Astrophysics Data System (ADS)

    Shyy, Wei; Cho, Young-Chang; Du, Wenbo; Gupta, Amit; Tseng, Chien-Chou; Sastry, Ann Marie

    2011-12-01

    Successful modeling and/or design of engineering systems often requires one to address the impact of multiple "design variables" on the prescribed outcome. There are often multiple, competing objectives based on which we assess the outcome of optimization. Since accurate, high fidelity models are typically time consuming and computationally expensive, comprehensive evaluations can be conducted only if an efficient framework is available. Furthermore, informed decisions of the model/hardware's overall performance rely on an adequate understanding of the global, not local, sensitivity of the individual design variables on the objectives. The surrogate-based approach, which involves approximating the objectives as continuous functions of design variables from limited data, offers a rational framework to reduce the number of important input variables, i.e., the dimension of a design or modeling space. In this paper, we review the fundamental issues that arise in surrogate-based analysis and optimization, highlighting concepts, methods, techniques, as well as modeling implications for mechanics problems. To aid the discussions of the issues involved, we summarize recent efforts in investigating cryogenic cavitating flows, active flow control based on dielectric barrier discharge concepts, and lithium (Li)-ion batteries. It is also stressed that many multi-scale mechanics problems can naturally benefit from the surrogate approach for "scale bridging."

  10. Dislocation Density-Based Constitutive Model for the Mechanical Behavior of Irradiated Cu

    SciTech Connect

    Arsenlis, A; Wirth, B D; Rhee, M

    2003-04-10

    Performance degradation of structural steels in nuclear environments results from the development of a high number density of nanometer scale defects. The defects observed in copper-based alloys are composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops, which impede dislocation glide and are evidenced in macroscopic uniaxial stress-strain curves as increased yield strengths, decreased total strain to failure, decreased work hardening and the appearance of a distinct upper yield point above a critical defect concentration (neutron dose). In this paper, we describe the development of an internal state variable model for the mechanical behavior of materials subject to these environments. This model has been developed within an information-passing multiscale materials modeling framework, in which molecular dynamics simulations of dislocation--radiation defect interactions, inform the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for radiation defect density evolution with dislocation interaction. The general behavior of the constitutive (single material point) model shows that as the defect density increases, the initial yield point increases and the initial strain hardening decreases. The final coarse-grained model is implemented into a finite element framework and used to simulate the behavior of tensile specimens with varying levels of irradiation induced material damage. The simulation results compare favorably with the experimentally observed mechanical properties of irradiated materials in terms of their increased strength, decreased hardening, and decreased ductility with increasing irradiation dose.

  11. A biophysically based mathematical model for the catalytic mechanism of glutathione reductase.

    PubMed

    Pannala, Venkat R; Bazil, Jason N; Camara, Amadou K S; Dash, Ranjan K

    2013-12-01

    Glutathione reductase (GR) catalyzes the reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH) using NADPH as the reducing cofactor, and thereby maintains a constant GSH level in the system. GSH scavenges superoxide (O2(*-)) and hydroxyl radicals (OH) nonenzymatically or by serving as an electron donor to several enzymes involved in reactive oxygen species (ROS) detoxification. In either case, GSH oxidizes to GSSG and is subsequently regenerated by the catalytic action of GR. Although the GR kinetic mechanism has been extensively studied under various experimental conditions with variable substrates and products, the catalytic mechanism has not been studied in terms of a mechanistic model that accounts for the effects of the substrates and products on the reaction kinetics. The aim of this study is therefore to develop a comprehensive mathematical model for the catalytic mechanism of GR. We use available experimental data on GR kinetics from various species/sources to develop the mathematical model and estimate the associated model parameters. The model simulations are consistent with the experimental observation that GR operates via both ping-pong and sequential branching mechanisms based on relevant concentrations of its reaction substrate GSSG. Furthermore, we show the observed pH-dependent substrate inhibition of GR activity by GSSG and bimodal behavior of GR activity with pH. The model presents a unique opportunity to understand the effects of products on the kinetics of GR. The model simulations show that under physiological conditions, where both substrates and products are present, the flux distribution depends on the concentrations of both GSSG and NADP(+), with ping-pong flux operating at low levels and sequential flux dominating at higher levels. The kinetic model of GR may serve as a key module for the development of integrated models for ROS-scavenging systems to understand protection of cells under normal and oxidative stress

  12. Nonlocal continuum-based modeling of mechanical characteristics of nanoscopic structures

    NASA Astrophysics Data System (ADS)

    Rafii-Tabar, Hashem; Ghavanloo, Esmaeal; Fazelzadeh, S. Ahmad

    2016-06-01

    Insight into the mechanical characteristics of nanoscopic structures is of fundamental interest and indeed poses a great challenge to the research communities around the world. These structures are ultra fine in size and consequently performing standard experiments to measure their various properties is an extremely difficult and expensive endeavor. Hence, to predict the mechanical characteristics of the nanoscopic structures, different theoretical models, numerical modeling techniques, and computer-based simulation methods have been developed. Among several proposed approaches, the nonlocal continuum-based modeling is of particular significance because the results obtained from this modeling for different nanoscopic structures are in very good agreement with the data obtained from both experimental and atomistic-based studies. A review of the essentials of this model together with its applications is presented here. Our paper is a self contained presentation of the nonlocal elasticity theory and contains the analysis of the recent works employing this model within the field of nanoscopic structures. In this review, the concepts from both the classical (local) and the nonlocal elasticity theories are presented and their applications to static and dynamic behavior of nanoscopic structures with various morphologies are discussed. We first introduce the various nanoscopic structures, both carbon-based and non carbon-based types, and then after a brief review of the definitions and concepts from classical elasticity theory, and the basic assumptions underlying size-dependent continuum theories, the mathematical details of the nonlocal elasticity theory are presented. A comprehensive discussion on the nonlocal version of the beam, the plate and the shell theories that are employed in modeling of the mechanical properties and behavior of nanoscopic structures is then provided. Next, an overview of the current literature discussing the application of the nonlocal models

  13. Models of dark matter halos based on statistical mechanics: The classical King model

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri; Lemou, Mohammed; Méhats, Florian

    2015-03-01

    We consider the possibility that dark matter halos are described by the Fermi-Dirac distribution at finite temperature. This is the case if dark matter is a self-gravitating quantum gas made of massive neutrinos at statistical equilibrium. This is also the case if dark matter can be treated as a self-gravitating collisionless gas experiencing Lynden-Bell's type of violent relaxation. In order to avoid the infinite mass problem and carry out a rigorous stability analysis, we consider the fermionic King model. In this paper, we study the nondegenerate limit leading to the classical King model. This model was initially introduced to describe globular clusters. We propose to apply it also to large dark matter halos where quantum effects are negligible. We determine the caloric curve and study the thermodynamical stability of the different configurations. Equilibrium states exist only above a critical energy Ec in the microcanonical ensemble and only above a critical temperature Tc in the canonical ensemble. For E model to the observations of large dark matter halos. Because of collisions and evaporation, the central density increases while the slope of the halo density profile decreases until an instability takes place. We show that large dark matter halos are relatively well described by the King model at, or close to, the point of marginal microcanonical stability. At that point, the King model generates a density profile that can be approximated by the modified Hubble profile. This profile has a flat core and decreases as r-3 at large distances, like the observational Burkert profile. Less steep halos are unstable. For large halos, the flat core is due to finite temperature effects, not to quantum mechanics. We argue that statistical

  14. A Micro-Mechanically Based Continuum Model for Strain-Induced Crystallization in Natural Rubber

    NASA Astrophysics Data System (ADS)

    Mistry, Sunny Jigger

    Recent experimental results show that strain-induced crystallization can substantially improve the crack growth resistance of natural rubber. While this might suggest superior designs of tires or other industrial applications where elastomers are used, a more thorough understanding of the underlying physics of strain-induced crystallization in natural rubber has to be developed before any design process can be started. The objective of this work is to develop a computationally-accessible micro-mechanically based continuum model, which is able to predict the macroscopic behavior of strain crystallizing natural rubber. While several researchers have developed micro-mechanical models of partially crystallized polymer chains, their results mainly give qualitative agreement with experimental data due to a lack of good micro-macro transition theories or the lack of computational power. However, recent developments in multiscale modeling in polymers provide new tools to continue this early work. In this thesis, a new model is proposed to model strain-induced crystallization in natural rubber. To this end, a micro-mechanical model of a constrained partially crystallized polymer chain with an extended-chain crystal is derived and connected to the macroscopic level using the non-affine micro-sphere model. On the macroscopic level, a thermodynamically consistent framework for strain-crystallizing materials is developed, and a description of the crystallization kinetics is introduced. For that matter, an evolution law for crystallization based on the gradient of the macroscopic Helmholtz free energy function (chemical potential) in combination with a simple threshold function is used. A numerical implementation of the model is proposed and its predictive performance assessed using published data.

  15. The Physical-Mechanism Based High-Temperature Thermal Contact Conductance Model with Experimental Verification

    NASA Astrophysics Data System (ADS)

    Liu, Dong-Huan; Shang, Xin-Chun

    2013-03-01

    The physical-mechanism based high-temperature thermal contact conductance model is proposed, in which the temperature effect on the material properties and interface radiation effect are considered. A testing platform of high temperature thermal contact conductance is also established, and the thermal contact conductance between three-dimensional braid C/C composite material and superalloy GH600 is tested under different interface roughness and temperatures. Experimental results verify the rationality of the present model. Results also show that it is necessary to take the effect of temperature into account especially at high temperatures, and the interface radiation effect is negligible compared to spot conduction under 850 K.

  16. Identifying significant covariates for anti-HIV treatment response: mechanism-based differential equation models and empirical semiparametric regression models.

    PubMed

    Huang, Yangxin; Liang, Hua; Wu, Hulin

    2008-10-15

    In this paper, the mechanism-based ordinary differential equation (ODE) model and the flexible semiparametric regression model are employed to identify the significant covariates for antiretroviral response in AIDS clinical trials. We consider the treatment effect as a function of three factors (or covariates) including pharmacokinetics, drug adherence and susceptibility. Both clinical and simulated data examples are given to illustrate these two different kinds of modeling approaches. We found that the ODE model is more powerful to model the mechanism-based nonlinear relationship between treatment effects and virological response biomarkers. The ODE model is also better in identifying the significant factors for virological response, although it is slightly liberal and there is a trend to include more factors (or covariates) in the model. The semiparametric mixed-effects regression model is very flexible to fit the virological response data, but it is too liberal to identify correct factors for the virological response; sometimes it may miss the correct factors. The ODE model is also biologically justifiable and good for predictions and simulations for various biological scenarios. The limitations of the ODE models include the high cost of computation and the requirement of biological assumptions that sometimes may not be easy to validate. The methodologies reviewed in this paper are also generally applicable to studies of other viruses such as hepatitis B virus or hepatitis C virus. PMID:18407583

  17. A quantum mechanics-based approach to model incident-induced dynamic driver behavior

    NASA Astrophysics Data System (ADS)

    Sheu, Jiuh-Biing

    2008-08-01

    A better understanding of the psychological factors influencing drivers, and the resulting driving behavior responding to incident-induced lane traffic phenomena while passing by an incident site is vital to the improvement of road safety. This paper presents a microscopic driver behavior model to explain the dynamics of the instantaneous driver decision process under lane-blocking incidents on adjacent lanes. The proposed conceptual framework decomposes the corresponding driver decision process into three sequential phases: (1) initial stimulus, (2) glancing-around car-following, and (3) incident-induced driving behavior. The theorem of quantum mechanics in optical flows is applied in the first phase to explain the motion-related perceptual phenomena while vehicles approach the incident site in adjacent lanes, followed by the incorporation of the effect of quantum optical flows in modeling the induced glancing-around car-following behavior in the second phase. Then, an incident-induced driving behavior model is formulated to reproduce the dynamics of driver behavior conducted in the process of passing by an incident site in the adjacent lanes. Numerical results of model tests using video-based incident data indicate the validity of the proposed traffic behavior model in analyzing the incident-induced lane traffic phenomena. It is also expected that such a proposed quantum-mechanics based methodology can throw more light if applied to driver psychology and response in anomalous traffic environments in order to improve road safety.

  18. The research Of Multilayer Thermal Insulation With Mechanical Properties Based On Model Analysis Test

    NASA Astrophysics Data System (ADS)

    Lianhua, Yin

    The heat shield of aircraft is made of the major thrusts structure with multilayer thermal insulation part. For protecting against thermo-radiation from larger thrusting force engine,the heat shield is installed around this engine nearby.The multilayer thermal insulation part with multilayer radiation/reflection structure is made of reflection layer and interval layer.At vacuum condition,these materials is higher heat insulation capability than other material,is applied for lots of pats on aircraft extensively.But because of these material is made of metal and nonmetal,it is impossible to receive it's mechanical properties of materials from mechanical tests.These paper describes a new measure of mechanical properties of materials in the heat shield based on model analysis test.At the requirement for the first order lateral frequency,these measure provide for the FEM analysis foundation on the optimization structure of the heat shield.

  19. Simulation based estimation of dynamic mechanical properties for viscoelastic materials used for vocal fold models

    NASA Astrophysics Data System (ADS)

    Rupitsch, Stefan J.; Ilg, Jürgen; Sutor, Alexander; Lerch, Reinhard; Döllinger, Michael

    2011-08-01

    In order to obtain a deeper understanding of the human phonation process and the mechanisms generating sound, realistic setups are built up containing artificial vocal folds. Usually, these vocal folds consist of viscoelastic materials (e.g., polyurethane mixtures). Reliable simulation based studies on the setups require the mechanical properties of the utilized viscoelastic materials. The aim of this work is the identification of mechanical material parameters (Young's modulus, Poisson's ratio, and loss factor) for those materials. Therefore, we suggest a low-cost measurement setup, the so-called vibration transmission analyzer (VTA) enabling to analyze the transfer behavior of viscoelastic materials for propagating mechanical waves. With the aid of a mathematical Inverse Method, the material parameters are adjusted in a convenient way so that the simulation results coincide with the measurement results for the transfer behavior. Contrary to other works, we determine frequency dependent functions for the mechanical properties characterizing the viscoelastic material in the frequency range of human speech (100-250 Hz). The results for three different materials clearly show that the Poisson's ratio is close to 0.5 and that the Young's modulus increases with higher frequencies. For a frequency of 400 Hz, the Young's modulus of the investigated viscoelastic materials is approximately 80% higher than for the static case (0 Hz). We verify the identified mechanical properties with experiments on fabricated vocal fold models. Thereby, only small deviations between measurements and simulations occur.

  20. Models of dark matter halos based on statistical mechanics: The fermionic King model

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri; Lemou, Mohammed; Méhats, Florian

    2015-12-01

    We discuss the nature of phase transitions in the fermionic King model which describes tidally truncated quantum self-gravitating systems. This distribution function takes into account the escape of high-energy particles and has a finite mass. On the other hand, the Pauli exclusion principle puts an upper bound on the phase-space density of the system and stabilizes it against gravitational collapse. As a result, there exists a statistical equilibrium state for all accessible values of energy and temperature. We plot the caloric curves and investigate the nature of phase transitions as a function of the degeneracy parameter in both microcanonical and canonical ensembles, extending the work of Chavanis [Int. J. Mod. Phys. B 20, 3113 (2006)] for box-confined configurations. We consider stable and metastable states and emphasize the importance of the latter for systems with long-range interactions. Phase transitions can take place between a "gaseous" phase unaffected by quantum mechanics and a "condensed" phase dominated by quantum mechanics. The phase diagram exhibits two critical points, one in each ensemble, beyond which the phase transitions disappear. There also exists a region of negative specific heats and a situation of ensemble inequivalence for sufficiently large systems. In the microcanonical ensemble, gravitational collapse (gravothermal catastrophe) results in the formation of a small degenerate object containing a small mass. This is accompanied by the expulsion of a hot envelope containing a large mass. In the canonical ensemble, gravitational collapse (isothermal collapse) leads to a small degenerate object containing almost all the mass. It is surrounded by a tenuous envelope. We apply the fermionic King model to the case of dark matter halos made of massive neutrinos following the work of de Vega, Salucci, and Sanchez [Mon. Not. R. Astron. Soc. 442, 2717 (2014)]. The gaseous phase describes large halos and the condensed phase describes dwarf halos

  1. A hierarchical lattice spring model to simulate the mechanics of 2-D materials-based composites

    NASA Astrophysics Data System (ADS)

    Brely, Lucas; Bosia, Federico; Pugno, Nicola

    2015-07-01

    In the field of engineering materials, strength and toughness are typically two mutually exclusive properties. Structural biological materials such as bone, tendon or dentin have resolved this conflict and show unprecedented damage tolerance, toughness and strength levels. The common feature of these materials is their hierarchical heterogeneous structure, which contributes to increased energy dissipation before failure occurring at different scale levels. These structural properties are the key to exceptional bioinspired material mechanical properties, in particular for nanocomposites. Here, we develop a numerical model in order to simulate the mechanisms involved in damage progression and energy dissipation at different size scales in nano- and macro-composites, which depend both on the heterogeneity of the material and on the type of hierarchical structure. Both these aspects have been incorporated into a 2-dimensional model based on a Lattice Spring Model, accounting for geometrical nonlinearities and including statistically-based fracture phenomena. The model has been validated by comparing numerical results to continuum and fracture mechanics results as well as finite elements simulations, and then employed to study how structural aspects impact on hierarchical composite material properties. Results obtained with the numerical code highlight the dependence of stress distributions on matrix properties and reinforcement dispersion, geometry and properties, and how failure of sacrificial elements is directly involved in the damage tolerance of the material. Thanks to the rapidly developing field of nanocomposite manufacture, it is already possible to artificially create materials with multi-scale hierarchical reinforcements. The developed code could be a valuable support in the design and optimization of these advanced materials, drawing inspiration and going beyond biological materials with exceptional mechanical properties.

  2. Semi-Mechanism-Based Population Pharmacokinetic Modeling of the Hedgehog Pathway Inhibitor Vismodegib.

    PubMed

    Lu, T; Wang, B; Gao, Y; Dresser, M; Graham, R A; Jin, J Y

    2015-11-01

    Vismodegib, approved for the treatment of advanced basal cell carcinoma, has shown unique pharmacokinetic (PK) nonlinearity and binding to α1-acid glycoprotein (AAG) in humans. A semi-mechanism-based population pharmacokinetic (PopPK) model was developed from a meta-dataset of 225 subjects enrolled in five clinical studies to quantitatively describe the clinical PK of vismodegib and identify sources of interindividual variability. Total and unbound vismodegib were analyzed simultaneously, together with time-varying AAG data. The PK of vismodegib was adequately described by a one-compartment model with first-order absorption, first-order elimination of unbound drug, and saturable binding to AAG with fast-equilibrium. The variability of total vismodegib concentration at steady-state was predominantly explained by the range of AAG level. The impact of AAG on unbound concentration was clinically insignificant. Various approaches were evaluated for model validation. The semi-mechanism-based PopPK model described herein provided insightful information on the nonlinear PK and has been utilized for various clinical applications. PMID:26783504

  3. Structure-Based Statistical Mechanical Model Accounts for the Causality and Energetics of Allosteric Communication

    PubMed Central

    Guarnera, Enrico; Berezovsky, Igor N.

    2016-01-01

    Allostery is one of the pervasive mechanisms through which proteins in living systems carry out enzymatic activity, cell signaling, and metabolism control. Effective modeling of the protein function regulation requires a synthesis of the thermodynamic and structural views of allostery. We present here a structure-based statistical mechanical model of allostery, allowing one to observe causality of communication between regulatory and functional sites, and to estimate per residue free energy changes. Based on the consideration of ligand free and ligand bound systems in the context of a harmonic model, corresponding sets of characteristic normal modes are obtained and used as inputs for an allosteric potential. This potential quantifies the mean work exerted on a residue due to the local motion of its neighbors. Subsequently, in a statistical mechanical framework the entropic contribution to allosteric free energy of a residue is directly calculated from the comparison of conformational ensembles in the ligand free and ligand bound systems. As a result, this method provides a systematic approach for analyzing the energetics of allosteric communication based on a single structure. The feasibility of the approach was tested on a variety of allosteric proteins, heterogeneous in terms of size, topology and degree of oligomerization. The allosteric free energy calculations show the diversity of ways and complexity of scenarios existing in the phenomenology of allosteric causality and communication. The presented model is a step forward in developing the computational techniques aimed at detecting allosteric sites and obtaining the discriminative power between agonistic and antagonistic effectors, which are among the major goals in allosteric drug design. PMID:26939022

  4. Structure-Based Statistical Mechanical Model Accounts for the Causality and Energetics of Allosteric Communication.

    PubMed

    Guarnera, Enrico; Berezovsky, Igor N

    2016-03-01

    Allostery is one of the pervasive mechanisms through which proteins in living systems carry out enzymatic activity, cell signaling, and metabolism control. Effective modeling of the protein function regulation requires a synthesis of the thermodynamic and structural views of allostery. We present here a structure-based statistical mechanical model of allostery, allowing one to observe causality of communication between regulatory and functional sites, and to estimate per residue free energy changes. Based on the consideration of ligand free and ligand bound systems in the context of a harmonic model, corresponding sets of characteristic normal modes are obtained and used as inputs for an allosteric potential. This potential quantifies the mean work exerted on a residue due to the local motion of its neighbors. Subsequently, in a statistical mechanical framework the entropic contribution to allosteric free energy of a residue is directly calculated from the comparison of conformational ensembles in the ligand free and ligand bound systems. As a result, this method provides a systematic approach for analyzing the energetics of allosteric communication based on a single structure. The feasibility of the approach was tested on a variety of allosteric proteins, heterogeneous in terms of size, topology and degree of oligomerization. The allosteric free energy calculations show the diversity of ways and complexity of scenarios existing in the phenomenology of allosteric causality and communication. The presented model is a step forward in developing the computational techniques aimed at detecting allosteric sites and obtaining the discriminative power between agonistic and antagonistic effectors, which are among the major goals in allosteric drug design. PMID:26939022

  5. Scapholunate ligament injury adversely alters in vivo wrist joint mechanics: an MRI-based modeling study.

    PubMed

    Johnson, Joshua E; Lee, Phil; McIff, Terence E; Toby, E Bruce; Fischer, Kenneth J

    2013-09-01

    We investigated the effects of scapholunate ligament injury on in vivo radiocarpal joint mechanics using image-based surface contact modeling. Magnetic resonance images of 10 injured and contralateral normal wrists were acquired at high resolution (hand relaxed) and during functional grasp. Three-dimensional surface models of the radioscaphoid and radiolunate articulations were constructed from the relaxed images, and image registration between the relaxed and grasp images provided kinematics. The displacement driven models were implemented in contact modeling software. Contact parameters were determined from interpenetration of interacting bodies and a linear contact rule. Peak and mean contact pressures, contact forces and contact areas were compared between the normal and injured wrists. Also measured were effective (direct) contact areas and intercentroid distances from the grasp images. Means of the model contact areas were within 10 mm(2) of the direct contact areas for both articulations. With injury, all contact parameters significantly increased in the radioscaphoid articulation, while only peak contact pressure and contact force significantly increased in the radiolunate articulation. Intercentroid distances also increased significantly with injury. This study provides novel in vivo contact mechanics data from scapholunate ligament injury and confirms detrimental alterations as a result of injury. PMID:23575966

  6. The Impacts of Information-Sharing Mechanisms on Spatial Market Formation Based on Agent-Based Modeling

    PubMed Central

    Li, Qianqian; Yang, Tao; Zhao, Erbo; Xia, Xing’ang; Han, Zhangang

    2013-01-01

    There has been an increasing interest in the geographic aspects of economic development, exemplified by P. Krugman’s logical analysis. We show in this paper that the geographic aspects of economic development can be modeled using multi-agent systems that incorporate multiple underlying factors. The extent of information sharing is assumed to be a driving force that leads to economic geographic heterogeneity across locations without geographic advantages or disadvantages. We propose an agent-based market model that considers a spectrum of different information-sharing mechanisms: no information sharing, information sharing among friends and pheromone-like information sharing. Finally, we build a unified model that accommodates all three of these information-sharing mechanisms based on the number of friends who can share information. We find that the no information-sharing model does not yield large economic zones, and more information sharing can give rise to a power-law distribution of market size that corresponds to the stylized fact of city size and firm size distributions. The simulations show that this model is robust. This paper provides an alternative approach to studying economic geographic development, and this model could be used as a test bed to validate the detailed assumptions that regulate real economic agglomeration. PMID:23484007

  7. The impacts of information-sharing mechanisms on spatial market formation based on agent-based modeling.

    PubMed

    Li, Qianqian; Yang, Tao; Zhao, Erbo; Xia, Xing'ang; Han, Zhangang

    2013-01-01

    There has been an increasing interest in the geographic aspects of economic development, exemplified by P. Krugman's logical analysis. We show in this paper that the geographic aspects of economic development can be modeled using multi-agent systems that incorporate multiple underlying factors. The extent of information sharing is assumed to be a driving force that leads to economic geographic heterogeneity across locations without geographic advantages or disadvantages. We propose an agent-based market model that considers a spectrum of different information-sharing mechanisms: no information sharing, information sharing among friends and pheromone-like information sharing. Finally, we build a unified model that accommodates all three of these information-sharing mechanisms based on the number of friends who can share information. We find that the no information-sharing model does not yield large economic zones, and more information sharing can give rise to a power-law distribution of market size that corresponds to the stylized fact of city size and firm size distributions. The simulations show that this model is robust. This paper provides an alternative approach to studying economic geographic development, and this model could be used as a test bed to validate the detailed assumptions that regulate real economic agglomeration. PMID:23484007

  8. Model-based evaluation of mechanisms and benefits of mainstream shortcut nitrogen removal processes.

    PubMed

    Al-Omari, Ahmed; Wett, Bernhard; Nopens, Ingmar; De Clippeleir, Haydee; Han, Mofei; Regmi, Pusker; Bott, Charles; Murthy, Sudhir

    2015-01-01

    The main challenge in implementing shortcut nitrogen removal processes for mainstream wastewater treatment is the out-selection of nitrite oxidizing bacteria (NOB) to limit nitrate production. A model-based approach was utilized to simulate the impact of individual features of process control strategies to achieve NO(-)(2)-N shunt via NOB out-selection. Simulations were conducted using a two-step nitrogen removal model from the literature. Nitrogen shortcut removal processes from two case studies were modeled to illustrate the contribution of NOB out-selection mechanisms. The paper highlights a comparison between two control schemes; one was based on online measured ammonia and the other was based on a target ratio of 1 for ammonia vs. NOx (nitrate + nitrite) (AVN). Results indicated that the AVN controller possesses unique features to nitrify only that amount of nitrogen that can be denitrified, which promotes better management of incoming organics and bicarbonate for a more efficient NOB out-selection. Finally, the model was used in a scenario analysis, simulating hypothetical optimized performance of the pilot process. An estimated potential saving of 60% in carbon addition for nitrogen removal by implementing full-scale mainstream deammonification was predicted. PMID:25812092

  9. Computer-based creativity enhanced conceptual design model for non-routine design of mechanical systems

    NASA Astrophysics Data System (ADS)

    Li, Yutong; Wang, Yuxin; Duffy, Alex H. B.

    2014-11-01

    Computer-based conceptual design for routine design has made great strides, yet non-routine design has not been given due attention, and it is still poorly automated. Considering that the function-behavior-structure(FBS) model is widely used for modeling the conceptual design process, a computer-based creativity enhanced conceptual design model(CECD) for non-routine design of mechanical systems is presented. In the model, the leaf functions in the FBS model are decomposed into and represented with fine-grain basic operation actions(BOA), and the corresponding BOA set in the function domain is then constructed. Choosing building blocks from the database, and expressing their multiple functions with BOAs, the BOA set in the structure domain is formed. Through rule-based dynamic partition of the BOA set in the function domain, many variants of regenerated functional schemes are generated. For enhancing the capability to introduce new design variables into the conceptual design process, and dig out more innovative physical structure schemes, the indirect function-structure matching strategy based on reconstructing the combined structure schemes is adopted. By adjusting the tightness of the partition rules and the granularity of the divided BOA subsets, and making full use of the main function and secondary functions of each basic structure in the process of reconstructing of the physical structures, new design variables and variants are introduced into the physical structure scheme reconstructing process, and a great number of simpler physical structure schemes to accomplish the overall function organically are figured out. The creativity enhanced conceptual design model presented has a dominant capability in introducing new deign variables in function domain and digging out simpler physical structures to accomplish the overall function, therefore it can be utilized to solve non-routine conceptual design problem.

  10. A Mechanism-based Model for Deformation Twinning in Polycrystalline FCC Steel

    SciTech Connect

    Wang, Yuan; Sun, Xin; Wang, Y. D.; Hu, Xiaohua; Zbib, Hussein M.

    2014-06-01

    Deformation twinning, a common and important plastic deformation mechanism, is the key contributor to the excellent combination of strength and ductility in twinning-induced plasticity (TWIP) steel. In the open literature, a significant amount of research has been reported on the microstructural characteristics of deformation twinning and its influence on the overall deformation behavior of TWIP steel. In this study, we examine the feasibility of a mechanism-based crystal plasticity model in simulating the microstructural level deformation characteristics of TWIP steel. To this end, a model considering both double-slip and double-twin is developed to investigate the stress-strain behavior and local microstructural features related to the formation and growth of micro-twins in low stacking fault energy (SFE) TWIP steel. The twin systems are described as pseudo-slips that can be activated when their resolved shear stress reaches the corresponding critical value. A hardening law that accounts for the interaction among the slip and twin systems is also developed. Numerical simulations for dDifferent mesh sizes and single crystal patch tests under different loading modes are carried out to verify the modeling procedure. Our simulation results reveal that, despite its simple nature, the double-slip/double-twin model can capture the key deformation features of TWIP steel, including twin volume fraction evolution, continuous strain hardening, and the final fracture in the form of strain localization.

  11. A mechanism based modeling approach to failure in fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Yerramalli, Chandra Sekher

    The increasing use of fiber reinforced polymer composites (FRPC) in civil and military applications has made it imperative that the behavior of FRPC be understood under a variety of loading conditions. It is known that the compressive load carrying capacity of FRPC is low compared to its tensile load carrying capacity. Thus, the compressive behavior of FRPC has been a limiting factor in the design of FRPC structures. In the current work, the compressive behavior of FRPC has been studied with an aim to identify and understand the important parameters affecting the compressive strength and failure mechanisms in FRPC, particularly under combined stress states. The purpose is to establish compressive strength degradation (or enhancement) in the presence of combined stress states. Results from experiments have led to the development of a mechanism based failure model, based on the principles of fracture mechanics for the splitting failure of FRPC. A mechanics model has been developed for both pure compression and combined compression-torsion loading. The predictions of the model were found to compare favorably with experimental data obtained from glass and carbon FRPC under pure compression and combined compression-torsion loading. A 3D finite element simulation of a representative cylindrical section of the composite was performed. The results indicated the importance of fiber diameter on the predicted compressive response of the composite. It also indicated the possibilities of fiber breakage under axial loading as a cause for the initiation of kinking in case of small diameter fiber reinforced composites. Pure compression tests were also conducted on hybrid (glass/carbon) composites under static and dynamic loading conditions. The static compressive strength of hybrid composites shows a non-monotonic behavior with respect to the hybrid ratio. The compressive strength first decreases and then increases as we approach either pure carbon or pure glass composites. The

  12. Model-based flaw localization from perturbations in the dynamic response of complex mechanical structures

    SciTech Connect

    Chambers, D H

    2009-02-24

    A new method of locating structural damage using measured differences in vibrational response and a numerical model of the undamaged structure has been presented. This method is particularly suited for complex structures with little or no symmetry. In a prior study the method successively located simulated damage from measurements of the vibrational response on two simple structures. Here we demonstrate that it can locate simulated damage in a complex structure. A numerical model of a complex structure was used to calculate the structural response before and after the introduction of a void. The method can now be considered for application to structures of programmatic interest. It could be used to monitor the structural integrity of complex mechanical structures and assemblies over their lifetimes. This would allow early detection of damage, when repair is relatively easy and inexpensive. It would also allow one to schedule maintenance based on actual damage instead of a time schedule.

  13. Mechanical properties of methacrylate-based model dentin adhesives: effect of loading rate and moisture exposure.

    PubMed

    Singh, Viraj; Misra, Anil; Parthasarathy, Ranganathan; Ye, Qiang; Park, Jonggu; Spencer, Paulette

    2013-11-01

    The aim of this study is to investigate the mechanical behavior of model methacrylate-based dentin adhesives under conditions that simulate the wet oral environment. A series of monotonic and creep experiments were performed on rectangular beam samples of dentin adhesive in three-point bending configuration under different moisture conditions. The monotonic test results show a significant effect of loading rate on the failure strength and the linear limit (yield point) of the stress-strain response. In addition, these tests show that the failure strength is low, and the failure occurs at a smaller deformation when the test is performed under continuously changing moisture conditions. The creep test results show that under constant moisture conditions, the model dentin adhesives can have a viscoelastic response under certain low loading levels. However, when the moisture conditions vary under the same low loading levels, the dentin adhesives have an anomalous creep response accompanied by large secondary creep and high strain accumulation. PMID:23744598

  14. Particle-Based Geometric and Mechanical Modelling of Woven Technical Textiles and Reinforcements for Composites

    NASA Astrophysics Data System (ADS)

    Samadi, Reza

    affecting the textile geometry and constitutive behaviour under evolving loading; 5) validating simulation results with experimental trials; and 6) demonstrating the applicability of the simulation procedure to textile reinforcements featuring large numbers of small fibres as used in PMCs. As a starting point, the effects of reinforcement configuration on the in-plane permeability of textile reinforcements, through-thickness thermal conductivity of PMCs and in-plane stiffness of unidirectional and bidirectional PMCs were quantified systematically and correlated with specific geometric parameters. Variability was quantified for each property at a constant fibre volume fraction. It was observed that variability differed strongly between properties; as such, the simulated behaviour can be related to variability levels seen in experimental measurements. The effects of the geometry of textile reinforcements on the aforementioned processing and performance properties of the textiles and PMCs made from these textiles was demonstrated and validated, but only for simple cases as thorough and credible geometric models were not available at the onset of this work. Outcomes of this work were published in a peer-reviewed journal [101]. Through this thesis it was demonstrated that predicting changes in textile geometry prior and during loading is feasible using the proposed particle-based modelling method. The particle-based modelling method relies on discrete mechanics and offers an alternative to more traditional methods based on continuum mechanics. Specifically it alleviates issues caused by large strains and management of intricate, evolving contact present in finite element simulations. The particle-based modelling method enables credible, intricate modelling of the geometry of textiles at the mesoscopic scale as well as faithful mechanical modelling under load. Changes to textile geometry and configuration due to the normal compaction pressure, stress relaxation, in-plane shear

  15. Modelling and Simulation Based on Matlab/Simulink: A Press Mechanism

    NASA Astrophysics Data System (ADS)

    Halicioglu, R.; Dulger, L. C.; Bozdana, A. T.

    2014-03-01

    In this study, design and kinematic analysis of a crank-slider mechanism for a crank press is studied. The crank-slider mechanism is the commonly applied one as direct and indirect drive alternatives in practice. Since inexpensiveness, flexibility and controllability are getting more and more important in many industrial applications especially in automotive industry, a crank press with servo actuator (servo crank press) is taken as an application. Design and kinematic analysis of representative mechanism is presented with geometrical analysis for the inverse kinematic of the mechanism by using desired motion concept of slider. The mechanism is modelled in MATLAB/Simulink platform. The simulation results are presented herein.

  16. Thermodynamics-based models for the magneto-mechanical response of magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    LaMaster, Douglas H.

    toward this i-direction. The energy required to rotate these magnetization vectors is called the anisotropy energy. Because MSMAs have unusually high anisotropy energy requirements [4, 5], it can become more energetically favorable to reorient variants into ξi and align the magnetic easy axis with the applied magnetic field, rather than to rotate the magnetization vector in the i-direction, toward the hard axis. In this manner, an MSMA can experience the same response to magnetic field as it does to a compressive stress: variant reorientation. As variants reorient, the MSMA will compress in one direction and elongate in another direction, enabling their use as actuators. Additionally, magnetization vectors change direction as they align with the short length of the reorienting variant. As the internal magnetization changes, the MSMA can produce changes in the external magnetic field, which can induce a current within a surrounding coil. Utilizing this can lead to the design of either power harvesters or sensors. This work builds upon that of others, notably that of Kiefer and Lagoudas [6-9], to present several thermodynamic-based continuum models to predict the response of an MSMA to magneto-mechanical loading. The first model is 2D, and allows for any magneto-mechanical loading in two directions. The 2D model includes evolution rules for domain fractions, magnetization vector rotation, and variant reorientation. The next two models are 3D, and include evolution rules for domain wall motion and variant re- orientation. The first 3D model neglects magnetization vector rotation to present a simpler model that is less computationally intensive, while the second 3D model in- cludes all known mechanisms present in the microstructure to give a more generalized and complete model. These models are all more general than any other continuum, thermodynamics-based model in the literature. No other 2D continuum, thermodynamics-based model allows for general 2D magneto-mechanical

  17. Microstructurally based mechanisms for modeling shrinkage of cement paste at multiple levels

    SciTech Connect

    Jennings, H.M.; Xi, Yunping

    1993-07-15

    Shrinkage of cement paste is controlled by a number of mechanisms that operate in various parts of the microstructure and at various length scales. A model for creep and shrinkage can be developed by combining several models that describe phenomena at each of several length scales, ranging from the nanometer to the meter. This model is described and preliminary results are discussed.

  18. Quantum mechanics based multiscale modeling of stress-induced phase transformations in iron

    NASA Astrophysics Data System (ADS)

    Lew, A.; Caspersen, K.; Carter, E. A.; Ortiz, M.

    2006-06-01

    The ground state crystal structure of Fe, ferromagnetic body-centered cubic (bcc), undergoes a stress-induced martensitic phase transformation to a hexagonally close-packed (hcp) structure. Both bcc and hcp have been observed to coexist over a large range deformations, such that the nonlinearities in the constitutive behavior of each phase need to be included for an accurate description. We present herein a methodology to construct high-fidelity quantum mechanics based nonlinear elastic energy densities, amenable to be included in microstructural optimization procedures like sequential lamination. We use the model to show that the transition pressure (TP) has a strong dependence on relatively small amounts of shear deformation, and to investigate the value of the TP under uniaxial compressions, presumably found in shock-loaded materials. Results hint that more complex deformation patterns may need be present to be consistent with measured experimental values.

  19. A Unified Model of Time Perception Accounts for Duration-Based and Beat-Based Timing Mechanisms

    PubMed Central

    Teki, Sundeep; Grube, Manon; Griffiths, Timothy D.

    2011-01-01

    Accurate timing is an integral aspect of sensory and motor processes such as the perception of speech and music and the execution of skilled movement. Neuropsychological studies of time perception in patient groups and functional neuroimaging studies of timing in normal participants suggest common neural substrates for perceptual and motor timing. A timing system is implicated in core regions of the motor network such as the cerebellum, inferior olive, basal ganglia, pre-supplementary, and supplementary motor area, pre-motor cortex as well as higher-level areas such as the prefrontal cortex. In this article, we assess how distinct parts of the timing system subserve different aspects of perceptual timing. We previously established brain bases for absolute, duration-based timing and relative, beat-based timing in the olivocerebellar and striato-thalamo-cortical circuits respectively (Teki et al., 2011). However, neurophysiological and neuroanatomical studies provide a basis to suggest that timing functions of these circuits may not be independent. Here, we propose a unified model of time perception based on coordinated activity in the core striatal and olivocerebellar networks that are interconnected with each other and the cerebral cortex through multiple synaptic pathways. Timing in this unified model is proposed to involve serial beat-based striatal activation followed by absolute olivocerebellar timing mechanisms. PMID:22319477

  20. Quantifying subpopulation synergy for antibiotic combinations via mechanism-based modeling and a sequential dosing design.

    PubMed

    Landersdorfer, Cornelia B; Ly, Neang S; Xu, Hongmei; Tsuji, Brian T; Bulitta, Jürgen B

    2013-05-01

    Quantitative modeling of combination therapy can describe the effects of each antibiotic against multiple bacterial populations. Our aim was to develop an efficient experimental and modeling strategy that evaluates different synergy mechanisms using a rapidly killing peptide antibiotic (nisin) combined with amikacin or linezolid as probe drugs. Serial viable counts over 48 h were obtained in time-kill experiments with all three antibiotics in monotherapy against a methicillin-resistant Staphylococcus aureus USA300 strain (inoculum, 10(8) CFU/ml). A sequential design (initial dosing of 8 or 32 mg/liter nisin, switched to amikacin or linezolid at 1.5 h) assessed the rate of killing by amikacin and linezolid against nisin-intermediate and nisin-resistant populations. Simultaneous combinations were additionally studied and all viable count profiles comodeled in S-ADAPT and NONMEM. A mechanism-based model with six populations (three for nisin times two for amikacin) yielded unbiased and precise (r = 0.99, slope = 1.00; S-ADAPT) individual fits. The second-order killing rate constants for nisin against the three populations were 5.67, 0.0664, and 0.00691 liter/(mg · h). For amikacin, the maximum killing rate constants were 10.1 h(-1) against its susceptible and 0.771 h(-1) against its less-susceptible populations, with 14.7 mg/liter amikacin causing half-maximal killing. After incorporating the effects of nisin and amikacin against each population, no additional synergy function was needed. Linezolid inhibited successful bacterial replication but did not efficiently kill populations less susceptible to nisin. Nisin plus amikacin achieved subpopulation synergy. The proposed sequential and simultaneous dosing design offers an efficient approach to quantitatively characterize antibiotic synergy over time and prospectively evaluate antibiotic combination dosing strategies. PMID:23478962

  1. A Comparative Data-Based Modeling Study on Respiratory CO2 Gas Exchange during Mechanical Ventilation

    PubMed Central

    Kim, Chang-Sei; Ansermino, J. Mark; Hahn, Jin-Oh

    2016-01-01

    The goal of this study is to derive a minimally complex but credible model of respiratory CO2 gas exchange that may be used in systematic design and pilot testing of closed-loop end-tidal CO2 controllers in mechanical ventilation. We first derived a candidate model that captures the essential mechanisms involved in the respiratory CO2 gas exchange process. Then, we simplified the candidate model to derive two lower-order candidate models. We compared these candidate models for predictive capability and reliability using experimental data collected from 25 pediatric subjects undergoing dynamically varying mechanical ventilation during surgical procedures. A two-compartment model equipped with transport delay to account for CO2 delivery between the lungs and the tissues showed modest but statistically significant improvement in predictive capability over the same model without transport delay. Aggregating the lungs and the tissues into a single compartment further degraded the predictive fidelity of the model. In addition, the model equipped with transport delay demonstrated superior reliability to the one without transport delay. Further, the respiratory parameters derived from the model equipped with transport delay, but not the one without transport delay, were physiologically plausible. The results suggest that gas transport between the lungs and the tissues must be taken into account to accurately reproduce the respiratory CO2 gas exchange process under conditions of wide-ranging and dynamically varying mechanical ventilation conditions. PMID:26870728

  2. A model-based simulator for testing rule-based decision support systems for mechanical ventilation of ARDS patients.

    PubMed Central

    Sailors, R. M.; East, T. D.

    1994-01-01

    A model-based simulator was developed for testing rule-based decision support systems that manages ventilator therapy of patients with the Adult Respiratory Distress Syndrome (ARDS). The simulator is based on a multi-compartment model of the human body and mathematical models of the gas exchange abnormalities associated with ARDS. Initial testing of this system indicates that model-based simulators are a viable tool for testing rule-based expert systems used in health-care. PMID:7949849

  3. Mechanical characterization and modelling of Lorentz force based MEMS magnetic field sensors

    NASA Astrophysics Data System (ADS)

    Gkotsis, P.; Lara-Castro, M.; López-Huerta, F.; Herrera-May, A. L.; Raskin, J.-P.

    2015-10-01

    In this work we present experimental results from dynamic and static tests on miniature magnetic field sensors which are based on Micro Electro Mechanical Systems (MEMS) technologies. These MEMS magnetometers were fabricated on SOI wafers using Si bulk micromachining techniques and they operate at the first resonant frequency under the action of the Lorentz force which arises when a current flows through them in the presence of an external magnetic field. Sensing is based on piezoresistive principles and high sensitivity is expected from devices that show high total quality factors Qtot. We investigate here the energy loss mechanisms and the temperature rise due to Joule heating effects in the resonators of the magnetometers by performing tests both in air and under vacuum conditions. Testing was performed using laser Doppler Vibrometry and white light interferometry. At each pressure different driving currents have been applied and Qtot was extracted. It is found that Qtot varies with pressure between two limiting values: a low one in air which was between 17 and 500 for the tested devices and a high one in vacuum which in the case of one of our devices was equal to 2800. The amplitude of the applied current is also affecting the Q value at a certain pressure due to the rise of thermal stress in the resonating structures. The sensitivity of the sensors in air was experimentally measured using a Helmholtz coil and an oscilloscope and values between 72 mV T-1 and 513 mV T-1 were obtained from the tested devices. We further attempt to estimate the temperature rise in the devices due to Joule heating effects by combining the topography scans which were experimentally obtained with results from thermomechanical analysis of the sensors using Finite Element Modelling.

  4. Volcanic plume height measured by seismic waves based on a mechanical model

    USGS Publications Warehouse

    Prejean, Stephanie G.; Brodsky, Emily E.

    2011-01-01

    In August 2008 an unmonitored, largely unstudied Aleutian volcano, Kasatochi, erupted catastrophically. Here we use seismic data to infer the height of large eruptive columns such as those of Kasatochi based on a combination of existing fluid and solid mechanical models. In so doing, we propose a connection between a common, observable, short-period seismic wave amplitude to the physics of an eruptive column. To construct a combined model, we estimate the mass ejection rate of material from the vent on the basis of the plume height, assuming that the height is controlled by thermal buoyancy for a continuous plume. Using the estimated mass ejection rate, we then derive the equivalent vertical force on the Earth through a momentum balance. Finally, we calculate the far-field surface waves resulting from the vertical force. The model performs well for recent eruptions of Kasatochi and Augustine volcanoes if v, the velocity of material exiting the vent, is 120-230 m s-1. The consistency between the seismically inferred and measured plume heights indicates that in these cases the far-field ~1 s seismic energy radiated by fluctuating flow in the volcanic jet during the eruption is a useful indicator of overall mass ejection rates. Thus, use of the model holds promise for characterizing eruptions and evaluating ash hazards to aircraft in real time on the basis of far-field short-period seismic data. This study emphasizes the need for better measurements of eruptive plume heights and a more detailed understanding of the full spectrum of seismic energy radiated coeruptively.

  5. Volcanic plume height measured by seismic waves based on a mechanical model

    NASA Astrophysics Data System (ADS)

    Prejean, Stephanie G.; Brodsky, Emily E.

    2011-01-01

    In August 2008 an unmonitored, largely unstudied Aleutian volcano, Kasatochi, erupted catastrophically. Here we use seismic data to infer the height of large eruptive columns such as those of Kasatochi based on a combination of existing fluid and solid mechanical models. In so doing, we propose a connection between a common, observable, short-period seismic wave amplitude to the physics of an eruptive column. To construct a combined model, we estimate the mass ejection rate of material from the vent on the basis of the plume height, assuming that the height is controlled by thermal buoyancy for a continuous plume. Using the estimated mass ejection rate, we then derive the equivalent vertical force on the Earth through a momentum balance. Finally, we calculate the far-field surface waves resulting from the vertical force. The model performs well for recent eruptions of Kasatochi and Augustine volcanoes if v, the velocity of material exiting the vent, is 120-230 m s-1. The consistency between the seismically inferred and measured plume heights indicates that in these cases the far-field ˜1 s seismic energy radiated by fluctuating flow in the volcanic jet during the eruption is a useful indicator of overall mass ejection rates. Thus, use of the model holds promise for characterizing eruptions and evaluating ash hazards to aircraft in real time on the basis of far-field short-period seismic data. This study emphasizes the need for better measurements of eruptive plume heights and a more detailed understanding of the full spectrum of seismic energy radiated coeruptively.

  6. Two mechanisms of killing of Pseudomonas aeruginosa by tobramycin assessed at multiple inocula via mechanism-based modeling.

    PubMed

    Bulitta, Jürgen B; Ly, Neang S; Landersdorfer, Cornelia B; Wanigaratne, Nicholin A; Velkov, Tony; Yadav, Rajbharan; Oliver, Antonio; Martin, Lisandra; Shin, Beom Soo; Forrest, Alan; Tsuji, Brian T

    2015-04-01

    Bacterial resistance is among the most serious threats to human health globally, and many bacterial isolates have emerged that are resistant to all antibiotics in monotherapy. Aminoglycosides are often used in combination therapies against severe infections by multidrug-resistant bacteria. However, models quantifying different antibacterial effects of aminoglycosides are lacking. While the mode of aminoglycoside action on protein synthesis has often been studied, their disruptive action on the outer membrane of Gram-negative bacteria remains poorly characterized. Here, we developed a novel quantitative model for these two mechanisms of aminoglycoside action, phenotypic tolerance at high bacterial densities, and adaptive bacterial resistance in response to an aminoglycoside (tobramycin) against three Pseudomonas aeruginosa strains. At low-intermediate tobramycin concentrations (<4 mg/liter), bacterial killing due to the effect on protein synthesis was most important, whereas disruption of the outer membrane was the predominant killing mechanism at higher tobramycin concentrations (≥8 mg/liter). The extent of killing was comparable across all inocula; however, the rate of bacterial killing and growth was substantially lower at the 10(8.9) CFU/ml inoculum than that at the lower inocula. At 1 to 4 mg/liter tobramycin for strain PAO1-RH, there was a 0.5- to 6-h lag time of killing that was modeled via the time to synthesize hypothetical lethal protein(s). Disruption of the outer bacterial membrane by tobramycin may be critical to enhance the target site penetration of antibiotics used in synergistic combinations with aminoglycosides and thereby combat multidrug-resistant bacteria. The two mechanisms of aminoglycoside action and the new quantitative model hold great promise to rationally design novel, synergistic aminoglycoside combination dosage regimens. PMID:25645838

  7. Experimental and modeling study on charge storage/transfer mechanism of graphene-based supercapacitors

    NASA Astrophysics Data System (ADS)

    Ban, Shuai; Jing, Xie; Zhou, Hongjun; Zhang, Lei; Zhang, Jiujun

    2014-12-01

    A symmetrical graphene-based supercapacitor is constructed for studying the charge-transfer mechanism within the graphene-based electrodes using both experiment measurements and molecular simulation. The in-house synthesized graphene is characterized by XRD, SEM and BET measurements for morphology and surface area. It is observed that the electric capacity of graphene electrode can be reduced by both high internal resistance and limited mass transfer. Computer modeling is conducted at the molecular level to characterize the diffusion behavior of electrolyte ions to the interior of electrode with emphasis on the unique 2D confinement imposed by graphene layers. Although graphene powder poses a moderate internal surface of 400 m2 g-1, the capacitance performance of graphene electrode can be as good as that of commercial activated carbon which has an overwhelming surface area of 1700 m2 g-1. An explanation to this abnormal correlation is that graphene material has an intrinsic capability of adaptively reorganizing its microporous structure in response to intercalation of ions and immergence of electrolyte solvent. The accessible surface of graphene is believed to be dramatically enlarged for ion adsorption during the charging process of capacitor.

  8. Dislocation mechanism based model for stage II fatigue crack propagation rate

    NASA Technical Reports Server (NTRS)

    Mazumdar, P. K.

    1986-01-01

    Repeated plastic deformation, which of course depends on dislocation mechanism, at or near the crack tip leads to the fatigue crack propagation. By involving the theory of thermally activated flow and the cumulative plastic strain criterion, an effort is made here to model the stage II fatigue crack propagation rate in terms of the dislocation mechanism. The model, therefore, provides capability to ascertain: (1) the dislocation mechanism (and hence the near crack tip microstructures) assisting the crack growth, (2) the relative resistance of dislocation mechanisms to the crack growth, and (3) the fracture surface characteristics and its interpretation in terms of the dislocation mechanism. The local microstructure predicted for the room temperature crack growth in copper by this model is in good agreement with the experimental results taken from the literature. With regard to the relative stability of such dislocation mechanisms as the cross-slip and the dislocation intersection, the model suggests an enhancement of crack growth rate with an ease of cross-slip which in general promotes dislocation cell formation and is common in material which has high stacking fault energy (produces wavy slips). Cross-slip apparently enhances crack growth rate by promoting slip irreversibility and fracture surface brittleness to a greater degree.

  9. Mechanism of Si and metal etching based on sticking reaction model

    NASA Astrophysics Data System (ADS)

    Izawa, Masaru

    2011-10-01

    Plasma etching technique has been wildly used in the fabrication of LSI device. With shrinking the device size, it is required to reduce CD shift and under-cutting as well as to improve uniformity in etching process. In development of etching apparatus and process, it has been necessary to understand the mechanism of the cause of CD shift. The CD shift and etching rate is determined by the reaction of incident species (ions, radicals), and surface materials. However, their mechanisms of the surface reactions are not explained quantitatively, although a portion of them was understood clearly. We proposed the mechanism taking a sticking reaction model on a wafer surface because the reaction is one of the key factors to determine the etching rate and CD shift. Because the surface reaction depends on the surface condition and temperature, the sticking coefficient S is formulated approximately as a function of them, S = = α[1-{1-(1- θ) [1-(1-Pr)n/L]}L], where α is the trapping coefficients, n and L is the vibration times and migration times until desorbing from the trapping state (physical adsorption), Pr is the chemical reaction probability from the state, and θ is the ratio of inactive site (coverage). n, L, Pr are functions of the surface temperature and potential energy barrier. In addition this equation can be expanded to chemical reactions. CD shift δCD is also formulated by assuming the taper angle determined by the balance of deposition and ion etching, δCD = 2h cot cos-1(Rd/YΓion) , where h is the film thickness, Rd is the deposition rate, YΓion is the sputtering rate of deposited film. By using these two equations, we have studied the mechanism of CD shift in Al etching and undercutting in Si etching. It was confirmed that temperature dependence of them are explained. In addition, by comparing the CD shift equation with another one based on the statistical analysis, it was found that RIE-lag was a factor of CD shift in gate etching.

  10. Mechanical responses of the periodontal ligament based on an exponential hyperelastic model: a combined experimental and finite element method.

    PubMed

    Huang, Huixiang; Tang, Wencheng; Yan, Bin; Wu, Bin; Cao, Dan

    2016-01-01

    The V-W exponential hyperelastic model is adopted to describe the instantaneous elastic response of the periodontal ligament (PDL). The general theoretical framework of constitutive modeling is described based on nonlinear continuum mechanics, and the elasticity tensor used to develop UMAT subroutine is formulated. Nanoindentation experiment is performed to characterize mechanical properties of an adult pig PDL specimen. Then the experiment is simulated by using the finite element (FE) analysis. Meanwhile, the optimized material parameters are identified by the inverse FE method. The good agreement between the simulated results and experimental data demonstrates that the V-W model is capable of describing the mechanical behavior of the PDL. Therefore, the model and its implementation into FE code are validated. By using the model, we simulate the tooth movement under orthodontic loading to predict the mechanical responses of the PDL. The results show that local concentrations of stress and strain in the PDL are found. PMID:25648914

  11. Unveiling the molecular mechanism of brassinosteroids: Insights from structure-based molecular modeling studies.

    PubMed

    Lei, Beilei; Liu, Jiyuan; Yao, Xiaojun

    2015-12-01

    Brassinosteroid (BR) phytohormones play indispensable roles in plant growth and development. Brassinolide (BL) and 24-epibrassinolide (24-epiBL) are the most active ones among the BRs reported thus far. Unfortunately, the extremely low natural content and intricate synthesis process limit their popularization in agricultural production. Earlier reports to discover alternative compounds have resulted in molecules with nearly same scaffold structure and without diversity in chemical space. In the present study, receptors structure based BRs regulation mechanism was analyzed. First, we examined the detailed binding interactions and their dynamic stability between BL and its receptor BRI1 and co-receptor BAK1. Then, the binding modes and binding free energies for 24-epiBL and a series of representative BRs binding with BRI1 and BRI1-BAK1 were carried out by molecular docking, energy minimization and MM-PBSA free energy calculation. The obtained binding structures and energetic results provided vital insights into the structural factors affecting the activity from both receptors and BRs aspects. Subsequently, the obtained knowledge will serve as valuable guidance to build pharmacophore models for rational screening of new scaffold alternative BRs. PMID:26362600

  12. Investigating the frequency spectrum of mechanical quality factor for piezoelectric materials based on phenomenological model

    NASA Astrophysics Data System (ADS)

    Shi, Weijia; Zhao, Hui; Ma, Jie; Yao, Yu; Uchino, Kenji

    2015-10-01

    Heat generation due to losses restricts piezoelectric materials from maintaining a high power density, which will further limit the miniaturization of piezoelectric devices. As an evaluation index of the loss level, the mechanical quality factor shows an opposite tendency with losses. The mechanical quality factor should therefore be evaluated. By new methods to determine the mechanical quality factor, the highest mechanical quality factor has been discovered within the working bandwidth other than the resonance and antiresonance frequencies, which is almost double the value at the resonance. In this study, the prime determinant of the maximum value has been experimentally investigated on the basis of the phenomenological model of the admittance phase. The investigation experimentally infers that the change in the tendency of the phase leads to the appearance of the maximum value. Thus, the new phenomenon is experimentally explained for the first time.

  13. Semantic Retrieval Based on Feature Element Constructional Model and Bias Competition Mechanism

    NASA Astrophysics Data System (ADS)

    Xu, Yin; Zhang, Yujin

    2003-01-01

    An original image retrieval framework is proposed and developed. Trying to achieve the semantic retrieval, a novel cognitive model - feature element constructional model is proposed. With its hierachical constructional structure and bias competition mechanism, the new model provides great power for semantic retrieval. Two types of retrieval mode are presented in the new system, which both try to analysis the semantic concept in the query image or semantic command. Then matching from the object to the feature element is carried out to obtain the final result, and our understanding of retrieval "to provide the way of approaching the accurate result" is also embodied.

  14. Analysis of the twin spacing and grain size effects on mechanical properties in hierarchically nanotwinned face-centered cubic metals based on a mechanism-based plasticity model

    NASA Astrophysics Data System (ADS)

    Zhu, Linli; Qu, Shaoxing; Guo, Xiang; Lu, Jian

    2015-03-01

    Hierarchical twin lamellae in polycrystalline face-centered cubic (fcc) metals possess a possibility to achieve higher strength with keeping an acceptable elongation. The present work is concerned with the analysis of twin spacing and grain size-dependent plastic performance in hierarchically nanotwinned fcc metals using a generalized strain-gradient plasticity model. The dislocation density-based physical model for constitutive description of nanotwinned fcc metals is expanded for the hierarchical structures of nanotwins. The strengthening mechanism and the failure behavior in these hierarchical nanostructures are studied to evaluate the strength and ductility. Moreover, the transition twin spacing between the strengthening and softening is obtained in different order of twin lamellae. A dislocation-based model on nucleating deformation twins is presented to predict the critical twin spacing in the lowest twin lamellae for generating the subordinate twin lamellae. Our simulation results demonstrate that the existence of the hierarchical nanotwins gives rise to a significant enhancement in the strength, and the resulting global flow stresses are sensitive to the twin spacings of the hierarchical twin lamellae and the grain size. Two softening stages are observed with variation of twin spacing, and the relevant transition twin spacing depends on the microstructural size in hierarchically nanotwinned metals. We further find that the predicted failure strain decreases with decreasing the twin spacing, which is quite different from the case of the individually nanotwinned fcc metals. The critical twin spacing for generating subordinate twins also depends on the twin spacing of superordinate twin lamellae and the grain size. These findings suggest that the high yield strength and good ductility can be achieved by optimizing the grain size and the twin spacings in the hierarchical twins.

  15. A Modified Wilson Cycle Scenario Based on Thermo-Mechanical Model

    NASA Astrophysics Data System (ADS)

    Baes, M.; Sobolev, S. V.

    2014-12-01

    The major problem of classical Wilson Cycle concept is the suggested conversion of the passive continental margin to the active subduction zone. Previous modeling studies assumed either unusually thick felsic continental crust at the margin (over 40 km) or unusually low lithospheric thickness (less than 70 km) to simulate this process. Here we propose a new triggering factor in subduction initiation process that is mantle suction force. Based on this proposal we suggest a modification of Wilson Cycle concept. Sometime after opening and extension of oceanic basin, continental passive margin moves over the slab remnants of the former active subduction zones in deep mantle. Such slab remnants or deep slabs of neighboring active subduction zones produce a suction mantle flow introducing additional compression at the passive margin. It results in the initiation of a new subduction zone, hence starting the closing phase of Wilson Cycle. In this scenario the weakness of continental crust near the passive margin which is inherited from the rifting phase and horizontal push force induced from far-field topographic gradient within the continent facilitate and speed up subduction initiation process. Our thermo-mechanical modeling shows that after a few tens of million years a shear zone may indeed develop along the passive margin that has typical two-layered 35 km thick continental crust and thermal lithosphere thicker than 100 km if there is a broad mantle down-welling flow below the margin. Soon after formation of this shear zone oceanic plate descends into mantle and subduction initiates. Subduction initiation occurs following over-thrusting of continental crust and retreating of future trench. In models without far-field topographic gradient within the continent subduction initiation requires weaker passive margin. Our results also indicate that subduction initiation depends on several parameters such as magnitude, domain size and location of suction mantle flow

  16. Model-based analysis of the effect of different operating conditions on fouling mechanisms in a membrane bioreactor.

    PubMed

    Sabia, Gianpaolo; Ferraris, Marco; Spagni, Alessandro

    2016-01-01

    This study proposes a model-based evaluation of the effect of different operating conditions with and without pre-denitrification treatment and applying three different solids retention times on the fouling mechanisms involved in membrane bioreactors (MBRs). A total of 11 fouling models obtained from literature were used to fit the transmembrane pressure variations measured in a pilot-scale MBR treating real wastewater for more than 1 year. The results showed that all the models represent reasonable descriptions of the fouling processes in the MBR tested. The model-based analysis confirmed that membrane fouling started by pore blocking (complete blocking model) and by a reduction of the pore diameter (standard blocking) while cake filtration became the dominant fouling mechanism over long-term operation. However, the different fouling mechanisms occurred almost simultaneously making it rather difficult to identify each one. The membrane "history" (i.e. age, lifespan, etc.) seems the most important factor affecting the fouling mechanism more than the applied operating conditions. Nonlinear regression of the most complex models (combined models) evaluated in this study sometimes demonstrated unreliable parameter estimates suggesting that the four basic fouling models (complete, standard, intermediate blocking and cake filtration) contain enough details to represent a reasonable description of the main fouling processes occurring in MBRs. PMID:26377972

  17. A meshfree method based on the peridynamic model of solid mechanics.

    SciTech Connect

    Silling, Stewart Andrew; Askari, Ebrahim

    2005-01-01

    An alternative theory of solid mechanics, known as the peridynamic theory, formulates problems in terms of integral equations rather than partial differential equations. This theory assumes that particles in a continuum interact with each other across a finite distance, as in molecular dynamics. Damage is incorporated in the theory at the level of these two-particle interactions, so localization and fracture occur as a natural outgrowth of the equation of motion and constitutive models. A numerical method for solving dynamic problems within the peridynamic theory is described. Accuracy and numerical stability are discussed. Examples illustrate the properties of the method for modeling brittle dynamic crack growth.

  18. Use of Agent-Based Modeling To Explore the Mechanisms of Intracellular Phosphorus Heterogeneity in Cultured Phytoplankton

    PubMed Central

    Fredrick, Neil D.; Berges, John A.; Twining, Benjamin S.; Nuñez-Milland, Daliangelis

    2013-01-01

    There can be significant intraspecific individual-level heterogeneity in the intracellular P of phytoplankton, which can affect the population-level growth rate. Several mechanisms can create this heterogeneity, including phenotypic variability in various physiological functions (e.g., nutrient uptake rate). Here, we use modeling to explore the contribution of various mechanisms to the heterogeneity in phytoplankton grown in a laboratory culture. An agent-based model simulates individual cells and their intracellular P. Heterogeneity is introduced by randomizing parameters (e.g., maximum uptake rate) of daughter cells at division. The model was calibrated to observations of the P quota of individual cells of the centric diatom Thalassiosira pseudonana, which were obtained using synchrotron X-ray fluorescence (SXRF). A number of simulations, with individual mechanisms of heterogeneity turned off, then were performed. Comparison of the coefficient of variation (CV) of these and the baseline simulation (i.e., all mechanisms turned on) provides an estimate of the relative contribution of these mechanisms. The results show that the mechanism with the largest contribution to variability is the parameter characterizing the maximum intracellular P, which, when removed, results in a CV of 0.21 compared to a CV of 0.37 with all mechanisms turned on. This suggests that nutrient/element storage capabilities/mechanisms are important determinants of intrapopulation heterogeneity. PMID:23666327

  19. Model of the catalytic mechanism of human aldose reductase based on quantum chemical calculations.

    SciTech Connect

    Cachau, R. C.; Howard, E. H.; Barth, P. B.; Mitschler, A. M.; Chevrier, B. C.; Lamour, V.; Joachimiak, A.; Sanishvili, R.; Van Zandt, M.; Sibley, E.; Moras, D.; Podjarny, A.; UPR de Biologie Structurale; National Cancer Inst.; Univ. Louis Pasteur; Inst. for Diabetes Discovery, Inc.

    2000-01-01

    Aldose Reductase is an enzyme involved in diabetic complications, thoroughly studied for the purpose of inhibitor development. The structure of an enzyme-inhibitor complex solved at sub-atomic resolution has been used to develop a model for the catalytic mechanism. This model has been refined using a combination of Molecular Dynamics and Quantum calculations. It shows that the proton donation, the subject of previous controversies, is the combined effect of three residues: Lys 77, Tyr 48 and His 110. Lys 77 polarises the Tyr 48 OH group, which donates the proton to His 110, which becomes doubly protonated. His 110 then moves and donates the proton to the substrate. The key information from the sub-atomic resolution structure is the orientation of the ring and the single protonafion of the His 110 in the enzyme-inhibitor complex. This model is in full agreement with all available experimental data.

  20. Regulation of amniotic fluid volume: mathematical model based on intramembranous transport mechanisms

    PubMed Central

    Anderson, Debra F.; Cheung, Cecilia Y.

    2014-01-01

    Experimentation in late-gestation fetal sheep has suggested that regulation of amniotic fluid (AF) volume occurs primarily by modulating the rate of intramembranous transport of water and solutes across the amnion into underlying fetal blood vessels. In order to gain insight into intramembranous transport mechanisms, we developed a computer model that allows simulation of experimentally measured changes in AF volume and composition over time. The model included fetal urine excretion and lung liquid secretion as inflows into the amniotic compartment plus fetal swallowing and intramembranous absorption as outflows. By using experimental flows and solute concentrations for urine, lung liquid, and swallowed fluid in combination with the passive and active transport mechanisms of the intramembranous pathway, we simulated AF responses to basal conditions, intra-amniotic fluid infusions, fetal intravascular infusions, urine replacement, and tracheoesophageal occlusion. The experimental data are consistent with four intramembranous transport mechanisms acting in concert: 1) an active unidirectional bulk transport of AF with all dissolved solutes out of AF into fetal blood presumably by vesicles; 2) passive bidirectional diffusion of solutes, such as sodium and chloride, between fetal blood and AF; 3) passive bidirectional water movement between AF and fetal blood; and 4) unidirectional transport of lactate into the AF. Further, only unidirectional bulk transport is dynamically regulated. The simulations also identified areas for future study: 1) identifying intramembranous stimulators and inhibitors, 2) determining the semipermeability characteristics of the intramembranous pathway, and 3) characterizing the vesicles that are the primary mediators of intramembranous transport. PMID:25186112

  1. Regulation of amniotic fluid volume: mathematical model based on intramembranous transport mechanisms.

    PubMed

    Brace, Robert A; Anderson, Debra F; Cheung, Cecilia Y

    2014-11-15

    Experimentation in late-gestation fetal sheep has suggested that regulation of amniotic fluid (AF) volume occurs primarily by modulating the rate of intramembranous transport of water and solutes across the amnion into underlying fetal blood vessels. In order to gain insight into intramembranous transport mechanisms, we developed a computer model that allows simulation of experimentally measured changes in AF volume and composition over time. The model included fetal urine excretion and lung liquid secretion as inflows into the amniotic compartment plus fetal swallowing and intramembranous absorption as outflows. By using experimental flows and solute concentrations for urine, lung liquid, and swallowed fluid in combination with the passive and active transport mechanisms of the intramembranous pathway, we simulated AF responses to basal conditions, intra-amniotic fluid infusions, fetal intravascular infusions, urine replacement, and tracheoesophageal occlusion. The experimental data are consistent with four intramembranous transport mechanisms acting in concert: 1) an active unidirectional bulk transport of AF with all dissolved solutes out of AF into fetal blood presumably by vesicles; 2) passive bidirectional diffusion of solutes, such as sodium and chloride, between fetal blood and AF; 3) passive bidirectional water movement between AF and fetal blood; and 4) unidirectional transport of lactate into the AF. Further, only unidirectional bulk transport is dynamically regulated. The simulations also identified areas for future study: 1) identifying intramembranous stimulators and inhibitors, 2) determining the semipermeability characteristics of the intramembranous pathway, and 3) characterizing the vesicles that are the primary mediators of intramembranous transport. PMID:25186112

  2. Development of Antipsychotic Medications with Novel Mechanisms of Action Based on Computational Modeling of Hippocampal Neuropathology

    PubMed Central

    Siekmeier, Peter J.; vanMaanen, David P.

    2013-01-01

    A large number of cellular level abnormalities have been identified in the hippocampus of schizophrenic subjects. Nonetheless, it remains uncertain how these pathologies interact at a system level to create clinical symptoms, and this has hindered the development of more effective antipsychotic medications. Using a 72-processor supercomputer, we created a tissue level hippocampal simulation, featuring multicompartmental neuron models with multiple ion channel subtypes and synaptic channels with realistic temporal dynamics. As an index of the schizophrenic phenotype, we used the specific inability of the model to attune to 40 Hz (gamma band) stimulation, a well-characterized abnormality in schizophrenia. We examined several possible combinations of putatively schizophrenogenic cellular lesions by systematically varying model parameters representing NMDA channel function, dendritic spine density, and GABA system integrity, conducting 910 trials in total. Two discrete “clusters” of neuropathological changes were identified. The most robust was characterized by co-occurring modest reductions in NMDA system function (-30%) and dendritic spine density (-30%). Another set of lesions had greater NMDA hypofunction along with low level GABA system dysregulation. To the schizophrenic model, we applied the effects of 1,500 virtual medications, which were implemented by varying five model parameters, independently, in a graded manner; the effects of known drugs were also applied. The simulation accurately distinguished agents that are known to lack clinical efficacy, and identified novel mechanisms (e.g., decrease in AMPA conductance decay time constant, increase in projection strength of calretinin-positive interneurons) and combinations of mechanisms that could re-equilibrate model behavior. These findings shed light on the mechanistic links between schizophrenic neuropathology and the gamma band oscillatory abnormalities observed in the illness. As such, they generate

  3. Coarsening of the Sn-Pb Solder Microstructure in Constitutive Model-Based Predictions of Solder Joint Thermal Mechanical Fatigue

    SciTech Connect

    Vianco, P.T.; Burchett, S.N.; Neilsen, M.K.; Rejent, J.A.; Frear, D.R.

    1999-04-12

    Thermal mechanical fatigue (TMF) is an important damage mechanism for solder joints exposed to cyclic temperature environments. Predicting the service reliability of solder joints exposed to such conditions requires two knowledge bases: first, the extent of fatigue damage incurred by the solder microstructure leading up to fatigue crack initiation, must be quantified in both time and space domains. Secondly, fatigue crack initiation and growth must be predicted since this metric determines, explicitly, the loss of solder joint functionality as it pertains to its mechanical fastening as well as electrical continuity roles. This paper will describe recent progress in a research effort to establish a microstructurally-based, constitutive model that predicts TMF deformation to 63Sn-37Pb solder in electronic solder joints up to the crack initiation step. The model is implemented using a finite element setting; therefore, the effects of both global and local thermal expansion mismatch conditions in the joint that would arise from temperature cycling.

  4. Alteration in refractive index profile during accommodation based on mechanical modelling

    PubMed Central

    Bahrami, Mehdi; Heidari, Ali; Pierscionek, Barbara K.

    2015-01-01

    The lens of the eye has a gradient refractive index (GRIN). Ocular accommodation, which alters the shape of the lens in response to visual demand, causes a redistribution of the internal structure of the lens leading to a change in the GRIN profile. The nature of this redistribution and the consequence of change in the GRIN profile are not understood. A modelling approach that considers how the GRIN profile may change with accommodation needs to take into account optical and mechanical parameters and be cognisant of individual variability in the shape and size of lenses. This study models the normalised axial GRIN profile during accommodation using reduced modelling and incorporating finite element analysis to connect inhomogenous mechanical characteristics of the lens to optical performance. The results show that simulated stretching changes the length of the plateau but does not alter the cortical gradient, which supports clinical findings. There is a very small change to the accommodated and non-accommodated profiles when normalised, yet this yields measurable changes in aberrations with around 11% and almost 13% difference in spherical aberration and astigmatism respectively. The results can be used in reconstruction of the refractive index and for investigating gradual changes with age. PMID:26819821

  5. Alteration in refractive index profile during accommodation based on mechanical modelling.

    PubMed

    Bahrami, Mehdi; Heidari, Ali; Pierscionek, Barbara K

    2016-01-01

    The lens of the eye has a gradient refractive index (GRIN). Ocular accommodation, which alters the shape of the lens in response to visual demand, causes a redistribution of the internal structure of the lens leading to a change in the GRIN profile. The nature of this redistribution and the consequence of change in the GRIN profile are not understood. A modelling approach that considers how the GRIN profile may change with accommodation needs to take into account optical and mechanical parameters and be cognisant of individual variability in the shape and size of lenses. This study models the normalised axial GRIN profile during accommodation using reduced modelling and incorporating finite element analysis to connect inhomogenous mechanical characteristics of the lens to optical performance. The results show that simulated stretching changes the length of the plateau but does not alter the cortical gradient, which supports clinical findings. There is a very small change to the accommodated and non-accommodated profiles when normalised, yet this yields measurable changes in aberrations with around 11% and almost 13% difference in spherical aberration and astigmatism respectively. The results can be used in reconstruction of the refractive index and for investigating gradual changes with age. PMID:26819821

  6. Plasma etching of Hf-based high-k thin films. Part III. Modeling the reaction mechanisms

    SciTech Connect

    Martin, Ryan M.; Chang, Jane P.

    2009-03-15

    A generalized etch rate model was formulated to describe metal oxide etching in complex plasma chemistries, based on the understanding gained from detailed plasma characterization and experimental investigation into the metal oxide etching mechanisms. Using a surface site balance-based approach, the correct etch rate dependencies on neutral-to-ion flux ratio, ion energy, competing deposition and etching reaction pathways, and film properties were successfully incorporated into the model. The applicability of the model was assessed by fitting to experimental etch rate data in both Cl{sub 2} and BCl{sub 3} chemistries. Plasma gas phase analysis as well as etch and deposition rate measurements were used to calculate initial values and appropriate ranges for model parameter variation. Physically meaningful parameter values were extracted from the modeling fitting to the experimental data, thereby demonstrating the applicability of this model in assessing the plasma etching of other complex materials systems.

  7. Microstructure-based modeling of snow mechanics: a discrete element approach

    NASA Astrophysics Data System (ADS)

    Hagenmuller, P.; Chambon, G.; Naaim, M.

    2015-10-01

    Rapid and large deformations of snow are mainly controlled by grain rearrangements, which occur through the failure of cohesive bonds and the creation of new contacts. We exploit a granular description of snow to develop a discrete element model based on the full 3-D microstructure captured by microtomography. The model assumes that snow is composed of rigid grains interacting through localized contacts accounting for cohesion and friction. The geometry of the grains and of the intergranular bonding system are explicitly defined from microtomographic data using geometrical criteria based on curvature and contiguity. Single grains are represented as rigid clumps of spheres. The model is applied to different snow samples subjected to confined compression tests. A detailed sensitivity analysis shows that artifacts introduced by the modeling approach and the influence of numerical parameters are limited compared to variations due to the geometry of the microstructure. The model shows that the compression behavior of snow is mainly controlled by the density of the samples, but that deviations from a pure density parameterization are not insignificant during the first phase of deformation. In particular, the model correctly predicts that, for a given density, faceted crystals are less resistant to compression than rounded grains or decomposed snow. For larger compression strains, no clear differences between snow types are observed.

  8. MRI-based modeling for evaluation of in vivo contact mechanics in the human wrist during active light grasp.

    PubMed

    Pillai, Ravi R; Thoomukuntla, Bhaskar; Ateshian, Gerard A; Fischer, Kenneth J

    2007-01-01

    Investigations of in vivo joint mechanics are important for understanding the joint function under functional loading and the mechanisms of pathology. In this study we used magnetic resonance imaging (MRI) based joint contact modeling to evaluate in vivo joint contact mechanics in the human wrist. MRI scans were performed on the wrists of four subjects while they maintained light grasp of a cylinder, and with the same wrist relaxed. 3D models of the radius, scaphoid and lunate, including cartilage surface data, were constructed from the relaxed image data. These models were transformed into the loaded configuration, as determined from the grasp image data, and contact mechanics were evaluated. The resulting contact pressures, areas and forces were then analyzed for each articulation and for each subject. Contact areas were measured directly from grasp MRI images for comparison to the model predictions. The first-ever estimates for in vivo radioscaphoid and radiolunate contact pressure agreed reasonably well with previous cadaveric studies. This investigation also produced novel in vivo scapholunate contact results that were similar to radiolunate data. The specimen-specific contact area comparison generally showed substantial variability between the models and the direct measurements from MRI. On average, the models were within about 10% of the direct MRI measurements for radioscaphoid and scapholunate contact areas, but radiolunate contact areas from the model were only within 55% of the direct measurements. Overall, the results of the study suggest that MRI-based modeling has substantial potential for evaluation of in vivo joint contact mechanics, especially as technology and methodology improve. PMID:17391678

  9. Statistical mechanics of competitive resource allocation using agent-based models

    NASA Astrophysics Data System (ADS)

    Chakraborti, Anirban; Challet, Damien; Chatterjee, Arnab; Marsili, Matteo; Zhang, Yi-Cheng; Chakrabarti, Bikas K.

    2015-01-01

    Demand outstrips available resources in most situations, which gives rise to competition, interaction and learning. In this article, we review a broad spectrum of multi-agent models of competition (El Farol Bar problem, Minority Game, Kolkata Paise Restaurant problem, Stable marriage problem, Parking space problem and others) and the methods used to understand them analytically. We emphasize the power of concepts and tools from statistical mechanics to understand and explain fully collective phenomena such as phase transitions and long memory, and the mapping between agent heterogeneity and physical disorder. As these methods can be applied to any large-scale model of competitive resource allocation made up of heterogeneous adaptive agent with non-linear interaction, they provide a prospective unifying paradigm for many scientific disciplines.

  10. Multiscale, structure-based modeling for the elastic mechanical behavior of arterial walls.

    PubMed

    Stylianopoulos, Triantafyllos; Barocas, Victor H

    2007-08-01

    Passive elastic behavior of arterial wall remains difficult to model. Although phenomenological and structural models exist, the question of how the three-dimensional network structure of the collagen in the artery determines its mechanical properties is still open. A model is presented that incorporates a collagen network as well as the noncollagenous material that comprise the artery. The collagen architecture is represented as a network of interconnected fibers, and a neo-Hookean constitutive equation is used to describe the contribution of the noncollagenous matrix. The model is multiscale in that volume-averaging theory is applied to the collagen network, and it is structural in that parameters of the microstructure of the collagen network were considered instead of a macroscopic constitutive law. The computational results provided a good fit to published experimental data for decellularized porcine carotid arteries. The model predicted increased circumferential compliance for increased axial stretch, consistent with previously published reports, and a relatively small sensitivity to open angle. Even at large extensions, the model predicted that the noncollagenous matrix would be in compression, preventing collapse of the collagen network. The incorporation of fiber-fiber interactions led to an accurate model of artery wall behavior with relatively few parameters. The counterintuitive result that the noncollagenous component is in compression during extension and inflation of the tissue suggests that the collagen is important even at small strains, with the noncollagenous components supporting the network, but not resisting the load directly. More accurate representation of the microstructure of the artery wall is needed to explore this issue further. PMID:17655483

  11. Mechanism-based model of a mass rapid transit system: A perspective

    NASA Astrophysics Data System (ADS)

    Legara, Erika Fille; Khoon, Lee Kee; Guang, Hung Gih; Monterola, Christopher

    2015-01-01

    In this paper, we discuss our findings on the spatiotemporal dynamics within the mass rapid transit (MRT) system of Singapore. We show that the trip distribution of Origin-Destination (OD) station pairs follows a power-law, implying the existence of critical OD pairs. We then present and discuss the empirically validated agent-based model (ABM) we have developed. The model allows recreation of the observed statistics and the setting up of various scenarios and their effects on the system, such as increasing the commuter population and the propagation of travel delays within the transportation network. The proposed model further enables identification of bottlenecks that can cause the MRT to break down, and consequently provide foresight on how such disruptions can possibly be managed. This can potentially provide a versatile approach for transport planners and government regulators to make quantifiable policies that optimally balance cost and convenience as a function of the number of the commuting public.

  12. Tracking control of nonlinear lumped mechanical continuous-time systems: A model-based iterative learning approach

    NASA Astrophysics Data System (ADS)

    Smolders, K.; Volckaert, M.; Swevers, J.

    2008-11-01

    This paper presents a nonlinear model-based iterative learning control procedure to achieve accurate tracking control for nonlinear lumped mechanical continuous-time systems. The model structure used in this iterative learning control procedure is new and combines a linear state space model and a nonlinear feature space transformation. An intuitive two-step iterative algorithm to identify the model parameters is presented. It alternates between the estimation of the linear and the nonlinear model part. It is assumed that besides the input and output signals also the full state vector of the system is available for identification. A measurement and signal processing procedure to estimate these signals for lumped mechanical systems is presented. The iterative learning control procedure relies on the calculation of the input that generates a given model output, so-called offline model inversion. A new offline nonlinear model inversion method for continuous-time, nonlinear time-invariant, state space models based on Newton's method is presented and applied to the new model structure. This model inversion method is not restricted to minimum phase models. It requires only calculation of the first order derivatives of the state space model and is applicable to multivariable models. For periodic reference signals the method yields a compact implementation in the frequency domain. Moreover it is shown that a bandwidth can be specified up to which learning is allowed when using this inversion method in the iterative learning control procedure. Experimental results for a nonlinear single-input-single-output system corresponding to a quarter car on a hydraulic test rig are presented. It is shown that the new nonlinear approach outperforms the linear iterative learning control approach which is currently used in the automotive industry on durability test rigs.

  13. MRI-based modeling for radiocarpal joint mechanics: validation criteria and results for four specimen-specific models.

    PubMed

    Fischer, Kenneth J; Johnson, Joshua E; Waller, Alexander J; McIff, Terence E; Toby, E Bruce; Bilgen, Mehmet

    2011-10-01

    The objective of this study was to validate the MRI-based joint contact modeling methodology in the radiocarpal joints by comparison of model results with invasive specimen-specific radiocarpal contact measurements from four cadaver experiments. We used a single validation criterion for multiple outcome measures to characterize the utility and overall validity of the modeling approach. For each experiment, a Pressurex film and a Tekscan sensor were sequentially placed into the radiocarpal joints during simulated grasp. Computer models were constructed based on MRI visualization of the cadaver specimens without load. Images were also acquired during the loaded configuration used with the direct experimental measurements. Geometric surface models of the radius, scaphoid and lunate (including cartilage) were constructed from the images acquired without the load. The carpal bone motions from the unloaded state to the loaded state were determined using a series of 3D image registrations. Cartilage thickness was assumed uniform at 1.0 mm with an effective compressive modulus of 4 MPa. Validation was based on experimental versus model contact area, contact force, average contact pressure and peak contact pressure for the radioscaphoid and radiolunate articulations. Contact area was also measured directly from images acquired under load and compared to the experimental and model data. Qualitatively, there was good correspondence between the MRI-based model data and experimental data, with consistent relative size, shape and location of radioscaphoid and radiolunate contact regions. Quantitative data from the model generally compared well with the experimental data for all specimens. Contact area from the MRI-based model was very similar to the contact area measured directly from the images. For all outcome measures except average and peak pressures, at least two specimen models met the validation criteria with respect to experimental measurements for both articulations

  14. Non-ablative hyperthermic mesenchymal regeneration: a proposed mechanism of action based on the Vivev model

    NASA Astrophysics Data System (ADS)

    Vos, Jeffrey A.; Livengood, Ryan H.; Jessop, Morris; Coad, James E.

    2011-03-01

    Novel non-ablative hyperthermic medical devices are currently being developed, in association with cryogen surface cooling, to rejuvenate tissues without collagen scarring. These devices have been designed to remodel skin, manage urinary stress incontinence, and more recently, treat vaginal laxity. In contrast to the thermal injury and reparative healing associated with higher energy ablation systems, these lower energy non-ablative systems are designed to subtly modify the collagen, stimulate the fibroblasts, and maintain a functional tissue architecture that subsequently promotes tissue rejuvenation and restoration. While these devices have primarily relied on clinical outcome questionnaires and satisfaction surveys to establish efficacy, a physiologic explanation for the induced tissue changes and tightening has not been well documented. Recent histology studies, using the Viveve ovine vaginal treatment model, have identified changes that propose both a mechanism of action and a tissue remodeling timeline for such non-ablative hyperthermic devices. The Viveve model results are consistent with subtle connective tissue changes leading to fibroblast stimulation and subsequent collagen replacement and augmentation. Unlike tissue ablation devices that cause thermal necrosis, these non-ablative devices renew the targeted tissue without dense collagenous scarring over a period of 3 or more months. The spectrum of histologic findings, as illustrated in the Viveve ovine vaginal model, further support the previously documented safety and efficacy profiles for low-dose non-ablative hyperthermic devices that rejuvenate and tighten submucosal tissues.

  15. Mechanical Model Analysis for Quantitative Evaluation of Liver Fibrosis Based on Ultrasound Tissue Elasticity Imaging

    NASA Astrophysics Data System (ADS)

    Shiina, Tsuyoshi; Maki, Tomonori; Yamakawa, Makoto; Mitake, Tsuyoshi; Kudo, Masatoshi; Fujimoto, Kenji

    2012-07-01

    Precise evaluation of the stage of chronic hepatitis C with respect to fibrosis has become an important issue to prevent the occurrence of cirrhosis and to initiate appropriate therapeutic intervention such as viral eradication using interferon. Ultrasound tissue elasticity imaging, i.e., elastography can visualize tissue hardness/softness, and its clinical usefulness has been studied to detect and evaluate tumors. We have recently reported that the texture of elasticity image changes as fibrosis progresses. To evaluate fibrosis progression quantitatively on the basis of ultrasound tissue elasticity imaging, we introduced a mechanical model of fibrosis progression and simulated the process by which hepatic fibrosis affects elasticity images and compared the results with those clinical data analysis. As a result, it was confirmed that even in diffuse diseases like chronic hepatitis, the patterns of elasticity images are related to fibrous structural changes caused by hepatic disease and can be used to derive features for quantitative evaluation of fibrosis stage.

  16. Locating and navigation mechanism based on place-cell and grid-cell models.

    PubMed

    Yan, Chuankui; Wang, Rubin; Qu, Jingyi; Chen, Guanrong

    2016-08-01

    Extensive experiments on rats have shown that environmental cues play an important role in goal locating and navigation. Major studies about locating and navigation are carried out based only on place cells. Nevertheless, it is known that navigation may also rely on grid cells. Therefore, we model locating and navigation based on both, thus developing a novel grid-cell model, from which firing fields of grid cells can be obtained. We found a continuous-time dynamic system to describe learning and direction selection. In our simulation experiment, according to the results from physiology experiments, we successfully rebuild place fields of place cells and firing fields of grid cells. We analyzed the factors affecting the locating accuracy. Results show that the learning rate, firing threshold and cell number can influence the outcomes from various tasks. We used our system model to perform a goal navigation task and showed that paths that are changed for every run in one experiment converged to a stable one after several runs. PMID:27468322

  17. Study of detecting mechanism of carbon nanotubes gas sensor based on multi-stable stochastic resonance model.

    PubMed

    Jingyi, Zhu

    2015-01-01

    The detecting mechanism of carbon nanotubes gas sensor based on multi-stable stochastic resonance (MSR) model was studied in this paper. A numerically stimulating model based on MSR was established. And gas-ionizing experiment by adding electronic white noise to induce 1.65 MHz periodic component in the carbon nanotubes gas sensor was performed. It was found that the signal-to-noise ratio (SNR) spectrum displayed 2 maximal values, which accorded to the change of the broken-line potential function. The experimental results of gas-ionizing experiment demonstrated that periodic component of 1.65 MHz had multiple MSR phenomena, which was in accordance with the numerical stimulation results. In this way, the numerical stimulation method provides an innovative method for the detecting mechanism research of carbon nanotubes gas sensor. PMID:26198910

  18. Study of detecting mechanism of carbon nanotubes gas sensor based on multi-stable stochastic resonance model

    PubMed Central

    Jingyi, Zhu

    2015-01-01

    The detecting mechanism of carbon nanotubes gas sensor based on multi-stable stochastic resonance (MSR) model was studied in this paper. A numerically stimulating model based on MSR was established. And gas-ionizing experiment by adding electronic white noise to induce 1.65 MHz periodic component in the carbon nanotubes gas sensor was performed. It was found that the signal-to-noise ratio (SNR) spectrum displayed 2 maximal values, which accorded to the change of the broken-line potential function. The experimental results of gas-ionizing experiment demonstrated that periodic component of 1.65 MHz had multiple MSR phenomena, which was in accordance with the numerical stimulation results. In this way, the numerical stimulation method provides an innovative method for the detecting mechanism research of carbon nanotubes gas sensor. PMID:26198910

  19. Mechanical analysis of congestive heart failure caused by bundle branch block based on an electromechanical canine heart model

    NASA Astrophysics Data System (ADS)

    Dou, Jianhong; Xia, Ling; Zhang, Yu; Shou, Guofa; Wei, Qing; Liu, Feng; Crozier, Stuart

    2009-01-01

    Asynchronous electrical activation, induced by bundle branch block (BBB), can cause reduced ventricular function. However, the effects of BBB on the mechanical function of heart are difficult to assess experimentally. Many heart models have been developed to investigate cardiac properties during BBB but have mainly focused on the electrophysiological properties. To date, the mechanical function of BBB has not been well investigated. Based on a three-dimensional electromechanical canine heart model, the mechanical properties of complete left and right bundle branch block (LBBB and RBBB) were simulated. The anatomical model as well as the fiber orientations of a dog heart was reconstructed from magnetic resonance imaging (MRI) and diffusion tensor MRI (DT-MRI). Using the solutions of reaction-diffusion equations and with a strategy of parallel computation, the asynchronous excitation propagation and intraventricular conduction in BBB was simulated. The mechanics of myocardial tissues were computed with time-, sarcomere length-dependent uniaxial active stress initiated at the time of depolarization. The quantification of mechanical intra- and interventricular asynchrony of BBB was then investigated using the finite-element method with an eight-node isoparametric element. The simulation results show that (1) there exists inter- and intraventricular systolic dyssynchrony during BBB; (2) RBBB may have more mechanical synchrony and better systolic function of the left ventricle (LV) than LBBB; (3) the ventricles always move toward the early-activated ventricle; and (4) the septum experiences higher stress than left and right ventricular free walls in BBB. The simulation results validate clinical and experimental recordings of heart deformation and provide regional quantitative estimates of ventricular wall strain and stress. The present work suggests that an electromechanical heart model, incorporating real geometry and fiber orientations, may be helpful for better

  20. Computational model for the cell-mechanical response of the osteocyte cytoskeleton based on self-stabilizing tensegrity structures.

    PubMed

    Kardas, Dieter; Nackenhorst, Udo; Balzani, Daniel

    2013-01-01

    The mechanism by which mechanical stimulation on osteocytes results in biochemical signals that initiate the remodeling process inside living bone tissue is largely unknown. Even the type of stimulation acting on these cells is not yet clearly identified. However, the cytoskeleton of osteocytes is suggested to play a major role in the mechanosensory process due to the direct connection to the nucleus. In this paper, a computational approach to model and simulate the cell structure of osteocytes based on self-stabilizing tensegrity structures is suggested. The computational model of the cell consists of the major components with respect to mechanical aspects: the integrins that connect the cell with the extracellular bone matrix, and different types of protein fibers (microtubules and intermediate filaments) that form the cytoskeleton, the membrane-cytoskeleton (microfilaments), the nucleus and the centrosome. The proposed geometrical cell models represent the cell in its physiological environment which is necessary in order to give a statement on the cell behavior in vivo. Studies on the mechanical response of osteocytes after physiological loading and in particular the mechanical response of the nucleus show that the load acting on the nucleus is rising with increasing deformation applied to the integrins. PMID:22527364

  1. Incorporating Micro-Mechanics Based Damage Models into Earthquake Rupture Simulations

    NASA Astrophysics Data System (ADS)

    Bhat, H.; Rosakis, A.; Sammis, C. G.

    2012-12-01

    The micromechanical damage mechanics formulated by Ashby and Sammis, 1990 and generalized by Deshpande and Evans 2008 has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated new crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces additional strain-rate sensitivity in the constitutive response. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over a wide range of strain rates. Model parameters determined from quasi-static experiments were used to predict the failure strength at higher loading rates. Agreement with experimental results was excellent. After this verification step the constitutive law was incorporated into a Finite Element Code focused on simulating dynamic earthquake ruptures with specific focus on the ends of the fault (fault tip process zone) and the resulting strong ground motion radiation was studied.

  2. Continuum-mechanical, Anisotropic Flow model for polar ice masses, based on an anisotropic Flow Enhancement factor

    NASA Astrophysics Data System (ADS)

    Placidi, Luca; Greve, Ralf; Seddik, Hakime; Faria, Sérgio H.

    2010-03-01

    A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is described by a generalization of Glen’s flow law, based on a scalar anisotropic enhancement factor. The enhancement factor depends on the orientation mass density, which is closely related to the orientation distribution function and describes the distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization) and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model is truly anisotropic despite the collinearity between the stress deviator and stretching tensors.

  3. An information diffusion model based on retweeting mechanism for online social media

    NASA Astrophysics Data System (ADS)

    Xiong, Fei; Liu, Yun; Zhang, Zhen-jiang; Zhu, Jiang; Zhang, Ying

    2012-06-01

    To characterize information propagation on online microblogs, we propose a diffusion model (SCIR) which contains four possible states: Susceptible, contacted, infected and refractory. Agents that read the information but have not decided to spread it, stay in the contacted state. They may become infected or refractory, and both the infected and refractory state are stable. Results show during the evolution process, more contacted agents appear in scale-free networks than in regular lattices. The degree based density of infected agents increases with the degree monotonously, but larger average network degree doesn't always mean less relaxation time.

  4. A Pulse-type Hardware Level Difference Detection Model Based on Sound Source Localization Mechanism in Barn Owl

    NASA Astrophysics Data System (ADS)

    Sakurai, Tsubasa; Sekine, Yoshifumi

    Auditory information processing is very important in the darkness where vision information is extremely limited. Barn owls have excellent hearing information processing function. Barn owls can detect a sound source in the high accuracy of less than two degrees in both of the vertical and horizontal directions. When they perform the sound source localization, the barn owls use the interaural time difference for localization in the horizontal plane, and the interaural level difference for localization in the vertical plane. We are constructing the two-dimensional sound source localization model using pulse-type hardware neuron models based on sound source localization mechanism of barn owl for the purpose of the engineering application. In this paper, we propose a pulse-type hardware model for level difference detection based on sound source localization mechanism of barn owl. Firstly, we discuss the response characteristics of the mathematical model for level difference detection. Next we discuss the response characteristics of the hardware mode. As a result, we show clearly that this proposal model can be used as a sound source localization model of vertical direction.

  5. Investigation of the best coseismic fault model of the 2006 Java tsunami earthquake based on mechanisms of postseismic deformation

    NASA Astrophysics Data System (ADS)

    Gunawan, Endra; Meilano, Irwan; Abidin, Hasanuddin Z.; Hanifa, Nuraini Rahma; Susilo

    2016-03-01

    We investigate three available coseismic fault models of the 2006 M7.8 Java tsunami earthquake, as reported by Fujii and Satake (2006), Bilek and Engdahl (2007), and Yagi and Fukahata (2011), in order to find the best coseismic model based on mechanisms of postseismic deformation associated with viscoelastic relaxation and afterslip. We construct a preliminary rheological model using vertical data, obtaining a final rheological model after we include horizontal and vertical components of afterslip in the further process. Our analysis indicates that the coseismic fault model of Fujii and Satake (2006) provides a better and more realistic result for a rheological model than the others. The best-fit rheological model calculated using the coseismic fault model of Fujii and Satake (2006) comprises a 60 ± 5 km elastic layer thickness with a viscosity of 2.0 ± 1.0 × 1017 Pa s in the asthenosphere. Also, we find that afterslip is dominant over the horizontal displacements, while viscoelastic relaxation is dominant over the vertical displacement. Additionally, in comparison to the coseismic displacement found through GPS data taken at BAKO station, our calculation indicates that Fujii and Satake (2006) modeled coseismic displacements with less GPS data misfit than the other examined models. Finally, we emphasize that our methodology for evaluating the best coseismic fault model can satisfactorily explain the postseismic deformation of the 2006 Java tsunami earthquake.

  6. Mechanical modeling of cholesterol crystallization in atherosclerotic plaques base on Micro-OCT images (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Luo, Yuemei; Liu, Xinyu; Chen, Si; Cui, Dongyao; Wang, Xianghong; Liu, Linbo

    2016-02-01

    Plaque rupture is the critical cause of cardiovascular thrombosis but this process is still under discussion. Recent studies show that, during crystallization, cholesterol crystals in atheromatous plaques accumulate rapidly in a limited space and may result in plaque rupture. However, the actual role of cholesterol crystals on plaque rupture remains unclear due to the lack of detailed morphological information of cholesterol crystals. In this study, we used a Micro-optical coherence tomography (µOCT) setup with 1-2 µm spatial resolution to extract the geometry of cholesterol crystals from human atherosclerotic artery ex vivo firstly. With measured dimensions of cholesterol crystals by this µOCT system (the average length and thickness of 269.1±80.16 µm and 3.0±0.33 µm), we developed a two-dimensional mechanical model in which rectangular shaped cholesterol crystals distribute at different locations spatially. We predicted the stress on the thin cap induced by the expansion of cholesterol crystals by use of finite-element method. Since a large portion of plaques (58%) rupture at points of peak circumferential stress (PCS), we used PCS as the primary indicator of plaque stability with blood pressure of 14.6 kPa on the lumen. The results demonstrate that loading of the concentrated crystals especially at the cap shoulder destabilize the plaque by proportionally increasing the PCS, while evenly distributed crystals loading along the cap might impose less PCS to the plaque than the concentrated case.

  7. A phase-contrast microscopy-based method for modeling the mechanical behavior of mesenchymal stem cells.

    PubMed

    Saeed, Mayssam; Sharabani-Yosef, Orna; Weihs, Daphne; Gefen, Amit

    2016-10-01

    We present three-dimensional (3D) finite element (FE) models of single, mesenchymal stem cells (MSCs), generated from images obtained by optical phase-contrast microscopy and used to quantify the structural responses of the studied cells to externally applied mechanical loads. Mechanical loading has been shown to affect cell morphology and structure, phenotype, motility and other biological functions. Cells experience mechanical loads naturally, yet under prolonged or sizable loading, damage and cell death may occur, which motivates research regarding the structural behavior of loaded cells. For example, near the weight-bearing boney prominences of the buttocks of immobile persons, tissues may become highly loaded, eventually leading to massive cell death that manifests as pressure ulcers. Cell-specific computational models have previously been developed by our group, allowing simulations of cell deformations under compressive or stretching loads. These models were obtained by reconstructing specific cell structures from series of 2D fluorescence, confocal image-slices, requiring cell-specific fluorescent-staining protocols and costly (confocal) microscopy equipment. Alternative modeling approaches represent cells simply as half-spheres or half-ellipsoids (i.e. idealized geometries), which neglects the curvature details of the cell surfaces associated with changes in concentrations of strains and stresses. Thus, we introduce here for the first time an optical image-based FE modeling, where loads are simulated on reconstructed 3D geometrical cell models from a single 2D, phase-contrast image. Our novel modeling method eliminates the need for confocal imaging and fluorescent staining preparations (both expensive), and makes cell-specific FE modeling affordable and accessible to the biomechanics community. We demonstrate the utility of this cost-effective modeling method by performing simulations of compression of MSCs embedded in a gel. PMID:26856632

  8. A comparison of a statistical-mechanics based plasticity model with discrete dislocation plasticity calculations

    NASA Astrophysics Data System (ADS)

    Yefimov, S.; Groma, I.; van der Giessen, E.

    2004-02-01

    A two-dimensional nonlocal version of continuum crystal plasticity theory is proposed, which is based on a statistical-mechanics description of the collective behavior of dislocations coupled to standard small-strain crystal continuum kinematics for single slip. It involves a set of transport equations for the total dislocation density field and for the net-Burgers vector density field, which include a slip system back stress associated to the gradient of the net-Burgers vector density. The theory is applied to the problem of shearing of a two-dimensional composite material with elastic reinforcements in a crystalline matrix. The results are compared to those of discrete dislocation simulations of the same problem. The continuum theory is shown to be able to pick up the distinct dependence on the size of the reinforcing particles for one of the morphologies being studied. Also, its predictions are consistent with the discrete dislocation results during unloading, showing a pronounced Bauschinger effect. None of these features are captured by standard local plasticity theories.

  9. Micro-mechanics based representative volume element modeling of heterogeneous cementitious materials

    NASA Astrophysics Data System (ADS)

    Shahzamanian Sichani, Mohammadmehdi

    The current work focuses on evaluation of the effective elastic properties of cementitious materials through a voxel based FEA approach. Voxels are generated for a heterogeneous cementitious material (Type-I cement) consisting of typical volume fractions of various constituent phases from digital microstructures. The microstructure is modeled as a micro-scale representative volume element (RVE) in ABAQUS to generate cubes several tens of microns in dimension and subjected to various prescribed deformation modes to generate the effective elastic tensor of the material. The RVE-calculated elastic properties such as moduli and Poisson's ratio are validated through an asymptotic expansion homogenization (AEH) and compared with rule of mixtures. Both Periodic (PBC) and Kinematic boundary conditions (KBC) are investigated to determine if the elastic properties are invariant due to boundary conditions. In addition the method of "Windowing" was used to assess the randomness of the constituents and to validate how the isotropic elastic properties were determined. The average elastic properties obtained from the displacement based FEA of various locally anisotropic micro-size cubes extracted from an RVE of size 100x100x100 microns showed that the overall RVE response was fully isotropic. The effects of domain size, degree of hydration, kinematic and periodic boundary conditions, domain sampling techniques, local anisotropy, particle size distribution (PSD), and random microstructure on elastic properties are studied.

  10. Based on Nucleotides Analysis of Tumor Cell Lines to Construct and Validate a Prediction Model of Mechanisms of Chemotherapeutics.

    PubMed

    Liu, Cuichai; Wang, Fang; Liu, Xi; Liu, Min; Liu, Zheng; Sun, Lixin

    2016-01-01

    Cancer is one of the diseases that seriously threaten to human life worldwide. Up to now, chemotherapy remains to be a critical means of cancer treatment, thus the development of chemotherapeutical drugs has become a top priority. An ion pair high performance liquid chromatography (ion pair RP-HPLC) was established for analyzing intracellular nucleotides of tumor cell lines. In this article, a partial least-squares discriminant analysis (PLS-DA) prediction model of mechanisms of chemotherapeutics was established based on four types of drugs with different mechanisms, including antimetabolic agents, antineoplastic agents that affect protein synthesis, agents directly acting on DNA, and RNA interference agents. Then four anti-tumor agents commonly used in clinical were used to validate the availability of the prediction model. Three natural compounds, including 16- dehydropregnenolone (16-DHP), apigenin (API) and diosgenin (DIO), were reported to display anti-tumor effect with unclear mechanisms. The three components were applied to this prediction model firstly. In conclusion, the recognition model was proved to be accurate and feasible to some degree and might become a promising auxiliary method in the process of chemotherapeutic drugs development. PMID:26234361

  11. Analysis of regulatory mechanism after ErbB4 gene mutation based on local modeling methodology.

    PubMed

    Chen, C L; Zhao, J W

    2016-01-01

    ErbB4 is an oncogene belonging to the epidermal growth factor receptor family and contributes to the occurrence and development of multiple cancers, such as gastric, breast, and colorectal cancers. Therefore, studies of the regulation of ErbB4 in cancerigenic pathway will advance molecular targeted therapy. Advanced bioinformatic analysis softwares, such as ExPASy, Predictprotei, QUARK, and I-TASSER, were used to analyze the regulatory mechanism after ErbB4 gene mutation in terms of amino acid sequence, primary, secondary, and tertiary structure of the protein and upstream-downstream receptor/ligands. Mutation of the 19th and 113th amino acids at the carboxyl terminus of ErbB4 protein did not affect its biological nature, but its secondary structure changed and protein binding sites were near 2 mutational sites; moreover, after mutation introduction, additional binding sites were observed. Tertiary structure modeling indicated that local structure of ErbB4 was changed from an α helical conformation into a β chain folding structure; the α helical conformation is the functional site of protein, while active sites are typically near junctions between helical regions, thus the helical structures are easily destroyed and change into folding structures or other structures after stretching. Mutable sites of ErbB4 is exact binding sites where dimer formed with other epidermal growth factor family proteins; mutation enabled the ErbB4 receptor to bind to neuregulin 1 ligand without dimer formation, disrupting the signal transduction pathway and affecting ErbB4 function. PMID:27323039

  12. Identification and design of novel polymer-based mechanical transducers: A nano-structural model for thin film indentation

    NASA Astrophysics Data System (ADS)

    Villanueva, Joshua; Huang, Qian; Sirbuly, Donald J.

    2014-09-01

    Mechanical characterization is important for understanding small-scale systems and developing devices, particularly at the interface of biology, medicine, and nanotechnology. Yet, monitoring sub-surface forces is challenging with current technologies like atomic force microscopes (AFMs) or optical tweezers due to their probe sizes and sophisticated feedback mechanisms. An alternative transducer design relying on the indentation mechanics of a compressible thin polymer would be an ideal system for more compact and versatile probes, facilitating measurements in situ or in vivo. However, application-specific tuning of a polymer's mechanical properties can be burdensome via experimental optimization. Therefore, efficient transducer design requires a fundamental understanding of how synthetic parameters such as the molecular weight and grafting density influence the bulk material properties that determine the force response. In this work, we apply molecular-level polymer scaling laws to a first order elastic foundation model, relating the conformational state of individual polymer chains to the macroscopic compression of thin film systems. A parameter sweep analysis was conducted to observe predicted model trends under various system conditions and to understand how nano-structural elements influence the material stiffness. We validate the model by comparing predicted force profiles to experimental AFM curves for a real polymer system and show that it has reasonable predictive power for initial estimates of the force response, displaying excellent agreement with experimental force curves. We also present an analysis of the force sensitivity of an example transducer system to demonstrate identification of synthetic protocols based on desired mechanical properties. These results highlight the usefulness of this simple model as an aid for the design of a new class of compact and tunable nanomechanical force transducers.

  13. Identification and design of novel polymer-based mechanical transducers: A nano-structural model for thin film indentation

    SciTech Connect

    Villanueva, Joshua; Huang, Qian; Sirbuly, Donald J.

    2014-09-14

    Mechanical characterization is important for understanding small-scale systems and developing devices, particularly at the interface of biology, medicine, and nanotechnology. Yet, monitoring sub-surface forces is challenging with current technologies like atomic force microscopes (AFMs) or optical tweezers due to their probe sizes and sophisticated feedback mechanisms. An alternative transducer design relying on the indentation mechanics of a compressible thin polymer would be an ideal system for more compact and versatile probes, facilitating measurements in situ or in vivo. However, application-specific tuning of a polymer's mechanical properties can be burdensome via experimental optimization. Therefore, efficient transducer design requires a fundamental understanding of how synthetic parameters such as the molecular weight and grafting density influence the bulk material properties that determine the force response. In this work, we apply molecular-level polymer scaling laws to a first order elastic foundation model, relating the conformational state of individual polymer chains to the macroscopic compression of thin film systems. A parameter sweep analysis was conducted to observe predicted model trends under various system conditions and to understand how nano-structural elements influence the material stiffness. We validate the model by comparing predicted force profiles to experimental AFM curves for a real polymer system and show that it has reasonable predictive power for initial estimates of the force response, displaying excellent agreement with experimental force curves. We also present an analysis of the force sensitivity of an example transducer system to demonstrate identification of synthetic protocols based on desired mechanical properties. These results highlight the usefulness of this simple model as an aid for the design of a new class of compact and tunable nanomechanical force transducers.

  14. Modelling Cochlear Mechanics

    PubMed Central

    Elliott, Stephen J.; Teal, Paul D.

    2014-01-01

    The cochlea plays a crucial role in mammal hearing. The basic function of the cochlea is to map sounds of different frequencies onto corresponding characteristic positions on the basilar membrane (BM). Sounds enter the fluid-filled cochlea and cause deflection of the BM due to pressure differences between the cochlear fluid chambers. These deflections travel along the cochlea, increasing in amplitude, until a frequency-dependent characteristic position and then decay away rapidly. The hair cells can detect these deflections and encode them as neural signals. Modelling the mechanics of the cochlea is of help in interpreting experimental observations and also can provide predictions of the results of experiments that cannot currently be performed due to technical limitations. This paper focuses on reviewing the numerical modelling of the mechanical and electrical processes in the cochlea, which include fluid coupling, micromechanics, the cochlear amplifier, nonlinearity, and electrical coupling. PMID:25136555

  15. Dissecting mechanisms of mouse embryonic stem cells heterogeneity through a model-based analysis of transcription factor dynamics.

    PubMed

    Herberg, Maria; Glauche, Ingmar; Zerjatke, Thomas; Winzi, Maria; Buchholz, Frank; Roeder, Ingo

    2016-04-01

    Pluripotent mouse embryonic stem cells (mESCs) show heterogeneous expression levels of transcription factors (TFs) involved in pluripotency regulation, among them Nanog and Rex1. The expression of both TFs can change dynamically between states of high and low activity, correlating with the cells' capacity for self-renewal. Stochastic fluctuations as well as sustained oscillations in gene expression are possible mechanisms to explain this behaviour, but the lack of suitable data hampered their clear distinction. Here, we present a systems biology approach in which novel experimental data on TF heterogeneity is complemented by an agent-based model of mESC self-renewal. Because the model accounts for intracellular interactions, cell divisions and heredity structures, it allows for evaluating the consistency of the proposed mechanisms with data on population growth and on TF dynamics after cell sorting. Our model-based analysis revealed that a bistable, noise-driven network model fulfils the minimal requirements to consistently explain Nanog and Rex1 expression dynamics in heterogeneous and sorted mESC populations. Moreover, we studied the impact of TF-related proliferation capacities on the frequency of state transitions and demonstrate that cellular genealogies can provide insights into the heredity structures of mESCs. PMID:27097654

  16. Modelling and simulations of the chemo-mechanical behaviour of leached cement-based materials: Interactions between damage and leaching

    SciTech Connect

    Stora, E.; Bary, B.; Deville, E.; Montarnal, P.

    2010-08-15

    The assessment of the durability of cement-based materials, which could be employed in underground structures for nuclear waste disposal, requires accounting for deterioration factors, such as chemical attacks and damage, and for the interactions between these phenomena. The objective of the present paper consists in investigating the long-term behaviour of cementitious materials by simulating their response to chemical and mechanical solicitations. In a companion paper (Stora et al., submitted to Cem. Concr. Res. 2008), the implementation of a multi-scale homogenization model into an integration platform has allowed for evaluating the evolution of the mineral composition, diffusive and elastic properties inside a concrete material subjected to leaching. To complete this previous work, an orthotropic micromechanical damage model is presently developed and incorporated in this numerical platform to estimate the mechanical and diffusive properties of damaged cement-based materials. Simulations of the chemo-mechanical behaviour of leached cementitious materials are performed with the tool thus obtained and compared with available experiments. The numerical results are insightful about the interactions between damage and chemical deteriorations.

  17. A mechanism-based model for the population pharmacokinetics of free and bound aflibercept in healthy subjects

    PubMed Central

    Thai, Hoai-Thu; Veyrat-Follet, Christine; Vivier, Nicole; Dubruc, Catherine; Sanderink, Gerard; Mentré, France; Comets, Emmanuelle

    2011-01-01

    AIM Aflibercept (VEGF-Trap), a novel anti-angiogenic agent that binds to VEGF, has been investigated for the treatment of cancer. The aim of this study was to develop a mechanism-based pharmacokinetic (PK) model for aflibercept to characterize its binding to VEGF and its PK properties in healthy subjects. METHODS Data from two phase I clinical studies with aflibercept administered as a single intravenous infusion were included in the analysis. Free and bound aflibercept concentration−time data were analysed using a nonlinear mixed-effects modelling approach with MONOLIX 3.1. RESULTS The best structural model involved two compartments for free aflibercept and one for bound aflibercept, with a Michaelis–Menten type binding of free aflibercept to VEGF from the peripheral compartment. The typical estimated clearances for free and bound aflibercept were 0.88 l day−1 and 0.14 l day−1, respectively. The central volume of distribution of free aflibercept was 4.94 l. The maximum binding capacity was 0.99 mg day−1 and the concentration of aflibercept corresponding to half of maximum binding capacity was 2.91 µg ml−1. Interindividual variability of model parameters was moderate, ranging from 13.6% (Vmax) to 49.8% (Q). CONCLUSION The present PK model for aflibercept adequately characterizes the underlying mechanism of disposition of aflibercept and its nonlinear binding to VEGF. PMID:21575034

  18. Agent-based modeling traction force mediated compaction of cell-populated collagen gels using physically realistic fibril mechanics.

    PubMed

    Reinhardt, James W; Gooch, Keith J

    2014-02-01

    Agent-based modeling was used to model collagen fibrils, composed of a string of nodes serially connected by links that act as Hookean springs. Bending mechanics are implemented as torsional springs that act upon each set of three serially connected nodes as a linear function of angular deflection about the central node. These fibrils were evaluated under conditions that simulated axial extension, simple three-point bending and an end-loaded cantilever. The deformation of fibrils under axial loading varied <0.001% from the analytical solution for linearly elastic fibrils. For fibrils between 100 μm and 200 μm in length experiencing small deflections, differences between simulated deflections and their analytical solutions were <1% for fibrils experiencing three-point bending and <7% for fibrils experiencing cantilever bending. When these new rules for fibril mechanics were introduced into a model that allowed for cross-linking of fibrils to form a network and the application of cell traction force, the fibrous network underwent macroscopic compaction and aligned between cells. Further, fibril density increased between cells to a greater extent than that observed macroscopically and appeared similar to matrical tracks that have been observed experimentally in cell-populated collagen gels. This behavior is consistent with observations in previous versions of the model that did not allow for the physically realistic simulation of fibril mechanics. The significance of the torsional spring constant value was then explored to determine its impact on remodeling of the simulated fibrous network. Although a stronger torsional spring constant reduced the degree of quantitative remodeling that occurred, the inclusion of torsional springs in the model was not necessary for the model to reproduce key qualitative aspects of remodeling, indicating that the presence of Hookean springs is essential for this behavior. These results suggest that traction force mediated matrix

  19. Electrophilic assistance to the cleavage of an RNA model phopshodiester via specific and general base-catalyzed mechanisms.

    PubMed

    Corona-Martínez, David Octavio; Gomez-Tagle, Paola; Yatsimirsky, Anatoly K

    2012-10-19

    Kinetics of transesterification of the RNA model substrate 2-hydroxypropyl 4-nitrophenyl phosphate promoted by Mg(2+) and Ca(2+), the most common biological metals acting as cofactors for nuclease enzymes and ribozymes, as well as by Co(NH(3))(6)(3+), Co(en)(3)(3+), Li(+), and Na(+) cations, often employed as mechanistic probes, was studied in 80% v/v (50 mol %) aqueous DMSO, a medium that allows one to discriminate easily specific base (OH(-)-catalyzed) and general base (buffer-catalyzed) reaction paths. All cations assist the specific base reaction, but only Mg(2+) and Na(+) assist the general base reaction. For Mg(2+)-assisted reactions, the solvent deuterium isotope effects are 1.23 and 0.25 for general base and specific base mechanisms, respectively. Rate constants for Mg(2+)-assisted general base reactions measured with different bases fit the Brønsted correlation with a slope of 0.38, significantly lower than the slope for the unassisted general base reaction (0.77). Transition state binding constants for catalysts in the specific base reaction (K(‡)(OH)) both in aqueous DMSO and pure water correlate with their binding constants to 4-nitrophenyl phosphate dianion (K(NPP)) used as a minimalist transition state model. It was found that K(‡)(OH) ≈ K(NPP) for "protic" catalysts (Co(NH(3))(6)(3+), Co(en)(3)(3+), guanidinium), but K(‡)(OH) ≫ K(NPP) for Mg(2+) and Ca(2+) acting as Lewis acids. It appears from results of this study that Mg(2+) is unique in its ability to assist efficiently the general base-catalyzed transesterification often occurring in active sites of nuclease enzymes and ribozymes. PMID:22991967

  20. Modeling of abnormal mechanical properties of nickel-based single crystal superalloy by three-dimensional discrete dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Yang, Hui; Li, Zhenhuan; Huang, Minsheng

    2014-12-01

    Unlike common single crystals, the nickel-based single crystal superalloy shows surprisingly anomalous flow strength (i.e. with the increase of temperature, the yield strength first increases to a peak value and then decreases) and tension-compression (TC) asymmetry. A comprehensive three-dimensional discrete dislocation dynamics (3D-DDD) procedure was developed to model these abnormal mechanical properties. For this purpose, a series of complicated dynamic evolution details of Kear-Wilsdorf (KW) locks, which are closely related to the flow strength anomaly and TC asymmetry, were incorporated into this 3D-DDD framework. Moreover, the activation of the cubic slip system, which is the origin of the decrease in yield strength with increasing temperature at relatively high temperatures, was especially taken into account by introducing a competition criterion between the unlocking of the KW locks and the activation of the cubic slip system. To test our framework, a series of 3D-DDD simulations were performed on a representative volume cell model with a cuboidal Ni3Al precipitate phase embedded in a nickel matrix. Results show that the present 3D-DDD procedure can successfully capture the dynamic evolution of KW locks, the flow strength anomaly and TC asymmetry. Then, the underlying dislocation mechanisms leading to these abnormal mechanical responses were investigated and discussed in detail. Finally, a cyclic deformation of the nickel-based single crystal superalloy was modeled by using the present DDD model, with a special focus on the influence of KW locks on the Bauschinger effect and cyclic softening.

  1. Research on the multicast mechanism based on physical-layer-impairment awareness model for OpenFlow optical network

    NASA Astrophysics Data System (ADS)

    Bai, Hui-feng; Zhou, Zi-guan; Song, Yan-bin

    2016-05-01

    A physical-layer-impairment (PLI)-awareness based optical multicast mechanism is proposed for OpenFlow controlled optical networks. This proposed approach takes the PLI models including linear and non-linear factors into optical multicast controlled by OpenFlow protocol. Thus, the proposed scheme is able to cover nearly all PLI factors of each optical link and to conduct optical multicast with better communication quality. Simulation results show that the proposed scheme can obtain the better performance of OpenFlow controlled optical multicast services.

  2. From Agents to Continuous Change via Aesthetics: Learning Mechanics with Visual Agent-Based Computational Modeling

    ERIC Educational Resources Information Center

    Sengupta, Pratim; Farris, Amy Voss; Wright, Mason

    2012-01-01

    Novice learners find motion as a continuous process of change challenging to understand. In this paper, we present a pedagogical approach based on agent-based, visual programming to address this issue. Integrating agent-based programming, in particular, Logo programming, with curricular science has been shown to be challenging in previous research…

  3. A physically-based continuum damage mechanics model for numerical prediction of damage growth in laminated composite plates

    NASA Astrophysics Data System (ADS)

    Williams, Kevin Vaughan

    Rapid growth in use of composite materials in structural applications drives the need for a more detailed understanding of damage tolerant and damage resistant design. Current analytical techniques provide sufficient understanding and predictive capabilities for application in preliminary design, but current numerical models applicable to composites are few and far between and their development into well tested, rigorous material models is currently one of the most challenging fields in composite materials. The present work focuses on the development, implementation, and verification of a plane-stress continuum damage mechanics based model for composite materials. A physical treatment of damage growth based on the extensive body of experimental literature on the subject is combined with the mathematical rigour of a continuum damage mechanics description to form the foundation of the model. The model has been implemented in the LS-DYNA3D commercial finite element hydrocode and the results of the application of the model are shown to be physically meaningful and accurate. Furthermore it is demonstrated that the material characterization parameters can be extracted from the results of standard test methodologies for which a large body of published data already exists for many materials. Two case studies are undertaken to verify the model by comparison with measured experimental data. The first series of analyses demonstrate the ability of the model to predict the extent and growth of damage in T800/3900-2 carbon fibre reinforced polymer (CFRP) plates subjected to normal impacts over a range of impact energy levels. The predicted force-time and force-displacement response of the panels compare well with experimental measurements. The damage growth and stiffness reduction properties of the T800/3900-2 CFRP are derived using published data from a variety of sources without the need for parametric studies. To further demonstrate the physical nature of the model, a IM6

  4. Radiation and mechanical unloading effects on mouse vertebral bone: Ground-based models of the spaceflight environment

    NASA Astrophysics Data System (ADS)

    Alwood, Joshua Stewart

    Astronauts on long-duration space missions experience increased ionizing radiation background levels and occasional acute doses of ionizing radiation from solar particle events, in addition to biological challenges introduced by weightlessness. Previous research indicates that cancer radiotherapy damages bone marrow cell populations and reduces mechanical strength of bone. However, the cumulative doses in radiotherapy are an order of magnitude or greater than dose predictions for long-duration space missions. Further detriments to the skeletal system are the disuse and mechanical unloading experienced during weightlessness, which causes osteopenia in weight-bearing cancellous bone (a sponge-like bony network of rods, plates and voids) and cortical bone (dense, compact bone). Studies of radiation exposure utilizing spaceflight-relevant types and doses, and in combination with mechanical unloading, have received little attention. Motivated by the future human exploration of the solar system, the effects of acute and increased background radiation on astronaut skeletal health are important areas of study in order to prevent osteopenic deterioration and, ultimately, skeletal fracture. This dissertation addresses how spaceflight-relevant radiation affects bone microarchitecture and mechanical properties in the cancellous-rich vertebrae and compares results to that of mechanical unloading. In addition, a period of re-ambulation is used to test whether animals recover skeletal tissue after irradiation. Whether radiation exposure displays synergism with mechanical unloading is further investigated. Finite element structural and statistical analyses are used to investigate how changes in architecture affect mechanical stress within the vertebra and to interpret the mechanical testing results. In this dissertation, ground-based models provide evidence that ionizing radiation, both highly energetic gamma-rays and charged iron ions, resulted in a persistent loss of cancellous

  5. A Physically-Based and Distributed Tool for Modeling the Hydrological and Mechanical Processes of Shallow Landslides

    NASA Astrophysics Data System (ADS)

    Arnone, E.; Noto, L. V.; Dialynas, Y. G.; Caracciolo, D.; Bras, R. L.

    2015-12-01

    This work presents the capabilities of a model, i.e. the tRIBS-VEGGIE-Landslide, in two different versions, i.e. developed within a probabilistic framework and coupled with a root cohesion module. The probabilistic model treats geotechnical and soil retention curve parameters as random variables across the basin and estimates theoretical probability distributions of slope stability and the associated "factor of safety" commonly used to describe the occurrence of shallow landslides. The derived distributions are used to obtain the spatio-temporal dynamics of probability of failure, conditioned on soil moisture dynamics at each watershed location. The framework has been tested in the Luquillo Experimental Forest (Puerto Rico) where shallow landslides are common. In particular, the methodology was used to evaluate how the spatial and temporal patterns of precipitation, whose variability is significant over the basin, affect the distribution of probability of failure. Another version of the model accounts for the additional cohesion exerted by vegetation roots. The approach is to use the Fiber Bundle Model (FBM) framework that allows for the evaluation of the root strength as a function of the stress-strain relationships of bundles of fibers. The model requires the knowledge of the root architecture to evaluate the additional reinforcement from each root diameter class. The root architecture is represented with a branching topology model based on Leonardo's rule. The methodology has been tested on a simple case study to explore the role of both hydrological and mechanical root effects. Results demonstrate that the effects of root water uptake can at times be more significant than the mechanical reinforcement; and that the additional resistance provided by roots depends heavily on the vegetation root structure and length.

  6. Mechanics and hydraulics of unsaturated soils: what makes interfaces an indispensable part of a physically-based model

    NASA Astrophysics Data System (ADS)

    Nikooee, E.; Hassanizadeh, S. M.

    2014-12-01

    The foundations of the current theories for hydraulics and mechanics of unsaturated soils have been mainly based on the empirically introduced equations. There are various characteristics of unsaturated soils for which lots of different empirical equations have been proposed such as hydraulic conductivity, water retention curve, and effective stress parameter. One of the remarkable challenges which all current models face is hysteresis, i.e., for a certain matric suction, values of saturation, hydraulic conductivity and effective stress parameter in drying state and wetting are different. Conventional models of hydraulic and mechanical behaviour of unsaturated soils try to account for the hysteresis phenomenon by means of different empirical equations for each hydraulic path. Hassanizadeh and Gray (1993) claimed that the hysteresis in capillary pressure-saturation curves can be modelled through the inclusion of air-water interfaces as a new independent variable [1]. It has recently been stated that the same conjecture can be made for suction stress [2]. Therefore, it seems to better portray hydraulic and mechanical behaviour of unsaturated soils, interfaces are required as an indispensable part of the framework [3, 4]. This presentation aims at introducing the drawbacks of current theories of hydraulics and mechanics of unsaturated soils. For this purpose, the role of interfaces in the mechanics and hydraulics of unsaturated soils is explained and different possibilities to account for the contribution of interfaces are discussed. Finally, current challenges and future research directions are set forth. References[1] Hassanizadeh, S.M. & Gray, W.G.: Thermodynamic basis of capillary pressure in porous media. Water Resour.Res. 29(1993), 3389-3405.[2] Nikooee, E., Habibagahi, G., Hassanizadeh, S.M. & Ghahramani, A.: Effective Stress in unsaturated Soils: a thermodynamic approach based on the interfacial energy and hydromechanical coupling. Transport porous Med. 96

  7. Determination of optimal excitation patterns for local mechanical inner ear stimulation using a physiologically-based model.

    PubMed

    Schurzig, Daniel; Rau, Thomas S; Wallaschek, Jörg; Lenarz, Thomas; Majdani, Omid

    2016-04-01

    Within the field of hearing prosthetics it is known that patients with sufficient residual hearing benefit from the simultaneous employment of hearing aid and cochlear implant. Several attempts have been proposed to combine the sources of the corresponding acoustic and electric stimuli in a single, implantable device. However, since only little is known about the effect of also applying the acoustic stimulus locally from within the inner ear, the current state of research lacks detailed knowledge on the optimal stimulation at the corresponding bionic interface. Within this manuscript, a simple but yet physiologically-based inner ear model is presented which was designed specifically for the analysis of local acoustic or mechanical inner ear stimulation. A detailed model analysis is performed showing that it is capable of mirroring the known mechanical phenomena of this particular stimulation approach. Using the model, it is demonstrated how amplitude and phase shift values of stimuli applied from within the inner ear should be chosen for optimal inner ear stimulation. PMID:27032960

  8. Modelling of the interaction between chemical and mechanical behaviour of ion exchange resins incorporated into a cement-based matrix

    NASA Astrophysics Data System (ADS)

    Neji, M.; Bary, B.; Burlion, N.; Le Bescop, P.

    2013-07-01

    In this paper, we present a predictive model, based on experimental data, to determine the macroscopic mechanical behavior of a material made up of ion exchange resins solidified into a CEM III cement paste. Some observations have shown that in some cases, a significant macroscopic expansion of this composite material may be expected, due to internal pressures generated in the resin. To build the model, we made the choice to break down the problem in two scale's studies. The first deals with the mechanical behavior of the different heterogeneities of the composite, i.e. the resin and the cement paste. The second upscales the information from the heterogeneities to the Representative Elementary Volume (REV) of the composite. The heterogeneities effects are taken into account in the REV by applying a homogenization method derived from the Eshelby theory combined with an interaction coefficient drawn from the poroelasticity theory. At the first scale, from the second thermodynamic law, a formulation is developed to estimate the resin microscopic swelling. The model response is illustrated on a simple example showing the impact of the calculated internal pressure, on the macroscopic strain.

  9. Microstructure Based Modeling of β Phase Influence on Mechanical Response of Cast AM Series Mg Alloys

    SciTech Connect

    Barker, Erin I.; Choi, Kyoo Sil; Sun, Xin; Deda, Erin; Allison, John; Li, Mei; Forsmark, Joy; Zindel, Jacob; Godlewski, Larry

    2014-09-30

    Magnesium alloys have become popular alternatives to aluminums and steels for the purpose of vehicle light-weighting. However, Mg alloys are hindered from wider application due to limited ductility as well as poor creep and corrosion performance. Understanding the impact of microstructural features on bulk response is key to improving Mg alloys for more widespread use and for moving towards truly predicting modeling capabilities. This study focuses on modeling the intrinsic features, particularly volume fraction and morphology of beta phase present, of cast Mg alloy microstructure and quantifying their impact on bulk performance. Computational results are compared to experimental measurements of cast plates of Mg alloy with varying aluminum content.

  10. Students' Problem-Solving in Mechanics: Preference of a Process Based Model.

    ERIC Educational Resources Information Center

    Stavy, Ruth; And Others

    Research in science and mathematics education has indicated that students often use inappropriate models for solving problems because they tend to mentally represent a problem according to surface features instead of referring to scientific concepts and features. The objective of the study reported in this paper was to determine whether 34 Israeli…

  11. Thermo-hydro-mechanical modeling and analysis of cement-based energy storages for small-scale dwellings

    NASA Astrophysics Data System (ADS)

    Hailemariam, Henok; Wuttke, Frank

    2016-04-01

    One of the common technologies for balancing the energy demand and supply in district heating, domestic hot water production, thermal power plants and thermal process industries in general is thermal energy storage. Thermal energy storage, in particular sensible heat storage as compared to latent heat storage and thermo-chemical storage, has recently gained much interest in the renewable energy storage sector due to its comparatively low cost and technical development. Sensible heat storages work on the principle of storing thermal energy by raising or lowering the temperature of liquid (commonly water) or solid media, and do not involve material phase change or conversion of thermal energy by chemical reactions or adsorption processes as in latent heat and thermo-chemical storages, respectively. In this study, the coupled thermo-hydro-mechanical behaviour of a cement-based thermal energy storage system for domestic applications has been modeled in both saturated as well as unsaturated conditions using the Finite Element method along with an extensive experimental analysis program for parameter detection. For this purpose, a prototype model is used with three well-known thermal energy storage materials, and the temperature and heat distribution of the system were investigated under specific thermo-hydro-mechanical conditions. Thermal energy samples with controlled water to solids ratio and stored in water for up to 28 days were used for the experimental program. The determination of parameters included: thermal conductivity, specific heat capacity and linear coefficient of thermal expansion (CTE) using a transient line-source measurement technique as well as a steady-state thermal conductivity and expansion meter; mechanical strength parameters such as uni-axial strength, young's modulus of elasticity, poisson's ratio and shear parameters using uniaxial, oedometer and triaxial tests; and hydraulic properties such as hydraulic permeability or conductivity under

  12. Research on geometrical model and mechanism for metal deformation based on plastic flow

    NASA Astrophysics Data System (ADS)

    An, H. P.; Rui, Z. Y.; Li, X.

    2015-12-01

    Starting with general conditions of metal plastic deformation, it analyses the relation between the percentage spread and geometric parameters of a forming body with typical machining process are studied. A geometrical model of deforming metal is set up according to the characteristic of a flowing metal particle. Starting from experimental results, the effect of technological parameters and friction between workpiece and dies on plastic deformation of a material were studied and a slippage deformation model of mass points within the material was proposed. Finally, the computing methods for strain and deformation energy and temperature rise are derived from homogeneous deformation. The results can be used to select technical parameters and compute physical quantities such as strain, deformation energy, and temperature rise.

  13. A Model-Based Product Evaluation Protocol for Comparison of Safety-Engineered Protection Mechanisms of Winged Blood Collection Needles.

    PubMed

    Haupt, C; Spaeth, J; Ahne, T; Goebel, U; Steinmann, D

    2016-05-01

    OBJECTIVE To evaluate differences in product characteristics and user preferences of safety-engineered protection mechanisms of winged blood collection needles. DESIGN Randomized model-based simulation study. SETTING University medical center. PARTICIPANTS A total of 33 third-year medical students. METHODS Venipuncture was performed using winged blood collection needles with 4 different safety mechanisms: (a) Venofix Safety, (b) BD Vacutainer Push Button, (c) Safety-Multifly, and (d) Surshield Surflo. Each needle type was used in 3 consecutive tries: there was an uninstructed first handling, then instructions were given according to the operating manual; subsequently, a first trial and second trial were conducted. Study end points included successful activation, activation time, single-handed activation, correct activation, possible risk of needlestick injury, possibility of deactivation, and preferred safety mechanism. RESULTS The overall successful activation rate during the second trial was equal for all 4 devices (94%-100%). Median activation time was (a) 7 s, (b) 2 s, (c) 9 s, and (d) 7 s. Single-handed activation during the second trial was (a) 18%, (b) 82%, (c) 15%, and (d) 45%. Correct activation during the second trial was (a) 3%, (b) 64%, (c) 15%, and (d) 39%. Possible risk of needlestick injury during the second trial was highest with (d). Possibility of deactivation was (a) 0%, (b) 12%, (c) 9%, and (d) 18%. Individual preferences for each system were (a) 11, (b) 17, (c) 5, and (d) 0. The main reason for preference was the comprehensive safety mechanism. CONCLUSION Significant differences exist between safety mechanisms of winged blood collection needles. Infect Control Hosp Epidemiol 2016;37:505-511. PMID:26868306

  14. Understanding Evapotranspiration Trends and their Driving Mechanisms: An investigation across CONUS based on numerical modeling

    NASA Astrophysics Data System (ADS)

    Parr, D.; Wang, G.; Fu, C.

    2015-12-01

    As shown by climate models, increasing global temperatures and enhanced greenhouse gas concentration such as CO2 have had major effects on the dynamics of the hydrologic cycle and the surface energy budget, in particular, on evapotranspiration (ET). ET has significant decadal variations whether it be regionally or globally and variations of ET have major environmental and socioeconomic impacts. A number of recent studies have found a global increase in annual mean ET around 7mm per year per decade from about 1982 to the late 1990s. These results correspond with what is expected from an intensification of the hydrological cycle. However, the increasing ET trend did not continue after 1998 and from 1998-2008 this global trend was replaced with a decreasing trend of similar magnitude. This study uses numerical modeling to investigate if similar changing ET trends emerge in the continental U.S and part of northern Mexico. After validating model simulated evaporative fluxes and comparing spatial patterns to the aforementioned studies, various changing trends of different signs are identified across the U.S., and specific regions with strong signals of change are chosen for further examination with the purpose of identifying the root causes of these changing trends and which variables are most influential towards change. Experimental simulations conducted to isolate the most influential factors towards ET reveal that precipitation amount as well as its characteristics have the greatest impact on the ET trends discovered, with other factors like wind and air temperatures displaying less influence over inter-annual trends. This study helps better understand terrestrial ET and it's interactions which will help facilitate better predictions of change in surface climate such as heatwaves and droughts as well as impacts on water resources.

  15. Formation Mechanism and Characteristics Research of Ball Lightning Based on Vortex Model

    NASA Astrophysics Data System (ADS)

    Li, Zi-Cheng; Yang, Guo-Hua

    2011-05-01

    The strange characteristics of ball lightning are considered as a question hard to explain. In order to solve the problem, in this paper a complete model of plasma vortex is presented for the ball lightning. By ideal MHD equations, through imposing disturbance to plasma column, the possibility of sausage and kink instability of the lightning channel is analyzed from the perspective the minimum potential energy. The conclusion is that the kink instability (m = 1) is most prone to occur. And when instability occurs, because of the difference of the magnetic field in the twisted area, the magnetic pressure makes the trend further and therefore forming the plasma vortex that may eventually turn into ball lightning if the energy of the vortex is large enough. The existence of the vortex makes ball lightning have a short period of time stability. By the proposed model, the ball lightning features that are hard to understand in the past are explained. In this paper, the reason for bead lightning is also explained from the perspective of the sausage instability.

  16. Mechanism of contact angle saturation and an energy-based model for electrowetting

    NASA Astrophysics Data System (ADS)

    Rui, Zhao; Zhong-Cheng, Liang

    2016-06-01

    Electrowetting, as a well-known approach to increasing droplet wettability on a solid surface by electrical bias, has broad applications. However, it is limited by contact angle saturation at large voltage. Although several debated hypotheses have been proposed to describe it, the physical origin of contact angle saturation still remains obscure. In this work, the physical factors responsible for the onset of contact angle saturation are explored, and the correlated theoretical models are established to characterize electrowetting behavior. Combination of the proper 3-phase system employed succeeds in dropping the saturating contact angle below 25°, and validates that the contact angle saturation is not a result of device-related imperfection. Project supported by the Fund from the Research Center of Optical Communications Engineering & Technology, Jiangsu Province, China (Grant No. ZSF0402).

  17. Interface transferring mechanism and error modification of FRP-OFBG strain sensor based on standard linear viscoelastic model

    NASA Astrophysics Data System (ADS)

    Li, Jilong; Zhou, Zhi; Ou, Jinping

    2006-03-01

    This paper presents the interface transferring mechanism and error modification of the Fiber Reinforced Polymer-Optical Fiber Bragg Grating (FRP-OFBG) sensing tendons, which including GFRP (Glass Fiber Reinforced Polymer) and CFRP (Carbon Fiber Reinforced Polymer), using standard linear viscoelastic model. The optical fiber is made up of glass, quartz or plastic, et al, which creep strain is very small at room temperature. So the tensile creep compliance of optical fiber is independent of time at room temperature. On the other hand, the FRP (GFRP or CFRP) is composed of a kind of polymeric matrix (epoxy resins or the others) with glass, carbon or aramid fibers, which shear creep strain is dependent of time at room temperature. Hence, the standard linear viscoelastic model is employed to describe the shear creep compliance of FRP along the fiber direction. The expression of interface strain transferring mechanism of FRP-OFBG sensors is derived based on the linear viscoelastic theory and the analytic solution of the error rate is given by the inverse Laplace transform. The effects of FRP viscoelasticity on the error rate of FRP-OFBG sensing tendons are included in the above expression. And the transient and steady-state error modified coefficient of FRP-OFBG sensors are obtained using initial value and final value theorems. Finally, a calculated example is given to explain the correct of theoretical prediction.

  18. Mechanisms based on piezoactuators

    NASA Astrophysics Data System (ADS)

    Claeyssen, Frank; Le Letty, Ronan; Barillot, Francois; Lhermet, Nicolas; Fabbro, H.; Guay, Philippe; Yorck, Mickael; Bouchilloux, Philippe

    2001-06-01

    In several fields (optics, space, aircraft, fluid control, biomedical, and manufacturing) there is a strong need for compact, robust and efficient positioning mechanisms that also offer high precision, short response times, low power consumption, low electromagnetic interference and multiple degrees of freedom. Piezoelectric actuators are generally good candidates for building such mechanisms. The products manufactured by Cedrat Recherche SA are piezoelectric actuators offering compact size, high deformation (up to 1%) and high stiffness. These actuators have successfully passed different qualification tests (air and space qualification, lifetime tests). They can easily be integrated in applications, as shown by examples of mechanisms taken from various fields: a super amplified actuator for a MRI biomedical device, a tip-tilt for mirrors, a chopper for X-ray diffraction, a helicopter flap mechanism and an XYZ stage for the AFM microscope of the MIDAS instrument of the ESA ROSETTA space mission.

  19. Mechanism-based crystal plasticity modeling of twin boundary migration in nanotwinned face-centered-cubic metals

    NASA Astrophysics Data System (ADS)

    Mirkhani, Hamidreza; Joshi, Shailendra P.

    2014-08-01

    Nanotwinned (nt) metals are an important subset of nanostructured materials because they exhibit impressive strength and ductility. Several recent investigations on nt face-centered-cubic (FCC) metals indicate that their macroscopic responses emerge from complex microscopic mechanisms that are dominated by dislocation-TB interactions. Under applied stimulus, nt microstructures evolve through migration of twin boundaries (TBs) that may have implications on the material strength and stability. This work focuses on modeling TB migration within finite element framework in an explicit manner and studying its effects on the micromechanics of twinned FCC metals under quasi-static loading conditions. The theoretical setting is developed using three-dimensional single crystal plasticity as a basis wherein the plastic slip on the {111}<1bar10> slip systems in an FCC crystal structure is modeled as visco-plastic behavior. Owing to their governing role, twins are modeled as discrete lamellas with full crystallographic anisotropy. To model TB migration, an additional visco-plastic slip-law for twinning partial systems ({111}<112bar>) based on the nucleation and motion of twin partial dislocations is introduced. This size-dependent constitutive law is presumed to prevail in the vicinity of the TB and naturally facilitates TB migration when combined with a twinning condition that is based on the accrual of the necessary shear strain. The constitutive development is implemented within a finite element framework through a User Material (UMAT) facility within ABAQUS/STANDARD®. Detailed micromechanics simulations on model microstructures involving single-grained and polycrystalline topologies are presented.

  20. A tribo-mechanical analysis of PVA-based building-blocks for implementation in a 2-layered skin model.

    PubMed

    Morales Hurtado, M; de Vries, E G; Zeng, X; van der Heide, E

    2016-09-01

    Poly(vinyl) alcohol hydrogel (PVA) is a well-known polymer widely used in the medical field due to its biocompatibility properties and easy manufacturing. In this work, the tribo-mechanical properties of PVA-based blocks are studied to evaluate their suitability as a part of a structure simulating the length scale dependence of human skin. Thus, blocks of pure PVA and PVA mixed with Cellulose (PVA-Cel) were synthesised via freezing/thawing cycles and their mechanical properties were determined by Dynamic Mechanical Analysis (DMA) and creep tests. The dynamic tests addressed to elastic moduli between 38 and 50kPa for the PVA and PVA-Cel, respectively. The fitting of the creep compliance tests in the SLS model confirmed the viscoelastic behaviour of the samples with retardation times of 23 and 16 seconds for the PVA and PVA-Cel, respectively. Micro indentation tests were also achieved and the results indicated elastic moduli in the same range of the dynamic tests. Specifically, values between 45-55 and 56-81kPa were obtained for the PVA and PVA-Cel samples, respectively. The tribological results indicated values of 0.55 at low forces for the PVA decreasing to 0.13 at higher forces. The PVA-Cel blocks showed lower friction even at low forces with values between 0.2 and 0.07. The implementation of these building blocks in the design of a 2-layered skin model (2LSM) is also presented in this work. The 2LSM was stamped with four different textures and their surface properties were evaluated. The hydration of the 2LSM was also evaluated with a corneometer and the results indicated a gradient of hydration comparable to the human skin. PMID:27236420

  1. Mechanical effects in cookoff modeling

    SciTech Connect

    Gross, R.J.; Baer, M.R.; Hobbs, M.L.

    1994-07-01

    Complete cookoff modeling of energetic material in confined geometries must couple thermal, chemical and mechanical effects. In the past, modeling has focused on the prediction of the onset of combustion behavior based only on thermal-chemistry effects with little or no regard to the mechanical behavior of the energetic material. In this paper, an analysis tool is outlined which couples thermal, chemical, and mechanical behavior for one-dimensional Geometries comprised of multi-materials. A reactive heat flow code, XCHEM, and a quasistatic mechanics code, SANTOS, have been completely coupled using, a reactive, elastic-plastic constitutive model describing pressurization of the energetic material. This new Thermally Reactive Elastic-plastic explosive code, TREX, was developed to assess the coupling, of mechanics with thermal chemistry making multidimensional cookoff analysis possible. In this study, TREX is applied to confined and unconfined systems. The confined systems simulate One-Dimensional Time to explosion (ODTX) experiments in both spherical and cylindrical configurations. The spherical ODTX system is a 1.27 cm diameter sphere of TATB confined by aluminum exposed to a constant external temperature. The cylindrical ODTX system is an aluminum tube filled with HMX, NC, and inert exposed to a constant temperature bath. Finally. an unconfined system consisting of a hollow steel cylinder filled with a propellant composed of Al, RMX, and NC, representative of a rocket motor, is considered. This model system is subjected to transient internal and external radiative/convective boundary conditions representative of 5 minutes exposure to a fire. The confined systems show significant pressure prior to ignition, and the unconfined system shows extrusion of the propellent suggesting that the energetic material becomes more shock sensitive.

  2. A statistical model for Windstorm Variability over the British Isles based on Large-scale Atmospheric and Oceanic Mechanisms

    NASA Astrophysics Data System (ADS)

    Kirchner-Bossi, Nicolas; Befort, Daniel J.; Wild, Simon B.; Ulbrich, Uwe; Leckebusch, Gregor C.

    2016-04-01

    Time-clustered winter storms are responsible for a majority of the wind-induced losses in Europe. Over last years, different atmospheric and oceanic large-scale mechanisms as the North Atlantic Oscillation (NAO) or the Meridional Overturning Circulation (MOC) have been proven to drive some significant portion of the windstorm variability over Europe. In this work we systematically investigate the influence of different large-scale natural variability modes: more than 20 indices related to those mechanisms with proven or potential influence on the windstorm frequency variability over Europe - mostly SST- or pressure-based - are derived by means of ECMWF ERA-20C reanalysis during the last century (1902-2009), and compared to the windstorm variability for the European winter (DJF). Windstorms are defined and tracked as in Leckebusch et al. (2008). The derived indices are then employed to develop a statistical procedure including a stepwise Multiple Linear Regression (MLR) and an Artificial Neural Network (ANN), aiming to hindcast the inter-annual (DJF) regional windstorm frequency variability in a case study for the British Isles. This case study reveals 13 indices with a statistically significant coupling with seasonal windstorm counts. The Scandinavian Pattern (SCA) showed the strongest correlation (0.61), followed by the NAO (0.48) and the Polar/Eurasia Pattern (0.46). The obtained indices (standard-normalised) are selected as predictors for a windstorm variability hindcast model applied for the British Isles. First, a stepwise linear regression is performed, to identify which mechanisms can explain windstorm variability best. Finally, the indices retained by the stepwise regression are used to develop a multlayer perceptron-based ANN that hindcasted seasonal windstorm frequency and clustering. Eight indices (SCA, NAO, EA, PDO, W.NAtl.SST, AMO (unsmoothed), EA/WR and Trop.N.Atl SST) are retained by the stepwise regression. Among them, SCA showed the highest linear

  3. Origami based mechanical metamaterials.

    PubMed

    Lv, Cheng; Krishnaraju, Deepakshyam; Konjevod, Goran; Yu, Hongyu; Jiang, Hanqing

    2014-01-01

    We describe mechanical metamaterials created by folding flat sheets in the tradition of origami, the art of paper folding, and study them in terms of their basic geometric and stiffness properties, as well as load bearing capability. A periodic Miura-ori pattern and a non-periodic Ron Resch pattern were studied. Unexceptional coexistence of positive and negative Poisson's ratio was reported for Miura-ori pattern, which are consistent with the interesting shear behavior and infinity bulk modulus of the same pattern. Unusually strong load bearing capability of the Ron Resch pattern was found and attributed to the unique way of folding. This work paves the way to the study of intriguing properties of origami structures as mechanical metamaterials. PMID:25099402

  4. Origami based Mechanical Metamaterials

    PubMed Central

    Lv, Cheng; Krishnaraju, Deepakshyam; Konjevod, Goran; Yu, Hongyu; Jiang, Hanqing

    2014-01-01

    We describe mechanical metamaterials created by folding flat sheets in the tradition of origami, the art of paper folding, and study them in terms of their basic geometric and stiffness properties, as well as load bearing capability. A periodic Miura-ori pattern and a non-periodic Ron Resch pattern were studied. Unexceptional coexistence of positive and negative Poisson's ratio was reported for Miura-ori pattern, which are consistent with the interesting shear behavior and infinity bulk modulus of the same pattern. Unusually strong load bearing capability of the Ron Resch pattern was found and attributed to the unique way of folding. This work paves the way to the study of intriguing properties of origami structures as mechanical metamaterials. PMID:25099402

  5. Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS

    NASA Astrophysics Data System (ADS)

    De Geeter, N.; Crevecoeur, G.; Leemans, A.; Dupré, L.

    2015-01-01

    In transcranial magnetic stimulation (TMS), an applied alternating magnetic field induces an electric field in the brain that can interact with the neural system. It is generally assumed that this induced electric field is the crucial effect exciting a certain region of the brain. More specifically, it is the component of this field parallel to the neuron’s local orientation, the so-called effective electric field, that can initiate neuronal stimulation. Deeper insights on the stimulation mechanisms can be acquired through extensive TMS modelling. Most models study simple representations of neurons with assumed geometries, whereas we embed realistic neural trajectories computed using tractography based on diffusion tensor images. This way of modelling ensures a more accurate spatial distribution of the effective electric field that is in addition patient and case specific. The case study of this paper focuses on the single pulse stimulation of the left primary motor cortex with a standard figure-of-eight coil. Including realistic neural geometry in the model demonstrates the strong and localized variations of the effective electric field between the tracts themselves and along them due to the interplay of factors such as the tract’s position and orientation in relation to the TMS coil, the neural trajectory and its course along the white and grey matter interface. Furthermore, the influence of changes in the coil orientation is studied. Investigating the impact of tissue anisotropy confirms that its contribution is not negligible. Moreover, assuming isotropic tissues lead to errors of the same size as rotating or tilting the coil with 10 degrees. In contrast, the model proves to be less sensitive towards the not well-known tissue conductivity values.

  6. The Conceptual Mechanism for Viable Organizational Learning Based on Complex System Theory and the Viable System Model

    ERIC Educational Resources Information Center

    Sung, Dia; You, Yeongmahn; Song, Ji Hoon

    2008-01-01

    The purpose of this research is to explore the possibility of viable learning organizations based on identifying viable organizational learning mechanisms. Two theoretical foundations, complex system theory and viable system theory, have been integrated to provide the rationale for building the sustainable organizational learning mechanism. The…

  7. Mechanics based model for predicting structure-induced rolling resistance (SRR) of the tire-pavement system

    NASA Astrophysics Data System (ADS)

    Shakiba, Maryam; Ozer, Hasan; Ziyadi, Mojtaba; Al-Qadi, Imad L.

    2016-05-01

    The structure-induced rolling resistance of pavements, and its impact on vehicle fuel consumption, is investigated in this study. The structural response of pavement causes additional rolling resistance and fuel consumption of vehicles through deformation of pavement and various dissipation mechanisms associated with inelastic material properties and damping. Accurate and computationally efficient models are required to capture these mechanisms and obtain realistic estimates of changes in vehicle fuel consumption. Two mechanistic-based approaches are currently used to calculate vehicle fuel consumption as related to structural rolling resistance: dissipation-induced and deflection-induced methods. The deflection-induced approach is adopted in this study, and realistic representation of pavement-vehicle interactions (PVIs) is incorporated. In addition to considering viscoelastic behavior of asphalt concrete layers, the realistic representation of PVIs in this study includes non-uniform three-dimensional tire contact stresses and dynamic analysis in pavement simulations. The effects of analysis type, tire contact stresses, pavement viscoelastic properties, pavement damping coefficients, vehicle speed, and pavement temperature are then investigated.

  8. Molecular modeling-based inclusion mechanism and stability studies of doxycycline and hydroxypropyl-β-cyclodextrin complex for ophthalmic delivery.

    PubMed

    Zhang, Haohao; Chen, Meiwan; He, Zixin; Wang, Zhouhua; Zhang, Meimei; He, Zhouyang; Wan, Qian; Liang, Dan; Repka, Michael A; Wu, Chuanbin

    2013-03-01

    The aim of the present study was to prepare a stable complex of doxycycline (Doxy) and hydroxypropyl-β-cyclodextrin (HPβCD) for ophthalmic delivery and investigate the inclusion mechanism and the inclusion effects on the stability of Doxy. The Doxy/HPβCD complex was prepared by solution stirring and then characterized by scanning electron microscopy and ultraviolet spectroscopy. Based on results of nuclear magnetic resonance, molecular model of Doxy/HPβCD complex was established using computational simulation of PM3 method implemented in Gaussian 03. Stabilities of Doxy/HPβCD complex in both aqueous solution and solid state at 25°C were evaluated by HPLC. Finally, in vitro antibacterial activity of the Doxy/HPβCD complex was evaluated by disk diffusion test. It was found that the stabilities of Doxy/HPβCD complex in both aqueous solution and solid state were improved obviously as compared with Doxy alone. This stability enhancement is consistent with the inclusion mechanism between HPβCD and Doxy, which showed that the unstable site of Doxy molecule at 6-CH3 was protected in the hydrophobic cavity of HPβCD, additionally, the chelation of Mg2+ provided a synergetic protection of the other unstable site of Doxy at 4-N(CH3)2. The antibacterial activity results indicated that Doxy/HPβCD complex might have potential for clinical applications. PMID:23160918

  9. A Collector Plate Mechanism-Based Classical Intergranular Precipitation Model for Al Alloys Sensitized at Different Temperatures

    NASA Astrophysics Data System (ADS)

    Yi, Gaosong; Derrick, Alexander T.; Zhu, Yakun; Free, Michael L.

    2015-11-01

    The sensitization behavior of Al 5xxx alloys is mainly caused by the formation of Mg-rich precipitates at grain boundaries. In this study, a classical nucleation-growth-coarsening theory for the description of intergranular precipitation is formulated, which adopts a collector plate mechanism, an equivalent average Mg concentration at the grain boundary, and new coarsening mechanisms. Three coarsening mechanisms, the modified Lifshitz-Slyozov-Wagner, the Kirchner mechanism, and a combination of these two mechanisms, are compared. Modeling results reveal that the Kirchner mechanism will breakdown when continuity ( √ {Nπ R2 } ) is close to 1. According to the new model, the coarsening still accounts for a small fraction (only 10 pct) in the final growth rate after aging at 343 K (70 °C) for 40 months, which is confirmed by the precipitate size distribution data. Thickness and continuity results predicted by the new model agree well with the experimental results obtained from scanning transmission electron microscopy images of Al 5083 H131 alloys aged at 343 K (70 °C) for different times. In addition, the new model is also applied to a high-temperature [453 K (180 °C)] situation, where coarsening of precipitates is observed.

  10. Prediction of chirality- and size-dependent elastic properties of single-walled boron nitride nanotubes based on an accurate molecular mechanics model

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Mirnezhad, M.; Sahmani, S.

    2015-04-01

    Molecular mechanics theory has been widely used to investigate the mechanical properties of nanostructures analytically. However, there is a limited number of research in which molecular mechanics model is utilized to predict the elastic properties of boron nitride nanotubes (BNNTs). In the current study, the mechanical properties of chiral single-walled BNNTs are predicted analytically based on an accurate molecular mechanics model. For this purpose, based upon the density functional theory (DFT) within the framework of the generalized gradient approximation (GGA), the exchange correlation of Perdew-Burke-Ernzerhof is adopted to evaluate force constants used in the molecular mechanics model. Afterwards, based on the principle of molecular mechanics, explicit expressions are given to calculate surface Young's modulus and Poisson's ratio of the single-walled BNNTs for different values of tube diameter and types of chirality. Moreover, the values of surface Young's modulus, Poisson's ratio and bending stiffness of boron nitride sheets are obtained via the DFT as byproducts. The results predicted by the present model are in reasonable agreement with those reported by other models in the literature.

  11. Global modelling of secondary organic aerosol from α-pinene oxidation using a parameterization based on a detailed chemical mechanism

    NASA Astrophysics Data System (ADS)

    Ceulemans, Karl; Müller, Jean-Francois; Compernolle, Steven; Stavrakou, Jenny

    2010-05-01

    Monoterpenes are oxidized in the atmosphere by ozone and the hydroxyl and nitrate radicals. The condensable products resulting from these reactions contribute to Secondary Organic Aerosol (SOA). We have developed a detailed α-pinene chemical mechanism BOREAM (Capouet et al. 2008), in which the primary gas phase chemistry is based on quantum-chemical results, structure activity relationships and experimental data. The secondary chemistry of the most important products is treated explicitly, while further chemistry is reduced by the aid of generic species classes. The partitioning between gas phase and SOA is modeled using Pankow's partitioning approach (Pankow 1994), with vapor pressures (Capouet and Müller 2006) and activity coefficients (Compernolle et al. 2009) obtained from group contribution methods. We will discuss the performance of BOREAM through comparison of model predictions for SOA formation with experimental SOA yields for a large number (>150) of photo-oxidation and dark ozonolysis experiments (Ceulemans et al. 2009). Although the BOREAM SOA yields are significantly higher than in several previous box modeling studies, a reasonable agreement is found in comparison with most laboratory measurements. For use in a global model, the detailed BOREAM chemistry is replaced by a parameterized scheme based on the two-product approach (Odum et al. 1996) with parameters obtained through regressions of full model simulations. The reduced scheme accounts for the dependence of SOA yield on the oxidant (ozone, OH or NO3) and the NOx regime. For example, the reaction of alpha-pinene with OH generates a peroxy radical which, upon reaction with either NO or HO2 leads to the formation of two condensable products. The branching ratios and partitioning coefficients are temperature dependent. We inserted the obtained parameterized scheme in the global model IMAGES, where it is used to represent the SOA formation due to the monoterpenes. For aromatics, isoprene and

  12. A mechanism-based pharmacokinetic/pharmacodynamic model for CYP3A1/2 induction by dexamethasone in rats

    PubMed Central

    Li, Liang; Li, Zai-quan; Deng, Chen-hui; Ning, Miao-ran; Li, Han-qing; Bi, Shan-shan; Zhou, Tian-yan; Lu, Wei

    2012-01-01

    Aim: To develop a pharmacokinetic/pharmacodynamic (PK/PD) model describing the receptor/gene-mediated induction of CYP3A1/2 by dexamethasone (DEX) in rats. Methods: A group of male Sprague-Dawley rats receiving DEX (100 mg/kg, ip) were sacrificed at various time points up to 60 h post-treatment. Their blood sample and liver were collected. The plasma concentration of DEX was determined with a reverse phase HPLC method. CYP3A1/2 mRNA, protein levels and enzyme activity were measured using RT-PCR, ELISA and the testosterone substrate assay, respectively. Data analyses were performed using a first-order conditional estimate (FOCE) with INTERACTION method in NONMEM version 7.1.2. Results: A two-compartment model with zero-order absorption was applied to describe the pharmacokinetic characteristics of DEX. Systemic clearance, the apparent volume of distribution and the duration of zero-order absorption were calculated to be 172.7 mL·kg−1·h−1, 657.4 mL/kg and 10.47 h, respectively. An indirect response model with a series of transit compartments was developed to describe the induction of CYP3A1/2 via PXR transactivation by DEX. The maximum induction of CYP3A1 and CYP3A2 mRNA levels was achieved, showing nearly 21.29- and 8.67-fold increases relative to the basal levels, respectively. The CYP3A1 and CYP3A2 protein levels were increased by 8.02-fold and 2.49-fold, respectively. The total enzyme activities of CYP3A1/2 were shown to increase by up to 2.79-fold, with a lag time of 40 h from the Tmax of the DEX plasma concentration. The final PK/PD model was able to recapitulate the delayed induction of CYP3A1/2 mRNA, protein and enzyme activity by DEX. Conclusion: A mechanism-based PK/PD model was developed to characterize the complex concentration-induction response relationship between DEX and CYP3A1/2 and to resolve the drug- and system-specific PK/PD parameters for the course of induction. PMID:22212433

  13. Gastric acid secretion in the dog: a mechanism-based pharmacodynamic model for histamine stimulation and irreversible inhibition by omeprazole.

    PubMed

    Abelö, Angela; Holstein, Björn; Eriksson, Ulf G; Gabrielsson, Johan; Karlsson, Mats O

    2002-08-01

    A mechanism-based pharmacodynamic model was used to describe the inhibitory effect by omeprazole on gastric acid secretion measured after histamine stimulation in the dog. The model identifies parameters that are related to the physiological system, the histamine stimulation, and the irreversible effect of omeprazole on the H+, K(+)-ATPase enzyme. Four different experiments with omeprazole (Exps. 1-4) and two placebo experiments were performed in each of the four Heidenhain pouch dogs used. For placebo and experiments 1-3, saline or omeprazole 0.81 mumol/kg was infused during 3 hr with measurements of histamine-stimulated gastric acid secretion in two periods of 3.5-6.5 hr, one period starting just before the omeprazole infusion and a second later period up to 29 hr post infusion. In experiment 4, 0.18 mumol/kg of omeprazole was infused for 22.5 min and gastric juice was collected for 5 hr post infusion. The response data was well described by the model. Similar parameter estimates were obtained by three different analysis methods; naïve pooling, two-stage method and nonlinear mixed effects modeling. The elimination rate constant for the H+, K(+)-ATPase enzyme, kout, was estimated to be 0.040 hr-1, corresponding to a half-life of about 17 hr. This rate constant determines the duration of omeprazole inhibition after long-term exposure. For short-term omeprazole exposure the duration is determined by the rate constant for transfer of enzymes from active to resting state, estimated to be 1.88 hr-1. The second-order rate constant for histamine stimulation was estimated to be 0.064 hr-1 per histamine concentration unit and the maximum acid secretion was estimated to be 5.0 mmol H+/30 min. The second-order rate constant for the irreversible binding of omeprazole to H+, K(+)-ATPase, kome, was estimated to be 2.39 L/mumol.hr. By modeling the histamine-induced baseline response simultaneously with active treatment, predictions of the response are possible not only

  14. Spatially explicit model of transposon-based genetic drive mechanisms for displacing fluctuating populations of anopheline vector mosquitoes.

    PubMed

    Kiszewski, A E; Spielman, A

    1998-07-01

    To evaluate the prospect of transposon-based genetic drive mechanisms for replacing African vectors of malaria with nonvector anopheline mosquitoes, we developed a spatially explicit simulation model that determined the likelihood that released transgenic mosquitoes may proceed to fixation or extinction under diverse conditions. We compared the effect on fixation of long breeding seasons with relatively subtle population fluctuations to short breeding seasons with severe bottlenecks. Assuming 100% transposition efficiency among heterozygotes with fitness varying between 50 and 100% of that of wild-type mosquitoes, we simulated releases of 1, 10, 50, 90, and 99% of transposon-bearers in relation to wild mosquitoes as well as 1 and 10% releases that were repeated annually. We also evaluated diverse patterns of release including linear, marginal, focused, and scattered distribution. Random dispersal provided the most rapid fixation of transposons within populations. More massive releases allowed longer persistence of transposon-bearers but did not promote fixation, especially when breeding seasons were long. Relative fitness of transposon-bearers, however, proved more powerful than pattern or number of releases in determining whether a construct will become fixed or extinct. Even when fitness approaches that of the wild-type, fixation of a construct may require 150 generations or more. PMID:9701949

  15. A musculo-mechanical model of esophageal transport based on an immersed boundary-finite element approach

    NASA Astrophysics Data System (ADS)

    Kou, Wenjun; Griffith, Boyce E.; Pandolfino, John E.; Kahrilas, Peter J.; Patankar, Neelesh A.

    2015-11-01

    This work extends a fiber-based immersed boundary (IB) model of esophageal transport by incorporating a continuum model of the deformable esophageal wall. The continuum-based esophagus model adopts finite element approach that is capable of describing more complex and realistic material properties and geometries. The leakage from mismatch between Lagrangian and Eulerian meshes resulting from large deformations of the esophageal wall is avoided by careful choice of interaction points. The esophagus model, which is described as a multi-layered, fiber-reinforced nonlinear elastic material, is coupled to bolus and muscle-activation models using the IB approach to form the esophageal transport model. Cases of esophageal transport with different esophagus models are studied. Results on the transport characteristics, including pressure field and esophageal wall kinematics and stress, are analyzed and compared. Support from NIH grant R01 DK56033 and R01 DK079902 is gratefully acknowledged. BEG is supported by NSF award ACI 1460334.

  16. Mechanisms of Hydrocarbon Based Polymer Etch

    NASA Astrophysics Data System (ADS)

    Lane, Barton; Ventzek, Peter; Matsukuma, Masaaki; Suzuki, Ayuta; Koshiishi, Akira

    2015-09-01

    Dry etch of hydrocarbon based polymers is important for semiconductor device manufacturing. The etch mechanisms for oxygen rich plasma etch of hydrocarbon based polymers has been studied but the mechanism for lean chemistries has received little attention. We report on an experimental and analytic study of the mechanism for etching of a hydrocarbon based polymer using an Ar/O2 chemistry in a single frequency 13.56 MHz test bed. The experimental study employs an analysis of transients from sequential oxidation and Ar sputtering steps using OES and surface analytics to constrain conceptual models for the etch mechanism. The conceptual model is consistent with observations from MD studies and surface analysis performed by Vegh et al. and Oehrlein et al. and other similar studies. Parameters of the model are fit using published data and the experimentally observed time scales.

  17. A measuring model study of a new coordinate-measuring machine based on the parallel kinematic mechanism

    NASA Astrophysics Data System (ADS)

    Liu, Dejun; Huang, Qingcheng; Che, Rensheng; Ai, Qinghui

    1999-11-01

    This paper introduces a new coordinate measuring machine (CMM) comprising a parallel kinematic mechanism with three spatial degrees of freedom and describes its structure, measuring theory and characteristics. Compared with the conventional CMM, this kind of CMM has a simple structure, a flexible probe posture, low moving errors, high stiffness and minimal deformations etc. In this paper, the measuring model of the new parallel CMM is established according to the theory of the spatial mechanics and verified by computer simulation. This research offers a theoretical basis for developing new CMMs.

  18. The Thermal-Mechanical Evolution of the Middle Hsuehshan Range in Taiwan Based on Zircon Thermochronology and Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Shyu, Chase J.; Tan, Eh; Kirstein, Linda A.; Stuart, Finlay M.; Chen, Yue-Gau

    2016-04-01

    The Hsuehshan Range is the second largest mountain belt in Taiwan. Despite extensive previous research, past thermo-mechanical studies of orogenesis in Taiwan have failed to adequately explain the origin of the Hseuhshan Range. In this study we present new zircon fission track and (U-Th)/He ages from the mid Hsuehshan Range (mid-HR). The data is used to provide thermochronological constraints on thermal-mechanical models. These models incorporate a cooling-rate-dependent closure temperature, rather than assuming that this is constant. With imposed constant uplift rate the thermochronological data are best explained if exhumation of the mid-HR started around 5.6 Ma with a rate of 2.0 km/Myr. We further simulate the formation of mid-HR with thermal-mechanical models. The model results suggest that the low strength of lithologies that comprise the Hsuehshan Range has led to homogeneous deformation of the mountain range and that the eastern part of mid-HR was an active deformation zone during the initial stages of orogenesis.

  19. Modelling the graphite fracture mechanisms

    SciTech Connect

    Jacquemoud, C.; Marie, S.; Nedelec, M.

    2012-07-01

    In order to define a design criterion for graphite components, it is important to identify the physical phenomena responsible for the graphite fracture, to include them in a more effective modelling. In a first step, a large panel of experiments have been realised in order to build up an important database; results of tensile tests, 3 and 4 point bending tests on smooth and notched specimens have been analysed and have demonstrated an important geometry related effects on the behavior up to fracture. Then, first simulations with an elastic or an elastoplastic bilinear constitutive law have not made it possible to simulate the experimental fracture stress variations with the specimen geometry, the fracture mechanisms of the graphite being at the microstructural scale. That is the reason why a specific F.E. model of the graphite structure has been developed in which every graphite grain has been meshed independently, the crack initiation along the basal plane of the particles as well as the crack propagation and coalescence have been modelled too. This specific model has been used to test two different approaches for fracture initiation: a critical stress criterion and two criteria of fracture mechanic type. They are all based on crystallographic considerations as a global critical stress criterion gave unsatisfactory results. The criteria of fracture mechanic type being extremely unstable and unable to represent the graphite global behaviour up to the final collapse, the critical stress criterion has been preferred to predict the results of the large range of available experiments, on both smooth and notched specimens. In so doing, the experimental observations have been correctly simulated: the geometry related effects on the experimental fracture stress dispersion, the specimen volume effects on the macroscopic fracture stress and the crack propagation at a constant stress intensity factor. In addition, the parameters of the criterion have been related to

  20. Mechanics Model of Plug Welding

    NASA Technical Reports Server (NTRS)

    Zuo, Q. K.; Nunes, A. C., Jr.

    2015-01-01

    An analytical model has been developed for the mechanics of friction plug welding. The model accounts for coupling of plastic deformation (material flow) and thermal response (plastic heating). The model predictions of the torque, energy, and pull force on the plug were compared to the data of a recent experiment, and the agreements between predictions and data are encouraging.

  1. Wear mechanism based on adhesion

    NASA Technical Reports Server (NTRS)

    Yamamoto, T.; Buckley, D. H.

    1982-01-01

    Various concepts concerning wear mechanisms and deformation behavior observed in the sliding wear track are surveyed. The mechanisms for wear fragment formation is discussed on the basis of adhesion. The wear process under unlubricated sliding conditions is explained in relation to the concept of adhesion at the interface during the sliding process. The mechanism for tearing away the surface layer from the contact area and forming the sliding track contour is explained by assuming the simplified process of material removal based on the adhesion theory.

  2. Human respiratory mechanics demonstration model.

    PubMed

    Anderson, Janelle; Goplen, Chris; Murray, Lynn; Seashore, Kristen; Soundarrajan, Malini; Lokuta, Andrew; Strang, Kevin; Chesler, Naomi

    2009-03-01

    Respiratory mechanics is a difficult topic for instructors and students alike. Existing respiratory mechanics models are limited in their abilities to demonstrate any effects of rib cage movement on alveolar and intrapleural pressures. We developed a model that can be used in both large and small classroom settings. This model contains digital pressure displays and computer integration for real-time demonstration of pressure changes that correspond to the different phases of breathing. Moving the simulated diaphragm and rib cage causes a volume change that results in pressure changes visible on the digital sensors and computer display. Device testing confirmed the model's ability to accurately demonstrate pressure changes in proportion to physiological values. Classroom testing in 427 surveyed students showed improved understanding of respiratory concepts (P < 0.05). We conclude that our respiratory mechanics model is a valuable instructional tool and provide detailed instructions for those who would like to create their own. PMID:19261761

  3. Mechanism test bed. Flexible body model report

    NASA Technical Reports Server (NTRS)

    Compton, Jimmy

    1991-01-01

    The Space Station Mechanism Test Bed is a six degree-of-freedom motion simulation facility used to evaluate docking and berthing hardware mechanisms. A generalized rigid body math model was developed which allowed the computation of vehicle relative motion in six DOF due to forces and moments from mechanism contact, attitude control systems, and gravity. No vehicle size limitations were imposed in the model. The equations of motion were based on Hill's equations for translational motion with respect to a nominal circular earth orbit and Newton-Euler equations for rotational motion. This rigid body model and supporting software were being refined.

  4. Dynamic mechanical response and a constitutive model of Fe-based high temperature alloy at high temperatures and strain rates.

    PubMed

    Su, Xiang; Wang, Gang; Li, Jianfeng; Rong, Yiming

    2016-01-01

    The effects of strain rate and temperature on the dynamic behavior of Fe-based high temperature alloy was studied. The strain rates were 0.001-12,000 s(-1), at temperatures ranging from room temperature to 800 °C. A phenomenological constitutive model (Power-Law constitutive model) was proposed considering adiabatic temperature rise and accurate material thermal physical properties. During which, the effects of the specific heat capacity on the adiabatic temperature rise was studied. The constitutive model was verified to be accurate by comparison between predicted and experimental results. PMID:27186468

  5. Nonlinear Dynamical Behavior in BS Evolution Model Based on Small-World Network Added with Mechanism of Preferential Connection

    NASA Astrophysics Data System (ADS)

    Zhang, Ying-Yue; Chen, Tian-Lun

    2006-03-01

    In this paper, we introduce a modified small-world network added with new links with preferential connection instead of adding randomly, then we apply Bak-Sneppen (BS) evolution model on this network. Several dynamical character of the model such as the evolution graph, f0 avalanche, the critical exponent D and τ, and the distribution of mutation times of all the nodes, show particular behaviors different from those of the model based on the regular network and the small-world network.

  6. Monitoring of intratidal lung mechanics: a Graphical User Interface for a model-based decision support system for PEEP-titration in mechanical ventilation.

    PubMed

    Buehler, S; Lozano-Zahonero, S; Schumann, S; Guttmann, J

    2014-12-01

    In mechanical ventilation, a careful setting of the ventilation parameters in accordance with the current individual state of the lung is crucial to minimize ventilator induced lung injury. Positive end-expiratory pressure (PEEP) has to be set to prevent collapse of the alveoli, however at the same time overdistension should be avoided. Classic approaches of analyzing static respiratory system mechanics fail in particular if lung injury already prevails. A new approach of analyzing dynamic respiratory system mechanics to set PEEP uses the intratidal, volume-dependent compliance which is believed to stay relatively constant during one breath only if neither atelectasis nor overdistension occurs. To test the success of this dynamic approach systematically at bedside or in an animal study, automation of the computing steps is necessary. A decision support system for optimizing PEEP in form of a Graphical User Interface (GUI) was targeted. Respiratory system mechanics were analyzed using the gliding SLICE method. The resulting shapes of the intratidal compliance-volume curve were classified into one of six categories, each associated with a PEEP-suggestion. The GUI should include a graphical representation of the results as well as a quality check to judge the reliability of the suggestion. The implementation of a user-friendly GUI was successfully realized. The agreement between modelled and measured pressure data [expressed as root-mean-square (RMS)] tested during the implementation phase with real respiratory data from two patient studies was below 0.2 mbar for data taken in volume controlled mode and below 0.4 mbar for data taken in pressure controlled mode except for two cases with RMS < 0.6 mbar. Visual inspections showed, that good and medium quality data could be reliably identified. The new GUI allows visualization of intratidal compliance-volume curves on a breath-by-breath basis. The automatic categorisation of curve shape into one of six shape

  7. Fundamental Study on Applicability of Powder-Based 3D Printer for Physical Modeling in Rock Mechanics

    NASA Astrophysics Data System (ADS)

    Fereshtenejad, Sayedalireza; Song, Jae-Joon

    2016-06-01

    Applications of 3D printing technology become more widespread in many research fields because of its rapid development and valuable capabilities. In rock mechanics and mining engineering, this technology has the potential to become a useful tool that might help implement a number of research studies previously considered impractical. Most commercial 3D printers cannot print prototypes with mechanical properties that match precisely those of natural rock samples. Therefore, some additional enhancements are required for 3D printers to be effectively utilized for rock mechanics applications. In this study, we printed and studied specimens using a powder-based commercial ZPrinter® 450 with ZP® 150 powder and Zb® 63 binder used as raw materials. The specimens printed by this 3D printer exhibited relatively low strength and ductile behavior, implying that it needs further improvements. Hence, we focused on several ways to determine the best combination of printing options and post-processing including the effects of the printing direction, printing layer thickness, binder saturation level, and heating process on the uniaxial compressive strength (UCS) and stress-strain behavior of the printed samples. The suggested procedures have demonstrated their effectiveness by obtaining the printed samples that behave similarly to the natural rocks with low UCS. Although our optimization methods were particularly successful, further improvements are required to expand 3D printer application in the area of rock mechanics.

  8. Length-scale dependent mechanical properties of Al-Cu eutectic alloy: Molecular dynamics based model and its experimental verification

    SciTech Connect

    Tiwary, C. S. Chattopadhyay, K.; Chakraborty, S.; Mahapatra, D. R.

    2014-05-28

    This paper attempts to gain an understanding of the effect of lamellar length scale on the mechanical properties of two-phase metal-intermetallic eutectic structure. We first develop a molecular dynamics model for the in-situ grown eutectic interface followed by a model of deformation of Al-Al{sub 2}Cu lamellar eutectic. Leveraging the insights obtained from the simulation on the behaviour of dislocations at different length scales of the eutectic, we present and explain the experimental results on Al-Al{sub 2}Cu eutectic with various different lamellar spacing. The physics behind the mechanism is further quantified with help of atomic level energy model for different length scale as well as different strain. An atomic level energy partitioning of the lamellae and the interface regions reveals that the energy of the lamellae core are accumulated more due to dislocations irrespective of the length-scale. Whereas the energy of the interface is accumulated more due to dislocations when the length-scale is smaller, but the trend is reversed when the length-scale is large beyond a critical size of about 80 nm.

  9. Neural mechanisms underlying the effects of face-based affective signals on memory for faces: a tentative model

    PubMed Central

    Tsukiura, Takashi

    2012-01-01

    In our daily lives, we form some impressions of other people. Although those impressions are affected by many factors, face-based affective signals such as facial expression, facial attractiveness, or trustworthiness are important. Previous psychological studies have demonstrated the impact of facial impressions on remembering other people, but little is known about the neural mechanisms underlying this psychological process. The purpose of this article is to review recent functional MRI (fMRI) studies to investigate the effects of face-based affective signals including facial expression, facial attractiveness, and trustworthiness on memory for faces, and to propose a tentative concept for understanding this affective-cognitive interaction. On the basis of the aforementioned research, three brain regions are potentially involved in the processing of face-based affective signals. The first candidate is the amygdala, where activity is generally modulated by both affectively positive and negative signals from faces. Activity in the orbitofrontal cortex (OFC), as the second candidate, increases as a function of perceived positive signals from faces; whereas activity in the insular cortex, as the third candidate, reflects a function of face-based negative signals. In addition, neuroscientific studies have reported that the three regions are functionally connected to the memory-related hippocampal regions. These findings suggest that the effects of face-based affective signals on memory for faces could be modulated by interactions between the regions associated with the processing of face-based affective signals and the hippocampus as a memory-related region. PMID:22837740

  10. Gate voltage dependent 1/f noise variance model based on physical noise generation mechanisms in n-channel metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Arai, Yukiko; Aoki, Hitoshi; Abe, Fumitaka; Todoroki, Shunichiro; Khatami, Ramin; Kazumi, Masaki; Totsuka, Takuya; Wang, Taifeng; Kobayashi, Haruo

    2015-04-01

    1/f noise is one of the most important characteristics for designing analog/RF circuits including operational amplifiers and oscillators. We have analyzed and developed a novel 1/f noise model in the strong inversion, saturation, and sub-threshold regions based on SPICE2 type model used in any public metal-oxide-semiconductor field-effect transistor (MOSFET) models developed by the University of California, Berkeley. Our model contains two noise generation mechanisms that are mobility and interface trap number fluctuations. Noise variability dependent on gate voltage is also newly implemented in our model. The proposed model has been implemented in BSIM4 model of a SPICE3 compatible circuit simulator. Parameters of the proposed model are extracted with 1/f noise measurements for simulation verifications. The simulation results show excellent agreements between measurement and simulations.

  11. Quantum-Mechanical QSPR Models for Polymerization Volume Change of Epoxides and Methacrylates Based on Mercury Dilatometry Results

    PubMed Central

    Miller, Matthew D.; Holder, Andrew J.; Kilway, Kathleen V.; Giese, Gregory J.; Finley, Jason E.; Travis, DeAnna M.; Iwai, Benjamin T.; Eick., J. David

    2007-01-01

    Polymerization volume change (PVC) was measured systematically using mercury dilatometry for 41 epoxide and methacrylate monomers with quartz filler. Quantitative structure property relationship (QSPR) models were developed based on this previously unreported data to gain insight in the data collection method for future models. Successful models included only data from those samples which polymerized to hardness. The most significant descriptors in these models related to monomer reactivity. In contrast, PVC data collected under experimental conditions which maximized monomer conversion resulted in descriptors describing size and branching, indicating conversion must be considered for future PVC measurements. A Rule of Mixtures (ROM) correction term improved correlations of the dilatometer data with varying quartz content, and an adjustment for conversion may similarly enable inclusion of data which had not polymerize to hardness. PMID:18066392

  12. Modeling Signal Propagation Mechanisms and Ligand-Based Conformational Dynamics of the Hsp90 Molecular Chaperone Full-Length Dimer

    PubMed Central

    Morra, Giulia; Verkhivker, Gennady; Colombo, Giorgio

    2009-01-01

    Hsp90 is a molecular chaperone essential for protein folding and activation in normal homeostasis and stress response. ATP binding and hydrolysis facilitate Hsp90 conformational changes required for client activation. Hsp90 plays an important role in disease states, particularly in cancer, where chaperoning of the mutated and overexpressed oncoproteins is important for function. Recent studies have illuminated mechanisms related to the chaperone function. However, an atomic resolution view of Hsp90 conformational dynamics, determined by the presence of different binding partners, is critical to define communication pathways between remote residues in different domains intimately affecting the chaperone cycle. Here, we present a computational analysis of signal propagation and long-range communication pathways in Hsp90. We carried out molecular dynamics simulations of the full-length Hsp90 dimer, combined with essential dynamics, correlation analysis, and a signal propagation model. All-atom MD simulations with timescales of 70 ns have been performed for complexes with the natural substrates ATP and ADP and for the unliganded dimer. We elucidate the mechanisms of signal propagation and determine “hot spots” involved in interdomain communication pathways from the nucleotide-binding site to the C-terminal domain interface. A comprehensive computational analysis of the Hsp90 communication pathways and dynamics at atomic resolution has revealed the role of the nucleotide in effecting conformational changes, elucidating the mechanisms of signal propagation. Functionally important residues and secondary structure elements emerge as effective mediators of communication between the nucleotide-binding site and the C-terminal interface. Furthermore, we show that specific interdomain signal propagation pathways may be activated as a function of the ligand. Our results support a “conformational selection model” of the Hsp90 mechanism, whereby the protein may exist in a

  13. A novel technique for modeling susceptibility-based contrast mechanisms for arbitrary microvascular geometries: the finite perturber method.

    PubMed

    Pathak, Arvind P; Ward, B Douglas; Schmainda, Kathleen M

    2008-04-15

    Recently, we demonstrated that vessel geometry is a significant determinant of susceptibility-induced contrast in MRI. This is especially relevant for susceptibility-contrast enhanced MRI of tumors with their characteristically abnormal vessel morphology. In order to better understand the biophysics of this contrast mechanism, it is of interest to model how various factors, including microvessel morphology contribute to the measured MR signal, and was the primary motivation for developing a novel computer modeling approach called the Finite Perturber Method (FPM). The FPM circumvents the limitations of traditional fixed-geometry approaches, and enables us to study susceptibility-induced contrast arising from arbitrary microvascular morphologies in 3D, such as those typically observed with brain tumor angiogenesis. Here we describe this new modeling methodology and some of its applications. The excellent agreement of the FPM with theory and the extant susceptibility modeling data, coupled with its computational efficiency demonstrates its potential to transform our understanding of the factors that engender susceptibility contrast in MRI. PMID:18308587

  14. Mechanical integrity of a carbon nanotube/copper-based through-silicon via for 3D integrated circuits: a multi-scale modeling approach.

    PubMed

    Awad, Ibrahim; Ladani, Leila

    2015-12-01

    Carbon nanotube (CNT)/copper (Cu) composite material is proposed to replace Cu-based through-silicon vias (TSVs) in micro-electronic packages. The proposed material is believed to offer extraordinary mechanical and electrical properties and the presence of CNTs in Cu is believed to overcome issues associated with miniaturization of Cu interconnects, such as electromigration. This study introduces a multi-scale modeling of the proposed TSV in order to evaluate its mechanical integrity under mechanical and thermo-mechanical loading conditions. Molecular dynamics (MD) simulation was used to determine CNT/Cu interface adhesion properties. A cohesive zone model (CZM) was found to be most appropriate to model the interface adhesion, and CZM parameters at the nanoscale were determined using MD simulation. CZM parameters were then used in the finite element analysis in order to understand the mechanical and thermo-mechanical behavior of composite TSV at micro-scale. From the results, CNT/Cu separation does not take place prior to plastic deformation of Cu in bending, and separation does not take place when standard thermal cycling is applied. Further investigation is recommended in order to alleviate the increased plastic deformation in Cu at the CNT/Cu interface in both loading conditions. PMID:26559788

  15. Mechanical integrity of a carbon nanotube/copper-based through-silicon via for 3D integrated circuits: a multi-scale modeling approach

    NASA Astrophysics Data System (ADS)

    Awad, Ibrahim; Ladani, Leila

    2015-12-01

    Carbon nanotube (CNT)/copper (Cu) composite material is proposed to replace Cu-based through-silicon vias (TSVs) in micro-electronic packages. The proposed material is believed to offer extraordinary mechanical and electrical properties and the presence of CNTs in Cu is believed to overcome issues associated with miniaturization of Cu interconnects, such as electromigration. This study introduces a multi-scale modeling of the proposed TSV in order to evaluate its mechanical integrity under mechanical and thermo-mechanical loading conditions. Molecular dynamics (MD) simulation was used to determine CNT/Cu interface adhesion properties. A cohesive zone model (CZM) was found to be most appropriate to model the interface adhesion, and CZM parameters at the nanoscale were determined using MD simulation. CZM parameters were then used in the finite element analysis in order to understand the mechanical and thermo-mechanical behavior of composite TSV at micro-scale. From the results, CNT/Cu separation does not take place prior to plastic deformation of Cu in bending, and separation does not take place when standard thermal cycling is applied. Further investigation is recommended in order to alleviate the increased plastic deformation in Cu at the CNT/Cu interface in both loading conditions.

  16. Patient-specific Modeling of Cardiovascular Mechanics

    PubMed Central

    Taylor, C.A.; Figueroa, C.A.

    2015-01-01

    Advances in numerical methods and three-dimensional imaging techniques have enabled the quantification of cardiovascular mechanics in subject-specific anatomic and physiologic models. Patient-specific models are being used to guide cell culture and animal experiments and test hypotheses related to the role of biomechanical factors in vascular diseases. Furthermore, biomechanical models based on noninvasive medical imaging could provide invaluable data on the in vivo service environment where cardiovascular devices are employed and the effect of the devices on physiologic function. Finally, the patient-specific modeling has enabled an entirely new application of cardiovascular mechanics, namely predicting outcomes of alternate therapeutic interventions for individual patients. We will review methods to create anatomic and physiologic models, obtain properties, assign boundary conditions, and solve the equations governing blood flow and vessel wall dynamics. Applications of patient-specific models of cardiovascular mechanics will be presented followed by a discussion of the challenges and opportunities that lie ahead. PMID:19400706

  17. A constitutive mechanical model for energetic materials

    SciTech Connect

    Hobbs, M.L.; Baer, M.R.; Gross, R.J.

    1994-06-01

    Cookoff modeling of energetic materials has traditionally addressed reactive heat flow with the goal of defining the onset of runaway combustion behavior. Current modeling efforts are now aimed toward predicting the violence of the event. Combined thermal, chemical, and mechanical response must be modeled, since confinement results in pressure buildup which can breach confinement or enhance gas-phase combustion rates leading to runaway combustion behavior. Thermally induced stresses can also cause gaps which inhibit heat flow. These mechanical effects must also be included in cookoff modeling. A new reactive elastic-plastic constitutive model for micromechanical response has been developed which represents a stress-strain relation for reacting materials such as explosives, propellants, pyrotechnics, or burning foams. This micromechanical model is based on bubble mechanics. A local force balance, with mass continuity constraints, forms the basis of the constitutive model requiring input of temperature and reacted fraction. This constitutive material model has been incorporated into a quasistatic mechanics code, SANTOS. To provide temperature and reacted gas fraction, the thermal-chemical solver, XCHEM, has been coupled to SANTOS. This paper summarizes the development of the micromechanical model with material property estimates for conventional energetic materials. This study shows that large pressures can arise from small reacted fractions which implies that cookoff modeling must consider the strong interaction between thermochemistry and mechanics.

  18. Native state dynamics and mechanical properties of human topoisomerase I within a structure-based coarse-grained model.

    PubMed

    Szklarczyk, Oliwia; Staroń, Krzysztof; Cieplak, Marek

    2009-11-01

    A coarse grained molecular dynamics model with an implicit solvent is used to elucidate properties of the human topoisomerase I. The model is defined through the native structure and it allows covering significantly longer time scales than in all atom simulations. Single residue and double residue motional characteristics are studied. The results are consistent with all atom simulations reported in the literature indicating usefulness of the model in further studies of this protein. Novel findings include broadening of the description of the dynamic behavior of the lip and hinge regions and a characterization of the motional properties of the RRM binding site of the enzyme. We also consider mechanical stretching of the protein and identify sources of the force peaks. The elastic properties of topoisomerase I are predicted to be average in comparison to other proteins, yielding a maximum force of resistance to pulling which should be of order 120 pN. The contact unraveling pattern is consistent with the understanding of the structure and function of the protein. We find supporting evidence for the hypothesis that the C-terminal domain acquires an ordered structure upon binding with the core enzyme even though it forms a molten globule when in isolation. PMID:19452556

  19. Spinal Mechanisms May Provide a Combination of Intermittent and Continuous Control of Human Posture: Predictions from a Biologically Based Neuromusculoskeletal Model

    PubMed Central

    Elias, Leonardo Abdala; Watanabe, Renato Naville; Kohn, André Fabio

    2014-01-01

    Several models have been employed to study human postural control during upright quiet stance. Most have adopted an inverted pendulum approximation to the standing human and theoretical models to account for the neural feedback necessary to keep balance. The present study adds to the previous efforts in focusing more closely on modelling the physiological mechanisms of important elements associated with the control of human posture. This paper studies neuromuscular mechanisms behind upright stance control by means of a biologically based large-scale neuromusculoskeletal (NMS) model. It encompasses: i) conductance-based spinal neuron models (motor neurons and interneurons); ii) muscle proprioceptor models (spindle and Golgi tendon organ) providing sensory afferent feedback; iii) Hill-type muscle models of the leg plantar and dorsiflexors; and iv) an inverted pendulum model for the body biomechanics during upright stance. The motor neuron pools are driven by stochastic spike trains. Simulation results showed that the neuromechanical outputs generated by the NMS model resemble experimental data from subjects standing on a stable surface. Interesting findings were that: i) an intermittent pattern of muscle activation emerged from this posture control model for two of the leg muscles (Medial and Lateral Gastrocnemius); and ii) the Soleus muscle was mostly activated in a continuous manner. These results suggest that the spinal cord anatomy and neurophysiology (e.g., motor unit types, synaptic connectivities, ordered recruitment), along with the modulation of afferent activity, may account for the mixture of intermittent and continuous control that has been a subject of debate in recent studies on postural control. Another finding was the occurrence of the so-called “paradoxical” behaviour of muscle fibre lengths as a function of postural sway. The simulations confirmed previous conjectures that reciprocal inhibition is possibly contributing to this effect, but on the

  20. Spinal mechanisms may provide a combination of intermittent and continuous control of human posture: predictions from a biologically based neuromusculoskeletal model.

    PubMed

    Elias, Leonardo Abdala; Watanabe, Renato Naville; Kohn, André Fabio

    2014-11-01

    Several models have been employed to study human postural control during upright quiet stance. Most have adopted an inverted pendulum approximation to the standing human and theoretical models to account for the neural feedback necessary to keep balance. The present study adds to the previous efforts in focusing more closely on modelling the physiological mechanisms of important elements associated with the control of human posture. This paper studies neuromuscular mechanisms behind upright stance control by means of a biologically based large-scale neuromusculoskeletal (NMS) model. It encompasses: i) conductance-based spinal neuron models (motor neurons and interneurons); ii) muscle proprioceptor models (spindle and Golgi tendon organ) providing sensory afferent feedback; iii) Hill-type muscle models of the leg plantar and dorsiflexors; and iv) an inverted pendulum model for the body biomechanics during upright stance. The motor neuron pools are driven by stochastic spike trains. Simulation results showed that the neuromechanical outputs generated by the NMS model resemble experimental data from subjects standing on a stable surface. Interesting findings were that: i) an intermittent pattern of muscle activation emerged from this posture control model for two of the leg muscles (Medial and Lateral Gastrocnemius); and ii) the Soleus muscle was mostly activated in a continuous manner. These results suggest that the spinal cord anatomy and neurophysiology (e.g., motor unit types, synaptic connectivities, ordered recruitment), along with the modulation of afferent activity, may account for the mixture of intermittent and continuous control that has been a subject of debate in recent studies on postural control. Another finding was the occurrence of the so-called "paradoxical" behaviour of muscle fibre lengths as a function of postural sway. The simulations confirmed previous conjectures that reciprocal inhibition is possibly contributing to this effect, but on the

  1. Renoprotective Mechanism of Remote Ischemic Preconditioning Based on Transcriptomic Analysis in a Porcine Renal Ischemia Reperfusion Injury Model

    PubMed Central

    Kim, Sook Young; Cho, Young In; Lee, Kwang Suk; Kim, Kwang Hyun; Yang, Seung Choul; Han, Woong Kyu

    2015-01-01

    Ischemic preconditioning (IPC) is a well-known phenomenon in which tissues are exposed to a brief period of ischemia prior to a longer ischemic event. This technique produces tissue tolerance to ischemia reperfusion injury (IRI). Currently, IPC’s mechanism of action is poorly understood. Using a porcine single kidney model, we performed remote IPC with renal IRI and evaluated the IPC mechanism of action. Following left nephrectomy, 15 female Yorkshire pigs were divided into three groups: no IPC and 90 minutes of warm ischemia (control), remote IPC immediately followed by 90 minutes of warm ischemia (rIPCe), and remote IPC with 90 minutes of warm ischemia performed 24 hours later (rIPCl). Differential gene expression analysis was performed using a porcine-specific microarray. The microarray analysis of porcine renal tissues identified 1,053 differentially expressed probes in preconditioned pigs. Among these, 179 genes had altered expression in both the rIPCe and rIPCl groups. The genes were largely related to oxidation reduction, apoptosis, and inflammatory response. In the rIPCl group, an additional 848 genes had altered expression levels. These genes were primarily related to immune response and inflammation, including those coding for cytokines and cytokine receptors and those that play roles in the complement system and coagulation cascade. In the complement system, the membrane attack complex was determined to be sublytic, because it colocalized with phosphorylated extracellular signal-regulated kinase. Furthermore, alpha 2 macroglobulin, tissue plasminogen activator, uterine plasmin trypsin inhibitor, and arginase-1 mRNA levels were elevated in the rIPCl group. These findings indicate that remote IPC produces renoprotective effects through multiple mechanisms, and these effects develop over a long timeframe rather than immediately following IPC. PMID:26489007

  2. 3D Progressive Damage Modeling for Laminated Composite Based on Crack Band Theory and Continuum Damage Mechanics

    NASA Technical Reports Server (NTRS)

    Wang, John T.; Pineda, Evan J.; Ranatunga, Vipul; Smeltzer, Stanley S.

    2015-01-01

    A simple continuum damage mechanics (CDM) based 3D progressive damage analysis (PDA) tool for laminated composites was developed and implemented as a user defined material subroutine to link with a commercially available explicit finite element code. This PDA tool uses linear lamina properties from standard tests, predicts damage initiation with an easy-to-implement Hashin-Rotem failure criteria, and in the damage evolution phase, evaluates the degradation of material properties based on the crack band theory and traction-separation cohesive laws. It follows Matzenmiller et al.'s formulation to incorporate the degrading material properties into the damaged stiffness matrix. Since nonlinear shear and matrix stress-strain relations are not implemented, correction factors are used for slowing the reduction of the damaged shear stiffness terms to reflect the effect of these nonlinearities on the laminate strength predictions. This CDM based PDA tool is implemented as a user defined material (VUMAT) to link with the Abaqus/Explicit code. Strength predictions obtained, using this VUMAT, are correlated with test data for a set of notched specimens under tension and compression loads.

  3. Development of a new physics-based internal coordinate mechanics force field (ICMFF) and its application to protein loop modeling

    PubMed Central

    Arnautova, Yelena A.; Abagyan, Ruben A.

    2010-01-01

    We report the development of ICMFF, new force field parameterized using a combination of experimental data for crystals of small molecules and quantum mechanics calculations. The main features of ICMFF include: (a) parameterization for the dielectric constant relevant to the condensed state (ε=2) instead of vacuum; (b) an improved description of hydrogen-bond interactions using duplicate sets of van der Waals parameters for heavy atom-hydrogen interactions; and (c) improved backbone covalent geometry and energetics achieved using novel backbone torsional potentials and inclusion of the bond angles at the Cα atoms into the internal variable set. The performance of ICMFF was evaluated through loop modeling simulations for 4-13 residue loops. ICMFF was combined with a solvent-accessible surface area solvation model optimized using a large set of loop decoys. Conformational sampling was carried out using the Biased Probability Monte Carlo method. Average/median backbone root-mean-square deviations of the lowest energy conformations from the native structures were 0.25/0.21 Å for 4 residues loops, 0.84/0.46 Å for 8 residue loops, and 1.16/0.73 Å for 12 residue loops. To our knowledge, these results are significantly better than or comparable to those reported to date for any loop modeling method that does not take crystal packing into account. Moreover, the accuracy of our method is on par with the best previously reported results obtained considering the crystal environment. We attribute this success to the high accuracy of the new ICM force field achieved by meticulous parameterization, to the optimized solvent model, and the efficiency of the search method. PMID:21069716

  4. Transport Mechanisms and Quality Changes During Frying of Chicken Nuggets--Hybrid Mixture Theory Based Modeling and Experimental Verification.

    PubMed

    Bansal, Harkirat S; Takhar, Pawan S; Alvarado, Christine Z; Thompson, Leslie D

    2015-12-01

    Hybrid mixture theory (HMT) based 2-scale fluid transport relations of Takhar coupled with a multiphase heat transfer equation were solved to model water, oil and gas movement during frying of chicken nuggets. A chicken nugget was treated as a heterogeneous material consisting of meat core with wheat-based coating. The coupled heat and fluid transfer equations were solved using the finite element method. Numerical simulations resulted in data on spatial and temporal profiles for moisture, rate of evaporation, temperature, oil, pore pressure, pressure in various phases, and coefficient of elasticity. Results showed that most of the oil stayed in the outer 1.5 mm of the coating region. Temperature values greater than 100 °C were observed in the coating after 30 s of frying. Negative gage-pore pressure (p(w) < p(g)) magnitudes were observed in simulations, which is in agreement with experimental observations of Sandhu and others. It is hypothesized that high water-phase capillary pressure (p(c) > p(g)) in the hydrophilic matrix causes p(w) < p(g), which further results in negative pore pressure. The coefficient of elasticity was the highest at the surface (2.5 × 10(5) Pa) for coating and the interface of coating and core (6 × 10(5) Pa). Kinetics equation for color change obtained from experiments was coupled with the HMT based model to predict the color (L, a, and b) as a function of frying time. PMID:26509578

  5. An error-model study of a new type of coordinate-measuring machine based on the parallel-link mechanism

    NASA Astrophysics Data System (ADS)

    Liu, Dejun; Che, Rensheng; Huang, Qingcheng; Ye, Dong

    2000-12-01

    Firstly, this paper establishes the inverse kinematic model of a new coordinate measuring machine (CMM) based on the parallel-link mechanism with three spatial degrees of freedom (3DOFs). Then, based on the differentiation of the kinematics, the relation between the input parameter errors, which consist of the position errors of the joints and the kinematic errors of the actuators, and the output errors at the probe of the new CMM, is derived; thereby the error model is presented. Finally, the error model is verified by computer simulation, and the result indicates that the error model established in this paper can approximately report the changing trend of the actual measuring errors where the input errors are small enough. This research provides an essential theoretical basis for calibrating the new parallel-link CMM.

  6. Architecture-based multiscale computational modeling of plant cell wall mechanics to examine the hydrogen-bonding hypothesis of cell wall network structure model

    SciTech Connect

    Yi, Hojae; Puri, Virendra M.

    2012-11-01

    A primary plant cell wall network was computationally modeled using the finite element approach to study the hypothesis of hemicellulose (HC) tethering with the cellulose microfibrils (CMFs) as one of the major load-bearing mechanisms of the growing cell wall. A computational primary cell wall network fragment (10 × 10 μm) comprising typical compositions and properties of CMFs and HC was modeled with well-aligned CMFs. The tethering of HC to CMFs is modeled in accordance with the strength of the hydrogen bonding by implementing a specific load-bearing connection (i.e. the joint element). The introduction of the CMF-HC interaction to the computational cell wall network model is a key to the quantitative examination of the mechanical consequences of cell wall structure models, including the tethering HC model. When the cell wall network models with and without joint elements were compared, the hydrogen bond exhibited a significant contribution to the overall stiffness of the cell wall network fragment. When the cell wall network model was stretched 1% in the transverse direction, the tethering of CMF-HC via hydrogen bonds was not strong enough to maintain its integrity. When the cell wall network model was stretched 1% in the longitudinal direction, the tethering provided comparable strength to maintain its integrity. This substantial anisotropy suggests that the HC tethering with hydrogen bonds alone does not manifest sufficient energy to maintain the integrity of the cell wall during its growth (i.e. other mechanisms are present to ensure the cell wall shape).

  7. Mechanisms for similarity based cooperation

    NASA Astrophysics Data System (ADS)

    Traulsen, A.

    2008-06-01

    Cooperation based on similarity has been discussed since Richard Dawkins introduced the term “green beard” effect. In these models, individuals cooperate based on an aribtrary signal (or tag) such as the famous green beard. Here, two different models for such tag based cooperation are analysed. As neutral drift is important in both models, a finite population framework is applied. The first model, which we term “cooperative tags” considers a situation in which groups of cooperators are formed by some joint signal. Defectors adopting the signal and exploiting the group can lead to a breakdown of cooperation. In this case, conditions are derived under which the average abundance of the more cooperative strategy exceeds 50%. The second model considers a situation in which individuals start defecting towards others that are not similar to them. This situation is termed “defective tags”. It is shown that in this case, individuals using tags to cooperate exclusively with their own kind dominate over unconditional cooperators.

  8. Determination of the mechanical and physical properties of cartilage by coupling poroelastic-based finite element models of indentation with artificial neural networks.

    PubMed

    Arbabi, Vahid; Pouran, Behdad; Campoli, Gianni; Weinans, Harrie; Zadpoor, Amir A

    2016-03-21

    One of the most widely used techniques to determine the mechanical properties of cartilage is based on indentation tests and interpretation of the obtained force-time or displacement-time data. In the current computational approaches, one needs to simulate the indentation test with finite element models and use an optimization algorithm to estimate the mechanical properties of cartilage. The modeling procedure is cumbersome, and the simulations need to be repeated for every new experiment. For the first time, we propose a method for fast and accurate estimation of the mechanical and physical properties of cartilage as a poroelastic material with the aid of artificial neural networks. In our study, we used finite element models to simulate the indentation for poroelastic materials with wide combinations of mechanical and physical properties. The obtained force-time curves are then divided into three parts: the first two parts of the data is used for training and validation of an artificial neural network, while the third part is used for testing the trained network. The trained neural network receives the force-time curves as the input and provides the properties of cartilage as the output. We observed that the trained network could accurately predict the properties of cartilage within the range of properties for which it was trained. The mechanical and physical properties of cartilage could therefore be estimated very fast, since no additional finite element modeling is required once the neural network is trained. The robustness of the trained artificial neural network in determining the properties of cartilage based on noisy force-time data was assessed by introducing noise to the simulated force-time data. We found that the training procedure could be optimized so as to maximize the robustness of the neural network against noisy force-time data. PMID:26944689

  9. Investigation of the mechanical behavior of kangaroo humeral head cartilage tissue by a porohyperelastic model based on the strain-rate-dependent permeability.

    PubMed

    Thibbotuwawa, Namal; Oloyede, Adekunle; Senadeera, Wijitha; Li, Tong; Gu, YuanTong

    2015-11-01

    Solid-interstitial fluid interaction, which depends on tissue permeability, is significant to the strain-rate-dependent mechanical behavior of humeral head (shoulder) cartilage. Due to anatomical and biomechanical similarities to that of the human shoulder, kangaroos present a suitable animal model. Therefore, indentation experiments were conducted on kangaroo shoulder cartilage tissues from low (10(-4)/s) to moderately high (10(-2)/s) strain-rates. A porohyperelastic model was developed based on the experimental characterization; and a permeability function that takes into account the effect of strain-rate on permeability (strain-rate-dependent permeability) was introduced into the model to investigate the effect of rate-dependent fluid flow on tissue response. The prediction of the model with the strain-rate-dependent permeability was compared with those of the models using constant permeability and strain-dependent permeability. Compared to the model with constant permeability, the models with strain-dependent and strain-rate-dependent permeability were able to better capture the experimental variation at all strain-rates (p < 0.05). Significant differences were not identified between models with strain-dependent and strain-rate-dependent permeability at strain-rate of 5 × 10(-3)/s (p = 0.179). However, at strain-rate of 10(-2)/s, the model with strain-rate-dependent permeability was significantly better at capturing the experimental results (p < 0.005). The findings thus revealed the significance of rate-dependent fluid flow on tissue behavior at large strain-rates, which provides insights into the mechanical deformation mechanisms of cartilage tissues. PMID:26275487

  10. Modeling of fluid injection and withdrawal induced fault activation using discrete element based hydro-mechanical and dynamic coupled simulator

    NASA Astrophysics Data System (ADS)

    Yoon, Jeoung Seok; Zang, Arno; Zimmermann, Günter; Stephansson, Ove

    2016-04-01

    Operation of fluid injection into and withdrawal from the subsurface for various purposes has been known to induce earthquakes. Such operations include hydraulic fracturing for shale gas extraction, hydraulic stimulation for Enhanced Geothermal System development and waste water disposal. Among these, several damaging earthquakes have been reported in the USA in particular in the areas of high-rate massive amount of wastewater injection [1] mostly with natural fault systems. Oil and gas production have been known to induce earthquake where pore fluid pressure decreases in some cases by several tens of Mega Pascal. One recent seismic event occurred in November 2013 near Azle, Texas where a series of earthquakes began along a mapped ancient fault system [2]. It was studied that a combination of brine production and waste water injection near the fault generated subsurface pressures sufficient to induced earthquakes on near-critically stressed faults. This numerical study aims at investigating the occurrence mechanisms of such earthquakes induced by fluid injection [3] and withdrawal by using hydro-geomechanical coupled dynamic simulator (Itasca's Particle Flow Code 2D). Generic models are setup to investigate the sensitivity of several parameters which include fault orientation, frictional properties, distance from the injection well to the fault, amount of fluid withdrawal around the injection well, to the response of the fault systems and the activation magnitude. Fault slip movement over time in relation to the diffusion of pore pressure is analyzed in detail. Moreover, correlations between the spatial distribution of pore pressure change and the locations of induced seismic events and fault slip rate are investigated. References [1] Keranen KM, Weingarten M, Albers GA, Bekins BA, Ge S, 2014. Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection, Science 345, 448, DOI: 10.1126/science.1255802. [2] Hornbach MJ, DeShon HR

  11. A Mechanism-Based Model for the Prediction of the Metabolic Sites of Steroids Mediated by Cytochrome P450 3A4.

    PubMed

    Dai, Zi-Ru; Ai, Chun-Zhi; Ge, Guang-Bo; He, Yu-Qi; Wu, Jing-Jing; Wang, Jia-Yue; Man, Hui-Zi; Jia, Yan; Yang, Ling

    2015-01-01

    Early prediction of xenobiotic metabolism is essential for drug discovery and development. As the most important human drug-metabolizing enzyme, cytochrome P450 3A4 has a large active cavity and metabolizes a broad spectrum of substrates. The poor substrate specificity of CYP3A4 makes it a huge challenge to predict the metabolic site(s) on its substrates. This study aimed to develop a mechanism-based prediction model based on two key parameters, including the binding conformation and the reaction activity of ligands, which could reveal the process of real metabolic reaction(s) and the site(s) of modification. The newly established model was applied to predict the metabolic site(s) of steroids; a class of CYP3A4-preferred substrates. 38 steroids and 12 non-steroids were randomly divided into training and test sets. Two major metabolic reactions, including aliphatic hydroxylation and N-dealkylation, were involved in this study. At least one of the top three predicted metabolic sites was validated by the experimental data. The overall accuracy for the training and test were 82.14% and 86.36%, respectively. In summary, a mechanism-based prediction model was established for the first time, which could be used to predict the metabolic site(s) of CYP3A4 on steroids with high predictive accuracy. PMID:26133240

  12. A Mechanism-Based Model for the Prediction of the Metabolic Sites of Steroids Mediated by Cytochrome P450 3A4

    PubMed Central

    Dai, Zi-Ru; Ai, Chun-Zhi; Ge, Guang-Bo; He, Yu-Qi; Wu, Jing-Jing; Wang, Jia-Yue; Man, Hui-Zi; Jia, Yan; Yang, Ling

    2015-01-01

    Early prediction of xenobiotic metabolism is essential for drug discovery and development. As the most important human drug-metabolizing enzyme, cytochrome P450 3A4 has a large active cavity and metabolizes a broad spectrum of substrates. The poor substrate specificity of CYP3A4 makes it a huge challenge to predict the metabolic site(s) on its substrates. This study aimed to develop a mechanism-based prediction model based on two key parameters, including the binding conformation and the reaction activity of ligands, which could reveal the process of real metabolic reaction(s) and the site(s) of modification. The newly established model was applied to predict the metabolic site(s) of steroids; a class of CYP3A4-preferred substrates. 38 steroids and 12 non-steroids were randomly divided into training and test sets. Two major metabolic reactions, including aliphatic hydroxylation and N-dealkylation, were involved in this study. At least one of the top three predicted metabolic sites was validated by the experimental data. The overall accuracy for the training and test were 82.14% and 86.36%, respectively. In summary, a mechanism-based prediction model was established for the first time, which could be used to predict the metabolic site(s) of CYP3A4 on steroids with high predictive accuracy. PMID:26133240

  13. Mechanical models for tanks containing two liquids

    SciTech Connect

    Tang, Y.

    1994-06-01

    The well-known Housner`s mechanical model for laterally excited rigid tanks that contain one liquid is generalized to permit consideration of tanks that contain two liquids under the horizontal and rocking base motions. Two mechanical models are developed herein; one is for rigid tanks and the other for flexible tanks. The model for rigid tanks has a rigidly attached mass and infinite number of elastically supported masses. The rigid attached mass which possesses a mass moment of inertia represents the impulsive component, whereas the elastically supported masses which do not possess mass moment of inertia represent the convective component of the response. These masses and their heights are chosen such that, under the same base motions, the base shear and base moments of the model match those of the original liquid-tank system. The spring stiffness constants for the elastically supported masses in the model are determined from the sloshing frequencies of the liquid-tank system. The model for flexible tanks, however, only represents the impulsive action of the hydrodynamic response. It has an elastically supported mass that does not possess mass moment of inertia and a member that has no mass but possesses a mass moment of inertia. This latter model is proposed for the study of the effect of the soil-structure interaction.

  14. Modeling the mechanical response of PBX 9501

    SciTech Connect

    Ragaswamy, Partha; Lewis, Matthew W; Liu, Cheng; Thompson, Darla G

    2010-01-01

    An engineering overview of the mechanical response of Plastic-Bonded eXplosives (PBXs), specifically PBX 9501, will be provided with emphasis on observed mechanisms associated with different types of mechanical testing. Mechanical tests in the form of uniaxial tension, compression, cyclic loading, creep (compression and tension), and Hopkinson bar show strain rate and temperature dependence. A range of mechanical behavior is observed which includes small strain recoverable response in the form of viscoelasticity; change in stiffness and softening beyond peak strength due to damage in the form microcracks, debonding, void formation and the growth of existing voids; inelastic response in the form of irrecoverable strain as shown in cyclic tests, and viscoelastic creep combined with plastic response as demonstrated in creep and recovery tests. The main focus of this paper is to elucidate the challenges and issues involved in modeling the mechanical behavior of PBXs for simulating thermo-mechanical responses in engineering components. Examples of validation of a constitutive material model based on a few of the observed mechanisms will be demonstrated against three point bending, split Hopkinson pressure bar and Brazilian disk geometry.

  15. Endocrine disrupting chemicals in fish: developing exposure indicators and predictive models of effects based on mechanism of action

    EPA Science Inventory

    Knowledge of possible toxic mechanisms/modes of action (MOA) of chemicals can provide valuable insights as to appropriate methods for assessing exposure and effects, such as reducing uncertainties related to extrapolation across species, endpoints and chemical structure. However,...

  16. Modeling mechanical signals on the surface of µCT and CAD based rapid prototype scaffold models to predict (early stage) tissue development.

    PubMed

    Hendrikson, W J; van Blitterswijk, C A; Verdonschot, N; Moroni, L; Rouwkema, J

    2014-09-01

    In the field of tissue engineering, mechano-regulation theories have been applied to help predict tissue development in tissue engineering scaffolds in the past. For this, finite element models (FEMs) were used to predict the distribution of strains within a scaffold. However, the strains reported in these studies are volumetric strains of the material or strains developed in the extracellular matrix occupying the pore space. The initial phase of cell attachment and growth on the biomaterial surface has thus far been neglected. In this study, we present a model that determines the magnitude of biomechanical signals on the biomaterial surface, enabling us to predict cell differentiation stimulus values at this initial stage. Results showed that magnitudes of the 2D strain--termed surface strain--were lower when compared to the 3D volumetric strain or the conventional octahedral shear strain as used in current mechano-regulation theories. Results of both µCT and CAD derived FEMs from the same scaffold were compared. Strain and fluid shear stress distributions, and subsequently the cell differentiation stimulus, were highly dependent on the pore shape. CAD models were not able to capture the distributions seen in the µCT FEM. The calculated mechanical stimuli could be combined with current mechanobiological models resulting in a tool to predict cell differentiation in the initial phase of tissue engineering. Although experimental data is still necessary to properly link mechanical signals to cell behavior in this specific setting, this model is an important step towards optimizing scaffold architecture and/or stimulation regimes. PMID:24824318

  17. ODP based UPT model

    NASA Astrophysics Data System (ADS)

    Berre, A. J.; Handegard, T.; Loevnes, K.; Skjellaug, B.; Aagedal, J. O.

    1994-01-01

    The report documents the experiments with object oriented modelling of Universal Personal Telecommunication (UPT) in a telecommunication environment based on the basic principles of open distributed processing (ODP). Through the object-oriented analysis and design technique Object Modelling Technique (OMT) the service is modelled as a collection of software objects distributed across multiple network nodes. A software platform provides the mechanisms for application objects to interact. The platform builds on the basic facilities in the native computing and communication environments, but hides the heterogeneity of these environments and provides distribution transparency at the application programmer's interface. The report closes with some thoughts about applying the paradigm of ODP to intelligent networks (IN), and the experience with OMT as a modelling technique for real time distributed applications.

  18. PC-based pseudo-model following discrete integral variable structure control of positions in slider-crank mechanisms

    NASA Astrophysics Data System (ADS)

    Chuang, Chin-Wen

    2007-04-01

    This paper proposes a pseudo-model following (PMF) discrete integral variable structure control (DIVSC) scheme to control the position of a slider crank coupled with a pseudo-model (PM) synchronous motor. Applying the Grey modeling method, the reference model and plant are on-line converted to pseudo-reference model and accumulated model, respectively. The advantage is that the least data and memory are used in this modeling procedure. The DIVSC is introduced to guide the model following motion. The integral controller is used to reduce the steady-state error. The switching controller is used to finish the sliding motion. The two existing condition of the discrete sliding mode are introduced in this paper, too. Finally, the position control of the slider crank is used to show the performance of the proposed control scheme. The simulation and experimental results show the robustness and the practicability.

  19. A chemo-mechanical free-energy-based approach to model durotaxis and extracellular stiffness-dependent contraction and polarization of cells.

    PubMed

    Shenoy, Vivek B; Wang, Hailong; Wang, Xiao

    2016-02-01

    We propose a chemo-mechanical model based on stress-dependent recruitment of myosin motors to describe how the contractility, polarization and strain in cells vary with the stiffness of their surroundings and their shape. A contractility tensor, which depends on the distribution of myosin motors, is introduced to describe the chemical free energy of the cell due to myosin recruitment. We explicitly include the contributions to the free energy that arise from mechanosensitive signalling pathways (such as the SFX, Rho-Rock and MLCK pathways) through chemo-mechanical coupling parameters. Taking the variations of the total free energy, which consists of the chemical and mechanical components, in accordance with the second law of thermodynamics provides equations for the temporal evolution of the active stress and the contractility tensor. Following this approach, we are able to recover the well-known Hill relation for active stresses, based on the fundamental principles of irreversible thermodynamics rather than phenomenology. We have numerically implemented our free energy-based approach to model spatial distribution of strain and contractility in (i) cells supported by flexible microposts, (ii) cells on two-dimensional substrates, and (iii) cells in three-dimensional matrices. We demonstrate how the polarization of the cells and the orientation of stress fibres can be deduced from the eigenvalues and eigenvectors of the contractility tensor. Our calculations suggest that the chemical free energy of the cell decreases with the stiffness of the extracellular environment as the cytoskeleton polarizes in response to stress-dependent recruitment of molecular motors. The mechanical energy, which includes the strain energy and motor potential energy, however, increases with stiffness, but the overall energy is lower for cells in stiffer environments. This provides a thermodynamic basis for durotaxis, whereby cells preferentially migrate towards stiffer regions of the

  20. Next-generation sequencing, FISH mapping and synteny-based modeling reveal mechanisms of decreasing dysploidy in Cucumis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the family of Cucurbitaceae, cucumber (Cucumis sativus) is the only species with 14 chromosomes. The majority of the remaining species, including melon and the sister species of cucumber, C. hystrix, have 24 chromosomes. To understand the underlying mechanisms of chromosome reduction from n=12 to...

  1. Effective Diffusion Coefficient and Controlling Process of P Diffusion in Si Based on the Pair Diffusion Models of Vacancy and Interstitial Mechanisms

    NASA Astrophysics Data System (ADS)

    Yoshida, Masayuki; Morooka, Masami; Takahashi, Manabu; Tomokage, Hajime

    2000-05-01

    Based on the pair diffusion models of vacancy and interstitial (V and I) mechanisms, the V and I components of effective P diffusion coefficient, DP^+,Veff and DP^+,Ieff, and the controlling process of P diffusion in Si are obtained. Assuming that the I mechanism is dominant, not only the I- concentration, CI^-, but also its gradient, d CI^-/d λ , is effective on DP^+,Ieff at high CP^+. DP^+,Ieff is large at d CI^-/d λ <0 and small at d CI^-/d λ >0. P+ and I- are generated by the dissociation of P-I pair. When excess I- thus generated is removed, d CI^-/d λ <0 is obtained. d CI^-/d λ <0 is also obtained by the decrease in quasi self-interstitial formation energy. Several diffusion models simulate the P diffusion profile well under an inert atmosphere. Applying the controlling process to them, the reason why they simulate the P profile well is investigated. Because all of them simulate the P profile well, it is difficult to conclude which model is correct. It is suggested that it is possible to conclude which model is correct from the P profile under oxidation at CP^+s >1× 1020 cm-3 (s: surface).

  2. Simulation modeling based method for choosing an effective set of fault tolerance mechanisms for real-time avionics systems

    NASA Astrophysics Data System (ADS)

    Bakhmurov, A. G.; Balashov, V. V.; Glonina, A. B.; Pashkov, V. N.; Smeliansky, R. L.; Volkanov, D. Yu.

    2013-12-01

    In this paper, the reliability allocation problem (RAP) for real-time avionics systems (RTAS) is considered. The proposed method for solving this problem consists of two steps: (i) creation of an RTAS simulation model at the necessary level of abstraction and (ii) application of metaheuristic algorithm to find an optimal solution (i. e., to choose an optimal set of fault tolerance techniques). When during the algorithm execution it is necessary to measure the execution time of some software components, the simulation modeling is applied. The procedure of simulation modeling also consists of the following steps: automatic construction of simulation model of the RTAS configuration and running this model in a simulation environment to measure the required time. This method was implemented as an experimental software tool. The tool works in cooperation with DYANA simulation environment. The results of experiments with the implemented method are presented. Finally, future plans for development of the presented method and tool are briefly described.

  3. A Simplified model of mutually inhibitory sleep-active and wake-active neuronal populations employing a noise-based switching mechanism.

    PubMed

    Patel, Mainak

    2016-04-01

    Infant rats switch randomly between the sleeping and waking states; during early infancy (up to postnatal day 8), sleep and wake bouts are random, brief (with means on the order of several seconds) and exponentially distributed, with the length of a particular bout independent of the length of prior bouts. As the rat ages during this early period, mean sleep and wake bout lengths gradually increase, though sleep and wake bouts remain exponentially distributed. Additionally, sleep and wake bouts are regulated independently of each other - alterations in the development of sleep (wake) bouts has no impact on the regulation wake (sleep) bouts. Sleep and wake bout behavior is associated with the activity of mutually inhibitory sleep-active and wake-active brainstem populations. In this work, I employ a simplified biophysical model of two mutually inhibitory populations consisting of ten integrate-and-fire neurons each and a noise-based switching mechanism. I show that such a noise-based switching mechanism naturally accounts for the experimentally observed features of sleep-wake switching during early infancy - random alternating activity bouts occur as a consequence of noise (provided inhibition is strong relative to excitation), bout durations are exponential (due to a lack of memory within the system), and cross-population inhibition or intrapopulation excitatory coupling provide mechanisms for changing and independently regulated sleep and wake bout means. PMID:26802484

  4. Exploring the Mechanisms of Ecological Land Change Based on the Spatial Autoregressive Model: A Case Study of the Poyang Lake Eco-Economic Zone, China

    PubMed Central

    Xie, Hualin; Liu, Zhifei; Wang, Peng; Liu, Guiying; Lu, Fucai

    2013-01-01

    Ecological land is one of the key resources and conditions for the survival of humans because it can provide ecosystem services and is particularly important to public health and safety. It is extremely valuable for effective ecological management to explore the evolution mechanisms of ecological land. Based on spatial statistical analyses, we explored the spatial disparities and primary potential drivers of ecological land change in the Poyang Lake Eco-economic Zone of China. The results demonstrated that the global Moran’s I value is 0.1646 during the 1990 to 2005 time period and indicated significant positive spatial correlation (p < 0.05). The results also imply that the clustering trend of ecological land changes weakened in the study area. Some potential driving forces were identified by applying the spatial autoregressive model in this study. The results demonstrated that the higher economic development level and industrialization rate were the main drivers for the faster change of ecological land in the study area. This study also tested the superiority of the spatial autoregressive model to study the mechanisms of ecological land change by comparing it with the traditional linear regressive model. PMID:24384778

  5. Endocrine Disrupting Chemicals in Fish: Developing Exposure Indicators and Predictive Models of Effects Based on Mechanism of Action

    EPA Science Inventory

    In this paper we provide an overview and illustrative results from a large, integrated project that assesses the effects of endocrine-disrupting chemicals (EDCs) on two small fish models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio). For this work a syste...

  6. Magneto-mechanical modeling study of CO-based amorphous micro- and nanowires for acoustic sensing medical applications

    NASA Astrophysics Data System (ADS)

    Atitoaie, Alexandru; Stancu, Alexandru; Ovari, Tibor-Adrian; Lupu, Nicoleta; Chiriac, Horia

    2016-04-01

    Magnetic nanowires are potential candidates for substituting, within enhanced cochlear implants, the role played by hair cilia from the inner ear, which are responsible for the transduction of acoustic vibrations into electric signals. The sound waves pressure that is bending the magnetic wires induces stresses that are leading to changes in magnetic properties, such as magnetization and permeability. These changes can be detected by a GMR sensor placed below the nanowire array or, in the case of different designs, by a pick-up coil wrapped around the fixed-end of the wires. For the latter case, we are studying the stress distributions caused by bending deformations using the COMSOL finite element software package. We are also proposing a theoretical method for the evaluation of magnetic permeability variation vs. induced stress dependence. The study is performed on CoFeSiB amorphous micro- and nanowires subjected to mechanical perturbations similar to the ones produced by sound pressure waves.

  7. Unifying model of carpal mechanics based on computationally derived isometric constraints and rules-based motion - the stable central column theory.

    PubMed

    Sandow, M J; Fisher, T J; Howard, C Q; Papas, S

    2014-05-01

    This study was part of a larger project to develop a (kinetic) theory of carpal motion based on computationally derived isometric constraints. Three-dimensional models were created from computed tomography scans of the wrists of ten normal subjects and carpal spatial relationships at physiological motion extremes were assessed. Specific points on the surface of the various carpal bones and the radius that remained isometric through range of movement were identified. Analysis of the isometric constraints and intercarpal motion suggests that the carpus functions as a stable central column (lunate-capitate-hamate-trapezoid-trapezium) with a supporting lateral column (scaphoid), which behaves as a 'two gear four bar linkage'. The triquetrum functions as an ulnar translation restraint, as well as controlling lunate flexion. The 'trapezoid'-shaped trapezoid places the trapezium anterior to the transverse plane of the radius and ulna, and thus rotates the principal axis of the central column to correspond to that used in the 'dart thrower's motion'. This study presents a forward kinematic analysis of the carpus that provides the basis for the development of a unifying kinetic theory of wrist motion based on isometric constraints and rules-based motion. PMID:24072199

  8. Strike-slip fault bridge fluid pumping mechanism: insights from field-based palaeostress analysis and numerical modelling

    NASA Astrophysics Data System (ADS)

    Nemčok, Michal; Henk, Andreas; Gayer, Rodney A.; Vandycke, Sara; Hathaway, Tanya M.

    2002-12-01

    We present a finite-element study of stress perturbation in evolving compressive and extensional strike-slip fault bridges. The results are compared with a fracture study of a compressive bridge at St Donats, UK. Horizontally interbedded calcareous mudstone and bioclastic calcilutite at St Donats have a distinct vertical permeability anisotropy. This sedimentary sequence behaves as a set of horizontal aquifers. The fluid flow in these aquifers is sensitive to mean stress gradients. Paleostress analysis of field fracture data, verified by finite-element modelling, indicates a rotation of σ1 towards parallelism with boundary faults inside the growing compressive bridge. Boundary faults and bridge faults recorded numerous fluid flow events. The modelled mean stress pattern shows a regional maximum within the bridge and local maxima/minima pairs at boundary fault tips. Finite-element modelling of an extensional bridge indicates that σ3 rotates towards parallelism with boundary faults. The mean stress pattern is similar to the pattern in compressive bridge but with maxima and minima locations interchanged. The stress patterns are reestablished by each stress build-up preceding the rupturation of the boundary faults throughout the development stages of strike-slip fault bridges. Mean stress gradients developed pre-failure control the fluid flow in fractures of the strike-slip fault system at and after the end of each stress build-up and the fluid flow in boundary faults post-failure. Fracture reactivation and new fracture generation within an evolving bridge is a process consisting of multiple successive events that retain the storage capacity of the bridge. Rupture and sealing of the main bounding-faults is a step-wise process that opens and closes fluid conduits between areas with different pressures.

  9. Scenario-based modelling of mass transfer mechanisms at a petroleum contaminated field site-numerical implications.

    PubMed

    Vasudevan, M; Nambi, Indumathi M; Suresh Kumar, G

    2016-06-15

    Knowledge about distribution of dissolved plumes and their influencing factors is essential for risk assessment and remediation of light non-aqueous phase liquid contamination in groundwater. Present study deals with the applicability of numerical model for simulating various hydro-geological scenarios considering non-uniform source distribution at a petroleum contaminated site in Chennai, India. The complexity associated with the hydrogeology of the site has limited scope for on-site quantification of petroleum pipeline spillage. The change in fuel composition under mass-transfer limited conditions was predicted by simultaneously comparing deviations in aqueous concentrations and activity coefficients (between Raoult's law and analytical approaches). The effects of source migration and weathering on the dissolution of major soluble fractions of petroleum fuel were also studied in relation to the apparent change in their activity coefficients and molar fractions. The model results were compared with field observations and found that field conditions were favourable for biodegradation, especially for the aromatic fraction (benzene and toluene (nearly 95% removal), polycyclic aromatic hydrocarbons (up to 65% removal) and xylene (nearly 45% removal). The results help to differentiate the effect of compositional non-ideality from rate-limited dissolution towards tailing of less soluble compounds (alkanes and trimethylbenzene). Although the effect of non-ideality decreased with distance from the source, the assumption of spatially varying residual saturation could effectively illustrate post-spill scenario by estimating the consequent decrease in mass transfer rate. PMID:27017268

  10. Alveolar mechanics using realistic acinar models

    NASA Astrophysics Data System (ADS)

    Kumar, Haribalan; Lin, Ching-Long; Tawhai, Merryn H.; Hoffman, Eric A.

    2009-11-01

    Accurate modeling of the mechanics in terminal airspaces of the lung is desirable for study of particle transport and pathology. The flow in the acinar region is traditionally studied by employing prescribed boundary conditions to represent rhythmic breathing and volumetric expansion. Conventional models utilize simplified spherical or polygonal units to represent the alveolar duct and sac. Accurate prediction of flow and transport characteristics may require geometries reconstructed from CT-based images and serve to understand the importance of physiologically realistic representation of the acinus. In this effort, we present a stabilized finite element framework, supplemented with appropriate boundary conditions at the alveolar mouth and septal borders for simulation of the alveolar mechanics and the resulting airflow. Results of material advection based on Lagrangian tracking are presented to complete the study of transport and compare the results with simplified acinar models. The current formulation provides improved understanding and realization of a dynamic framework for parenchymal mechanics with incorporation of alveolar pressure and traction stresses.

  11. Application of the Johnson-Kendall-Roberts model in AFM-based mechanical measurements on cells and gel.

    PubMed

    Efremov, Yu M; Bagrov, D V; Kirpichnikov, M P; Shaitan, K V

    2015-10-01

    The force-distance curves (FCs) obtained by the atomic force microscope (AFM) with colloid probes contain information about both the viscoelastic properties and adhesion of a sample. Here, we processed both the approach and retraction parts of FCs obtained on polyacrylamide gels (in water or PBS) and Vero cells (in a culture medium). The Johnson-Kendall-Roberts model was applied to the retraction curves to account for the adhesion. The effects of loading rate, holding time and indentation depth on adhesion force and Young's modulus, calculated from approach and retraction curves, were studied. It was shown that both bulk and local interfacial viscoelasticity can affect the observed approach-retraction hysteresis and measured parameters. The addition of 1% bovine serum albumin (BSA) decreased adhesion of the probe to the PAA gel surface, so interfacial viscoelasticity effects were diminished. On the contrary, the adhesiveness of Vero cells increased after BSA addition, indicating the complex nature of the cell-probe interaction. PMID:26186106

  12. Familial Dysautonomia: Mechanisms and Models.

    PubMed

    Dietrich, Paula; Dragatsis, Ioannis

    2016-08-01

    Hereditary Sensory and Autonomic Neuropathies (HSANs) compose a heterogeneous group of genetic disorders characterized by sensory and autonomic dysfunctions. Familial Dysautonomia (FD), also known as HSAN III, is an autosomal recessive disorder that affects 1/3,600 live births in the Ashkenazi Jewish population. The major features of the disease are already present at birth and are attributed to abnormal development and progressive degeneration of the sensory and autonomic nervous systems. Despite clinical interventions, the disease is inevitably fatal. FD is caused by a point mutation in intron 20 of the IKBKAP gene that results in severe reduction in expression of IKAP, its encoded protein. In vitro and in vivo studies have shown that IKAP is involved in multiple intracellular processes, and suggest that failed target innervation and/or impaired neurotrophic retrograde transport are the primary causes of neuronal cell death in FD. However, FD is far more complex, and appears to affect several other organs and systems in addition to the peripheral nervous system. With the recent generation of mouse models that recapitulate the molecular and pathological features of the disease, it is now possible to further investigate the mechanisms underlying different aspects of the disorder, and to test novel therapeutic strategies. PMID:27494199

  13. CHEMICAL AND PHYSICAL PROCESS AND MECHANISM MODELING

    EPA Science Inventory

    The goal of this task is to develop and test chemical and physical mechanisms for use in the chemical transport models of EPA's Models-3. The target model for this research is the Community Multiscale Air Quality (CMAQ) model. These mechanisms include gas and aqueous phase ph...

  14. Determination of focal mechanisms of intermediate-magnitude earthquakes in Mexico, based on Greens functions calculated for a 3D Earth model

    NASA Astrophysics Data System (ADS)

    Rodrigo Rodríguez Cardozo, Félix; Hjörleifsdóttir, Vala

    2015-04-01

    One important ingredient in the study of the complex active tectonics in Mexico is the analysis of earthquake focal mechanisms, or the seismic moment tensor. They can be determined trough the calculation of Green functions and subsequent inversion for moment-tensor parameters. However, this calculation is gets progressively more difficult as the magnitude of the earthquakes decreases. Large earthquakes excite waves of longer periods that interact weakly with laterally heterogeneities in the crust. For these earthquakes, using 1D velocity models to compute the Greens fucntions works well. The opposite occurs for smaller and intermediate sized events, where the relatively shorter periods excited interact strongly with lateral heterogeneities in the crust and upper mantle and requires more specific or regional 3D models. In this study, we calculate Greens functions for earthquakes in Mexico using a laterally heterogeneous seismic wave speed model, comprised of mantle model S362ANI (Kustowski et al 2008) and crustal model CRUST 2.0 (Bassin et al 1990). Subsequently, we invert the observed seismograms for the seismic moment tensor using a method developed by Liu et al (2004) an implemented by Óscar de La Vega (2014) for earthquakes in Mexico. By following a brute force approach, in which we include all observed Rayleigh and Love waves of the Mexican National Seismic Network (Servicio Sismológico Naciona, SSN), we obtain reliable focal mechanisms for events that excite a considerable amount of low frequency waves (Mw > 4.8). However, we are not able to consistently estimate focal mechanisms for smaller events using this method, due to high noise levels in many of the records. Excluding the noisy records, or noisy parts of the records manually, requires interactive edition of the data, using an efficient tool for the editing. Therefore, we developed a graphical user interface (GUI), based on python and the python library ObsPy, that allows the edition of observed and

  15. Cellobiose as a model system to reveal cellulose dissolution mechanism in acetate-based ionic liquids: Density functional theory study substantiated by NMR spectra.

    PubMed

    Cao, Bobo; Du, Jiuyao; Du, Dongmei; Sun, Haitao; Zhu, Xiao; Fu, Hui

    2016-09-20

    Cellulose dissolution mechanism in acetate-based ionic liquids was systematically studied in Nuclear Magnetic Resonance (NMR) spectra and Density Functional Theory (DFT) methods by using cellobiose and 1-butyl-3-methylimidazolium acetate (BmimAc) as a model system. The solubility of cellulose in ionic liquid increased with temperature increase in the range of 90-140°C. NMR spectra suggested OAc(-) preferred to form stronger hydrogen bonds with hydrogen of hydroxyl in cellulose. Electrostatic potential method was employed to predict the most possible reaction sites and locate the most stable configuration. Atoms in molecules (AIM) theory was used to study the features of bonds at bond critical points and the variations of bond types. Simultaneously, noncovalent interactions were characterized and visualized by employing reduced density gradient analysis combined with Visual Molecular Dynamics (VMD) program. Natural bond orbital (NBO) theory was applied to study the noncovalent nature and characterize the orbital interactions between cellobiose and Bmim[OAc]. PMID:27261759

  16. Model of a mechanical clock escapement

    NASA Astrophysics Data System (ADS)

    Moline, David; Wagner, John; Volk, Eugene

    2012-07-01

    The mechanical tower clock originated in Europe during the 14th century to sound hourly bells and later display hands on a dial. An important innovation was the escapement mechanism, which converts stored energy into oscillatory motion for fixed time intervals through the pendulum swing. Previous work has modeled the escapement mechanism in terms of inelastic and elastic collisions. We derive and experimentally verify a theoretical model in terms of impulsive differential equations for the Graham escapement mechanism in a Seth Thomas tower clock. The model offers insight into the clock's mechanical behavior and the functionality of the deadbeat escapement mechanism.

  17. Thermal, chemical, and mechanical cookoff modeling

    SciTech Connect

    Hobbs, M.L.; Baer, M.R.; Gross, R.J.

    1994-08-01

    A Thermally Reactive, Elastic-plastic eXplosive code, TREX, has been developed to analyze coupled thermal, chemical and mechanical effects associated with cookoff simulation of confined or unconfined energetic materials. In confined systems, pressure buildup precedes thermal runaway, and unconfined energetic material expands to relieve high stress. The model was developed based on nucleation, decomposition chemistry, and elastic/plastic mechanical behavior of a material with a distribution of internal defects represented as clusters of spherical inclusions. A local force balance, with mass continuity constraints, forms the basis of the model requiring input of temperature and reacted gas fraction. This constitutive material model has been incorporated into a quasistatic mechanics code SANTOS as a material module which predicts stress history associated with a given strain history. The thermal-chemical solver XCHEM has been coupled to SANTOS to provide temperature and reacted gas fraction. Predicted spatial history variables include temperature, chemical species, solid/gas pressure, solid/gas density, local yield stress, and gas volume fraction. One-Dimensional Time to explosion (ODTX) experiments for TATB and PBX 9404 (HMX and NC) are simulated using global multistep kinetic mechanisms and the reactive elastic-plastic constitutive model. Pressure explosions, rather than thermal runaway, result in modeling slow cookoff experiments of confined conventional energetic materials such as TATB. For PBX 9404, pressure explosions also occur at fast cookoff conditions because of low temperature reactions of nitrocellulose resulting in substantial pressurization. A demonstrative calculation is also presented for reactive heat flow in a hollow, propellant-filled, stainless steel cylinder, representing a rocket motor. This example simulation show

  18. Multiscale mechanical modeling of soft biological tissues

    NASA Astrophysics Data System (ADS)

    Stylianopoulos, Triantafyllos

    2008-10-01

    Soft biological tissues include both native and artificial tissues. In the human body, tissues like the articular cartilage, arterial wall, and heart valve leaflets are examples of structures composed of an underlying network of collagen fibers, cells, proteins and molecules. Artificial tissues are less complex than native tissues and mainly consist of a fiber polymer network with the intent of replacing lost or damaged tissue. Understanding of the mechanical function of these materials is essential for many clinical treatments (e.g. arterial clamping, angioplasty), diseases (e.g. arteriosclerosis) and tissue engineering applications (e.g. engineered blood vessels or heart valves). This thesis presents the derivation and application of a multiscale methodology to describe the macroscopic mechanical function of soft biological tissues incorporating directly their structural architecture. The model, which is based on volume averaging theory, accounts for structural parameters such as the network volume fraction and orientation, the realignment of the fibers in response to strain, the interactions among the fibers and the interactions between the fibers and the interstitial fluid in order to predict the overall tissue behavior. Therefore, instead of using a constitutive equation to relate strain to stress, the tissue microstructure is modeled within a representative volume element (RVE) and the macroscopic response at any point in the tissue is determined by solving a micromechanics problem in the RVE. The model was applied successfully to acellular collagen gels, native blood vessels, and electrospun polyurethane scaffolds and provided accurate predictions for permeability calculations in isotropic and oriented fiber networks. The agreement of model predictions with experimentally determined mechanical properties provided insights into the mechanics of tissues and tissue constructs, while discrepancies revealed limitations of the model framework.

  19. Development of a fracture mechanics/threshold behavior model to assess the effects of competing mechanisms induced by shot peening on cyclic life of a nickel-base superalloy, Rene 88DT

    NASA Astrophysics Data System (ADS)

    Tufft, Marsha Klopmeier

    This research establishes an improved lower-bound predictive method for the cyclic life of shot peened specimens made from a nickel-base superalloy, Rene 88DT. Based on previous work, shot peening is noted to induce the equivalent of fatigue damage, in addition to the beneficial compressive residual stresses. The ability to quantify the relative effects of various shot peening treatments on cyclic life capability provides a basis for more economic use of shot peening, and selection of shot peening parameters to meet design and life requirements, while minimizing production costs. The predictive method developed consists of two major elements: (1) a Fracture Mechanics Model, which accounts for changes in microstructure, residual stress and topography induced by shot peening, and (2) a Threshold Behavior Map which identifies both crack nucleation and crack propagation thresholds. When both thresholds are crossed, life capability can be evaluated using the Fracture Mechanics model developed. When the crack propagation threshold is exceeded but the crack nucleation threshold is not, the FM method produces a conservative lower-bound estimate of life capability. A unique contribution is the characterization of damage induced by peening by an initial flaw size from microstructural observations of slip depth. Observations of crack formation along slip band in a model disk provide reinforcement for defining a flaw size from slip measurements. Supporting research includes: (1) metallurgical and microstructural evaluation of single impact dimples and production peened coupons, (2) instrumented Single Particle Impact Tests, characterizing changes in material response due to variations in impact conditions (particle size, incidence angle, velocity), (3) duplication of 16 peening conditions used in a designed experiment, characterizing slip depth, residual stress profiles, surface roughness and velocity measurements taken during production peening conditions.

  20. Modeling of hydro-thermo-mechanical behavior of Nafion NRE212 for Polymer Electrolyte Membrane Fuel Cells using the Finite Viscoplasticity Theory Based on Overstress for Polymers (FVBOP)

    NASA Astrophysics Data System (ADS)

    Colak, Ozgen U.; Acar, Alperen

    2013-08-01

    The primary aim of this work is to present the modifications made to the Finite Viscoplasticity Theory Based on Overstress for Polymers (FVBOP). This is a unified state variable theory and the proposed changes are designed to account for humidity and temperature effects relevant to the modeling of the hydrothermal deformation behavior of ionomer membranes used in Polymer Electrolyte Membrane Fuel Cells (PEMFC). Towards that end, the flow function, which is responsible for conferring rate dependency in FVBOP, is modified. A secondary objective of this work was to investigate the feasibility of using the storage modulus obtained by Dynamic Mechanical Analysis (DMA) in place of the elasticity modulus obtained from conventional tensile/compressive tests, and find the correlation between the storage modulus and the elasticity modulus. The numerical simulations were juxtaposed against data from tensile monotonic loading and unloading experiments on perfluorosulfonic acid (PFSA) membrane Nafion NRE212 samples which are used extensively as a membrane material in PEMFC. The deformation behavior was modeled at four different temperatures (298, 323, 338, and 353 K—all values below the glass transition temperature of Nafion) and at three water content levels (3, 7 and 8 % swelling). The effects of strain rate, temperature, and hydration were captured well with the modified FVBOP model.

  1. A mechanical model of overnight hair curling.

    PubMed

    Xiao, Hang; Chen, Xi

    2015-09-01

    Based on the observation of overnight hair curling procedure, we establish a mechanical model to describe the temporary wave formation of straight hair (initial curvature is zero), which incorporates the contact between hair and hair roller. Systematic studies are carried out to explore the effects of radius ratio between hair and hair roller, hair's average axial strain, creep time, Poisson's ratio and gravity on the curl retention. The variation of curl retention with respect to time obtained from our numerical model is validated by a simple theoretical model and by overnight curling experiments on hair samples. The results of simulation show that overnight hair curling is suitable to create a wavy hairstyle within about 7 hours, while the combined usage with hair fixatives enables a wavy hairstyle with desired curvature that lasts for a day or more. PMID:26338501

  2. Statistical mechanics based on fractional classical and quantum mechanics

    SciTech Connect

    Korichi, Z.; Meftah, M. T.

    2014-03-15

    The purpose of this work is to study some problems in statistical mechanics based on the fractional classical and quantum mechanics. At first stage we have presented the thermodynamical properties of the classical ideal gas and the system of N classical oscillators. In both cases, the Hamiltonian contains fractional exponents of the phase space (position and momentum). At the second stage, in the context of the fractional quantum mechanics, we have calculated the thermodynamical properties for the black body radiation, studied the Bose-Einstein statistics with the related problem of the condensation and the Fermi-Dirac statistics.

  3. Methods for modeling contact dynamics of capture mechanisms

    NASA Technical Reports Server (NTRS)

    Williams, Philip J.; Tobbe, Patrick A.; Glaese, John

    1991-01-01

    In this paper, an analytical approach for studying the contact dynamics of space-based vehicles during docking/berthing maneuvers is presented. Methods for modeling physical contact between docking/berthing mechanisms, examples of how these models have been used to evaluate the dynamic behavior of automated capture mechanisms, and experimental verification of predicted results are shown.

  4. Mechanisms and Geochemical Models of Core Formation

    NASA Astrophysics Data System (ADS)

    David Rubie; Seth Andrew Jacobson

    2016-03-01

    The formation of the Earth's core is a consequence of planetary accretion and processes in the Earth's interior. The mechanical process of planetary differentiation is likely to occur in large, if not global, magma oceans created by the collisions of planetary embryos. Metal-silicate segregation in magma oceans occurs rapidly and efficiently unlike grain scale percolation according to laboratory experiments and calculations. Geochemical models of the core formation process as planetary accretion proceeds are becoming increasingly realistic. Single stage and continuous core formation models have evolved into multi-stage models that are couple to the output of dynamical models of the giant impact phase of planet formation. The models that are most successful in matching the chemical composition of the Earth's mantle, based on experimentally-derived element partition coefficients, show that the temperature and pressure of metal-silicate equilibration must increase as a function of time and mass accreted and so must the oxygen fugacity of the equilibrating material. The latter can occur if silicon partitions into the core and through the late delivery of oxidized material. Coupled dynamical accretion and multi-stage core formation models predict the evolving mantle and core compositions of all the terrestrial planets simultaneously and also place strong constraints on the bulk compositions and oxidation states of primitive bodies in the protoplanetary disk.

  5. Modelling a Simple Mechanical System.

    ERIC Educational Resources Information Center

    Morland, Tim

    1999-01-01

    Provides an example of the modeling power of Mathematics, demonstrated in a piece of A-Level student coursework which was undertaken as part of the MEI Structured Mathematics scheme. A system of two masses and two springs oscillating in one dimension is found to be accurately modeled by a system of linear differential equations. (Author/ASK)

  6. Feedback Mechanisms in a Mechanical Model of Cell Polarization

    PubMed Central

    Wang, Xinxin; Carlsson, Anders E.

    2014-01-01

    Directed cell migration requires a spatially polarized distribution of polymerized actin. We develop and treat a mechanical model of cell polarization based on polymerization and depolymerization of actin filaments at the two ends of a cell, modulated by forces at either end that are coupled by the cell membrane. We solve this model using both a simulation approach that treats filament nucleation, polymerization, and depolymerization stochastically, and a rate-equation approach based on key properties such as the number of filaments N and the number of polymerized subunits F at either end of the cell. The rate-equation approach agrees closely with the stochastic approach at steady state and, when appropriately generalized, also predicts the dynamic behavior accurately. The calculated transitions from symmetric to polarized states show that polarization is enhanced by a high free-actin concentration, a large pointed-end off-rate, a small barbed-end off-rate, and a small spontaneous nucleation rate. The rate-equation approach allows us to perform a linear-stability analysis to pin down the key interactions that drive the polarization. The polarization is driven by a positive-feedback loop having two interactions. First, an increase in F at one side of the cell lengthens the filaments and thus reduces the decay rate of N (increasing N); second, increasing N enhances F because the force per growing filament tip is reduced. We find that the transitions induced by changing system properties result from supercritical pitchfork bifurcations. The filament lifetime depends strongly on the average filament length, and this effect is crucial for obtaining polarization correctly. PMID:25313164

  7. Nanoscale resistive switching devices: mechanisms and modeling

    NASA Astrophysics Data System (ADS)

    Yang, Yuchao; Lu, Wei

    2013-10-01

    Resistive switching devices (also termed memristive devices or memristors) are two-terminal nonlinear dynamic electronic devices that can have broad applications in the fields of nonvolatile memory, reconfigurable logic, analog circuits, and neuromorphic computing. Current rapid advances in memristive devices in turn demand better understanding of the switching mechanism and the development of physics-based as well as simplified device models to guide future device designs and circuit-level applications. In this article, we review the physical processes behind resistive switching (memristive) phenomena and discuss the experimental and modeling efforts to explain these effects. In this article three categories of devices, in which the resistive switching effects are driven by cation migration, anion migration, and electronic effects, will be discussed. The fundamental driving forces and the stochastic nature of resistive switching will also be discussed.

  8. Nanoscale resistive switching devices: mechanisms and modeling.

    PubMed

    Yang, Yuchao; Lu, Wei

    2013-11-01

    Resistive switching devices (also termed memristive devices or memristors) are two-terminal nonlinear dynamic electronic devices that can have broad applications in the fields of nonvolatile memory, reconfigurable logic, analog circuits, and neuromorphic computing. Current rapid advances in memristive devices in turn demand better understanding of the switching mechanism and the development of physics-based as well as simplified device models to guide future device designs and circuit-level applications. In this article, we review the physical processes behind resistive switching (memristive) phenomena and discuss the experimental and modeling efforts to explain these effects. In this article three categories of devices, in which the resistive switching effects are driven by cation migration, anion migration, and electronic effects, will be discussed. The fundamental driving forces and the stochastic nature of resistive switching will also be discussed. PMID:24057010

  9. A computational study of discrete mechanical tissue models.

    PubMed

    Pathmanathan, P; Cooper, J; Fletcher, A; Mirams, G; Murray, P; Osborne, J; Pitt-Francis, J; Walter, A; Chapman, S J

    2009-01-01

    A computational study of discrete 'cell-centre' approaches to modelling the evolution of a collection of cells is undertaken. The study focuses on the mechanical aspects of the tissue, in order to separate the passive mechanical response of the model from active effects such as cell-growth and cell division. Issues which arise when implementing these models are described, and a series of numerical mechanical experiments is performed. It is shown that discrete tissues modelled this way typically exhibit elastic-plastic behaviour under slow compression, and act as a brittle linear elastic solid under slow tension. Both overlapping spheres and Voronoi-tessellation-based models are examined, and the effect of different cell-cell interaction force laws on the bulk mechanical properties of the tissue is determined. This correspondence allows parameters in the cell-based model to be chosen to be compatible with bulk tissue measurements. PMID:19369704

  10. Neurocomputational Nosology: Malfunctions of Models and Mechanisms

    PubMed Central

    Barack, David L.; Platt, Michael L.

    2016-01-01

    Executive dysfunctions, psychopathologies arising from problems in the control and regulation of behavior, can occur as a result of the faulty execution of formal information processing models or as a result of malfunctioning neural mechanisms. The models correspond to the formal descriptions of how signals in the environment must be transformed in order to behave adaptively, and the mechanisms correspond to the signal transformations that nervous systems implement in order to execute those cognitive functions. Mechanisms in the form of repeated patterns of neural dynamics execute information processing models. Two distinct modes of malfunction can occur when neural dynamics execute models of information processing. The processing models describing behavior may fail to be executed correctly by neural mechanisms. Or, the neural mechanisms may malfunction, failing to implement the right computation. As an example of malfunctioning models in executive cognition, purported failures of rule following can be understood as failures to appropriately execute a suite of processing models. As an example of malfunctioning mechanisms of executive cognition, maladaptive behavior resulting from dysfunction in the medial prefrontal cortex (mPFC) can be understood as failures in the signal transformations carried out therein. The purpose of these examples is to illustrate the potential benefits of considering models and mechanisms in the diagnosis and etiology of neuropsychological illness and dysfunction, especially disorders of executive cognition. PMID:27199835

  11. Neurocomputational Nosology: Malfunctions of Models and Mechanisms.

    PubMed

    Barack, David L; Platt, Michael L

    2016-01-01

    Executive dysfunctions, psychopathologies arising from problems in the control and regulation of behavior, can occur as a result of the faulty execution of formal information processing models or as a result of malfunctioning neural mechanisms. The models correspond to the formal descriptions of how signals in the environment must be transformed in order to behave adaptively, and the mechanisms correspond to the signal transformations that nervous systems implement in order to execute those cognitive functions. Mechanisms in the form of repeated patterns of neural dynamics execute information processing models. Two distinct modes of malfunction can occur when neural dynamics execute models of information processing. The processing models describing behavior may fail to be executed correctly by neural mechanisms. Or, the neural mechanisms may malfunction, failing to implement the right computation. As an example of malfunctioning models in executive cognition, purported failures of rule following can be understood as failures to appropriately execute a suite of processing models. As an example of malfunctioning mechanisms of executive cognition, maladaptive behavior resulting from dysfunction in the medial prefrontal cortex (mPFC) can be understood as failures in the signal transformations carried out therein. The purpose of these examples is to illustrate the potential benefits of considering models and mechanisms in the diagnosis and etiology of neuropsychological illness and dysfunction, especially disorders of executive cognition. PMID:27199835

  12. The mechanism of myrmekite formation deduced from steady-diffusion modeling based on petrography: Case study of the Okueyama granitic body, Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Yuguchi, Takashi; Nishiyama, Tadao

    2008-12-01

    Myrmekite is an intergrowth texture consisting of vermicular quartz and albitic plagioclase (Ab 93An 7 in this study), typically occurring between K-feldspar and plagioclase. It occurs ubiquitously in both metamorphic and granitic rocks; however, its genesis has been an enigma. This paper describes myrmekite's petrography and discusses its genesis from the Okueyama granitic body (OKG), which is a young (14 Ma) granite in Southwest Japan with no evidence of deformation after solidification. The genesis of a newly observed texture, the 'reaction rim', will be also discussed in relation to myrmekite. The reaction rim is an albite layer (Ab 95An 5) with no vermicular quartz between K-feldspar and plagioclase, and it occasionally makes a composite texture with myrmekite. Both myrmekite and the reaction rim are accompanied by a diffusive boundary layer (Olg-layer) with a mean composition of oligoclase (Ab 75An 25) in the rim of neighboring plagioclase rim. The overall reactions in an open system for the formation of myrmekite and that for the reaction rim are derived based on the following two models: 1) one based on the assumption of conservation of solid volume with arbitrarily specified closure components, and 2) the other based on the assumption of closure of AlO 3/2 together with an arbitrarily specified volume factor. Steady diffusion modeling in an open system based on the overall reaction thus derived defines the stability field of myrmekite and of the reaction rim in terms of the ratios of phenomenological coefficients ( L-ratios). The steady diffusion models for the above two models have essentially the same features. Myrmekite is stable for large values (> 10) of LAlAl/ LCaCa, for moderate values of LAlAl/ LSiSi, and for only small values (< 1) of LAlAl/ LNaNa. In the case of the reaction rim, the stability field is much wider in a plot of LAlAl/ LCaCa vs. LAlAl/ LNaNa, and its dependence on LAlAl/ LSiSi is stronger than that of myrmekite. The reaction rim is

  13. Mechanical modelling of tooth wear.

    PubMed

    Karme, Aleksis; Rannikko, Janina; Kallonen, Aki; Clauss, Marcus; Fortelius, Mikael

    2016-07-01

    Different diets wear teeth in different ways and generate distinguishable wear and microwear patterns that have long been the basis of palaeodiet reconstructions. Little experimental research has been performed to study them together. Here, we show that an artificial mechanical masticator, a chewing machine, occluding real horse teeth in continuous simulated chewing (of 100 000 chewing cycles) is capable of replicating microscopic wear features and gross wear on teeth that resemble wear in specimens collected from nature. Simulating pure attrition (chewing without food) and four plant material diets of different abrasives content (at n = 5 tooth pairs per group), we detected differences in microscopic wear features by stereomicroscopy of the chewing surface in the number and quality of pits and scratches that were not always as expected. Using computed tomography scanning in one tooth per diet, absolute wear was quantified as the mean height change after the simulated chewing. Absolute wear increased with diet abrasiveness, originating from phytoliths and grit. In combination, our findings highlight that differences in actual dental tissue loss can occur at similar microwear patterns, cautioning against a direct transformation of microwear results into predictions about diet or tooth wear rate. PMID:27411727

  14. Computational Models for Mechanics of Morphogenesis

    PubMed Central

    Wyczalkowski, Matthew A.; Chen, Zi; Filas, Benjamen A.; Varner, Victor D.; Taber, Larry A.

    2012-01-01

    In the developing embryo, tissues differentiate, deform, and move in an orchestrated manner to generate various biological shapes driven by the complex interplay between genetic, epigenetic, and environmental factors. Mechanics plays a key role in regulating and controlling morphogenesis, and quantitative models help us understand how various mechanical forces combine to shape the embryo. Models allow for the quantitative, unbiased testing of physical mechanisms, and when used appropriately, can motivate new experimental directions. This knowledge benefits biomedical researchers who aim to prevent and treat congenital malformations, as well as engineers working to create replacement tissues in the laboratory. In this review, we first give an overview of fundamental mechanical theories for morphogenesis, and then focus on models for specific processes, including pattern formation, gastrulation, neurulation, organogenesis, and wound healing. The role of mechanical feedback in development is also discussed. Finally, some perspectives are given on the emerging challenges in morphomechanics and mechanobiology. PMID:22692887

  15. Base Flow Model Validation

    NASA Technical Reports Server (NTRS)

    Sinha, Neeraj; Brinckman, Kevin; Jansen, Bernard; Seiner, John

    2011-01-01

    A method was developed of obtaining propulsive base flow data in both hot and cold jet environments, at Mach numbers and altitude of relevance to NASA launcher designs. The base flow data was used to perform computational fluid dynamics (CFD) turbulence model assessments of base flow predictive capabilities in order to provide increased confidence in base thermal and pressure load predictions obtained from computational modeling efforts. Predictive CFD analyses were used in the design of the experiments, available propulsive models were used to reduce program costs and increase success, and a wind tunnel facility was used. The data obtained allowed assessment of CFD/turbulence models in a complex flow environment, working within a building-block procedure to validation, where cold, non-reacting test data was first used for validation, followed by more complex reacting base flow validation.

  16. Mechanical models for slosh of liquid fuel

    NASA Technical Reports Server (NTRS)

    Buseck, R.; Benaroya, H.

    1993-01-01

    This paper concentrates on equilibrium behavior of fluids in low or zero gravity, and sloshing in normal and low gravity. Included are a background and review of the literature, and an introduction to a new equivalent mechanical model.

  17. An automated dynamic fracture procedure and a continuum damage mechanics based model for finite element simulations of delamination failure in laminated composites

    NASA Astrophysics Data System (ADS)

    Aminjikarai Vedagiri, Srinivasa Babu

    An active field of research that has developed due to the increasing use of computational techniques like finite element simulations for analysis of highly complex structural mechanics problems and the increasing use of composite laminates in varied industries such as aerospace, automotive, bio-medical, etc. is the development of numerical models to capture the behavior of composite materials. One of the big challenges not yet overcome convincingly in this field is the modeling of delamination failure which is one of the primary modes of damage in composite laminates. Hence, the primary aim of this work is to develop two numerical models for finite element simulations of delamination failure in composite laminates and implement them in the explicit finite element software DYNA3D/LS-DYNA. Dynamic fracture mechanics is an example of a complex structural analysis problem for which finite element simulations seem to be the only possible way to extract detailed information on sophisticated physical quantities of the crack-tip at any instant of time along a highly transient history of fracture. However, general purpose, commercial finite element software which have capabilities to do fracture analyses are still limited in their use to stationary cracks and crack propagation along trajectories known a priori. Therefore, an automated dynamic fracture procedure capable of simulating dynamic propagation of through-thickness cracks in arbitrary directions in linear, isotropic materials without user-intervention is first developed and implemented in DYNA3D for its default 8-node solid (brick) element. Dynamic energy release rate and stress intensity factors are computed in the model using integral expressions particularly well-suited for the finite element method. Energy approach is used to check for crack propagation and the maximum circumferential stress criterion is used to determine the direction of crack growth. Since the re-meshing strategy used to model crack growth

  18. Trait-based tests of coexistence mechanisms.

    PubMed

    Adler, Peter B; Fajardo, Alex; Kleinhesselink, Andrew R; Kraft, Nathan J B

    2013-10-01

    Recent functional trait studies have shown that trait differences may favour certain species (environmental filtering) while simultaneously preventing competitive exclusion (niche partitioning). However, phenomenological trait-dispersion analyses do not identify the mechanisms that generate niche partitioning, preventing trait-based prediction of future changes in biodiversity. We argue that such predictions require linking functional traits with recognised coexistence mechanisms involving spatial or temporal environmental heterogeneity, resource partitioning and natural enemies. We first demonstrate the limitations of phenomenological approaches using simulations, and then (1) propose trait-based tests of coexistence, (2) generate hypotheses about which plant functional traits are likely to interact with particular mechanisms and (3) review the literature for evidence for these hypotheses. Theory and data suggest that all four classes of coexistence mechanisms could act on functional trait variation, but some mechanisms will be stronger and more widespread than others. The highest priority for future research is studies of interactions between environmental heterogeneity and trait variation that measure environmental variables at within-community scales and quantify species' responses to the environment in the absence of competition. Evidence that similar trait-based coexistence mechanisms operate in many ecosystems would simplify biodiversity forecasting and represent a rare victory for generality over contingency in community ecology. PMID:23910482

  19. Modeling biofilms with dual extracellular electron transfer mechanisms

    PubMed Central

    Renslow, Ryan; Babauta, Jerome; Kuprat, Andrew; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim; Beyenal, Haluk

    2013-01-01

    Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as terminal electron acceptors for their metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce the requisite components for both mechanisms. In this study, a generic model is presented that incorporates the diffusion- and the conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to S. oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found in the literature. Our simulation results show that 1) biofilms having both mechanisms available, especially if they can interact, may have a metabolic advantage over biofilms that can use only a single mechanism; 2) the thickness of G. sulfurreducens biofilms is likely not limited by conductivity; 3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and 4) the local biofilm potential and redox potential are two distinct parameters and cannot be assumed to have identical values. Finally, we determined that simulated cyclic and squarewave voltammetry based on our model are currently not capable of determining the specific percentages of extracellular electron transfer mechanisms in a biofilm. The developed model will be a critical tool for designing experiments to explain EET mechanisms. PMID:24113651

  20. Modeling biofilms with dual extracellular electron transfer mechanisms.

    PubMed

    Renslow, Ryan; Babauta, Jerome; Kuprat, Andrew; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim; Beyenal, Haluk

    2013-11-28

    Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as terminal electron acceptors for their metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce the requisite components for both mechanisms. In this study, a generic model is presented that incorporates the diffusion- and the conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to S. oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found in the literature. Our simulation results show that (1) biofilms having both mechanisms available, especially if they can interact, may have a metabolic advantage over biofilms that can use only a single mechanism; (2) the thickness of G. sulfurreducens biofilms is likely not limited by conductivity; (3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and (4) the local biofilm potential and redox potential are two distinct parameters and cannot be assumed to have identical values. Finally, we determined that simulated cyclic and squarewave voltammetry based on our model are currently not capable of determining the specific percentages of extracellular electron transfer mechanisms in a biofilm. The developed model will be a critical tool for designing experiments to explain EET mechanisms. PMID:24113651

  1. Putting mechanisms into crop production models

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Crop simulation models dynamically predict processes of carbon, nitrogen, and water balance on daily or hourly time-steps to the point of predicting yield and production at crop maturity. A brief history of these models is reviewed, and their level of mechanism for assimilation and respiration, ran...

  2. Mathematical model of a telomerase transcriptional regulatory network developed by cell-based screening: analysis of inhibitor effects and telomerase expression mechanisms.

    PubMed

    Bilsland, Alan E; Stevenson, Katrina; Liu, Yu; Hoare, Stacey; Cairney, Claire J; Roffey, Jon; Keith, W Nicol

    2014-02-01

    Cancer cells depend on transcription of telomerase reverse transcriptase (TERT). Many transcription factors affect TERT, though regulation occurs in context of a broader network. Network effects on telomerase regulation have not been investigated, though deeper understanding of TERT transcription requires a systems view. However, control over individual interactions in complex networks is not easily achievable. Mathematical modelling provides an attractive approach for analysis of complex systems and some models may prove useful in systems pharmacology approaches to drug discovery. In this report, we used transfection screening to test interactions among 14 TERT regulatory transcription factors and their respective promoters in ovarian cancer cells. The results were used to generate a network model of TERT transcription and to implement a dynamic Boolean model whose steady states were analysed. Modelled effects of signal transduction inhibitors successfully predicted TERT repression by Src-family inhibitor SU6656 and lack of repression by ERK inhibitor FR180204, results confirmed by RT-QPCR analysis of endogenous TERT expression in treated cells. Modelled effects of GSK3 inhibitor 6-bromoindirubin-3'-oxime (BIO) predicted unstable TERT repression dependent on noise and expression of JUN, corresponding with observations from a previous study. MYC expression is critical in TERT activation in the model, consistent with its well known function in endogenous TERT regulation. Loss of MYC caused complete TERT suppression in our model, substantially rescued only by co-suppression of AR. Interestingly expression was easily rescued under modelled Ets-factor gain of function, as occurs in TERT promoter mutation. RNAi targeting AR, JUN, MXD1, SP3, or TP53, showed that AR suppression does rescue endogenous TERT expression following MYC knockdown in these cells and SP3 or TP53 siRNA also cause partial recovery. The model therefore successfully predicted several aspects of TERT

  3. Finite element modeling of retinal prosthesis mechanics

    NASA Astrophysics Data System (ADS)

    Basinger, B. C.; Rowley, A. P.; Chen, K.; Humayun, M. S.; Weiland, J. D.

    2009-10-01

    Epiretinal prostheses used to treat degenerative retina diseases apply stimulus via an electrode array fixed to the ganglion cell side of the retina. Mechanical pressure applied by these arrays to the retina, both during initial insertion and throughout chronic use, could cause sufficient retinal damage to reduce the device's effectiveness. In order to understand and minimize potential mechanical damage, we have used finite element analysis to model mechanical interactions between an electrode array and the retina in both acute and chronic loading configurations. Modeling indicates that an acute tacking force distributes stress primarily underneath the tack site and heel edge of the array, while more moderate chronic stresses are distributed more evenly underneath the array. Retinal damage in a canine model chronically implanted with a similar array occurred in correlating locations, and model predictions correlate well with benchtop eyewall compression tests. This model provides retinal prosthesis researchers with a tool to optimize the mechanical electrode array design, but the techniques used here represent a unique effort to combine a modifiable device and soft biological tissues in the same model and those techniques could be extended to other devices that come into mechanical contact with soft neural tissues.

  4. Time-independent Anisotropic Plastic Behavior by Mechanical Subelement Models

    NASA Technical Reports Server (NTRS)

    Pian, T. H. H.

    1983-01-01

    The paper describes a procedure for modelling the anisotropic elastic-plastic behavior of metals in plane stress state by the mechanical sub-layer model. In this model the stress-strain curves along the longitudinal and transverse directions are represented by short smooth segments which are considered as piecewise linear for simplicity. The model is incorporated in a finite element analysis program which is based on the assumed stress hybrid element and the iscoplasticity-theory.

  5. Mechanical model of a single tendon finger

    NASA Astrophysics Data System (ADS)

    Rossi, Cesare; Savino, Sergio

    2013-10-01

    The mechanical model of a single tendon three phalanxes finger is presented. By means of the model both kinematic and dynamical behavior of the finger itself can be studied. This finger is a part of a more complex mechanical system that consists in a four finger grasping device for robots or in a five finger human hand prosthesis. A first prototype has been realized in our department in order to verify the real behavior of the model. Some results of both kinematic and dynamical behavior are presented.

  6. Experimental verification of a progressive damage model for composite laminates based on continuum damage mechanics. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Coats, Timothy William

    1994-01-01

    Progressive failure is a crucial concern when using laminated composites in structural design. Therefore the ability to model damage and predict the life of laminated composites is vital. The purpose of this research was to experimentally verify the application of the continuum damage model, a progressive failure theory utilizing continuum damage mechanics, to a toughened material system. Damage due to tension-tension fatigue was documented for the IM7/5260 composite laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables, respectively, to predict stiffness loss. A damage dependent finite element code qualitatively predicted trends in transverse matrix cracking, axial splits and local stress-strain distributions for notched quasi-isotropic laminates. The predictions were similar to the experimental data and it was concluded that the continuum damage model provided a good prediction of stiffness loss while qualitatively predicting damage growth in notched laminates.

  7. A fully coupled thermal, chemical, mechanical cookoff model

    SciTech Connect

    Hobbs, M.L.; Baer, M.R.; Gross, R.J.

    1994-05-01

    Cookoff modeling of confined energetic materials involves the coupling of thermal, chemical and mechanical effects. In the past, modeling has focussed on the prediction of thermal runaway with little regard to the effects of mechanical behavior of the energetic material. To address the mechanical response of the energetic material, a constitutive submodel has been developed which can be incorporated into thermal-chemical-mechanical analysis. This work presents development of this submodel and its incorporation into a fully coupled one-dimensional, thermal-chemical-mechanical computer code to simulate thermal initiation of energetic materials. Model predictions include temperature, chemical species, stress, strain, solid/gas pressure, solid/gas density, yield function, and gas volume fraction. Sample results from a scaled aluminum tube filled with RDX exposed to a constant temperature bath at 500 K will be displayed. The micromechanical submodel is based on bubble mechanics which describes nucleation, decomposition, and elastic/plastic mechanical behavior. This constitutive material description requires input of temperatures and reacted fraction of the energetic material as provided by the reactive heat flow code, XCHEM, and the mechanical response is predicted using a quasistatic mechanics code, SANTOS. A parametric sensitivity analysis indicates that a small degree of decomposition causes significant pressurization of the energetic material, which implies that cookoff modeling must consider the strong interaction between thermal-chemistry and mechanics. This document consists of view graphs from the poster session.

  8. Secondary Inorganic Soluble Aerosol in Hong Kong: Continuous Measurements, Formation Mechanism Discussion and Improvement of an Observation-Based Model to Study Control Strategies

    NASA Astrophysics Data System (ADS)

    Xue, Jian

    Work in this thesis focuses on half-hourly or hourly measurements of PM2.5 secondary inorganic aerosols (SIA) in two locations in Hong Kong (HK) using a continuous system, PILS (Particle-into-Liquid System) coupled to two ion chromatographs. The high-resolution data sets allow the examination of SIA temporal dynamics in the scale of hours that the filter-based approach is incapable of providing. (1) Impacts of local emissions, regional transports and their interactions on chemical composition and concentrations of PM2.5 SIA and other ionic species were investigated at the Hong Kong University of Science and Technology (HKUST), a receptor site, under three synoptic conditions. (2) Chemical compositions and size characteristics of ionic species were investigated at Tung Chung, a new town area located in the Southwest part of HK. The sampling period was from 17 to 26 December 2009, covering both normal conditions and an aerosol episode. The three major secondary inorganic ions, SO42, NH4+ and NO 3-, accounted for 47 +/- 6% of PM2.5 mass. Further examination of size characteristics of NO3 - shows that fine mode NO3- is more likely to occur in environments when the fine particles are less acidic and the sea-salt aerosol contributions are low. (3) The ionic chemical composition of PM2.5 and meteorological parameters (e.g., temperature, RH) obtained at the HKUST site under all three different synoptic conditions are input into Aerosol Inorganic Model (AIM-III) for estimation of in situ pH through calculation of H+ amount and aerosol liquid water content (LWC). The second part of this thesis work is to improve an observation-based model (OBAMAP) for SIA, which was first developed by Dr. Zibing Yuan (2006) to evaluate the sensitivity of formation of nitrate ad sulfate to changes in the emissions of their precursors (i.e., NOx, SO2, and VOCs). The improvement work includes incorporating updated chemical mechanisms, thermodynamic equilibrium for gas-aerosol phase

  9. Control mechanisms for a nonlinear model of international relations

    SciTech Connect

    Pentek, A.; Kadtke, J.; Lenhart, S.; Protopopescu, V.

    1997-07-15

    Some issues of control in complex dynamical systems are considered. The authors discuss two control mechanisms, namely: a short range, reactive control based on the chaos control idea and a long-term strategic control based on an optimal control algorithm. They apply these control ideas to simple examples in a discrete nonlinear model of a multi-nation arms race.

  10. Thermal shock fracture mechanics analysis of a semi-infinite medium based on the dual-phase-lag heat conduction model

    PubMed Central

    Wang, B.; Li, J. E.; Yang, C.

    2015-01-01

    The generalized lagging behaviour in solids is very important in understanding heat conduction in small-scale and high-rate heating. In this paper, an edge crack in a semi-infinite medium subjected to a heat shock on its surface is studied under the framework of the dual-phase-lag (DPL) heat conduction model. The transient thermal stress in the medium without crack is obtained first. This stress is used as the crack surface traction with an opposite sign to formulate the crack problem. Numerical results of thermal stress intensity factor are obtained as the functions of crack length and thermal shock time. Crack propagation predictions are conducted and results based on the DPL model and those based on the classical Fourier heat conduction model are compared. The thermal shock strength that the medium can sustain without catastrophic failure is established according to the maximum local stress criterion and the stress intensity factor criterion. PMID:25663805

  11. Reliability mechanisms in distributed data base systems

    SciTech Connect

    Son, S.H.

    1986-01-01

    Distributed database systems operate in computer networking environments where component failures are inevitable during normal operation. Failures not only threaten normal operation of the system, but they may destroy the correctness of the data base by direct damage to the storage subsystem. In order to cope with these failures, distributed data base systems must provide reliability mechanisms that maintain the system consistency. There are two major parts in this dissertation. In the first part, mechanisms are presented for recovery management in distributed data base system. The recovery management of a distributed data bases system consists of two parts: the preparation for the recovery by saving necessary information during normal operation of the data base system, and the coordination of the actual recovery in order to avoid the possible inconsistency after the recovery. The preparation for the recovery is done through the checkpointing and logging. A new scheme is proposed for reconstruction of the data base in distributed environments. In the second part, a token-based resiliency control scheme for replicated distributed data base systems. The proposed control scheme increases the reliability as well as the degree of concurrency while maintaining the consistency of the system.

  12. Model based manipulator control

    NASA Technical Reports Server (NTRS)

    Petrosky, Lyman J.; Oppenheim, Irving J.

    1989-01-01

    The feasibility of using model based control (MBC) for robotic manipulators was investigated. A double inverted pendulum system was constructed as the experimental system for a general study of dynamically stable manipulation. The original interest in dynamically stable systems was driven by the objective of high vertical reach (balancing), and the planning of inertially favorable trajectories for force and payload demands. The model-based control approach is described and the results of experimental tests are summarized. Results directly demonstrate that MBC can provide stable control at all speeds of operation and support operations requiring dynamic stability such as balancing. The application of MBC to systems with flexible links is also discussed.

  13. Glutamate transporter homolog-based model predicts that anion-π interaction is the mechanism for the voltage-dependent response of prestin.

    PubMed

    Lovas, Sándor; He, David Z Z; Liu, Huizhan; Tang, Jie; Pecka, Jason L; Hatfield, Marcus P D; Beisel, Kirk W

    2015-10-01

    Prestin is the motor protein of cochlear outer hair cells. Its unique capability to perform direct, rapid, and reciprocal electromechanical conversion depends on membrane potential and interaction with intracellular anions. How prestin senses the voltage change and interacts with anions are still unknown. Our three-dimensional model of prestin using molecular dynamics simulations predicts that prestin contains eight transmembrane-spanning segments and two helical re-entry loops and that tyrosyl residues are the structural specialization of the molecule for the unique function of prestin. Using site-directed mutagenesis and electrophysiological techniques, we confirmed that residues Tyr(367), Tyr(486), Tyr(501), and Tyr(508) contribute to anion binding, interacting with intracellular anions through novel anion-π interactions. Such weak interactions, sensitive to voltage and mechanical stimulation, confer prestin with a unique capability to perform electromechanical and mechanoelectric conversions with exquisite sensitivity. This novel mechanism is completely different from all known mechanisms seen in ion channels, transporters, and motor proteins. PMID:26283790

  14. Modeling thermal/chemical/mechanical response of energetic materials

    SciTech Connect

    Baer, M.R.; Hobbs, M.L.; Gross, R.J.

    1995-07-01

    An overview of modeling at Sandia National Laboratories is presented which describes coupled thermal, chemical and mechanical response of energetic materials. This modeling addresses cookoff scenarios for safety assessment studies in systems containing energetic materials. Foundation work is discussed which establishes a method for incorporating chemistry and mechanics into multidimensional analysis. Finite element analysis offers the capabilities to simultaneously resolve reactive heat transfer and structural mechanics in complex geometries. Nonlinear conduction heat transfer, with multiple step finite-rate chemistry, is resolved using a thermal finite element code. Rate equations are solved element-by-element using a modified matrix-free stiff solver This finite element software was developed for the simulation of systems requiring large numbers of finite elements. An iterative implicit scheme, based on the conjugate gradient method, is used and a hemi-cube algorithm is employed for the determination of view factors in surface-to-surface radiation transfer The critical link between the reactive heat transfer and mechanics is the introduction of an appropriate constitutive material model providing a stress-strain relationship for quasi-static mechanics analysis. This model is formally derived from bubble nucleation theory, and parameter variations of critical model parameters indicate that a small degree of decomposition leads to significant mechanical response. Coupled thermal/chemical/mechanical analysis is presented which simulates experiments designed to probe cookoff thermal-mechanical response of energetic materials.

  15. Modeling Transport and Flow Regulatory Mechanisms of the Kidney

    PubMed Central

    Layton, Anita T.

    2013-01-01

    The kidney plays an indispensable role in the regulation of whole-organism water balance, electrolyte balance, and acid-base balance, and in the excretion of metabolic wastes and toxins. In this paper, we review representative mathematical models that have been developed to better understand kidney physiology and pathophysiology, including the regulation of glomerular filtration, the regulation of renal blood flow by means of the tubuloglomerular feedback mechanisms and of the myogenic mechanism, the urine concentrating mechanism, and regulation of renal oxygen transport. We discuss how such modeling efforts have significantly expanded our understanding of renal function in both health and disease. PMID:23914303

  16. Mechanical model of the recovery from stumbling.

    PubMed

    Cordero, A Forner; Koopman, H J F M; van der Helm, F C T

    2004-10-01

    Several strategies have been described as a reaction to a stumble during gait. The elevating strategy, which tries to proceed with the perturbed step, was executed as a response to a perturbation during early swing. The lowering strategy, bringing the perturbed leg to the ground and overtaking the obstacle with the contralateral limb, was executed more frequently when the perturbation appeared at mid or late swing. The goal of this paper is to analyze which mechanical factors determine the most advantageous strategy. In order to determine these factors, a mechanical model of the recovery was developed and used to analyze a series of perturbation experiments. It was assumed that the goal of the recovery reaction was to control the trunk as an inverted pendulum during the double-stance phase. In order to be able to control the trunk angle, one foot should be up front and one foot should be behind the hips; otherwise it would be impossible to generate the required trunk torques. The trunk dynamics were expressed in terms of the ground reaction forces and their application point. A larger step (elevation strategy) gives the opportunity to dissolve the perturbation in one step. A small step (lowering strategy) necessarily results in a second quick step, after which the perturbation energy can be dissipated in the second double-stance phase. If a recovery step is too slow, it becomes impossible to counteract the forward flexion of the trunk. It is suggested that a measure of the ability to recover from a stumble could be based on the ability to perform quick steps. PMID:15378375

  17. Selected aspects of modelling monetary transmission mechanism by BVAR model

    NASA Astrophysics Data System (ADS)

    Vaněk, Tomáš; Dobešová, Anna; Hampel, David

    2013-10-01

    In this paper we use the BVAR model with the specifically defined prior to evaluate data including high-lag dependencies. The results are compared to both restricted and common VAR model. The data depicts the monetary transmission mechanism in the Czech Republic and Slovakia from January 2002 to February 2013. The results point to the inadequacy of the common VAR model. The restricted VAR model and the BVAR model appear to be similar in the sense of impulse responses.

  18. Modeling biofilms with dual extracellular electron transfer mechanisms

    SciTech Connect

    Renslow, Ryan S.; Babauta, Jerome T.; Kuprat, Andrew P.; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim K.; Beyenal, Haluk

    2013-11-28

    Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as their terminal electron acceptor for metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce components requisite for both mechanisms. In this study, a generic model is presented that incorporates both diffusion- and conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to Shewanella oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found the literature. Our simulation results showed that 1) biofilms having both mechanisms available, especially if they can interact, may have metabolic advantage over biofilms that can use only a single mechanism; 2) the thickness of Geobacter sulfurreducens biofilms is likely not limited by conductivity; 3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and 4) the local biofilm potential and redox potential are two distinct measurements and cannot be assumed to have identical values. Finally, we determined that cyclic and squarewave voltammetry are currently not good tools to determine the specific percentage of extracellular electron transfer mechanisms used by biofilms. The developed model will be a critical tool in designing experiments to explain EET mechanisms.

  19. Quantum Mechanical Modeling of Ballistic MOSFETs

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, Bryan (Technical Monitor)

    2001-01-01

    The objective of this project was to develop theory, approximations, and computer code to model quasi 1D structures such as nanotubes, DNA, and MOSFETs: (1) Nanotubes: Influence of defects on ballistic transport, electro-mechanical properties, and metal-nanotube coupling; (2) DNA: Model electron transfer (biochemistry) and transport experiments, and sequence dependence of conductance; and (3) MOSFETs: 2D doping profiles, polysilicon depletion, source to drain and gate tunneling, understand ballistic limit.

  20. Statistical mechanics of ontology based annotations

    NASA Astrophysics Data System (ADS)

    Hoyle, David C.; Brass, Andrew

    2016-01-01

    We present a statistical mechanical theory of the process of annotating an object with terms selected from an ontology. The term selection process is formulated as an ideal lattice gas model, but in a highly structured inhomogeneous field. The model enables us to explain patterns recently observed in real-world annotation data sets, in terms of the underlying graph structure of the ontology. By relating the external field strengths to the information content of each node in the ontology graph, the statistical mechanical model also allows us to propose a number of practical metrics for assessing the quality of both the ontology, and the annotations that arise from its use. Using the statistical mechanical formalism we also study an ensemble of ontologies of differing size and complexity; an analysis not readily performed using real data alone. Focusing on regular tree ontology graphs we uncover a rich set of scaling laws describing the growth in the optimal ontology size as the number of objects being annotated increases. In doing so we provide a further possible measure for assessment of ontologies.

  1. A contact mechanics based model for partially-closed randomly distributed surface microcracks and their effect on acoustic nonlinearity in Rayleigh surface waves

    NASA Astrophysics Data System (ADS)

    Oberhardt, Tobias; Kim, Jin-Yeon; Qu, Jianmin; Jacobs, Laurence J.

    2016-02-01

    This research investigates the modeling of randomly distributed surface-breaking microcracks and the dependency of higher harmonic generation in Rayleigh surface waves on microcrack density. The microcrack model is based on micromechanical considerations of rough surface contact. An effective stress-strain relationship is derived to describe the nonlinear behavior of a single microcrack and implemented into a finite-element model via a hyperelastic constitutive law. Finite-element simulations of nonlinear wave propagation in a solid with distributed surface microcracks are performed for a range of microcrack densities. The evolution of fundamental and second harmonic amplitudes along the propagation distance is studied and the acoustic nonlinearity parameter is calculated. The results show that the nonlinearity parameter increases with crack density. While, for small crack densities (dilute concentration of microcracks) a proportionality between crack density and acoustic nonlinearity is observed, this is not valid for higher crack densities, as the microcracks start to interact.

  2. Modelling approaches for evaluating multiscale tendon mechanics.

    PubMed

    Fang, Fei; Lake, Spencer P

    2016-02-01

    Tendon exhibits anisotropic, inhomogeneous and viscoelastic mechanical properties that are determined by its complicated hierarchical structure and varying amounts/organization of different tissue constituents. Although extensive research has been conducted to use modelling approaches to interpret tendon structure-function relationships in combination with experimental data, many issues remain unclear (i.e. the role of minor components such as decorin, aggrecan and elastin), and the integration of mechanical analysis across different length scales has not been well applied to explore stress or strain transfer from macro- to microscale. This review outlines mathematical and computational models that have been used to understand tendon mechanics at different scales of the hierarchical organization. Model representations at the molecular, fibril and tissue levels are discussed, including formulations that follow phenomenological and microstructural approaches (which include evaluations of crimp, helical structure and the interaction between collagen fibrils and proteoglycans). Multiscale modelling approaches incorporating tendon features are suggested to be an advantageous methodology to understand further the physiological mechanical response of tendon and corresponding adaptation of properties owing to unique in vivo loading environments. PMID:26855747

  3. Modeling mechanical interactions between cancerous mammary acini

    NASA Astrophysics Data System (ADS)

    Wang, Jeffrey; Liphardt, Jan; Rycroft, Chris

    2015-03-01

    The rules and mechanical forces governing cell motility and interactions with the extracellular matrix of a tissue are often critical for understanding the mechanisms by which breast cancer is able to spread through the breast tissue and eventually metastasize. Ex vivo experimentation has demonstrated the the formation of long collagen fibers through collagen gels between the cancerous mammary acini responsible for milk production, providing a fiber scaffolding along which cancer cells can disorganize. We present a minimal mechanical model that serves as a potential explanation for the formation of these collagen fibers and the resultant motion. Our working hypothesis is that cancerous cells induce this fiber formation by pulling on the gel and taking advantage of the specific mechanical properties of collagen. To model this system, we employ a new Eulerian, fixed grid simulation method to model the collagen as a nonlinear viscoelastic material subject to various forces coupled with a multi-agent model to describe individual cancer cells. We find that these phenomena can be explained two simple ideas: cells pull collagen radially inwards and move towards the tension gradient of the collagen gel, while being exposed to standard adhesive and collision forces.

  4. Biaxial mechanical modeling of the small intestine.

    PubMed

    Bellini, Chiara; Glass, Paul; Sitti, Metin; Di Martino, Elena S

    2011-11-01

    Capsule endoscopes are pill-size devices provided with a camera that capture images of the small intestine from inside the body after being ingested by a patient. The interaction between intestinal tissue and capsule endoscopes needs to be investigated to optimize capsule design while preventing tissue damage. To that purpose, a constitutive model that can reliably predict the mechanical response of the intestinal tissue under complex mechanical loading is required. This paper describes the development and numerical validation of a phenomenological constitutive model for the porcine duodenum, jejunum and ileum. Parameters characterizing the mechanical behavior of the material were estimated from planar biaxial test data, where intestinal tissue specimens were simultaneously loaded along the circumferential and longitudinal directions. Specimen-specific Fung constitutive models were able to accurately predict the planar stress-strain behavior of the tested samples under a wide range of loading conditions. To increase model generality, average anisotropic constitutive relationships were also generated for each tissue region by fitting average stress-strain curves to the Fung potential. Due to the observed variability in the direction of maximum stiffness, the average Fung models were less anisotropic than the specimen-specific models. Hence, average isotropic models in the Neo-Hookean and Mooney-Rivlin forms were attempted, but they could not adequately describe the degree of nonlinearity in the tissue. Values of the R2 for the nonlinear regressions were 0.17, 0.44 and 0.93 for the average Neo-Hookean, Mooney-Rivlin and Fung models, respectively. Average models were successfully implemented into FORTRAN routines and used to simulate capsule deployment with a finite element method analysis. PMID:22098873

  5. QSPR models based on molecular mechanics and quantum chemical calculations. 1. Construction of Boltzmann-averaged descriptors for alkanes, alcohols, diols, ethers and cyclic compounds.

    PubMed

    Dyekjaer, Jane; Rasmussen, Kjeld; Jónsdóttir, Svava

    2002-09-01

    Values for nine descriptors for QSPR (quantitative structure-property relationships) modeling of physical properties of 96 alkanes, alcohols, ethers, diols, triols and cyclic alkanes and alcohols in conjunction with the program Codessa are presented. The descriptors are Boltzmann-averaged by selection of the most relevant conformers out of a set of possible molecular conformers generated by a systematic scheme presented in this paper. Six of these descriptors are calculated with molecular mechanics and three with quantum chemical methods. Especially interesting descriptors are the relative van der Waals energies and the molecular polarizabilities, which correlate very well with boiling points. Five more simple descriptors that only depend on the molecular constitutional formula are also discussed briefly. PMID:12415333

  6. Symmetry-based reciprocity: evolutionary constraints on a proximate mechanism

    PubMed Central

    Campennì, Marco

    2016-01-01

    Background. While the evolution of reciprocal cooperation has attracted an enormous attention, the proximate mechanisms underlying the ability of animals to cooperate reciprocally are comparatively neglected. Symmetry-based reciprocity is a hypothetical proximate mechanism that has been suggested to be widespread among cognitively unsophisticated animals. Methods. We developed two agent-based models of symmetry-based reciprocity (one relying on an arbitrary tag and the other on interindividual proximity) and tested their ability both to reproduce significant emergent features of cooperation in group living animals and to promote the evolution of cooperation. Results. Populations formed by agents adopting symmetry-based reciprocity showed differentiated “social relationships” and a positive correlation between cooperation given and received: two common aspects of animal cooperation. However, when reproduction and selection across multiple generations were added to the models, agents adopting symmetry-based reciprocity were outcompeted by selfish agents that never cooperated. Discussion. In order to evolve, hypothetical proximate mechanisms must be able to stand competition from alternative strategies. While the results of our simulations require confirmation using analytical methods, we provisionally suggest symmetry-based reciprocity is to be abandoned as a possible proximate mechanism underlying the ability of animals to reciprocate cooperative interactions. PMID:26998412

  7. Modelling of volatility in monetary transmission mechanism

    SciTech Connect

    Dobešová, Anna; Klepáč, Václav; Kolman, Pavel; Bednářová, Petra

    2015-03-10

    The aim of this paper is to compare different approaches to modeling of volatility in monetary transmission mechanism. For this purpose we built time-varying parameter VAR (TVP-VAR) model with stochastic volatility and VAR-DCC-GARCH model with conditional variance. The data from three European countries are included in the analysis: the Czech Republic, Germany and Slovakia. Results show that VAR-DCC-GARCH system captures higher volatility of observed variables but main trends and detected breaks are generally identical in both approaches.

  8. A new mechanism for regional atmospheric chemistry modeling

    NASA Astrophysics Data System (ADS)

    Stockwell, William R.; Kirchner, Frank; Kuhn, Michael; Seefeld, Stephan

    1997-11-01

    A new gas-phase chemical mechanism for the modeling of regional atmospheric chemistry, the "Regional Atmospheric Chemistry Mechanism" (RACM) is presented. The mechanism is intended to be valid for remote to polluted conditions and from the Earth's surface through the upper troposphere. The RACM mechanism is based upon the earlier Regional Acid Deposition Model, version 2 (RADM2) mechanism [Stockwell et al., 1990] and the more detailed Euro-RADM mechanism [Stockwell and Kley, 1994]. The RACM mechanism includes rate constants and product yields from the most recent laboratory measurements, and it has been tested against environmental chamber data. A new condensed reaction mechanism is included for biogenic compounds: isoprene, α-pinene, and d-limonene. The branching ratios for alkane decay were reevaluated, and in the revised mechanism the aldehyde to ketone ratios were significantly reduced. The relatively large amounts of nitrates resulting from the reactions of unbranched alkenes with NO3 are now included, and the production of HO from the ozonolysis of alkenes has a much greater yield. The aromatic chemistry has been revised through the use of new laboratory data. The yield of cresol production from aromatics was reduced, while the reactions of HO, NO3, and O3 with unsaturated dicarbonyl species and unsaturated peroxynitrate are now included in the RACM mechanism. The peroxyacetyl nitrate chemistry and the organic peroxy radical-peroxy radical reactions were revised, and organic peroxy radical +NO3 reactions were added.

  9. Systematic comparison of model polymer nanocomposite mechanics.

    PubMed

    Xiao, Senbo; Peter, Christine; Kremer, Kurt

    2016-01-01

    Polymer nanocomposites render a range of outstanding materials from natural products such as silk, sea shells and bones, to synthesized nanoclay or carbon nanotube reinforced polymer systems. In contrast to the fast expanding interest in this type of material, the fundamental mechanisms of their mixing, phase behavior and reinforcement, especially for higher nanoparticle content as relevant for bio-inorganic composites, are still not fully understood. Although polymer nanocomposites exhibit diverse morphologies, qualitatively their mechanical properties are believed to be governed by a few parameters, namely their internal polymer network topology, nanoparticle volume fraction, particle surface properties and so on. Relating material mechanics to such elementary parameters is the purpose of this work. By taking a coarse-grained molecular modeling approach, we study an range of different polymer nanocomposites. We vary polymer nanoparticle connectivity, surface geometry and volume fraction to systematically study rheological/mechanical properties. Our models cover different materials, and reproduce key characteristics of real nanocomposites, such as phase separation, mechanical reinforcement. The results shed light on establishing elementary structure, property and function relationship of polymer nanocomposites. PMID:27623170

  10. Comparing fluid mechanics models with experimental data.

    PubMed Central

    Spedding, G R

    2003-01-01

    The art of modelling the physical world lies in the appropriate simplification and abstraction of the complete problem. In fluid mechanics, the Navier-Stokes equations provide a model that is valid under most circumstances germane to animal locomotion, but the complexity of solutions provides strong incentive for the development of further, more simplified practical models. When the flow organizes itself so that all shearing motions are collected into localized patches, then various mathematical vortex models have been very successful in predicting and furthering the physical understanding of many flows, particularly in aerodynamics. Experimental models have the significant added convenience that the fluid mechanics can be generated by a real fluid, not a model, provided the appropriate dimensionless groups have similar values. Then, analogous problems can be encountered in making intelligible but independent descriptions of the experimental results. Finally, model predictions and experimental results may be compared if, and only if, numerical estimates of the likely variations in the tested quantities are provided. Examples from recent experimental measurements of wakes behind a fixed wing and behind a bird in free flight are used to illustrate these principles. PMID:14561348

  11. cyp51A-based mechanism of azole resistance in Aspergillus fumigatus: Illustration by a new 3D Structural Model of Aspergillus fumigatus CYP51A protein.

    PubMed

    Liu, Musang; Zheng, Nan; Li, Dongmei; Zheng, Hailin; Zhang, Lili; Ge, Hu; Liu, Weida

    2016-05-01

    Mutations of CYP51A protein (Cytochrome P450 14-α Sterol demethylase) play a central role in the azole resistance of Aspergillus fumigatus The available structural models of CYP51A protein ofA. fumigatus are built based on that of Homo sapiens and that of Mycobacterium tuberculosis, of which the amino acid homology is only 38% and 29% compared with CYP51A protein ofA. fumigatus, respectively. In the present study, we constructed a new 3D structural model ofA. fumigatus CYP51A protein based on a recently resolved crystal structure of the homologous protein in the fungus S. cerevisiae, which shares 50% amino acid homology with A. fumigatus CYP51A protein. Three azole molecules, itraconazole, voriconazole, and posaconazole, were docked to the wild-type and the mutant A. fumigatus CYP51A protein models, respectively, to illustrate the impact of cyp51A mutations to azole-resistance. We found the mutations that occurred at L98, M220, and Y431 positions would decrease the binding affinity of azoles to the CYP51A protein and therefore would reduce their inhibitory effects. Additionally, the mutations of L98 and G432 would reduce the stability of the protein, which might lead to conformational change of its binding pocket and eventually the resistance to azoles. PMID:26768370

  12. In vivo evaluation of bioactive PMMA-based bone cement with unchanged mechanical properties in a load-bearing model on rabbits.

    PubMed

    Fottner, Andreas; Nies, Berthold; Kitanovic, Denis; Steinbrück, Arnd; Hausdorf, Jörg; Mayer-Wagner, Susanne; Pohl, Ulrich; Jansson, Volkmar

    2015-07-01

    Polymethylmethacrylate-based bone cements are widely used for fixation of joint replacements. To improve the long-term outcome, bioactive bone cements are aspired to advance the bone-cement interface. This study evaluated the in vivo properties of a new polymethylmethacrylate-based bioactive bone cement with addition of amphiphilic phosphorylated 2-hydroxyethylmethacrylate. Previous in vitro studies confirmed bioactive properties in cell culture, as well as unchanged mechanical properties are tests according to ISO 5833:2002.Three different variations of the cement (polymethylmethacrylate + phosphorylated 2-hydroxyethylmethacrylate, polymethylmethacrylate + phosphorylated 2-hydroxyethylmethacrylate + CaCl2 and polymethylmethacrylate + phosphorylated 2-hydroxyethylmethacrylate + CaCl2 + Na2CO3) were compared to conventional polymethylmethacrylate cement. To evaluate the properties under load-bearing conditions, a spacer prosthesis was implanted into the femoral diaphysis of 24 rabbits. Additionally, a cement plug was installed into the proximal tibia. After three months, polished sections with Giemsa surface staining were prepared. The bioactivity was determined using the bone affinity index.The sections showed a good osseointegration of the bioactive bone cement without cement cracks under load-bearing conditions. Regarding the bone affinity index, the bioactive bone cement revealed a significantly higher value in the proximal tibia (25.9-37.7%) and around the spacer prosthesis (36.8-58.9%) compared to the conventional polymethylmethacrylate cement (12.8-17.0%).The results confirm the in vivo bioactivity of this bone cement. The absence of cement cracks indicates a sufficient mechanical stability to fix prostheses with this bioactive cement, but for a final assessment long-term tests are necessary. PMID:25627649

  13. Collision-based mechanics of bipedal hopping.

    PubMed

    Gutmann, Anne K; Lee, David V; McGowan, Craig P

    2013-08-23

    The muscle work required to sustain steady-speed locomotion depends largely upon the mechanical energy needed to redirect the centre of mass and the degree to which this energy can be stored and returned elastically. Previous studies have found that large bipedal hoppers can elastically store and return a large fraction of the energy required to hop, whereas small bipedal hoppers can only elastically store and return a relatively small fraction. Here, we consider the extent to which large and small bipedal hoppers (tammar wallabies, approx. 7 kg, and desert kangaroo rats, approx. 0.1 kg) reduce the mechanical energy needed to redirect the centre of mass by reducing collisions. We hypothesize that kangaroo rats will reduce collisions to a greater extent than wallabies since kangaroo rats cannot elastically store and return as high a fraction of the mechanical energy of hopping as wallabies. We find that kangaroo rats use a significantly smaller collision angle than wallabies by employing ground reaction force vectors that are more vertical and center of mass velocity vectors that are more horizontal and thereby reduce their mechanical cost of transport. A collision-based approach paired with tendon morphometry may reveal this effect more generally among bipedal runners and quadrupedal trotters. PMID:23843217

  14. A quantum-mechanical relaxation model

    NASA Astrophysics Data System (ADS)

    Skomski, R.; Kashyap, A.; Sellmyer, D. J.

    2012-04-01

    The atomic origin of micromagnetic damping is investigated by developing and solving a quantum-mechanical relaxation model. A projection-operator technique is used to derive an analytical expression for the relaxation time as a function of the heat-bath and interaction parameters. The present findings are consistent with earlier research beyond the Landau-Lifshitz-Gilbert (LLG) equation and show that the underlying relaxation mechanism is very general. Zermelo's recurrence paradox means that there is no true irreversibility in non-interacting nanoparticles, but the corresponding recurrence times are very long and can be ignored in many cases.

  15. A fuzzy logic controller based approach to model the switching mechanism of the mammalian central carbon metabolic pathway in normal and cancer cells.

    PubMed

    Dasgupta, Abhijit; Paul, Debjyoti; De, Rajat K

    2016-07-19

    Dynamics of large nonlinear complex systems, like metabolic networks, depend on several parameters. A metabolic pathway may switch to another pathway in accordance with the current state of parameters in both normal and cancer cells. Here, most of the parameter values are unknown to us. A fuzzy logic controller (FLC) has been developed here for the purpose of modeling metabolic networks by approximating the reasons for the behaviour of a system and applying expert knowledge to track switching between metabolic pathways. The simulation results can track the switching between glycolysis and gluconeogenesis, as well as glycolysis and pentose phosphate pathways (PPP) in normal cells. Unlike normal cells, pyruvate kinase (M2 isoform) (PKM2) switches alternatively between its two oligomeric forms, i.e. an active tetramer and a relatively low activity dimer, in cancer cells. Besides, there is a coordination among PKM2 switching and enzymes catalyzing PPP. These phenomena help cancer cells to maintain their high energy demand and macromolecular synthesis. However, the reduction of initial adenosine triphosphate (ATP) to a very low concentration, decreasing initial glucose uptake, destroying coordination between glycolysis and PPP, and replacement of PKM2 by its relatively inactive oligomeric form (dimer) or inhibition of the translation of PKM2 may destabilize the mutated control mechanism of the mammalian central carbon metabolic (CCM) pathway in cancer cells. The performance of the model is compared appropriately with some existing ones. PMID:27225801

  16. Mechanical analyses on the digital behaviour of the Tokay gecko (Gekko gecko) based on a multi-level directional adhesion model

    PubMed Central

    Wu, Xuan; Wang, Xiaojie; Mei, Tao; Sun, Shaoming

    2015-01-01

    This paper proposes a multi-level hierarchical model for the Tokay gecko (Gekko gecko) adhesive system and analyses the digital behaviour of the G. gecko under macro/meso-level scale. The model describes the structures of G. gecko's adhesive system from the nano-level spatulae to the sub-millimetre-level lamella. The G. gecko's seta is modelled using inextensible fibril based on Euler's elastica theorem. Considering the side contact of the spatular pads of the seta on the flat and rigid substrate, the directional adhesion behaviour of the seta has been investigated. The lamella-induced attachment and detachment have been modelled to simulate the active digital hyperextension (DH) and the digital gripping (DG) phenomena. The results suggest that a tiny angular displacement within 0.25° of the lamellar proximal end is necessary in which a fast transition from attachment to detachment or vice versa is induced. The active DH helps release the torque to induce setal non-sliding detachment, while the DG helps apply torque to make the setal adhesion stable. The lamella plays a key role in saving energy during detachment to adapt to its habitat and provides another adhesive function which differs from the friction-dependent setal adhesion system controlled by the dynamic of G. gecko's body. PMID:26345081

  17. Physical modeling of the deformation mechanisms of semisolid bodies and a mechanical criterion for hot tearing

    NASA Astrophysics Data System (ADS)

    Lahaie, D. J.; Bouchard, M.

    2001-08-01

    The mechanical response of a semisolid body to an applied, uniaxial strain rate has been expressed as a function of strain by modifying an existing analysis based on an idealized representation of the microstructure. An existing mechanical criterion for hot tearing of the semisolid body has been adapted to the deformation mechanisms. The resulting hot tearing model shows that the strength of the body depends on the strain, the viscosity of the intergranular fluid, the solid fraction, the isothermal compressibility of the fluid, the surface tension of the liquid, the limiting liquid-film thickness for viscous flow and a parameter m, which describes microstructure. The effect of each parameter on the mechanical response and the onset of hot tearing has been examined for ranges of values relevant to aluminum alloys and the direct-chill (DC) casting process. The parameter testing has shown that the mechanical response predicted by the model agrees well with some experimental data for both the mechanisms of fracture and the parameters that govern the process. An adjustment of unknown model parameters to experimental data would permit use of the model as a constitutive law and a fracture criterion for numerical modeling of hot tearing during the solidification of Al alloys by DC casting.

  18. Model-Based Systems

    NASA Technical Reports Server (NTRS)

    Frisch, Harold P.

    2007-01-01

    Engineers, who design systems using text specification documents, focus their work upon the completed system to meet Performance, time and budget goals. Consistency and integrity is difficult to maintain within text documents for a single complex system and more difficult to maintain as several systems are combined into higher-level systems, are maintained over decades, and evolve technically and in performance through updates. This system design approach frequently results in major changes during the system integration and test phase, and in time and budget overruns. Engineers who build system specification documents within a model-based systems environment go a step further and aggregate all of the data. They interrelate all of the data to insure consistency and integrity. After the model is constructed, the various system specification documents are prepared, all from the same database. The consistency and integrity of the model is assured, therefore the consistency and integrity of the various specification documents is insured. This article attempts to define model-based systems relative to such an environment. The intent is to expose the complexity of the enabling problem by outlining what is needed, why it is needed and how needs are being addressed by international standards writing teams.

  19. Realist model approach to quantum mechanics

    NASA Astrophysics Data System (ADS)

    Hájíček, P.

    2013-06-01

    The paper proves that quantum mechanics is compatible with the constructive realism of modern philosophy of science. The proof is based on the observation that properties of quantum systems that are uniquely determined by their preparations can be assumed objective without the difficulties that are encountered by the same assumption about values of observables. The resulting realist interpretation of quantum mechanics is made rigorous by studying the space of quantum states—the convex set of state operators. Prepared states are classified according to their statistical structure into indecomposable and decomposable instead of pure and mixed. Simple objective properties are defined and showed to form a Boolean lattice.

  20. Implementing and Assessing Computational Modeling in Introductory Mechanics

    ERIC Educational Resources Information Center

    Caballero, Marcos D.; Kohlmyer, Matthew A.; Schatz, Michael F.

    2012-01-01

    Students taking introductory physics are rarely exposed to computational modeling. In a one-semester large lecture introductory calculus-based mechanics course at Georgia Tech, students learned to solve physics problems using the VPython programming environment. During the term, 1357 students in this course solved a suite of 14 computational…

  1. Development of a mechanism and an accurate and simple mathematical model for the description of drug release: Application to a relevant example of acetazolamide-controlled release from a bio-inspired elastin-based hydrogel.

    PubMed

    Fernández-Colino, A; Bermudez, J M; Arias, F J; Quinteros, D; Gonzo, E

    2016-04-01

    Transversality between mathematical modeling, pharmacology, and materials science is essential in order to achieve controlled-release systems with advanced properties. In this regard, the area of biomaterials provides a platform for the development of depots that are able to achieve controlled release of a drug, whereas pharmacology strives to find new therapeutic molecules and mathematical models have a connecting function, providing a rational understanding by modeling the parameters that influence the release observed. Herein we present a mechanism which, based on reasonable assumptions, explains the experimental data obtained very well. In addition, we have developed a simple and accurate “lumped” kinetics model to correctly fit the experimentally observed drug-release behavior. This lumped model allows us to have simple analytic solutions for the mass and rate of drug release as a function of time without limitations of time or mass of drug released, which represents an important step-forward in the area of in vitro drug delivery when compared to the current state of the art in mathematical modeling. As an example, we applied the mechanism and model to the release data for acetazolamide from a recombinant polymer. Both materials were selected because of a need to develop a suitable ophthalmic formulation for the treatment of glaucoma. The in vitro release model proposed herein provides a valuable predictive tool for ensuring product performance and batch-to-batch reproducibility, thus paving the way for the development of further pharmaceutical devices. PMID:26838852

  2. Effect of alcohol aggregation on the retention factors of chiral solutes with an amylose-based sorbent: modeling and implications for the adsorption mechanism.

    PubMed

    Tsui, Hung-Wei; Franses, Elias I; Wang, Nien-Hwa Linda

    2014-02-01

    Various displacement models in the literature have been widely used for understanding the adsorption mechanisms of solutes in various chromatography systems. The models were used for describing the often-observed linear plots of the logarithms of the retention factor versus the logarithms of the polar modifier concentration CI(0). The slopes of such a plot was inferred to be equal to the number of the displaced modifier molecules upon adsorption of one solute molecule, and were generally found to be greater than 1. In this study, the retention factors of four structurally related chiral solutes, ethyl lactate (EL), methyl mandelate (MM), benzoin (B), and pantolactone (PL), were measured for the amylose tris[(S)-α-methylbenzylcarbamate] sorbent, or AS, as a function of the concentration of isopropanol (IPA) in n-hexane. With increasing IPA concentration CI(0), the slopes increase from less than 1, at a concentration range from 0.13 to 1.3M, to slightly more than 1 at higher concentrations. Such slopes cannot be explained by the conventional retention models. It was found previously for monovalent solutes that such slopes can only be explained when the aggregation of the mobile phase modifier, isopropyl alcohol, was accounted for. A new retention model is presented here, accounting for alcohol aggregation, multivalent solute adsorption, multivalent solute-alcohol complexation, alcohol adsorption, and solute intra hydrogen-bonding, which occur in these four solutes. The slope is found to be controlled by three key dimensionless groups, the fraction of the sorbent binding sites covered by IPA, the fraction of the solute molecules in complex form, and the fraction of the IPA molecules in aggregate form. The limiting slope at a very high IPA concentration is equal to the value of (x+y)/n, where x is the number of the solute-sorbent binding sites and y is the number of the alcohol molecules in the solute-alcohol complex, and n is the alcohol aggregation number. The model

  3. Modeling Quantum Mechanical Observers via Neural-Glial Networks

    NASA Astrophysics Data System (ADS)

    Konishi, Eiji

    2012-07-01

    We investigate the theory of observers in the quantum mechanical world by using a novel model of the human brain which incorporates the glial network into the Hopfield model of the neural network. Our model is based on a microscopic construction of a quantum Hamiltonian of the synaptic junctions. Using the Eguchi-Kawai large N reduction, we show that, when the number of neurons and astrocytes is exponentially large, the degrees of freedom (d.o.f) of the dynamics of the neural and glial networks can be completely removed and, consequently, that the retention time of the superposition of the wavefunctions in the brain is as long as that of the microscopic quantum system of pre-synaptics sites. Based on this model, the classical information entropy of the neural-glial network is introduced. Using this quantity, we propose a criterion for the brain to be a quantum mechanical observer.

  4. Model Based Definition

    NASA Technical Reports Server (NTRS)

    Rowe, Sidney E.

    2010-01-01

    In September 2007, the Engineering Directorate at the Marshall Space Flight Center (MSFC) created the Design System Focus Team (DSFT). MSFC was responsible for the in-house design and development of the Ares 1 Upper Stage and the Engineering Directorate was preparing to deploy a new electronic Configuration Management and Data Management System with the Design Data Management System (DDMS) based upon a Commercial Off The Shelf (COTS) Product Data Management (PDM) System. The DSFT was to establish standardized CAD practices and a new data life cycle for design data. Of special interest here, the design teams were to implement Model Based Definition (MBD) in support of the Upper Stage manufacturing contract. It is noted that this MBD does use partially dimensioned drawings for auxiliary information to the model. The design data lifecycle implemented several new release states to be used prior to formal release that allowed the models to move through a flow of progressive maturity. The DSFT identified some 17 Lessons Learned as outcomes of the standards development, pathfinder deployments and initial application to the Upper Stage design completion. Some of the high value examples are reviewed.

  5. Numerical modeling of polar mesocyclones generation mechanisms

    NASA Astrophysics Data System (ADS)

    Sergeev, Dennis; Stepanenko, Victor

    2013-04-01

    Polar mesocyclones, commonly referred to as polar lows, remain of great interest due to their complicated dynamics. These mesoscale vortices are small short-living objects that are formed over the observation-sparse high-latitude oceans, and therefore, their evolution can hardly be observed and predicted numerically. The origin of polar mesoscale cyclones is still a matter of uncertainty, though the recent numerical investigations [3] have exposed a strong dependence of the polar mesocyclone development upon the magnitude of baroclinicity. Nevertheless, most of the previous studies focused on the individual polar low (the so-called case studies), with too many factors affecting it simultaneously. None of the earlier studies suggested a clear picture of polar mesocyclone generation within an idealized experiment, where it is possible to look deeper into each single physical process. The present paper concentrates on the initial triggering mechanism of the polar mesocyclone. As it is reported by many researchers, some mesocyclones are formed by the surface forcing, namely the uneven distribution of heat fluxes. That feature is common on the ice boundaries [2], where intense air stream flows from the cold ice surface to the warm sea surface. Hence, the resulting conditions are shallow baroclinicity and strong surface heat fluxes, which provide an arising polar mesocyclone with potential energy source converting it to the kinetic energy of the vortex. It is shown in this paper that different surface characteristics, including thermal parameters and, for example, the shape of an ice edge, determine an initial phase of a polar low life cycle. Moreover, it is shown what initial atmospheric state is most preferable for the formation of a new polar mesocyclone or in maintaining and reinforcing the existing one. The study is based on idealized high-resolution (~2 km) numerical experiment in which baroclinicity, stratification, initial wind profile and disturbance, surface

  6. Diagnosis of Photochemical Ozone Production Rates and Limiting Factors based on Observation-based Modeling Approach over East Asia: Impact of Radical Chemistry Mechanism and Ozone-Control Implications

    NASA Astrophysics Data System (ADS)

    Kanaya, Y.

    2015-12-01

    Growth of tropospheric ozone, causing health and climate impacts, is concerned over East Asia, because emissions of precursors have dramatically increased. Photochemical production rates of ozone and limiting factors, primarily studied for urban locations, have been poorly assessed within a perspective of regional-scale air pollution over East Asia. We performed comprehensive observations of ozone precursors at several locations with regional representativeness and made such assessment based on the observation-based modeling approach. Here, diagnosis at Fukue Island (32.75°N, 128.68°E) remotely located in western Japan (May 2009) is highlighted, where the highest 10% of hourly ozone concentrations reached 72‒118 ppb during May influenced by Asian continental outflow. The average in-situ ozone production rate was estimated to be 6.8 ppb per day, suggesting that in-travel production was still active, while larger buildup must have occurred beforehand. Information on the chemical status of the air mass arriving in Japan is important, because it affects how further ozone production occurs after precursor addition from Japanese domestic emissions. The main limiting factor of ozone production was usually NOx, suggesting that domestic NOx emission control is important in reducing further ozone production and the incidence of warning issuance (>120 ppb). VOCs also increased the ozone production rate, and occasionally (14% of time) became dominant. This analysis implies that the VOC reduction legislation recently enacted should be effective. The uncertainty in the radical chemistry mechanism governing ozone production had a non-negligible impact, but the main conclusion relevant to policy was not altered. When chain termination was augmented by HO2-H2O + NO/NO2 reactions and by heterogeneous loss of HO2 on aerosol particle surfaces, the daily ozone production rate decreased by <24%, and the fraction of hours when the VOC-limited condition occurred varied from 14% to 13

  7. Unraveling the binding mechanism of polyoxyethylene sorbitan esters with bovine serum albumin: a novel theoretical model based on molecular dynamic simulations.

    PubMed

    Delgado-Magnero, Karelia H; Valiente, Pedro A; Ruiz-Peña, Miriam; Pérez-Gramatges, Aurora; Pons, Tirso

    2014-04-01

    To gain a better understanding of the interactions governing the binding mechanism of proteins with non-ionic surfactants, the association processes of Tween 20 and Tween 80 with the bovine serum albumin (BSA) protein were investigated using molecular dynamics (MD) simulations. Protein:surfactant molar ratios were chosen according to the critical micelle concentration (CMC) of each surfactant in the presence of BSA. It was found that both the hydrophilic and the hydrophobic groups of the BSA equally contribute to the surface area of interaction with the non-ionic surfactants. A novel theoretical model for the interactions between BSA and these surfactants at the atomic level is proposed, where both surfactants bind to non-specific domains of the BSA three-dimensional structure mainly through their polyoxyethylene groups, by hydrogen bonds and van der Waals interactions. This is well supported by the strong electrostatic and van der Waals interaction energies obtained in the calculations involving surfactant polyoxyethylene groups and different protein regions. The results obtained from the MD simulations suggest that the formation of surfactant clusters over the BSA structure, due to further cooperative self-assembly of Tween molecules, could increase the protein conformational stability. These results extend the current knowledge on molecular interactions between globular proteins and non-ionic surfactants, and contribute to the fine-tuning design of protein formulations using polysorbates as excipients for minimizing the undesirable effects of protein adsorption and aggregation. PMID:24309134

  8. Computational Modeling of Morphogenesis Regulated by Mechanical Feedback

    PubMed Central

    Ramasubramanian, Ashok; Taber, Larry A.

    2008-01-01

    Mechanical forces cause changes in form during embryogenesis and likely play a role in regulating these changes. This paper explores the idea that changes in homeostatic tissue stress (target stress), possibly modulated by genes, drive some morphogenetic processes. Computational models are presented to illustrate how regional variations in target stress can cause a range of complex behaviors involving the bending of epithelia. These models include growth and cytoskeletal contraction regulated by stress-based mechanical feedback. All simulations were carried out using the commercial finite element code ABAQUS, with growth and contraction included by modifying the zero-stress state in the material constitutive relations. Results presented for bending of bilayered beams and invagination of cylindrical and spherical shells provide insight into some of the mechanical aspects that must be considered in studying morphogenetic mechanisms. PMID:17318485

  9. Mechanism of Actin-Based Motility

    NASA Astrophysics Data System (ADS)

    Pantaloni, Dominique; Le Clainche, Christophe; Carlier, Marie-France

    2001-05-01

    Spatially controlled polymerization of actin is at the origin of cell motility and is responsible for the formation of cellular protrusions like lamellipodia. The pathogens Listeria monocytogenes and Shigella flexneri, which undergo actin-based propulsion, are acknowledged models of the leading edge of lamellipodia. Actin-based motility of the bacteria or of functionalized microspheres can be reconstituted in vitro from only five pure proteins. Movement results from the regulated site-directed treadmilling of actin filaments, consistent with observations of actin dynamics in living motile cells and with the biochemical properties of the components of the synthetic motility medium.

  10. Mechanical model for fiber-laden membranes

    NASA Astrophysics Data System (ADS)

    Rey, Alejandro D.; Murugesan, Yogesh K.

    2011-01-01

    An integrated mechanical model for fiber-laden membranes is presented and representative predictions of relevance to cellulose ordering and orientation in the plant cell wall are presented. The model describes nematic liquid crystalline self-assembly of rigid fibers on an arbitrarily curved fluid membrane. The mechanics of the fluid membrane is described by the Helfrich bending-torsion model, the fiber self-assembly is described by the 2D Landau-de Gennes quadrupolar Q-tensor order parameter model, and the fiber-membrane interactions (inspired by an extension of the 2D Maier-Saupe model to curved surfaces) include competing curvo-philic (curvature-seeking) and curvo-phobic (curvature-avoiding) effects. Analysis of the free energy reveals three fiber orientation regimes: (a) along the major curvature, (b) along the minor curvature, (c) away from the principal curvatures, according to the competing curvo-philic and curvo-phobic interactions. The derived shape equation (normal stress balance) now includes curvature-nematic ordering contributions, with both bending and torsion renormalizations. Integration of the shape and nematic order equations gives a complete model whose solution describes the coupled membrane shape/fiber order state. Applications to cylindrical membranes, relevant to the plant cell wall, shows how growth decreases the fiber order parameter and moves the fibers' director from the axial direction towards the azimuthal orientation, eventually leading to a state of stress predicted by pure membranes. The ubiquitous 54.7° cellulose fibril orientation with respect to the long axis in a cylindrical plant cell wall is shown to be predicted by the preset model when the ratio of curvo-phobic and curvo-philic interactions is in the range of the cylinder radius.

  11. Mechanical-mathematical modeling for landslide process

    NASA Astrophysics Data System (ADS)

    Svalova, V.

    2009-04-01

    500 m and displacement of a landslide in the plan over 1 m. Last serious activization of a landslide has taken place in 2002 with a motion on 53 cm. Catastrophic activization of the deep blockglide landslide in the area of Khoroshevo in Moscow took place in 2006-2007. A crack of 330 m long appeared in the old sliding circus, along which a new 220 m long creeping block was separated from the plateau and began sinking with a displaced surface of the plateau reaching to 12 m. Such activization of the landslide process was not observed in Moscow since mid XIX century. The sliding area of Khoroshevo was stable during long time without manifestations of activity. Revealing of the reasons of deformation and development of ways of protection from deep landslide motions is extremely actual and difficult problem which decision is necessary for preservation of valuable historical monuments and modern city constructions. The reasons of activization and protective measures are discussed. Structure of monitoring system for urban territories is elaborated. Mechanical-mathematical model of high viscous fluid was used for modeling of matter behavior on landslide slopes. Equation of continuity and an approximated equation of the Navier-Stockes for slow motions in a thin layer were used. The results of modelling give possibility to define the place of highest velocity on landslide surface, which could be the best place for monitoring post position. Model can be used for calibration of monitoring equipment and gives possibility to investigate some fundamental aspects of matter movement on landslide slope.

  12. Nucleation in models of damage mechanics

    NASA Astrophysics Data System (ADS)

    Gran, J. D.; Rundle, J. B.; Klein, W.; Turcotte, D. L.

    2010-12-01

    A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study two cellular automaton models of damage mechanics which. The first model is a modified slider-block model with failure threshold weakening. A block is considered partially damaged after its first slip, and any subsequent failure of that block will occur at reduced failure threshold. Damage here is defined as the fraction of blocks that have a reduced failure threshold. The threshold weakening parameter is viewed as a scaling field similar to the occupation probability in site percolation. The second model is time-dependent fiber-bundle model, where the time to failure for each element is specified from a Poissonian distribution and the hazard rate is assumed to have a power-law dependence on stress. Damage here is defined to be the fraction of blocks or fibers that have failed. Because there is no healing, catastrophic failure occurs. The transient behavior prior to rupture propagation is studied and scaling laws are obtained. We compare both models to mean-field percolation which has been shown to be representative of spinodal nucleation and to laboratory experiments that display power-law behavior.

  13. A Retinal Mechanism Inspired Color Constancy Model.

    PubMed

    Zhang, Xian-Shi; Gao, Shao-Bing; Li, Ruo-Xuan; Du, Xin-Yu; Li, Chao-Yi; Li, Yong-Jie

    2016-03-01

    In this paper, we propose a novel model for the computational color constancy, inspired by the amazing ability of the human vision system (HVS) to perceive the color of objects largely constant as the light source color changes. The proposed model imitates the color processing mechanisms in the specific level of the retina, the first stage of the HVS, from the adaptation emerging in the layers of cone photoreceptors and horizontal cells (HCs) to the color-opponent mechanism and disinhibition effect of the non-classical receptive field in the layer of retinal ganglion cells (RGCs). In particular, HC modulation provides a global color correction with cone-specific lateral gain control, and the following RGCs refine the processing with iterative adaptation until all the three opponent channels reach their stable states (i.e., obtain stable outputs). Instead of explicitly estimating the scene illuminant(s), such as most existing algorithms, our model directly removes the effect of scene illuminant. Evaluations on four commonly used color constancy data sets show that the proposed model produces competitive results in comparison with the state-of-the-art methods for the scenes under either single or multiple illuminants. The results indicate that single opponency, especially the disinhibitory effect emerging in the receptive field's subunit-structured surround of RGCs, plays an important role in removing scene illuminant(s) by inherently distinguishing the spatial structures of surfaces from extensive illuminant(s). PMID:26766375

  14. Instability-based mechanism for body undulations in centipede locomotion

    NASA Astrophysics Data System (ADS)

    Aoi, Shinya; Egi, Yoshimasa; Tsuchiya, Kazuo

    2013-01-01

    Centipedes have many body segments and legs and they generate body undulations during terrestrial locomotion. Centipede locomotion has the characteristic that body undulations are absent at low speeds but appear at faster speeds; furthermore, their amplitude and wavelength increase with increasing speed. There are conflicting reports regarding whether the muscles along the body axis resist or support these body undulations and the underlying mechanisms responsible for the body undulations remain largely unclear. In the present study, we investigated centipede locomotion dynamics using computer simulation with a body-mechanical model and experiment with a centipede-like robot and then conducted dynamic analysis with a simple model to clarify the mechanism. The results reveal that body undulations in these models occur due to an instability caused by a supercritical Hopf bifurcation. We subsequently compared these results with data obtained using actual centipedes. The model and actual centipedes exhibit similar dynamic properties, despite centipedes being complex, nonlinear dynamic systems. Based on our findings, we propose a possible passive mechanism for body undulations in centipedes, similar to a follower force or jackknife instability. We also discuss the roles of the muscles along the body axis in generating body undulations in terms of our physical model.

  15. Physical modeling of transverse drainage mechanisms

    NASA Astrophysics Data System (ADS)

    Douglass, J. C.; Schmeeckle, M. W.

    2005-12-01

    Streams that incise across bedrock highlands such as anticlines, upwarps, cuestas, or horsts are termed transverse drainages. Their relevance today involves such diverse matters as highway and dam construction decisions, location of wildlife corridors, better-informed sediment budgets, and detailed studies into developmental histories of late Cenozoic landscapes. The transient conditions responsible for transverse drainage incision have been extensively studied on a case-by-case basis, and the dominate mechanisms proposed include: antecedence, superimposition, overflow, and piracy. Modeling efforts have been limited to antecedence, and such the specific erosional conditions required for transverse drainage incision, with respect to the individual mechanisms, remains poorly understood. In this study, fifteen experiments attempted to simulate the four mechanisms and constructed on a 9.15 m long, 2.1 m wide, and 0.45 m deep stream table. Experiments lasted between 50 and 220 minutes. The stream table was filled with seven tons of sediment consisting of a silt and clay (30%) and a fine to coarse sand (70%) mixture. The physical models highlighted the importance of downstream aggradation with regard to antecedent incision versus possible defeat and diversion. The overflow experiments indicate that retreating knickpoints across a basin outlet produce a high probability of downstream flooding when associated with a deep lake. Misters used in a couple of experiments illustrate a potential complication with regard to headward erosion driven piracy. Relatively level asymmetrically sloped ridges allow for the drainage divide across the ridge to retreat from headward erosion, but hindered when the ridge's apex undulates or when symmetrically sloped. Although these physical models cannot strictly simulate natural transverse drainages, the observed processes, their development over time, and resultant landforms roughly emulate their natural counterparts. Proposed originally from

  16. Mechanical Model of Traditional Thai Massage for Integrated Healthcare.

    PubMed

    Rattanaphan, Salinee; Srichandr, Panya

    2015-01-01

    In this study, a mechanical model was developed, aiming to provide standardized and programmable traditional Thai massage (TTM) therapy to patients. The TTM was modeled and integrated into a mechanical hand (MH) system, and a prototype massage chair was built and tested for user satisfaction. Three fundamental principles of Thai massage were integrated: pull, press, and pin. Based on these principles, the mechanics of Thai massage was studied and a mathematical model was developed to describe the dynamics and conditions for the design and prototyping of an MH. On average, it was found that users were satisfied with the treatment and felt that the treatment was similar to that performed by human hands. According to the interview results, users indicated that they were likely to utilize the MH as an alternative to traditional massage. Therefore, integrated TTM with an MH may help healthcare providers deliver standardized, programmable massage therapy to patients as opposed to variable, inconsistent human massage. PMID:26288887

  17. Mechanism and models for zinc metal morphology in alkaline media

    NASA Technical Reports Server (NTRS)

    May, C. E.; Kautz, H. E.

    1981-01-01

    Based on experimental observations, a mechanism is presented to explain existence of the different morphologies of electrodeposited zinc in alkaline solution. The high current density dendrites appear to be due to more rapid growth on the nonbasal crystallographic planes than on the basal plane. The low current density moss apparently results from dissolution from the nonbasal planes at low cathodic voltages. Electrochemical models were sought which would produce such a phenomenon. The fundamental plating mechanism alone accounts only for different rates on different planes, not for zinc dissolution from a plane in the cathodic region. Fourteen models were explored; two models were in accord with the proposed mechanism. One involves rapid disproportionation of the zinc +1 species on the nonbasal planes. The other involves a redox reaction (corrosion) between the zinc-zincate and hydrogen-water systems.

  18. Mechanical contact by constraints and split-based preconditioning

    SciTech Connect

    Dmitry Karpeyev; Derek Gaston; Jason Hales; Steven Novascone

    2014-03-01

    An accurate implementation of glued mechanical contact was developed in MOOSE based on its Constraint system. This approach results in a superior convergence of elastic structure problems, in particular in BISON. Adaptation of this technique to frictionless and frictional contact models is under way. Additionally, the improved convergence of elastic problems results from the application of the split-based preconditioners to constraint-based systems. This yields a substantial increase in the robustness of elastic solvers when the number of nodes in contact is increased and/or the mesh is refined.

  19. Mechanical model of an earthquake fault

    NASA Technical Reports Server (NTRS)

    Carlson, J. M.; Langer, J. S.

    1989-01-01

    The dynamic behavior of a simple mechanical model of an earthquake fault is studied. This model, introduced originally by Burridge and Knopoff (1967), consists of an elastically coupled chain of masses in contact with a moving rough surface. The present version of the model retains the full Newtonian dynamics with inertial effects and contains no externally imposed stochasticity or spatial inhomogeneity. The only nonlinear feature is a velocity-weakening stick-slip friction force between the masses and the moving surface. This system is being driven persistently toward a slipping instability and therefore exhibits noisy sequences of earthquakelike events. These events are observed in numerical simulations, and many of their features can be predicted analytically.

  20. A Separable, Dynamically Local Ontological Model of Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Pienaar, Jacques

    2016-01-01

    A model of reality is called separable if the state of a composite system is equal to the union of the states of its parts, located in different regions of space. Spekkens has argued that it is trivial to reproduce the predictions of quantum mechanics using a separable ontological model, provided one allows for arbitrary violations of `dynamical locality'. However, since dynamical locality is strictly weaker than local causality, this leaves open the question of whether an ontological model for quantum mechanics can be both separable and dynamically local. We answer this question in the affirmative, using an ontological model based on previous work by Deutsch and Hayden. Although the original formulation of the model avoids Bell's theorem by denying that measurements result in single, definite outcomes, we show that the model can alternatively be cast in the framework of ontological models, where Bell's theorem does apply. We find that the resulting model violates local causality, but satisfies both separability and dynamical locality, making it a candidate for the `most local' ontological model of quantum mechanics.

  1. Investigation of mechanism of bone regeneration in a porous biodegradable calcium phosphate (CaP) scaffold by a combination of a multi-scale agent-based model and experimental optimization/validation

    NASA Astrophysics Data System (ADS)

    Zhang, Le; Qiao, Minna; Gao, Hongjie; Hu, Bin; Tan, Hua; Zhou, Xiaobo; Li, Chang Ming

    2016-08-01

    Herein, we have developed a novel approach to investigate the mechanism of bone regeneration in a porous biodegradable calcium phosphate (CaP) scaffold by a combination of a multi-scale agent-based model, experimental optimization of key parameters and experimental data validation of the predictive power of the model. The advantages of this study are that the impact of mechanical stimulation on bone regeneration in a porous biodegradable CaP scaffold is considered, experimental design is used to investigate the optimal combination of growth factors loaded on the porous biodegradable CaP scaffold to promote bone regeneration and the training, testing and analysis of the model are carried out by using experimental data, a data-mining algorithm and related sensitivity analysis. The results reveal that mechanical stimulation has a great impact on bone regeneration in a porous biodegradable CaP scaffold and the optimal combination of growth factors that are encapsulated in nanospheres and loaded into porous biodegradable CaP scaffolds layer-by-layer can effectively promote bone regeneration. Furthermore, the model is robust and able to predict the development of bone regeneration under specified conditions.

  2. Investigation of mechanism of bone regeneration in a porous biodegradable calcium phosphate (CaP) scaffold by a combination of a multi-scale agent-based model and experimental optimization/validation.

    PubMed

    Zhang, Le; Qiao, Minna; Gao, Hongjie; Hu, Bin; Tan, Hua; Zhou, Xiaobo; Li, Chang Ming

    2016-08-21

    Herein, we have developed a novel approach to investigate the mechanism of bone regeneration in a porous biodegradable calcium phosphate (CaP) scaffold by a combination of a multi-scale agent-based model, experimental optimization of key parameters and experimental data validation of the predictive power of the model. The advantages of this study are that the impact of mechanical stimulation on bone regeneration in a porous biodegradable CaP scaffold is considered, experimental design is used to investigate the optimal combination of growth factors loaded on the porous biodegradable CaP scaffold to promote bone regeneration and the training, testing and analysis of the model are carried out by using experimental data, a data-mining algorithm and related sensitivity analysis. The results reveal that mechanical stimulation has a great impact on bone regeneration in a porous biodegradable CaP scaffold and the optimal combination of growth factors that are encapsulated in nanospheres and loaded into porous biodegradable CaP scaffolds layer-by-layer can effectively promote bone regeneration. Furthermore, the model is robust and able to predict the development of bone regeneration under specified conditions. PMID:27460959

  3. Rock mechanics models evaluation report. [Contains glossary

    SciTech Connect

    Not Available

    1987-08-01

    This report documents the evaluation of the thermal and thermomechanical models and codes for repository subsurface design and for design constraint analysis. The evaluation was based on a survey of the thermal and thermomechanical codes and models that are applicable to subsurface design, followed by a Kepner-Tregoe (KT) structured decision analysis of the codes and models. The primary recommendations of the analysis are that the DOT code be used for two-dimensional thermal analysis and that the STEALTH and HEATING 5/6 codes be used for three-dimensional and complicated two-dimensional thermal analysis. STEALTH and SPECTROM 32 are recommended for thermomechanical analyses. The other evaluated codes should be considered for use in certain applications. A separate review of salt creep models indicate that the commonly used exponential time law model is appropriate for use in repository design studies. 38 refs., 1 fig., 7 tabs.

  4. Modeling equine race surface vertical mechanical behaviors in a musculoskeletal modeling environment.

    PubMed

    Symons, Jennifer E; Fyhrie, David P; Hawkins, David A; Upadhyaya, Shrinivasa K; Stover, Susan M

    2015-02-26

    Race surfaces have been associated with the incidence of racehorse musculoskeletal injury, the leading cause of racehorse attrition. Optimal race surface mechanical behaviors that minimize injury risk are unknown. Computational models are an economical method to determine optimal mechanical behaviors. Previously developed equine musculoskeletal models utilized ground reaction floor models designed to simulate a stiff, smooth floor appropriate for a human gait laboratory. Our objective was to develop a computational race surface model (two force-displacement functions, one linear and one nonlinear) that reproduced experimental race surface mechanical behaviors for incorporation in equine musculoskeletal models. Soil impact tests were simulated in a musculoskeletal modeling environment and compared to experimental force and displacement data collected during initial and repeat impacts at two racetracks with differing race surfaces - (i) dirt and (ii) synthetic. Best-fit model coefficients (7 total) were compared between surface types and initial and repeat impacts using a mixed model ANCOVA. Model simulation results closely matched empirical force, displacement and velocity data (Mean R(2)=0.930-0.997). Many model coefficients were statistically different between surface types and impacts. Principal component analysis of model coefficients showed systematic differences based on surface type and impact. In the future, the race surface model may be used in conjunction with previously developed the equine musculoskeletal models to understand the effects of race surface mechanical behaviors on limb dynamics, and determine race surface mechanical behaviors that reduce the incidence of racehorse musculoskeletal injury through modulation of limb dynamics. PMID:25634662

  5. Modeling of mechanical properties in alpha/beta-titanium alloys

    NASA Astrophysics Data System (ADS)

    Kar, Sujoy Kumar

    2005-11-01

    The accelerated insertion of titanium alloys in component application requires the development of predictive capabilities for various aspects of their behavior, for example, phase stability, microstructural evolution and property-microstructure relationships over a wide range of length and time scales. In this presentation some navel aspects of property-microstructure relationships and microstructural evolution in alpha/beta Ti alloys will be discussed. Neural Network (NN) Models based on a Bayesian framework have been developed to predict the mechanical properties of alpha/beta Ti alloys. The development of such rules-based model requires the population of extensive databases, which in the present case are microstructurally-based. The steps involved in database development include producing controlled variations of the microstructure using novel approaches to heat-treatments, the use of standardized stereology protocols to characterize and quantify microstructural features rapidly, and mechanical testing of the heat-treated specimens. These databases have been used to train and test NN Models for prediction of mechanical properties. In addition, these models have been used to identify the influence of individual microstructural features on the mechanical properties, consequently guiding the efforts towards development of more robust mechanistically based models. In order to understand the property-microstructure relationships, a detailed understanding of microstructure evolution is imperative. The crystallography of the microstructure developing as a result of the solid-state beta → beta+alpha transformation has been studied in detail by employing Scanning Electron Microscopy (SEM), Orientation Imaging Microscopy (in a high resolution SEM), site-specific TEM sample preparation using focused ion beam, and TEM based techniques. The influence of variant selection on the evolution of microstructure will be specifically addressed.

  6. Mechanisms and models of somatic cell reprogramming

    PubMed Central

    Buganim, Yosef; Faddah, Dina A.; Jaenisch, Rudolf

    2014-01-01

    Conversion of somatic cells to pluripotency by defined factors is a long and complex process that yields embryonic stem cell-like cells that vary in their developmental potential. To improve the quality of resulting induced pluripotent stem cells (iPSCs), which is important for potential therapeutic applications, and to address fundamental questions about control of cell identity, molecular mechanisms of the reprogramming process must be understood. Here we discuss recent discoveries regarding the role of reprogramming factors in remodeling the genome, including new insights into the function of c-Myc, and describe the different phases, markers and emerging models of reprogramming. PMID:23681063

  7. Mechanical Models of Fault-Related Folding

    SciTech Connect

    Johnson, A. M.

    2003-01-09

    The subject of the proposed research is fault-related folding and ground deformation. The results are relevant to oil-producing structures throughout the world, to understanding of damage that has been observed along and near earthquake ruptures, and to earthquake-producing structures in California and other tectonically-active areas. The objectives of the proposed research were to provide both a unified, mechanical infrastructure for studies of fault-related foldings and to present the results in computer programs that have graphical users interfaces (GUIs) so that structural geologists and geophysicists can model a wide variety of fault-related folds (FaRFs).

  8. Statistical Mechanics Model of Solids with Defects

    NASA Astrophysics Data System (ADS)

    Kaufman, M.; Walters, P. A.; Ferrante, J.

    1997-03-01

    Previously(M.Kaufman, J.Ferrante,NASA Tech. Memor.,1996), we examined the phase diagram for the failure of a solid under isotropic expansion and compression as a function of stress and temperature with the "springs" modelled by the universal binding energy relation (UBER)(J.H.Rose, J.R.Smith, F.Guinea, J.Ferrante, Phys.Rev.B29, 2963 (1984)). In the previous calculation we assumed that the "springs" failed independently and that the strain is uniform. In the present work, we have extended this statistical model of mechanical failure by allowing for correlations between "springs" and for thermal fluctuations in strains. The springs are now modelled in the harmonic approximation with a failure threshold energy E0, as an intermediate step in future studies to reinclude the full non-linear dependence of the UBER for modelling the interactions. We use the Migdal-Kadanoff renormalization-group method to determine the phase diagram of the model and to compute the free energy.

  9. Fluid mechanical model of the Helmholtz resonator

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Walker, B.

    1977-01-01

    A semi-empirical fluid mechanical model of the acoustic behavior of Helmholtz resonators is presented which predicts impedance as a function of the amplitude and frequency of the incident sound pressure field and resonator geometry. The model assumes that the particle velocity approaches the orifice in a spherical manner. The incident and cavity sound fields are connected by solving the governing oscillating mass and momentum conservation equations. The model is in agreement with the Rayleigh slug-mass model at low values of incident sound pressure level. At high values, resistance is predicted to be independent of frequency, proportional to the square root of the amplitude of the incident sound pressure field, and virtually independent of resonator geometry. Reactance is predicted to depend in a very complicated way upon resonator geometry, incident sound pressure level, and frequency. Nondimensional parameters are defined that divide resonator impedance into three categories corresponding to low, moderately low, and intense incident sound pressure amplitudes. The two-microphone method was used to measure the impedance of a variety of resonators. The data were used to refine and verify the model.

  10. EFFECTS OF PHOTOCHEMICAL KINETIC MECHANISMS ON OXIDANT MODEL PREDICTIONS

    EPA Science Inventory

    The comparative effects of kinetic mechanisms on oxidant model predictions have been tested using two different mechanisms (the Carbon-Bond Mechanism II (CBM-II) and the Demerjian Photochemical Box Model (DPBM) mechanism) in three air quality models (the OZIPM/EKMA, the Urban Air...

  11. Seismic metamaterials based on isochronous mechanical oscillators

    SciTech Connect

    Finocchio, G. Garescì, F.; Azzerboni, B.; Casablanca, O.; Chiappini, M.; Ricciardi, G.; Alibrandi, U.

    2014-05-12

    This Letter introduces a seismic metamaterial (SM) composed by a chain of mass-in-mass system able to filter the S-waves of an earthquake. We included the effect of the SM into the mono dimensional model for the soil response analysis. The SM modifies the soil behavior and in presence of an internal damping the amplitude of the soil amplification function is reduced also in a region near the resonance frequency. This SM can be realized by a continuous structure with inside a 3d-matrix of isochronous oscillators based on a sphere rolling over a cycloidal trajectory.

  12. A mechanical model of retinal detachment

    NASA Astrophysics Data System (ADS)

    Chou, Tom; Siegel, Michael

    2012-08-01

    We present a model of the mechanical and fluid forces associated with exudative retinal detachments where the retinal photoreceptor cells separate, typically from the underlying retinal pigment epithelium (RPE). By computing the total fluid volume flow arising from transretinal, vascular and RPE pump currents, we determine the conditions under which the subretinal fluid pressure exceeds the maximum yield stress holding the retina and RPE together, giving rise to an irreversible, extended retinal delamination. We also investigate localized, blister-like retinal detachments by balancing mechanical tension in the retina with both the retina-RPE adhesion energy and the hydraulic pressure jump across the retina. For detachments induced by traction forces, we find a critical radius beyond which the blister is unstable to growth. Growth of a detached blister can also be driven by inflamed lesions in which the tissue has a higher choroidal hydraulic conductivity, has insufficient RPE pump activity, or has defective adhesion bonds. We determine the parameter regimes in which the blister either becomes unstable to growth, remains stable and finite-sized, or shrinks, allowing possible healing. The corresponding stable blister radius and shape are calculated. Our analysis provides a quantitative description of the physical mechanisms involved in exudative retinal detachments and can help guide the development of retinal reattachment protocols or preventative procedures.

  13. Melanoma Brain Metastasis: Mechanisms, Models, and Medicine.

    PubMed

    Kircher, David A; Silvis, Mark R; Cho, Joseph H; Holmen, Sheri L

    2016-01-01

    The development of brain metastases in patients with advanced stage melanoma is common, but the molecular mechanisms responsible for their development are poorly understood. Melanoma brain metastases cause significant morbidity and mortality and confer a poor prognosis; traditional therapies including whole brain radiation, stereotactic radiotherapy, or chemotherapy yield only modest increases in overall survival (OS) for these patients. While recently approved therapies have significantly improved OS in melanoma patients, only a small number of studies have investigated their efficacy in patients with brain metastases. Preliminary data suggest that some responses have been observed in intracranial lesions, which has sparked new clinical trials designed to evaluate the efficacy in melanoma patients with brain metastases. Simultaneously, recent advances in our understanding of the mechanisms of melanoma cell dissemination to the brain have revealed novel and potentially therapeutic targets. In this review, we provide an overview of newly discovered mechanisms of melanoma spread to the brain, discuss preclinical models that are being used to further our understanding of this deadly disease and provide an update of the current clinical trials for melanoma patients with brain metastases. PMID:27598148

  14. A unified creep-plasticity model suitable for thermo-mechanical loading

    NASA Technical Reports Server (NTRS)

    Slavik, D.; Sehitoglu, H.

    1988-01-01

    An experimentally based unified creep-plasticity constitutive model was implemented for 1070 steel. Accurate rate and temperature effects were obtained for isothermal and thermo-mechanical loading by incorporating deformation mechanisms into the constitutive equations in a simple way.

  15. Models on the boundary between classical and quantum mechanics.

    PubMed

    Hooft, Gerard 't

    2015-08-01

    Arguments that quantum mechanics cannot be explained in terms of any classical theory using only classical logic seem to be based on sound mathematical considerations: there cannot be physical laws that require 'conspiracy'. It may therefore be surprising that there are several explicit quantum systems where these considerations apparently do not apply. In this report, several such counterexamples are shown. These are quantum models that do have a classical origin. The most curious of these models is superstring theory. So now the question is asked: how can such a model feature 'conspiracy', and how bad is that? Is there conspiracy in the vacuum fluctuations? Arguments concerning Bell's theorem are further sharpened. PMID:26124246

  16. Systematic development of reduced reaction mechanisms for dynamic modeling

    NASA Technical Reports Server (NTRS)

    Frenklach, M.; Kailasanath, K.; Oran, E. S.

    1986-01-01

    A method for systematically developing a reduced chemical reaction mechanism for dynamic modeling of chemically reactive flows is presented. The method is based on the postulate that if a reduced reaction mechanism faithfully describes the time evolution of both thermal and chain reaction processes characteristic of a more complete mechanism, then the reduced mechanism will describe the chemical processes in a chemically reacting flow with approximately the same degree of accuracy. Here this postulate is tested by producing a series of mechanisms of reduced accuracy, which are derived from a full detailed mechanism for methane-oxygen combustion. These mechanisms were then tested in a series of reactive flow calculations in which a large-amplitude sinusoidal perturbation is applied to a system that is initially quiescent and whose temperature is high enough to start ignition processes. Comparison of the results for systems with and without convective flow show that this approach produces reduced mechanisms that are useful for calculations of explosions and detonations. Extensions and applicability to flames are discussed.

  17. Physical vs. Mathematical Models in Rock Mechanics

    NASA Astrophysics Data System (ADS)

    Morozov, I. B.; Deng, W.

    2013-12-01

    One of the less noted challenges in understanding the mechanical behavior of rocks at both in situ and lab conditions is the character of theoretical approaches being used. Currently, the emphasis is made on spatial averaging theories (homogenization and numerical models of microstructure), empirical models for temporal behavior (material memory, compliance functions and complex moduli), and mathematical transforms (Laplace and Fourier) used to infer the Q-factors and 'relaxation mechanisms'. In geophysical applications, we have to rely on such approaches for very broad spatial and temporal scales which are not available in experiments. However, the above models often make insufficient use of physics and utilize, for example, the simplified 'correspondence principle' instead of the laws of viscosity and friction. As a result, the commonly-used time- and frequency dependent (visco)elastic moduli represent apparent properties related to the measurement procedures and not necessarily to material properties. Predictions made from such models may therefore be inaccurate or incorrect when extrapolated beyond the lab scales. To overcome the above challenge, we need to utilize the methods of micro- and macroscopic mechanics and thermodynamics known in theoretical physics. This description is rigorous and accurate, uses only partial differential equations, and allows straightforward numerical implementations. One important observation from the physical approach is that the analysis should always be done for the specific geometry and parameters of the experiment. Here, we illustrate these methods on axial deformations of a cylindrical rock sample in the lab. A uniform, isotropic elastic rock with a thermoelastic effect is considered in four types of experiments: 1) axial extension with free transverse boundary, 2) pure axial extension with constrained transverse boundary, 3) pure bulk expansion, and 4) axial loading harmonically varying with time. In each of these cases, an

  18. A Hydro-mechanical Model and Analytical Solutions for Geomechanical Modeling of Carbon Dioxide Geological Sequestration

    SciTech Connect

    Xu, Zhijie; Fang, Yilin; Scheibe, Timothy D.; Bonneville, Alain

    2012-05-15

    We present a hydro-mechanical model for geological sequestration of carbon dioxide. The model considers the poroelastic effects by taking into account the coupling between the geomechanical response and the fluid flow in greater detail. The simplified hydro-mechanical model includes the geomechanical part that relies on the linear elasticity, while the fluid flow is based on the Darcy’s law. Two parts were coupled using the standard linear poroelasticity. Analytical solutions for pressure field were obtained for a typical geological sequestration scenario. The model predicts the temporal and spatial variation of pressure field and effects of permeability and elastic modulus of formation on the fluid pressure distribution.

  19. Theory of fracture mechanics based upon plasticity

    NASA Technical Reports Server (NTRS)

    Lee, J. D.

    1976-01-01

    A theory of fracture mechanics is formulated on the foundation of continuum mechanics. Fracture surface is introduced as an unknown quantity and is incorporated into boundary and initial conditions. Surface energy is included in the global form of energy conservation law and the dissipative mechanism is formulated into constitutive equations which indicate the thermodynamic irreversibility and the irreversibility of fracture process as well.

  20. Arctic Sea Ice Reemergence Mechanisms in a Model Hierarchy

    NASA Astrophysics Data System (ADS)

    Bushuk, M.; Giannakis, D.

    2015-12-01

    Lagged correlation analysis of Arctic sea ice area anomalies reveals that melt season sea ice anomalies tend to recur the following growth season, and growth season anomalies tend to recur the following melt season. In this work, the regional and temporal characteristics of this phenomenon, termed sea-ice reemergence, are investigated in a hierarchy of climate models. Coupled nonlinear Laplacian spectral analysis (NLSA), a multivariate data analysis technique, is used to study the covariability of Arctic sea-ice concentration (SIC), sea-surface temperature (SST), sea-level pressure (SLP), and sea-ice thickness (SIT). Two mechanisms related to melt season to growth season reemergence are identified: (1) An SST-SIC mechanism, related to local imprinting and persistence of SST anomalies in the seasonal ice zones, and (2) an SLP-SIC mechanism, related to winter-to-winter regime persistence of large-scale SLP teleconnection patterns. An SIT-SIC growth season to melt season reemergence mechanism is also identified, related to winter persistence of SIT anomalies in the central Arctic. The representation of these mechanisms is investigated using the model hierarchy to determine the relative roles of the ocean, atmosphere, and sea ice itself in producing reemergence. It is found that the SST-based and SIT-based mechanisms can exist as stand-alone processes, whereas the SLP mechanism cannot. Dynamical feedback from the ocean to the atmosphere is found to be essential in creating large-scale organized patterns of SIC-SLP covariability. A set of reemergence metrics is introduced, by which one can judge the amplitude and phase of reemergence events and associated mechanisms.

  1. Synaptic dynamics at the neuromuscular junction: mechanisms and models.

    PubMed

    Van Essen, D C; Gordon, H; Soha, J M; Fraser, S E

    1990-01-01

    During development, the neuromuscular junction passes through a stage of extensive polyinnervation followed by a period of wholesale synapse elimination. In this report we discuss mechanisms and interactions that could mediate many of the key aspects of these important developmental events. Our emphasis is on (1) establishing an overall conceptual framework within which the role of many distinct cellular interactions and molecular factors can be evaluated, and (2) generating computer simulations that systematically test the adequacy of different models in accounting for a wide range of biological data. Our analysis indicates that several relatively simple mechanisms are each capable of explaining a variety of experimental observations. On the other hand, no one mechanism can account for the full spectrum of experimental results. Thus, it is important to consider models that are based on interactions among multiple mechanisms. A potentially powerful combination is one based on (1) a scaffold within the basal lamina or in the postsynaptic membrane which is induced by nerve terminals and which serves to stabilize terminals by a positive feedback mechanism; (2) a sprouting factor whose release by muscle fibers is down-regulated by activity and perhaps other factors; and (3) an intrinsic tendency of motor neurons to withdraw some connections while allowing others to grow. PMID:2181065

  2. Macrocomposite mechanical design, modeling, and behavior of physical models of bioinspired fish armor

    NASA Astrophysics Data System (ADS)

    Browning, Ashley; Ortiz, Christine; Boyce, Mary C.

    2012-02-01

    The macrocomposite design of flexible biological exoskeletons, consisting of overlapping mineralized armor units embedded in a compliant tissue, is a key determinant of their mechanical function (e.g penetration resistance and biomechanical flexibility). Here, we investigate the role of macrocomposite structure, composition, geometric orientation, and spatial distribution in a flexible model natural armor system present in the majority of teleost fish species. Physical multi-material composite models are fabricated using a combination of 3-D printing and molding methods. Mechanical experiments using digital image correlation enable measurement of both the macroscopic response and underlying deformation mechanisms during various loading scenarios. Finite element-based mechanical models yield detailed insights into the roles and the tradeoffs of the composite structure providing constraint, shear, and bending mechanisms to impart protection and flexibility.

  3. Neurologic autoimmunity: mechanisms revealed by animal models.

    PubMed

    Bradl, Monika; Lassmann, Hans

    2016-01-01

    Over the last decade, neurologic autoimmunity has become a major consideration in the diagnosis and management of patients with many neurologic presentations. The nature of the associated antibodies and their targets has led to appreciation of the importance of the accessibility of the target antigen to antibodies, and a partial understanding of the different mechanisms that can follow antibody binding. This chapter will first describe the basic principles of autoimmune inflammation and tissue damage in the central and peripheral nervous system, and will then demonstrate what has been learnt about neurologic autoimmunity from circumstantial clinical evidence and from passive, active, and occasionally spontaneous or genetic animal models. It will cover neurologic autoimmune diseases ranging from disorders of neuromuscular transmission, peripheral and ganglionic neuropathy, to diseases of the central nervous system, where autoantibodies are either pathogenic and cause destruction or changes in function of their targets, where they are harmless bystanders of T-cell-mediated tissue damage, or are not involved at all. Finally, this chapter will summarize the relevance of current animal models for studying the different neurologic autoimmune diseases, and it will identify aspects where future animal models need to be improved to better reflect the disease reality experienced by affected patients, e.g., the chronicity or the relapsing/remitting nature of their disease. PMID:27112675

  4. Coupled Thermal-Chemical-Mechanical Modeling of Validation Cookoff Experiments

    SciTech Connect

    ERIKSON,WILLIAM W.; SCHMITT,ROBERT G.; ATWOOD,A.I.; CURRAN,P.D.

    2000-11-27

    The cookoff of energetic materials involves the combined effects of several physical and chemical processes. These processes include heat transfer, chemical decomposition, and mechanical response. The interaction and coupling between these processes influence both the time-to-event and the violence of reaction. The prediction of the behavior of explosives during cookoff, particularly with respect to reaction violence, is a challenging task. To this end, a joint DoD/DOE program has been initiated to develop models for cookoff, and to perform experiments to validate those models. In this paper, a series of cookoff analyses are presented and compared with data from a number of experiments for the aluminized, RDX-based, Navy explosive PBXN-109. The traditional thermal-chemical analysis is used to calculate time-to-event and characterize the heat transfer and boundary conditions. A reaction mechanism based on Tarver and McGuire's work on RDX{sup 2} was adjusted to match the spherical one-dimensional time-to-explosion data. The predicted time-to-event using this reaction mechanism compares favorably with the validation tests. Coupled thermal-chemical-mechanical analysis is used to calculate the mechanical response of the confinement and the energetic material state prior to ignition. The predicted state of the material includes the temperature, stress-field, porosity, and extent of reaction. There is little experimental data for comparison to these calculations. The hoop strain in the confining steel tube gives an estimation of the radial stress in the explosive. The inferred pressure from the measured hoop strain and calculated radial stress agree qualitatively. However, validation of the mechanical response model and the chemical reaction mechanism requires more data. A post-ignition burn dynamics model was applied to calculate the confinement dynamics. The burn dynamics calculations suffer from a lack of characterization of the confinement for the flaw

  5. An agent based model of genotype editing

    SciTech Connect

    Rocha, L. M.; Huang, C. F.

    2004-01-01

    This paper presents our investigation on an agent-based model of Genotype Editing. This model is based on several characteristics that are gleaned from the RNA editing system as observed in several organisms. The incorporation of editing mechanisms in an evolutionary agent-based model provides a means for evolving agents with heterogenous post-transcriptional processes. The study of this agent-based genotype-editing model has shed some light into the evolutionary implications of RNA editing as well as established an advantageous evolutionary computation algorithm for machine learning. We expect that our proposed model may both facilitate determining the evolutionary role of RNA editing in biology, and advance the current state of research in agent-based optimization.

  6. effects of driving mechanisms in geodynamo models

    NASA Astrophysics Data System (ADS)

    Kutzner, Carsten; Christensen, Ulrich

    2000-01-01

    We compare the influence of different mechanisms for driving convection in the Earth's core on the structure of the magnetic and velocity fields using a 3D numerical dynamo model. We find dynamos with a dipolar magnetic field in cases of chemical convection or convection driven by an imposed temperature contrast. With purely internal heating we obtain only dynamos with a quadrupolar or more complex field. The relative strength of convection and magnetic field generation in the regions close to the poles depends on whether a condition of fixed composition or of fixed chemical flux is specified on the inner core boundary. If applicable to the geodynamo, our results favor the dominance of chemical convection during the past 3 Gyr.

  7. Tensegrity finite element models of mechanical tests of individual cells.

    PubMed

    Bursa, Jiri; Lebis, Radek; Holata, Jakub

    2012-01-01

    A three-dimensional finite element model of a vascular smooth muscle cell is based on models published recently; it comprehends elements representing cell membrane, cytoplasm and nucleus, and a complex tensegrity structure representing the cytoskeleton. In contrast to previous models of eucaryotic cells, this tensegrity structure consists of several parts. Its external and internal parts number 30 struts, 60 cables each, and their nodes are interconnected by 30 radial members; these parts represent cortical, nuclear and deep cytoskeletons, respectively. This arrangement enables us to simulate load transmission from the extracellular space to the nucleus or centrosome via membrane receptors (focal adhesions); the ability of the model was tested by simulation of some mechanical tests with isolated vascular smooth muscle cells. Although material properties of components defined on the basis of the mechanical tests are ambiguous, modelling of different types of tests has shown the ability of the model to simulate substantial global features of cell behaviour, e.g. "action at a distance effect" or the global load-deformation response of the cell under various types of loading. Based on computational simulations, the authors offer a hypothesis explaining the scatter of experimental results of indentation tests. PMID:22508025

  8. Modelling mechanical characteristics of microbial biofilms by network theory

    PubMed Central

    Ehret, Alexander E.; Böl, Markus

    2013-01-01

    In this contribution, we present a constitutive model to describe the mechanical behaviour of microbial biofilms based on classical approaches in the continuum theory of polymer networks. Although the model is particularly developed for the well-studied biofilms formed by mucoid Pseudomonas aeruginosa strains, it could easily be adapted to other biofilms. The basic assumption behind the model is that the network of extracellular polymeric substances can be described as a superposition of worm-like chain networks, each connected by transient junctions of a certain lifetime. Several models that were applied to biofilms previously are included in the presented approach as special cases, and for small shear strains, the governing equations are those of four parallel Maxwell elements. Rheological data given in the literature are very adequately captured by the proposed model, and the simulated response for a series of compression tests at large strains is in good qualitative agreement with reported experimental behaviour. PMID:23034354

  9. Distinguishing Feedback Mechanisms in Clock Models

    NASA Astrophysics Data System (ADS)

    Golden, Alexander; Lubensky, David

    Biological oscillators are very diverse but can be classified based on dynamical motifs such as type of feedback. The S. Elongatus circadian oscillator is a novel circadian oscillator that can operate at constant protein number by modifying covalent states. It can be reproduced in vitro with only 3 different purified proteins: KaiA, KaiB, and KaiC. We use computational and analytic techniques to compare models of the S. Elongatus post-translational oscillator that rely on positive feedback with models that rely on negative feedback. We show that introducing a protein that binds competitively with KaiA to the KaiB-KaiC complex can distinguish between positive and negative feedback as the primary driver of the rhythm, which has so far been difficult to address experimentally. NSF Grant DMR-1056456.

  10. Conduction Mechanisms in Lillie's Iron-Wire Model of Nerve

    PubMed Central

    Wei, Ling Y.; Neuman, R. H.

    1970-01-01

    Based on theory and experiment, we found that the conduction through the oxide film in Lillie's iron-wire model is dominated by Schottky emission at low fields (below 106 v/cm), by electron tunneling from trap to trap at intermediate fields and by direct tunneling (Fowler-Nordheim type) at higher fields (above 3 × 106 v/cm). The trap-to-trap tunneling is considered to give rise to the negative resistance and the fixed position of the current maximum as observed. Some of the nervelike properties of the Lillie's model are interpreted on this tunneling mechanism. ImagesFigure 2Figure 3 PMID:5496904

  11. Piezoelectric compliant mechanism energy harvesters under large base excitations

    NASA Astrophysics Data System (ADS)

    Ma, Xiaokun; Trolier-McKinstry, Susan; Rahn, Christopher D.

    2016-09-01

    A piezoelectric compliant mechanism (PCM) energy harvester is designed, modeled, and analyzed that consists of a polyvinylidene diflouoride, PVDF unimorph clamped at its base and attached to a compliant mechanism at its tip. The compliant hinge stiffness is carefully tuned to approach a low frequency first mode with an efficient (nearly quadratic) shape that provides a uniform strain distribution. A nonlinear model of the PCM energy harvester under large base excitation is derived to determine the maximum power that can be generated by the device. Experiments with a fabricated PCM energy harvester prototype show that the compliant mechanism introduces a stiffening effect and a much wider bandwidth than a benchmark proof mass cantilever design. The PCM bridge structure self-limits the displacement and maximum strain at large excitations compared with the proof mass cantilever, improving the device robustness. The PCM outperforms the cantilever in both average power and power-strain sensitivity at high accelerations due to the PCM axial stretching effect and its more uniform strain distribution.

  12. Computational tool for modeling and simulation of mechanically ventilated patients.

    PubMed

    Serna, Leidy Y; Hernandez, Alher M; Mananas, Miguel A

    2010-01-01

    The mechanical ventilator settings in patients with respiratory diseases like chronic obstructive pulmonary disease (COPD) during episodes of acute respiratory failure (ARF) is not a simple task that in most cases is successful based on the experience of physicians. This paper describes an interactive tool based in mathematical models, developed to make easier the study of the interaction between a mechanical ventilator and a patient. It describes all stages of system development, including simulated ventilatory modes, the pathologies of interest and interaction between the user and the system through a graphical interface developed in Matlab and Simulink. The developed computational tool allows the study of most widely used ventilatory modes and its advantages in the treatment of different kind of patients. The graphical interface displays all variables and parameters in the common way of last generation mechanical ventilators do and it is totally interactive, making possible its use by clinical personal, hiding the complexity of implemented mathematical models to the user. The evaluation in different clinical simulated scenes adjusts properly with recent findings in mechanical ventilation scientific literature. PMID:21096101

  13. Qualitative mechanism models and the rationalization of procedures

    NASA Technical Reports Server (NTRS)

    Farley, Arthur M.

    1989-01-01

    A qualitative, cluster-based approach to the representation of hydraulic systems is described and its potential for generating and explaining procedures is demonstrated. Many ideas are formalized and implemented as part of an interactive, computer-based system. The system allows for designing, displaying, and reasoning about hydraulic systems. The interactive system has an interface consisting of three windows: a design/control window, a cluster window, and a diagnosis/plan window. A qualitative mechanism model for the ORS (Orbital Refueling System) is presented to coordinate with ongoing research on this system being conducted at NASA Ames Research Center.

  14. Model-Based Reasoning

    ERIC Educational Resources Information Center

    Ifenthaler, Dirk; Seel, Norbert M.

    2013-01-01

    In this paper, there will be a particular focus on mental models and their application to inductive reasoning within the realm of instruction. A basic assumption of this study is the observation that the construction of mental models and related reasoning is a slowly developing capability of cognitive systems that emerges effectively with proper…

  15. Extended model of the photoinitiation mechanisms in photopolymer materials

    SciTech Connect

    Liu Shui; Gleeson, Michael R.; Sabol, Dusan; Sheridan, John T.

    2009-11-15

    In order to further improve photopolymer materials for applications such as data storage, a deeper understanding of the photochemical mechanisms which are present during the formation of holographic gratings has become ever more crucial. This is especially true of the photoinitiation processes, since holographic data storage requires multiple sequential short exposures. Previously, models describing the temporal variation in the photosensitizer (dye) concentration as a function of exposure have been presented and applied to two different types of photosensitizer, i.e., Methylene Blue and Erythrosine B, in a polyvinyl alcohol/acrylamide based photopolymer. These models include the effects of photosensitizer recovery and bleaching under certain limiting conditions. In this paper, based on a detailed study of the photochemical reactions, the previous models are further developed to more physically represent these effects. This enables a more accurate description of the time varying dye absorption, recovery, and bleaching, and therefore of the generation of primary radicals in photopolymers containing such dyes.

  16. Model-based software design

    NASA Technical Reports Server (NTRS)

    Iscoe, Neil; Liu, Zheng-Yang; Feng, Guohui; Yenne, Britt; Vansickle, Larry; Ballantyne, Michael

    1992-01-01

    Domain-specific knowledge is required to create specifications, generate code, and understand existing systems. Our approach to automating software design is based on instantiating an application domain model with industry-specific knowledge and then using that model to achieve the operational goals of specification elicitation and verification, reverse engineering, and code generation. Although many different specification models can be created from any particular domain model, each specification model is consistent and correct with respect to the domain model.

  17. Principles of models based engineering

    SciTech Connect

    Dolin, R.M.; Hefele, J.

    1996-11-01

    This report describes a Models Based Engineering (MBE) philosophy and implementation strategy that has been developed at Los Alamos National Laboratory`s Center for Advanced Engineering Technology. A major theme in this discussion is that models based engineering is an information management technology enabling the development of information driven engineering. Unlike other information management technologies, models based engineering encompasses the breadth of engineering information, from design intent through product definition to consumer application.

  18. Strains, Mechanism, and Perspective: Salmonella-Based Cancer Therapy

    PubMed Central

    Wang, Cheng-Zhi; Kazmierczak, Robert A.; Eisenstark, Abraham

    2016-01-01

    Recently, investigation of bacterial-based tumor therapy has regained focus due to progress in molecular, cellular, and microbial biology. Many bacteria such as Salmonella, Listeria, Escherichia, and Clostridium have proved to have tumor targeting and in some cases even tumor-destroying phenotypes. Furthermore, bacterial clinical treatments for cancer have been improved by combination with other therapeutic methods such as chemotherapeutic drugs and radioactive agents. Synthetic biology techniques have also driven the development of new bacterial-based cancer therapies. However, basic questions about the mechanisms of bacterial-mediated tumor targeting and destruction are still being elucidated. In this review, we focus on three tumor-therapeutic Salmonella models, the most intensively studied bacterial genus in this field. One of these Salmonella models is our Salmonella enterica serovar Typhimurium LT2 derived strain CRC2631, engineered to minimize toxicity but maximize tumor-targeting and destruction effects. The other two are VNP20009 and A1-R. We compare the means by which these therapeutic candidate strain models were selected for study, their tumor targeting and tumor destruction phenotypes in vitro and in vivo, and what is currently known about the mechanisms by which they target and destroy tumors. PMID:27190519

  19. Oral biofilm models for mechanical plaque removal.

    PubMed

    Verkaik, Martinus J; Busscher, Henk J; Rustema-Abbing, Minie; Slomp, Anje M; Abbas, Frank; van der Mei, Henny C

    2010-08-01

    In vitro plaque removal studies require biofilm models that resemble in vivo dental plaque. Here, we compare contact and non-contact removal of single and dual-species biofilms as well as of biofilms grown from human whole saliva in vitro using different biofilm models. Bacteria were adhered to a salivary pellicle for 2 h or grown after adhesion for 16 h, after which, their removal was evaluated. In a contact mode, no differences were observed between the manual, rotating, or sonic brushing; and removal was on average 39%, 84%, and 95% for Streptococcus mutans, Streptococcus oralis, and Actinomyces naeslundii, respectively, and 90% and 54% for the dual- and multi-species biofilms, respectively. However, in a non-contact mode, rotating and sonic brushes still removed considerable numbers of bacteria (24-40%), while the manual brush as a control (5-11%) did not. Single A. naeslundii and dual-species (A. naeslundii and S. oralis) biofilms were more difficult to remove after 16 h growth than after 2 h adhesion (on average, 62% and 93% for 16- and 2-h-old biofilms, respectively), while in contrast, biofilms grown from whole saliva were easier to remove (97% after 16 h and 54% after 2 h of growth). Considering the strong adhesion of dual-species biofilms and their easier more reproducible growth compared with biofilms grown from whole saliva, dual-species biofilms of A. naeslundii and S. oralis are suggested to be preferred for use in mechanical plaque removal studies in vitro. PMID:19565279

  20. Normal brain ageing: models and mechanisms

    PubMed Central

    Toescu, Emil C

    2005-01-01

    Normal ageing is associated with a degree of decline in a number of cognitive functions. Apart from the issues raised by the current attempts to expand the lifespan, understanding the mechanisms and the detailed metabolic interactions involved in the process of normal neuronal ageing continues to be a challenge. One model, supported by a significant amount of experimental evidence, views the cellular ageing as a metabolic state characterized by an altered function of the metabolic triad: mitochondria–reactive oxygen species (ROS)–intracellular Ca2+. The perturbation in the relationship between the members of this metabolic triad generate a state of decreased homeostatic reserve, in which the aged neurons could maintain adequate function during normal activity, as demonstrated by the fact that normal ageing is not associated with widespread neuronal loss, but become increasingly vulnerable to the effects of excessive metabolic loads, usually associated with trauma, ischaemia or neurodegenerative processes. This review will concentrate on some of the evidence showing altered mitochondrial function with ageing and also discuss some of the functional consequences that would result from such events, such as alterations in mitochondrial Ca2+ homeostasis, ATP production and generation of ROS. PMID:16321805

  1. Fracture mechanics of model fiber composites

    SciTech Connect

    Wang Chi.

    1992-01-01

    Fracture of matrix material caused by a tensile break in a fiber was investigated. A model was constructed, consisting of two inextensible fibers touching end-to-end and embedded in an elastic block. Energy release rates were calculated by FEA for a circular crack growing outwards from the point where the fiber ends separated as they were pulled apart. The results are compared with experimental observations on steel rod/silicone resin systems. It is found that, when a fiber breaks, a circular crack grows outward in a stable way under increasing load. After the crack reaches a certain size, approximately halfway to the edge of the resin block, the strain energy release reaches a minimum value and then increases, and the crack accelerates. The force required to propagate a crack is predicted successfully by linear elastic fracture mechanics at all stages of crack growth. In particular, good agreement was obtained with the maximum force that the system could support - the breaking load. Fracture of fiber composites under shear deformation was simulated by applying a tension to the rod in a bush mounting.

  2. Cardiac mechanical parameter calibration based on the unscented transform.

    PubMed

    Marchesseau, Stéphanie; Delingette, Hervé; Sermesant, Maxime; Rhode, Kawal; Duckett, Simon G; Rinaldi, C Aldo; Razavi, Reza; Ayache, Nicholas

    2012-01-01

    Patient-specific cardiac modelling can help in understanding pathophysiology and predict therapy planning. However it requires to personalize the model geometry, kinematics, electrophysiology and mechanics. Calibration aims at providing global values (space invariant) of parameters before performing the personalization stage which involves solving an inverse problem to find regional values. We propose an automatic calibration method of the mechanical parameters of the Bestel-Clément-Sorine (BCS) electromechanical model of the heart based on the Unscented Transform algorithm. A sensitivity analysis is performed that reveals which observations on the volume and pressure evolution are significant to characterize the global behaviour of the myocardium. We show that the calibration method gives satisfying results by optimizing up to 7 parameters of the BCS model in only one iteration. This method was evaluated on 7 volunteers and 2 heart failure patients, with a mean relative error from the real data of 11%. This calibration enabled furthermore a preliminary study of the specific parameters to the studied pathologies. PMID:23286030

  3. Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates

    NASA Astrophysics Data System (ADS)

    Meng, Qinghua; Wang, Zhenqing

    2016-05-01

    Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of ​​impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.

  4. A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules

    NASA Astrophysics Data System (ADS)

    Andriollo, Tito; Thorborg, Jesper; Tiedje, Niels; Hattel, Jesper

    2016-06-01

    In this paper, the thermo-elastic behavior of the graphite nodules contained in ductile iron is derived on the basis of recent transmission electron microscopy investigations of their real internal structure. The proposed model is initially validated by performing a finite element homogenization analysis to verify its consistency with the room-temperature elastic properties of ductile iron measured at the macro scale. Subsequently, it is used to investigate the formation of local residual stresses around the graphite particles by simulating the manufacturing process of a typical ferritic ductile iron grade, and the results are compared with preliminary measurements using synchrotron x-rays. Finally, the obtained accurate description of the stress & strain field at the micro scale is used to shed light on common failure modes reported for the nodules and on some peculiar properties observed in ductile iron at both micro and macro scale.

  5. SFT based cosmological models

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexey S.

    2010-11-01

    We consider the appearance of multiple scalar fields in SFT inspired non-local models with a single scalar field at late times. In this regime all the scalar fields are free. This system minimally coupled to gravity is mainly analyzed in this note. We build one exact solution to the equations of motion. We consider an exactly solvable model which obeys a simple exact solution in the cosmological context for the Friedmann equations and that reproduces the behavior expected from SFT in the asymptotic regime.

  6. Thermal-mechanical-noise-based CMUT characterization and sensing.

    PubMed

    Gurun, Gokce; Hochman, Michael; Hasler, Paul; Degertekin, F Levent

    2012-06-01

    When capacitive micromachined ultrasonic transducers (CMUTs) are monolithically integrated with custom-designed low-noise electronics, the output noise of the system can be dominated by the CMUT thermal-mechanical noise both in air and in immersion even for devices with low capacitance. Because the thermal-mechanical noise can be related to the electrical admittance of the CMUTs, this provides an effective means of device characterization. This approach yields a novel method to test the functionality and uniformity of CMUT arrays and the integrated electronics when a direct connection to CMUT array element terminals is not available. Because these measurements can be performed in air at the wafer level, the approach is suitable for batch manufacturing and testing. We demonstrate this method on the elements of an 800-μm-diameter CMUT-on-CMOS array designed for intravascular imaging in the 10 to 20 MHz range. Noise measurements in air show the expected resonance behavior and spring softening effects. Noise measurements in immersion for the same array provide useful information on both the acoustic cross talk and radiation properties of the CMUT array elements. The good agreement between a CMUT model based on finite difference and boundary element methods and the noise measurements validates the model and indicates that the output noise is indeed dominated by thermal-mechanical noise. The measurement method can be exploited to implement CMUT-based passive sensors to measure immersion medium properties, or other parameters affecting the electro-mechanics of the CMUT structure. PMID:22718877

  7. The statistical mechanics of several Hamiltonian models

    NASA Astrophysics Data System (ADS)

    Lee, Chi-Lun

    This thesis has two major parts. The first part concerns studies of the equilibrium thermodynamics on different models using a self-consistent Ornstein-Zernike approximation (SCOZA). For most approximate correlation-function theories there exists an inconsistency for thermodynamic quantities evaluated from different thermodynamic routes. In SCOZA one solves this inconsistency through a renormalization procedure, which is based on the enforcement of thermodynamic consistency for quantities evaluated from the energy and the compressibility routes. This procedure has resulted in remarkable accuracy of thermodynamics for most phase regions. We apply several versions of SCOZA to study different models such as the two-dimensional lattice gas, the hard-core Yukawa fluid, and the polymer fluid. Our main objective is to develop a simple non-perturbative approximation that can give accurate results for thermodynamic quantities even when the system stays very close to its critical point. The second part is focused on a study of the protein-folding dynamics using a statistical energy landscape theory. A protein molecule is modelled as a heterogeneous polymer with randomized interaction energies characterized by a statistical distribution. This results in an funnel-like energy landscape with local fluctuations (roughness) and an overall bias towards the folded state. With the introduction of an order parameter, the direction of folding can be characterized. The statistical energy landscape is then mapped into a one-dimensional continuous-time random walk along the order parameter, in which the dynamics is represented through a generalized Fokker-Planck equation. By solving the equation numerically we find a transition from exponential to non-exponential kinetics in the distribution of the first-passage time to the folded state. In our results the non-exponential kinetics has a distribution which resembles a truncated Levy distribution in time.

  8. Monochloramination of resorcinol: mechanism and kinetic modeling.

    PubMed

    Cimetiere, Nicolas; Dossier-Berne, Florence; De Laat, Joseph

    2009-12-15

    The kinetics of monochloramination of resorcinol, 4-chlororesorcinol, and 4,6-dichlororesorcinol have been investigated over the pH range of 5-12, at 23 +/- 2 degrees C. Monochloramine solutions were prepared with ammonia-to-chlorine ratios (N/Cl) ranging from 1.08 to 31 mol/mol. Under conditions that minimize free chlorine reactions (N/Cl > 2 mol/mol), the apparent second-order rate constants of monochloramination of resorcinol compounds show a maximum at pH values between 8.6 and 10.2. The intrinsic second-order rate constants for the reaction of monochloramine with the acid-base forms of the dihydroxybenzenes (Ar(OH)(2), Ar(OH)O(-), and Ar(O(-))(2)) were calculated from the apparent second-order rate constants. The stoichiometric coefficients for the formation of 4-chlororesorcinol by monochloramination of resorcinol and 4,6-dichlororesorcinol by monochloramination of 4-chlororesorcinol were found to be equal to 0.66 +/- 0.05 and 0.25 +/- 0.02 mol/mol, respectively at pH 8.6. A kinetic model that incorporates reactions of free chlorine and monochloramine with the different acid-base forms of resorcinol compounds simulated well the initial rates of degradation of resorcinol compounds and was useful to evaluate the contribution of free chlorine reactions to the overall rates of degradation of resorcinol at low N/Cl ratios. PMID:20000532

  9. Quantum Mechanical Models Of The Fermi Shuttle

    SciTech Connect

    Sternberg, James

    2011-06-01

    The Fermi shuttle is a mechanism in which high energy electrons are produced in an atomic collision by multiple collisions with a target and a projectile atom. It is normally explained purely classically in terms of the electron's orbits prescribed in the collision. Common calculations to predict the Fermi shuttle use semi-classical methods, but these methods still rely on classical orbits. In reality such collisions belong to the realm of quantum mechanics, however. In this paper we discuss several purely quantum mechanical calculations which can produce the Fermi shuttle. Being quantum mechanical in nature, these calculations produce these features by wave interference, rather than by classical orbits.

  10. Mechanism-Based Competitive Binding Model to Investigate the Effect of Neonatal Fc Receptor Binding Affinity on the Pharmacokinetic of Humanized Anti-VEGF Monoclonal IgG1 Antibody in Cynomolgus Monkey.

    PubMed

    Ng, Chee M; Fielder, Paul J; Jin, Jin; Deng, Rong

    2016-07-01

    The quantitative relationship between neonatal Fc receptor (FcRn) binding affinity at both acidic and physiological pH and the pharmacokinetics of protein engineered FcRn IgG1 variants has not yet been reported. Our objective was to develop a quantitatively mechanism-based competitive binding model to describe the effects of FcRn binding affinity at acidic and physiological pH on the pharmacokinetics of anti-VEGF IgG1 antibodies when both endogenous and exogenous antibodies are competing for the same FcRn. Pharmacokinetic (PK) and FcRn binding data from five Fc variants of humanized anti-VEGF IgG1 monoclonal antibodies with wide range of FcRn binding affinity were used for the analysis. Sixty-seven anti-VEGF IgG1 antibody-treated animals and 25 control animals with simulated endogenous IgG levels were used to develop the final model. A hybrid iterative two stages and Monte Carlo parametric expectation-maximization method was used to obtain the final model parameters estimates. The final model well described the observed PK data. Quantitative FcRn binding affinity-pharmacokinetics relationships was constructed to provide important biological insights in better understanding of the FcRn binding effect on pharmacokinetics of anti-VEGF IgG1 antibodies in cynomolgus monkeys and served as an important model-based drug discovery platform to guide the design and development of the future generation of anti-VEGF or other therapeutic IgG1 antibodies. PMID:27075465

  11. Particle-Based Multidimensional Multispecies Biofilm Model

    PubMed Central

    Picioreanu, Cristian; Kreft, Jan-Ulrich; van Loosdrecht, Mark C. M.

    2004-01-01

    In this paper we describe a spatially multidimensional (two-dimensional [2-D] and three-dimensional [3-D]) particle-based approach for modeling the dynamics of multispecies biofilms growing on multiple substrates. The model is based on diffusion-reaction mass balances for chemical species coupled with microbial growth and spreading of biomass represented by hard spherical particles. Effectively, this is a scaled-up version of a previously proposed individual-based biofilm model. Predictions of this new particle-based model were quantitatively compared with those obtained with an established one-dimensional (1-D) multispecies model for equivalent problems. A nitrifying biofilm containing aerobic ammonium and nitrite oxidizers, anaerobic ammonium oxidizers, and inert biomass was chosen as an example. The 2-D and 3-D models generally gave the same results. If only the average flux of nutrients needs to be known, 2-D and 1-D models are very similar. However, the behavior of intermediates, which are produced and consumed in different locations within the biofilm, is better described in 2-D and 3-D models because of the multidirectional concentration gradients. The predictions of 2-D or 3-D models are also different from those of 1-D models for slowly growing or minority species in the biofilm. This aspect is related to the mechanism of biomass spreading or advection implemented in the models and should receive more attention in future experimental studies. PMID:15128564

  12. Rule-based simulation models

    NASA Technical Reports Server (NTRS)

    Nieten, Joseph L.; Seraphine, Kathleen M.

    1991-01-01

    Procedural modeling systems, rule based modeling systems, and a method for converting a procedural model to a rule based model are described. Simulation models are used to represent real time engineering systems. A real time system can be represented by a set of equations or functions connected so that they perform in the same manner as the actual system. Most modeling system languages are based on FORTRAN or some other procedural language. Therefore, they must be enhanced with a reaction capability. Rule based systems are reactive by definition. Once the engineering system has been decomposed into a set of calculations using only basic algebraic unary operations, a knowledge network of calculations and functions can be constructed. The knowledge network required by a rule based system can be generated by a knowledge acquisition tool or a source level compiler. The compiler would take an existing model source file, a syntax template, and a symbol table and generate the knowledge network. Thus, existing procedural models can be translated and executed by a rule based system. Neural models can be provide the high capacity data manipulation required by the most complex real time models.

  13. High performance liquid chromatography of substituted aromatics with the metal-organic framework MIL-100(Fe): Mechanism analysis and model-based prediction.

    PubMed

    Qin, Weiwei; Silvestre, Martin Eduardo; Li, Yongli; Franzreb, Matthias

    2016-02-01

    Metal-organic framework (MOF) MIL-100(Fe) with well-defined thickness was homogenously coated onto the outer surface of magnetic microparticles via a liquid-phase epitaxy method. The as-synthesized MIL-100(Fe) was used as stationary phase for high-performance liquid chromatography (HPLC) and separations of two groups of mixed aromatic hydrocarbons (toluene, styrene and p-xylene; acetanilide, 2-nirtoaniline and 1-naphthylamine) using methanol/water as mobile phase were performed to evaluate its performance. Increasing water content of the mobile phase composition can greatly improve the separations on the expense of a longer elution time. Stepwise elution significantly shortens the elution time of acetanilide, 2-nirtoaniline and 1-naphthylamine mixtures, while still achieving a baseline separation. Combining the experimental results and in-depth modeling using a recently developed chromatographic software (ChromX), adsorption equilibrium parameters, including the affinities and maximum capacities, for each analyte toward the MIL-100(Fe) are obtained. In addition, the pore diffusivity of aromatic hydrocarbons within MIL-100(Fe) was determined to be 5×10(-12)m(2)s(-1). While the affinities of MIL-100(Fe) toward the analyte molecules differs much, the maximum capacities of the analytes are in a narrow range with q*MOFmax,toluene=3.55molL(-1), q*MOFmax,styrene or p-xylene=3.53molL(-1), and q*MOFmax,anilines=3.12molL(-1) corresponding to approximately 842 toluene and 838 styrene or p-xylene, and 740 aniline molecules per MIL-100(Fe) unit cell, respectively. PMID:26787165

  14. Auto Mechanics: Time for a Model Change?

    ERIC Educational Resources Information Center

    Aun, Emil Michael

    1970-01-01

    There were 825,000 auto mechanics and repairmen in 1968 and the net number is rising at a rate of 16,400 a year. However, officials of the Automotive Services Industry Association estimate that 125,000 to 200,000 more repairmen and mechanics are needed now. Occupational problems and possible solutions are discussed. (BC)

  15. Estimating seabed scattering mechanisms via Bayesian model selection.

    PubMed

    Steininger, Gavin; Dosso, Stan E; Holland, Charles W; Dettmer, Jan

    2014-10-01

    A quantitative inversion procedure is developed and applied to determine the dominant scattering mechanism (surface roughness and/or volume scattering) from seabed scattering-strength data. The classification system is based on trans-dimensional Bayesian inversion with the deviance information criterion used to select the dominant scattering mechanism. Scattering is modeled using first-order perturbation theory as due to one of three mechanisms: Interface scattering from a rough seafloor, volume scattering from a heterogeneous sediment layer, or mixed scattering combining both interface and volume scattering. The classification system is applied to six simulated test cases where it correctly identifies the true dominant scattering mechanism as having greater support from the data in five cases; the remaining case is indecisive. The approach is also applied to measured backscatter-strength data where volume scattering is determined as the dominant scattering mechanism. Comparison of inversion results with core data indicates the method yields both a reasonable volume heterogeneity size distribution and a good estimate of the sub-bottom depths at which scatterers occur. PMID:25324059

  16. Statistical mechanical and quantum mechanical modeling of condensed phase systems

    NASA Astrophysics Data System (ADS)

    Labrosse, Matthew R.

    Understanding adsorption in nanoporous media is vital to improving their use in industrial applications such as fluid storage and separations processes. One major objective of this research is to shed light on an on-going controversy in literature over where gases adsorb on single walled carbon nanotube bundles. Grand-canonical Monte Carlo simulations have been performed using models of carbon nanotube bundles composed of tubes of all the same diameter (homogeneous) and tubes of different diameters (heterogeneous). We used three metrics with which we compared our simulation results to those found in experiments on carbon nanotubes: the specific surface area, the isosteric heat of adsorption, and the adsorption capacity. Simulations of classically behaved fluids Ar, CH4, and Xe indicate that nanotubes prepared by the HiPco process are best described by a heterogeneous bundle model with ˜11% of the nanotubes opened. Ne gas requires additional considerations to describe the quantum effects at the temperatures of interest, which have been implemented by the Feynman-Hibbs approximation. Overall, calculated results from Ne simulations are consistent with those from classical fluids. However, Ne simulations strongly indicate that the small interstitial channels formed by exactly three nanotubes are closed. Combined with previous studies on classically behaved fluids Ar, CH4, and Xe, experimental data including Ne are best matched by hetergeneous bundles with ˜11% open-ended nanotubes. The development of a heterogeneous Co/C/O reactive force field (ReaxFF) potential has also been a major objective of this research. ReaxFF provides a method to describe bond-breaking and bond-forming events that can be applied to large-scale molecular dynamics (MD) simulations. This many-bodied semi-empirical potential has been trained from ab initio density functional theory (DFT) calculations. The training set originally included descriptions of bulk and surface condensed phase cobalt

  17. Mechanical properties and modeling of seal-forming lithologies

    SciTech Connect

    Kronenberg, A.K.; Russell, J.E.; Carter, N.L.; Ibanez, W.; Mazariegos, R.

    1992-04-01

    Both rocksalt and shale lithologies are actively deformed in response to gravitational loads associated with deposition, and both form effective seals to petroleum and natural gas. Thus, the shapes of seal-forming units, and the nature of fractures and faults that may breach them depend upon either the mechanical properties of salt or those of shale, and the loading histories to which they have been subjected. The objectives of this research include the determination of the mechanical properties under controlled conditions of well-characterized shales, and the numerical modeling of rocksalt (and eventually shale) formations using laboratory-based rheologies. Progress has been made towards these goals over this project period, both in our experimental program on shale deformation and model development for the growth of salt diapirs. The mechanical anisotropy of an illite-bearing shale from Louisiana has been determined and related to the preferred orientation and distribution of clays. Its strength in the absence of pore fluids has been determined at confining pressures of up to 250 MPa and at high pressure we have investigated the effects of deformation rate and temperature. A numerical finite difference code has been developed to solve the incompressible Navier-Stokes equations and validated using a two- layer linear viscous model for which analytic solutions are available. Although the code has only been validated for the linear viscous case, it is capable of solving for highly nonlinear constitutive laws as well as solving for arbitrary interfaces between the salt and overburden.

  18. Modeling cochlear dynamics: interrelation between cochlea mechanics and psychoacoustics.

    PubMed

    Epp, Bastian; Verhey, Jesko L; Mauermann, Manfred

    2010-10-01

    A model of the cochlea was used to bridge the gap between model approaches commonly used to investigate phenomena related to otoacoustic emissions and more filter-based model approaches often used in psychoacoustics. In the present study, a nonlinear and active one-dimensional transmission line model was developed that accounts for several aspects of physiological data with a single fixed parameter set. The model shows plausible excitation patterns and an input-output function similar to the linear-compressive-linear function as hypothesized in psychoacoustics. The model shows realistic results in a two-tone suppression paradigm and a plausible growth function of the 2f(1)-f(2) component of distortion product otoacoustic emissions. Finestructure was found in simulated stimulus-frequency otoacoustic emissions (SFOAE) with realistic levels and rapid phase rotation. A plausible "threshold in quiet" including finestructure and spontaneous otoacoustic emissions (SOAE) could be simulated. It is further shown that psychoacoustical data of modulation detection near threshold can be explained by the mechanical dynamics of the modeled healthy cochlea. It is discussed that such a model can be used to investigate the representation of acoustic signals in healthy and impaired cochleae at this early stage of the auditory pathway for both, physiological as well as psychoacoustical paradigms. PMID:20968359

  19. Video-based problems in introductory mechanics physics courses

    NASA Astrophysics Data System (ADS)

    Gröber, Sebastian; Klein, Pascal; Kuhn, Jochen

    2014-09-01

    Introductory mechanics physics courses at the transition from school to university are a challenge for students. They are faced with an abrupt and necessary increase of theoretical content and requirements on their conceptual understanding of phyiscs. In order to support this transition we replaced part of the mandatory weekly theory-based paper-and-pencil problems with video analysis problems of equal content and level of difficulty. Video-based problems (VBP) are a new problem format for teaching physics from a linked sequence of theoretical and video-based experimental tasks. Experimental tasks are related to the well-known concept of video motion analysis. This introduction of an experimental part in recitations allows the establishment of theory-experiment interplay as well as connections between physical content and context fields such as nature, technique, everyday life and applied physics by conducting model-and context-related experiments. Furthermore, laws and formulas as predominantly representative forms are extended by the use of diagrams and vectors. In this paper we give general reasons for this approach, describe the structure and added values of VBP, and show that they cover a relevant part of mechanics courses at university. Emphasis is put on theory-experiment interplay as a structural added value of VBP to promote students' construction of knowledge and conceptual understanding.

  20. Stochastical modeling for Viral Disease: Statistical Mechanics and Network Theory

    NASA Astrophysics Data System (ADS)

    Zhou, Hao; Deem, Michael

    2007-04-01

    Theoretical methods of statistical mechanics are developed and applied to study the immunological response against viral disease, such as dengue. We use this theory to show how the immune response to four different dengue serotypes may be sculpted. It is the ability of avian influenza, to change and to mix, that has given rise to the fear of a new human flu pandemic. Here we propose to utilize a scale free network based stochastic model to investigate the mitigation strategies and analyze the risk.

  1. Shear mechanical properties of the spleen: experiment and analytical modelling.

    PubMed

    Nicolle, S; Noguer, L; Palierne, J-F

    2012-05-01

    This paper aims at providing the first shear mechanical properties of spleen tissue. Rheometric tests on porcine splenic tissues were performed in the linear and nonlinear regime, revealing a weak frequency dependence of the dynamic moduli in linear regime and a distinct strain-hardening effect in nonlinear regime. These behaviours are typical of soft tissues such as kidney and liver, with however a less pronounced strain-hardening for the spleen. An analytical model based on power laws is then proposed to describe the general shear viscoelastic behaviour of the spleen. PMID:22498291

  2. Impeller leakage flow modeling for mechanical vibration control

    NASA Technical Reports Server (NTRS)

    Palazzolo, Alan B.

    1996-01-01

    HPOTP and HPFTP vibration test results have exhibited transient and steady characteristics which may be due to impeller leakage path (ILP) related forces. For example, an axial shift in the rotor could suddenly change the ILP clearances and lengths yielding dynamic coefficient and subsequent vibration changes. ILP models are more complicated than conventional-single component-annular seal models due to their radial flow component (coriolis and centrifugal acceleration), complex geometry (axial/radial clearance coupling), internal boundary (transition) flow conditions between mechanical components along the ILP and longer length, requiring moment as well as force coefficients. Flow coupling between mechanical components results from mass and energy conservation applied at their interfaces. Typical components along the ILP include an inlet seal, curved shroud, and an exit seal, which may be a stepped labyrinth type. Von Pragenau (MSFC) has modeled labyrinth seals as a series of plain annular seals for leakage and dynamic coefficient prediction. These multi-tooth components increase the total number of 'flow coupled' components in the ILP. Childs developed an analysis for an ILP consisting of a single, constant clearance shroud with an exit seal represented by a lumped flow-loss coefficient. This same geometry was later extended to include compressible flow. The objective of the current work is to: supply ILP leakage-force impedance-dynamic coefficient modeling software to MSFC engineers, base on incompressible/compressible bulk flow theory; design the software to model a generic geometry ILP described by a series of components lying along an arbitrarily directed path; validate the software by comparison to available test data, CFD and bulk models; and develop a hybrid CFD-bulk flow model of an ILP to improve modeling accuracy within practical run time constraints.

  3. Tractor Mechanic--Teacher's Guide. Competency Based Education Curriculum.

    ERIC Educational Resources Information Center

    McCann, Edward W.

    This teacher's guide is designed to accompany the Tractor Mechanic Competency Based Education (CBE) Curriculum (CE 022 480). The following information is included: a discussion of the uses of the Tractor Mechanic CBE curriculum; definitions of related terms; the table of contents for the Tractor Mechanic CBE curriculum; a list of competencies by…

  4. Mechanical model of kinesin moving on microtubule

    NASA Astrophysics Data System (ADS)

    To, Kiwing; Chou, Ya-Chang; Hsiao, Yi-Feng; Chen, Kuan-Hua

    Kinesins are biomolecules that serve as intercellular motors for carrying cellular cargos along microtubules. Although the mechanism of converting the chemical energy of ATP to mechanical work is not fully understood, the motion of a kinesin on a microtubule has been measured and two different mechanisms, namely the ``hand-over-hand'' and ``inchworm'', has been proposed. The particular shape of kinesin and microtubules suggest a possible mechanism for force generation similar to Brownian ratchet. Using a bead chain connected to two heads that are attracted to a vibrated ratchet plate as a scaled up analog of the kinesinmicrotubule system, we manage to simulate both ``handoverhand'' and ``inchworm'' motion [Chou, et. al., Physica A443, 66 (2015)]. In addition, we find that chain, which play the role of the stalk in a kinesin molecule, can also generate force by interacting with the ratchet plate [Chen, et. al. Phys. Rev. E87, 012711 (2013)].

  5. The cognitive life of mechanical molecular models.

    PubMed

    Charbonneau, Mathieu

    2013-12-01

    The use of physical models of molecular structures as research tools has been central to the development of biochemistry and molecular biology. Intriguingly, it has received little attention from scholars of science. In this paper, I argue that these physical models are not mere three-dimensional representations but that they are in fact very special research tools: they are cognitive augmentations. Despite the fact that they are external props, these models serve as cognitive tools that augment and extend the modeler's cognitive capacities and performance in molecular modeling tasks. This cognitive enhancement is obtained because of the way the modeler interacts with these models, the models' materiality contributing to the solving of the molecule's structure. Furthermore, I argue that these material models and their component parts were designed, built and used specifically to serve as cognitive facilitators and cognitive augmentations. PMID:23910718

  6. Differential Geometry Based Multiscale Models

    PubMed Central

    Wei, Guo-Wei

    2010-01-01

    Large chemical and biological systems such as fuel cells, ion channels, molecular motors, and viruses are of great importance to the scientific community and public health. Typically, these complex systems in conjunction with their aquatic environment pose a fabulous challenge to theoretical description, simulation, and prediction. In this work, we propose a differential geometry based multiscale paradigm to model complex macromolecular systems, and to put macroscopic and microscopic descriptions on an equal footing. In our approach, the differential geometry theory of surfaces and geometric measure theory are employed as a natural means to couple the macroscopic continuum mechanical description of the aquatic environment with the microscopic discrete atom-istic description of the macromolecule. Multiscale free energy functionals, or multiscale action functionals are constructed as a unified framework to derive the governing equations for the dynamics of different scales and different descriptions. Two types of aqueous macromolecular complexes, ones that are near equilibrium and others that are far from equilibrium, are considered in our formulations. We show that generalized Navier–Stokes equations for the fluid dynamics, generalized Poisson equations or generalized Poisson–Boltzmann equations for electrostatic interactions, and Newton's equation for the molecular dynamics can be derived by the least action principle. These equations are coupled through the continuum-discrete interface whose dynamics is governed by potential driven geometric flows. Comparison is given to classical descriptions of the fluid and electrostatic interactions without geometric flow based micro-macro interfaces. The detailed balance of forces is emphasized in the present work. We further extend the proposed multiscale paradigm to micro-macro analysis of electrohydrodynamics, electrophoresis, fuel cells, and ion channels. We derive generalized Poisson–Nernst–Planck equations that

  7. Model based vibration monitoring

    SciTech Connect

    Esat, I.; Paya, B.; Badi, M.N.M.

    1996-11-01

    The principal source of vibratory excitation of gear system is the unsteady component of the relative angular motion of pair of meshing spur gears. This vibratory excitation is described by the transmission error. The transmission error present itself as a varying force at the contact point of the meshing gear teeth. The varying force is also influenced by the varying tooth stiffness due to change of orientation of teeth relative to each other, during the contact phase of each pair. Such a varying force produces both lateral and torsional excitation to the gear system. This paper presents analytical formulation of a simple two meshing spur gear system as a three mass system (18 DOF). The mathematical model also incorporates the analytical formulation of the tooth stiffness. The analytical results are compared with the experimental results. At this stage of analysis the procedure developed for handling the nonlinear influences of the tooth geometry is not fully implemented and the tooth stiffness taken as a constant value representing the average tooth stiffness. The comparison between the analytical and experimental results are encouraging as three main frequency obtained from FFT of the experimental results correlates very closely with the analytical results.

  8. A damage mechanics based general purpose interface/contact element

    NASA Astrophysics Data System (ADS)

    Yan, Chengyong

    Most of the microelectronics packaging structures consist of layered substrates connected with bonding materials, such as solder or epoxy. Predicting the thermomechanical behavior of these multilayered structures is a challenging task in electronic packaging engineering. In a layered structure the most complex part is always the interfaces between the strates. Simulating the thermo-mechanical behavior of such interfaces, is the main theme of this dissertation. The most commonly used solder material, Pb-Sn alloy, has a very low melting temperature 180sp°C, so that the material demonstrates a highly viscous behavior. And, creep usually dominates the failure mechanism. Hence, the theory of viscoplasticity is adapted to describe the constitutive behavior. In a multilayered assembly each layer has a different coefficient of thermal expansion. Under thermal cycling, due to heat dissipated from circuits, interfaces and interconnects experience low cycle fatigue. Presently, the state-of-the art damage mechanics model used for fatigue life predictions is based on Kachanov (1986) continuum damage model. This model uses plastic strain as a damage criterion. Since plastic strain is a stress path dependent value, the criterion does not yield unique damage values for the same state of stress. In this dissertation a new damage evolution equation based on the second law of thermodynamic is proposed. The new criterion is based on the entropy of the system and it yields unique damage values for all stress paths to the final state of stress. In the electronics industry, there is a strong desire to develop fatigue free interconnections. The proposed interface/contact element can also simulate the behavior of the fatigue free Z-direction thin film interconnections as well as traditional layered interconnects. The proposed interface element can simulate behavior of a bonded interface or unbonded sliding interface, also called contact element. The proposed element was verified against

  9. The Two-Capacitor Problem Revisited: A Mechanical Harmonic Oscillator Model Approach

    ERIC Educational Resources Information Center

    Lee, Keeyung

    2009-01-01

    The well-known two-capacitor problem, in which exactly half the stored energy disappears when a charged capacitor is connected to an identical capacitor, is discussed based on the mechanical harmonic oscillator model approach. In the mechanical harmonic oscillator model, it is shown first that "exactly half" the work done by a constant applied…

  10. Reconstruction of Sedimentary Rock Based on MechanicalProperties

    SciTech Connect

    Jin, Guodong; Patzek, Tad W.; Silin, Dmitry B.

    2004-05-04

    We describe a general, physics-based approach to numericalreconstruction of the geometrical structure and mechanical properties ofnatural sedimentary rock in 3D. Our procedure consists of three mainsteps: sedimentation, compaction, and diagenesis, followed by theverification of rock mechanical properties. The dynamic geologicprocesses of grain sedimentation and compaction are simulated by solvinga dimensionless form of Newton's equations of motion for an ensemble ofgrains. The diagenetic rock transformation is modeled using a cementationalgorithm, which accounts for the effect of rock grain size on therelative rate of cement overgrowth. Our emphasis is on unconsolidatedsand and sandstone. The main input parameters are the grain sizedistribution, the final rock porosity, the type and amount of cement andclay minerals, and grain mechanical properties: the inter-grain frictioncoefficient, the cement strength, and the grain stiffness moduli. We usea simulated 2D Fontainebleau sandstone to obtain the grain mechanicalproperties. This Fontainebleau sandstone is also used to study theinitiation, growth, and coalescence of micro-cracks under increasingvertical stress. The box fractal dimension of the micro-crackdistribution, and its variation with the applied stress areestimated.

  11. Model-Based Safety Analysis

    NASA Technical Reports Server (NTRS)

    Joshi, Anjali; Heimdahl, Mats P. E.; Miller, Steven P.; Whalen, Mike W.

    2006-01-01

    System safety analysis techniques are well established and are used extensively during the design of safety-critical systems. Despite this, most of the techniques are highly subjective and dependent on the skill of the practitioner. Since these analyses are usually based on an informal system model, it is unlikely that they will be complete, consistent, and error free. In fact, the lack of precise models of the system architecture and its failure modes often forces the safety analysts to devote much of their effort to gathering architectural details about the system behavior from several sources and embedding this information in the safety artifacts such as the fault trees. This report describes Model-Based Safety Analysis, an approach in which the system and safety engineers share a common system model created using a model-based development process. By extending the system model with a fault model as well as relevant portions of the physical system to be controlled, automated support can be provided for much of the safety analysis. We believe that by using a common model for both system and safety engineering and automating parts of the safety analysis, we can both reduce the cost and improve the quality of the safety analysis. Here we present our vision of model-based safety analysis and discuss the advantages and challenges in making this approach practical.

  12. A model of the proton translocation mechanism of complex I.

    PubMed

    Treberg, Jason R; Brand, Martin D

    2011-05-20

    Despite decades of speculation, the proton pumping mechanism of complex I (NADH-ubiquinone oxidoreductase) is unknown and continues to be controversial. Recent descriptions of the architecture of the hydrophobic region of complex I have resolved one vital issue: this region appears to have multiple proton transporters that are mechanically interlinked. Thus, transduction of conformational changes to drive the transmembrane transporters linked by a "connecting rod" during the reduction of ubiquinone (Q) can account for two or three of the four protons pumped per NADH oxidized. The remaining proton(s) must be pumped by direct coupling at the Q-binding site. Here, we present a mixed model based on a crucial constraint: the strong dependence on the pH gradient across the membrane (ΔpH) of superoxide generation at the Q-binding site of complex I. This model combines direct and indirect coupling mechanisms to account for the pumping of the four protons. It explains the observed properties of the semiquinone in the Q-binding site, the rapid superoxide production from this site during reverse electron transport, its low superoxide production during forward electron transport except in the presence of inhibitory Q-analogs and high protonmotive force, and the strong dependence of both modes of superoxide production on ΔpH. PMID:21454533

  13. A Model of the Proton Translocation Mechanism of Complex I*

    PubMed Central

    Treberg, Jason R.; Brand, Martin D.

    2011-01-01

    Despite decades of speculation, the proton pumping mechanism of complex I (NADH-ubiquinone oxidoreductase) is unknown and continues to be controversial. Recent descriptions of the architecture of the hydrophobic region of complex I have resolved one vital issue: this region appears to have multiple proton transporters that are mechanically interlinked. Thus, transduction of conformational changes to drive the transmembrane transporters linked by a “connecting rod” during the reduction of ubiquinone (Q) can account for two or three of the four protons pumped per NADH oxidized. The remaining proton(s) must be pumped by direct coupling at the Q-binding site. Here, we present a mixed model based on a crucial constraint: the strong dependence on the pH gradient across the membrane (ΔpH) of superoxide generation at the Q-binding site of complex I. This model combines direct and indirect coupling mechanisms to account for the pumping of the four protons. It explains the observed properties of the semiquinone in the Q-binding site, the rapid superoxide production from this site during reverse electron transport, its low superoxide production during forward electron transport except in the presence of inhibitory Q-analogs and high protonmotive force, and the strong dependence of both modes of superoxide production on ΔpH. PMID:21454533

  14. Inverse modeling of geochemical and mechanical compaction in sedimentary basins

    NASA Astrophysics Data System (ADS)

    Colombo, Ivo; Porta, Giovanni Michele; Guadagnini, Alberto

    2015-04-01

    We study key phenomena driving the feedback between sediment compaction processes and fluid flow in stratified sedimentary basins formed through lithification of sand and clay sediments after deposition. Processes we consider are mechanic compaction of the host rock and the geochemical compaction due to quartz cementation in sandstones. Key objectives of our study include (i) the quantification of the influence of the uncertainty of the model input parameters on the model output and (ii) the application of an inverse modeling technique to field scale data. Proper accounting of the feedback between sediment compaction processes and fluid flow in the subsurface is key to quantify a wide set of environmentally and industrially relevant phenomena. These include, e.g., compaction-driven brine and/or saltwater flow at deep locations and its influence on (a) tracer concentrations observed in shallow sediments, (b) build up of fluid overpressure, (c) hydrocarbon generation and migration, (d) subsidence due to groundwater and/or hydrocarbons withdrawal, and (e) formation of ore deposits. Main processes driving the diagenesis of sediments after deposition are mechanical compaction due to overburden and precipitation/dissolution associated with reactive transport. The natural evolution of sedimentary basins is characterized by geological time scales, thus preventing direct and exhaustive measurement of the system dynamical changes. The outputs of compaction models are plagued by uncertainty because of the incomplete knowledge of the models and parameters governing diagenesis. Development of robust methodologies for inverse modeling and parameter estimation under uncertainty is therefore crucial to the quantification of natural compaction phenomena. We employ a numerical methodology based on three building blocks: (i) space-time discretization of the compaction process; (ii) representation of target output variables through a Polynomial Chaos Expansion (PCE); and (iii) model

  15. Computational study of dislocation based mechanisms in FCC materials

    NASA Astrophysics Data System (ADS)

    Yellakara, Ranga Nikhil

    Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechanical behavior of metallic alloys, particularly focusing on face centered cubic (FCC) structured metals through a unique computational methodology called three-dimensional dislocation dynamics (3D-DD). In these simulations, the equations of motion for dislocations are mathematically solved to determine the evolution and interaction of dislocations. Microstructure details and stress-strain curves are a direct observation in the simulation and can be used to validate experimental results. The effect of initial dislocation microstructure on the yield strength has been studied. It has been shown that dislocation density based crystal plasticity formulations only work when dislocation densities/numbers are sufficiently large so that a statistically accurate description of the microstructure can be obtainable. The evolution of the flow stress for grain sizes ranging from 0.5 to 10 mum under uniaxial tension was simulated using an improvised model by integrating dislocation pile-up mechanism at grain boundaries has been performed. This study showed that for a same initial dislocation density, the Hall--Petch relationship holds well at small grain sizes (0.5--2 mum), beyond which the yield strength remains constant as the grain size increases. Various dislocation-particle interaction mechanisms have been introduced and investigations were made on their effect on the uniaxial tensile properties. These studies suggested that increase in particle volume fraction and decrease in particle

  16. Constraint Based Modeling Going Multicellular

    PubMed Central

    Martins Conde, Patricia do Rosario; Sauter, Thomas; Pfau, Thomas

    2016-01-01

    Constraint based modeling has seen applications in many microorganisms. For example, there are now established methods to determine potential genetic modifications and external interventions to increase the efficiency of microbial strains in chemical production pipelines. In addition, multiple models of multicellular organisms have been created including plants and humans. While initially the focus here was on modeling individual cell types of the multicellular organism, this focus recently started to switch. Models of microbial communities, as well as multi-tissue models of higher organisms have been constructed. These models thereby can include different parts of a plant, like root, stem, or different tissue types in the same organ. Such models can elucidate details of the interplay between symbiotic organisms, as well as the concerted efforts of multiple tissues and can be applied to analyse the effects of drugs or mutations on a more systemic level. In this review we give an overview of the recent development of multi-tissue models using constraint based techniques and the methods employed when investigating these models. We further highlight advances in combining constraint based models with dynamic and regulatory information and give an overview of these types of hybrid or multi-level approaches. PMID:26904548

  17. Modelling for the mechanical behavior of cementitious granular materials

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoxiong

    Crack damages due to load application are commonly observed in cementitious granular materials such as concrete, cemented sand, and ceramic materials. Previous analytical models for these types of materials have been developed based on continuum mechanics using a phenomenological approach. However, the theories of continuum mechanics have limitations when used for analyzing fracture mechanism and localized damages at a micro-scale level. Therefore, a microstructural approach is desirable for the analysis of these types of materials. In this dissertation, a contact law was derived for the inter-particle behavior of two particles connected by a cement binder. Microcracking process within binder was fully taken into account by regarding crack length as a basic damage factor. The binder initially contains small-size cracks which propagate and grow under external loading. As a result the binder is weakened with lower strength in shear and tension. Theory of fracture mechanics was employed to model the propagation and growth of these microcracks for both the shear fracture mode and normal fracture mode. The contact law was then incorporated in the analysis for the overall damage behaviors of cementitious granular material using the statistical micromechanics approach and the distinct element method. These overall damage behaviors include the stress-strain relationship, fracture strength, development of damage zone, and fatigue deformation. The micro-parameters affecting these behaviors are mainly the microcrack length and density, binder toughness, and binder elastic constants. In the numerical simulations, the cementitious granular materials were represented by 2-D random assemblies of rods bonded by cement binders with preexisting microcracks. Stress-strain relationships were modeled and validated for the uniaxial tension and compression tests, biaxial tension and compression tests, and double cantilever beam test. Force-deflection relationship and fatigue deformation

  18. Visual-adaptation-mechanism based underwater object extraction

    NASA Astrophysics Data System (ADS)

    Chen, Zhe; Wang, Huibin; Xu, Lizhong; Shen, Jie

    2014-03-01

    Due to the major obstacles originating from the strong light absorption and scattering in a dynamic underwater environment, underwater optical information acquisition and processing suffer from effects such as limited range, non-uniform lighting, low contrast, and diminished colors, causing it to become the bottleneck for marine scientific research and projects. After studying and generalizing the underwater biological visual mechanism, we explore its advantages in light adaption which helps animals to precisely sense the underwater scene and recognize their prey or enemies. Then, aiming to transform the significant advantage of the visual adaptation mechanism into underwater computer vision tasks, a novel knowledge-based information weighting fusion model is established for underwater object extraction. With this bionic model, the dynamical adaptability is given to the underwater object extraction task, making them more robust to the variability of the optical properties in different environments. The capability of the proposed method to adapt to the underwater optical environments is shown, and its outperformance for the object extraction is demonstrated by comparison experiments.

  19. Modeling Guru: Knowledge Base for NASA Modelers

    NASA Astrophysics Data System (ADS)

    Seablom, M. S.; Wojcik, G. S.; van Aartsen, B. H.

    2009-05-01

    Modeling Guru is an on-line knowledge-sharing resource for anyone involved with or interested in NASA's scientific models or High End Computing (HEC) systems. Developed and maintained by the NASA's Software Integration and Visualization Office (SIVO) and the NASA Center for Computational Sciences (NCCS), Modeling Guru's combined forums and knowledge base for research and collaboration is becoming a repository for the accumulated expertise of NASA's scientific modeling and HEC communities. All NASA modelers and associates are encouraged to participate and provide knowledge about the models and systems so that other users may benefit from their experience. Modeling Guru is divided into a hierarchy of communities, each with its own set forums and knowledge base documents. Current modeling communities include those for space science, land and atmospheric dynamics, atmospheric chemistry, and oceanography. In addition, there are communities focused on NCCS systems, HEC tools and libraries, and programming and scripting languages. Anyone may view most of the content on Modeling Guru (available at http://modelingguru.nasa.gov/), but you must log in to post messages and subscribe to community postings. The site offers a full range of "Web 2.0" features, including discussion forums, "wiki" document generation, document uploading, RSS feeds, search tools, blogs, email notification, and "breadcrumb" links. A discussion (a.k.a. forum "thread") is used to post comments, solicit feedback, or ask questions. If marked as a question, SIVO will monitor the thread, and normally respond within a day. Discussions can include embedded images, tables, and formatting through the use of the Rich Text Editor. Also, the user can add "Tags" to their thread to facilitate later searches. The "knowledge base" is comprised of documents that are used to capture and share expertise with others. The default "wiki" document lets users edit within the browser so others can easily collaborate on the

  20. "Piekara's Chair": Mechanical Model for Atomic Energy Levels.

    ERIC Educational Resources Information Center

    Golab-Meyer, Zofia

    1991-01-01

    Uses the teaching method of models or analogies, specifically the model called "Piekara's chair," to show how teaching classical mechanics can familiarize students with the notion of energy levels in atomic physics. (MDH)

  1. 16. YAZOO BACKWATER PUMPING STATION MODEL, YAZOO RIVER BASIN. MECHANICAL ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    16. YAZOO BACKWATER PUMPING STATION MODEL, YAZOO RIVER BASIN. MECHANICAL AND HYDRAULIC ENGINEERS EXAMINING MODEL PUMPS. - Waterways Experiment Station, Hydraulics Laboratory, Halls Ferry Road, 2 miles south of I-20, Vicksburg, Warren County, MS

  2. Mechanically based generative laws of morphogenesis

    NASA Astrophysics Data System (ADS)

    Beloussov, Lev V.

    2008-03-01

    A deep (although at the first glance naïve) question which may be addressed to embryonic development is why during this process quite definite and accurately reproduced successions of precise and complicated shapes are taking place, or why, in several cases, the result of development is highly precise in spite of an extensive variability of intermediate stages. This problem can be attacked in two different ways. One of them, up to now just slightly employed, is to formulate robust macroscopic generative laws from which the observed successions of shapes could be derived. Another one, which dominates in modern embryology, regards the development as a succession of highly precise 'micropatterns', each of them arising due to the action of specific factors, having, as a rule, nothing in common with each other. We argue that the latter view contradicts a great bulk of firmly established data and gives no satisfactory answers to the main problems of development. Therefore we intend to follow the first way. By doing this, we regard developing embryos as self-organized systems transpierced by feedbacks among which we pay special attention to those linked with mechanical stresses (MS). We formulate a hypothesis of so-called MS hyper-restoration as a common basis for the developmentally important feedback loops. We present a number of examples confirming this hypothesis and use it for reconstructing prolonged chains of developmental events. Finally, we discuss the application of the same set of assumptions to the first steps of egg development and to the internal differentiation of embryonic cells.

  3. Model to Estimate Threshold Mechanical Stability of Lower Lateral Cartilage

    PubMed Central

    Kim, James Hakjune; Hamamoto, Ashley; Kiyohara, Nicole; Wong, Brian J. F.

    2015-01-01

    IMPORTANCE In rhinoplasty, techniques used to alter the shape of the nasal tip often compromise the structural stability of the cartilage framework in the nose. Determining the minimum threshold level of cartilage stiffness required to maintain long-term structural stability is a critical aspect in performing these surgical maneuvers. OBJECTIVE To quantify the minimum threshold mechanical stability (elastic modulus) of lower lateral cartilage (LLC) according to expert opinion. METHODS Five anatomically correct LLC phantoms were made from urethane via a 3-dimensional computer modeling and injection molding process. All 5 had identical geometry but varied in stiffness along the intermediate crural region (0.63–30.6 MPa). DESIGN, SETTING, AND PARTICIPANTS A focus group of experienced rhinoplasty surgeons (n = 33) was surveyed at a regional professional meeting on October 25, 2013. Each survey participant was presented the 5 phantoms in a random order and asked to arrange the phantoms in order of increasing stiffness based on their sense of touch. Then, they were asked to select a single phantom out of the set that they believed to have the minimum acceptable mechanical stability for LLC to maintain proper form and function. MAIN OUTCOMES AND MEASURES A binary logistic regression was performed to calculate the probability of mechanical acceptability as a function of the elastic modulus of the LLC based on survey data. A Hosmer-Lemeshow test was performed to measure the goodness of fit between the logistic regression and survey data. The minimum threshold mechanical stability for LLC was taken at a 50% acceptability rating. RESULTS Phantom 4 was selected most frequently by the participants as having the minimum acceptable stiffness for LLC intermediate care. The minimum threshold mechanical stability for LLC was determined to be 3.65 MPa. The Hosmer-Lemeshow test revealed good fit between the logistic regression and survey data ( χ32=0.92 , P = .82). CONCLUSIONS AND

  4. Hierarchical parameter identification in models of respiratory mechanics.

    PubMed

    Schranz, C; Knöbel, C; Kretschmer, J; Zhao, Z; Möller, K

    2011-11-01

    Potential harmful effects of ventilation therapy could be reduced by model-based predictions of the effects of ventilator settings to the patient. To obtain optimal predictions, the model has to be individualized based on patients' data. Given a nonlinear model, the result of parameter identification using iterative numerical methods depends on initial estimates. In this work, a feasible hierarchical identification process is proposed and compared to the commonly implemented direct approach with randomized initial values. The hierarchical approach is exemplarily illustrated by identifying the viscoelastic model (VEM) of respiratory mechanics, whose a priori identifiability was proven. To demonstrate its advantages over the direct approach, two different data sources were employed. First, correctness of the approach was shown with simulation data providing controllable conditions. Second, the clinical potential was evaluated under realistic conditions using clinical data from 13 acute respiratory distress syndrome (ARDS) patients. Simulation data revealed that the success rate of the direct approach exponentially decreases with increasing deviation of the initial estimates while the hierarchical approach always obtained the correct solution. The average computing time using clinical data for the direct approach equals 4.77 s (SD  =  1.32) and 2.41 s (SD  =  0.01) for the hierarchical approach. These investigations demonstrate that a hierarchical approach may be beneficial with respect to robustness and efficiency using simulated and clinical data. PMID:21880567

  5. Solitons in Skyrme - Faddeev spinor model and quantum mechanics

    NASA Astrophysics Data System (ADS)

    Rybakov, Y.

    2016-07-01

    We discuss the possibility of unification of Skyrme and Faddeev approaches for the description of baryons and leptons respectively as topological solitons within the scope of 16-spinor model. The motivation for such a unification is based on a special 8- semispinor identity invented by the Italian geometrician F. Brioschi. This remarkable identity permits one to realize baryon or lepton states through the effect of spontaneous symmetry breaking emerging due to special structure of the Higgs potential in the model. At large distances from the particle - soliton small excitation of the vacuum satisfies Klein - Gordon equation with some mass that permits one to establish the correspondence with quantum mechanics in special stochastic representation of the wave function for extended particles - solitons. Finally, we illustrate the peculiar properties of stochastic representation by the famous T. Young's experiment with n slits in soliton realization.

  6. Pathway Model and Nonextensive Statistical Mechanics

    NASA Astrophysics Data System (ADS)

    Mathai, A. M.; Haubold, H. J.; Tsallis, C.

    2015-12-01

    The established technique of eliminating upper or lower parameters in a general hypergeometric series is profitably exploited to create pathways among confluent hypergeometric functions, binomial functions, Bessel functions, and exponential series. One such pathway, from the mathematical statistics point of view, results in distributions which naturally emerge within nonextensive statistical mechanics and Beck-Cohen superstatistics, as pursued in generalizations of Boltzmann-Gibbs statistics.

  7. New Mechanical Model for the Transmutation Fuel Performance Code

    SciTech Connect

    Gregory K. Miller

    2008-04-01

    A new mechanical model has been developed for implementation into the TRU fuel performance code. The new model differs from the existing FRAPCON 3 model, which it is intended to replace, in that it will include structural deformations (elasticity, plasticity, and creep) of the fuel. Also, the plasticity algorithm is based on the “plastic strain–total strain” approach, which should allow for more rapid and assured convergence. The model treats three situations relative to interaction between the fuel and cladding: (1) an open gap between the fuel and cladding, such that there is no contact, (2) contact between the fuel and cladding where the contact pressure is below a threshold value, such that axial slippage occurs at the interface, and (3) contact between the fuel and cladding where the contact pressure is above a threshold value, such that axial slippage is prevented at the interface. The first stage of development of the model included only the fuel. In this stage, results obtained from the model were compared with those obtained from finite element analysis using ABAQUS on a problem involving elastic, plastic, and thermal strains. Results from the two analyses showed essentially exact agreement through both loading and unloading of the fuel. After the cladding and fuel/clad contact were added, the model demonstrated expected behavior through all potential phases of fuel/clad interaction, and convergence was achieved without difficulty in all plastic analysis performed. The code is currently in stand alone form. Prior to implementation into the TRU fuel performance code, creep strains will have to be added to the model. The model will also have to be verified against an ABAQUS analysis that involves contact between the fuel and cladding.

  8. Bipotential continuum models for granular mechanics

    NASA Astrophysics Data System (ADS)

    Goddard, Joe

    2014-03-01

    Most currently popular continuum models for granular media are special cases of a generalized Maxwell fluid model, which describes the evolution of stress and internal variables such as granular particle fraction and fabric,in terms of imposed strain rate. It is shown how such models can be obtained from two scalar potentials, a standard elastic free energy and a ``dissipation potential'' given rigorously by the mathematical theory of Edelen. This allows for a relatively easy derivation of properly invariant continuum models for granular media and fluid-particle suspensions within a thermodynamically consistent framework. The resulting continuum models encompass all the prominent regimes of granular flow, ranging from the quasi-static to rapidly sheared, and are readily extended to include higher-gradient or Cosserat effects. Models involving stress diffusion, such as that proposed recently by Kamrin and Koval (PRL 108 178301), provide an alternative approach that is mentioned in passing. This paper provides a brief overview of a forthcoming review articles by the speaker (The Princeton Companion to Applied Mathematics, and Appl. Mech. Rev.,in the press, 2013).

  9. Model-based machine learning

    PubMed Central

    Bishop, Christopher M.

    2013-01-01

    Several decades of research in the field of machine learning have resulted in a multitude of different algorithms for solving a broad range of problems. To tackle a new application, a researcher typically tries to map their problem onto one of these existing methods, often influenced by their familiarity with specific algorithms and by the availability of corresponding software implementations. In this study, we describe an alternative methodology for applying machine learning, in which a bespoke solution is formulated for each new application. The solution is expressed through a compact modelling language, and the corresponding custom machine learning code is then generated automatically. This model-based approach offers several major advantages, including the opportunity to create highly tailored models for specific scenarios, as well as rapid prototyping and comparison of a range of alternative models. Furthermore, newcomers to the field of machine learning do not have to learn about the huge range of traditional methods, but instead can focus their attention on understanding a single modelling environment. In this study, we show how probabilistic graphical models, coupled with efficient inference algorithms, provide a very flexible foundation for model-based machine learning, and we outline a large-scale commercial application of this framework involving tens of millions of users. We also describe the concept of probabilistic programming as a powerful software environment for model-based machine learning, and we discuss a specific probabilistic programming language called Infer.NET, which has been widely used in practical applications. PMID:23277612

  10. Model-based machine learning.

    PubMed

    Bishop, Christopher M

    2013-02-13

    Several decades of research in the field of machine learning have resulted in a multitude of different algorithms for solving a broad range of problems. To tackle a new application, a researcher typically tries to map their problem onto one of these existing methods, often influenced by their familiarity with specific algorithms and by the availability of corresponding software implementations. In this study, we describe an alternative methodology for applying machine learning, in which a bespoke solution is formulated for each new application. The solution is expressed through a compact modelling language, and the corresponding custom machine learning code is then generated automatically. This model-based approach offers several major advantages, including the opportunity to create highly tailored models for specific scenarios, as well as rapid prototyping and comparison of a range of alternative models. Furthermore, newcomers to the field of machine learning do not have to learn about the huge range of traditional methods, but instead can focus their attention on understanding a single modelling environment. In this study, we show how probabilistic graphical models, coupled with efficient inference algorithms, provide a very flexible foundation for model-based machine learning, and we outline a large-scale commercial application of this framework involving tens of millions of users. We also describe the concept of probabilistic programming as a powerful software environment for model-based machine learning, and we discuss a specific probabilistic programming language called Infer.NET, which has been widely used in practical applications. PMID:23277612

  11. A poroviscohyperelastic model for numerical analysis of mechanical behavior of single chondrocyte.

    PubMed

    Nguyen, Trung Dung; Oloyede, Adekunle; Gu, Yuantong

    2016-01-01

    The aim of this paper is to use a poroviscohyperelastic (PVHE) model, which is developed based on the porohyperelastic (PHE) model to explore the mechanical deformation properties of single chondrocytes. Both creep and relaxation responses are investigated by using finite element analysis models of micropipette aspiration and atomic force microscopy experiments, respectively. The newly developed PVHE model is compared thoroughly with the standard neo-Hookean solid and PHE models. It has been found that the PVHE can accurately capture both creep and stress relaxation behaviors of chondrocytes better than other two models. Hence, the PVHE is a promising model to investigate mechanical properties of single chondrocytes. PMID:25588670

  12. Mouse models of neural tube defects: investigating preventive mechanisms.

    PubMed

    Greene, Nicholas D E; Copp, Andrew J

    2005-05-15

    Neural tube defects (NTD), including anencephaly and spina bifida, are a group of severe congenital abnormalities in which the future brain and/or spinal cord fail to close. In mice, NTD may result from genetic mutations or knockouts, or from exposure to teratogenic agents, several of which are known risk factors in humans. Among the many mouse NTD models that have been identified to date, a number have been tested for possible primary prevention of NTD by exogenous agents, such as folic acid. In genetic NTD models such as Cart1, splotch, Cited2, and crooked tail, and NTD induced by teratogens including valproic acid and fumonisins, the incidence of defects is reduced by maternal folic acid supplementation. These folate-responsive models provide an opportunity to investigate the possible mechanisms underlying prevention of NTD by folic acid in humans. In another group of mouse models, that includes curly tail, axial defects, and the Ephrin-A5 knockout, NTD are not preventable by folic acid, reflecting the situation in humans in which a subset of NTD appear resistant to folic acid therapy. In this group of mutants alternative preventive agents, including inositol and methionine, have been shown to be effective. Overall, the data from mouse models suggests that a broad-based in utero therapy may offer scope for prevention of a greater proportion of NTD than is currently possible. PMID:15800852

  13. Insight into model mechanisms through automatic parameter fitting: a new methodological framework for model development

    PubMed Central

    2014-01-01

    Background Striking a balance between the degree of model complexity and parameter identifiability, while still producing biologically feasible simulations using modelling is a major challenge in computational biology. While these two elements of model development are closely coupled, parameter fitting from measured data and analysis of model mechanisms have traditionally been performed separately and sequentially. This process produces potential mismatches between model and data complexities that can compromise the ability of computational frameworks to reveal mechanistic insights or predict new behaviour. In this study we address this issue by presenting a generic framework for combined model parameterisation, comparison of model alternatives and analysis of model mechanisms. Results The presented methodology is based on a combination of multivariate metamodelling (statistical approximation of the input–output relationships of deterministic models) and a systematic zooming into biologically feasible regions of the parameter space by iterative generation of new experimental designs and look-up of simulations in the proximity of the measured data. The parameter fitting pipeline includes an implicit sensitivity analysis and analysis of parameter identifiability, making it suitable for testing hypotheses for model reduction. Using this approach, under-constrained model parameters, as well as the coupling between parameters within the model are identified. The methodology is demonstrated by refitting the parameters of a published model of cardiac cellular mechanics using a combination of measured data and synthetic data from an alternative model of the same system. Using this approach, reduced models with simplified expressions for the tropomyosin/crossbridge kinetics were found by identification of model components that can be omitted without affecting the fit to the parameterising data. Our analysis revealed that model parameters could be constrained to a standard

  14. Uncertainty quantification in modeling HIV viral mechanics.

    PubMed

    Banks, H T; Baraldi, Robert; Cross, Karissa; Flores, Kevin; McChesney, Christina; Poag, Laura; Thorpe, Emma

    2015-10-01

    We consider an in-host model for HIV-1 infection dynamics developed and validated with patient data in earlier work [7]. We revisit the earlier model in light of progress over the last several years in understanding HIV-1 progression in humans. We then consider statistical models to describe the data and use these with residual plots in generalized least squares problems to develop accurate descriptions of the proper weights for the data. We use recent parameter subset selection techniques [5,6] to investigate the impact of estimated parameters on the corresponding selection scores. Bootstrapping and asymptotic theory are compared in the context of confidence intervals for the resulting parameter estimates. PMID:26280189

  15. Understanding the mechanism of base development of HSQ

    SciTech Connect

    Kim, Jihoon; Chao, Weilun; Griedel, Brian; Liang, Xiaogan; Lewis, Mark; Hilken, Dawn; Olynick, Deirdre

    2009-06-16

    We study the dissolution mechanism of HSQ (hydrogen silsesquioxane) in base solutions with the addition of chloride salts to elucidate the development mechanism. Reaction mechanisms are proposed based on the dissolution mechanism of quartz. Development kinetics points to two dose-dependent development mechanisms. Considering ion sizes, both hydrated and non-hydrated, and ion exchange, we propose that a combination of a surface dominated reaction at higher doses and a matrix dominated reaction at lower doses accounts for the high development contrast with a NaOH base/NaCl salt mixture. The interplay between the hydrated and non-hydrated ion size leads to higher contrast developers, such as tetramethyl ammonium hydroxide (TMAH) with NaCl.

  16. Gallium nitride-based micro-opto-electro-mechanical systems

    NASA Astrophysics Data System (ADS)

    Stonas, Andreas Robert

    Gallium Nitride and its associated alloys InGaN and AlGaN have many material properties that are highly desirable for micro-electro-mechanical systems (MEMS), and more specifically micro-opto-electro-mechanical systems (MOEMS). The group III-nitrides are tough, stiff, optically transparent, direct bandgap, chemically inert, highly piezoelectric, and capable of functioning at high temperatures. There is currently no other semiconductor system that possesses all of these properties. Taken together, these attributes make the nitrides prime candidates not only for creating new versions of existing device structures, but also for creating entirely unique devices which combine these properties in novel ways. Unfortunately, their chemical resiliency also makes the group III-nitrides extraordinarily difficult to shape into devices. In particular, until this research, no undercut etch technology existed that could controllably separate a selected part of a MEMS device from its sapphire or silicon carbide substrate. This has effectively prevented GaN-based MEMS from being developed. This dissertation describes how this fabrication obstacle was overcome by a novel etching geometry (bandgap-selective backside-illuminated photoelectochemical (BS-BIPEC) etching) and its resulting morphologies. Several gallium-nitride based MEMS devices were created, actuated, and modelled, including cantilevers and membranes. We describe in particular our pursuit of one of the many novel device elements that is possible only in this material system: a transducer that uses an externally applied strain to dynamically change the optical transition energy of a quantum well. While the device objective of a dynamically tunable quantum well was not achieved, we have demonstrated sufficient progress to believe that such a device will be possible soon. We have observed a shift (5.5meV) of quantum well transition energies in released structures, and we have created structures that can apply large biaxial

  17. Pyrolysis mechanisms of lignin model compounds

    SciTech Connect

    Britt, P.F.; Buchanan, A.C. III; Cooney, M.J.

    1997-06-01

    The flash vacuum pyrolysis of lignin model compounds was studied under conditions optimized for the production of liquid products to provide mechanistic insight into the reaction pathways that lead to product formation. The major reaction products can be explained by cleavage of the C-O either linkage by a free radial or concerted 1,2-elimination.

  18. Quark Model in the Quantum Mechanics Curriculum.

    ERIC Educational Resources Information Center

    Hussar, P. E.; And Others

    1980-01-01

    This article discusses in detail the totally symmetric three-quark karyonic wave functions. The two-body mesonic states are also discussed. A brief review of the experimental efforts to identify the quark model multiplets is given. (Author/SK)

  19. Putting mechanisms into crop production models.

    PubMed

    Boote, Kenneth J; Jones, James W; White, Jeffrey W; Asseng, Senthold; Lizaso, Jon I

    2013-09-01

    Crop growth models dynamically simulate processes of C, N and water balance on daily or hourly time-steps to predict crop growth and development and at season-end, final yield. Their ability to integrate effects of genetics, environment and crop management have led to applications ranging from understanding gene function to predicting potential impacts of climate change. The history of crop models is reviewed briefly, and their level of mechanistic detail for assimilation and respiration, ranging from hourly leaf-to-canopy assimilation to daily radiation-use efficiency is discussed. Crop models have improved steadily over the past 30-40 years, but much work remains. Improvements are needed for the prediction of transpiration response to elevated CO₂ and high temperature effects on phenology and reproductive fertility, and simulation of root growth and nutrient uptake under stressful edaphic conditions. Mechanistic improvements are needed to better connect crop growth to genetics and to soil fertility, soil waterlogging and pest damage. Because crop models integrate multiple processes and consider impacts of environment and management, they have excellent potential for linking research from genomics and allied disciplines to crop responses at the field scale, thus providing a valuable tool for deciphering genotype by environment by management effects. PMID:23600481

  20. Dynamic modeling and identification of a slider-crank mechanism

    NASA Astrophysics Data System (ADS)

    Ha, Jih-Lian; Fung, Rong-Fong; Chen, Kun-Yung; Hsien, Shao-Chien

    2006-02-01

    In this paper, Hamilton's principle, Lagrange multiplier, geometric constraints and partitioning method are employed to derive the dynamic equations of a slider-crank mechanism driven by a servomotor. The formulation is expressed by only one independent variable and considers the effects of mass, external force and motor electric inputs. Comparing the dynamic responses between the experimental results and numerical simulations, the dynamic modeling gives a wonderful interpretation of a slider-crank mechanism. The parameters of many industrial machines are difficult to obtain if these machines cannot be taken apart. In this paper, a new identification method based on the real-coded genetic algorithm (RGA) is presented to identify the parameters of a slider-crank mechanism. The method promotes the calculation efficiency very much, and is calculated by the real-code without the operations of encoding and decoding. The results of numerical simulations and the experiments prove that the identification method is feasible. Finally, the experimental results by the RGA and the recursive least squares (RLS) are also compared.

  1. Statistical mechanical models of virus capsid assembly

    NASA Astrophysics Data System (ADS)

    Hicks, Stephen Daniel

    Viruses have become an increasingly popular subject of physics investigation, particularly in the last decade. Advances in imaging of virus capsids---the protective protein shells---in a wide variety of stages of assembly have encouraged physical assembly models at a similarly wide variety of scales, while the apparent simplicity of the capsid system---typically, many identical units assembling spontaneously into an icosahedrally symmetric (rather than amorphous) shell---makes the problem particularly interesting. We take a look at the existing physical assembly models in light of the question of how a particular assembly target can be consistently achieved in the presence of so many possible incorrect results. This review leads us to pose our own model of fully irreversible virus assembly, which we study in depth using a large ensemble of simulated assembled capsids, generated under a variety of capsid shell elastic parameters. While this irreversible model (predictably) did not yield consistently symmetric results, we do glean some insight into the effect of elasticity on growth, as well as an understanding of common failure modes. In particular, we found that (i) capsid size depends strongly on the spontaneous curvature and weakly on the ratio of bending to stretching elastic stiffnesses, (ii) the probability of successful capsid completion decays exponentially with capsid size, and (iii) the degree of localization of Gaussian curvature depends heavily on the ratio of elastic stiffnesses. We then go on to consider more thoroughly the nature of the ensemble of symmetric and almost-symmetric capsids---ultimately computing a phase diagram of minimum-energy capsids as a function of the two above-mentioned elastic parameters---and also look at a number of modifications we can make to our irreversible model, finally putting forth a rather different type of model potentially appropriate for understanding immature HIV assembly, and concluding with a fit of this new

  2. Statistical mechanical modeling: Computer simulations, analysis and applications

    NASA Astrophysics Data System (ADS)

    Subramanian, Balakrishna

    This thesis describes the applications of statistical mechanical models and tools, especially computational techniques to the study of several problems in science. We study in chapter 2, various properties of a non-equilibrium cellular automaton model, the Toom model. We obtain numerically the exponents describing the fluctuations of the interface between the two stable phases of the model. In chapter 3, we introduce a binary alloy model with three-body potentials. Unlike the usual Ising-type models with two-body interactions, this model is not symmetric in its components. We calculate the exact low temperature phase diagram using Pirogov-Sinai theory and also find the mean-field equilibrium properties of this model. We then study the kinetics of phase segregation following a quenching in this model. We find that the results are very similar to those obtained for Ising-type models with pair interactions, indicating universality. In chapter 4, we discuss the statistical properties of "Contact Maps". These maps, are used to represent three-dimensional structures of proteins in modeling problems. We find that this representation space has particular properties that make it a convenient choice. The maps representing native folds of proteins correspond to compact structures which in turn correspond to maps with low degeneracy, making it easier to translate the map into the detailed 3-dimensional structure. The early stage of formation of a river network is described in Chapter 5 using quasi-random spanning trees on a square lattice. We observe that the statistical properties generated by these models are quite similar (better than some of the earlier models) to the empirical laws and results presented by geologists for real river networks. Finally, in chapter 6 we present a brief note on our study of the problem of progression of heterogeneous breast tumors. We investigate some of the possible pathways of progression based on the traditional notions of DCIS (Ductal

  3. Studies on sulfate attack: Mechanisms, test methods, and modeling

    NASA Astrophysics Data System (ADS)

    Santhanam, Manu

    concentration of the solution were seen to change the rate and mechanism of the attack in both sodium and magnesium sulfate solutions. The test results from these experiments were used to generate models for prediction of physical properties such as expansion and mass change, which could be used either for service life predictions, or for designing more reliable laboratory tests. Lastly, mechanisms for the attack by sodium and magnesium sulfate were proposed, based on the observations in the various studies. These mechanisms were able to simplify the understanding of the sulfate attack phenomenon.

  4. Sketch-based geologic modeling

    NASA Astrophysics Data System (ADS)

    Rood, M. P.; Jackson, M.; Hampson, G.; Brazil, E. V.; de Carvalho, F.; Coda, C.; Sousa, M. C.; Zhang, Z.; Geiger, S.

    2015-12-01

    Two-dimensional (2D) maps and cross-sections, and 3D conceptual models, are fundamental tools for understanding, communicating and modeling geology. Yet geologists lack dedicated and intuitive tools that allow rapid creation of such figures and models. Standard drawing packages produce only 2D figures that are not suitable for quantitative analysis. Geologic modeling packages can produce 3D models and are widely used in the groundwater and petroleum communities, but are often slow and non-intuitive to use, requiring the creation of a grid early in the modeling workflow and the use of geostatistical methods to populate the grid blocks with geologic information. We present an alternative approach to rapidly create figures and models using sketch-based interface and modelling (SBIM). We leverage methods widely adopted in other industries to prototype complex geometries and designs. The SBIM tool contains built-in geologic rules that constrain how sketched lines and surfaces interact. These rules are based on the logic of superposition and cross-cutting relationships that follow from rock-forming processes, including deposition, deformation, intrusion and modification by diagenesis or metamorphism. The approach allows rapid creation of multiple, geologically realistic, figures and models in 2D and 3D using a simple, intuitive interface. The user can sketch in plan- or cross-section view. Geologic rules are used to extrapolate sketched lines in real time to create 3D surfaces. Quantitative analysis can be carried our directly on the models. Alternatively, they can be output as simple figures or imported directly into other modeling tools. The software runs on a tablet PC and can be used in a variety of settings including the office, classroom and field. The speed and ease of use of SBIM enables multiple interpretations to be developed from limited data, uncertainty to be readily appraised, and figures and models to be rapidly updated to incorporate new data or concepts.

  5. Tractor Mechanic--Student Material. Competency Based Education Curriculum.

    ERIC Educational Resources Information Center

    McCann, Edward W.

    Developed to assist vocational agricultural mechanics students in learning to be tractor mechanics, this curriculum guide contains all the student competency sheets which comprise this competency-based curriculum. These competency sheets are categorized under sixteen instructional units. The first two units cover employment opportunities and…

  6. Carbon-based nano-electro-mechanical systems

    NASA Astrophysics Data System (ADS)

    Kaul, A. B.; Khan, A. R.; Megerian, K. G.; Epp, L.; LeDuc, H. G.; Bagge, L.; Jennings, A. T.; Jang, D.; Greer, J. R.

    2010-04-01

    We provide an overview of our work where carbon-based nanostructures have been applied to twodimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were implemented for forming bridge-type 2D NEMS switches, where switching voltages were on the order of a few volts. In the second configuration, vertically oriented carbon nanofibers (CNFs) synthesized using plasma-enhanced (PE) CVD have been explored for their potential application in 3D NEMS. We have performed nanomechanical measurements on such vertically oriented tubes using nanoindentation to determine the mechanical properties of the CNFs. Electrostatic switching was demonstrated in the CNFs synthesized on refractory metallic nitride substrates, where a nanoprobe was used as the actuating electrode inside a scanning-electron-microscope. The switching voltages were determined to be in the tens of volts range and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical pull-in voltage which was compared to experimental results.

  7. Carbon-Based Nano-Electro-Mechanical-Systems

    NASA Technical Reports Server (NTRS)

    Kaul, A. B.; Khan, A. R.; Megerian, K. G.; Epp, L.; LeDuc, G.; Bagge, L.; Jennings, A. T.; Jang, D.; Greer, J. R.

    2011-01-01

    We provide an overview of our work where carbon-based nanostructures have been applied to two-dimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were implemented for forming bridge-type 2D NEMS switches, where switching voltages were on the order of a few volts. In the second configuration, vertically oriented carbon nanofibers (CNFs) synthesized using plasma-enhanced (PE) CVD have been explored for their potential application in 3D NEMS. We have performed nanomechanical measurements on such vertically oriented tubes using nanoindentation to determine the mechanical properties of the CNFs. Electrostatic switching was demonstrated in the CNFs synthesized on refractory metallic nitride substrates, where a nanoprobe was used as the actuating electrode inside a scanning-electron-microscope. The switching voltages were determined to be in the tens of volts range and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical pull-in voltage which was compared to experimental results.

  8. A Computer-based Course in Classical Mechanics.

    ERIC Educational Resources Information Center

    Kane, D.; Sherwood, B.

    1980-01-01

    Describes and illustrates the tutorial and homework exercise lessons, student routing, course organization, administration, and evaluation of a PLATO computer-based course in classical mechanics. An appendix lists 41 lessons developed for the course. (CMV)

  9. A polycrystalline modeling of the mechanical behavior of neutron irradiated zirconium alloys

    NASA Astrophysics Data System (ADS)

    Onimus, Fabien; Béchade, Jean-Luc

    2009-02-01

    Zirconium alloys used as fuel cladding tubes in the nuclear industry undergo important changes after neutron irradiation in the microstructure as well as in the mechanical properties. However, the effects of the specific post-irradiation deformation mechanisms on the mechanical behavior are not clearly understood and modeled. Based on experimental results it is discussed that the kinematic strain hardening is increased by the plastic strain localization inside the dislocation channels as well as the only basal slip activation observed for specific mechanical tests. From this analysis, the first polycrystalline model is developed for irradiated zirconium alloys, taking into account the irradiation induced hardening, the intra-granular softening as well as the intra-granular kinematic strain hardening due to the plastic strain localization inside the channels. This physically based model reproduces the mechanical behavior in agreement with the slip systems observed. In addition, this model reproduces the Bauschinger effect observed during low cycle fatigue as well as the cyclic strain softening.

  10. MODELING GLUTAMATERGIC SYNAPSES: INSIGHTS INTO MECHANISMS REGULATING SYNAPTIC EFFICACY

    PubMed Central

    BOUTEILLER, JEAN-MARIE C.; BAUDRY, MICHEL; ALLAM, SUSHMITA L.; GREGET, RENAUD J.; BISCHOFF, SERGE; BERGER, THEODORE W.

    2010-01-01

    The hippocampal formation is critically involved for the long-term storage of various forms of information, and it is widely believed that the phenomenon of long-term potentiation (LTP) of synaptic transmission is a molecular/cellular mechanism participating in memory formation. Although several high level models of hippocampal function have been developed, they do not incorporate detailed molecular information of the type necessary to understand the contribution of individual molecular events to the mechanisms underlying LTP and learning and memory. We are therefore developing new technological tools based on mathematical modeling and computer simulation of the molecular processes taking place in realistic biological networks to reach such an understanding. This article briefly summarizes the approach we are using and illustrates it by presenting data regarding the effects of changing the number of AMPA receptors on various features of glutamatergic transmission, including NMDA receptor-mediated responses and paired-pulse facilitation. We conclude by discussing the significance of these results and providing some ideas for future directions with this approach. PMID:18763719

  11. Modeling tailed bacteriophage adsorption: Insight into mechanisms.

    PubMed

    Storms, Zachary J; Sauvageau, Dominic

    2015-11-01

    The process of a bacteriophage attaching to its host cell is a combination of physical diffusion, biochemical surface interactions, and reaction-induced conformational changes in receptor proteins. Local variations in the physico-chemical properties of the medium, the phage׳s mode of action, and the physiology of the host cell also all influence adsorption kinetics. These characteristics can affect a specific phage׳s binding capabilities and the susceptibility of the host cell to phage attack. Despite the complexity of this process, describing adsorption kinetics of a population of bacteriophages binding to a culture of cells has been accomplished with relatively simple equations governed by the laws of mass-action. Many permutations and modifications to the basic set of reactions have been suggested through the years. While no single solution emerges as a universal answer, this review provides the fundamentals of current phage adsorption modeling and will guide researchers in the selection of valid, appropriate models. PMID:26331682

  12. A model of the mechanism of cooperativity and associativity of long-term potentiation in the hippocampus: a fundamental mechanism of associative memory and learning.

    PubMed

    Kitajima, T; Hara, K

    1991-01-01

    Long-Term Potentiation (LTP) has three properties: (1) input specificity, (2) cooperativity and (3) associativity. In a previous paper, we proposed an integrated model of the mechanisms of the induction and maintenance of LTP with input specificity. In this paper, a model of the mechanism of cooperative and associative LTP is described. According to computer simulations of the model, its mechanism is based on the spread of synaptic potentials. PMID:2049412

  13. Fluid mechanics in stented arterial model

    NASA Astrophysics Data System (ADS)

    Bernad, S. I.; Totorean, A.; Bosioc, A.; Crainic, N.; Hudrea, C.; Bernad, E. S.

    2015-12-01

    Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. Strut shape, strut thickness and the distance between consecutive struts have been associated clinically with the with post-intervention clinical outcomes. Hemodynamically favorable designs according to computational modeling can reduced in-stent restenosis after coronary stenting intervention.

  14. Quantum mechanical model in gravity theory

    NASA Astrophysics Data System (ADS)

    Losyakov, V. V.

    2016-05-01

    We consider a model of a real massive scalar field defined as homogeneous on a d-dimensional sphere such that the sphere radius, time scale, and scalar field are related by the equations of the general theory of relativity. We quantize this system with three degrees of freedom, define the observables, and find dynamical mean values of observables in the regime where the scalar field mass is much less than the Planck mass.

  15. Statistical mechanics model of angiogenic tumor growth.

    PubMed

    Ferreira, António Luis; Lipowska, Dorota; Lipowski, Adam

    2012-01-01

    We examine a lattice model of tumor growth where the survival of tumor cells depends on the supplied nutrients. When such a supply is random, the extinction of tumors belongs to the directed percolation universality class. However, when the supply is correlated with the distribution of tumor cells, which as we suggest might mimic the angiogenic growth, the extinction shows different critical behavior. Such a correlation affects also the morphology of the growing tumors and drastically raises tumor-survival probability. PMID:22400505

  16. Mathematical model of depolarization mechanism of conducted vasoreactivity

    NASA Astrophysics Data System (ADS)

    Neganova, Anastasiia Y.; Stiukhina, Elena S.; Postnov, Dmitry E.

    2015-03-01

    We address the problem of conducted vasodilation, the phenomenon which is also known as functional hyperemia. Specifically, we test the mechanism of nondecremental propagation of electric signals along endothelial cell layer recently hypothesized by Figueroa et al. By means of functional modeling we focus on possible nonlinear mechanisms that can underlie such regenerative pulse transmission (RPT). Since endothelial cells (EC) are generally known as electrically inexcitable, the possible role of ECs in RPT mechanisms is not evident. By means of mathematical modeling we check the dynamical self-consistency of Figueroa's hypothesis, as well as estimate the possible contribution of specific ionic currents to the suggested RPT mechanism.

  17. Mechanical modeling of the growth of salt structures

    SciTech Connect

    Alfaro, R.A.M.

    1993-05-01

    A 2D numerical model for studying the morphology and history of salt structures by way of computer simulations is presented. The model is based on conservation laws for physical systems, a fluid marker equation to keep track of the salt/sediments interface, and two constitutive laws for rocksalt. When buoyancy alone is considered, the fluid-assisted diffusion model predicts evolution of salt structures 2.5 times faster than the power-law creep model. Both rheological laws predict strain rates of the order of 4.0 {times} 10{sup {minus}15}s{sup {minus}1} for similar structural maturity level of salt structures. Equivalent stresses and viscosities predicted by the fluid-assisted diffusion law are 10{sup 2} times smaller than those predicted by the power-law creep rheology. Use of East Texas Basin sedimentation rates and power-law creep rheology indicate that differential loading is an effective mechanism to induce perturbations that amplify and evolve to mature salt structures, similar to those observed under natural geological conditions.

  18. An Action-Based Fine-Grained Access Control Mechanism for Structured Documents and Its Application

    PubMed Central

    Su, Mang; Li, Fenghua; Tang, Zhi; Yu, Yinyan; Zhou, Bo

    2014-01-01

    This paper presents an action-based fine-grained access control mechanism for structured documents. Firstly, we define a describing model for structured documents and analyze the application scenarios. The describing model could support the permission management on chapters, pages, sections, words, and pictures of structured documents. Secondly, based on the action-based access control (ABAC) model, we propose a fine-grained control protocol for structured documents by introducing temporal state and environmental state. The protocol covering different stages from document creation, to permission specification and usage control are given by using the Z-notation. Finally, we give the implementation of our mechanism and make the comparisons between the existing methods and our mechanism. The result shows that our mechanism could provide the better solution of fine-grained access control for structured documents in complicated networks. Moreover, it is more flexible and practical. PMID:25136651

  19. Exploring host-guest complexation mechanisms by a molecular dynamics/quantum mechanics/continuum solvent model approach

    NASA Astrophysics Data System (ADS)

    Ye, Renlong; Nie, Xuemei; Zhou, Yumei; Wong, Chung F.; Gong, Xuedong; Jiang, Wei; Tang, Weihua; Wang, Yan A.; Heine, Thomas; Zhou, Baojing

    2016-03-01

    We introduce a molecular dynamics/quantum mechanics/continuum solvent model (MD/QM/CSM) approach to investigate binding mechanisms of host-guest systems. The representative conformations of host, guest, and their complex generated from MD simulations at the molecular-mechanics level are used for binding free energy calculations based on a QM/CSM model. We use this approach to explore the binding mechanisms of β-cyclodextrin (β-CD) and 2, 6-di-methyl-β-CD (DM-β-CD) with various guest molecules. Our results suggest that solvent effects play a more important role in determining the relative binding affinities of DM-β-CD than those of β-CD mainly because the former is more flexible than the latter.

  20. RASopathies: unraveling mechanisms with animal models

    PubMed Central

    Jindal, Granton A.; Goyal, Yogesh; Burdine, Rebecca D.; Rauen, Katherine A.; Shvartsman, Stanislav Y.

    2015-01-01

    ABSTRACT RASopathies are developmental disorders caused by germline mutations in the Ras-MAPK pathway, and are characterized by a broad spectrum of functional and morphological abnormalities. The high incidence of these disorders (∼1/1000 births) motivates the development of systematic approaches for their efficient diagnosis and potential treatment. Recent advances in genome sequencing have greatly facilitated the genotyping and discovery of mutations in affected individuals, but establishing the causal relationships between molecules and disease phenotypes is non-trivial and presents both technical and conceptual challenges. Here, we discuss how these challenges could be addressed using genetically modified model organisms that have been instrumental in delineating the Ras-MAPK pathway and its roles during development. Focusing on studies in mice, zebrafish and Drosophila, we provide an up-to-date review of animal models of RASopathies at the molecular and functional level. We also discuss how increasingly sophisticated techniques of genetic engineering can be used to rigorously connect changes in specific components of the Ras-MAPK pathway with observed functional and morphological phenotypes. Establishing these connections is essential for advancing our understanding of RASopathies and for devising rational strategies for their management and treatment. PMID:26203125

  1. RASopathies: unraveling mechanisms with animal models.

    PubMed

    Jindal, Granton A; Goyal, Yogesh; Burdine, Rebecca D; Rauen, Katherine A; Shvartsman, Stanislav Y

    2015-08-01

    RASopathies are developmental disorders caused by germline mutations in the Ras-MAPK pathway, and are characterized by a broad spectrum of functional and morphological abnormalities. The high incidence of these disorders (∼1/1000 births) motivates the development of systematic approaches for their efficient diagnosis and potential treatment. Recent advances in genome sequencing have greatly facilitated the genotyping and discovery of mutations in affected individuals, but establishing the causal relationships between molecules and disease phenotypes is non-trivial and presents both technical and conceptual challenges. Here, we discuss how these challenges could be addressed using genetically modified model organisms that have been instrumental in delineating the Ras-MAPK pathway and its roles during development. Focusing on studies in mice, zebrafish and Drosophila, we provide an up-to-date review of animal models of RASopathies at the molecular and functional level. We also discuss how increasingly sophisticated techniques of genetic engineering can be used to rigorously connect changes in specific components of the Ras-MAPK pathway with observed functional and morphological phenotypes. Establishing these connections is essential for advancing our understanding of RASopathies and for devising rational strategies for their management and treatment. PMID:26203125

  2. Material removal mechanism of copper chemical mechanical polishing in a periodate-based slurry

    NASA Astrophysics Data System (ADS)

    Cheng, Jie; Wang, Tongqing; He, Yongyong; Lu, Xinchun

    2015-05-01

    The material removal mechanism of copper in a periodate-based slurry during barrier layer chemical mechanical polishing (CMP) has not been intensively investigated. This paper presents a study of the copper surface film chemistry and mechanics in a periodate-based slurry. On this basis, the controlling factor of the copper CMP material removal mechanism is proposed. The results show that the chemical and electrochemical reaction products on the copper surface are complex and vary considerably as a function of the solution pH. Under acidic conditions (pH 4) the copper surface underwent strong chemical dissolution while the corrosion was mild and uniform under alkaline conditions (pH 11). The corrosion effect was the lowest in near neutral solutions because the surface was covered with non-uniform Cu(IO3)2·H2O/Cu-periodate/copper oxides films, which had better passivation effect. The surface film thickness and mechanical removal properties were studied by AES and AFM nano-scratch tests. Based on the combined surface film analysis and CMP experiment results, it can be concluded that the controlling factor during copper CMP in a periodate-based slurry is the chemical-enhanced mechanical removal of the surface films. The periodate-based slurry should be modified by the addition of corrosion inhibitors and complexing agents to achieve a good copper surface quality with moderate chemical dissolution.

  3. PHYSIOLOGICALLY-BASED PHARMACOKINETIC MODELING

    EPA Science Inventory

    Physiologically-based pharmacokinetic (PB-PK) models attempt to provide both a realistic anatomic description of the animal to which a drug or toxic chemical has been administered and a biologically accurate representation of the physiological pathways for chemical storage, metab...

  4. Aging mechanism in model Pickering emulsion.

    PubMed

    Fouilloux, Sarah; Malloggi, Florent; Daillant, Jean; Thill, Antoine

    2016-01-21

    We study the stability of a model Pickering emulsion system using fluorinated oil and functionalized silica nanoparticles. A special counter-flow microfluidic set-up was used to prepare monodisperse oil droplets in water. The wettability of the monodisperse silica nanoparticles (NPs) could be tuned by surface grafting and the surface coverage of the droplets was controlled using the microfluidic setup. For surface coverage as low as 23%, we observed a regime of Pickering emulsion stability where the surface coverage of emulsion droplets of constant size increases with time, coexisting with an excess of oil phase. Our results demonstrate that the previously observed limited coalescence regime where surface coverage tends to control the average size of the final droplets must be put in a broader perspective. PMID:26549639

  5. An improved anti-leech mechanism based on session identifier

    NASA Astrophysics Data System (ADS)

    Zhang, Jianbiao; Zhu, Tong; Zhang, Han; Lin, Li

    2012-01-01

    With the rapid development of information technology and extensive requirement of network resource sharing, plenty of resource hotlinking phenomenons appear on the internet. The hotlinking problem not only harms the interests of legal websites but also leads to a great affection to fair internet environment. The anti-leech technique based on session identifier is highly secure, but the transmission of session identifier in plaintext form causes some security flaws. In this paper, a proxy hotlinking technique based on session identifier is introduced firstly to illustrate these security flaws; next, this paper proposes an improved anti-leech mechanism based on session identifier, the mechanism takes the random factor as the core and detects hotlinking request using a map table that contains random factor, user's information and time stamp; at last the paper analyzes the security of mechanism in theory. The result reveals that the improved mechanism has the merits of simple realization, high security and great flexibility.

  6. An improved anti-leech mechanism based on session identifier

    NASA Astrophysics Data System (ADS)

    Zhang, Jianbiao; Zhu, Tong; Zhang, Han; Lin, Li

    2011-12-01

    With the rapid development of information technology and extensive requirement of network resource sharing, plenty of resource hotlinking phenomenons appear on the internet. The hotlinking problem not only harms the interests of legal websites but also leads to a great affection to fair internet environment. The anti-leech technique based on session identifier is highly secure, but the transmission of session identifier in plaintext form causes some security flaws. In this paper, a proxy hotlinking technique based on session identifier is introduced firstly to illustrate these security flaws; next, this paper proposes an improved anti-leech mechanism based on session identifier, the mechanism takes the random factor as the core and detects hotlinking request using a map table that contains random factor, user's information and time stamp; at last the paper analyzes the security of mechanism in theory. The result reveals that the improved mechanism has the merits of simple realization, high security and great flexibility.

  7. United polarizable multipole water model for molecular mechanics simulation

    NASA Astrophysics Data System (ADS)

    Qi, Rui; Wang, Lee-Ping; Wang, Qiantao; Pande, Vijay S.; Ren, Pengyu

    2015-07-01

    We report the development of a united AMOEBA (uAMOEBA) polarizable water model, which is computationally 3-5 times more efficient than the three-site AMOEBA03 model in molecular dynamics simulations while providing comparable accuracy for gas-phase and liquid properties. In this coarse-grained polarizable water model, both electrostatic (permanent and induced) and van der Waals representations have been reduced to a single site located at the oxygen atom. The permanent charge distribution is described via the molecular dipole and quadrupole moments and the many-body polarization via an isotropic molecular polarizability, all located at the oxygen center. Similarly, a single van der Waals interaction site is used for each water molecule. Hydrogen atoms are retained only for the purpose of defining local frames for the molecular multipole moments and intramolecular vibrational modes. The parameters have been derived based on a combination of ab initio quantum mechanical and experimental data set containing gas-phase cluster structures and energies, and liquid thermodynamic properties. For validation, additional properties including dimer interaction energy, liquid structures, self-diffusion coefficient, and shear viscosity have been evaluated. The results demonstrate good transferability from the gas to the liquid phase over a wide range of temperatures, and from nonpolar to polar environments, due to the presence of molecular polarizability. The water coordination, hydrogen-bonding structure, and dynamic properties given by uAMOEBA are similar to those derived from the all-atom AMOEBA03 model and experiments. Thus, the current model is an accurate and efficient alternative for modeling water.

  8. United polarizable multipole water model for molecular mechanics simulation

    PubMed Central

    Qi, Rui; Wang, Lee-Ping; Wang, Qiantao; Pande, Vijay S.; Ren, Pengyu

    2015-01-01

    We report the development of a united AMOEBA (uAMOEBA) polarizable water model, which is computationally 3–5 times more efficient than the three-site AMOEBA03 model in molecular dynamics simulations while providing comparable accuracy for gas-phase and liquid properties. In this coarse-grained polarizable water model, both electrostatic (permanent and induced) and van der Waals representations have been reduced to a single site located at the oxygen atom. The permanent charge distribution is described via the molecular dipole and quadrupole moments and the many-body polarization via an isotropic molecular polarizability, all located at the oxygen center. Similarly, a single van der Waals interaction site is used for each water molecule. Hydrogen atoms are retained only for the purpose of defining local frames for the molecular multipole moments and intramolecular vibrational modes. The parameters have been derived based on a combination of ab initio quantum mechanical and experimental data set containing gas-phase cluster structures and energies, and liquid thermodynamic properties. For validation, additional properties including dimer interaction energy, liquid structures, self-diffusion coefficient, and shear viscosity have been evaluated. The results demonstrate good transferability from the gas to the liquid phase over a wide range of temperatures, and from nonpolar to polar environments, due to the presence of molecular polarizability. The water coordination, hydrogen-bonding structure, and dynamic properties given by uAMOEBA are similar to those derived from the all-atom AMOEBA03 model and experiments. Thus, the current model is an accurate and efficient alternative for modeling water. PMID:26156485

  9. United polarizable multipole water model for molecular mechanics simulation.

    PubMed

    Qi, Rui; Wang, Lee-Ping; Wang, Qiantao; Pande, Vijay S; Ren, Pengyu

    2015-07-01

    We report the development of a united AMOEBA (uAMOEBA) polarizable water model, which is computationally 3-5 times more efficient than the three-site AMOEBA03 model in molecular dynamics simulations while providing comparable accuracy for gas-phase and liquid properties. In this coarse-grained polarizable water model, both electrostatic (permanent and induced) and van der Waals representations have been reduced to a single site located at the oxygen atom. The permanent charge distribution is described via the molecular dipole and quadrupole moments and the many-body polarization via an isotropic molecular polarizability, all located at the oxygen center. Similarly, a single van der Waals interaction site is used for each water molecule. Hydrogen atoms are retained only for the purpose of defining local frames for the molecular multipole moments and intramolecular vibrational modes. The parameters have been derived based on a combination of ab initio quantum mechanical and experimental data set containing gas-phase cluster structures and energies, and liquid thermodynamic properties. For validation, additional properties including dimer interaction energy, liquid structures, self-diffusion coefficient, and shear viscosity have been evaluated. The results demonstrate good transferability from the gas to the liquid phase over a wide range of temperatures, and from nonpolar to polar environments, due to the presence of molecular polarizability. The water coordination, hydrogen-bonding structure, and dynamic properties given by uAMOEBA are similar to those derived from the all-atom AMOEBA03 model and experiments. Thus, the current model is an accurate and efficient alternative for modeling water. PMID:26156485

  10. United polarizable multipole water model for molecular mechanics simulation

    SciTech Connect

    Qi, Rui; Wang, Qiantao; Ren, Pengyu; Wang, Lee-Ping; Pande, Vijay S.

    2015-07-07

    We report the development of a united AMOEBA (uAMOEBA) polarizable water model, which is computationally 3–5 times more efficient than the three-site AMOEBA03 model in molecular dynamics simulations while providing comparable accuracy for gas-phase and liquid properties. In this coarse-grained polarizable water model, both electrostatic (permanent and induced) and van der Waals representations have been reduced to a single site located at the oxygen atom. The permanent charge distribution is described via the molecular dipole and quadrupole moments and the many-body polarization via an isotropic molecular polarizability, all located at the oxygen center. Similarly, a single van der Waals interaction site is used for each water molecule. Hydrogen atoms are retained only for the purpose of defining local frames for the molecular multipole moments and intramolecular vibrational modes. The parameters have been derived based on a combination of ab initio quantum mechanical and experimental data set containing gas-phase cluster structures and energies, and liquid thermodynamic properties. For validation, additional properties including dimer interaction energy, liquid structures, self-diffusion coefficient, and shear viscosity have been evaluated. The results demonstrate good transferability from the gas to the liquid phase over a wide range of temperatures, and from nonpolar to polar environments, due to the presence of molecular polarizability. The water coordination, hydrogen-bonding structure, and dynamic properties given by uAMOEBA are similar to those derived from the all-atom AMOEBA03 model and experiments. Thus, the current model is an accurate and efficient alternative for modeling water.

  11. Links between fluid mechanics and quantum mechanics: a model for information in economics?

    PubMed

    Haven, Emmanuel

    2016-05-28

    This paper tallies the links between fluid mechanics and quantum mechanics, and attempts to show whether those links can aid in beginning to build a formal template which is usable in economics models where time is (a)symmetric and memory is absent or present. An objective of this paper is to contemplate whether those formalisms can allow us to model information in economics in a novel way. PMID:27091173

  12. A simple polymeric model describes cell nuclear mechanical response

    NASA Astrophysics Data System (ADS)

    Banigan, Edward; Stephens, Andrew; Marko, John

    The cell nucleus must continually resist inter- and intracellular mechanical forces, and proper mechanical response is essential to basic cell biological functions as diverse as migration, differentiation, and gene regulation. Experiments probing nuclear mechanics reveal that the nucleus stiffens under strain, leading to two characteristic regimes of force response. This behavior depends sensitively on the intermediate filament protein lamin A, which comprises the outer layer of the nucleus, and the properties of the chromatin interior. To understand these mechanics, we study a simulation model of a polymeric shell encapsulating a semiflexible polymer. This minimalistic model qualitatively captures the typical experimental nuclear force-extension relation and observed nuclear morphologies. Using a Flory-like theory, we explain the simulation results and mathematically estimate the force-extension relation. The model and experiments suggest that chromatin organization is a dominant contributor to nuclear mechanics, while the lamina protects cell nuclei from large deformations.

  13. Knowledge-based design of complex mechanical systems

    SciTech Connect

    Ishii, K.

    1988-01-01

    The recent development of Artificial Intelligence (AI) techniques allows incorporation of qualitative aspects of design into the computer aids. This thesis presents a framework for applying AI techniques to the design of complex mechanical systems. A complex, yet well-understood design example as a vehicle for the effort is used. The author first reviews how experienced designers use knowledge at various stages of system design. He then proposes a knowledge-based model of the design process and develop frameworks for applying knowledge engineering in order to construct a consultation system for the designers. He proposes four such frameworks for use at different stages of design: (1) Design Compatibility Analysis (DCA) analyzes the compatibility of the designer's design alternatives with the design specification, (2) Initial Design Suggestion (IDS) provides the designer with reasonable initial estimates of the design variables, (3) Rule-based Sensitivity Analysis (RSA) guides the user through redesign, and (4) Active Constraint Deduction (ACD) identifies the bottlenecks of design by heuristic knowledge. These frameworks eliminate unnecessary iterations and allows the user to obtain a satisfactory solution rapidly.

  14. Wetting mechanisms of gel-based controlled-release fertilizers.

    PubMed

    Shavit, U; Reiss, M; Shaviv, A

    2003-02-14

    The release mechanism of gel-based controlled release fertilizers (CRFs) involves water penetration into dry mixtures of fertilizers and gel forming polymers. Water penetration provides an upper limit to the whole release process. Where wetting prediction is often based on models that describe the flow of the liquid phase, vapor motion may become significant when a sharp wetting front exists. In this study we examine the role of vapor and fluid flows in the wetting process of CRFs consisting of urea or KNO(3) mixed with polyacrylamide (PAM). Vapor adsorption isotherms were obtained for typical fertilizer-PAM mixtures. Wetting and release experiments were conducted by dividing the CRFs into regions alternately filled with a pure fertilizer and mixtures of PAM and fertilizer. The experiments were designed in such a way that when the wetting front reaches a mixtures interface, its motion depends on the gradient imposed by the difference in osmotic potential (OP). The coupled equations of vapor and liquid flow in initially dry conditions were solved numerically to demonstrate the conceptual understanding gained by the experiments. The results show that wetting front motion is affected by transport and adsorption of vapor. It was also shown that the release rate is different when wetting is governed by vapor flow or by liquid flow. The release pattern from a multi-regions device was consistent with the wetting pattern, demonstrating the possibility to tailor the release according to periods of peak demand. PMID:12586505

  15. Market-based control mechanisms for patient safety

    PubMed Central

    Coiera, E; Braithwaite, J

    2009-01-01

    A new model is proposed for enhancing patient safety using market-based control (MBC), inspired by successful approaches to environmental governance. Emissions trading, enshrined in the Kyoto protocol, set a carbon price and created a carbon market—is it possible to set a patient safety price and let the marketplace find ways of reducing clinically adverse events? To “cap and trade,” a regulator would need to establish system-wide and organisation-specific targets, based on the cost of adverse events, create a safety market for trading safety credits and then police the market. Organisations are given a clear policy signal to reduce adverse event rates, are told by how much, but are free to find mechanisms best suited to their local needs. The market would inevitably generate novel ways of creating safety credits, and accountability becomes hard to evade when adverse events are explicitly measured and accounted for in an organisation’s bottom line. PMID:19342522

  16. A new algorithm for modeling friction in dynamic mechanical systems

    NASA Technical Reports Server (NTRS)

    Hill, R. E.

    1988-01-01

    A method of modeling friction forces that impede the motion of parts of dynamic mechanical systems is described. Conventional methods in which the friction effect is assumed a constant force, or torque, in a direction opposite to the relative motion, are applicable only to those cases where applied forces are large in comparison to the friction, and where there is little interest in system behavior close to the times of transitions through zero velocity. An algorithm is described that provides accurate determination of friction forces over a wide range of applied force and velocity conditions. The method avoids the simulation errors resulting from a finite integration interval used in connection with a conventional friction model, as is the case in many digital computer-based simulations. The algorithm incorporates a predictive calculation based on initial conditions of motion, externally applied forces, inertia, and integration step size. The predictive calculation in connection with an external integration process provides an accurate determination of both static and Coulomb friction forces and resulting motions in dynamic simulations. Accuracy of the results is improved over that obtained with conventional methods and a relatively large integration step size is permitted. A function block for incorporation in a specific simulation program is described. The general form of the algorithm facilitates implementation with various programming languages such as FORTRAN or C, as well as with other simulation programs.

  17. Observations and Modeling of the Component Mechanisms in Deflagration

    NASA Astrophysics Data System (ADS)

    Smilowitz, Laura; Henson, Bryan; Oschwald, David; Novak, Alan; Holmes, Matthew

    2013-06-01

    We have used dynamic x-ray and proton radiography to observe the behavior of a series of HMX based energetic materials formulations undergoing thermal explosions. The result of these observations is a mechanism for deflagration based on both gas phase convective burning and solid phase conductive burning. The velocities for both the convective and conductive burns are tied together by the single combustion pressure driving both in a single experiment. The convective rate is directly measured as the burn front in the radiographs. The pressure associated with that rate is inferred from independently measured burn rate verses pressure data. This same pressure is then assumed to drive the conductive burning which begins as the convective burn front lights the material surface. Using a single, independently validated particle size distribution for damaged HMX, the combination of pressure driven convective lighting and conductive consumption is then calculated and compared to the measured transmission data sets. This same model with different initial pressurizations is used to successfully model deflagration in PBX9501, PBXN-9, and LX-07. In addition, a correlation between initial pressurization, convective/conductive velocity, and final ``reaction violence'' is observed. This leads us to the use of convective velocity as a metric for final energy release rate and therefore overall reaction violence.

  18. Mechanical models for the self-organization of tubular patterns

    PubMed Central

    2013-01-01

    Organogenesis, such as long tubule self-organization, requires long-range coordination of cell mechanics to arrange cell positions and to remodel the extracellular matrix. While the current mainstream in the field of tissue morphogenesis focuses primarily on genetics and chemical signaling, the influence of cell mechanics on the programming of patterning cues in tissue morphogenesis has not been adequately addressed. Here, we review experimental evidence and propose quantitative mechanical models by which cells can create tubular patterns. PMID:23719257

  19. A Simplified Quantum Mechanical Model of Diatomic Molecules

    ERIC Educational Resources Information Center

    Nielsen, Lars Drud

    1978-01-01

    Introduces a simple one-dimensional model of a diatomic molecule that can explain all the essential features of a real two particle quantum mechanical system and gives quantitative results in fair agreement with those of a hydrogen molecule. (GA)

  20. Modeling complex diffusion mechanisms in L1 2 -structured compounds

    NASA Astrophysics Data System (ADS)

    Zacate, M. O.; Lape, M.; Stufflebeam, M.; Evenson, W. E.

    2010-04-01

    We report on a procedure developed to create stochastic models of hyperfine interactions for complex diffusion mechanisms and demonstrate its application to simulate perturbed angular correlation spectra for the divacancy and 6-jump cycle diffusion mechanisms in L12-structured compounds.

  1. Haptics-based dynamic implicit solid modeling.

    PubMed

    Hua, Jing; Qin, Hong

    2004-01-01

    This paper systematically presents a novel, interactive solid modeling framework, Haptics-based Dynamic Implicit Solid Modeling, which is founded upon volumetric implicit functions and powerful physics-based modeling. In particular, we augment our modeling framework with a haptic mechanism in order to take advantage of additional realism associated with a 3D haptic interface. Our dynamic implicit solids are semi-algebraic sets of volumetric implicit functions and are governed by the principles of dynamics, hence responding to sculpting forces in a natural and predictable manner. In order to directly manipulate existing volumetric data sets as well as point clouds, we develop a hierarchical fitting algorithm to reconstruct and represent discrete data sets using our continuous implicit functions, which permit users to further design and edit those existing 3D models in real-time using a large variety of haptic and geometric toolkits, and visualize their interactive deformation at arbitrary resolution. The additional geometric and physical constraints afford more sophisticated control of the dynamic implicit solids. The versatility of our dynamic implicit modeling enables the user to easily modify both the geometry and the topology of modeled objects, while the inherent physical properties can offer an intuitive haptic interface for direct manipulation with force feedback. PMID:15794139

  2. Quantum Mechanical Model Of Pulsar Glitches And Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Warszawski, Lila; Berloff, N. G.; Melatos, A.

    2009-12-01

    We present a quantum mechanical model of the timing irregularities (glitches) in pulsars. The model relies on the build up of differential rotation between the stellar crust and the interior superfluid due to the presence of pinned superfluid vortices. We employ the Gross-Pitaevskii equation to model computationally the dynamics of the superfluid condensate. By invoking conservation of angular momentum between the interior superfluid and the stellar crust, we provide proof of principle that stick-slip vortex motion, due to vortex pinning, can result in discrete changes in the spin frequency of the crust, analogous to glitches in pulsars. Using the time-varying superfluid velocity field (and hence time-varying current quadrupole moment), we calculate the amplitude, polarization, and frequency content of the burst gravitational wave signal from a single glitch, and cross-correlate the waveform with standard templates in burst pipelines. We also set out the conditions for the signal to be detectable by Advanced LIGO. Radio timing data show that glitch sizes follow a power law with an index that varies between pulsars, and the waiting times between successive glitches have a Poissonian distribution. Based on these statistical distributions, we estimate the combined stochastic gravitational wave signal emanating from a realistically distributed pulsar population in a Milky-Way-type galaxy.

  3. Applied mechanics modeling of granulated ceramic powder compaction

    SciTech Connect

    Mahoney, F.M.; Readey, M.J.

    1995-08-01

    In ceramic manufacturing processes such as dry-pressing, correlations between applied compacting pressure and resultant powder compact density are essential for defining reliable process conditions for ceramic components. Pressure-density diagrams have been developed as a tool for both process control and for understanding the compaction behavior of different powders. These types of diagrams, however, pertain only to the averag@ properties of a powder compact and do not address a significant issue in powder compaction processes: the formation of density gradients within the compact. Continuum-based mechanics models of varying complexity have addressed the influence of frictional forces acting at the powder-die wall interface which dissipate the applied pressure throughout the compact. Resulting pressure distribution models are then typically coupled with empirical functions relating pressure and density to obtain a green density distribution in the compact. All of these models predict similar trends; however, none predict the distribution with sufficient accuracy to be considered as a design tool for industrial applications.

  4. Generation Mechanism of Alternans in Luo-Rudy Model

    NASA Astrophysics Data System (ADS)

    Kitajima, Hiroyuki; Ioka, Eri; Yazawa, Toru

    Electrical alternans is the alternating amplitude from beat to beat in the action potential of the cardiac cell. It has been associated with ventricular arrhythmias in many clinical studies; however, its dynamical mechanisms remain unknown. The reason is that we do not have realistic network models of the heart system. Recently, Yazawa clarified the network structure of the heart and the central nerve system in the crustacean heart. In this study, we construct a simple model of the heart system based on Yazawa’s experimental data. Using this model, we clarify that two parameters (the conductance of sodium ions and free concentration of potassium ions in the extracellular compartment) play the key roles of generating alternans. In particular, we clarify that the inactivation gate of the time-independent potassium channel is the most important parameter. Moreover, interaction between the membrane potential and potassium ionic currents is significant for generating alternate rhythms. This result indicates that if the muscle cell has problems such as channelopathies, there is great risk of generating alternans.

  5. Benefits of detailed models of muscle activation and mechanics

    NASA Technical Reports Server (NTRS)

    Lehman, S. L.; Stark, L.

    1981-01-01

    Recent biophysical and physiological studies identified some of the detailed mechanisms involved in excitation-contraction coupling, muscle contraction, and deactivation. Mathematical models incorporating these mechanisms allow independent estimates of key parameters, direct interplay between basic muscle research and the study of motor control, and realistic model behaviors, some of which are not accessible to previous, simpler, models. The existence of previously unmodeled behaviors has important implications for strategies of motor control and identification of neural signals. New developments in the analysis of differential equations make the more detailed models feasible for simulation in realistic experimental situations.

  6. Evaluating Arctic warming mechanisms in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Franzke, Christian L. E.; Lee, Sukyoung; Feldstein, Steven B.

    2016-07-01

    Arctic warming is one of the most striking signals of global warming. The Arctic is one of the fastest warming regions on Earth and constitutes, thus, a good test bed to evaluate the ability of climate models to reproduce the physics and dynamics involved in Arctic warming. Different physical and dynamical mechanisms have been proposed to explain Arctic amplification. These mechanisms include the surface albedo feedback and poleward sensible and latent heat transport processes. During the winter season when Arctic amplification is most pronounced, the first mechanism relies on an enhancement in upward surface heat flux, while the second mechanism does not. In these mechanisms, it has been proposed that downward infrared radiation (IR) plays a role to a varying degree. Here, we show that the current generation of CMIP5 climate models all reproduce Arctic warming and there are high pattern correlations—typically greater than 0.9—between the surface air temperature (SAT) trend and the downward IR trend. However, we find that there are two groups of CMIP5 models: one with small pattern correlations between the Arctic SAT trend and the surface vertical heat flux trend (Group 1), and the other with large correlations (Group 2) between the same two variables. The Group 1 models exhibit higher pattern correlations between Arctic SAT and 500 hPa geopotential height trends, than do the Group 2 models. These findings suggest that Arctic warming in Group 1 models is more closely related to changes in the large-scale atmospheric circulation, whereas in Group 2, the albedo feedback effect plays a more important role. Interestingly, while Group 1 models have a warm or weak bias in their Arctic SAT, Group 2 models show large cold biases. This stark difference in model bias leads us to hypothesize that for a given model, the dominant Arctic warming mechanism and trend may be dependent on the bias of the model mean state.

  7. Inferring brain-computational mechanisms with models of activity measurements.

    PubMed

    Kriegeskorte, Nikolaus; Diedrichsen, Jörn

    2016-10-01

    High-resolution functional imaging is providing increasingly rich measurements of brain activity in animals and humans. A major challenge is to leverage such data to gain insight into the brain's computational mechanisms. The first step is to define candidate brain-computational models (BCMs) that can perform the behavioural task in question. We would then like to infer which of the candidate BCMs best accounts for measured brain-activity data. Here we describe a method that complements each BCM by a measurement model (MM), which simulates the way the brain-activity measurements reflect neuronal activity (e.g. local averaging in functional magnetic resonance imaging (fMRI) voxels or sparse sampling in array recordings). The resulting generative model (BCM-MM) produces simulated measurements. To avoid having to fit the MM to predict each individual measurement channel of the brain-activity data, we compare the measured and predicted data at the level of summary statistics. We describe a novel particular implementation of this approach, called probabilistic representational similarity analysis (pRSA) with MMs, which uses representational dissimilarity matrices (RDMs) as the summary statistics. We validate this method by simulations of fMRI measurements (locally averaging voxels) based on a deep convolutional neural network for visual object recognition. Results indicate that the way the measurements sample the activity patterns strongly affects the apparent representational dissimilarities. However, modelling of the measurement process can account for these effects, and different BCMs remain distinguishable even under substantial noise. The pRSA method enables us to perform Bayesian inference on the set of BCMs and to recognize the data-generating model in each case.This article is part of the themed issue 'Interpreting BOLD: a dialogue between cognitive and cellular neuroscience'. PMID:27574316

  8. A numerical model for the mechanical behavior of intraplate volcanoes

    NASA Astrophysics Data System (ADS)

    Chevallier, Luc; Verwoerd, Wilhelm J.

    1988-05-01

    A new approach toward understanding the mechanical behavior of intraplate volcanoes is offered by first postulating a geological model of the internal structure and then developing an axisymmetric numerical simulation using the finite element method. This enables one to consider the types of fracturing at various depths in terms of state of stress under specific conditions of loading. The geological model is based on comparative field studies of three volcanically active oceanic islands (Marion, Tristan da Cunha, and Reunion) and a dormant one (Gough). The model contains a shallow (3 km deep) magma chamber with distinguishable floor, wall, and roof sections. A magma column rises from the chamber toward a central cone at the surface. Depending on the structural level at which they originate, different dyke and fracture patterns are generated. For the numerical simulation the medium is assumed to be linear elastic, continuous, and isotropic. Different loading combinations are applied, including hydrostatic pressure plus magmatic pressure in the chamber and external pressure that represents regional tectonic effects. It appears that the structural levels of the geological model can be adequately explained by variations in the distribution, intensity, and trajectories of principal stresses σ1, σ2, and σ3. It is concluded that the shape of the magma source is a major factor in the stress pattern. The effect of the driving pressure (Pmag - Pext) on the orientation of the principal stresses σ1 and σ2 is also considered. The sloped surface of the volcanic edifice is found to cause local rotation of the stress field. Finally, the evolution of the stress field with loading path is related to successive structural levels in a dynamic eruptive model.

  9. Thermal fluid-solid interaction model and experimental validation for hydrostatic mechanical face seals

    NASA Astrophysics Data System (ADS)

    Huang, Weifeng; Liao, Chuanjun; Liu, Xiangfeng; Suo, Shuangfu; Liu, Ying; Wang, Yuming

    2014-09-01

    Hydrostatic mechanical face seals for reactor coolant pumps are very important for the safety and reliability of pressurized-water reactor power plants. More accurate models on the operating mechanism of the seals are needed to help improve their performance. The thermal fluid-solid interaction (TFSI) mechanism of the hydrostatic seal is investigated in this study. Numerical models of the flow field and seal assembly are developed. Based on the mechanism for the continuity condition of the physical quantities at the fluid-solid interface, an on-line numerical TFSI model for the hydrostatic mechanical seal is proposed using an iterative coupling method. Dynamic mesh technology is adopted to adapt to the changing boundary shape. Experiments were performed on a test rig using a full-size test seal to obtain the leakage rate as a function of the differential pressure. The effectiveness and accuracy of the TFSI model were verified by comparing the simulation results and experimental data. Using the TFSI model, the behavior of the seal is presented, including mechanical and thermal deformation, and the temperature field. The influences of the rotating speed and differential pressure of the sealing device on the temperature field, which occur widely in the actual use of the seal, are studied. This research proposes an on-line and assembly-based TFSI model for hydrostatic mechanical face seals, and the model is validated by full-sized experiments.

  10. Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet

    SciTech Connect

    Frisch, Josef; Chang, Allison; Decker, Valentin; Doyle, Eric; Eriksson, Leif; Hendrickson, Linda; Himel, Thomas; Markiewicz, Thomas; Partridge, Richard; Seryi, Andrei; /SLAC

    2006-09-28

    The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system.

  11. Shape memory-based actuators and release mechanisms therefrom

    NASA Technical Reports Server (NTRS)

    Vaidyanathan, Rajan (Inventor); Snyder, Daniel W. (Inventor); Schoenwald, David K. (Inventor); Lam, Nhin S. (Inventor); Watson, Daniel S. (Inventor); Krishnan, Vinu B. (Inventor); Noebe, Ronald D. (Inventor)

    2012-01-01

    SM-based actuators (110) and release mechanisms (100) therefrom and systems (500) including one or more release mechanisms (100). The actuators (110) comprise a SM member (118) and a deformable member (140) mechanically coupled to the SM member (118) which deforms upon a shape change of the SM member triggered by a phase transition of the SM member. A retaining element (160) is mechanically coupled to the deformable member (140), wherein the retaining element (160) moves upon the shape change. Release mechanism (100) include an actuator, a rotatable mechanism (120) including at least one restraining feature (178) for restraining rotational movement of the retaining element (160) before the shape change, and at least one spring (315) that provides at least one locked spring-loaded position when the retaining element is in the restraining feature and at least one released position that is reached when the retaining element is in a position beyond the restraining feature (178). The rotatable mechanism (120) includes at least one load-bearing protrusion (310). A hitch (400) is for mechanically coupling to the load, wherein the hitch is supported on the load bearing protrusion (310) when the rotatable mechanism is in the locked spring-loaded position.

  12. Mechanism of the Exchange Reaction in HRAS from Multiscale Modeling

    PubMed Central

    Kapoor, Abhijeet; Travesset, Alex

    2014-01-01

    HRAS regulates cell growth promoting signaling processes by cycling between active (GTP-bound) and inactive (GDP-bound) states. Understanding the transition mechanism is central for the design of small molecules to inhibit the formation of RAS-driven tumors. Using a multiscale approach involving coarse-grained (CG) simulations, all-atom classical molecular dynamics (CMD; total of 3.02 µs), and steered molecular dynamics (SMD) in combination with Principal Component Analysis (PCA), we identified the structural features that determine the nucleotide (GDP) exchange reaction. We show that weakening the coupling between the SwitchI (residues 25–40) and SwitchII (residues 59–75) accelerates the opening of SwitchI; however, an open conformation of SwitchI is unstable in the absence of guanine nucleotide exchange factors (GEFs) and rises up towards the bound nucleotide to close the nucleotide pocket. Both I21 and Y32, play a crucial role in SwitchI transition. We show that an open SwitchI conformation is not necessary for GDP destabilization but is required for GDP/Mg escape from the HRAS. Further, we present the first simulation study showing displacement of GDP/Mg away from the nucleotide pocket. Both SwitchI and SwitchII, delays the escape of displaced GDP/Mg in the absence of GEF. Based on these results, a model for the mechanism of GEF in accelerating the exchange process is hypothesized. PMID:25272152

  13. Statistical mechanics of the Huxley-Simmons model

    NASA Astrophysics Data System (ADS)

    Caruel, M.; Truskinovsky, L.

    2016-06-01

    The chemomechanical model of Huxley and Simmons (HS) [A. F. Huxley and R. M. Simmons, Nature 233, 533 (1971), 10.1038/233533a0] provides a paradigmatic description of mechanically induced collective conformational changes relevant in a variety of biological contexts, from muscles power stroke and hair cell gating to integrin binding and hairpin unzipping. We develop a statistical mechanical perspective on the HS model by exploiting a formal analogy with a paramagnetic Ising model. We first study the equilibrium HS model with a finite number of elements and compute explicitly its mechanical and thermal properties. To model kinetics, we derive a master equation and solve it for several loading protocols. The developed formalism is applicable to a broad range of allosteric systems with mean-field interactions.

  14. Mechanisms and models of effective thermal conductivities of nanofluids.

    SciTech Connect

    Yu, W.; France, D. M.; Singh, D.; Timofeeva, E. V.; Smith, D. S.; Routbort, J. L.; Univ. of Illinois

    2010-08-01

    The physical mechanisms and mathematical models of the effective thermal conductivities of nanofluids have long been of interest to the nanofluid research community because the effective thermal conductivities of nanofluids cannot generally be fully explained and predicted by classical effective medium theories. This review article summarizes considerable progress made on this topic. Specifically, the physical mechanisms and mathematical models of the effective thermal conductivities of nanofluids are reviewed, the potential contributions of those physical mechanisms are evaluated, and the comparisons of the theoretical predictions and experimental data are presented along with opportunities for future research.

  15. SAFOD Brittle Microstructure and Mechanics Knowledge Base (BM2KB)

    NASA Astrophysics Data System (ADS)

    Babaie, Hassan A.; Broda Cindi, M.; Hadizadeh, Jafar; Kumar, Anuj

    2013-07-01

    Scientific drilling near Parkfield, California has established the San Andreas Fault Observatory at Depth (SAFOD), which provides the solid earth community with short range geophysical and fault zone material data. The BM2KB ontology was developed in order to formalize the knowledge about brittle microstructures in the fault rocks sampled from the SAFOD cores. A knowledge base, instantiated from this domain ontology, stores and presents the observed microstructural and analytical data with respect to implications for brittle deformation and mechanics of faulting. These data can be searched on the knowledge base‧s Web interface by selecting a set of terms (classes, properties) from different drop-down lists that are dynamically populated from the ontology. In addition to this general search, a query can also be conducted to view data contributed by a specific investigator. A search by sample is done using the EarthScope SAFOD Core Viewer that allows a user to locate samples on high resolution images of core sections belonging to different runs and holes. The class hierarchy of the BM2KB ontology was initially designed using the Unified Modeling Language (UML), which was used as a visual guide to develop the ontology in OWL applying the Protégé ontology editor. Various Semantic Web technologies such as the RDF, RDFS, and OWL ontology languages, SPARQL query language, and Pellet reasoning engine, were used to develop the ontology. An interactive Web application interface was developed through Jena, a java based framework, with AJAX technology, jsp pages, and java servlets, and deployed via an Apache tomcat server. The interface allows the registered user to submit data related to their research on a sample of the SAFOD core. The submitted data, after initial review by the knowledge base administrator, are added to the extensible knowledge base and become available in subsequent queries to all types of users. The interface facilitates inference capabilities in the

  16. Model-based tomographic reconstruction

    DOEpatents

    Chambers, David H.; Lehman, Sean K.; Goodman, Dennis M.

    2012-06-26

    A model-based approach to estimating wall positions for a building is developed and tested using simulated data. It borrows two techniques from geophysical inversion problems, layer stripping and stacking, and combines them with a model-based estimation algorithm that minimizes the mean-square error between the predicted signal and the data. The technique is designed to process multiple looks from an ultra wideband radar array. The processed signal is time-gated and each section processed to detect the presence of a wall and estimate its position, thickness, and material parameters. The floor plan of a building is determined by moving the array around the outside of the building. In this paper we describe how the stacking and layer stripping algorithms are combined and show the results from a simple numerical example of three parallel walls.

  17. Mechanical testing and modelling of the Universal 2 implant.

    PubMed

    Gislason, M K; Foster, E; Main, D; Fusiek, G; Niewczas, P; Bransby-Zachary, M; Nash, D H

    2016-06-01

    Understanding the load mechanics of orthopaedic implants is important to be able to predict their behaviour in-vivo. Much research, both mechanical and clinical, has been carried out on hip and knee implants, but less has been written about the mechanics of wrist implants. In this paper, the load mechanics of the Universal 2 wrist implant have been measured using two types of measuring techniques, strain gauges and Fibre Bragg Grating measurements to measure strains. The results were compared to a finite element model of the implant. The results showed that the computational results were in good agreement with the experimental results. Better understanding of the load mechanics of wrist implants, using models and experimental results can catalyse the development of future generation implants. PMID:27083120

  18. Mechanical Slosh Models for Rocket-Propelled Spacecraft

    NASA Technical Reports Server (NTRS)

    Jang, Jiann-Woei; Alaniz, Abram; Yang, Lee; Powers. Joseph; Hall, Charles

    2013-01-01

    Several analytical mechanical slosh models for a cylindrical tank with flat bottom are reviewed. Even though spacecrafts use cylinder shaped tanks, most of those tanks usually have elliptical domes. To extend the application of the analytical models for a cylindrical tank with elliptical domes, the modified slosh parameter models are proposed in this report by mapping an elliptical dome cylindrical tank to a flat top/bottom cylindrical tank while maintaining the equivalent liquid volume. For the low Bond number case, the low-g slosh models were also studied. Those low-g models can be used for Bond number > 10. The current low-g slosh models were also modified to extend their applications for the case that liquid height is smaller than the tank radius. All modified slosh models are implemented in MATLAB m-functions and are collected in the developed MST (Mechanical Slosh Toolbox).

  19. Model-based safety assessments

    SciTech Connect

    Carlson, D.D.; Jones, T.R.

    1998-04-01

    Sandia National Laboratories performs systems analysis of high risk, high consequence systems. In particular, Sandia is responsible for the engineering of nuclear weapons, exclusive of the explosive physics package. In meeting this responsibility, Sandia has developed fundamental approaches to safety and a process for evaluating safety based on modeling and simulation. These approaches provide confidence in the safety of our nuclear weapons. Similar concepts may be applied to improve the safety of other high consequence systems.

  20. A comparison of chemical mechanisms based on TRAMP-2006 field data

    NASA Astrophysics Data System (ADS)

    Chen, Shuang; Ren, Xinrong; Mao, Jingqiu; Chen, Zhong; Brune, William H.; Lefer, Barry; Rappenglück, Bernhard; Flynn, James; Olson, Jennifer; Crawford, James H.

    2010-10-01

    A comparison of a model using five widely known mechanisms (RACM, CB05, LaRC, SAPRC-99, SAPRC-07, and MCMv3.1) has been conducted based on the TexAQS II Radical and Aerosol Measurement Project (TRAMP-2006) field data in 2006. The concentrations of hydroxyl (OH) and hydroperoxy (HO 2) radicals were calculated by a zero-dimensional box model with each mechanism and then compared with the OH and HO 2 measurements. The OH and HO 2 calculated by the model with different mechanisms show similarities and differences with each other and with the measurements. First, measured OH and HO 2 are generally greater than modeled for all mechanisms, with the median modeled-to-measured ratios ranging from about 0.8 (CB05) to about 0.6 (SAPRC-99). These differences indicate that either measurement errors, the effects of unmeasured species or chemistry errors in the model or the mechanisms, with some errors being independent of the mechanism used. Second, the modeled and measured ratios of HO 2/OH agree when NO is about 1 ppbv, but the modeled ratio is too high when NO was less and too low when NO is more, as seen in previous studies. Third, mechanism-mechanism HO x differences are sensitive to the environmental conditions - in more polluted conditions, the mechanism-mechanism differences are less. This result suggests that, in polluted conditions, the mechanistic details are less important than in cleaner conditions, probably because of the dominance of reactive nitrogen chemistry under polluted conditions.

  1. Toward a rule-based biome model

    SciTech Connect

    Neilson, R.P.; King, G.A.; Koerper, G.

    1991-01-01

    Current projections of the response of the biosphere to global climatic change indicate as much as 50% to 90% spatial displacement of extratropical biomes. The mechanism of spatial shift could be dominated by either (1) competitive displacement of northern biomes by southern biomes, or (2) drought-induced dieback of areas susceptible to change. The current suite of global biosphere models cannot distinguish between these two processes, thus determining the need for a mechanistically based biome model. The model is in an early stage of development and will require several enhancements, including explicit simulation of potential evapotranspiration, extension to boreal and tropical biomes, a shift from steady-state to transient dynamics, and validation on other continents.

  2. Transfer function modeling of damping mechanisms in distributed parameter models

    NASA Technical Reports Server (NTRS)

    Slater, J. C.; Inman, D. J.

    1994-01-01

    This work formulates a method for the modeling of material damping characteristics in distributed parameter models which may be easily applied to models such as rod, plate, and beam equations. The general linear boundary value vibration equation is modified to incorporate hysteresis effects represented by complex stiffness using the transfer function approach proposed by Golla and Hughes. The governing characteristic equations are decoupled through separation of variables yielding solutions similar to those of undamped classical theory, allowing solution of the steady state as well as transient response. Example problems and solutions are provided demonstrating the similarity of the solutions to those of the classical theories and transient responses of nonviscous systems.

  3. A Simple Mechanical Model for the Isotropic Harmonic Oscillator

    ERIC Educational Resources Information Center

    Nita, Gelu M.

    2010-01-01

    A constrained elastic pendulum is proposed as a simple mechanical model for the isotropic harmonic oscillator. The conceptual and mathematical simplicity of this model recommends it as an effective pedagogical tool in teaching basic physics concepts at advanced high school and introductory undergraduate course levels. (Contains 2 figures.)

  4. A mechanical approach to mean field spin models

    NASA Astrophysics Data System (ADS)

    Genovese, Giuseppe; Barra, Adriano

    2009-05-01

    Inspired by the bridge pioneered by Guerra among statistical mechanics on lattice and analytical mechanics on 1+1 continuous Euclidean space time, we built a self-consistent method to solve for the thermodynamics of mean field models defined on lattice, whose order parameters self-average. We show the whole procedure by analyzing in full detail the simplest test case, namely, the Curie-Weiss model. Further, we report some applications also to models whose order parameters do not self-average by using the Sherrington-Kirkpatrick spin glass as a guide.

  5. Mechanical Regulation of Bone Regeneration: Theories, Models, and Experiments

    PubMed Central

    Betts, Duncan Colin; Müller, Ralph

    2014-01-01

    How mechanical forces influence the regeneration of bone remains an open question. Their effect has been demonstrated experimentally, which has allowed mathematical theories of mechanically driven tissue differentiation to be developed. Many simulations driven by these theories have been presented, however, validation of these models has remained difficult due to the number of independent parameters considered. An overview of these theories and models is presented along with a review of experimental studies and the factors they consider. Finally limitations of current experimental data and how this influences modeling are discussed and potential solutions are proposed. PMID:25540637

  6. Density functional theory and quantum mechanics/molecular mechanics study of cysteine protease inhibition by nitrile-based inhibitors.

    NASA Astrophysics Data System (ADS)

    De Visser, Sam; Quesne, Matthew; Ward, Richard

    2013-12-01

    Cysteine protease enzymes are important for human physiology and catalyze key protein degradation pathways. These enzymes react via a nucleophilic reaction mechanism that involves a cysteine residue and the proton of a proximal histidine. Particularly efficient inhibitors of these enzymes are nitrile-based, however, the details of the catalytic reaction mechanism currently are poorly understood. To gain further insight into the inhibition of these molecules, we have performed a combined density functional theory and quantum mechanics/molecular mechanics study on the reaction of a nitrile-based inhibitor with the enzyme active site amino acids. We show here that small perturbations to the inhibitor structure can have dramatic effects on the catalysis and inhibition processes. Thus, we investigated a range of inhibitor templates and show that specific structural changes reduce the inhibitory efficiency by several orders of magnitude. Moreover, as the reaction takes place on a polar surface, we find strong differences between the DFT and QM/MM calculated energetics. In particular, the DFT model led to dramatic distortions from the starting structure and the convergence to a structure that would not fit the enzyme active site. In the subsequent QM/MM study we investigated the use of mechanical versus electronic embedding on the kinetics, thermodynamics and geometries along the reaction mechanism. We find minor effects on the kinetics of the reaction but large geometric and thermodynamics differences as a result of inclusion of electronic embedding corrections. The work here highlights the importance of model choice in the investigation of this biochemical reaction mechanism.

  7. The von Neumann model of measurement in quantum mechanics

    SciTech Connect

    Mello, Pier A.

    2014-01-08

    We describe how to obtain information on a quantum-mechanical system by coupling it to a probe and detecting some property of the latter, using a model introduced by von Neumann, which describes the interaction of the system proper with the probe in a dynamical way. We first discuss single measurements, where the system proper is coupled to one probe with arbitrary coupling strength. The goal is to obtain information on the system detecting the probe position. We find the reduced density operator of the system, and show how Lüders rule emerges as the limiting case of strong coupling. The von Neumann model is then generalized to two probes that interact successively with the system proper. Now we find information on the system by detecting the position-position and momentum-position correlations of the two probes. The so-called 'Wigner's formula' emerges in the strong-coupling limit, while 'Kirkwood's quasi-probability distribution' is found as the weak-coupling limit of the above formalism. We show that successive measurements can be used to develop a state-reconstruction scheme. Finally, we find a generalized transform of the state and the observables based on the notion of successive measurements.

  8. Statistical mechanics models for motion and force planning

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.

    1990-01-01

    The models of statistical mechanics provide an alternative to the methods of classical mechanics more traditionally used in robotics. They have a potential to: improve analysis of object collisions; handle kinematic and dynamic contact interactions within the same frmework; and reduce the need for perfect deterministic world model information. The statistical mechanics models characterize the state of the system as a probability density function (p.d.f.) whose time evolution is governed by a partial differential equation subject to boundary and initial conditions. The boundary conditions when rigid objects collide reflect the conservation of momentum. The models are being developed to embedd in remote semi-autonomous systems with a need to reason and interact with a multiobject environment.

  9. Modeling Selection and Extinction Mechanisms of Biological Systems

    NASA Astrophysics Data System (ADS)

    Amirjanov, Adil

    In this paper, the behavior of a genetic algorithm is modeled to enhance its applicability as a modeling tool of biological systems. A new description model for selection mechanism is introduced which operates on a portion of individuals of population. The extinction and recolonization mechanism is modeled, and solving the dynamics analytically shows that the genetic drift in the population with extinction/recolonization is doubled. The mathematical analysis of the interaction between selection and extinction/recolonization processes is carried out to assess the dynamics of motion of the macroscopic statistical properties of population. Computer simulations confirm that the theoretical predictions of described models are in good approximations. A mathematical model of GA dynamics was also examined, which describes the anti-predator vigilance in an animal group with respect to a known analytical solution of the problem, and showed a good agreement between them to find the evolutionarily stable strategies.

  10. Modeling Mechanisms of Saucer-Shaped Sill Formation

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Bunger, A.

    2006-12-01

    Magmatic sills have a basic tendency to form concave-upward saucer shapes. This morphology is observed in numerous seismic images and in the striking formations which dominate the landscape in South Africa's Karoo Basin. The propensity of sills to curve upward has also been suggested as a mechanism for magma ascent, particularly in compressive tectonic regions. Recent efforts that are focused on understanding the fundamental mechanisms controlling the saucer curvature indicate that saucer-shaped growth should be understood to result from asymmetry in the induced stress field near the fracture tip that results when the sill attains a size similar to its depth. Here we explore this phenomenon numerically and extend the consideration to examine the tendency of sills that are growing in a naturally layered environment to curve upward as they mechanically interact with a stiffer underlying layer or softer overlying layer. Our numerical model is based on the displacement discontinuity method, where the presence of three layers is accounted for explicitly in the plane strain linear elastic fundamental solution upon which the method is built. The equations governing fluid flow in the fracture are solved using a finite difference method, but here we consider only the limiting case where the effects of viscous dissipation are shown to be negligible so that the internal fluid pressure is uniform. The numerical results are first compared with laboratory experiments performed by injecting glycerin or glucose- based fluids to form hydraulic fractures in PMMA or glass specimens. The particular case of a fracture growing near a free-surface is examined. Reasonable agreement for the curving fracture path is found between the numerical model and experimental results up until the point where the initial radial symmetry in the experiments breaks down and the fracture elongates to become egg-shaped in plan view as growth favors one direction over the others. The numerical model is then

  11. Enhanced mathematical modeling of the displacement amplification ratio for piezoelectric compliant mechanisms

    NASA Astrophysics Data System (ADS)

    Ling, Mingxiang; Cao, Junyi; Zeng, Minghua; Lin, Jing; Inman, Daniel J.

    2016-07-01

    Piezo-actuated, flexure hinge-based compliant mechanisms have been frequently used in precision engineering in the last few decades. There have been a considerable number of publications on modeling the displacement amplification behavior of rhombus-type and bridge-type compliant mechanisms. However, due to an unclear geometric approximation and mechanical assumption between these two flexures, it is very difficult to obtain an exact description of the kinematic performance using previous analytical models, especially when the designed angle of the compliant mechanisms is small. Therefore, enhanced theoretical models of the displacement amplification ratio for rhombus-type and bridge-type compliant mechanisms are proposed to improve the prediction accuracy based on the distinct force analysis between these two flexures. The energy conservation law and the elastic beam theory are employed for modeling with consideration of the translational and rotational stiffness. Theoretical and finite elemental results show that the prediction errors of the displacement amplification ratio will be enlarged if the bridge-type flexure is simplified as a rhombic structure to perform mechanical modeling. More importantly, the proposed models exhibit better performance than the previous models, which is further verified by experiments.

  12. Designing Competency-Based Materials for the Automotive Mechanics Curriculum

    ERIC Educational Resources Information Center

    Richardson, Roger L.

    1977-01-01

    Describes the Career Education Center's (Florida State University) development of the "Automotive Mechanics Catalog" (a job inventory noting performance objectives for specific occupational programs), using the Vocational-Technical Education Consortium of States (V-TECS) model. Also describes the development of curriculum materials using the…

  13. Crowdsourcing Based 3d Modeling

    NASA Astrophysics Data System (ADS)

    Somogyi, A.; Barsi, A.; Molnar, B.; Lovas, T.

    2016-06-01

    Web-based photo albums that support organizing and viewing the users' images are widely used. These services provide a convenient solution for storing, editing and sharing images. In many cases, the users attach geotags to the images in order to enable using them e.g. in location based applications on social networks. Our paper discusses a procedure that collects open access images from a site frequently visited by tourists. Geotagged pictures showing the image of a sight or tourist attraction are selected and processed in photogrammetric processing software that produces the 3D model of the captured object. For the particular investigation we selected three attractions in Budapest. To assess the geometrical accuracy, we used laser scanner and DSLR as well as smart phone photography to derive reference values to enable verifying the spatial model obtained from the web-album images. The investigation shows how detailed and accurate models could be derived applying photogrammetric processing software, simply by using images of the community, without visiting the site.

  14. Constitutive Modeling of the Mechanical Properties of Optical Fibers

    NASA Technical Reports Server (NTRS)

    Moeti, L.; Moghazy, S.; Veazie, D.; Cuddihy, E.

    1998-01-01

    Micromechanical modeling of the composite mechanical properties of optical fibers was conducted. Good agreement was obtained between the values of Young's modulus obtained by micromechanics modeling and those determined experimentally for a single mode optical fiber where the wave guide and the jacket are physically coupled. The modeling was also attempted on a polarization-maintaining optical fiber (PANDA) where the wave guide and the jacket are physically decoupled, and found not to applicable since the modeling required perfect bonding at the interface. The modeling utilized constituent physical properties such as the Young's modulus, Poisson's ratio, and shear modulus to establish bounds on the macroscopic behavior of the fiber.

  15. Inference on biological mechanisms using an integrated phenotype prediction model.

    PubMed

    Enomoto, Yumi; Ushijima, Masaru; Miyata, Satoshi; Matsuura, Masaaki; Ohtaki, Megu

    2008-03-01

    We propose a methodology for constructing an integrated phenotype prediction model that accounts for multiple pathways regulating a targeted phenotype. The method uses multiple prediction models, each expressing a particular pattern of gene-to-gene interrelationship, such as epistasis. We also propose a methodology using Gene Ontology annotations to infer a biological mechanism from the integrated phenotype prediction model. To construct the integrated models, we employed multiple logistic regression models using a two-step learning approach to examine a number of patterns of gene-to-gene interrelationships. We first selected individual prediction models with acceptable goodness of fit, and then combined the models. The resulting integrated model predicts phenotype as a logical sum of predicted results from the individual models. We used published microarray data on neuroblastoma from Ohira et al (2005) for illustration, constructing an integrated model to predict prognosis and infer the biological mechanisms controlling prognosis. Although the resulting integrated model comprised a small number of genes compared to a previously reported analysis of these data, the model demonstrated excellent performance, with an error rate of 0.12 in a validation analysis. Gene Ontology analysis suggested that prognosis of patients with neuroblastoma may be influenced by biological processes such as cell growth, G-protein signaling, phosphoinositide-mediated signaling, alcohol metabolism, glycolysis, neurophysiological processes, and catecholamine catabolism. PMID:18578362

  16. Coupled thermal/chemical/mechanical modeling of insensitive explosives in thermal environments

    SciTech Connect

    Nichols, A.L. III

    1996-05-01

    The ability to predict the response of a weapon system that contains insensitive explosives to elevated temperatures is important in understanding its safety characteristics. To model such a system at elevated temperatures in a finite element computer code requires a variety of capabilities. These modeling capabilities include thermal diffusion and convection to transport the heat to the explosives in the weapon system, temperature based chemical reaction modeling of the decomposition of the explosive materials, and mechanical modeling of both the metal casing and the unreacted and decomposed explosive. The Chemical TOPAZ code has been developed to model coupled thermal/chemical problems where we do not need to model the mass motion. We have also developed the LYNX2D code, based on PALM2D and Chemical TOPAZ, which is an implicit, two-dimensional coupled thermal/chemical/mechanical finite element model computer code. Some representative examples are shown. {copyright} {ital 1996 American Institute of Physics.}

  17. Probabilistic model for pressure vessel reliability incorporating fracture mechanics and nondestructive examination

    SciTech Connect

    Tow, D.M.; Reuter, W.G.

    1998-03-01

    A probabilistic model has been developed for predicting the reliability of structures based on fracture mechanics and the results of nondestructive examination (NDE). The distinctive feature of this model is the way in which inspection results and the probability of detection (POD) curve are used to calculate a probability density function (PDF) for the number of flaws and the distribution of those flaws among the various size ranges. In combination with a probabilistic fracture mechanics model, this density function is used to estimate the probability of failure (POF) of a structure in which flaws have been detected by NDE. The model is useful for parametric studies of inspection techniques and material characteristics.

  18. STATISTICAL MECHANICS MODELING OF MESOSCALE DEFORMATION IN METALS

    SciTech Connect

    Anter El-Azab

    2013-04-08

    The research under this project focused on a theoretical and computational modeling of dislocation dynamics of mesoscale deformation of metal single crystals. Specifically, the work aimed to implement a continuum statistical theory of dislocations to understand strain hardening and cell structure formation under monotonic loading. These aspects of crystal deformation are manifestations of the evolution of the underlying dislocation system under mechanical loading. The project had three research tasks: 1) Investigating the statistical characteristics of dislocation systems in deformed crystals. 2) Formulating kinetic equations of dislocations and coupling these kinetics equations and crystal mechanics. 3) Computational solution of coupled crystal mechanics and dislocation kinetics. Comparison of dislocation dynamics predictions with experimental results in the area of statistical properties of dislocations and their field was also a part of the proposed effort. In the first research task, the dislocation dynamics simulation method was used to investigate the spatial, orientation, velocity, and temporal statistics of dynamical dislocation systems, and on the use of the results from this investigation to complete the kinetic description of dislocations. The second task focused on completing the formulation of a kinetic theory of dislocations that respects the discrete nature of crystallographic slip and the physics of dislocation motion and dislocation interaction in the crystal. Part of this effort also targeted the theoretical basis for establishing the connection between discrete and continuum representation of dislocations and the analysis of discrete dislocation simulation results within the continuum framework. This part of the research enables the enrichment of the kinetic description with information representing the discrete dislocation systems behavior. The third task focused on the development of physics-inspired numerical methods of solution of the coupled

  19. Experience on a cryogenic linear mechanism based on superconducting levitation

    NASA Astrophysics Data System (ADS)

    Serrano-Tellez, Javier; Romera-Juarez, Fernando; González-de-María, David; Lamensans, Mikel; Argelaguet-Vilaseca, Heribert; Pérez-Díaz, José-Luis; Sánchez-Casarrubios, Juan; Díez-Jiménez, Efrén.; Valiente-Blanco, Ignacio

    2012-09-01

    The instrumentation of many space missions requires operation in cryogenic temperatures. In all the cases, the use of mechanisms in this environment is a matter of concern, especially when long lifetime is required. With the aim of removing lifetime concerns and to benefit from the cryogenic environment, a cryogenic contactless linear mechanism has been developed. It is based on the levitation of a permanent magnet over superconductor disks. The mechanism has been designed, built, and tested to assess the performances of such technology. The levitation system solves the mechanical contact problems due to cold-welding effects, material degradation by fatigue, wearing, backlash, lubrication...etc, at cryogenic temperatures. In fact, the lower is the temperature the better the superconductor levitation systems work. The mechanism provides a wide stroke (18mm) and high resolution motion (1μm), where position is controlled by changing the magnetic field of its environment using electric-magnets. During the motion, the moving part of the mechanism levitates supported by the magnetic interaction with the high temperature type II superconductors after reaching the superconductor state down to 90K. This paper describes the results of the complete levitation system development, including extensive cryogenic testing to measure optically the motion range, resolution, run-outs and rotations in order to characterize the levitation mechanism and to verify its performance in a cryogenic environment.

  20. Coupling multi-physics models to cardiac mechanics.

    PubMed

    Nordsletten, D A; Niederer, S A; Nash, M P; Hunter, P J; Smith, N P

    2011-01-01

    We outline and review the mathematical framework for representing mechanical deformation and contraction of the cardiac ventricles, and how this behaviour integrates with other processes crucial for understanding and modelling heart function. Building on general conservation principles of space, mass and momentum, we introduce an arbitrary Eulerian-Lagrangian framework governing the behaviour of both fluid and solid components. Exploiting the natural alignment of cardiac mechanical properties with the tissue microstructure, finite deformation measures and myocardial constitutive relations are referred to embedded structural axes. Coupling approaches for solving this large deformation mechanics framework with three dimensional fluid flow, coronary hemodynamics and electrical activation are described. We also discuss the potential of cardiac mechanics modelling for clinical applications. PMID:19917304

  1. Model-based Utility Functions

    NASA Astrophysics Data System (ADS)

    Hibbard, Bill

    2012-05-01

    Orseau and Ring, as well as Dewey, have recently described problems, including self-delusion, with the behavior of agents using various definitions of utility functions. An agent's utility function is defined in terms of the agent's history of interactions with its environment. This paper argues, via two examples, that the behavior problems can be avoided by formulating the utility function in two steps: 1) inferring a model of the environment from interactions, and 2) computing utility as a function of the environment model. Basing a utility function on a model that the agent must learn implies that the utility function must initially be expressed in terms of specifications to be matched to structures in the learned model. These specifications constitute prior assumptions about the environment so this approach will not work with arbitrary environments. But the approach should work for agents designed by humans to act in the physical world. The paper also addresses the issue of self-modifying agents and shows that if provided with the possibility to modify their utility functions agents will not choose to do so, under some usual assumptions.

  2. A Relevance Feedback Mechanism for Content-Based Image Retrieval.

    ERIC Educational Resources Information Center

    Ciocca, G.; Schettini, R.

    1999-01-01

    Describes a relevance-feedback mechanism for content-based image retrieval that evaluates the feature distributions of the images judged relevant by the user and updates both the similarity measure and the query to accurately represent the user's information needs. (Author/LRW)

  3. Modeling Aging and Mechanical Rejuvenation of Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Semkiv, Mykhailo; Hütter, Markus

    2016-04-01

    The elasto-viscoplasticity of amorphous solids is modeled, with a focus on the effects of physical aging and mechanical rejuvenation. Using nonequilibrium thermodynamics, the concept of kinetic and configurational subsystems has been employed. The Hamiltonian structure of reversible dynamics is exploited to derive a constitutive relation for the stress tensor. Furthermore, it is demonstrated that accounting for mechanical rejuvenation results in a modification of the driving force for viscoplastic flow.

  4. Mechanism-Based Design of Green Oxidation Catalysts

    SciTech Connect

    Rybak-Akimova, Elena

    2015-03-16

    situation. Growing families of synthetic iron complexes that resemble active sites of metalloenzymes produce metal-based intermediates (rather than hydroxyl radicals) in reactions with oxygen donors. These complexes are very promising for selective oxygen and peroxide activation. In order to understand the mechanisms of metal-based small molecule activation, kinetically competent metal-oxygen intermediates must be identified. One of the grand challenges identified by the Department of Energy workshop "Catalysis for Energy" is understanding mechanisms and dynamics of catalyzed reactions. The research summarized herein focuses on detailed characterization of the formation and reactivity of various iron-peroxo- and iron-oxo intermediates that are involved in catalysis. Rates of rapid reactions were studied at low temperatures by a specialized technique termed cryogenic stopped-flow spectrophotometry. These measurements identified reaction conditions which favor the formation of catalytically competent oxidants. Chemical structures of reactive complexes was determined, and new, efficient catalysts for hydrocarbon oxidation were synthesized. Importantly, these catalysts are selective, they promote oxidation of hydrocarbons at a specific site. The catalysts are also efficient and robust, hundreds of cycles of substrate oxidation occur within minutes at room temperature. Furthermore, they enable utilization of environmentally friendly oxidants, such as hydrogen peroxide, which produces water as the only byproduct. Mechanistic insights uncovered the role of various acid-containing additives in catalytic oxidations. Proton delivery to the active catalytic sites facilitated oxidations, similarly to the catalytic pathways in metal-containing enzymes. Under certain conditions, two metals in one complex can act in concert, modeling the reactivity of a bacterial enzyme which converts methane into methanol. In related studies, a family of nickel complexes that react with carbon dioxide at

  5. A Comparison of Chemical Mechanisms Based on TRAMP-2006 Field Data

    NASA Astrophysics Data System (ADS)

    Chen, S.; Ren, X.; Mao, J.; Chen, Z.; Brune, W. H.; Lefer, B.; Rappenglueck, B.; Flynn, J.; Olson, J.; Crawford, J. H.

    2008-12-01

    A comparison of five widely used mechanisms (RACM, CB05, LaRC, SAPRC99, SAPRC07, and MCMv3.1) has been conducted based on the TexAQS II Radical and Aerosol Measurement Project (TRAMP) field data in summer 2006 in Houston. The concentrations of hydroxyl (OH) and hydroperoxy (HO2) radicals (called HOx collectively) were calculated by a zero-dimensional box model with each mechanism and then compared with the OH and HO2 measurements. The OH and HO2 calculated by the different mechanisms show similarities and differences with each other and with the measurements. First, OH and HO2 are generally underestimated by all mechanisms, with the median modeled-to-measured ratios ranging from about 0.8 (CB05) to about 0.6 (SAPRC-99). These differences indicate that the measurements of precursor species (including unmeasured species) were in error or that all mechanisms have a common chemistry error. Second, the modeled and measured ratio of HO2/OH agree when NO was about 1 ppbv, although the ratio is too high when NO was less and too low when NO was more, as seen in previous studies. Third, mechanism-mechanism difference in HOx is sensitive to the environmental conditions: in more polluted conditions, the mechanism-mechanism differences are less. This result suggests that, in polluted conditions, the mechanistic details are less important than in cleaner conditions, probably because of the dominance of reactive nitrogen chemistry under polluted conditions.

  6. Modeling the Interactions Between Multiple Crack Closure Mechanisms at Threshold

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Riddell, William T.; Piascik, Robert S.

    2003-01-01

    A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs.

  7. Experimental Verification of a Cracked Fuel Mechanical Model

    SciTech Connect

    Williford, R. E.

    1982-12-01

    This report describes the results of a series of laboratory experiments conducted to independently verify a model that describes the nonlinear mechanical behavior of cracked fuel in pelletized UO{sub 2}/Zircaloy nuclear fuel rods under normal operating conditions. After a brief description of the analytical model, each experiment is discussed in detail. Experiments were conducted to verify the general behavior and numerical values for the three primary independent modelling parameters (effective crack roughness, effective gap roughness, and total crack length), and to verify the model predictions that the effective Young's moduli for cracked fuel systems were substantially less than those for solid UO{sub 2} pellets. In general, the model parameters and predictions were confirmed, and new insight was gained concerning the complexities of cracked fuel mechanics.

  8. Mechanical behavior in living cells consistent with the tensegrity model

    NASA Technical Reports Server (NTRS)

    Wang, N.; Naruse, K.; Stamenovic, D.; Fredberg, J. J.; Mijailovich, S. M.; Tolic-Norrelykke, I. M.; Polte, T.; Mannix, R.; Ingber, D. E.

    2001-01-01

    Alternative models of cell mechanics depict the living cell as a simple mechanical continuum, porous filament gel, tensed cortical membrane, or tensegrity network that maintains a stabilizing prestress through incorporation of discrete structural elements that bear compression. Real-time microscopic analysis of cells containing GFP-labeled microtubules and associated mitochondria revealed that living cells behave like discrete structures composed of an interconnected network of actin microfilaments and microtubules when mechanical stresses are applied to cell surface integrin receptors. Quantitation of cell tractional forces and cellular prestress by using traction force microscopy confirmed that microtubules bear compression and are responsible for a significant portion of the cytoskeletal prestress that determines cell shape stability under conditions in which myosin light chain phosphorylation and intracellular calcium remained unchanged. Quantitative measurements of both static and dynamic mechanical behaviors in cells also were consistent with specific a priori predictions of the tensegrity model. These findings suggest that tensegrity represents a unified model of cell mechanics that may help to explain how mechanical behaviors emerge through collective interactions among different cytoskeletal filaments and extracellular adhesions in living cells.

  9. Optimum selection of mechanism type for heavy manipulators based on particle swarm optimization method

    NASA Astrophysics Data System (ADS)

    Zhao, Yong; Chen, Genliang; Wang, Hao; Lin, Zhongqin

    2013-07-01

    The mechanism type plays a decisive role in the mechanical performance of robotic manipulators. Feasible mechanism types can be obtained by applying appropriate type synthesis theory, but there is still a lack of effective and efficient methods for the optimum selection among different types of mechanism candidates. This paper presents a new strategy for the purpose of optimum mechanism type selection based on the modified particle swarm optimization method. The concept of sub-swarm is introduced to represent the different mechanisms generated by the type synthesis, and a competitive mechanism is employed between the sub-swarms to reassign their population size according to the relative performances of the mechanism candidates to implement the optimization. Combining with a modular modeling approach for fast calculation of the performance index of the potential candidates, the proposed method is applied to determine the optimum mechanism type among the potential candidates for the desired manipulator. The effectiveness and efficiency of the proposed method is demonstrated through a case study on the optimum selection of mechanism type of a heavy manipulator where six feasible candidates are considered with force capability as the specific performance index. The optimization result shows that the fitness of the optimum mechanism type for the considered heavy manipulator can be up to 0.578 5. This research provides the instruction in optimum selection of mechanism types for robotic manipulators.

  10. Theoretical Modeling of Mechanical-Electrical Coupling of Carbon Nanotubes

    SciTech Connect

    Lu, Jun-Qiang; Jiang, Hanqiang

    2008-01-01

    Carbon nanotubes have been studied extensively due to their unique properties, ranging from electrical, mechanical, optical, to thermal properties. The coupling between the electrical and mechanical properties of carbon nanotubes has emerged as a new field, which raises both interesting fundamental problems and huge application potentials. In this article, we will review our recently work on the theoretical modeling on mechanical-electrical coupling of carbon nanotubes subject to various loading conditions, including tension/compression, torsion, and squashing. Some related work by other groups will be also mentioned.

  11. Innovating Method of Existing Mechanical Product Based on TRIZ Theory

    NASA Astrophysics Data System (ADS)

    Zhao, Cunyou; Shi, Dongyan; Wu, Han

    Main way of product development is adaptive design and variant design based on existing product. In this paper, conceptual design frame and its flow model of innovating products is put forwar