Multiple Export Mechanisms for mRNAs

Science.gov (United States)

Delaleau, Mildred; Borden, Katherine L. B.

2015-01-01

Nuclear mRNA export plays an important role in gene expression. We describe the mechanisms of mRNA export including the importance of mRNP assembly, docking with the nuclear basket of the nuclear pore complex (NPC), transit through the central channel of the NPC and cytoplasmic release. We describe multiple mechanisms of mRNA export including NXF1 and CRM1 mediated pathways. Selective groups of mRNAs can be preferentially transported in order to respond to cellular stimuli. RNAs can be selected based on the presence of specific cis-acting RNA elements and binding of specific adaptor proteins. The role that dysregulation of this process plays in human disease is also discussed. PMID:26343730

Multiscale modelling of DNA mechanics

International Nuclear Information System (INIS)

Dršata, Tomáš; Lankaš, Filip

2015-01-01

Mechanical properties of DNA are important not only in a wide range of biological processes but also in the emerging field of DNA nanotechnology. We review some of the recent developments in modeling these properties, emphasizing the multiscale nature of the problem. Modern atomic resolution, explicit solvent molecular dynamics simulations have contributed to our understanding of DNA fine structure and conformational polymorphism. These simulations may serve as data sources to parameterize rigid base models which themselves have undergone major development. A consistent buildup of larger entities involving multiple rigid bases enables us to describe DNA at more global scales. Free energy methods to impose large strains on DNA, as well as bead models and other approaches, are also briefly discussed. (topical review)

Fluid mechanics and heat transfer advances in nonlinear dynamics modeling

CERN Document Server

Asli, Kaveh Hariri

2015-01-01

This valuable new book focuses on new methods and techniques in fluid mechanics and heat transfer in mechanical engineering. The book includes the research of the authors on the development of optimal mathematical models and also uses modern computer technology and mathematical methods for the analysis of nonlinear dynamic processes. It covers technologies applicable to both fluid mechanics and heat transfer problems, which include a combination of physical, mechanical, and thermal techniques. The authors develop a new method for the calculation of mathematical models by computer technology, using parametric modeling techniques and multiple analyses for mechanical system. The information in this book is intended to help reduce the risk of system damage or failure. Included are sidebar discussions, which contain information and facts about each subject area that help to emphasize important points to remember.

Disconnection as a Mechanism for Cognitive Dysfunction in Multiple Sclerosis

Science.gov (United States)

Dineen, R. A.; Vilisaar, J.; Hlinka, J.; Bradshaw, C. M.; Morgan, P. S.; Constantinescu, C. S.; Auer, D. P.

2009-01-01

Disconnection of cognitively important processing regions by injury to the interconnecting white matter provides a potential mechanism for cognitive dysfunction in multiple sclerosis. The contribution of tract-specific white matter injury to dysfunction in different cognitive domains in patients with multiple sclerosis has not previously been…

Multiple Scattering in Random Mechanical Systems and Diffusion Approximation

Science.gov (United States)

Feres, Renato; Ng, Jasmine; Zhang, Hong-Kun

2013-10-01

This paper is concerned with stochastic processes that model multiple (or iterated) scattering in classical mechanical systems of billiard type, defined below. From a given (deterministic) system of billiard type, a random process with transition probabilities operator P is introduced by assuming that some of the dynamical variables are random with prescribed probability distributions. Of particular interest are systems with weak scattering, which are associated to parametric families of operators P h , depending on a geometric or mechanical parameter h, that approaches the identity as h goes to 0. It is shown that ( P h - I)/ h converges for small h to a second order elliptic differential operator on compactly supported functions and that the Markov chain process associated to P h converges to a diffusion with infinitesimal generator . Both P h and are self-adjoint (densely) defined on the space of square-integrable functions over the (lower) half-space in , where η is a stationary measure. This measure's density is either (post-collision) Maxwell-Boltzmann distribution or Knudsen cosine law, and the random processes with infinitesimal generator respectively correspond to what we call MB diffusion and (generalized) Legendre diffusion. Concrete examples of simple mechanical systems are given and illustrated by numerically simulating the random processes.

Rapidity correlations at fixed multiplicity in cluster emission models

CERN Document Server

Berger, M C

1975-01-01

Rapidity correlations in the central region among hadrons produced in proton-proton collisions of fixed final state multiplicity n at NAL and ISR energies are investigated in a two-step framework in which clusters of hadrons are emitted essentially independently, via a multiperipheral-like model, and decay isotropically. For n>or approximately=/sup 1///sub 2/(n), these semi-inclusive distributions are controlled by the reaction mechanism which dominates production in the central region. Thus, data offer cleaner insight into the properties of this mechanism than can be obtained from fully inclusive spectra. A method of experimental analysis is suggested to facilitate the extraction of new dynamical information. It is shown that the n independence of the magnitude of semi-inclusive correlation functions reflects directly the structure of the internal cluster multiplicity distribution. This conclusion is independent of certain assumptions concerning the form of the single cluster density in rapidity space. (23 r...

Multiple-collision model for pion production in relativistic nucleus-nucleus collisions

International Nuclear Information System (INIS)

Vary, J.P.

1978-01-01

A simple model for pion production in relativistic heavy-ion collisions is developed based on nucleon-nucleon data, nuclear density distribution, and the assumption of straight-line trajectories. Multiplicity distributions for total pion production and for negative-pion production are predicted for 40 Ar incident on a Pb 3 O 4 target at 1.8 GeV/nucleon. Production through intermediate baryon resonances reduces the high-multiplicity region but insufficiently to yield agreement with data. This implies the need for a coherent production mechanism

Three mechanical models for blebbing and multi-blebbing

KAUST Repository

Woolley, T. E.

2014-06-17

Membrane protrusions known as blebs play important roles in many cellular phenomena. Here we present three mathematical models of the bleb formation, which use biological insights to produce phenotypically accurate pressure-driven expansions. First, we introduce a recently suggested solid mechanics framework that is able to create blebs through stretching the membrane. This framework is then extended to include reference state reconfigurations, which models membrane growth. Finally, the stretching and reconfiguring mechanical models are compared with a much simpler geometrically constrained solution. This allows us to demonstrate that simpler systems are able to capture much of the biological complexity despite more restrictive assumptions. Moreover, the simplicity of the spherical model allows us to consider multiple blebs in a tractable framework. © 2014 The authors 2014. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved.

Multiple Indicator Stationary Time Series Models.

Science.gov (United States)

Sivo, Stephen A.

2001-01-01

Discusses the propriety and practical advantages of specifying multivariate time series models in the context of structural equation modeling for time series and longitudinal panel data. For time series data, the multiple indicator model specification improves on classical time series analysis. For panel data, the multiple indicator model…

Study on the mechanism of seepage flow in the grouting for multiple fractured model

International Nuclear Information System (INIS)

Nishigaki, Makoto; Mikake, Shin-ichiro

2002-01-01

The purpose of study is to improve the grouting method for fractured rock masses. In this paper, the results on the fundamental phenomenon for grasping the properties of grouting injection and seepage flow are discussed. The case of grouting stage is studied about the multiple hydraulic fractured apertures in the injected borehole. So the theory on the mechanism is constructed, and experiment is executed in order to verify the availability of the theory. From the results, it is shown that Bernoulli's law is able to prove the behavior of the grouting. And the theoretical evaluation is executed on the experiential procedure of the grouting. (author)

Computation of Hydration Free Energies Using the Multiple Environment Single System Quantum Mechanical/Molecular Mechanical Method.

Science.gov (United States)

König, Gerhard; Mei, Ye; Pickard, Frank C; Simmonett, Andrew C; Miller, Benjamin T; Herbert, John M; Woodcock, H Lee; Brooks, Bernard R; Shao, Yihan

2016-01-12

A recently developed MESS-E-QM/MM method (multiple-environment single-system quantum mechanical molecular/mechanical calculations with a Roothaan-step extrapolation) is applied to the computation of hydration free energies for the blind SAMPL4 test set and for 12 small molecules. First, free energy simulations are performed with a classical molecular mechanics force field using fixed-geometry solute molecules and explicit TIP3P solvent, and then the non-Boltzmann-Bennett method is employed to compute the QM/MM correction (QM/MM-NBB) to the molecular mechanical hydration free energies. For the SAMPL4 set, MESS-E-QM/MM-NBB corrections to the hydration free energy can be obtained 2 or 3 orders of magnitude faster than fully converged QM/MM-NBB corrections, and, on average, the hydration free energies predicted with MESS-E-QM/MM-NBB fall within 0.10-0.20 kcal/mol of full-converged QM/MM-NBB results. Out of five density functionals (BLYP, B3LYP, PBE0, M06-2X, and ωB97X-D), the BLYP functional is found to be most compatible with the TIP3P solvent model and yields the most accurate hydration free energies against experimental values for solute molecules included in this study.

Multiple mechanisms enable invasive species to suppress native species.

Science.gov (United States)

Bennett, Alison E; Thomsen, Meredith; Strauss, Sharon Y

2011-07-01

Invasive plants represent a significant threat to ecosystem biodiversity. To decrease the impacts of invasive species, a major scientific undertaking of the last few decades has been aimed at understanding the mechanisms that drive invasive plant success. Most studies and theories have focused on a single mechanism for predicting the success of invasive plants and therefore cannot provide insight as to the relative importance of multiple interactions in predicting invasive species' success. We examine four mechanisms that potentially contribute to the success of invasive velvetgrass Holcus lanatus: direct competition, indirect competition mediated by mammalian herbivores, interference competition via allelopathy, and indirect competition mediated by changes in the soil community. Using a combination of field and greenhouse approaches, we focus on the effects of H. lanatus on a common species in California coastal prairies, Erigeron glaucus, where the invasion is most intense. We found that H. lanatus had the strongest effects on E. glaucus via direct competition, but it also influenced the soil community in ways that feed back to negatively influence E. glaucus and other native species after H. lanatus removal. This approach provided evidence for multiple mechanisms contributing to negative effects of invasive species, and it identified when particular strategies were most likely to be important. These mechanisms can be applied to eradication of H. lanatus and conservation of California coastal prairie systems, and they illustrate the utility of an integrated set of experiments for determining the potential mechanisms of invasive species' success.

Monte Carlo simulation of a statistical mechanical model of multiple protein sequence alignment.

Science.gov (United States)

Kinjo, Akira R

2017-01-01

A grand canonical Monte Carlo (MC) algorithm is presented for studying the lattice gas model (LGM) of multiple protein sequence alignment, which coherently combines long-range interactions and variable-length insertions. MC simulations are used for both parameter optimization of the model and production runs to explore the sequence subspace around a given protein family. In this Note, I describe the details of the MC algorithm as well as some preliminary results of MC simulations with various temperatures and chemical potentials, and compare them with the mean-field approximation. The existence of a two-state transition in the sequence space is suggested for the SH3 domain family, and inappropriateness of the mean-field approximation for the LGM is demonstrated.

Tuning Cell and Tissue Development by Combining Multiple Mechanical Signals.

Science.gov (United States)

Sinha, Ravi; Verdonschot, Nico; Koopman, Bart; Rouwkema, Jeroen

2017-10-01

Mechanical signals offer a promising way to control cell and tissue development. It has been established that cells constantly probe their mechanical microenvironment and employ force feedback mechanisms to modify themselves and when possible, their environment, to reach a homeostatic state. Thus, a correct mechanical microenvironment (external forces and mechanical properties and shapes of cellular surroundings) is necessary for the proper functioning of cells. In vitro or in the case of nonbiological implants in vivo, where cells are in an artificial environment, addition of the adequate mechanical signals can, therefore, enable the cells to function normally as in vivo. Hence, a wide variety of approaches have been developed to apply mechanical stimuli (such as substrate stretch, flow-induced shear stress, substrate stiffness, topography, and modulation of attachment area) to cells in vitro. These approaches have not just revealed the effects of the mechanical signals on cells but also provided ways for probing cellular molecules and structures that can provide a mechanistic understanding of the effects. However, they remain lower in complexity compared with the in vivo conditions, where the cellular mechanical microenvironment is the result of a combination of multiple mechanical signals. Therefore, combinations of mechanical stimuli have also been applied to cells in vitro. These studies have had varying focus-developing novel platforms to apply complex combinations of mechanical stimuli, observing the co-operation/competition between stimuli, combining benefits of multiple stimuli toward an application, or uncovering the underlying mechanisms of their action. In general, they provided new insights that could not have been predicted from previous knowledge. We present here a review of several such studies and the insights gained from them, thereby making a case for such studies to be continued and further developed.

Correlations in multiple production on nuclei and Glauber model of multiple scattering

International Nuclear Information System (INIS)

Zoller, V.R.; Nikolaev, N.N.

1982-01-01

Critical analysis of possibility for describing correlation phenomena during multiple production on nuclei within the framework of the Glauber multiple seattering model generalized for particle production processes with Capella, Krziwinski and Shabelsky has been performed. It was mainly concluded that the suggested generalization of the Glauber model gives dependences on Ng(Np) (where Ng-the number of ''grey'' tracess, and Np-the number of protons flying out of nucleus) and, eventually, on #betta# (where #betta#-the number of intranuclear interactions) contradicting experience. Independent of choice of relation between #betta# and Ng(Np) in the model the rapidity corrletor Rsub(eta) is overstated in the central region and understated in the region of nucleus fragmentation. In mean multiplicities these two contradictions of experience are disguised with random compensation and agreement with experience in Nsub(S) (function of Ng) cannot be an argument in favour of the model. It is concluded that eiconal model doesn't permit to quantitatively describe correlation phenomena during the multiple production on nuclei

Multiple sclerosis : Mechanisms of myelin phagocytosis and lesion expansion

NARCIS (Netherlands)

Hendrickx, D.A.E.

2018-01-01

Multiple sclerosis (MS) is characterized by immune activation and focal demyelination in the central nervous system. The aim of this thesis was to gain more insight into the mechanisms of myelin phagocytosis by resident microglia and infiltrating macrophages. We first evaluated the expression of the

Should researchers use single indicators, best indicators, or multiple indicators in structural equation models?

Directory of Open Access Journals (Sweden)

Hayduk Leslie A

2012-10-01

Full Text Available Abstract Background Structural equation modeling developed as a statistical melding of path analysis and factor analysis that obscured a fundamental tension between a factor preference for multiple indicators and path modeling’s openness to fewer indicators. Discussion Multiple indicators hamper theory by unnecessarily restricting the number of modeled latents. Using the few best indicators – possibly even the single best indicator of each latent – encourages development of theoretically sophisticated models. Additional latent variables permit stronger statistical control of potential confounders, and encourage detailed investigation of mediating causal mechanisms. Summary We recommend the use of the few best indicators. One or two indicators are often sufficient, but three indicators may occasionally be helpful. More than three indicators are rarely warranted because additional redundant indicators provide less research benefit than single indicators of additional latent variables. Scales created from multiple indicators can introduce additional problems, and are prone to being less desirable than either single or multiple indicators.

Modeling Instruction in AP Physics C: Mechanics and Electricity and Magnetism

Science.gov (United States)

Belcher, Nathan Tillman

This action research study used data from multiple assessments in Mechanics and Electricity and Magnetism to determine the viability of Modeling Instruction as a pedagogy for students in AP Physics C: Mechanics and Electricity and Magnetism. Modeling Instruction is a guided-inquiry approach to teaching science in which students progress through the Modeling Cycle to develop a fully-constructed model for a scientific concept. AP Physics C: Mechanics and Electricity and Magnetism are calculus-based physics courses, approximately equivalent to first-year calculus-based physics courses at the collegiate level. Using a one-group pretest-posttest design, students were assessed in Mechanics using the Force Concept Inventory, Mechanics Baseline Test, and 2015 AP Physics C: Mechanics Practice Exam. With the same design, students were assessed in Electricity and Magnetism on the Brief Electricity and Magnetism Assessment, Electricity and Magnetism Conceptual Assessment, and 2015 AP Physics C: Electricity and Magnetism Practice Exam. In a one-shot case study design, student scores were collected from the 2017 AP Physics C: Mechanics and Electricity and Magnetism Exams. Students performed moderately well on the assessments in Mechanics and Electricity and Magnetism, demonstrating that Modeling Instruction is a viable pedagogy in AP Physics C: Electricity and Magnetism.

Chemo-mechanical modeling of tumor growth in elastic epithelial tissue

Energy Technology Data Exchange (ETDEWEB)

Bratsun, Dmitry A., E-mail: bratsun@pspu.ru [Department of Applied Physics, Perm National Research Polytechnical University, Perm, 614990 (Russian Federation); Zakharov, Andrey P. [Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel (Israel); Theoretical Physics Department, Perm State Humanitarian Pedagogical University, Perm, 614990 (Russian Federation); Pismen, Len [Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel (Israel)

2016-08-02

We propose a multiscale chemo-mechanical model of the cancer tumor development in the epithelial tissue. The epithelium is represented by an elastic 2D array of polygonal cells with its own gene regulation dynamics. The model allows the simulation of the evolution of multiple cells interacting via the chemical signaling or mechanically induced strain. The algorithm includes the division and intercalation of cells as well as the transformation of normal cells into a cancerous state triggered by a local failure of the spatial synchronization of the cellular rhythms driven by transcription/translation processes. Both deterministic and stochastic descriptions of the system are given for chemical signaling. The transformation of cells means the modification of their respective parameters responsible for chemo-mechanical interactions. The simulations reproduce a distinct behavior of invasive and localized carcinoma. Generally, the model is designed in such a way that it can be readily modified to take account of any newly understood gene regulation processes and feedback mechanisms affecting chemo-mechanical properties of cells.

Chemo-mechanical modeling of tumor growth in elastic epithelial tissue

Science.gov (United States)

Bratsun, Dmitry A.; Zakharov, Andrey P.; Pismen, Len

2016-08-01

We propose a multiscale chemo-mechanical model of the cancer tumor development in the epithelial tissue. The epithelium is represented by an elastic 2D array of polygonal cells with its own gene regulation dynamics. The model allows the simulation of the evolution of multiple cells interacting via the chemical signaling or mechanically induced strain. The algorithm includes the division and intercalation of cells as well as the transformation of normal cells into a cancerous state triggered by a local failure of the spatial synchronization of the cellular rhythms driven by transcription/translation processes. Both deterministic and stochastic descriptions of the system are given for chemical signaling. The transformation of cells means the modification of their respective parameters responsible for chemo-mechanical interactions. The simulations reproduce a distinct behavior of invasive and localized carcinoma. Generally, the model is designed in such a way that it can be readily modified to take account of any newly understood gene regulation processes and feedback mechanisms affecting chemo-mechanical properties of cells.

Different Mechanisms of Inflammation Induced in Virus and Autoimmune-Mediated Models of Multiple Sclerosis in C57BL6 Mice

Directory of Open Access Journals (Sweden)

Abhinoy Kishore

2013-01-01

Full Text Available Multiple sclerosis (MS is an inflammatory demyelinating disease of the human central nervous system (CNS. Neurotropic demyelinating strain of MHV (MHV-A59 or its isogenic recombinant strain RSA59 induces MS-like disease in mice mediated by microglia, along with a small population of T cells. The mechanism of demyelination is at least in part due to microglia-mediated myelin stripping, with some direct axonal injury. Immunization with myelin oligodendrocyte glycoprotein (MOG induces experimental autoimmune encephalomyelitis (EAE, a mainly CD4+ T-cell-mediated disease, although CD8+ T cells may play a significant role in demyelination. It is possible that both autoimmune and nonimmune mechanisms such as direct viral toxicity may induce MS. Our study directly compares CNS pathology in autoimmune and viral-induced MS models. Mice with viral-induced and EAE demyelinating diseases demonstrated similar patterns and distributions of demyelination that accumulated over the course of the disease. However, significant differences in acute inflammation were noted. Inflammation was restricted mainly to white matter at all times in EAE, whereas inflammation initially largely involved gray matter in acute MHV-induced disease and then is subsequently localized only in white matter in the chronic disease phase. The presence of dual mechanisms of demyelination may be responsible for the failure of immunosuppression to promote long-term remission in many MS patients.

Testing for Nonuniform Differential Item Functioning with Multiple Indicator Multiple Cause Models

Science.gov (United States)

Woods, Carol M.; Grimm, Kevin J.

2011-01-01

In extant literature, multiple indicator multiple cause (MIMIC) models have been presented for identifying items that display uniform differential item functioning (DIF) only, not nonuniform DIF. This article addresses, for apparently the first time, the use of MIMIC models for testing both uniform and nonuniform DIF with categorical indicators. A…

Collaboration Mechanism for Equipment Instruction of Multiple Energy Systems

Science.gov (United States)

Wang, Dong; Wang, Tuo; Wang, Qi; Zhang, Zhao; Zhao, Mingyu; Wang, Yinghui

2018-01-01

When multiple energy systems execute optimization instructions simultaneously, and the same equipment is Shared, the instruction conflict may occur. Aiming at the above problems, taking into account the control objectives of each system, the characteristics of different systems, such as comprehensive clean energy, energy efficiency, and peak filling, etc., designed the instruction coordination mechanism for the daemon. This mechanism mainly acts on the main station of the system, and form a final optimization instruction. For some specific scenarios, the collaboration mechanism of unlocking the terminal is supplemented. The mechanism determines the specific execution instructions based on the arrival time of the instruction. Finally, the experiment in Tianjin eco-city shows that this algorithm can meet the instruction and collaboration requirements of multi-energy systems, and ensure the safe operation of the equipment.

A modeling and numerical algorithm for thermoporomechanics in multiple porosity media for naturally fractured reservoirs

Science.gov (United States)

Kim, J.; Sonnenthal, E. L.; Rutqvist, J.

2011-12-01

Rigorous modeling of coupling between fluid, heat, and geomechanics (thermo-poro-mechanics), in fractured porous media is one of the important and difficult topics in geothermal reservoir simulation, because the physics are highly nonlinear and strongly coupled. Coupled fluid/heat flow and geomechanics are investigated using the multiple interacting continua (MINC) method as applied to naturally fractured media. In this study, we generalize constitutive relations for the isothermal elastic dual porosity model proposed by Berryman (2002) to those for the non-isothermal elastic/elastoplastic multiple porosity model, and derive the coupling coefficients of coupled fluid/heat flow and geomechanics and constraints of the coefficients. When the off-diagonal terms of the total compressibility matrix for the flow problem are zero, the upscaled drained bulk modulus for geomechanics becomes the harmonic average of drained bulk moduli of the multiple continua. In this case, the drained elastic/elastoplastic moduli for mechanics are determined by a combination of the drained moduli and volume fractions in multiple porosity materials. We also determine a relation between local strains of all multiple porosity materials in a gridblock and the global strain of the gridblock, from which we can track local and global elastic/plastic variables. For elastoplasticity, the return mapping is performed for all multiple porosity materials in the gridblock. For numerical implementation, we employ and extend the fixed-stress sequential method of the single porosity model to coupled fluid/heat flow and geomechanics in multiple porosity systems, because it provides numerical stability and high accuracy. This sequential scheme can be easily implemented by using a porosity function and its corresponding porosity correction, making use of the existing robust flow and geomechanics simulators. We implemented the proposed modeling and numerical algorithm to the reaction transport simulator

Modeling of MEMS Mirrors Actuated by Phase-Change Mechanism

Directory of Open Access Journals (Sweden)

David Torres

2017-04-01

Full Text Available Given the multiple applications for micro-electro-mechanical system (MEMS mirror devices, most of the research efforts are focused on improving device performance in terms of tilting angles, speed, and their integration into larger arrays or systems. The modeling of these devices is crucial for enabling a platform, in particular, by allowing for the future control of such devices. In this paper, we present the modeling of a MEMS mirror structure with four actuators driven by the phase-change of a thin film. The complexity of the device structure and the nonlinear behavior of the actuation mechanism allow for a comprehensive study that encompasses simpler electrothermal designs, thus presenting a general approach that can be adapted to most MEMS mirror designs based on this operation principle. The MEMS mirrors presented in this work are actuated by Joule heating and tested using optical techniques. Mechanical and thermal models including both pitch and roll displacements are developed by combining theoretical analysis (using both numerical and analytical tools with experimental data and subsequently verifying with quasi-static and dynamic experiments.

Multiscale Mechanics of Articular Cartilage: Potentials and Challenges of Coupling Musculoskeletal, Joint, and Microscale Computational Models

Science.gov (United States)

Halloran, J. P.; Sibole, S.; van Donkelaar, C. C.; van Turnhout, M. C.; Oomens, C. W. J.; Weiss, J. A.; Guilak, F.; Erdemir, A.

2012-01-01

Articular cartilage experiences significant mechanical loads during daily activities. Healthy cartilage provides the capacity for load bearing and regulates the mechanobiological processes for tissue development, maintenance, and repair. Experimental studies at multiple scales have provided a fundamental understanding of macroscopic mechanical function, evaluation of the micromechanical environment of chondrocytes, and the foundations for mechanobiological response. In addition, computational models of cartilage have offered a concise description of experimental data at many spatial levels under healthy and diseased conditions, and have served to generate hypotheses for the mechanical and biological function. Further, modeling and simulation provides a platform for predictive risk assessment, management of dysfunction, as well as a means to relate multiple spatial scales. Simulation-based investigation of cartilage comes with many challenges including both the computational burden and often insufficient availability of data for model development and validation. This review outlines recent modeling and simulation approaches to understand cartilage function from a mechanical systems perspective, and illustrates pathways to associate mechanics with biological function. Computational representations at single scales are provided from the body down to the microstructure, along with attempts to explore multiscale mechanisms of load sharing that dictate the mechanical environment of the cartilage and chondrocytes. PMID:22648577

Multiple-walled BN nanotubes obtained with a mechanical alloying technique

International Nuclear Information System (INIS)

Rosas, G.; Sistos, J.; Ascencio, J.A.; Medina, A.; Perez, R.

2005-01-01

An experimental method to obtain multiple-walled nanotubes of BN using low energy is presented. The method is based on the use of mechanical alloying techniques with elemental boron powders and nitrogen gas mixed in an autoclave at room temperature. The chemical and structural characteristics of the multiple-walled nanotubes were obtained using different techniques, such as X-ray diffraction, transmission electron microscopy, EELS microanalysis, high-resolution electron microscopy images and theoretical simulations based on the multisliced approach of the electron diffraction theory. This investigation clearly illustrates the production of multiple-wall BN nanotubes at room temperature. These results open up a new kind of synthesis method with low expense and important perspectives for use in large-quantity production. (orig.)

Quantum Mechanics/Molecular Mechanics Modeling of Drug Metabolism: Mexiletine N-Hydroxylation by Cytochrome P450 1A2.

Science.gov (United States)

Lonsdale, Richard; Fort, Rachel M; Rydberg, Patrik; Harvey, Jeremy N; Mulholland, Adrian J

2016-06-20

The mechanism of cytochrome P450(CYP)-catalyzed hydroxylation of primary amines is currently unclear and is relevant to drug metabolism; previous small model calculations have suggested two possible mechanisms: direct N-oxidation and H-abstraction/rebound. We have modeled the N-hydroxylation of (R)-mexiletine in CYP1A2 with hybrid quantum mechanics/molecular mechanics (QM/MM) methods, providing a more detailed and realistic model. Multiple reaction barriers have been calculated at the QM(B3LYP-D)/MM(CHARMM27) level for the direct N-oxidation and H-abstraction/rebound mechanisms. Our calculated barriers indicate that the direct N-oxidation mechanism is preferred and proceeds via the doublet spin state of Compound I. Molecular dynamics simulations indicate that the presence of an ordered water molecule in the active site assists in the binding of mexiletine in the active site, but this is not a prerequisite for reaction via either mechanism. Several active site residues play a role in the binding of mexiletine in the active site, including Thr124 and Phe226. This work reveals key details of the N-hydroxylation of mexiletine and further demonstrates that mechanistic studies using QM/MM methods are useful for understanding drug metabolism.

Authority inside the firm: multiple mechanisms of coordination

OpenAIRE

Bernard Baudry; Bruno Tinel

2004-01-01

In the last twenty years, through a growing awareness of contractual incompleteness, the concept of authority has regained primacy in the analysis of the employment relationship. This article pursues two goals. First, we assess the famous controversy between Coase and Alchian and Demsetz via an analysis of the foundations of intra-firm authority. Second, we argue that intra-firm authority cannot hinge on a single variable and, to the contrary, rests on multiple mechanisms. The employer's auth...

Modeling Rabbit Responses to Single and Multiple Aerosol ...

Science.gov (United States)

Journal Article Survival models are developed here to predict response and time-to-response for mortality in rabbits following exposures to single or multiple aerosol doses of Bacillus anthracis spores. Hazard function models were developed for a multiple dose dataset to predict the probability of death through specifying dose-response functions and the time between exposure and the time-to-death (TTD). Among the models developed, the best-fitting survival model (baseline model) has an exponential dose-response model with a Weibull TTD distribution. Alternative models assessed employ different underlying dose-response functions and use the assumption that, in a multiple dose scenario, earlier doses affect the hazard functions of each subsequent dose. In addition, published mechanistic models are analyzed and compared with models developed in this paper. None of the alternative models that were assessed provided a statistically significant improvement in fit over the baseline model. The general approach utilizes simple empirical data analysis to develop parsimonious models with limited reliance on mechanistic assumptions. The baseline model predicts TTDs consistent with reported results from three independent high-dose rabbit datasets. More accurate survival models depend upon future development of dose-response datasets specifically designed to assess potential multiple dose effects on response and time-to-response. The process used in this paper to dev

The curvature calculation mechanism based on simple cell model.

Science.gov (United States)

Yu, Haiyang; Fan, Xingyu; Song, Aiqi

2017-07-20

A conclusion has not yet been reached on how exactly the human visual system detects curvature. This paper demonstrates how orientation-selective simple cells can be used to construct curvature-detecting neural units. Through fixed arrangements, multiple plurality cells were constructed to simulate curvature cells with a proportional output to their curvature. In addition, this paper offers a solution to the problem of narrow detection range under fixed resolution by selecting an output value under multiple resolution. Curvature cells can be treated as concrete models of an end-stopped mechanism, and they can be used to further understand "curvature-selective" characteristics and to explain basic psychophysical findings and perceptual phenomena in current studies.

Modeling and Control of the Redundant Parallel Adjustment Mechanism on a Deployable Antenna Panel

Directory of Open Access Journals (Sweden)

Lili Tian

2016-10-01

Full Text Available With the aim of developing multiple input and multiple output (MIMO coupling systems with a redundant parallel adjustment mechanism on the deployable antenna panel, a structural control integrated design methodology is proposed in this paper. Firstly, the modal information from the finite element model of the structure of the antenna panel is extracted, and then the mathematical model is established with the Hamilton principle; Secondly, the discrete Linear Quadratic Regulator (LQR controller is added to the model in order to control the actuators and adjust the shape of the panel. Finally, the engineering practicality of the modeling and control method based on finite element analysis simulation is verified.

Direct and indirect stabilisation mechanisms in multiple electron capture

Energy Technology Data Exchange (ETDEWEB)

Roncin, P. [Paris-11 Univ., 91 - Orsay (France). Lab. de Collisions Atomiques et Moleculaires; Barat, M. [Paris-11 Univ., 91 - Orsay (France). Lab. de Collisions Atomiques et Moleculaires; Gaboriaud, M.N. [Paris-11 Univ., 91 -Orsay (France). Lab. de Collisions Atomiques et Moleculaires; Szilagyi, Z.S. [Paris-11 Univ., 91 - Orsay (France). Lab. de Collisions Atomiques et Moleculaires; Kazansky, A.K. [Paris-11 Univ., 91 - Orsay (France). Lab. de Collisions Atomiques et Moleculaires

1995-05-01

During the last years both experimental and theoretical works have focused on the problem of the stabilisation of two excited electrons on the projectile. In this contribution we would like to give experimental examples of the two suggested mechanisms and their extension to multiple electron capture. Our data are discussed together with those obtained with other experimental techniques and with theoretical predictions. (orig./WL).

Simultaneous Measurement of Multiple Mechanical Properties of Single Cells Using AFM by Indentation and Vibration.

Science.gov (United States)

Zhang, Chuang; Shi, Jialin; Wang, Wenxue; Xi, Ning; Wang, Yuechao; Liu, Lianqing

2017-12-01

The mechanical properties of cells, which are the main characteristics determining their physical performance and physiological functions, have been actively studied in the fields of cytobiology and biomedical engineering and for the development of medicines. In this study, an indentation-vibration-based method is proposed to simultaneously measure the mechanical properties of cells in situ, including cellular mass (m), elasticity (k), and viscosity (c). The proposed measurement method is implemented based on the principle of forced vibration stimulated by simple harmonic force using an atomic force microscope (AFM) system integrated with a piezoelectric transducer as the substrate vibrator. The corresponding theoretical model containing the three mechanical properties is derived and used to perform simulations and calculations. Living and fixed human embryonic kidney 293 (HEK 293) cells were subjected to indentation and vibration to measure and compare their mechanical parameters and verify the proposed approach. The results that the fixed sample cells are more viscous and elastic than the living sample cells and the measured mechanical properties of cell are consistent within, but not outside of the central region of the cell, are in accordance with the previous studies. This work provides an approach to simultaneous measurement of the multiple mechanical properties of single cells using an integrated AFM system based on the principle force vibration and thickness-corrected Hertz model. This study should contribute to progress in biomedical engineering, cytobiology, medicine, early diagnosis, specific therapy and cell-powered robots.

Shared Authentic Leadership in Research Teams: Testing a Multiple Mediation Model.

Science.gov (United States)

Guenter, Hannes; Gardner, William L; Davis McCauley, Kelly; Randolph-Seng, Brandon; Prabhu, Veena P

2017-12-01

Research teams face complex leadership and coordination challenges. We propose shared authentic leadership (SAL) as a timely approach to addressing these challenges. Drawing from authentic and functional leadership theories, we posit a multiple mediation model that suggests three mechanisms whereby SAL influences team effectiveness: shared mental models (SMM), team trust, and team coordination. To test our hypotheses, we collected survey data on leadership and teamwork within 142 research teams that recently published an article in a peer-reviewed management journal. The results indicate team coordination represents the primary mediating mechanism accounting for the relationship between SAL and research team effectiveness. While teams with high trust and SMM felt more successful and were more satisfied, they were less successful in publishing in high-impact journals. We also found the four SAL dimensions (i.e., self-awareness, relational transparency, balanced processing, and internalized moral perspective) to associate differently with team effectiveness.

Multiplicity distributions in the dual parton model

International Nuclear Information System (INIS)

Batunin, A.V.; Tolstenkov, A.N.

1985-01-01

Multiplicity distributions are calculated by means of a new mechanism of production of hadrons in a string, which was proposed previously by the authors and takes into account explicitly the valence character of the ends of the string. It is shown that allowance for this greatly improves the description of the low-energy multiplicity distributions. At superhigh energies, the contribution of the ends of the strings becomes negligibly small, but in this case multi-Pomeron contributions must be taken into account

Multiple stressor effects in Chlamydomonas reinhardtii – Toward understanding mechanisms of interaction between effects of ultraviolet radiation and chemical pollutants

Energy Technology Data Exchange (ETDEWEB)

Korkaric, Muris [Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf (Switzerland); ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zürich (Switzerland); Behra, Renata; Fischer, Beat B. [Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf (Switzerland); Junghans, Marion [Swiss Center for Applied Ecotoxicology Eawag-EPFL, 8600, Duebendorf (Switzerland); Eggen, Rik I.L., E-mail: rik.eggen@eawag.ch [Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600, Duebendorf (Switzerland); ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zürich (Switzerland)

2015-05-15

Highlights: • Systematic study of multiple stressor effects of UVR and chemicals in C. reinhardtii. • UVR and chemicals did not act independently on algal photosynthesis and reproduction. • Multiple stressor effects of UVR and chemicals depended on chemical MOA. • Synergistic effect interactions not limited to oxidative stress inducing chemicals. • Multiple MOAs of UVR may limit applicability of current prediction models. - Abstract: The effects of chemical pollutants and environmental stressors, such as ultraviolet radiation (UVR), can interact when organisms are simultaneously exposed, resulting in higher (synergistic) or lower (antagonistic) multiple stressor effects than expected based on the effects of single stressors. Current understanding of interactive effects is limited due to a lack of mechanism-based multiple stressor studies. It has been hypothesized that effect interactions may generally occur if chemical and non-chemical stressors cause similar physiological effects in the organism. To test this hypothesis, we exposed the model green alga Chlamydomonas reinhardtii to combinations of UVR and single chemicals displaying modes of action (MOA) similar or dissimilar to the impact of UVR on photosynthesis. Stressor interactions were analyzed based on the independent action model. Effect interactions were found to depend on the MOA of the chemicals, and also on their concentrations, the exposure time and the measured endpoint. Indeed, only chemicals assumed to cause effects on photosynthesis similar to UVR showed interactions with UVR on photosynthetic yield: synergistic in case of Cd(II) and paraquat and antagonistic in case of diuron. No interaction on photosynthesis was observed for S-metolachlor, which acts dissimilarly to UVR. However, combined effects of S-metolachlor and UVR on algal reproduction were synergistic, highlighting the importance of considering additional MOA of UVR. Possible mechanisms of stressor effect interactions are

Multiple stressor effects in Chlamydomonas reinhardtii – Toward understanding mechanisms of interaction between effects of ultraviolet radiation and chemical pollutants

International Nuclear Information System (INIS)

Korkaric, Muris; Behra, Renata; Fischer, Beat B.; Junghans, Marion; Eggen, Rik I.L.

2015-01-01

Highlights: • Systematic study of multiple stressor effects of UVR and chemicals in C. reinhardtii. • UVR and chemicals did not act independently on algal photosynthesis and reproduction. • Multiple stressor effects of UVR and chemicals depended on chemical MOA. • Synergistic effect interactions not limited to oxidative stress inducing chemicals. • Multiple MOAs of UVR may limit applicability of current prediction models. - Abstract: The effects of chemical pollutants and environmental stressors, such as ultraviolet radiation (UVR), can interact when organisms are simultaneously exposed, resulting in higher (synergistic) or lower (antagonistic) multiple stressor effects than expected based on the effects of single stressors. Current understanding of interactive effects is limited due to a lack of mechanism-based multiple stressor studies. It has been hypothesized that effect interactions may generally occur if chemical and non-chemical stressors cause similar physiological effects in the organism. To test this hypothesis, we exposed the model green alga Chlamydomonas reinhardtii to combinations of UVR and single chemicals displaying modes of action (MOA) similar or dissimilar to the impact of UVR on photosynthesis. Stressor interactions were analyzed based on the independent action model. Effect interactions were found to depend on the MOA of the chemicals, and also on their concentrations, the exposure time and the measured endpoint. Indeed, only chemicals assumed to cause effects on photosynthesis similar to UVR showed interactions with UVR on photosynthetic yield: synergistic in case of Cd(II) and paraquat and antagonistic in case of diuron. No interaction on photosynthesis was observed for S-metolachlor, which acts dissimilarly to UVR. However, combined effects of S-metolachlor and UVR on algal reproduction were synergistic, highlighting the importance of considering additional MOA of UVR. Possible mechanisms of stressor effect interactions are

Plants-Derived Neuroprotective Agents: Cutting the Cycle of Cell Death through Multiple Mechanisms

Directory of Open Access Journals (Sweden)

Taiwo Olayemi Elufioye

2017-01-01

Full Text Available Neuroprotection is the preservation of the structure and function of neurons from insults arising from cellular injuries induced by a variety of agents or neurodegenerative diseases (NDs. The various NDs including Alzheimer’s, Parkinson’s, and Huntington’s diseases as well as amyotropic lateral sclerosis affect millions of people around the world with the main risk factor being advancing age. Each of these diseases affects specific neurons and/or regions in the brain and involves characteristic pathological and molecular features. Hence, several in vitro and in vivo study models specific to each disease have been employed to study NDs with the aim of understanding their underlying mechanisms and identifying new therapeutic strategies. Of the most prevalent drug development efforts employed in the past few decades, mechanisms implicated in the accumulation of protein-based deposits, oxidative stress, neuroinflammation, and certain neurotransmitter deficits such as acetylcholine and dopamine have been scrutinized in great detail. In this review, we presented classical examples of plant-derived neuroprotective agents by highlighting their structural class and specific mechanisms of action. Many of these natural products that have shown therapeutic efficacies appear to be working through the above-mentioned key multiple mechanisms of action.

A mechanical characterisation on multiple timescales of electroconductive magnetorheological elastomers

Science.gov (United States)

Schümann, M.; Morich, J.; Kaufhold, T.; Böhm, V.; Zimmermann, K.; Odenbach, S.

2018-05-01

Magnetorheological elastomers are a type of smart hybrid material which combines elastic properties of a soft elastomer matrix with magnetic properties of magnetic micro particles. This leads to a material with magnetically controllable mechanical properties of which the magnetorheological effect is the best known. The addition of electroconductive particles to the polymer mix adds electrical properties to the material behaviour. The resulting electrical resistance of the sample can be manipulated by external magnetic fields and mechanical loads. This results in a distinct interplay of mechanical, electrical and magnetic effects with a highly complex time behaviour. In this paper a mechanical characterisation on multiple time scales was conducted to get an insight on the short and long-term electrical and mechanical behaviour of this novel material. The results show a complex resistivity behaviour on several timescales, sensitive to magnetic fields and strain velocity. The observed material exhibits fatigue and relaxation behaviour, whereas the magnetorheological effect appears not to interfere with the piezoresistive properties.

Multiple trapping on a comb structure as a model of electron transport in disordered nanostructured semiconductors

International Nuclear Information System (INIS)

Sibatov, R. T.; Morozova, E. V.

2015-01-01

A model of dispersive transport in disordered nanostructured semiconductors has been proposed taking into account the percolation structure of a sample and joint action of several mechanisms. Topological and energy disorders have been simultaneously taken into account within the multiple trapping model on a comb structure modeling the percolation character of trajectories. The joint action of several mechanisms has been described within random walks with a mixture of waiting time distributions. Integral transport equations with fractional derivatives have been obtained for an arbitrary density of localized states. The kinetics of the transient current has been calculated within the proposed new model in order to analyze time-of-flight experiments for nanostructured semiconductors

Geometrical model of multiple production

International Nuclear Information System (INIS)

Chikovani, Z.E.; Jenkovszky, L.L.; Kvaratshelia, T.M.; Struminskij, B.V.

1988-01-01

The relation between geometrical and KNO-scaling and their violation is studied in a geometrical model of multiple production of hadrons. Predictions concerning the behaviour of correlation coefficients at future accelerators are given

Multiplicity Control in Structural Equation Modeling

Science.gov (United States)

Cribbie, Robert A.

2007-01-01

Researchers conducting structural equation modeling analyses rarely, if ever, control for the inflated probability of Type I errors when evaluating the statistical significance of multiple parameters in a model. In this study, the Type I error control, power and true model rates of famsilywise and false discovery rate controlling procedures were…

Multiplicative point process as a model of trading activity

Science.gov (United States)

Gontis, V.; Kaulakys, B.

2004-11-01

Signals consisting of a sequence of pulses show that inherent origin of the 1/ f noise is a Brownian fluctuation of the average interevent time between subsequent pulses of the pulse sequence. In this paper, we generalize the model of interevent time to reproduce a variety of self-affine time series exhibiting power spectral density S( f) scaling as a power of the frequency f. Furthermore, we analyze the relation between the power-law correlations and the origin of the power-law probability distribution of the signal intensity. We introduce a stochastic multiplicative model for the time intervals between point events and analyze the statistical properties of the signal analytically and numerically. Such model system exhibits power-law spectral density S( f)∼1/ fβ for various values of β, including β= {1}/{2}, 1 and {3}/{2}. Explicit expressions for the power spectra in the low-frequency limit and for the distribution density of the interevent time are obtained. The counting statistics of the events is analyzed analytically and numerically, as well. The specific interest of our analysis is related with the financial markets, where long-range correlations of price fluctuations largely depend on the number of transactions. We analyze the spectral density and counting statistics of the number of transactions. The model reproduces spectral properties of the real markets and explains the mechanism of power-law distribution of trading activity. The study provides evidence that the statistical properties of the financial markets are enclosed in the statistics of the time interval between trades. A multiplicative point process serves as a consistent model generating this statistics.

On the thermoluminescent interactive multiple-trap system (IMTS) model: is it a simple model?

International Nuclear Information System (INIS)

Gil T, M. I.; Perez C, L.; Cruz Z, E.; Furetta, C.; Roman L, J.

2016-10-01

In the thermally stimulated luminescence phenomenon, named thermoluminescence (Tl), the electrons and holes generated by the radiation-matter interaction can be trapped by the metastable levels in the band gap of the solid. Following, the electron can be thermally releases into the conduction band and a radiatively recombination with hole close to the recombination center occurred and the glow curve is emitted. However, the complex mechanism of trapping and thermally releases occurred in the band gap of solid. Some models, such as; first, second and general-order kinetics, have been well established to explain the behaviour of the glow curves and their defects recombination mechanism. In this work, expressions for and Interactive Multiple-Trap System model (IMTS) was obtained assuming: a set of discrete electron traps (active traps At), another set of thermally disconnected trap (TDT) and a recombination center (Rc) too. A numerical analysis based on the Levenberg-Marquardt method in conjunction with an implicit Rosenbrock method was taken into account to simulate the glow curve. The numerical method was tested through synthetic Tl glow curves for a wide range of trap parameters. The activation energy and kinetics order were determined using values from the General Order Kinetics (GOK) model as entry data to IMTS model. This model was tested using the experimental glow curves obtained from Ce or Eu-doped MgF 2 (LiF) polycrystals samples. Results shown that the IMTS model can predict more accurately the behavior of the Tl glow curves that those obtained by the GOK modified by Rasheedy and by the Mixed Order Kinetics model. (Author)

Relative efficiency of joint-model and full-conditional-specification multiple imputation when conditional models are compatible: The general location model.

Science.gov (United States)

Seaman, Shaun R; Hughes, Rachael A

2018-06-01

Estimating the parameters of a regression model of interest is complicated by missing data on the variables in that model. Multiple imputation is commonly used to handle these missing data. Joint model multiple imputation and full-conditional specification multiple imputation are known to yield imputed data with the same asymptotic distribution when the conditional models of full-conditional specification are compatible with that joint model. We show that this asymptotic equivalence of imputation distributions does not imply that joint model multiple imputation and full-conditional specification multiple imputation will also yield asymptotically equally efficient inference about the parameters of the model of interest, nor that they will be equally robust to misspecification of the joint model. When the conditional models used by full-conditional specification multiple imputation are linear, logistic and multinomial regressions, these are compatible with a restricted general location joint model. We show that multiple imputation using the restricted general location joint model can be substantially more asymptotically efficient than full-conditional specification multiple imputation, but this typically requires very strong associations between variables. When associations are weaker, the efficiency gain is small. Moreover, full-conditional specification multiple imputation is shown to be potentially much more robust than joint model multiple imputation using the restricted general location model to mispecification of that model when there is substantial missingness in the outcome variable.

Introducing memory and association mechanism into a biologically inspired visual model.

Science.gov (United States)

Qiao, Hong; Li, Yinlin; Tang, Tang; Wang, Peng

2014-09-01

A famous biologically inspired hierarchical model (HMAX model), which was proposed recently and corresponds to V1 to V4 of the ventral pathway in primate visual cortex, has been successfully applied to multiple visual recognition tasks. The model is able to achieve a set of position- and scale-tolerant recognition, which is a central problem in pattern recognition. In this paper, based on some other biological experimental evidence, we introduce the memory and association mechanism into the HMAX model. The main contributions of the work are: 1) mimicking the active memory and association mechanism and adding the top down adjustment to the HMAX model, which is the first try to add the active adjustment to this famous model and 2) from the perspective of information, algorithms based on the new model can reduce the computation storage and have a good recognition performance. The new model is also applied to object recognition processes. The primary experimental results show that our method is efficient with a much lower memory requirement.

Numerical solution of fractured horizontal wells in shale gas reservoirs considering multiple transport mechanisms

Science.gov (United States)

Zhao, Yu-long; Tang, Xu-chuan; Zhang, Lie-hui; Tang, Hong-ming; Tao, Zheng-Wu

2018-06-01

The multiscale pore size and specific gas storage mechanism in organic-rich shale gas reservoirs make gas transport in such reservoirs complicated. Therefore, a model that fully incorporates all transport mechanisms and employs an accurate numerical method is urgently needed to simulate the gas production process. In this paper, a unified model of apparent permeability was first developed, which took into account multiple influential factors including slip flow, Knudsen diffusion (KD), surface diffusion, effects of the adsorbed layer, permeability stress sensitivity, and ad-/desorption phenomena. Subsequently, a comprehensive mathematical model, which included the model of apparent permeability, was derived to describe gas production behaviors. Thereafter, on the basis of unstructured perpendicular bisection grids and finite volume method, a fully implicit numerical simulator was developed using Matlab software. The validation and application of the new model were confirmed using a field case reported in the literature. Finally, the impacts of related influencing factors on gas production were analyzed. The results showed that KD resulted in a negligible impact on gas production in the proposed model. The smaller the pore size was, the more obvious the effects of the adsorbed layer on the well production rate would be. Permeability stress sensitivity had a slight effect on well cumulative production in shale gas reservoirs. Adsorbed gas made a major contribution to the later flow period of the well; the greater the adsorbed gas content, the greater the well production rate would be. This paper can improve the understanding of gas production in shale gas reservoirs for petroleum engineers.

3-D thermo-mechanical laboratory modeling of plate-tectonics: modeling scheme, technique and first experiments

Directory of Open Access Journals (Sweden)

D. Boutelier

2011-05-01

Full Text Available We present an experimental apparatus for 3-D thermo-mechanical analogue modeling of plate tectonic processes such as oceanic and continental subductions, arc-continent or continental collisions. The model lithosphere, made of temperature-sensitive elasto-plastic analogue materials with strain softening, is submitted to a constant temperature gradient causing a strength reduction with depth in each layer. The surface temperature is imposed using infrared emitters, which allows maintaining an unobstructed view of the model surface and the use of a high resolution optical strain monitoring technique (Particle Imaging Velocimetry. Subduction experiments illustrate how the stress conditions on the interplate zone can be estimated using a force sensor attached to the back of the upper plate and adjusted via the density and strength of the subducting lithosphere or the lubrication of the plate boundary. The first experimental results reveal the potential of the experimental set-up to investigate the three-dimensional solid-mechanics interactions of lithospheric plates in multiple natural situations.

Cannabidiol inhibits angiogenesis by multiple mechanisms.

Science.gov (United States)

Solinas, M; Massi, P; Cantelmo, A R; Cattaneo, M G; Cammarota, R; Bartolini, D; Cinquina, V; Valenti, M; Vicentini, L M; Noonan, D M; Albini, A; Parolaro, D

2012-11-01

Several studies have demonstrated anti-proliferative and pro-apoptotic actions of cannabinoids on various tumours, together with their anti-angiogenic properties. The non-psychoactive cannabinoid cannabidiol (CBD) effectively inhibits the growth of different types of tumours in vitro and in vivo and down-regulates some pro-angiogenic signals produced by glioma cells. As its anti-angiogenic properties have not been thoroughly investigated to date, and given its very favourable pharmacological and toxicological profile, here, we evaluated the ability of CBD to modulate tumour angiogenesis. Firstly, we evaluated the effect of CBD on human umbilical vein endothelial cell (HUVEC) proliferation and viability - through [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and FACS analysis - and in vitro motility - both in a classical Boyden chamber test and in a wound-healing assay. We next investigated CBD effects on different angiogenesis-related proteins released by HUVECs, using an angiogenesis array kit and an ELISA directed at MMP2. Then we evaluated its effects on in vitro angiogenesis in treated HUVECs invading a Matrigel layer and in HUVEC spheroids embedded into collagen gels, and further characterized its effects in vivo using a Matrigel sponge model of angiogenesis in C57/BL6 mice. CBD induced HUVEC cytostasis without inducing apoptosis, inhibited HUVEC migration, invasion and sprouting in vitro, and angiogenesis in vivo in Matrigel sponges. These effects were associated with the down-modulation of several angiogenesis-related molecules. This study reveals that CBD inhibits angiogenesis by multiple mechanisms. Its dual effect on both tumour and endothelial cells supports the hypothesis that CBD has potential as an effective agent in cancer therapy. © 2012 The Authors. British Journal of Pharmacology © 2012 The British Pharmacological Society.

Geophysical Factor Resolving of Rainfall Mechanism for Super Typhoons by Using Multiple Spatiotemporal Components Analysis

Science.gov (United States)

Huang, Chien-Lin; Hsu, Nien-Sheng

2016-04-01

This study develops a novel methodology to resolve the geophysical cause of typhoon-induced rainfall considering diverse dynamic co-evolution at multiple spatiotemporal components. The multi-order hidden patterns of complex hydrological process in chaos are detected to understand the fundamental laws of rainfall mechanism. The discovered spatiotemporal features are utilized to develop a state-of-the-art descriptive statistical model for mechanism validation, modeling and further prediction during typhoons. The time series of hourly typhoon precipitation from different types of moving track, atmospheric field and landforms are respectively precede the signal analytical process to qualify each type of rainfall cause and to quantify the corresponding affected degree based on the measured geophysical atmospheric-hydrological variables. This study applies the developed methodology in Taiwan Island which is constituted by complex diverse landform formation. The identified driving-causes include: (1) cloud height to ground surface; (2) co-movement effect induced by typhoon wind field with monsoon; (3) stem capacity; (4) interaction between typhoon rain band and terrain; (5) structural intensity variance of typhoon; and (6) integrated cloudy density of rain band. Results show that: (1) for the central maximum wind speed exceeding 51 m/sec, Causes (1) and (3) are the primary ones to generate rainfall; (2) for the typhoon moving toward the direction of 155° to 175°, Cause (2) is the primary one; (3) for the direction of 90° to 155°, Cause (4) is the primary one; (4) for the typhoon passing through mountain chain which above 3500 m, Cause (5) is the primary one; and (5) for the moving speed lower than 18 km/hr, Cause (6) is the primary one. Besides, the multiple geophysical component-based precipitation modeling can achieve 81% of average accuracy and 0.732 of average correlation coefficient (CC) within average 46 hours of duration, that improve their predictability.

Integration of multiple, excess, backup, and expected covering models

OpenAIRE

M S Daskin; K Hogan; C ReVelle

1988-01-01

The concepts of multiple, excess, backup, and expected coverage are defined. Model formulations using these constructs are reviewed and contrasted to illustrate the relationships between them. Several new formulations are presented as is a new derivation of the expected covering model which indicates more clearly the relationship of the model to other multi-state covering models. An expected covering model with multiple time standards is also presented.

Evolving Four Part Harmony Using a Multiple Worlds Model

DEFF Research Database (Denmark)

Scirea, Marco; Brown, Joseph Alexander

2015-01-01

This application of the Multiple Worlds Model examines a collaborative fitness model for generating four part harmonies. In this model we have multiple populations and the fitness of the individuals is based on the ability of a member from each population to work with the members of other...

Mechanism of chimera formation during the Multiple Displacement Amplification reaction

Directory of Open Access Journals (Sweden)

Stockwell Timothy B

2007-04-01

Full Text Available Abstract Background Multiple Displacement Amplification (MDA is a method used for amplifying limiting DNA sources. The high molecular weight amplified DNA is ideal for DNA library construction. While this has enabled genomic sequencing from one or a few cells of unculturable microorganisms, the process is complicated by the tendency of MDA to generate chimeric DNA rearrangements in the amplified DNA. Determining the source of the DNA rearrangements would be an important step towards reducing or eliminating them. Results Here, we characterize the major types of chimeras formed by carrying out an MDA whole genome amplification from a single E. coli cell and sequencing by the 454 Life Sciences method. Analysis of 475 chimeras revealed the predominant reaction mechanisms that create the DNA rearrangements. The highly branched DNA synthesized in MDA can assume many alternative secondary structures. DNA strands extended on an initial template can be displaced becoming available to prime on a second template creating the chimeras. Evidence supports a model in which branch migration can displace 3'-ends freeing them to prime on the new templates. More than 85% of the resulting DNA rearrangements were inverted sequences with intervening deletions that the model predicts. Intramolecular rearrangements were favored, with displaced 3'-ends reannealing to single stranded 5'-strands contained within the same branched DNA molecule. In over 70% of the chimeric junctions, the 3' termini had initiated priming at complimentary sequences of 2–21 nucleotides (nts in the new templates. Conclusion Formation of chimeras is an important limitation to the MDA method, particularly for whole genome sequencing. Identification of the mechanism for chimera formation provides new insight into the MDA reaction and suggests methods to reduce chimeras. The 454 sequencing approach used here will provide a rapid method to assess the utility of reaction modifications.

A mechanical model for deformable and mesh pattern wheel of lunar roving vehicle

Science.gov (United States)

Liang, Zhongchao; Wang, Yongfu; Chen, Gang (Sheng); Gao, Haibo

2015-12-01

As an indispensable tool for astronauts on lunar surface, the lunar roving vehicle (LRV) is of great significance for manned lunar exploration. An LRV moves on loose and soft lunar soil, so the mechanical property of its wheels directly affects the mobility performance. The wheels used for LRV have deformable and mesh pattern, therefore, the existing mechanical theory of vehicle wheel cannot be used directly for analyzing the property of LRV wheels. In this paper, a new mechanical model for LRV wheel is proposed. At first, a mechanical model for a rigid normal wheel is presented, which involves in multiple conventional parameters such as vertical load, tangential traction force, lateral force, and slip ratio. Secondly, six equivalent coefficients are introduced to amend the rigid normal wheel model to fit for the wheels with deformable and mesh-pattern in LRV application. Thirdly, the values of the six equivalent coefficients are identified by using experimental data obtained in an LRV's single wheel testing. Finally, the identified mechanical model for LRV's wheel with deformable and mesh pattern are further verified and validated by using additional experimental results.

Double-multiple streamtube model for Darrieus in turbines

Science.gov (United States)

Paraschivoiu, I.

1981-01-01

An analytical model is proposed for calculating the rotor performance and aerodynamic blade forces for Darrieus wind turbines with curved blades. The method of analysis uses a multiple-streamtube model, divided into two parts: one modeling the upstream half-cycle of the rotor and the other, the downstream half-cycle. The upwind and downwind components of the induced velocities at each level of the rotor were obtained using the principle of two actuator disks in tandem. Variation of the induced velocities in the two parts of the rotor produces larger forces in the upstream zone and smaller forces in the downstream zone. Comparisons of the overall rotor performance with previous methods and field test data show the important improvement obtained with the present model. The calculations were made using the computer code CARDAA developed at IREQ. The double-multiple streamtube model presented has two major advantages: it requires a much shorter computer time than the three-dimensional vortex model and is more accurate than multiple-streamtube model in predicting the aerodynamic blade loads.

Mechanisms for integration of information models across related domains

Science.gov (United States)

Atkinson, Rob

2010-05-01

It is well recognised that there are opportunities and challenges in cross-disciplinary data integration. A significant barrier, however, is creating a conceptual model of the combined domains and the area of integration. For example, a groundwater domain application may require information from several related domains: geology, hydrology, water policy, etc. Each domain may have its own data holdings and conceptual models, but these will share various common concepts (eg. The concept of an aquifer). These areas of semantic overlap present significant challenges, firstly to choose a single representation (model) of a concept that appears in multiple disparate models,, then to harmonise these other models with the single representation. In addition, models may exist at different levels of abstraction depending on how closely aligned they are with a particular implementation. This makes it hard for modellers in one domain to introduce elements from another domain without either introducing a specific style of implementation, or conversely dealing with a set of abstract patterns that are hard to integrate with existing implementations. Models are easier to integrate if they are broken down into small units, with common concepts implemented using common models from well-known, and predictably managed shared libraries. This vision however requires development of a set of mechanisms (tools and procedures) for implementing and exploiting libraries of model components. These mechanisms need to handle publication, discovery, subscription, versioning and implementation of models in different forms. In this presentation a coherent suite of such mechanisms is proposed, using a scenario based on re-use of geosciences models. This approach forms the basis of a comprehensive strategy to empower domain modellers to create more interoperable systems. The strategy address a range of concerns and practice, and includes methodologies, an accessible toolkit, improvements to available

A multiple-field coupled resistive transition model for superconducting Nb3Sn

Science.gov (United States)

Yang, Lin; Ding, He; Zhang, Xin; Qiao, Li

2016-12-01

A study on the superconducting transition width as functions of the applied magnetic field and strain is performed in superconducting Nb3Sn. A quantitative, yet universal phenomenological resistivity model is proposed. The numerical simulation by the proposed model shows predicted resistive transition characteristics under variable magnetic fields and strain, which in good agreement with the experimental observations. Furthermore, a temperature-modulated magnetoresistance transition behavior in filamentary Nb3Sn conductors can also be well described by the given model. The multiple-field coupled resistive transition model is helpful for making objective determinations of the high-dimensional critical surface of Nb3Sn in the multi-parameter space, offering some preliminary information about the basic vortex-pinning mechanisms, and guiding the design of the quench protection system of Nb3Sn superconducting magnets.

On the thermoluminescent interactive multiple-trap system (IMTS) model: is it a simple model?

Energy Technology Data Exchange (ETDEWEB)

Gil T, M. I.; Perez C, L. [UNAM, Facultad de Quimica, Ciudad Universitaria, 04510 Ciudad de Mexico (Mexico); Cruz Z, E.; Furetta, C.; Roman L, J., E-mail: ecruz@nucleares.unam.mx [UNAM, Instituto de Ciencias Nucleares, Ciudad Universitaria, 04510 Ciudad de Mexico (Mexico)

2016-10-15

In the thermally stimulated luminescence phenomenon, named thermoluminescence (Tl), the electrons and holes generated by the radiation-matter interaction can be trapped by the metastable levels in the band gap of the solid. Following, the electron can be thermally releases into the conduction band and a radiatively recombination with hole close to the recombination center occurred and the glow curve is emitted. However, the complex mechanism of trapping and thermally releases occurred in the band gap of solid. Some models, such as; first, second and general-order kinetics, have been well established to explain the behaviour of the glow curves and their defects recombination mechanism. In this work, expressions for and Interactive Multiple-Trap System model (IMTS) was obtained assuming: a set of discrete electron traps (active traps At), another set of thermally disconnected trap (TDT) and a recombination center (Rc) too. A numerical analysis based on the Levenberg-Marquardt method in conjunction with an implicit Rosenbrock method was taken into account to simulate the glow curve. The numerical method was tested through synthetic Tl glow curves for a wide range of trap parameters. The activation energy and kinetics order were determined using values from the General Order Kinetics (GOK) model as entry data to IMTS model. This model was tested using the experimental glow curves obtained from Ce or Eu-doped MgF{sub 2}(LiF) polycrystals samples. Results shown that the IMTS model can predict more accurately the behavior of the Tl glow curves that those obtained by the GOK modified by Rasheedy and by the Mixed Order Kinetics model. (Author)

Dual mechanisms regulating glutamate decarboxylases and accumulation of gamma-aminobutyric acid in tea (Camellia sinensis) leaves exposed to multiple stresses.

Science.gov (United States)

Mei, Xin; Chen, Yiyong; Zhang, Lingyun; Fu, Xiumin; Wei, Qing; Grierson, Don; Zhou, Ying; Huang, Yahui; Dong, Fang; Yang, Ziyin

2016-03-29

γ-Aminobutyric acid (GABA) is one of the major inhibitory neurotransmitters in the central nervous system. It has multiple positive effects on mammalian physiology and is an important bioactive component of tea (Camellia sinensis). GABA generally occurs at a very low level in plants but GABA content increases substantially after exposure to a range of stresses, especially oxygen-deficiency. During processing of tea leaves, a combination of anoxic stress and mechanical damage are essential for the high accumulation of GABA. This is believed to be initiated by a change in glutamate decarboxylase activity, but the underlying mechanisms are unclear. In the present study we characterized factors regulating the expression and activity of three tea glutamate decarboxylase genes (CsGAD1, 2, and 3), and their encoded enzymes. The results suggests that, unlike the model plant Arabidopsis thaliana, there are dual mechanisms regulating the accumulation of GABA in tea leaves exposed to multiple stresses, including activation of CsGAD1 enzymatic activity by calmodulin upon the onset of the stress and accumulation of high levels of CsGAD2 mRNA induced by a combination of anoxic stress and mechanical damage.

History, rare, and multiple events of mechanical unfolding of repeat proteins

Science.gov (United States)

Sumbul, Fidan; Marchesi, Arin; Rico, Felix

2018-03-01

Mechanical unfolding of proteins consisting of repeat domains is an excellent tool to obtain large statistics. Force spectroscopy experiments using atomic force microscopy on proteins presenting multiple domains have revealed that unfolding forces depend on the number of folded domains (history) and have reported intermediate states and rare events. However, the common use of unspecific attachment approaches to pull the protein of interest holds important limitations to study unfolding history and may lead to discarding rare and multiple probing events due to the presence of unspecific adhesion and uncertainty on the pulling site. Site-specific methods that have recently emerged minimize this uncertainty and would be excellent tools to probe unfolding history and rare events. However, detailed characterization of these approaches is required to identify their advantages and limitations. Here, we characterize a site-specific binding approach based on the ultrastable complex dockerin/cohesin III revealing its advantages and limitations to assess the unfolding history and to investigate rare and multiple events during the unfolding of repeated domains. We show that this approach is more robust, reproducible, and provides larger statistics than conventional unspecific methods. We show that the method is optimal to reveal the history of unfolding from the very first domain and to detect rare events, while being more limited to assess intermediate states. Finally, we quantify the forces required to unfold two molecules pulled in parallel, difficult when using unspecific approaches. The proposed method represents a step forward toward more reproducible measurements to probe protein unfolding history and opens the door to systematic probing of rare and multiple molecule unfolding mechanisms.

Integrative modelling reveals mechanisms linking productivity and plant species richness.

Science.gov (United States)

Grace, James B; Anderson, T Michael; Seabloom, Eric W; Borer, Elizabeth T; Adler, Peter B; Harpole, W Stanley; Hautier, Yann; Hillebrand, Helmut; Lind, Eric M; Pärtel, Meelis; Bakker, Jonathan D; Buckley, Yvonne M; Crawley, Michael J; Damschen, Ellen I; Davies, Kendi F; Fay, Philip A; Firn, Jennifer; Gruner, Daniel S; Hector, Andy; Knops, Johannes M H; MacDougall, Andrew S; Melbourne, Brett A; Morgan, John W; Orrock, John L; Prober, Suzanne M; Smith, Melinda D

2016-01-21

How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.

Modeling mechanical inhomogeneities in small populations of proliferating monolayers and spheroids.

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Lejeune, Emma; Linder, Christian

2018-06-01

Understanding the mechanical behavior of multicellular monolayers and spheroids is fundamental to tissue culture, organism development, and the early stages of tumor growth. Proliferating cells in monolayers and spheroids experience mechanical forces as they grow and divide and local inhomogeneities in the mechanical microenvironment can cause individual cells within the multicellular system to grow and divide at different rates. This differential growth, combined with cell division and reorganization, leads to residual stress. Multiple different modeling approaches have been taken to understand and predict the residual stresses that arise in growing multicellular systems, particularly tumor spheroids. Here, we show that by using a mechanically robust agent-based model constructed with the peridynamic framework, we gain a better understanding of residual stresses in multicellular systems as they grow from a single cell. In particular, we focus on small populations of cells (1-100 s) where population behavior is highly stochastic and prior investigation has been limited. We compare the average strain energy density of cells in monolayers and spheroids using different growth and division rules and find that, on average, cells in spheroids have a higher strain energy density than cells in monolayers. We also find that cells in the interior of a growing spheroid are, on average, in compression. Finally, we demonstrate the importance of accounting for stochastic fluctuations in the mechanical environment, particularly when the cellular response to mechanical cues is nonlinear. The results presented here serve as a starting point for both further investigation with agent-based models, and for the incorporation of major findings from agent-based models into continuum scale models when explicit representation of individual cells is not computationally feasible.

Probability distributions in conservative energy exchange models of multiple interacting agents

International Nuclear Information System (INIS)

Scafetta, Nicola; West, Bruce J

2007-01-01

Herein we study energy exchange models of multiple interacting agents that conserve energy in each interaction. The models differ regarding the rules that regulate the energy exchange and boundary effects. We find a variety of stochastic behaviours that manifest energy equilibrium probability distributions of different types and interaction rules that yield not only the exponential distributions such as the familiar Maxwell-Boltzmann-Gibbs distribution of an elastically colliding ideal particle gas, but also uniform distributions, truncated exponential distributions, Gaussian distributions, Gamma distributions, inverse power law distributions, mixed exponential and inverse power law distributions, and evolving distributions. This wide variety of distributions should be of value in determining the underlying mechanisms generating the statistical properties of complex phenomena including those to be found in complex chemical reactions

Multiple model cardinalized probability hypothesis density filter

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Georgescu, Ramona; Willett, Peter

2011-09-01

The Probability Hypothesis Density (PHD) filter propagates the first-moment approximation to the multi-target Bayesian posterior distribution while the Cardinalized PHD (CPHD) filter propagates both the posterior likelihood of (an unlabeled) target state and the posterior probability mass function of the number of targets. Extensions of the PHD filter to the multiple model (MM) framework have been published and were implemented either with a Sequential Monte Carlo or a Gaussian Mixture approach. In this work, we introduce the multiple model version of the more elaborate CPHD filter. We present the derivation of the prediction and update steps of the MMCPHD particularized for the case of two target motion models and proceed to show that in the case of a single model, the new MMCPHD equations reduce to the original CPHD equations.

[Disease concept, etiology and mechanisms of multiple sclerosis].

Science.gov (United States)

Kira, Jun-Ichi

2014-11-01

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system(CNS). MS is assumed to be caused by a complex interplay between genes and environments. Autoimmune mechanisms targeting CNS myelin has long been proposed, yet it has not been proved. Th17 cells producing interleukin-17 and Th1 cells producing interferon-gamma are postulated to play major roles in initiating inflammation while regulatory T cell functions are dampened. The forth nationwide survey of MS in Japan revealed that MS prevalence showed four-folds increase over 30 years and the increase was especially prominent in female. Thus, westernized life style and improved sanitation are suspected to increase MS susceptibility. Genome-wide association studies in Western MS patients disclosed more than 100 disease-susceptibility genes, most of which are immune-related genes. It therefore supports immune-mediated mechanisms to be operative. Detailed magnetic resonance imaging studies revealed an early atrophy of the cerebral gray matter where T cell infiltration is pathologically scarce. Therefore, neurodegenerative process also takes place in the early course beside neuroinflammation.

Hybrid Multiple Soft-Sensor Models of Grinding Granularity Based on Cuckoo Searching Algorithm and Hysteresis Switching Strategy

Directory of Open Access Journals (Sweden)

Jie-Sheng Wang

2015-01-01

Full Text Available According to the characteristics of grinding process and accuracy requirements of technical indicators, a hybrid multiple soft-sensor modeling method of grinding granularity is proposed based on cuckoo searching (CS algorithm and hysteresis switching (HS strategy. Firstly, a mechanism soft-sensor model of grinding granularity is deduced based on the technique characteristics and a lot of experimental data of grinding process. Meanwhile, the BP neural network soft-sensor model and wavelet neural network (WNN soft-sensor model are set up. Then, the hybrid multiple soft-sensor model based on the hysteresis switching strategy is realized. That is to say, the optimum model is selected as the current predictive model according to the switching performance index at each sampling instant. Finally the cuckoo searching algorithm is adopted to optimize the performance parameters of hysteresis switching strategy. Simulation results show that the proposed model has better generalization results and prediction precision, which can satisfy the real-time control requirements of grinding classification process.

Mean multiplicity in the Regge models with rising cross sections

International Nuclear Information System (INIS)

Chikovani, Z.E.; Kobylisky, N.A.; Martynov, E.S.

1979-01-01

Behaviour of the mean multiplicity and the total cross section σsub(t) of hadron-hadron interactions is considered in the framework of the Regge models at high energies. Generating function was plotted for models of dipole and froissaron, and the mean multiplicity and multiplicity moments were calculated. It is shown that approximately ln 2 S (energy square) in the dipole model, which is in good agreement with the experiment. It is also found that in various Regge models approximately σsub(t)lnS

A multiple-field coupled resistive transition model for superconducting Nb3Sn

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Lin Yang

2016-12-01

Full Text Available A study on the superconducting transition width as functions of the applied magnetic field and strain is performed in superconducting Nb3Sn. A quantitative, yet universal phenomenological resistivity model is proposed. The numerical simulation by the proposed model shows predicted resistive transition characteristics under variable magnetic fields and strain, which in good agreement with the experimental observations. Furthermore, a temperature-modulated magnetoresistance transition behavior in filamentary Nb3Sn conductors can also be well described by the given model. The multiple-field coupled resistive transition model is helpful for making objective determinations of the high-dimensional critical surface of Nb3Sn in the multi-parameter space, offering some preliminary information about the basic vortex-pinning mechanisms, and guiding the design of the quench protection system of Nb3Sn superconducting magnets.

Mathematical modelling in solid mechanics

CERN Document Server

Sofonea, Mircea; Steigmann, David

2017-01-01

This book presents new research results in multidisciplinary fields of mathematical and numerical modelling in mechanics. The chapters treat the topics: mathematical modelling in solid, fluid and contact mechanics nonconvex variational analysis with emphasis to nonlinear solid and structural mechanics numerical modelling of problems with non-smooth constitutive laws, approximation of variational and hemivariational inequalities, numerical analysis of discrete schemes, numerical methods and the corresponding algorithms, applications to mechanical engineering numerical aspects of non-smooth mechanics, with emphasis on developing accurate and reliable computational tools mechanics of fibre-reinforced materials behaviour of elasto-plastic materials accounting for the microstructural defects definition of structural defects based on the differential geometry concepts or on the atomistic basis interaction between phase transformation and dislocations at nano-scale energetic arguments bifurcation and post-buckling a...

Statistics, synergy, and mechanism of multiple photogeneration of excitons in quantum dots: Fundamental and applied aspects

International Nuclear Information System (INIS)

Oksengendler, B. L.; Turaeva, N. N.; Uralov, I.; Marasulov, M. B.

2012-01-01

The effect of multiple exciton generation is analyzed based on statistical physics, quantum mechanics, and synergetics. Statistical problems of the effect of multiple exciton generation (MEG) are broadened and take into account not only exciton generation, but also background excitation. The study of the role of surface states of quantum dots is based on the synergy of self-catalyzed electronic reactions. An analysis of the MEG mechanism is based on the idea of electronic shaking using the sudden perturbation method in quantum mechanics. All of the above-mentioned results are applied to the problem of calculating the limiting efficiency to transform solar energy into electric energy. (authors)

Multiple model adaptive control with mixing

Science.gov (United States)

Kuipers, Matthew

Despite the remarkable theoretical accomplishments and successful applications of adaptive control, the field is not sufficiently mature to solve challenging control problems requiring strict performance and safety guarantees. Towards addressing these issues, a novel deterministic multiple-model adaptive control approach called adaptive mixing control is proposed. In this approach, adaptation comes from a high-level system called the supervisor that mixes into feedback a number of candidate controllers, each finely-tuned to a subset of the parameter space. The mixing signal, the supervisor's output, is generated by estimating the unknown parameters and, at every instant of time, calculating the contribution level of each candidate controller based on certainty equivalence. The proposed architecture provides two characteristics relevant to solving stringent, performance-driven applications. First, the full-suite of linear time invariant control tools is available. A disadvantage of conventional adaptive control is its restriction to utilizing only those control laws whose solutions can be feasibly computed in real-time, such as model reference and pole-placement type controllers. Because its candidate controllers are computed off line, the proposed approach suffers no such restriction. Second, the supervisor's output is smooth and does not necessarily depend on explicit a priori knowledge of the disturbance model. These characteristics can lead to improved performance by avoiding the unnecessary switching and chattering behaviors associated with some other multiple adaptive control approaches. The stability and robustness properties of the adaptive scheme are analyzed. It is shown that the mean-square regulation error is of the order of the modeling error. And when the parameter estimate converges to its true value, which is guaranteed if a persistence of excitation condition is satisfied, the adaptive closed-loop system converges exponentially fast to a closed

Toward modular biological models: defining analog modules based on referent physiological mechanisms.

Science.gov (United States)

Petersen, Brenden K; Ropella, Glen E P; Hunt, C Anthony

2014-08-16

Currently, most biomedical models exist in isolation. It is often difficult to reuse or integrate models or their components, in part because they are not modular. Modular components allow the modeler to think more deeply about the role of the model and to more completely address a modeling project's requirements. In particular, modularity facilitates component reuse and model integration for models with different use cases, including the ability to exchange modules during or between simulations. The heterogeneous nature of biology and vast range of wet-lab experimental platforms call for modular models designed to satisfy a variety of use cases. We argue that software analogs of biological mechanisms are reasonable candidates for modularization. Biomimetic software mechanisms comprised of physiomimetic mechanism modules offer benefits that are unique or especially important to multi-scale, biomedical modeling and simulation. We present a general, scientific method of modularizing mechanisms into reusable software components that we call physiomimetic mechanism modules (PMMs). PMMs utilize parametric containers that partition and expose state information into physiologically meaningful groupings. To demonstrate, we modularize four pharmacodynamic response mechanisms adapted from an in silico liver (ISL). We verified the modularization process by showing that drug clearance results from in silico experiments are identical before and after modularization. The modularized ISL achieves validation targets drawn from propranolol outflow profile data. In addition, an in silico hepatocyte culture (ISHC) is created. The ISHC uses the same PMMs and required no refactoring. The ISHC achieves validation targets drawn from propranolol intrinsic clearance data exhibiting considerable between-lab variability. The data used as validation targets for PMMs originate from both in vitro to in vivo experiments exhibiting large fold differences in time scale. This report demonstrates

Design of Xen Hybrid Multiple Police Model

Science.gov (United States)

Sun, Lei; Lin, Renhao; Zhu, Xianwei

2017-10-01

Virtualization Technology has attracted more and more attention. As a popular open-source virtualization tools, XEN is used more and more frequently. Xsm, XEN security model, has also been widespread concern. The safety status classification has not been established in the XSM, and it uses the virtual machine as a managed object to make Dom0 a unique administrative domain that does not meet the minimum privilege. According to these questions, we design a Hybrid multiple police model named SV_HMPMD that organically integrates multiple single security policy models include DTE,RBAC,BLP. It can fullfill the requirement of confidentiality and integrity for security model and use different particle size to different domain. In order to improve BLP’s practicability, the model introduce multi-level security labels. In order to divide the privilege in detail, we combine DTE with RBAC. In order to oversize privilege, we limit the privilege of domain0.

A novel mechanical lung model of pulmonary diseases to assist with teaching and training

Directory of Open Access Journals (Sweden)

Shaw Geoffrey M

2006-08-01

Full Text Available Abstract Background A design concept of low-cost, simple, fully mechanical model of a mechanically ventilated, passively breathing lung is developed. An example model is built to simulate a patient under mechanical ventilation with accurate volumes and compliances, while connected directly to a ventilator. Methods The lung is modelled with multiple units, represented by rubber bellows, with adjustable weights placed on bellows to simulate compartments of different superimposed pressure and compliance, as well as different levels of lung disease, such as Acute Respiratory Distress Syndrome (ARDS. The model was directly connected to a ventilator and the resulting pressure volume curves recorded. Results The model effectively captures the fundamental lung dynamics for a variety of conditions, and showed the effects of different ventilator settings. It was particularly effective at showing the impact of Positive End Expiratory Pressure (PEEP therapy on lung recruitment to improve oxygenation, a particulary difficult dynamic to capture. Conclusion Application of PEEP therapy is difficult to teach and demonstrate clearly. Therefore, the model provide opportunity to train, teach, and aid further understanding of lung mechanics and the treatment of lung diseases in critical care, such as ARDS and asthma. Finally, the model's pure mechanical nature and accurate lung volumes mean that all results are both clearly visible and thus intuitively simple to grasp.

Supersymmetric U(1)' model with multiple dark matters

International Nuclear Information System (INIS)

Hur, Taeil; Lee, Hye-Sung; Nasri, Salah

2008-01-01

We consider a scenario where a supersymmetric model has multiple dark matter particles. Adding a U(1) ' gauge symmetry is a well-motivated extension of the minimal supersymmetric standard model (MSSM). It can cure the problems of the MSSM such as the μ problem or the proton decay problem with high-dimensional lepton number and baryon number violating operators which R parity allows. An extra parity (U parity) may arise as a residual discrete symmetry after U(1) ' gauge symmetry is spontaneously broken. The lightest U-parity particle (LUP) is stable under the new parity becoming a new dark matter candidate. Up to three massive particles can be stable in the presence of the R parity and the U parity. We numerically illustrate that multiple stable particles in our model can satisfy both constraints from the relic density and the direct detection, thus providing a specific scenario where a supersymmetric model has well-motivated multiple dark matters consistent with experimental constraints. The scenario provides new possibilities in the present and upcoming dark matter searches in the direct detection and collider experiments

Multiple Social Networks, Data Models and Measures for

DEFF Research Database (Denmark)

Magnani, Matteo; Rossi, Luca

2017-01-01

Multiple Social Network Analysis is a discipline defining models, measures, methodologies, and algorithms to study multiple social networks together as a single social system. It is particularly valuable when the networks are interconnected, e.g., the same actors are present in more than one...

Multiple Response Regression for Gaussian Mixture Models with Known Labels.

Science.gov (United States)

Lee, Wonyul; Du, Ying; Sun, Wei; Hayes, D Neil; Liu, Yufeng

2012-12-01

Multiple response regression is a useful regression technique to model multiple response variables using the same set of predictor variables. Most existing methods for multiple response regression are designed for modeling homogeneous data. In many applications, however, one may have heterogeneous data where the samples are divided into multiple groups. Our motivating example is a cancer dataset where the samples belong to multiple cancer subtypes. In this paper, we consider modeling the data coming from a mixture of several Gaussian distributions with known group labels. A naive approach is to split the data into several groups according to the labels and model each group separately. Although it is simple, this approach ignores potential common structures across different groups. We propose new penalized methods to model all groups jointly in which the common and unique structures can be identified. The proposed methods estimate the regression coefficient matrix, as well as the conditional inverse covariance matrix of response variables. Asymptotic properties of the proposed methods are explored. Through numerical examples, we demonstrate that both estimation and prediction can be improved by modeling all groups jointly using the proposed methods. An application to a glioblastoma cancer dataset reveals some interesting common and unique gene relationships across different cancer subtypes.

SDG and qualitative trend based model multiple scale validation

Science.gov (United States)

Gao, Dong; Xu, Xin; Yin, Jianjin; Zhang, Hongyu; Zhang, Beike

2017-09-01

Verification, Validation and Accreditation (VV&A) is key technology of simulation and modelling. For the traditional model validation methods, the completeness is weak; it is carried out in one scale; it depends on human experience. The SDG (Signed Directed Graph) and qualitative trend based multiple scale validation is proposed. First the SDG model is built and qualitative trends are added to the model. And then complete testing scenarios are produced by positive inference. The multiple scale validation is carried out by comparing the testing scenarios with outputs of simulation model in different scales. Finally, the effectiveness is proved by carrying out validation for a reactor model.

A Multiple Items EPQ/EOQ Model for a Vendor and Multiple Buyers System with Considering Continuous and Discrete Demand Simultaneously

Science.gov (United States)

Jonrinaldi; Rahman, T.; Henmaidi; Wirdianto, E.; Zhang, D. Z.

2018-03-01

This paper proposed a mathematical model for multiple items Economic Production and Order Quantity (EPQ/EOQ) with considering continuous and discrete demand simultaneously in a system consisting of a vendor and multiple buyers. This model is used to investigate the optimal production lot size of the vendor and the number of shipments policy of orders to multiple buyers. The model considers the multiple buyers’ holding cost as well as transportation cost, which minimize the total production and inventory costs of the system. The continuous demand from any other customers can be fulfilled anytime by the vendor while the discrete demand from multiple buyers can be fulfilled by the vendor using the multiple delivery policy with a number of shipments of items in the production cycle time. A mathematical model is developed to illustrate the system based on EPQ and EOQ model. Solution procedures are proposed to solve the model using a Mixed Integer Non Linear Programming (MINLP) and algorithm methods. Then, the numerical example is provided to illustrate the system and results are discussed.

Iterative integral parameter identification of a respiratory mechanics model.

Science.gov (United States)

Schranz, Christoph; Docherty, Paul D; Chiew, Yeong Shiong; Möller, Knut; Chase, J Geoffrey

2012-07-18

Patient-specific respiratory mechanics models can support the evaluation of optimal lung protective ventilator settings during ventilation therapy. Clinical application requires that the individual's model parameter values must be identified with information available at the bedside. Multiple linear regression or gradient-based parameter identification methods are highly sensitive to noise and initial parameter estimates. Thus, they are difficult to apply at the bedside to support therapeutic decisions. An iterative integral parameter identification method is applied to a second order respiratory mechanics model. The method is compared to the commonly used regression methods and error-mapping approaches using simulated and clinical data. The clinical potential of the method was evaluated on data from 13 Acute Respiratory Distress Syndrome (ARDS) patients. The iterative integral method converged to error minima 350 times faster than the Simplex Search Method using simulation data sets and 50 times faster using clinical data sets. Established regression methods reported erroneous results due to sensitivity to noise. In contrast, the iterative integral method was effective independent of initial parameter estimations, and converged successfully in each case tested. These investigations reveal that the iterative integral method is beneficial with respect to computing time, operator independence and robustness, and thus applicable at the bedside for this clinical application.

Multiple commodities in statistical microeconomics: Model and market

Science.gov (United States)

Baaquie, Belal E.; Yu, Miao; Du, Xin

2016-11-01

A statistical generalization of microeconomics has been made in Baaquie (2013). In Baaquie et al. (2015), the market behavior of single commodities was analyzed and it was shown that market data provides strong support for the statistical microeconomic description of commodity prices. The case of multiple commodities is studied and a parsimonious generalization of the single commodity model is made for the multiple commodities case. Market data shows that the generalization can accurately model the simultaneous correlation functions of up to four commodities. To accurately model five or more commodities, further terms have to be included in the model. This study shows that the statistical microeconomics approach is a comprehensive and complete formulation of microeconomics, and which is independent to the mainstream formulation of microeconomics.

Stabilization of multiple rib fractures in a canine model.

Science.gov (United States)

Huang, Ke-Nan; Xu, Zhi-Fei; Sun, Ju-Xian; Ding, Xin-Yu; Wu, Bin; Li, Wei; Qin, Xiong; Tang, Hua

2014-12-01

Operative stabilization is frequently used in the clinical treatment of multiple rib fractures (MRF); however, no ideal material exists for use in this fixation. This study investigates a newly developed biodegradable plate system for the stabilization of MRF. Silk fiber-reinforced polycaprolactone (SF/PCL) plates were developed for rib fracture stabilization and studied using a canine flail chest model. Adult mongrel dogs were divided into three groups: one group received the SF/PCL plates, one group received standard clinical steel plates, and the final group did not undergo operative fracture stabilization (n = 6 for each group). Radiographic, mechanical, and histologic examination was performed to evaluate the effectiveness of the biodegradable material for the stabilization of the rib fractures. No nonunion and no infections were found when using SF-PCL plates. The fracture sites collapsed in the untreated control group, leading to obvious chest wall deformity not encountered in the two groups that underwent operative stabilization. Our experimental study shows that the SF/PCL plate has the biocompatibility and mechanical strength suitable for fixation of MRF and is potentially ideal for the treatment of these injuries. Copyright © 2014 Elsevier Inc. All rights reserved.

AgMIP Training in Multiple Crop Models and Tools

Science.gov (United States)

Boote, Kenneth J.; Porter, Cheryl H.; Hargreaves, John; Hoogenboom, Gerrit; Thornburn, Peter; Mutter, Carolyn

2015-01-01

The Agricultural Model Intercomparison and Improvement Project (AgMIP) has the goal of using multiple crop models to evaluate climate impacts on agricultural production and food security in developed and developing countries. There are several major limitations that must be overcome to achieve this goal, including the need to train AgMIP regional research team (RRT) crop modelers to use models other than the ones they are currently familiar with, plus the need to harmonize and interconvert the disparate input file formats used for the various models. Two activities were followed to address these shortcomings among AgMIP RRTs to enable them to use multiple models to evaluate climate impacts on crop production and food security. We designed and conducted courses in which participants trained on two different sets of crop models, with emphasis on the model of least experience. In a second activity, the AgMIP IT group created templates for inputting data on soils, management, weather, and crops into AgMIP harmonized databases, and developed translation tools for converting the harmonized data into files that are ready for multiple crop model simulations. The strategies for creating and conducting the multi-model course and developing entry and translation tools are reviewed in this chapter.

Taking a(c)count of eye movements: Multiple mechanisms underlie fixations during enumeration.

Science.gov (United States)

Paul, Jacob M; Reeve, Robert A; Forte, Jason D

2017-03-01

We habitually move our eyes when we enumerate sets of objects. It remains unclear whether saccades are directed for numerosity processing as distinct from object-oriented visual processing (e.g., object saliency, scanning heuristics). Here we investigated the extent to which enumeration eye movements are contingent upon the location of objects in an array, and whether fixation patterns vary with enumeration demands. Twenty adults enumerated random dot arrays twice: first to report the set cardinality and second to judge the perceived number of subsets. We manipulated the spatial location of dots by presenting arrays at 0°, 90°, 180°, and 270° orientations. Participants required a similar time to enumerate the set or the perceived number of subsets in the same array. Fixation patterns were systematically shifted in the direction of array rotation, and distributed across similar locations when the same array was shown on multiple occasions. We modeled fixation patterns and dot saliency using a simple filtering model and show participants judged groups of dots in close proximity (2°-2.5° visual angle) as distinct subsets. Modeling results are consistent with the suggestion that enumeration involves visual grouping mechanisms based on object saliency, and specific enumeration demands affect spatial distribution of fixations. Our findings highlight the importance of set computation, rather than object processing per se, for models of numerosity processing.

Efficient Adoption and Assessment of Multiple Process Improvement Reference Models

Directory of Open Access Journals (Sweden)

Simona Jeners

2013-06-01

Full Text Available A variety of reference models such as CMMI, COBIT or ITIL support IT organizations to improve their processes. These process improvement reference models (IRMs cover different domains such as IT development, IT Services or IT Governance but also share some similarities. As there are organizations that address multiple domains and need to coordinate their processes in their improvement we present MoSaIC, an approach to support organizations to efficiently adopt and conform to multiple IRMs. Our solution realizes a semantic integration of IRMs based on common meta-models. The resulting IRM integration model enables organizations to efficiently implement and asses multiple IRMs and to benefit from synergy effects.

Adaptive Active Noise Suppression Using Multiple Model Switching Strategy

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Quanzhen Huang

2017-01-01

Full Text Available Active noise suppression for applications where the system response varies with time is a difficult problem. The computation burden for the existing control algorithms with online identification is heavy and easy to cause control system instability. A new active noise control algorithm is proposed in this paper by employing multiple model switching strategy for secondary path varying. The computation is significantly reduced. Firstly, a noise control system modeling method is proposed for duct-like applications. Then a multiple model adaptive control algorithm is proposed with a new multiple model switching strategy based on filter-u least mean square (FULMS algorithm. Finally, the proposed algorithm was implemented on Texas Instruments digital signal processor (DSP TMS320F28335 and real time experiments were done to test the proposed algorithm and FULMS algorithm with online identification. Experimental verification tests show that the proposed algorithm is effective with good noise suppression performance.

Active Vertex Model for cell-resolution description of epithelial tissue mechanics.

Science.gov (United States)

Barton, Daniel L; Henkes, Silke; Weijer, Cornelis J; Sknepnek, Rastko

2017-06-01

We introduce an Active Vertex Model (AVM) for cell-resolution studies of the mechanics of confluent epithelial tissues consisting of tens of thousands of cells, with a level of detail inaccessible to similar methods. The AVM combines the Vertex Model for confluent epithelial tissues with active matter dynamics. This introduces a natural description of the cell motion and accounts for motion patterns observed on multiple scales. Furthermore, cell contacts are generated dynamically from positions of cell centres. This not only enables efficient numerical implementation, but provides a natural description of the T1 transition events responsible for local tissue rearrangements. The AVM also includes cell alignment, cell-specific mechanical properties, cell growth, division and apoptosis. In addition, the AVM introduces a flexible, dynamically changing boundary of the epithelial sheet allowing for studies of phenomena such as the fingering instability or wound healing. We illustrate these capabilities with a number of case studies.

Unified thalamic model generates multiple distinct oscillations with state-dependent entrainment by stimulation.

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Guoshi Li

2017-10-01

Full Text Available The thalamus plays a critical role in the genesis of thalamocortical oscillations, yet the underlying mechanisms remain elusive. To understand whether the isolated thalamus can generate multiple distinct oscillations, we developed a biophysical thalamic model to test the hypothesis that generation of and transition between distinct thalamic oscillations can be explained as a function of neuromodulation by acetylcholine (ACh and norepinephrine (NE and afferent synaptic excitation. Indeed, the model exhibited four distinct thalamic rhythms (delta, sleep spindle, alpha and gamma oscillations that span the physiological states corresponding to different arousal levels from deep sleep to focused attention. Our simulation results indicate that generation of these distinct thalamic oscillations is a result of both intrinsic oscillatory cellular properties and specific network connectivity patterns. We then systematically varied the ACh/NE and input levels to generate a complete map of the different oscillatory states and their transitions. Lastly, we applied periodic stimulation to the thalamic network and found that entrainment of thalamic oscillations is highly state-dependent. Our results support the hypothesis that ACh/NE modulation and afferent excitation define thalamic oscillatory states and their response to brain stimulation. Our model proposes a broader and more central role of the thalamus in the genesis of multiple distinct thalamo-cortical rhythms than previously assumed.

A test for the parameters of multiple linear regression models ...

African Journals Online (AJOL)

A test for the parameters of multiple linear regression models is developed for conducting tests simultaneously on all the parameters of multiple linear regression models. The test is robust relative to the assumptions of homogeneity of variances and absence of serial correlation of the classical F-test. Under certain null and ...

Mechanical and mathematical models of multi-stage horizontal fracturing strings and their application

Directory of Open Access Journals (Sweden)

Zhanghua Lian

2015-03-01

Full Text Available Multi-stage SRV fracturing in horizontal wells is a new technology developed at home and abroad in recent years to effectively develop shale gas or low-permeability reservoirs, but on the other hand makes the mechanical environment of fracturing strings more complicated at the same time. In view of this, based on the loading features of tubing strings during the multi-stage fracturing of a horizontal well, mechanical models were established for three working cases of multiple packer setting, open differential-pressure sliding sleeve, and open ball-injection sliding sleeve under a hold-down packer. Moreover, mathematical models were respectively built for the above three cases. According to the Lame formula and Von Mises stress calculation formula for the thick-walled cylinder in the theory of elastic mechanics, a mathematical model was also established to calculate the equivalent stress for tubing string safety evaluation when the fracturing string was under the combined action of inner pressure, external squeezing force and axial stress, and another mathematical model was built for the mechanical strength and safety evaluation of multi-stage fracturing strings. In addition, a practical software was developed for the mechanical safety evaluation of horizontal well multi-stage fracturing strings according to the mathematical model developed for the mechanical calculation of the multi-packer string in horizontal wells. The research results were applied and verified in a gas well of Tahe Oilfield in the Tarim Basin with excellent effects, providing a theoretical basis and a simple and reliable technical means for optimal design and safety evaluation of safe operational parameters of multi-stage fracturing strings in horizontal wells.

Parametric modeling for damped sinusoids from multiple channels

DEFF Research Database (Denmark)

Zhou, Zhenhua; So, Hing Cheung; Christensen, Mads Græsbøll

2013-01-01

frequencies and damping factors are then computed with the multi-channel weighted linear prediction method. The estimated sinusoidal poles are then matched to each channel according to the extreme value theory of distribution of random fields. Simulations are performed to show the performance advantages......The problem of parametric modeling for noisy damped sinusoidal signals from multiple channels is addressed. Utilizing the shift invariance property of the signal subspace, the number of distinct sinusoidal poles in the multiple channels is first determined. With the estimated number, the distinct...... of the proposed multi-channel sinusoidal modeling methodology compared with existing methods....

A model for diagnosing and explaining multiple disorders.

Science.gov (United States)

Jamieson, P W

1991-08-01

The ability to diagnose multiple interacting disorders and explain them in a coherent causal framework has only partially been achieved in medical expert systems. This paper proposes a causal model for diagnosing and explaining multiple disorders whose key elements are: physician-directed hypotheses generation, object-oriented knowledge representation, and novel explanation heuristics. The heuristics modify and link the explanations to make the physician aware of diagnostic complexities. A computer program incorporating the model currently is in use for diagnosing peripheral nerve and muscle disorders. The program successfully diagnoses and explains interactions between diseases in terms of underlying pathophysiologic concepts. The model offers a new architecture for medical domains where reasoning from first principles is difficult but explanation of disease interactions is crucial for the system's operation.

Technical report on micro-mechanical versus conventional modelling in non-linear fracture mechanics

International Nuclear Information System (INIS)

2001-07-01

While conventional fracture mechanics is capable of predicting crack growth behaviour if sufficient experimental observations are available, micro-mechanical modelling can both increase the accuracy of these predictions and model phenomena that are inaccessible by the conventional theory such as the ductile-cleavage temperature transition. A common argument against micro-mechanical modelling is that it is too complicated for use in routine engineering applications. This is both a computational and an educational problem. That micro-mechanical modelling is unnecessarily complicated is certainly true in many situations. The on-going development of micro-mechanical models, computational algorithms and computer speed will however most probably diminish the computational problem rather rapidly. Compare for instance the rate of development of computational methods for structural analysis. Meanwhile micro-mechanical modelling may serve as a tool by which more simplified engineering methods can be validated. The process of receiving a wide acceptance of the new methods is probably much slower. This involves many steps. First the research community must be in reasonable agreement on the methods and their use. Then the methods have to be implemented into computer software and into code procedures. The development and acceptance of conventional fracture mechanics may serve as an historical example of the time required before a new methodology has received a wide usage. The CSNI Working Group on Integrity and Ageing (IAGE) decided to carry out a report on micro-mechanical modeling to promote this promising and valuable technique. The report presents a comparison with non-linear fracture mechanics and highlights key aspects that could lead to a better knowledge and accurate predictions. Content: - 1. Introduction; - 2. Concepts of non-linear fracture mechanics with point crack tip modelling; - 3. Micro-mechanical models for cleavage fracture; - 4, Micro-mechanical modelling of

Iterative integral parameter identification of a respiratory mechanics model

Directory of Open Access Journals (Sweden)

Schranz Christoph

2012-07-01

Full Text Available Abstract Background Patient-specific respiratory mechanics models can support the evaluation of optimal lung protective ventilator settings during ventilation therapy. Clinical application requires that the individual’s model parameter values must be identified with information available at the bedside. Multiple linear regression or gradient-based parameter identification methods are highly sensitive to noise and initial parameter estimates. Thus, they are difficult to apply at the bedside to support therapeutic decisions. Methods An iterative integral parameter identification method is applied to a second order respiratory mechanics model. The method is compared to the commonly used regression methods and error-mapping approaches using simulated and clinical data. The clinical potential of the method was evaluated on data from 13 Acute Respiratory Distress Syndrome (ARDS patients. Results The iterative integral method converged to error minima 350 times faster than the Simplex Search Method using simulation data sets and 50 times faster using clinical data sets. Established regression methods reported erroneous results due to sensitivity to noise. In contrast, the iterative integral method was effective independent of initial parameter estimations, and converged successfully in each case tested. Conclusion These investigations reveal that the iterative integral method is beneficial with respect to computing time, operator independence and robustness, and thus applicable at the bedside for this clinical application.

Pellet Cladding Mechanical Interaction Modeling Using the Extended Finite Element Method

Energy Technology Data Exchange (ETDEWEB)

Spencer, Benjamin W.; Jiang, Wen; Dolbow, John E.; Peco, Christian

2016-09-01

As a brittle material, the ceramic UO2 used as light water reactor fuel experiences significant fracturing throughout its life, beginning with the first rise to power of fresh fuel. This has multiple effects on the thermal and mechanical response of the fuel/cladding system. One such effect that is particularly important is that when there is mechanical contact between the fuel and cladding, cracks that extending from the outer surface of the fuel into the volume of the fuel cause elevated stresses in the adjacent cladding, which can potentially lead to cladding failure. Modeling the thermal and mechanical response of the cladding in the vicinity of these surface-breaking cracks in the fuel can provide important insights into this behavior to help avoid operating conditions that could lead to cladding failure. Such modeling has traditionally been done in the context of finite-element-based fuel performance analysis by modifying the fuel mesh to introduce discrete cracks. While this approach is effective in capturing the important behavior at the fuel/cladding interface, there are multiple drawbacks to explicitly incorporating the cracks in the finite element mesh. Because the cracks are incorporated in the original mesh, the mesh must be modified for cracks of specified location and depth, so it is difficult to account for crack propagation and the formation of new cracks at other locations. The extended finite element method (XFEM) has emerged in recent years as a powerful method to represent arbitrary, evolving, discrete discontinuities within the context of the finite element method. Development work is underway by the authors to implement XFEM in the BISON fuel performance code, and this capability has previously been demonstrated in simulations of fracture propagation in ceramic nuclear fuel. These preliminary demonstrations have included only the fuel, and excluded the cladding for simplicity. This paper presents initial results of efforts to apply XFEM to

Solid mechanics theory, modeling, and problems

CERN Document Server

Bertram, Albrecht

2015-01-01

This textbook offers an introduction to modeling the mechanical behavior of solids within continuum mechanics and thermodynamics. To illustrate the fundamental principles, the book starts with an overview of the most important models in one dimension. Tensor calculus, which is called for in three-dimensional modeling, is concisely presented in the second part of the book. Once the reader is equipped with these essential mathematical tools, the third part of the book develops the foundations of continuum mechanics right from the beginning. Lastly, the book’s fourth part focuses on modeling the mechanics of materials and in particular elasticity, viscoelasticity and plasticity. Intended as an introductory textbook for students and for professionals interested in self-study, it also features numerous worked-out examples to aid in understanding.

Financial power laws: Empirical evidence, models, and mechanisms

International Nuclear Information System (INIS)

Lux, Thomas; Alfarano, Simone

2016-01-01

Financial markets (share markets, foreign exchange markets and others) are all characterized by a number of universal power laws. The most prominent example is the ubiquitous finding of a robust, approximately cubic power law characterizing the distribution of large returns. A similarly robust feature is long-range dependence in volatility (i.e., hyperbolic decline of its autocorrelation function). The recent literature adds temporal scaling of trading volume and multi-scaling of higher moments of returns. Increasing awareness of these properties has recently spurred attempts at theoretical explanations of the emergence of these key characteristics form the market process. In principle, different types of dynamic processes could be responsible for these power-laws. Examples to be found in the economics literature include multiplicative stochastic processes as well as dynamic processes with multiple equilibria. Though both types of dynamics are characterized by intermittent behavior which occasionally generates large bursts of activity, they can be based on fundamentally different perceptions of the trading process. The present paper reviews both the analytical background of the power laws emerging from the above data generating mechanisms as well as pertinent models proposed in the economics literature.

Multiple stressor effects in Chlamydomonas reinhardtii--toward understanding mechanisms of interaction between effects of ultraviolet radiation and chemical pollutants.

Science.gov (United States)

Korkaric, Muris; Behra, Renata; Fischer, Beat B; Junghans, Marion; Eggen, Rik I L

2015-05-01

The effects of chemical pollutants and environmental stressors, such as ultraviolet radiation (UVR), can interact when organisms are simultaneously exposed, resulting in higher (synergistic) or lower (antagonistic) multiple stressor effects than expected based on the effects of single stressors. Current understanding of interactive effects is limited due to a lack of mechanism-based multiple stressor studies. It has been hypothesized that effect interactions may generally occur if chemical and non-chemical stressors cause similar physiological effects in the organism. To test this hypothesis, we exposed the model green alga Chlamydomonas reinhardtii to combinations of UVR and single chemicals displaying modes of action (MOA) similar or dissimilar to the impact of UVR on photosynthesis. Stressor interactions were analyzed based on the independent action model. Effect interactions were found to depend on the MOA of the chemicals, and also on their concentrations, the exposure time and the measured endpoint. Indeed, only chemicals assumed to cause effects on photosynthesis similar to UVR showed interactions with UVR on photosynthetic yield: synergistic in case of Cd(II) and paraquat and antagonistic in case of diuron. No interaction on photosynthesis was observed for S-metolachlor, which acts dissimilarly to UVR. However, combined effects of S-metolachlor and UVR on algal reproduction were synergistic, highlighting the importance of considering additional MOA of UVR. Possible mechanisms of stressor effect interactions are discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

Application of Multiple Evaluation Models in Brazil

Directory of Open Access Journals (Sweden)

Rafael Victal Saliba

2008-07-01

Full Text Available Based on two different samples, this article tests the performance of a number of Value Drivers commonly used for evaluating companies by finance practitioners, through simple regression models of cross-section type which estimate the parameters associated to each Value Driver, denominated Market Multiples. We are able to diagnose the behavior of several multiples in the period 1994-2004, with an outlook also on the particularities of the economic activities performed by the sample companies (and their impacts on the performance through a subsequent analysis with segregation of companies in the sample by sectors. Extrapolating simple multiples evaluation standards from analysts of the main financial institutions in Brazil, we find that adjusting the ratio formulation to allow for an intercept does not provide satisfactory results in terms of pricing errors reduction. Results found, in spite of evidencing certain relative and absolute superiority among the multiples, may not be generically representative, given samples limitation.

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

Science.gov (United States)

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

Linking definitions, mechanisms, and modeling of drought-induced tree death.

Science.gov (United States)

Anderegg, William R L; Berry, Joseph A; Field, Christopher B

2012-12-01

Tree death from drought and heat stress is a critical and uncertain component in forest ecosystem responses to a changing climate. Recent research has illuminated how tree mortality is a complex cascade of changes involving interconnected plant systems over multiple timescales. Explicit consideration of the definitions, dynamics, and temporal and biological scales of tree mortality research can guide experimental and modeling approaches. In this review, we draw on the medical literature concerning human death to propose a water resource-based approach to tree mortality that considers the tree as a complex organism with a distinct growth strategy. This approach provides insight into mortality mechanisms at the tree and landscape scales and presents promising avenues into modeling tree death from drought and temperature stress. Copyright © 2012 Elsevier Ltd. All rights reserved.

Study on the dynamic recrystallization model and mechanism of nuclear grade 316LN austenitic stainless steel

International Nuclear Information System (INIS)

Wang, Shenglong; Zhang, Mingxian; Wu, Huanchun; Yang, Bin

2016-01-01

In this study, the dynamic recrystallization behaviors of a nuclear grade 316LN austenitic stainless steel were researched through hot compression experiment performed on a Gleeble-1500 simulator at temperatures of 900–1250 °C and strain rates of 0.01–1 s −1 . By multiple linear regressions of the flow stress-strain data, the dynamic recrystallization mathematical models of this steel as functions of strain rate, strain and temperature were developed. Then these models were verified in a real experiment. Furthermore, the dynamic recrystallization mechanism of the steel was determined. The results indicated that the subgrains in this steel are formed through dislocations polygonization and then grow up through subgrain boundaries migration towards high density dislocation areas and subgrain coalescence mechanism. Dynamic recrystallization nucleation performs in grain boundary bulging mechanism and subgrain growth mechanism. The nuclei grow up through high angle grain boundaries migration. - Highlights: •Establish the DRX mathematical models of nuclear grade 316LN stainless steel •Determine the DRX mechanism of this steel •Subgrains are formed through dislocations polygonization. •Subgrains grow up through subgrain boundaries migration and coalescence mechanism. •DRX nucleation performs in grain boundary bulging mechanism and subgrain growth mechanism.

Multiple attractors and crisis route to chaos in a model food-chain

International Nuclear Information System (INIS)

Upadhyay, Ranjit Kumar

2003-01-01

An attempt has been made to identify the mechanism, which is responsible for the existence of chaos in narrow parameter range in a realistic ecological model food-chain. Analytical and numerical studies of a three species food-chain model similar to a situation likely to be seen in terrestrial ecosystems has been carried out. The study of the model food chain suggests that the existence of chaos in narrow parameter ranges is caused by the crisis-induced sudden death of chaotic attractors. Varying one of the critical parameters in its range while keeping all the others constant, one can monitor the changes in the dynamical behaviour of the system, thereby fixing the regimes in which the system exhibits chaotic dynamics. The computed bifurcation diagrams and basin boundary calculations indicate that crisis is the underlying factor which generates chaotic dynamics in this model food-chain. We investigate sudden qualitative changes in chaotic dynamical behaviour, which occur at a parameter value a 1 =1.7804 at which the chaotic attractor destroyed by boundary crisis with an unstable periodic orbit created by the saddle-node bifurcation. Multiple attractors with riddled basins and fractal boundaries are also observed. If ecological systems of interacting species do indeed exhibit multiple attractors etc., the long term dynamics of such systems may undergo vast qualitative changes following epidemics or environmental catastrophes due to the system being pushed into the basin of a new attractor by the perturbation. Coupled with stochasticity, such complex behaviours may render such systems practically unpredictable

Deterministic integer multiple firing depending on initial state in Wang model

Energy Technology Data Exchange (ETDEWEB)

Xie Yong [Institute of Nonlinear Dynamics, MSSV, Department of Engineering Mechanics, Xi' an Jiaotong University, Xi' an 710049 (China)]. E-mail: yxie@mail.xjtu.edu.cn; Xu Jianxue [Institute of Nonlinear Dynamics, MSSV, Department of Engineering Mechanics, Xi' an Jiaotong University, Xi' an 710049 (China); Jiang Jun [Institute of Nonlinear Dynamics, MSSV, Department of Engineering Mechanics, Xi' an Jiaotong University, Xi' an 710049 (China)

2006-12-15

We investigate numerically dynamical behaviour of the Wang model, which describes the rhythmic activities of thalamic relay neurons. The model neuron exhibits Type I excitability from a global view, but Type II excitability from a local view. There exists a narrow range of bistability, in which a subthreshold oscillation and a suprathreshold firing behaviour coexist. A special firing pattern, integer multiple firing can be found in the certain part of the bistable range. The characteristic feature of such firing pattern is that the histogram of interspike intervals has a multipeaked structure, and the peaks are located at about integer multiples of a basic interspike interval. Since the Wang model is noise-free, the integer multiple firing is a deterministic firing pattern. The existence of bistability leads to the deterministic integer multiple firing depending on the initial state of the model neuron, i.e., the initial values of the state variables.

Deterministic integer multiple firing depending on initial state in Wang model

International Nuclear Information System (INIS)

Xie Yong; Xu Jianxue; Jiang Jun

2006-01-01

We investigate numerically dynamical behaviour of the Wang model, which describes the rhythmic activities of thalamic relay neurons. The model neuron exhibits Type I excitability from a global view, but Type II excitability from a local view. There exists a narrow range of bistability, in which a subthreshold oscillation and a suprathreshold firing behaviour coexist. A special firing pattern, integer multiple firing can be found in the certain part of the bistable range. The characteristic feature of such firing pattern is that the histogram of interspike intervals has a multipeaked structure, and the peaks are located at about integer multiples of a basic interspike interval. Since the Wang model is noise-free, the integer multiple firing is a deterministic firing pattern. The existence of bistability leads to the deterministic integer multiple firing depending on the initial state of the model neuron, i.e., the initial values of the state variables

Multiple regression and beyond an introduction to multiple regression and structural equation modeling

CERN Document Server

Keith, Timothy Z

2014-01-01

Multiple Regression and Beyond offers a conceptually oriented introduction to multiple regression (MR) analysis and structural equation modeling (SEM), along with analyses that flow naturally from those methods. By focusing on the concepts and purposes of MR and related methods, rather than the derivation and calculation of formulae, this book introduces material to students more clearly, and in a less threatening way. In addition to illuminating content necessary for coursework, the accessibility of this approach means students are more likely to be able to conduct research using MR or SEM--and more likely to use the methods wisely. Covers both MR and SEM, while explaining their relevance to one another Also includes path analysis, confirmatory factor analysis, and latent growth modeling Figures and tables throughout provide examples and illustrate key concepts and techniques For additional resources, please visit: http://tzkeith.com/.

Modified random hinge transport mechanics and multiple scattering step-size selection in EGS5

International Nuclear Information System (INIS)

Wilderman, S.J.; Bielajew, A.F.

2005-01-01

The new transport mechanics in EGS5 allows for significantly longer electron transport step sizes and hence shorter computation times than required for identical problems in EGS4. But as with all Monte Carlo electron transport algorithms, certain classes of problems exhibit step-size dependencies even when operating within recommended ranges, sometimes making selection of step-sizes a daunting task for novice users. Further contributing to this problem, because of the decoupling of multiple scattering and continuous energy loss in the dual random hinge transport mechanics of EGS5, there are two independent step sizes in EGS5, one for multiple scattering and one for continuous energy loss, each of which influences speed and accuracy in a different manner. Further, whereas EGS4 used a single value of fractional energy loss (ESTEPE) to determine step sizes at all energies, to increase performance by decreasing the amount of effort expended simulating lower energy particles, EGS5 permits the fractional energy loss values which are used to determine both the multiple scattering and continuous energy loss step sizes to vary with energy. This results in requiring the user to specify four fractional energy loss values when optimizing computations for speed. Thus, in order to simplify step-size selection and to mitigate step-size dependencies, a method has been devised to automatically optimize step-size selection based on a single material dependent input related to the size of problem tally region. In this paper we discuss the new transport mechanics in EGS5 and describe the automatic step-size optimization algorithm. (author)

A Novel Multiple-Bits Collision Attack Based on Double Detection with Error-Tolerant Mechanism

Directory of Open Access Journals (Sweden)

Ye Yuan

2018-01-01

Full Text Available Side-channel collision attacks are more powerful than traditional side-channel attack without knowing the leakage model or establishing the model. Most attack strategies proposed previously need quantities of power traces with high computational complexity and are sensitive to mistakes, which restricts the attack efficiency seriously. In this paper, we propose a multiple-bits side-channel collision attack based on double distance voting detection (DDVD and also an improved version, involving the error-tolerant mechanism, which can find all 120 relations among 16 key bytes when applied to AES (Advanced Encryption Standard algorithm. In addition, we compare our collision detection method called DDVD with the Euclidean distance and the correlation-enhanced collision method under different intensity of noise, which indicates that our detection technique performs better in the circumstances of noise. Furthermore, 4-bit model of our collision detection method is proven to be optimal in theory and in practice. Meanwhile the corresponding practical attack experiments are also performed on a hardware implementation of AES-128 on FPGA board successfully. Results show that our strategy needs less computation time but more traces than LDPC method and the online time for our strategy is about 90% less than CECA and 96% less than BCA with 90% success rate.

Mechanism study of pulsus paradoxus using mechanical models.

Directory of Open Access Journals (Sweden)

Chang-yang Xing

Full Text Available Pulsus paradoxus is an exaggeration of the normal inspiratory decrease in systolic blood pressure. Despite a century of attempts to explain this sign consensus is still lacking. To solve the controversy and reveal the exact mechanism, we reexamined the characteristic anatomic arrangement of the circulation system in the chest and designed these mechanical models based on related hydromechanic principles. Model 1 was designed to observe the primary influence of respiratory intrathoracic pressure change (RIPC on systemic and pulmonary venous return systems (SVR and PVR respectively. Model 2, as an equivalent mechanical model of septal swing, was to study the secondary influence of RIPC on the motion of the interventriclar septum (IVS, which might be the direct cause for pulsus paradoxus. Model 1 demonstrated that the simulated RIPC had different influence on the simulated SVR and PVR. It increased the volume of the simulated right ventricle (SRV when the internal pressure was kept constant (8.16 cmH2O, while it had the opposite effect on PVR. Model 2 revealed the three major factors determining the respiratory displacement of IVS in normal and different pathophysiological conditions: the magnitude of RIPC, the pressure difference between the two ventricles and the intrapericardial pressure. Our models demonstrate that the different anatomical arrangement of the two venous return systems leads to a different effect of RIPC on right and left ventricles, and thus a pressure gradient across IVS that tends to shift IVS left- and rightwards. When the leftward displacement of IVS reaches a considerable amplitude in some pathologic condition such as cardiac tamponade, the pulsus paradoxus occurs.

New Hybrid Variational Recovery Model for Blurred Images with Multiplicative Noise

DEFF Research Database (Denmark)

Dong, Yiqiu; Zeng, Tieyong

2013-01-01

A new hybrid variational model for recovering blurred images in the presence of multiplicative noise is proposed. Inspired by previous work on multiplicative noise removal, an I-divergence technique is used to build a strictly convex model under a condition that ensures the uniqueness...

Microstructural response and grain refinement mechanism of commercially pure titanium subjected to multiple laser shock peening impacts

International Nuclear Information System (INIS)

Lu, J.Z.; Wu, L.J.; Sun, G.F.; Luo, K.Y.; Zhang, Y.K.; Cai, J.; Cui, C.Y.; Luo, X.M.

2017-01-01

The microstructural response and grain subdivision process in commercially pure (CP) titanium subjected to multiple laser shock peening (LSP) impacts were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The micro-hardness curves as a function of the impact time were also determined. The deformation-induced grain refinement mechanism of the close-packed hexagonal (hcp) material by laser shock wave was subsequently analyzed. Experimental results showed that uniform equiaxed grains with an average size of less than 50 nm were generated due to the ultra-high plastic strain induced by multiple LSP impacts. Special attention was paid to four types of novel deformation-induced microstructural features, including a layered slip band in the tension deformation zone, and inverse-transformation martensite, micro-twin grating and micro-twin collision in the compression deformation zone. Furthermore, the grain refinement mechanism in the near-surface layer of CP titanium subjected to multiple LSP impacts contains two types of simultaneous subdivision modes: multi-directional mechanical twin (MT)-MT intersections at (sub)micrometer scale, and the intersection between longitudinal secondary MTs and transverse dislocation walls at nanometer scale. In addition, both grain refinement (nanocrystallization) and the existence of a small amount of inverse-transformation martensite induced by multiple LSP impacts contribute to an increase in the micro-hardness of the near-surface layer.

ONKALO rock mechanics model (RMM). Version 2.3

Energy Technology Data Exchange (ETDEWEB)

Haekkinen, T.; Merjama, S.; Moenkkoenen, H. [WSP Finland, Helsinki (Finland)

2014-07-15

The Rock Mechanics Model of the ONKALO rock volume includes the most important rock mechanics features and parameters at the Olkiluoto site. The main objective of the model is to be a tool to predict rock properties, rock quality and hence provide an estimate for the rock stability of the potential repository at Olkiluoto. The model includes a database of rock mechanics raw data and a block model in which the rock mechanics parameters are estimated through block volumes based on spatial rock mechanics raw data. In this version 2.3, special emphasis was placed on refining the estimation of the block model. The model was divided into rock mechanics domains which were used as constraints during the block model estimation. During the modelling process, a display profile and toolbar were developed for the GEOVIA Surpac software to improve visualisation and access to the rock mechanics data for the Olkiluoto area. (orig.)

Mathematical Modeling of Loop Heat Pipes with Multiple Capillary Pumps and Multiple Condensers. Part 1; Stead State Stimulations

Science.gov (United States)

Hoang, Triem T.; OConnell, Tamara; Ku, Jentung

2004-01-01

Loop Heat Pipes (LHPs) have proven themselves as reliable and robust heat transport devices for spacecraft thermal control systems. So far, the LHPs in earth-orbit satellites perform very well as expected. Conventional LHPs usually consist of a single capillary pump for heat acquisition and a single condenser for heat rejection. Multiple pump/multiple condenser LHPs have shown to function very well in ground testing. Nevertheless, the test results of a dual pump/condenser LHP also revealed that the dual LHP behaved in a complicated manner due to the interaction between the pumps and condensers. Thus it is redundant to say that more research is needed before they are ready for 0-g deployment. One research area that perhaps compels immediate attention is the analytical modeling of LHPs, particularly the transient phenomena. Modeling a single pump/single condenser LHP is difficult enough. Only a handful of computer codes are available for both steady state and transient simulations of conventional LHPs. No previous effort was made to develop an analytical model (or even a complete theory) to predict the operational behavior of the multiple pump/multiple condenser LHP systems. The current research project offered a basic theory of the multiple pump/multiple condenser LHP operation. From it, a computer code was developed to predict the LHP saturation temperature in accordance with the system operating and environmental conditions.

Mechanical Systems, Classical Models

CERN Document Server

Teodorescu, Petre P

2009-01-01

This third volume completes the Work Mechanical Systems, Classical Models. The first two volumes dealt with particle dynamics and with discrete and continuous mechanical systems. The present volume studies analytical mechanics. Topics like Lagrangian and Hamiltonian mechanics, the Hamilton-Jacobi method, and a study of systems with separate variables are thoroughly discussed. Also included are variational principles and canonical transformations, integral invariants and exterior differential calculus, and particular attention is given to non-holonomic mechanical systems. The author explains in detail all important aspects of the science of mechanics, regarded as a natural science, and shows how they are useful in understanding important natural phenomena and solving problems of interest in applied and engineering sciences. Professor Teodorescu has spent more than fifty years as a Professor of Mechanics at the University of Bucharest and this book relies on the extensive literature on the subject as well as th...

A Bayesian Hierarchical Model for Relating Multiple SNPs within Multiple Genes to Disease Risk

Directory of Open Access Journals (Sweden)

Lewei Duan

2013-01-01

Full Text Available A variety of methods have been proposed for studying the association of multiple genes thought to be involved in a common pathway for a particular disease. Here, we present an extension of a Bayesian hierarchical modeling strategy that allows for multiple SNPs within each gene, with external prior information at either the SNP or gene level. The model involves variable selection at the SNP level through latent indicator variables and Bayesian shrinkage at the gene level towards a prior mean vector and covariance matrix that depend on external information. The entire model is fitted using Markov chain Monte Carlo methods. Simulation studies show that the approach is capable of recovering many of the truly causal SNPs and genes, depending upon their frequency and size of their effects. The method is applied to data on 504 SNPs in 38 candidate genes involved in DNA damage response in the WECARE study of second breast cancers in relation to radiotherapy exposure.

Predictive performance models and multiple task performance

Science.gov (United States)

Wickens, Christopher D.; Larish, Inge; Contorer, Aaron

1989-01-01

Five models that predict how performance of multiple tasks will interact in complex task scenarios are discussed. The models are shown in terms of the assumptions they make about human operator divided attention. The different assumptions about attention are then empirically validated in a multitask helicopter flight simulation. It is concluded from this simulation that the most important assumption relates to the coding of demand level of different component tasks.

MFAM: Multiple Frequency Adaptive Model-Based Indoor Localization Method.

Science.gov (United States)

Tuta, Jure; Juric, Matjaz B

2018-03-24

This paper presents MFAM (Multiple Frequency Adaptive Model-based localization method), a novel model-based indoor localization method that is capable of using multiple wireless signal frequencies simultaneously. It utilizes indoor architectural model and physical properties of wireless signal propagation through objects and space. The motivation for developing multiple frequency localization method lies in the future Wi-Fi standards (e.g., 802.11ah) and the growing number of various wireless signals present in the buildings (e.g., Wi-Fi, Bluetooth, ZigBee, etc.). Current indoor localization methods mostly rely on a single wireless signal type and often require many devices to achieve the necessary accuracy. MFAM utilizes multiple wireless signal types and improves the localization accuracy over the usage of a single frequency. It continuously monitors signal propagation through space and adapts the model according to the changes indoors. Using multiple signal sources lowers the required number of access points for a specific signal type while utilizing signals, already present in the indoors. Due to the unavailability of the 802.11ah hardware, we have evaluated proposed method with similar signals; we have used 2.4 GHz Wi-Fi and 868 MHz HomeMatic home automation signals. We have performed the evaluation in a modern two-bedroom apartment and measured mean localization error 2.0 to 2.3 m and median error of 2.0 to 2.2 m. Based on our evaluation results, using two different signals improves the localization accuracy by 18% in comparison to 2.4 GHz Wi-Fi-only approach. Additional signals would improve the accuracy even further. We have shown that MFAM provides better accuracy than competing methods, while having several advantages for real-world usage.

MFAM: Multiple Frequency Adaptive Model-Based Indoor Localization Method

Directory of Open Access Journals (Sweden)

Jure Tuta

2018-03-01

Full Text Available This paper presents MFAM (Multiple Frequency Adaptive Model-based localization method, a novel model-based indoor localization method that is capable of using multiple wireless signal frequencies simultaneously. It utilizes indoor architectural model and physical properties of wireless signal propagation through objects and space. The motivation for developing multiple frequency localization method lies in the future Wi-Fi standards (e.g., 802.11ah and the growing number of various wireless signals present in the buildings (e.g., Wi-Fi, Bluetooth, ZigBee, etc.. Current indoor localization methods mostly rely on a single wireless signal type and often require many devices to achieve the necessary accuracy. MFAM utilizes multiple wireless signal types and improves the localization accuracy over the usage of a single frequency. It continuously monitors signal propagation through space and adapts the model according to the changes indoors. Using multiple signal sources lowers the required number of access points for a specific signal type while utilizing signals, already present in the indoors. Due to the unavailability of the 802.11ah hardware, we have evaluated proposed method with similar signals; we have used 2.4 GHz Wi-Fi and 868 MHz HomeMatic home automation signals. We have performed the evaluation in a modern two-bedroom apartment and measured mean localization error 2.0 to 2.3 m and median error of 2.0 to 2.2 m. Based on our evaluation results, using two different signals improves the localization accuracy by 18% in comparison to 2.4 GHz Wi-Fi-only approach. Additional signals would improve the accuracy even further. We have shown that MFAM provides better accuracy than competing methods, while having several advantages for real-world usage.

Modelling Cochlear Mechanics

Directory of Open Access Journals (Sweden)

Guangjian Ni

2014-01-01

Full Text Available 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.

Mechanical model for ductility loss

International Nuclear Information System (INIS)

Hu, W.L.

1980-01-01

A mechanical model was constructed to probe into the mechanism of ductility loss. Fracture criterion based on critical localized deformation was undertaken. Two microstructure variables were considered in the model. Namely, the strength ratio of grain boundary affected area to the matrix, Ω, and the linear fraction, x, of grain boundary affected area. A parametrical study was carried out. The study shows that the ductility is very sensitive to those microstructure parameters. The functional dependence of ductility to temperature as well as strain-rate, suggested by the model, is demonstrated to be consistent with the observation

Petiveria alliacea extracts uses multiple mechanisms to inhibit growth of human and mouse tumoral cells

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Kaur Punit

2008-11-01

Full Text Available Abstract Background There is ethnopharmacological evidence that Petiveria alliacea can have antitumor activity; however, the mechanism of its cytotoxic activity is not well understood. We assessed multiple in vitro biological activities of an ethyl acetate soluble plant fraction over several tumor cell lines. Methods Tumor cell lines were evaluated using the following tests: trypan blue exclusion test, MTT [3-(4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide], flow cytometry, cytoskeleton organization analysis, cell cycle, mitochondria membrane depolarization, clonogenicity test, DNA fragmentation test and differential protein expression by HPLC-Chip/MS analysis. F4 fraction characterization was made by HPLC-MS. Results Petiveria alliacea fraction characterized by de-replication was found to alter actin cytoskeleton organization, induce G2 cell cycle arrest and cause apoptotic cell death in a mitochondria independent way. In addition, we found down regulation of cytoskeleton, chaperone, signal transduction proteins, and proteins involved in metabolic pathways. Finally up regulation of proteins involved in translation and intracellular degradation was also observed. Conclusion The results of this study indicate that Petiveria alliacea exerts multiple biological activities in vitro consistent with cytotoxicity. Further studies in animal models are needed but Petiveria alliacea appears to be a good candidate to be used as an antitumor agent.

Petiveria alliacea extracts uses multiple mechanisms to inhibit growth of human and mouse tumoral cells.

Science.gov (United States)

Urueña, Claudia; Cifuentes, Claudia; Castañeda, Diana; Arango, Amparo; Kaur, Punit; Asea, Alexzander; Fiorentino, Susana

2008-11-18

There is ethnopharmacological evidence that Petiveria alliacea can have antitumor activity; however, the mechanism of its cytotoxic activity is not well understood. We assessed multiple in vitro biological activities of an ethyl acetate soluble plant fraction over several tumor cell lines. Tumor cell lines were evaluated using the following tests: trypan blue exclusion test, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide], flow cytometry, cytoskeleton organization analysis, cell cycle, mitochondria membrane depolarization, clonogenicity test, DNA fragmentation test and differential protein expression by HPLC-Chip/MS analysis. F4 fraction characterization was made by HPLC-MS. Petiveria alliacea fraction characterized by de-replication was found to alter actin cytoskeleton organization, induce G2 cell cycle arrest and cause apoptotic cell death in a mitochondria independent way. In addition, we found down regulation of cytoskeleton, chaperone, signal transduction proteins, and proteins involved in metabolic pathways. Finally up regulation of proteins involved in translation and intracellular degradation was also observed. The results of this study indicate that Petiveria alliacea exerts multiple biological activities in vitro consistent with cytotoxicity. Further studies in animal models are needed but Petiveria alliacea appears to be a good candidate to be used as an antitumor agent.

Multiple Scattering Model for Optical Coherence Tomography with Rytov Approximation

KAUST Repository

Li, Muxingzi

2017-01-01

of speckles due to multiple scatterers within the coherence length, and other random noise. Motivated by the above two challenges, a multiple scattering model based on Rytov approximation and Gaussian beam optics is proposed for the OCT setup. Some previous

Timescales and Mechanisms of Sigh-Like Bursting and Spiking in Models of Rhythmic Respiratory Neurons.

Science.gov (United States)

Wang, Yangyang; Rubin, Jonathan E

2017-12-01

Neural networks generate a variety of rhythmic activity patterns, often involving different timescales. One example arises in the respiratory network in the pre-Bötzinger complex of the mammalian brainstem, which can generate the eupneic rhythm associated with normal respiration as well as recurrent low-frequency, large-amplitude bursts associated with sighing. Two competing hypotheses have been proposed to explain sigh generation: the recruitment of a neuronal population distinct from the eupneic rhythm-generating subpopulation or the reconfiguration of activity within a single population. Here, we consider two recent computational models, one of which represents each of the hypotheses. We use methods of dynamical systems theory, such as fast-slow decomposition, averaging, and bifurcation analysis, to understand the multiple-timescale mechanisms underlying sigh generation in each model. In the course of our analysis, we discover that a third timescale is required to generate sighs in both models. Furthermore, we identify the similarities of the underlying mechanisms in the two models and the aspects in which they differ.

Multiple post-transcriptional regulatory mechanisms in ferritin gene expression

International Nuclear Information System (INIS)

Mattia, E.; Den Blaauwen, J.; Van Renswoude, J.; Ashwell, G.

1989-01-01

The authors have investigated the mechanisms involved in the regulation of ferritin biosynthesis in K562 human erythroleukemia cells during prolonged exposure to iron. They show that, upon addition of hemin (an efficient iron donor) to the cell culture, the rate of ferritin biosynthesis reaches a maximum after a few hours and then decreases. During a 24-hr incubation with the iron donor the concentrations of total ferritin heavy (H) and light (L) subunit mRNAs rise 2- to 5-fold and 2- to 3-fold, respectively, over the control values, while the amount of the protein increases 10- to 30-fold. The hemin-induced increment in ferritin subunit mRNA is not prevented by deferoxamine, suggesting that it is not directly mediated by chelatable iron. In vitro nuclear transcription analyses performed on nuclei isolated from control cells and cells grown in the presence of hemin indicate that the rates of synthesis of H- and L-subunit mRNAs remain constant. They conclude that iron-induced ferritin biosynthesis is governed by multiple post-transcriptional regulatory mechanisms. They propose that exposure of cells to iron leads to stabilization of ferritin mRNAs, in addition to activation and translation of stored H-and L-subunit mRNAs

MODEL PENSKORAN PARTIAL CREDIT PADA BUTIR MULTIPLE TRUE-FALSE BIDANG FISIKA

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Wasis Wasis

2013-01-01

Full Text Available Tujuan penelitian ini menghasilkan model penskoran politomus untuk respons butir multiple true-false, sehingga dapat mengestimasi secara lebih akurat kemampuan di bidang fisika. Pengembangan penskoran menggunakan Four-D model dan diuji akurasinya melalui penelitian empiris dan simulasi. Penelitian empiris menggunakan 15 butir multiple true-false yang diambil dari soal UMPTN tahun 1996-2006 dan dikenakan pada 410 mahasiswa baru FMIPA Universitas Negeri Surabaya angkatan tahun 2007. Respons peserta tes diskor dengan tiga model partial credit (PCM I; II; dan III dan secara dikotomus. Hasil penskoran dianalisis dengan program Quest untuk mendapat-kan estimasi tingkat kesukaran butir (δ dan estimasi ke-mampuan peserta (θ untuk menentukan nilai fungsi informasi tes dan kesalahan baku estimasi. Penelitian simulasi mengguna-kan data bangkitan berdasarkan parameter empiris (δ dan θ memakai program statistik SAS dan akurasi estimasinya di-analisis dengan metode root mean squared error (RMSE. Hasil penelitian ini menunjukkan: (i Penskoran PCM dengan pem-bobotan mampu mengestimasi kemampuan lebih akurat di-bandingkan tanpa pembobotan maupun secara dikotomus; (ii Semakin banyak jumlah kategori dalam penskoran partial credit, semakin akurat. Kata kunci: model penskoran partial credit, butir multiple true-false ____________________________________________________________ THE PARTIAL CREDIT SCORING MODEL FOR THE MULTIPLE TRUE-FALSE BUTIRS IN PHYSICS Abstract This study is an attempt to overcome the weaknesses. This study aims to produce a polytomous scoring model for responses to multiple true-false butirs in order to get a more accurate estimation of abilities in physics. It adopts the Four-D model and its accuracy is assessed through empirical and simulation studies. The empirical study employed 15 multiple true-false butirs taken from the New Students Entrance Test of State University the year of 1996–2006. It administered to 410 new students enrolled

A perspective on multiple waves of influenza pandemics.

Science.gov (United States)

Mummert, Anna; Weiss, Howard; Long, Li-Ping; Amigó, José M; Wan, Xiu-Feng

2013-01-01

A striking characteristic of the past four influenza pandemic outbreaks in the United States has been the multiple waves of infections. However, the mechanisms responsible for the multiple waves of influenza or other acute infectious diseases are uncertain. Understanding these mechanisms could provide knowledge for health authorities to develop and implement prevention and control strategies. We exhibit five distinct mechanisms, each of which can generate two waves of infections for an acute infectious disease. The first two mechanisms capture changes in virus transmissibility and behavioral changes. The third mechanism involves population heterogeneity (e.g., demography, geography), where each wave spreads through one sub-population. The fourth mechanism is virus mutation which causes delayed susceptibility of individuals. The fifth mechanism is waning immunity. Each mechanism is incorporated into separate mathematical models, and outbreaks are then simulated. We use the models to examine the effects of the initial number of infected individuals (e.g., border control at the beginning of the outbreak) and the timing of and amount of available vaccinations. Four models, individually or in any combination, reproduce the two waves of the 2009 H1N1 pandemic in the United States, both qualitatively and quantitatively. One model reproduces the two waves only qualitatively. All models indicate that significantly reducing or delaying the initial numbers of infected individuals would have little impact on the attack rate. Instead, this reduction or delay results in a single wave as opposed to two waves. Furthermore, four of these models also indicate that a vaccination program started earlier than October 2009 (when the H1N1 vaccine was initially distributed) could have eliminated the second wave of infection, while more vaccine available starting in October would not have eliminated the second wave.

A perspective on multiple waves of influenza pandemics.

Directory of Open Access Journals (Sweden)

Anna Mummert

Full Text Available A striking characteristic of the past four influenza pandemic outbreaks in the United States has been the multiple waves of infections. However, the mechanisms responsible for the multiple waves of influenza or other acute infectious diseases are uncertain. Understanding these mechanisms could provide knowledge for health authorities to develop and implement prevention and control strategies.We exhibit five distinct mechanisms, each of which can generate two waves of infections for an acute infectious disease. The first two mechanisms capture changes in virus transmissibility and behavioral changes. The third mechanism involves population heterogeneity (e.g., demography, geography, where each wave spreads through one sub-population. The fourth mechanism is virus mutation which causes delayed susceptibility of individuals. The fifth mechanism is waning immunity. Each mechanism is incorporated into separate mathematical models, and outbreaks are then simulated. We use the models to examine the effects of the initial number of infected individuals (e.g., border control at the beginning of the outbreak and the timing of and amount of available vaccinations.Four models, individually or in any combination, reproduce the two waves of the 2009 H1N1 pandemic in the United States, both qualitatively and quantitatively. One model reproduces the two waves only qualitatively. All models indicate that significantly reducing or delaying the initial numbers of infected individuals would have little impact on the attack rate. Instead, this reduction or delay results in a single wave as opposed to two waves. Furthermore, four of these models also indicate that a vaccination program started earlier than October 2009 (when the H1N1 vaccine was initially distributed could have eliminated the second wave of infection, while more vaccine available starting in October would not have eliminated the second wave.

Multiple environment single system quantum mechanical/molecular mechanical (MESS-QM/MM) calculations. 1. Estimation of polarization energies.

Science.gov (United States)

Sodt, Alexander J; Mei, Ye; König, Gerhard; Tao, Peng; Steele, Ryan P; Brooks, Bernard R; Shao, Yihan

2015-03-05

In combined quantum mechanical/molecular mechanical (QM/MM) free energy calculations, it is often advantageous to have a frozen geometry for the quantum mechanical (QM) region. For such multiple-environment single-system (MESS) cases, two schemes are proposed here for estimating the polarization energy: the first scheme, termed MESS-E, involves a Roothaan step extrapolation of the self-consistent field (SCF) energy; whereas the other scheme, termed MESS-H, employs a Newton-Raphson correction using an approximate inverse electronic Hessian of the QM region (which is constructed only once). Both schemes are extremely efficient, because the expensive Fock updates and SCF iterations in standard QM/MM calculations are completely avoided at each configuration. They produce reasonably accurate QM/MM polarization energies: MESS-E can predict the polarization energy within 0.25 kcal/mol in terms of the mean signed error for two of our test cases, solvated methanol and solvated β-alanine, using the M06-2X or ωB97X-D functionals; MESS-H can reproduce the polarization energy within 0.2 kcal/mol for these two cases and for the oxyluciferin-luciferase complex, if the approximate inverse electronic Hessians are constructed with sufficient accuracy.

A collaborative scheduling model for the supply-hub with multiple suppliers and multiple manufacturers.

Science.gov (United States)

Li, Guo; Lv, Fei; Guan, Xu

2014-01-01

This paper investigates a collaborative scheduling model in the assembly system, wherein multiple suppliers have to deliver their components to the multiple manufacturers under the operation of Supply-Hub. We first develop two different scenarios to examine the impact of Supply-Hub. One is that suppliers and manufacturers make their decisions separately, and the other is that the Supply-Hub makes joint decisions with collaborative scheduling. The results show that our scheduling model with the Supply-Hub is a NP-complete problem, therefore, we propose an auto-adapted differential evolution algorithm to solve this problem. Moreover, we illustrate that the performance of collaborative scheduling by the Supply-Hub is superior to separate decision made by each manufacturer and supplier. Furthermore, we also show that the algorithm proposed has good convergence and reliability, which can be applicable to more complicated supply chain environment.

A Technique of Fuzzy C-Mean in Multiple Linear Regression Model toward Paddy Yield

Science.gov (United States)

Syazwan Wahab, Nur; Saifullah Rusiman, Mohd; Mohamad, Mahathir; Amira Azmi, Nur; Che Him, Norziha; Ghazali Kamardan, M.; Ali, Maselan

2018-04-01

In this paper, we propose a hybrid model which is a combination of multiple linear regression model and fuzzy c-means method. This research involved a relationship between 20 variates of the top soil that are analyzed prior to planting of paddy yields at standard fertilizer rates. Data used were from the multi-location trials for rice carried out by MARDI at major paddy granary in Peninsular Malaysia during the period from 2009 to 2012. Missing observations were estimated using mean estimation techniques. The data were analyzed using multiple linear regression model and a combination of multiple linear regression model and fuzzy c-means method. Analysis of normality and multicollinearity indicate that the data is normally scattered without multicollinearity among independent variables. Analysis of fuzzy c-means cluster the yield of paddy into two clusters before the multiple linear regression model can be used. The comparison between two method indicate that the hybrid of multiple linear regression model and fuzzy c-means method outperform the multiple linear regression model with lower value of mean square error.

Thermo-kinetic mechanisms for grain boundary structure multiplicity, thermal instability and defect interactions

International Nuclear Information System (INIS)

Burbery, N.J.; Das, R.; Ferguson, W.G.

2016-01-01

Grain boundaries (GBs) provide a source and/or a sink for crystal defects and store elastic energy due to the non-uniform atomic bonding structure of the GB core. GB structures are thermodynamically driven to transition to the lowest energy configuration possible; however to date there has been little evidence to explain why specific GB structures have a low energy state. Furthermore, there is little quantitative demonstration of the significance of physical and GB structure characteristics on the GB energy, thermal stability, and the effect of temporary local GB structure transformations on defect interactions. This paper evaluates the defect interactions and structure stability of multiple Σ5(310) GB structures in bi-crystals of pure aluminium, and systematically investigates the features at 0 K to characterise multiple metastable structures. Structure stability is evaluated by utilising unstable vacancy defects to initiate GB transformations, and using nudged elastic band simulations to quantify this with the activation energy. The emission of stable vacancy defects from the ‘stable’ and metastable grain boundaries is also evaluated in the same manner. A detailed analysis of dislocation nucleation at the atomistic scale demonstrates that local transformations of GB structure between stable and metastable intermediates can provide a mechanism to accommodate the generation of crystal defects. Kinetic (time-dependent) effects that compete with energetic driving forces for structural transformations of GBs are shown to cause a significant effect on the activation properties that may exceed the influence of GB potential energy. The results demonstrate that GB structural multiplicity can be associated with the generation and absorption of dislocations and vacancies. This paper demonstrates the suitability of atomistic simulations coupled with nudged elastic band simulations to evaluate fundamental thermodynamic properties of pure FCC metals. Overall, this paper

Thermo-kinetic mechanisms for grain boundary structure multiplicity, thermal instability and defect interactions

Energy Technology Data Exchange (ETDEWEB)

Burbery, N.J. [Department of Mechanical Engineering, University of Auckland, Auckland 1010 (New Zealand); Das, R., E-mail: r.das@auckland.ac.nz [Department of Mechanical Engineering, University of Auckland, Auckland 1010 (New Zealand); Ferguson, W.G. [Department of Chemical and Materials Engineering, University of Auckland, Auckland 1010 (New Zealand)

2016-08-15

Grain boundaries (GBs) provide a source and/or a sink for crystal defects and store elastic energy due to the non-uniform atomic bonding structure of the GB core. GB structures are thermodynamically driven to transition to the lowest energy configuration possible; however to date there has been little evidence to explain why specific GB structures have a low energy state. Furthermore, there is little quantitative demonstration of the significance of physical and GB structure characteristics on the GB energy, thermal stability, and the effect of temporary local GB structure transformations on defect interactions. This paper evaluates the defect interactions and structure stability of multiple Σ5(310) GB structures in bi-crystals of pure aluminium, and systematically investigates the features at 0 K to characterise multiple metastable structures. Structure stability is evaluated by utilising unstable vacancy defects to initiate GB transformations, and using nudged elastic band simulations to quantify this with the activation energy. The emission of stable vacancy defects from the ‘stable’ and metastable grain boundaries is also evaluated in the same manner. A detailed analysis of dislocation nucleation at the atomistic scale demonstrates that local transformations of GB structure between stable and metastable intermediates can provide a mechanism to accommodate the generation of crystal defects. Kinetic (time-dependent) effects that compete with energetic driving forces for structural transformations of GBs are shown to cause a significant effect on the activation properties that may exceed the influence of GB potential energy. The results demonstrate that GB structural multiplicity can be associated with the generation and absorption of dislocations and vacancies. This paper demonstrates the suitability of atomistic simulations coupled with nudged elastic band simulations to evaluate fundamental thermodynamic properties of pure FCC metals. Overall, this paper

From fracture mechanics to damage mechanics: how to model structural deterioration

International Nuclear Information System (INIS)

Nicolet, S.; Lorentz, E.; Barbier, G.

1998-01-01

Modelling of structural deteriorations of thermo-mechanical origin is highly enhanced when using damage mechanics. Indeed, the latter offers both a fine description of the material behaviour and an ability to deal with any loading conditions, moving away the current limits of fracture mechanics. But new difficulties can arise, depending on the examined problem: if forecasts of rack initiation are well mastered, the study of crack propagation remains more complex and needs sophisticated modelizations, which are nevertheless on the point of being well understood too. (authors)

Reduction of bias in neutron multiplicity assay using a weighted point model

Energy Technology Data Exchange (ETDEWEB)

Geist, W. H. (William H.); Krick, M. S. (Merlyn S.); Mayo, D. R. (Douglas R.)

2004-01-01

Accurate assay of most common plutonium samples was the development goal for the nondestructive assay technique of neutron multiplicity counting. Over the past 20 years the technique has been proven for relatively pure oxides and small metal items. Unfortunately, the technique results in large biases when assaying large metal items. Limiting assumptions, such as unifoh multiplication, in the point model used to derive the multiplicity equations causes these biases for large dense items. A weighted point model has been developed to overcome some of the limitations in the standard point model. Weighting factors are detemiined from Monte Carlo calculations using the MCNPX code. Monte Carlo calculations give the dependence of the weighting factors on sample mass and geometry, and simulated assays using Monte Carlo give the theoretical accuracy of the weighted-point-model assay. Measured multiplicity data evaluated with both the standard and weighted point models are compared to reference values to give the experimental accuracy of the assay. Initial results show significant promise for the weighted point model in reducing or eliminating biases in the neutron multiplicity assay of metal items. The negative biases observed in the assay of plutonium metal samples are caused by variations in the neutron multiplication for neutrons originating in various locations in the sample. The bias depends on the mass and shape of the sample and depends on the amount and energy distribution of the ({alpha},n) neutrons in the sample. When the standard point model is used, this variable-multiplication bias overestimates the multiplication and alpha values of the sample, and underestimates the plutonium mass. The weighted point model potentially can provide assay accuracy of {approx}2% (1 {sigma}) for cylindrical plutonium metal samples < 4 kg with {alpha} < 1 without knowing the exact shape of the samples, provided that the ({alpha},n) source is uniformly distributed throughout the

Active joint mechanism driven by multiple actuators made of flexible bags: a proposal of dual structural actuator.

Science.gov (United States)

Kimura, Hitoshi; Matsuzaki, Takuya; Kataoka, Mokutaro; Inou, Norio

2013-01-01

An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0 Nm load torque under 0.15 MPa air input.

Targeting multiple pathogenic mechanisms with polyphenols for the treatment of Alzheimer’s disease: Experimental approach and therapeutic implications

Directory of Open Access Journals (Sweden)

Jun eWang

2014-03-01

Full Text Available Alzheimer’s disease (AD is the most prevalent neurodegenerative disease of aging and currently has no cure. Its onset and progression are influenced by multiple factors. There is growing consensus that successful treatment will rely on simultaneously targeting multiple pathological features of AD. Polyphenol compounds have many proven health benefits. In this study, we tested the hypothesis that combining three polyphenolic preparations (grape seed extract, resveratrol and Concord grape juice extract, with different polyphenolic compositions and partially redundant bioactivities, may simultaneously and synergistically mitigate amyloid-β (Aβ mediated neuropathology and cognitive impairments in a mouse model of AD. We found that administration of the polyphenols in combination did not alter the profile of bioactive polyphenol metabolites in the brain. We also found that combination treatment resulted in better protection against cognitive impairments compared to individual treatments, in J20 AD mice. Electrophysiological examination showed that acute treatment with select brain penetrating polyphenol metabolites, derived from these polyphenols, improved oligomeric Aβ (oAβ-induced long term potentiation (LTP deficits in hippocampal slices. Moreover, we found greatly reduced total amyloid content in the brain following combination treatment. Our studies provided experimental evidence that application of polyphenols targeting multiple disease-mechanisms may yield a greater likelihood of therapeutic efficacy.

Prediction of mechanical properties for hexagonal boron nitride nanosheets using molecular mechanics model

Energy Technology Data Exchange (ETDEWEB)

Natsuki, Toshiaki [Shinshu University, Faculty of Textile Science and Technology, Ueda (Japan); Shinshu University, Institute of Carbon Science and Technology, Nagano (Japan); Natsuki, Jun [Shinshu University, Institute of Carbon Science and Technology, Nagano (Japan)

2017-04-15

Mechanical behaviors of nanomaterials are not easy to be evaluated in the laboratory because of their extremely small size and difficulty controlling. Thus, a suitable model for the estimation of the mechanical properties for nanomaterials becomes very important. In this study, the elastic properties of boron nitride (BN) nanosheets, including the elastic modulus, the shear modulus, and the Poisson's ratio, are predicted using a molecular mechanics model. The molecular mechanics force filed is established to directly incorporate the Morse potential function into the constitutive model of nanostructures. According to the molecular mechanics model, the chirality effect of hexagonal BN nanosheets on the elastic modulus is investigated through a closed-form solution. The simulated result shows that BN nanosheets exhibit an isotropic elastic property. The present analysis yields a set of very simple formulas and is able to be served as a good approximation on the mechanical properties for the BN nanosheets. (orig.)

Prediction of mechanical properties for hexagonal boron nitride nanosheets using molecular mechanics model

International Nuclear Information System (INIS)

Natsuki, Toshiaki; Natsuki, Jun

2017-01-01

Mechanical behaviors of nanomaterials are not easy to be evaluated in the laboratory because of their extremely small size and difficulty controlling. Thus, a suitable model for the estimation of the mechanical properties for nanomaterials becomes very important. In this study, the elastic properties of boron nitride (BN) nanosheets, including the elastic modulus, the shear modulus, and the Poisson's ratio, are predicted using a molecular mechanics model. The molecular mechanics force filed is established to directly incorporate the Morse potential function into the constitutive model of nanostructures. According to the molecular mechanics model, the chirality effect of hexagonal BN nanosheets on the elastic modulus is investigated through a closed-form solution. The simulated result shows that BN nanosheets exhibit an isotropic elastic property. The present analysis yields a set of very simple formulas and is able to be served as a good approximation on the mechanical properties for the BN nanosheets. (orig.)

Infinite Multiple Membership Relational Modeling for Complex Networks

DEFF Research Database (Denmark)

Mørup, Morten; Schmidt, Mikkel Nørgaard; Hansen, Lars Kai

Learning latent structure in complex networks has become an important problem fueled by many types of networked data originating from practically all fields of science. In this paper, we propose a new non-parametric Bayesian multiplemembership latent feature model for networks. Contrary to existing...... multiplemembership models that scale quadratically in the number of vertices the proposedmodel scales linearly in the number of links admittingmultiple-membership analysis in large scale networks. We demonstrate a connection between the single membership relational model and multiple membership models and show...

Single-process versus multiple-strategy models of decision making: evidence from an information intrusion paradigm.

Science.gov (United States)

Söllner, Anke; Bröder, Arndt; Glöckner, Andreas; Betsch, Tilmann

2014-02-01

When decision makers are confronted with different problems and situations, do they use a uniform mechanism as assumed by single-process models (SPMs) or do they choose adaptively from a set of available decision strategies as multiple-strategy models (MSMs) imply? Both frameworks of decision making have gathered a lot of support, but only rarely have they been contrasted with each other. Employing an information intrusion paradigm for multi-attribute decisions from givens, SPM and MSM predictions on information search, decision outcomes, attention, and confidence judgments were derived and tested against each other in two experiments. The results consistently support the SPM view: Participants seemingly using a "take-the-best" (TTB) strategy do not ignore TTB-irrelevant information as MSMs would predict, but adapt the amount of information searched, choose alternative choice options, and show varying confidence judgments contingent on the quality of the "irrelevant" information. The uniformity of these findings underlines the adequacy of the novel information intrusion paradigm and comprehensively promotes the notion of a uniform decision making mechanism as assumed by single-process models. Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

Experimental Autoimmune Encephalomyelitis (EAE) as Animal Models of Multiple Sclerosis (MS).

Science.gov (United States)

Glatigny, Simon; Bettelli, Estelle

2018-01-08

Multiple sclerosis (MS) is a multifocal demyelinating disease of the central nervous system (CNS) leading to the progressive destruction of the myelin sheath surrounding axons. It can present with variable clinical and pathological manifestations, which might reflect the involvement of distinct pathogenic processes. Although the mechanisms leading to the development of the disease are not fully understood, numerous evidences indicate that MS is an autoimmune disease, the initiation and progression of which are dependent on an autoimmune response against myelin antigens. In addition, genetic susceptibility and environmental triggers likely contribute to the initiation of the disease. At this time, there is no cure for MS, but several disease-modifying therapies (DMTs) are available to control and slow down disease progression. A good number of these DMTs were identified and tested using animal models of MS referred to as experimental autoimmune encephalomyelitis (EAE). In this review, we will recapitulate the characteristics of EAE models and discuss how they help shed light on MS pathogenesis and help test new treatments for MS patients. Copyright © 2018 Cold Spring Harbor Laboratory Press; all rights reserved.

Optimization of the Darrieus wind turbines with double-multiple-streamtube model

International Nuclear Information System (INIS)

Paraschivoiu, I.

1985-01-01

This paper discusses a new improvement of the double-multiple-stream tube model by considering the stream tube expansion effects on the Darrieus wind turbine. These effects, allowing a more realistic modeling of the upwind/downwind flow field asymmetries inherent in the Darrieus rotor, were calculated by using CARDAAX computer code. When the dynamic stall is introduced in the double-multiple-stream tube model, the aerodynamic loads and performance show significant changes in the range of low tip-speed ratio

Application of multiple objective models to water resources planning and management

International Nuclear Information System (INIS)

North, R.M.

1993-01-01

Over the past 30 years, we have seen the birth and growth of multiple objective analysis from an idea without tools to one with useful applications. Models have been developed and applications have been researched to address the multiple purposes and objectives inherent in the development and management of water resources. A practical approach to multiple objective modelling incorporates macroeconomic-based policies and expectations in order to optimize the results from both engineering (structural) and management (non-structural) alternatives, while taking into account the economic and environmental trade-offs. (author). 27 refs, 4 figs, 3 tabs

A Collaborative Scheduling Model for the Supply-Hub with Multiple Suppliers and Multiple Manufacturers

Directory of Open Access Journals (Sweden)

Guo Li

2014-01-01

Full Text Available This paper investigates a collaborative scheduling model in the assembly system, wherein multiple suppliers have to deliver their components to the multiple manufacturers under the operation of Supply-Hub. We first develop two different scenarios to examine the impact of Supply-Hub. One is that suppliers and manufacturers make their decisions separately, and the other is that the Supply-Hub makes joint decisions with collaborative scheduling. The results show that our scheduling model with the Supply-Hub is a NP-complete problem, therefore, we propose an auto-adapted differential evolution algorithm to solve this problem. Moreover, we illustrate that the performance of collaborative scheduling by the Supply-Hub is superior to separate decision made by each manufacturer and supplier. Furthermore, we also show that the algorithm proposed has good convergence and reliability, which can be applicable to more complicated supply chain environment.

A Collaborative Scheduling Model for the Supply-Hub with Multiple Suppliers and Multiple Manufacturers

Science.gov (United States)

Lv, Fei; Guan, Xu

2014-01-01

This paper investigates a collaborative scheduling model in the assembly system, wherein multiple suppliers have to deliver their components to the multiple manufacturers under the operation of Supply-Hub. We first develop two different scenarios to examine the impact of Supply-Hub. One is that suppliers and manufacturers make their decisions separately, and the other is that the Supply-Hub makes joint decisions with collaborative scheduling. The results show that our scheduling model with the Supply-Hub is a NP-complete problem, therefore, we propose an auto-adapted differential evolution algorithm to solve this problem. Moreover, we illustrate that the performance of collaborative scheduling by the Supply-Hub is superior to separate decision made by each manufacturer and supplier. Furthermore, we also show that the algorithm proposed has good convergence and reliability, which can be applicable to more complicated supply chain environment. PMID:24892104

Multiple Time Series Ising Model for Financial Market Simulations

International Nuclear Information System (INIS)

Takaishi, Tetsuya

2015-01-01

In this paper we propose an Ising model which simulates multiple financial time series. Our model introduces the interaction which couples to spins of other systems. Simulations from our model show that time series exhibit the volatility clustering that is often observed in the real financial markets. Furthermore we also find non-zero cross correlations between the volatilities from our model. Thus our model can simulate stock markets where volatilities of stocks are mutually correlated

Security-Based Mechanism for Proactive Routing Schema Using Game Theory Model

Directory of Open Access Journals (Sweden)

Hicham Amraoui

2016-01-01

Full Text Available Game theory may offer a useful mechanism to address many problems in mobile ad hoc networks (MANETs. One of the key concepts in the research field of such networks with Optimized Link State Routing Protocol (OLSR is the security problem. Relying on applying game theory to study this problem, we consider two strategies during this suggested model: cooperate and not-cooperate. However, in such networks, it is not easy to identify different actions of players. In this paper, we have essentially been inspired from recent advances provided in game theory to propose a new model for security in MANETs. Our proposal presents a powerful tool with a large number of players where interactions are played multiple times. Moreover, each node keeps a cooperation rate (CR record of other nodes to cope with the behaviors and mitigate aggregate effect of other malicious devices. Additionally, our suggested security mechanism does not only take into consideration security requirements, but also take into account system resources and network performances. The simulation results using Network Simulator 3 are presented to illustrate the effectiveness of the proposal.

Alternative approaches to reliability modeling of a multiple engineered barrier system

International Nuclear Information System (INIS)

Ananda, M.M.A.; Singh, A.K.

1994-01-01

The lifetime of the engineered barrier system used for containment of high-level radioactive waste will significantly impact the total performance of a geological repository facility. Currently two types of designs are under consideration for an engineered barrier system, single engineered barrier system and multiple engineered barrier system. Multiple engineered barrier system consists of several metal barriers and the waste form (cladding). Some recent work show that a significant improvement of performance can be achieved by utilizing multiple engineered barrier systems. Considering sequential failures for each barrier, we model the reliability of the multiple engineered barrier system. Weibull and exponential lifetime distributions are used through out the analysis. Furthermore, the number of failed engineered barrier systems in a repository at a given time is modeled using a poisson approximation

Development of 3D Oxide Fuel Mechanics Models

Energy Technology Data Exchange (ETDEWEB)

Spencer, B. W. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Casagranda, A. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Pitts, S. A. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Jiang, W. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2017-07-27

This report documents recent work to improve the accuracy and robustness of the mechanical constitutive models used in the BISON fuel performance code. These developments include migration of the fuel mechanics models to be based on the MOOSE Tensor Mechanics module, improving the robustness of the smeared cracking model, implementing a capability to limit the time step size based on material model response, and improving the robustness of the return mapping iterations used in creep and plasticity models.

Model of the regulation of the rate of multiplication of the stem cells of the bone marrow. [X radiation, gamma radiation

Energy Technology Data Exchange (ETDEWEB)

Gruzdev, G P; Monichev, A Ya

1975-01-01

A mathematical model of regulation of the rate of multiplication of the stem cells of the bone marrow has been constructed and investigated. Two possible variants of regulation of the proliferative activity of the irradiated stem cells are compared: at the level of tissue and subtissue units. Comparison of the results of modeling with the results of experimental investigations supports the latter mechanism of regulation of the proliferation of the stem cells.

Feedback structure based entropy approach for multiple-model estimation

Institute of Scientific and Technical Information of China (English)

Shen-tu Han; Xue Anke; Guo Yunfei

2013-01-01

The variable-structure multiple-model (VSMM) approach, one of the multiple-model (MM) methods, is a popular and effective approach in handling problems with mode uncertainties. The model sequence set adaptation (MSA) is the key to design a better VSMM. However, MSA methods in the literature have big room to improve both theoretically and practically. To this end, we propose a feedback structure based entropy approach that could find the model sequence sets with the smallest size under certain conditions. The filtered data are fed back in real time and can be used by the minimum entropy (ME) based VSMM algorithms, i.e., MEVSMM. Firstly, the full Markov chains are used to achieve optimal solutions. Secondly, the myopic method together with particle filter (PF) and the challenge match algorithm are also used to achieve sub-optimal solutions, a trade-off between practicability and optimality. The numerical results show that the proposed algorithm provides not only refined model sets but also a good robustness margin and very high accuracy.

A PDP model of the simultaneous perception of multiple objects

Science.gov (United States)

Henderson, Cynthia M.; McClelland, James L.

2011-06-01

Illusory conjunctions in normal and simultanagnosic subjects are two instances where the visual features of multiple objects are incorrectly 'bound' together. A connectionist model explores how multiple objects could be perceived correctly in normal subjects given sufficient time, but could give rise to illusory conjunctions with damage or time pressure. In this model, perception of two objects benefits from lateral connections between hidden layers modelling aspects of the ventral and dorsal visual pathways. As with simultanagnosia, simulations of dorsal lesions impair multi-object recognition. In contrast, a large ventral lesion has minimal effect on dorsal functioning, akin to dissociations between simple object manipulation (retained in visual form agnosia and semantic dementia) and object discrimination (impaired in these disorders) [Hodges, J.R., Bozeat, S., Lambon Ralph, M.A., Patterson, K., and Spatt, J. (2000), 'The Role of Conceptual Knowledge: Evidence from Semantic Dementia', Brain, 123, 1913-1925; Milner, A.D., and Goodale, M.A. (2006), The Visual Brain in Action (2nd ed.), New York: Oxford]. It is hoped that the functioning of this model might suggest potential processes underlying dorsal and ventral contributions to the correct perception of multiple objects.

MODEL PENSKORAN PARTIAL CREDIT PADA BUTIR MULTIPLE TRUE-FALSE BIDANG FISIKA

OpenAIRE

Wasis Wasis

2013-01-01

Tujuan penelitian ini menghasilkan model penskoran politomus untuk respons butir multiple true-false, sehingga dapat mengestimasi secara lebih akurat kemampuan di bidang fisika. Pengembangan penskoran menggunakan Four-D model dan diuji akurasinya melalui penelitian empiris dan simulasi. Penelitian empiris menggunakan 15 butir multiple true-false yang diambil dari soal UMPTN tahun 1996-2006 dan dikenakan pada 410 mahasiswa baru FMIPA Universitas Negeri Surabaya angkatan tahun 2007. Respons pes...

Modeling the effector - regulatory T cell cross-regulation reveals the intrinsic character of relapses in Multiple Sclerosis

Directory of Open Access Journals (Sweden)

Torrealdea Javier

2011-07-01

Full Text Available Abstract Background The relapsing-remitting dynamics is a hallmark of autoimmune diseases such as Multiple Sclerosis (MS. Although current understanding of both cellular and molecular mechanisms involved in the pathogenesis of autoimmune diseases is significant, how their activity generates this prototypical dynamics is not understood yet. In order to gain insight about the mechanisms that drive these relapsing-remitting dynamics, we developed a computational model using such biological knowledge. We hypothesized that the relapsing dynamics in autoimmunity can arise through the failure in the mechanisms controlling cross-regulation between regulatory and effector T cells with the interplay of stochastic events (e.g. failure in central tolerance, activation by pathogens that are able to trigger the immune system. Results The model represents five concepts: central tolerance (T-cell generation by the thymus, T-cell activation, T-cell memory, cross-regulation (negative feedback between regulatory and effector T-cells and tissue damage. We enriched the model with reversible and irreversible tissue damage, which aims to provide a comprehensible link between autoimmune activity and clinical relapses and active lesions in the magnetic resonances studies in patients with Multiple Sclerosis. Our analysis shows that the weakness in this negative feedback between effector and regulatory T-cells, allows the immune system to generate the characteristic relapsing-remitting dynamics of autoimmune diseases, without the need of additional environmental triggers. The simulations show that the timing at which relapses appear is highly unpredictable. We also introduced targeted perturbations into the model that mimicked immunotherapies that modulate effector and regulatory populations. The effects of such therapies happened to be highly dependent on the timing and/or dose, and on the underlying dynamic of the immune system. Conclusion The relapsing dynamic in MS

Hybrid approaches for multiple-species stochastic reaction–diffusion models

International Nuclear Information System (INIS)

Spill, Fabian; Guerrero, Pilar; Alarcon, Tomas; Maini, Philip K.; Byrne, Helen

2015-01-01

Reaction–diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction–diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model. - Highlights: • A novel hybrid stochastic/deterministic reaction–diffusion simulation method is given. • Can massively speed up stochastic simulations while preserving stochastic effects. • Can handle multiple reacting species. • Can handle moving boundaries

Hybrid approaches for multiple-species stochastic reaction–diffusion models

Energy Technology Data Exchange (ETDEWEB)

Spill, Fabian, E-mail: fspill@bu.edu [Department of Biomedical Engineering, Boston University, 44 Cummington Street, Boston, MA 02215 (United States); Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Guerrero, Pilar [Department of Mathematics, University College London, Gower Street, London WC1E 6BT (United Kingdom); Alarcon, Tomas [Centre de Recerca Matematica, Campus de Bellaterra, Edifici C, 08193 Bellaterra (Barcelona) (Spain); Departament de Matemàtiques, Universitat Atonòma de Barcelona, 08193 Bellaterra (Barcelona) (Spain); Maini, Philip K. [Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Oxford OX2 6GG (United Kingdom); Byrne, Helen [Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Oxford OX2 6GG (United Kingdom); Computational Biology Group, Department of Computer Science, University of Oxford, Oxford OX1 3QD (United Kingdom)

2015-10-15

Reaction–diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction–diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model. - Highlights: • A novel hybrid stochastic/deterministic reaction–diffusion simulation method is given. • Can massively speed up stochastic simulations while preserving stochastic effects. • Can handle multiple reacting species. • Can handle moving boundaries.

Dealing with Multiple Solutions in Structural Vector Autoregressive Models.

Science.gov (United States)

Beltz, Adriene M; Molenaar, Peter C M

2016-01-01

Structural vector autoregressive models (VARs) hold great potential for psychological science, particularly for time series data analysis. They capture the magnitude, direction of influence, and temporal (lagged and contemporaneous) nature of relations among variables. Unified structural equation modeling (uSEM) is an optimal structural VAR instantiation, according to large-scale simulation studies, and it is implemented within an SEM framework. However, little is known about the uniqueness of uSEM results. Thus, the goal of this study was to investigate whether multiple solutions result from uSEM analysis and, if so, to demonstrate ways to select an optimal solution. This was accomplished with two simulated data sets, an empirical data set concerning children's dyadic play, and modifications to the group iterative multiple model estimation (GIMME) program, which implements uSEMs with group- and individual-level relations in a data-driven manner. Results revealed multiple solutions when there were large contemporaneous relations among variables. Results also verified several ways to select the correct solution when the complete solution set was generated, such as the use of cross-validation, maximum standardized residuals, and information criteria. This work has immediate and direct implications for the analysis of time series data and for the inferences drawn from those data concerning human behavior.

Modeling the Coupled Chemo-Thermo-Mechanical Behavior of Amorphous Polymer Networks.

Energy Technology Data Exchange (ETDEWEB)

Zimmerman, Jonathan A. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Nguyen, Thao D. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Xiao, Rui [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

2015-02-01

Amorphous polymers exhibit a rich landscape of time-dependent behavior including viscoelasticity, structural relaxation, and viscoplasticity. These time-dependent mechanisms can be exploited to achieve shape-memory behavior, which allows the material to store a programmed deformed shape indefinitely and to recover entirely the undeformed shape in response to specific environmental stimulus. The shape-memory performance of amorphous polymers depends on the coordination of multiple physical mechanisms, and considerable opportunities exist to tailor the polymer structure and shape-memory programming procedure to achieve the desired performance. The goal of this project was to use a combination of theoretical, numerical and experimental methods to investigate the effect of shape memory programming, thermo-mechanical properties, and physical and environmental aging on the shape memory performance. Physical and environmental aging occurs during storage and through exposure to solvents, such as water, and can significantly alter the viscoelastic behavior and shape memory behavior of amorphous polymers. This project – executed primarily by Professor Thao Nguyen and Graduate Student Rui Xiao at Johns Hopkins University in support of a DOE/NNSA Presidential Early Career Award in Science and Engineering (PECASE) – developed a theoretical framework for chemothermo- mechanical behavior of amorphous polymers to model the effects of physical aging and solvent-induced environmental factors on their thermoviscoelastic behavior.

Mechanics Model of Plug Welding

Science.gov (United States)

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.

A constitutive mechanical model for gas hydrate bearing sediments incorporating inelastic mechanisms

KAUST Repository

Sánchez, Marcelo

2016-11-30

Gas hydrate bearing sediments (HBS) are natural soils formed in permafrost and sub-marine settings where the temperature and pressure conditions are such that gas hydrates are stable. If these conditions shift from the hydrate stability zone, hydrates dissociate and move from the solid to the gas phase. Hydrate dissociation is accompanied by significant changes in sediment structure and strongly affects its mechanical behavior (e.g., sediment stiffenss, strength and dilatancy). The mechanical behavior of HBS is very complex and its modeling poses great challenges. This paper presents a new geomechanical model for hydrate bearing sediments. The model incorporates the concept of partition stress, plus a number of inelastic mechanisms proposed to capture the complex behavior of this type of soil. This constitutive model is especially well suited to simulate the behavior of HBS upon dissociation. The model was applied and validated against experimental data from triaxial and oedometric tests conducted on manufactured and natural specimens involving different hydrate saturation, hydrate morphology, and confinement conditions. Particular attention was paid to model the HBS behavior during hydrate dissociation under loading. The model performance was highly satisfactory in all the cases studied. It managed to properly capture the main features of HBS mechanical behavior and it also assisted to interpret the behavior of this type of sediment under different loading and hydrate conditions.

Dynamic Bus Travel Time Prediction Models on Road with Multiple Bus Routes.

Science.gov (United States)

Bai, Cong; Peng, Zhong-Ren; Lu, Qing-Chang; Sun, Jian

2015-01-01

Accurate and real-time travel time information for buses can help passengers better plan their trips and minimize waiting times. A dynamic travel time prediction model for buses addressing the cases on road with multiple bus routes is proposed in this paper, based on support vector machines (SVMs) and Kalman filtering-based algorithm. In the proposed model, the well-trained SVM model predicts the baseline bus travel times from the historical bus trip data; the Kalman filtering-based dynamic algorithm can adjust bus travel times with the latest bus operation information and the estimated baseline travel times. The performance of the proposed dynamic model is validated with the real-world data on road with multiple bus routes in Shenzhen, China. The results show that the proposed dynamic model is feasible and applicable for bus travel time prediction and has the best prediction performance among all the five models proposed in the study in terms of prediction accuracy on road with multiple bus routes.

Dynamic Bus Travel Time Prediction Models on Road with Multiple Bus Routes

Science.gov (United States)

Bai, Cong; Peng, Zhong-Ren; Lu, Qing-Chang; Sun, Jian

2015-01-01

Accurate and real-time travel time information for buses can help passengers better plan their trips and minimize waiting times. A dynamic travel time prediction model for buses addressing the cases on road with multiple bus routes is proposed in this paper, based on support vector machines (SVMs) and Kalman filtering-based algorithm. In the proposed model, the well-trained SVM model predicts the baseline bus travel times from the historical bus trip data; the Kalman filtering-based dynamic algorithm can adjust bus travel times with the latest bus operation information and the estimated baseline travel times. The performance of the proposed dynamic model is validated with the real-world data on road with multiple bus routes in Shenzhen, China. The results show that the proposed dynamic model is feasible and applicable for bus travel time prediction and has the best prediction performance among all the five models proposed in the study in terms of prediction accuracy on road with multiple bus routes. PMID:26294903

Green communication: The enabler to multiple business models

DEFF Research Database (Denmark)

Lindgren, Peter; Clemmensen, Suberia; Taran, Yariv

2010-01-01

Companies stand at the forefront of a new business model reality with new potentials - that will change their basic understanding and practice of running their business models radically. One of the drivers to this change is green communication, its strong relation to green business models and its...... possibility to enable lower energy consumption. This paper shows how green communication enables innovation of green business models and multiple business models running simultaneously in different markets to different customers.......Companies stand at the forefront of a new business model reality with new potentials - that will change their basic understanding and practice of running their business models radically. One of the drivers to this change is green communication, its strong relation to green business models and its...

The Mechanisms of Water Exchange: The Regulatory Roles of Multiple Interactions in Social Wasps.

Science.gov (United States)

Agrawal, Devanshu; Karsai, Istvan

2016-01-01

Evolutionary benefits of task fidelity and improving information acquisition via multiple transfers of materials between individuals in a task partitioned system have been shown before, but in this paper we provide a mechanistic explanation of these phenomena. Using a simple mathematical model describing the individual interactions of the wasps, we explain the functioning of the common stomach, an information center, which governs construction behavior and task change. Our central hypothesis is a symmetry between foragers who deposit water and foragers who withdraw water into and out of the common stomach. We combine this with a trade-off between acceptance and resistance to water transfer. We ultimately derive a mathematical function that relates the number of interactions that foragers complete with common stomach wasps during a foraging cycle. We use field data and additional model assumptions to calculate values of our model parameters, and we use these to explain why the fullness of the common stomach stabilizes just below 50 percent, why the average number of successful interactions between foragers and the wasps forming the common stomach is between 5 and 7, and why there is a variation in this number of interactions over time. Our explanation is that our proposed water exchange mechanism places natural bounds on the number of successful interactions possible, water exchange is set to optimize mediation of water through the common stomach, and the chance that foragers abort their task prematurely is very low.

A computational framework for 3D mechanical modeling of plant morphogenesis with cellular resolution.

Directory of Open Access Journals (Sweden)

Frédéric Boudon

2015-01-01

Full Text Available The link between genetic regulation and the definition of form and size during morphogenesis remains largely an open question in both plant and animal biology. This is partially due to the complexity of the process, involving extensive molecular networks, multiple feedbacks between different scales of organization and physical forces operating at multiple levels. Here we present a conceptual and modeling framework aimed at generating an integrated understanding of morphogenesis in plants. This framework is based on the biophysical properties of plant cells, which are under high internal turgor pressure, and are prevented from bursting because of the presence of a rigid cell wall. To control cell growth, the underlying molecular networks must interfere locally with the elastic and/or plastic extensibility of this cell wall. We present a model in the form of a three dimensional (3D virtual tissue, where growth depends on the local modulation of wall mechanical properties and turgor pressure. The model shows how forces generated by turgor-pressure can act both cell autonomously and non-cell autonomously to drive growth in different directions. We use simulations to explore lateral organ formation at the shoot apical meristem. Although different scenarios lead to similar shape changes, they are not equivalent and lead to different, testable predictions regarding the mechanical and geometrical properties of the growing lateral organs. Using flower development as an example, we further show how a limited number of gene activities can explain the complex shape changes that accompany organ outgrowth.

Conduction mechanism in amorphous InGaZnO thin film transistors

NARCIS (Netherlands)

Bhoolokam, A.; Nag, M.; Steudel, S.; Genoe, J.; Gelinck, G.; Kadashchuk, A.; Groeseneken, G.; Heremans, P.

2016-01-01

We validate a model which is a combination of multiple trapping and release and percolation model for describing the conduction mechanism in amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFT). We show that using just multiple trapping and release or percolation model is

Mechanism for multiplicity of steady states with distinct cell concentration in continuous culture of mammalian cells.

Science.gov (United States)

Yongky, Andrew; Lee, Jongchan; Le, Tung; Mulukutla, Bhanu Chandra; Daoutidis, Prodromos; Hu, Wei-Shou

2015-07-01

Continuous culture for the production of biopharmaceutical proteins offers the possibility of steady state operations and thus more consistent product quality and increased productivity. Under some conditions, multiplicity of steady states has been observed in continuous cultures of mammalian cells, wherein with the same dilution rate and feed nutrient composition, steady states with very different cell and product concentrations may be reached. At those different steady states, cells may exhibit a high glycolysis flux with high lactate production and low cell concentration, or a low glycolysis flux with low lactate and high cell concentration. These different steady states, with different cell concentration, also have different productivity. Developing a mechanistic understanding of the occurrence of steady state multiplicity and devising a strategy to steer the culture toward the desired steady state is critical. We establish a multi-scale kinetic model that integrates a mechanistic intracellular metabolic model and cell growth model in a continuous bioreactor. We show that steady state multiplicity exists in a range of dilution rate in continuous culture as a result of the bistable behavior in glycolysis. The insights from the model were used to devise strategies to guide the culture to the desired steady state in the multiple steady state region. The model provides a guideline principle in the design of continuous culture processes of mammalian cells. © 2015 Wiley Periodicals, Inc.

Mechanical Impedance Modeling of Human Arm: A survey

Science.gov (United States)

Puzi, A. Ahmad; Sidek, S. N.; Sado, F.

2017-03-01

Human arm mechanical impedance plays a vital role in describing motion ability of the upper limb. One of the impedance parameters is stiffness which is defined as the ratio of an applied force to the measured deformation of the muscle. The arm mechanical impedance modeling is useful in order to develop a better controller for system that interacts with human as such an automated robot-assisted platform for automated rehabilitation training. The aim of the survey is to summarize the existing mechanical impedance models of human upper limb so to justify the need to have an improved version of the arm model in order to facilitate the development of better controller of such systems with ever increase in complexity. In particular, the paper will address the following issue: Human motor control and motor learning, constant and variable impedance models, methods for measuring mechanical impedance and mechanical impedance modeling techniques.

A statistical model of uplink inter-cell interference with slow and fast power control mechanisms

KAUST Repository

Tabassum, Hina; Yilmaz, Ferkan; Dawy, Zaher; Alouini, Mohamed-Slim

2013-01-01

Uplink power control is in essence an interference mitigation technique that aims at minimizing the inter-cell interference (ICI) in cellular networks by reducing the transmit power levels of the mobile users while maintaining their target received signal quality levels at base stations. Power control mechanisms directly impact the interference dynamics and, thus, affect the overall achievable capacity and consumed power in cellular networks. Due to the stochastic nature of wireless channels and mobile users' locations, it is important to derive theoretical models for ICI that can capture the impact of design alternatives related to power control mechanisms. To this end, we derive and verify a novel statistical model for uplink ICI in Generalized-K composite fading environments as a function of various slow and fast power control mechanisms. The derived expressions are then utilized to quantify numerically key network performance metrics that include average resource fairness, average reduction in power consumption, and ergodic capacity. The accuracy of the derived expressions is validated via Monte-Carlo simulations. Results are generated for multiple network scenarios, and insights are extracted to assess various power control mechanisms as a function of system parameters. © 1972-2012 IEEE.

A statistical model of uplink inter-cell interference with slow and fast power control mechanisms

KAUST Repository

Tabassum, Hina

2013-09-01

Uplink power control is in essence an interference mitigation technique that aims at minimizing the inter-cell interference (ICI) in cellular networks by reducing the transmit power levels of the mobile users while maintaining their target received signal quality levels at base stations. Power control mechanisms directly impact the interference dynamics and, thus, affect the overall achievable capacity and consumed power in cellular networks. Due to the stochastic nature of wireless channels and mobile users\\' locations, it is important to derive theoretical models for ICI that can capture the impact of design alternatives related to power control mechanisms. To this end, we derive and verify a novel statistical model for uplink ICI in Generalized-K composite fading environments as a function of various slow and fast power control mechanisms. The derived expressions are then utilized to quantify numerically key network performance metrics that include average resource fairness, average reduction in power consumption, and ergodic capacity. The accuracy of the derived expressions is validated via Monte-Carlo simulations. Results are generated for multiple network scenarios, and insights are extracted to assess various power control mechanisms as a function of system parameters. © 1972-2012 IEEE.

Adaption of Ulva pertusa to multiple-contamination of heavy metals and nutrients: Biological mechanism of outbreak of Ulva sp. green tide.

Science.gov (United States)

Ge, Changzi; Yu, Xiru; Kan, Manman; Qu, Chunfeng

2017-12-15

The multiple-contamination of heavy metals and nutrients worsens increasingly and Ulva sp. green tide occurs almost simultaneously. To reveal the biological mechanism for outbreak of the green tide, Ulva pertusa was exposed to seven-day-multiple-contamination. The relation between pH variation (V pH ), Chl a content, ratio of (Chl a content)/(Chl b content) (R chla/chlb ), SOD activity of U. pertusa (A SOD ) and contamination concentration is [Formula: see text] (pcontamination concentrations of seawaters where Ulva sp. green tide occurred and the contamination concentrations set in the present work, U. pertusa can adapt to multiple-contaminations in these waters. Thus, the adaption to multiple-contamination may be one biological mechanism for the outbreak of Ulva sp. green tide. Copyright © 2017 Elsevier Ltd. All rights reserved.

p38 mediates mechanical allodynia in a mouse model of type 2 diabetes

Directory of Open Access Journals (Sweden)

Hong Yu

2010-05-01

Full Text Available Abstract Background Painful Diabetic Neuropathy (PDN affects more than 25% of patients with type 2 diabetes; however, the pathogenesis remains unclear due to lack of knowledge of the molecular mechanisms leading to PDN. In our current study, we use an animal model of type 2 diabetes in order to understand the roles of p38 in PDN. Previously, we have demonstrated that the C57BLK db/db (db/db mouse, a model of type 2 diabetes that carries the loss-of-function leptin receptor mutant, develops mechanical allodynia in the hind paws during the early stage (6-12 wk of age of diabetes. Using this timeline of PDN, we can investigate the signaling mechanisms underlying mechanical allodynia in the db/db mouse. Results We studied the role of p38 in lumbar dorsal root ganglia (LDRG during the development of mechanical allodynia in db/db mice. p38 phosphorylation was detected by immunoblots at the early stage of mechanical allodynia in LDRG of diabetic mice. Phosphorylated p38 (pp38 immunoreactivity was detected mostly in the small- to medium-sized LDRG neurons during the time period of mechanical allodynia. Treatment with an antibody against nerve growth factor (NGF significantly inhibited p38 phosphorylation in LDRG of diabetic mice. In addition, we detected higher levels of inflammatory mediators, including cyclooxygenase (COX 2, inducible nitric oxide synthases (iNOS, and tumor necrosis factor (TNF-α in LDRG neurons of db/db mice compared to non-diabetic db+ mice. Intrathecal delivery of SB203580, a p38 inhibitor, significantly inhibited the development of mechanical allodynia and the upregulation of COX2, iNOS and TNF-α. Conclusions Our findings suggest that NGF activated-p38 phosphorylation mediates mechanical allodynia in the db/db mouse by upregulation of multiple inflammatory mediators in LDRG.

An extension of the multiple-trapping model

International Nuclear Information System (INIS)

Shkilev, V. P.

2012-01-01

The hopping charge transport in disordered semiconductors is considered. Using the concept of the transport energy level, macroscopic equations are derived that extend a multiple-trapping model to the case of semiconductors with both energy and spatial disorders. It is shown that, although both types of disorder can cause dispersive transport, the frequency dependence of conductivity is determined exclusively by the spatial disorder.

Quantitative analysis of multiple biokinetic models using a dynamic water phantom: A feasibility study

Science.gov (United States)

Chiang, Fu-Tsai; Li, Pei-Jung; Chung, Shih-Ping; Pan, Lung-Fa; Pan, Lung-Kwang

2016-01-01

ABSTRACT This study analyzed multiple biokinetic models using a dynamic water phantom. The phantom was custom-made with acrylic materials to model metabolic mechanisms in the human body. It had 4 spherical chambers of different sizes, connected by 8 ditches to form a complex and adjustable water loop. One infusion and drain pole connected the chambers to an auxiliary silicon-based hose, respectively. The radio-active compound solution (TC-99m-MDP labeled) formed a sealed and static water loop inside the phantom. As clean feed water was infused to replace the original solution, the system mimicked metabolic mechanisms for data acquisition. Five cases with different water loop settings were tested and analyzed, with case settings changed by controlling valve poles located in the ditches. The phantom could also be changed from model A to model B by transferring its vertical configuration. The phantom was surveyed with a clinical gamma camera to determine the time-dependent intensity of every chamber. The recorded counts per pixel in each chamber were analyzed and normalized to compare with theoretical estimations from the MATLAB program. Every preset case was represented by uniquely defined, time-dependent, simultaneous differential equations, and a corresponding MATLAB program optimized the solutions by comparing theoretical calculations and practical measurements. A dimensionless agreement (AT) index was recommended to evaluate the comparison in each case. ATs varied from 5.6 to 48.7 over the 5 cases, indicating that this work presented an acceptable feasibility study. PMID:27286096

A Multiple Model Prediction Algorithm for CNC Machine Wear PHM

Directory of Open Access Journals (Sweden)

Huimin Chen

2011-01-01

Full Text Available The 2010 PHM data challenge focuses on the remaining useful life (RUL estimation for cutters of a high speed CNC milling machine using measurements from dynamometer, accelerometer, and acoustic emission sensors. We present a multiple model approach for wear depth estimation of milling machine cutters using the provided data. The feature selection, initial wear estimation and multiple model fusion components of the proposed algorithm are explained in details and compared with several alternative methods using the training data. The final submission ranked #2 among professional and student participants and the method is applicable to other data driven PHM problems.

Modeling the Evolution of Beliefs Using an Attentional Focus Mechanism.

Directory of Open Access Journals (Sweden)

Dimitrije Marković

2015-10-01

Full Text Available For making decisions in everyday life we often have first to infer the set of environmental features that are relevant for the current task. Here we investigated the computational mechanisms underlying the evolution of beliefs about the relevance of environmental features in a dynamical and noisy environment. For this purpose we designed a probabilistic Wisconsin card sorting task (WCST with belief solicitation, in which subjects were presented with stimuli composed of multiple visual features. At each moment in time a particular feature was relevant for obtaining reward, and participants had to infer which feature was relevant and report their beliefs accordingly. To test the hypothesis that attentional focus modulates the belief update process, we derived and fitted several probabilistic and non-probabilistic behavioral models, which either incorporate a dynamical model of attentional focus, in the form of a hierarchical winner-take-all neuronal network, or a diffusive model, without attention-like features. We used Bayesian model selection to identify the most likely generative model of subjects' behavior and found that attention-like features in the behavioral model are essential for explaining subjects' responses. Furthermore, we demonstrate a method for integrating both connectionist and Bayesian models of decision making within a single framework that allowed us to infer hidden belief processes of human subjects.

The Effects of Multiple Sets of Squats and Jump Squats on Mechanical Variables.

Science.gov (United States)

Rossetti, Michael L; Munford, Shawn N; Snyder, Brandon W; Davis, Shala E; Moir, Gavin L

2017-07-28

The mechanical responses to two non-ballistic squat and two ballistic jump squat protocols performed over multiple sets were investigated. One protocol from each of the two non-ballistic and ballistic conditions incorporated a pause between the eccentric and concentric phases of the movements in order to determine the influence of the coupling time on the mechanical variables and post-activation potentiation (PAP). Eleven men (age: 21.9 ± 1.8 years; height: 1.79 ± 0.05 m; mass: 87.0 ± 7.4 kg) attended four sessions where they performed multiple sets of squats and jump squats with a load equivalent to 30% 1-repeititon maximum under one of the following conditions: 1) 3 × 4 repetitions of non-ballistic squats (30N-B); 2) 3 × 4 repetitions of non-ballistic squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PN-B); 3) 3 × 4 repetitions of ballistic jump squats (30B); 4) 3 × 4 repetitions of ballistic jump squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PB). Force plates were used to calculate variables including average vertical velocity, average vertical force (GRF), and average power output (PO). Vertical velocities during the ballistic conditions were significantly greater than those attained during the non-ballistic conditions (mean differences: 0.21 - 0.25 m/s, p0.05). Ballistic jump squats may be an effective exercise for developing PO given the high velocities and forces generated in these exercises. Furthermore, the completion of multiple sets of jump squats may induce PAP to enhance PO. The coupling times between the eccentric and concentric phases of the jump squats should be short in order to maximize the GRF and PO across the sets.

Multiple mechanisms involved in diabetes protection by lipopolysaccharide in non-obese diabetic mice

Energy Technology Data Exchange (ETDEWEB)

Wang, Jun [Department of Pharmacology, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan (China); Department of Pharmacology, College of Medicine, Wuhan University of Science and Technology, Wuhan (China); Cao, Hui [Department of Pharmacology, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan (China); Wang, Hongjie [Section of Neurobiology, Torrey Pines Institute for Molecular Studies, Port Saint Lucie, FL (United States); Yin, Guoxiao; Du, Jiao; Xia, Fei; Lu, Jingli [Department of Pharmacology, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan (China); Xiang, Ming, E-mail: xiangming@mails.tjmu.edu.cn [Department of Pharmacology, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan (China)

2015-06-15

Toll-like receptor 4 (TLR4) activation has been proposed to be important for islet cell inflammation and eventually β cell loss in the course of type 1 diabetes (T1D) development. However, according to the “hygiene hypothesis”, bacterial endotoxin lipopolysaccharide (LPS), an agonist on TLR4, inhibits T1D progression. Here we investigated possible mechanisms for the protective effect of LPS on T1D development in non-obese diabetic (NOD) mice. We found that LPS administration to NOD mice during the prediabetic state neither prevented nor reversed insulitis, but delayed the onset and decreased the incidence of diabetes, and that a multiple-injection protocol is more effective than a single LPS intervention. Further, LPS administration suppressed spleen T lymphocyte proliferation, increased the generation of CD4{sup +}CD25{sup +}Foxp3{sup +} regulatory T cells (Tregs), reduced the synthesis of strong Th1 proinflammatory cytokines, and downregulated TLR4 and its downstream MyD88-dependent signaling pathway. Most importantly, multiple injections of LPS induced a potential tolerogenic dendritic cell (DC) subset with low TLR4 expression without influencing the DC phenotype. Explanting DCs from repeated LPS-treated NOD mice into NOD/SCID diabetic mice conferred sustained protective effects against the progression of diabetes in the recipients. Overall, these results suggest that multiple mechanisms are involved in the protective effects of LPS against the development of diabetes in NOD diabetic mice. These include Treg induction, down-regulation of TLR4 and its downstream MyD88-dependent signaling pathway, and the emergence of a potential tolerogenic DC subset. - Highlights: • Administration of lipopolysaccharide (LPS) prevented type 1 diabetes in NOD mice. • Downregulating TLR4 level and MyD88-dependent pathway contributed to protection of LPS. • LPS administration also hampered DC maturation and promoted Treg differentiation.

Multiple mechanisms involved in diabetes protection by lipopolysaccharide in non-obese diabetic mice

International Nuclear Information System (INIS)

Wang, Jun; Cao, Hui; Wang, Hongjie; Yin, Guoxiao; Du, Jiao; Xia, Fei; Lu, Jingli; Xiang, Ming

2015-01-01

Toll-like receptor 4 (TLR4) activation has been proposed to be important for islet cell inflammation and eventually β cell loss in the course of type 1 diabetes (T1D) development. However, according to the “hygiene hypothesis”, bacterial endotoxin lipopolysaccharide (LPS), an agonist on TLR4, inhibits T1D progression. Here we investigated possible mechanisms for the protective effect of LPS on T1D development in non-obese diabetic (NOD) mice. We found that LPS administration to NOD mice during the prediabetic state neither prevented nor reversed insulitis, but delayed the onset and decreased the incidence of diabetes, and that a multiple-injection protocol is more effective than a single LPS intervention. Further, LPS administration suppressed spleen T lymphocyte proliferation, increased the generation of CD4 + CD25 + Foxp3 + regulatory T cells (Tregs), reduced the synthesis of strong Th1 proinflammatory cytokines, and downregulated TLR4 and its downstream MyD88-dependent signaling pathway. Most importantly, multiple injections of LPS induced a potential tolerogenic dendritic cell (DC) subset with low TLR4 expression without influencing the DC phenotype. Explanting DCs from repeated LPS-treated NOD mice into NOD/SCID diabetic mice conferred sustained protective effects against the progression of diabetes in the recipients. Overall, these results suggest that multiple mechanisms are involved in the protective effects of LPS against the development of diabetes in NOD diabetic mice. These include Treg induction, down-regulation of TLR4 and its downstream MyD88-dependent signaling pathway, and the emergence of a potential tolerogenic DC subset. - Highlights: • Administration of lipopolysaccharide (LPS) prevented type 1 diabetes in NOD mice. • Downregulating TLR4 level and MyD88-dependent pathway contributed to protection of LPS. • LPS administration also hampered DC maturation and promoted Treg differentiation

Multiplicity of Mathematical Modeling Strategies to Search for Molecular and Cellular Insights into Bacteria Lung Infection.

Science.gov (United States)

Cantone, Martina; Santos, Guido; Wentker, Pia; Lai, Xin; Vera, Julio

2017-01-01

Even today two bacterial lung infections, namely pneumonia and tuberculosis, are among the 10 most frequent causes of death worldwide. These infections still lack effective treatments in many developing countries and in immunocompromised populations like infants, elderly people and transplanted patients. The interaction between bacteria and the host is a complex system of interlinked intercellular and the intracellular processes, enriched in regulatory structures like positive and negative feedback loops. Severe pathological condition can emerge when the immune system of the host fails to neutralize the infection. This failure can result in systemic spreading of pathogens or overwhelming immune response followed by a systemic inflammatory response. Mathematical modeling is a promising tool to dissect the complexity underlying pathogenesis of bacterial lung infection at the molecular, cellular and tissue levels, and also at the interfaces among levels. In this article, we introduce mathematical and computational modeling frameworks that can be used for investigating molecular and cellular mechanisms underlying bacterial lung infection. Then, we compile and discuss published results on the modeling of regulatory pathways and cell populations relevant for lung infection and inflammation. Finally, we discuss how to make use of this multiplicity of modeling approaches to open new avenues in the search of the molecular and cellular mechanisms underlying bacterial infection in the lung.

Mechanics model for actin-based motility.

Science.gov (United States)

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.

Sound propagation in dilute suspensions of spheres: Analytical comparison between coupled phase model and multiple scattering theory.

Science.gov (United States)

Valier-Brasier, Tony; Conoir, Jean-Marc; Coulouvrat, François; Thomas, Jean-Louis

2015-10-01

Sound propagation in dilute suspensions of small spheres is studied using two models: a hydrodynamic model based on the coupled phase equations and an acoustic model based on the ECAH (ECAH: Epstein-Carhart-Allegra-Hawley) multiple scattering theory. The aim is to compare both models through the study of three fundamental kinds of particles: rigid particles, elastic spheres, and viscous droplets. The hydrodynamic model is based on a Rayleigh-Plesset-like equation generalized to elastic spheres and viscous droplets. The hydrodynamic forces for elastic spheres are introduced by analogy with those of droplets. The ECAH theory is also modified in order to take into account the velocity of rigid particles. Analytical calculations performed for long wavelength, low dilution, and weak absorption in the ambient fluid show that both models are strictly equivalent for the three kinds of particles studied. The analytical calculations show that dilatational and translational mechanisms are modeled in the same way by both models. The effective parameters of dilute suspensions are also calculated.

Selecting Tools to Model Integer and Binomial Multiplication

Science.gov (United States)

Pratt, Sarah Smitherman; Eddy, Colleen M.

2017-01-01

Mathematics teachers frequently provide concrete manipulatives to students during instruction; however, the rationale for using certain manipulatives in conjunction with concepts may not be explored. This article focuses on area models that are currently used in classrooms to provide concrete examples of integer and binomial multiplication. The…

Comparative study between a QCD inspired model and a multiple diffraction model

International Nuclear Information System (INIS)

Luna, E.G.S.; Martini, A.F.; Menon, M.J.

2003-01-01

A comparative study between a QCD Inspired Model (QCDIM) and a Multiple Diffraction Model (MDM) is presented, with focus on the results for pp differential cross section at √s = 52.8 GeV. It is shown that the MDM predictions are in agreement with experimental data, except for the dip region and that the QCDIM describes only the diffraction peak region. Interpretations in terms of the corresponding eikonals are also discussed. (author)

Modeling and Generating Strategy Games Mechanics

DEFF Research Database (Denmark)

Mahlmann, Tobias

of the game is, how players may manipulate the game world, etc. We present the Strategy Games Description Language (SGDL), a tree-based approach to model the game mechanics of strategy games. SGDL allows game designers to rapid prototype their game ideas with the help of our customisable game engine. We...... their games to individual players’ preferences by creating game content adaptively to how the player plays (and likes) a game. W we extend the notion of “procedural game content generation” by “game mechanics”. Game mechanics herein refer to the way that objects in a game may interact, what the goal...... present several example games to demonstrate the capabilities of the language and how to model common strategy game elements. Furthermore, we present methods to procedurally generate and evaluate game mechanics modelled in SGDL in terms of enjoyability. We argue that an evolutionary process can be used...

ANALYSIS AND MODELING OF GENEVA MECHANISM

Directory of Open Access Journals (Sweden)

HARAGA Georgeta

2015-06-01

Full Text Available The paper presents some aspects theoretical and practical based on the finite element analysis and modelling of Geneva mechanism with four slots, using the CATIA graphic program. This type of mechanism is an example of intermittent gearing that translates a continuous rotation into an intermittent rotary motion. It consists of alternate periods of motion and rest without reversing direction. In this paper, some design parameters with specify a Geneva mechanism will be defined precisely such as number of driving cranks, number of slots, wheel diameter, pin diameter, etc. Finite element analysis (FEA can be used for creating a finite element model (preprocessing and visualizing the analysis results (postprocessing, and use other solvers for processing.

Learning with multiple representations: an example of a revision lesson in mechanics

Science.gov (United States)

Wong, Darren; Poo, Sng Peng; Eng Hock, Ng; Loo Kang, Wee

2011-03-01

We describe an example of learning with multiple representations in an A-level revision lesson on mechanics. The context of the problem involved the motion of a ball thrown vertically upwards in air and studying how the associated physical quantities changed during its flight. Different groups of students were assigned to look at the ball's motion using various representations: motion diagrams, vector diagrams, free-body diagrams, verbal description, equations and graphs, drawn against time as well as against displacement. Overall, feedback from students about the lesson was positive. We further discuss the benefits of using computer simulation to support and extend student learning.

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Directory of Open Access Journals (Sweden)

Davidovic Marco

2017-09-01

Full Text Available A single-hole n-dodecane spray flame is studied in a Large-Eddy Simulation (LES framework under Diesel-relevant conditions using a Multiple Representative Interactive Flamelets (MRIF combustion model. Diesel spray combustion is strongly affected by the mixture formation process, which is dominated by several physical processes such as the flow within the injector, break-up of the liquid fuel jet, evaporation and turbulent mixing with the surrounding gas. While the effects of nozzle-internal flow and primary breakup are captured within tuned model parameters in traditional Lagrangian spray models, an alternative approach is applied in this study, where the initial droplet conditions and primary fuel jet breakup are modeled based on results from highly resolved multiphase simulations with resolved interface. A highly reduced chemical mechanism consisting of 57 species and 217 reactions has been developed for n-dodecane achiving a good computational performance at solving the chemical reactions. The MRIF model, which has demonstrated its capability of capturing combustion and pollutant formation under typical Diesel conditions in Reynolds-Averaged Navier-Stokes (RANS simulations is extended for the application in LES. In the standard RIF combustion model, representative chemistry conditioned on mixture fraction is solved interactively with the flow. Subfilter-scale mixing is modeled by the scalar dissipation rate. While the standard RIF model only includes temporal changes of the scalar dissipation rate, the spatial distribution can be accounted for by extending the model to multiple flamelets, which also enables the possibility of capturing different fuel residence times. Overall, the model shows good agreement with experimental data regarding both, low and high temperature combustion characteristics. It is shown that the ignition process and pollutant formation are affected by turbulent mixing. First, a cool flame is initiated at approximately

Multiple impacts in dissipative granular chains

CERN Document Server

Nguyen, Ngoc Son

2014-01-01

The extension of collision models for single impacts between two bodies, to the case of multiple impacts (which take place when several collisions occur at the same time in a multibody system) is a challenge in Solid Mechanics, due to the complexity of such phenomena, even in the frictionless case. This monograph aims at presenting the main multiple collision rules proposed in the literature. Such collisions typically occur in granular materials, the simplest of which are made of chains of aligned balls. These chains are used throughout the book to analyze various multiple impact rules which extend the classical Newton (kinematic restitution), Poisson (kinetic restitution) and Darboux-Keller (energetic or kinetic restitution) approaches for impact modelling. The shock dynamics in various types of chains of aligned balls (monodisperse, tapered, decorated, stepped chains) is carefully studied and shown to depend on several parameters: restitution coefficients, contact stiffness ratios, elasticity coefficients (...

Multiplicative formulation of quantum mechanics

International Nuclear Information System (INIS)

Voros, A.; Leboeuf, P.

1991-01-01

A general semi-classical description for the eigenfunctions of the multidimensional Schroedinger operator cannot be based on the WKB method which is incompatible with classically ergodic behavior. An alternative, more general multiplicative parametrization of quantum wave functions is suggested, whereby the semi-classical behavior of eigenfunctions can be traced in the presence of classical ergodicity, in the form of diffusive patterns of phase-space zeros in the quantum wave functions. (author) 24 refs.; 4 figs

An introduction to mathematical modeling a course in mechanics

CERN Document Server

Oden, Tinsley J

2011-01-01

A modern approach to mathematical modeling, featuring unique applications from the field of mechanics An Introduction to Mathematical Modeling: A Course in Mechanics is designed to survey the mathematical models that form the foundations of modern science and incorporates examples that illustrate how the most successful models arise from basic principles in modern and classical mathematical physics. Written by a world authority on mathematical theory and computational mechanics, the book presents an account of continuum mechanics, electromagnetic field theory, quantum mechanics, and statistical mechanics for readers with varied backgrounds in engineering, computer science, mathematics, and physics. The author streamlines a comprehensive understanding of the topic in three clearly organized sections: Nonlinear Continuum Mechanics introduces kinematics as well as force and stress in deformable bodies; mass and momentum; balance of linear and angular momentum; conservation of energy; and constitutive equation...

Optimized production planning model for a multi-plant cultivation system under uncertainty

Science.gov (United States)

Ke, Shunkui; Guo, Doudou; Niu, Qingliang; Huang, Danfeng

2015-02-01

An inexact multi-constraint programming model under uncertainty was developed by incorporating a production plan algorithm into the crop production optimization framework under the multi-plant collaborative cultivation system. In the production plan, orders from the customers are assigned to a suitable plant under the constraints of plant capabilities and uncertainty parameters to maximize profit and achieve customer satisfaction. The developed model and solution method were applied to a case study of a multi-plant collaborative cultivation system to verify its applicability. As determined in the case analysis involving different orders from customers, the period of plant production planning and the interval between orders can significantly affect system benefits. Through the analysis of uncertain parameters, reliable and practical decisions can be generated using the suggested model of a multi-plant collaborative cultivation system.

A statistical mechanical model of economics

Science.gov (United States)

Lubbers, Nicholas Edward Williams

Statistical mechanics pursues low-dimensional descriptions of systems with a very large number of degrees of freedom. I explore this theme in two contexts. The main body of this dissertation explores and extends the Yard Sale Model (YSM) of economic transactions using a combination of simulations and theory. The YSM is a simple interacting model for wealth distributions which has the potential to explain the empirical observation of Pareto distributions of wealth. I develop the link between wealth condensation and the breakdown of ergodicity due to nonlinear diffusion effects which are analogous to the geometric random walk. Using this, I develop a deterministic effective theory of wealth transfer in the YSM that is useful for explaining many quantitative results. I introduce various forms of growth to the model, paying attention to the effect of growth on wealth condensation, inequality, and ergodicity. Arithmetic growth is found to partially break condensation, and geometric growth is found to completely break condensation. Further generalizations of geometric growth with growth in- equality show that the system is divided into two phases by a tipping point in the inequality parameter. The tipping point marks the line between systems which are ergodic and systems which exhibit wealth condensation. I explore generalizations of the YSM transaction scheme to arbitrary betting functions to develop notions of universality in YSM-like models. I find that wealth vi condensation is universal to a large class of models which can be divided into two phases. The first exhibits slow, power-law condensation dynamics, and the second exhibits fast, finite-time condensation dynamics. I find that the YSM, which exhibits exponential dynamics, is the critical, self-similar model which marks the dividing line between the two phases. The final chapter develops a low-dimensional approach to materials microstructure quantification. Modern materials design harnesses complex

Multi-scale Multi-mechanism Toughening of Hydrogels

Science.gov (United States)

Zhao, Xuanhe

Hydrogels are widely used as scaffolds for tissue engineering, vehicles for drug delivery, actuators for optics and fluidics, and model extracellular matrices for biological studies. The scope of hydrogel applications, however, is often severely limited by their mechanical properties. Inspired by the mechanics and hierarchical structures of tough biological tissues, we propose that a general principle for the design of tough hydrogels is to implement two mechanisms for dissipating mechanical energy and maintaining high elasticity in hydrogels. A particularly promising strategy for the design is to integrate multiple pairs of mechanisms across multiple length scales into a hydrogel. We develop a multiscale theoretical framework to quantitatively guide the design of tough hydrogels. On the network level, we have developed micro-physical models to characterize the evolution of polymer networks under deformation. On the continuum level, we have implemented constitutive laws formulated from the network-level models into a coupled cohesive-zone and Mullins-effect model to quantitatively predict crack propagation and fracture toughness of hydrogels. Guided by the design principle and quantitative model, we will demonstrate a set of new hydrogels, based on diverse types of polymers, yet can achieve extremely high toughness superior to their natural counterparts such as cartilages. The work was supported by NSF(No. CMMI- 1253495) and ONR (No. N00014-14-1-0528).

Multiple mechanisms of PCB neurotoxicity

Energy Technology Data Exchange (ETDEWEB)

Carpenter, D.O.; Stoner, C.T.; Lawrence, D.A. [Univ. of New York, Albany, NY (United States)] [and others

1996-12-31

Polychlorinated biphenyls (PCBs) have been implicated in cancer, but many of the symptoms in humans exposed to PCBs are related to the nervous system and behavior. We demonstrated three different direct mechanisms whereby PCBs are neurotoxic in rats. By using flow cytometry, we demonstrated that the orthosubstituted PCB congener 2,4,4{prime}, but neither TCDD nor the coplanar PCB congener 3,4,5,3{prime},4{prime}, causes rapid death of cerebellar granule cells. The ortho-substituted congener 2,4,4{prime} reduced long-term potentiation, an indicator of cognitive potential, in hippocampal brain slices, but a similar effect was observed for the coplanar congener 3,4,3{prime},4{prime}, indicating that this effect may be caused by both ortho- and coplanar congeners by mechanisms presumably not mediated via the Ah receptor. It was previously shown that some ortho-substituted PCB congeners cause a reduction in levels of the neurotransmitter dopamine, and we present in vitro and in vivo evidence that this is due to reduction of synthesis of dopamine via inhibition of the enzyme tyrosine hydroxylase. Thus, PCBs have a variety of mechanisms of primary neurotoxicity, and neurotoxicity is a characteristic of ortho-substituted, non-dioxin-like congeners as well as some coplanar congeners. The relative contribution of each of these mechanisms to the loss of cognitive function in humans exposed to PCBs remains to be determined. 42 refs., 3 figs., 1 tab.

Understanding comorbidity among internalizing problems: Integrating latent structural models of psychopathology and risk mechanisms

Science.gov (United States)

Hankin, Benjamin L.; Snyder, Hannah R.; Gulley, Lauren D.; Schweizer, Tina H.; Bijttebier, Patricia; Nelis, Sabine; Toh, Gim; Vasey, Michael W.

2016-01-01

It is well known that comorbidity is the rule, not the exception, for categorically defined psychiatric disorders, and this is also the case for internalizing disorders of depression and anxiety. This theoretical review paper addresses the ubiquity of comorbidity among internalizing disorders. Our central thesis is that progress in understanding this co-occurrence can be made by employing latent dimensional structural models that organize both psychopathology as well as vulnerabilities and risk mechanisms and by connecting the multiple levels of risk and psychopathology outcomes together. Different vulnerabilities and risk mechanisms are hypothesized to predict different levels of the structural model of psychopathology. We review the present state of knowledge based on concurrent and developmental sequential comorbidity patterns among common discrete psychiatric disorders in youth, and then we advocate for the use of more recent bifactor dimensional models of psychopathology (e.g., p factor, Caspi et al., 2014) that can help to explain the co-occurrence among internalizing symptoms. In support of this relatively novel conceptual perspective, we review six exemplar vulnerabilities and risk mechanisms, including executive function, information processing biases, cognitive vulnerabilities, positive and negative affectivity aspects of temperament, and autonomic dysregulation, along with the developmental occurrence of stressors in different domains, to show how these vulnerabilities can predict the general latent psychopathology factor, a unique latent internalizing dimension, as well as specific symptom syndrome manifestations. PMID:27739389

Workshop on multifactor aging mechanisms and models

Science.gov (United States)

Agarwal, V. K.

1992-10-01

There have been considerable efforts to understand the aging and failure mechanisms of insulation in electrical systems. However, progress has been slow because of the complex nature of the subject particularly when dealing with multiple stresses e.g. electrical, thermal, mechanical, radiation, humidity and other environmental factors. When an insulating material is exposed to just one stress factor e.g. electric field, one must devise test(s) which are not only economically efficient and practical but which take into account the nature of electric field (ac, dc and pulsed), duration and level or field strength, and field configurations. Any additional stress factor(s) make the matrix of measurements and the understanding of resulting degradation processes more complex, time consuming and expensive.

Time-dependent pharmacokinetics of dexamethasone and its efficacy in human breast cancer xenograft mice: a semi-mechanism-based pharmacokinetic/pharmacodynamic model.

Science.gov (United States)

Li, Jian; Chen, Rong; Yao, Qing-Yu; Liu, Sheng-Jun; Tian, Xiu-Yun; Hao, Chun-Yi; Lu, Wei; Zhou, Tian-Yan

2018-03-01

Dexamethasone (DEX) is the substrate of CYP3A. However, the activity of CYP3A could be induced by DEX when DEX was persistently administered, resulting in auto-induction and time-dependent pharmacokinetics (pharmacokinetics with time-dependent clearance) of DEX. In this study we investigated the pharmacokinetic profiles of DEX after single or multiple doses in human breast cancer xenograft nude mice and established a semi-mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) model for characterizing the time-dependent PK of DEX as well as its anti-cancer effect. The mice were orally given a single or multiple doses (8 mg/kg) of DEX, and the plasma concentrations of DEX were assessed using LC-MS/MS. Tumor volumes were recorded daily. Based on the experimental data, a two-compartment model with first order absorption and time-dependent clearance was established, and the time-dependence of clearance was modeled by a sigmoid E max equation. Moreover, a semi-mechanism-based PK/PD model was developed, in which the auto-induction effect of DEX on its metabolizing enzyme CYP3A was integrated and drug potency was described using an E max equation. The PK/PD model was further used to predict the drug efficacy when the auto-induction effect was or was not considered, which further revealed the necessity of adding the auto-induction effect into the final PK/PD model. This study established a semi-mechanism-based PK/PD model for characterizing the time-dependent pharmacokinetics of DEX and its anti-cancer effect in breast cancer xenograft mice. The model may serve as a reference for DEX dose adjustments or optimization in future preclinical or clinical studies.

Natural Antioxidants: Multiple Mechanisms to Protect Skin From Solar Radiation

Directory of Open Access Journals (Sweden)

Spencer Dunaway

2018-04-01

Full Text Available Human skin exposed to solar ultraviolet radiation (UVR results in a dramatic increase in the production of reactive oxygen species (ROS. The sudden increase in ROS shifts the natural balance toward a pro-oxidative state, resulting in oxidative stress. The detrimental effects of oxidative stress occur through multiple mechanisms that involve alterations to proteins and lipids, induction of inflammation, immunosuppression, DNA damage, and activation of signaling pathways that affect gene transcription, cell cycle, proliferation, and apoptosis. All of these alterations promote carcinogenesis and therefore, regulation of ROS levels is critical to the maintenance of normal skin homeostasis. Several botanical products have been found to exhibit potent antioxidant capacity and the ability to counteract UV-induced insults to the skin. These natural products exert their beneficial effects through multiple pathways, including some known to be negatively affected by solar UVR. Aging of the skin is also accelerated by UVR exposure, in particular UVA rays that penetrate deep into the epidermis and the dermis where it causes the degradation of collagen and elastin fibers via oxidative stress and activation of matrix metalloproteinases (MMPs. Because natural compounds are capable of attenuating some of the UV-induced aging effects in the skin, increased attention has been generated in the area of cosmetic sciences. The focus of this review is to cover the most prominent phytoproducts with potential to mitigate the deleterious effects of solar UVR and suitability for use in topical application.

Review of Monte Carlo methods for particle multiplicity evaluation

CERN Document Server

Armesto-Pérez, Nestor

2005-01-01

I present a brief review of the existing models for particle multiplicity evaluation in heavy ion collisions which are at our disposal in the form of Monte Carlo simulators. Models are classified according to the physical mechanisms with which they try to describe the different stages of a high-energy collision between heavy nuclei. A comparison of predictions, as available at the beginning of year 2000, for multiplicities in central AuAu collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and PbPb collisions at the CERN Large Hadron Collider (LHC) is provided.

Review of Monte Carlo methods for particle multiplicity evaluation

International Nuclear Information System (INIS)

Armesto, Nestor

2005-01-01

I present a brief review of the existing models for particle multiplicity evaluation in heavy ion collisions which are at our disposal in the form of Monte Carlo simulators. Models are classified according to the physical mechanisms with which they try to describe the different stages of a high-energy collision between heavy nuclei. A comparison of predictions, as available at the beginning of year 2000, for multiplicities in central AuAu collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and PbPb collisions at the CERN Large Hadron Collider (LHC) is provided

Improving ecosystem-scale modeling of evapotranspiration using ecological mechanisms that account for compensatory responses following disturbance

Science.gov (United States)

Millar, David J.; Ewers, Brent E.; Mackay, D. Scott; Peckham, Scott; Reed, David E.; Sekoni, Adewale

2017-09-01

Mountain pine beetle outbreaks in western North America have led to extensive forest mortality, justifiably generating interest in improving our understanding of how this type of ecological disturbance affects hydrological cycles. While observational studies and simulations have been used to elucidate the effects of mountain beetle mortality on hydrological fluxes, an ecologically mechanistic model of forest evapotranspiration (ET) evaluated against field data has yet to be developed. In this work, we use the Terrestrial Regional Ecosystem Exchange Simulator (TREES) to incorporate the ecohydrological impacts of mountain pine beetle disturbance on ET for a lodgepole pine-dominated forest equipped with an eddy covariance tower. An existing degree-day model was incorporated that predicted the life cycle of mountain pine beetles, along with an empirically derived submodel that allowed sap flux to decline as a function of temperature-dependent blue stain fungal growth. The eddy covariance footprint was divided into multiple cohorts for multiple growing seasons, including representations of recently attacked trees and the compensatory effects of regenerating understory, using two different spatial scaling methods. Our results showed that using a multiple cohort approach matched eddy covariance-measured ecosystem-scale ET fluxes well, and showed improved performance compared to model simulations assuming a binary framework of only areas of live and dead overstory. Cumulative growing season ecosystem-scale ET fluxes were 8 - 29% greater using the multicohort approach during years in which beetle attacks occurred, highlighting the importance of including compensatory ecological mechanism in ET models.

Docosahexaenoic Acid Reduces Amyloid β Production via Multiple Pleiotropic Mechanisms*

Science.gov (United States)

Grimm, Marcus O. W.; Kuchenbecker, Johanna; Grösgen, Sven; Burg, Verena K.; Hundsdörfer, Benjamin; Rothhaar, Tatjana L.; Friess, Petra; de Wilde, Martijn C.; Broersen, Laus M.; Penke, Botond; Péter, Mária; Vígh, László; Grimm, Heike S.; Hartmann, Tobias

2011-01-01

Alzheimer disease is characterized by accumulation of the β-amyloid peptide (Aβ) generated by β- and γ-secretase processing of the amyloid precursor protein (APP). The intake of the polyunsaturated fatty acid docosahexaenoic acid (DHA) has been associated with decreased amyloid deposition and a reduced risk in Alzheimer disease in several epidemiological trials; however, the exact underlying molecular mechanism remains to be elucidated. Here, we systematically investigate the effect of DHA on amyloidogenic and nonamyloidogenic APP processing and the potential cross-links to cholesterol metabolism in vivo and in vitro. DHA reduces amyloidogenic processing by decreasing β- and γ-secretase activity, whereas the expression and protein levels of BACE1 and presenilin1 remain unchanged. In addition, DHA increases protein stability of α-secretase resulting in increased nonamyloidogenic processing. Besides the known effect of DHA to decrease cholesterol de novo synthesis, we found cholesterol distribution in plasma membrane to be altered. In the presence of DHA, cholesterol shifts from raft to non-raft domains, and this is accompanied by a shift in γ-secretase activity and presenilin1 protein levels. Taken together, DHA directs amyloidogenic processing of APP toward nonamyloidogenic processing, effectively reducing Aβ release. DHA has a typical pleiotropic effect; DHA-mediated Aβ reduction is not the consequence of a single major mechanism but is the result of combined multiple effects. PMID:21324907

Eye Movement Abnormalities in Multiple Sclerosis: Pathogenesis, Modeling, and Treatment

Directory of Open Access Journals (Sweden)

Alessandro Serra

2018-02-01

Full Text Available Multiple sclerosis (MS commonly causes eye movement abnormalities that may have a significant impact on patients’ disability. Inflammatory demyelinating lesions, especially occurring in the posterior fossa, result in a wide range of disorders, spanning from acquired pendular nystagmus (APN to internuclear ophthalmoplegia (INO, among the most common. As the control of eye movements is well understood in terms of anatomical substrate and underlying physiological network, studying ocular motor abnormalities in MS provides a unique opportunity to gain insights into mechanisms of disease. Quantitative measurement and modeling of eye movement disorders, such as INO, may lead to a better understanding of common symptoms encountered in MS, such as Uhthoff’s phenomenon and fatigue. In turn, the pathophysiology of a range of eye movement abnormalities, such as APN, has been clarified based on correlation of experimental model with lesion localization by neuroimaging in MS. Eye movement disorders have the potential of being utilized as structural and functional biomarkers of early cognitive deficit, and possibly help in assessing disease status and progression, and to serve as platform and functional outcome to test novel therapeutic agents for MS. Knowledge of neuropharmacology applied to eye movement dysfunction has guided testing and use of a number of pharmacological agents to treat some eye movement disorders found in MS, such as APN and other forms of central nystagmus.

Modeling mechanical interactions between cancerous mammary acini

Science.gov (United States)

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.

Pairing mechanism in oxide superconductors

International Nuclear Information System (INIS)

Hirsch, J.E.

1988-01-01

A useful way to learn about the pairing mechanism that is responsible for high T c superconductivity is to study properties of model Hamiltonians on small systems. The goal is to find the simplest model that can describe the essential physics of high T c superconductivity. The authors have used Monte Carlo simulation and exact diagonalization techniques to study properties of systems of up to 64 sites. Their results show that spin fluctuations and other spin related mechanisms induced by a Hubbard on-site repulsion U are not likely to give rise to pairing, neither in one nor in multiple band models. In contrast, charge fluctuations in a model with both strong U and V (repulsion between Cu and O) are shown to give rise to pairing and it is suggested that this model provides a plausible mechanism for high T c superconductivity

Estimation of causal mediation effects for a dichotomous outcome in multiple-mediator models using the mediation formula.

Science.gov (United States)

Wang, Wei; Nelson, Suchitra; Albert, Jeffrey M

2013-10-30

Mediators are intermediate variables in the causal pathway between an exposure and an outcome. Mediation analysis investigates the extent to which exposure effects occur through these variables, thus revealing causal mechanisms. In this paper, we consider the estimation of the mediation effect when the outcome is binary and multiple mediators of different types exist. We give a precise definition of the total mediation effect as well as decomposed mediation effects through individual or sets of mediators using the potential outcomes framework. We formulate a model of joint distribution (probit-normal) using continuous latent variables for any binary mediators to account for correlations among multiple mediators. A mediation formula approach is proposed to estimate the total mediation effect and decomposed mediation effects based on this parametric model. Estimation of mediation effects through individual or subsets of mediators requires an assumption involving the joint distribution of multiple counterfactuals. We conduct a simulation study that demonstrates low bias of mediation effect estimators for two-mediator models with various combinations of mediator types. The results also show that the power to detect a nonzero total mediation effect increases as the correlation coefficient between two mediators increases, whereas power for individual mediation effects reaches a maximum when the mediators are uncorrelated. We illustrate our approach by applying it to a retrospective cohort study of dental caries in adolescents with low and high socioeconomic status. Sensitivity analysis is performed to assess the robustness of conclusions regarding mediation effects when the assumption of no unmeasured mediator-outcome confounders is violated. Copyright © 2013 John Wiley & Sons, Ltd.

Estimation of Causal Mediation Effects for a Dichotomous Outcome in Multiple-Mediator Models using the Mediation Formula

Science.gov (United States)

Nelson, Suchitra; Albert, Jeffrey M.

2013-01-01

Mediators are intermediate variables in the causal pathway between an exposure and an outcome. Mediation analysis investigates the extent to which exposure effects occur through these variables, thus revealing causal mechanisms. In this paper, we consider the estimation of the mediation effect when the outcome is binary and multiple mediators of different types exist. We give a precise definition of the total mediation effect as well as decomposed mediation effects through individual or sets of mediators using the potential outcomes framework. We formulate a model of joint distribution (probit-normal) using continuous latent variables for any binary mediators to account for correlations among multiple mediators. A mediation formula approach is proposed to estimate the total mediation effect and decomposed mediation effects based on this parametric model. Estimation of mediation effects through individual or subsets of mediators requires an assumption involving the joint distribution of multiple counterfactuals. We conduct a simulation study that demonstrates low bias of mediation effect estimators for two-mediator models with various combinations of mediator types. The results also show that the power to detect a non-zero total mediation effect increases as the correlation coefficient between two mediators increases, while power for individual mediation effects reaches a maximum when the mediators are uncorrelated. We illustrate our approach by applying it to a retrospective cohort study of dental caries in adolescents with low and high socioeconomic status. Sensitivity analysis is performed to assess the robustness of conclusions regarding mediation effects when the assumption of no unmeasured mediator-outcome confounders is violated. PMID:23650048

Multiple Imputation of Predictor Variables Using Generalized Additive Models

NARCIS (Netherlands)

de Jong, Roel; van Buuren, Stef; Spiess, Martin

2016-01-01

The sensitivity of multiple imputation methods to deviations from their distributional assumptions is investigated using simulations, where the parameters of scientific interest are the coefficients of a linear regression model, and values in predictor variables are missing at random. The

Model Seleksi Premi Asuransi Jiwa Dwiguna untuk Kasus Multiple Decrement

OpenAIRE

Cita, Devi Ramana; Pane, Rolan; ', Harison

2015-01-01

This article discusses a select survival model for the case of multiple decrements in evaluating endowment life insurance premium for person currently aged ( + ) years, who is selected at age with ℎ years selection period. The case of multiple decrements in this case is limited to two cases. The calculation of the annual premium is done by prior evaluating of the single premium, and the present value of annuity depends on theconstant force assumption.

A new adaptive control scheme based on the interacting multiple model (IMM) estimation

International Nuclear Information System (INIS)

Afshari, Hamed H.; Al-Ani, Dhafar; Habibi, Saeid

2016-01-01

In this paper, an Interacting multiple model (IMM) adaptive estimation approach is incorporated to design an optimal adaptive control law for stabilizing an Unmanned vehicle. Due to variations of the forward velocity of the Unmanned vehicle, its aerodynamic derivatives are constantly changing. In order to stabilize the unmanned vehicle and achieve the control objectives for in-flight conditions, one seeks for an adaptive control strategy that can adjust itself to varying flight conditions. In this context, a bank of linear models is used to describe the vehicle dynamics in different operating modes. Each operating mode represents a particular dynamic with a different forward velocity. These models are then used within an IMM filter containing a bank of Kalman filters (KF) in a parallel operating mechanism. To regulate and stabilize the vehicle, a Linear quadratic regulator (LQR) law is designed and implemented for each mode. The IMM structure determines the particular mode based on the stored models and in-flight input-output measurements. The LQR controller also provides a set of controllers; each corresponds to a particular flight mode and minimizes the tracking error. Finally, the ultimate control law is obtained as a weighted summation of all individual controllers whereas weights are obtained using mode probabilities of each operating mode.

A model of mechanical interactions between heart and lungs.

Science.gov (United States)

Fontecave Jallon, Julie; Abdulhay, Enas; Calabrese, Pascale; Baconnier, Pierre; Gumery, Pierre-Yves

2009-12-13

To study the mechanical interactions between heart, lungs and thorax, we propose a mathematical model combining a ventilatory neuromuscular model and a model of the cardiovascular system, as described by Smith et al. (Smith, Chase, Nokes, Shaw & Wake 2004 Med. Eng. Phys.26, 131-139. (doi:10.1016/j.medengphy.2003.10.001)). The respiratory model has been adapted from Thibault et al. (Thibault, Heyer, Benchetrit & Baconnier 2002 Acta Biotheor. 50, 269-279. (doi:10.1023/A:1022616701863)); using a Liénard oscillator, it allows the activity of the respiratory centres, the respiratory muscles and rib cage internal mechanics to be simulated. The minimal haemodynamic system model of Smith includes the heart, as well as the pulmonary and systemic circulation systems. These two modules interact mechanically by means of the pleural pressure, calculated in the mechanical respiratory system, and the intrathoracic blood volume, calculated in the cardiovascular model. The simulation by the proposed model provides results, first, close to experimental data, second, in agreement with the literature results and, finally, highlighting the presence of mechanical cardiorespiratory interactions.

Modeling the mechanical response of PBX 9501

Energy Technology Data Exchange (ETDEWEB)

Ragaswamy, Partha [Los Alamos National Laboratory; Lewis, Matthew W [Los Alamos National Laboratory; Liu, Cheng [Los Alamos National Laboratory; Thompson, Darla G [Los Alamos National Laboratory

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.

A multiple shock model for common cause failures using discrete Markov chain

International Nuclear Information System (INIS)

Chung, Dae Wook; Kang, Chang Soon

1992-01-01

The most widely used models in common cause analysis are (single) shock models such as the BFR, and the MFR. But, single shock model can not treat the individual common cause separately and has some irrational assumptions. Multiple shock model for common cause failures is developed using Markov chain theory. This model treats each common cause shock as separately and sequently occuring event to implicate the change in failure probability distribution due to each common cause shock. The final failure probability distribution is evaluated and compared with that from the BFR model. The results show that multiple shock model which minimizes the assumptions in the BFR model is more realistic and conservative than the BFR model. The further work for application is the estimations of parameters such as common cause shock rate and component failure probability given a shock,p, through the data analysis

The Answering Process for Multiple-Choice Questions in Collaborative Learning: A Mathematical Learning Model Analysis

Science.gov (United States)

Nakamura, Yasuyuki; Nishi, Shinnosuke; Muramatsu, Yuta; Yasutake, Koichi; Yamakawa, Osamu; Tagawa, Takahiro

2014-01-01

In this paper, we introduce a mathematical model for collaborative learning and the answering process for multiple-choice questions. The collaborative learning model is inspired by the Ising spin model and the model for answering multiple-choice questions is based on their difficulty level. An intensive simulation study predicts the possibility of…

Protein structure modeling for CASP10 by multiple layers of global optimization.

Science.gov (United States)

Joo, Keehyoung; Lee, Juyong; Sim, Sangjin; Lee, Sun Young; Lee, Kiho; Heo, Seungryong; Lee, In-Ho; Lee, Sung Jong; Lee, Jooyoung

2014-02-01

In the template-based modeling (TBM) category of CASP10 experiment, we introduced a new protocol called protein modeling system (PMS) to generate accurate protein structures in terms of side-chains as well as backbone trace. In the new protocol, a global optimization algorithm, called conformational space annealing (CSA), is applied to the three layers of TBM procedure: multiple sequence-structure alignment, 3D chain building, and side-chain re-modeling. For 3D chain building, we developed a new energy function which includes new distance restraint terms of Lorentzian type (derived from multiple templates), and new energy terms that combine (physical) energy terms such as dynamic fragment assembly (DFA) energy, DFIRE statistical potential energy, hydrogen bonding term, etc. These physical energy terms are expected to guide the structure modeling especially for loop regions where no template structures are available. In addition, we developed a new quality assessment method based on random forest machine learning algorithm to screen templates, multiple alignments, and final models. For TBM targets of CASP10, we find that, due to the combination of three stages of CSA global optimizations and quality assessment, the modeling accuracy of PMS improves at each additional stage of the protocol. It is especially noteworthy that the side-chains of the final PMS models are far more accurate than the models in the intermediate steps. Copyright © 2013 Wiley Periodicals, Inc.

An Overview of Mechanical Properties and Material Modeling of Polylactide (PLA) for Medical Applications.

Science.gov (United States)

Bergström, Jörgen S; Hayman, Danika

2016-02-01

This article provides an overview of the connection between the microstructural state and the mechanical response of various bioresorbable polylactide (PLA) devices for medical applications. PLLA is currently the most commonly used material for bioresorbable stents and sutures, and its use is increasing in many other medical applications. The non-linear mechanical response of PLLA, due in part to its low glass transition temperature (T g ≈ 60 °C), is highly sensitive to the molecular weight and molecular orientation field, the degree of crystallinity, and the physical aging time. These microstructural parameters can be tailored for specific applications using different resin formulations and processing conditions. The stress-strain, deformation, and degradation response of a bioresorbable medical device is also strongly dependent on the time history of applied loads and boundary conditions. All of these factors can be incorporated into a suitable constitutive model that captures the multiple physics that are involved in the device response. Currently developed constitutive models already provide powerful computations simulation tools, and more progress in this area is expected to occur in the coming years.

Multiple mechanisms quench passive spiral galaxies

Science.gov (United States)

Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin; Dolley, Tim; Bonne, Nicolas J.

2018-02-01

We examine the properties of a sample of 35 nearby passive spiral galaxies in order to determine their dominant quenching mechanism(s). All five low-mass (M⋆ environments. We postulate that cluster-scale gas stripping and heating mechanisms operating only in rich clusters are required to quench low-mass passive spirals, and ram-pressure stripping and strangulation are obvious candidates. For higher mass passive spirals, while trends are present, the story is less clear. The passive spiral bar fraction is high: 74 ± 15 per cent, compared with 36 ± 5 per cent for a mass, redshift and T-type matched comparison sample of star-forming spiral galaxies. The high mass passive spirals occur mostly, but not exclusively, in groups, and can be central or satellite galaxies. The passive spiral group fraction of 74 ± 15 per cent is similar to that of the comparison sample of star-forming galaxies at 61 ± 7 per cent. We find evidence for both quenching via internal structure and environment in our passive spiral sample, though some galaxies have evidence of neither. From this, we conclude no one mechanism is responsible for quenching star formation in passive spiral galaxies - rather, a mixture of mechanisms is required to produce the passive spiral distribution we see today.

Interacting Multiple Model (IMM Fifth-Degree Spherical Simplex-Radial Cubature Kalman Filter for Maneuvering Target Tracking

Directory of Open Access Journals (Sweden)

Hua Liu

2017-06-01

Full Text Available For improving the tracking accuracy and model switching speed of maneuvering target tracking in nonlinear systems, a new algorithm named the interacting multiple model fifth-degree spherical simplex-radial cubature Kalman filter (IMM5thSSRCKF is proposed in this paper. The new algorithm is a combination of the interacting multiple model (IMM filter and the fifth-degree spherical simplex-radial cubature Kalman filter (5thSSRCKF. The proposed algorithm makes use of Markov process to describe the switching probability among the models, and uses 5thSSRCKF to deal with the state estimation of each model. The 5thSSRCKF is an improved filter algorithm, which utilizes the fifth-degree spherical simplex-radial rule to improve the filtering accuracy. Finally, the tracking performance of the IMM5thSSRCKF is evaluated by simulation in a typical maneuvering target tracking scenario. Simulation results show that the proposed algorithm has better tracking performance and quicker model switching speed when disposing maneuver models compared with the interacting multiple model unscented Kalman filter (IMMUKF, the interacting multiple model cubature Kalman filter (IMMCKF and the interacting multiple model fifth-degree cubature Kalman filter (IMM5thCKF.

Interacting Multiple Model (IMM) Fifth-Degree Spherical Simplex-Radial Cubature Kalman Filter for Maneuvering Target Tracking.

Science.gov (United States)

Liu, Hua; Wu, Wen

2017-06-13

For improving the tracking accuracy and model switching speed of maneuvering target tracking in nonlinear systems, a new algorithm named the interacting multiple model fifth-degree spherical simplex-radial cubature Kalman filter (IMM5thSSRCKF) is proposed in this paper. The new algorithm is a combination of the interacting multiple model (IMM) filter and the fifth-degree spherical simplex-radial cubature Kalman filter (5thSSRCKF). The proposed algorithm makes use of Markov process to describe the switching probability among the models, and uses 5thSSRCKF to deal with the state estimation of each model. The 5thSSRCKF is an improved filter algorithm, which utilizes the fifth-degree spherical simplex-radial rule to improve the filtering accuracy. Finally, the tracking performance of the IMM5thSSRCKF is evaluated by simulation in a typical maneuvering target tracking scenario. Simulation results show that the proposed algorithm has better tracking performance and quicker model switching speed when disposing maneuver models compared with the interacting multiple model unscented Kalman filter (IMMUKF), the interacting multiple model cubature Kalman filter (IMMCKF) and the interacting multiple model fifth-degree cubature Kalman filter (IMM5thCKF).

Comparing Multiple-Group Multinomial Log-Linear Models for Multidimensional Skill Distributions in the General Diagnostic Model. Research Report. ETS RR-08-35

Science.gov (United States)

Xu, Xueli; von Davier, Matthias

2008-01-01

The general diagnostic model (GDM) utilizes located latent classes for modeling a multidimensional proficiency variable. In this paper, the GDM is extended by employing a log-linear model for multiple populations that assumes constraints on parameters across multiple groups. This constrained model is compared to log-linear models that assume…

Linear systems with unstructured multiplicative uncertainty: Modeling and robust stability analysis.

Directory of Open Access Journals (Sweden)

Radek Matušů

Full Text Available This article deals with continuous-time Linear Time-Invariant (LTI Single-Input Single-Output (SISO systems affected by unstructured multiplicative uncertainty. More specifically, its aim is to present an approach to the construction of uncertain models based on the appropriate selection of a nominal system and a weight function and to apply the fundamentals of robust stability investigation for considered sort of systems. The initial theoretical parts are followed by three extensive illustrative examples in which the first order time-delay, second order and third order plants with parametric uncertainty are modeled as systems with unstructured multiplicative uncertainty and subsequently, the robust stability of selected feedback loops containing constructed models and chosen controllers is analyzed and obtained results are discussed.

Multiple purpose electrical profit; Emprendimiento electrico de prestacion multiple

Energy Technology Data Exchange (ETDEWEB)

Assennato, H. [Electrica de Azul Ltda., Buenos Aires (Argentina)

1986-12-31

This paper shows the multiple purpose aspects of electrification projects in rural and isolated areas. The multiple aspects involved in the electrification process may include, over electric power supply: improvement of life quality, irrigation and rural mechanization. 4 figs., 6 tabs., 4 refs.

Experimental approach and micro-mechanical modeling of the mechanical behavior of irradiated zirconium alloys

International Nuclear Information System (INIS)

Onimus, F.

2003-12-01

Zirconium alloys cladding tubes containing nuclear fuel of the Pressurized Water Reactors constitute the first safety barrier against the dissemination of radioactive elements. Thus, it is essential to predict the mechanical behavior of the material in-reactor conditions. This study aims, on the one hand, to identify and characterize the mechanisms of the plastic deformation of irradiated zirconium alloys and, on the other hand, to propose a micro-mechanical modeling based on these mechanisms. The experimental analysis shows that, for the irradiated material, the plastic deformation occurs by dislocation channeling. For transverse tensile test and internal pressure test this channeling occurs in the basal planes. However, for axial tensile test, the study revealed that the plastic deformation also occurs by channeling but in the prismatic and pyramidal planes. In addition, the study of the macroscopic mechanical behavior, compared to the deformation mechanisms observed by TEM, suggested that the internal stress is higher in the case of irradiated material than in the case of non-irradiated material, because of the very heterogeneous character of the plastic deformation. This analysis led to a coherent interpretation of the mechanical behavior of irradiated materials, in terms of deformation mechanisms. The mechanical behavior of irradiated materials was finally modeled by applying homogenization methods for heterogeneous materials. This model is able to reproduce adequately the mechanical behavior of the irradiated material, in agreement with the TEM observations. (author)

Nonsmooth mechanics models, dynamics and control

CERN Document Server

Brogliato, Bernard

2016-01-01

Now in its third edition, this standard reference is a comprehensive treatment of nonsmooth mechanical systems refocused to give more prominence to control and modelling. It covers Lagrangian and Newton–Euler systems, detailing mathematical tools such as convex analysis and complementarity theory. The ways in which nonsmooth mechanics influence and are influenced by well-posedness analysis, numerical analysis and simulation, modelling and control are explained. Contact/impact laws, stability theory and trajectory-tracking control are given in-depth exposition connected by a framework formed from complementarity systems and measure-differential inclusions. Links are established with electrical circuits with set-valued nonsmooth elements and with other nonsmooth dynamical systems like impulsive and piecewise linear systems. Nonsmooth Mechanics (third edition) has been substantially rewritten, edited and updated to account for the significant body of results that have emerged in the twenty-first century—incl...

The hydro-mechanical modeling of the fractured media

International Nuclear Information System (INIS)

Kadiri, I.

2002-10-01

The hydro-mechanical modeling of the fractured media is quite complex. Simplifications are necessary for the modeling of such media, but, not always justified, Only permeable fractures are often considered. The rest of the network is approximated by an equivalent continuous medium. Even if we suppose that this approach is validated, the hydraulic and mechanical properties of the fractures and of the continuous medium are seldom known. Calibrations are necessary for the determination of these properties. Until now, one does not know very well the nature of measurements which must be carried out in order to carry on a modeling in discontinuous medium, nor elements of enough robust validation for this kind of modeling. For a better understanding of the hydro-mechanical phenomena in fractured media, two different sites have been selected for the work. The first is the site of Grimsel in Switzerland in which an underground laboratory is located at approximately 400 m of depth. The FEBEX experiment aims at the in-situ study of the consecutive phenomena due to the installation of a heat source representative of radioactive waste in the last 17 meters of the FEBEX tunnel in the laboratory of Grimsel. Only, the modeling of the hydro-mechanical of the excavation was model. The modeling of the Febex enabled us to establish a methodology of calibration of the hydraulic properties in the discontinuous media. However, this kind of study on such complex sites does not make possible to answer all the questions which arise on the hydro-mechanical behavior of the fractured media. We thus carried out modeling on an other site, smaller than the fist one and more accessible. The experimental site of Coaraze, in the Maritime Alps, is mainly constituted of limestone and fractures. Then the variation of water pressure along fractures is governed by the opening/closure sequence of a water gate. Normal displacement as well as the pore pressure along these fractures are recorded, and then

Stochastic modelling in design of mechanical properties of nanometals

International Nuclear Information System (INIS)

Tengen, T.B.; Wejrzanowski, T.; Iwankiewicz, R.; Kurzydlowski, K.J.

2010-01-01

Polycrystalline nanometals are being fabricated through different processing routes and conditions. The consequence is that nanometals having the same mean grain size may have different grain size dispersion and, hence, may have different material properties. This has often led to conflicting reports from both theoretical and experimental findings about the evolutions of the mechanical properties of nanomaterials. The present paper employs stochastic model to study the impact of microstructure evolution during grain growth on the mechanical properties of polycrystalline nanometals. The stochastic model for grain growth and the stochastic model for changes in mechanical properties of nanomaterials are proposed. The model for the mechanical properties developed is tested on aluminium samples.Many salient features of the mechanical properties of the aluminium samples are revealed. The results show that the different mechanisms of grain growth impart different nature of response to the material mechanical properties. The conventional, homologous and anomalous temperature dependences of the yield stress have also been revealed to be due to different nature of interactions of the microstructures during evolution.

A latent class multiple constraint multiple discrete-continuous extreme value model of time use and goods consumption.

Science.gov (United States)

2016-06-01

This paper develops a microeconomic theory-based multiple discrete continuous choice model that considers: (a) that both goods consumption and time allocations (to work and non-work activities) enter separately as decision variables in the utility fu...

An investigation of multidisciplinary complex health care interventions - steps towards an integrative treatment model in the rehabilitation of People with Multiple Sclerosis

Directory of Open Access Journals (Sweden)

Skovgaard Lasse

2012-04-01

Full Text Available Abstract Background The Danish Multiple Sclerosis Society initiated a large-scale bridge building and integrative treatment project to take place from 2004–2010 at a specialized Multiple Sclerosis (MS hospital. In this project, a team of five conventional health care practitioners and five alternative practitioners was set up to work together in developing and offering individualized treatments to 200 people with MS. The purpose of this paper is to present results from the six year treatment collaboration process regarding the development of an integrative treatment model. Discussion The collaborative work towards an integrative treatment model for people with MS, involved six steps: 1 Working with an initial model 2 Unfolding the different treatment philosophies 3 Discussing the elements of the Intervention-Mechanism-Context-Outcome-scheme (the IMCO-scheme 4 Phrasing the common assumptions for an integrative MS program theory 5 Developing the integrative MS program theory 6 Building the integrative MS treatment model. The model includes important elements of the different treatment philosophies represented in the team and thereby describes a common understanding of the complexity of the courses of treatment. Summary An integrative team of practitioners has developed an integrative model for combined treatments of People with Multiple Sclerosis. The model unites different treatment philosophies and focuses on process-oriented factors and the strengthening of the patients’ resources and competences on a physical, an emotional and a cognitive level.

Hybrid approaches for multiple-species stochastic reaction-diffusion models

Science.gov (United States)

Spill, Fabian; Guerrero, Pilar; Alarcon, Tomas; Maini, Philip K.; Byrne, Helen

2015-10-01

Reaction-diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction-diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model.

Hybrid approaches for multiple-species stochastic reaction-diffusion models.

KAUST Repository

Spill, Fabian; Guerrero, Pilar; Alarcon, Tomas; Maini, Philip K; Byrne, Helen

2015-01-01

Reaction-diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction-diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model.

Hybrid approaches for multiple-species stochastic reaction-diffusion models.

KAUST Repository

Spill, Fabian

2015-10-01

Reaction-diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction-diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model.

Risk Prediction Models for Other Cancers or Multiple Sites

Science.gov (United States)

Developing statistical models that estimate the probability of developing other multiple cancers over a defined period of time will help clinicians identify individuals at higher risk of specific cancers, allowing for earlier or more frequent screening and counseling of behavioral changes to decrease risk.

Exclusive description of multiple production on nuclei in the additive quark model. Multiplicity distributions in interactions with heavy nuclei

International Nuclear Information System (INIS)

Levchenko, B.B.; Nikolaev, N.N.

1985-01-01

In the framework of the additive quark model of multiple production on nuclei we calculate the multiplicity distributions of secondary particles and the correlations between secondary particles in πA and pA interactions with heavy nuclei. We show that intranuclear cascades are responsible for up to 50% of the nuclear increase of the multiplicity of fast particles. We analyze the sensitivity of the multiplicities and their correlations to the choice of the quark-hadronization function. We show that with good accuracy the yield of relativistic secondary particles from heavy and intermediate nuclei depends only on the number N/sub p/ of protons knocked out of the nucleus, and not on the mass number of the nucleus (N/sub p/ scaling)

A quantitative evaluation of multiple biokinetic models using an assembled water phantom: A feasibility study.

Directory of Open Access Journals (Sweden)

Da-Ming Yeh

Full Text Available This study examined the feasibility of quantitatively evaluating multiple biokinetic models and established the validity of the different compartment models using an assembled water phantom. Most commercialized phantoms are made to survey the imaging system since this is essential to increase the diagnostic accuracy for quality assurance. In contrast, few customized phantoms are specifically made to represent multi-compartment biokinetic models. This is because the complicated calculations as defined to solve the biokinetic models and the time-consuming verifications of the obtained solutions are impeded greatly the progress over the past decade. Nevertheless, in this work, five biokinetic models were separately defined by five groups of simultaneous differential equations to obtain the time-dependent radioactive concentration changes inside the water phantom. The water phantom was assembled by seven acrylic boxes in four different sizes, and the boxes were linked to varying combinations of hoses to signify the multiple biokinetic models from the biomedical perspective. The boxes that were connected by hoses were then regarded as a closed water loop with only one infusion and drain. 129.1±24.2 MBq of Tc-99m labeled methylene diphosphonate (MDP solution was thoroughly infused into the water boxes before gamma scanning; then the water was replaced with de-ionized water to simulate the biological removal rate among the boxes. The water was driven by an automatic infusion pump at 6.7 c.c./min, while the biological half-life of the four different-sized boxes (64, 144, 252, and 612 c.c. was 4.8, 10.7, 18.8, and 45.5 min, respectively. The five models of derived time-dependent concentrations for the boxes were estimated either by a self-developed program run in MATLAB or by scanning via a gamma camera facility. Either agreement or disagreement between the practical scanning and the theoretical prediction in five models was thoroughly discussed. The

Multiple attribute decision making model and application to food safety risk evaluation.

Science.gov (United States)

Ma, Lihua; Chen, Hong; Yan, Huizhe; Yang, Lifeng; Wu, Lifeng

2017-01-01

Decision making for supermarket food purchase decisions are characterized by network relationships. This paper analyzed factors that influence supermarket food selection and proposes a supplier evaluation index system based on the whole process of food production. The author established the intuitive interval value fuzzy set evaluation model based on characteristics of the network relationship among decision makers, and validated for a multiple attribute decision making case study. Thus, the proposed model provides a reliable, accurate method for multiple attribute decision making.

Dynamical nexus of water supply, hydropower and environment based on the modeling of multiple socio-natural processes: from socio-hydrological perspective

Science.gov (United States)

Liu, D.; Wei, X.; Li, H. Y.; Lin, M.; Tian, F.; Huang, Q.

2017-12-01

In the socio-hydrological system, the ecological functions and environmental services, which are chosen to maintain, are determined by the preference of the society, which is making the trade-off among the values of riparian vegetation, fish, river landscape, water supply, hydropower, navigation and so on. As the society develops, the preference of the value will change and the ecological functions and environmental services which are chosen to maintain will change. The aim of the study is to focus on revealing the feedback relationship of water supply, hydropower and environment and the dynamical feedback mechanism at macro-scale, and to establish socio-hydrological evolution model of the watershed based on the modeling of multiple socio-natural processes. The study will aim at the Han River in China, analyze the impact of the water supply and hydropower on the ecology, hydrology and other environment elements, and study the effect on the water supply and hydropower to ensure the ecological and environmental water of the different level. Water supply and ecology are usually competitive. In some reservoirs, hydropower and ecology are synergic relationship while they are competitive in some reservoirs. The study will analyze the multiple mechanisms to implement the dynamical feedbacks of environment to hydropower, set up the quantitative relationship description of the feedback mechanisms, recognize the dominant processes in the feedback relationships of hydropower and environment and then analyze the positive and negative feedbacks in the feedback networks. The socio-hydrological evolution model at the watershed scale will be built and applied to simulate the long-term evolution processes of the watershed of the current situation. Dynamical nexus of water supply, hydropower and environment will be investigated.

Estimating intratidal nonlinearity of respiratory system mechanics: a model study using the enhanced gliding-SLICE method

International Nuclear Information System (INIS)

Schumann, Stefan; Burcza, Boris; Guttmann, Josef; Haberthür, Christoph; Lichtwarck-Aschoff, Michael

2009-01-01

In the clinical situation and in most research work, the analysis of respiratory system mechanics is limited to the estimation of single-value compliances during static or quasi-static conditions. In contrast, our SLICE method analyses intratidal nonlinearity under the dynamic conditions of mechanical ventilation by calculating compliance and resistance for six conjoined volume portions (slices) of the pressure–volume loop by multiple linear regression analysis. With the gliding-SLICE method we present a new approach to determine continuous intratidal nonlinear compliance. The performance of the gliding-SLICE method was tested both in computer simulations and in a physical model of the lung, both simulating different intratidal compliance profiles. Compared to the original SLICE method, the gliding-SLICE method resulted in smaller errors when calculating the compliance or pressure course (all p 2 O s L −1 to 0.8 ± 0.3 cmH 2 O s L −1 (mathematical model) and from 7.2 ± 3.9 cmH 2 O s L −1 to 0.4 ± 0.2 cmH 2 O s L −1 (physical model) (all p < 0.001). We conclude that the new gliding-SLICE method allows detailed assessment of intratidal nonlinear respiratory system mechanics without discontinuity error

Utilized social support and self-esteem mediate the relationship between perceived social support and suicide ideation. A test of a multiple mediator model.

Science.gov (United States)

Kleiman, Evan M; Riskind, John H

2013-01-01

While perceived social support has received considerable research as a protective factor for suicide ideation, little attention has been given to the mechanisms that mediate its effects. We integrated two theoretical models, Joiner's (2005) interpersonal theory of suicide and Leary's (Leary, Tambor, Terdal, & Downs, 1995) sociometer theory of self-esteem to investigate two hypothesized mechanisms, utilization of social support and self-esteem. Specifically, we hypothesized that individuals must utilize the social support they perceive that would result in increased self-esteem, which in turn buffers them from suicide ideation. Participants were 172 college students who completed measures of social support, self-esteem, and suicide ideation. Tests of simple mediation indicate that utilization of social support and self-esteem may each individually help to mediate the perceived social support/suicide ideation relationship. Additionally, a test of multiple mediators using bootstrapping supported the hypothesized multiple-mediator model. The use of a cross-sectional design limited our ability to find true cause-and-effect relationships. Results suggested that utilized social support and self-esteem both operate as individual moderators in the social support/self-esteem relationship. Results further suggested, in a comprehensive model, that perceived social support buffers suicide ideation through utilization of social support and increases in self-esteem.

Penerapan Model Pembelajaran Atraktif Berbasis Multiple Intelligences Tentang Pemantulan Cahaya pada Cermin

Directory of Open Access Journals (Sweden)

Intan Kusumawati

2016-03-01

Full Text Available Penelitian ini bertujuan untuk mengetahui efektivitas penerapan model pembelajaran atraktif berbasis multiple intelligences dalam meremediasi miskonsepsi siswa tentang pemantulan cahaya pada cermin. Pada penelitian ini digunakan bentuk pre-eksperimental design dengan rancangan one group pretest-post test design. Alat pengumpulan data berupa tes pilihan ganda dengan reasoning. Hasil validitas sebesar 4,08 dan reliabilitas 0,537. Siswa dibagi menjadi lima kelompok kecerdasan, yaitu kelompok linguistic intelligence, mathematical-logical intelligence, visual-spatial intelligence, bodily-khinestetic intelligence, dan musical intelligence. Siswa membahas konsep fisika sesuai kelompok kecerdasannya dalam bentuk pembuatan pantun-puisi, teka-teki silang, menggambar kreatif, drama, dan mengarang lirik lagu. Efektivitas penerapan model pembelajaran multiple intelligences menggunakan persamaan effect size. Ditemukan bahwa skor effect size masing-masing kelompok berkategori tinggi sebesar 5,76; 3,76; 4,60; 1,70; dan 1,34. Penerapan model pembelajaran atraktif berbasis multiple intelligences efektif dalam meremediasi miskonsepsi siswa. Penelitian ini diharapkan dapat digunakan pada materi fisika dan sekolah lainnya.

Modeling of a new electron-streamer acceleration mechanism

Science.gov (United States)

Ihaddadene, K. M. A.; Dwyer, J. R.; Liu, N.; Celestin, S. J.

2017-12-01

Lightning stepped leaders and laboratory spark discharges in air are known to produce X-rays [e.g., Dwyer et al., Geophys. Res. lett., 32, L20809, 2005; Kochkin et al., J. Phys. D: Appl. Phys., 45, 425202, 2012]. However, the processes behind the production of these X-rays are still not very well understood. During discharges, encounters between streamers of different polarities are very common. For example, during the formation of a new leader step, the negative streamer zone around the tip of a negative leader and the positive streamers initiated from the posiive part of a bidirectional space leader strongly interact. In laboratory experiments, when streamers are approaching a sharp electrode, streamers with the opposite polarity are initiated from the electrode and collide with the former streamers. Recently, the encounter between negative and positive streamers has been proposed as a plausible mechanism for the production of X-rays by spark discharges [Cooray et la., JASTP, 71, 1890, 2009; Kochkin et al., J. Phys. D: Appl. Phys., 45, 425202, 2012], but modeling results have shown later that the increase of the electric field involved in this process, which is above the conventional breakdown threshold field, is accompanied by a strong increase of the electron density. The resulting increase in the conductivity, in turn, causes this electric field to collapse over a few tens of picoseconds, preventing the electrons reaching high energies and producing significant X-ray emissions [e.g., Ihaddadene and Celestin, Geophys. Res. Lett., 45, 5644, 2015]. In this work, we will present simulation results of a new electron acceleration mechanism for producing runaway electron energies above hundred keV. The mechanism couples multiple single streamers and streamer head-on collisions, similar to a laboratory discharge, and is suitable for explaining the high-energy X-rays produced by discharges in air and by lightning stepped leaders.

Quantum mechanical models for the Fermi shuttle

Science.gov (United States)

Sternberg, James; Ovchinnikov, S. Yu.; Macek, J. H.

2009-05-01

Although the Fermi shuttle was originally proposed as an explanation for highly energetic cosmic rays, it is also a mechanism for the production of high energy electrons in atomic collisions [1]. The Fermi shuttle is usually thought of as a classical effect and most models of this process rely on classical or semi-classical approximations. In this work we explore several quantum mechanical models for ion-atom collisions and examine the evidence for the Fermi shuttle in these models. [4pt] [1] B. Sulik, Cs. Koncz, K. Tok'esi, A. Orb'an, and D. Ber'enyi, Phys Rev. Lett. 88 073201 (2002)

Mechanical Slosh Models for Rocket-Propelled Spacecraft

Science.gov (United States)

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).

A basket two-part model to analyze medical expenditure on interdependent multiple sectors.

Science.gov (United States)

Sugawara, Shinya; Wu, Tianyi; Yamanishi, Kenji

2018-05-01

This study proposes a novel statistical methodology to analyze expenditure on multiple medical sectors using consumer data. Conventionally, medical expenditure has been analyzed by two-part models, which separately consider purchase decision and amount of expenditure. We extend the traditional two-part models by adding the step of basket analysis for dimension reduction. This new step enables us to analyze complicated interdependence between multiple sectors without an identification problem. As an empirical application for the proposed method, we analyze data of 13 medical sectors from the Medical Expenditure Panel Survey. In comparison with the results of previous studies that analyzed the multiple sector independently, our method provides more detailed implications of the impacts of individual socioeconomic status on the composition of joint purchases from multiple medical sectors; our method has a better prediction performance.

MMOSS-I: a CANDU multiple-channel thermosyphoning flow stability model

Energy Technology Data Exchange (ETDEWEB)

Gulshani, P [Atomic Energy of Canada Ltd., Mississauga, ON (Canada); Huynh, H [Hydro-Quebec, Montreal, PQ (Canada)

1996-12-31

This paper presents a multiple-channel flow stability model, dubbed MMOSS, developed to predict the conditions for the onset of flow oscillations in a CANDU-type multiple-channel heat transport system under thermosyphoning conditions. The model generalizes that developed previously to account for the effects of any channel flow reversal. Two-phase thermosyphoning conditions are predicted by thermalhydraulic codes for some postulated accident scenarios in CANDU. Two-phase thermosyphoning experiments in the multiple-channel RD-14M facility have indicated that pass-to-pass out-of-phase oscillations in the loop conditions caused the flow in some of the heated channels to undergo sustained reversal in direction. This channel flow reversal had significant effects on the channel and loop conditions. It is, therefore, important to understand the nature of the oscillations and be able to predict the conditions for the onset of the oscillations or for stable flow in RD-14M and the reactor. For stable flow conditions, oscillation-induced channel flow reversal is not expected. MMOSS was developed for a figure-of-eight system with any number of channels. The system characteristic equation was derived from a linearization of the conservation equations. In this paper, the MMOSS characteristic equation is solved for a system of N identical channel assemblies. The resulting model is called MMOSS-I. This simplification provides valuable physical insight and reasonably accurate results. MMOSS-I and a previously-developed steady-state model THERMOSYPHON are used to predict thermosyphoning flow stability maps for RD-14M and the Gentilly 2 reactor. (author). 11 refs., 7 figs.

A 1D thermomechanical network transition constitutive model coupled with multiple structural relaxation for shape memory polymers

Science.gov (United States)

Zeng, Hao; Xie, Zhimin; Gu, Jianping; Sun, Huiyu

2018-03-01

A new thermomechanical network transition constitutive model is proposed in the study to describe the viscoelastic behavior of shape memory polymers (SMPs). Based on the microstructure of semi-crystalline SMPs, a new simplified transformation equation is proposed to describe the transform of transient networks. And the generalized fractional Maxwell model is introduced in the paper to estimate the temperature-dependent storage modulus. In addition, a neo-KAHR theory with multiple discrete relaxation processes is put forward to study the structural relaxation of the nonlinear thermal strain in cooling/heating processes. The evolution equations of the time- and temperature-dependent stress and strain response are developed. In the model, the thermodynamical and mechanical characteristics of SMPs in the typical thermomechanical cycle are described clearly and the irreversible deformation is studied in detail. Finally, the typical thermomechanical cycles are simulated using the present constitutive model, and the simulation results agree well with the experimental results.

Model for nucleus-nucleus, hadron-nucleus and hadron-proton multiplicity distributions

International Nuclear Information System (INIS)

Singh, C.P.; Shyam, M.; Tuli, S.K.

1986-07-01

A model relating hadron-proton, hadron-nucleus and nucleus-nucleus multiplicity distributions is proposed and some interesting consequences are derived. The values of the parameters are the same for all the processes and are given by the QCD hypothesis of ''universal'' hadronic multiplicities which are found to be asymptotically independent of target and beam in hadronic and current induced reactions in particle physics. (author)

Multiple attribute decision making model and application to food safety risk evaluation.

Directory of Open Access Journals (Sweden)

Lihua Ma

Full Text Available Decision making for supermarket food purchase decisions are characterized by network relationships. This paper analyzed factors that influence supermarket food selection and proposes a supplier evaluation index system based on the whole process of food production. The author established the intuitive interval value fuzzy set evaluation model based on characteristics of the network relationship among decision makers, and validated for a multiple attribute decision making case study. Thus, the proposed model provides a reliable, accurate method for multiple attribute decision making.

Hierarchical Multiple Markov Chain Model for Unsupervised Texture Segmentation

Czech Academy of Sciences Publication Activity Database

Scarpa, G.; Gaetano, R.; Haindl, Michal; Zerubia, J.

2009-01-01

Roč. 18, č. 8 (2009), s. 1830-1843 ISSN 1057-7149 R&D Projects: GA ČR GA102/08/0593 EU Projects: European Commission(XE) 507752 - MUSCLE Institutional research plan: CEZ:AV0Z10750506 Keywords : Classification * texture analysis * segmentation * hierarchical image models * Markov process Subject RIV: BD - Theory of Information Impact factor: 2.848, year: 2009 http://library.utia.cas.cz/separaty/2009/RO/haindl-hierarchical multiple markov chain model for unsupervised texture segmentation.pdf

A Convex Variational Model for Restoring Blurred Images with Multiplicative Noise

DEFF Research Database (Denmark)

Dong, Yiqiu; Tieyong Zeng

2013-01-01

In this paper, a new variational model for restoring blurred images with multiplicative noise is proposed. Based on the statistical property of the noise, a quadratic penalty function technique is utilized in order to obtain a strictly convex model under a mild condition, which guarantees...

A Mechanism of Virus-Induced Demyelination

Directory of Open Access Journals (Sweden)

Jayasri Das Sarma

2010-01-01

Full Text Available Myelin forms an insulating sheath surrounding axons in the central and peripheral nervous systems and is essential for rapid propagation of neuronal action potentials. Demyelination is an acquired disorder in which normally formed myelin degenerates, exposing axons to the extracellular environment. The result is dysfunction of normal neuron-to-neuron communication and in many cases, varying degrees of axonal degeneration. Numerous central nervous system demyelinating disorders exist, including multiple sclerosis. Although demyelination is the major manifestation of most of the demyelinating diseases, recent studies have clearly documented concomitant axonal loss to varying degrees resulting in long-term disability. Axonal injury may occur secondary to myelin damage (outside-in model or myelin damage may occur secondary to axonal injury (inside-out model. Viral induced demyelination models, has provided unique imminent into the cellular mechanisms of myelin destruction. They illustrate mechanisms of viral persistence, including latent infections, virus reactivation and viral-induced tissue damage. These studies have also provided excellent paradigms to study the interactions between the immune system and the central nervous system (CNS. In this review we will discuss potential cellular and molecular mechanism of central nervous system axonal loss and demyelination in a viral induced mouse model of multiple sclerosis.

Alemtuzumab in Multiple Sclerosis: Mechanism of Action and Beyond

Directory of Open Access Journals (Sweden)

Tobias Ruck

2015-07-01

Full Text Available Alemtuzumab is a humanized monoclonal antibody against CD52 (cluster of differentiation 52 and is approved for the therapy of relapsing-remitting multiple sclerosis. The application of alemtuzumab leads to a rapid, but long-lasting depletion predominantly of CD52-bearing B and T cells with reprogramming effects on immune cell composition resulting in the restoration of tolerogenic networks. Alemtuzumab has proven high efficacy in clinical phase II and III trials, where interferon β-1a was used as active comparator. However, alemtuzumab is associated with frequent and considerable risks. Most importantly secondary autoimmune disease affects 30%–40% of patients, predominantly impairing thyroid function. Extensive monitoring and early intervention allow for an appropriate risk management. However, new and reliable biomarkers for individual risk stratification and treatment response to improve patient selection and therapy guidance are a significant unmet need. Only a deeper understanding of the underlying mechanisms of action (MOA will reveal such markers, maximizing the best potential risk-benefit ratio for the individual patient. This review provides and analyses the current knowledge on the MOA of alemtuzumab. Most recent data on efficacy and safety of alemtuzumab are presented and future research opportunities are discussed.

The empirical content of models with multiple equilibria in economies with social interactions

OpenAIRE

Alberto Bisin; Andrea Moro; Giorgio Topa

2011-01-01

We study a general class of models with social interactions that might display multiple equilibria. We propose an estimation procedure for these models and evaluate its efficiency and computational feasibility relative to different approaches taken to the curse of dimensionality implied by the multiplicity. Using data on smoking among teenagers, we implement the proposed estimation procedure to understand how group interactions affect health-related choices. We find that interaction effects a...

Links between fluid mechanics and quantum mechanics: a model for information in economics?

Science.gov (United States)

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. © 2016 The Author(s).

Dynamic coordinated control laws in multiple agent models

International Nuclear Information System (INIS)

Morgan, David S.; Schwartz, Ira B.

2005-01-01

We present an active control scheme of a kinetic model of swarming. It has been shown previously that the global control scheme for the model, presented in [Systems Control Lett. 52 (2004) 25], gives rise to spontaneous collective organization of agents into a unified coherent swarm, via steering controls and utilizing long-range attractive and short-range repulsive interactions. We extend these results by presenting control laws whereby a single swarm is broken into independently functioning subswarm clusters. The transition between one coordinated swarm and multiple clustered subswarms is managed simply with a homotopy parameter. Additionally, we present as an alternate formulation, a local control law for the same model, which implements dynamic barrier avoidance behavior, and in which swarm coherence emerges spontaneously

Petiveria alliacea extracts uses multiple mechanisms to inhibit growth of human and mouse tumoral cells

OpenAIRE

Urue?a, Claudia; Cifuentes, Claudia; Casta?eda, Diana; Arango, Amparo; Kaur, Punit; Asea, Alexzander; Fiorentino, Susana

2008-01-01

Abstract Background There is ethnopharmacological evidence that Petiveria alliacea can have antitumor activity; however, the mechanism of its cytotoxic activity is not well understood. We assessed multiple in vitro biological activities of an ethyl acetate soluble plant fraction over several tumor cell lines. Methods Tumor cell lines were evaluated using the following tests: trypan blue exclusion test, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide], flow cytometry, cytosk...

Flexible Modeling of Survival Data with Covariates Subject to Detection Limits via Multiple Imputation.

Science.gov (United States)

Bernhardt, Paul W; Wang, Huixia Judy; Zhang, Daowen

2014-01-01

Models for survival data generally assume that covariates are fully observed. However, in medical studies it is not uncommon for biomarkers to be censored at known detection limits. A computationally-efficient multiple imputation procedure for modeling survival data with covariates subject to detection limits is proposed. This procedure is developed in the context of an accelerated failure time model with a flexible seminonparametric error distribution. The consistency and asymptotic normality of the multiple imputation estimator are established and a consistent variance estimator is provided. An iterative version of the proposed multiple imputation algorithm that approximates the EM algorithm for maximum likelihood is also suggested. Simulation studies demonstrate that the proposed multiple imputation methods work well while alternative methods lead to estimates that are either biased or more variable. The proposed methods are applied to analyze the dataset from a recently-conducted GenIMS study.

A feedback control model for network flow with multiple pure time delays

Science.gov (United States)

Press, J.

1972-01-01

A control model describing a network flow hindered by multiple pure time (or transport) delays is formulated. Feedbacks connect each desired output with a single control sector situated at the origin. The dynamic formulation invokes the use of differential difference equations. This causes the characteristic equation of the model to consist of transcendental functions instead of a common algebraic polynomial. A general graphical criterion is developed to evaluate the stability of such a problem. A digital computer simulation confirms the validity of such criterion. An optimal decision making process with multiple delays is presented.

Multiple Model Adaptive Attitude Control of LEO Satellite with Angular Velocity Constraints

Science.gov (United States)

Shahrooei, Abolfazl; Kazemi, Mohammad Hosein

2018-04-01

In this paper, the multiple model adaptive control is utilized to improve the transient response of attitude control system for a rigid spacecraft. An adaptive output feedback control law is proposed for attitude control under angular velocity constraints and its almost global asymptotic stability is proved. The multiple model adaptive control approach is employed to counteract large uncertainty in parameter space of the inertia matrix. The nonlinear dynamics of a low earth orbit satellite is simulated and the proposed control algorithm is implemented. The reported results show the effectiveness of the suggested scheme.

Thymic Atrophy and Apoptosis of CD4+CD8+ Thymocytes in the Cuprizone Model of Multiple Sclerosis

DEFF Research Database (Denmark)

Solti, Izabella; Kvell, Krisztian; Talaber, Gergely

2015-01-01

Previous studies on the degenerative animal model of multiple sclerosis suggested that the copper-chelator cuprizone might directly suppress T-cell functions. Peripheral T-cell function in the cuprizone model has already been explored; therefore, in the present study, we investigated, for the first...... mitochondria, myelin-bodies, large lipid droplets, and large lysosomes in the thymi of cuprizone-treated mice. Some of these features were similar to those in physiological and steroid-induced accelerated aging. According to our results, apoptosis was mainly of mitochondrial origin mediated by both caspase-3......- and apoptosis inducing factor-mediated mechanisms. Additionally, mitogen activated protein kinase activation and increased pro-apoptotic B cell lymphoma-2 family protein expression were the major underlying processes. Our results do not indicate a functional relationship between cuprizone-induced thymus...

Skin mechanical properties and modeling: A review.

Science.gov (United States)

Joodaki, Hamed; Panzer, Matthew B

2018-04-01

The mechanical properties of the skin are important for various applications. Numerous tests have been conducted to characterize the mechanical behavior of this tissue, and this article presents a review on different experimental methods used. A discussion on the general mechanical behavior of the skin, including nonlinearity, viscoelasticity, anisotropy, loading history dependency, failure properties, and aging effects, is presented. Finally, commonly used constitutive models for simulating the mechanical response of skin are discussed in the context of representing the empirically observed behavior.

Phase transitions in multiplicative competitive processes

International Nuclear Information System (INIS)

Shimazaki, Hideaki; Niebur, Ernst

2005-01-01

We introduce a discrete multiplicative process as a generic model of competition. Players with different abilities successively join the game and compete for finite resources. Emergence of dominant players and evolutionary development occur as a phase transition. The competitive dynamics underlying this transition is understood from a formal analogy to statistical mechanics. The theory is applicable to bacterial competition, predicting novel population dynamics near criticality

Improving the Pattern Reproducibility of Multiple-Point-Based Prior Models Using Frequency Matching

DEFF Research Database (Denmark)

Cordua, Knud Skou; Hansen, Thomas Mejer; Mosegaard, Klaus

2014-01-01

Some multiple-point-based sampling algorithms, such as the snesim algorithm, rely on sequential simulation. The conditional probability distributions that are used for the simulation are based on statistics of multiple-point data events obtained from a training image. During the simulation, data...... events with zero probability in the training image statistics may occur. This is handled by pruning the set of conditioning data until an event with non-zero probability is found. The resulting probability distribution sampled by such algorithms is a pruned mixture model. The pruning strategy leads...... to a probability distribution that lacks some of the information provided by the multiple-point statistics from the training image, which reduces the reproducibility of the training image patterns in the outcome realizations. When pruned mixture models are used as prior models for inverse problems, local re...

Dynamic modeling and hierarchical compound control of a novel 2-DOF flexible parallel manipulator with multiple actuation modes

Science.gov (United States)

Liang, Dong; Song, Yimin; Sun, Tao; Jin, Xueying

2018-03-01

This paper addresses the problem of rigid-flexible coupling dynamic modeling and active control of a novel flexible parallel manipulator (PM) with multiple actuation modes. Firstly, based on the flexible multi-body dynamics theory, the rigid-flexible coupling dynamic model (RFDM) of system is developed by virtue of the augmented Lagrangian multipliers approach. For completeness, the mathematical models of permanent magnet synchronous motor (PMSM) and piezoelectric transducer (PZT) are further established and integrated with the RFDM of mechanical system to formulate the electromechanical coupling dynamic model (ECDM). To achieve the trajectory tracking and vibration suppression, a hierarchical compound control strategy is presented. Within this control strategy, the proportional-differential (PD) feedback controller is employed to realize the trajectory tracking of end-effector, while the strain and strain rate feedback (SSRF) controller is developed to restrain the vibration of the flexible links using PZT. Furthermore, the stability of the control algorithm is demonstrated based on the Lyapunov stability theory. Finally, two simulation case studies are performed to illustrate the effectiveness of the proposed approach. The results indicate that, under the redundant actuation mode, the hierarchical compound control strategy can guarantee the flexible PM achieves singularity-free motion and vibration attenuation within task workspace simultaneously. The systematic methodology proposed in this study can be conveniently extended for the dynamic modeling and efficient controller design of other flexible PMs, especially the emerging ones with multiple actuation modes.

The reverse effects of random perturbation on discrete systems for single and multiple population models

International Nuclear Information System (INIS)

Kang, Li; Tang, Sanyi

2016-01-01

Highlights: • The discrete single species and multiple species models with random perturbation are proposed. • The complex dynamics and interesting bifurcation behavior have been investigated. • The reverse effects of random perturbation on discrete systems have been discussed and revealed. • The main results can be applied for pest control and resources management. - Abstract: The natural species are likely to present several interesting and complex phenomena under random perturbations, which have been confirmed by simple mathematical models. The important questions are: how the random perturbations influence the dynamics of the discrete population models with multiple steady states or multiple species interactions? and is there any different effects for single species and multiple species models with random perturbation? To address those interesting questions, we have proposed the discrete single species model with two stable equilibria and the host-parasitoid model with Holling type functional response functions to address how the random perturbation affects the dynamics. The main results indicate that the random perturbation does not change the number of blurred orbits of the single species model with two stable steady states compared with results for the classical Ricker model with same random perturbation, but it can strength the stability. However, extensive numerical investigations depict that the random perturbation does not influence the complexities of the host-parasitoid models compared with the results for the models without perturbation, while it does increase the period of periodic orbits doubly. All those confirm that the random perturbation has a reverse effect on the dynamics of the discrete single and multiple population models, which could be applied in reality including pest control and resources management.

Theoretical Models of Protostellar Binary and Multiple Systems with AMR Simulations

Science.gov (United States)

Matsumoto, Tomoaki; Tokuda, Kazuki; Onishi, Toshikazu; Inutsuka, Shu-ichiro; Saigo, Kazuya; Takakuwa, Shigehisa

2017-05-01

We present theoretical models for protostellar binary and multiple systems based on the high-resolution numerical simulation with an adaptive mesh refinement (AMR) code, SFUMATO. The recent ALMA observations have revealed early phases of the binary and multiple star formation with high spatial resolutions. These observations should be compared with theoretical models with high spatial resolutions. We present two theoretical models for (1) a high density molecular cloud core, MC27/L1521F, and (2) a protobinary system, L1551 NE. For the model for MC27, we performed numerical simulations for gravitational collapse of a turbulent cloud core. The cloud core exhibits fragmentation during the collapse, and dynamical interaction between the fragments produces an arc-like structure, which is one of the prominent structures observed by ALMA. For the model for L1551 NE, we performed numerical simulations of gas accretion onto protobinary. The simulations exhibit asymmetry of a circumbinary disk. Such asymmetry has been also observed by ALMA in the circumbinary disk of L1551 NE.

Study on modeling of operator's learning mechanism

International Nuclear Information System (INIS)

Yoshimura, Seichi; Hasegawa, Naoko

1998-01-01

One effective method to analyze the causes of human errors is to model the behavior of human and to simulate it. The Central Research Institute of Electric Power Industry (CRIEPI) has developed an operator team behavior simulation system called SYBORG (Simulation System for the Behavior of an Operating Group) to analyze the human errors and to establish the countermeasures for them. As an operator behavior model which composes SYBORG has no learning mechanism and the knowledge of a plant is fixed, it cannot take suitable actions when unknown situations occur nor learn anything from the experience. However, considering actual operators, learning is an essential human factor to enhance their abilities to diagnose plant anomalies. In this paper, Q learning with 1/f fluctuation was proposed as a learning mechanism of an operator and simulation using the mechanism was conducted. The results showed the effectiveness of the learning mechanism. (author)

Systematic comparison of model polymer nanocomposite mechanics.

Science.gov (United States)

Xiao, Senbo; Peter, Christine; Kremer, Kurt

2016-09-13

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.

ONKALO rock mechanics model (RMM) - Version 2.0

International Nuclear Information System (INIS)

Moenkkoenen, H.; Hakala, M.; Paananen, M.; Laine, E.

2012-02-01

The Rock Mechanics Model of the ONKALO rock volume is a description of the significant features and parameters related to rock mechanics. The main objective is to develop a tool to predict the rock properties, quality and hence the potential for stress failure which can then be used for continuing design of the ONKALO and the repository. This is the second implementation of the Rock Mechanics Model and it includes sub-models of the intact rock strength, in situ stress, thermal properties, rock mass quality and properties of the brittle deformation zones. Because of the varying quantities of available data for the different parameters, the types of presentations also vary: some data sets can be presented in the style of a 3D block model but, in other cases, a single distribution represents the whole rock volume hosting the ONKALO. (orig.)

Nonlinear structural mechanics theory, dynamical phenomena and modeling

CERN Document Server

Lacarbonara, Walter

2013-01-01

Nonlinear Structural Mechanics: Theory, Dynamical Phenomena and Modeling offers a concise, coherent presentation of the theoretical framework of nonlinear structural mechanics, computational methods, applications, parametric investigations of nonlinear phenomena and their mechanical interpretation towards design. The theoretical and computational tools that enable the formulation, solution, and interpretation of nonlinear structures are presented in a systematic fashion so as to gradually attain an increasing level of complexity of structural behaviors, under the prevailing assumptions on the geometry of deformation, the constitutive aspects and the loading scenarios. Readers will find a treatment of the foundations of nonlinear structural mechanics towards advanced reduced models, unified with modern computational tools in the framework of the prominent nonlinear structural dynamic phenomena while tackling both the mathematical and applied sciences. Nonlinear Structural Mechanics: Theory, Dynamical Phenomena...

Vehicle coordinated transportation dispatching model base on multiple crisis locations

Science.gov (United States)

Tian, Ran; Li, Shanwei; Yang, Guoying

2018-05-01

Many disastrous events are often caused after unconventional emergencies occur, and the requirements of disasters are often different. It is difficult for a single emergency resource center to satisfy such requirements at the same time. Therefore, how to coordinate the emergency resources stored by multiple emergency resource centers to various disaster sites requires the coordinated transportation of emergency vehicles. In this paper, according to the problem of emergency logistics coordination scheduling, based on the related constraints of emergency logistics transportation, an emergency resource scheduling model based on multiple disasters is established.

A P-value model for theoretical power analysis and its applications in multiple testing procedures

Directory of Open Access Journals (Sweden)

Fengqing Zhang

2016-10-01

Full Text Available Abstract Background Power analysis is a critical aspect of the design of experiments to detect an effect of a given size. When multiple hypotheses are tested simultaneously, multiplicity adjustments to p-values should be taken into account in power analysis. There are a limited number of studies on power analysis in multiple testing procedures. For some methods, the theoretical analysis is difficult and extensive numerical simulations are often needed, while other methods oversimplify the information under the alternative hypothesis. To this end, this paper aims to develop a new statistical model for power analysis in multiple testing procedures. Methods We propose a step-function-based p-value model under the alternative hypothesis, which is simple enough to perform power analysis without simulations, but not too simple to lose the information from the alternative hypothesis. The first step is to transform distributions of different test statistics (e.g., t, chi-square or F to distributions of corresponding p-values. We then use a step function to approximate each of the p-value’s distributions by matching the mean and variance. Lastly, the step-function-based p-value model can be used for theoretical power analysis. Results The proposed model is applied to problems in multiple testing procedures. We first show how the most powerful critical constants can be chosen using the step-function-based p-value model. Our model is then applied to the field of multiple testing procedures to explain the assumption of monotonicity of the critical constants. Lastly, we apply our model to a behavioral weight loss and maintenance study to select the optimal critical constants. Conclusions The proposed model is easy to implement and preserves the information from the alternative hypothesis.

Sorption mechanisms and sorption models

International Nuclear Information System (INIS)

Fedoroff, M.; Lefevre, G.; Duc, M.; Neskovic, C.; Milonjic, S.

2004-01-01

Sorption at the solid-liquid interfaces play a major role in many phenomena and technologies: chemical separations, catalysis, biological processes, transport of toxic and radioactive species in surface and underground waters. The long term safety of radioactive waste repositories is based on artificial and natural barriers, intended to sorb radionuclides after the moment when the storage matrixes and containers will be corroded. Predictions on the efficiency of sorption for more than 10 6 years have to be done in order to demonstrate the safety of such depositories, what is a goal never encountered in the history of sciences and technology. For all these purposes, and, especially for the long term prediction, acquiring of sorption data constitutes only a first step of studies. Modeling based on a very good knowledge of sorption mechanisms is needed. In this review, we shall examine the main approaches and models used to quantify sorption processes, including results taken from the literature and from our own studies. We shall compare sorption models and examine their adequacy with sorption mechanisms. The cited references are only a few examples of the numerous articles published in that field. (orig.)

Modeling Multiple Causes of Carcinogenesis

Energy Technology Data Exchange (ETDEWEB)

Jones, T D

1999-01-24

An array of epidemiological results and databases on test animal indicate that risk of cancer and atherosclerosis can be up- or down-regulated by diet through a range of 200%. Other factors contribute incrementally and include the natural terrestrial environment and various human activities that jointly produce complex exposures to endotoxin-producing microorganisms, ionizing radiations, and chemicals. Ordinary personal habits and simple physical irritants have been demonstrated to affect the immune response and risk of disease. There tends to be poor statistical correlation of long-term risk with single agent exposures incurred throughout working careers. However, Agency recommendations for control of hazardous exposures to humans has been substance-specific instead of contextually realistic even though there is consistent evidence for common mechanisms of toxicological and carcinogenic action. That behavior seems to be best explained by molecular stresses from cellular oxygen metabolism and phagocytosis of antigenic invasion as well as breakdown of normal metabolic compounds associated with homeostatic- and injury-related renewal of cells. There is continually mounting evidence that marrow stroma, comprised largely of monocyte-macrophages and fibroblasts, is important to phagocytic and cytokinetic response, but the complex action of the immune process is difficult to infer from first-principle logic or biomarkers of toxic injury. The many diverse database studies all seem to implicate two important processes, i.e., the univalent reduction of molecular oxygen and breakdown of aginuine, an amino acid, by hydrolysis or digestion of protein which is attendant to normal antigen-antibody action. This behavior indicates that protection guidelines and risk coefficients should be context dependent to include reference considerations of the composite action of parameters that mediate oxygen metabolism. A logic of this type permits the realistic common-scale modeling of

Infinite Random Graphs as Statistical Mechanical Models

DEFF Research Database (Denmark)

Durhuus, Bergfinnur Jøgvan; Napolitano, George Maria

2011-01-01

We discuss two examples of infinite random graphs obtained as limits of finite statistical mechanical systems: a model of two-dimensional dis-cretized quantum gravity defined in terms of causal triangulated surfaces, and the Ising model on generic random trees. For the former model we describe a ...

Challenges in LCA modelling of multiple loops for aluminium cans

DEFF Research Database (Denmark)

Niero, Monia; Olsen, Stig Irving

considered the case of closed-loop recycling for aluminium cans, where body and lid are different alloys, and discussed the abovementioned challenge. The Life Cycle Inventory (LCI) modelling of aluminium processes is traditionally based on a pure aluminium flow, therefore neglecting the presence of alloying...... elements. We included the effect of alloying elements on the LCA modelling of aluminium can recycling. First, we performed a mass balance of the main alloying elements (Mn, Fe, Si, Cu) in aluminium can recycling at increasing levels of recycling rate. The analysis distinguished between different aluminium...... packaging scrap sources (i.e. used beverage can and mixed aluminium packaging) to understand the limiting factors for multiple loop aluminium can recycling. Secondly, we performed a comparative LCA of aluminium can production and recycling in multiple loops considering the two aluminium packaging scrap...

A minimal unified model of disease trajectories captures hallmarks of multiple sclerosis

KAUST Repository

Kannan, Venkateshan

2017-03-29

Multiple Sclerosis (MS) is an autoimmune disease targeting the central nervous system (CNS) causing demyelination and neurodegeneration leading to accumulation of neurological disability. Here we present a minimal, computational model involving the immune system and CNS that generates the principal subtypes of the disease observed in patients. The model captures several key features of MS, especially those that distinguish the chronic progressive phase from that of the relapse-remitting. In addition, a rare subtype of the disease, progressive relapsing MS naturally emerges from the model. The model posits the existence of two key thresholds, one in the immune system and the other in the CNS, that separate dynamically distinct behavior of the model. Exploring the two-dimensional space of these thresholds, we obtain multiple phases of disease evolution and these shows greater variation than the clinical classification of MS, thus capturing the heterogeneity that is manifested in patients.

Modelling multiple cycles of static and dynamic recrystallisation using a fully implicit isotropic material model based on dislocation density

Science.gov (United States)

Jansen van Rensburg, Gerhardus J.; Kok, Schalk; Wilke, Daniel N.

2018-03-01

This paper presents the development and numerical implementation of a state variable based thermomechanical material model, intended for use within a fully implicit finite element formulation. Plastic hardening, thermal recovery and multiple cycles of recrystallisation can be tracked for single peak as well as multiple peak recrystallisation response. The numerical implementation of the state variable model extends on a J2 isotropic hypo-elastoplastic modelling framework. The complete numerical implementation is presented as an Abaqus UMAT and linked subroutines. Implementation is discussed with detailed explanation of the derivation and use of various sensitivities, internal state variable management and multiple recrystallisation cycle contributions. A flow chart explaining the proposed numerical implementation is provided as well as verification on the convergence of the material subroutine. The material model is characterised using two high temperature data sets for cobalt and copper. The results of finite element analyses using the material parameter values characterised on the copper data set are also presented.

Equilibrium statistical mechanics of lattice models

CERN Document Server

Lavis, David A

2015-01-01

Most interesting and difficult problems in equilibrium statistical mechanics concern models which exhibit phase transitions. For graduate students and more experienced researchers this book provides an invaluable reference source of approximate and exact solutions for a comprehensive range of such models. Part I contains background material on classical thermodynamics and statistical mechanics, together with a classification and survey of lattice models. The geometry of phase transitions is described and scaling theory is used to introduce critical exponents and scaling laws. An introduction is given to finite-size scaling, conformal invariance and Schramm—Loewner evolution. Part II contains accounts of classical mean-field methods. The parallels between Landau expansions and catastrophe theory are discussed and Ginzburg—Landau theory is introduced. The extension of mean-field theory to higher-orders is explored using the Kikuchi—Hijmans—De Boer hierarchy of approximations. In Part III the use of alge...

Binding and segmentation via a neural mass model trained with Hebbian and anti-Hebbian mechanisms.

Science.gov (United States)

Cona, Filippo; Zavaglia, Melissa; Ursino, Mauro

2012-04-01

Synchronization of neural activity in the gamma band, modulated by a slower theta rhythm, is assumed to play a significant role in binding and segmentation of multiple objects. In the present work, a recent neural mass model of a single cortical column is used to analyze the synaptic mechanisms which can warrant synchronization and desynchronization of cortical columns, during an autoassociation memory task. The model considers two distinct layers communicating via feedforward connections. The first layer receives the external input and works as an autoassociative network in the theta band, to recover a previously memorized object from incomplete information. The second realizes segmentation of different objects in the gamma band. To this end, units within both layers are connected with synapses trained on the basis of previous experience to store objects. The main model assumptions are: (i) recovery of incomplete objects is realized by excitatory synapses from pyramidal to pyramidal neurons in the same object; (ii) binding in the gamma range is realized by excitatory synapses from pyramidal neurons to fast inhibitory interneurons in the same object. These synapses (both at points i and ii) have a few ms dynamics and are trained with a Hebbian mechanism. (iii) Segmentation is realized with faster AMPA synapses, with rise times smaller than 1 ms, trained with an anti-Hebbian mechanism. Results show that the model, with the previous assumptions, can correctly reconstruct and segment three simultaneous objects, starting from incomplete knowledge. Segmentation of more objects is possible but requires an increased ratio between the theta and gamma periods.

Aerodynamic and Mechanical System Modelling

DEFF Research Database (Denmark)

Jørgensen, Martin Felix

This thesis deals with mechanical multibody-systems applied to the drivetrain of a 500 kW wind turbine. Particular focus has been on gearbox modelling of wind turbines. The main part of the present project involved programming multibody systems to investigate the connection between forces, moments...

Distinguishing Antimicrobial Models with Different Resistance Mechanisms via Population Pharmacodynamic Modeling.

Directory of Open Access Journals (Sweden)

Matthieu Jacobs

2016-03-01

Full Text Available Semi-mechanistic pharmacokinetic-pharmacodynamic (PK-PD modeling is increasingly used for antimicrobial drug development and optimization of dosage regimens, but systematic simulation-estimation studies to distinguish between competing PD models are lacking. This study compared the ability of static and dynamic in vitro infection models to distinguish between models with different resistance mechanisms and support accurate and precise parameter estimation. Monte Carlo simulations (MCS were performed for models with one susceptible bacterial population without (M1 or with a resting stage (M2, a one population model with adaptive resistance (M5, models with pre-existing susceptible and resistant populations without (M3 or with (M4 inter-conversion, and a model with two pre-existing populations with adaptive resistance (M6. For each model, 200 datasets of the total bacterial population were simulated over 24h using static antibiotic concentrations (256-fold concentration range or over 48h under dynamic conditions (dosing every 12h; elimination half-life: 1h. Twelve-hundred random datasets (each containing 20 curves for static or four curves for dynamic conditions were generated by bootstrapping. Each dataset was estimated by all six models via population PD modeling to compare bias and precision. For M1 and M3, most parameter estimates were unbiased (<10% and had good imprecision (<30%. However, parameters for adaptive resistance and inter-conversion for M2, M4, M5 and M6 had poor bias and large imprecision under static and dynamic conditions. For datasets that only contained viable counts of the total population, common statistical criteria and diagnostic plots did not support sound identification of the true resistance mechanism. Therefore, it seems advisable to quantify resistant bacteria and characterize their MICs and resistance mechanisms to support extended simulations and translate from in vitro experiments to animal infection models and

Computational modelling in fluid mechanics

International Nuclear Information System (INIS)

Hauguel, A.

1985-01-01

The modelling of the greatest part of environmental or industrial flow problems gives very similar types of equations. The considerable increase in computing capacity over the last ten years consequently allowed numerical models of growing complexity to be processed. The varied group of computer codes presented are now a complementary tool of experimental facilities to achieve studies in the field of fluid mechanics. Several codes applied in the nuclear field (reactors, cooling towers, exchangers, plumes...) are presented among others [fr

Persistent visual impairment in multiple sclerosis: prevalence, mechanisms and resulting disability.

Science.gov (United States)

Jasse, Laurence; Vukusic, Sandra; Durand-Dubief, Françoise; Vartin, Cristina; Piras, Carolina; Bernard, Martine; Pélisson, Denis; Confavreux, Christian; Vighetto, Alain; Tilikete, Caroline

2013-10-01

The objective of this article is to evaluate in multiple sclerosis (MS) patients the prevalence of persistent complaints of visual disturbances and the mechanisms and resulting functional disability of persistent visual complaints (PVCs). Firstly, the prevalence of PVCs was calculated in 303 MS patients. MS-related data of patients with or without PVCs were compared. Secondly, 70 patients with PVCs performed an extensive neuro-ophthalmologic assessment and a vision-related quality of life questionnaire, the National Eye Institute Visual Functionary Questionnaire (NEI-VFQ-25). PVCs were reported in 105 MS patients (34.6%). Patients with PVCs had more frequently primary progressive MS (30.5% vs 13.6%) and more neuro-ophthalmologic relapses (1.97 vs 1.36) than patients without PVCs. In the mechanisms/disability study, an afferent visual and an ocular-motor pathways dysfunction were respectively diagnosed in 41 and 59 patients, mostly related to bilateral optic neuropathy and bilateral internuclear ophthalmoplegia. The NEI-VFQ 25 score was poor and significantly correlated with the number of impaired neuro-ophthalmologic tests. Our study emphasizes the high prevalence of PVC in MS patients. Regarding the nature of neuro-ophthalmologic deficit, our results suggest that persistent optic neuropathy, as part of the progressive evolution of the disease, is not rare. We also demonstrate that isolated ocular motor dysfunctions induce visual disability in daily life.

Method of experimental and theoretical modeling for multiple pressure tube rupture for RBMK reactor

International Nuclear Information System (INIS)

Medvedeva, N.Y.; Goldstein, R.V.; Burrows, J.A.

2001-01-01

The rupture of single RBMK reactor channels has occurred at a number of stations with a variety of initiating events. It is assumed in RBMK Safety Cases that the force of the escaping fluid will not cause neighbouring channels to break. This assumption has not been justified. A chain reaction of tube breaks could over-pressurise the reactor cavity leading to catastrophic failure of the containment. To validate the claims of the RBMK Safety Cases the Electrogorsk Research and Engineering Centre, in participation with experts from the Institute of Mechanics of RAS, has developed the method of interacting multiscale physical and mathematical modelling for coupled thermophysical, hydrogasodynamic processes and deformation and break processes causing and (or) accompanying potential failures, design and beyond the design RBMK reactor accidents. To realise the method the set of rigs, physical and mathematical models and specialized computer codes are under creation. This article sets out an experimental philosophy and programme for achieving this objective to solve the problem of credibility or non-credibility for multiple fuel channel rupture in RBMK.(author)

A dynamical model of car-following with the consideration of the multiple information of preceding cars

International Nuclear Information System (INIS)

Peng, G.H.; Sun, D.H.

2010-01-01

An improved multiple car-following (MCF) model is proposed, based on the full velocity difference (FVD) model, but taking into consideration multiple information inputs from preceding vehicles. The linear stability condition of the model is obtained by using the linear stability theory. Through nonlinear analysis, the modified Korteweg-de Vries (mKdV) equation is derived to describe the traffic behavior near the critical point. Numerical simulation shows that the proposed model is theoretically an improvement over others, while retaining many strong points in the previous ones by adjusting the information of the multiple leading vehicles.

Multiple sequential failure model: A probabilistic approach to quantifying human error dependency

International Nuclear Information System (INIS)

Samanta

1985-01-01

This paper rpesents a probabilistic approach to quantifying human error dependency when multiple tasks are performed. Dependent human failures are dominant contributors to risks from nuclear power plants. An overview of the Multiple Sequential Failure (MSF) model developed and its use in probabilistic risk assessments (PRAs) depending on the available data are discussed. A small-scale psychological experiment was conducted on the nature of human dependency and the interpretation of the experimental data by the MSF model show remarkable accommodation of the dependent failure data. The model, which provides an unique method for quantification of dependent failures in human reliability analysis, can be used in conjunction with any of the general methods currently used for performing the human reliability aspect in PRAs

Double-multiple streamtube model for studying vertical-axis wind turbines

Science.gov (United States)

Paraschivoiu, Ion

1988-08-01

This work describes the present state-of-the-art in double-multiple streamtube method for modeling the Darrieus-type vertical-axis wind turbine (VAWT). Comparisons of the analytical results with the other predictions and available experimental data show a good agreement. This method, which incorporates dynamic-stall and secondary effects, can be used for generating a suitable aerodynamic-load model for structural design analysis of the Darrieus rotor.

Multiple Surrogate Modeling for Wire-Wrapped Fuel Assembly Optimization

International Nuclear Information System (INIS)

Raza, Wasim; Kim, Kwang-Yong

2007-01-01

In this work, shape optimization of seven pin wire wrapped fuel assembly has been carried out in conjunction with RANS analysis in order to evaluate the performances of surrogate models. Previously, Ahmad and Kim performed the flow and heat transfer analysis based on the three-dimensional RANS analysis. But numerical optimization has not been applied to the design of wire-wrapped fuel assembly, yet. Surrogate models are being widely used in multidisciplinary optimization. Queipo et al. reviewed various surrogates based models used in aerospace applications. Goel et al. developed weighted average surrogate model based on response surface approximation (RSA), radial basis neural network (RBNN) and Krigging (KRG) models. In addition to the three basic models, RSA, RBNN and KRG, the multiple surrogate model, PBA also has been employed. Two geometric design variables and a multi-objective function with a weighting factor have been considered for this problem

Neocortical dynamics at multiple scales: EEG standing waves, statistical mechanics, and physical analogs.

Science.gov (United States)

Ingber, Lester; Nunez, Paul L

2011-02-01

The dynamic behavior of scalp potentials (EEG) is apparently due to some combination of global and local processes with important top-down and bottom-up interactions across spatial scales. In treating global mechanisms, we stress the importance of myelinated axon propagation delays and periodic boundary conditions in the cortical-white matter system, which is topologically close to a spherical shell. By contrast, the proposed local mechanisms are multiscale interactions between cortical columns via short-ranged non-myelinated fibers. A mechanical model consisting of a stretched string with attached nonlinear springs demonstrates the general idea. The string produces standing waves analogous to large-scale coherent EEG observed in some brain states. The attached springs are analogous to the smaller (mesoscopic) scale columnar dynamics. Generally, we expect string displacement and EEG at all scales to result from both global and local phenomena. A statistical mechanics of neocortical interactions (SMNI) calculates oscillatory behavior consistent with typical EEG, within columns, between neighboring columns via short-ranged non-myelinated fibers, across cortical regions via myelinated fibers, and also derives a string equation consistent with the global EEG model. Copyright © 2010 Elsevier Inc. All rights reserved.

Modeling and optimization of a utility system containing multiple extractions steam turbines

International Nuclear Information System (INIS)

Luo, Xianglong; Zhang, Bingjian; Chen, Ying; Mo, Songping

2011-01-01

Complex turbines with multiple controlled and/or uncontrolled extractions are popularly used in the processing industry and cogeneration plants to provide steam of different levels, electric power, and driving power. To characterize thermodynamic behavior under varying conditions, nonlinear mathematical models are developed based on energy balance, thermodynamic principles, and semi-empirical equations. First, the complex turbine is decomposed into several simple turbines from the controlled extraction stages and modeled in series. THM (The turbine hardware model) developing concept is applied to predict the isentropic efficiency of the decomposed simple turbines. Stodola's formulation is also used to simulate the uncontrolled extraction steam parameters. The thermodynamic properties of steam and water are regressed through linearization or piece-wise linearization. Second, comparison between the simulated results using the proposed model and the data in the working condition diagram provided by the manufacturer is conducted over a wide range of operations. The simulation results yield small deviation from the data in the working condition diagram where the maximum modeling error is 0.87% among the compared seven operation conditions. Last, the optimization model of a utility system containing multiple extraction turbines is established and a detailed case is analyzed. Compared with the conventional operation strategy, a maximum of 5.47% of the total operation cost is saved using the proposed optimization model. -- Highlights: → We develop a complete simulation model for steam turbine with multiple extractions. → We test the simulation model using the performance data of commercial turbines. → The simulation error of electric power generation is no more than 0.87%. → We establish a utility system operational optimization model. → The optimal industrial operation scheme featured with 5.47% of cost saving.

Modelling the Dynamics of Intracellular Processes as an Organisation of Multiple Agents

NARCIS (Netherlands)

Bosse, T.; Jonker, C.M.; Treur, J.; Armano, G.; Merelli, E.; Denzinger, J.; Martin, A.; Miles, S.; Tianfield, H.; Unland, R.

2005-01-01

This paper explores how the dynamics of complex biological processes can be modeled as an organisation of multiple agents. This modelling perspective identifies organisational structure occurring in complex decentralised processes and handles complexity of the analysis of the dynamics by structuring

Use of Computational Modeling to Evaluate Hypotheses About the Molecular and Cellular Mechanisms of Bystander Effects

Energy Technology Data Exchange (ETDEWEB)

Zhao, Yuchao; Conolly, Rory B; Andersen, Melvin E.

2006-11-21

This report describes the development of a computational systems biology approach to evaluate the hypotheses of molecular and cellular mechanisms of adaptive response to low dose ionizing radiation. Our concept is that computational models of signaling pathways can be developed and linked to biologically based dose response models to evaluate the underlying molecular mechanisms which lead to adaptive response. For development of quantitatively accurate, predictive models, it will be necessary to describe tissues consisting of multiple cell types where the different types each contribute in their own way to the overall function of the tissue. Such a model will probably need to incorporate not only cell type-specific data but also spatial information on the architecture of the tissue and on intercellular signaling. The scope of the current model was more limited. Data obtained in a number of different biological systems were synthesized to describe a chimeric, “average” population cell. Biochemical signaling pathways involved in sensing of DNA damage and in the activation of cell cycle checkpoint controls and the apoptotic path were also included. As with any computational modeling effort, it was necessary to develop these simplified initial descriptions (models) that can be iteratively refined. This preliminary model is a starting point which, with time, can evolve to a level of refinement where large amounts of detailed biological information are synthesized and a capability for robust predictions of dose- and time-response behaviors is obtained.

Mechanical characterization of bioprinted in vitro soft tissue models

International Nuclear Information System (INIS)

Zhang, Ting; Ouyang, Liliang; Sun, Wei; Yan, Karen Chang

2013-01-01

Recent development in bioprinting technology enables the fabrication of complex, precisely controlled cell-encapsulated tissue constructs. Bioprinted tissue constructs have potential in both therapeutic applications and nontherapeutic applications such as drug discovery and screening, disease modelling and basic biological studies such as in vitro tissue modelling. The mechanical properties of bioprinted in vitro tissue models play an important role in mimicking in vivo the mechanochemical microenvironment. In this study, we have constructed three-dimensional in vitro soft tissue models with varying structure and porosity based on the 3D cell-assembly technique. Gelatin/alginate hybrid materials were used as the matrix material and cells were embedded. The mechanical properties of these models were assessed via compression tests at various culture times, and applicability of three material constitutive models was examined for fitting the experimental data. An assessment of cell bioactivity in these models was also carried out. The results show that the mechanical properties can be improved through structure design, and the compression modulus and strength decrease with respect to time during the first week of culture. In addition, the experimental data fit well with the Ogden model and experiential function. These results provide a foundation to further study the mechanical properties, structural and combined effects in the design and the fabrication of in vitro soft tissue models. (paper)

Multiplicity in Early Stellar Evolution

Science.gov (United States)

Reipurth, B.; Clarke, C. J.; Boss, A. P.; Goodwin, S. P.; Rodríguez, L. F.; Stassun, K. G.; Tokovinin, A.; Zinnecker, H.

Observations from optical to centimeter wavelengths have demonstrated that multiple systems of two or more bodies is the norm at all stellar evolutionary stages. Multiple systems are widely agreed to result from the collapse and fragmentation of cloud cores, despite the inhibiting influence of magnetic fields. Surveys of class 0 protostars with millimeter interferometers have revealed a very high multiplicity frequency of about 2/3, even though there are observational difficulties in resolving close protobinaries, thus supporting the possibility that all stars could be born in multiple systems. Near-infrared adaptive optics observations of class I protostars show a lower binary frequency relative to the class 0 phase, a declining trend that continues through the class II/III stages to the field population. This loss of companions is a natural consequence of dynamical interplay in small multiple systems, leading to ejection of members. We discuss observational consequences of this dynamical evolution, and its influence on circumstellar disks, and we review the evolution of circumbinary disks and their role in defining binary mass ratios. Special attention is paid to eclipsing PMS binaries, which allow for observational tests of evolutionary models of early stellar evolution. Many stars are born in clusters and small groups, and we discuss how interactions in dense stellar environments can significantly alter the distribution of binary separations through dissolution of wider binaries. The binaries and multiples we find in the field are the survivors of these internal and external destructive processes, and we provide a detailed overview of the multiplicity statistics of the field, which form a boundary condition for all models of binary evolution. Finally, we discuss various formation mechanisms for massive binaries, and the properties of massive trapezia.

Mechanisms of Osteoarthritic Pain. Studies in Humans and Experimental Models

Directory of Open Access Journals (Sweden)

Annett Eitner

2017-11-01

Full Text Available Pain due to osteoarthritis (OA is one of the most frequent causes of chronic pain. However, the mechanisms of OA pain are poorly understood. This review addresses the mechanisms which are thought to be involved in OA pain, derived from studies on pain mechanisms in humans and in experimental models of OA. Three areas will be considered, namely local processes in the joint associated with OA pain, neuronal mechanisms involved in OA pain, and general factors which influence OA pain. Except the cartilage all structures of the joints are innervated by nociceptors. Although the hallmark of OA is the degradation of the cartilage, OA joints show multiple structural alterations of cartilage, bone and synovial tissue. In particular synovitis and bone marrow lesions have been proposed to determine OA pain whereas the contribution of the other pathologies to pain generation has been studied less. Concerning the peripheral neuronal mechanisms of OA pain, peripheral nociceptive sensitization was shown, and neuropathic mechanisms may be involved at some stages. Structural changes of joint innervation such as local loss and/or sprouting of nerve fibers were shown. In addition, central sensitization, reduction of descending inhibition, descending excitation and cortical atrophies were observed in OA. The combination of different neuronal mechanisms may define the particular pain phenotype in an OA patient. Among mediators involved in OA pain, nerve growth factor (NGF is in the focus because antibodies against NGF significantly reduce OA pain. Several studies show that neutralization of interleukin-1β and TNF may reduce OA pain. Many patients with OA exhibit comorbidities such as obesity, low grade systemic inflammation and diabetes mellitus. These comorbidities can significantly influence the course of OA, and pain research just began to study the significance of such factors in pain generation. In addition, psychologic and socioeconomic factors may aggravate

Teaching and Evaluation Materials Utilizing Multiple Representations in Mechanics

Science.gov (United States)

Savinainen, A.; Nieminen, P.; Makynen, A.; Viiri, J.

2013-01-01

In this paper, we present materials and teaching ideas utilizing multiple representations in the contexts of kinematics and the force concept. These ideas and materials are substantiated by evidence and can be readily used in teaching with no special training. In addition, we briefly discuss two multiple-choice tests based on physics education…

Model selection with multiple regression on distance matrices leads to incorrect inferences.

Directory of Open Access Journals (Sweden)

Ryan P Franckowiak

Full Text Available In landscape genetics, model selection procedures based on Information Theoretic and Bayesian principles have been used with multiple regression on distance matrices (MRM to test the relationship between multiple vectors of pairwise genetic, geographic, and environmental distance. Using Monte Carlo simulations, we examined the ability of model selection criteria based on Akaike's information criterion (AIC, its small-sample correction (AICc, and the Bayesian information criterion (BIC to reliably rank candidate models when applied with MRM while varying the sample size. The results showed a serious problem: all three criteria exhibit a systematic bias toward selecting unnecessarily complex models containing spurious random variables and erroneously suggest a high level of support for the incorrectly ranked best model. These problems effectively increased with increasing sample size. The failure of AIC, AICc, and BIC was likely driven by the inflated sample size and different sum-of-squares partitioned by MRM, and the resulting effect on delta values. Based on these findings, we strongly discourage the continued application of AIC, AICc, and BIC for model selection with MRM.

Multiple Temperature Model for Near Continuum Flows

International Nuclear Information System (INIS)

XU, Kun; Liu, Hongwei; Jiang, Jianzheng

2007-01-01

In the near continuum flow regime, the flow may have different translational temperatures in different directions. It is well known that for increasingly rarefied flow fields, the predictions from continuum formulation, such as the Navier-Stokes equations, lose accuracy. These inaccuracies may be partially due to the single temperature assumption in the Navier-Stokes equations. Here, based on the gas-kinetic Bhatnagar-Gross-Krook (BGK) equation, a multitranslational temperature model is proposed and used in the flow calculations. In order to fix all three translational temperatures, two constraints are additionally proposed to model the energy exchange in different directions. Based on the multiple temperature assumption, the Navier-Stokes relation between the stress and strain is replaced by the temperature relaxation term, and the Navier-Stokes assumption is recovered only in the limiting case when the flow is close to the equilibrium with the same temperature in different directions. In order to validate the current model, both the Couette and Poiseuille flows are studied in the transition flow regime

A toy MCT model for multiple glass transitions: Double swallow tail singularity

Energy Technology Data Exchange (ETDEWEB)

Ryzhov, V.N. [Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk 142190, Moscow region (Russian Federation); Moscow Institute of Physics and Technology, 141700 Moscow (Russian Federation); Tareyeva, E.E. [Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk 142190, Moscow region (Russian Federation)

2014-11-07

We propose a toy model to describe in the frame of Mode Coupling Theory multiple glass transitions. The model is based on the postulated simple form for static structure factor as a sum of two delta-functions. This form makes it possible to solve the MCT equations in almost analytical way. The phase diagram is governed by two swallow tails resulting from two A{sub 4} singularities and includes liquid–glass transition and multiple glasses. The diagram has much in common with those of binary and quasibinary systems. - Highlights: • A simple toy model is proposed for description of glass–glass transitions. • The static structure factor of the model has the form of a sum of delta-functions. • The phase diagram contains A{sub 4} bifurcation singularities and A{sub 3} end points. • The results can be applied for the qualitative description of quasibinary systems.

Validation and calibration of structural models that combine information from multiple sources.

Science.gov (United States)

Dahabreh, Issa J; Wong, John B; Trikalinos, Thomas A

2017-02-01

Mathematical models that attempt to capture structural relationships between their components and combine information from multiple sources are increasingly used in medicine. Areas covered: We provide an overview of methods for model validation and calibration and survey studies comparing alternative approaches. Expert commentary: Model validation entails a confrontation of models with data, background knowledge, and other models, and can inform judgments about model credibility. Calibration involves selecting parameter values to improve the agreement of model outputs with data. When the goal of modeling is quantitative inference on the effects of interventions or forecasting, calibration can be viewed as estimation. This view clarifies issues related to parameter identifiability and facilitates formal model validation and the examination of consistency among different sources of information. In contrast, when the goal of modeling is the generation of qualitative insights about the modeled phenomenon, calibration is a rather informal process for selecting inputs that result in model behavior that roughly reproduces select aspects of the modeled phenomenon and cannot be equated to an estimation procedure. Current empirical research on validation and calibration methods consists primarily of methodological appraisals or case-studies of alternative techniques and cannot address the numerous complex and multifaceted methodological decisions that modelers must make. Further research is needed on different approaches for developing and validating complex models that combine evidence from multiple sources.

Modeling oscillatory dynamics in brain microcircuits as a way to help uncover neurological disease mechanisms: A proposal

Energy Technology Data Exchange (ETDEWEB)

Skinner, F. K. [Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto Western Hospital, 60 Leonard Street, 7th floor, 7KD411, Toronto, Ontario M5T 2S8 (Canada); Department of Medicine (Neurology), University of Toronto, 200 Elizabeth Street, Toronto, Ontario M5G 2C4 (Canada); Department of Physiology, University of Toronto Medical Sciences Building, 3rd Floor, 1 King' s College Circle, Toronto, Ontario M5S 1A8 (Canada); Ferguson, K. A. [Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto Western Hospital, 60 Leonard Street, 7th floor, 7KD411, Toronto, Ontario M5T 2S8 (Canada); Department of Physiology, University of Toronto Medical Sciences Building, 3rd Floor, 1 King' s College Circle, Toronto, Ontario M5S 1A8 (Canada)

2013-12-15

There is an undisputed need and requirement for theoretical and computational studies in Neuroscience today. Furthermore, it is clear that oscillatory dynamical output from brain networks is representative of various behavioural states, and it is becoming clear that one could consider these outputs as measures of normal and pathological brain states. Although mathematical modeling of oscillatory dynamics in the context of neurological disease exists, it is a highly challenging endeavour because of the many levels of organization in the nervous system. This challenge is coupled with the increasing knowledge of cellular specificity and network dysfunction that is associated with disease. Recently, whole hippocampus in vitro preparations from control animals have been shown to spontaneously express oscillatory activities. In addition, when using preparations derived from animal models of disease, these activities show particular alterations. These preparations present an opportunity to address challenges involved with using models to gain insight because of easier access to simultaneous cellular and network measurements, and pharmacological modulations. We propose that by developing and using models with direct links to experiment at multiple levels, which at least include cellular and microcircuit, a cycling can be set up and used to help us determine critical mechanisms underlying neurological disease. We illustrate our proposal using our previously developed inhibitory network models in the context of these whole hippocampus preparations and show the importance of having direct links at multiple levels.

Multiple sclerosis, relapses, and the mechanism of action of adrenocorticotropic hormone (ACTH

Directory of Open Access Journals (Sweden)

Amy ePerrin Ross

2013-03-01

Full Text Available Relapses in multiple sclerosis (MS are disruptive and frequently disabling for patients, and their treatment is often a challenge to clinicians. Despite progress in the understanding of the pathophysiology of MS and development of new treatments for long-term management of MS, options for treating relapses have not changed substantially over the past few decades. Corticosteroids, a component of the HPA axis that modulate immune responses and reduce inflammation, are currently the mainstay of relapse treatment. Adrenocorticotropic hormone (ACTH gel is another treatment option. Although it has long been assumed that the efficacy of ACTH in treating relapses depends on the peptide’s ability to increase endogenous corticosteroid production, evidence from research on the melanocortin system suggests that steroidogenesis may only partly account for ACTH influences. Indeed, the melanocortin peptides (ACTH and α-, β-, γ-melanocyte-stimulating hormones [MSH] and their receptors (MCRs exert multiple actions, including modulation of inflammatory and immune mediator production. Melanocortin receptors are widely distributed within the central nervous system and in peripheral tissues including immune cells (eg, macrophages. This suggests that the mechanism of action of ACTH includes not only steroid-mediated indirect effects, but also direct anti-inflammatory and immune-modulating actions via the melanocortin system. An increased understanding of the role of the melanocortin system, particularly ACTH, in the immune and inflammatory processes underlying relapses may help to improve relapse management.

Mechanics and model-based control of advanced engineering systems

CERN Document Server

Irschik, Hans; Krommer, Michael

2014-01-01

Mechanics and Model-Based Control of Advanced Engineering Systems collects 32 contributions presented at the International Workshop on Advanced Dynamics and Model Based Control of Structures and Machines, which took place in St. Petersburg, Russia in July 2012. The workshop continued a series of international workshops, which started with a Japan-Austria Joint Workshop on Mechanics and Model Based Control of Smart Materials and Structures and a Russia-Austria Joint Workshop on Advanced Dynamics and Model Based Control of Structures and Machines. In the present volume, 10 full-length papers based on presentations from Russia, 9 from Austria, 8 from Japan, 3 from Italy, one from Germany and one from Taiwan are included, which represent the state of the art in the field of mechanics and model based control, with particular emphasis on the application of advanced structures and machines.

Modeling Spatial Dependence of Rainfall Extremes Across Multiple Durations

Science.gov (United States)

Le, Phuong Dong; Leonard, Michael; Westra, Seth

2018-03-01

Determining the probability of a flood event in a catchment given that another flood has occurred in a nearby catchment is useful in the design of infrastructure such as road networks that have multiple river crossings. These conditional flood probabilities can be estimated by calculating conditional probabilities of extreme rainfall and then transforming rainfall to runoff through a hydrologic model. Each catchment's hydrological response times are unlikely to be the same, so in order to estimate these conditional probabilities one must consider the dependence of extreme rainfall both across space and across critical storm durations. To represent these types of dependence, this study proposes a new approach for combining extreme rainfall across different durations within a spatial extreme value model using max-stable process theory. This is achieved in a stepwise manner. The first step defines a set of common parameters for the marginal distributions across multiple durations. The parameters are then spatially interpolated to develop a spatial field. Storm-level dependence is represented through the max-stable process for rainfall extremes across different durations. The dependence model shows a reasonable fit between the observed pairwise extremal coefficients and the theoretical pairwise extremal coefficient function across all durations. The study demonstrates how the approach can be applied to develop conditional maps of the return period and return level across different durations.

A model for chemically-induced mechanical loading on MEMS

DEFF Research Database (Denmark)

Amiot, Fabien

2007-01-01

The development of full displacement field measurements as an alternative to the optical lever technique to measure the mechanical response for microelectro-mechanical systems components in their environment calls for a modeling of chemically-induced mechanical fields (stress, strain, and displac......The development of full displacement field measurements as an alternative to the optical lever technique to measure the mechanical response for microelectro-mechanical systems components in their environment calls for a modeling of chemically-induced mechanical fields (stress, strain...... of the system free energy and its dependence on the surface amount. It is solved in the cantilever case thanks to an asymptotic analysis, and an approached closed-form solution is obtained for the interfacial stress field. Finally, some conclusions regarding the transducer efficiency of cantilevers are drawn...

Contraction Options and Optimal Multiple-Stopping in Spectrally Negative Lévy Models

Energy Technology Data Exchange (ETDEWEB)

Yamazaki, Kazutoshi, E-mail: kyamazak@kansai-u.ac.jp [Kansai University, Department of Mathematics, Faculty of Engineering Science (Japan)

2015-08-15

This paper studies the optimal multiple-stopping problem arising in the context of the timing option to withdraw from a project in stages. The profits are driven by a general spectrally negative Lévy process. This allows the model to incorporate sudden declines of the project values, generalizing greatly the classical geometric Brownian motion model. We solve the one-stage case as well as the extension to the multiple-stage case. The optimal stopping times are of threshold-type and the value function admits an expression in terms of the scale function. A series of numerical experiments are conducted to verify the optimality and to evaluate the efficiency of the algorithm.

Contraction Options and Optimal Multiple-Stopping in Spectrally Negative Lévy Models

International Nuclear Information System (INIS)

Yamazaki, Kazutoshi

2015-01-01

This paper studies the optimal multiple-stopping problem arising in the context of the timing option to withdraw from a project in stages. The profits are driven by a general spectrally negative Lévy process. This allows the model to incorporate sudden declines of the project values, generalizing greatly the classical geometric Brownian motion model. We solve the one-stage case as well as the extension to the multiple-stage case. The optimal stopping times are of threshold-type and the value function admits an expression in terms of the scale function. A series of numerical experiments are conducted to verify the optimality and to evaluate the efficiency of the algorithm

Binocular contrast discrimination needs monocular multiplicative noise

Science.gov (United States)

Ding, Jian; Levi, Dennis M.

2016-01-01

The effects of signal and noise on contrast discrimination are difficult to separate because of a singularity in the signal-detection-theory model of two-alternative forced-choice contrast discrimination (Katkov, Tsodyks, & Sagi, 2006). In this article, we show that it is possible to eliminate the singularity by combining that model with a binocular combination model to fit monocular, dichoptic, and binocular contrast discrimination. We performed three experiments using identical stimuli to measure the perceived phase, perceived contrast, and contrast discrimination of a cyclopean sine wave. In the absence of a fixation point, we found a binocular advantage in contrast discrimination both at low contrasts (discrimination mechanisms: a nonlinear contrast transducer and multiplicative noise (MN). A binocular combination model (the DSKL model; Ding, Klein, & Levi, 2013b) was first fitted to both the perceived-phase and the perceived-contrast data sets, then combined with either the nonlinear contrast transducer or the MN mechanism to fit the contrast-discrimination data. We found that the best model combined the DSKL model with early MN. Model simulations showed that, after going through interocular suppression, the uncorrelated noise in the two eyes became anticorrelated, resulting in less binocular noise and therefore a binocular advantage in the discrimination task. Combining a nonlinear contrast transducer or MN with a binocular combination model (DSKL) provides a powerful method for evaluating the two putative contrast-discrimination mechanisms. PMID:26982370

Effect of multiple forming tools on geometrical and mechanical properties in incremental sheet forming

Science.gov (United States)

Wernicke, S.; Dang, T.; Gies, S.; Tekkaya, A. E.

2018-05-01

The tendency to a higher variety of products requires economical manufacturing processes suitable for the production of prototypes and small batches. In the case of complex hollow-shaped parts, single point incremental forming (SPIF) represents a highly flexible process. The flexibility of this process comes along with a very long process time. To decrease the process time, a new incremental forming approach with multiple forming tools is investigated. The influence of two incremental forming tools on the resulting mechanical and geometrical component properties compared to SPIF is presented. Sheets made of EN AW-1050A were formed to frustums of a pyramid using different tool-path strategies. Furthermore, several variations of the tool-path strategy are analyzed. A time saving between 40% and 60% was observed depending on the tool-path and the radii of the forming tools while the mechanical properties remained unchanged. This knowledge can increase the cost efficiency of incremental forming processes.

Continuum mechanics the birthplace of mathematical models

CERN Document Server

Allen, Myron B

2015-01-01

Continuum mechanics is a standard course in many graduate programs in engineering and applied mathematics as it provides the foundations for the various differential equations and mathematical models that are encountered in fluid mechanics, solid mechanics, and heat transfer.  This book successfully makes the topic more accessible to advanced undergraduate mathematics majors by aligning the mathematical notation and language with related courses in multivariable calculus, linear algebra, and differential equations; making connections with other areas of applied mathematics where parial differe

Model Pembelajaran Berbasis Penstimulasian Multiple Intelligences Siswa

Directory of Open Access Journals (Sweden)

Edy Legowo

2017-03-01

Full Text Available Tulisan ini membahas mengenai penerapan teori multiple intelligences dalam pembelajaran di sekolah. Pembahasan diawali dengan menguraikan perkembangan konsep inteligensi dan multiple intelligences. Diikuti dengan menjelaskan dampak teori multiple intelligences dalam bidang pendidikan dan pembelajaran di sekolah. Bagian selanjutnya menguraikan tentang implementasi teori multiple intelligences dalam praktik pembelajaran di kelas yaitu bagaimana pemberian pengalaman belajar siswa yang difasilitasi guru dapat menstimulasi multiple intelligences siswa. Evaluasi hasil belajar siswa dari pandangan penerapan teori multiple intelligences seharusnya dilakukan menggunakan authentic assessment dan portofolio yang lebih memfasilitasi para siswa mengungkapkan atau mengaktualisasikan hasil belajarnya melalui berbagai cara sesuai dengan kekuatan jenis inteligensinya.

Increased multiaxial lumbar motion responses during multiple-impulse mechanical force manually assisted spinal manipulation

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Gunzburg Robert

2006-04-01

Full Text Available Abstract Background Spinal manipulation has been found to create demonstrable segmental and intersegmental spinal motions thought to be biomechanically related to its mechanisms. In the case of impulsive-type instrument device comparisons, significant differences in the force-time characteristics and concomitant motion responses of spinal manipulative instruments have been reported, but studies investigating the response to multiple thrusts (multiple impulse trains have not been conducted. The purpose of this study was to determine multi-axial segmental and intersegmental motion responses of ovine lumbar vertebrae to single impulse and multiple impulse spinal manipulative thrusts (SMTs. Methods Fifteen adolescent Merino sheep were examined. Tri-axial accelerometers were attached to intraosseous pins rigidly fixed to the L1 and L2 lumbar spinous processes under fluoroscopic guidance while the animals were anesthetized. A hand-held electromechanical chiropractic adjusting instrument (Impulse was used to apply single and repeated force impulses (13 total over a 2.5 second time interval at three different force settings (low, medium, and high along the posteroanterior axis of the T12 spinous process. Axial (AX, posteroanterior (PA, and medial-lateral (ML acceleration responses in adjacent segments (L1, L2 were recorded at a rate of 5000 samples per second. Peak-peak segmental accelerations (L1, L2 and intersegmental acceleration transfer (L1–L2 for each axis and each force setting were computed from the acceleration-time recordings. The initial acceleration response for a single thrust and the maximum acceleration response observed during the 12 multiple impulse trains were compared using a paired observations t-test (POTT, alpha = .05. Results Segmental and intersegmental acceleration responses mirrored the peak force magnitude produced by the Impulse Adjusting Instrument. Accelerations were greatest for AX and PA measurement axes. Compared to

A multiple objective mixed integer linear programming model for power generation expansion planning

Energy Technology Data Exchange (ETDEWEB)

Antunes, C. Henggeler; Martins, A. Gomes [INESC-Coimbra, Coimbra (Portugal); Universidade de Coimbra, Dept. de Engenharia Electrotecnica, Coimbra (Portugal); Brito, Isabel Sofia [Instituto Politecnico de Beja, Escola Superior de Tecnologia e Gestao, Beja (Portugal)

2004-03-01

Power generation expansion planning inherently involves multiple, conflicting and incommensurate objectives. Therefore, mathematical models become more realistic if distinct evaluation aspects, such as cost and environmental concerns, are explicitly considered as objective functions rather than being encompassed by a single economic indicator. With the aid of multiple objective models, decision makers may grasp the conflicting nature and the trade-offs among the different objectives in order to select satisfactory compromise solutions. This paper presents a multiple objective mixed integer linear programming model for power generation expansion planning that allows the consideration of modular expansion capacity values of supply-side options. This characteristic of the model avoids the well-known problem associated with continuous capacity values that usually have to be discretized in a post-processing phase without feedback on the nature and importance of the changes in the attributes of the obtained solutions. Demand-side management (DSM) is also considered an option in the planning process, assuming there is a sufficiently large portion of the market under franchise conditions. As DSM full costs are accounted in the model, including lost revenues, it is possible to perform an evaluation of the rate impact in order to further inform the decision process (Author)

Multiplicative Attribute Graph Model of Real-World Networks

Energy Technology Data Exchange (ETDEWEB)

Kim, Myunghwan [Stanford Univ., CA (United States); Leskovec, Jure [Stanford Univ., CA (United States)

2010-10-20

Large scale real-world network data, such as social networks, Internet andWeb graphs, is ubiquitous in a variety of scientific domains. The study of such social and information networks commonly finds patterns and explain their emergence through tractable models. In most networks, especially in social networks, nodes also have a rich set of attributes (e.g., age, gender) associatedwith them. However, most of the existing network models focus only on modeling the network structure while ignoring the features of nodes in the network. Here we present a class of network models that we refer to as the Multiplicative Attribute Graphs (MAG), which naturally captures the interactions between the network structure and node attributes. We consider a model where each node has a vector of categorical features associated with it. The probability of an edge between a pair of nodes then depends on the product of individual attributeattribute similarities. The model yields itself to mathematical analysis as well as fit to real data. We derive thresholds for the connectivity, the emergence of the giant connected component, and show that the model gives rise to graphs with a constant diameter. Moreover, we analyze the degree distribution to show that the model can produce networks with either lognormal or power-law degree distribution depending on certain conditions.

Analysis of the benefits of designing and implementing a virtual didactic model of multiple choice exam and problem-solving heuristic report, for first year engineering students

OpenAIRE

Bennun, Leonardo; Santibanez, Mauricio

2015-01-01

Improvements in performance and approval obtained by first year engineering students from University of Concepcion, Chile, were studied, once a virtual didactic model of multiple-choice exam, was implemented. This virtual learning resource was implemented in the Web ARCO platform and allows training, by facing test models comparable in both time and difficulty to those that they will have to solve during the course. It also provides a feedback mechanism for both: 1) The students, since they c...

Towards an automatic model transformation mechanism from UML state machines to DEVS models

Directory of Open Access Journals (Sweden)

Ariel González

2015-08-01

Full Text Available The development of complex event-driven systems requires studies and analysis prior to deployment with the goal of detecting unwanted behavior. UML is a language widely used by the software engineering community for modeling these systems through state machines, among other mechanisms. Currently, these models do not have appropriate execution and simulation tools to analyze the real behavior of systems. Existing tools do not provide appropriate libraries (sampling from a probability distribution, plotting, etc. both to build and to analyze models. Modeling and simulation for design and prototyping of systems are widely used techniques to predict, investigate and compare the performance of systems. In particular, the Discrete Event System Specification (DEVS formalism separates the modeling and simulation; there are several tools available on the market that run and collect information from DEVS models. This paper proposes a model transformation mechanism from UML state machines to DEVS models in the Model-Driven Development (MDD context, through the declarative QVT Relations language, in order to perform simulations using tools, such as PowerDEVS. A mechanism to validate the transformation is proposed. Moreover, examples of application to analyze the behavior of an automatic banking machine and a control system of an elevator are presented.

Anti-inflammatory mechanisms of IFN-γ studied in experimental autoimmune encephalomyelitis reveal neutrophils as a potential target in multiple sclerosis

Directory of Open Access Journals (Sweden)

Nichole M Miller

2015-08-01

Full Text Available Multiple sclerosis (MS is an autoimmune disease of the central nervous system (CNS mediated by T helper (h1 and/or Th17 CD4 T cells that drive inflammatory lesion development along with demyelination and neuronal damage. Defects in immune regulatory mechanisms are thought to play a role in the pathogenesis of MS. While an early clinical trial indicated that IFN-γ administration was detrimental to MS, studies in the mouse model of MS, experimental autoimmune encephalomyelitis (EAE, indicated that IFN-γ exhibits a number of anti-inflammatory properties within the CNS. These mechanisms include inhibition of IL-17 production, induction of regulatory T cells, T cell apoptosis and regulation of chemokine production. Mice deficient in IFN-γ or its receptor were instrumental in deciphering the anti-inflammatory properties of IFN-γ in the CNS. In particular, they revealed that IFN-γ is a major regulator of neutrophil recruitment into the CNS, which by a variety of mechanisms including disruption of the blood-brain-barrier (BBB and production of reactive oxygen species are thought to contribute to the onset and progression of EAE. Neutrophils were also shown to be instrumental in EAE relapses. To date neutrophils have not been appreciated as a driver of MS, but more recently based largely on the strong EAE data this view is being reevaluated by some investigators in the field.

Prediction Model of Mechanical Extending Limits in Horizontal Drilling and Design Methods of Tubular Strings to Improve Limits

Directory of Open Access Journals (Sweden)

Wenjun Huang

2017-01-01

Full Text Available Mechanical extending limit in horizontal drilling means the maximum horizontal extending length of a horizontal well under certain ground and down-hole mechanical constraint conditions. Around this concept, the constrained optimization model of mechanical extending limits is built and simplified analytical results for pick-up and slack-off operations are deduced. The horizontal extending limits for kinds of tubular strings under different drilling parameters are calculated and drawn. To improve extending limits, an optimal design model of drill strings is built and applied to a case study. The results indicate that horizontal extending limits are underestimated a lot when the effects of friction force on critical helical buckling loads are neglected. Horizontal extending limits firstly increase and tend to stable values with vertical depths. Horizontal extending limits increase faster but finally become smaller with the increase of horizontal pushing forces for tubular strings of smaller modulus-weight ratio. Sliding slack-off is the main limit operation and high axial friction is the main constraint factor constraining horizontal extending limits. A sophisticated installation of multiple tubular strings can greatly inhibit helical buckling and increase horizontal extending limits. The optimal design model is called only once to obtain design results, which greatly increases the calculation efficiency.

An electro-mechanical impedance model of a cracked composite beam with adhesively bonded piezoelectric patches

Science.gov (United States)

Yan, Wei; Cai, J. B.; Chen, W. Q.

2011-01-01

A model of a laminated composite beam including multiple non-propagating part-through surface cracks as well as installed PZT transducers is presented based on the method of reverberation-ray matrix (MRRM) in this paper. Toward determining the local flexibility characteristics induced by the individual cracks, the concept of the massless rotational spring is applied. A Timoshenko beam theory is then used to simulate the behavior of the composite beam with open cracks. As a result, transverse shear and rotatory inertia effects are included in the model. Only one-dimensional axial vibration of the PZT wafer is considered and the imperfect interfacial bonding between PZT patches and the host beam is further investigated based on a Kelvin-type viscoelastic model. Then, an accurate electro-mechanical impedance (EMI) model can be established for crack detection in laminated beams. In this model, the effects of various parameters such as the ply-angle, fibre volume fraction, crack depth and position on the EMI signatures are highlighted. Furthermore, comparison with existent numerical results is presented to validate the present analysis.

INCORPORATING MULTIPLE OBJECTIVES IN PLANNING MODELS OF LOW-RESOURCE FARMERS

OpenAIRE

Flinn, John C.; Jayasuriya, Sisira; Knight, C. Gregory

1980-01-01

Linear goal programming provides a means of formally incorporating the multiple goals of a household into the analysis of farming systems. Using this approach, the set of plans which come as close as possible to achieving a set of desired goals under conditions of land and cash scarcity are derived for a Filipino tenant farmer. A challenge in making LGP models empirically operational is the accurate definition of the goals of the farm household being modelled.

Problem solving based learning model with multiple representations to improve student's mental modelling ability on physics

Science.gov (United States)

Haili, Hasnawati; Maknun, Johar; Siahaan, Parsaoran

2017-08-01

Physics is a lessons that related to students' daily experience. Therefore, before the students studying in class formally, actually they have already have a visualization and prior knowledge about natural phenomenon and could wide it themselves. The learning process in class should be aimed to detect, process, construct, and use students' mental model. So, students' mental model agree with and builds in the right concept. The previous study held in MAN 1 Muna informs that in learning process the teacher did not pay attention students' mental model. As a consequence, the learning process has not tried to build students' mental modelling ability (MMA). The purpose of this study is to describe the improvement of students' MMA as a effect of problem solving based learning model with multiple representations approach. This study is pre experimental design with one group pre post. It is conducted in XI IPA MAN 1 Muna 2016/2017. Data collection uses problem solving test concept the kinetic theory of gasses and interview to get students' MMA. The result of this study is clarification students' MMA which is categorized in 3 category; High Mental Modelling Ability (H-MMA) for 7Mental Modelling Ability (M-MMA) for 3Mental Modelling Ability (L-MMA) for 0 ≤ x ≤ 3 score. The result shows that problem solving based learning model with multiple representations approach can be an alternative to be applied in improving students' MMA.

Exploring the Use of Multiple Analogical Models when Teaching and Learning Chemical Equilibrium

Science.gov (United States)

Harrison, Allan G.; De Jong, Onno

2005-01-01

This study describes the multiple analogical models used to introduce and teach Grade 12 chemical equilibrium. We examine the teacher's reasons for using models, explain each model's development during the lessons, and analyze the understandings students derived from the models. A case study approach was used and the data were drawn from the…

Medicare capitation model, functional status, and multiple comorbidities: model accuracy

Science.gov (United States)

Noyes, Katia; Liu, Hangsheng; Temkin-Greener, Helena

2012-01-01

Objective This study examined financial implications of CMS-Hierarchical Condition Categories (HCC) risk-adjustment model on Medicare payments for individuals with comorbid chronic conditions. Study Design The study used 1992-2000 data from the Medicare Current Beneficiary Survey and corresponding Medicare claims. The pairs of comorbidities were formed based on the prior evidence about possible synergy between these conditions and activities of daily living (ADL) deficiencies and included heart disease and cancer, lung disease and cancer, stroke and hypertension, stroke and arthritis, congestive heart failure (CHF) and osteoporosis, diabetes and coronary artery disease, CHF and dementia. Methods For each beneficiary, we calculated the actual Medicare cost ratio as the ratio of the individual’s annualized costs to the mean annual Medicare cost of all people in the study. The actual Medicare cost ratios, by ADLs, were compared to the HCC ratios under the CMS-HCC payment model. Using multivariate regression models, we tested whether having the identified pairs of comorbidities affects the accuracy of CMS-HCC model predictions. Results The CMS-HCC model underpredicted Medicare capitation payments for patients with hypertension, lung disease, congestive heart failure and dementia. The difference between the actual costs and predicted payments was partially explained by beneficiary functional status and less than optimal adjustment for these chronic conditions. Conclusions Information about beneficiary functional status should be incorporated in reimbursement models since underpaying providers for caring for population with multiple comorbidities may provide severe disincentives for managed care plans to enroll such individuals and to appropriately manage their complex and costly conditions. PMID:18837646

Mathematical Modeling of Protein Misfolding Mechanisms in Neurological Diseases: A Historical Overview.

Science.gov (United States)

Carbonell, Felix; Iturria-Medina, Yasser; Evans, Alan C

2018-01-01

Protein misfolding refers to a process where proteins become structurally abnormal and lose their specific 3-dimensional spatial configuration. The histopathological presence of misfolded protein (MP) aggregates has been associated as the primary evidence of multiple neurological diseases, including Prion diseases, Alzheimer's disease, Parkinson's disease, and Creutzfeldt-Jacob disease. However, the exact mechanisms of MP aggregation and propagation, as well as their impact in the long-term patient's clinical condition are still not well understood. With this aim, a variety of mathematical models has been proposed for a better insight into the kinetic rate laws that govern the microscopic processes of protein aggregation. Complementary, another class of large-scale models rely on modern molecular imaging techniques for describing the phenomenological effects of MP propagation over the whole brain. Unfortunately, those neuroimaging-based studies do not take full advantage of the tremendous capabilities offered by the chemical kinetics modeling approach. Actually, it has been barely acknowledged that the vast majority of large-scale models have foundations on previous mathematical approaches that describe the chemical kinetics of protein replication and propagation. The purpose of the current manuscript is to present a historical review about the development of mathematical models for describing both microscopic processes that occur during the MP aggregation and large-scale events that characterize the progression of neurodegenerative MP-mediated diseases.

Fracture mechanics model of fragmentation

International Nuclear Information System (INIS)

Glenn, L.A.; Gommerstadt, B.Y.; Chudnovsky, A.

1986-01-01

A model of the fragmentation process is developed, based on the theory of linear elastic fracture mechanics, which predicts the average fragment size as a function of strain rate and material properties. This approach permits a unification of previous results, yielding Griffith's solution in the low-strain-rate limit and Grady's solution at high strain rates

On the identification of multiple space dependent ionic parameters in cardiac electrophysiology modelling

Science.gov (United States)

Abidi, Yassine; Bellassoued, Mourad; Mahjoub, Moncef; Zemzemi, Nejib

2018-03-01

In this paper, we consider the inverse problem of space dependent multiple ionic parameters identification in cardiac electrophysiology modelling from a set of observations. We use the monodomain system known as a state-of-the-art model in cardiac electrophysiology and we consider a general Hodgkin-Huxley formalism to describe the ionic exchanges at the microscopic level. This formalism covers many physiological transmembrane potential models including those in cardiac electrophysiology. Our main result is the proof of the uniqueness and a Lipschitz stability estimate of ion channels conductance parameters based on some observations on an arbitrary subdomain. The key idea is a Carleman estimate for a parabolic operator with multiple coefficients and an ordinary differential equation system.

Learned helplessness, discouraged workers, and multiple unemployment equilibria in a search model

OpenAIRE

Bjørnstad, Roger

2001-01-01

Abstract: Unemployment varies strongly between countries with comparable economic structure. Some economists have tried to explain these differences with institutional differences in the labour market. Instead, this paper focuses on a model with multiple equilibria so that the same socioeconomic structure can give rise to different levels of unemployment. Unemployed workers' search efficiency are modelled within an equilibrium search model and lay behind these results. In the model learned...

Open Business Models: New Compensation Mechanisms for ...

International Development Research Centre (IDRC) Digital Library (Canada)

Open Business Models: New Compensation Mechanisms for Creativity and Inclusion ... This research aims to explore important new business models in the networked society ... Linking research to urban planning at the ICLEI World Congress 2018 ... In partnership with UNESCO's Organization for Women in Science for the ...

Multiple Authorities Attribute-Based Verification Mechanism for Blockchain Mircogrid Transactions

Directory of Open Access Journals (Sweden)

Sarmadullah Khan

2018-05-01

Full Text Available Recently, advancements in energy distribution models have fulfilled the needs of microgrids in finding a suitable energy distribution model between producer and consumer without the need of central controlling authority. Most of the energy distribution model deals with energy transactions and losses without considering the security aspects such as information tampering. The transaction data could be accessible online to keep track of the energy distribution between the consumer and producer (e.g., online payment records and supplier profiles. However this data is prone to modification and misuse if a consumer moves from one producer to other. Blockchain is considered to be one solution to allow users to exchange energy related data and keep track of it without exposing it to modification. In this paper, electrical transactions embedded in blockchain are validated using the signatures of multiple producers based on their assigned attributes. These signatures are verified and endorsed by the consumers satisfying those attributes without revealing any information. The public and private keys for these consumers are generated by the producers and endorsement procedure using these keys ensures that these consumers are authorized. This approach does not need any central authority. To resist against collision attacks, producers are given a secret pseudorandom function seed. The comparative analysis shows the efficiency of proposed approach over the existing ones.

The effects of a driving mechanism on Oslo models

International Nuclear Information System (INIS)

Pan, Gui-Jun; Pan, Yong-Cai

2010-01-01

Isotropic and anisotropic Oslo models (IOM and AOM) under a bulk driving mechanism have been investigated. We apply the moment analysis to evaluate critical exponents and the finite size scaling method to consistently test the obtained results. We find that both types of Oslo model have different critical behaviour. However, the critical exponents are the same for deterministic and random IOMs, and are independent of the strength of the anisotropy for the AOM. In contrast to a boundary driving mechanism, we find that the critical exponents depend crucially on the driving mechanism for the IOM, and are independent of the driving mechanism for the AOM.

Fast analytical model of MZI micro-opto-mechanical pressure sensor

Science.gov (United States)

Rochus, V.; Jansen, R.; Goyvaerts, J.; Neutens, P.; O’Callaghan, J.; Rottenberg, X.

2018-06-01

This paper presents a fast analytical procedure in order to design a micro-opto-mechanical pressure sensor (MOMPS) taking into account the mechanical nonlinearity and the optical losses. A realistic model of the photonic MZI is proposed, strongly coupled to a nonlinear mechanical model of the membrane. Based on the membrane dimensions, the residual stress, the position of the waveguide, the optical wavelength and the phase variation due to the opto-mechanical coupling, we derive an analytical model which allows us to predict the response of the total system. The effect of the nonlinearity and the losses on the total performance are carefully studied and measurements on fabricated devices are used to validate the model. Finally, a design procedure is proposed in order to realize fast design of this new type of pressure sensor.

Quality-Aware Incentive Mechanism for Mobile Crowd Sensing

Directory of Open Access Journals (Sweden)

Ling-Yun Jiang

2017-01-01

Full Text Available Mobile crowd sensing (MCS is a novel sensing paradigm which can sense human-centered daily activities and the surrounding environment. The impact of mobility and selfishness of participants on the data reliability cannot be ignored in most mobile crowd sensing systems. To address this issue, we present a universal system model based on the reverse auction framework and formulate the problem as the Multiple Quality Multiple User Selection (MQMUS problem. The quality-aware incentive mechanism (QAIM is proposed to meet the quality requirement of data reliability. We demonstrate that the proposed incentive mechanism achieves the properties of computational efficiency, individual rationality, and truthfulness. And meanwhile, we evaluate the performance and validate the theoretical properties of our incentive mechanism through extensive simulation experiments.

Model Pembelajaran Berbasis Penstimulasian Multiple Intelligences Siswa

OpenAIRE

Edy Legowo

2017-01-01

Tulisan ini membahas mengenai penerapan teori multiple intelligences dalam pembelajaran di sekolah. Pembahasan diawali dengan menguraikan perkembangan konsep inteligensi dan multiple intelligences. Diikuti dengan menjelaskan dampak teori multiple intelligences dalam bidang pendidikan dan pembelajaran di sekolah. Bagian selanjutnya menguraikan tentang implementasi teori multiple intelligences dalam praktik pembelajaran di kelas yaitu bagaimana pemberian pengalaman belajar siswa yang difasilita...

Toy Models of a Nonassociative Quantum Mechanics

International Nuclear Information System (INIS)

Dzhunushaliev, V.

2007-01-01

Toy models of a nonassociative quantum mechanics are presented. The Heisenberg equation of motion is modified using a nonassociative commutator. Possible physical applications of a nonassociative quantum mechanics are considered. The idea is discussed that a nonassociative algebra could be the operator language for the nonperturbative quantum theory. In such approach the nonperturbative quantum theory has observables and un observables quantities.

Skewed factor models using selection mechanisms

KAUST Repository

Kim, Hyoung-Moon

2015-12-21

Traditional factor models explicitly or implicitly assume that the factors follow a multivariate normal distribution; that is, only moments up to order two are involved. However, it may happen in real data problems that the first two moments cannot explain the factors. Based on this motivation, here we devise three new skewed factor models, the skew-normal, the skew-tt, and the generalized skew-normal factor models depending on a selection mechanism on the factors. The ECME algorithms are adopted to estimate related parameters for statistical inference. Monte Carlo simulations validate our new models and we demonstrate the need for skewed factor models using the classic open/closed book exam scores dataset.

Skewed factor models using selection mechanisms

KAUST Repository

Kim, Hyoung-Moon; Maadooliat, Mehdi; Arellano-Valle, Reinaldo B.; Genton, Marc G.

2015-01-01

Traditional factor models explicitly or implicitly assume that the factors follow a multivariate normal distribution; that is, only moments up to order two are involved. However, it may happen in real data problems that the first two moments cannot explain the factors. Based on this motivation, here we devise three new skewed factor models, the skew-normal, the skew-tt, and the generalized skew-normal factor models depending on a selection mechanism on the factors. The ECME algorithms are adopted to estimate related parameters for statistical inference. Monte Carlo simulations validate our new models and we demonstrate the need for skewed factor models using the classic open/closed book exam scores dataset.

Second-Generation Non-Covalent NAAA Inhibitors are Protective in a Model of Multiple Sclerosis.

Science.gov (United States)

Migliore, Marco; Pontis, Silvia; Fuentes de Arriba, Angel Luis; Realini, Natalia; Torrente, Esther; Armirotti, Andrea; Romeo, Elisa; Di Martino, Simona; Russo, Debora; Pizzirani, Daniela; Summa, Maria; Lanfranco, Massimiliano; Ottonello, Giuliana; Busquet, Perrine; Jung, Kwang-Mook; Garcia-Guzman, Miguel; Heim, Roger; Scarpelli, Rita; Piomelli, Daniele

2016-09-05

Palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) are endogenous lipid mediators that suppress inflammation. Their actions are terminated by the intracellular cysteine amidase, N-acylethanolamine acid amidase (NAAA). Even though NAAA may offer a new target for anti-inflammatory therapy, the lipid-like structures and reactive warheads of current NAAA inhibitors limit the use of these agents as oral drugs. A series of novel benzothiazole-piperazine derivatives that inhibit NAAA in a potent and selective manner by a non-covalent mechanism are described. A prototype member of this class (8) displays high oral bioavailability, access to the central nervous system (CNS), and strong activity in a mouse model of multiple sclerosis (MS). This compound exemplifies a second generation of non-covalent NAAA inhibitors that may be useful in the treatment of MS and other chronic CNS disorders. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Obesity resistance and multiple mechanisms of triglyceride synthesis in mice lacking Dgat.

Science.gov (United States)

Smith, S J; Cases, S; Jensen, D R; Chen, H C; Sande, E; Tow, B; Sanan, D A; Raber, J; Eckel, R H; Farese, R V

2000-05-01

Triglycerides (or triacylglycerols) represent the major form of stored energy in eukaryotes. Triglyceride synthesis has been assumed to occur primarily through acyl CoA:diacylglycerol transferase (Dgat), a microsomal enzyme that catalyses the final and only committed step in the glycerol phosphate pathway. Therefore, Dgat has been considered necessary for adipose tissue formation and essential for survival. Here we show that Dgat-deficient (Dgat-/-) mice are viable and can still synthesize triglycerides. Moreover, these mice are lean and resistant to diet-induced obesity. The obesity resistance involves increased energy expenditure and increased activity. Dgat deficiency also alters triglyceride metabolism in other tissues, including the mammary gland, where lactation is defective in Dgat-/- females. Our findings indicate that multiple mechanisms exist for triglyceride synthesis and suggest that the selective inhibition of Dgat-mediated triglyceride synthesis may be useful for treating obesity.

Exploring potential mechanisms of action of natalizumab in secondary progressive multiple sclerosis

DEFF Research Database (Denmark)

Sellebjerg, Finn; Cadavid, Diego; Steiner, Deborah

2016-01-01

progressive MS (SPMS), for which approved disease-modifying therapies are limited. In this review, we summarize the pathophysiological mechanisms involved in the development of SPMS and the rationale and clinical potential for natalizumab, which is currently approved for the treatment of relapsing forms of MS......Multiple sclerosis (MS) is a common and chronic central nervous system (CNS) demyelinating disease and a leading cause of permanent disability. Patients most often present with a relapsing-remitting disease course, typically progressing over time to a phase of relentless advancement in secondary......, to exert beneficial effects in reducing disease progression unrelated to relapses in SPMS. In both forms of MS, active brain-tissue injury is associated with inflammation; but in SPMS, the inflammatory response occurs at least partly behind the blood-brain barrier and is followed by a cascade of events...

Impedance model for quantum-mechanical barrier problems

International Nuclear Information System (INIS)

Nelin, Evgenii A

2007-01-01

Application of the impedance model to typical quantum-mechanical barrier problems, including those for structures with resonant electron tunneling, is discussed. The efficiency of the approach is illustrated. The physical transparency and compactness of the model and its potential as a teaching and learning tool are discussed. (methodological notes)

Searching for Variables and Models to Investigate Mediators of Learning from Multiple Representations

Science.gov (United States)

Rau, Martina A.; Scheines, Richard

2012-01-01

Although learning from multiple representations has been shown to be effective in a variety of domains, little is known about the mechanisms by which it occurs. We analyzed log data on error-rate, hint-use, and time-spent obtained from two experiments with a Cognitive Tutor for fractions. The goal of the experiments was to compare learning from…

Testing effect of a drug using multiple nested models for the dose–response

DEFF Research Database (Denmark)

Baayen, C.; Hougaard, P.; Pipper, C. B.

2015-01-01

of the assumed dose–response model. Bretz et al. (2005, Biometrics 61, 738–748) suggested a combined approach, which selects one or more suitable models from a set of candidate models using a multiple comparison procedure. The method initially requires a priori estimates of any non-linear parameters...

Heat Recovery from Multiple-Fracture Enhanced Geothermal Systems: The Effect of Thermoelastic Fracture Interactions

DEFF Research Database (Denmark)

Vik, Hedda Slatlem; Salimzadeh, Saeed; Nick, Hamid

2018-01-01

This study investigates the effect of thermoelastic interactions between multiple parallel fractures on energy production from a multiple-fracture enhanced geothermal system. A coupled thermo-hydro-mechanical finite element model has been developed that accounts for non-isothermal fluid flow within...... increased to maximise the net energy production from the system. Otherwise, the multiple-fracture system fails to improve the energy recovery from the geothermal reservoir, as initially intended....... aperture in the adjacent fracture, and facilitates the creation of favourable flow pathways between the injection and production wells. These flow paths reduce the energy production from the system. The effects of fracture spacing, reservoir temperature gradient and mechanical properties of the rock matrix...

A discrete model to study reaction-diffusion-mechanics systems.

Science.gov (United States)

Weise, Louis D; Nash, Martyn P; Panfilov, Alexander V

2011-01-01

This article introduces a discrete reaction-diffusion-mechanics (dRDM) model to study the effects of deformation on reaction-diffusion (RD) processes. The dRDM framework employs a FitzHugh-Nagumo type RD model coupled to a mass-lattice model, that undergoes finite deformations. The dRDM model describes a material whose elastic properties are described by a generalized Hooke's law for finite deformations (Seth material). Numerically, the dRDM approach combines a finite difference approach for the RD equations with a Verlet integration scheme for the equations of the mass-lattice system. Using this framework results were reproduced on self-organized pacemaking activity that have been previously found with a continuous RD mechanics model. Mechanisms that determine the period of pacemakers and its dependency on the medium size are identified. Finally it is shown how the drift direction of pacemakers in RDM systems is related to the spatial distribution of deformation and curvature effects.

A discrete model to study reaction-diffusion-mechanics systems.

Directory of Open Access Journals (Sweden)

Louis D Weise

Full Text Available This article introduces a discrete reaction-diffusion-mechanics (dRDM model to study the effects of deformation on reaction-diffusion (RD processes. The dRDM framework employs a FitzHugh-Nagumo type RD model coupled to a mass-lattice model, that undergoes finite deformations. The dRDM model describes a material whose elastic properties are described by a generalized Hooke's law for finite deformations (Seth material. Numerically, the dRDM approach combines a finite difference approach for the RD equations with a Verlet integration scheme for the equations of the mass-lattice system. Using this framework results were reproduced on self-organized pacemaking activity that have been previously found with a continuous RD mechanics model. Mechanisms that determine the period of pacemakers and its dependency on the medium size are identified. Finally it is shown how the drift direction of pacemakers in RDM systems is related to the spatial distribution of deformation and curvature effects.

A new spatial multiple discrete-continuous modeling approach to land use change analysis.

Science.gov (United States)

2013-09-01

This report formulates a multiple discrete-continuous probit (MDCP) land-use model within a : spatially explicit economic structural framework for land-use change decisions. The spatial : MDCP model is capable of predicting both the type and intensit...

Using hidden Markov models to align multiple sequences.

Science.gov (United States)

Mount, David W

2009-07-01

A hidden Markov model (HMM) is a probabilistic model of a multiple sequence alignment (msa) of proteins. In the model, each column of symbols in the alignment is represented by a frequency distribution of the symbols (called a "state"), and insertions and deletions are represented by other states. One moves through the model along a particular path from state to state in a Markov chain (i.e., random choice of next move), trying to match a given sequence. The next matching symbol is chosen from each state, recording its probability (frequency) and also the probability of going to that state from a previous one (the transition probability). State and transition probabilities are multiplied to obtain a probability of the given sequence. The hidden nature of the HMM is due to the lack of information about the value of a specific state, which is instead represented by a probability distribution over all possible values. This article discusses the advantages and disadvantages of HMMs in msa and presents algorithms for calculating an HMM and the conditions for producing the best HMM.

Hair length, facial attractiveness, personality attribution: A multiple fitness model of hairdressing

OpenAIRE

Bereczkei, Tamas; Mesko, Norbert

2007-01-01

Multiple Fitness Model states that attractiveness varies across multiple dimensions, with each feature representing a different aspect of mate value. In the present study, male raters judged the attractiveness of young females with neotenous and mature facial features, with various hair lengths. Results revealed that the physical appearance of long-haired women was rated high, regardless of their facial attractiveness being valued high or low. Women rated as most attractive were those whose f...

Steam consumption minimization model in a multiple evaporation effect in a sugar plant

International Nuclear Information System (INIS)

Villada, Fernando; Valencia, Jaime A; Moreno, German; Murillo, J. Joaquin

1992-01-01

In this work, a mathematical model to minimize the steam consumption in a multiple effect evaporation system is shown. The model is based in the dynamic programming technique and the results are tested in a Colombian sugar mill

Quantum Mechanical Modeling of Ballistic MOSFETs

Science.gov (United States)

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.

Eikonal multiple scattering model within the framework of Feynman's positron theory

International Nuclear Information System (INIS)

Tekou, A.

1986-07-01

The Bethe Salpeter equation for nucleon-nucleon, nucleon-nucleus and nucleus-nucleus scattering is eikonalized. Multiple scattering series is obtained. Contributions of three body interations are included. The model presented below may be used to investigate atomic collisions. (author)

A novel variational Bayes multiple locus Z-statistic for genome-wide association studies with Bayesian model averaging

Science.gov (United States)

Logsdon, Benjamin A.; Carty, Cara L.; Reiner, Alexander P.; Dai, James Y.; Kooperberg, Charles

2012-01-01

Motivation: For many complex traits, including height, the majority of variants identified by genome-wide association studies (GWAS) have small effects, leaving a significant proportion of the heritable variation unexplained. Although many penalized multiple regression methodologies have been proposed to increase the power to detect associations for complex genetic architectures, they generally lack mechanisms for false-positive control and diagnostics for model over-fitting. Our methodology is the first penalized multiple regression approach that explicitly controls Type I error rates and provide model over-fitting diagnostics through a novel normally distributed statistic defined for every marker within the GWAS, based on results from a variational Bayes spike regression algorithm. Results: We compare the performance of our method to the lasso and single marker analysis on simulated data and demonstrate that our approach has superior performance in terms of power and Type I error control. In addition, using the Women's Health Initiative (WHI) SNP Health Association Resource (SHARe) GWAS of African-Americans, we show that our method has power to detect additional novel associations with body height. These findings replicate by reaching a stringent cutoff of marginal association in a larger cohort. Availability: An R-package, including an implementation of our variational Bayes spike regression (vBsr) algorithm, is available at http://kooperberg.fhcrc.org/soft.html. Contact: blogsdon@fhcrc.org Supplementary information: Supplementary data are available at Bioinformatics online. PMID:22563072

Mechanical characterization and constitutive modeling of Mg alloy sheets

International Nuclear Information System (INIS)

Mekonen, M. Nebebe; Steglich, D.; Bohlen, J.; Letzig, D.; Mosler, J.

2012-01-01

Highlights: ► Material characterization of the Mg alloys AZ31 and ZE10 at elevated temperatures. ► Distortion of the yield locus does not depend on the strain rate. ► Novel constitutive model suitable for the analysis of sheet forming of magnesium. ► Strain-dependent r-values are included within the model. ► The model is thermodynamically consistent and accounts for distortional hardening. - Abstract: In this paper, an experimental mechanical characterization of the magnesium alloys ZE10 and AZ31 is performed and a suitable constitutive model is established. The mechanical characterization is based on uniaxial tensile tests. In order to avoid poor formability at room temperature, the tests were conducted at elevated temperature (200 °C). The uniaxial tensile tests reveal sufficient ductility allowing sheet forming processes at this temperature. The differences in yield stresses and plastic strain ratios (r-values) confirm the anisotropic response of the materials under study. The constitutive model is established so that the characteristic mechanical features observed in magnesium alloys such as anisotropy and compression-tension asymmetry can be accommodated. This model is thermodynamically consistent, incorporates rate effect, is formulated based on finite strain plasticity theory and is applicable in sheet forming simulations of magnesium alloys. More precisely, a model originally proposed by Cazacu and Barlat in 2004 and later modified to account for the evolution of the material anisotropy is rewritten in a thermodynamically consistent framework. The calibrated constitutive model is shown to capture the characteristic mechanical features observed in magnesium alloy sheets.

Integrated assessment by multiple gene expression analysis of quercetin bioactivity on anticancer-related mechanisms in colon cancer cells in vitro

NARCIS (Netherlands)

Erk, van M.J.; Roepman, P.; Lende, van der T.R.; Stierum, R.H.; Aarts, J.M.M.J.G.; Bladeren, van P.J.; Ommen, van B.

2005-01-01

Background Many different mechanisms are involved in nutrient¿related prevention of colon cancer. In this study, a comprehensive assessment of the spectrum of possible biological actions of the bioactive compound quercetin is made using multiple gene expression analysis. Quercetin is a flavonoid

A multiple relevance feedback strategy with positive and negative models.

Directory of Open Access Journals (Sweden)

Yunlong Ma

Full Text Available A commonly used strategy to improve search accuracy is through feedback techniques. Most existing work on feedback relies on positive information, and has been extensively studied in information retrieval. However, when a query topic is difficult and the results from the first-pass retrieval are very poor, it is impossible to extract enough useful terms from a few positive documents. Therefore, the positive feedback strategy is incapable to improve retrieval in this situation. Contrarily, there is a relatively large number of negative documents in the top of the result list, and it has been confirmed that negative feedback strategy is an important and useful way for adapting this scenario by several recent studies. In this paper, we consider a scenario when the search results are so poor that there are at most three relevant documents in the top twenty documents. Then, we conduct a novel study of multiple strategies for relevance feedback using both positive and negative examples from the first-pass retrieval to improve retrieval accuracy for such difficult queries. Experimental results on these TREC collections show that the proposed language model based multiple model feedback method which is generally more effective than both the baseline method and the methods using only positive or negative model.

Protein Structure Classification and Loop Modeling Using Multiple Ramachandran Distributions

KAUST Repository

Najibi, Seyed Morteza; Maadooliat, Mehdi; Zhou, Lan; Huang, Jianhua Z.; Gao, Xin

2017-01-01

Recently, the study of protein structures using angular representations has attracted much attention among structural biologists. The main challenge is how to efficiently model the continuous conformational space of the protein structures based on the differences and similarities between different Ramachandran plots. Despite the presence of statistical methods for modeling angular data of proteins, there is still a substantial need for more sophisticated and faster statistical tools to model the large-scale circular datasets. To address this need, we have developed a nonparametric method for collective estimation of multiple bivariate density functions for a collection of populations of protein backbone angles. The proposed method takes into account the circular nature of the angular data using trigonometric spline which is more efficient compared to existing methods. This collective density estimation approach is widely applicable when there is a need to estimate multiple density functions from different populations with common features. Moreover, the coefficients of adaptive basis expansion for the fitted densities provide a low-dimensional representation that is useful for visualization, clustering, and classification of the densities. The proposed method provides a novel and unique perspective to two important and challenging problems in protein structure research: structure-based protein classification and angular-sampling-based protein loop structure prediction.

Protein Structure Classification and Loop Modeling Using Multiple Ramachandran Distributions

KAUST Repository

Najibi, Seyed Morteza

2017-02-08

Recently, the study of protein structures using angular representations has attracted much attention among structural biologists. The main challenge is how to efficiently model the continuous conformational space of the protein structures based on the differences and similarities between different Ramachandran plots. Despite the presence of statistical methods for modeling angular data of proteins, there is still a substantial need for more sophisticated and faster statistical tools to model the large-scale circular datasets. To address this need, we have developed a nonparametric method for collective estimation of multiple bivariate density functions for a collection of populations of protein backbone angles. The proposed method takes into account the circular nature of the angular data using trigonometric spline which is more efficient compared to existing methods. This collective density estimation approach is widely applicable when there is a need to estimate multiple density functions from different populations with common features. Moreover, the coefficients of adaptive basis expansion for the fitted densities provide a low-dimensional representation that is useful for visualization, clustering, and classification of the densities. The proposed method provides a novel and unique perspective to two important and challenging problems in protein structure research: structure-based protein classification and angular-sampling-based protein loop structure prediction.

Sequential optimization of a terrestrial biosphere model constrained by multiple satellite based products

Science.gov (United States)

Ichii, K.; Kondo, M.; Wang, W.; Hashimoto, H.; Nemani, R. R.

2012-12-01

Various satellite-based spatial products such as evapotranspiration (ET) and gross primary productivity (GPP) are now produced by integration of ground and satellite observations. Effective use of these multiple satellite-based products in terrestrial biosphere models is an important step toward better understanding of terrestrial carbon and water cycles. However, due to the complexity of terrestrial biosphere models with large number of model parameters, the application of these spatial data sets in terrestrial biosphere models is difficult. In this study, we established an effective but simple framework to refine a terrestrial biosphere model, Biome-BGC, using multiple satellite-based products as constraints. We tested the framework in the monsoon Asia region covered by AsiaFlux observations. The framework is based on the hierarchical analysis (Wang et al. 2009) with model parameter optimization constrained by satellite-based spatial data. The Biome-BGC model is separated into several tiers to minimize the freedom of model parameter selections and maximize the independency from the whole model. For example, the snow sub-model is first optimized using MODIS snow cover product, followed by soil water sub-model optimized by satellite-based ET (estimated by an empirical upscaling method; Support Vector Regression (SVR) method; Yang et al. 2007), photosynthesis model optimized by satellite-based GPP (based on SVR method), and respiration and residual carbon cycle models optimized by biomass data. As a result of initial assessment, we found that most of default sub-models (e.g. snow, water cycle and carbon cycle) showed large deviations from remote sensing observations. However, these biases were removed by applying the proposed framework. For example, gross primary productivities were initially underestimated in boreal and temperate forest and overestimated in tropical forests. However, the parameter optimization scheme successfully reduced these biases. Our analysis

Mechanical behavior of the ATLAS B0 model coil

CERN Document Server

Foussat, A; Acerbi, E; Alessandria, F; Berthier, R; Broggi, F; Daël, A; Dudarev, A; Mayri, C; Miele, P; Reytier, M; Rossi, L; Sorbi, M; Sun, Z; ten Kate, H H J; Vanenkov, I; Volpini, G

2002-01-01

The ATLAS B0 model coil has been developed and constructed to verify the design parameters and the manufacture techniques of the Barrel Toroid coils (BT) that are under construction for the ATLAS Detector. Essential for successful operation is the mechanical behavior of the superconducting coil and its support structure. In the ATLAS magnet test facility, a magnetic mirror is used to reproduce in the model coil the electromagnetic forces of the BT coils when assembled in the final Barrel Toroid magnet system. The model coil is extensively equipped with mechanical instrumentation to monitor stresses and force levels as well as contraction during a cooling down and excitation up to nominal current. The installed set up of strain gauges, position sensors and capacitive force transducers is presented. Moreover the first mechanical results in terms of expected main stress, strain and deformation values are presented based on detailed mechanical analysis of the design. (7 refs).

Effects of the Ordering of Natural Selection and Population Regulation Mechanisms on Wright-Fisher Models.

Science.gov (United States)

He, Zhangyi; Beaumont, Mark; Yu, Feng

2017-07-05

We explore the effect of different mechanisms of natural selection on the evolution of populations for one- and two-locus systems. We compare the effect of viability and fecundity selection in the context of the Wright-Fisher model with selection under the assumption of multiplicative fitness. We show that these two modes of natural selection correspond to different orderings of the processes of population regulation and natural selection in the Wright-Fisher model. We find that under the Wright-Fisher model these two different orderings can affect the distribution of trajectories of haplotype frequencies evolving with genetic recombination. However, the difference in the distribution of trajectories is only appreciable when the population is in significant linkage disequilibrium. We find that as linkage disequilibrium decays the trajectories for the two different models rapidly become indistinguishable. We discuss the significance of these findings in terms of biological examples of viability and fecundity selection, and speculate that the effect may be significant when factors such as gene migration maintain a degree of linkage disequilibrium. Copyright © 2017 He et al.

Asbestos-related diseases in automobile mechanics.

Science.gov (United States)

Ameille, Jacques; Rosenberg, Nicole; Matrat, Mireille; Descatha, Alexis; Mompoint, Dominique; Hamzi, Lounis; Atassi, Catherine; Vasile, Manuela; Garnier, Robert; Pairon, Jean-Claude

2012-01-01

Automobile mechanics have been exposed to asbestos in the past, mainly due to the presence of chrysotile asbestos in brakes and clutches. Despite the large number of automobile mechanics, little is known about the non-malignant respiratory diseases observed in this population. The aim of this retrospective multicenter study was to analyse the frequency of pleural and parenchymal abnormalities on high-resolution computed tomography (HRCT) in a population of automobile mechanics. The study population consisted of 103 automobile mechanics with no other source of occupational exposure to asbestos, referred to three occupational health departments in the Paris area for systematic screening of asbestos-related diseases. All subjects were examined by HRCT and all images were reviewed separately by two independent readers; who in the case of disagreement discussed until they reached agreement. Multiple logistic regression models were constructed to investigate factors associated with pleural plaques. Pleural plaques were observed in five cases (4.9%) and interstitial abnormalities consistent with asbestosis were observed in one case. After adjustment for age, smoking status, and a history of non-asbestos-related respiratory diseases, multiple logistic regression models showed a significant association between the duration of exposure to asbestos and pleural plaques. The asbestos exposure experienced by automobile mechanics may lead to pleural plaques. The low prevalence of non-malignant asbestos-related diseases, using a very sensitive diagnostic tool, is in favor of a low cumulative exposure to asbestos in this population of workers.

Asbestos-related diseases in automobile mechanics

Science.gov (United States)

Ameille, Jacques; Rosenberg, Nicole; Matrat, Mireille; Descatha, Alexis; Mompoint, Dominique; Hamzi, Lounis; Atassi, Catherine; Vasile, Manuela; Garnier, Robert; Pairon, Jean-Claude

2012-01-01

Purpose Automobile mechanics have been exposed to asbestos in the past, mainly due to the presence of chrysotile asbestos in brakes and clutches. Despite the large number of automobile mechanics, little is known about the non-malignant respiratory diseases observed in this population. The aim of this retrospective multicenter study was to analyze the frequency of pleural and parenchymal abnormalities on HRCT in a population of automobile mechanics. Methods The study population consisted of 103 automobile mechanics with no other source of occupational exposure to asbestos, referred to three occupational health departments in the Paris area for systematic screening of asbestos–related diseases. All subjects were examined by HRCT and all images were reviewed separately by two independent readers, with further consensus in the case of disagreement. Multiple logistic regression models were constructed to investigate factors associated with pleural plaques. Results Pleural plaques were observed in 5 cases (4.9%) and interstitial abnormalities consistent with asbestosis were observed in 1 case. After adjustment for age, smoking status, and a history of non-asbestos-related respiratory diseases, multiple logistic regression models showed a significant association between the duration of exposure to asbestos and pleural plaques. Conclusions The asbestos exposure experienced by automobile mechanics may lead to pleural plaques. The low prevalence of non-malignant asbestos-related diseases, using a very sensitive diagnostic tool, is in favor of a low cumulative exposure to asbestos in this population of workers. PMID:21965465

Laplace transform analysis of a multiplicative asset transfer model

Science.gov (United States)

Sokolov, Andrey; Melatos, Andrew; Kieu, Tien

2010-07-01

We analyze a simple asset transfer model in which the transfer amount is a fixed fraction f of the giver’s wealth. The model is analyzed in a new way by Laplace transforming the master equation, solving it analytically and numerically for the steady-state distribution, and exploring the solutions for various values of f∈(0,1). The Laplace transform analysis is superior to agent-based simulations as it does not depend on the number of agents, enabling us to study entropy and inequality in regimes that are costly to address with simulations. We demonstrate that Boltzmann entropy is not a suitable (e.g. non-monotonic) measure of disorder in a multiplicative asset transfer system and suggest an asymmetric stochastic process that is equivalent to the asset transfer model.

Modelling of diffuse solar fraction with multiple predictors

Energy Technology Data Exchange (ETDEWEB)

Ridley, Barbara; Boland, John [Centre for Industrial and Applied Mathematics, University of South Australia, Mawson Lakes Boulevard, Mawson Lakes, SA 5095 (Australia); Lauret, Philippe [Laboratoire de Physique du Batiment et des Systemes, University of La Reunion, Reunion (France)

2010-02-15

For some locations both global and diffuse solar radiation are measured. However, for many locations, only global radiation is measured, or inferred from satellite data. For modelling solar energy applications, the amount of radiation on a tilted surface is needed. Since only the direct component on a tilted surface can be calculated from direct on some other plane using trigonometry, we need to have diffuse radiation on the horizontal plane available. There are regression relationships for estimating the diffuse on a tilted surface from diffuse on the horizontal. Models for estimating the diffuse on the horizontal from horizontal global that have been developed in Europe or North America have proved to be inadequate for Australia. Boland et al. developed a validated model for Australian conditions. Boland et al. detailed our recent advances in developing the theoretical framework for the use of the logistic function instead of piecewise linear or simple nonlinear functions and was the first step in identifying the means for developing a generic model for estimating diffuse from global and other predictors. We have developed a multiple predictor model, which is much simpler than previous models, and uses hourly clearness index, daily clearness index, solar altitude, apparent solar time and a measure of persistence of global radiation level as predictors. This model performs marginally better than currently used models for locations in the Northern Hemisphere and substantially better for Southern Hemisphere locations. We suggest it can be used as a universal model. (author)

Assessments of Future Maize Yield Potential Changes in the Korean Peninsula Using Multiple Crop Models

Science.gov (United States)

Kim, S. H.; Lim, C. H.; Kim, J.; Lee, W. K.; Kafatos, M.

2016-12-01

The Korean Peninsula has unique agricultural environment due to the differences of political and socio-economical system between Republic of Korea (SK, hereafter) and Democratic Peoples' Republic of Korea (NK, hereafter). NK has been suffering lack of food supplies caused by natural disasters, land degradation and political failure. The neighboring developed country SK has better agricultural system but very low food self-sufficiency rate. Maize is an important crop in both countries since it is staple food for NK and SK is No. 2 maize importing country in the world after Japan. Therefore, evaluating maize yield potential (Yp) in the two distinct regions is essential to assess food security under climate change and variability. In this study, we utilized multiple process-based crop models, having ability of regional scale assessment, to evaluate maize Yp and assess the model uncertainties -EPIC, GEPIC, DSSAT, and APSIM model that has capability of regional scale expansion (apsimRegions). First we evaluated each crop model for 3 years from 2012 to 2014 using reanalysis data (RDAPS; Regional Data Assimilation and Prediction System produced by Korea Meteorological Agency) and observed yield data. Each model performances were compared over the different regions in the Korean Peninsula having different local climate characteristics. To quantify of the major influence of at each climate variables, we also conducted sensitivity test using 20 years of climatology in historical period from 1981 to 2000. Lastly, the multi-crop model ensemble analysis was performed for future period from 2031 to 2050. The required weather variables projected for mid-century were employed from COordinated Regional climate Downscaling EXperiment (CORDEX) East Asia. The high-resolution climate data were obtained from multiple regional climate models (RCM) driven by multiple climate scenarios projected from multiple global climate models (GCMs) in conjunction with multiple greenhouse gas

Mechanical Model Development for Composite Structural Supercapacitors

Science.gov (United States)

Ricks, Trenton M.; Lacy, Thomas E., Jr.; Santiago, Diana; Bednarcyk, Brett A.

2016-01-01

Novel composite structural supercapacitor concepts have recently been developed as a means both to store electrical charge and to provide modest mechanical load carrying capability. Double-layer composite supercapacitors are often fabricated by impregnating a woven carbon fiber fabric, which serves as the electrodes, with a structural polymer electrolyte. Polypropylene or a glass fabric is often used as the separator material. Recent research has been primarily limited to evaluating these composites experimentally. In this study, mechanical models based on the Multiscale Generalized Method of Cells (MSGMC) were developed and used to calculate the shear and tensile properties and response of two composite structural supercapacitors from the literature. The modeling approach was first validated against traditional composite laminate data. MSGMC models for composite supercapacitors were developed, and accurate elastic shear/tensile properties were obtained. It is envisioned that further development of the models presented in this work will facilitate the design of composite components for aerospace and automotive applications and can be used to screen candidate constituent materials for inclusion in future composite structural supercapacitor concepts.

An explicit statistical model of learning lexical segmentation using multiple cues

NARCIS (Netherlands)

Çöltekin, Ça ̆grı; Nerbonne, John; Lenci, Alessandro; Padró, Muntsa; Poibeau, Thierry; Villavicencio, Aline

2014-01-01

This paper presents an unsupervised and incremental model of learning segmentation that combines multiple cues whose use by children and adults were attested by experimental studies. The cues we exploit in this study are predictability statistics, phonotactics, lexical stress and partial lexical

Mechanical modeling for magnetorheological elastomer isolators based on constitutive equations and electromagnetic analysis

Science.gov (United States)

Wang, Qi; Dong, Xufeng; Li, Luyu; Ou, Jinping

2018-06-01

As constitutive models are too complicated and existing mechanical models lack universality, these models are beyond satisfaction for magnetorheological elastomer (MRE) devices. In this article, a novel universal method is proposed to build concise mechanical models. Constitutive model and electromagnetic analysis were applied in this method to ensure universality, while a series of derivations and simplifications were carried out to obtain a concise formulation. To illustrate the proposed modeling method, a conical MRE isolator was introduced. Its basic mechanical equations were built based on equilibrium, deformation compatibility, constitutive equations and electromagnetic analysis. An iteration model and a highly efficient differential equation editor based model were then derived to solve the basic mechanical equations. The final simplified mechanical equations were obtained by re-fitting the simulations with a novel optimal algorithm. In the end, verification test of the isolator has proved the accuracy of the derived mechanical model and the modeling method.

Multiple imputation to account for measurement error in marginal structural models

Science.gov (United States)

Edwards, Jessie K.; Cole, Stephen R.; Westreich, Daniel; Crane, Heidi; Eron, Joseph J.; Mathews, W. Christopher; Moore, Richard; Boswell, Stephen L.; Lesko, Catherine R.; Mugavero, Michael J.

2015-01-01

Background Marginal structural models are an important tool for observational studies. These models typically assume that variables are measured without error. We describe a method to account for differential and non-differential measurement error in a marginal structural model. Methods We illustrate the method estimating the joint effects of antiretroviral therapy initiation and current smoking on all-cause mortality in a United States cohort of 12,290 patients with HIV followed for up to 5 years between 1998 and 2011. Smoking status was likely measured with error, but a subset of 3686 patients who reported smoking status on separate questionnaires composed an internal validation subgroup. We compared a standard joint marginal structural model fit using inverse probability weights to a model that also accounted for misclassification of smoking status using multiple imputation. Results In the standard analysis, current smoking was not associated with increased risk of mortality. After accounting for misclassification, current smoking without therapy was associated with increased mortality [hazard ratio (HR): 1.2 (95% CI: 0.6, 2.3)]. The HR for current smoking and therapy (0.4 (95% CI: 0.2, 0.7)) was similar to the HR for no smoking and therapy (0.4; 95% CI: 0.2, 0.6). Conclusions Multiple imputation can be used to account for measurement error in concert with methods for causal inference to strengthen results from observational studies. PMID:26214338

Multiple Imputation to Account for Measurement Error in Marginal Structural Models.

Science.gov (United States)

Edwards, Jessie K; Cole, Stephen R; Westreich, Daniel; Crane, Heidi; Eron, Joseph J; Mathews, W Christopher; Moore, Richard; Boswell, Stephen L; Lesko, Catherine R; Mugavero, Michael J

2015-09-01

Marginal structural models are an important tool for observational studies. These models typically assume that variables are measured without error. We describe a method to account for differential and nondifferential measurement error in a marginal structural model. We illustrate the method estimating the joint effects of antiretroviral therapy initiation and current smoking on all-cause mortality in a United States cohort of 12,290 patients with HIV followed for up to 5 years between 1998 and 2011. Smoking status was likely measured with error, but a subset of 3,686 patients who reported smoking status on separate questionnaires composed an internal validation subgroup. We compared a standard joint marginal structural model fit using inverse probability weights to a model that also accounted for misclassification of smoking status using multiple imputation. In the standard analysis, current smoking was not associated with increased risk of mortality. After accounting for misclassification, current smoking without therapy was associated with increased mortality (hazard ratio [HR]: 1.2 [95% confidence interval [CI] = 0.6, 2.3]). The HR for current smoking and therapy [0.4 (95% CI = 0.2, 0.7)] was similar to the HR for no smoking and therapy (0.4; 95% CI = 0.2, 0.6). Multiple imputation can be used to account for measurement error in concert with methods for causal inference to strengthen results from observational studies.

A minimal unified model of disease trajectories captures hallmarks of multiple sclerosis

KAUST Repository

Kannan, Venkateshan; Kiani, Narsis A.; Piehl, Fredrik; Tegner, Jesper

2017-01-01

Multiple Sclerosis (MS) is an autoimmune disease targeting the central nervous system (CNS) causing demyelination and neurodegeneration leading to accumulation of neurological disability. Here we present a minimal, computational model involving

Generic skills requirements (KSA model) towards future mechanical ...

African Journals Online (AJOL)

... Statistics and Discriminant Analysis (DA) as required to achieve the objective of the study. This study will guide all future engineers, especially in the field of Mechanical Engineering in Malaysia to penetrate the job market according to the current market needs. Keywords: generic skills; KSA model; mechanical engineers; ...

Study of gap conductance model for thermo mechanical fully coupled finite element model

International Nuclear Information System (INIS)

Kim, Hyo Cha; Yang, Yong Sik; Kim, Dae Ho; Bang, Je Geon; Kim, Sun Ki; Koo, Yang Hyun

2012-01-01

A light water reactor (LWR) fuel rod consists of zirconium alloy cladding and uranium dioxide pellets, with a slight gap between them. Therefore, the mechanical integrity of zirconium alloy cladding is the most critical issue, as it is an important barrier for fission products released into the environment. To evaluate the stress and strain of the cladding during operation, fuel performance codes with a one-dimensional (1D) approach have been reported since the 1970s. However, it is difficult for a 1D model to simulate the stress and strain of the cladding accurately owing to a lack of degree of freedom. A LWR fuel performance code should include thermo-mechanical coupled model owing to the existence of the fuel-cladding gap. Generally, the gap that is filled with helium gas results in temperature drop along radius direction. The gap conductance that determines temperature gradient within the gap is very sensitive to gap thickness. For instance, once the gap size increases up to several microns in certain region, difference of surface temperatures increases up to 100 Kelvin. Therefore, iterative thermo-mechanical coupled analysis is required to solve temperature distribution throughout pellet and cladding. Consequently, the Finite Element (FE) module, which can simulate a higher degree of freedom numerically, is an indispensable requirement to understand the thermomechanical behavior of cladding. FRAPCON-3, which is reliable performance code, has iterative loop for thermo-mechanical coupled calculation to solve 1D gap conductance model. In FEMAXI-III, 1D thermal analysis module and FE module for stress-strain analysis were separated. 1D thermal module includes iterative analysis between them. DIONISIO code focused on thermal contact model as function of surface roughness and contact pressure when the gap is closed. In previous works, gap conductance model has been developed only for 1D model or hybrid model (1D and FE). To simulate temperature, stress and strain

Modeling single versus multiple systems in implicit and explicit memory.

Science.gov (United States)

Starns, Jeffrey J; Ratcliff, Roger; McKoon, Gail

2012-04-01

It is currently controversial whether priming on implicit tasks and discrimination on explicit recognition tests are supported by a single memory system or by multiple, independent systems. In a Psychological Review article, Berry and colleagues used mathematical modeling to address this question and provide compelling evidence against the independent-systems approach. Copyright © 2012 Elsevier Ltd. All rights reserved.

On the practical modeling of conceptual overlap among multiple facets in ontology domain concepts (Mini-thesis)

OpenAIRE

Rodriguez-Castro, Benedicto; Glaser, Hugh; Carr, Leslie

2007-01-01

This report presents a study on the practical modelling of the conceptual overlap that might exist among the multiple facets that define a particular ontology domain concept. The notions of conceptual overlap and facet are defined, together with their relation to scenarios of multiple inheritance in ontology models. Starting from the notion of a value partition, a terminology of ontology modelling constructs is introduced that allows the characterization of two types of conceptual overlap wit...

Bioinformatics Mining and Modeling Methods for the Identification of Disease Mechanisms in Neurodegenerative Disorders

Directory of Open Access Journals (Sweden)

Martin Hofmann-Apitius

2015-12-01

Full Text Available Since the decoding of the Human Genome, techniques from bioinformatics, statistics, and machine learning have been instrumental in uncovering patterns in increasing amounts and types of different data produced by technical profiling technologies applied to clinical samples, animal models, and cellular systems. Yet, progress on unravelling biological mechanisms, causally driving diseases, has been limited, in part due to the inherent complexity of biological systems. Whereas we have witnessed progress in the areas of cancer, cardiovascular and metabolic diseases, the area of neurodegenerative diseases has proved to be very challenging. This is in part because the aetiology of neurodegenerative diseases such as Alzheimer´s disease or Parkinson´s disease is unknown, rendering it very difficult to discern early causal events. Here we describe a panel of bioinformatics and modeling approaches that have recently been developed to identify candidate mechanisms of neurodegenerative diseases based on publicly available data and knowledge. We identify two complementary strategies—data mining techniques using genetic data as a starting point to be further enriched using other data-types, or alternatively to encode prior knowledge about disease mechanisms in a model based framework supporting reasoning and enrichment analysis. Our review illustrates the challenges entailed in integrating heterogeneous, multiscale and multimodal information in the area of neurology in general and neurodegeneration in particular. We conclude, that progress would be accelerated by increasing efforts on performing systematic collection of multiple data-types over time from each individual suffering from neurodegenerative disease. The work presented here has been driven by project AETIONOMY; a project funded in the course of the Innovative Medicines Initiative (IMI; which is a public-private partnership of the European Federation of Pharmaceutical Industry Associations

A tactical supply chain planning model with multiple flexibility options

DEFF Research Database (Denmark)

Esmaeilikia, Masoud; Fahimnia, Behnam; Sarkis, Joeseph

2016-01-01

Supply chain flexibility is widely recognized as an approach to manage uncertainty. Uncertainty in the supply chain may arise from a number of sources such as demand and supply interruptions and lead time variability. A tactical supply chain planning model with multiple flexibility options...... incorporated in sourcing, manufacturing and logistics functions can be used for the analysis of flexibility adjustment in an existing supply chain. This paper develops such a tactical supply chain planning model incorporating a realistic range of flexibility options. A novel solution method is designed...

Modelling and simulation of multiple single - phase induction motor in parallel connection

Directory of Open Access Journals (Sweden)

Sujitjorn, S.

2006-11-01

Full Text Available A mathematical model for parallel connected n-multiple single-phase induction motors in generalized state-space form is proposed in this paper. The motor group draws electric power from one inverter. The model is developed by the dq-frame theory and was tested against four loading scenarios in which satisfactory results were obtained.

An adaptation model for trabecular bone at different mechanical levels

Directory of Open Access Journals (Sweden)

Lv Linwei

2010-07-01

Full Text Available Abstract Background Bone has the ability to adapt to mechanical usage or other biophysical stimuli in terms of its mass and architecture, indicating that a certain mechanism exists for monitoring mechanical usage and controlling the bone's adaptation behaviors. There are four zones describing different bone adaptation behaviors: the disuse, adaptation, overload, and pathologic overload zones. In different zones, the changes of bone mass, as calculated by the difference between the amount of bone formed and what is resorbed, should be different. Methods An adaptation model for the trabecular bone at different mechanical levels was presented in this study based on a number of experimental observations and numerical algorithms in the literature. In the proposed model, the amount of bone formation and the probability of bone remodeling activation were proposed in accordance with the mechanical levels. Seven numerical simulation cases under different mechanical conditions were analyzed as examples by incorporating the adaptation model presented in this paper with the finite element method. Results The proposed bone adaptation model describes the well-known bone adaptation behaviors in different zones. The bone mass and architecture of the bone tissue within the adaptation zone almost remained unchanged. Although the probability of osteoclastic activation is enhanced in the overload zone, the potential of osteoblasts to form bones compensate for the osteoclastic resorption, eventually strengthening the bones. In the disuse zone, the disuse-mode remodeling removes bone tissue in disuse zone. Conclusions The study seeks to provide better understanding of the relationships between bone morphology and the mechanical, as well as biological environments. Furthermore, this paper provides a computational model and methodology for the numerical simulation of changes of bone structural morphology that are caused by changes of mechanical and biological

Improved double-multiple streamtube model for the Darrieus-type vertical axis wind turbine

Science.gov (United States)

Berg, D. E.

Double streamtube codes model the curved blade (Darrieus-type) vertical axis wind turbine (VAWT) as a double actuator fish arrangement (one half) and use conservation of momentum principles to determine the forces acting on the turbine blades and the turbine performance. Sandia National Laboratories developed a double multiple streamtube model for the VAWT which incorporates the effects of the incident wind boundary layer, nonuniform velocity between the upwind and downwind sections of the rotor, dynamic stall effects and local blade Reynolds number variations. The theory underlying this VAWT model is described, as well as the code capabilities. Code results are compared with experimental data from two VAWT's and with the results from another double multiple streamtube and a vortex filament code. The effects of neglecting dynamic stall and horizontal wind velocity distribution are also illustrated.