Sample records for accommodate multibody dynamics

  1. Multibody dynamic simulation of knee contact mechanics

    PubMed Central

    Bei, Yanhong; Fregly, Benjamin J.

    2006-01-01

    Multibody dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to knee joint degeneration and restoration. Current three-dimensional multi-body knee models are either quasi-static with deformable contact or dynamic with rigid contact. This study proposes a computationally efficient methodology for combining multibody dynamic simulation methods with a deformable contact knee model. The methodology requires preparation of the articular surface geometry, development of efficient methods to calculate distances between contact surfaces, implementation of an efficient contact solver that accounts for the unique characteristics of human joints, and specification of an application programming interface for integration with any multibody dynamic simulation environment. The current implementation accommodates natural or artificial tibiofemoral joint models, small or large strain contact models, and linear or nonlinear material models. Applications are presented for static analysis (via dynamic simulation) of a natural knee model created from MRI and CT data and dynamic simulation of an artificial knee model produced from manufacturer’s CAD data. Small and large strain natural knee static analyses required 1 min of CPU time and predicted similar contact conditions except for peak pressure, which was higher for the large strain model. Linear and nonlinear artificial knee dynamic simulations required 10 min of CPU time and predicted similar contact force and torque but different contact pressures, which were lower for the nonlinear model due to increased contact area. This methodology provides an important step toward the realization of dynamic musculoskeletal models that can predict in vivo knee joint motion and loading simultaneously. PMID:15564115

  2. Computational Workbench for Multibody Dynamics

    NASA Technical Reports Server (NTRS)

    Edmonds, Karina

    2007-01-01

    PyCraft is a computer program that provides an interactive, workbenchlike computing environment for developing and testing algorithms for multibody dynamics. Examples of multibody dynamic systems amenable to analysis with the help of PyCraft include land vehicles, spacecraft, robots, and molecular models. PyCraft is based on the Spatial-Operator- Algebra (SOA) formulation for multibody dynamics. The SOA operators enable construction of simple and compact representations of complex multibody dynamical equations. Within the Py-Craft computational workbench, users can, essentially, use the high-level SOA operator notation to represent the variety of dynamical quantities and algorithms and to perform computations interactively. PyCraft provides a Python-language interface to underlying C++ code. Working with SOA concepts, a user can create and manipulate Python-level operator classes in order to implement and evaluate new dynamical quantities and algorithms. During use of PyCraft, virtually all SOA-based algorithms are available for computational experiments.

  3. Solving Equations of Multibody Dynamics

    NASA Technical Reports Server (NTRS)

    Jain, Abhinandan; Lim, Christopher

    2007-01-01

    Darts++ is a computer program for solving the equations of motion of a multibody system or of a multibody model of a dynamic system. It is intended especially for use in dynamical simulations performed in designing and analyzing, and developing software for the control of, complex mechanical systems. Darts++ is based on the Spatial-Operator- Algebra formulation for multibody dynamics. This software reads a description of a multibody system from a model data file, then constructs and implements an efficient algorithm that solves the dynamical equations of the system. The efficiency and, hence, the computational speed is sufficient to make Darts++ suitable for use in realtime closed-loop simulations. Darts++ features an object-oriented software architecture that enables reconfiguration of system topology at run time; in contrast, in related prior software, system topology is fixed during initialization. Darts++ provides an interface to scripting languages, including Tcl and Python, that enable the user to configure and interact with simulation objects at run time.

  4. Reduced gravity multibody dynamics testing

    NASA Technical Reports Server (NTRS)

    Sillanpaa, Meija

    1993-01-01

    The Final Report on reduced gravity multibody dynamics testing is presented. Tests were conducted on board the NASA KC-135 RGA in Houston, Texas. The objective was to analyze the effects of large angle rotations on flexible, multi-segmented structures. The flight experiment was conducted to provide data which will be compared to the data gathered from ground tests of the same configurations. The flight and ground tested data will be used to validate the TREETOPS software, software which models dynamic multibody systems, and other multibody codes. The flight experiment consisted of seven complete flights on board the KC-135 RGA during two one-week periods. The first period of testing was 4-9 Apr. 1993. The second period of testing was 13-18 Jun. 1993.

  5. Recursive dynamics for flexible multibody systems using spatial operators

    NASA Technical Reports Server (NTRS)

    Jain, A.; Rodriguez, G.

    1990-01-01

    Due to their structural flexibility, spacecraft and space manipulators are multibody systems with complex dynamics and possess a large number of degrees of freedom. Here the spatial operator algebra methodology is used to develop a new dynamics formulation and spatially recursive algorithms for such flexible multibody systems. A key feature of the formulation is that the operator description of the flexible system dynamics is identical in form to the corresponding operator description of the dynamics of rigid multibody systems. A significant advantage of this unifying approach is that it allows ideas and techniques for rigid multibody systems to be easily applied to flexible multibody systems. The algorithms use standard finite-element and assumed modes models for the individual body deformation. A Newton-Euler Operator Factorization of the mass matrix of the multibody system is first developed. It forms the basis for recursive algorithms such as for the inverse dynamics, the computation of the mass matrix, and the composite body forward dynamics for the system. Subsequently, an alternative Innovations Operator Factorization of the mass matrix, each of whose factors is invertible, is developed. It leads to an operator expression for the inverse of the mass matrix, and forms the basis for the recursive articulated body forward dynamics algorithm for the flexible multibody system. For simplicity, most of the development here focuses on serial chain multibody systems. However, extensions of the algorithms to general topology flexible multibody systems are described. While the computational cost of the algorithms depends on factors such as the topology and the amount of flexibility in the multibody system, in general, it appears that in contrast to the rigid multibody case, the articulated body forward dynamics algorithm is the more efficient algorithm for flexible multibody systems containing even a small number of flexible bodies. The variety of algorithms described

  6. Spatial Operator Algebra for multibody system dynamics

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.; Jain, A.; Kreutz-Delgado, K.

    1992-01-01

    The Spatial Operator Algebra framework for the dynamics of general multibody systems is described. The use of a spatial operator-based methodology permits the formulation of the dynamical equations of motion of multibody systems in a concise and systematic way. The dynamical equations of progressively more complex grid multibody systems are developed in an evolutionary manner beginning with a serial chain system, followed by a tree topology system and finally, systems with arbitrary closed loops. Operator factorizations and identities are used to develop novel recursive algorithms for the forward dynamics of systems with closed loops. Extensions required to deal with flexible elements are also discussed.

  7. Spatial operator algebra framework for multibody system dynamics

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.; Jain, Abhinandan; Kreutz, K.

    1989-01-01

    The Spatial Operator Algebra framework for the dynamics of general multibody systems is described. The use of a spatial operator-based methodology permits the formulation of the dynamical equations of motion of multibody systems in a concise and systematic way. The dynamical equations of progressively more complex grid multibody systems are developed in an evolutionary manner beginning with a serial chain system, followed by a tree topology system and finally, systems with arbitrary closed loops. Operator factorizations and identities are used to develop novel recursive algorithms for the forward dynamics of systems with closed loops. Extensions required to deal with flexible elements are also discussed.

  8. Recursive flexible multibody system dynamics using spatial operators

    NASA Technical Reports Server (NTRS)

    Jain, A.; Rodriguez, G.

    1992-01-01

    This paper uses spatial operators to develop new spatially recursive dynamics algorithms for flexible multibody systems. The operator description of the dynamics is identical to that for rigid multibody systems. Assumed-mode models are used for the deformation of each individual body. The algorithms are based on two spatial operator factorizations of the system mass matrix. The first (Newton-Euler) factorization of the mass matrix leads to recursive algorithms for the inverse dynamics, mass matrix evaluation, and composite-body forward dynamics for the systems. The second (innovations) factorization of the mass matrix, leads to an operator expression for the mass matrix inverse and to a recursive articulated-body forward dynamics algorithm. The primary focus is on serial chains, but extensions to general topologies are also described. A comparison of computational costs shows that the articulated-body, forward dynamics algorithm is much more efficient than the composite-body algorithm for most flexible multibody systems.

  9. G-DYN Multibody Dynamics Engine

    NASA Technical Reports Server (NTRS)

    Acikmese, Behcet; Blackmore, James C.; Broderick, Daniel

    2011-01-01

    G-DYN is a multi-body dynamic simulation software engine that automatically assembles and integrates equations of motion for arbitrarily connected multibody dynamic systems. The algorithm behind G-DYN is based on a primal-dual formulation of the dynamics that captures the position and velocity vectors (primal variables) of each body and the interaction forces (dual variables) between bodies, which are particularly useful for control and estimation analysis and synthesis. It also takes full advantage of the spare matrix structure resulting from the system dynamics to numerically integrate the equations of motion efficiently. Furthermore, the dynamic model for each body can easily be replaced without re-deriving the overall equations of motion, and the assembly of the equations of motion is done automatically. G-DYN proved an essential software tool in the simulation of spacecraft systems used for small celestial body surface sampling, specifically in simulating touch-and-go (TAG) maneuvers of a robotic sampling system from a comet and asteroid. It is used extensively in validating mission concepts for small body sample return, such as Comet Odyssey and Galahad New Frontiers proposals.

  10. Constraint Embedding Technique for Multibody System Dynamics

    NASA Technical Reports Server (NTRS)

    Woo, Simon S.; Cheng, Michael K.

    2011-01-01

    Multibody dynamics play a critical role in simulation testbeds for space missions. There has been a considerable interest in the development of efficient computational algorithms for solving the dynamics of multibody systems. Mass matrix factorization and inversion techniques and the O(N) class of forward dynamics algorithms developed using a spatial operator algebra stand out as important breakthrough on this front. Techniques such as these provide the efficient algorithms and methods for the application and implementation of such multibody dynamics models. However, these methods are limited only to tree-topology multibody systems. Closed-chain topology systems require different techniques that are not as efficient or as broad as those for tree-topology systems. The closed-chain forward dynamics approach consists of treating the closed-chain topology as a tree-topology system subject to additional closure constraints. The resulting forward dynamics solution consists of: (a) ignoring the closure constraints and using the O(N) algorithm to solve for the free unconstrained accelerations for the system; (b) using the tree-topology solution to compute a correction force to enforce the closure constraints; and (c) correcting the unconstrained accelerations with correction accelerations resulting from the correction forces. This constraint-embedding technique shows how to use direct embedding to eliminate local closure-loops in the system and effectively convert the system back to a tree-topology system. At this point, standard tree-topology techniques can be brought to bear on the problem. The approach uses a spatial operator algebra approach to formulating the equations of motion. The operators are block-partitioned around the local body subgroups to convert them into aggregate bodies. Mass matrix operator factorization and inversion techniques are applied to the reformulated tree-topology system. Thus in essence, the new technique allows conversion of a system with

  11. Linked-List-Based Multibody Dynamics (MBDyn) Engine

    NASA Technical Reports Server (NTRS)

    MacLean, John; Brain, Thomas; Wuiocho, Leslie; Huynh, An; Ghosh, Tushar

    2012-01-01

    This new release of MBDyn is a software engine that calculates the dynamics states of kinematic, rigid, or flexible multibody systems. An MBDyn multibody system may consist of multiple groups of articulated chains, trees, or closed-loop topologies. Transient topologies are handled through conservation of energy and momentum. The solution for rigid-body systems is exact, and several configurable levels of nonlinear term fidelity are available for flexible dynamics systems. The algorithms have been optimized for efficiency and can be used for both non-real-time (NRT) and real-time (RT) simulations. Interfaces are currently compatible with NASA's Trick Simulation Environment. This new release represents a significant advance in capability and ease of use. The two most significant new additions are an application programming interface (API) that clarifies and simplifies use of MBDyn, and a link-list infrastructure that allows a single MBDyn instance to propagate an arbitrary number of interacting groups of multibody top ologies. MBDyn calculates state and state derivative vectors for integration using an external integration routine. A Trickcompatible interface is provided for initialization, data logging, integration, and input/output.

  12. Substructured multibody molecular dynamics.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Grest, Gary Stephen; Stevens, Mark Jackson; Plimpton, Steven James

    2006-11-01

    We have enhanced our parallel molecular dynamics (MD) simulation software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator, lammps.sandia.gov) to include many new features for accelerated simulation including articulated rigid body dynamics via coupling to the Rensselaer Polytechnic Institute code POEMS (Parallelizable Open-source Efficient Multibody Software). We use new features of the LAMMPS software package to investigate rhodopsin photoisomerization, and water model surface tension and capillary waves at the vapor-liquid interface. Finally, we motivate the recipes of MD for practitioners and researchers in numerical analysis and computational mechanics.

  13. Constrained multibody system dynamics: An automated approach

    NASA Technical Reports Server (NTRS)

    Kamman, J. W.; Huston, R. L.

    1982-01-01

    The governing equations for constrained multibody systems are formulated in a manner suitable for their automated, numerical development and solution. The closed loop problem of multibody chain systems is addressed. The governing equations are developed by modifying dynamical equations obtained from Lagrange's form of d'Alembert's principle. The modifications is based upon a solution of the constraint equations obtained through a zero eigenvalues theorem, is a contraction of the dynamical equations. For a system with n-generalized coordinates and m-constraint equations, the coefficients in the constraint equations may be viewed as constraint vectors in n-dimensional space. In this setting the system itself is free to move in the n-m directions which are orthogonal to the constraint vectors.

  14. Graph Theoretic Foundations of Multibody Dynamics Part I: Structural Properties

    PubMed Central

    Jain, Abhinandan

    2011-01-01

    This is the first part of two papers that use concepts from graph theory to obtain a deeper understanding of the mathematical foundations of multibody dynamics. The key contribution is the development of a unifying framework that shows that key analytical results and computational algorithms in multibody dynamics are a direct consequence of structural properties and require minimal assumptions about the specific nature of the underlying multibody system. This first part focuses on identifying the abstract graph theoretic structural properties of spatial operator techniques in multibody dynamics. The second part paper exploits these structural properties to develop a broad spectrum of analytical results and computational algorithms. Towards this, we begin with the notion of graph adjacency matrices and generalize it to define block-weighted adjacency (BWA) matrices and their 1-resolvents. Previously developed spatial operators are shown to be special cases of such BWA matrices and their 1-resolvents. These properties are shown to hold broadly for serial and tree topology multibody systems. Specializations of the BWA and 1-resolvent matrices are referred to as spatial kernel operators (SKO) and spatial propagation operators (SPO). These operators and their special properties provide the foundation for the analytical and algorithmic techniques developed in the companion paper. We also use the graph theory concepts to study the topology induced sparsity structure of these operators and the system mass matrix. Similarity transformations of these operators are also studied. While the detailed development is done for the case of rigid-link multibody systems, the extension of these techniques to a broader class of systems (e.g. deformable links) are illustrated. PMID:22102790

  15. Geometric stiffening in multibody dynamics formulations

    NASA Technical Reports Server (NTRS)

    Sharf, Inna

    1993-01-01

    In this paper we discuss the issue of geometric stiffening as it arises in the context of multibody dynamics. This topic has been treated in a number of previous publications in this journal and appears to be a debated subject. The controversy revolves primarily around the 'correct' methodology for incorporating the stiffening effect into dynamics formulations. The main goal of this work is to present the different approaches that have been developed for this problem through an in-depth review of several publications dealing with this subject. This is done with the goal of contributing to a precise understanding of the existing methodologies for modelling the stiffening effects in multibody systems. Thus, in presenting the material we attempt to illuminate the key characteristics of the various methods as well as show how they relate to each other. In addition, we offer a number of novel insights and clarifying interpretations of these schemes. The paper is completed with a general classification and comparison of the different approaches.

  16. Spatial operator algebra for flexible multibody dynamics

    NASA Technical Reports Server (NTRS)

    Jain, A.; Rodriguez, G.

    1993-01-01

    This paper presents an approach to modeling the dynamics of flexible multibody systems such as flexible spacecraft and limber space robotic systems. A large number of degrees of freedom and complex dynamic interactions are typical in these systems. This paper uses spatial operators to develop efficient recursive algorithms for the dynamics of these systems. This approach very efficiently manages complexity by means of a hierarchy of mathematical operations.

  17. Nonrecursive formulations of multibody dynamics and concurrent multiprocessing

    NASA Technical Reports Server (NTRS)

    Kurdila, Andrew J.; Menon, Ramesh

    1993-01-01

    Since the late 1980's, research in recursive formulations of multibody dynamics has flourished. Historically, much of this research can be traced to applications of low dimensionality in mechanism and vehicle dynamics. Indeed, there is little doubt that recursive order N methods are the method of choice for this class of systems. This approach has the advantage that a minimal number of coordinates are utilized, parallelism can be induced for certain system topologies, and the method is of order N computational cost for systems of N rigid bodies. Despite the fact that many authors have dismissed redundant coordinate formulations as being of order N(exp 3), and hence less attractive than recursive formulations, we present recent research that demonstrates that at least three distinct classes of redundant, nonrecursive multibody formulations consistently achieve order N computational cost for systems of rigid and/or flexible bodies. These formulations are as follows: (1) the preconditioned range space formulation; (2) penalty methods; and (3) augmented Lagrangian methods for nonlinear multibody dynamics. The first method can be traced to its foundation in equality constrained quadratic optimization, while the last two methods have been studied extensively in the context of coercive variational boundary value problems in computational mechanics. Until recently, however, they have not been investigated in the context of multibody simulation, and present theoretical questions unique to nonlinear dynamics. All of these nonrecursive methods have additional advantages with respect to recursive order N methods: (1) the formalisms retain the highly desirable order N computational cost; (2) the techniques are amenable to concurrent simulation strategies; (3) the approaches do not depend upon system topology to induce concurrency; and (4) the methods can be derived to balance the computational load automatically on concurrent multiprocessors. In addition to the presentation of

  18. Dynamic analysis of space structures including elastic, multibody, and control behavior

    NASA Technical Reports Server (NTRS)

    Pinson, Larry; Soosaar, Keto

    1989-01-01

    The problem is to develop analysis methods, modeling stategies, and simulation tools to predict with assurance the on-orbit performance and integrity of large complex space structures that cannot be verified on the ground. The problem must incorporate large reliable structural models, multi-body flexible dynamics, multi-tier controller interaction, environmental models including 1g and atmosphere, various on-board disturbances, and linkage to mission-level performance codes. All areas are in serious need of work, but the weakest link is multi-body flexible dynamics.

  19. System Theory Aspects of Multi-Body Dynamics.

    DTIC Science & Technology

    1978-08-18

    systems are described from a system theory point of view. Various system theory concepts and research topics which have applicability to this class of...systems are identified and briefly described. The subject of multi-body dynamics is presented in a vector space setting and is related to system theory concepts. (Author)

  20. Approaches and possible improvements in the area of multibody dynamics modeling

    NASA Technical Reports Server (NTRS)

    Lips, K. W.; Singh, R.

    1987-01-01

    A wide ranging look is taken at issues involved in the dynamic modeling of complex, multibodied orbiting space systems. Capabilities and limitations of two major codes (DISCOS, TREETOPS) are assessed and possible extensions to the CONTOPS software are outlined. In addition, recommendations are made concerning the direction future development should take in order to achieve higher fidelity, more computationally efficient multibody software solutions.

  1. Simbody: multibody dynamics for biomedical research.

    PubMed

    Sherman, Michael A; Seth, Ajay; Delp, Scott L

    Multibody software designed for mechanical engineering has been successfully employed in biomedical research for many years. For real time operation some biomedical researchers have also adapted game physics engines. However, these tools were built for other purposes and do not fully address the needs of biomedical researchers using them to analyze the dynamics of biological structures and make clinically meaningful recommendations. We are addressing this problem through the development of an open source, extensible, high performance toolkit including a multibody mechanics library aimed at the needs of biomedical researchers. The resulting code, Simbody, supports research in a variety of fields including neuromuscular, prosthetic, and biomolecular simulation, and related research such as biologically-inspired design and control of humanoid robots and avatars. Simbody is the dynamics engine behind OpenSim, a widely used biomechanics simulation application. This article reviews issues that arise uniquely in biomedical research, and reports on the architecture, theory, and computational methods Simbody uses to address them. By addressing these needs explicitly Simbody provides a better match to the needs of researchers than can be obtained by adaptation of mechanical engineering or gaming codes. Simbody is a community resource, free for any purpose. We encourage wide adoption and invite contributions to the code base at https://simtk.org/home/simbody.

  2. Masticatory biomechanics in the rabbit: a multi-body dynamics analysis.

    PubMed

    Watson, Peter J; Gröning, Flora; Curtis, Neil; Fitton, Laura C; Herrel, Anthony; McCormack, Steven W; Fagan, Michael J

    2014-10-06

    Multi-body dynamics is a powerful engineering tool which is becoming increasingly popular for the simulation and analysis of skull biomechanics. This paper presents the first application of multi-body dynamics to analyse the biomechanics of the rabbit skull. A model has been constructed through the combination of manual dissection and three-dimensional imaging techniques (magnetic resonance imaging and micro-computed tomography). Individual muscles are represented with multiple layers, thus more accurately modelling muscle fibres with complex lines of action. Model validity was sought through comparing experimentally measured maximum incisor bite forces with those predicted by the model. Simulations of molar biting highlighted the ability of the masticatory system to alter recruitment of two muscle groups, in order to generate shearing or crushing movements. Molar shearing is capable of processing a food bolus in all three orthogonal directions, whereas molar crushing and incisor biting are predominately directed vertically. Simulations also show that the masticatory system is adapted to process foods through several cycles with low muscle activations, presumably in order to prevent rapidly fatiguing fast fibres during repeated chewing cycles. Our study demonstrates the usefulness of a validated multi-body dynamics model for investigating feeding biomechanics in the rabbit, and shows the potential for complementing and eventually reducing in vivo experiments.

  3. Masticatory biomechanics in the rabbit: a multi-body dynamics analysis

    PubMed Central

    Watson, Peter J.; Gröning, Flora; Curtis, Neil; Fitton, Laura C.; Herrel, Anthony; McCormack, Steven W.; Fagan, Michael J.

    2014-01-01

    Multi-body dynamics is a powerful engineering tool which is becoming increasingly popular for the simulation and analysis of skull biomechanics. This paper presents the first application of multi-body dynamics to analyse the biomechanics of the rabbit skull. A model has been constructed through the combination of manual dissection and three-dimensional imaging techniques (magnetic resonance imaging and micro-computed tomography). Individual muscles are represented with multiple layers, thus more accurately modelling muscle fibres with complex lines of action. Model validity was sought through comparing experimentally measured maximum incisor bite forces with those predicted by the model. Simulations of molar biting highlighted the ability of the masticatory system to alter recruitment of two muscle groups, in order to generate shearing or crushing movements. Molar shearing is capable of processing a food bolus in all three orthogonal directions, whereas molar crushing and incisor biting are predominately directed vertically. Simulations also show that the masticatory system is adapted to process foods through several cycles with low muscle activations, presumably in order to prevent rapidly fatiguing fast fibres during repeated chewing cycles. Our study demonstrates the usefulness of a validated multi-body dynamics model for investigating feeding biomechanics in the rabbit, and shows the potential for complementing and eventually reducing in vivo experiments. PMID:25121650

  4. Constraint Embedding for Multibody System Dynamics

    NASA Technical Reports Server (NTRS)

    Jain, Abhinandan

    2009-01-01

    This paper describes a constraint embedding approach for the handling of local closure constraints in multibody system dynamics. The approach uses spatial operator techniques to eliminate local-loop constraints from the system and effectively convert the system into tree-topology systems. This approach allows the direct derivation of recursive O(N) techniques for solving the system dynamics and avoiding the expensive steps that would otherwise be required for handling the closedchain dynamics. The approach is very effective for systems where the constraints are confined to small-subgraphs within the system topology. The paper provides background on the spatial operator O(N) algorithms, the extensions for handling embedded constraints, and concludes with some examples of such constraints.

  5. Multibody dynamics model building using graphical interfaces

    NASA Technical Reports Server (NTRS)

    Macala, Glenn A.

    1989-01-01

    In recent years, the extremely laborious task of manually deriving equations of motion for the simulation of multibody spacecraft dynamics has largely been eliminated. Instead, the dynamicist now works with commonly available general purpose dynamics simulation programs which generate the equations of motion either explicitly or implicitly via computer codes. The user interface to these programs has predominantly been via input data files, each with its own required format and peculiarities, causing errors and frustrations during program setup. Recent progress in a more natural method of data input for dynamics programs: the graphical interface, is described.

  6. Simulating coupled dynamics of a rigid-flexible multibody system and compressible fluid

    NASA Astrophysics Data System (ADS)

    Hu, Wei; Tian, Qiang; Hu, HaiYan

    2018-04-01

    As a subsequent work of previous studies of authors, a new parallel computation approach is proposed to simulate the coupled dynamics of a rigid-flexible multibody system and compressible fluid. In this approach, the smoothed particle hydrodynamics (SPH) method is used to model the compressible fluid, the natural coordinate formulation (NCF) and absolute nodal coordinate formulation (ANCF) are used to model the rigid and flexible bodies, respectively. In order to model the compressible fluid properly and efficiently via SPH method, three measures are taken as follows. The first is to use the Riemann solver to cope with the fluid compressibility, the second is to define virtual particles of SPH to model the dynamic interaction between the fluid and the multibody system, and the third is to impose the boundary conditions of periodical inflow and outflow to reduce the number of SPH particles involved in the computation process. Afterwards, a parallel computation strategy is proposed based on the graphics processing unit (GPU) to detect the neighboring SPH particles and to solve the dynamic equations of SPH particles in order to improve the computation efficiency. Meanwhile, the generalized-alpha algorithm is used to solve the dynamic equations of the multibody system. Finally, four case studies are given to validate the proposed parallel computation approach.

  7. Transport in Dynamical Astronomy and Multibody Problems

    NASA Astrophysics Data System (ADS)

    Dellnitz, Michael; Junge, Oliver; Koon, Wang Sang; Lekien, Francois; Lo, Martin W.; Marsden, Jerrold E.; Padberg, Kathrin; Preis, Robert; Ross, Shane D.; Thiere, Bianca

    We combine the techniques of almost invariant sets (using tree structured box elimination and graph partitioning algorithms) with invariant manifold and lobe dynamics techniques. The result is a new computational technique for computing key dynamical features, including almost invariant sets, resonance regions as well as transport rates and bottlenecks between regions in dynamical systems. This methodology can be applied to a variety of multibody problems, including those in molecular modeling, chemical reaction rates and dynamical astronomy. In this paper we focus on problems in dynamical astronomy to illustrate the power of the combination of these different numerical tools and their applicability. In particular, we compute transport rates between two resonance regions for the three-body system consisting of the Sun, Jupiter and a third body (such as an asteroid). These resonance regions are appropriate for certain comets and asteroids.

  8. Recursive multibody dynamics and discrete-time optimal control

    NASA Technical Reports Server (NTRS)

    Deleuterio, G. M. T.; Damaren, C. J.

    1989-01-01

    A recursive algorithm is developed for the solution of the simulation dynamics problem for a chain of rigid bodies. Arbitrary joint constraints are permitted, that is, joints may allow translational and/or rotational degrees of freedom. The recursive procedure is shown to be identical to that encountered in a discrete-time optimal control problem. For each relevant quantity in the multibody dynamics problem, there exists an analog in the context of optimal control. The performance index that is minimized in the control problem is identified as Gibbs' function for the chain of bodies.

  9. A variational approach to dynamics of flexible multibody systems

    NASA Technical Reports Server (NTRS)

    Wu, Shih-Chin; Haug, Edward J.; Kim, Sung-Soo

    1989-01-01

    This paper presents a variational formulation of constrained dynamics of flexible multibody systems, using a vector-variational calculus approach. Body reference frames are used to define global position and orientation of individual bodies in the system, located and oriented by position of its origin and Euler parameters, respectively. Small strain linear elastic deformation of individual components, relative to their body references frames, is defined by linear combinations of deformation modes that are induced by constraint reaction forces and normal modes of vibration. A library of kinematic couplings between flexible and/or rigid bodies is defined and analyzed. Variational equations of motion for multibody systems are obtained and reduced to mixed differential-algebraic equations of motion. A space structure that must deform during deployment is analyzed, to illustrate use of the methods developed.

  10. Evolution of Flexible Multibody Dynamics for Simulation Applications Supporting Human Spaceflight

    NASA Technical Reports Server (NTRS)

    Huynh, An; Brain, Thomas A.; MacLean, John R.; Quiocho, Leslie J.

    2016-01-01

    During the course of transition from the Space Shuttle and International Space Station programs to the Orion and Journey to Mars exploration programs, a generic flexible multibody dynamics formulation and associated software implementation has evolved to meet an ever changing set of requirements at the NASA Johnson Space Center (JSC). Challenging problems related to large transitional topologies and robotic free-flyer vehicle capture/ release, contact dynamics, and exploration missions concept evaluation through simulation (e.g., asteroid surface operations) have driven this continued development. Coupled with this need is the requirement to oftentimes support human spaceflight operations in real-time. Moreover, it has been desirable to allow even more rapid prototyping of on-orbit manipulator and spacecraft systems, to support less complex infrastructure software for massively integrated simulations, to yield further computational efficiencies, and to take advantage of recent advances and availability of multi-core computing platforms. Since engineering analysis, procedures development, and crew familiarity/training for human spaceflight is fundamental to JSC's charter, there is also a strong desire to share and reuse models in both the non-realtime and real-time domains, with the goal of retaining as much multibody dynamics fidelity as possible. Three specific enhancements are reviewed here: (1) linked list organization to address large transitional topologies, (2) body level model order reduction, and (3) parallel formulation/implementation. This paper provides a detailed overview of these primary updates to JSC's flexible multibody dynamics algorithms as well as a comparison of numerical results to previous formulations and associated software.

  11. Online Kinematic and Dynamic-State Estimation for Constrained Multibody Systems Based on IMUs

    PubMed Central

    Torres-Moreno, José Luis; Blanco-Claraco, José Luis; Giménez-Fernández, Antonio; Sanjurjo, Emilio; Naya, Miguel Ángel

    2016-01-01

    This article addresses the problems of online estimations of kinematic and dynamic states of a mechanism from a sequence of noisy measurements. In particular, we focus on a planar four-bar linkage equipped with inertial measurement units (IMUs). Firstly, we describe how the position, velocity, and acceleration of all parts of the mechanism can be derived from IMU signals by means of multibody kinematics. Next, we propose the novel idea of integrating the generic multibody dynamic equations into two variants of Kalman filtering, i.e., the extended Kalman filter (EKF) and the unscented Kalman filter (UKF), in a way that enables us to handle closed-loop, constrained mechanisms, whose state space variables are not independent and would normally prevent the direct use of such estimators. The proposal in this work is to apply those estimators over the manifolds of allowed positions and velocities, by means of estimating a subset of independent coordinates only. The proposed techniques are experimentally validated on a testbed equipped with encoders as a means of establishing the ground-truth. Estimators are run online in real-time, a feature not matched by any previous procedure of those reported in the literature on multibody dynamics. PMID:26959027

  12. Leveraging natural dynamical structures to explore multi-body systems

    NASA Astrophysics Data System (ADS)

    Bosanac, Natasha

    Multi-body systems have become the target of an increasing number of mission concepts and observations, supplying further information about the composition, origin and dynamical environment of bodies within the solar system and beyond. In many of these scenarios, identification and characterization of the particular solutions that exist in a circular restricted three-body model is valuable. This insight into the underlying natural dynamical structures is achieved via the application of dynamical systems techniques. One application of such analysis is trajectory design for CubeSats, which are intended to explore cislunar space and other planetary systems. These increasingly complex mission objectives necessitate innovative trajectory design strategies for spacecraft within our solar system, as well as the capability for rapid and well-informed redesign. Accordingly, a trajectory design framework is constructed using dynamical systems techniques and demonstrated for the Lunar IceCube mission. An additional application explored in this investigation involves the motion of an exoplanet near a binary star system. Due to the strong gravitational field near a binary star, physicists have previously leveraged these systems as testbeds for examining the validity of gravitational and relativistic theories. In this investigation, a preliminary analysis into the effect of an additional three-body interaction on the dynamical environment near a large mass ratio binary system is conducted. As demonstrated through both of these sample applications, identification and characterization of the natural particular solutions that exist within a multi-body system supports a well-informed and guided analysis.

  13. Dynamics and Embedded Internet of Things Input Shaping Control for Overhead Cranes Transporting Multibody Payloads.

    PubMed

    Peláez, Gerardo; Vaugan, Joshua; Izquierdo, Pablo; Rubio, Higinio; García-Prada, Juan Carlos

    2018-06-04

    Input shaping is an Optimal Control feedforward strategy whose ability to define how and when a flexible dynamical system defined by Ordinary Differential Equations (ODEs) and computer controlled would move into its operative space, without command induced unwanted dynamics, has been exhaustively demonstrated. This work examines the issue of Embedded Internet of Things (IoT) Input Shaping with regard to real time control of multibody oscillatory systems whose dynamics are better described by differential algebraic equations (DAEs). An overhead crane hanging a double link multibody payload has been appointed as a benchmark case; it is a multibody, multimode system. This might be worst scenario to implement Input Shaping. The reasons can be found in the wide array of constraints that arise. Firstly, the reliability of the multibody model was tested on a Functional Mock-Up Interface (FMI) with the two link payload suspended from the trolley by comparing the experimental video tapping signals in time domain faced with the signals extracted from the multibody model. The FFTs of the simulated and the experimental signal contain the same frequency harmonics only with somewhat different power due to the real world light damping in the joints. The application of this approach may be extended to other cases i.e., the usefulness of mobile hydraulic cranes is limited because the payload is supported by an overhead cable under tension that allows oscillation to occur during crane motion. If the payload size is not negligible small when compared with the cable length may introduce an additional oscillatory mode that creates a multibody double pendulum. To give the insight into the double pendulum dynamics by Lagrangian methods two slender rods as payloads are analyzed dealing with the overhead crane and a composite revolute-revolute joint is proposed to model the cable of the hydraulic crane, both assumptions facilitates an affordable analysis. This allows developing a general

  14. Partition method and experimental validation for impact dynamics of flexible multibody system

    NASA Astrophysics Data System (ADS)

    Wang, J. Y.; Liu, Z. Y.; Hong, J. Z.

    2018-06-01

    The impact problem of a flexible multibody system is a non-smooth, high-transient, and strong-nonlinear dynamic process with variable boundary. How to model the contact/impact process accurately and efficiently is one of the main difficulties in many engineering applications. The numerical approaches being used widely in impact analysis are mainly from two fields: multibody system dynamics (MBS) and computational solid mechanics (CSM). Approaches based on MBS provide a more efficient yet less accurate analysis of the contact/impact problems, while approaches based on CSM are well suited for particularly high accuracy needs, yet require very high computational effort. To bridge the gap between accuracy and efficiency in the dynamic simulation of a flexible multibody system with contacts/impacts, a partition method is presented considering that the contact body is divided into two parts, an impact region and a non-impact region. The impact region is modeled using the finite element method to guarantee the local accuracy, while the non-impact region is modeled using the modal reduction approach to raise the global efficiency. A three-dimensional rod-plate impact experiment is designed and performed to validate the numerical results. The principle for how to partition the contact bodies is proposed: the maximum radius of the impact region can be estimated by an analytical method, and the modal truncation orders of the non-impact region can be estimated by the highest frequency of the signal measured. The simulation results using the presented method are in good agreement with the experimental results. It shows that this method is an effective formulation considering both accuracy and efficiency. Moreover, a more complicated multibody impact problem of a crank slider mechanism is investigated to strengthen this conclusion.

  15. Multi-body Dynamic Contact Analysis Tool for Transmission Design

    DTIC Science & Technology

    2003-04-01

    frequencies were computed in COSMIC NASTRAN, and were validated against the published experimental modal analysis [17]. • Using assumed time domain... modal superposition. • Results from the structural analysis (mode shapes or forced response) were converted into IDEAS universal format (dataset 55...ARMY RESEARCH LABORATORY Multi-body Dynamic Contact Analysis Tool for Transmission Design SBIR Phase II Final Report by

  16. Connection forces in deformable multibody dynamics

    NASA Technical Reports Server (NTRS)

    Shabana, A. A.; Chang, C. W.

    1989-01-01

    In the dynamic formulation of holonomic and nonholonomic systems based on D'Alembert-Lagrange equation, the forces of constraints are maintained in the dynamic equations by introducing auxiliary variables, called Lagrange multipliers. This approach introduces a set of generalized reaction forces associated with the system generalized coordinates. Different sets of variables can be used as generalized coordinates and accordingly, the generalized reactions associated with these generalized coordinates may not be the actual reaction forces at the joints. In rigid body dynamics, the generalized reaction forces and the actual reaction forces at the joints represent equipollent systems of forces since they produce the same total forces and moments at and about any point on the rigid body. This is not, however, the case in deformable body analyses wherein the generalized reaction forces depend on the system generalized reference and elastic coordinates. In this paper, a method for determining the actual reaction forces at the joints from the generalized reaction forces in deformable multibody systems is presented.

  17. Multibody dynamical modeling for spacecraft docking process with spring-damper buffering device: A new validation approach

    NASA Astrophysics Data System (ADS)

    Daneshjou, Kamran; Alibakhshi, Reza

    2018-01-01

    In the current manuscript, the process of spacecraft docking, as one of the main risky operations in an on-orbit servicing mission, is modeled based on unconstrained multibody dynamics. The spring-damper buffering device is utilized here in the docking probe-cone system for micro-satellites. Owing to the impact occurs inevitably during docking process and the motion characteristics of multibody systems are remarkably affected by this phenomenon, a continuous contact force model needs to be considered. Spring-damper buffering device, keeping the spacecraft stable in an orbit when impact occurs, connects a base (cylinder) inserted in the chaser satellite and the end of docking probe. Furthermore, by considering a revolute joint equipped with torsional shock absorber, between base and chaser satellite, the docking probe can experience both translational and rotational motions simultaneously. Although spacecraft docking process accompanied by the buffering mechanisms may be modeled by constrained multibody dynamics, this paper deals with a simple and efficient formulation to eliminate the surplus generalized coordinates and solve the impact docking problem based on unconstrained Lagrangian mechanics. By an example problem, first, model verification is accomplished by comparing the computed results with those recently reported in the literature. Second, according to a new alternative validation approach, which is based on constrained multibody problem, the accuracy of presented model can be also evaluated. This proposed verification approach can be applied to indirectly solve the constrained multibody problems by minimum required effort. The time history of impact force, the influence of system flexibility and physical interaction between shock absorber and penetration depth caused by impact are the issues followed in this paper. Third, the MATLAB/SIMULINK multibody dynamic analysis software will be applied to build impact docking model to validate computed results and

  18. A decoupled recursive approach for constrained flexible multibody system dynamics

    NASA Technical Reports Server (NTRS)

    Lai, Hao-Jan; Kim, Sung-Soo; Haug, Edward J.; Bae, Dae-Sung

    1989-01-01

    A variational-vector calculus approach is employed to derive a recursive formulation for dynamic analysis of flexible multibody systems. Kinematic relationships for adjacent flexible bodies are derived in a companion paper, using a state vector notation that represents translational and rotational components simultaneously. Cartesian generalized coordinates are assigned for all body and joint reference frames, to explicitly formulate deformation kinematics under small deformation kinematics and an efficient flexible dynamics recursive algorithm is developed. Dynamic analysis of a closed loop robot is performed to illustrate efficiency of the algorithm.

  19. New Finite Element/Multibody System Algorithm for Modeling Flexible Tracked Vehicles

    DTIC Science & Technology

    2011-08-01

    U.S. Army RDECOM-TARDEC & 2 University of Illinois at Chicago ABSTRACT The dynamic simulation of multibody tracked vehicles offers engineers a...bodies. Then in a follow-on structural analysis, the loads from the multibody dynamic simulation are input to calculate strains and stresses within the...multibody dynamic simulation environment allowing for an integrated solution. In addition, a new formulation for the interaction between the rigid sprocket

  20. Multibody dynamic analysis using a rotation-free shell element with corotational frame

    NASA Astrophysics Data System (ADS)

    Shi, Jiabei; Liu, Zhuyong; Hong, Jiazhen

    2018-03-01

    Rotation-free shell formulation is a simple and effective method to model a shell with large deformation. Moreover, it can be compatible with the existing theories of finite element method. However, a rotation-free shell is seldom employed in multibody systems. Using a derivative of rigid body motion, an efficient nonlinear shell model is proposed based on the rotation-free shell element and corotational frame. The bending and membrane strains of the shell have been simplified by isolating deformational displacements from the detailed description of rigid body motion. The consistent stiffness matrix can be obtained easily in this form of shell model. To model the multibody system consisting of the presented shells, joint kinematic constraints including translational and rotational constraints are deduced in the context of geometric nonlinear rotation-free element. A simple node-to-surface contact discretization and penalty method are adopted for contacts between shells. A series of analyses for multibody system dynamics are presented to validate the proposed formulation. Furthermore, the deployment of a large scaled solar array is presented to verify the comprehensive performance of the nonlinear shell model.

  1. Effects of Age on Dynamic Accommodation

    PubMed Central

    Lockhart, Thurmon E.; Shi, Wen

    2010-01-01

    Visual accommodation plays a critical role in one’s visual perception and activities of daily living. Age-related accommodation loss poses an increased risk to older adults’ safety and independence. Although extensive effort has been made towards understanding the effect of age on steady-state accommodation, dynamic aspects of accommodation is still unknown. A study was therefore conducted to investigate age-related dynamic accommodative characteristics utilizing a modified autorefractor. Ten individuals from each of three age groups (i.e., younger group: 20 to 29 years old, middle-aged group: 40 to 49 years old, and older group: 60 to 69 years old) were recruited and their dynamic accommodation responses were examined. The laboratory experiment was designed to assess dynamic accommodation associated with an abrupt change from a constant far target (400 cm, 50 cd/m2) to a near target (70 cm, 100 cd/m2 or 20 cd/m2), which aimed to simulate car dashboard reading behavior while driving. The results of the study indicated that age and target intensity both had a significant impact on dynamic accommodation. These effects were attributed to both the age-related physiological limitation of the eye as well as to central neural processing delay. A method of measuring dynamic accommodation and the implications of the study are discussed. PMID:20582770

  2. A verification library for multibody simulation software

    NASA Technical Reports Server (NTRS)

    Kim, Sung-Soo; Haug, Edward J.; Frisch, Harold P.

    1989-01-01

    A multibody dynamics verification library, that maintains and manages test and validation data is proposed, based on RRC Robot arm and CASE backhoe validation and a comparitive study of DADS, DISCOS, and CONTOPS that are existing public domain and commercial multibody dynamic simulation programs. Using simple representative problems, simulation results from each program are cross checked, and the validation results are presented. Functionalities of the verification library are defined, in order to automate validation procedure.

  3. An innovations approach to decoupling of multibody dynamics and control

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.

    1989-01-01

    The problem of hinged multibody dynamics is solved using an extension of the innovations approach of linear filtering and prediction theory to the problem of mechanical system modeling and control. This approach has been used quite effectively to diagonalize the equations for filtering and prediction for linear state space systems. It has similar advantages in the study of dynamics and control of multibody systems. The innovations approach advanced here consists of expressing the equations of motion in terms of two closely related processes: (1) the innovations process e, a sequence of moments, obtained from the applied moments T by means of a spatially recursive Kalman filter that goes from the tip of the manipulator to its base; (2) a residual process, a sequence of velocities, obtained from the joint-angle velocities by means of an outward smoothing operations. The innovations e and the applied moments T are related by means of the relationships e = (I - L)T and T = (I + K)e. The operation (I - L) is a causal lower triangular matrix which is generated by a spatially recursive Kalman filter and the corresponding discrete-step Riccati equation. Hence, the innovations and the applied moments can be obtained from each other by means of a causal operation which is itself casually invertible.

  4. A NASTRAN/TREETOPS solution to a flexible, multi-body dynamics and controls problem on a UNIX workstation

    NASA Technical Reports Server (NTRS)

    Benavente, Javier E.; Luce, Norris R.

    1989-01-01

    Demands for nonlinear time history simulations of large, flexible multibody dynamic systems has created a need for efficient interfaces between finite-element modeling programs and time-history simulations. One such interface, TREEFLX, an interface between NASTRAN and TREETOPS, a nonlinear dynamics and controls time history simulation for multibody structures, is presented and demonstrated via example using the proposed Space Station Mobile Remote Manipulator System (MRMS). The ability to run all three programs (NASTRAN, TREEFLX and TREETOPS), in addition to other programs used for controller design and model reduction (such as DMATLAB and TREESEL, both described), under a UNIX Workstation environment demonstrates the flexibility engineers now have in designing, developing and testing control systems for dynamically complex systems.

  5. Advances in Chimera Grid Tools for Multi-Body Dynamics Simulations and Script Creation

    NASA Technical Reports Server (NTRS)

    Chan, William M.

    2004-01-01

    This viewgraph presentation contains information about (1) Framework for multi-body dynamics - Geometry Manipulation Protocol (GMP), (2) Simulation procedure using Chimera Grid Tools (CGT) and OVERFLOW-2 (3) Further recent developments in Chimera Grid Tools OVERGRID, Grid modules, Script library and (4) Future work.

  6. Computationally efficient multibody simulations

    NASA Technical Reports Server (NTRS)

    Ramakrishnan, Jayant; Kumar, Manoj

    1994-01-01

    Computationally efficient approaches to the solution of the dynamics of multibody systems are presented in this work. The computational efficiency is derived from both the algorithmic and implementational standpoint. Order(n) approaches provide a new formulation of the equations of motion eliminating the assembly and numerical inversion of a system mass matrix as required by conventional algorithms. Computational efficiency is also gained in the implementation phase by the symbolic processing and parallel implementation of these equations. Comparison of this algorithm with existing multibody simulation programs illustrates the increased computational efficiency.

  7. Vergence accommodation and monocular closed loop blur accommodation have similar dynamic characteristics.

    PubMed

    Suryakumar, Rajaraman; Meyers, Jason P; Irving, Elizabeth L; Bobier, William R

    2007-02-01

    Retinal blur and disparity are two different sensory signals known to cause a change in accommodative response. These inputs have differing neurological correlates that feed into a final common pathway. The purpose of this study was to investigate the dynamic properties of monocular blur driven accommodation and binocular disparity driven vergence-accommodation (VA) in human subjects. The results show that when response amplitudes are matched, blur accommodation and VA share similar dynamic properties.

  8. Development of High Fidelity Mobility Simulation of an Autonomous Vehicle in an Off-Road Scenario Using Integrated Sensor, Controller, and Multi-Body Dynamics

    DTIC Science & Technology

    2011-08-04

    AND MULTI-BODY DYNAMICS Jayakumar , Smith, Ross, Jategaonkar, Konarzewski 4 August 2011 UNCLASSIFIED: Distribution Statement A. Approved for public...Autonomous Vehicle in an Off-Road Scenario Using Integrated Sensor, Controller, and Multi-Body Dynamics 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM...Cannot neglect vehicle dynamics 4 August 2011 3 UNCLASSIFIED Importance of Simulation Fidelity • Performance evaluation requires entire system

  9. Spatial operator approach to flexible multibody system dynamics and control

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.

    1991-01-01

    The inverse and forward dynamics problems for flexible multibody systems were solved using the techniques of spatially recursive Kalman filtering and smoothing. These algorithms are easily developed using a set of identities associated with mass matrix factorization and inversion. These identities are easily derived using the spatial operator algebra developed by the author. Current work is aimed at computational experiments with the described algorithms and at modelling for control design of limber manipulator systems. It is also aimed at handling and manipulation of flexible objects.

  10. Nonlinear dynamic analysis of flexible multibody systems

    NASA Technical Reports Server (NTRS)

    Bauchau, Olivier A.; Kang, Nam Kook

    1991-01-01

    Two approaches are developed to analyze the dynamic behavior of flexible multibody systems. In the first approach each body is modeled with a modal methodology in a local non-inertial frame of reference, whereas in the second approach, each body is modeled with a finite element methodology in the inertial frame. In both cases, the interaction among the various elastic bodies is represented by constraint equations. The two approaches were compared for accuracy and efficiency: the first approach is preferable when the nonlinearities are not too strong but it becomes cumbersome and expensive to use when many modes must be used. The second approach is more general and easier to implement but could result in high computation costs for a large system. The constraints should be enforced in a time derivative fashion for better accuracy and stability.

  11. Dynamic accommodation responses following adaptation to defocus.

    PubMed

    Cufflin, Matthew P; Mallen, Edward A H

    2008-10-01

    Adaptation to defocus is known to influence the subjective sensitivity to blur in both emmetropes and myopes. Blur is a major contributing factor in the closed-loop dynamic accommodation response. Previous investigations have examined the magnitude of the accommodation response following blur adaptation. We have investigated whether a period of blur adaptation influences the dynamic accommodation response to step and sinusoidal changes in target vergence. Eighteen subjects (six emmetropes, six early onset myopes, and six late onset myopes) underwent 30 min of adaptation to 0.00 D (control), +1.00 D or +3.00 D myopic defocus. Following this adaptation period, accommodation responses to a 2.00 D step change and 2.00 D sinusoidal change (0.2 Hz) in target vergence were recorded continuously using an autorefractor. Adaptation to defocus failed to influence accommodation latency times, but did influence response times to a step change in target vergence. Adaptation to both +1.00 and +3.00 D induced significant increases in response times (p = 0.002 and p = 0.012, respectively) and adaptation to +3.00 D increased the change in accommodation response magnitude (p = 0.014) for a 2.00 D step change in demand. Blur adaptation also significantly increased the peak-to-peak phase lag for accommodation responses to a sinusoidally oscillating target, although failed to influence the accommodation gain. These changes in accommodative response were equivalent across all refractive groups. Adaptation to a degraded stimulus causes an increased level of accommodation for dynamic targets moving towards an observer and increases response times and phase lags. It is suggested that the contrast constancy theory may explain these changes in dynamic behavior.

  12. Brownian dynamics simulations of a flexible polymer chain which includes continuous resistance and multibody hydrodynamic interactions

    NASA Astrophysics Data System (ADS)

    Butler, Jason E.; Shaqfeh, Eric S. G.

    2005-01-01

    Using methods adapted from the simulation of suspension dynamics, we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules. The polymer molecule is modeled as a chain composed of a series of inextensible, rigid rods with constraints at each joint to ensure continuity of the chain. The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor [J. Fluid Mech. 44, 419 (1970)]. To include hydrodynamic interactions between the segments of the chain, the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment, where the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution is specified by a center of mass force, couple, and stresslet on each segment. This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers [O. G. Harlen, R. R. Sundararajakumar, and D. L. Koch, J. Fluid Mech. 388, 355 (1999); J. E. Butler and E. S. G. Shaqfeh, J. Fluid Mech. 468, 204 (2002)]. The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique. Comparisons are made for different levels of approximation of the hydrodynamic interactions, including multibody interactions, two-body interactions, and the "freely draining" case with no interactions. For the short polymer chains studied in this paper, the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions.

  13. Modeling the Multi-Body System Dynamics of a Flexible Solar Sail Spacecraft

    NASA Technical Reports Server (NTRS)

    Kim, Young; Stough, Robert; Whorton, Mark

    2005-01-01

    Solar sail propulsion systems enable a wide range of space missions that are not feasible with current propulsion technology. Hardware concepts and analytical methods have matured through ground development to the point that a flight validation mission is now realizable. Much attention has been given to modeling the structural dynamics of the constituent elements, but to date an integrated system level dynamics analysis has been lacking. Using a multi-body dynamics and control analysis tool called TREETOPS, the coupled dynamics of the sailcraft bus, sail membranes, flexible booms, and control system sensors and actuators of a representative solar sail spacecraft are investigated to assess system level dynamics and control issues. With this tool, scaling issues and parametric trade studies can be performed to study achievable performance, control authority requirements, and control/structure interaction assessments.

  14. A comparative study on dynamic stiffness in typical finite element model and multi-body model of C6-C7 cervical spine segment.

    PubMed

    Wang, Yawei; Wang, Lizhen; Du, Chengfei; Mo, Zhongjun; Fan, Yubo

    2016-06-01

    In contrast to numerous researches on static or quasi-static stiffness of cervical spine segments, very few investigations on their dynamic stiffness were published. Currently, scale factors and estimated coefficients were usually used in multi-body models for including viscoelastic properties and damping effects, meanwhile viscoelastic properties of some tissues were unavailable for establishing finite element models. Because dynamic stiffness of cervical spine segments in these models were difficult to validate because of lacking in experimental data, we tried to gain some insights on current modeling methods through studying dynamic stiffness differences between these models. A finite element model and a multi-body model of C6-C7 segment were developed through using available material data and typical modeling technologies. These two models were validated with quasi-static response data of the C6-C7 cervical spine segment. Dynamic stiffness differences were investigated through controlling motions of C6 vertebrae at different rates and then comparing their reaction forces or moments. Validation results showed that both the finite element model and the multi-body model could generate reasonable responses under quasi-static loads, but the finite element segment model exhibited more nonlinear characters. Dynamic response investigations indicated that dynamic stiffness of this finite element model might be underestimated because of the absence of dynamic stiffen effect and damping effects of annulus fibrous, while representation of these effects also need to be improved in current multi-body model. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

  15. Evaluation of constraint stabilization procedures for multibody dynamical systems

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Chiou, J. C.

    1987-01-01

    Comparative numerical studies of four constraint treatment techniques for the simulation of general multibody dynamic systems are presented, and results are presented for the example of a classical crank mechanism and for a simplified version of the seven-link manipulator deployment problem. The staggered stabilization technique (Park, 1986) is found to yield improved accuracy and robustness over Baumgarte's (1972) technique, the singular decomposition technique (Walton and Steeves, 1969), and the penalty technique (Lotstedt, 1979). Furthermore, the staggered stabilization technique offers software modularity, and the only data each solution module needs to exchange with the other is a set of vectors plus a common module to generate the gradient matrix of the constraints, B.

  16. Multi-Body Dynamic Contact Analysis. Tool for Transmission Design SBIR Phase II Final Report

    DTIC Science & Technology

    2003-04-01

    shapes and natural frequencies were computed in COSMIC NASTRAN, and were validated against the published experimental modal analysis [17]. • Using...COSMIC NASTRAN via modal superposition. • Results from the structural analysis (mode shapes or forced response) were converted into IDEAS universal...ARMY RESEARCH LABORATORY Multi-body Dynamic Contact Analysis Tool for Transmission Design SBIR Phase II Final Report by

  17. Brownian dynamics simulations of a flexible polymer chain which includes continuous resistance and multibody hydrodynamic interactions.

    PubMed

    Butler, Jason E; Shaqfeh, Eric S G

    2005-01-01

    Using methods adapted from the simulation of suspension dynamics, we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules. The polymer molecule is modeled as a chain composed of a series of inextensible, rigid rods with constraints at each joint to ensure continuity of the chain. The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor [J. Fluid Mech. 44, 419 (1970)]. To include hydrodynamic interactions between the segments of the chain, the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment, where the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution is specified by a center of mass force, couple, and stresslet on each segment. This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers [O. G. Harlen, R. R. Sundararajakumar, and D. L. Koch, J. Fluid Mech. 388, 355 (1999); J. E. Butler and E. S. G. Shaqfeh, J. Fluid Mech. 468, 204 (2002)]. The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique. Comparisons are made for different levels of approximation of the hydrodynamic interactions, including multibody interactions, two-body interactions, and the "freely draining" case with no interactions. For the short polymer chains studied in this paper, the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions. (c) 2005 American Institute of Physics.

  18. Some fundamentals regarding kinematics and generalized forces for multibody dynamics

    NASA Technical Reports Server (NTRS)

    Hodges, Dewey H.

    1990-01-01

    In order to illustrate the various forms in which generalized forces can arise from diverse subsystem analyses in multibody dynamics, intrinsic dynamical equations for the rotational dynamics of a rigid body are derived from Hamilton's principle. Two types of generalized forces are derived: (1) those associated with the virtual rotation vector in some orthogonal basis, and (2) those associated with varying generalized coordinates. As one physical or kinematical result (such as a frequency or a specific direction cosine) cannot rely on this selection, a 'blind' coupling of two models in which generalized forces are calculated in different ways would be wrong. Both types should use the same rotational coordinates and should denote the virtual rotation on a similar basis according to method 1, or in terms of common rotational coordinates and their diversifications as in method 2. Alternatively, the generalized forces and coordinates of one model may be transformed to those of the other.

  19. Bond graph modelling of multibody dynamics and its symbolic scheme

    NASA Astrophysics Data System (ADS)

    Kawase, Takehiko; Yoshimura, Hiroaki

    A bond graph method of modeling multibody dynamics is demonstrated. Specifically, a symbolic generation scheme which fully utilizes the bond graph information is presented. It is also demonstrated that structural understanding and representation in bond graph theory is quite powerful for the modeling of such large scale systems, and that the nonenergic multiport of junction structure, which is a multiport expression of the system structure, plays an important role, as first suggested by Paynter. The principal part of the proposed symbolic scheme, that is, the elimination of excess variables, is done through tearing and interconnection in the sense of Kron using newly defined causal and causal coefficient arrays.

  20. Recursive thoughts on the simulation of the flexible multibody dynamics of slender offshore structures

    NASA Astrophysics Data System (ADS)

    Schilder, J.; Ellenbroek, M.; de Boer, A.

    2017-12-01

    In this work, the floating frame of reference formulation is used to create a flexible multibody model of slender offshore structures such as pipelines and risers. It is shown that due to the chain-like topology of the considered structures, the equation of motion can be expressed in terms of absolute interface coordinates. In the presented form, kinematic constraint equations are satisfied explicitly and the Lagrange multipliers are eliminated from the equations. Hence, the structures can be conveniently coupled to finite element or multibody models of for example seabed and vessel. The chain-like topology enables the efficient use of recursive solution procedures for both transient dynamic analysis and equilibrium analysis. For this, the transfer matrix method is used. In order to improve the convergence of the equilibrium analysis, the analytical solution of an ideal catenary is used as an initial configuration, reducing the number of required iterations.

  1. Adaptive Calibration of Dynamic Accommodation—Implications for Accommodating Intraocular Lenses

    PubMed Central

    Schor, Clifton M.; Bharadwaj, Shrikant R.

    2009-01-01

    PURPOSE When the aging lens is replaced with prosthetic accommodating intraocular lenses (IOLs), with effective viscoelasticities different from those of the natural lens, mismatches could arise between the neural control of accommodation and the biomechanical properties of the new lens. These mismatches could lead to either unstable oscillations or sluggishness of dynamic accommodation. Using computer simulations, we investigated whether optimal accommodative responses could be restored through recalibration of the neural control of accommodation. Using human experiments, we also investigated whether the accommodative system has the capacity for adaptive recalibration in response to changes in lens biomechanics. METHODS Dynamic performance of two accommodating IOL prototypes was simulated for a 45-year-old accommodative system, before and after neural recalibration, using a dynamic model of accommodation. Accommodating IOL I, a prototype for an injectable accommodating IOL, was less stiff and less viscous than the natural 45-year-old lens. Accommodating IOL II, a prototype for a translating accommodating IOL, was less stiff and more viscous than the natural 45-year-old lens. Short-term adaptive recalibration of dynamic accommodation was stimulated using a double-step adaptation paradigm that optically induced changes in neuromuscular effort mimicking responses to changes in lens biomechanics. RESULTS Model simulations indicate that the unstable oscillations or sluggishness of dynamic accommodation resulting from mismatches between neural control and lens biomechanics might be restored through neural recalibration. CONCLUSIONS Empirical measures reveal that the accommodative system is capable of adaptive recalibration in response to optical loads that simulate effects of changing lens biomechanics. PMID:19044245

  2. Simulation studies using multibody dynamics code DART

    NASA Technical Reports Server (NTRS)

    Keat, James E.

    1989-01-01

    DART is a multibody dynamics code developed by Photon Research Associates for the Air Force Astronautics Laboratory (AFAL). The code is intended primarily to simulate the dynamics of large space structures, particularly during the deployment phase of their missions. DART integrates nonlinear equations of motion numerically. The number of bodies in the system being simulated is arbitrary. The bodies' interconnection joints can have an arbitrary number of degrees of freedom between 0 and 6. Motions across the joints can be large. Provision for simulating on-board control systems is provided. Conservation of energy and momentum, when applicable, are used to evaluate DART's performance. After a brief description of DART, studies made to test the program prior to its delivery to AFAL are described. The first is a large angle reorientating of a flexible spacecraft consisting of a rigid central hub and four flexible booms. Reorientation was accomplished by a single-cycle sine wave shape torque input. In the second study, an appendage, mounted on a spacecraft, was slewed through a large angle. Four closed-loop control systems provided control of this appendage and of the spacecraft's attitude. The third study simulated the deployment of the rim of a bicycle wheel configuration large space structure. This system contained 18 bodies. An interesting and unexpected feature of the dynamics was a pulsing phenomena experienced by the stays whole playout was used to control the deployment. A short description of the current status of DART is given.

  3. Applications of Multi-Body Dynamical Environments: The ARTEMIS Transfer Trajectory Design

    NASA Technical Reports Server (NTRS)

    Folta, David C.; Woodard, Mark; Howell, Kathleen; Patterson, Chris; Schlei, Wayne

    2010-01-01

    The application of forces in multi-body dynamical environments to pennit the transfer of spacecraft from Earth orbit to Sun-Earth weak stability regions and then return to the Earth-Moon libration (L1 and L2) orbits has been successfully accomplished for the first time. This demonstrated transfer is a positive step in the realization of a design process that can be used to transfer spacecraft with minimal Delta-V expenditures. Initialized using gravity assists to overcome fuel constraints; the ARTEMIS trajectory design has successfully placed two spacecraft into EarthMoon libration orbits by means of these applications.

  4. Static analysis of large-scale multibody system using joint coordinates and spatial algebra operator.

    PubMed

    Omar, Mohamed A

    2014-01-01

    Initial transient oscillations inhibited in the dynamic simulations responses of multibody systems can lead to inaccurate results, unrealistic load prediction, or simulation failure. These transients could result from incompatible initial conditions, initial constraints violation, and inadequate kinematic assembly. Performing static equilibrium analysis before the dynamic simulation can eliminate these transients and lead to stable simulation. Most exiting multibody formulations determine the static equilibrium position by minimizing the system potential energy. This paper presents a new general purpose approach for solving the static equilibrium in large-scale articulated multibody. The proposed approach introduces an energy drainage mechanism based on Baumgarte constraint stabilization approach to determine the static equilibrium position. The spatial algebra operator is used to express the kinematic and dynamic equations of the closed-loop multibody system. The proposed multibody system formulation utilizes the joint coordinates and modal elastic coordinates as the system generalized coordinates. The recursive nonlinear equations of motion are formulated using the Cartesian coordinates and the joint coordinates to form an augmented set of differential algebraic equations. Then system connectivity matrix is derived from the system topological relations and used to project the Cartesian quantities into the joint subspace leading to minimum set of differential equations.

  5. Recursive mass matrix factorization and inversion: An operator approach to open- and closed-chain multibody dynamics

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.; Kreutz, K.

    1988-01-01

    This report advances a linear operator approach for analyzing the dynamics of systems of joint-connected rigid bodies.It is established that the mass matrix M for such a system can be factored as M=(I+H phi L)D(I+H phi L) sup T. This yields an immediate inversion M sup -1=(I-H psi L) sup T D sup -1 (I-H psi L), where H and phi are given by known link geometric parameters, and L, psi and D are obtained recursively by a spatial discrete-step Kalman filter and by the corresponding Riccati equation associated with this filter. The factors (I+H phi L) and (I-H psi L) are lower triangular matrices which are inverses of each other, and D is a diagonal matrix. This factorization and inversion of the mass matrix leads to recursive algortihms for forward dynamics based on spatially recursive filtering and smoothing. The primary motivation for advancing the operator approach is to provide a better means to formulate, analyze and understand spatial recursions in multibody dynamics. This is achieved because the linear operator notation allows manipulation of the equations of motion using a very high-level analytical framework (a spatial operator algebra) that is easy to understand and use. Detailed lower-level recursive algorithms can readily be obtained for inspection from the expressions involving spatial operators. The report consists of two main sections. In Part 1, the problem of serial chain manipulators is analyzed and solved. Extensions to a closed-chain system formed by multiple manipulators moving a common task object are contained in Part 2. To retain ease of exposition in the report, only these two types of multibody systems are considered. However, the same methods can be easily applied to arbitrary multibody systems formed by a collection of joint-connected regid bodies.

  6. Newton-Euler Dynamic Equations of Motion for a Multi-body Spacecraft

    NASA Technical Reports Server (NTRS)

    Stoneking, Eric

    2007-01-01

    The Magnetospheric MultiScale (MMS) mission employs a formation of spinning spacecraft with several flexible appendages and thruster-based control. To understand the complex dynamic interaction of thruster actuation, appendage motion, and spin dynamics, each spacecraft is modeled as a tree of rigid bodies connected by spherical or gimballed joints. The method presented facilitates assembling by inspection the exact, nonlinear dynamic equations of motion for a multibody spacecraft suitable for solution by numerical integration. The building block equations are derived by applying Newton's and Euler's equations of motion to an "element" consisting of two bodies and one joint (spherical and gimballed joints are considered separately). Patterns in the "mass" and L'force" matrices guide assembly by inspection of a general N-body tree-topology system. Straightforward linear algebra operations are employed to eliminate extraneous constraint equations, resulting in a minimum-dimension system of equations to solve. This method thus combines a straightforward, easily-extendable, easily-mechanized formulation with an efficient computer implementation.

  7. Static Analysis of Large-Scale Multibody System Using Joint Coordinates and Spatial Algebra Operator

    PubMed Central

    Omar, Mohamed A.

    2014-01-01

    Initial transient oscillations inhibited in the dynamic simulations responses of multibody systems can lead to inaccurate results, unrealistic load prediction, or simulation failure. These transients could result from incompatible initial conditions, initial constraints violation, and inadequate kinematic assembly. Performing static equilibrium analysis before the dynamic simulation can eliminate these transients and lead to stable simulation. Most exiting multibody formulations determine the static equilibrium position by minimizing the system potential energy. This paper presents a new general purpose approach for solving the static equilibrium in large-scale articulated multibody. The proposed approach introduces an energy drainage mechanism based on Baumgarte constraint stabilization approach to determine the static equilibrium position. The spatial algebra operator is used to express the kinematic and dynamic equations of the closed-loop multibody system. The proposed multibody system formulation utilizes the joint coordinates and modal elastic coordinates as the system generalized coordinates. The recursive nonlinear equations of motion are formulated using the Cartesian coordinates and the joint coordinates to form an augmented set of differential algebraic equations. Then system connectivity matrix is derived from the system topological relations and used to project the Cartesian quantities into the joint subspace leading to minimum set of differential equations. PMID:25045732

  8. Study on accommodation by autorefraction and dynamic refraction in children.

    PubMed

    Krishnacharya, Prabhakar Srinivasapur

    2014-01-01

    Childhood accommodation interferes with accurate diagnosis of the latent refractive errors. Dynamic retinoscopy offers accurate measurements of accommodative response, while an autorefractometer can predict the accommodative system activation in children. A correlation of the accommodative effort with the dynamic refraction has been investigated in emmetropic children, before and after cycloplegia. A prospective clinical study of accommodative effort in 149 emmetropic children, in the age group 3-16 years, has been conducted using TOPCON AR RM-8000B autorefractor. Dynamic refraction was performed by monocular estimation method before and after cycloplegia, using the retinoscope mirror light as target. Retinoscopic reflex produced 'with the motion' was corrected with positive spherical lenses, and that 'against the motion' was corrected with negative spherical lenses, to achieve neutralization. Mean accommodative effort measured for 149 children included in the study was -0.63±0.69D and dynamic refraction was -0.07±0.44D before cycloplegia, while the mean was+0.52D after cycloplegia, irrespective of the method used. Autorefractor measured -0.17D of accommodative effort per unit change in dynamic refraction before cycloplegia and +0.90D after cycloplegia. The performance of TOPCON AR RM-8000B autorefractor was comparable to dynamic retinoscopy. Presence of many children, and in turn, large number of accommodative response data in 11-13 and 14-15 years group is probably linked to prolonged reading/writing. The accuracy and the agreement of the actual accommodative measurements revealed after cycloplegia. Copyright © 2013 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

  9. [Monochromatic aberration in accommodation. Dynamic wavefront analysis].

    PubMed

    Fritzsch, M; Dawczynski, J; Jurkutat, S; Vollandt, R; Strobel, J

    2011-06-01

    Monochromatic aberrations may influence the visual acuity of the eye. They are not stable and can be affected by different factors. The subject of the following paper is the dynamic investigation of the changes in wavefront aberration with accommodation. Dynamic measurement of higher and lower order aberrations was performed with a WASCA Wavefront Analyzer (Carl-Zeiss-Meditec) and a specially constructed target device for aligning objects in far and near distances on 25 subjects aged from 15 to 27 years old. Wavefront aberrations showed some significant changes in accommodation. In addition to the characteristic sphere reaction accompanying miosis and changes in horizontal prism (Z(1) (1)) in the sense of a convergence movement of the eyeball also occurred. Furthermore defocus rose (Z(2) (0)) and astigmatism (Z(2) (-2)) changed. In higher-order aberrations a decrease in coma-like Zernike polynomials (Z(3) (-1), Z(3) (1)) was found. The most obvious change appeared in spherical aberration (Z(4) (0)) which increased and changed from positive to negative. In addition the secondary astigmatism (Z(4) (-2)) and quadrafoil (Z(4) (4)) rise also increased. The total root mean square (RMS), as well as the higher-order aberrations (RMS-HO) significantly increased in accommodation which is associated with a theoretical reduction of visual acuity. An analysis of the influence of pupil size on aberrations showed significant increases in defocus, spherical aberration, quadrafoil, RMS and RMS HO by increasing pupil diameter. By accommodation-associated miosis, the growing aberrations are partially compensated by focusing on near objects. Temporal analysis of the accommodation process with dynamic wavefront analysis revealed significant delays in pupil response and changing of prism in relation to the sphere reaction. In accommodation to near objects a discrete time ahead of third order aberrations in relation to the sphere response was found. Using dynamic wavefront measurement

  10. Design and Implementation of the ARTEMIS Lunar Transfer Using Multi-Body Dynamics

    NASA Technical Reports Server (NTRS)

    Folta, David; Woodard, Mark; Sweetser, Theodore; Broschart, Stephen B.; Cosgrove, Daniel

    2011-01-01

    The use of multi-body dynamics to design the transfer of spacecraft from Earth elliptical orbits to the Earth-Moon libration (L(sub 1) and L(sub 2)) orbits has been successfully demonstrated by the Acceleration Reconnection and Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission. Operational support of the two ARTEMIS spacecraft is a final step in the realization of a design process that can be used to transfer spacecraft with restrictive operational constraints and fuel limitations. The focus of this paper is to describe in detail the processes and implementation of this successful approach.

  11. Study on accommodation by autorefraction and dynamic refraction in children

    PubMed Central

    Krishnacharya, Prabhakar Srinivasapur

    2014-01-01

    Purpose Childhood accommodation interferes with accurate diagnosis of the latent refractive errors. Dynamic retinoscopy offers accurate measurements of accommodative response, while an autorefractometer can predict the accommodative system activation in children. A correlation of the accommodative effort with the dynamic refraction has been investigated in emmetropic children, before and after cycloplegia. Methods A prospective clinical study of accommodative effort in 149 emmetropic children, in the age group 3–16 years, has been conducted using TOPCON AR RM-8000B autorefractor. Dynamic refraction was performed by monocular estimation method before and after cycloplegia, using the retinoscope mirror light as target. Retinoscopic reflex produced ‘with the motion’ was corrected with positive spherical lenses, and that ‘against the motion’ was corrected with negative spherical lenses, to achieve neutralization. Results Mean accommodative effort measured for 149 children included in the study was −0.63 ± 0.69 D and dynamic refraction was −0.07 ± 0.44 D before cycloplegia, while the mean was + 0.52 D after cycloplegia, irrespective of the method used. Autorefractor measured −0.17 D of accommodative effort per unit change in dynamic refraction before cycloplegia and +0.90 D after cycloplegia. Conclusions The performance of TOPCON AR RM-8000B autorefractor was comparable to dynamic retinoscopy. Presence of many children, and in turn, large number of accommodative response data in 11–13 and 14–15 years group is probably linked to prolonged reading/writing. The accuracy and the agreement of the actual accommodative measurements revealed after cycloplegia. PMID:25130066

  12. Comparative multibody dynamics analysis of falls from playground climbing frames.

    PubMed

    Forero Rueda, M A; Gilchrist, M D

    2009-10-30

    This paper shows the utility of multibody dynamics in evaluating changes in injury related parameters of the head and lower limbs of children following falls from playground climbing frames. A particular fall case was used as a starting point to analyze the influence of surface properties, posture of the body at impact, and intermediate collisions against the climbing frame before impacting the ground. Simulations were made using the 6-year-old pedestrian MADYMO rigid body model and scaled head contact characteristics. Energy absorbing surfaces were shown to reduce injury severity parameters by up to 30-80% of those of rigid surfaces, depending on impact posture and surface. Collisions against components of a climbing frame during a fall can increase injury severity of the final impact of the head with the ground by more than 90%. Negligible changes are associated with lower limb injury risks when different surfacing materials are used. Computer reconstructions of actual falls that are intended to quantify the severity of physical injuries rely on accurate knowledge of initial conditions prior to falling, intermediate kinematics of the fall and the orientation of the body when it impacts against the ground. Multibody modelling proved to be a valuable tool to analyze the quality of eyewitness information and analyze the relative injury risk associated with changes in components influencing fall injuries from playground climbing frames. Such simulations can also support forensic investigations by evaluating alternative hypotheses for the sequence of kinematic motion of falls which result in known injuries.

  13. Multibody modeling and verification

    NASA Technical Reports Server (NTRS)

    Wiens, Gloria J.

    1989-01-01

    A summary of a ten week project on flexible multibody modeling, verification and control is presented. Emphasis was on the need for experimental verification. A literature survey was conducted for gathering information on the existence of experimental work related to flexible multibody systems. The first portion of the assigned task encompassed the modeling aspects of flexible multibodies that can undergo large angular displacements. Research in the area of modeling aspects were also surveyed, with special attention given to the component mode approach. Resulting from this is a research plan on various modeling aspects to be investigated over the next year. The relationship between the large angular displacements, boundary conditions, mode selection, and system modes is of particular interest. The other portion of the assigned task was the generation of a test plan for experimental verification of analytical and/or computer analysis techniques used for flexible multibody systems. Based on current and expected frequency ranges of flexible multibody systems to be used in space applications, an initial test article was selected and designed. A preliminary TREETOPS computer analysis was run to ensure frequency content in the low frequency range, 0.1 to 50 Hz. The initial specifications of experimental measurement and instrumentation components were also generated. Resulting from this effort is the initial multi-phase plan for a Ground Test Facility of Flexible Multibody Systems for Modeling Verification and Control. The plan focusses on the Multibody Modeling and Verification (MMV) Laboratory. General requirements of the Unobtrusive Sensor and Effector (USE) and the Robot Enhancement (RE) laboratories were considered during the laboratory development.

  14. Age-Related Changes in Accommodative Dynamics from Preschool to Adulthood

    PubMed Central

    Glasser, Adrian; Manny, Ruth E.; Stuebing, Karla K.

    2010-01-01

    Purpose. To study variations in dynamic measures of accommodation and disaccommodation with age in subjects ranging from preschool to adulthood. Methods. Accommodative responses to a step stimulus cartoon movie alternating from distance to near were recorded with a dynamic infrared photorefractor. Subjects viewed at least three stimulus cycles of far and near for four near stimulus demands (2, 3, 4, and 5 D). Latencies, peak velocities, and the magnitude of accommodative microfluctuations were calculated from the responses and compared in 41 subjects from 3 to 38 years of age. Results. Mean accommodative and disaccommodative latencies decreased linearly with age. The magnitude of accommodative microfluctuations during sustained near accommodation had a significant quadratic relationship to age, with subjects in the first decade of life having the largest fluctuations and subjects in the third decade of life having the smallest for all stimulus demands. Accommodative peak velocities were fastest in subjects in the first two decades of life, compared with subjects in the third and fourth decades; however, disaccommodative peak velocities showed no significant age differences. Conclusions. Age-related changes in dynamics occur in accommodative and disaccommodative latencies, accommodative peak velocities, and accommodative microfluctuations, all of which decrease with increasing age from preschool to adulthood. Disaccommodative peak velocities showed no change with age. PMID:19684002

  15. On computing stress in polymer systems involving multi-body potentials from molecular dynamics simulation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fu, Yao, E-mail: fu5@mailbox.sc.edu, E-mail: jhsong@cec.sc.edu; Song, Jeong-Hoon, E-mail: fu5@mailbox.sc.edu, E-mail: jhsong@cec.sc.edu

    2014-08-07

    Hardy stress definition has been restricted to pair potentials and embedded-atom method potentials due to the basic assumptions in the derivation of a symmetric microscopic stress tensor. Force decomposition required in the Hardy stress expression becomes obscure for multi-body potentials. In this work, we demonstrate the invariance of the Hardy stress expression for a polymer system modeled with multi-body interatomic potentials including up to four atoms interaction, by applying central force decomposition of the atomic force. The balance of momentum has been demonstrated to be valid theoretically and tested under various numerical simulation conditions. The validity of momentum conservation justifiesmore » the extension of Hardy stress expression to multi-body potential systems. Computed Hardy stress has been observed to converge to the virial stress of the system with increasing spatial averaging volume. This work provides a feasible and reliable linkage between the atomistic and continuum scales for multi-body potential systems.« less

  16. On computing stress in polymer systems involving multi-body potentials from molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Fu, Yao; Song, Jeong-Hoon

    2014-08-01

    Hardy stress definition has been restricted to pair potentials and embedded-atom method potentials due to the basic assumptions in the derivation of a symmetric microscopic stress tensor. Force decomposition required in the Hardy stress expression becomes obscure for multi-body potentials. In this work, we demonstrate the invariance of the Hardy stress expression for a polymer system modeled with multi-body interatomic potentials including up to four atoms interaction, by applying central force decomposition of the atomic force. The balance of momentum has been demonstrated to be valid theoretically and tested under various numerical simulation conditions. The validity of momentum conservation justifies the extension of Hardy stress expression to multi-body potential systems. Computed Hardy stress has been observed to converge to the virial stress of the system with increasing spatial averaging volume. This work provides a feasible and reliable linkage between the atomistic and continuum scales for multi-body potential systems.

  17. Non-recursive augmented Lagrangian algorithms for the forward and inverse dynamics of constrained flexible multibodies

    NASA Technical Reports Server (NTRS)

    Bayo, Eduardo; Ledesma, Ragnar

    1993-01-01

    A technique is presented for solving the inverse dynamics of flexible planar multibody systems. This technique yields the non-causal joint efforts (inverse dynamics) as well as the internal states (inverse kinematics) that produce a prescribed nominal trajectory of the end effector. A non-recursive global Lagrangian approach is used in formulating the equations for motion as well as in solving the inverse dynamics equations. Contrary to the recursive method previously presented, the proposed method solves the inverse problem in a systematic and direct manner for both open-chain as well as closed-chain configurations. Numerical simulation shows that the proposed procedure provides an excellent tracking of the desired end effector trajectory.

  18. Multibody dynamics driving GNC and system design in tethered nets for active debris removal

    NASA Astrophysics Data System (ADS)

    Benvenuto, Riccardo; Lavagna, Michèle; Salvi, Samuele

    2016-07-01

    Debris removal in Earth orbits is an urgent issue to be faced for space exploitation durability. Among different techniques, tethered-nets present appealing benefits and some open points to fix. Former and latter are discussed in the paper, supported by the exploitation of a multibody dynamics tool. With respect to other proposed capture mechanisms, tethered-net solutions are characterised by a safer capturing distance, a passive angular momentum damping effect and the highest flexibility to unknown shape, material and attitude of the target to interface with. They also allow not considering the centre of gravity alignment with thrust axis as a constraint, as it is for any rigid link solution. Furthermore, the introduction of a closing thread around the net perimeter ensures safer and more reliable grasping and holding. In the paper, a six degrees of freedom multibody dynamics simulator is presented: it was developed at Politecnico di Milano - Department of Aerospace Science and Technologies - and it is able to describe the orbital and attitude dynamics of tethered-nets systems and end-bodies during different phases, with great flexibility in dealing with different topologies and configurations. Critical phases as impact and wrapping are analysed by simulation to address the tethered-stack controllability. It is shown how the role of contact modelling is fundamental to describe the coupled dynamics: it is demonstrated, as a major novel contribution, how friction between the net and a tumbling target allows reducing its angular motion, stabilizing the system and allowing safer towing operations. Moreover, the so-called tethered space tug is analysed: after capture, the two objects, one passive and one active, are connected by the tethered-net flexible link, the motion of the system being excited by the active spacecraft thrusters. The critical modes prevention during this phase, by means of a closed-loop control synthesis is shown. Finally, the connection between

  19. Research on The Construction of Flexible Multi-body Dynamics Model based on Virtual Components

    NASA Astrophysics Data System (ADS)

    Dong, Z. H.; Ye, X.; Yang, F.

    2018-05-01

    Focus on the harsh operation condition of space manipulator, which cannot afford relative large collision momentum, this paper proposes a new concept and technology, called soft-contact technology. In order to solve the problem of collision dynamics of flexible multi-body system caused by this technology, this paper also proposes the concepts of virtual components and virtual hinges, and constructs flexible dynamic model based on virtual components, and also studies on its solutions. On this basis, this paper uses NX to carry out model and comparison simulation for space manipulator in 3 different modes. The results show that using the model of multi-rigid body + flexible body hinge + controllable damping can make effective control on amplitude for the force and torque caused by target satellite collision.

  20. Short-Term Adaptive Modification of Dynamic Ocular Accommodation

    PubMed Central

    Bharadwaj, Shrikant R.; Vedamurthy, Indu; Schor, Clifton M.

    2009-01-01

    Purpose Indirect observations suggest that the neural control of accommodation may undergo adaptive recalibration in response to age-related biomechanical changes in the accommodative system. However, there has been no direct demonstration of such an adaptive capability. This investigation was conducted to demonstrate short-term adaptation of accommodative step response dynamics to optically induced changes in neuromuscular demands. Methods Repetitive changes in accommodative effort were induced in 15 subjects (18–34 years) with a double-step adaptation paradigm wherein an initial 2-D step change in blur was followed 350 ms later by either a 2-D step increase in blur (increasing-step paradigm) or a 1.75-D step decrease in blur (decreasing-step paradigm). Peak velocity, peak acceleration, and latency of 2-D single-step test responses were assessed before and after 1.5 hours of training with these paradigms. Results Peak velocity and peak acceleration of 2-D step responses increased after adaptation to the increasing-step paradigm (9/12 subjects), and they decreased after adaptation to the decreasing-step paradigm (4/9 subjects). Adaptive changes in peak velocity and peak acceleration generalized to responses that were smaller (1 D) and larger (3 D) than the 2-D adaptation stimulus. The magnitude of adaptation correlated poorly with the subject's age, but it was significantly negatively correlated with the preadaptation dynamics. Response latency decreased after adaptation, irrespective of the direction of adaptation. Conclusions Short-term adaptive changes in accommodative step response dynamics could be induced, at least in some of our subjects between 18 and 34 years, with a directional bias toward increasing rather than decreasing the dynamics. PMID:19255153

  1. Human dynamic closed-loop accommodation augmented by sympathetic inhibition.

    PubMed

    Culhane, H M; Winn, B; Gilmartin, B

    1999-05-01

    A ciliary alpha-adrenoceptor accommodative effect has been proposed, caused by a small population of alpha1-inhibitory receptors in excised human ciliary muscle. This study was intended to investigate the effect on the closed-loop dynamic accommodative process of modulating alpha1-adrenoceptor activity by topical instillation of the alpha1-adrenergic agonist, phenylephrine hydrochloride. A group of 10 visually normal subjects viewed a photopic (30 candela/m2) high-contrast Maltese cross, which was modulated sinusoidally (0.05-0.6Hz) and stepwise over a 2-D range (2-4 D). Monocular temporal accommodation responses were measured using a continuously recording dynamic tracking infrared optometer under two trial conditions: after instillation of saline control solution and 50 minutes subsequent to the instillation of 0.27 microl 0.4% benoxinate hydrochloride and 0.27 microl 2.5% phenylephrine hydrochloride. Pupil size and accommodative amplitude were measured at 90-second intervals for 50 minutes after drug instillation. All accommodative measurements were recorded through a fixed 4-mm pupil. A significant reduction in accommodative amplitude (11%; P < 0.05) was recorded, whereas pupil size showed a significant increase (33%; P < 0.05). No significant change in step-response dynamics was observed. However, phenylephrine hydrochloride caused a significant increase in accommodative gain in the low and midtemporal frequency ranges compared with the effect of a saline control treatment. No significant variation in phase lag was observed. For the first time in humans, this study shows that augmentation of the alpha1-inhibitory sympathetic contribution results in increased accommodative gain at low and midtemporal frequencies, which is consistent with findings in animal studies.

  2. Attitude coordination of multi-HUG formation based on multibody system theory

    NASA Astrophysics Data System (ADS)

    Xue, Dong-yang; Wu, Zhi-liang; Qi, Er-mai; Wang, Yan-hui; Wang, Shu-xin

    2017-04-01

    Application of multiple hybrid underwater gliders (HUGs) is a promising method for large scale, long-term ocean survey. Attitude coordination has become a requisite for task execution of multi-HUG formation. In this paper, a multibody model is presented for attitude coordination among agents in the HUG formation. The HUG formation is regarded as a multi-rigid body system. The interaction between agents in the formation is described by artificial potential field (APF) approach. Attitude control torque is composed of a conservative torque generated by orientation potential field and a dissipative term related with angular velocity. Dynamic modeling of the multibody system is presented to analyze the dynamic process of the HUG formation. Numerical calculation is carried out to simulate attitude synchronization with two kinds of formation topologies. Results show that attitude synchronization can be fulfilled based on the multibody method described in this paper. It is also indicated that different topologies affect attitude control quality with respect to energy consumption and adjusting time. Low level topology should be adopted during formation control scheme design to achieve a better control effect.

  3. Multibody aircraft study, volume 2

    NASA Technical Reports Server (NTRS)

    Moore, J. W.; Craven, E. P.; Farmer, B. T.; Honrath, J. F.; Stephens, R. E.; Bronson, C. E., Jr.; Meyer, R. T.; Hogue, J. G.

    1981-01-01

    The potential benefits of a multibody aircraft when compared to a single body aircraft are presented. The analyses consist principally of a detailed point design analysis of three multibody and one single body aircraft, based on a selected payload of 350,000 kg (771,618 lb), for final aircraft definitions; sensitivity studies to evaluate the effects of variations in payload, wing semispan body locations, and fuel price; recommendations as to the research and technology requirements needed to validate the multibody concept. Two, two body, one, three body, and one single body aircraft were finalized for the selected payload, with DOC being the prime figure of merit. When compared to the single body, the multibody aircraft showed a reduction in DOC by as much as 11.3 percent. Operating weight was reduced up to 14 percent, and fly away cost reductions ranged from 8.6 to 13.4 percent. Weight reduction, hence cost, of the multibody aircraft resulted primarily from the wing bending relief afforded by the bodies being located outboard on the wing.

  4. Multibody aircraft study, volume 1

    NASA Technical Reports Server (NTRS)

    Moore, J. W.; Craven, E. P.; Farmer, B. T.; Honrath, J. F.; Stephens, R. E.; Bronson, C. E., Jr.; Meyer, R. T.; Hogue, J. H.

    1982-01-01

    The potential benefits of a multibody aircraft when compared to a single body aircraft are presented. The analyses consist principally of a detailed point design analysis of three multibody and one single body aircraft, based on a selected payload of 350,000 kg (771,618 lb), for final aircraft definitions; sensitivity studies to evaluate the effects of variations in payload, wing semispan body locations, and fuel price; recommendations as to the research and technology requirements needed to validate the multibody concept. Two, two body, one, three body, and one single body aircraft were finalized for the selected payload, with DOC being the prime figure of merit. When compared to the single body, the multibody aircraft showed a reduction in DOC by as much as 11.3 percent. Operating weight was reduced up to 14 percent, and fly away cost reductions ranged from 8.6 to 13.4 percent. Weight reduction, hence cost, of the multibody aircraft resulted primarily from the wing bending relief afforded by the bodies being located outboard on the wing.

  5. A computational procedure for multibody systems including flexible beam dynamics

    NASA Technical Reports Server (NTRS)

    Downer, J. D.; Park, K. C.; Chiou, J. C.

    1990-01-01

    A computational procedure suitable for the solution of equations of motions for flexible multibody systems has been developed. A fully nonlinear continuum approach capable of accounting for both finite rotations and large deformations has been used to model a flexible beam component. The beam kinematics are referred directly to an inertial reference frame such that the degrees of freedom embody both the rigid and flexible deformation motions. As such, the beam inertia expression is identical to that of rigid body dynamics. The nonlinear coupling between gross body motion and elastic deformation is contained in the internal force expression. Numerical solution procedures for the integration of spatial kinematic systems can be directily applied to the generalized coordinates of both the rigid and flexible components. An accurate computation of the internal force term which is invariant to rigid motions is incorporated into the general solution procedure.

  6. A program for the investigation of the Multibody Modeling, Verification, and Control Laboratory

    NASA Technical Reports Server (NTRS)

    Tobbe, Patrick A.; Christian, Paul M.; Rakoczy, John M.; Bulter, Marlon L.

    1993-01-01

    The Multibody Modeling, Verification, and Control (MMVC) Laboratory is under development at NASA MSFC in Huntsville, Alabama. The laboratory will provide a facility in which dynamic tests and analyses of multibody flexible structures representative of future space systems can be conducted. The purpose of the tests are to acquire dynamic measurements of the flexible structures undergoing large angle motions and use the data to validate the multibody modeling code, TREETOPS, developed under sponsorship of NASA. Advanced control systems design and system identification methodologies will also be implemented in the MMVC laboratory. This paper describes the ground test facility, the real-time control system, and the experiments. A top-level description of the TREETOPS code is also included along with the validation plan for the MMVC program. Dynamic test results from component testing are also presented and discussed. A detailed discussion of the test articles, which manifest the properties of large flexible space structures, is included along with a discussion of the various candidate control methodologies to be applied in the laboratory.

  7. Dynamic Behavior of Wind Turbine by a Mixed Flexible-Rigid Multi-Body Model

    NASA Astrophysics Data System (ADS)

    Wang, Jianhong; Qin, Datong; Ding, Yi

    A mixed flexible-rigid multi-body model is presented to study the dynamic behavior of a horizontal axis wind turbine. The special attention is given to flexible body: flexible rotor is modeled by a newly developed blade finite element, support bearing elasticities, variations in the number of teeth in contact as well as contact tooth's elasticities are mainly flexible components in the power train. The couple conditions between different subsystems are established by constraint equations. The wind turbine model is generated by coupling models of rotor, power train and generator with constraint equations together. Based on this model, an eigenproblem analysis is carried out to show the mode shape of rotor and power train at a few natural frequencies. The dynamic responses and contact forces among gears under constant wind speed and fixed pitch angle are analyzed.

  8. Multibody dynamics: Modeling component flexibility with fixed, free, loaded, constraint, and residual modes

    NASA Technical Reports Server (NTRS)

    Spanos, John T.; Tsuha, Walter S.

    1989-01-01

    The assumed-modes method in multibody dynamics allows the elastic deformation of each component in the system to be approximated by a sum of products of spatial and temporal functions commonly known as modes and modal coordinates respectively. The choice of component modes used to model articulating and non-articulating flexible multibody systems is examined. Attention is directed toward three classical Component Mode Synthesis (CMS) methods whereby component normal modes are generated by treating the component interface (I/F) as either fixed, free, or loaded with mass and stiffness contributions from the remaining components. The fixed and free I/F normal modes are augmented by static shape functions termed constraint and residual modes respectively. A mode selection procedure is outlined whereby component modes are selected from the Craig-Bampton (fixed I/F plus constraint), MacNeal-Rubin (free I/F plus residual), or Benfield-Hruda (loaded I/F) mode sets in accordance with a modal ordering scheme derived from balance realization theory. The success of the approach is judged by comparing the actuator-to-sensor frequency response of the reduced order system with that of the full order system over the frequency range of interest. A finite element model of the Galileo spacecraft serves as an example in demonstrating the effectiveness of the proposed mode selection method.

  9. Chain Dynamic Formulations for Multibody System Tracked Vehicles

    DTIC Science & Technology

    2012-08-01

    CONTRACT NUMBER W911NF-07-D-0001 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Paramsothy Jayakumar ; Michael Letherwood; Michael Wallin...Hamed, M. A., Shabana, A. A., Jayakumar , P., and Letherwood, M. D., 2011, “Nonstructural geometric discontinuities in finite element/multibody system... Jayakumar , P., and Letherwood, M. D. 2012, “Use of B- Spline in the Finite Element Analysis: Comparison with ANCF Geometry,” Journal of Computational and

  10. Development of High Fidelity Mobility Simulation of an Autonomous Vehicle in an Off-Road Scenario Using Integrated Sensor, Controller, and Multi-Body Dynamics

    DTIC Science & Technology

    2011-08-01

    VEHICLE IN AN OFF-ROAD SCENARIO USING INTEGRATED SENSOR, CONTROLLER, AND MULTI-BODY DYNAMICS Paramsothy Jayakumar , PhD William Smith US Army...environment for a control system, mechanical system dynamics , and sensor simulation for an improved assessment of the vehicle system performance...improve vehicle dynamic performance; we must also evaluate and improve the sensor suite employed on the vehicle, and the controller used to operate

  11. Staggered solution procedures for multibody dynamics simulation

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Chiou, J. C.; Downer, J. D.

    1990-01-01

    The numerical solution procedure for multibody dynamics (MBD) systems is termed a staggered MBD solution procedure that solves the generalized coordinates in a separate module from that for the constraint force. This requires a reformulation of the constraint conditions so that the constraint forces can also be integrated in time. A major advantage of such a partitioned solution procedure is that additional analysis capabilities such as active controller and design optimization modules can be easily interfaced without embedding them into a monolithic program. After introducing the basic equations of motion for MBD system in the second section, Section 3 briefly reviews some constraint handling techniques and introduces the staggered stabilized technique for the solution of the constraint forces as independent variables. The numerical direct time integration of the equations of motion is described in Section 4. As accurate damping treatment is important for the dynamics of space structures, we have employed the central difference method and the mid-point form of the trapezoidal rule since they engender no numerical damping. This is in contrast to the current practice in dynamic simulations of ground vehicles by employing a set of backward difference formulas. First, the equations of motion are partitioned according to the translational and the rotational coordinates. This sets the stage for an efficient treatment of the rotational motions via the singularity-free Euler parameters. The resulting partitioned equations of motion are then integrated via a two-stage explicit stabilized algorithm for updating both the translational coordinates and angular velocities. Once the angular velocities are obtained, the angular orientations are updated via the mid-point implicit formula employing the Euler parameters. When the two algorithms, namely, the two-stage explicit algorithm for the generalized coordinates and the implicit staggered procedure for the constraint Lagrange

  12. Mathematical modeling of a class of multibody flexible spacecraft structures

    NASA Technical Reports Server (NTRS)

    Kelkar, Atul, G.

    1994-01-01

    A mathematical model for a general multibody flexible spacecraft is obtained. The generic spacecraft considered consists of a flexible central body to which a number of flexible multibody structures are attached. The coordinate systems used in the derivation allow effective decoupling of the translational motion of the entire spacecraft from its rotational motion about its center of mass. The derivation assumes that the deformations in the bodies are only due to elastic motions. The dynamic model derived is a closed-form vector-matrix differential equation. The model developed can be used for analysis and simulation of many realistic spacecraft configurations.

  13. Static and dynamic crystalline lens accommodation evaluated using quantitative 3-D OCT.

    PubMed

    Gambra, Enrique; Ortiz, Sergio; Perez-Merino, Pablo; Gora, Michalina; Wojtkowski, Maciej; Marcos, Susana

    2013-01-01

    Custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT) provided with automatic quantification and distortion correction algorithms was used to characterize three-dimensionally (3-D) the human crystalline lens in vivo in four subjects, for accommodative demands between 0 to 6 D in 1 D steps. Anterior and posterior lens radii of curvature decreased with accommodative demand at rates of 0.73 and 0.20 mm/D, resulting in an increase of the estimated optical power of the eye of 0.62 D per diopter of accommodative demand. Dynamic fluctuations in crystalline lens radii of curvature, anterior chamber depth and lens thickness were also estimated from dynamic 2-D OCT images (14 Hz), acquired during 5-s of steady fixation, for different accommodative demands. Estimates of the eye power from dynamical geometrical measurements revealed an increase of the fluctuations of the accommodative response from 0.07 D to 0.47 D between 0 and 6 D (0.044 D per D of accommodative demand). A sensitivity analysis showed that the fluctuations of accommodation were driven by dynamic changes in the lens surfaces, particularly in the posterior lens surface.

  14. Static and dynamic crystalline lens accommodation evaluated using quantitative 3-D OCT

    PubMed Central

    Gambra, Enrique; Ortiz, Sergio; Perez-Merino, Pablo; Gora, Michalina; Wojtkowski, Maciej; Marcos, Susana

    2013-01-01

    Custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT) provided with automatic quantification and distortion correction algorithms was used to characterize three-dimensionally (3-D) the human crystalline lens in vivo in four subjects, for accommodative demands between 0 to 6 D in 1 D steps. Anterior and posterior lens radii of curvature decreased with accommodative demand at rates of 0.73 and 0.20 mm/D, resulting in an increase of the estimated optical power of the eye of 0.62 D per diopter of accommodative demand. Dynamic fluctuations in crystalline lens radii of curvature, anterior chamber depth and lens thickness were also estimated from dynamic 2-D OCT images (14 Hz), acquired during 5-s of steady fixation, for different accommodative demands. Estimates of the eye power from dynamical geometrical measurements revealed an increase of the fluctuations of the accommodative response from 0.07 D to 0.47 D between 0 and 6 D (0.044 D per D of accommodative demand). A sensitivity analysis showed that the fluctuations of accommodation were driven by dynamic changes in the lens surfaces, particularly in the posterior lens surface. PMID:24049680

  15. Flexible multibody simulation of automotive systems with non-modal model reduction techniques

    NASA Astrophysics Data System (ADS)

    Shiiba, Taichi; Fehr, Jörg; Eberhard, Peter

    2012-12-01

    The stiffness of the body structure of an automobile has a strong relationship with its noise, vibration, and harshness (NVH) characteristics. In this paper, the effect of the stiffness of the body structure upon ride quality is discussed with flexible multibody dynamics. In flexible multibody simulation, the local elastic deformation of the vehicle has been described traditionally with modal shape functions. Recently, linear model reduction techniques from system dynamics and mathematics came into the focus to find more sophisticated elastic shape functions. In this work, the NVH-relevant states of a racing kart are simulated, whereas the elastic shape functions are calculated with modern model reduction techniques like moment matching by projection on Krylov-subspaces, singular value decomposition-based reduction techniques, and combinations of those. The whole elastic multibody vehicle model consisting of tyres, steering, axle, etc. is considered, and an excitation with a vibration characteristics in a wide frequency range is evaluated in this paper. The accuracy and the calculation performance of those modern model reduction techniques is investigated including a comparison of the modal reduction approach.

  16. Musculoskeletal multibody dynamics simulation of the contact mechanics and kinematics of a natural knee joint during a walking cycle.

    PubMed

    Hu, Jiayu; Chen, Zhenxian; Xin, Hua; Zhang, Qida; Jin, Zhongmin

    2018-05-01

    Detailed knowledge of the in vivo loading and kinematics in the knee joint is essential to understand its normal functions and the aetiology of osteoarthritis. Computer models provide a viable non-invasive solution for estimating joint loading and kinematics during different physiological activities. However, the joint loading and kinematics of the tibiofemoral and patellofemoral joints during a gait cycle were not typically investigated concurrently in previous computational simulations. In this study, a natural knee architecture was incorporated into a lower extremity musculoskeletal multibody dynamics model based on a force-dependent kinematics approach to investigate the contact mechanics and kinematics of a natural knee joint during a walking cycle. Specifically, the contact forces between the femoral/tibial articular cartilages and menisci and between the femoral and tibial/patellar articular cartilages were quantified. The contact forces and kinematics of the tibiofemoral and patellofemoral joints and the muscle activations and ligament forces were predicted simultaneously with a reasonable level of accuracy. The developed musculoskeletal multibody dynamics model with a natural knee architecture can serve as a potential platform for assisting clinical decision-making and postoperative rehabilitation planning.

  17. Effect of third-order aberrations on dynamic accommodation.

    PubMed

    López-Gil, Norberto; Rucker, Frances J; Stark, Lawrence R; Badar, Mustanser; Borgovan, Theodore; Burke, Sean; Kruger, Philip B

    2007-03-01

    We investigate the potential for the third-order aberrations coma and trefoil to provide a signed cue to accommodation. It is first demonstrated theoretically (with some assumptions) that the point spread function is insensitive to the sign of spherical defocus in the presence of odd-order aberrations. In an experimental investigation, the accommodation response to a sinusoidal change in vergence (1-3D, 0.2Hz) of a monochromatic stimulus was obtained with a dynamic infrared optometer. Measurements were obtained in 10 young visually normal individuals with and without custom contact lenses that induced low and high values of r.m.s. trefoil (0.25, 1.03 microm) and coma (0.34, 0.94 microm). Despite variation between subjects, we did not find any statistically significant increase or decrease in the accommodative gain for low levels of trefoil and coma, although effects approached or reached significance for the high levels of trefoil and coma. Theoretical and experimental results indicate that the presence of Zernike third-order aberrations on the eye does not seem to play a crucial role in the dynamics of the accommodation response.

  18. 6 DOF articulated-arm robot and mobile platform: Dynamic modelling as Multibody System and its validation via Experimental Modal Analysis.

    NASA Astrophysics Data System (ADS)

    Toledo Fuentes, A.; Kipfmueller, M.; José Prieto, M. A.

    2017-10-01

    Mobile manipulators are becoming a key instrument to increase the flexibility in industrial processes. Some of their requirements include handling of objects with different weights and sizes and their “fast” transportation, without jeopardizing production workers and machines. The compensation of forces affecting the system dynamic is therefore needed to avoid unwanted oscillations and tilting by sudden accelerations and decelerations. One general solution may be the implementation of external positioning elements to active stabilize the system. To accomplish the approach, the dynamic behavior of a robotic arm and a mobile platform was investigated to develop the stabilization mechanism using multibody simulations. The methodology used was divided into two phases for each subsystem: their natural frequencies and modal shapes were obtained using experimental modal analyses. Then, based on these experimental results, multibody simulation models (MBS) were set up and its dynamical parameters adjusted. Their modal shapes together with their obtained natural frequencies allowed a quantitative and qualitative analysis. In summary, the MBS models were successfully validated with the real subsystems, with a maximal percentage error of 15%. These models will serve as the basis for future steps in the design of the external actuators and its control strategy using a co-simulation tool.

  19. Dynamic accommodation with simulated targets blurred with high order aberrations

    PubMed Central

    Gambra, Enrique; Wang, Yinan; Yuan, Jing; Kruger, Philip B.; Marcos, Susana

    2010-01-01

    High order aberrations have been suggested to play a role in determining the direction of accommodation. We have explored the effect of retinal blur induced by high order aberrations on dynamic accommodation by measuring the accommodative response to sinusoidal variations in accommodative demand (1–3 D). The targets were blurred with 0.3 and 1 μm (for a 3-mm pupil) of defocus, coma, trefoil and spherical aberration. Accommodative gain decreased significantly when 1-μm of aberration was induced. We found a strong correlation between the relative accommodative gain (and phase lag) and the contrast degradation imposed on the target at relevant spatial frequencies. PMID:20600230

  20. A class of stabilizing controllers for flexible multibody systems

    NASA Technical Reports Server (NTRS)

    Joshi, Suresh M.; Kelkar, Atul G.; Maghami, Peiman G.

    1995-01-01

    The problem of controlling a class of nonlinear multibody flexible space systems consisting of a flexible central body to which a number of articulated appendages are attached is considered. Collocated actuators and sensors are assumed, and global asymptotic stability of such systems is established under a nonlinear dissipative control law. The stability is shown to be robust to unmodeled dynamics and parametric uncertainties. For a special case in which the attitude motion of the central body is small, the system, although still nonlinear, is shown to be stabilized by linear dissipative control laws. Two types of linear controllers are considered: static dissipative (constant gain) and dynamic dissipative. The static dissipative control law is also shown to provide robust stability in the presence of certain classes of actuator and sensor nonlinearities and actuator dynamics. The results obtained for this special case can also be readily applied for controlling single-body linear flexible space structures. For this case, a synthesis technique for the design of a suboptimal dynamic dissipative controller is also presented. The results obtained in this paper are applicable to a broad class of multibody and single-body systems such as flexible multilink manipulators, multipayload space platforms, and space antennas. The stability proofs use the Lyapunov approach and exploit the inherent passivity of such systems.

  1. Amplitude, Latency, and Peak Velocity in Accommodation and Disaccommodation Dynamics

    PubMed Central

    Papadatou, Eleni; Ferrer-Blasco, Teresa; Montés-Micó, Robert

    2017-01-01

    The aim of this work was to ascertain whether there are differences in amplitude, latency, and peak velocity of accommodation and disaccommodation responses when different analysis strategies are used to compute them, such as fitting different functions to the responses or for smoothing them prior to computing the parameters. Accommodation and disaccommodation responses from four subjects to pulse changes in demand were recorded by means of aberrometry. Three different strategies were followed to analyze such responses: fitting an exponential function to the experimental data; fitting a Boltzmann sigmoid function to the data; and smoothing the data. Amplitude, latency, and peak velocity of the responses were extracted. Significant differences were found between the peak velocity in accommodation computed by fitting an exponential function and smoothing the experimental data (mean difference 2.36 D/s). Regarding disaccommodation, significant differences were found between latency and peak velocity, calculated with the two same strategies (mean difference of 0.15 s and −3.56 D/s, resp.). The strategy used to analyze accommodation and disaccommodation responses seems to affect the parameters that describe accommodation and disaccommodation dynamics. These results highlight the importance of choosing the most adequate analysis strategy in each individual to obtain the parameters that characterize accommodation and disaccommodation dynamics. PMID:29226128

  2. Path lumping: An efficient algorithm to identify metastable path channels for conformational dynamics of multi-body systems

    NASA Astrophysics Data System (ADS)

    Meng, Luming; Sheong, Fu Kit; Zeng, Xiangze; Zhu, Lizhe; Huang, Xuhui

    2017-07-01

    Constructing Markov state models from large-scale molecular dynamics simulation trajectories is a promising approach to dissect the kinetic mechanisms of complex chemical and biological processes. Combined with transition path theory, Markov state models can be applied to identify all pathways connecting any conformational states of interest. However, the identified pathways can be too complex to comprehend, especially for multi-body processes where numerous parallel pathways with comparable flux probability often coexist. Here, we have developed a path lumping method to group these parallel pathways into metastable path channels for analysis. We define the similarity between two pathways as the intercrossing flux between them and then apply the spectral clustering algorithm to lump these pathways into groups. We demonstrate the power of our method by applying it to two systems: a 2D-potential consisting of four metastable energy channels and the hydrophobic collapse process of two hydrophobic molecules. In both cases, our algorithm successfully reveals the metastable path channels. We expect this path lumping algorithm to be a promising tool for revealing unprecedented insights into the kinetic mechanisms of complex multi-body processes.

  3. Computational Methods for Structural Mechanics and Dynamics

    NASA Technical Reports Server (NTRS)

    Stroud, W. Jefferson (Editor); Housner, Jerrold M. (Editor); Tanner, John A. (Editor); Hayduk, Robert J. (Editor)

    1989-01-01

    Topics addressed include: transient dynamics; transient finite element method; transient analysis in impact and crash dynamic studies; multibody computer codes; dynamic analysis of space structures; multibody mechanics and manipulators; spatial and coplanar linkage systems; flexible body simulation; multibody dynamics; dynamical systems; and nonlinear characteristics of joints.

  4. Space Station Common Berthing Mechanism, a multi-body simulation application

    NASA Technical Reports Server (NTRS)

    Searle, Ian

    1993-01-01

    This paper discusses an application of multi-body dynamic analysis conducted at the Boeing Company in connection with the Space Station (SS) Common Berthing Mechanism (CBM). After introducing the hardware and analytical objectives we will focus on some of the day-to-day computational issues associated with this type of analysis.

  5. Multibody local approximation: Application to conformational entropy calculations on biomolecules

    NASA Astrophysics Data System (ADS)

    Suárez, Ernesto; Suárez, Dimas

    2012-08-01

    Multibody type expansions like mutual information expansions are widely used for computing or analyzing properties of large composite systems. The power of such expansions stems from their generality. Their weaknesses, however, are the large computational cost of including high order terms due to the combinatorial explosion and the fact that truncation errors do not decrease strictly with the expansion order. Herein, we take advantage of the redundancy of multibody expansions in order to derive an efficient reformulation that captures implicitly all-order correlation effects within a given cutoff, avoiding the combinatory explosion. This approach, which is cutoff dependent rather than order dependent, keeps the generality of the original expansions and simultaneously mitigates their limitations provided that a reasonable cutoff can be used. An application of particular interest can be the computation of the conformational entropy of flexible peptide molecules from molecular dynamics trajectories. By combining the multibody local estimations of conformational entropy with average values of the rigid-rotor and harmonic-oscillator entropic contributions, we obtain by far a tighter upper bound of the absolute entropy than the one obtained by the broadly used quasi-harmonic method.

  6. Multibody local approximation: application to conformational entropy calculations on biomolecules.

    PubMed

    Suárez, Ernesto; Suárez, Dimas

    2012-08-28

    Multibody type expansions like mutual information expansions are widely used for computing or analyzing properties of large composite systems. The power of such expansions stems from their generality. Their weaknesses, however, are the large computational cost of including high order terms due to the combinatorial explosion and the fact that truncation errors do not decrease strictly with the expansion order. Herein, we take advantage of the redundancy of multibody expansions in order to derive an efficient reformulation that captures implicitly all-order correlation effects within a given cutoff, avoiding the combinatory explosion. This approach, which is cutoff dependent rather than order dependent, keeps the generality of the original expansions and simultaneously mitigates their limitations provided that a reasonable cutoff can be used. An application of particular interest can be the computation of the conformational entropy of flexible peptide molecules from molecular dynamics trajectories. By combining the multibody local estimations of conformational entropy with average values of the rigid-rotor and harmonic-oscillator entropic contributions, we obtain by far a tighter upper bound of the absolute entropy than the one obtained by the broadly used quasi-harmonic method.

  7. Simulation and Analyses of Multi-Body Separation in Launch Vehicle Staging Environment

    NASA Technical Reports Server (NTRS)

    Pamadi, Bandu N.; Hotchko, Nathaniel J.; Samareh, Jamshid; Covell, Peter F.; Tartabini, Paul V.

    2006-01-01

    The development of methodologies, techniques, and tools for analysis and simulation of multi-body separation is critically needed for successful design and operation of next generation launch vehicles. As a part of this activity, ConSep simulation tool is being developed. ConSep is a generic MATLAB-based front-and-back-end to the commercially available ADAMS. solver, an industry standard package for solving multi-body dynamic problems. This paper discusses the 3-body separation capability in ConSep and its application to the separation of the Shuttle Solid Rocket Boosters (SRBs) from the External Tank (ET) and the Orbiter. The results are compared with STS-1 flight data.

  8. Further Results of Soft-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses

    NASA Technical Reports Server (NTRS)

    Masarati, Pierangelo; Quaranta, Giuseppe; Piatak, David J.; Singleton, Jeffrey D.

    2004-01-01

    This investigation focuses on the development of multibody analytical models to predict the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model. Comprehensive rotorcraft-based multibody analyses enable modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry and joint deadband may be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of the tiltrotor model are examined. A parametric study of the design parameters which may have influence on the aeromechanics of the soft-inplane rotor system are also included in this investigation.

  9. Development of Constraint Force Equation Methodology for Application to Multi-Body Dynamics Including Launch Vehicle Stage Seperation

    NASA Technical Reports Server (NTRS)

    Pamadi, Bandu N.; Toniolo, Matthew D.; Tartabini, Paul V.; Roithmayr, Carlos M.; Albertson, Cindy W.; Karlgaard, Christopher D.

    2016-01-01

    The objective of this report is to develop and implement a physics based method for analysis and simulation of multi-body dynamics including launch vehicle stage separation. The constraint force equation (CFE) methodology discussed in this report provides such a framework for modeling constraint forces and moments acting at joints when the vehicles are still connected. Several stand-alone test cases involving various types of joints were developed to validate the CFE methodology. The results were compared with ADAMS(Registered Trademark) and Autolev, two different industry standard benchmark codes for multi-body dynamic analysis and simulations. However, these two codes are not designed for aerospace flight trajectory simulations. After this validation exercise, the CFE algorithm was implemented in Program to Optimize Simulated Trajectories II (POST2) to provide a capability to simulate end-to-end trajectories of launch vehicles including stage separation. The POST2/CFE methodology was applied to the STS-1 Space Shuttle solid rocket booster (SRB) separation and Hyper-X Research Vehicle (HXRV) separation from the Pegasus booster as a further test and validation for its application to launch vehicle stage separation problems. Finally, to demonstrate end-to-end simulation capability, POST2/CFE was applied to the ascent, orbit insertion, and booster return of a reusable two-stage-to-orbit (TSTO) vehicle concept. With these validation exercises, POST2/CFE software can be used for performing conceptual level end-to-end simulations, including launch vehicle stage separation, for problems similar to those discussed in this report.

  10. Static and Dynamic Measurements of Accommodation in Individuals with Down Syndrome

    PubMed Central

    Manny, Ruth E.; Glasser, Adrian; Stuebing, Karla K.

    2011-01-01

    Purpose. To identify whether static and dynamic aspects of accommodation other than accuracy are deficient in individuals with Down syndrome (DS) and whether poor accommodation is related to sensory or motor pathway deficits. Methods. Static aspects of accommodation (maximum accommodative response and lag) were measured with an autorefractor for both proximal and minus lens demands. Dynamic aspects of accommodation (latency, peak velocity, microfluctuations) were recorded at 30 Hz with a custom-built photorefractor as subjects viewed a movie switching between 11 m and 50, 33, 25, or 20 cm. Thirty-six subjects with DS were recruited (age 3 to 39 years), and 24 (67%) had useable responses for at least one study measurement for comparison with 140 controls (3 to 40 years) from a previously published cohort. Results. DS subjects had lower maximum accommodative responses (mean = 2.52 ± 1.66 D) and higher lags (1.81 ± 1.30 D for 33 cm demand) than controls for both proximal and minus lens stimuli. DS subjects had greater microfluctuations (one-way ANCOVA, P < 0.001), and a small percentage of the total number of latency measurements (17% accommodative and 16% disaccommodative) were longer than controls. Peak velocities of accommodation and disaccommodation were not different between groups (one-way ANCOVA, P = 0.143). Conclusions. Peak velocities of accommodation and disaccommodation (primarily motor aspects) did not differ between controls and DS subjects; however, latencies (primarily sensory) and microfluctuations (combined motor and sensory) were poorer in DS subjects. These results suggest that poor accommodative accuracy in individuals with DS may be predominantly related to sensory deficits. PMID:20739471

  11. Multi-body dynamics modelling of seated human body under exposure to whole-body vibration.

    PubMed

    Yoshimura, Takuya; Nakai, Kazuma; Tamaoki, Gen

    2005-07-01

    In vehicle systems occupational drivers might expose themselves to vibration for a long time. This may cause illness of the spine such as chronic lumbago or low back pain. Therefore, it is necessary to evaluate the influence of vibration to the spinal column and to make up appropriate guidelines or counter plans. In ISO2631-1 or ISO2631-5 assessment of vibration effects to human in the view of adverse-health effect was already presented. However, it is necessary to carry out further research to understand the effect of vibration to human body to examine their validity and to prepare for the future revision. This paper shows the detail measurement of human response to vibration, and the modelling of the seated human body for the assessment of the vibration risk. The vibration transmissibilities from the seat surface to the spinal column and to the head are measured during the exposure to vertical excitation. The modal paramters of seated subject are extracted in order to understand the dominant natural modes. For the evaluation of adverse-health effect the multi-body modelling of the spinal column is introduced. A simplified model having 10 DOFs is counstructed so that the transmissibilities of the model fit to those of experiment. The transient response analysis is illustrated when a half-sine input is applied. The relative displacements of vertebrae are evaluated, which can be a basis for the assessment of vibration risk. It is suggested that the multi-body dynamic model is used to evaluate the vibration effect to the spinal column for seated subjects.

  12. Dynamic performance of accommodating intraocular lenses in a negative feedback control system: a simulation-based study.

    PubMed

    Schor, Clifton M; Bharadwaj, Shrikant R; Burns, Christopher D

    2007-07-01

    A dynamic model of ocular accommodation is used to simulate the stability and dynamic performance of accommodating intraocular lenses (A-IOLs) that replace the hardened natural ocular lens that is unable to change focus. Accommodation simulations of an older eye with A-IOL materials having biomechanical properties of a younger eye illustrate overshoots and oscillations resulting from decreased visco-elasticity of the A-IOL. Stable dynamics of an A-IOL are restored by adaptation of phasic and tonic neural-control properties of accommodation. Simulations indicate that neural control must be recalibrated to avoid unstable dynamic accommodation with A-IOLs. An interactive web-model of A-IOL illustrating these properties is available at http://schorlab.berkeley.edu.

  13. Planning and executing motions for multibody systems in free-fall. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Cameron, Jonathan M.

    1991-01-01

    The purpose of this research is to develop an end-to-end system that can be applied to a multibody system in free-fall to analyze its possible motions, save those motions in a database, and design a controller that can execute those motions. A goal is for the process to be highly automated and involve little human intervention. Ideally, the output of the system would be data and algorithms that could be put in ROM to control the multibody system in free-fall. The research applies to more than just robots in space. It applies to any multibody system in free-fall. Mathematical techniques from nonlinear control theory were used to study the nature of the system dynamics and its possible motions. Optimization techniques were applied to plan motions. Image compression techniques were proposed to compress the precomputed motion data for storage. A linearized controller was derived to control the system while it executes preplanned trajectories.

  14. Transfer matrix method for dynamics modeling and independent modal space vibration control design of linear hybrid multibody system

    NASA Astrophysics Data System (ADS)

    Rong, Bao; Rui, Xiaoting; Lu, Kun; Tao, Ling; Wang, Guoping; Ni, Xiaojun

    2018-05-01

    In this paper, an efficient method of dynamics modeling and vibration control design of a linear hybrid multibody system (MS) is studied based on the transfer matrix method. The natural vibration characteristics of a linear hybrid MS are solved by using low-order transfer equations. Then, by constructing the brand-new body dynamics equation, augmented operator and augmented eigenvector, the orthogonality of augmented eigenvector of a linear hybrid MS is satisfied, and its state space model expressed in each independent model space is obtained easily. According to this dynamics model, a robust independent modal space-fuzzy controller is designed for vibration control of a general MS, and the genetic optimization of some critical control parameters of fuzzy tuners is also presented. Two illustrative examples are performed, which results show that this method is computationally efficient and with perfect control performance.

  15. An Efficient Solution Method for Multibody Systems with Loops Using Multiple Processors

    NASA Technical Reports Server (NTRS)

    Ghosh, Tushar K.; Nguyen, Luong A.; Quiocho, Leslie J.

    2015-01-01

    This paper describes a multibody dynamics algorithm formulated for parallel implementation on multiprocessor computing platforms using the divide-and-conquer approach. The system of interest is a general topology of rigid and elastic articulated bodies with or without loops. The algorithm divides the multibody system into a number of smaller sets of bodies in chain or tree structures, called "branches" at convenient joints called "connection points", and uses an Order-N (O (N)) approach to formulate the dynamics of each branch in terms of the unknown spatial connection forces. The equations of motion for the branches, leaving the connection forces as unknowns, are implemented in separate processors in parallel for computational efficiency, and the equations for all the unknown connection forces are synthesized and solved in one or several processors. The performances of two implementations of this divide-and-conquer algorithm in multiple processors are compared with an existing method implemented on a single processor.

  16. Static and Dynamic Measurement of Accommodation Using the Grand Seiko WAM-5500 Autorefractor

    PubMed Central

    Win-Hall, Dorothy M.; Houser, Jaime; Glasser, Adrian

    2013-01-01

    Purpose The Grand Seiko WR-5500 (WAM) is an open field autorefractor capable of measuring accommodation and pupil diameter dynamically. This study was undertaken to compare static and dynamic accommodation measurements with this instrument in young, phakic subjects. Methods Fifteen subjects, aged 20–28 years (23.8±0.58; mean±SD) participated. Accommodation was stimulated with text printed on a transparent sheet presented at various distances. In static mode, subjects focused on the near text and three measurements were taken for each stimulus amplitude. In dynamic mode, the 5 Hz recording was started and subjects alternately looked through the transparent near chart and focused on a letter chart at 6 m for 5 seconds and then focused on the near letter chart for 5 seconds for a total of 30 seconds. After smoothing the raw data, the highest three individual values recorded in each 5 second interval of focusing at near were averaged for each stimulus amplitude. ANOVA and Bland-Altman analysis were used to compare the static and dynamic measurements. A calibration was performed with +3.00 to -10.00 D trial lenses behind an IR filter, in 1.00 D steps in 5 of the 15 subjects. Results Stimulus-response graphs from static and dynamic modes were not significantly different in the lower stimulus range (< 5.00 D, p = 0.93), but differed significantly for the higher stimulus amplitudes (p = 0.0027). One of 15 subjects showed a significant difference between the static and dynamic modes. Corresponding pupil diameter could be recorded along with the accommodation responses for the subjects and pupil diameter decreased with increasing stimulus demand. Calibration curves for static and dynamic measurements were not significantly different from the 1:1 line or from each other (p = 0.32). Conclusion Although slight differences between the dynamically and statically recorded responses were identified, the Grand-Seiko WAM autorefractor provides the ability to measure both. Dynamic

  17. On the Modeling of Shells in Multibody Dynamics

    NASA Technical Reports Server (NTRS)

    Bauchau, Olivier A.; Choi, Jou-Young; Bottasso, Carlo L.

    2000-01-01

    Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material nonlinearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of shells are treated in a rigorous manner, and the material nonlinearities can be handled when the, constitutive laws stem from the existence of a strain energy density function. The efficiency and robustness of the proposed approach is illustrated with specific numerical examples that also demonstrate the need for integration schemes possessing high frequency numerical dissipation.

  18. Modeling of control forces for kinematical constraints in the dynamics of multibody systems: A new approach

    NASA Technical Reports Server (NTRS)

    Ider, Sitki Kemal

    1989-01-01

    Conventionally kinematical constraints in multibody systems are treated similar to geometrical constraints and are modeled by constraint reaction forces which are perpendicular to constraint surfaces. However, in reality, one may want to achieve the desired kinematical conditions by control forces having different directions in relation to the constraint surfaces. The conventional equations of motion for multibody systems subject to kinematical constraints are generalized by introducing general direction control forces. Conditions for the selections of the control force directions are also discussed. A redundant robotic system subject to prescribed end-effector motion is analyzed to illustrate the methods proposed.

  19. Molecular-dynamics study on characteristics of energy and tangential momentum accommodation coefficients

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hiroki; Matsuda, Yu; Niimi, Tomohide

    2017-07-01

    Gas-surface interaction is studied by the molecular dynamics method to investigate qualitatively characteristics of accommodation coefficients. A large number of trajectories of gas molecules colliding to and scattering from a surface are statistically analyzed to calculate the energy (thermal) accommodation coefficient (EAC) and the tangential momentum accommodation coefficient (TMAC). Considering experimental measurements of the accommodation coefficients, the incident velocities are stochastically sampled to represent a bulk condition. The accommodation coefficients for noble gases show qualitative coincidence with experimental values. To investigate characteristics of these accommodation coefficients in detail, the gas-surface interaction is parametrically studied by varying the molecular mass of gas, the gas-surface interaction strength, and the molecular size of gas, one by one. EAC increases with increasing every parameter, while TMAC increases with increasing the interaction strength, but decreases with increasing the molecular mass and the molecular size. Thus, contradictory results in experimentally measured TMAC for noble gases could result from the difference between the surface conditions employed in the measurements in the balance among the effective parameters of molecular mass, interaction strength, and molecular size, due to surface roughness and/or adsorbed molecules. The accommodation coefficients for a thermo-fluid dynamics field with a temperature difference between gas and surface and a bulk flow at the same time are also investigated.

  20. An assessment of multibody simulation tools for articulated spacecraft

    NASA Technical Reports Server (NTRS)

    Man, Guy K.; Sirlin, Samuel W.

    1989-01-01

    A survey of multibody simulation codes was conducted in the spring of 1988, to obtain an assessment of the state of the art in multibody simulation codes from the users of the codes. This survey covers the most often used articulated multibody simulation codes in the spacecraft and robotics community. There was no attempt to perform a complete survey of all available multibody codes in all disciplines. Furthermore, this is not an exhaustive evaluation of even robotics and spacecraft multibody simulation codes, as the survey was designed to capture feedback on issues most important to the users of simulation codes. We must keep in mind that the information received was limited and the technical background of the respondents varied greatly. Therefore, only the most often cited observations from the questionnaire are reported here. In this survey, it was found that no one code had both many users (reports) and no limitations. The first section is a report on multibody code applications. Following applications is a discussion of execution time, which is the most troublesome issue for flexible multibody codes. The representation of component flexible bodies, which affects both simulation setup time as well as execution time, is presented next. Following component data preparation, two sections address the accessibility or usability of a code, evaluated by considering its user interface design and examining the overall simulation integrated environment. A summary of user efforts at code verification is reported, before a tabular summary of the questionnaire responses. Finally, some conclusions are drawn.

  1. A Constraint Embedding Approach for Complex Vehicle Suspension Dynamics

    DTIC Science & Technology

    2015-04-24

    Complex Vehicle Suspension Dynamics ECCOMAS Thematic Conference on Multibody Dynamics 2015 Abhinandan Jain∗, Calvin Kuo#, Paramsothy Jayakumar †, Jonathan...Suspension Dynamics ECCOMAS Thematic Conference on Multibody Dynamics 2015 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6...13. SUPPLEMENTARY NOTES ECCOMAS Thematic Conference on Multibody Dynamics 2015, June 29-July 2, 2015, Barcelona, Catalonia, Spain 14. ABSTRACT See

  2. Verification of component mode techniques for flexible multibody systems

    NASA Technical Reports Server (NTRS)

    Wiens, Gloria J.

    1990-01-01

    Investigations were conducted in the modeling aspects of flexible multibodies undergoing large angular displacements. Models were to be generated and analyzed through application of computer simulation packages employing the 'component mode synthesis' techniques. Multibody Modeling, Verification and Control Laboratory (MMVC) plan was implemented, which includes running experimental tests on flexible multibody test articles. From these tests, data was to be collected for later correlation and verification of the theoretical results predicted by the modeling and simulation process.

  3. A computational procedure for large rotational motions in multibody dynamics

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Chiou, J. C.

    1987-01-01

    A computational procedure suitable for the solution of equations of motion for multibody systems is presented. The present procedure adopts a differential partitioning of the translational motions and the rotational motions. The translational equations of motion are then treated by either a conventional explicit or an implicit direct integration method. A principle feature of this procedure is a nonlinearly implicit algorithm for updating rotations via the Euler four-parameter representation. This procedure is applied to the rolling of a sphere through a specific trajectory, which shows that it yields robust solutions.

  4. Human eyes do not need monochromatic aberrations for dynamic accommodation.

    PubMed

    Bernal-Molina, Paula; Marín-Franch, Iván; Del Águila-Carrasco, Antonio J; Esteve-Taboada, Jose J; López-Gil, Norberto; Kruger, Philip B; Montés-Micó, Robert

    2017-09-01

    To determine if human accommodation uses the eye's own monochromatic aberrations to track dynamic accommodative stimuli. Wavefront aberrations were measured while subjects monocularly viewed a monochromatic Maltese cross moving sinusoidally around 2D of accommodative demand with 1D amplitude at 0.2 Hz. The amplitude and phase (delay) of the accommodation response were compared to the actual vergence of the stimulus to obtain gain and temporal phase, calculated from wavefront aberrations recorded over time during experimental trials. The tested conditions were as follows: Correction of all the subject's aberrations except defocus (C); Correction of all the subject's aberrations except defocus and habitual second-order astigmatism (AS); Correction of all the subject's aberrations except defocus and odd higher-order aberrations (HOAs); Correction of all the subject's aberrations except defocus and even HOAs (E); Natural aberrations of the subject's eye, i.e., the adaptive-optics system only corrected the optical system's aberrations (N); Correction of all the subject's aberrations except defocus and fourth-order spherical aberration (SA). The correction was performed at 20 Hz and each condition was repeated six times in randomised order. Average gain (±2 standard errors of the mean) varied little across conditions; between 0.55 ± 0.06 (SA), and 0.62 ± 0.06 (AS). Average phase (±2 standard errors of the mean) also varied little; between 0.41 ± 0.02 s (E), and 0.47 ± 0.02 s (O). After Bonferroni correction, no statistically significant differences in gain or phase were found in the presence of specific monochromatic aberrations or in their absence. These results show that the eye's monochromatic aberrations are not necessary for accommodation to track dynamic accommodative stimuli. © 2017 The Authors. Ophthalmic and Physiological Optics published by John Wiley & Sons Ltd on behalf of College of Optometrists.

  5. Sub-domain decomposition methods and computational controls for multibody dynamical systems. [of spacecraft structures

    NASA Technical Reports Server (NTRS)

    Menon, R. G.; Kurdila, A. J.

    1992-01-01

    This paper presents a concurrent methodology to simulate the dynamics of flexible multibody systems with a large number of degrees of freedom. A general class of open-loop structures is treated and a redundant coordinate formulation is adopted. A range space method is used in which the constraint forces are calculated using a preconditioned conjugate gradient method. By using a preconditioner motivated by the regular ordering of the directed graph of the structures, it is shown that the method is order N in the total number of coordinates of the system. The overall formulation has the advantage that it permits fine parallelization and does not rely on system topology to induce concurrency. It can be efficiently implemented on the present generation of parallel computers with a large number of processors. Validation of the method is presented via numerical simulations of space structures incorporating large number of flexible degrees of freedom.

  6. Effect of temporal location of correction of monochromatic aberrations on the dynamic accommodation response

    PubMed Central

    Hampson, Karen M.; Chin, Sem Sem; Mallen, Edward A. H.

    2010-01-01

    Dynamic correction of monochromatic aberrations of the eye is known to affect the accommodation response to a step change in stimulus vergence. We used an adaptive optics system to determine how the temporal location of the correction affects the response. The system consists of a Shack-Hartmann sensor sampling at 20 Hz and a 37-actuator piezoelectric deformable mirror. An extra sensing channel allows for an independent measure of the accommodation level of the eye. The accommodation response of four subjects was measured during a +/− 0.5 D step change in stimulus vergence whilst aberrations were corrected at various time locations. We found that continued correction of aberrations after the step change decreased the gain for disaccommodation, but increased the gain for accommodation. These results could be explained based on the initial lag of accommodation to the stimulus and changes in the level of aberrations before and after the stimulus step change. Future considerations for investigations of the effect of monochromatic aberrations on the dynamic accommodation response are discussed. PMID:21258515

  7. Investigating the running abilities of Tyrannosaurus rex using stress-constrained multibody dynamic analysis

    PubMed Central

    Pond, Stuart B.; Brassey, Charlotte A.; Manning, Philip L.; Bates, Karl T.

    2017-01-01

    The running ability of Tyrannosaurus rex has been intensively studied due to its relevance to interpretations of feeding behaviour and the biomechanics of scaling in giant predatory dinosaurs. Different studies using differing methodologies have produced a very wide range of top speed estimates and there is therefore a need to develop techniques that can improve these predictions. Here we present a new approach that combines two separate biomechanical techniques (multibody dynamic analysis and skeletal stress analysis) to demonstrate that true running gaits would probably lead to unacceptably high skeletal loads in T. rex. Combining these two approaches reduces the high-level of uncertainty in previous predictions associated with unknown soft tissue parameters in dinosaurs, and demonstrates that the relatively long limb segments of T. rex—long argued to indicate competent running ability—would actually have mechanically limited this species to walking gaits. Being limited to walking speeds contradicts arguments of high-speed pursuit predation for the largest bipedal dinosaurs like T. rex, and demonstrates the power of multiphysics approaches for locomotor reconstructions of extinct animals. PMID:28740745

  8. Investigating the running abilities of Tyrannosaurus rex using stress-constrained multibody dynamic analysis.

    PubMed

    Sellers, William I; Pond, Stuart B; Brassey, Charlotte A; Manning, Philip L; Bates, Karl T

    2017-01-01

    The running ability of Tyrannosaurus rex has been intensively studied due to its relevance to interpretations of feeding behaviour and the biomechanics of scaling in giant predatory dinosaurs. Different studies using differing methodologies have produced a very wide range of top speed estimates and there is therefore a need to develop techniques that can improve these predictions. Here we present a new approach that combines two separate biomechanical techniques (multibody dynamic analysis and skeletal stress analysis) to demonstrate that true running gaits would probably lead to unacceptably high skeletal loads in T. rex . Combining these two approaches reduces the high-level of uncertainty in previous predictions associated with unknown soft tissue parameters in dinosaurs, and demonstrates that the relatively long limb segments of T. rex -long argued to indicate competent running ability-would actually have mechanically limited this species to walking gaits. Being limited to walking speeds contradicts arguments of high-speed pursuit predation for the largest bipedal dinosaurs like T. rex , and demonstrates the power of multiphysics approaches for locomotor reconstructions of extinct animals.

  9. Space Solar Power Multi-body Dynamics and Controls, Concepts for the Integrated Symmetrical Concentrator Configuration

    NASA Technical Reports Server (NTRS)

    Glaese, John R.; McDonald, Emmett J.

    2000-01-01

    Orbiting space solar power systems are currently being investigated for possible flight in the time frame of 2015-2020 and later. Such space solar power (SSP) satellites are required to be extremely large in order to make practical the process of collection, conversion to microwave radiation, and reconversion to electrical power at earth stations or at remote locations in space. These large structures are expected to be very flexible presenting unique problems associated with their dynamics and control. The purpose of this project is to apply the expanded TREETOPS multi-body dynamics analysis computer simulation program (with expanded capabilities developed in the previous activity) to investigate the control problems associated with the integrated symmetrical concentrator (ISC) conceptual SSP system. SSP satellites are, as noted, large orbital systems having many bodies (perhaps hundreds) with flexible arrays operating in an orbiting environment where the non-uniform gravitational forces may be the major load producers on the structure so that a high fidelity gravity model is required. The current activity arises from our NRA8-23 SERT proposal. Funding, as a supplemental selection, has been provided by NASA with reduced scope from that originally proposed.

  10. Effect of correction of aberration dynamics on chaos in human ocular accommodation.

    PubMed

    Hampson, Karen M; Cufflin, Matthew P; Mallen, Edward A H

    2013-11-15

    We used adaptive optics to determine the effect of monochromatic aberration dynamics on the level of chaos in the accommodation control system. Four participants viewed a stationary target while the dynamics of their aberrations were either left uncorrected, defocus was corrected, or all aberrations except defocus were corrected. Chaos theory analysis was used to discern changes in the accommodative microfluctuations. We found a statistically significant reduction in the chaotic nature of the accommodation microfluctuations during correction of defocus, but not when all aberrations except defocus were corrected. The Lyapunov exponent decreased from 0.71 ± 0.07 D/s (baseline) to 0.55 ± 0.03 D/s (correction of defocus fluctuations). As the reduction of chaos in physiological signals is indicative of stress to the system, the results indicate that for the participants included in this study, fluctuations in defocus have a more profound effect than those of the other aberrations. There were no changes in the power spectrum between experimental conditions. Hence chaos theory analysis is a more subtle marker of changes in the accommodation control system and will be of value in the study of myopia onset and progression.

  11. [Objective accommodation parameters depending on accommodation task].

    PubMed

    Tarutta, E P; Tarasova, N A; Dolzhenko, O O

    2011-01-01

    62 myopic patients were examined to study objective accommodation parameters in different conditions of accommodation stimulus presenting (use of convex lenses). Objective accommodation response (OAR) was studied using binocular open-field autorefractometer in different conditions of stimulus presenting: complete myopia correction and adding of convex lenses with increasing power from +1.0 till +3.0 D. In 88,5% of children and adolescents showed significant decrease of OAR for 1,5-2,75D in 3.0D stimulus. Additional correction with convex lenses with increasing power leads to further reduce of accommodation response. As a result induced dynamic refraction in eye-lens system is lower than accommodation task. Only addition of +2,5D lense approximates it to required index of -3.0D.

  12. Mass accommodation of water: bridging the gap between molecular dynamics simulations and kinetic condensation models.

    PubMed

    Julin, Jan; Shiraiwa, Manabu; Miles, Rachael E H; Reid, Jonathan P; Pöschl, Ulrich; Riipinen, Ilona

    2013-01-17

    The condensational growth of submicrometer aerosol particles to climate relevant sizes is sensitive to their ability to accommodate vapor molecules, which is described by the mass accommodation coefficient. However, the underlying processes are not yet fully understood. We have simulated the mass accommodation and evaporation processes of water using molecular dynamics, and the results are compared to the condensation equations derived from the kinetic gas theory to shed light on the compatibility of the two. Molecular dynamics simulations were performed for a planar TIP4P-Ew water surface at four temperatures in the range 268-300 K as well as two droplets, with radii of 1.92 and 4.14 nm at T = 273.15 K. The evaporation flux from molecular dynamics was found to be in good qualitative agreement with that predicted by the simple kinetic condensation equations. Water droplet growth was also modeled with the kinetic multilayer model KM-GAP of Shiraiwa et al. [Atmos. Chem. Phys. 2012, 12, 2777]. It was found that, due to the fast transport across the interface, the growth of a pure water droplet is controlled by gas phase diffusion. These facts indicate that the simple kinetic treatment is sufficient in describing pure water condensation and evaporation. The droplet size was found to have minimal effect on the value of the mass accommodation coefficient. The mass accommodation coefficient was found to be unity (within 0.004) for all studied surfaces, which is in agreement with previous simulation work. Additionally, the simulated evaporation fluxes imply that the evaporation coefficient is also unity. Comparing the evaporation rates of the mass accommodation and evaporation simulations indicated that the high collision flux, corresponding to high supersaturation, present in typical molecular dynamics mass accommodation simulations can under certain conditions lead to an increase in the evaporation rate. Consequently, in such situations the mass accommodation coefficient

  13. Mass Accommodation of Water: Bridging the Gap Between Molecular Dynamics Simulations and Kinetic Condensation Models

    PubMed Central

    2012-01-01

    The condensational growth of submicrometer aerosol particles to climate relevant sizes is sensitive to their ability to accommodate vapor molecules, which is described by the mass accommodation coefficient. However, the underlying processes are not yet fully understood. We have simulated the mass accommodation and evaporation processes of water using molecular dynamics, and the results are compared to the condensation equations derived from the kinetic gas theory to shed light on the compatibility of the two. Molecular dynamics simulations were performed for a planar TIP4P-Ew water surface at four temperatures in the range 268–300 K as well as two droplets, with radii of 1.92 and 4.14 nm at T = 273.15 K. The evaporation flux from molecular dynamics was found to be in good qualitative agreement with that predicted by the simple kinetic condensation equations. Water droplet growth was also modeled with the kinetic multilayer model KM-GAP of Shiraiwa et al. [Atmos. Chem. Phys.2012, 117, 2777]. It was found that, due to the fast transport across the interface, the growth of a pure water droplet is controlled by gas phase diffusion. These facts indicate that the simple kinetic treatment is sufficient in describing pure water condensation and evaporation. The droplet size was found to have minimal effect on the value of the mass accommodation coefficient. The mass accommodation coefficient was found to be unity (within 0.004) for all studied surfaces, which is in agreement with previous simulation work. Additionally, the simulated evaporation fluxes imply that the evaporation coefficient is also unity. Comparing the evaporation rates of the mass accommodation and evaporation simulations indicated that the high collision flux, corresponding to high supersaturation, present in typical molecular dynamics mass accommodation simulations can under certain conditions lead to an increase in the evaporation rate. Consequently, in such situations the mass accommodation

  14. Multi-Body Analysis of the 1/5 Scale Wind Tunnel Model of the V-22 Tiltrotor

    NASA Technical Reports Server (NTRS)

    Ghiringhelli, G. L.; Masarati, P.; Mantegazza, P.; Nixon, M. W.

    1999-01-01

    The paper presents a multi-body analysis of the 1/5 scale wind tunnel model of the V-22 tiltrotor, the Wing and Rotor Aeroelastic Testing System (WRATS), currently tested at NASA Langley Research Center. An original multi-body formulation has been developed at the Dipartimento di Ingegneria Aerospaziale of the Politecnico di Milano, Italy. It is based on the direct writing of the equilibrium equations of independent rigid bodies, connected by kinematic constraints that result in the addition of algebraic constraint equations, and by dynamic constraints, that directly contribute to the equilibrium equations. The formulation has been extended to the simultaneous solution of interdisciplinary problems by modeling electric and hydraulic networks, for aeroservoelastic problems. The code has been tailored to the modeling of rotorcrafts while preserving a complete generality. A family of aerodynamic elements has been introduced to model high aspect aerodynamic surfaces, based on the strip theory, with quasi-steady aerodynamic coefficients, compressibility, post-stall interpolation of experimental data, dynamic stall modeling, and radial flow drag. Different models for the induced velocity of the rotor can be used, from uniform velocity to dynamic in flow. A complete dynamic and aeroelastic analysis of the model of the V-22 tiltrotor has been performed, to assess the validity of the formulation and to exploit the unique features of multi-body analysis with respect to conventional comprehensive rotorcraft codes; These are the ability to model the exact kinematics of mechanical systems, and the possibility to simulate unusual maneuvers and unusual flight conditions, that are particular to the tiltrotor, e.g. the conversion maneuver. A complete modal validation of the analytical model has been performed, to assess the ability to reproduce the correct dynamics of the system with a relatively coarse beam model of the semispan wing, pylon and rotor. Particular care has been used

  15. Dynamic and thermal response finite element models of multi-body space structural configurations

    NASA Technical Reports Server (NTRS)

    Edighoffer, Harold H.

    1987-01-01

    Presented is structural dynamics modeling of two multibody space structural configurations. The first configuration is a generic space station model of a cylindrical habitation module, two solar array panels, radiator panel, and central connecting tube. The second is a 15-m hoop-column antenna. Discussed is the special joint elimination sequence used for these large finite element models, so that eigenvalues could be extracted. The generic space station model aided test configuration design and analysis/test data correlation. The model consisted of six finite element models, one of each substructure and one of all substructures as a system. Static analysis and tests at the substructure level fine-tuned the finite element models. The 15-m hoop-column antenna is a truss column and structural ring interconnected with tension stabilizing cables. To the cables, pretensioned mesh membrane elements were attached to form four parabolic shaped antennae, one per quadrant. Imposing thermal preloads in the cables and mesh elements produced pretension in the finite element model. Thermal preload variation in the 96 control cables was adjusted to maintain antenna shape within the required tolerance and to give pointing accuracy.

  16. Hypernetted-chain-like closure of Ornstein-Zernike equation in multibody dissipative particle dynamics

    NASA Astrophysics Data System (ADS)

    Mo, Chao-jie; Qin, Li-zi; Yang, Li-jun

    2017-10-01

    We have derived a hypernetted-chain-like (HNC-like) approximate closure of the Ornstein-Zernike equation for multibody dissipative particle dynamics (MDPD) system in which the classic closures are not directly practicable. We first point out that the Percus's method is applicable to MDPD system in which particles interact with a density-dependent potential. And then an HNC-like closure is derived using Percus's idea and the saddle-point approximation of particle free energy. This HNC-like closure is compared with results of previous researchers, and in many cases, it demonstrates better agreement with computer simulation results. The HNC-like closure is used to predict the cluster crystallization in MDPD. We determine whether the cluster crystallization will happen in a system utilizing the widely applicable Hansen-Verlet freezing criterion and by observing the radial distribution function. The conclusions drawn from the results of the HNC-like closure are in agreement with computer simulation results. We evaluate different weight functions to determine whether they are prone to cluster crystallization. A new effective density-dependent pairwise potential is also proposed to help to explain the tendency to cluster crystallization of MDPD systems.

  17. A computational procedure for multibody systems including flexible beam dynamics

    NASA Technical Reports Server (NTRS)

    Downer, J. D.; Park, K. C.; Chiou, J. C.

    1990-01-01

    A computational procedure suitable for the solution of equations of motions for flexible multibody systems has been developed. The flexible beams are modeled using a fully nonlinear theory which accounts for both finite rotations and large deformations. The present formulation incorporates physical measures of conjugate Cauchy stress and covariant strain increments. As a consequence, the beam model can easily be interfaced with real-time strain measurements and feedback control systems. A distinct feature of the present work is the computational preservation of total energy for undamped systems; this is obtained via an objective strain increment/stress update procedure combined with an energy-conserving time integration algorithm which contains an accurate update of angular orientations. The procedure is demonstrated via several example problems.

  18. Multibody simulation of vehicles equipped with an automatic transmission

    NASA Astrophysics Data System (ADS)

    Olivier, B.; Kouroussis, G.

    2016-09-01

    Nowadays automotive vehicles remain as one of the most used modes of transportation. Furthermore automatic transmissions are increasingly used to provide a better driving comfort and a potential optimization of the engine performances (by placing the gear shifts at specific engine and vehicle speeds). This paper presents an effective modeling of the vehicle using the multibody methodology (numerically computed under EasyDyn, an open source and in-house library dedicated to multibody simulations). However, the transmission part of the vehicle is described by the usual equations of motion computed using a systematic matrix approach: del Castillo's methodology for planetary gear trains. By coupling the analytic equations of the transmission and the equations computed by the multibody methodology, the performances of any vehicle can be obtained if the characteristics of each element in the vehicle are known. The multibody methodology offers the possibilities to develop the vehicle modeling from 1D-motion to 3D-motion by taking into account the rotations and implementing tire models. The modeling presented in this paper remains very efficient and provides an easy and quick vehicle simulation tool which could be used in order to calibrate the automatic transmission.

  19. Method of Obtaining High Resolution Intrinsic Wire Boom Damping Parameters for Multi-Body Dynamics Simulations

    NASA Technical Reports Server (NTRS)

    Yew, Alvin G.; Chai, Dean J.; Olney, David J.

    2010-01-01

    The goal of NASA's Magnetospheric MultiScale (MMS) mission is to understand magnetic reconnection with sensor measurements from four spinning satellites flown in a tight tetrahedron formation. Four of the six electric field sensors on each satellite are located at the end of 60- meter wire booms to increase measurement sensitivity in the spin plane and to minimize motion coupling from perturbations on the main body. A propulsion burn however, might induce boom oscillations that could impact science measurements if oscillations do not damp to values on the order of 0.1 degree in a timely fashion. Large damping time constants could also adversely affect flight dynamics and attitude control performance. In this paper, we will discuss the implementation of a high resolution method for calculating the boom's intrinsic damping, which was used in multi-body dynamics simulations. In summary, experimental data was obtained with a scaled-down boom, which was suspended as a pendulum in vacuum. Optical techniques were designed to accurately measure the natural decay of angular position and subsequently, data processing algorithms resulted in excellent spatial and temporal resolutions. This method was repeated in a parametric study for various lengths, root tensions and vacuum levels. For all data sets, regression models for damping were applied, including: nonlinear viscous, frequency-independent hysteretic, coulomb and some combination of them. Our data analysis and dynamics models have shown that the intrinsic damping for the baseline boom is insufficient, thereby forcing project management to explore mitigation strategies.

  20. Multiphysics modelling of multibody systems: application to car semi-active suspensions

    NASA Astrophysics Data System (ADS)

    Docquier, N.; Poncelet, A.; Delannoy, M.; Fisette, P.

    2010-12-01

    The goal of the present article is to analyse the performances of a modern vehicle equipped with a novel suspension system linking front, rear, right and left cylinders via a semi-active hydraulic circuit, developed by the Tenneco Automotive company. In addition to improving the vehicle's vertical performances (in terms of comfort), both the stiff roll motion of the carbody and the soft wrap motion of the rear/front wheel-axle units can be obtained and tuned via eight electrovalves. The proposed system avoids the use of classical anti-roll bars, which would be incompatible with the wrap performance. A major problem of the project is to produce a realistic and efficient 3D multibody dynamic model of an Audi A6 coupled, at the equational level, with an hydraulic model of the suspension including cylinders, accumulators, valve characteristics, oil compressibility and pipe dynamics. As regards the hydraulic submodel, a particular attention is paid to assemble resistive components properly without resorting to the use of artificial volumes, as proposed by some software dealing with the dynamics of hydraulic systems. According to Tenneco Automotive requirements, this model must be produced in a Matlab/Simulink form, in particular for control purposes. Thanks to the symbolic approach underlying our multibody program; a unified hybrid model can be obtained as a unique plant dynamic block to be real-time integrated in the Simulink environment on a standard computer. Simulation results highlight the advantages of this new suspension system, in particular regarding the behaviour of the car which can remain stiff in roll for curve negotiation, while maintaining a soft wrap behaviour on uneven surfaces.

  1. Analytical and multibody modeling for the power analysis of standing jumps.

    PubMed

    Palmieri, G; Callegari, M; Fioretti, S

    2015-01-01

    Two methods for the power analysis of standing jumps are proposed and compared in this article. The first method is based on a simple analytical formulation which requires as input the coordinates of the center of gravity in three specified instants of the jump. The second method is based on a multibody model that simulates the jumps processing the data obtained by a three-dimensional (3D) motion capture system and the dynamometric measurements obtained by the force platforms. The multibody model is developed with OpenSim, an open-source software which provides tools for the kinematic and dynamic analyses of 3D human body models. The study is focused on two of the typical tests used to evaluate the muscular activity of lower limbs, which are the counter movement jump and the standing long jump. The comparison between the results obtained by the two methods confirms that the proposed analytical formulation is correct and represents a simple tool suitable for a preliminary analysis of total mechanical work and the mean power exerted in standing jumps.

  2. Implementation of 3-D isoparametric finite elements on supercomputer for the formulation of recursive dynamical equations of multi-body systems

    NASA Technical Reports Server (NTRS)

    Shareef, N. H.; Amirouche, F. M. L.

    1991-01-01

    A computational algorithmic procedure is developed and implemented for the dynamic analysis of a multibody system with rigid/flexible interconnected bodies. The algorithm takes into consideration the large rotation/translation and small elastic deformations associated with the rigid-body degrees of freedom and the flexibility of the bodies in the system respectively. Versatile three-dimensional isoparametric brick elements are employed for the modeling of the geometric configurations of the bodies. The formulation of the recursive dynamical equations of motion is based on the recursive Kane's equations, strain energy concepts, and the techniques of component mode synthesis. In order to minimize CPU-intensive matrix multiplication operations and speed up the execution process, the concepts of indexed arrays is utilized in the formulation of the equations of motion. A spin-up maneuver of a space robot with three flexible links carrying a solar panel is used as an illustrative example.

  3. Random Changes of Accommodation Stimuli: An Automated Extension of the Flippers Accommodative Facility Test.

    PubMed

    Otero, Carles; Aldaba, Mikel; López, Silvia; Díaz-Doutón, Fernando; Vera-Díaz, Fuensanta A; Pujol, Jaume

    2018-06-01

    To study the accommodative dynamics for predictable and unpredictable stimuli using manual and automated accommodative facility tests Materials and Methods: Seventeen young healthy subjects were tested monocularly in two consecutive sessions, using five different conditions. Two conditions replicated the conventional monocular accommodative facility tests for far and near distances, performed with manually held flippers. The other three conditions were automated and conducted using an electro-optical system and open-field autorefractor. Two of the three automated conditions replicated the predictable manual accommodative facility tests. The last automated condition was a hybrid approach using a novel method whereby far and near-accommodative-facility tests were randomly integrated into a single test of four unpredictable accommodative demands. The within-subject standard deviations for far- and near-distance-accommodative reversals were (±1,±1) cycles per minute (cpm) for the manual flipper accommodative facility conditions and (±3, ±4) cpm for the automated conditions. The 95% limits of agreement between the manual and the automated conditions for far and near distances were poor: (-18, 12) and (-15, 3). During the hybrid unpredictable condition, the response time and accommodative response parameters were significantly (p < 0.05) larger for accommodation than disaccommodation responses for high accommodative demands only. The response times during the transitions 0.17/2.17 D and 0.50/4.50 D appeared to be indistinguishable between the hybrid unpredictable and the conventional predictable automated tests. The automated accommodative facility test does not agree with the manual flipper test results. Operator delays in flipping the lens may account for these differences. This novel test, using unpredictable stimuli, provides a more comprehensive examination of accommodative dynamics than conventional manual accommodative facility tests. Unexpectedly, the

  4. Modeling Multibody Stage Separation Dynamics Using Constraint Force Equation Methodology

    NASA Technical Reports Server (NTRS)

    Tartabini, Paul V.; Roithmayr, Carlos M.; Toniolo, Matthew D.; Karlgaard, Christopher D.; Pamadi, Bandu N.

    2011-01-01

    This paper discusses the application of the constraint force equation methodology and its implementation for multibody separation problems using three specially designed test cases. The first test case involves two rigid bodies connected by a fixed joint, the second case involves two rigid bodies connected with a universal joint, and the third test case is that of Mach 7 separation of the X-43A vehicle. For the first two cases, the solutions obtained using the constraint force equation method compare well with those obtained using industry- standard benchmark codes. For the X-43A case, the constraint force equation solutions show reasonable agreement with the flight-test data. Use of the constraint force equation method facilitates the analysis of stage separation in end-to-end simulations of launch vehicle trajectories

  5. Changes in dynamics of accommodation after accommodative facility training in myopes and emmetropes.

    PubMed

    Allen, Peter M; Charman, W Neil; Radhakrishnan, Hema

    2010-05-12

    This study evaluates the effect of accommodative facility training in myopes and emmetropes. Monocular accommodative facility was measured in nine myopes and nine emmetropes for distance and near. Subjective facility was recorded with automated flippers and objective measurements were simultaneously taken with a PowerRefractor. Accommodative facility training (a sequence of 5 min monocular right eye, 5 min monocular left eye, 5 min binocular) was given on three consecutive days and facility was re-assessed on the fifth day. The results showed that training improved the facility rate in both groups. The improvement in facility rates were linked to the time constants and peak velocity of accommodation. Some changes in amplitude seen in emmetropes indicate an improvement in facility rate at the expense of an accurate accommodation response. Copyright 2010 Elsevier Ltd. All rights reserved.

  6. Development of Viscoelastic Multi-Body Simulation and Impact Response Analysis of a Ballasted Railway Track under Cyclic Loading.

    PubMed

    Nishiura, Daisuke; Sakaguchi, Hide; Aikawa, Akira

    2017-06-03

    Simulation of a large number of deformable bodies is often difficult because complex high-level modeling is required to address both multi-body contact and viscoelastic deformation. This necessitates the combined use of a discrete element method (DEM) and a finite element method (FEM). In this study, a quadruple discrete element method (QDEM) was developed for dynamic analysis of viscoelastic materials using a simpler algorithm compared to the standard FEM. QDEM easily incorporates the contact algorithm used in DEM. As the first step toward multi-body simulation, the fundamental performance of QDEM was investigated for viscoelastic analysis. The amplitude and frequency of cantilever elastic vibration were nearly equal to those obtained by the standard FEM. A comparison of creep recovery tests with an analytical solution showed good agreement between them. In addition, good correlation between the attenuation degree and the real physical viscosity was confirmed for viscoelastic vibration analysis. Therefore, the high accuracy of QDEM in the fundamental analysis of infinitesimal viscoelastic deformations was verified. Finally, the impact response of a ballast and sleeper under cyclic loading on a railway track was analyzed using QDEM as an application of deformable multi-body dynamics. The results showed that the vibration of the ballasted track was qualitatively in good agreement with the actual measurements. Moreover, the ballast layer with high friction reduced the ballasted track deterioration. This study suggests that QDEM, as an alternative to DEM and FEM, can provide deeper insights into the contact dynamics of a large number of deformable bodies.

  7. Development of Viscoelastic Multi-Body Simulation and Impact Response Analysis of a Ballasted Railway Track under Cyclic Loading

    PubMed Central

    Nishiura, Daisuke; Sakaguchi, Hide; Aikawa, Akira

    2017-01-01

    Simulation of a large number of deformable bodies is often difficult because complex high-level modeling is required to address both multi-body contact and viscoelastic deformation. This necessitates the combined use of a discrete element method (DEM) and a finite element method (FEM). In this study, a quadruple discrete element method (QDEM) was developed for dynamic analysis of viscoelastic materials using a simpler algorithm compared to the standard FEM. QDEM easily incorporates the contact algorithm used in DEM. As the first step toward multi-body simulation, the fundamental performance of QDEM was investigated for viscoelastic analysis. The amplitude and frequency of cantilever elastic vibration were nearly equal to those obtained by the standard FEM. A comparison of creep recovery tests with an analytical solution showed good agreement between them. In addition, good correlation between the attenuation degree and the real physical viscosity was confirmed for viscoelastic vibration analysis. Therefore, the high accuracy of QDEM in the fundamental analysis of infinitesimal viscoelastic deformations was verified. Finally, the impact response of a ballast and sleeper under cyclic loading on a railway track was analyzed using QDEM as an application of deformable multi-body dynamics. The results showed that the vibration of the ballasted track was qualitatively in good agreement with the actual measurements. Moreover, the ballast layer with high friction reduced the ballasted track deterioration. This study suggests that QDEM, as an alternative to DEM and FEM, can provide deeper insights into the contact dynamics of a large number of deformable bodies. PMID:28772974

  8. Constraint Force Equation Methodology for Modeling Multi-Body Stage Separation Dynamics

    NASA Technical Reports Server (NTRS)

    Toniolo, Matthew D.; Tartabini, Paul V.; Pamadi, Bandu N.; Hotchko, Nathaniel

    2008-01-01

    This paper discusses a generalized approach to the multi-body separation problems in a launch vehicle staging environment based on constraint force methodology and its implementation into the Program to Optimize Simulated Trajectories II (POST2), a widely used trajectory design and optimization tool. This development facilitates the inclusion of stage separation analysis into POST2 for seamless end-to-end simulations of launch vehicle trajectories, thus simplifying the overall implementation and providing a range of modeling and optimization capabilities that are standard features in POST2. Analysis and results are presented for two test cases that validate the constraint force equation methodology in a stand-alone mode and its implementation in POST2.

  9. Multi-Body Analysis of a Tiltrotor Configuration

    NASA Technical Reports Server (NTRS)

    Ghiringhelli, G. L.; Masarati, P.; Mantegazza, P.; Nixon, M. W.

    1997-01-01

    The paper describes the aeroelastic analysis of a tiltrotor configuration. The 1/5 scale wind tunnel semispan model of the V-22 tiltrotor aircraft is considered. The analysis is performed by means of a multi-body code, based on an original formulation. The differential equilibrium problem is stated in terms of first order differential equations. The equilibrium equations of every rigid body are written, together with the definitions of the momenta. The bodies are connected by kinematic constraints, applied in form of Lagrangian multipliers. Deformable components are mainly modelled by means of beam elements, based on an original finite volume formulation. Multi-disciplinar problems can be solved by adding user-defined differential equations. In the presented analysis the equations related to the control of the swash-plate of the model are considered. Advantages of a multi-body aeroelastic code over existing comprehensive rotorcraft codes include the exact modelling of the kinematics of the hub, the detailed modelling of the flexibility of critical hub components, and the possibility to simulate steady flight conditions as well as wind-up and maneuvers. The simulations described in the paper include: 1) the analysis of the aeroelastic stability, with particular regard to the proprotor/pylon instability that is peculiar to tiltrotors, 2) the determination of the dynamic behavior of the system and of the loads due to typical maneuvers, with particular regard to the conversion from helicopter to airplane mode, and 3) the stress evaluation in critical components, such as the pitch links and the conversion downstop spring.

  10. A multibody knee model with discrete cartilage prediction of tibio-femoral contact mechanics.

    PubMed

    Guess, Trent M; Liu, Hongzeng; Bhashyam, Sampath; Thiagarajan, Ganesh

    2013-01-01

    Combining musculoskeletal simulations with anatomical joint models capable of predicting cartilage contact mechanics would provide a valuable tool for studying the relationships between muscle force and cartilage loading. As a step towards producing multibody musculoskeletal models that include representation of cartilage tissue mechanics, this research developed a subject-specific multibody knee model that represented the tibia plateau cartilage as discrete rigid bodies that interacted with the femur through deformable contacts. Parameters for the compliant contact law were derived using three methods: (1) simplified Hertzian contact theory, (2) simplified elastic foundation contact theory and (3) parameter optimisation from a finite element (FE) solution. The contact parameters and contact friction were evaluated during a simulated walk in a virtual dynamic knee simulator, and the resulting kinematics were compared with measured in vitro kinematics. The effects on predicted contact pressures and cartilage-bone interface shear forces during the simulated walk were also evaluated. The compliant contact stiffness parameters had a statistically significant effect on predicted contact pressures as well as all tibio-femoral motions except flexion-extension. The contact friction was not statistically significant to contact pressures, but was statistically significant to medial-lateral translation and all rotations except flexion-extension. The magnitude of kinematic differences between model formulations was relatively small, but contact pressure predictions were sensitive to model formulation. The developed multibody knee model was computationally efficient and had a computation time 283 times faster than a FE simulation using the same geometries and boundary conditions.

  11. Constraint treatment techniques and parallel algorithms for multibody dynamic analysis. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Chiou, Jin-Chern

    1990-01-01

    Computational procedures for kinematic and dynamic analysis of three-dimensional multibody dynamic (MBD) systems are developed from the differential-algebraic equations (DAE's) viewpoint. Constraint violations during the time integration process are minimized and penalty constraint stabilization techniques and partitioning schemes are developed. The governing equations of motion, a two-stage staggered explicit-implicit numerical algorithm, are treated which takes advantage of a partitioned solution procedure. A robust and parallelizable integration algorithm is developed. This algorithm uses a two-stage staggered central difference algorithm to integrate the translational coordinates and the angular velocities. The angular orientations of bodies in MBD systems are then obtained by using an implicit algorithm via the kinematic relationship between Euler parameters and angular velocities. It is shown that the combination of the present solution procedures yields a computationally more accurate solution. To speed up the computational procedures, parallel implementation of the present constraint treatment techniques, the two-stage staggered explicit-implicit numerical algorithm was efficiently carried out. The DAE's and the constraint treatment techniques were transformed into arrowhead matrices to which Schur complement form was derived. By fully exploiting the sparse matrix structural analysis techniques, a parallel preconditioned conjugate gradient numerical algorithm is used to solve the systems equations written in Schur complement form. A software testbed was designed and implemented in both sequential and parallel computers. This testbed was used to demonstrate the robustness and efficiency of the constraint treatment techniques, the accuracy of the two-stage staggered explicit-implicit numerical algorithm, and the speed up of the Schur-complement-based parallel preconditioned conjugate gradient algorithm on a parallel computer.

  12. Multi-body coalescence in Pickering emulsions

    NASA Astrophysics Data System (ADS)

    Wu, Tong; Wang, Haitao; Jing, Benxin; Liu, Fang; Burns, Peter C.; Na, Chongzheng

    2015-01-01

    Particle-stabilized Pickering emulsions have shown unusual behaviours such as the formation of non-spherical droplets and the sudden halt of coalescence between individual droplets. Here we report another unusual behaviour of Pickering emulsions—the simultaneous coalescence of multiple droplets in a single event. Using latex particles, silica particles and carbon nanotubes as model stabilizers, we show that multi-body coalescence can occur in both water-in-oil and oil-in-water emulsions. The number of droplets involved in the nth coalscence event equals four times the corresponding number of the tetrahedral sequence in close packing. Furthermore, coalescence is promoted by repulsive latex and silica particles but inhibited by attractive carbon nanotubes. The revelation of multi-body coalescence is expected to help better understand Pickering emulsions in natural systems and improve their designs in engineering applications.

  13. Short-term adaptation of accommodation, accommodative vergence and disparity vergence facility.

    PubMed

    Maxwell, James; Tong, Jianliang; Schor, Clifton M

    2012-06-01

    Previous studies have found that subjects can increase the velocity of accommodation using visual exercises such as pencil push ups, flippers, Brock strings and the like and myriad papers have shown improvement in accommodation facility (speed) and sufficiency (amplitude) using subjective tests following vision training but few have objectively measured accommodation before and after training in either normal subjects or in patients diagnosed with accommodative infacility (abnormally slow dynamics). Accommodation is driven either directly by blur or indirectly by way of neural crosslinks from the vergence system. Until now, no study has objectively measured both accommodation and accommodative-vergence before and after vision training and the role vergence might play in modifying the speed of accommodation. In the present study, accommodation and accommodative-vergence were measured with a Purkinje Eye Tracker/optometer before and after normal subjects trained in a flipper-like task in which the stimulus stepped between 0 and 2.5 diopters and back for over 200 cycles. Most subjects increased their speed of accommodation as well as their speed of accommodative vergence. Accommodative vergence led the accommodation response by approximately 77 ms before training and 100 ms after training and the vergence lead was most prominent in subjects with high accommodation and vergence velocities and the vergence leads tended to increase in conjunction with increases in accommodation velocity. We surmise that volitional vergence may help increase accommodation velocity by way of vergence-accommodation cross links. Copyright © 2012 Elsevier Ltd. All rights reserved.

  14. Short-Term Adaptation of Accommodation, Accommodative Vergence and Disparity Vergence Facility

    PubMed Central

    Maxwell, James; Tong, Jianliang; Schor, Clifton M.

    2012-01-01

    Previous studies have found that subjects can increase the velocity of accommodation using visual exercises such as pencil push ups, flippers, Brock strings and the like and myriad papers have shown improvement in accommodation facility (speed) and sufficiency (amplitude) using subjective tests following vision training but few have objectively measured accommodation before and after training in either normal subjects or in patients diagnosed with accommodative infacility (abnormally slow dynamics). Accommodation is driven either directly by blur or indirectly by way of neural crosslinks from the vergence system. Until now, no study has objectively measured both accommodation and accommodative-vergence before and after vision training and the role vergence might play in modifying the speed of accommodation. In the present study, accommodation and accommodative-vergence were measured with a Purkinje Eye Tracker/Optometer before and after normal subjects trained in a flipper-like task in which the stimulus stepped between 0 and 2.5 diopters and back for over 200 cycles. Most subjects increased their speed of accommodation as well as their speed of accommodative vergence. Accommodative vergence led the accommodation response by approximately 77 msec before training and 100 msec after training and the vergence lead was most prominent in subjects with high accommodation and vergence velocities and the vergence leads tended to increase in conjunction with increases in accommodation velocity. We surmise that volitional vergence may help increase accommodation velocity by way of vergence-accommodation cross links. PMID:22480879

  15. Recursive linearization of multibody dynamics equations of motion

    NASA Technical Reports Server (NTRS)

    Lin, Tsung-Chieh; Yae, K. Harold

    1989-01-01

    The equations of motion of a multibody system are nonlinear in nature, and thus pose a difficult problem in linear control design. One approach is to have a first-order approximation through the numerical perturbations at a given configuration, and to design a control law based on the linearized model. Here, a linearized model is generated analytically by following the footsteps of the recursive derivation of the equations of motion. The equations of motion are first written in a Newton-Euler form, which is systematic and easy to construct; then, they are transformed into a relative coordinate representation, which is more efficient in computation. A new computational method for linearization is obtained by applying a series of first-order analytical approximations to the recursive kinematic relationships. The method has proved to be computationally more efficient because of its recursive nature. It has also turned out to be more accurate because of the fact that analytical perturbation circumvents numerical differentiation and other associated numerical operations that may accumulate computational error, thus requiring only analytical operations of matrices and vectors. The power of the proposed linearization algorithm is demonstrated, in comparison to a numerical perturbation method, with a two-link manipulator and a seven degrees of freedom robotic manipulator. Its application to control design is also demonstrated.

  16. A unifying framework for rigid multibody dynamics and serial and parallel computational issues

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Jain, Abhinandan

    1989-01-01

    A unifying framework for various formulations of the dynamics of open-chain rigid multibody systems is discussed. Their suitability for serial and parallel processing is assessed. The framework is based on the derivation of intrinsic, i.e., coordinate-free, equations of the algorithms which provides a suitable abstraction and permits a distinction to be made between the computational redundancy in the intrinsic and extrinsic equations. A set of spatial notation is used which allows the derivation of the various algorithms in a common setting and thus clarifies the relationships among them. The three classes of algorithms viz., O(n), O(n exp 2) and O(n exp 3) or the solution of the dynamics problem are investigated. Researchers begin with the derivation of O(n exp 3) algorithms based on the explicit computation of the mass matrix and it provides insight into the underlying basis of the O(n) algorithms. From a computational perspective, the optimal choice of a coordinate frame for the projection of the intrinsic equations is discussed and the serial computational complexity of the different algorithms is evaluated. The three classes of algorithms are also analyzed for suitability for parallel processing. It is shown that the problem belongs to the class of N C and the time and processor bounds are of O(log2/2(n)) and O(n exp 4), respectively. However, the algorithm that achieves the above bounds is not stable. Researchers show that the fastest stable parallel algorithm achieves a computational complexity of O(n) with O(n exp 4), respectively. However, the algorithm that achieves the above bounds is not stable. Researchers show that the fastest stable parallel algorithm achieves a computational complexity of O(n) with O(n exp 2) processors, and results from the parallelization of the O(n exp 3) serial algorithm.

  17. Making a meaningful impact: modelling simultaneous frictional collisions in spatial multibody systems

    PubMed Central

    Uchida, Thomas K.; Sherman, Michael A.; Delp, Scott L.

    2015-01-01

    Impacts are instantaneous, computationally efficient approximations of collisions. Current impact models sacrifice important physical principles to achieve that efficiency, yielding qualitative and quantitative errors when applied to simultaneous impacts in spatial multibody systems. We present a new impact model that produces behaviour similar to that of a detailed compliant contact model, while retaining the efficiency of an instantaneous method. In our model, time and configuration are fixed, but the impact is resolved into distinct compression and expansion phases, themselves comprising sliding and rolling intervals. A constrained optimization problem is solved for each interval to compute incremental impulses while respecting physical laws and principles of contact mechanics. We present the mathematical model, algorithms for its practical implementation, and examples that demonstrate its effectiveness. In collisions involving materials of various stiffnesses, our model can be more than 20 times faster than integrating through the collision using a compliant contact model. This work extends the use of instantaneous impact models to scientific and engineering applications with strict accuracy requirements, where compliant contact models would otherwise be required. An open-source implementation is available in Simbody, a C++ multibody dynamics library widely used in biomechanical and robotic applications. PMID:27547093

  18. Integrated Aeromechanics with Three-Dimensional Solid-Multibody Structures

    NASA Technical Reports Server (NTRS)

    Datta, Anubhav; Johnson, Wayne

    2014-01-01

    A full three-dimensional finite element-multibody structural dynamic solver is coupled to a three-dimensional Reynolds-averaged Navier-Stokes solver for the prediction of integrated aeromechanical stresses and strains on a rotor blade in forward flight. The objective is to lay the foundations of all major pieces of an integrated three-dimensional rotor dynamic analysis - from model construction to aeromechanical solution to stress/strain calculation. The primary focus is on the aeromechanical solution. Two types of three-dimensional CFD/CSD interfaces are constructed for this purpose with an emphasis on resolving errors from geometry mis-match so that initial-stage approximate structural geometries can also be effectively analyzed. A three-dimensional structural model is constructed as an approximation to a UH-60A-like fully articulated rotor. The aerodynamic model is identical to the UH-60A rotor. For preliminary validation measurements from a UH-60A high speed flight is used where CFD coupling is essential to capture the advancing side tip transonic effects. The key conclusion is that an integrated aeromechanical analysis is indeed possible with three-dimensional structural dynamics but requires a careful description of its geometry and discretization of its parts.

  19. A joint-space numerical model of metabolic energy expenditure for human multibody dynamic system.

    PubMed

    Kim, Joo H; Roberts, Dustyn

    2015-09-01

    Metabolic energy expenditure (MEE) is a critical performance measure of human motion. In this study, a general joint-space numerical model of MEE is derived by integrating the laws of thermodynamics and principles of multibody system dynamics, which can evaluate MEE without the limitations inherent in experimental measurements (phase delays, steady state and task restrictions, and limited range of motion) or muscle-space models (complexities and indeterminacies from excessive DOFs, contacts and wrapping interactions, and reliance on in vitro parameters). Muscle energetic components are mapped to the joint space, in which the MEE model is formulated. A constrained multi-objective optimization algorithm is established to estimate the model parameters from experimental walking data also used for initial validation. The joint-space parameters estimated directly from active subjects provide reliable MEE estimates with a mean absolute error of 3.6 ± 3.6% relative to validation values, which can be used to evaluate MEE for complex non-periodic tasks that may not be experimentally verifiable. This model also enables real-time calculations of instantaneous MEE rate as a function of time for transient evaluations. Although experimental measurements may not be completely replaced by model evaluations, predicted quantities can be used as strong complements to increase reliability of the results and yield unique insights for various applications. Copyright © 2015 John Wiley & Sons, Ltd.

  20. Particle-based solid for nonsmooth multidomain dynamics

    NASA Astrophysics Data System (ADS)

    Nordberg, John; Servin, Martin

    2018-04-01

    A method for simulation of elastoplastic solids in multibody systems with nonsmooth and multidomain dynamics is developed. The solid is discretised into pseudo-particles using the meshfree moving least squares method for computing the strain tensor. The particle's strain and stress tensor variables are mapped to a compliant deformation constraint. The discretised solid model thus fit a unified framework for nonsmooth multidomain dynamics simulations including rigid multibodies with complex kinematic constraints such as articulation joints, unilateral contacts with dry friction, drivelines, and hydraulics. The nonsmooth formulation allows for impact impulses to propagate instantly between the rigid multibody and the solid. Plasticity is introduced through an associative perfectly plastic modified Drucker-Prager model. The elastic and plastic dynamics are verified for simple test systems, and the capability of simulating tracked terrain vehicles driving on a deformable terrain is demonstrated.

  1. Substructuring of multibody systems for numerical transfer path analysis in internal combustion engines

    NASA Astrophysics Data System (ADS)

    Acri, Antonio; Offner, Guenter; Nijman, Eugene; Rejlek, Jan

    2016-10-01

    Noise legislations and the increasing customer demands determine the Noise Vibration and Harshness (NVH) development of modern commercial vehicles. In order to meet the stringent legislative requirements for the vehicle noise emission, exact knowledge of all vehicle noise sources and their acoustic behavior is required. Transfer path analysis (TPA) is a fairly well established technique for estimating and ranking individual low-frequency noise or vibration contributions via the different transmission paths. Transmission paths from different sources to target points of interest and their contributions can be analyzed by applying TPA. This technique is applied on test measurements, which can only be available on prototypes, at the end of the designing process. In order to overcome the limits of TPA, a numerical transfer path analysis methodology based on the substructuring of a multibody system is proposed in this paper. Being based on numerical simulation, this methodology can be performed starting from the first steps of the designing process. The main target of the proposed methodology is to get information of noise sources contributions of a dynamic system considering the possibility to have multiple forces contemporary acting on the system. The contributions of these forces are investigated with particular focus on distribute or moving forces. In this paper, the mathematical basics of the proposed methodology and its advantages in comparison with TPA will be discussed. Then, a dynamic system is investigated with a combination of two methods. Being based on the dynamic substructuring (DS) of the investigated model, the methodology proposed requires the evaluation of the contact forces at interfaces, which are computed with a flexible multi-body dynamic (FMBD) simulation. Then, the structure-borne noise paths are computed with the wave based method (WBM). As an example application a 4-cylinder engine is investigated and the proposed methodology is applied on the

  2. Multibody Parachute Flight Simulations for Planetary Entry Trajectories Using "Equilibrium Points"

    NASA Technical Reports Server (NTRS)

    Raiszadeh, Ben

    2003-01-01

    A method has been developed to reduce numerical stiffness and computer CPU requirements of high fidelity multibody flight simulations involving parachutes for planetary entry trajectories. Typical parachute entry configurations consist of entry bodies suspended from a parachute, connected by flexible lines. To accurately calculate line forces and moments, the simulations need to keep track of the point where the flexible lines meet (confluence point). In previous multibody parachute flight simulations, the confluence point has been modeled as a point mass. Using a point mass for the confluence point tends to make the simulation numerically stiff, because its mass is typically much less that than the main rigid body masses. One solution for stiff differential equations is to use a very small integration time step. However, this results in large computer CPU requirements. In the method described in the paper, the need for using a mass as the confluence point has been eliminated. Instead, the confluence point is modeled using an "equilibrium point". This point is calculated at every integration step as the point at which sum of all line forces is zero (static equilibrium). The use of this "equilibrium point" has the advantage of both reducing the numerical stiffness of the simulations, and eliminating the dynamical equations associated with vibration of a lumped mass on a high-tension string.

  3. ESA multibody simulator for spacecrafts' ascent and landing in a microgravity environment

    NASA Astrophysics Data System (ADS)

    Toso, Mario; Pennestrì, Ettore; Rossi, Valerio

    2015-09-01

    The investigation of planets, moons and small bodies, including comets and asteroids can contribute substantially to our understanding of the formation and history of the solar system. In situ observations by landers play an important role in this field: for example, the Rosetta Lander Philae has been the first spacecraft to accomplish a soft touchdown on a comet. Since the last decade, the urgency to anticipate hardware performance and correlate testing results with mathematical models is generating the trend for more extensively applying multibody approach in supporting the design and verification of complex aerospace systems, from the early phases of the project. Some of the essential multibody technologies assisting the analysis of this class of problems consist of a reliable attitude control algorithm, a variable-step and variable-order numerical integrator and a consistent contact-friction formulation. This paper illustrates the particular implementation of these crucial features in the European Space Agency's multibody software DCAP and shows a direct application to a feasibility case study.

  4. Real-Time and High-Fidelity Simulation Environment for Autonomous Ground Vehicle Dynamics

    DTIC Science & Technology

    2013-08-01

    ENGINEERING AND TECHNOLOGY SYMPOSIUM (GVSETS), SET FOR AUG. 21-22, 2013 14. ABSTRACT briefing charts 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17...EDL & Aero-Flight DSENDS Airships Planetary & Terrain models SimScape Simulation framework Dshell Flex & Multibody dynamics DARTS 3D...7 DARTS Rigid/Flexible Real-Time Multibody Dynamics Engine Recipient of the NASA Software of the Year Award. Abhinandan Jain, "Robot and

  5. Exploration of molecular interactions in cholesterol superlattices: effect of multibody interactions.

    PubMed

    Huang, Juyang

    2002-08-01

    Experimental evidences have indicated that cholesterol may adapt highly regular lateral distributions (i.e., superlattices) in a phospholipid bilayer. We investigated the formations of superlattices at cholesterol mole fraction of 0.154, 0.25, 0.40, and 0.5 using Monte Carlo simulation. We found that in general, conventional pairwise-additive interactions cannot produce superlattices. Instead, a multibody (nonpairwise) interaction is required. Cholesterol superlattice formation reveals that although the overall interaction between cholesterol and phospholipids is favorable, it contains two large opposing components: an interaction favoring cholesterol-phospholipid mixing and an unfavorable acyl chain multibody interaction that increases nonlinearly with the number of cholesterol contacts. The magnitudes of interactions are in the order of kT. The physical origins of these interactions can be explained by our umbrella model. They most likely come from the requirement for polar phospholipid headgroups to cover the nonpolar cholesterol to avoid the exposure of cholesterol to water and from the sharp decreasing of acyl chain conformation entropy due to cholesterol contact. This study together with our previous work demonstrate that the driving force of cholesterol-phospholipid mixing is a hydrophobic interaction, and multibody interactions dominate others over a wide range of cholesterol concentration.

  6. Data-driven train set crash dynamics simulation

    NASA Astrophysics Data System (ADS)

    Tang, Zhao; Zhu, Yunrui; Nie, Yinyu; Guo, Shihui; Liu, Fengjia; Chang, Jian; Zhang, Jianjun

    2017-02-01

    Traditional finite element (FE) methods are arguably expensive in computation/simulation of the train crash. High computational cost limits their direct applications in investigating dynamic behaviours of an entire train set for crashworthiness design and structural optimisation. On the contrary, multi-body modelling is widely used because of its low computational cost with the trade-off in accuracy. In this study, a data-driven train crash modelling method is proposed to improve the performance of a multi-body dynamics simulation of train set crash without increasing the computational burden. This is achieved by the parallel random forest algorithm, which is a machine learning approach that extracts useful patterns of force-displacement curves and predicts a force-displacement relation in a given collision condition from a collection of offline FE simulation data on various collision conditions, namely different crash velocities in our analysis. Using the FE simulation results as a benchmark, we compared our method with traditional multi-body modelling methods and the result shows that our data-driven method improves the accuracy over traditional multi-body models in train crash simulation and runs at the same level of efficiency.

  7. Temporal Co-Variation between Eye Lens Accommodation and Trapezius Muscle Activity during a Dynamic Near-Far Visual Task

    PubMed Central

    Zetterberg, Camilla; Richter, Hans O.; Forsman, Mikael

    2015-01-01

    Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy controls and 12 patients with a history of visual and neck/shoulder symptoms performed a Near-Far visual task under three different viewing conditions; one neutral condition with no trial lenses, one condition with negative trial lenses to create increased accommodation, and one condition with positive trial lenses to create decreased accommodation. Eye lens accommodation and trapezius muscle activity were continuously recorded. The trapezius muscle activity was significantly higher during Near than during Far focusing periods for both groups within the neutral viewing condition, and there was a significant co-variation in time between accommodation and trapezius muscle activity within the neutral and positive viewing conditions for the control group. In conclusion, these results reveal a connection between Near focusing and increased muscle activity during dynamic changes in focus between a nearby and a far target. A direct link, from the accommodation/vergence system to the trapezius muscles cannot be ruled out, but the connection may also be explained by an increased need for eye-neck (head) stabilization when focusing on a nearby target as compared to a more distant target. PMID:25961299

  8. Temporal Co-Variation between Eye Lens Accommodation and Trapezius Muscle Activity during a Dynamic Near-Far Visual Task.

    PubMed

    Zetterberg, Camilla; Richter, Hans O; Forsman, Mikael

    2015-01-01

    Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy controls and 12 patients with a history of visual and neck/shoulder symptoms performed a Near-Far visual task under three different viewing conditions; one neutral condition with no trial lenses, one condition with negative trial lenses to create increased accommodation, and one condition with positive trial lenses to create decreased accommodation. Eye lens accommodation and trapezius muscle activity were continuously recorded. The trapezius muscle activity was significantly higher during Near than during Far focusing periods for both groups within the neutral viewing condition, and there was a significant co-variation in time between accommodation and trapezius muscle activity within the neutral and positive viewing conditions for the control group. In conclusion, these results reveal a connection between Near focusing and increased muscle activity during dynamic changes in focus between a nearby and a far target. A direct link, from the accommodation/vergence system to the trapezius muscles cannot be ruled out, but the connection may also be explained by an increased need for eye-neck (head) stabilization when focusing on a nearby target as compared to a more distant target.

  9. Integrating Multibody Simulation and CFD: toward Complex Multidisciplinary Design Optimization

    NASA Astrophysics Data System (ADS)

    Pieri, Stefano; Poloni, Carlo; Mühlmeier, Martin

    This paper describes the use of integrated multidisciplinary analysis and optimization of a race car model on a predefined circuit. The objective is the definition of the most efficient geometric configuration that can guarantee the lowest lap time. In order to carry out this study it has been necessary to interface the design optimization software modeFRONTIER with the following softwares: CATIA v5, a three dimensional CAD software, used for the definition of the parametric geometry; A.D.A.M.S./Motorsport, a multi-body dynamic simulation software; IcemCFD, a mesh generator, for the automatic generation of the CFD grid; CFX, a Navier-Stokes code, for the fluid-dynamic forces prediction. The process integration gives the possibility to compute, for each geometrical configuration, a set of aerodynamic coefficients that are then used in the multiboby simulation for the computation of the lap time. Finally an automatic optimization procedure is started and the lap-time minimized. The whole process is executed on a Linux cluster running CFD simulations in parallel.

  10. Planar reorientation maneuvers of space multibody systems using internal controls

    NASA Technical Reports Server (NTRS)

    Reyhanoglu, Mahmut; Mcclamroch, N. H.

    1992-01-01

    In this paper a reorientation maneuvering strategy for an interconnection of planar rigid bodies in space is developed. It is assumed that there are no exogeneous torques, and torques generated by joint motors are used as means of control so that the total angular momentum of the multibody system is a constant, assumed to be zero in this paper. The maneuver strategy uses the nonintegrability of the expression for the angular momentum. We demonstrate that large-angle maneuvers can be designed to achieve an arbitrary reorientation of the multibody system with respect to an inertial frame. The theoretical background for carrying out the required maneuvers is briefly summarized. Specifications and computer simulations of a specific reorientation maneuver, and the corresponding control strategies, are described.

  11. The dynamic response of visual accommodation over a seven-day period

    NASA Technical Reports Server (NTRS)

    Randle, R. J.; Murphy, M. R.

    1974-01-01

    Four college students, ranging in age from 18 to 21 years, were tested on their dynamic, monocular accommodation responses to a square wave stimulus and sine waves of two frequencies. The tests were conducted over a period of seven days in a controlled environment, each subject being tested once every three hours. Latency, magnitude, velocity, gain and phase lag of the responses were measured, and means and standard deviations were computed. The latency of response was stable throughout and agreed fairly well with previous studies. The response magnitude was relatively stable. Three of the subjects had higher velocities on receding targets; one was faster on approaching targets. The group mean velocity increased over the seven days of the study. In keeping with the trend to faster dynamics over the seven days, both gain and phase lag improved.

  12. Two body and multibody interaction in a cold Rydberg gas

    NASA Astrophysics Data System (ADS)

    Han, Jianing; Gallagher, Tom

    2009-05-01

    Cold Rydberg atoms trapped in a Magneto Optical Trap (MOT) are not isolated and they tend to bond through dipole-dipole and multiple-multiple interactions between Rydberg atoms. The dipole-dipole interaction and van der Waals interaction between two atoms have been intensively studied. However, the fact that the dipole-dipole interaction and van der Waals interaction show the same size of broadening, studied by Raithel's group, and there is transition between two molecular states, studied by Farooqi and Overstreet, can not be explained by the two atom picture. The purpose of this paper is to show the multibody nature of a dense cold Rydberg gas by studying the molecular state microwave spectrum. Specifically, single body, two body and three body interaction regions are separated. Moreover, the multibody energy levels for selected geometries are calculated. In addition, multibody blockade will be discussed. [3pt] [1] A. Reinhard, K. C. Younge, T. Cubel Liebisch, B. Knuffman, P. R. Berman, and G. Raithel, Phys. Rev. Lett. 100, 233201 (2008).[0pt] [2] S.M. Farooqi, D. Tong, S. Krishnan, J. Stanojevic,Y.P. Zhang, J.R. Ensher, A.S. Estrin, C. Boisseau, R. Cote, E.E. Eyler, and P.L. Gould, Phys. Rev. Lett. 91, 183002 (2003).[0pt] [3] K. Richard Overstreet, Arne Schwettmann, Jonathan Tallant, and James P. Shaffer, Phys. Rev. A 76, 011403 (2007).

  13. Search for exclusive multibody non- decays at the resonance.

    PubMed

    Huang, G S; Miller, D H; Pavlunin, V; Sanghi, B; Shipsey, I P J; Adams, G S; Cravey, M; Cummings, J P; Danko, I; Napolitano, J; He, Q; Muramatsu, H; Park, C S; Thorndike, E H; Coan, T E; Gao, Y S; Liu, F; Artuso, M; Boulahouache, C; Blusk, S; Butt, J; Dorjkhaidav, O; Li, J; Menaa, N; Mountain, R; Nandakumar, R; Randrianarivony, K; Redjimi, R; Sia, R; Skwarnicki, T; Stone, S; Wang, J C; Zhang, K; Csorna, S E; Bonvicini, G; Cinabro, D; Dubrovin, M; Briere, R A; Chen, G P; Chen, J; Ferguson, T; Tatishvili, G; Vogel, H; Watkins, M E; Rosner, J L; Adam, N E; Alexander, J P; Berkelman, K; Cassel, D G; Crede, V; Duboscq, J E; Ecklund, K M; Ehrlich, R; Fields, L; Galik, R S; Gibbons, L; Gittelman, B; Gray, R; Gray, S W; Hartill, D L; Heltsley, B K; Hertz, D; Jones, C D; Kandaswamy, J; Kreinick, D L; Kuznetsov, V E; Mahlke-Krüger, H; Meyer, T O; Onyisi, P U E; Patterson, J R; Peterson, D; Phillips, E A; Pivarski, J; Riley, D; Ryd, A; Sadoff, A J; Schwarthoff, H; Shi, X; Shepherd, M R; Stroiney, S; Sun, W M; Urner, D; Wilksen, T; Weaver, K M; Weinberger, M; Athar, S B; Avery, P; Breva-Newell, L; Patel, R; Potlia, V; Stoeck, H; Yelton, J; Rubin, P; Cawlfield, C; Eisenstein, B I; Gollin, G D; Karliner, I; Kim, D; Lowrey, N; Naik, P; Sedlack, C; Selen, M; White, E J; Williams, J; Wiss, J; Edwards, K W; Besson, D; Pedlar, T K; Cronin-Hennessy, D; Gao, K Y; Gong, D T; Hietala, J; Kubota, Y; Klein, T; Lang, B W; Li, S Z; Poling, R; Scott, A W; Smith, A; Dobbs, S; Metreveli, Z; Seth, K K; Tomaradze, A; Zweber, P; Ernst, J; Severini, H; Asner, D M; Dytman, S A; Love, W; Mehrabyan, S; Mueller, J A; Savinov, V; Li, Z; Lopez, A; Mendez, H; Ramirez, J

    2006-01-27

    Using data collected at the psi(3770) resonance with the CLEO-c detector at the Cornell e+e- storage ring, we present searches for 25 charmless decay modes of the psi(3770), mostly multibody final states. No evidence for charmless decays is found.

  14. Multibody Simulation Software Testbed for Small-Body Exploration and Sampling

    NASA Technical Reports Server (NTRS)

    Acikmese, Behcet; Blackmore, James C.; Mandic, Milan

    2011-01-01

    G-TAG is a software tool for the multibody simulation of a spacecraft with a robotic arm and a sampling mechanism, which performs a touch-and-go (TAG) maneuver for sampling from the surface of a small celestial body. G-TAG utilizes G-DYN, a multi-body simulation engine described in the previous article, and interfaces to controllers, estimators, and environmental forces that affect the spacecraft. G-TAG can easily be adapted for the analysis of the mission stress cases to support the design of a TAG system, as well as for comprehensive Monte Carlo simulations to analyze and evaluate a particular TAG system design. Any future small-body mission will benefit from using G-TAG, which has already been extensively used in Comet Odyssey and Galahad Asteroid New Frontiers proposals.

  15. GPU-accelerated computing for Lagrangian coherent structures of multi-body gravitational regimes

    NASA Astrophysics Data System (ADS)

    Lin, Mingpei; Xu, Ming; Fu, Xiaoyu

    2017-04-01

    Based on a well-established theoretical foundation, Lagrangian Coherent Structures (LCSs) have elicited widespread research on the intrinsic structures of dynamical systems in many fields, including the field of astrodynamics. Although the application of LCSs in dynamical problems seems straightforward theoretically, its associated computational cost is prohibitive. We propose a block decomposition algorithm developed on Compute Unified Device Architecture (CUDA) platform for the computation of the LCSs of multi-body gravitational regimes. In order to take advantage of GPU's outstanding computing properties, such as Shared Memory, Constant Memory, and Zero-Copy, the algorithm utilizes a block decomposition strategy to facilitate computation of finite-time Lyapunov exponent (FTLE) fields of arbitrary size and timespan. Simulation results demonstrate that this GPU-based algorithm can satisfy double-precision accuracy requirements and greatly decrease the time needed to calculate final results, increasing speed by approximately 13 times. Additionally, this algorithm can be generalized to various large-scale computing problems, such as particle filters, constellation design, and Monte-Carlo simulation.

  16. Development of New Generation of Multibody System Computer Software

    DTIC Science & Technology

    2012-04-12

    DEVELOPMENT OF NEW GENERATION OF MULTIBODY SYSTEM COMPUTER SOFTWARE Ahmed A. Shabana University of Illinois at Chicago Paramsothy Jayakumar ...Paramsothy Jayakumar ; Michael Letherwood 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES

  17. Creation of 3D Multi-Body Orthodontic Models by Using Independent Imaging Sensors

    PubMed Central

    Barone, Sandro; Paoli, Alessandro; Razionale, Armando Viviano

    2013-01-01

    In the field of dental health care, plaster models combined with 2D radiographs are widely used in clinical practice for orthodontic diagnoses. However, complex malocclusions can be better analyzed by exploiting 3D digital dental models, which allow virtual simulations and treatment planning processes. In this paper, dental data captured by independent imaging sensors are fused to create multi-body orthodontic models composed of teeth, oral soft tissues and alveolar bone structures. The methodology is based on integrating Cone-Beam Computed Tomography (CBCT) and surface structured light scanning. The optical scanner is used to reconstruct tooth crowns and soft tissues (visible surfaces) through the digitalization of both patients' mouth impressions and plaster casts. These data are also used to guide the segmentation of internal dental tissues by processing CBCT data sets. The 3D individual dental tissues obtained by the optical scanner and the CBCT sensor are fused within multi-body orthodontic models without human supervisions to identify target anatomical structures. The final multi-body models represent valuable virtual platforms to clinical diagnostic and treatment planning. PMID:23385416

  18. Creation of 3D multi-body orthodontic models by using independent imaging sensors.

    PubMed

    Barone, Sandro; Paoli, Alessandro; Razionale, Armando Viviano

    2013-02-05

    In the field of dental health care, plaster models combined with 2D radiographs are widely used in clinical practice for orthodontic diagnoses. However, complex malocclusions can be better analyzed by exploiting 3D digital dental models, which allow virtual simulations and treatment planning processes. In this paper, dental data captured by independent imaging sensors are fused to create multi-body orthodontic models composed of teeth, oral soft tissues and alveolar bone structures. The methodology is based on integrating Cone-Beam Computed Tomography (CBCT) and surface structured light scanning. The optical scanner is used to reconstruct tooth crowns and soft tissues (visible surfaces) through the digitalization of both patients' mouth impressions and plaster casts. These data are also used to guide the segmentation of internal dental tissues by processing CBCT data sets. The 3D individual dental tissues obtained by the optical scanner and the CBCT sensor are fused within multi-body orthodontic models without human supervisions to identify target anatomical structures. The final multi-body models represent valuable virtual platforms to clinical diagnostic and treatment planning.

  19. Accommodative Lag by Autorefraction and Two Dynamic Retinoscopy Methods

    PubMed Central

    2008-01-01

    Purpose To evaluate two clinical procedures, MEM and Nott retinoscopy, for detecting accommodative lags 1.00 diopter (D) or greater in children as identified by an open-field autorefractor. Methods 168 children 8 to <12 years old with low myopia, normal visual acuity, and no strabismus participated as part of an ancillary study within the screening process for a randomized trial. Accommodative response to a 3.00 D demand was first assessed by MEM and Nott retinoscopy, viewing binocularly with spherocylindrical refractive error corrected, with testing order randomized and each performed by a different masked examiner. The response was then determined viewing monocularly with spherical equivalent refractive error corrected, using an open-field autorefractor, which was the gold standard used for eligibility for the clinical trial. Sensitivity and specificity for accommodative lags of 1.00 D or more were calculated for each retinoscopy method compared to the autorefractor. Results 116 (69%) of the 168 children had accommodative lag of 1.00 D or more by autorefraction. MEM identified 66 children identified by autorefraction for a sensitivity of 57% (95% CI = 47% to 66%) and a specificity of 63% (95% CI = 49% to 76%). Nott retinoscopy identified 35 children for a sensitivity of 30% (95% CI = 22% to 39%) and a specificity of 81% (95% CI = 67% to 90%). Analysis of receiver operating characteristic (ROC) curves constructed for MEM and for Nott retinoscopy failed to reveal alternate cut points that would improve the combination of sensitivity and specificity for identifying accommodative lag ≥ 1.00 D as defined by autorefraction. Conclusions Neither MEM nor Nott retinoscopy provided adequate sensitivity and specificity to identify myopic children with accommodative lag ≥ 1.00 D as determined by autorefraction. A variety of methodological differences between the techniques may contribute to the modest to poor agreement. PMID:19214130

  20. Research on Equivalent Tests of Dynamics of On-orbit Soft Contact Technology Based on On-Orbit Experiment Data

    NASA Astrophysics Data System (ADS)

    Yang, F.; Dong, Z. H.; Ye, X.

    2018-05-01

    Currently, space robots have been become a very important means of space on-orbit maintenance and support. Many countries are taking deep research and experiment on this. Because space operation attitude is very complicated, it is difficult to model them in research lab. This paper builds up a complete equivalent experiment framework according to the requirement of proposed space soft-contact technology. Also, this paper carries out flexible multi-body dynamics parameters verification for on-orbit soft-contact mechanism, which combines on-orbit experiment data, the built soft-contact mechanism equivalent model and flexible multi-body dynamics equivalent model that is based on KANE equation. The experiment results approve the correctness of the built on-orbit soft-contact flexible multi-body dynamics.

  1. Acceleration characteristics of human ocular accommodation.

    PubMed

    Bharadwaj, Shrikant R; Schor, Clifton M

    2005-01-01

    Position and velocity of accommodation are known to increase with stimulus magnitude, however, little is known about acceleration properties. We investigated three acceleration properties: peak acceleration, time-to-peak acceleration and total duration of acceleration to step changes in defocus. Peak velocity and total duration of acceleration increased with response magnitude. Peak acceleration and time-to-peak acceleration remained independent of response magnitude. Independent first-order and second-order dynamic components of accommodation demonstrate that neural control of accommodation has an initial open-loop component that is independent of response magnitude and a closed-loop component that increases with response magnitude.

  2. Attitude and Configuration Control of Flexible Multi-Body Spacecraft

    NASA Astrophysics Data System (ADS)

    Cho, Sung-Ki; Cochran, John E., Jr.

    2002-06-01

    Multi-body spacecraft attitude and configuration control formulations based on the use of collaborative control theory are considered. The control formulations are based on two-player, nonzero-sum, differential game theory applied using a Nash strategy. It is desired that the control laws allow different components of the multi-body system to perform different tasks. For example, it may be desired that one body points toward a fixed star while another body in the system slews to track another satellite. Although similar to the linear quadratic regulator formulation, the collaborative control formulation contains a number of additional design parameters because the problem is formulated as two control problems coupled together. The use of the freedom of the partitioning of the total problem into two coupled control problems and the selection of the elements of the cross-coupling matrices are specific problems addressed in this paper. Examples are used to show that significant improvement in performance, as measured by realistic criteria, of collaborative control over conventional linear quadratic regulator control can be achieved by using proposed design guidelines.

  3. Computer simulation of multigrid body dynamics and control

    NASA Technical Reports Server (NTRS)

    Swaminadham, M.; Moon, Young I.; Venkayya, V. B.

    1990-01-01

    The objective is to set up and analyze benchmark problems on multibody dynamics and to verify the predictions of two multibody computer simulation codes. TREETOPS and DISCOS have been used to run three example problems - one degree-of-freedom spring mass dashpot system, an inverted pendulum system, and a triple pendulum. To study the dynamics and control interaction, an inverted planar pendulum with an external body force and a torsional control spring was modeled as a hinge connected two-rigid body system. TREETOPS and DISCOS affected the time history simulation of this problem. System state space variables and their time derivatives from two simulation codes were compared.

  4. Nonlinear finite element formulation for the large displacement analysis in multibody system dynamics

    NASA Technical Reports Server (NTRS)

    Rismantab-Sany, J.; Chang, B.; Shabana, A. A.

    1989-01-01

    A total Lagrangian finite element formulation for the deformable bodies in multibody mechanical systems that undergo finite relative rotations is developed. The deformable bodies are discretized using finite element methods. The shape functions that are used to describe the displacement field are required to include the rigid body modes that describe only large translational displacements. This does not impose any limitations on the technique because most commonly used shape functions satisfy this requirement. The configuration of an element is defined using four sets of coordinate systems: Body, Element, Intermediate element, Global. The body coordinate system serves as a unique standard for the assembly of the elements forming the deformable body. The element coordinate system is rigidly attached to the element and therefore it translates and rotates with the element. The intermediate element coordinate system, whose axes are initially parallel to the element axes, has an origin which is rigidly attached to the origin of the body coordinate system and is used to conveniently describe the configuration of the element in undeformed state with respect to the body coordinate system.

  5. Analog-to-Digital Conversion to Accommodate the Dynamics of Live Music in Hearing Instruments

    PubMed Central

    Bahlmann, Frauke; Fulton, Bernadette

    2012-01-01

    Hearing instrument design focuses on the amplification of speech to reduce the negative effects of hearing loss. Many amateur and professional musicians, along with music enthusiasts, also require their hearing instruments to perform well when listening to the frequent, high amplitude peaks of live music. One limitation, in most current digital hearing instruments with 16-bit analog-to-digital (A/D) converters, is that the compressor before the A/D conversion is limited to 95 dB (SPL) or less at the input. This is more than adequate for the dynamic range of speech; however, this does not accommodate the amplitude peaks present in live music. The hearing instrument input compression system can be adjusted to accommodate for the amplitudes present in music that would otherwise be compressed before the A/D converter in the hearing instrument. The methodology behind this technological approach will be presented along with measurements to demonstrate its effectiveness. PMID:23258618

  6. Analog-to-digital conversion to accommodate the dynamics of live music in hearing instruments.

    PubMed

    Hockley, Neil S; Bahlmann, Frauke; Fulton, Bernadette

    2012-09-01

    Hearing instrument design focuses on the amplification of speech to reduce the negative effects of hearing loss. Many amateur and professional musicians, along with music enthusiasts, also require their hearing instruments to perform well when listening to the frequent, high amplitude peaks of live music. One limitation, in most current digital hearing instruments with 16-bit analog-to-digital (A/D) converters, is that the compressor before the A/D conversion is limited to 95 dB (SPL) or less at the input. This is more than adequate for the dynamic range of speech; however, this does not accommodate the amplitude peaks present in live music. The hearing instrument input compression system can be adjusted to accommodate for the amplitudes present in music that would otherwise be compressed before the A/D converter in the hearing instrument. The methodology behind this technological approach will be presented along with measurements to demonstrate its effectiveness.

  7. Multibody model reduction by component mode synthesis and component cost analysis

    NASA Technical Reports Server (NTRS)

    Spanos, J. T.; Mingori, D. L.

    1990-01-01

    The classical assumed-modes method is widely used in modeling the dynamics of flexible multibody systems. According to the method, the elastic deformation of each component in the system is expanded in a series of spatial and temporal functions known as modes and modal coordinates, respectively. This paper focuses on the selection of component modes used in the assumed-modes expansion. A two-stage component modal reduction method is proposed combining Component Mode Synthesis (CMS) with Component Cost Analysis (CCA). First, each component model is truncated such that the contribution of the high frequency subsystem to the static response is preserved. Second, a new CMS procedure is employed to assemble the system model and CCA is used to further truncate component modes in accordance with their contribution to a quadratic cost function of the system output. The proposed method is demonstrated with a simple example of a flexible two-body system.

  8. Thrust Force Analysis of Tripod Constant Velocity Joint Using Multibody Model

    NASA Astrophysics Data System (ADS)

    Sugiura, Hideki; Matsunaga, Tsugiharu; Mizutani, Yoshiteru; Ando, Yosei; Kashiwagi, Isashi

    A tripod constant velocity joint is used in the driveshaft of front wheel drive vehicles. Thrust force generated by this joint causes lateral vibration in these vehicles. To analyze the thrust force, a detailed model is constructed based on a multibody dynamics approach. This model includes all principal parts of the joint defined as rigid bodies and all force elements of contact and friction acting among these parts. This model utilizes a new contact modeling method of needle roller bearings for more precise and faster computation. By comparing computational and experimental results, the appropriateness of this model is verified and the principal factors inducing the second and third rotating order components of the thrust force are clarified. This paper also describes the influence of skewed needle rollers on the thrust force and evaluates the contribution of friction forces at each contact region to the thrust force.

  9. Model updating in flexible-link multibody systems

    NASA Astrophysics Data System (ADS)

    Belotti, R.; Caneva, G.; Palomba, I.; Richiedei, D.; Trevisani, A.

    2016-09-01

    The dynamic response of flexible-link multibody systems (FLMSs) can be predicted through nonlinear models based on finite elements, to describe the coupling between rigid- body and elastic behaviour. Their accuracy should be as high as possible to synthesize controllers and observers. Model updating based on experimental measurements is hence necessary. By taking advantage of the experimental modal analysis, this work proposes a model updating procedure for FLMSs and applies it experimentally to a planar robot. Indeed, several peculiarities of the model of FLMS should be carefully tackled. On the one hand, nonlinear models of a FLMS should be linearized about static equilibrium configurations. On the other, the experimental mode shapes should be corrected to be consistent with the elastic displacements represented in the model, which are defined with respect to a fictitious moving reference (the equivalent rigid link system). Then, since rotational degrees of freedom are also represented in the model, interpolation of the experimental data should be performed to match the model displacement vector. Model updating has been finally cast as an optimization problem in the presence of bounds on the feasible values, by also adopting methods to improve the numerical conditioning and to compute meaningful updated inertial and elastic parameters.

  10. The relationship between refractive and biometric changes during Edinger–Westphal stimulated accommodation in rhesus monkeys

    PubMed Central

    Vilupuru, Abhiram S.; Glasser, Adrian

    2010-01-01

    Experiments were undertaken to understand the relationship between dynamic accommodative refractive and biometric (lens thickness (LT), anterior chamber depth (ACD) and anterior segment length (ASL=ACD+LT)) changes during Edinger–Westphal stimulated accommodation in rhesus monkeys. Experiments were conducted on three rhesus monkeys (aged 11·5, 4·75 and 4·75 years) which had undergone prior, bilateral, complete iridectomies and implantation of a stimulating electrode in the Edinger–Westphal (EW) nucleus. Accommodative refractive responses were first measured dynamically with video-based infrared photorefraction and then ocular biometric responses were measured dynamically with continuous ultrasound biometry (CUB) during EW stimulation. The same stimulus amplitudes were used for the refractive and biometric measurements to allow them to be compared. Main sequence relationships (ratio of peak velocity to amplitude) were calculated. Dynamic accommodative refractive changes are linearly correlated with the biometric changes and accommodative biometric changes in ACD, ASL and LT show systematic linear correlations with increasing accommodative amplitudes. The relationships are relatively similar for the eyes of the different monkeys. Dynamic analysis showed that main sequence relationships for both biometry and refraction are linear. Although accommodative refractive changes in the eye occur primarily due to changes in lens surface curvature, the refractive changes are well correlated with A-scan measured accommodative biometric changes. Accommodative changes in ACD, LT and ASL are all well correlated over the full extent of the accommodative response. PMID:15721617

  11. The mechanisms of plastic strain accommodation and post critical behavior of heterogeneous reactive composites subject to dynamic loading

    NASA Astrophysics Data System (ADS)

    Olney, Karl L.

    The dynamic behavior of granular/porous and laminate reactive materials is of interest due to their practical applications; reactive structural components, reactive fragments, etc. The mesostructural properties control meso- and macro-scale dynamic behavior of these heterogeneous composites including the behavior during the post-critical stage of deformation. They heavily influence mechanisms of fragment generation and the in situ development of local hot spots, which act as sites of ignition in these materials. This dissertation concentrates on understanding the mechanisms of plastic strain accommodation in two representative reactive material systems with different heterogeneous mesostructrues: Aluminum-Tungsten granular/porous and Nickel-Aluminum laminate composites. The main focus is on the interpretation of results of the following dynamic experiments conducted at different strain and strain rates: drop weight tests, explosively expanded ring experiments, and explosively collapsed thick walled cylinder experiments. Due to the natural limitations in the evaluation of the mesoscale behavior of these materials experimentally and the large variation in the size scales between the mesostructural level and the sample, it is extremely difficult, if not impossible, to examine the mesoscale behavior in situ. Therefore, numerical simulations of the corresponding experiments are used as the main tool to explore material behavior at the mesoscale. Numerical models were developed to elucidate the mechanisms of plastic strain accommodation and post critical behavior in these heterogeneous composites subjected to dynamic loading. These simulations were able to reproduce the qualitative and quantitative features that were observable in the experiments and provided insight into the evolution of the mechanisms of plastic strain accommodation and post critical behavior in these materials with complex mesotructure. Additionally, these simulations provided a framework to examine

  12. Flexible Multi-Body Spacecraft Simulator: Design, Construction, and Experiments

    DTIC Science & Technology

    2017-12-01

    BODY SPACECRAFT SIMULATOR: DESIGN , CONSTRUCTION, AND EXPERIMENTS by Adam L. Atwood December 2017 Thesis Advisor: Mark Karpenko Second...TYPE AND DATES COVERED Master’s thesis 4. TITLE AND SUBTITLE FLEXIBLE MULTI-BODY SPACECRAFT SIMULATOR: DESIGN , CONSTRUCTION, AND EXPERIMENTS 5...spacecraft simulator for use in testing optimal control-based slew and maneuver designs . The simulator is modified from an earlier prototype, which

  13. Validation of Multibody Program to Optimize Simulated Trajectories II Parachute Simulation with Interacting Forces

    NASA Technical Reports Server (NTRS)

    Raiszadeh, Behzad; Queen, Eric M.; Hotchko, Nathaniel J.

    2009-01-01

    A capability to simulate trajectories of multiple interacting rigid bodies has been developed, tested and validated. This capability uses the Program to Optimize Simulated Trajectories II (POST 2). The standard version of POST 2 allows trajectory simulation of multiple bodies without force interaction. In the current implementation, the force interaction between the parachute and the suspended bodies has been modeled using flexible lines, allowing accurate trajectory simulation of the individual bodies in flight. The POST 2 multibody capability is intended to be general purpose and applicable to any parachute entry trajectory simulation. This research paper explains the motivation for multibody parachute simulation, discusses implementation methods, and presents validation of this capability.

  14. Distributed digital signal processors for multi-body flexible structures

    NASA Technical Reports Server (NTRS)

    Lee, Gordon K. F.

    1992-01-01

    Multi-body flexible structures, such as those currently under investigation in spacecraft design, are large scale (high-order) dimensional systems. Controlling and filtering such structures is a computationally complex problem. This is particularly important when many sensors and actuators are located along the structure and need to be processed in real time. This report summarizes research activity focused on solving the signal processing (that is, information processing) issues of multi-body structures. A distributed architecture is developed in which single loop processors are employed for local filtering and control. By implementing such a philosophy with an embedded controller configuration, a supervising controller may be used to process global data and make global decisions as the local devices are processing local information. A hardware testbed, a position controller system for a servo motor, is employed to illustrate the capabilities of the embedded controller structure. Several filtering and control structures which can be modeled as rational functions can be implemented on the system developed in this research effort. Thus the results of the study provide a support tool for many Control/Structure Interaction (CSI) NASA testbeds such as the Evolutionary model and the nine-bay truss structure.

  15. Gain and movement time of convergence-accommodation in preschool children.

    PubMed

    Suryakumar, R; Bobier, W R

    2004-11-01

    Convergence-accommodation is the synkinetic change in accommodation driven by vergence. A few studies have investigated the static and dynamic properties of this cross-link in adults but little is known about convergence-accommodation in children. The purpose of this study was to develop a technique for measuring convergence-accommodation and to study its dynamics (gain and movement time) in a sample of pre-school children. Convergence-accommodation measures were examined on thiry-seven normal pre-school children (mean age = 4.0 +/- 1.31 yrs). Stimulus CA/C (sCA/C) ratios and movement time measures of convergence-accommodation were assessed using a photorefractor while subjects viewed a DOG target. Repeated measures were obtained on eight normal adults (mean age = 23 +/- 0.2 yrs). The mean sCA/C ratios and movement times were not significantly different between adults and children (0.10 D/Delta [0.61 D/M.A.], 743 +/- 70 ms and 0.11 D/Delta [0.50 D/M.A.], 787 +/- 216 ms). Repeated measures on adults showed a non-significant mean difference of 0.001 D/Delta. The results suggest that the possible differences in crystalline lens (plant) characteristics between children and adults do not appear to influence convergence-accommodation gain or duration.

  16. Gas-surface interactions using accommodation coefficients for a dilute and a dense gas in a micro- or nanochannel: heat flux predictions using combined molecular dynamics and Monte Carlo techniques.

    PubMed

    Nedea, S V; van Steenhoven, A A; Markvoort, A J; Spijker, P; Giordano, D

    2014-05-01

    The influence of gas-surface interactions of a dilute gas confined between two parallel walls on the heat flux predictions is investigated using a combined Monte Carlo (MC) and molecular dynamics (MD) approach. The accommodation coefficients are computed from the temperature of incident and reflected molecules in molecular dynamics and used as effective coefficients in Maxwell-like boundary conditions in Monte Carlo simulations. Hydrophobic and hydrophilic wall interactions are studied, and the effect of the gas-surface interaction potential on the heat flux and other characteristic parameters like density and temperature is shown. The heat flux dependence on the accommodation coefficient is shown for different fluid-wall mass ratios. We find that the accommodation coefficient is increasing considerably when the mass ratio is decreased. An effective map of the heat flux depending on the accommodation coefficient is given and we show that MC heat flux predictions using Maxwell boundary conditions based on the accommodation coefficient give good results when compared to pure molecular dynamics heat predictions. The accommodation coefficients computed for a dilute gas for different gas-wall interaction parameters and mass ratios are transferred to compute the heat flux predictions for a dense gas. Comparison of the heat fluxes derived using explicit MD, MC with Maxwell-like boundary conditions based on the accommodation coefficients, and pure Maxwell boundary conditions are discussed. A map of the heat flux dependence on the accommodation coefficients for a dense gas, and the effective accommodation coefficients for different gas-wall interactions are given. In the end, this approach is applied to study the gas-surface interactions of argon and xenon molecules on a platinum surface. The derived accommodation coefficients are compared with values of experimental results.

  17. FAST Simulation Tool Containing Methods for Predicting the Dynamic Response of Wind Turbines

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jonkman, Jason

    2015-08-12

    FAST is a simulation tool (computer software) for modeling tlie dynamic response of horizontal-axis wind turbines. FAST employs a combined modal and multibody structural-dynamics formulation in the time domain.

  18. Multibody Modeling and Simulation for the Mars Phoenix Lander Entry, Descent and Landing

    NASA Technical Reports Server (NTRS)

    Queen, Eric M.; Prince, Jill L.; Desai, Prasun N.

    2008-01-01

    A multi-body flight simulation for the Phoenix Mars Lander has been developed that includes high fidelity six degree-of-freedom rigid-body models for the parachute and lander system. The simulation provides attitude and rate history predictions of all bodies throughout the flight, as well as loads on each of the connecting lines. In so doing, a realistic behavior of the descending parachute/lander system dynamics can be simulated that allows assessment of the Phoenix descent performance and identification of potential sensitivities for landing. This simulation provides a complete end-to-end capability of modeling the entire entry, descent, and landing sequence for the mission. Time histories of the parachute and lander aerodynamic angles are presented. The response of the lander system to various wind models and wind shears is shown to be acceptable. Monte Carlo simulation results are also presented.

  19. Noise coupling between accommodation and accommodative vergence

    NASA Technical Reports Server (NTRS)

    Wilson, D.

    1973-01-01

    For monocular viewing, the fluctuations in accommodative lens power in the frequency range from 0.5 to 3 Hz were found to be considerably greater than those in accommodative vergence movements of the covered eye. Considering the close synkinesis between these motor responses for step changes or slow variations in accommodative stimulus, this finding is unexpected. This apparent lack of synkinesis is found to result mainly from the fact that the decrease in small-signal linear gain with increasing frequency is more rapid in the case of the accommodative vergence system than in the case of the accommodation system, rather than from some nonlinear phenomenon.

  20. Red-green opponent channel mediation of control of human ocular accommodation.

    PubMed Central

    Kotulak, J C; Morse, S E; Billock, V A

    1995-01-01

    1. It has been hypothesized, but not verified empirically, that the control of human ocular accommodation is mediated by either the red-green or yellow-blue colour channels. Our goal was to determine experimentally whether the red-green channel by itself could influence the accommodative response. 2. To find out, we isolated the red-green channel through chromatic bandpass filtering and measured accommodation under dynamic and static conditions. The effect of this filtering was to modulate the red-green channel without disturbing either the yellow-blue or luminance channels. 3. Accommodative gain (ratio of response to stimulus amplitude) declined monotonically with decreasing bandwidth under dynamic conditions. Because the outputs of both the luminance and yellow-blue colour channels did not vary with bandwidth, the only explanation is that the red-green opponent process was responsible for the effect. 4. Under static conditions, however, accommodation was independent of bandwidth. This may be attributable to the decreased sensitivity to chromatic contrast that occurs at low temporal frequencies. PMID:7738858

  1. Differences in the Stimulus Accommodative Convergence/Accommodation Ratio using Various Techniques and Accommodative Stimuli.

    PubMed

    Satou, Tsukasa; Ito, Misae; Shinomiya, Yuma; Takahashi, Yoshiaki; Hara, Naoto; Niida, Takahiro

    2018-04-04

    To investigate differences in the stimulus accommodative convergence/accommodation (AC/A) ratio using various techniques and accommodative stimuli, and to describe a method for determining the stimulus AC/A ratio. A total of 81 subjects with a mean age of 21 years (range, 20-23 years) were enrolled. The relationship between ocular deviation and accommodation was assessed using two methods. Ocular deviation was measured by varying the accommodative requirement using spherical plus/minus lenses to create an accommodative stimulus of 10.00 diopters (D) (in 1.00 D steps). Ocular deviation was assessed using the alternate prism cover test in method 1 at distance (5 m) and near (1/3 m), and the major amblyoscope in method 2. The stimulus AC/A ratios obtained using methods 1 and 2 were calculated and defined as the stimulus AC/A ratios with low and high accommodation, respectively, using the following analysis method. The former was calculated as the difference between the convergence response to an accommodative stimulus of 3 D and 0 D, divided by 3. The latter was calculated as the difference between the convergence response to a maximum (max) accommodative stimulus with distinct vision of the subject and an accommodative stimulus of max minus 3.00 D, divided by 3. The median stimulus AC/A ratio with low accommodation (1.0 Δ/D for method 1 at distance, 2.0 Δ/D for method 1 at near, and 2.7 Δ/D for method 2) differed significantly among the measurement methods (P < 0.01). Differences in the median stimulus AC/A ratio with high accommodation (4.0 Δ/D for method 1 at distance, 3.7 Δ/D for method 1 at near, and 4.7 Δ/D for method 2) between method 1 at distance and method 2 were statistically significant (P < 0.05), while method 1 at near was not significantly different compared with other methods. Differences in the stimulus AC/A ratio value were significant according to measurement technique and accommodative stimuli. However, differences caused by

  2. Update: Advancement of Contact Dynamics Modeling for Human Spaceflight Simulation Applications

    NASA Technical Reports Server (NTRS)

    Brain, Thomas A.; Kovel, Erik B.; MacLean, John R.; Quiocho, Leslie J.

    2017-01-01

    Pong is a new software tool developed at the NASA Johnson Space Center that advances interference-based geometric contact dynamics based on 3D graphics models. The Pong software consists of three parts: a set of scripts to extract geometric data from 3D graphics models, a contact dynamics engine that provides collision detection and force calculations based on the extracted geometric data, and a set of scripts for visualizing the dynamics response with the 3D graphics models. The contact dynamics engine can be linked with an external multibody dynamics engine to provide an integrated multibody contact dynamics simulation. This paper provides a detailed overview of Pong including the overall approach and modeling capabilities, which encompasses force generation from contact primitives and friction to computational performance. Two specific Pong-based examples of International Space Station applications are discussed, and the related verification and validation using this new tool are also addressed.

  3. Quantification of the ciliary muscle and crystalline lens interaction during accommodation with synchronous OCT imaging

    PubMed Central

    Ruggeri, Marco; de Freitas, Carolina; Williams, Siobhan; Hernandez, Victor M.; Cabot, Florence; Yesilirmak, Nilufer; Alawa, Karam; Chang, Yu-Cherng; Yoo, Sonia H.; Gregori, Giovanni; Parel, Jean-Marie; Manns, Fabrice

    2016-01-01

    Abstract: Two SD-OCT systems and a dual channel accommodation target were combined and precisely synchronized to simultaneously image the anterior segment and the ciliary muscle during dynamic accommodation. The imaging system simultaneously generates two synchronized OCT image sequences of the anterior segment and ciliary muscle with an imaging speed of 13 frames per second. The system was used to acquire OCT image sequences of a non-presbyopic and a pre-presbyopic subject accommodating in response to step changes in vergence. The image sequences were processed to extract dynamic morphological data from the crystalline lens and the ciliary muscle. The synchronization between the OCT systems allowed the precise correlation of anatomical changes occurring in the crystalline lens and ciliary muscle at identical time points during accommodation. To describe the dynamic interaction between the crystalline lens and ciliary muscle, we introduce accommodation state diagrams that display the relation between anatomical changes occurring in the accommodating crystalline lens and ciliary muscle. PMID:27446660

  4. Quantification of the ciliary muscle and crystalline lens interaction during accommodation with synchronous OCT imaging.

    PubMed

    Ruggeri, Marco; de Freitas, Carolina; Williams, Siobhan; Hernandez, Victor M; Cabot, Florence; Yesilirmak, Nilufer; Alawa, Karam; Chang, Yu-Cherng; Yoo, Sonia H; Gregori, Giovanni; Parel, Jean-Marie; Manns, Fabrice

    2016-04-01

    Two SD-OCT systems and a dual channel accommodation target were combined and precisely synchronized to simultaneously image the anterior segment and the ciliary muscle during dynamic accommodation. The imaging system simultaneously generates two synchronized OCT image sequences of the anterior segment and ciliary muscle with an imaging speed of 13 frames per second. The system was used to acquire OCT image sequences of a non-presbyopic and a pre-presbyopic subject accommodating in response to step changes in vergence. The image sequences were processed to extract dynamic morphological data from the crystalline lens and the ciliary muscle. The synchronization between the OCT systems allowed the precise correlation of anatomical changes occurring in the crystalline lens and ciliary muscle at identical time points during accommodation. To describe the dynamic interaction between the crystalline lens and ciliary muscle, we introduce accommodation state diagrams that display the relation between anatomical changes occurring in the accommodating crystalline lens and ciliary muscle.

  5. Are high lags of accommodation in myopic children due to motor deficits?

    PubMed

    Labhishetty, Vivek; Bobier, William R

    2017-01-01

    Children with a progressing myopia exhibit an abnormal pattern of high accommodative lags coupled with high accommodative convergence (AC/A) and high accommodative adaptation. This is not predicted by the current models of accommodation and vergence. Reduced accommodative plant gain and reduced sensitivity to blur have been suggested as potential causes for this abnormal behavior. These etiologies were tested by altering parameters (sensory, controller and plant gains) in the Simulink model of accommodation. Predictions were then compared to the static and dynamic blur accommodation (BA) measures taken using a Badal optical system on 12 children (6 emmetropes and 6 myopes, 8-13years) and 6 adults (20-35years). Other critical parameters such as CA/C, AC/A, and accommodative adaptation were also measured. Usable BA responses were classified as either typical or atypical. Typical accommodation data confirmed the abnormal pattern of myopia along with an unchanged CA/C. Main sequence relationship remained invariant between myopic and nonmyopic children. An overall reduction was noted in the response dynamics such as peak velocity and acceleration with age. Neither a reduced plant gain nor reduced blur sensitivity could predict the abnormal accommodative behavior. A model adjustment reflecting a reduced accommodative sensory gain (ASG) coupled with an increased AC cross-link gain and reduced vergence adaptive gain does predict the empirical findings. Empirical measures also showed a greater frequency of errors in accommodative response generation (atypical responses) in both myopic and control children compared to adults. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Accommodation and pupil responses to random-dot stereograms

    PubMed Central

    Suryakumar, Rajaraman; Allison, Robert

    2015-01-01

    We investigated the dynamics of accommodative and pupillary responses to random-dot stereograms presented in crossed and uncrossed disparity in six visually normal young adult subjects (mean age = 25.8 ± 3.1 years). Accommodation and pupil measures were monitored monocularly with a custom built photorefraction system while subjects fixated at the center of a random-dot stereogram. On each trial, the stereogram initially depicted a flat plane and then changed to depict a sinusoidal corrugation in depth while fixation remained constant. Increase in disparity specified depth resulted in pupil constriction during both crossed and uncrossed disparity presentations. The change in pupil size between crossed and uncrossed disparity conditions was not significantly different (p > 0.05). The change in pupil size was also accompanied by a small concomitant increase in accommodation. In addition, the dynamic properties of pupil responses varied as a function of their initial (starting) diameter. The finding that accommodation and pupil responses increased with disparity regardless of the sign of retinal disparity suggests that these responses were driven by apparent depth rather than shifts in mean simulated distance of the stimulus. Presumably the need for the increased depth of focus when viewing stimuli extended in depth results in pupil constriction which also results in a concomitant change in accommodation. Starting position effects in pupil response confirm the non-linearity in the operating range of the pupil. PMID:25891121

  7. Experimental and analytical investigation of inertial propulsion mechanisms and motion simulation of rigid multi-body mechanical systems

    NASA Astrophysics Data System (ADS)

    Almesallmy, Mohammed

    Methodologies are developed for dynamic analysis of mechanical systems with emphasis on inertial propulsion systems. This work adopted the Lagrangian methodology. Lagrangian methodology is the most efficient classical computational technique, which we call Equations of Motion Code (EOMC). The EOMC is applied to several simple dynamic mechanical systems for easier understanding of the method and to aid other investigators in developing equations of motion of any dynamic system. In addition, it is applied to a rigid multibody system, such as Thomson IPS [Thomson 1986]. Furthermore, a simple symbolic algorithm is developed using Maple software, which can be used to convert any nonlinear n-order ordinary differential equation (ODE) systems into 1st-order ODE system in ready format to be used in Matlab software. A side issue, but equally important, we have started corresponding with the U.S. Patent office to persuade them that patent applications, claiming gross linear motion based on inertial propulsion systems should be automatically rejected. The precedent is rejection of patent applications involving perpetual motion machines.

  8. Dynamics of Multibody Systems Near Lagrangian Points

    NASA Astrophysics Data System (ADS)

    Wong, Brian

    This thesis examines the dynamics of a physically connected multi-spacecraft system in the vicinity of the Lagrangian points of a Circular Restricted Three-Body System. The spacecraft system is arranged in a wheel-spoke configuration with smaller and less massive satellites connected to a central hub using truss/beams or tether connectors. The kinematics of the system is first defined, and the kinetic, gravitational potential energy and elastic potential energy of the system are derived. The Assumed Modes Method is used to discretize the continuous variables of the system, and a general set of ordinary differential equations describing the dynamics of the connectors and the central hub are obtained using the Lagrangian method. The flexible body dynamics of the tethered and truss connected systems are examined using numerical simulations. The results show that these systems experienced only small elastic deflections when they are naturally librating or rotating at moderate angular velocities, and these deflections have relatively small effect on the attitude dynamics of the systems. Based on these results, it is determined that the connectors can be modeled as rigid when only the attitude dynamics of the system is of interest. The equations of motion of rigid satellites stationed at the Lagrangian points are linearized, and the stability conditions of the satellite are obtained from the linear equations. The required conditions are shown to be similar to those of geocentric satellites. Study of the linear equations also revealed the resonant conditions of rigid Lagrangian point satellites, when a librational natural frequency of the satellite matches the frequency of its station-keeping orbit leading to large attitude motions. For tethered satellites, the linear analysis shows that the tethers are in stable equilibrium when they lie along a line joining the two primary celestial bodies of the Three-Body System. Numerical simulations are used to study the long term

  9. Biomechanical investigation of thoracolumbar spine in different postures during ejection using a combined finite element and multi-body approach.

    PubMed

    Du, Chengfei; Mo, Zhongjun; Tian, Shan; Wang, Lizhen; Fan, Jie; Liu, Songyang; Fan, Yubo

    2014-11-01

    The aim of this study is to investigate the dynamic response of a multi-segment model of the thoracolumbar spine and determine how the sitting posture affects the response under the impact of ejection. A nonlinear finite element model of the thoracolumbar-pelvis complex (T9-S1) was developed and validated. A multi-body dynamic model of a pilot was also constructed so an ejection seat restraint system could be incorporated into the finite element model. The distribution of trunk mass on each vertebra was also considered in the model. Dynamics analysis showed that ejection impact induced obvious axial compression and anterior flexion of the spine, which may contribute to spinal injuries. Compared with a normal posture, the relaxed posture led to an increase in stress on the cortical wall, endplate, and intradiscal pressure of 43%, 10%, 13%, respectively, and accordingly increased the risk of inducing spinal injuries. Copyright © 2014 John Wiley & Sons, Ltd.

  10. Temporal accommodation response measured by photorefractive accommodation measurement device

    NASA Astrophysics Data System (ADS)

    Song, Byoungsub; Leportier, Thibault; Park, Min-Chul

    2017-02-01

    Although accommodation response plays an important role in the human vision system for perception of distance, some three-dimensional (3D) displays offer depth stimuli regardless of the accommodation response. The consequence is that most observers watching 3D displays have complained about visual fatigue. The measurement of the accommodation response is therefore necessary to develop human-friendly 3D displays. However, only few studies about accommodation measurement have been reported. Most of the investigations have been focused on the measurement and analysis of monocular accommodation responses only because the accommodation response works individually in each eye. Moreover, a main eye perceives dominantly the object distance. However, the binocular accommodation response should be examined because both eyes are used to watch the 3D display in natural conditions. The ophthalmic instrument that we developed enabled to measure changes in the accommodation response of the two eyes simultaneously. Two cameras acquired separately the infrared images reflected from each eyes after the reflected beams passed through a cylindrical lens. The changes in the accommodation response could then be estimated from the changes in the astigmatism ratio of the infrared images that were acquired in real time. In this paper, we compared the accommodation responses of main eye between the monocular and the binocular conditions. The two eyes were measured one by one, with only one eye opened, during measurement for monocular condition. Then the two eyes were examined simultaneously for binocular condition. The results showed similar tendencies for main eye accommodation response in both cases.

  11. Modal identities for multibody elastic spacecraft: An aid to selecting modes for simulation

    NASA Technical Reports Server (NTRS)

    Hablani, Hari B.

    1989-01-01

    The question: Which set of modes furnishes a higher fidelity math model of dynamics of a multibody, deformable spacecraft (hinges-free or hinges-locked vehicle modes) is answered. Two sets of general, discretized, linear equations of motion of a spacecraft with an arbitrary number of deformable appendages, each articulated directly to the core body, are obtained using the above two families of modes. By a comparison of these equations, ten sets of modal identities are constructed which involve modal momenta coefficients and frequencies associated with both classes of modes. The sums of infinite series that appear in the identities are obtained in terms of mass, and first and second moments of inertia of the appendages, core body, and vehicle by using certain basic identities concerning appendage modes. Applying the above identities to a four-body spacecraft, the hinges-locked vehicle modes are found to yield a higher fidelity model than hinges-free modes, because the latter modes have nonconverging modal coefficients; a characteristic proved and illustrated.

  12. State and force observers based on multibody models and the indirect Kalman filter

    NASA Astrophysics Data System (ADS)

    Sanjurjo, Emilio; Dopico, Daniel; Luaces, Alberto; Naya, Miguel Ángel

    2018-06-01

    The aim of this work is to present two new methods to provide state observers by combining multibody simulations with indirect extended Kalman filters. One of the methods presented provides also input force estimation. The observers have been applied to two mechanism with four different sensor configurations, and compared to other multibody-based observers found in the literature to evaluate their behavior, namely, the unscented Kalman filter (UKF), and the indirect extended Kalman filter with simplified Jacobians (errorEKF). The new methods have some more computational cost than the errorEKF, but still much less than the UKF. Regarding their accuracy, both are better than the errorEKF. The method with input force estimation outperforms also the UKF, while the method without force estimation achieves results almost identical to those of the UKF. All the methods have been implemented as a reusable MATLAB® toolkit which has been released as Open Source in https://github.com/MBDS/mbde-matlab.

  13. Water Accommodation on Bare and Coated Ice

    NASA Astrophysics Data System (ADS)

    Kong, Xiangrui

    2015-04-01

    A good understanding of water accommodation on ice surfaces is essential for quantitatively predicting the evolution of clouds, and therefore influences the effectiveness of climate models. However, the accommodation coefficient is poorly constrained within the literature where reported values vary by up to three orders of magnitude. In addition, the complexity of the chemical composition of the atmosphere plays an important role in ice phase behavior and dynamics. We employ an environmental molecular beam (EMB) technique to investigate molecular water interactions with bare and impurity coated ice at temperatures from 170 K to 200 K. In this work, we summarize results of water accommodation experiments on bare ice (Kong et al., 2014) and on ice coated by methanol (Thomson et al., 2013), butanol (Thomson et al., 2013) and acetic acid (Papagiannakopoulos et al., 2014), and compare those results with analogous experiments using hexanol and nitric acid coatings. Hexanol is chosen as a complementary chain alcohol to methanol and butanol, while nitric acid is a common inorganic compound in the atmosphere. The results show a strong negative temperature dependence of water accommodation on bare ice, which can be quantitatively described by a precursor model. Acidic adlayers tend to enhance water uptake indicating that the system kinetics are thoroughly changed compared to bare ice. Adsorbed alcohols influence the temperature dependence of the accommodation coefficient and water molecules generally spend less time on the surfaces before desorbing, although the measured accommodation coefficients remain high and comparable to bare ice for the investigated systems. We conclude that impurities can either enhance or restrict water uptake in ways that are influenced by several factors including temperature and type of adsorbant, with potential implications for the description of ice particle growth in the atmosphere. This work was supported by the Swedish Research Council and

  14. Accommodating environmental variation in population models: metaphysiological biomass loss accounting.

    PubMed

    Owen-Smith, Norman

    2011-07-01

    1. There is a pressing need for population models that can reliably predict responses to changing environmental conditions and diagnose the causes of variation in abundance in space as well as through time. In this 'how to' article, it is outlined how standard population models can be modified to accommodate environmental variation in a heuristically conducive way. This approach is based on metaphysiological modelling concepts linking populations within food web contexts and underlying behaviour governing resource selection. Using population biomass as the currency, population changes can be considered at fine temporal scales taking into account seasonal variation. Density feedbacks are generated through the seasonal depression of resources even in the absence of interference competition. 2. Examples described include (i) metaphysiological modifications of Lotka-Volterra equations for coupled consumer-resource dynamics, accommodating seasonal variation in resource quality as well as availability, resource-dependent mortality and additive predation, (ii) spatial variation in habitat suitability evident from the population abundance attained, taking into account resource heterogeneity and consumer choice using empirical data, (iii) accommodating population structure through the variable sensitivity of life-history stages to resource deficiencies, affecting susceptibility to oscillatory dynamics and (iv) expansion of density-dependent equations to accommodate various biomass losses reducing population growth rate below its potential, including reductions in reproductive outputs. Supporting computational code and parameter values are provided. 3. The essential features of metaphysiological population models include (i) the biomass currency enabling within-year dynamics to be represented appropriately, (ii) distinguishing various processes reducing population growth below its potential, (iii) structural consistency in the representation of interacting populations and

  15. Finite element based N-Port model for preliminary design of multibody systems

    NASA Astrophysics Data System (ADS)

    Sanfedino, Francesco; Alazard, Daniel; Pommier-Budinger, Valérie; Falcoz, Alexandre; Boquet, Fabrice

    2018-02-01

    This article presents and validates a general framework to build a linear dynamic Finite Element-based model of large flexible structures for integrated Control/Structure design. An extension of the Two-Input Two-Output Port (TITOP) approach is here developed. The authors had already proposed such framework for simple beam-like structures: each beam was considered as a TITOP sub-system that could be interconnected to another beam thanks to the ports. The present work studies bodies with multiple attaching points by allowing complex interconnections among several sub-structures in tree-like assembly. The TITOP approach is extended to generate NINOP (N-Input N-Output Port) models. A Matlab toolbox is developed integrating beam and bending plate elements. In particular a NINOP formulation of bending plates is proposed to solve analytic two-dimensional problems. The computation of NINOP models using the outputs of a MSC/Nastran modal analysis is also investigated in order to directly use the results provided by a commercial finite element software. The main advantage of this tool is to provide a model of a multibody system under the form of a block diagram with a minimal number of states. This model is easy to operate for preliminary design and control. An illustrative example highlights the potential of the proposed approach: the synthesis of the dynamical model of a spacecraft with two deployable and flexible solar arrays.

  16. STS payload data collection and accommodations analysis study. Volume 3: Accommodations analysis

    NASA Technical Reports Server (NTRS)

    1978-01-01

    Payload requirements were compared to launch site accommodations and flight accommodations for a number of Spacelab payloads. Experiment computer operating system accommodations were also considered. A summary of accommodations in terms of resources available for payload discretionary use and recommendations for Spacelab/STS accommodation improvements are presented.

  17. Non-linearity of the response accommodative convergence to accommodation ratio.

    PubMed

    Johnston, Miriam S; Firth, Alison Y

    2013-09-01

    Previous studies have reported variation in stimulus accommodative convergence to accommodation (AC/A) ratio across differing accommodative stimuli. Response AC/A ratio was assessed across 4 accommodative demands to determine if these differences could be due to accommodative inaccuracies to stimuli. Twenty-three student participants aged 18 to 26 years (mean age 20.3 ± 1.7 years) successfully completed all testing conditions. The modified Thorington technique was used at 4 m to measure heterophoria. The Shin Nippon SRW 5000 infrared autorefractor was used to determine accommodative change to -1.50, -3.00, -4.50, and -6.00D lens stimuli. Significant differences were found in response AC/A ratio between different minus lens stimulated accommodative demands (p < 0.001). Mean AC/A ratio values were 3.11 ± 1.29 with the -1.50D lens stimulus; 4.03 ± 2.11 with -3.00D; 4.14 ± 1.40 with -4.50D; and 4.48 ± 1.56 with -6.00D. No differences in linearity were noted between myopes and non-myopic participants, but myopes tended to have higher response AC/A ratios than non-myopes, mean 4.88 ± 1.89 for myopes vs 3.61 ± 1.47 for non-myopes (p = 0.045). Response AC/A ratio did not display linearity across 4 minus lens accommodative stimuli, but tended to increase with accommodative demand. Significant variability in response AC/A ratio was found, both within individuals to different accommodative demands, and between individuals across the data set.

  18. [One-year longitudinal change in parameters of myopic school children trained by a new accommodative training device--uncorrected visual acuity, refraction, axial length, accommodation, and pupil reaction].

    PubMed

    Watanabe, Kumiko; Hara, Naoto; Kimijima, Masumi; Kotegawa, Yasue; Ohno, Koji; Arimoto, Ako; Mukuno, Kazuo; Hisahara, Satoru; Horie, Hidenori

    2012-10-01

    School children with myopia were trained using a visual stimulation device that generated an isolated blur stimulus on a visual target, with a constant retinal image size and constant brightness. Uncorrected visual acuity, cycloplegic refraction, axial length, dynamic accommodation and papillary reaction were measured to investigate the effectiveness of the training. There were 45 school children with myopia without any other ophthalmic diseases. The mean age of the children was 8.9 +/- 2.0 years (age range; 6-16)and the mean refraction was -1.56 +/- 0.58 D (mean +/- standard deviation). As a visual stimulus, a white ring on a black background with a constant ratio of visual target size to retinal image size, irrespective of the distance, was displayed on a liquid crystal display (LCD), and the LCD was quickly moved from a proximal to a distal position to produce an isolated blur stimulus. Training with this visual stimulus was carried out in the relaxation phase of accommodation. Uncorrected visual acuity, cycloplegic refraction, axial length, dynamic accommodation and pupillary reaction were investigated before training and every 3 months during the training. Of the 45 subjects, 42 (93%) could be trained for 3 consecutive months, 33 (73%) for 6 months, 23 (51%) for 9 months, and 21 (47%) for 12 months. The mean refraction decreased by 0.83 +/- 0.56 D (mean +/- standard deviation) and the mean axial length increased by 0.47 +/- 0.16 mm at 1 year, showing that the training bad some effect in improving the visual acuity. In the tests of the dynamic accommodative responses, the latency of the accommodative-phase decreased from 0.4 +/- 0.2 sec to 0.3 +/- 0.1 sec at 1 year, the gain of the accommodative-phase improved from 69.0 +/- 27.0% to 93.3 +/- 13.4%, the maximum speed of the accommodative-phase increased from 5.1 +/- 2.2 D/sec to 6.8 +/- 2.2 D/sec and the gain of the relaxation-phase significantly improved from 52.1 +/- 26.0% to 72.7 +/- 13.7% (corresponding t

  19. Constraint elimination in dynamical systems

    NASA Technical Reports Server (NTRS)

    Singh, R. P.; Likins, P. W.

    1989-01-01

    Large space structures (LSSs) and other dynamical systems of current interest are often extremely complex assemblies of rigid and flexible bodies subjected to kinematical constraints. A formulation is presented for the governing equations of constrained multibody systems via the application of singular value decomposition (SVD). The resulting equations of motion are shown to be of minimum dimension.

  20. Computer-animated model of accommodation and presbyopia.

    PubMed

    Goldberg, Daniel B

    2015-02-01

    To understand, demonstrate, and further research the mechanisms of accommodation and presbyopia. Private practice, Little Silver, New Jersey, USA. Experimental study. The CAMA 2.0 computer-animated model of accommodation and presbyopia was produced in collaboration with an experienced medical animator using Autodesk Maya animation software and Adobe After Effects. The computer-animated model demonstrates the configuration and synchronous movements of all accommodative elements. A new classification of the zonular apparatus based on structure and function is proposed. There are 3 divisions of zonular fibers; that is, anterior, crossing, and posterior. The crossing zonular fibers form a scaffolding to support the lens; the anterior and posterior zonular fibers work reciprocally to achieve focused vision. The model demonstrates the important support function of Weiger ligament. Dynamic movement of the ora serrata demonstrates that the forces of ciliary muscle contraction store energy for disaccommodation in the elastic choroid. The flow of aqueous and vitreous provides strong evidence for our understanding of the hydrodynamic interactions during the accommodative cycle. The interaction may result from the elastic stretch in the choroid transmitted to the vitreous rather than from vitreous pressue. The model supports the concept that presbyopia results from loss of elasticity and increasing ocular rigidity in both the lenticular and extralenticular structures. The computer-animated model demonstrates the structures of accommodation moving in synchrony and might enhance understanding of the mechanisms of accommodation and presbyopia. Dr. Goldberg is a consultant to Acevision, Inc., and Bausch & Lomb. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  1. Potential role for microfluctuations as a temporal directional cue to accommodation

    PubMed Central

    Metlapally, Sangeetha; Tong, Jianliang L.; Tahir, Humza J.; Schor, Clifton M.

    2016-01-01

    The goal was to revisit an important, yet unproven notion that accommodative microfluctuations facilitate the determination of direction (sign) of abrupt focus changes in the stimulus to accommodation. We contaminated the potential temporal cues from natural accommodative microfluctuations by presenting uncorrelated external (screen) temporal defocus noise that combined with the retinal image effects of natural microfluctuations. A polychromatic Maltese spoke pattern thus either modulated defocus at a combination of two temporal frequencies (on-screen noise condition) or was static (control condition). The on-screen conditions were combined with step changes in optical vergence that were randomized in direction and magnitude. Five subjects monocularly viewed stimuli through a Badal optical system in a Maxwellian view. An artificial 4-mm aperture was imaged at the entrance pupil of the eye. Wavefront aberrations were measured dynamically at 50 Hz using a custom Shack–Hartmann aberrometer. Dynamic changes in the Zernike defocus term with step changes in optical vergence were analyzed. We calculated the percentage of correct directional responses for 1, 2, and 3 D accommodative and disaccommodative step stimuli using preset criteria for latency, velocity, and persistence of the response. The on-screen noise condition reduced the percent-correct responses compared to the static stimulus, suggesting that this manipulation affected the detectability of the sign of the accommodative stimulus. Several possible reasons and implications of this result are discussed. PMID:27120075

  2. Can current models of accommodation and vergence predict accommodative behavior in myopic children?

    PubMed

    Sreenivasan, Vidhyapriya; Irving, Elizabeth L; Bobier, William R

    2014-08-01

    Investigations into the progression of myopia in children have long considered the role of accommodation as a cause and solution. Myopic children show high levels of accommodative adaptation, coupled with accommodative lag and high response AC/A (accommodative convergence per diopter of accommodation). This pattern differs from that predicted by current models of interaction between accommodation and vergence, where weakened reflex responses and a high AC/A would be associated with a low not high levels of accommodative adaptation. However, studies of young myopes were limited to only part of the accommodative vergence synkinesis and the reciprocal components of vergence adaptation and convergence accommodation were not studied in tandem. Accordingly, we test the hypothesis that the accommodative behavior of myopic children is not predicted by current models and whether that departure is explained by differences in the accommodative plant of the myopic child. Responses to incongruent stimuli (-2D, +2D adds, 10 prism diopter base-out prism) were investigated in 28 myopic and 25 non-myopic children aged 7-15 years. Subjects were divided into phoria groups - exo, ortho and eso based upon their near phoria. The school aged myopes showed high levels of accommodative adaptation but with reduced accommodation and high AC/A. This pattern is not explained by current adult models and could reflect a sluggish gain of the accommodative plant (ciliary muscle and lens), changes in near triad innervation or both. Further, vergence adaptation showed a predictable reciprocal relationship with the high accommodative adaptation, suggesting that departures from adult models were limited to accommodation not vergence behavior. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Spacecraft transfer trajectory design exploiting resonant orbits in multi-body environments

    NASA Astrophysics Data System (ADS)

    Vaquero Escribano, Tatiana Mar

    Historically, resonant orbits have been employed in mission design for multiple planetary flyby trajectories and, more recently, as a source of long-term orbital stability. For instance, in support of a mission concept in NASA's Outer Planets Program, the Jupiter Europa Orbiter spacecraft is designed to encounter two different resonances with Europa during the 'endgame' phase, leading to Europa orbit insertion on the final pass. In 2011, the Interstellar Boundary Explorer spacecraft was inserted into a stable out-of-plane lunar-resonant orbit, the first of this type for a spacecraft in a long-term Earth orbit. However, resonant orbits have not yet been significantly explored as transfer mechanisms between non-resonant orbits in multi-body systems. This research effort focuses on incorporating resonant orbits into the design process to potentially enable the construction of more efficient or even novel transfer scenarios. Thus, the goals in this investigation are twofold: i) to expand the orbit architecture in multi-body environments by cataloging families of resonant orbits, and ii) to assess the role of such families in the design of transfer trajectories with specific patterns and itineraries. The benefits and advantages of employing resonant orbits in the design process are demonstrated through a variety of astrodynamics applications in several multi-body systems. In the Earth-Moon system, locally optimal transfer trajectories from low Earth orbit to selected libration point orbits are designed by leveraging conic arcs and invariant manifolds associated with resonant orbits. Resonant manifolds in the Earth-Moon system offer trajectories that tour the entire space within reasonable time intervals, facilitating the design of libration point orbit tours as well as Earth-Moon cyclers. In the Saturnian system, natural transitions between resonant and libration point orbits are sought and the problem of accessing Hyperion from orbits that are resonant with Titan is

  4. Accommodation and vergence latencies in human infants

    PubMed Central

    Tondel, Grazyna M.; Candy, T. Rowan

    2008-01-01

    Purpose Achieving simultaneous single and clear visual experience during postnatal development depends on the temporal relationship between accommodation and vergence, in addition to their accuracies. This study was designed to examine one component of the dynamic relationship, the latencies of the responses. Methods Infants and adults were tested in three conditions i) Binocular viewing of a target moving in depth at 5cm/s (closed loop) ii) monocular viewing of the same target (vergence open loop) iii) binocular viewing of a low spatial frequency Difference of Gaussian target during a prism induced step change in retinal disparity (accommodation open loop). Results There was a significant correlation between accommodation and vergence latencies in binocular conditions for infants from 7 to 23 weeks of age. Some of the infants, as young as 7 or 8 weeks, generated adult-like latencies of less than 0.5 s. Latencies in the vergence open loop and accommodation open loop conditions tended to be shorter for the stimulated system than the open loop system in both cases, and all latencies were typically less than 2 seconds across the infant age range. Conclusions Many infants between 7 and 23 weeks of age were able to generate accommodation and vergence responses with latencies of less than a second in full binocular closed loop conditions. The correlation between the latencies in the two systems suggests that they are limited by related factors from the earliest ages tested. PMID:18199466

  5. Accommodation and vergence latencies in human infants.

    PubMed

    Tondel, Grazyna M; Candy, T Rowan

    2008-02-01

    Achieving simultaneous single and clear visual experience during postnatal development depends on the temporal relationship between accommodation and vergence, in addition to their accuracies. This study was designed to examine one component of the dynamic relationship, the latencies of the responses. Infants and adults were tested in three conditions (i) binocular viewing of a target moving in depth at 5 cm/s (closed loop) (ii) monocular viewing of the same target (vergence open loop) (iii) binocular viewing of a low spatial frequency Difference of Gaussian target during a prism induced step change in retinal disparity (accommodation open loop). There was a significant correlation between accommodation and vergence latencies in binocular conditions for infants from 7 to 23 weeks of age. Some of the infants, as young as 7 or 8 weeks, generated adult-like latencies of less than 0.5 s. Latencies in the vergence open loop and accommodation open loop conditions tended to be shorter for the stimulated system than the open loop system in both cases, and all latencies were typically less than 2 s across the infant age range. Many infants between 7 and 23 weeks of age were able to generate accommodation and vergence responses with latencies of less than a second in full binocular closed loop conditions. The correlation between the latencies in the two systems suggests that they are limited by related factors from the earliest ages tested.

  6. Imaging and full-length biometry of the eye during accommodation using spectral domain OCT with an optical switch.

    PubMed

    Ruggeri, Marco; Uhlhorn, Stephen R; De Freitas, Carolina; Ho, Arthur; Manns, Fabrice; Parel, Jean-Marie

    2012-07-01

    An optical switch was implemented in the reference arm of an extended depth SD-OCT system to sequentially acquire OCT images at different depths into the eye ranging from the cornea to the retina. A custom-made accommodation module was coupled with the delivery of the OCT system to provide controlled step stimuli of accommodation and disaccommodation that preserve ocular alignment. The changes in the lens shape were imaged and ocular distances were dynamically measured during accommodation and disaccommodation. The system is capable of dynamic in vivo imaging of the entire anterior segment and eye-length measurement during accommodation in real-time.

  7. Effect of planform and body on supersonic aerodynamics of multibody configurations

    NASA Technical Reports Server (NTRS)

    Mcmillin, S. Naomi; Bauer, Steven X. S.; Howell, Dorothy T.

    1992-01-01

    An experimental and theoretical investigation of the effect of the wing planform and bodies on the supersonic aerodynamics of a low-fineness-ratio, multibody configuration has been conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.60, 1.80, 2.00, and 2.16. Force and moment data, flow-visualization data, and surface-pressure data were obtained on eight low-fineness-ratio, twin-body configurations. These configurations varied in inboard wing planform shape, outboard wing planform shape, outboard wing planform size, and presence of the bodies. The force and moment data showed that increasing the ratio of outboard wing area to total wing area or increasing the leading-edge sweep of the inboard wing influenced the aerodynamic characteristics. The flow-visualization data showed a complex flow-field system of shocks, shock-induced separation, and body vortex systems occurring between the side bodies. This flow field was substantially affected by the inboard wing planform shape but minimally affected by the outboard wing planform shape. The flow-visualization and surface-pressure data showed that flow over the outboard wing developed as expected with changes in angle of attack and Mach number and was affected by the leading-edge sweep of the inboard wing and the presence of the bodies. Evaluation of the linear-theory prediction methods revealed their general inability to consistently predict the characteristics of these multibody configurations.

  8. A Cervico-Thoraco-Lumbar Multibody Dynamic Model for the Estimation of Joint Loads and Muscle Forces.

    PubMed

    Khurelbaatar, Tsolmonbaatar; Kim, Kyungsoo; Hyuk Kim, Yoon

    2015-11-01

    Computational musculoskeletal models have been developed to predict mechanical joint loads on the human spine, such as the forces and moments applied to vertebral and facet joints and the forces that act on ligaments and muscles because of difficulties in the direct measurement of joint loads. However, many whole-spine models lack certain elements. For example, the detailed facet joints in the cervical region or the whole spine region may not be implemented. In this study, a detailed cervico-thoraco-lumbar multibody musculoskeletal model with all major ligaments, separated structures of facet contact and intervertebral disk joints, and the rib cage was developed. The model was validated by comparing the intersegmental rotations, ligament tensile forces, facet joint contact forces, compressive and shear forces on disks, and muscle forces were to those reported in previous experimental and computational studies both by region (cervical, thoracic, or lumbar regions) and for the whole model. The comparisons demonstrated that our whole spine model is consistent with in vitro and in vivo experimental studies and with computational studies. The model developed in this study can be used in further studies to better understand spine structures and injury mechanisms of spinal disorders.

  9. The effect of monocular and binocular viewing on the accommodation response to real targets in emmetropia and myopia.

    PubMed

    Seidel, Dirk; Gray, Lyle S; Heron, Gordon

    2005-04-01

    Decreased blur-sensitivity found in myopia has been linked with reduced accommodation responses and myopigenesis. Although the mechanism for myopia progression remains unclear, it is commonly known that myopic patients rarely report near visual symptoms and are generally very sensitive to small changes in their distance prescription. This experiment investigated the effect of monocular and binocular viewing on static and dynamic accommodation in emmetropes and myopes for real targets to monitor whether inaccuracies in the myopic accommodation response are maintained when a full set of visual cues, including size and disparity, is available. Monocular and binocular steady-state accommodation responses were measured with a Canon R1 autorefractor for target vergences ranging from 0-5 D in emmetropes (EMM), late-onset myopes (LOM), and early-onset myopes (EOM). Dynamic closed-loop accommodation responses for a stationary target at 0.25 m and step stimuli of two different magnitudes were recorded for both monocular and binocular viewing. All refractive groups showed similar accommodation stimulus response curves consistent with previously published data. Viewing a stationary near target monocularly, LOMs demonstrated slightly larger accommodation microfluctuations compared with EMMs and EOMs; however, this difference was absent under binocular viewing conditions. Dynamic accommodation step responses revealed significantly (p < 0.05) longer response times for the myopic subject groups for a number of step stimuli. No significant difference in either reaction time or the number of correct responses for a given number of step-vergence changes was found between the myopic groups and EMMs. When viewing real targets with size and disparity cues available, no significant differences in the accuracy of static and dynamic accommodation responses were found among EMM, EOM, and LOM. The results suggest that corrected myopes do not experience dioptric blur levels that are

  10. Implicit gas-kinetic unified algorithm based on multi-block docking grid for multi-body reentry flows covering all flow regimes

    NASA Astrophysics Data System (ADS)

    Peng, Ao-Ping; Li, Zhi-Hui; Wu, Jun-Lin; Jiang, Xin-Yu

    2016-12-01

    Based on the previous researches of the Gas-Kinetic Unified Algorithm (GKUA) for flows from highly rarefied free-molecule transition to continuum, a new implicit scheme of cell-centered finite volume method is presented for directly solving the unified Boltzmann model equation covering various flow regimes. In view of the difficulty in generating the single-block grid system with high quality for complex irregular bodies, a multi-block docking grid generation method is designed on the basis of data transmission between blocks, and the data structure is constructed for processing arbitrary connection relations between blocks with high efficiency and reliability. As a result, the gas-kinetic unified algorithm with the implicit scheme and multi-block docking grid has been firstly established and used to solve the reentry flow problems around the multi-bodies covering all flow regimes with the whole range of Knudsen numbers from 10 to 3.7E-6. The implicit and explicit schemes are applied to computing and analyzing the supersonic flows in near-continuum and continuum regimes around a circular cylinder with careful comparison each other. It is shown that the present algorithm and modelling possess much higher computational efficiency and faster converging properties. The flow problems including two and three side-by-side cylinders are simulated from highly rarefied to near-continuum flow regimes, and the present computed results are found in good agreement with the related DSMC simulation and theoretical analysis solutions, which verify the good accuracy and reliability of the present method. It is observed that the spacing of the multi-body is smaller, the cylindrical throat obstruction is greater with the flow field of single-body asymmetrical more obviously and the normal force coefficient bigger. While in the near-continuum transitional flow regime of near-space flying surroundings, the spacing of the multi-body increases to six times of the diameter of the single

  11. Attention-deficit/hyperactivity disorder children exhibit an impaired accommodative response.

    PubMed

    Redondo, Beatriz; Vera, Jesús; Molina, Rubén; García, José Antonio; Ouadi, Miriam; Muñoz-Hoyos, Antonio; Jiménez, Raimundo

    2018-05-01

    Attention-deficit/hyperactivity disorder (ADHD) is one of the most common paediatric neurobehavioural disorders causing multiple functional impairments in children. Based on the relationship between the neural system that controls attention and ocular dynamics, the present study compares the magnitude and variability of accommodation between a group of non-medicated ADHD children and an age-matched control group. The magnitude and variability of the accommodative response were objectively measured in 36 children using the WAM-5500 autorefractometer for 90 consecutive seconds at three static viewing distances (500, 40, and 20 cm). Participants were divided into ADHD (n = 18) or control (n = 18) groups based on clinically validated criteria. Children with ADHD exhibited higher lags of accommodation (p = 0.024), increasing at closer viewing distances, in comparison to the control group. Marginal statistical differences were found for the variability of accommodation (p = 0.066), with the ADHD group showing a trend towards higher variability. Our analysis showed that the magnitude and variability of accommodation did not vary over time between groups (p > 0.05). Our data suggest that children with ADHD have a less accurate accommodative response. These results provide a new ocular index that could help to clarify the relationship between accommodative response and attentional deficits, which could have a direct impact on the academic, cognitive, and visual performance of ADHD children.

  12. Imaging and full-length biometry of the eye during accommodation using spectral domain OCT with an optical switch

    PubMed Central

    Ruggeri, Marco; Uhlhorn, Stephen R.; De Freitas, Carolina; Ho, Arthur; Manns, Fabrice; Parel, Jean-Marie

    2012-01-01

    Abstract: An optical switch was implemented in the reference arm of an extended depth SD-OCT system to sequentially acquire OCT images at different depths into the eye ranging from the cornea to the retina. A custom-made accommodation module was coupled with the delivery of the OCT system to provide controlled step stimuli of accommodation and disaccommodation that preserve ocular alignment. The changes in the lens shape were imaged and ocular distances were dynamically measured during accommodation and disaccommodation. The system is capable of dynamic in vivo imaging of the entire anterior segment and eye-length measurement during accommodation in real-time. PMID:22808424

  13. Inter-individual variability in the dynamics of natural accommodation in humans: relation to age and refractive errors.

    PubMed Central

    Schaeffel, F; Wilhelm, H; Zrenner, E

    1993-01-01

    1. To study the relationship between accommodation under natural viewing conditions, age and refractive errors, we have measured time courses of accommodation in thirty-nine human subjects aged 5-49 years using a newly developed technique. The technique is based on infrared photoretinoscopy and involves fully automated on-line image processing of digitized video images of the eyes with a sampling rate of 5.3 Hz. 2. The distance between the subject and the video camera was about 1.3 m. Head movements of the subject required little restriction because the eyes were automatically tracked in the video image by the computer program. All subjects were tested under binocular viewing conditions. 3. Both refraction of the right eye and pupil diameter were measured with a precision of 0.2-0.4 dioptres (D) and 0.1 mm, respectively, and were plotted on-line. The data were subsequently automatically analysed. 4. Automated infrared photoretinoscopy proved to be very convenient and easy to handle in both children and adults. 5. The maximal speed of accommodation for a target at a distance of 5 D declined in the subjects with age (from up to 21.7 D s-1 for accommodation and 32.7 D s-1 for subsequent accommodation to a distant target ('near to far accommodation') in children down to 2-18 D s-1 in adults). There was a striking inter-individual variability in the maximum possible speed of accommodation and near to far accommodation. 6. Speed of accommodation and of near to far accommodation was correlated for each subject. However, in most of the subjects, the process of near to far accommodation was faster than accommodation (P < 0.005, if averaged over all subjects). This correlation was independent of age. 7. The accommodation-induced pupillary constriction (pupillary near response) was absent in children for a 4 D target; even at 10 D, there was no reliable pupillary response. The pupillary near response increased to about 1.6 mm D-1 of accommodation at the age of 47. Since a

  14. A fast recursive algorithm for molecular dynamics simulation

    NASA Technical Reports Server (NTRS)

    Jain, A.; Vaidehi, N.; Rodriguez, G.

    1993-01-01

    The present recursive algorithm for solving molecular systems' dynamical equations of motion employs internal variable models that reduce such simulations' computation time by an order of magnitude, relative to Cartesian models. Extensive use is made of spatial operator methods recently developed for analysis and simulation of the dynamics of multibody systems. A factor-of-450 speedup over the conventional O(N-cubed) algorithm is demonstrated for the case of a polypeptide molecule with 400 residues.

  15. The influence of interactions between accommodation and convergence on the lag of accommodation.

    PubMed

    Schor, C

    1999-03-01

    Several models of myopia predict that growth of axial length is stimulated by blur. Accommodative lag has been suggested as an important source of blur in the development of myopia and this study has modeled how cross-link interactions between accommodation and convergence might interact with uncorrected distance heterophoria and refractive error to influence accommodative lag. Accommodative lag was simulated with two models of interactions between accommodation and convergence (one with and one without adaptable tonic elements). Simulations of both models indicate that both uncorrected hyperopia and esophoria increase the lag of accommodative and uncorrected myopia and exophoria decrease the lag or introduce a lead of accommodation in response to the near (40 cm) stimulus. These effects were increased when gain of either cross-link, accommodative convergence (AC/A) or convergence accommodation (CA/C), was increased within a moderate range of values while the other was fixed at a normal value (clamped condition). These effects were exaggerated when both the AC/A and CA/C ratios were increased (covaried condition) and affects of cross-link gain were negated when an increase of one cross-link (e.g. AC/A) was accompanied by a reduction of the other cross-link (e.g. CA/C) (reciprocal condition). The inclusion of tonic adaptation in the model reduced steady state errors of accommodation for all conditions except when the AC/A ratio was very high (2 MA/D). Combinations of cross-link interactions between accommodation and convergence that resemble either clamped or reciprocal patterns occur naturally in clinical populations. Simulations suggest that these two patterns of abnormal cross-link interactions could affect the progression of myopia differently. Adaptable tonic accommodation and tonic vergence could potentially reduce the progression of myopia by reducing the lag of accommodation.

  16. Simultaneous refraction measurement and OCT axial biometry of the eye during accommodation (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    De Freitas, Carolina; Hernandez, Victor M.; Ruggeri, Marco; Durkee, Heather A.; Williams, Siobhan; Gregori, Giovanni; Ho, Arthur; Manns, Fabrice; Parel, Jean-Marie

    2016-03-01

    The purpose of this project is to design and evaluate a system that will enable objective assessment of the optical accommodative response in real-time while acquiring axial biometric information. The system combines three sub-systems which were integrated and mounted on a joystick x-y-z adjustable modified slit-lamp base to facilitate alignment and data acquisition: (1) a Shack-Hartmann wavefront sensor for dynamic refraction measurement, provided software calculates sphere, cylinder and axis values, (2) an extended-depth Optical Coherence Tomography (OCT) system using an optical switch records high-resolution cross-sectional images across the length of the eye, from which, dynamic axial biometry (corneal thickness, anterior chamber depth, crystalline lens thickness and vitreous depth) can be extracted, and (3) a modified dual-channel accommodation stimulus unit based on the Badal optometer for providing a step change in accommodative stimulus. The prototypal system is capable of taking simultaneous measurements of both the optical and the mechanical response of lens accommodation. These measurements can provide insight into correlating changes in lens shape with changes in lens power and ocular refraction and ultimately provide a more comprehensive understanding of accommodation, presbyopia and an objective assessment of presbyopia correction techniques.

  17. Application of video-based technology for the simultaneous measurement of accommodation and vergence.

    PubMed

    Suryakumar, Rajaraman; Meyers, Jason P; Irving, Elizabeth L; Bobier, William R

    2007-01-01

    Accommodation and vergence are two ocular motor systems that interact during binocular vision. Independent measurement of the response dynamics of each system has been achieved by the application of optometers and eye trackers. However, relatively few devices, typically earlier model optometers, allow the simultaneous assessment of accommodation and vergence. In this study we describe the development and application of a custom designed high-speed digital photorefractor that allows for rapid measures of accommodation (up to 75Hz). In addition the photorefractor was also synchronized with a video-based stereo eye tracker to allow a simultaneous measurement of accommodation and vergence. Analysis of accommodation and vergence could then be conducted offline. The new instrumentation is suitable for investigation of young children and could be potentially used for clinical populations.

  18. Multibody dynamics simulation of an all-wheel-drive motorcycle for handling and energy efficiency investigations

    NASA Astrophysics Data System (ADS)

    Griffin, J. W.; Popov, A. A.

    2018-07-01

    It is now possible, through electrical, hydraulic or mechanical means, to power the front wheel of a motorcycle. The aim of this is often to improve performance in limit-handling scenarios including off-road low-traction conditions and on-road high-speed cornering. Following on from research into active torque distribution in 4-wheeled vehicles, the possibility exists for efficiency improvements to be realised by reducing the total amount of energy dissipated as slip at the wheel-road contact. This paper presents the results of an investigation into the effect that varying the torque distribution ratio has on the energy consumption of the two-wheeled vehicle. A 13-degree of freedom multibody model was created, which includes the effects of suspension, aerodynamics and gyroscopic bodies. SimMechanics, from the MathWorks?, is used for automatic generation of equations of motion and time-domain simulation, in conjunction with MATLAB and Simulink. A simple driver model is used to control the speed and yaw rate of the motorcycle. The handling characteristics of the motorcycle are quantitatively analysed, and the impact of torque distribution on energy consumption is considered during straight line and cornering situations. The investigation has shown that only a small improvement in efficiency can be made by transferring a portion of the drive torque to the front wheel. Tyre longevity could be improved by reduced slip energy dissipation.

  19. Simulation of spacecraft attitude dynamics using TREETOPS and model-specific computer Codes

    NASA Technical Reports Server (NTRS)

    Cochran, John E.; No, T. S.; Fitz-Coy, Norman G.

    1989-01-01

    The simulation of spacecraft attitude dynamics and control using the generic, multi-body code called TREETOPS and other codes written especially to simulate particular systems is discussed. Differences in the methods used to derive equations of motion--Kane's method for TREETOPS and the Lagrangian and Newton-Euler methods, respectively, for the other two codes--are considered. Simulation results from the TREETOPS code are compared with those from the other two codes for two example systems. One system is a chain of rigid bodies; the other consists of two rigid bodies attached to a flexible base body. Since the computer codes were developed independently, consistent results serve as a verification of the correctness of all the programs. Differences in the results are discussed. Results for the two-rigid-body, one-flexible-body system are useful also as information on multi-body, flexible, pointing payload dynamics.

  20. Relationship of ocular accommodation and motor skills performance in developmental coordination disorder.

    PubMed

    Rafique, Sara A; Northway, Nadia

    2015-08-01

    Ocular accommodation provides a well-focussed image, feedback for accurate eye movement control, and cues for depth perception. To accurately perform visually guided motor tasks, integration of ocular motor systems is essential. Children with motor coordination impairment are established to be at higher risk of accommodation anomalies. The aim of the present study was to examine the relationship between ocular accommodation and motor tasks, which are often overlooked, in order to better understand the problems experienced by children with motor coordination impairment. Visual function, gross and fine motor skills were assessed in children with developmental coordination disorder (DCD) and typically developing control children. Children with DCD had significantly poorer accommodation facility and amplitude dynamics compared to controls. Results indicate a relationship between impaired accommodation and motor skills. Specifically, accommodation anomalies correlated with visual motor, upper limb and fine dexterity task performance. Consequently, we argue accommodation anomalies influence the ineffective coordination of action and perception in DCD. Furthermore, reading disabilities were related to poorer motor performance. We postulate the role of the fastigial nucleus as a common pathway for accommodation and motor deficits. Implications of the findings and recommended visual screening protocols are discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

  1. Disabling accommodation barriers: A study exploring how to better accommodate government employees with anxiety disorders.

    PubMed

    Mellifont, Damian; Smith-Merry, Jennifer; Scanlan, Justin Newton

    2016-11-22

    Accommodating mental health in the workplace is challenging. Despite policy efforts to encourage the availability of mental health accommodations in the workplace, employees experiencing mental illness are missing out on accommodations that they need. To inform vocational rehabilitation professionals and managers in the public service of best practice accommodations for government employees with anxiety disorders. Thematic analysis was applied to data collected from the online Accommodating Government Employees with Anxiety Disorders Survey undertaken by 71 Australian public service employees diagnosed with at least one anxiety disorder. Our research results include theme and sub-theme representations of accommodations received, accommodations reported as missing, accommodations that study participants felt they couldn't request, along with rejected accommodations. From the study participants' accounts, three key findings supporting desirable vocational outcomes become apparent. First, that the availability of 'standard' flexible work arrangements, along with personalised accommodations, can assist persons with anxiety disorders (where needed) to reach and retain government positions. Second, the chief barriers reported to making accommodation requests revolve around fears of being stigmatised and penalised. Finally, there is a need for managerial decision-makers to remain open-minded, particularly when assessing requests for accommodations that may break from government norms.

  2. Pupil movements to light and accommodative stimulation - A comparative study.

    NASA Technical Reports Server (NTRS)

    Semmlow, J.; Stark, L.

    1973-01-01

    Isolation and definition of specific response components in pupil reflexes through comparison of the dynamic features of light-induced and accommodation-induced pupil movements. A quantitative analysis of the behavior of the complex nonlinear pupil responses reveals the presence of two independent nonlinear characteristics: a range-dependent gain and a direction dependence or movement asymmetry. These nonlinear properties are attributed to motor processes because they are observable in pupil responses to both light and accommodation stimuli. The possible mechanisms and consequences of these pupil response characteristics are quantitatively defined and discussed.

  3. [Effects of orthokeratology lenses on the magnitude of accommodative lag and accommodativeconvergence/accommodation].

    PubMed

    Ren, Qiujin; Yue, Hui; Zhou, Qing

    2016-02-01

    To evaluate the change in accommodative lag and accommodation convergence/accommodation (AC/A) after patients with myopia wear orthokeratology lenses. 
 A total of 48 myopic subjects (a test group), who wore orthokeratology lenses regularly, and 48 myopic subjects (a control group), who wore spectacles regularly, were enrolled for this study from January 2011 to January 2013 in Optometric Center, the Forth Hospital of Changsha. Accommodative lag was measured by fused cross cylinder method, where the patients should gaze at the front optotypes 40 cm away. Gradient of the AC/A ratio was measured by Von Grafe method to check closer distance heterophoria. Accommodative lag and AC/A ratio were analyzed by statistics.
 After 1-year follow-up, accommodative lag and AC/A rate in patients with low or moderate myopia in the test group was decreased in 1, 3, 6 months or 1 year compared with that in the control group (P<0.05). 
 Compared with spectacles, orthokeratology lenses are able to decrease accommodative lag and high AC/A rate in patients with low or moderate myopia. The relationship between accommodation and convergence is improved by orthokeratology lenses. Orthokeratology is an effective way to control myopia.

  4. Prediction of elbow joint contact mechanics in the multibody framework.

    PubMed

    Rahman, Munsur; Cil, Akin; Stylianou, Antonis P

    2016-03-01

    Computational multibody musculoskeletal models of the elbow joint that are capable of simultaneous and accurate predictions of muscle and ligament forces, along with cartilage contact mechanics can be immensely useful in clinical practice. As a step towards producing a musculoskeletal model that includes the interaction between cartilage and muscle loading, the goal of this study was to develop subject-specific multibody models of the elbow joint with discretized humerus cartilage representation interacting with the radius and ulna cartilages through deformable contacts. The contact parameters for the compliant contact law were derived using simplified elastic foundation contact theory. The models were then validated by placing the model in a virtual mechanical tester for flexion-extension motion similar to a cadaver experiment, and the resulting kinematics were compared. Two cadaveric upper limbs were used in this study. The humeral heads were subjected to axial motion in a mechanical tester and the resulting kinematics from three bones were recorded for model validation. The maximum RMS error between the predicted and measured kinematics during the complete testing cycle was 2.7 mm medial-lateral translation and 9.7° varus-valgus rotation of radius relative to humerus (for elbow 2). After model validation, a lateral ulnar collateral ligament (LUCL) deficient condition was simulated and, contact pressures and kinematics were compared to the intact elbow model. A noticeable difference in kinematics, contact area, and contact pressure were observed for LUCL deficient condition. LUCL deficiency induced higher internal rotations for both the radius and ulna during flexion and an associated medial shift of the articular contact area. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

  5. Improving Accommodations Outcomes: Monitoring Instructional and Assessment Accommodations for Students with Disabilities

    ERIC Educational Resources Information Center

    Christensen, Laurene L.; Thurlow, Martha L.; Wang, Ting

    2009-01-01

    This document presents a five-step process for schools, districts, and states to use in monitoring accommodations for instruction and assessment. This document was designed to be a companion to the "Council of Chief State School Officers' Accommodations Manual: How to Select, Administer, and Evaluate Use of Accommodations for Instruction and…

  6. Systematic generation of multibody equations of motion suitable for recursive and parallel manipulation

    NASA Technical Reports Server (NTRS)

    Nikravesh, Parviz E.; Gim, Gwanghum; Arabyan, Ara; Rein, Udo

    1989-01-01

    The formulation of a method known as the joint coordinate method for automatic generation of the equations of motion for multibody systems is summarized. For systems containing open or closed kinematic loops, the equations of motion can be reduced systematically to a minimum number of second order differential equations. The application of recursive and nonrecursive algorithms to this formulation, computational considerations and the feasibility of implementing this formulation on multiprocessor computers are discussed.

  7. Visual accommodation trainer-tester

    NASA Technical Reports Server (NTRS)

    Randle, R. J., Jr. (Inventor)

    1983-01-01

    An apparatus for training of the human visual accommodation system is presented, specifically, useful for training a person to volitionally control his focus to his far point (normaly infinity) from a position of myopia due to functional causes. The functional causes could be due, for example, to a behavioral accommodative spasm or the effects of an empty field. The device may also be used to measure accommodation, the accommodation resting position and the near and far points of vision.

  8. The Accommodation Operation. Accommodation Management Module. Operational Management Programme.

    ERIC Educational Resources Information Center

    Chapman, Janet

    This module on accommodation operation is intended to help supervisors or managers achieve a balance in the day-to-day running of the premises and plan for a smooth and successful future. Much of the material is concerned with the housekeeping aspects of accommodation management. The material is presented in a self-instructional format in seven…

  9. Effect of the accommodation-vergence conflict on vergence eye movements.

    PubMed

    Vienne, Cyril; Sorin, Laurent; Blondé, Laurent; Huynh-Thu, Quan; Mamassian, Pascal

    2014-07-01

    With the broader use of stereoscopic displays, a flurry of research activity about the accommodation-vergence conflict has emerged to highlight the implications for the human visual system. In stereoscopic displays, the introduction of binocular disparities requires the eyes to make vergence movements. In this study, we examined vergence dynamics with regard to the conflict between the stimulus-to-accommodation and the stimulus-to-vergence. In a first experiment, we evaluated the immediate effect of the conflict on vergence responses by presenting stimuli with conflicting disparity and focus on a stereoscopic display (i.e. increasing the stereoscopic demand) or by presenting stimuli with matched disparity and focus using an arrangement of displays and a beam splitter (i.e. focus and disparity specifying the same locations). We found that the dynamics of vergence responses were slower overall in the first case due to the conflict between accommodation and vergence. In a second experiment, we examined the effect of a prolonged exposure to the accommodation-vergence conflict on vergence responses, in which participants judged whether an oscillating depth pattern was in front or behind the fixation plane. An increase in peak velocity was observed, thereby suggesting that the vergence system has adapted to the stereoscopic demand. A slight increase in vergence latency was also observed, thus indicating a small decline of vergence performance. These findings offer a better understanding and document how the vergence system behaves in stereoscopic displays. We describe what stimuli in stereo-movies might produce these oculomotor effects, and discuss potential applications perspectives. Copyright © 2014 Elsevier B.V. All rights reserved.

  10. New Factorization Techniques and Parallel (log N) Algorithms for Forward Dynamics Solution of Single Closed-Chain Robot Manipulators

    NASA Technical Reports Server (NTRS)

    Fijany, Amir

    1993-01-01

    In this paper parallel 0(log N) algorithms for dynamic simulation of single closed-chain rigid multibody system as specialized to the case of a robot manipulatoar in contact with the environment are developed.

  11. [Energy and memory efficient calculation of the accommodation demand in the artificial accommodation system].

    PubMed

    Nagel, J A; Beck, C; Harms, H; Stiller, P; Guth, H; Stachs, O; Bretthauer, G

    2010-12-01

    Presbyopia and cataract are gaining more and more importance in the ageing society. Both age-related complaints are accompanied with a loss of the eye's ability to accommodate. A new approach to restore accommodation is the Artificial Accommodation System, an autonomous micro system, which will be implanted into the capsular bag instead of a rigid intraocular lens. The Artificial Accommodation System will, depending on the actual demand for accommodation, autonomously adapt the refractive power of its integrated optical element. One possibility to measure the demand for accommodation non-intrusively is to analyse eye movements. We present an efficient algorithm, based on the CORDIC technique, to calculate the demand for accommodation from magnetic field sensor data. It can be shown that specialised algorithms significantly shorten calculation time without violating precision requirements. Additionally, a communication strategy for the wireless exchange of sensor data between the implants of the left and right eye is introduced. The strategy allows for a one-sided calculation of the demand for accommodation, resulting in an overall reduction of calculation time by 50 %. The presented methods enable autonomous microsystems, such as the Artificial Accommodation System, to save significant amounts of energy, leading to extended autonomous run-times. © Georg Thieme Verlag KG Stuttgart · New York.

  12. Simulations and Measurements of Human Middle Ear Vibrations Using Multi-Body Systems and Laser-Doppler Vibrometry with the Floating Mass Transducer.

    PubMed

    Böhnke, Frank; Bretan, Theodor; Lehner, Stefan; Strenger, Tobias

    2013-10-22

    The transfer characteristic of the human middle ear with an applied middle ear implant (floating mass transducer) is examined computationally with a Multi-body System approach and compared with experimental results. For this purpose, the geometry of the middle ear was reconstructed from μ-computer tomography slice data and prepared for a Multi-body System simulation. The transfer function of the floating mass transducer, which is the ratio of the input voltage and the generated force, is derived based on a physical context. The numerical results obtained with the Multi-body System approach are compared with experimental results by Laser Doppler measurements of the stapes footplate velocities of five different specimens. Although slightly differing anatomical structures were used for the calculation and the measurement, a high correspondence with respect to the course of stapes footplate displacement along the frequency was found. Notably, a notch at frequencies just below 1 kHz occurred. Additionally, phase courses of stapes footplate displacements were determined computationally if possible and compared with experimental results. The examinations were undertaken to quantify stapes footplate displacements in the clinical practice of middle ear implants and, also, to develop fitting strategies on a physical basis for hearing impaired patients aided with middle ear implants.

  13. Reasonable Accommodation Information Tracking System

    EPA Pesticide Factsheets

    The Reasonable Accommodation Information Tracking System (RAITS) is a case management system that allows the National Reasonable Accommodation Coordinator (NRAC) and the Local Reasonable Accommodation Coordinators (LORAC) to manage information related to Reasonable Accommodation (RA) requests. It provides a data base system in compliance with Executive Order 13164 and required by the Equal Employment Opportunity Commission (EEOC) Regulations and American Federation of Government Employees (AFGE) Bargaining Unit as described in the AFGE National Reasonable Accommodation Procedures. It is a tool that was internally developed in Lotus Notes to track requests for reasonable accommodation and was custom-configured to meet EPA's specific needs and infrastructure.

  14. Retinal Image Quality During Accommodation

    PubMed Central

    López-Gil, N.; Martin, J.; Liu, T.; Bradley, A.; Díaz-Muñoz, D.; Thibos, L.

    2013-01-01

    Purpose We asked if retinal image quality is maximum during accommodation, or sub-optimal due to accommodative error, when subjects perform an acuity task. Methods Subjects viewed a monochromatic (552nm), high-contrast letter target placed at various viewing distances. Wavefront aberrations of the accommodating eye were measured near the endpoint of an acuity staircase paradigm. Refractive state, defined as the optimum target vergence for maximising retinal image quality, was computed by through-focus wavefront analysis to find the power of the virtual correcting lens that maximizes visual Strehl ratio. Results Despite changes in ocular aberrations and pupil size during binocular viewing, retinal image quality and visual acuity typically remain high for all target vergences. When accommodative errors lead to sub-optimal retinal image quality, acuity and measured image quality both decline. However, the effect of accommodation errors of on visual acuity are mitigated by pupillary constriction associated with accommodation and binocular convergence and also to binocular summation of dissimilar retinal image blur. Under monocular viewing conditions some subjects displayed significant accommodative lag that reduced visual performance, an effect that was exacerbated by pharmacological dilation of the pupil. Conclusions Spurious measurement of accommodative error can be avoided when the image quality metric used to determine refractive state is compatible with the focusing criteria used by the visual system to control accommodation. Real focusing errors of the accommodating eye do not necessarily produce a reliably measurable loss of image quality or clinically significant loss of visual performance, probably because of increased depth-of-focus due to pupil constriction. When retinal image quality is close to maximum achievable (given the eye’s higher-order aberrations), acuity is also near maximum. A combination of accommodative lag, reduced image quality, and reduced

  15. Concentration dependent carriers dynamics in CsPbBr3 perovskite nanocrystals film with transient grating

    NASA Astrophysics Data System (ADS)

    Wang, Yinghui; Wang, Yanting; Dev Verma, Sachin; Tan, Mingrui; Liu, Qinghui; Yuan, Qilin; Sui, Ning; Kang, Zhihui; Zhou, Qiang; Zhang, Han-Zhuang

    2017-05-01

    The concentration dependence of the carrier dynamics is a key parameter to describe the photo-physical properties of semiconductor films. Here, we investigate the carrier dynamics in the CsPbBr3 perovskite nanocrystal film by employing the transient grating (TG) technique with continuous bias light. The concentration of initial carriers is determined by the average number of photons per nanocrystals induced by pump light (⟨N⟩). The multi-body interaction would appear and accelerate the TG dynamics with ⟨N⟩. When ⟨N⟩ is more than 3.0, the TG dynamics slightly changes, which implies that the Auger recombination would be the highest order multi-body interaction in carrier recombination dynamics. The concentration of non-equilibrium carriers in the film is controlled by the average number of photons per nanocrystals excited by continuous bias light (⟨nne⟩). Increasing ⟨nne⟩ would improve the trapping-detrapping process by filling the trapping state, which would accelerate the carrier diffusion and add the complexity of the mono-molecular recombination mechanism. The results should be useful to further understand the mechanism of carrier dynamics in the CsPbBr3 perovskite nanocrystal film and of great importance for the operation of the corresponding optoelectronic devices.

  16. Asymmetrical accommodation in hyperopic anisometropic amblyopia

    PubMed Central

    Toor, Sonia; Riddell, Patricia

    2018-01-01

    Background/aims To investigate the presence of asymmetrical accommodation in hyperopic anisometropic amblyopia. Methods Accommodation in each eye and binocular vergence were measured simultaneously using a PlusoptiX SO4 photorefractor in 26 children aged 4–8 years with hyperopic anisometropic amblyopia and 13 controls (group age-matched) while they viewed a detailed target moving in depth. Results Without spectacles, only 5 (19%) anisometropes demonstrated symmetrical accommodation (within the 95% CI of the mean gain of the sound eye of the anisometropic group), whereas 21 (81%) demonstrated asymmetrical accommodation. Of those, 15 (58%) showed aniso-accommodation and 6 (23%) demonstrated ‘anti-accommodation’ (greater accommodation for distance than for near). In those with anti-accommodation, the response gain in the sound eye was (0.93±0.20) while that of the amblyopic eye showed a negative accommodation gain of (−0.44±0.23). Anti-accommodation resolved with spectacles. Vergence gains were typical in those with symmetrical and asymmetrical accommodation. Conclusion The majority of hyperopic anisometropic amblyopes demonstrated non-consensual asymmetrical accommodation. Approximately one in four demonstrated anti-accommodation. PMID:29051327

  17. Movement Characteristics Analysis and Dynamic Simulation of Collaborative Measuring Robot

    NASA Astrophysics Data System (ADS)

    guoqing, MA; li, LIU; zhenglin, YU; guohua, CAO; yanbin, ZHENG

    2017-03-01

    Human-machine collaboration is becoming increasingly more necessary, and so collaborative robot applications are also in high demand. We selected a UR10 robot as our research subject for this study. First, we applied D-H coordinate transformation of the robot to establish a link system, and we then used inverse transformation to solve the robot’s inverse kinematics and find all the joints. Use Lagrange method to analysis UR robot dynamics; use ADAMS multibody dynamics simulation software to dynamic simulation; verifying the correctness of the derived kinetic models.

  18. Computer aided design environment for the analysis and design of multi-body flexible structures

    NASA Technical Reports Server (NTRS)

    Ramakrishnan, Jayant V.; Singh, Ramen P.

    1989-01-01

    A computer aided design environment consisting of the programs NASTRAN, TREETOPS and MATLAB is presented in this paper. With links for data transfer between these programs, the integrated design of multi-body flexible structures is significantly enhanced. The CAD environment is used to model the Space Shuttle/Pinhole Occulater Facility. Then a controller is designed and evaluated in the nonlinear time history sense. Recent enhancements and ongoing research to add more capabilities are also described.

  19. Job Accommodation Network

    MedlinePlus

    ADA LIBRARY PUBLICATIONS AND RESOURCES SEARCH ACCOMMODATIONS DATABASE A-Z OF DISABILITIES AND ACCOMMODATIONS NEWS Hot Topics How to Use this Site JAN en Español Print this Page A A A Text Size Connect with JAN (800)526-7234 (Voice) (877)781-9403 ( ...

  20. Fast Auroral Snapshot performance using a multi-body dynamic simulation

    NASA Technical Reports Server (NTRS)

    Zimbelman, Darrell; Walker, Mary

    1993-01-01

    This paper examines the complex dynamic interaction between two 2.6 m long stacer booms, four 30 m long flexible wire booms and the attitude control system of the Fast Auroral SnapshoT (FAST) spacecraft. The FAST vehicle will nominally operate as a negative orbit spinner, positioned in a 83 deg inclination, 350 x 4200 km orbit. For this study, a three-axis, non-linear, seven body dynamic simulation is developed using the TREETOPS software package. The significance of this approach is the ability to model each component of the FAST spacecraft as an individual member and connect them together in order to better understand the dynamic coupling between structures and the control system. Both the wire and stacer booms are modeled as separate bodies attached to a rigid central body. The wire booms are oriented perpendicular to the spin axis at right angles relative to each other, whereas the stacer booms are aligned with the spin axis. The analysis consists of a comparison between the simulated in-plane and out-of-plane boom motions with theoretically derived frequencies, and an examination of the dynamic coupling between the control system and boom oscillations. Results show that boom oscillations of up to 0.36 deg are acceptable in order to meet the performance requirements. The dynamic motion is well behaved when the precession coil is operating, however, activation of the spin coil produces an erratic trend in the spin rate which approaches the spin rate requirement.

  1. EBooks and Accommodations: Is This the Future of Print Accommodation?

    ERIC Educational Resources Information Center

    Cavanaugh, Terence

    2002-01-01

    This article explains the three components of eBooks: an eBook file, software to read the eBook, and a hardware device to read it on. The use of eBooks for students with special needs, the advantages of eBooks, built in accommodations, and creating accommodations are discussed. EBook resources are included. (Contains references.) (CR)

  2. Retinal image quality during accommodation.

    PubMed

    López-Gil, Norberto; Martin, Jesson; Liu, Tao; Bradley, Arthur; Díaz-Muñoz, David; Thibos, Larry N

    2013-07-01

    We asked if retinal image quality is maximum during accommodation, or sub-optimal due to accommodative error, when subjects perform an acuity task. Subjects viewed a monochromatic (552 nm), high-contrast letter target placed at various viewing distances. Wavefront aberrations of the accommodating eye were measured near the endpoint of an acuity staircase paradigm. Refractive state, defined as the optimum target vergence for maximising retinal image quality, was computed by through-focus wavefront analysis to find the power of the virtual correcting lens that maximizes visual Strehl ratio. Despite changes in ocular aberrations and pupil size during binocular viewing, retinal image quality and visual acuity typically remain high for all target vergences. When accommodative errors lead to sub-optimal retinal image quality, acuity and measured image quality both decline. However, the effect of accommodation errors of on visual acuity are mitigated by pupillary constriction associated with accommodation and binocular convergence and also to binocular summation of dissimilar retinal image blur. Under monocular viewing conditions some subjects displayed significant accommodative lag that reduced visual performance, an effect that was exacerbated by pharmacological dilation of the pupil. Spurious measurement of accommodative error can be avoided when the image quality metric used to determine refractive state is compatible with the focusing criteria used by the visual system to control accommodation. Real focusing errors of the accommodating eye do not necessarily produce a reliably measurable loss of image quality or clinically significant loss of visual performance, probably because of increased depth-of-focus due to pupil constriction. When retinal image quality is close to maximum achievable (given the eye's higher-order aberrations), acuity is also near maximum. A combination of accommodative lag, reduced image quality, and reduced visual function may be a useful

  3. Developing a musculoskeletal model of the primate skull: predicting muscle activations, bite force, and joint reaction forces using multibody dynamics analysis and advanced optimisation methods.

    PubMed

    Shi, Junfen; Curtis, Neil; Fitton, Laura C; O'Higgins, Paul; Fagan, Michael J

    2012-10-07

    An accurate, dynamic, functional model of the skull that can be used to predict muscle forces, bite forces, and joint reaction forces would have many uses across a broad range of disciplines. One major issue however with musculoskeletal analyses is that of muscle activation pattern indeterminacy. A very large number of possible muscle force combinations will satisfy a particular functional task. This makes predicting physiological muscle recruitment patterns difficult. Here we describe in detail the process of development of a complex multibody computer model of a primate skull (Macaca fascicularis), that aims to predict muscle recruitment patterns during biting. Using optimisation criteria based on minimisation of muscle stress we predict working to balancing side muscle force ratios, peak bite forces, and joint reaction forces during unilateral biting. Validation of such models is problematic; however we have shown comparable working to balancing muscle activity and TMJ reaction ratios during biting to those observed in vivo and that peak predicted bite forces compare well to published experimental data. To our knowledge the complexity of the musculoskeletal model is greater than any previously reported for a primate. This complexity, when compared to more simple representations provides more nuanced insights into the functioning of masticatory muscles. Thus, we have shown muscle activity to vary throughout individual muscle groups, which enables them to function optimally during specific masticatory tasks. This model will be utilised in future studies into the functioning of the masticatory apparatus. Copyright © 2012 Elsevier Ltd. All rights reserved.

  4. FDI and Accommodation Using NN Based Techniques

    NASA Astrophysics Data System (ADS)

    Garcia, Ramon Ferreiro; de Miguel Catoira, Alberto; Sanz, Beatriz Ferreiro

    Massive application of dynamic backpropagation neural networks is used on closed loop control FDI (fault detection and isolation) tasks. The process dynamics is mapped by means of a trained backpropagation NN to be applied on residual generation. Process supervision is then applied to discriminate faults on process sensors, and process plant parameters. A rule based expert system is used to implement the decision making task and the corresponding solution in terms of faults accommodation and/or reconfiguration. Results show an efficient and robust FDI system which could be used as the core of an SCADA or alternatively as a complement supervision tool operating in parallel with the SCADA when applied on a heat exchanger.

  5. Tonic accommodation predicts closed-loop accommodation responses.

    PubMed

    Liu, Chunming; Drew, Stefanie A; Borsting, Eric; Escobar, Amy; Stark, Lawrence; Chase, Christopher

    2016-12-01

    The purpose of this study is to examine the potential relationship between tonic accommodation (TA), near work induced TA-adaptation and the steady state closed-loop accommodation response (AR). Forty-two graduate students participated in the study. Various aspects of their accommodation system were objectively measured using an open-field infrared auto-refractor (Grand Seiko WAM-5500). Tonic accommodation was assessed in a completely dark environment. The association between TA and closed-loop AR was assessed using linear regression correlations and t-test comparisons. Initial mean baseline TA was 1.84diopter (D) (SD±1.29D) with a wide distribution range (-0.43D to 5.14D). For monocular visual tasks, baseline TA was significantly correlated with the closed-loop AR. The slope of the best fit line indicated that closed-loop AR varied by approximately 0.3D for every 1D change in TA. This ratio was consistent across a variety of viewing distances and different near work tasks, including both static targets and continuous reading. Binocular reading conditions weakened the correlation between baseline TA and AR, although results remained statistically significant. The 10min near reading task with a 3D demand did not reveal significant near work induced TA-adaptation for either monocular or binocular conditions. Consistently, the TA-adaptation did not show any correlation with AR during reading. This study found a strong association between open-loop TA and closed-loop AR across a variety of viewing distances and different near work tasks. Difference between the correlations under monocular and binocular reading condition suggests a potential role for vergence compensation during binocular closed-loop AR. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Integration of car-body flexibility into train-track coupling system dynamics analysis

    NASA Astrophysics Data System (ADS)

    Ling, Liang; Zhang, Qing; Xiao, Xinbiao; Wen, Zefeng; Jin, Xuesong

    2018-04-01

    The resonance vibration of flexible car-bodies greatly affects the dynamics performances of high-speed trains. In this paper, we report a three-dimensional train-track model to capture the flexible vibration features of high-speed train carriages based on the flexible multi-body dynamics approach. The flexible car-body is modelled using both the finite element method (FEM) and the multi-body dynamics (MBD) approach, in which the rigid motions are obtained by using the MBD theory and the structure deformation is calculated by the FEM and the modal superposition method. The proposed model is applied to investigate the influence of the flexible vibration of car-bodies on the dynamics performances of train-track systems. The dynamics performances of a high-speed train running on a slab track, including the car-body vibration behaviour, the ride comfort, and the running safety, calculated by the numerical models with rigid and flexible car-bodies are compared in detail. The results show that the car-body flexibility not only significantly affects the vibration behaviour and ride comfort of rail carriages, but also can has an important influence on the running safety of trains. The rigid car-body model underestimates the vibration level and ride comfort of rail vehicles, and ignoring carriage torsional flexibility in the curving safety evaluation of trains is conservative.

  7. Cumulant-based expressions for the multibody terms for the correlation between local and electrostatic interactions in the united-residue force field

    NASA Astrophysics Data System (ADS)

    Liwo, Adam; Czaplewski, Cezary; Pillardy, Jarosław; Scheraga, Harold A.

    2001-08-01

    A general method to derive site-site or united-residue potentials is presented. The basic principle of the method is the separation of the degrees of freedom of a system into the primary and secondary ones. The primary degrees of freedom describe the basic features of the system, while the secondary ones are averaged over when calculating the potential of mean force, which is hereafter referred to as the restricted free energy (RFE) function. The RFE can be factored into one-, two-, and multibody terms, using the cluster-cumulant expansion of Kubo. These factors can be assigned the functional forms of the corresponding lowest-order nonzero generalized cumulants, which can, in most cases, be evaluated analytically, after making some simplifying assumptions. This procedure to derive coarse-grain force fields is very valuable when applied to multibody terms, whose functional forms are hard to deduce in another way (e.g., from structural databases). After the functional forms have been derived, they can be parametrized based on the RFE surfaces of model systems obtained from all-atom models or on the statistics derived from structural databases. The approach has been applied to our united-residue force field for proteins. Analytical expressions were derived for the multibody terms pertaining to the correlation between local and electrostatic interactions within the polypeptide backbone; these expressions correspond to up to sixth-order terms in the cumulant expansion of the RFE. These expressions were subsequently parametrized by fitting to the RFEs of selected peptide fragments, calculated with the empirical conformational energy program for peptides force field. The new multibody terms enable not only the heretofore predictable α-helical segments, but also regular β-sheets, to form as the lowest-energy structures, as assessed by test calculations on a model helical protein A, as well as a model 20-residue polypeptide (betanova); the latter was not possible without

  8. Habitability sleep accommodations

    NASA Technical Reports Server (NTRS)

    Fisher, H. T.

    1985-01-01

    Schematic outlines are presented with various design requirements for the accommodation of the spacecrew of Space Stations. The primary concern is for sleeping accommodations. Some other general requirements given are for a rest place, entertainment, dressing area, personal item stowage, body restraint, total privacy, external viewing, and grooming provisions. Several plans are given for sleep quarters concepts.

  9. Nonverbal Accommodation in Healthcare Communication

    PubMed Central

    D’Agostino, Thomas A.; Bylund, Carma L.

    2016-01-01

    This exploratory study examined patterns of nonverbal accommodation within healthcare interactions and investigated the impact of communication skills training and gender concordance on nonverbal accommodation behavior. The Nonverbal Accommodation Analysis System (NAAS) was used to code the nonverbal behavior of physicians and patients within 45 oncology consultations. Cases were then placed in one of seven categories based on patterns of accommodation observed across the interaction. Results indicated that across all NAAS behavior categories, physician-patient interactions were most frequently categorized as Joint Convergence, followed closely by Asymmetrical-Patient Convergence. Among paraverbal behaviors, talk time, interruption, and pausing were most frequently characterized by Joint Convergence. Among nonverbal behaviors, eye contact, laughing, and gesturing were most frequently categorized as Asymmetrical-Physician Convergence. Differences were predominantly non-significant in terms of accommodation behavior between pre and post-communication skills training interactions. Only gesturing proved significant, with post-communication skills training interactions more likely to be categorized as Joint Convergence or Asymmetrical-Physician Convergence. No differences in accommodation were noted between gender concordant and non-concordant interactions. The importance of accommodation behavior in healthcare communication is considered from a patient-centered care perspective. PMID:24138223

  10. Employer benefits from making workplace accommodations.

    PubMed

    Solovieva, Tatiana I; Dowler, Denetta L; Walls, Richard T

    2011-01-01

    This study explored workplace disability accommodations and their benefits. The participants were employers and human resource professionals who had not used the services of the Job Accommodation Network (JAN). The companies included large businesses (more than 499 employees) and small businesses (fewer than 500 employees). The intent of this investigation was to assess the disability accommodations and benefits for the employers. The study used responses to online survey from194 employers to discuss disability-related accommodations for an employee or potential employee. The survey included 128 employers who reported having had a person with a disability who requested an accommodation. As reported by the employers, the most frequently mentioned direct benefits from implementing workplace accommodations were (a) retained a qualified employee, (b) increased worker productivity, and (c) eliminated the cost of training a new employee. The most frequently mentioned indirect benefits from accommodations were (a) improved interactions with coworkers, (b) increased overall company morale, and (c) increased overall company productivity. The most frequently reported types of implemented accommodations were buying equipment and changing work schedules. Most of the respondents estimated the direct benefits of having made an accommodation at more than $1000. The findings heighten awareness of benefits associated with making accommodations for people with disabilities in the workplace. These benefits signify value for business, coworkers, and individuals with disabilities for whom accommodations are critical for successful employment. Published by Elsevier Inc.

  11. 43 CFR 17.211 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Reasonable accommodation. (a) A recipient shall make reasonable accommodation to the known physical or mental... that the accommodation would impose an undue hardship on the operation of its program or activity. (b... accommodation would impose an undue hardship on the operation of a recipient's program or activity, factors to...

  12. Uncertain dynamic analysis for rigid-flexible mechanisms with random geometry and material properties

    NASA Astrophysics Data System (ADS)

    Wu, Jinglai; Luo, Zhen; Zhang, Nong; Zhang, Yunqing; Walker, Paul D.

    2017-02-01

    This paper proposes an uncertain modelling and computational method to analyze dynamic responses of rigid-flexible multibody systems (or mechanisms) with random geometry and material properties. Firstly, the deterministic model for the rigid-flexible multibody system is built with the absolute node coordinate formula (ANCF), in which the flexible parts are modeled by using ANCF elements, while the rigid parts are described by ANCF reference nodes (ANCF-RNs). Secondly, uncertainty for the geometry of rigid parts is expressed as uniform random variables, while the uncertainty for the material properties of flexible parts is modeled as a continuous random field, which is further discretized to Gaussian random variables using a series expansion method. Finally, a non-intrusive numerical method is developed to solve the dynamic equations of systems involving both types of random variables, which systematically integrates the deterministic generalized-α solver with Latin Hypercube sampling (LHS) and Polynomial Chaos (PC) expansion. The benchmark slider-crank mechanism is used as a numerical example to demonstrate the characteristics of the proposed method.

  13. Weak decays of doubly heavy baryons: multi-body decay channels

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Ji; Wang, Wei; Xing, Ye; Xu, Ji

    2018-01-01

    The newly-discovered Ξ _{cc}^{++} decays into the Λ c^+ K^-π ^+π ^+, but the experimental data has indicated that this decay is not saturated by any two-body intermediate state. In this work, we analyze the multi-body weak decays of doubly heavy baryons Ξ _{cc}, Ω _{cc}, Ξ _{bc}, Ω _{bc}, Ξ _{bb} and Ω _{bb}, in particular the three-body nonleptonic decays and four-body semileptonic decays. We classify various decay modes according to the quark-level transitions and present an estimate of the typical branching fractions for a few golden decay channels. Decay amplitudes are then parametrized in terms of a few SU(3) irreducible amplitudes. With these amplitudes, we find a number of relations for decay widths, which can be examined in future.

  14. Computational strategies in the dynamic simulation of constrained flexible MBS

    NASA Technical Reports Server (NTRS)

    Amirouche, F. M. L.; Xie, M.

    1993-01-01

    This research focuses on the computational dynamics of flexible constrained multibody systems. At first a recursive mapping formulation of the kinematical expressions in a minimum dimension as well as the matrix representation of the equations of motion are presented. The method employs Kane's equation, FEM, and concepts of continuum mechanics. The generalized active forces are extended to include the effects of high temperature conditions, such as creep, thermal stress, and elastic-plastic deformation. The time variant constraint relations for rolling/contact conditions between two flexible bodies are also studied. The constraints for validation of MBS simulation of gear meshing contact using a modified Timoshenko beam theory are also presented. The last part deals with minimization of vibration/deformation of the elastic beam in multibody systems making use of time variant boundary conditions. The above methodologies and computational procedures developed are being implemented in a program called DYAMUS.

  15. An Integrated Approach to Damage Accommodation in Flight Control

    NASA Technical Reports Server (NTRS)

    Boskovic, Jovan D.; Knoebel, Nathan; Mehra, Raman K.; Gregory, Irene

    2008-01-01

    In this paper we present an integrated approach to in-flight damage accommodation in flight control. The approach is based on Multiple Models, Switching and Tuning (MMST), and consists of three steps: In the first step the main objective is to acquire a realistic aircraft damage model. Modeling of in-flight damage is a highly complex problem since there is a large number of issues that need to be addressed. One of the most important one is that there is strong coupling between structural dynamics, aerodynamics, and flight control. These effects cannot be studied separately due to this coupling. Once a realistic damage model is available, in the second step a large number of models corresponding to different damage cases are generated. One possibility is to generate many linear models and interpolate between them to cover a large portion of the flight envelope. Once these models have been generated, we will implement a recently developed-Model Set Reduction (MSR) technique. The technique is based on parameterizing damage in terms of uncertain parameters, and uses concepts from robust control theory to arrive at a small number of "centered" models such that the controllers corresponding to these models assure desired stability and robustness properties over a subset in the parametric space. By devising a suitable model placement strategy, the entire parametric set is covered with a relatively small number of models and controllers. The third step consists of designing a Multiple Models, Switching and Tuning (MMST) strategy for estimating the current operating regime (damage case) of the aircraft, and switching to the corresponding controller to achieve effective damage accommodation and the desired performance. In the paper present a comprehensive approach to damage accommodation using Model Set Design,MMST, and Variable Structure compensation for coupling nonlinearities. The approach was evaluated on a model of F/A-18 aircraft dynamics under control effector damage

  16. Vestibular-ocular accommodation reflex in man

    NASA Technical Reports Server (NTRS)

    Clark, B.; Randle, R. J.; Stewart, J. D.

    1975-01-01

    Stimulation of the vestibular system by angular acceleration produces widespread sensory and motor effects. The present paper studies a motor effect which has not been reported in the literature, i.e., the influence of rotary acceleration of the body on ocular accommodation. The accommodation of 10 young men was recorded before and after a high-level deceleration to zero velocity following 30 sec of rotating. Accommodation was recorded continuously on an infrared optometer for 110 sec under two conditions: while the subjects observed a target set at the far point, and while they viewed the same target through a 0.3-mm pinhole. Stimulation by high-level rotary deceleration produced positive accommodation or a pseudomyopia under both conditions, but the positive accommodation was substantially greater and lasted much longer during fixation through the pinhole. It is hypothesized that this increase in accommodation is a result of a vestibular-ocular accommodation reflex.

  17. Influence of accommodative lag upon the far-gradient measurement of accommodative convergence to accommodation ratio in strabismic patients.

    PubMed

    Miyata, Manabu; Hasebe, Satoshi; Ohtsuki, Hiroshi

    2006-01-01

    To determine the influence of the lag of accommodation (LOA) on the accommodative convergence to accommodation (AC/A) ratio measured by the far-gradient method in strabismic patients. The AC/A ratio was measured with a distance target viewed with and without -3.00 diopter (D) addition lenses in 63 patients with different types of strabismus (age range, 7-34 years; range of strabismic angle, -60 to +40 prism diopters; refractive error range, -7.33 to +6.63 D). The LOA for the same lens was measured with an open-view-type autorefractometer. The stimulus AC/A ratio and the AC/A ratio adjusted by the individually measured LOA (adjusted AC/A ratio) were compared. The mean +/- SD of the LOA to the -3.00 D lenses was 1.06 +/- 0.43 D. The mean adjusted AC/A ratio was 41% greater than the stimulus AC/A ratio. The LOA differed widely among patients (0.13 to 2.14 D), and a large LOA tended to appear in myopic or young patients. The AC/A ratio obtained using the conventional far-gradient method is significantly biased by the LOA, and thus does not always represent the actual relationship between accommodation and vergence control systems. Copyright Japanese Ophthalmological Society 2006.

  18. Technique to eliminate computational instability in multibody simulations employing the Lagrange multiplier

    NASA Technical Reports Server (NTRS)

    Watts, G.

    1992-01-01

    A programming technique to eliminate computational instability in multibody simulations that use the Lagrange multiplier is presented. The computational instability occurs when the attached bodies drift apart and violate the constraints. The programming technique uses the constraint equation, instead of integration, to determine the coordinates that are not independent. Although the equations of motion are unchanged, a complete derivation of the incorporation of the Lagrange multiplier into the equation of motion for two bodies is presented. A listing of a digital computer program which uses the programming technique to eliminate computational instability is also presented. The computer program simulates a solid rocket booster and parachute connected by a frictionless swivel.

  19. Medial rectus Faden operations with or without recession for partially accommodative esotropia associated with a high accommodative convergence to accommodation ratio.

    PubMed

    Akar, Serpil; Gokyigit, Birsen; Sayin, Nihat; Demirok, Ahmet; Yilmaz, Omer Faruk

    2013-01-01

    To evaluate the results of Faden operations on the medial rectus (MR) muscles with or without recession for the treatment of partially accommodative esotropia associated with a high accommodative convergence to accommodation (AC : A) ratio and to determine whether there was a decrease in the effects of posterior fixation over time. In this retrospective study, 108 of 473 patients who underwent surgery for partially accommodative esotropia with a high AC : A ratio received Faden operations on both MR muscles, and 365 received symmetric MR muscle recessions combined with a Faden operation. For the Faden operation, a satisfactory outcome of 76.9% at 1 month postoperation, decreased to 71.3% by the final follow-up visit (mean 4.8 years). A moderate positive correlation was observed between the increase in the postoperative near deviation and postoperative time. For the Faden operations combined with MR recession, a satisfactory outcome of 78.9% at 1 month post-operation, decreased to 78.4% by the final follow-up visit. A Faden operation of the MR muscles with or without recession is an effective surgical option for treating partially accommodative esotropia associated with a high AC : A ratio. For Faden operations of the MR muscles without recession, the effects of the posterior fixation decline over time.

  20. Magnifications of Single and Dual Element Accommodative Intraocular Lenses: Paraxial Optics Analysis

    PubMed Central

    Ale, Jit B; Manns, Fabrice; Ho, Arthur

    2010-01-01

    the translation (or the achieved accommodative amplitude) are important parameters in determining the magnifications of the AIOLs. The results highlight the need for caution in the prescribing of AIOL. Aniso-accommodation or inter-ocular differences in AIOL designs (or relative to the natural lens of the contralateral eye) may introduce dynamic aniseikonia and consequent impaired binocular vision. Nevertheless, some designs, offering greater increases in magnification on accommodation, may provide enhanced near vision depending on patient needs. PMID:21054469

  1. Vestibular-ocular accommodation reflex in man.

    PubMed

    Clark, B R; Randle, R J; Stewart, J D

    1975-11-01

    Stimulation of the vestibular system by angular acceleration produces widespread sensory and motor effects. The present study was designed to study a motor effect which has not been reported in the literature, i.e., the influence of rotary acceleration of the body on ocular accommodation. The accommodation of 10 young men was recorded before and after a high-level deceleration to zero velocity following 30 s of rotation. Accommodation was recorded continuously on an infrared optometer for 110 s under two conditions; while the subjects observed a target set at the far point, and while they viewed the same target through a 0.3-mm pinhole. Stimulation by high-level rotary deceleration produced positive accommodation or a pseudomyopia under both conditions, but the positive accommodation was substantially greater and lasted much longer during fixation through the pinhole. It is hypothesized that this increase in accommodation is a result of a vestibular-ocular accommodation reflex.

  2. A centre for accommodative vergence motor control

    NASA Technical Reports Server (NTRS)

    Wilson, D.

    1973-01-01

    Latencies in accommodation, accommodative-vergence, and pupil-diameter responses to changing accommodation stimuli, as well as latencies in pupil response to light-intensity changes were measured. From the information obtained, a block diagram has been derived that uses the least number of blocks for representing the accommodation, accommodative-vergence, and pupil systems. The signal transmission delays over the various circuits of the model have been determined and compared to known experimental physiological-delay data. The results suggest the existence of a motor center that controls the accommodative vergence and is completely independent of the accommodation system.

  3. Experimental study of visual accommodation

    NASA Technical Reports Server (NTRS)

    Cornsweet, T. N.; Crane, H. D.

    1972-01-01

    A summary report of a research effort related to the human visual accommodation system is presented. A theoretical study of the accommodation system was made. Subsequent effort was aimed at the development of specialized instrumentation for experiments designed to lead to understanding the nature of the control system in human accommodation. The necessary instrumentation consisted primarily of: (1) an automatic optometer to measure the state of eye focus, (2) a focus stimulator device to control the apparent optical distance to any target, and (3) a two-dimensional eye tracker. The concepts and designs of the first two instruments have been published in the open literature, but this report contains the first detailed treatment of the Purkinje eye tracker developed under this program. The report also discusses an accommodation lag model to explain the ability of the eye to apparently know the polarity of focus error even though the blur on the retina is to a first-approximation an even function. The interaction of the accommodation and eye movement systems is also discussed, as is the ability to train the visual accommodation system to a surprisingly responsive condition in only a few hours of training.

  4. Handbook of Reasonable Accommodation.

    ERIC Educational Resources Information Center

    Heaton, Sandra M.; And Others

    The booklet discusses a basic concept in affirmative action and nondiscrimination for the handicapped, which requires federal agencies to make reasonable accommodation to the physical or mental limitations of a qualified handicapped applicant or employee unless the accommodation would impose an undue hardship on the agency. Reasonable…

  5. Accommodative insufficiency in a student population in Iran.

    PubMed

    Hashemi, Hassan; Khabazkhoob, Mehdi; Nabovati, Payam; Shahraki, Fatemeh Azad; Ostadimoghaddam, Hadi; Faghihi, Mohammad; Aghamirsalim, Mohamadreza; Doostdar, Asgar; Yekta, Abbasali

    2018-05-22

    To determine the prevalence of accommodative insufficiency (AI) and its relation with age, gender, and refractive errors in a college-age student population in Iran. The present study was conducted cross-sectionally in 2017. All students had optometric tests including measurement of visual acuity, objective and subjective refraction, as well as binocular vision and accommodative examinations. Amplitude of accommodation was measured with the Donders' push-up method using the Royal Air Force (RAF) rule. Monocular accommodative facility was measured with ±2.00diopter flipper lenses. The accommodative response was tested using dynamic retinoscopy with the monocular estimation method (MEM). The prevalence of AI in the studied population was 4.07% (95% CI: 2.61-5.52). The rate was 6.04% (95% CI: 3.58-8.50) in females and 2.01% (95% CI: 0.53-3.48) in males, and logistic regression showed a significantly higher odds of AI in females (OR=3.14, 95% CI: 1.33-7.45, p-value=0.009). The prevalence of AI was 2.59% (95% CI: 0.55-7.56) in the 18-19-year-old age group and 4.08% (95% CI: 0.09-8.07) in the 24-25-year-old group (p-value=0.848). The prevalence of AI among emmetropic, myopic, and hyperopic individuals was 3.74% (95% CI: 1.88-5.61), 4.44% (95% CI: 2.07-6.81), and 5.26% (95% CI: 4.79-16.32), respectively (p-value=0.869). In the multiple regression model, only gender showed significant relationship with AI (Odds ratio=3.14, 95% CI: 1.33-7.45; p-values=0.009). The prevalence of AI in the present study is lower than the most prevalence rates reported in previous studies. In the present study, gender and AI showed a strong association, such that AI prevalence was significantly higher in females than males. Copyright © 2018 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

  6. Receding and disparity cues aid relaxation of accommodation

    PubMed Central

    Horwood, Anna M; Riddell, Patricia M

    2015-01-01

    Purpose Accommodation can mask hyperopia and reduce the accuracy of non-cycloplegic refraction. It is therefore important to minimize accommodation to obtain as accurate a measure of hyperopia as possible. In order to characterize the parameters required to measure the maximally hyperopic error using photorefraction, we used different target types and distances to determine which target was most likely to maximally relax accommodation and thus more accurately detect hyperopia in an individual. Methods A PlusoptiX SO4 infra-red photorefractor was mounted in a remote haploscope which presented the targets. All participants were tested with targets at four fixation distances between 0.3m and 2m containing all combinations of blur, disparity and proximity/looming cues. 38 infants (6-44 wks) were studied longitudinally, and 104 children (4 -15 yrs (mean 6.4)) and 85 adults, with a range of refractive errors and binocular vision status, were tested once. Cycloplegic refraction data was available for a sub-set of 59 participants spread across the age range. Results The maximally hyperopic refraction (MHR) found at any time in the session was most frequently found when fixating the most distant targets and those containing disparity and dynamic proximity/looming cues. Presence or absence of blur was less significant, and targets in which only single cues to depth were present were also less likely to produce MHR. MHR correlated closely with cycloplegic refraction (r = 0.93,mean difference 0.07D,p=n.s.,95%CI ±<0.25D) after correction by a calibration factor. Conclusion Maximum relaxation of accommodation occurred for binocular targets receding into the distance. Proximal and disparity cues aid relaxation of accommodation to a greater extent than blur, and thus non-cycloplegic refraction targets should incorporate these cues. This is especially important in screening contexts with a brief opportunity to test for significant hyperopia. MHR in our laboratory was found to be a

  7. Accommodation-Amplitudes following an Accommodative Lens Refilling Procedure — an in vivo Update

    PubMed Central

    Nishi, Okihiro; Nishi, Yutaro; Chang, S.; Nishi, Kayo

    2014-01-01

    Purpose To investigate whether a newly developed lens refilling procedure can provide some accommodation in monkey eyes and to evaluate the difference in accommodation with different degrees of capsular bag refilling. Setting Jinshikai Medical Foundation, Nishi Eye Hospital, Osaka, Japan. Design Experimental monkey study. Methods Following a central 3–4 mm continuous curvilinear capsulorhexis, phacoemulsification was performed in the usual manner. A novel accommodative membrane intraocular lens for sealing capsular opening was implanted into the capsular bag. Silicone polymers were injected beneath the intraocular lens into the capsular bag through the delivery hole. In three study groups, each with six monkey eyes, the lens capsule was refilled with 0.08 ml corresponding to 65% bag volume, 0.1 ml corresponding to 80% bag volume, and 0.125 ml of silicone polymers corresponding to 100% bag volume, respectively. To calculate the accommodation-amplitudes achieved, automated refractometry was performed before and 1 hour after the topical 4% pilocarpine application before and four weeks after surgery. Results The refilling technique was successful in all monkeys without polymer leakage. Accommodation-amplitudes attained were 2.56 ± 0.74 dioptries (D), 2.42 ± 1.00D, and 2.71 ± 0.63D, respectively, 4 weeks after surgery in the three study groups. Conclusions Using the technique, some accommodation could be obtained in the young monkey eyes. Leakage of the injectable silicone polymer and anterior capsular opacification at least in the visual axis could be avoided. The results suggest that this lens refilling procedure warrants further studies for a possible clinical application. PMID:24461501

  8. Evaluation of Verisyse and Artiflex phakic intraocular lenses during accommodation using Visante optical coherence tomography.

    PubMed

    Güell, José Luis; Morral, Merce; Gris, Oscar; Gaytan, Javier; Sisquella, Maite; Manero, Felicidad

    2007-08-01

    To perform a dynamic study of the relationship between Verisyse (AMO) and Artiflex (Ophtec B.V.) phakic intraocular lenses (pIOLs) and anterior chamber structures during accommodation using optical coherence tomography (OCT) (Visante, Carl Zeiss Meditec, Inc.) Institutional practice. Eleven myopic patients were randomly selected to have implantation of a Verisyse pIOL in 1 eye and an Artiflex pIOL in the other. Using a 2-dimensional image, dynamic measurements of the relationship between the anterior surface of the pIOL and the corneal endothelium, the posterior surface of the pIOL and the anterior surface of the crystalline lens, and the pupil diameter were performed using Visante OCT. Physiological accommodation was stimulated by adding lenses in 1.00 diopter (D) steps from +1.00 to -7.00 D. Both groups had a significant decrease in pupil diameter (P<.0001, generalized linear model [GLM]) and in the distance between the anterior surface of the pIOL and the corneal endothelium (P<.0001, GLM) with accommodation. There were no statistically significant changes in the distance between the posterior surface of either pIOL and the anterior surface of the crystalline lens (P = .2845, GLM). There were no statistically significant differences between the 2 pIOLs in any measurement (P>.05, GLM). The results fit with Helmholtz' theory of accommodation as forward movement of the diaphragm iris-crystalline lens was seen. There was a decrease in the distance between the pIOL and corneal endothelium and in the pupil diameter, whereas the distance between both pIOLs and the crystalline lens remained constant throughout the accommodation examination. This suggests that the risk for cataract from intermittent contact between the crystalline lens and IOL from accommodative effort is unlikely.

  9. Experimental verification of dynamic simulation

    NASA Technical Reports Server (NTRS)

    Yae, K. Harold; Hwang, Howyoung; Chern, Su-Tai

    1989-01-01

    The dynamics model here is a backhoe, which is a four degree of freedom manipulator from the dynamics standpoint. Two types of experiment are chosen that can also be simulated by a multibody dynamics simulation program. In the experiment, recorded were the configuration and force histories; that is, velocity and position, and force output and differential pressure change from the hydraulic cylinder, in the time domain. When the experimental force history is used as driving force in the simulation model, the forward dynamics simulation produces a corresponding configuration history. Then, the experimental configuration history is used in the inverse dynamics analysis to generate a corresponding force history. Therefore, two sets of configuration and force histories--one set from experiment, and the other from the simulation that is driven forward and backward with the experimental data--are compared in the time domain. More comparisons are made in regard to the effects of initial conditions, friction, and viscous damping.

  10. Numerical methods for the simulation of complex multi-body flows with applications for the integrated Space Shuttle vehicle

    NASA Technical Reports Server (NTRS)

    Chan, William M.

    1992-01-01

    The following papers are presented: (1) numerical methods for the simulation of complex multi-body flows with applications for the Integrated Space Shuttle vehicle; (2) a generalized scheme for 3-D hyperbolic grid generation; (3) collar grids for intersecting geometric components within the Chimera overlapped grid scheme; and (4) application of the Chimera overlapped grid scheme to simulation of Space Shuttle ascent flows.

  11. Computational methods and software systems for dynamics and control of large space structures

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Felippa, C. A.; Farhat, C.; Pramono, E.

    1990-01-01

    Two key areas of crucial importance to the computer-based simulation of large space structures are discussed. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area involves massively parallel computers.

  12. 24 CFR 8.11 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... make reasonable accommodation to the known physical or mental limitations of an otherwise qualified... accommodation would impose an undue hardship on the operation of its program. (b) Reasonable accommodation may... hardship on the operation of a recipient's program, factors to be considered include: (1) The overall size...

  13. Independent and reciprocal accommodation in anisometropic amblyopia

    PubMed Central

    Horwood, Anna M.; Riddell, Patricia M

    2015-01-01

    Accommodation is considered to be a symmetrical response, and to be driven by the least ametropic and nonamblyopic eye in anisometropia. We report a case of a 4-year-old child with anisometropic amblyopia who accommodates asymmetrically, reliably demonstrating normal accommodation in the nonamblyopic eye and anti-accommodation of the amblyopic eye to near targets. The abnormal accommodation of the amblyopic eye remained largely unchanged over seven subsequent testing sessions undertaken over the course of therapy. We suggest that a congenital dysinnervation syndrome may result in relaxation of accommodation in relation to near cues and might be a hitherto-unconsidered additional etiologic factor in anisometropic amblyopia. PMID:20863728

  14. 22 CFR 217.12 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... accommodation. (a) A recipient shall make reasonable accommodation to the known physical or mental limitations... the accommodation would impose an undue hardship on the operation of its program or activity. (b... would impose an undue hardship on the operation of a recipient's program or activity, factors to be...

  15. Design of multi-body Lambert type orbits with specified departure and arrival positions

    NASA Astrophysics Data System (ADS)

    Ishii, Nobuaki; Kawaguchi, Jun'ichiro; Matsuo, Hiroki

    1991-10-01

    A new procedure for designing a multi-body Lambert type orbit comprising a multiple swingby process is developed, aiming at relieving a numerical difficulty inherent to a highly nonlinear swingby mechanism. The proposed algorithm, Recursive Multi-Step Linearization, first divides a whole orbit into several trajectory segments. Then, with a maximum use of piecewised transition matrices, a segmentized orbit is repeatedly upgraded until an approximated orbit initially based on a patched conics method eventually converges. In application to the four body earth-moon system with sun's gravitation, one of the double lunar swingby orbits including 12 lunar swingbys is successfully designed without any velocity mismatch.

  16. Effect of heterophoria measurement technique on the clinical accommodative convergence to accommodation ratio.

    PubMed

    Escalante, Jaime Bernal; Rosenfield, Mark

    2006-05-01

    Measurement of the stimulus accommodative convergence to accommodation (AC/A) ratio is a standard procedure in clinical optometric practice. Typically, heterophoria is assessed at several accommodative stimulus levels, and the gradient of the vergence to accommodation function computed. A number of procedures are available for the subjective measurement of heterophoria, but it is unclear whether the use of different vergence measurement techniques will alter the obtained AC/A value. Accordingly, the current study compared AC/A ratios measured using 3 clinical subjective heterophoria tests, namely the von Graefe (VG), Maddox Rod (MR), and Modified Thorington (MT) procedures. The AC/A ratio was measured in 60 visually normal subjects between 20 and 25 years of age using each of the 3 procedures listed above. The accommodative stimulus was varied by the introduction of +/-1.00 diopter (D) spherical lenses over the distance refractive correction while subjects viewed a target at a viewing distance of 40 cm. To examine the repeatability of each procedure, the AC/A ratio was measured on 2 separate occasions for each measurement technique, with the 2 sessions being separated by at least 24 hours. Mean values of stimulus AC/A ratio measured using the VG, MR, and MT procedures were 3.47, 2.99, and 2.46Delta/D, respectively. These differences were significant (p=0.0001). In addition, the coefficient of repeatability for the 3 techniques was 2.22, 1.99, and 1.20 Delta/D, respectively. Ratios obtained using the Modified Thorington technique with +/-1.00 D lenses showed the best repeatability, whereas the poorest repeatability was found with the von Graefe technique when only +1.00 D lenses were used to vary the accommodative stimulus. Accordingly, we recommend that that Modified Thorington procedure with +/-1.00 D lenses be used to quantify heterophoria during clinical measurement of the stimulus AC/A ratio.

  17. High fidelity quasi steady-state aerodynamic model effects on race vehicle performance predictions using multi-body simulation

    NASA Astrophysics Data System (ADS)

    Mohrfeld-Halterman, J. A.; Uddin, M.

    2016-07-01

    We described in this paper the development of a high fidelity vehicle aerodynamic model to fit wind tunnel test data over a wide range of vehicle orientations. We also present a comparison between the effects of this proposed model and a conventional quasi steady-state aerodynamic model on race vehicle simulation results. This is done by implementing both of these models independently in multi-body quasi steady-state simulations to determine the effects of the high fidelity aerodynamic model on race vehicle performance metrics. The quasi steady state vehicle simulation is developed with a multi-body NASCAR Truck vehicle model, and simulations are conducted for three different types of NASCAR race tracks, a short track, a one and a half mile intermediate track, and a higher speed, two mile intermediate race track. For each track simulation, the effects of the aerodynamic model on handling, maximum corner speed, and drive force metrics are analysed. The accuracy of the high-fidelity model is shown to reduce the aerodynamic model error relative to the conventional aerodynamic model, and the increased accuracy of the high fidelity aerodynamic model is found to have realisable effects on the performance metric predictions on the intermediate tracks resulting from the quasi steady-state simulation.

  18. 46 CFR 108.143 - Accommodation space.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Accommodation space. 108.143 Section 108.143 Shipping... EQUIPMENT Construction and Arrangement Structural Fire Protection § 108.143 Accommodation space. (a) Each corridor bulkhead in an accommodation space must be an A class or B class bulkhead except if an A class...

  19. 46 CFR 108.143 - Accommodation space.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Accommodation space. 108.143 Section 108.143 Shipping... EQUIPMENT Construction and Arrangement Structural Fire Protection § 108.143 Accommodation space. (a) Each corridor bulkhead in an accommodation space must be an A class or B class bulkhead except if an A class...

  20. 46 CFR 108.143 - Accommodation space.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Accommodation space. 108.143 Section 108.143 Shipping... EQUIPMENT Construction and Arrangement Structural Fire Protection § 108.143 Accommodation space. (a) Each corridor bulkhead in an accommodation space must be an A class or B class bulkhead except if an A class...

  1. 46 CFR 108.143 - Accommodation space.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Accommodation space. 108.143 Section 108.143 Shipping... EQUIPMENT Construction and Arrangement Structural Fire Protection § 108.143 Accommodation space. (a) Each corridor bulkhead in an accommodation space must be an A class or B class bulkhead except if an A class...

  2. 46 CFR 108.143 - Accommodation space.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Accommodation space. 108.143 Section 108.143 Shipping... EQUIPMENT Construction and Arrangement Structural Fire Protection § 108.143 Accommodation space. (a) Each corridor bulkhead in an accommodation space must be an A class or B class bulkhead except if an A class...

  3. The effect of bifocal add on accommodative lag in myopic children with high accommodative lag.

    PubMed

    Berntsen, David A; Mutti, Donald O; Zadnik, Karla

    2010-12-01

    To determine the effect of a bifocal add and manifest correction on accommodative lag in myopic children with high accommodative lag, who have been reported to have the greatest reduction in myopia progression with progressive addition lenses (PALs). Monocular accommodative lag to a 4-D Badal stimulus was measured on two occasions 6 months apart in 83 children (mean ± SD age, 9.9 ± 1.3 years) with high lag randomized to wearing single-vision lenses (SVLs) or PALs. Accommodative lag was measured with the following corrections: habitual, manifest, manifest with +2.00-D add, and habitual with +2.00-D add (6-month visit only). At baseline, accommodative lag was higher (1.72 ± 0.37 D; mean ± SD) when measured with manifest correction than with habitual correction (1.51 ± 0.50; P < 0.05). This higher lag with manifest correction correlated with a larger amount of habitual undercorrection at baseline (r = -0.29, P = 0.009). A +2.00-D add over the manifest correction reduced lag by 0.45 ± 0.34 D at baseline and 0.33 ± 0.38 D at the 6-month visit. Lag results at 6 months were not different between PAL and SVL wearers (P = 0.92). A +2.00-D bifocal add did not eliminate accommodative lag and reduced lag by less than 25% of the bifocal power, indicating that children mainly responded to a bifocal by decreasing accommodation. If myopic progression is substantial, measuring lag with full correction can overestimate the hyperopic retinal blur that a child most recently experienced. (ClinicalTrials.gov number, NCT00335049.).

  4. The Effect of Bifocal Add on Accommodative Lag in Myopic Children with High Accommodative Lag

    PubMed Central

    Mutti, Donald O.; Zadnik, Karla

    2010-01-01

    Purpose. To determine the effect of a bifocal add and manifest correction on accommodative lag in myopic children with high accommodative lag, who have been reported to have the greatest reduction in myopia progression with progressive addition lenses (PALs). Methods. Monocular accommodative lag to a 4-D Badal stimulus was measured on two occasions 6 months apart in 83 children (mean ± SD age, 9.9 ± 1.3 years) with high lag randomized to wearing single-vision lenses (SVLs) or PALs. Accommodative lag was measured with the following corrections: habitual, manifest, manifest with +2.00-D add, and habitual with +2.00-D add (6-month visit only). Results. At baseline, accommodative lag was higher (1.72 ± 0.37 D; mean ± SD) when measured with manifest correction than with habitual correction (1.51 ± 0.50; P < 0.05). This higher lag with manifest correction correlated with a larger amount of habitual undercorrection at baseline (r = −0.29, P = 0.009). A +2.00-D add over the manifest correction reduced lag by 0.45 ± 0.34 D at baseline and 0.33 ± 0.38 D at the 6-month visit. Lag results at 6 months were not different between PAL and SVL wearers (P = 0.92). Conclusions. A +2.00-D bifocal add did not eliminate accommodative lag and reduced lag by less than 25% of the bifocal power, indicating that children mainly responded to a bifocal by decreasing accommodation. If myopic progression is substantial, measuring lag with full correction can overestimate the hyperopic retinal blur that a child most recently experienced. (ClinicalTrials.gov number, NCT00335049.) PMID:20688729

  5. Numerical integration and optimization of motions for multibody dynamic systems

    NASA Astrophysics Data System (ADS)

    Aguilar Mayans, Joan

    This thesis considers the optimization and simulation of motions involving rigid body systems. It does so in three distinct parts, with the following topics: optimization and analysis of human high-diving motions, efficient numerical integration of rigid body dynamics with contacts, and motion optimization of a two-link robot arm using Finite-Time Lyapunov Analysis. The first part introduces the concept of eigenpostures, which we use to simulate and analyze human high-diving motions. Eigenpostures are used in two different ways: first, to reduce the complexity of the optimal control problem that we solve to obtain such motions, and second, to generate an eigenposture space to which we map existing real world motions to better analyze them. The benefits of using eigenpostures are showcased through different examples. The second part reviews an extensive list of integration algorithms used for the integration of rigid body dynamics. We analyze the accuracy and stability of the different integrators in the three-dimensional space and the rotation space SO(3). Integrators with an accuracy higher than first order perform more efficiently than integrators with first order accuracy, even in the presence of contacts. The third part uses Finite-time Lyapunov Analysis to optimize motions for a two-link robot arm. Finite-Time Lyapunov Analysis diagnoses the presence of time-scale separation in the dynamics of the optimized motion and provides the information and methodology for obtaining an accurate approximation to the optimal solution, avoiding the complications that timescale separation causes for alternative solution methods.

  6. Stimulating human accommodation without changes in focus.

    PubMed

    Weiss, Monika; Seidemann, Anne; Schaeffel, Frank

    2004-05-01

    Inspired by the finding in chickens that preferential stimulation of the ON retinal system suppresses myopia induced by negative spectacle lens wear and that stimulation of the OFF system suppresses the hyperopia induced by positive lens wear, we sought to determine whether stimulation of the ON-OFF retinal systems could drive directional accommodation responses in humans. If emmetropisation and accommodation use similar image processing algorithms, more accommodation would be expected with OFF stimulation. Accommodation responses were measured while viewing a computer-generated pattern designed to stimulate the ON-OFF systems. The stimulus comprised a rectangular field (12 x 9.5 cm) on a black background filled with 196 discs (diameters: 0.4-1.0 cm). These were presented on an LCD monitor in a dark room at a viewing distance of 55 cm (1.8 D). Thirteen subjects aged 21-37 years took part. The individual discs had saw-tooth shaped temporal luminance profiles with the same time period but with random phases with respect to each other, so that the mean brightness of the stimulus was constant. To eliminate accommodation responses based on other cues (i.e. proximity) a 0.5 mm artificial pupil was used to open the accommodation loop. Refraction in the vertical pupil meridian was continuously recorded with an infrared photorefractor (the PowerRefractor). To verify that computer-based stimuli presented within our experimental design were effective in driving accommodation, previously studied stimuli were also tested: changes in size (looming) and incremental low pass filtering. Preferential stimulation of the ON or OFF subsystems produced a convincing depth illusion in all subjects (which was psychophysically confirmed in four subjects). Although the stimulus appeared to move in depth it did not produce accommodation responses that were consistent with that, i.e. the accommodation system did not appear to fluctuate in rhythm with the temporal oscillations of the stimulus

  7. Visual accommodation trainer-tester

    NASA Technical Reports Server (NTRS)

    Randle, Robert J. (Inventor)

    1988-01-01

    An apparatus for training the human visual accommodation system is described. Specifically, the apparatus is useful for training personnel to volitionally control focus to the far point (normally infinity) from a position of myopia due to functional causes. The functional causes could be due, for example, to a behavioral accommodative spasm or the effects of an empty field. The device may also be used to measure accommodation, the accommodation resting position and the near and far points of vision. The device comprises a number of optical elements arranged on a single optical axis. Several of the elements are arranged in order on a movable stage in fixed relationship to each other: a light source, a lens, a target, an aperture and/or a second lens. On a base and in fixed relationship to each other are eyepiece and third lens. A stage generates an image of the target and the stage is movable with respect to the base by means of a knob. The device is utilized for the various training and test functions by following a series of procedural steps, and interchanging the apertures as necessary for the selected procedure.

  8. Multi-body modeling method for rollover using MADYMO

    NASA Astrophysics Data System (ADS)

    Liu, Changye; Lin, Zhigui; Lv, Juncheng; Luo, Qinyue; Qin, Zhenyao; Zhang, Pu; Chen, Tao

    2017-04-01

    Rollovers are complex road accidents causing a big deal of fatalities. FE model for rollover study will costtoo much time due to its long duration.A new multi-body modeling method is proposed in this paper which can save a lot of time and has high-fidelity meanwhile. Following works were carried out to validate this new method. First, a small van was tested following the FMVSS 208 protocol for the validation of the proposed modeling method. Second, a MADYMO model of this small van was reconstructed. The vehicle body was divided into two main parts, the deformable upper body and the rigid lower body, modeled by different waysbased on an FE model. The specific method of modeling is offered in this paper. Finally, the trajectories of the vehicle from test and simulation were comparedand the match was very good. Acceleration of left B pillar was taken into consideration, which turned out fitting the test result well in the time of event. The final deformation status of the vehicle in test and simulation showed similar trend. This validated model provides a reliable wayfor further research in occupant injuries during rollovers.

  9. Sub-discretized surface model with application to contact mechanics in multi-body simulation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Johnson, S; Williams, J

    2008-02-28

    The mechanics of contact between rough and imperfectly spherical adhesive powder grains are often complicated by a variety of factors, including several which vary over sub-grain length scales. These include several traction factors that vary spatially over the surface of the individual grains, including high energy electron and acceptor sites (electrostatic), hydrophobic and hydrophilic sites (electrostatic and capillary), surface energy (general adhesion), geometry (van der Waals and mechanical), and elasto-plastic deformation (mechanical). For mechanical deformation and reaction, coupled motions, such as twisting with bending and sliding, as well as surface roughness add an asymmetry to the contact force which invalidatesmore » assumptions for popular models of contact, such as the Hertzian and its derivatives, for the non-adhesive case, and the JKR and DMT models for adhesive contacts. Though several contact laws have been offered to ameliorate these drawbacks, they are often constrained to particular loading paths (most often normal loading) and are relatively complicated for computational implementation. This paper offers a simple and general computational method for augmenting contact law predictions in multi-body simulations through characterization of the contact surfaces using a hierarchically-defined surface sub-discretization. For the case of adhesive contact between powder grains in low stress regimes, this technique can allow a variety of existing contact laws to be resolved across scales, allowing for moments and torques about the contact area as well as normal and tangential tractions to be resolved. This is especially useful for multi-body simulation applications where the modeler desires statistical distributions and calibration for parameters in contact laws commonly used for resolving near-surface contact mechanics. The approach is verified against analytical results for the case of rough, elastic spheres.« less

  10. 46 CFR 169.317 - Accommodations.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... of the stem. The space must not be located totally below the deepest load waterline. (b) Bulkheads separating accommodations from machinery spaces, paint lockers, storerooms, washrooms, and toilet facilities... and Arrangement Living Spaces § 169.317 Accommodations. (a) Quarters must have sufficient fresh air...

  11. 46 CFR 169.317 - Accommodations.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... of the stem. The space must not be located totally below the deepest load waterline. (b) Bulkheads separating accommodations from machinery spaces, paint lockers, storerooms, washrooms, and toilet facilities... and Arrangement Living Spaces § 169.317 Accommodations. (a) Quarters must have sufficient fresh air...

  12. 46 CFR 169.317 - Accommodations.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... of the stem. The space must not be located totally below the deepest load waterline. (b) Bulkheads separating accommodations from machinery spaces, paint lockers, storerooms, washrooms, and toilet facilities... and Arrangement Living Spaces § 169.317 Accommodations. (a) Quarters must have sufficient fresh air...

  13. 46 CFR 169.317 - Accommodations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Accommodations. 169.317 Section 169.317 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) NAUTICAL SCHOOLS SAILING SCHOOL VESSELS Construction and Arrangement Living Spaces § 169.317 Accommodations. (a) Quarters must have sufficient fresh air...

  14. 46 CFR 169.317 - Accommodations.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Accommodations. 169.317 Section 169.317 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) NAUTICAL SCHOOLS SAILING SCHOOL VESSELS Construction and Arrangement Living Spaces § 169.317 Accommodations. (a) Quarters must have sufficient fresh air...

  15. Accommodation to wavefront vergence and chromatic aberration.

    PubMed

    Wang, Yinan; Kruger, Philip B; Li, James S; Lin, Peter L; Stark, Lawrence R

    2011-05-01

    Longitudinal chromatic aberration (LCA) provides a cue to accommodation with small pupils. However, large pupils increase monochromatic aberrations, which may obscure chromatic blur. In this study, we examined the effect of pupil size and LCA on accommodation. Accommodation was recorded by infrared optometer while observers (nine normal trichromats) viewed a sinusoidally moving Maltese cross target in a Badal stimulus system. There were two illumination conditions: white (3000 K; 20 cd/m) and monochromatic (550 nm with 10 nm bandwidth; 20 cd/m) and two artificial pupil conditions (3 and 5.7 mm). Separately, static measurements of wavefront aberration were made with the eye accommodating to targets between 0 and 4 D (COAS, Wavefront Sciences). Large individual differences in accommodation to wavefront vergence and to LCA are a hallmark of accommodation. LCA continues to provide a signal at large pupil sizes despite higher levels of monochromatic aberrations. Monochromatic aberrations may defend against chromatic blur at high spatial frequencies, but accommodation responds best to optical vergence and to LCA at 3 c/deg where blur from higher order aberrations is less.

  16. Anthropometric accommodation in USAF cockpits

    NASA Technical Reports Server (NTRS)

    Zehner, Gregory F.

    1994-01-01

    Over the past three years, a new set of methodologies has been developed to specify and evaluate anthropometric accommodation in USAF crewstation designs. These techniques are used to improve the ability of the pilot to reach controls, to safely escape the aircraft, to achieve adequate mobility and comfort, and to assure full access to the visual field both inside and outside the aircraft. This paper summarized commonly encountered aircraft accommodation problems, explains the failure of the traditional 'percentile man' design concept to resolve these difficulties, and suggests an alternative approach for improving cockpit design to better accommodate today's more heterogeneous flying population.

  17. Supercomputer optimizations for stochastic optimal control applications

    NASA Technical Reports Server (NTRS)

    Chung, Siu-Leung; Hanson, Floyd B.; Xu, Huihuang

    1991-01-01

    Supercomputer optimizations for a computational method of solving stochastic, multibody, dynamic programming problems are presented. The computational method is valid for a general class of optimal control problems that are nonlinear, multibody dynamical systems, perturbed by general Markov noise in continuous time, i.e., nonsmooth Gaussian as well as jump Poisson random white noise. Optimization techniques for vector multiprocessors or vectorizing supercomputers include advanced data structures, loop restructuring, loop collapsing, blocking, and compiler directives. These advanced computing techniques and superconducting hardware help alleviate Bellman's curse of dimensionality in dynamic programming computations, by permitting the solution of large multibody problems. Possible applications include lumped flight dynamics models for uncertain environments, such as large scale and background random aerospace fluctuations.

  18. Magnetour: Surfing planetary systems on electromagnetic and multi-body gravity fields

    NASA Astrophysics Data System (ADS)

    Lantoine, Gregory; Russell, Ryan P.; Anderson, Rodney L.; Garrett, Henry B.

    2017-09-01

    A comprehensive tour of the complex outer planet systems is a central goal in space science. However, orbiting multiple moons of the same planet would be extremely prohibitive using traditional propulsion and power technologies. In this paper, a new mission concept, named Magnetour, is presented to facilitate the exploration of outer planet systems and address both power and propulsion challenges. This approach would enable a single spacecraft to orbit and travel between multiple moons of an outer planet, without significant propellant or onboard power source. To achieve this free-lunch 'Grand Tour', Magnetour exploits the unexplored combination of magnetic and multi-body gravitational fields of planetary systems, with a unique focus on using a bare electrodynamic tether for power and propulsion. Preliminary results indicate that the Magnetour concept is sound and is potentially highly promising at Jupiter.

  19. A Review of Worksite Lactation Accommodations.

    PubMed

    Hilliard, Elizabeth Dianne

    2017-01-01

    The purpose of this review was to examine workplace lactation accommodations, and their association with breastfeeding duration, and identify strategies occupational health professionals can use to promote lactation improvements. This study included literature published from 1985 through 2015 and listed in PubMed and CINAHL. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), 11 articles were identified for review. Presence of a corporate lactation program, on-site child care, and return to work/telephone lactation consultation were consistently associated with breastfeeding at 6 months. Other breastfeeding accommodations (i.e., lactation spaces, lactation breaks, worksite lactation policies, and supervisor/coworker support) were not consistently associated with breastfeeding duration. Occupational health professionals can play key roles in improving the effectiveness of lactation accommodations. Assuring adequate implementation of accommodations, increasing communication and marketing of accommodations, and promoting supervisor and coworker support are areas that occupational health professionals should explore for improving lactation duration.

  20. Exploring the Relationship Between Students Needing Accommodations and Instructor Self-Efficacy in Complying with Accommodations

    ERIC Educational Resources Information Center

    Wright, Anna M.; Meyer, Kevin R.

    2017-01-01

    The willingness and flexibility of university instructors to comply with and provide accommodations for students with disabilities is critical to academic success. The authors examine how communication between students needing accommodations and university instructors impacts instructor self-efficacy, or instructors' perception that they can meet…

  1. Accommodative spasm in siblings: A unique finding

    PubMed Central

    Rutstein, Robert P

    2010-01-01

    Accommodative spasm is a rare condition occurring in children, adolescents, and young adults. A familial tendency for this binocular vision disorder has not been reported. I describe accommodative spasm occurring in a brother and sister. Both children presented on the same day with complaints of headaches and blurred vision. Treatment included cycloplegia drops and bifocals. Siblings of patients having accommodative spasm should receive a detailed eye exam with emphasis on recognition of accommodative spasm. PMID:20534925

  2. Accommodation, accommodative convergence, and response AC/A ratios before and at the onset of myopia in children.

    PubMed

    Gwiazda, Jane; Thorn, Frank; Held, Richard

    2005-04-01

    The purpose of this study was to investigate accommodation, accommodative convergence, and AC/A ratios before and at the onset of myopia in children. Refractive error, accommodation, and phorias were measured annually over a period of 3 years in 80 6- to 18-year-old children (mean age at first visit = 11.1 years), including 26 who acquired myopia of at least -0.50 D and 54 who remained emmetropic (-0.25 to + 0.75 D). Refraction was measured by noncycloplegic distance retinoscopy. Concomitant measures of accommodation and phorias were taken for letter targets at 4.0 m and 0.33 m using the Canon R-1 open field-of-view autorefractor with an attached motorized Risley prism and Maddox rod. The accommodation and phoria measurements were used to calculate response AC/A ratios. Compared with children who remained emmetropic, those who became myopic had elevated response AC/A ratios at 1 and 2 years before the onset of myopia, in addition to at onset and 1 year later (t's = -2.97 to -4.04, p < 0.01 at all times). The significantly higher AC/A ratios in the children who became myopic are a result of significantly reduced accommodation. Accommodative convergence was significantly greater in myopes only at onset. These findings suggest that the abnormal oculomotor factors found before the onset of myopia may contribute to myopigenesis by producing hyperopic retinal defocus when a child is engaged in near-viewing tasks.

  3. Accommodative Performance of Children With Unilateral Amblyopia

    PubMed Central

    Manh, Vivian; Chen, Angela M.; Tarczy-Hornoch, Kristina; Cotter, Susan A.; Candy, T. Rowan

    2015-01-01

    Purpose. The purpose of this study was to compare the accommodative performance of the amblyopic eye of children with unilateral amblyopia to that of their nonamblyopic eye, and also to that of children without amblyopia, during both monocular and binocular viewing. Methods. Modified Nott retinoscopy was used to measure accommodative performance of 38 subjects with unilateral amblyopia and 25 subjects with typical vision from 3 to 13 years of age during monocular and binocular viewing at target distances of 50, 33, and 25 cm. The relationship between accommodative demand and interocular difference (IOD) in accommodative error was assessed in each group. Results. The mean IOD in monocular accommodative error for amblyopic subjects across all three viewing distances was 0.49 diopters (D) (95% confidence interval [CI], ±1.12 D) in the 180° meridian and 0.54 D (95% CI, ±1.27 D) in the 90° meridian, with the amblyopic eye exhibiting greater accommodative errors on average. Interocular difference in monocular accommodative error increased significantly with increasing accommodative demand; 5%, 47%, and 58% of amblyopic subjects had monocular errors in the amblyopic eye that fell outside the upper 95% confidence limit for the better eye of control subjects at viewing distances of 50, 33, and 25 cm, respectively. Conclusions. When viewing monocularly, children with unilateral amblyopia had greater mean accommodative errors in their amblyopic eyes than in their nonamblyopic eyes, and when compared with control subjects. This could lead to unintended retinal image defocus during patching therapy for amblyopia. PMID:25626970

  4. 46 CFR 108.211 - Miscellaneous accommodation spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Miscellaneous accommodation spaces. 108.211 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.211 Miscellaneous accommodation spaces. (a) Each unit must have enough facilities for personnel to wash their own clothes...

  5. 46 CFR 108.211 - Miscellaneous accommodation spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Miscellaneous accommodation spaces. 108.211 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.211 Miscellaneous accommodation spaces. (a) Each unit must have enough facilities for personnel to wash their own clothes...

  6. 46 CFR 108.211 - Miscellaneous accommodation spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Miscellaneous accommodation spaces. 108.211 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.211 Miscellaneous accommodation spaces. (a) Each unit must have enough facilities for personnel to wash their own clothes...

  7. 46 CFR 108.211 - Miscellaneous accommodation spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Miscellaneous accommodation spaces. 108.211 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.211 Miscellaneous accommodation spaces. (a) Each unit must have enough facilities for personnel to wash their own clothes...

  8. 46 CFR 108.211 - Miscellaneous accommodation spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Miscellaneous accommodation spaces. 108.211 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.211 Miscellaneous accommodation spaces. (a) Each unit must have enough facilities for personnel to wash their own clothes...

  9. Employer Accommodation and Labor Supply of Disabled Workers*

    PubMed Central

    Hill, Matthew J.; Maestas, Nicole; Mullen, Kathleen J.

    2016-01-01

    We examine the factors that influence employer accommodation of newly disabled workers and how effective such accommodations are in retaining workers and discouraging disability insurance applications. Using the Health and Retirement Study, we find that only a quarter of newly disabled older workers in their 50s are accommodated by their employers in some way following onset of a disability. Importantly, we find that few employer characteristics explain which workers are accommodated; rather, employee characteristics, particularly the presence of personality traits correlated with assertiveness and open communication, are highly predictive of accommodation. We also find that if employer accommodation rates could be increased, disabled workers would be significantly more likely to delay labor force exit for up to two years. However, accommodation does not appear to reduce subsequent disability insurance claiming. PMID:27840560

  10. 46 CFR 108.195 - Location of accommodation spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Location of accommodation spaces. 108.195 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.195 Location of accommodation spaces. (a) On surface type units, accommodation spaces must not be located forward of a vertical...

  11. 46 CFR 108.195 - Location of accommodation spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Location of accommodation spaces. 108.195 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.195 Location of accommodation spaces. (a) On surface type units, accommodation spaces must not be located forward of a vertical...

  12. 46 CFR 108.195 - Location of accommodation spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Location of accommodation spaces. 108.195 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.195 Location of accommodation spaces. (a) On surface type units, accommodation spaces must not be located forward of a vertical...

  13. 46 CFR 108.195 - Location of accommodation spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Location of accommodation spaces. 108.195 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.195 Location of accommodation spaces. (a) On surface type units, accommodation spaces must not be located forward of a vertical...

  14. 46 CFR 108.195 - Location of accommodation spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Location of accommodation spaces. 108.195 Section 108... DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.195 Location of accommodation spaces. (a) On surface type units, accommodation spaces must not be located forward of a vertical...

  15. Accommodation to Wavefront Vergence and Chromatic Aberration

    PubMed Central

    Wang, Yinan; Kruger, Philip B.; Li, James S.; Lin, Peter L.; Stark, Lawrence R.

    2011-01-01

    Purpose Longitudinal chromatic aberration (LCA) provides a cue to accommodation with small pupils. However, large pupils increase monochromatic aberrations, which may obscure chromatic blur. In the present study, we examined the effect of pupil size and LCA on accommodation. Methods Accommodation was recorded by infrared optometer while observers (nine normal trichromats) viewed a sinusoidally moving Maltese cross target in a Badal stimulus system. There were two illumination conditions: white (3000 K; 20 cd/m2) and monochromatic (550 nm with 10 nm bandwidth; 20 cd/m2) and two artificial pupil conditions (3 mm and 5.7 mm). Separately, static measurements of wavefront aberration were made with the eye accommodating to targets between 0 and 4 D (COAS, Wavefront Sciences). Results Large individual differences in accommodation to wavefront vergence and to LCA are a hallmark of accommodation. LCA continues to provide a signal at large pupil sizes despite higher levels of monochromatic aberrations. Conclusions Monochromatic aberrations may defend against chromatic blur at high spatial frequencies, but accommodation responds best to optical vergence and to LCA at 3 c/deg where blur from higher order aberrations is less. PMID:21317666

  16. Determination of the Accommodation Coefficient Using Vapor/gas Bubble Dynamics in an Acoustic Field

    NASA Technical Reports Server (NTRS)

    Gumerov, Nail A.; Hsiao, Chao-Tsung; Goumilevski, Alexei G.; Allen, Jeff (Technical Monitor)

    2001-01-01

    Nonequilibrium liquid/vapor phase transformations can occur in superheated or subcooled liquids in fast processes such as in evaporation in a vacuum. The rate at which such a phase transformation occurs depends on the "condensation" or "accommodation" coefficient, Beta, which is a property of the interface. Existing measurement techniques for Beta are complex and expensive. The development of a relatively inexpensive and reliable technique for measurement of Beta for a wide range of substances and temperatures is of great practical importance. The dynamics of a bubble in an acoustic field strongly depends on the value of Beta. It is known that near the saturation temperature, small vapor bubbles grow under the action of an acoustic field due to "rectified heat transfer." This finding can be used as the basis for an effective measurement technique of Beta. We developed a theory of vapor bubble behavior in an isotropic acoustic wave and in a plane standing acoustic wave. A numerical code was developed which enables simulation of a variety of experimental situations and accurately takes into account slowly evolving temperature. A parametric study showed that the measurement of Beta can be made over a broad range of frequencies and bubble sizes. We found several interesting regimes and conditions which can be efficiently used for measurements of Beta. Measurements of Beta can be performed in both reduced and normal gravity environments.

  17. Spinal circuits can accommodate interaction torques during multijoint limb movements.

    PubMed

    Buhrmann, Thomas; Di Paolo, Ezequiel A

    2014-01-01

    The dynamic interaction of limb segments during movements that involve multiple joints creates torques in one joint due to motion about another. Evidence shows that such interaction torques are taken into account during the planning or control of movement in humans. Two alternative hypotheses could explain the compensation of these dynamic torques. One involves the use of internal models to centrally compute predicted interaction torques and their explicit compensation through anticipatory adjustment of descending motor commands. The alternative, based on the equilibrium-point hypothesis, claims that descending signals can be simple and related to the desired movement kinematics only, while spinal feedback mechanisms are responsible for the appropriate creation and coordination of dynamic muscle forces. Partial supporting evidence exists in each case. However, until now no model has explicitly shown, in the case of the second hypothesis, whether peripheral feedback is really sufficient on its own for coordinating the motion of several joints while at the same time accommodating intersegmental interaction torques. Here we propose a minimal computational model to examine this question. Using a biomechanics simulation of a two-joint arm controlled by spinal neural circuitry, we show for the first time that it is indeed possible for the neuromusculoskeletal system to transform simple descending control signals into muscle activation patterns that accommodate interaction forces depending on their direction and magnitude. This is achieved without the aid of any central predictive signal. Even though the model makes various simplifications and abstractions compared to the complexities involved in the control of human arm movements, the finding lends plausibility to the hypothesis that some multijoint movements can in principle be controlled even in the absence of internal models of intersegmental dynamics or learned compensatory motor signals.

  18. Reproducibility of carbachol stimulated accommodation in rhesus monkeys.

    PubMed

    Wendt, Mark; Glasser, Adrian

    2012-06-01

    Approaches are being explored to restore accommodation to the presbyopic eye. Some of these approaches can be tested in monkeys by stimulating accommodation in various ways including using carbachol iontophoresis. Knowledge of the repeatability of carbachol iontophoresis stimulated accommodation in the monkey phakic eye is necessary to understand the variability of this method of evaluating accommodation. Data from 9 to 10 separate carbachol iontophoresis experiments performed on phakic eyes from 8 monkeys were retrospectively analyzed. For each experiment, carbachol was applied iontophoretically to the eyes of anesthetized monkeys and refraction generally measured every two minutes until accommodation reached a plateau. Repeated experiments were performed in each monkey over periods ranging from 10 to 18 months. Maximum accommodation measured for each monkey ranged from 11.1 D to 18.3 D with standard deviations from 0.8 D to 2.1 D and differences in accommodative amplitude varying from 2.2 D to 7.5 D. Time to reach maximum accommodation ranged from 18 to 64 min in individual experiments. Averaged time-courses indicate that maximum accommodation is generally achieved between 10 and 20 min after carbachol administration. Although carbachol iontophoresis is considered a reliable method to stimulate maximum accommodation in anesthetized monkeys, the amplitude achieved typically varies by more than 2 D. Presbyopia treatments evaluated in this way in phakic monkeys would need to show an increase in accommodation of over 2 D to clearly demonstrate that the treatments work when being tested with carbachol iontophoresis stimulation. Copyright © 2012 Elsevier Ltd. All rights reserved.

  19. Accommodation in Astigmatic Children During Visual Task Performance

    PubMed Central

    Harvey, Erin M.; Miller, Joseph M.; Apple, Howard P.; Parashar, Pavan; Twelker, J. Daniel; Crescioni, Mabel; Davis, Amy L.; Leonard-Green, Tina K.; Campus, Irene; Sherrill, Duane L.

    2014-01-01

    Purpose. To determine the accuracy and stability of accommodation in uncorrected children during visual task performance. Methods. Subjects were second- to seventh-grade children from a highly astigmatic population. Measurements of noncycloplegic right eye spherical equivalent (Mnc) were obtained while uncorrected subjects performed three visual tasks at near (40 cm) and distance (2 m). Tasks included reading sentences with stimulus letter size near acuity threshold and an age-appropriate letter size (high task demands) and viewing a video (low task demand). Repeated measures ANOVA assessed the influence of astigmatism, task demand, and accommodative demand on accuracy (mean Mnc) and variability (mean SD of Mnc) of accommodation. Results. For near and distance analyses, respectively, sample size was 321 and 247, mean age was 10.37 (SD 1.77) and 10.30 (SD 1.74) years, mean cycloplegic M was 0.48 (SD 1.10) and 0.79 diopters (D) (SD 1.00), and mean astigmatism was 0.99 (SD 1.15) and 0.75 D (SD 0.96). Poor accommodative accuracy was associated with high astigmatism, low task demand (video viewing), and high accommodative demand. The negative effect of accommodative demand on accuracy increased with increasing astigmatism, with the poorest accommodative accuracy observed in high astigmats (≥3.00 D) with high accommodative demand/high hyperopia (1.53 D and 2.05 D of underaccommodation for near and distant stimuli, respectively). Accommodative variability was greatest in high astigmats and was uniformly high across task condition. No/low and moderate astigmats showed higher variability for the video task than the reading tasks. Conclusions. Accuracy of accommodation is reduced in uncorrected children with high astigmatism and high accommodative demand/high hyperopia, but improves with increased visual task demand (reading). High astigmats showed the greatest variability in accommodation. PMID:25103265

  20. Decreased accommodation during decompensation of distance exotropia.

    PubMed

    Horwood, Anna M; Riddell, Patricia M

    2012-04-01

    Disparity cues can be a major drive to accommodation via the convergence accommodation to convergence (CA/C) linkage, but, on decompensation of exotropia, disparity cues are extinguished by suppression so this drive is lost. This study investigated accommodation and vergence responses to disparity, blur and proximal cues in a group of distance exotropes aged between 4 and 11 years both during decompensation and when exotropic. 19 participants with distance exotropia were tested using a PlusoptiXSO4 photo refractor set in a remote haploscopic device that assessed simultaneous vergence and accommodation to a range of targets incorporating different combinations of blur, disparity and proximal cues at four fixation distances between 2 m and 33 cm. Responses on decompensation were compared with those from the same children when their deviation was controlled. Manifest exotropia was more common in the more impoverished cue conditions. When decompensated for near, mean accommodation gain for the all-cue (naturalistic) target was significantly reduced (p<0.0001), with resultant mean under-accommodation of 2.33 D at 33 cm. The profile of near cues usage changed after decompensation, with blur and proximity driving residual responses, but these remaining cues did not compensate for loss of accommodation caused by the removal of disparity. Accommodation often reduces on decompensation of distance exotropia as the drive from convergence is extinguished, providing a further reason to try to prevent decompensation for near.

  1. Decreased accommodation during decompensation of distance exotropia

    PubMed Central

    Horwood, Anna M; Riddell, Patricia M

    2015-01-01

    Objective Disparity cues can be a major drive to accommodation via the CA/C (convergence accommodation to convergence) linkage but, on decompensation of exotropia, disparity cues are extinguished by suppression, so this drive is lost. This study investigated accommodation and vergence responses to disparity, blur and proximal cues in a group of distance exotropes aged between 4-11 years both during decompensation and when exotropic. Methods 19 participants with distance exotropia were tested using a PlusoptiXSO4 photorefractor set in a remote haploscopic device which assessed simultaneous vergence and accommodation to a range of targets incorporating different combinations of blur, disparity and proximal cues at four fixation distances between 2m and 33cm. Responses on decompensation were compared to those from the same children when their deviation was controlled. Results Manifest exotropia was more common in the more impoverished cue conditions. When decompensated for near, mean accommodation gain for the all-cue (naturalistic) target reduced significantly (p<0.0001), with resultant mean under-accommodation of 2.33D at 33cm. The profile of near cues usage changed after decompensation, with blur and proximity driving residual responses, but these remaining cues did not compensate for loss of accommodation caused by the removal of disparity. Conclusions Accommodation often reduces on decompensation of distance exotropia as the drive from convergence is extinguished, providing a further reason to try to prevent decompensation for near. PMID:21873311

  2. Effect of Phenylephrine on the Accommodative System

    PubMed Central

    Del Águila-Carrasco, Antonio J.; Bernal-Molina, Paula; Ferrer-Blasco, Teresa; López-Gil, Norberto; Montés-Micó, Robert

    2016-01-01

    Accommodation is controlled by the action of the ciliary muscle and mediated primarily by parasympathetic input through postganglionic fibers that originate from neurons in the ciliary and pterygopalatine ganglia. During accommodation the pupil constricts to increase the depth of focus of the eye and improve retinal image quality. Researchers have traditionally faced the challenge of measuring the accommodative properties of the eye through a small pupil and thus have relied on pharmacological agents to dilate the pupil. Achieving pupil dilation (mydriasis) without affecting the accommodative ability of the eye (cycloplegia) could be useful in many clinical and research contexts. Phenylephrine hydrochloride (PHCl) is a sympathomimetic agent that is used clinically to dilate the pupil. Nevertheless, first investigations suggested some loss of functional accommodation in the human eye after PHCl instillation. Subsequent studies, based on different measurement procedures, obtained contradictory conclusions, causing therefore an unexpected controversy that has been spread almost to the present days. This manuscript reviews and summarizes the main research studies that have been performed to analyze the effect of PHCl on the accommodative system and provides clear conclusions that could help clinicians know the real effects of PHCl on the accommodative system of the human eye. PMID:28053778

  3. Teleworkers with disabilities: characteristics and accommodation use.

    PubMed

    Linden, Maureen; Milchus, Karen

    2014-01-01

    The prevalence of telework among people with disabilities is not as great as the general population, despite the accommodative benefits of telework. This study of employment and accommodation use patterns of people with disabilities investigates relationships between functional abilities, work location and nature, and accommodation use. Currently employed subjects with disabilities were recruited from client lists of research, technical assistance, and service provision centers, as well as through over 100 social networking venues focused on individuals with disabilities. A national, cross-sectional survey was administered electronically. Details of accommodation use for 373 individuals were compared using Chi-Square distribution analysis. Those in white-collar and knowledge-based jobs were twice as likely to telework as other worker types, and teleworkers were twice as likely to use flexible scheduling. Only 47% of teleworkers reported telework as a job accommodation. Of those, 57% were satisfied with telework and 76% reported it as important to job task completion. Increased use of flexible scheduling, particularly among those who view telework as an accommodation, suggests the primary accommodative benefit of telework is to reduce pain and fatigue-related barriers to traditional employment. Relatively low satisfaction with telework suggests that it presents other employment-related barriers.

  4. Modeling the convergence accommodation of stereo vision for binocular endoscopy.

    PubMed

    Gao, Yuanqian; Li, Jinhua; Li, Jianmin; Wang, Shuxin

    2018-02-01

    The stereo laparoscope is an important tool for achieving depth perception in robot-assisted minimally invasive surgery (MIS). A dynamic convergence accommodation algorithm is proposed to improve the viewing experience and achieve accurate depth perception. Based on the principle of the human vision system, a positional kinematic model of the binocular view system is established. The imaging plane pair is rectified to ensure that the two rectified virtual optical axes intersect at the fixation target to provide immersive depth perception. Stereo disparity was simulated with the roll and pitch movements of the binocular system. The chessboard test and the endoscopic peg transfer task were performed, and the results demonstrated the improved disparity distribution and robustness of the proposed convergence accommodation method with respect to the position of the fixation target. This method offers a new solution for effective depth perception with the stereo laparoscopes used in robot-assisted MIS. Copyright © 2017 John Wiley & Sons, Ltd.

  5. Analysis of composite/difference field scattering properties between a slightly rough optical surface and multi-body defects.

    PubMed

    Gong, Lei; Wu, Zhensen; Gao, Ming; Qu, Tan

    2018-03-20

    The effective extraction of optical surface roughness and defect characteristic provide important realistic values to improve optical system efficiency. Based on finite difference time domain/multi-resolution time domain (FDTD/MRTD) mixed approach, composite scattering between a slightly rough optical surface and multi-body defect particles with different positions is investigated. The scattering contribution of defect particles or the slightly rough optical surface is presented. Our study provides a theoretical and technological basis for the nondestructive examination and optical performance design of nanometer structures.

  6. Surface accommodation of molecular contaminants

    NASA Technical Reports Server (NTRS)

    Chen, Philip T.; Hedgeland, Randy J.; Thomson, Shaun R.

    1990-01-01

    Theoretical consideration and supporting data are presented regarding the nature of the transport mechanisms which cause the adsorption of gases on spacecraft surfaces. Particular attention is given to the concept of a sticking coefficient which is the ratio of the thermally accommodated mass to the total incident mass. Existing molecular accommodation data are examined in terms of spacecraft applications and recent contamination-control data are introduced. Two distinct yet linked concepts emerge which are the accommodation and sticking coefficients, and surface roughness contributes significantly to both coefficients. A general equation regarding the coefficients is developed, and the data are found to fit the equation basically. It is concluded that a more precise characterization of the coefficients can be obtained through experimentation under simulated spacecraft conditions.

  7. Sliding mode-based lateral vehicle dynamics control using tyre force measurements

    NASA Astrophysics Data System (ADS)

    Kunnappillil Madhusudhanan, Anil; Corno, Matteo; Holweg, Edward

    2015-11-01

    In this work, a lateral vehicle dynamics control based on tyre force measurements is proposed. Most of the lateral vehicle dynamics control schemes are based on yaw rate whereas tyre forces are the most important variables in vehicle dynamics as tyres are the only contact points between the vehicle and road. In the proposed method, active front steering is employed to uniformly distribute the required lateral force among the front left and right tyres. The force distribution is quantified through the tyre utilisation coefficients. In order to address the nonlinearities and uncertainties of the vehicle model, a gain scheduling sliding-mode control technique is used. In addition to stabilising the lateral dynamics, the proposed controller is able to maintain maximum lateral acceleration. The proposed method is tested and validated on a multi-body vehicle simulator.

  8. Advanced Solar Observatory (ASO) accommodations requirements study

    NASA Technical Reports Server (NTRS)

    1989-01-01

    Results of an accommodations analysis for the Advanced Solar Observatory on Space Station Freedom are reported. Concepts for the High Resolution Telescope Cluster, Pinhole/Occulter Facility, and High Energy Cluster were developed which can be accommodated on Space Station Freedom. It is shown that workable accommodations concepts are possible. Areas of emphasis for the next stage of engineering development are identified.

  9. 77 FR 38833 - Job Accommodation Network

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-29

    ... DEPARTMENT OF LABOR Job Accommodation Network AGENCY: Office of Disability Employment Policy, Department of Labor. Announcement Type: New Notice of Availability of Funds and Solicitation for Grant... cooperative agreement to manage and operate its Job Accommodation Network (JAN), a national technical...

  10. A sensitivity study of the effects of evaporation/condensation accommodation coefficients on transient heat pipe modeling

    NASA Astrophysics Data System (ADS)

    Hall, Michael L.; Doster, J. Michael

    1990-03-01

    The dynamic behavior of liquid metal heat pipe models is strongly influenced by the choice of evaporation and condensation modeling techniques. Classic kinetic theory descriptions of the evaporation and condensation processes are often inadequate for real situations; empirical accommodation coefficients are commonly utilized to reflect nonideal mass transfer rates. The complex geometries and flow fields found in proposed heat pipe systems cause considerable deviation from the classical models. the THROHPUT code, which has been described in previous works, was developed to model transient liquid metal heat pipe behavior from frozen startup conditions to steady state full power operation. It is used here to evaluate the sensitivity of transient liquid metal heat pipe models to the choice of evaporation and condensation accommodation coefficients. Comparisons are made with experimental liquid metal heat pipe data. It is found that heat pipe behavior can be predicted with the proper choice of the accommodation coefficients. However, the common assumption of spatially constant accommodation coefficients is found to be a limiting factor in the model.

  11. Gender differences in early accommodation and vergence development.

    PubMed

    Horwood, Anna M; Riddell, Patricia M

    2008-03-01

    A remote haploscopic photorefractor was used to assess objective binocular vergence and accommodation responses in 157 full-term healthy infants aged 1-6 months while fixating a brightly coloured target moving between fixation distances at 2, 1, 0.5 and 0.33 m. Vergence and accommodation response gain matured rapidly from 'flat' neonatal responses at an intercept of approximately 2 dioptres (D) for accommodation and 2.5 metre angles(MA) for vergence, reaching adult-like values at 4 months. Vergence gain was marginally higher in females (p = 0.064), but accommodation gain (p = 0.034) was higher and accommodative intercept closer to zero (p = 0.004) in males in the first 3 months as they relaxed accommodation more appropriately for distant targets. More females showed flat accommodation responses (p = 0.029). More males behaved hypermetropically in the first two months of life, but when these hypermetropic infants were excluded from the analysis, the gender difference remained. Gender differences disappeared after three months. Data showed variable responses and infants could behave appropriately and simultaneously on both, neither or only one measure at all ages. If accommodation was appropriate (gain between 0.7 and 1.3; r(2) > 0.7) but vergence was not, males over- and under-converged equally, while the females who accommodated appropriately were more likely to overconverge (p = 0.008). The apparent earlier maturity of the male accommodative responses may be due to refractive error differences but could also reflect gender-specific male preference for blur cues while females show earlier preference for disparity, which may underpin the earlier emerging, disparity dependent, stereopsis and full vergence found in females in other studies.

  12. Chromatic aberration, accommodation, and color preference in asthenopia.

    PubMed

    Drew, Stefanie A; Borsting, Eric; Stark, Lawrence R; Chase, Chris

    2012-07-01

    Asthenopia is a common problem associated with near work and reports suggest that colored lenses or overlays may be applied to reduce symptoms. In this study, we examine the relationship between eyestrain, color preferences, and function of the accommodation and vergence system. Specifically, we examine whether symptomatic observers select colors that reduce accommodative demand based on longitudinal chromatic aberration (LCA). Forty-seven undergraduate students participated in this study. Visual discomfort symptoms were assessed using the Conlon survey. A Mark 2 Intuitive Colorimeter was used to obtain optimal colored light preferences. LCA was modeled using the Chromatic Eye and spectral power density data. A comprehensive evaluation of accommodation and vergence was performed following standard procedures. A significant negative correlation (r = -0.51) was found between eyestrain symptoms and the International Commission on Illumination (CIE) v' axis of colors preferences. Additionally, a significant negative correlation (r = -0.31) was found between eyestrain symptoms and LCA accommodation. Two thirds of the participants in the high discomfort group chose colors that decreased accommodative demand. Accommodative amplitude and vergence facility also correlated with LCA, accounting for 25% of the variance. The color preferences of individuals are systematically influenced by the functioning of their accommodation and vergence systems with increased symptomatology resulting in color selections that reduce LCA accommodative stimulus demand.

  13. Dynamic analysis of the deployment for mesh reflector deployable antennas with the cable-net structure

    NASA Astrophysics Data System (ADS)

    Zhang, Yiqun; Li, Na; Yang, Guigeng; Ru, Wenrui

    2017-02-01

    This paper presents a dynamic analysis approach for the composite structure of a deployable truss and cable-net system. An Elastic Catenary Element is adopted to model the slack/tensioned cables. Then, from the energy standpoint, the kinetic energy, elasticity-potential energy and geopotential energy of the cable-net structure and deployable truss are derived. Thus, the flexible multi-body dynamic model of the deployable antenna is built based on the Lagrange equation. The effect of the cable-net tension on the antenna truss is discussed and compared with previous publications and a dynamic deployment analysis is performed. Both the simulation and experimental results verify the validity of the method presented.

  14. Dynamic analysis of multirigid-body system based on the Gauss principle

    NASA Astrophysics Data System (ADS)

    Lilov, L.; Lorer, M.

    Two different approaches can be used for solving the basic dynamic problem in the case of a multirigid body system. The first approach is based on the derivation of the nonlinear equations of motion of the mechanical system, while the second approach is concerned with the direct derivation of the unknown accelerations. Using the Gauss principle, the accelerations can be determined by using the condition for the minimum of a functional. The present investigation is concerned with an algorithm for a dynamical study of a multibody system on the basis of the Gauss principle. The system may contain an arbitrary number of closed loops. The main purpose of the proposed algorithm is the investigation of the dynamics of industrial manipulators, robots, and similar mechanisms.

  15. 14 CFR 1251.201 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... OF HANDICAP Employment Practices § 1251.201 Reasonable accommodation. (a) A recipient shall make reasonable accommodation to the known physical or mental limitations of an otherwise qualified handicapped... facilities used by employees readily accessible to and usable by handicapped persons; and (2) Job...

  16. 14 CFR 1251.201 - Reasonable accommodation.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... OF HANDICAP Employment Practices § 1251.201 Reasonable accommodation. (a) A recipient shall make reasonable accommodation to the known physical or mental limitations of an otherwise qualified handicapped... facilities used by employees readily accessible to and usable by handicapped persons; and (2) Job...

  17. 14 CFR 1251.201 - Reasonable accommodation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... OF HANDICAP Employment Practices § 1251.201 Reasonable accommodation. (a) A recipient shall make reasonable accommodation to the known physical or mental limitations of an otherwise qualified handicapped... facilities used by employees readily accessible to and usable by handicapped persons; and (2) Job...

  18. 14 CFR 1251.201 - Reasonable accommodation.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... OF HANDICAP Employment Practices § 1251.201 Reasonable accommodation. (a) A recipient shall make reasonable accommodation to the known physical or mental limitations of an otherwise qualified handicapped... facilities used by employees readily accessible to and usable by handicapped persons; and (2) Job...

  19. Dynamics simulation and controller interfacing for legged robots

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Reichler, J.A.; Delcomyn, F.

    2000-01-01

    Dynamics simulation can play a critical role in the engineering of robotic control code, and there exist a variety of strategies both for building physical models and for interacting with these models. This paper presents an approach to dynamics simulation and controller interfacing for legged robots, and contrasts it to existing approaches. The authors describe dynamics algorithms and contact-resolution strategies for multibody articulated mobile robots based on the decoupled tree-structure approach, and present a novel scripting language that provides a unified framework for control-code interfacing, user-interface design, and data analysis. Special emphasis is placed on facilitating the rapid integration ofmore » control algorithms written in a standard object-oriented language (C++), the production of modular, distributed, reusable controllers, and the use of parameterized signal-transmission properties such as delay, sampling rate, and noise.« less

  20. Experimental investigations of pupil accommodation factors.

    PubMed

    Lee, Eui Chul; Lee, Ji Woo; Park, Kang Ryoung

    2011-08-17

    PURPOSE. The contraction and dilation of the iris muscle that controls the amount of light entering the retina causes pupil accommodation. In this study, experiments were performed and two of the three factors that influence pupil accommodation were analyzed: lighting conditions and depth fixations. The psychological benefits were not examined, because they could not be quantified. METHODS. A head-wearable eyeglasses-based, eye-capturing device was designed to measure pupil size. It included a near-infrared (NIR) camera and an NIR light-emitting diode. Twenty-four subjects watched two-dimensional (2D) and three-dimensional (3D) stereoscopic videos of the same content, and the changes in pupil size were measured by using the eye-capturing device and image-processing methods: RESULTS. The pupil size changed with the intensity of the videos and the disparities between the left and right images of a 3D stereoscopic video. There was correlation between the pupil size and average intensity. The pupil diameter could be estimated as being contracted from approximately 5.96 to 4.25 mm as the intensity varied from 0 to 255. Further, from the changes in the depth fixation for the pupil accommodation, it was confirmed that the depth fixation also affected accommodation of pupil size. CONCLUSIONS. It was confirmed that the lighting condition was an even more significant factor in pupil accommodation than was depth fixation (significance ratio: approximately 3.2:1) when watching 3D stereoscopic video. Pupil accommodation was more affected by depth fixation in the real world than was the binocular convergence in the 3D stereoscopic display.

  1. Overview for Attached Payload Accommodations and Environments

    NASA Technical Reports Server (NTRS)

    Schaffer, Craig; Cook, Gene; Nabizadeh, Rodney; Phillion, James

    2007-01-01

    External payload accommodations are provided at attach sites on the U.S provided ELC, U.S. Truss, the Japanese Experiment Module Exposed Facility (JEM EF) and the Columbus EPF (External Payload Facilities). The Integrated Truss Segment (ITS) provides the backbone structure for the ISS. It attaches the solar and thermal control arrays to the rest of the complex, and houses cable distribution trays Extravehicular Activity (EVA) support equipment such as handholds and lighting; and providing for Extravehicular Robotic (EVR) accommodations using the Mobile Servicing System (MSS). It also provides logistics and maintenance, and payload attachment sites. The attachment sites accommodate logistics and maintenance and payloads carriers, zenith and nadir. The JEM-EF, a back porch-like attachment to the JEM Pressurized Module, accommodates up to eight payloads, which can be serviced by the crew via the JEM PM's airlock and dedicated robotic arm. The Columbus-EPF is another porch-like platform that can accommodate two zenith and two nadir looking payloads.

  2. Combining the Vortex Particle-Mesh method with a Multi-Body System solver for the simulation of self-propelled articulated swimmers

    NASA Astrophysics Data System (ADS)

    Bernier, Caroline; Gazzola, Mattia; Ronsse, Renaud; Chatelain, Philippe

    2017-11-01

    We present a 2D fluid-structure interaction simulation method with a specific focus on articulated and actuated structures. The proposed algorithm combines a viscous Vortex Particle-Mesh (VPM) method based on a penalization technique and a Multi-Body System (MBS) solver. The hydrodynamic forces and moments acting on the structure parts are not computed explicitly from the surface stresses; they are rather recovered from the projection and penalization steps within the VPM method. The MBS solver accounts for the body dynamics via the Euler-Lagrange formalism. The deformations of the structure are dictated by the hydrodynamic efforts and actuation torques. Here, we focus on simplified swimming structures composed of neutrally buoyant ellipses connected by virtual joints. The joints are actuated through a simple controller in order to reproduce the swimming patterns of an eel-like swimmer. The method enables to recover the histories of torques applied on each hinge along the body. The method is verified on several benchmarks: an impulsively started elastically mounted cylinder and free swimming articulated fish-like structures. Validation will be performed by means of an experimental swimming robot that reproduces the 2D articulated ellipses.

  3. Appropriate Accommodations for Individual Needs Allowable by State Guidelines

    ERIC Educational Resources Information Center

    Jordan, Ashley Sokol

    2009-01-01

    Accommodation decisions should be based on the validity and accountability to provide the least restrictive accommodations for students with learning disabilities. Accommodations are based upon the allowable guidelines set by the Ohio Department of Education but the scribing accommodations do not meet the least restrictive criteria for many…

  4. New EEOC guidance details responsibilities for job accommodation.

    PubMed

    1999-04-02

    The Equal Employment Opportunity Commission (EEOC) released new guidelines on how employers should accommodate the needs of workers with disabilities. Guidelines address using leave as an accommodation, the duty of offering reassignment as a form of reasonable accommodation, and an employer's cost of accommodation. Among the clarifications, the EEOC states that employers do not have to provide more paid leave than workers in similar situations receive. Employees must be qualified for reassignments, and the employer is not obligated to provide training for the new position. The EEOC disagrees with the Americans with Disabilities Act reasoning that employers should not be forced to accommodate if a cost-benefit analysis reveals undue hardship on the employer. Contact information is provided.

  5. 46 CFR 177.810 - Overnight accommodations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... TONS) CONSTRUCTION AND ARRANGEMENT Passenger Accommodations § 177.810 Overnight accommodations. (a) A... three high and must be constructed of wood, fiber reinforced plastic, or metal. A berth located more... construction and arrangement of berths and other furniture must allow free and unobstructed access to each...

  6. 10 CFR 1040.67 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... known physical or mental limitations of an otherwise qualified handicapped applicant or employee unless the recipient can demonstrate that the accommodation would impose an undue hardship on the operation... accommodation would impose an undue hardship on the operation of a recipient's program or activity, factors to...

  7. 45 CFR 84.12 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... physical or mental limitations of an otherwise qualified handicapped applicant or employee unless the recipient can demonstrate that the accommodation would impose an undue hardship on the operation of its... an accommodation would impose an undue hardship on the operation of a recipient's program or activity...

  8. 45 CFR 1232.10 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... shall make reasonable accommodation to the known physical or mental limitations of an otherwise... accommodation would impose an undue hardship on the operation of its program or activity. (b) Reasonable... would impose an undue hardship on the operation of a recipient's program or activity, factors to be...

  9. 10 CFR 4.123 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... shall make reasonable accommodation to the known physical or mental limitations of an otherwise... would impose an undue hardship on the operation of its program or activity. (b) Reasonable accommodation... on the operation of a recipient's program or activity, factors to be considered include: (1) The...

  10. [Comparison study on subjective and objective measurements of the accommodative convergence to accommodation ratio].

    PubMed

    Xu, Jing-jing; Xu, Dan; Huang, Tao; Jiang, Jian; Lü, Fan

    2012-05-01

    To detect the accommodative convergence to accommodation (AC/A) ratios measured respectively by objective and subjective methods. The differences and its relative factors were explored. Forty young volunteers were measured by eye tracker to get the amount of convergence when fixating at the target at 100 cm, 50 cm, 33 cm and 25 cm and were measured by infrared auto-refractor to get corresponding accommodative responses. AC/A ratio based on these two measurements were compared with the calculated and the gradient AC/A ratio from Von Graefe tests. Mean value of stimulated AC/A ratio measured by eye tracker was higher than the calculated and gradient AC/A ratio by Von Graefe method (P = 0.003, 0.001). There are statistic correlation (r = 0.871, P = 0.000) and difference (P = 0.000) between stimulated AC/A ratio and response AC/A ratios both measured by eye tracker, and the difference trends to be greater with the higher AC/A ratio. The objective AC/A ratio is usually higher than the clinical subjective measurement because of more proximal effect. The response AC/A ratio measured objectively may reveal realistically the mutual effect and relationship between accommodation and convergence and it seems to be more credible to be the monitor parameter on progression of myopia in clinics.

  11. 46 CFR 108.197 - Construction of accommodation spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Construction of accommodation spaces. 108.197 Section... UNITS DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.197 Construction of accommodation spaces. (a) Each sleeping, mess, recreational, or hospital space that is adjacent to or...

  12. 46 CFR 108.197 - Construction of accommodation spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Construction of accommodation spaces. 108.197 Section... UNITS DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.197 Construction of accommodation spaces. (a) Each sleeping, mess, recreational, or hospital space that is adjacent to or...

  13. 46 CFR 108.197 - Construction of accommodation spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Construction of accommodation spaces. 108.197 Section... UNITS DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.197 Construction of accommodation spaces. (a) Each sleeping, mess, recreational, or hospital space that is adjacent to or...

  14. 46 CFR 108.197 - Construction of accommodation spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Construction of accommodation spaces. 108.197 Section... UNITS DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.197 Construction of accommodation spaces. (a) Each sleeping, mess, recreational, or hospital space that is adjacent to or...

  15. 46 CFR 108.197 - Construction of accommodation spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Construction of accommodation spaces. 108.197 Section... UNITS DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.197 Construction of accommodation spaces. (a) Each sleeping, mess, recreational, or hospital space that is adjacent to or...

  16. Minus-Lens–Stimulated Accommodative Amplitude Decreases Sigmoidally with Age: A Study of Objectively Measured Accommodative Amplitudes from Age 3

    PubMed Central

    Anderson, Heather A.; Hentz, Gloria; Glasser, Adrian; Stuebing, Karla K.; Manny, Ruth E.

    2009-01-01

    Purpose Guidelines for predicting accommodative amplitude by age are often based on subjective push-up test data that overestimate the accommodative response. Studies in which objective measurements were used have defined expected amplitudes for adults, but expected amplitudes for children remain unknown. In this study, objective methods were used to measure accommodative amplitude in a wide age range of individuals, to define the relationship of amplitude and age from age 3. Methods Accommodative responses were measured in 140 subjects aged 3 to 40 years. Measurements were taken with the Grand Seiko autorefractor (RyuSyo Industrial Co., Ltd., Kagawa, Japan) as the subjects viewed a high-contrast target at 33 cm through minus lenses of increasing power until the responses showed no further increase in accommodation. Results The maximum accommodative amplitude of each subject was plotted by age, and a curvilinear function fit to the data: y = 7.33 − 0.0035(age − 3)2 (P < 0.001). Tangent analysis of the fit indicated that the accommodative amplitude remained relatively stable until age 20. Data from this study were then pooled with objective amplitudes from previous studies of adults up to age 70. A sigmoidal function was fit to the data: y = 7.083/(1 + e[0.2031(age-36.2)−0.6109]) (P < 0.001). The sigmoidal function indicated relatively stable amplitudes below age 20 years, a rapid linear decline between 20 and 50 years, and a taper to 0 beyond 50 years. Conclusions These data indicate that accommodative amplitude decreases in a curvilinear manner from 3 to 40 years. When combined with data from previous studies, a sigmoidal function describes the overall trend throughout life with the biggest decrease occurring between 20 and 50 years. PMID:18326693

  17. Long-term follow-up of acute isolated accommodation insufficiency.

    PubMed

    Lee, Jung Jin; Baek, Seung-Hee; Kim, Ungsoo Samuel

    2013-04-01

    To define the long-term results of accommodation insufficiency and to investigate the correlation between accommodation insufficiency and other factors including near point of convergence (NPC), age, and refractive errors. From January 2008 to December 2009, 11 patients with acute near vision disturbance and remote near point of accommodation (NPA) were evaluated. Full ophthalmologic examinations, including best corrected visual acuity, manifest refraction and prism cover tests were performed. Accommodation ability was measured by NPA using the push-up method. We compared accommodation insufficiency and factors including age, refractive errors and NPC. We also investigated the recovery from loss of accommodation in patients. Mean age of patients was 20 years (range, 9 to 34 years). Five of the 11 patients were female. Mean refractive error was -0.6 diopters (range, -3.5 to +0.25 diopters) and 8 of 11 patients (73%) had emmetropia (+0.50 to -0.50 diopters). No abnormalities were found in brain imaging tests. Refractive errors were not correlated with NPA or NPC (rho = 0.148, p = 0.511; rho = 0.319, p = 0.339; respectively). The correlation between age and NPA was not significant (rho = -395, p = 0.069). However, the correlation between age and NPC was negative (rho = -0.508, p = 0.016). Three of 11 patients were lost to follow-up, and 6 of 8 patients had permanent insufficiency of accommodation. Accommodation insufficiency is most common in emmetropia, however, refractive errors and age are not correlated with accommodation insufficiency. Dysfunction of accommodation can be permanent in the isolated accommodation insufficiency.

  18. Long-term Follow-up of Acute Isolated Accommodation Insufficiency

    PubMed Central

    Lee, Jung Jin; Baek, Seung-Hee

    2013-01-01

    Purpose To define the long-term results of accommodation insufficiency and to investigate the correlation between accommodation insufficiency and other factors including near point of convergence (NPC), age, and refractive errors. Methods From January 2008 to December 2009, 11 patients with acute near vision disturbance and remote near point of accommodation (NPA) were evaluated. Full ophthalmologic examinations, including best corrected visual acuity, manifest refraction and prism cover tests were performed. Accommodation ability was measured by NPA using the push-up method. We compared accommodation insufficiency and factors including age, refractive errors and NPC. We also investigated the recovery from loss of accommodation in patients. Results Mean age of patients was 20 years (range, 9 to 34 years). Five of the 11 patients were female. Mean refractive error was -0.6 diopters (range, -3.5 to +0.25 diopters) and 8 of 11 patients (73%) had emmetropia (+0.50 to -0.50 diopters). No abnormalities were found in brain imaging tests. Refractive errors were not correlated with NPA or NPC (rho = 0.148, p = 0.511; rho = 0.319, p = 0.339; respectively). The correlation between age and NPA was not significant (rho = -395, p = 0.069). However, the correlation between age and NPC was negative (rho = -0.508, p = 0.016). Three of 11 patients were lost to follow-up, and 6 of 8 patients had permanent insufficiency of accommodation. Conclusions Accommodation insufficiency is most common in emmetropia, however, refractive errors and age are not correlated with accommodation insufficiency. Dysfunction of accommodation can be permanent in the isolated accommodation insufficiency. PMID:23543051

  19. Accommodation training in foreign workers.

    PubMed

    Takada, Masumi; Miyao, Masaru; Matsuura, Yasuyuki; Takada, Hiroki

    2013-01-01

    By relaxing the contracted focus-adjustment muscles around the eyeball, known as the ciliary and extraocular muscles, the degree of pseudomyopia can be reduced. This understanding has led to accommodation training in which a visual target is presented in stereoscopic video clips. However, it has been pointed out that motion sickness can be induced by viewing stereoscopic video clips. In Measurement 1 of the present study, we verified whether the new 3D technology reduced the severity of motion sickness in accordance with stabilometry. We then evaluated the short-term effects of accommodation training using new stereoscopic video clips on foreign workers (11 females) suffering from eye fatigue in Measurement 2. The foreign workers were trained for three days. As a result, visual acuity was statistically improved by continuous accommodation training, which will help promote ciliary muscle stretching.

  20. 38 CFR 18.412 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... known physical or mental limitations of a handicapped applicant or employee if such accommodation would... that the accommodation would impose an undue hardship on the operation of its program or activity. (b... impose an undue hardship on the operation of a recipient's program or activity, factors to be considered...

  1. Accommodation Outcomes and the ICF Framework

    ERIC Educational Resources Information Center

    Schreuer, Naomi

    2009-01-01

    Accommodation of the environment and technology is one of the key mediators of adjustment to disability and participation in community. In this article, accommodations are tested empirically as facilitators of return to work and participation, as defined by the "International Classification of Disability, Function, and Health" (ICF) and…

  2. Beyond Psychometric Evaluation of the Student--Task Determinants of Accommodation: Why Students with Learning Disabilities May Not Need to Be Accommodated

    ERIC Educational Resources Information Center

    Roberts, Barbara L.

    2012-01-01

    Students with learning disabilities obtain a wide range of recommended accommodations in secondary school, which they anticipate will continue into postsecondary education. Although the student's specific learning disability (SLD) contributes to the accommodation planning process, it is not the sole determinant of appropriate accommodation.…

  3. Stress stiffening and approximate equations in flexible multibody dynamics

    NASA Technical Reports Server (NTRS)

    Padilla, Carlos E.; Vonflotow, Andreas H.

    1993-01-01

    A useful model for open chains of flexible bodies undergoing large rigid body motions, but small elastic deformations, is one in which the equations of motion are linearized in the small elastic deformations and deformation rates. For slow rigid body motions, the correctly linearized, or consistent, set of equations can be compared to prematurely linearized, or inconsistent, equations and to 'oversimplified,' or ruthless, equations through the use of open loop dynamic simulations. It has been shown that the inconsistent model should never be used, while the ruthless model should be used whenever possible. The consistent and inconsistent models differ by stress stiffening terms. These are due to zeroth-order stresses effecting virtual work via nonlinear strain-displacement terms. In this paper we examine in detail the nature of these stress stiffening terms and conclude that they are significant only when the associated zeroth-order stresses approach 'buckling' stresses. Finally it is emphasized that when the stress stiffening terms are negligible the ruthlessly linearized equations should be used.

  4. Job Accommodation System: Project TIE (Technology in Employment).

    ERIC Educational Resources Information Center

    Roberts, Gary; Zimbrich, Karen; Butterworth, John; Hart, Debra

    This manual presents a comprehensive evaluation tool that can be used by employees with disabilities, by rehabilitation practitioners, and by consultants to develop job accommodations in a variety of employment settings. The Job Accommodation System is designed to help in identifying, selecting, and implementing job accommodations and consists of…

  5. [Accommodation to monochromatic targets in people with different color vision statuses].

    PubMed

    Qian, Yishan; Huang, Jia; Chu, Renyuan

    2015-01-01

    To compare the accommodation response (AR) to monochromatic targets in subjects with different color vision statuses, and to investigate the role of color vision in the control of accommodation and emmetropization. It was a case-control study. Accommodation was measured with a dynamic infrared optometer while subjects [17 protans, 47 deutans, and 23 normals; mean age: (20.0 ± 4.4) years] viewed a (1) red on black or (2) green on black vertical square-wave gratings of iso-luminance (3 cycles/deg; 0.9 contrast) in a Badal optic system. The grating stepped 1.00 D towards the eye from an initial position of 0 D until 5.00 D. With red-black targets, the AR in the protans (AR = 1.98 D) was worse than that in the normals (AR = 2.55 D) when the accommodation stimulus (AS) was 4.00 D (LSD, P = 0.031). The AR in the deutans were worse than that in the normals when the AS was 3.00, 4.00, and 5.00 D (3.00 D: 1.23 D vs. 1.69 D, P = 0.002; 4.00 D: 1.89 D vs. 2.55 D, P = 0.002; 5.00 D: 2.40 D vs. 3.17 D, P = 0.003). With green-black targets, the AR in the protans were worse than that in the normals when the AS was 3.00 and 4.00 D (3.00 D: 1.13 D vs. 1.61 D, P = 0.004; 4.00 D: 1.80 D vs. 2.34 D, P = 0.021). In the deutans, the AR was worse with stimuli of 3.00, 4.00, and 5.00 D (3.00 D: 1.21 D vs. 1.61 D, P = 0.003; 4.00 D: 1.65 D vs. 2.34 D, P < 0.001; 5.00 D: 2.36 D vs. 2.93 D, P = 0.007). No significant differences between the protans and deutans were found for all the stimulus conditions. In the protans, accommodation to red-black targets was better than that to green-black targets when the stimulus was 2.00, 3.00, and 5.00 D (2.00 D: t = -2.81, P = 0.013; 3.00 D: t = -4.55, P < 0.001; 5.00 D: t = -3.15, P = 0.006). In the deutans, accommodation to red-black targets was better than that to green-black targets when the stimulus was 4.00 D (t = -2.19, P = 0.034). In the normals, accommodation to red-black targets were better than that to green-black targets when the stimulus

  6. Accommodations Manual: How to Select, Administer, and Evaluate Use of Accommodations for Instruction and Assessment of Students with Disabilities. Third Edition

    ERIC Educational Resources Information Center

    Christensen, L.; Carver, W.; VanDeZande, J.; Lazarus, S.

    2011-01-01

    The Council of Chief State School Officers' "Accommodations Manual: How to Select, Administer, and Evaluate the Use of Accommodations for Instruction and Assessment of Students with Disabilities" was first developed to establish guidelines for states to use for the selection, administration, and evaluation of accommodations for…

  7. Lenticular accommodation in relation to ametropia: the chick model.

    PubMed

    Choh, Vivian; Sivak, Jacob G

    2005-03-04

    Our goal was to determine whether experimentally induced ametropias have an effect on lenticular accommodation and spherical aberration. Form-deprivation myopia and hyperopia were induced in one eye of hatchling chicks by application of a translucent goggle and +15 D lens, respectively. After 7 days, eyes were enucleated and lenses were optically scanned prior to accommodation, during accommodation, and after accommodation. Accommodation was induced by electrical stimulation of the ciliary nerve. Lenticular focal lengths for form-deprived eyes were significantly shorter than for their controls and accommodation-associated changes in focal length were significantly smaller in myopic eyes compared to their controls. For eyes imposed with +15 D blur, focal lengths were longer than those for their controls and accommodative changes were greater. Spherical aberration of the lens increased with accommodation in both form-deprived and lens-treated birds, but induction of ametropia had no effect on lenticular spherical aberration in general. Nonmonotonicity from lenticular spherical aberration increased during accommodation but effects of refractive error were equivocal. The crystalline lens contributes to refractive error changes of the eye both in the case of myopia and hyperopia. These changes are likely attributable to global changes in the size and shape of the eye.

  8. Transitions: Times of Change and Accommodation.

    ERIC Educational Resources Information Center

    Rice, Mabel L.; O'Brien, Marion

    1990-01-01

    The research literature is reviewed for transitions from birth to eight years. A model describes transition as a change in ecocultural niche, requiring accommodations in daily routines for a child, family, and service providers and transition impact measures the number of accommodations required and the sustainability of daily routines.…

  9. Real-space finite-difference approach for multi-body systems: path-integral renormalization group method and direct energy minimization method.

    PubMed

    Sasaki, Akira; Kojo, Masashi; Hirose, Kikuji; Goto, Hidekazu

    2011-11-02

    The path-integral renormalization group and direct energy minimization method of practical first-principles electronic structure calculations for multi-body systems within the framework of the real-space finite-difference scheme are introduced. These two methods can handle higher dimensional systems with consideration of the correlation effect. Furthermore, they can be easily extended to the multicomponent quantum systems which contain more than two kinds of quantum particles. The key to the present methods is employing linear combinations of nonorthogonal Slater determinants (SDs) as multi-body wavefunctions. As one of the noticeable results, the same accuracy as the variational Monte Carlo method is achieved with a few SDs. This enables us to study the entire ground state consisting of electrons and nuclei without the need to use the Born-Oppenheimer approximation. Recent activities on methodological developments aiming towards practical calculations such as the implementation of auxiliary field for Coulombic interaction, the treatment of the kinetic operator in imaginary-time evolutions, the time-saving double-grid technique for bare-Coulomb atomic potentials and the optimization scheme for minimizing the total-energy functional are also introduced. As test examples, the total energy of the hydrogen molecule, the atomic configuration of the methylene and the electronic structures of two-dimensional quantum dots are calculated, and the accuracy, availability and possibility of the present methods are demonstrated.

  10. Momentum-Based Dynamics for Spacecraft with Chained Revolute Appendages

    NASA Technical Reports Server (NTRS)

    Queen, Steven; London, Ken; Gonzalez, Marcelo

    2005-01-01

    An efficient formulation is presented for a sub-class of multi-body dynamics problems that involve a six degree-of-freedom base body and a chain of N rigid linkages connected in series by single degree-of-freedom revolute joints. This general method is particularly well suited for simulations of spacecraft dynamics and control that include the modeling of an orbiting platform with or without internal degrees of freedom such as reaction wheels, dampers, and/or booms. In the present work, particular emphasis is placed on dynamic simulation of multi-linkage robotic manipulators. The differential equations of motion are explicitly given in terms of linear and angular momentum states, which can be evaluated recursively along a serial chain of linkages for an efficient real-time solution on par with the best of the O(N3) methods.

  11. The Use of IMMUs in a Water Environment: Instrument Validation and Application of 3D Multi-Body Kinematic Analysis in Medicine and Sport

    PubMed Central

    Mangia, Anna Lisa; Cortesi, Matteo; Fantozzi, Silvia; Giovanardi, Andrea; Borra, Davide; Gatta, Giorgio

    2017-01-01

    The aims of the present study were the instrumental validation of inertial-magnetic measurements units (IMMUs) in water, and the description of their use in clinical and sports aquatic applications applying customized 3D multi-body models. Firstly, several tests were performed to map the magnetic field in the swimming pool and to identify the best volume for experimental test acquisition with a mean dynamic orientation error lower than 5°. Successively, the gait and the swimming analyses were explored in terms of spatiotemporal and joint kinematics variables. The extraction of only spatiotemporal parameters highlighted several critical issues and the joint kinematic information has shown to be an added value for both rehabilitative and sport training purposes. Furthermore, 3D joint kinematics applied using the IMMUs provided similar quantitative information than that of more expensive and bulky systems but with a simpler and faster setup preparation, a lower time consuming processing phase, as well as the possibility to record and analyze a higher number of strides/strokes without limitations imposed by the cameras. PMID:28441739

  12. The Use of IMMUs in a Water Environment: Instrument Validation and Application of 3D Multi-Body Kinematic Analysis in Medicine and Sport.

    PubMed

    Mangia, Anna Lisa; Cortesi, Matteo; Fantozzi, Silvia; Giovanardi, Andrea; Borra, Davide; Gatta, Giorgio

    2017-04-22

    The aims of the present study were the instrumental validation of inertial-magnetic measurements units (IMMUs) in water, and the description of their use in clinical and sports aquatic applications applying customized 3D multi-body models. Firstly, several tests were performed to map the magnetic field in the swimming pool and to identify the best volume for experimental test acquisition with a mean dynamic orientation error lower than 5°. Successively, the gait and the swimming analyses were explored in terms of spatiotemporal and joint kinematics variables. The extraction of only spatiotemporal parameters highlighted several critical issues and the joint kinematic information has shown to be an added value for both rehabilitative and sport training purposes. Furthermore, 3D joint kinematics applied using the IMMUs provided similar quantitative information than that of more expensive and bulky systems but with a simpler and faster setup preparation, a lower time consuming processing phase, as well as the possibility to record and analyze a higher number of strides/strokes without limitations imposed by the cameras.

  13. Stabilization of computational procedures for constrained dynamical systems

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Chiou, J. C.

    1988-01-01

    A new stabilization method of treating constraints in multibody dynamical systems is presented. By tailoring a penalty form of the constraint equations, the method achieves stabilization without artificial damping and yields a companion matrix differential equation for the constraint forces; hence, the constraint forces are obtained by integrating the companion differential equation for the constraint forces in time. A principal feature of the method is that the errors committed in each constraint condition decay with its corresponding characteristic time scale associated with its constraint force. Numerical experiments indicate that the method yields a marked improvement over existing techniques.

  14. A painless and constraint-free method to estimate viscoelastic passive dynamics of limbs' joints to support diagnosis of neuromuscular diseases.

    PubMed

    Venture, Gentiane; Nakamura, Yoshihiko; Yamane, Katsu; Hirashima, Masaya

    2007-01-01

    Though seldom identified, the human joints dynamics is important in the fields of medical robotics and medical research. We present a general solution to estimate in-vivo and simultaneously the passive dynamics of the human limbs' joints. It is based on the use of the multi-body description of the human body and its kinematics and dynamics computations. The linear passive joint dynamics of the shoulders and the elbows: stiffness, viscosity and friction, is estimated simultaneously using the linear least squares method. Acquisition of movements is achieved with an optical motion capture studio on one examinee during the clinical diagnosis of neuromuscular diseases. Experimental results are given and discussed.

  15. A Case Study of Dynamic Response Analysis and Safety Assessment for a Suspended Monorail System

    PubMed Central

    Bao, Yulong; Li, Yongle; Ding, Jiajie

    2016-01-01

    A suspended monorail transit system is a category of urban rail transit, which is effective in alleviating traffic pressure and injury prevention. Meanwhile, with the advantages of low cost and short construction time, suspended monorail transit systems show vast potential for future development. However, the suspended monorail has not been systematically studied in China, and there is a lack of relevant knowledge and analytical methods. To ensure the health and reliability of a suspended monorail transit system, the driving safety of vehicles and structure dynamic behaviors when vehicles are running on the bridge should be analyzed and evaluated. Based on the method of vehicle-bridge coupling vibration theory, the finite element method (FEM) software ANSYS and multi-body dynamics software SIMPACK are adopted respectively to establish the finite element model for bridge and the multi-body vehicle. A co-simulation method is employed to investigate the vehicle-bridge coupling vibration for the transit system. The traffic operation factors, including train formation, track irregularity and tire stiffness, are incorporated into the models separately to analyze the bridge and vehicle responses. The results show that the coupling of dynamic effects of the suspended monorail system between vehicle and bridge are significant in the case studied, and it is strongly suggested to take necessary measures for vibration suppression. The simulation of track irregularity is a critical factor for its vibration safety, and the track irregularity of A-level road roughness negatively influences the system vibration safety. PMID:27834923

  16. A Case Study of Dynamic Response Analysis and Safety Assessment for a Suspended Monorail System.

    PubMed

    Bao, Yulong; Li, Yongle; Ding, Jiajie

    2016-11-10

    A suspended monorail transit system is a category of urban rail transit, which is effective in alleviating traffic pressure and injury prevention. Meanwhile, with the advantages of low cost and short construction time, suspended monorail transit systems show vast potential for future development. However, the suspended monorail has not been systematically studied in China, and there is a lack of relevant knowledge and analytical methods. To ensure the health and reliability of a suspended monorail transit system, the driving safety of vehicles and structure dynamic behaviors when vehicles are running on the bridge should be analyzed and evaluated. Based on the method of vehicle-bridge coupling vibration theory, the finite element method (FEM) software ANSYS and multi-body dynamics software SIMPACK are adopted respectively to establish the finite element model for bridge and the multi-body vehicle. A co-simulation method is employed to investigate the vehicle-bridge coupling vibration for the transit system. The traffic operation factors, including train formation, track irregularity and tire stiffness, are incorporated into the models separately to analyze the bridge and vehicle responses. The results show that the coupling of dynamic effects of the suspended monorail system between vehicle and bridge are significant in the case studied, and it is strongly suggested to take necessary measures for vibration suppression. The simulation of track irregularity is a critical factor for its vibration safety, and the track irregularity of A-level road roughness negatively influences the system vibration safety.

  17. Maternal emotion regulation during child distress, child anxiety accommodation, and links between maternal and child anxiety.

    PubMed

    Kerns, Caroline E; Pincus, Donna B; McLaughlin, Katie A; Comer, Jonathan S

    2017-08-01

    Environmental contributions are thought to play a primary role in the familial aggregation of anxiety, but parenting influences remain poorly understood. We examined dynamic relations between maternal anxiety, maternal emotion regulation (ER) during child distress, maternal accommodation of child distress, and child anxiety. Mothers (N=45) of youth ages 3-8 years (M=4.8) participated in an experimental task during which they listened to a standardized audio recording of a child in anxious distress pleading for parental intervention. Measures of maternal and child anxiety, mothers' affective states, mothers' ER strategies during the child distress, and maternal accommodation of child anxiety were collected. Mothers' resting respiratory sinus arrhythmia (RSA) reactivity during the recording was also acquired. Higher maternal negative affect and greater maternal ER switching (i.e., using multiple ER strategies in a short time without positive regulatory results) during child distress were associated with child anxiety. Sequential mediation modeling showed that maternal anxiety predicted ineffective maternal ER during child distress exposure, which in turn predicted greater maternal accommodation, which in turn predicted higher child anxiety. Findings support the mediating roles of maternal ER and accommodation in linking maternal and child anxiety, and suggest that ineffective maternal ER and subsequent attempts to accommodate child distress may act as mechanisms underlying the familial aggregation of anxiety. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Phacoemulsification and implantation of an accommodating IOL after PRK.

    PubMed

    Aslanides, loannis M; Plainis, Sotiris; Kumar, Vinod; Ginis, Harilaos

    2006-01-01

    To present a case of phacoemulsification and implantation of an accommodating intraocular lens (IOL) in a patient with cataract formation after previous refractive surgery. A 50-year-old man, who initially had photorefractive keratectomy to correct moderate myopia, developed a cataract in one eye. He subsequently underwent phacoemulsification and implantation of a 1CU accommodating IOL, as he wished to remain spectacle independent. The patient's distance vision was fully restored. However, accommodative function, which was assessed using subjective and novice objective techniques, was only partially restored. Although the accommodating IOL fully restored the patient's distance vision, accommodative function was only partially restored.

  19. Framing Appropriate Accommodations in Terms of Individual Need: Examining the Fit of Four Approaches to Selecting Test Accommodations of English Language Learners

    ERIC Educational Resources Information Center

    Koran, Jennifer; Kopriva, Rebecca J.

    2017-01-01

    Providing appropriate test accommodations to most English language learners (ELLs) is important to facilitate meaningful inferences about learning. This study compared teacher large-scale test accommodation recommendations to those from a literature- and practitioner-grounded accommodation selection taxonomy. The taxonomy links student-specific…

  20. Investigation of solid plume simulation criteria to produce flight plume effects on multibody configuration in wind tunnel tests

    NASA Technical Reports Server (NTRS)

    Frost, A. L.; Dill, C. C.

    1986-01-01

    An investigation to determine the sensitivity of the space shuttle base and forebody aerodynamics to the size and shape of various solid plume simulators was conducted. Families of cones of varying angle and base diameter, at various axial positions behind a Space Shuttle launch vehicle model, were wind tunnel tested. This parametric evaluation yielded base pressure and force coefficient data which indicated that solid plume simulators are an inexpensive, quick method of approximating the effect of engine exhaust plumes on the base and forebody aerodynamics of future, complex multibody launch vehicles.

  1. Bearing-Mounting Concept Accommodates Thermal Expansion

    NASA Technical Reports Server (NTRS)

    Nespodzany, Robert; Davis, Toren S.

    1995-01-01

    Pins or splines allow radial expansion without slippage. Design concept for mounting rotary bearing accommodates differential thermal expansion between bearing and any structure(s) to which bearing connected. Prevents buildup of thermal stresses by allowing thermal expansion to occur freely but accommodating expansion in such way not to introduce looseness. Pin-in-slot configuration also maintains concentricity.

  2. Corneal changes with accommodation using dual Scheimpflug photography.

    PubMed

    Sisó-Fuertes, Irene; Domínguez-Vicent, Alberto; del Águila-Carrasco, Antonio; Ferrer-Blasco, Teresa; Montés-Micó, Robert

    2015-05-01

    To assess whether corneal parameters and aberrations are affected by accommodation. Optics Department, University of Valencia, Valencia, Spain. Prospective cross-sectional study. The Galilei G4 dual Scheimpflug device was used to obtain data on the anterior and posterior axial curvatures, total corneal power (TCP), and corneal pachymetry from 3 corneal zones (central: 0.0 up to 4.0 mm; paracentral or mid: 4.0 up to 7.0 mm; peripheral: 7.0 up to 10.0 mm) in young emmetropic eyes in the unaccommodated and 4 accommodated states (from -1.0 to -4.0 diopters [D] in 1.0 D steps). The 2nd-, 3rd-, and 4th-order aberrations as well as the root mean square (RMS) were also determined for the entire cornea at the same accommodative demands. The study evaluated 7 subjects (12 eyes). No significant changes in any measured parameter were found during accommodation for any corneal zone (P > .05). Statistically significant differences were found in the various corneal zones when it was assumed they were constant with accommodation (P < .01). A stable linear trend with accommodation was also found for corneal aberrations, although individual variations existed because of the high standard deviation values. Different parameters in various zones of the cornea as well as corneal aberrations were stable during accommodation. Crown Copyright © 2015. Published by Elsevier Inc. All rights reserved.

  3. What Works? Toward a New Classification System for Mental Health Supported Accommodation Services: The Simple Taxonomy for Supported Accommodation (STAX-SA)

    PubMed Central

    McPherson, Peter; Krotofil, Joanna

    2018-01-01

    Inconsistent terminology and variation in service models have made synthesis of the supported accommodation literature challenging. To overcome this, we developed a brief, categorical taxonomy that aimed to capture the defining features of different supported accommodation models: the simple taxonomy for supported accommodation (STAX-SA). Data from a previous review of existing classification systems were used to develop the taxonomy structure. After initial testing and amendments, the STAX-SA and an existing taxonomy were applied to 132 supported accommodation service descriptions drawn from two systematic reviews and their performance compared. To assess external validity, the STAX-SA was distributed to a sample of supported accommodation managers in England and they were asked to use it to classify their services. The final version of the STAX-SA comprised of five supported accommodation ‘types’, based on four domains; Staffing location; Level of support; Emphasis on move-on; and Physical setting. The STAX-SA accurately categorized 71.1% (n = 94) of service descriptions, outperforming the comparison tool, and was not affected by publication date or research design. The STAX-SA effectively discriminated between ‘real world’ service models in England and 53.2% (n = 17) of service managers indicated that the taxonomy was ‘Very effective’ or ‘Extremely effective’ in capturing key characteristics of their service. The STAX-SA is an effective tool for classifying supported accommodation models and represents a promising approach to synthesizing the extant effectiveness literature. The authors recommend the development of reporting guidelines for future supported accommodation publications to facilitate comparison between models. PMID:29364171

  4. What Works? Toward a New Classification System for Mental Health Supported Accommodation Services: The Simple Taxonomy for Supported Accommodation (STAX-SA).

    PubMed

    McPherson, Peter; Krotofil, Joanna; Killaspy, Helen

    2018-01-24

    Inconsistent terminology and variation in service models have made synthesis of the supported accommodation literature challenging. To overcome this, we developed a brief, categorical taxonomy that aimed to capture the defining features of different supported accommodation models: the simple taxonomy for supported accommodation (STAX-SA). Data from a previous review of existing classification systems were used to develop the taxonomy structure. After initial testing and amendments, the STAX-SA and an existing taxonomy were applied to 132 supported accommodation service descriptions drawn from two systematic reviews and their performance compared. To assess external validity, the STAX-SA was distributed to a sample of supported accommodation managers in England and they were asked to use it to classify their services. The final version of the STAX-SA comprised of five supported accommodation 'types', based on four domains; Staffing location ; Level of support ; Emphasis on move-on ; and Physical setting . The STAX-SA accurately categorized 71.1% ( n = 94) of service descriptions, outperforming the comparison tool, and was not affected by publication date or research design. The STAX-SA effectively discriminated between 'real world' service models in England and 53.2% ( n = 17) of service managers indicated that the taxonomy was ' Very effective ' or ' Extremely effective ' in capturing key characteristics of their service. The STAX-SA is an effective tool for classifying supported accommodation models and represents a promising approach to synthesizing the extant effectiveness literature. The authors recommend the development of reporting guidelines for future supported accommodation publications to facilitate comparison between models.

  5. Functional spasm of accommodation: Changes on scheimpflug imaging

    PubMed Central

    Sukhija, Jaspreet; Dogra, Mangat R.; Zadeng, Thara; Ram, Jagat

    2014-01-01

    Spasm of accommodation is a rare condition characterized by a sudden increase in myopia. It can occur in emmetropes, hypermetropes and myopes. All the physiological changes that occur in normal accommodation are exaggerated. Mostly the cause is functional disorder and the condition gradually improves. We hereby present the changes occurring in spasm of accommodation as seen on Scheimpflug imaging. PMID:25378883

  6. Fault Accommodation in Control of Flexible Systems

    NASA Technical Reports Server (NTRS)

    Maghami, Peiman G.; Sparks, Dean W., Jr.; Lim, Kyong B.

    1998-01-01

    New synthesis techniques for the design of fault accommodating controllers for flexible systems are developed. Three robust control design strategies, static dissipative, dynamic dissipative and mu-synthesis, are used in the approach. The approach provides techniques for designing controllers that maximize, in some sense, the tolerance of the closed-loop system against faults in actuators and sensors, while guaranteeing performance robustness at a specified performance level, measured in terms of the proximity of the closed-loop poles to the imaginary axis (the degree of stability). For dissipative control designs, nonlinear programming is employed to synthesize the controllers, whereas in mu-synthesis, the traditional D-K iteration is used. To demonstrate the feasibility of the proposed techniques, they are applied to the control design of a structural model of a flexible laboratory test structure.

  7. A lateral dynamics of a wheelchair: identification and analysis of tire parameters.

    PubMed

    Silva, L C A; Corrêa, F C; Eckert, J J; Santiciolli, F M; Dedini, F G

    2017-02-01

    In vehicle dynamics studies, the tire behaviour plays an important role in planar motion of the vehicle. Therefore, a correct representation of tire is a necessity. This paper describes a mathematical model for wheelchair tire based on the Magic Formula model. This model is widely used to represent forces and moments between the tire and the ground; however some experimental parameters must be determined. The purpose of this work is to identify the tire parameters for the wheelchair tire model, implementing them in a dynamic model of the wheelchair. For this, we developed an experimental test rig to measure the tires parameters for the lateral dynamics of a wheelchair. This dynamic model was made using a multi-body software and the wheelchair behaviour was analysed and discussed according to the tire parameters. The result of this work is one step further towards the understanding of wheelchair dynamics.

  8. Vehicle response-based track geometry assessment using multi-body simulation

    NASA Astrophysics Data System (ADS)

    Kraft, Sönke; Causse, Julien; Coudert, Frédéric

    2018-02-01

    The assessment of the geometry of railway tracks is an indispensable requirement for safe rail traffic. Defects which represent a risk for the safety of the train have to be identified and the necessary measures taken. According to current standards, amplitude thresholds are applied to the track geometry parameters measured by recording cars. This geometry-based assessment has proved its value but suffers from the low correlation between the geometry parameters and the vehicle reactions. Experience shows that some defects leading to critical vehicle reactions are underestimated by this approach. The use of vehicle responses in the track geometry assessment process allows identifying critical defects and improving the maintenance operations. This work presents a vehicle response-based assessment method using multi-body simulation. The choice of the relevant operation conditions and the estimation of the simulation uncertainty are outlined. The defects are identified from exceedances of track geometry and vehicle response parameters. They are then classified using clustering methods and the correlation with vehicle response is analysed. The use of vehicle responses allows the detection of critical defects which are not identified from geometry parameters.

  9. Communication Accommodation between Chinese and Australian Students and Academic Staff.

    ERIC Educational Resources Information Center

    Gallois, Cynthia; And Others

    A study tested paths predicted by Communication Accommodation Theory (CAT) in the context of interactions between 105 Chinese and 283 Anglo-Australian students and 98 academic staff in situations of potential conflict. Videotapes of student-lecturer interactions in which speakers accommodated, over-accommodated, or under-accommodated were rated by…

  10. 28 CFR 36.310 - Transportation provided by public accommodations.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 28 Judicial Administration 1 2010-07-01 2010-07-01 false Transportation provided by public... BASIS OF DISABILITY BY PUBLIC ACCOMMODATIONS AND IN COMMERCIAL FACILITIES Specific Requirements § 36.310 Transportation provided by public accommodations. (a) General. (1) A public accommodation that provides...

  11. Operationalizing workplace accommodations for individuals with disabilities: A scoping review.

    PubMed

    Sundar, Vidya

    2017-01-01

    The provision of workplace accommodations is a proven strategy in supporting individuals with disabilities at work. Accommodations include a wide range of supports and strategies that are not very well defined beyond the Americans with Disabilities Act in the United States. Understanding the landscape of accommodations is important to measure the impact of programs that support employment of individuals with disabilities. To conduct a scoping review and thematic analysis of research literature to identify how workplace accommodations are operationalized and to identify knowledge gaps in its conceptualization. Keywords searches were conducted in seven electronic databases. Title, abstract, and full text screening was conducted followed by a thematic analysis of the content to identify how workplace accommodations are operationalized. Overall, 47 studies were selected for review. 433 different types of accommodations were identified, of which assistive technology and specialized equipment represented the most frequently reported type of accommodation (40%). A very small percentage of studies included policy changes (9%) and human assistance (5%) as an accommodation strategy. This scoping review aims to clarify how accommodations are operationalized in the research literature. Key knowledge gaps identified include the systematic exclusion of certain types of supports or disability types.

  12. Anthropometric Accommodation in Space Suit Design

    NASA Technical Reports Server (NTRS)

    Rajulu, Sudhakar; Thaxton, Sherry

    2007-01-01

    Design requirements for next generation hardware are in process at NASA. Anthropometry requirements are given in terms of minimum and maximum sizes for critical dimensions that hardware must accommodate. These dimensions drive vehicle design and suit design, and implicitly have an effect on crew selection and participation. At this stage in the process, stakeholders such as cockpit and suit designers were asked to provide lists of dimensions that will be critical for their design. In addition, they were asked to provide technically feasible minimum and maximum ranges for these dimensions. Using an adjusted 1988 Anthropometric Survey of U.S. Army (ANSUR) database to represent a future astronaut population, the accommodation ranges provided by the suit critical dimensions were calculated. This project involved participation from the Anthropometry and Biomechanics facility (ABF) as well as suit designers, with suit designers providing expertise about feasible hardware dimensions and the ABF providing accommodation analysis. The initial analysis provided the suit design team with the accommodation levels associated with the critical dimensions provided early in the study. Additional outcomes will include a comparison of principal components analysis as an alternate method for anthropometric analysis.

  13. Maximum human objectively measured pharmacologically stimulated accommodative amplitude.

    PubMed

    Grzybowski, Andrzej; Schachar, Ronald A; Gaca-Wysocka, Magdalena; Schachar, Ira H; Pierscionek, Barbara K

    2018-01-01

    To measure the maximum, objectively measured, accommodative amplitude, produced by pharmacologic stimulation. Thirty-seven healthy subjects were enrolled, with a mean age of 20.2±1.1 years, corrected visual acuity of 20/20, and mean spherical equivalent refraction (SER) =-0.83±1.60 diopters. For each subject, the right pupil was dilated with phenylephrine 10%. After 30 minutes, the pupil was measured, the left eye was patched, and the right eye was autorefracted. Pilocarpine 4% was then instilled in the right eye, followed by phenylephrine. At 45 minutes after the pilocarpine, autorefraction and pupil size were again measured. Mean pupil size pre- and postpilocarpine was 8.0±0.8 mm and 4.4±1.9 mm, respectively. Pre- and postpilocarpine, the mean SER was -0.83±1.60 and -10.55±4.26 diopters, respectively. The mean pilocarpine-induced accommodative amplitude was 9.73±3.64 diopters. Five subjects had accommodative amplitudes ≥14.00 diopters. Accommodative amplitude was not significantly related to baseline SER ( p -value =0.24), pre- or postpilocarpine pupil size ( p -values =0.13 and 0.74), or change in pupil size ( p -value =0.37). Iris color did not statistically significantly affect accommodative amplitude ( p -value =0.83). Following topically applied pilocarpine, the induced objectively measured accommodation in the young eye is greater than or equal to the reported subjectively measured voluntary maximum accommodative amplitude.

  14. Restoration of accommodation: surgical options for correction of presbyopia

    PubMed Central

    Glasser, Adrian

    2010-01-01

    Accommodation is a dioptric change in the power of the eye to see clearly at near. Ciliary muscle contraction causes a release in zonular tension at the lens equator, which permits the elastic capsule to mould the young lens into an accommodated form. Presbyopia, the gradual age-related loss of accommodation, occurs primarily through a gradual age-related stiffening of the lens. While there are many possible options for relieving the symptoms of presbyopia, only relatively recently has consideration been given to surgical restoration of accommodation to the presbyopic eye. To understand how this might be achieved, it is necessary to understand the accommodative anatomy, the mechanism of accommodation and the causes of presbyopia. A variety of different kinds of surgical procedures has been considered for restoring accommodation to the presbyopic eye, including surgical expansion of the sclera, using femtosecond lasers to treat the lens or with so-called accommodative intraocular lenses (IOLs). Evidence suggests that scleral expansion cannot and does not restore accommodation. Laser treatments of the lens are in their early infancy. Development and testing of accommodative IOLs are proliferating. They are designed to produce a myopic refractive change in the eye in response to ciliary muscle contraction either through a movement of an optic or through a change in surface curvature. Three general design principles are being considered. These are single optic IOLs that rely on a forward shift of the optic, dual optic IOLs that rely on an increased separation between the two optics, or IOLs that permit a change in surface curvature to produce an increase in optical power in response to ciliary muscle contraction. Several of these different IOLs are available and being used clinically, while many are still in research and development. PMID:18399800

  15. Microstructural Dynamics and Rheology of Suspensions of Rigid Fibers

    NASA Astrophysics Data System (ADS)

    Butler, Jason E.; Snook, Braden

    2018-01-01

    The dynamics and rheology of suspensions of rigid, non-Brownian fibers in Newtonian fluids are reviewed. Experiments, theories, and computer simulations are considered, with an emphasis on suspensions at semidilute and concentrated conditions. In these suspensions, interactions between the particles strongly influence the microstructure and rheological properties of the suspension. The interactions can arise from hydrodynamic disturbances, giving multibody interactions at long ranges and pairwise lubrication forces over short distances. For concentrated suspensions, additional interactions due to excluded volume (contacts) and adhesive forces are addressed. The relative importance of the various interactions as a function of fiber concentration is assessed.

  16. Objective measurement of accommodative biometric changes using ultrasound biomicroscopy

    PubMed Central

    Ramasubramanian, Viswanathan; Glasser, Adrian

    2015-01-01

    PURPOSE To demonstrate that ultrasound biomicroscopy (UBM) can be used for objective quantitative measurements of anterior segment accommodative changes. SETTING College of Optometry, University of Houston, Houston, Texas, USA. DESIGN Prospective cross-sectional study. METHODS Anterior segment biometric changes in response to 0 to 6.0 diopters (D) of accommodative stimuli in 1.0 D steps were measured in eyes of human subjects aged 21 to 36 years. Imaging was performed in the left eye using a 35 MHz UBM (Vumax) and an A-scan ultrasound (A-5500) while the right eye viewed the accommodative stimuli. An automated Matlab image-analysis program was developed to measure the biometry parameters from the UBM images. RESULTS The UBM-measured accommodative changes in anterior chamber depth (ACD), lens thickness, anterior lens radius of curvature, posterior lens radius of curvature, and anterior segment length were statistically significantly (P < .0001) linearly correlated with accommodative stimulus amplitudes. Standard deviations of the UBM-measured parameters were independent of the accommodative stimulus demands (ACD 0.0176 mm, lens thickness 0.0294 mm, anterior lens radius of curvature 0.3350 mm, posterior lens radius of curvature 0.1580 mm, and anterior segment length 0.0340 mm). The mean difference between the A-scan and UBM measurements was −0.070 mm for ACD and 0.166 mm for lens thickness. CONCLUSIONS Accommodating phakic eyes imaged using UBM allowed visualization of the accommodative response, and automated image analysis of the UBM images allowed reliable, objective, quantitative measurements of the accommodative intraocular biometric changes. PMID:25804579

  17. Assessment of launch site accommodations versus Spacelab payload requirements

    NASA Technical Reports Server (NTRS)

    1977-01-01

    The Kennedy launch site capability for accommodating spacelab payload operations was assessed. Anomalies between facility accommodations and requirements for the Spacelab III (Strawman), OA Mission 83-2, Dedicated Life Sciences, and Combined Astronomy missions are noted. Recommendations for revision of the accommodations handbook are summarized.

  18. Ocular Aberrations Across the Visual Field During Accommodation

    NASA Astrophysics Data System (ADS)

    Liu, Tao

    Myopia is classically defined as a mismatch between the optical power of the relaxed eye and its dioptric length. This definition is entirely foveocentric without concern for the contributions of peripheral refractive errors to myopia development. Long periods of steady near-work was considered to cause myopia development due to inadequate accommodation. Consequently, not only the on-axis optical features but also off-axis ones should be probed to gain insight about myopia progression. Moreover, these features need to be understood not only for the relaxed eye, but also for the accommodating eye. To acquire complete data set, a custom-built Indiana Scanning Aberrometer for Wavefront (I SAW) was developed to measure wavefront aberration along 37 line-of-sights at 8 different accommodation states in the central 30 degree visual field. We found that ocular refractive state changed uniformly over the central visual field as the eye accommodates up to 6D, and the accuracy of accommodation across the central visual field is similar to that measured in the fovea. No systematic difference between emmetropic and myopic eyes was evident. Then, a linear vector-summation rule for axial and oblique astigmatism was found to account for their interaction over the central visual field. Using this combination rule, our experimental evidence revealed no systematic effect of accommodation on axial or oblique astigmatism for two adult populations. The axial and oblique astigmatism of the whole eye is less than for the cornea alone, indicating a compensatory role for internal optics at all accommodative states. This compensation mechanism was further validated theoretically with schematic eye model. Lastly, we developed a hybrid method yielding customized eye models that accurately reproduce the empirical measurements and reasonably represent the anatomical structure, thus providing a mechanistic explanation for the changes in the eye's aberration structure that occur over the central

  19. An Analysis and Rejection of Arguments for Religious Accommodation

    ERIC Educational Resources Information Center

    Kline, Lisa Anne

    2009-01-01

    This dissertation provides a comprehensive critical analysis of six main arguments for religious accommodation, with a specific focus on fundamentalist religious groups and the accommodation of their practices within liberal democratic societies. This analysis reveals that the types of practices that these arguments aim to accommodate primarily…

  20. Long-term reproducibility of Edinger-Westphal stimulated accommodation in rhesus monkeys.

    PubMed

    He, Lin; Wendt, Mark; Glasser, Adrian

    2013-08-01

    If longitudinal studies of accommodation or accommodation restoration procedures are undertaken in rhesus monkeys, the methods used to induce and measure accommodation must remain reproducible over the study period. Stimulation of the Edinger-Westphal (EW) nucleus in anesthetized rhesus monkeys is a valuable method to understand various aspects of accommodation. A prior study showed reproducibility of EW-stimulated accommodation over 14 months after chronic electrode implantation. However, reproducibility over a period longer than this has not been investigated and therefore remains unknown. To address this, accommodation stimulation experiments in four eyes of two rhesus monkeys (13.7 and 13.8 years old) were evaluated over a period of 68 months. Carbachol iontophoresis stimulated accommodation was first measured with a Hartinger coincidence refractometer (HCR) two weeks before electrode implantation to determine maximum accommodative amplitudes. EW stimulus-response curves were initially measured with the HCR one month after electrode implantation and then repeated at least six times for each eye in the following 60 months. At 64 months, carbachol iontophoresis induced accommodation was measured again. At 68 months, EW stimulus-response curves were measured with an HCR and photorefraction every week over four consecutive weeks to evaluate the short-term reproducibility over one month. In the four eyes studied, long-term EW-stimulated accommodation decreased by 7.00 D, 3.33 D, 4.63 D, and 2.03 D, whereas carbachol stimulated accommodation increased by 0.18 D-0.49 D over the same time period. The short-term reproducibility of maximum EW-stimulated accommodation (standard deviations) over a period of four weeks at 68 months after electrode implantation was 0.48 D, 0.79 D, 0.55 D and 0.39 D in the four eyes. Since the long-term decrease in EW-stimulated accommodation is not matched by similar decreases in carbachol iontophoresis stimulated accommodation, the decline

  1. Effective techniques for the identification and accommodation of disturbances

    NASA Technical Reports Server (NTRS)

    Johnson, C. D.

    1989-01-01

    The successful control of dynamic systems such as space stations, or launch vehicles, requires a controller design methodology that acknowledges and addresses the disruptive effects caused by external and internal disturbances that inevitably act on such systems. These disturbances, technically defined as uncontrollable inputs, typically vary with time in an uncertain manner and usually cannot be directly measured in real time. A relatively new non-statistical technique for modeling, and (on-line) identification, of those complex uncertain disturbances that are not as erratic and capricious as random noise is described. This technique applies to multi-input cases and to many of the practical disturbances associated with the control of space stations, or launch vehicles. Then, a collection of smart controller design techniques that allow controlled dynamic systems, with possible multi-input controls, to accommodate (cope with) such disturbances with extraordinary effectiveness are associated. These new smart controllers are designed by non-statistical techniques and typically turn out to be unconventional forms of dynamic linear controllers (compensators) with constant coefficients. The simplicity and reliability of linear, constant coefficient controllers is well-known in the aerospace field.

  2. Accommodations: Assisting Students with Disabilities. Third Edition

    ERIC Educational Resources Information Center

    Beech, Marty

    2010-01-01

    This document updates "Accommodations: Assisting Students with Disabilities. A Guide for Educators," published by the Florida Department of Education (FDOE) in 2003. This document is written to assist school district personnel and parents when making decisions about the use of accommodations by students with disabilities in instructional…

  3. 14 CFR § 1251.201 - Reasonable accommodation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... ON BASIS OF HANDICAP Employment Practices § 1251.201 Reasonable accommodation. (a) A recipient shall... handicapped applicant or employee unless the recipient can demonstrate that the accommodation would impose an...) Making facilities used by employees readily accessible to and usable by handicapped persons; and (2) Job...

  4. 7 CFR 15b.13 - Reasonable accommodation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...) A recipient shall make reasonable accommodation to the known physical or mental limitations of an... accommodation would impose an undue hardship on the operation of its program or activity. (b) Reasonable... undue hardship on the operation of a recipient's programs or activities, factors to be considered...

  5. Recommendations for Accommodations: Implications of (In)consistency

    ERIC Educational Resources Information Center

    Ketterlin-Geller, Leanne R.

    2007-01-01

    When accurately assigned and administered appropriately, testing accommodations help ameliorate the effects of personal characteristics that limit access to critical information and prevent a person from demonstrating his or her true abilities in the tested domain. Inaccurate assignment or misuse of accommodations may counteract the benefits of…

  6. 46 CFR 154.325 - Accommodation, service, and control spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Accommodation, service, and control spaces. 154.325... Equipment Ship Arrangements § 154.325 Accommodation, service, and control spaces. (a) Accommodation, service, and control spaces must be outside the cargo area. (b) If a hold space having a cargo containment...

  7. 46 CFR 154.325 - Accommodation, service, and control spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Accommodation, service, and control spaces. 154.325... Equipment Ship Arrangements § 154.325 Accommodation, service, and control spaces. (a) Accommodation, service, and control spaces must be outside the cargo area. (b) If a hold space having a cargo containment...

  8. 46 CFR 154.325 - Accommodation, service, and control spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Accommodation, service, and control spaces. 154.325... Equipment Ship Arrangements § 154.325 Accommodation, service, and control spaces. (a) Accommodation, service, and control spaces must be outside the cargo area. (b) If a hold space having a cargo containment...

  9. Effects of visual imagery on the accommodation response

    NASA Technical Reports Server (NTRS)

    Malmstrom, F. V.; Randle, R. J.

    1976-01-01

    Twenty-seven naive male subjects were tested to determine whether they could effect appropriate accommodation changes in an empty field by 'thinking near' and 'thinking far'. Evidence indicated that naive subjects could effect significant and appropriate accommodation changes, but only about a steady-state value of 1.0 diopter. Additionally, the data support the hypothesis that the resting state of accommodation is not at the visual far point, but, rather, at about 1.0 diopter.

  10. Verification of a Constraint Force Equation Methodology for Modeling Multi-Body Stage Separation

    NASA Technical Reports Server (NTRS)

    Tartabini, Paul V.; Roithmayr, Carlos; Toniolo, Matthew D.; Karlgaard, Christopher; Pamadi, Bandu N.

    2008-01-01

    This paper discusses the verification of the Constraint Force Equation (CFE) methodology and its implementation in the Program to Optimize Simulated Trajectories II (POST2) for multibody separation problems using three specially designed test cases. The first test case involves two rigid bodies connected by a fixed joint; the second case involves two rigid bodies connected with a universal joint; and the third test case is that of Mach 7 separation of the Hyper-X vehicle. For the first two cases, the POST2/CFE solutions compared well with those obtained using industry standard benchmark codes, namely AUTOLEV and ADAMS. For the Hyper-X case, the POST2/CFE solutions were in reasonable agreement with the flight test data. The CFE implementation in POST2 facilitates the analysis and simulation of stage separation as an integral part of POST2 for seamless end-to-end simulations of launch vehicle trajectories.

  11. Workplace accommodations for people with mental illness: a scoping review.

    PubMed

    McDowell, Caitlin; Fossey, Ellie

    2015-03-01

    Disability discrimination legislation means that employees with a disability or mental illness are legally entitled to reasonable workplace accommodations that enable them to work effectively and safely. This scoping review aims to investigate the types of workplace accommodations provided for people with mental illness, and their costs and benefits. A literature search was conducted using five electronic databases. Peer reviewed research articles published between 1993 and June 2013 were included in this scoping review and their quality was assessed. Opinion papers, reports, and case descriptions were excluded. Nine studies explored workplace accommodations for people with mental illness. The most commonly reported work-related accommodations were flexible scheduling/reduced hours, modified training and supervision, and modified job duties/descriptions. The least common type of accommodation was physical modification to the workplace. For employees with persistent mental illness who were accessing a supported employment agency, the majority of accommodations related to support from the job coach or employment specialist, such as facilitating communication with the employer during hiring or on the job. The quality of the studies varied considerably and the benefits of the accommodations are not yet well documented. There is limited evidence that a larger number of workplace accommodations are associated with longer job tenure. Workplace accommodations appear to be important to support employees with mental illness, but more accessible information about how disability discrimination legislation applies to this population is needed. Future research should address the implementation and effectiveness of mental health-related workplace accommodations.

  12. Vergence driven accommodation with simulated disparity in myopia and emmetropia.

    PubMed

    Maiello, Guido; Kerber, Kristen L; Thorn, Frank; Bex, Peter J; Vera-Diaz, Fuensanta A

    2018-01-01

    The formation of focused and corresponding foveal images requires a close synergy between the accommodation and vergence systems. This linkage is usually decoupled in virtual reality systems and may be dysfunctional in people who are at risk of developing myopia. We study how refractive error affects vergence-accommodation interactions in stereoscopic displays. Vergence and accommodative responses were measured in 21 young healthy adults (n=9 myopes, 22-31 years) while subjects viewed naturalistic stimuli on a 3D display. In Step 1, vergence was driven behind the monitor using a blurred, non-accommodative, uncrossed disparity target. In Step 2, vergence and accommodation were driven back to the monitor plane using naturalistic images that contained structured depth and focus information from size, blur and/or disparity. In Step 1, both refractive groups converged towards the stereoscopic target depth plane, but the vergence-driven accommodative change was smaller in emmetropes than in myopes (F 1,19 =5.13, p=0.036). In Step 2, there was little effect of peripheral depth cues on accommodation or vergence in either refractive group. However, vergence responses were significantly slower (F 1,19 =4.55, p=0.046) and accommodation variability was higher (F 1,19 =12.9, p=0.0019) in myopes. Vergence and accommodation responses are disrupted in virtual reality displays in both refractive groups. Accommodation responses are less stable in myopes, perhaps due to a lower sensitivity to dioptric blur. Such inaccuracies of accommodation may cause long-term blur on the retina, which has been associated with a failure of emmetropization. Copyright © 2017 Elsevier Ltd. All rights reserved.

  13. Extended Time Testing Accommodations: What Does the Research Say?

    ERIC Educational Resources Information Center

    Lovett, Benjamin J.

    2011-01-01

    Extended time is among the most common testing accommodations given to students with a wide range of disabilities. However, although school psychologists are often involved in accommodation decisions, many are unaware of research from the past decade that has changed their understanding of extended time. Used properly, testing accommodations let…

  14. Normal and Tangential Momentum Accommodation for Earth Satellite Conditions

    NASA Technical Reports Server (NTRS)

    Knechtel, Earl D.; Pitts, William C.

    1973-01-01

    Momentum accommodation was determined experimentally for gas-surface interactions simulating in a practical way those of near-earth satellites. Throughout the ranges of gas energies and incidence angles of interest for earth-conditions, two components of force were measured by means of a vacuum microbalance to determine the normal and tangential momentum-accommodation coefficients for nitrogen ions on technical-quality aluminum surfaces. For these experimental conditions, the electrodynamics of ion neutralization near the surface indicate that results for nitrogen ions should differ relatively little from those for nitrogen molecules, which comprise the largest component of momentum flux for near-earth satellites. The experimental results indicated that both normal and tangential momentum-accommodation coefficients varied widely with energy, tending to be relatively well accommodated at the higher energies, but becoming progressively less accommodated as the energy was reduced to and below that for earth-satellite speeds. Both coefficients also varied greatly with incidence angle, the normal momentum becoming less accommodated as the incidence angle became more glancing, whereas the tangential momentum generally became more fully accommodated. For each momentum coefficient, an empirical correlation function was obtained which closely approximated the experimental results over the ranges of energy and incidence angle. Most of the observed variations of momentum accommodation with energy and incidence angle were qualitatively indicated by a calculation using a three-dimensional model that simulated the target surface by a one-dimensional attractive potential and hard sphere reflectors.

  15. 46 CFR 127.260 - Ventilation for accommodations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Ventilation for accommodations. 127.260 Section 127.260... ARRANGEMENTS Particular Construction and Arrangements § 127.260 Ventilation for accommodations. (a) Each... vessel of 100 or more gross tons must be provided with a mechanical ventilation system unless the...

  16. Dynamic accommodative response to different visual stimuli (2D vs 3D) while watching television and while playing Nintendo 3DS console.

    PubMed

    Oliveira, Sílvia; Jorge, Jorge; González-Méijome, José M

    2012-09-01

    The aim of the present study was to compare the accommodative response to the same visual content presented in two dimensions (2D) and stereoscopically in three dimensions (3D) while participants were either watching a television (TV) or Nintendo 3DS console. Twenty-two university students, with a mean age of 20.3 ± 2.0 years (mean ± S.D.), were recruited to participate in the TV experiment and fifteen, with a mean age of 20.1 ± 1.5 years took part in the Nintendo 3DS console study. The accommodative response was measured using a Grand Seiko WAM 5500 autorefractor. In the TV experiment, three conditions were used initially: the film was viewed in 2D mode (TV2D without glasses), the same sequence was watched in 2D whilst shutter-glasses were worn (TV2D with glasses) and the sequence was viewed in 3D mode (TV3D). Measurements were taken for 5 min in each condition, and these sections were sub-divided into ten 30-s segments to examine changes within the film. In addition, the accommodative response to three points of different disparity of one 3D frame was assessed for 30 s. In the Nintendo experiment, two conditions were employed - 2D viewing and stereoscopic 3D viewing. In the TV experiment no statistically significant differences were found between the accommodative response with TV2D without glasses (-0.38 ± 0.32D, mean ± S.D.) and TV3D (-0.37 ± 0.34D). Also, no differences were found between the various segments of the film, or between the accommodative response to different points of one frame (p > 0.05). A significant difference (p = 0.015) was found, however, between the TV2D with (-0.32 ± 0.32D) and without glasses (-0.38 ± 0.32D). In the Nintendo experiment the accommodative responses obtained in modes 2D (-2.57 ± 0.30D) and 3D (-2.49 ± 0.28D) were significantly different (paired t-test p = 0.03). The need to use shutter-glasses may affect the accommodative response during the viewing of displays, and the accommodative response when playing

  17. The provision of workplace accommodations following cancer: survivor, provider, and employer perspectives.

    PubMed

    Stergiou-Kita, Mary; Pritlove, Cheryl; van Eerd, Dwayne; Holness, Linn D; Kirsh, Bonnie; Duncan, Andrea; Jones, Jennifer

    2016-06-01

    With improvements in screening, diagnosis, and treatment, the number of persons surviving cancer and staying at or returning to work is increasing. While workplace accommodations optimize workers' abilities to participate in the workforce, there has been little in-depth investigation of the types of accommodations reported to have been provided to cancer survivors and the processes relevant to ensuring their successful implementation. We employed an exploratory qualitative method and conducted 40 semi-structured interviews with three groups: (i) cancers survivors (n = 16), (ii) health/vocational service providers (n = 16), and (iii) employer representatives (n = 8) to explore return to work and accommodation processes, successes, and challenges. An inductive thematic analysis approach was used to analyze the data. Four types of accommodations were recommended: (1) graduated return to work plans and flexible scheduling, (2) modification of work duties and performance expectations, (3) retraining and supports at the workplace, and (4) modification of the physical work environment and/or the provision of adaptive aids/technologies. Processes relevant to ensuring effective accommodations included: (1) developing knowledge about accommodations, (2) employer's ability to accommodate, (3) negotiating reasonable accommodations, (4) customizing accommodations, and (5) implementing and monitoring accommodation plans. Accommodation challenges included: (1) survivors' fears requesting accommodations, (2) developing clear and specific accommodations, (3) difficult to accommodate jobs, and (4) workplace challenges, including strained pre-cancer workplace relationships, insufficient/inflexible workplace policies, employer concerns regarding productivity and precedent setting, and limited modified duties. Accommodations need to be customized and clearly linked to survivors' specific job demands, work context, and available workplace supports. Survivors need to feel

  18. Utility accommodation and conflict tracker (UACT) : user manual

    DOT National Transportation Integrated Search

    2009-02-01

    Project 0-5475 performed a comprehensive analysis of utility conflict data/information flows between utility : accommodation stakeholders in the Texas Department of Transportation project development process, : developed data models to accommodate wo...

  19. 46 CFR 30.10-2 - Accommodation space-TB/ALL.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 1 2012-10-01 2012-10-01 false Accommodation space-TB/ALL. 30.10-2 Section 30.10-2... Accommodation space—TB/ALL. The term accommodation space means any public space such as a hall, dining room... that contains no cooking appliances, and a similar space open to the passengers and crew. [CGD 74-127...

  20. 46 CFR 30.10-2 - Accommodation space-TB/ALL.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 1 2010-10-01 2010-10-01 false Accommodation space-TB/ALL. 30.10-2 Section 30.10-2... Accommodation space—TB/ALL. The term accommodation space means any public space such as a hall, dining room... that contains no cooking appliances, and a similar space open to the passengers and crew. [CGD 74-127...

  1. 46 CFR 30.10-2 - Accommodation space-TB/ALL.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 1 2014-10-01 2014-10-01 false Accommodation space-TB/ALL. 30.10-2 Section 30.10-2... Accommodation space—TB/ALL. The term accommodation space means any public space such as a hall, dining room... that contains no cooking appliances, and a similar space open to the passengers and crew. [CGD 74-127...

  2. 46 CFR 30.10-2 - Accommodation space-TB/ALL.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 1 2011-10-01 2011-10-01 false Accommodation space-TB/ALL. 30.10-2 Section 30.10-2... Accommodation space—TB/ALL. The term accommodation space means any public space such as a hall, dining room... that contains no cooking appliances, and a similar space open to the passengers and crew. [CGD 74-127...

  3. 46 CFR 30.10-2 - Accommodation space-TB/ALL.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 1 2013-10-01 2013-10-01 false Accommodation space-TB/ALL. 30.10-2 Section 30.10-2... Accommodation space—TB/ALL. The term accommodation space means any public space such as a hall, dining room... that contains no cooking appliances, and a similar space open to the passengers and crew. [CGD 74-127...

  4. Accommodating Picky Palates

    ERIC Educational Resources Information Center

    Lum, Lydia

    2007-01-01

    Healthy gourmet offerings are fast becoming the norm at college dining halls around the country. At a time when the children of Baby Boomers are hitting higher education in record numbers, college officials have scrambled to accommodate their picky palates and their insistence for healthier meals than were served to past generations. At the same…

  5. Prediction of anthropometric accommodation in aircraft cockpits

    NASA Astrophysics Data System (ADS)

    Zehner, Gregory Franklin

    Designing aircraft cockpits to accommodate the wide range of body sizes existing in the U.S. population has always been a difficult problem for Crewstation Engineers. The approach taken in the design of military aircraft has been to restrict the range of body sizes allowed into flight training, and then to develop standards and specifications to ensure that the majority of the pilots are accommodated. Accommodation in this instance is defined as the ability to: (1) Adequately see, reach, and actuate controls; (2) Have external visual fields so that the pilot can see to land, clear for other aircraft, and perform a wide variety of missions (ground support/attack or air to air combat); and (3) Finally, if problems arise, the pilot has to be able to escape safely. Each of these areas is directly affected by the body size of the pilot. Unfortunately, accommodation problems persist and may get worse. Currently the USAF is considering relaxing body size entrance requirements so that smaller and larger people could become pilots. This will make existing accommodation problems much worse. This dissertation describes a methodology for correcting this problem and demonstrates the method by predicting pilot fit and performance in the USAF T-38A aircraft based on anthropometric data. The methods described can be applied to a variety of design applications where fitting the human operator into a system is a major concern. A systematic approach is described which includes: defining the user population, setting functional requirements that operators must be able to perform, testing the ability of the user population to perform the functional requirements, and developing predictive equations for selecting future users of the system. Also described is a process for the development of new anthropometric design criteria and cockpit design methods that assure body size accommodation is improved in the future.

  6. Evidence that convergence rather than accommodation controls intermittent distance exotropia

    PubMed Central

    Horwood, Anna M; Riddell, Patricia M

    2015-01-01

    Purpose This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Methods 19 distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2m and 33cm. Stimulus and response AC/A and CA/C ratios were calculated. Results Accommodation responses for near targets (p=0.017) response gains (p=0.026) were greater in the exotropes than the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p=0.02), but significantly higher CA/C ratios (p=0.02). All the exotropes, whether the angle changed most with lenses (“controlled by accommodation”) or on occlusion (“controlled by fusion”), used binocular disparity not blur as their main cue to target distance. Conclusions Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting over-accommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios. PMID:22280437

  7. Accommodation measurements of horizontally scanning holographic display.

    PubMed

    Takaki, Yasuhiro; Yokouchi, Masahito

    2012-02-13

    Eye accommodation is considered to function properly for three-dimensional (3D) images generated by holography. We developed a horizontally scanning holographic display technique that enlarges both the screen size and viewing zone angle. A 3D image generated by this technique can be easily seen by both eyes. In this study, we measured the accommodation responses to a 3D image generated by the horizontally scanning holographic display technique that has a horizontal viewing zone angle of 14.6° and screen size of 4.3 in. We found that the accommodation responses to a 3D image displayed within 400 mm from the display screen were similar to those of a real object.

  8. Choosing Accommodations: Signed Language Interpreting and the Absence of Choice.

    PubMed

    Burke, Teresa Blankmeyer

    This paper carves out a topic space for discussion about the ethical question of whether input from signing Deaf consumers of interpreting services ought to be included in the provision of signed language interpreter accommodations. The first section provides background about disability accommodations and practices, including how signed language interpreting accommodations are similar and dissimilar to other kinds of disability accommodations. In the second section, I offer a personal narrative of my experience as a Deaf academic who has been excluded from the interpreter selection process, highlighting some of the harmful consequences of such exclusion. In the subsequent two sections, I describe and analyze the process of choosing interpreter accommodations, starting with the process of requesting signed language interpreters and the institutionalization of this process, followed by a brief overview of privacy and autonomy concerns from the standpoint of the signing Deaf consumer. The penultimate section considers some objections to the proposal of involving more consumer choice in signed language accommodations. I conclude the paper with some concrete suggestions for a more Deaf-centered, inclusive process for choosing interpreter accommodations.

  9. Nonlinear Vibrations, Stability, and Dynamics of Structures and Mechanisms Conference (4th) Held in Blacksburg, Virginia on June 7-11, 1992

    DTIC Science & Technology

    1992-11-01

    Subharmonic Forced Traveling Waves in a Thin Perfect Circular Disk T. A. Nayfeh and A. F. Vakakis, University of Illinois at Urbana -Champaign, Urbana ...of Illinois at Urbana -Champaign, Urbana , IL and J. Awrejcewicz, The University of Tokyo, Tokyo, JAPAN 0830-1010 On the Nonlinear Parametric Excitation...and A. F. Vakakis, University of Illinois at Urbana -Champaign, Urbana , IL Thursday, June 11 Session 15. Multibody Dynamics I/ Chairmen: G. Anderson

  10. The effect of incipient presbyopia on the correspondence between accommodation and vergence.

    PubMed

    Baker, Fiona J; Gilmartin, Bernard

    2002-06-01

    To investigate the accommodation-convergence relationship during the incipient phase of presbyopia. The study aimed to differentiate between the current theories of presbyopia and to explore the mechanisms by which the oculomotor system compensates for the change in the accommodation-convergence relationship contingent on a declining amplitude of accommodation. Using a Canon R-1 open-view autorefractor and a haploscope device, measurements were made of the stimulus and response accommodative convergence/accommodation ratios and the convergence accommodation/convergence ratio of 28 subjects aged 35-45 years at the commencement of the study. Amplitude of accommodation was assessed using a push-down technique. The measurements were repeated at 4-monthly intervals over a 2-year period. The results showed that with the decline in the amplitude of accommodation there is an increase in the accommodative convergence response per unit of accommodative response and a decrease in the convergence accommodation response per unit of convergence. The results of this study fail to support the Hess-Gullstrand theory of presbyopia in that the ciliary muscle effort required to produce a unit change in accommodation increases, rather than stays constant, with age. Data show that the near vision response is limited to the maximum vergence response that can be tolerated and, despite being within the amplitude of accommodation, a stimulus may still appear blurred because the vergence component determines the proportion of available accommodation utilised during near vision.

  11. [Accommodation effects of the audiovisual stimulation in the patients experiencing eyestrain with the concomitant disturbances of psychological adaptation].

    PubMed

    Shakula, A V; Emel'ianov, G A

    2014-01-01

    The present study was designed to evaluate the effectiveness of audiovisual stimulation on the state of the eye accommodation system in the patients experiencing eyes train with the concomitant disturbances of psychological. It was shown that a course of audiovisual stimulation (seeing a psychorelaxing film accompanied by a proper music) results in positive (5.9-21.9%) dynamics of the objective accommodation parameters and of the subjective status (4.5-33.2%). Taken together, these findings whole allow this method to be regarded as "relaxing preparation" in the integral complex of the measures for the preservation of the professional vision in this group of the patients.

  12. Wavefront aberration changes caused by a gradient of increasing accommodation stimuli

    PubMed Central

    Zhou, X-Y; Wang, L; Zhou, X-T; Yu, Z-Q

    2015-01-01

    Purpose The aim of this study was to investigate the wavefront aberration changes in human eyes caused by a gradient of increasing accommodation stimuli. Design This is a prospective, single-site study. Methods Healthy volunteers (n=22) aged 18–28 years whose refraction states were emmetropia or mild myopia, with astigmatism <1 diopter (D), were included in this study. After dilating the right pupil with 0.5% phenylephrine drops, the wavefront aberration of the right eye was measured continuously either without or with 1, 2, 3, 4, 5, or 6D accommodation stimuli (WFA1000B psychophysical aberrometer). The root mean square (RMS) values of the total wavefront aberrations, higher-order aberrations, and 35 individual Zernike aberrations under different accommodation stimuli were calculated and compared. Results The average induced accommodations using 1, 2, 3, 4, 5, or 6D accommodation stimuli were 0.848, 1.626, 2.375, 3.249, 4.181, or 5.085 D, respectively. The RMS of total wavefront aberrations, as well as higher-order aberrations, showed no significant effects with 1–3 D accommodation stimuli, but increased significantly under 4, 5, and 6 D accommodation stimuli compared with relaxed accommodation. Zernike coefficients of significantly decreased with increasing levels of accommodation. Conclusion Higher-order wavefront aberrations in human eyes changed with increased accommodation. These results are consistent with Schachar's accommodation theory. PMID:25341432

  13. Spatial multibody modeling and vehicle dynamics analysis of advanced vehicle technologies

    NASA Astrophysics Data System (ADS)

    Letherwood, Michael D.; Gunter, David D.; Gorsich, David J.; Udvare, Thomas B.

    2004-08-01

    The US Army vision, announced in October of 1999, encompasses people, readiness, and transformation. The goal of the Army vision is to transition the entire Army into a force that is strategically responsive and dominant at every point of the spectrum of operations. The transformation component will be accomplished in three ways: the Objective Force, the Legacy (current) Force, and the Interim Force. The objective force is not platform driven, but rather the focus is on achieving capabilities that will operate as a "system of systems." As part of the Objective Force, the US Army plans to begin production of the Future Combat System (FCS) in FY08 and field the first unit by FY10 as currently defined in the FCS solicitation(1). As part of the FCS program, the Future Tactical Truck System (FTTS) encompasses all US Army tactical wheeled vehicles and its initial efforts will focus only on the heavy class. The National Automotive Center (NAC) is using modeling and simulation to demonstrate the feasibility and operational potential of advanced commercial and military technologies with application to new and existing tactical vehicles and to describe potential future vehicle capabilities. This document will present the results of computer-based, vehicle dynamics performance assessments of FTTS concepts with such features as hybrid power sources, active suspensions, skid steering, and in-hub electric drive motors. Fully three-dimensional FTTS models are being created using commercially available modeling and simulation methodologies such as ADAMS and DADS and limited vehicle dynamics validation studies are will be performed.

  14. Occlusal accommodation and mouthguards for prevention of orofacial trauma.

    PubMed

    Geary, Julian Lindsay; Clifford, Thomas Joseph; Kinirons, Martin James

    2009-01-01

    The aim of this study was to investigate the effect of two types of occlusal accommodation on the arch separation in centric and eccentric arch positions and to assess the opposing tooth contacts in professionally made, thermoformed sports mouthguards. Maxillary and mandibular alginate impressions, a wax interocclusal record of centric occlusion together with maxillary/condylar face-bow registrations, were recorded clinically for 10 undergraduate dental students who are sports activist volunteers of the School of Medicine and Dentistry, Queen's University Belfast. Two ethylene vinyl acetate thermoformed maxillary mouthguards were made for each player (N = 20) using a standardised procedure. Ten mouthguards served both as the control (i.e. the non-accommodated) group and also the accommodated, occlusally 'imprinted' group. The other 10 mouthguards served as the accommodated, occlusally 'ground' group. Casts were articulated, each non-accommodated and accommodated mouthguard was seated and the extent of the interocclusal opening was recorded in all three arch relationships. The number of mouthguard and mandibular tooth contacts were also recorded in each position. The increased vertical occlusal dimension that was found in the presence of non-accommodated mouthguards equated to the full-sheet thickness of the material that was used to form the mouthguards. Only mouthguards accommodated by grinding retained high levels of occlusal contact in all arch relationships that were tested. Within the limitations of this study, the modification of the occlusal surface made by flat grinding reduced the arch separation in eccentric movements and increased the opposing tooth contacts in custom-made mouthguards. This may contribute to increased comfort, compliance and the protective effect of these appliances thus resulting in a reduction of injuries to the teeth, arches and soft tissues.

  15. Comparison of tests of accommodation for computer users.

    PubMed

    Kolker, David; Hutchinson, Robert; Nilsen, Erik

    2002-04-01

    With the increased use of computers in the workplace and at home, optometrists are finding more patients presenting with symptoms of Computer Vision Syndrome. Among these symptomatic individuals, research supports that accommodative disorders are the most common vision finding. A prepresbyopic group (N= 30) and a presbyopic group (N = 30) were selected from a private practice. Assignment to a group was determined by age, accommodative amplitude, and near visual acuity with their distance prescription. Each subject was given a thorough vision and ocular health examination, then administered several nearpoint tests of accommodation at a computer working distance. All the tests produced similar results in the presbyopic group. For the prepresbyopic group, the tests yielded very different results. To effectively treat symptomatic VDT users, optometrists must assess the accommodative system along with the binocular and refractive status. For presbyopic patients, all nearpoint tests studied will yield virtually the same result. However, the method of testing accommodation, as well as the test stimulus presented, will yield significantly different responses for prepresbyopic patients. Previous research indicates that a majority of patients prefer the higher plus prescription yielded by the Gaussian image test.

  16. Accommodation in pediatric oncology: parental experiences, preferences and unmet needs.

    PubMed

    Daniel, Gunar; Wakefield, Claire E; Ryan, Barbara; Fleming, Catharine Ak; Levett, Nicole; Cohn, Richard J

    2013-01-01

    For families of children diagnosed with cancer, proximity to the treatment center and staying close to immediate family members are essential for proper patient management. Accommodation services are therefore a key consideration in pediatric oncology. This descriptive study explored the accommodation used, and preferred, by parents of pediatric cancer patients at Sydney Children's Hospital, Randwick (SCH), Australia, and investigated their accommodation and practical needs. Forty-two parents from 25 families participated in individual semi-structured telephone interviews. Interviews were recorded, transcribed verbatim and coded line-by-line. Coding was facilitated by data analysis software QSR NVivo v8 (www.qsrinternational.com). Emergent themes were numerically assessed to minimize the potential for researcher bias. Nine families (36%) lived near SCH and were able to stay at their own residence during treatment (mean distance of 15.4 km from SCH). The remaining families were categorized 'local, but requiring accommodation' (n=3 families represented by five parent interviews; mean distance of 82.22 km from SCH),'inner regional' (IR) (n=8 families, 15 parent interviews; mean distance of 396.75 km from SCH) or 'outer regional' (OR) (n=3 families, 5 interviews; mean distance of 547.4 km from SCH) according to the Australian Standard Geographical Classification (ASGC) remoteness ratings. Accommodation provided for families from both IR and OR areas was mixed, with several families using multiple accommodation options during treatment, including Ronald Macdonald House (RMH), private accommodation or a rental property close to the hospital for the duration of the treatment. Six IR and one OR family utilized hotel or motel accommodation as an alternative to RMH due to unavailability of rooms. The majority of parents (37/42) preferred to stay on the hospital campus, near their child. Seven out of 11 IR and OR mothers preferred self-contained accommodation, while three out

  17. A model to predict accommodations needed by disabled persons.

    PubMed

    Babski-Reeves, Kari; Williams, Sabrina; Waters, Tzer Nan; Crumpton-Young, Lesia L; McCauley-Bell, Pamela

    2005-09-01

    In this paper, several approaches to assist employers in the accommodation process for disabled employees are discussed and a mathematical model is proposed to assist employers in predicting the accommodation level needed by an individual with a mobility-related disability. This study investigates the validity and reliability of this model in assessing the accommodation level needed by individuals utilizing data collected from twelve individuals with mobility-related disabilities. Based on the results of the statistical analyses, this proposed model produces a feasible preliminary measure for assessing the accommodation level needed for persons with mobility-related disabilities. Suggestions for practical application of this model in an industrial setting are addressed.

  18. Simulation of diatomic gas-wall interaction and accommodation coefficients for negative ion sources and accelerators.

    PubMed

    Sartori, E; Brescaccin, L; Serianni, G

    2016-02-01

    Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production-detrimental for high current negative ion systems such as beam sources for fusion-are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient and energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared.

  19. Simulation of diatomic gas-wall interaction and accommodation coefficients for negative ion sources and accelerators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sartori, E., E-mail: emanuele.sartori@igi.cnr.it; Serianni, G.; Brescaccin, L.

    2016-02-15

    Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production—detrimental for high current negative ion systems such as beam sources for fusion—are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient andmore » energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared.« less

  20. Evidence that convergence rather than accommodation controls intermittent distance exotropia.

    PubMed

    Horwood, Anna M; Riddell, Patricia M

    2012-03-01

    This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios. © 2012 The Authors. Acta Ophthalmologica © 2012 Acta Ophthalmologica Scandinavica Foundation.

  1. Accommodation and Phoria in Children Wearing Multifocal Contact Lenses

    PubMed Central

    Gong, Celia R; Troilo, David; Richdale, Kathryn

    2017-01-01

    Purpose To determine the effect of multifocal contact lenses on accommodation and phoria in children. Methods This was a prospective, non-dispensing, randomized, crossover, single visit study. Myopic children with normal accommodation and binocularity and no history of myopia control treatment were enrolled and fitted with Coopervision Biofinity single vision (SV) and multifocal (MF, +2.50D center distance add) contact lenses. Accommodative responses (photorefraction) and phorias (Modified Thorington) were measured at 4 distances (>3m, 100cm, 40cm, 25cm). Secondary measures included high and low contrast logMAR acuity, accommodative amplitude and facility. Differences between contact lens designs were analyzed using repeated measures regression and paired t-tests. Results A total of 16 subjects, aged 10-15 years, completed the study. There was a small decrease in high (SV: -0.08, MF: +0.01) and low illumination (SV:-0.03, MF: +0.08) (both p<0.01) visual acuity, and contrast sensitivity (SV: 2.0, MF: 1.9 log units, p=0.015) with multifocals. Subjects were more exophoric at 40 cm (SV: -0.41, MF: -2.06 Δ) and 25cm (SV: -0.83, MF: -4.30 Δ) (both p<0.01). With multifocals, subjects had decreased accommodative responses at distance (SV: -0.04; MF: -0.37 D, p=0.02), 100 cm (SV: +0.37; MF: -0.35 D, p<0.01), 40 cm (SV: +1.82; MF: +0.62 D, p<0.01), and 25 cm (SV: +3.38; MF: +1.75 D, p<0.01). There were no significant differences in accommodative amplitude (p=0.66) or facility (p=0.54). Conclusions Children wearing multifocal contact lenses exhibited reduced accommodative responses and more exophoria at increasingly higher accommodative demands than with single vision contact lenses. This suggests that children may be relaxing their accommodation and using the positive addition or increased depth of focus from added spherical aberration of the multifocals. Further studies are needed to evaluate other lens designs, different amounts of positive addition and aberrations, and

  2. On the identifiability of inertia parameters of planar Multi-Body Space Systems

    NASA Astrophysics Data System (ADS)

    Nabavi-Chashmi, Seyed Yaser; Malaek, Seyed Mohammad-Bagher

    2018-04-01

    This work describes a new formulation to study the identifiability characteristics of Serially Linked Multi-body Space Systems (SLMBSS). The process exploits the so called "Lagrange Formulation" to develop a linear form of Equations of Motion w.r.t the system Inertia Parameters (IPs). Having developed a specific form of regressor matrix, we aim to expedite the identification process. The new approach allows analytical as well as numerical identification and identifiability analysis for different SLMBSSs' configurations. Moreover, the explicit forms of SLMBSSs identifiable parameters are derived by analyzing the identifiability characteristics of the robot. We further show that any SLMBSS designed with Variable Configurations Joint allows all IPs to be identifiable through comparing two successive identification outcomes. This feature paves the way to design new class of SLMBSS for which accurate identification of all IPs is at hand. Different case studies reveal that proposed formulation provides fast and accurate results, as required by the space applications. Further studies might be necessary for cases where planar-body assumption becomes inaccurate.

  3. The determinants of transitions into sheltered accommodation in later life in England and Wales

    PubMed Central

    Vlachantoni, Athina; Maslovskaya, Olga; Evandrou, Maria; Falkingham, Jane

    2016-01-01

    Background Population ageing is a global challenge and understanding the dynamics of living arrangements in later life and their implications for the design of appropriate housing and long-term care is a critical policy issue. Existing research has focused on the study of transitions into residential care in the UK. This paper investigates transitions into sheltered accommodation among older people in England and Wales between 1993 and 2008. Methods The study uses longitudinal data constructed from pooled observations across waves 2–18 of the British Household Panel Survey (BHPS) data, focusing on individuals aged 65 and over who lived in private housing at baseline and who were observed for two consecutive time points. A discrete-time logistic regression model was used to examine the association of transitioning into sheltered accommodation with a range of demographic, health and socioeconomic predictors. Results Demographic (age, region), socioeconomic factors (housing tenure, having a washing machine) and contact with health professionals (number of visits to the general practitioner, start in use of health visitor) were significant determinants of an older person's move into sheltered accommodation. Conclusions Transitions into sheltered accommodation are associated with a range of demographic and socioeconomic characteristics as well as service use but not with health. Such results indicate that this type of housing option may be accessible by individuals with relatively good health, but may be limited to those who are referred by gatekeepers. Policymakers could consider making such housing option available to everyone, as well as providing incentives for building lifecourse-sensitive housing in the future. PMID:26896519

  4. The accommodation index measures the perturbation associated with insertions and deletions in coiled‐coils: Application to understand signaling in histidine kinases

    PubMed Central

    Schmidt, Nathan W.; Grigoryan, Gevorg

    2017-01-01

    Abstract Coiled‐coils are essential components of many protein complexes. First discovered in structural proteins such as keratins, they have since been found to figure largely in the assembly and dynamics required for diverse functions, including membrane fusion, signal transduction and motors. Coiled‐coils have a characteristic repeating seven‐residue geometric and sequence motif, which is sometimes interrupted by the insertion of one or more residues. Such insertions are often highly conserved and critical to interdomain communication in signaling proteins such as bacterial histidine kinases. Here we develop the “accommodation index” as a parameter that allows automatic detection and classification of insertions based on the three dimensional structure of a protein. This method allows precise identification of the type of insertion and the “accommodation length” over which the insertion is structurally accommodated. A simple theory is presented that predicts the structural perturbations of 1, 3, 4 residue insertions as a function of the length over which the insertion is accommodated. Analysis of experimental structures is in good agreement with theory, and shows that short accommodation lengths give rise to greater perturbation of helix packing angles, changes in local helical phase, and increased structural asymmetry relative to long accommodation lengths. Cytoplasmic domains of histidine kinases in different signaling states display large changes in their accommodation lengths, which can now be seen to underlie diverse structural transitions including symmetry/asymmetry and local variations in helical phase that accompany signal transduction. PMID:27977891

  5. Accommodation Practices for English Language Learners in States' Mathematics Assessments

    ERIC Educational Resources Information Center

    Wolf, Mikyung Kim; Kao, Jenny C.; Rivera, Nichole M.; Chang, Sandy M.

    2012-01-01

    Background/Context: Testing accommodations have been widely utilized as a way of increasing the validity of content assessments for English language learner (ELL) students. However, concerns have also arisen regarding the appropriateness of accommodation use, including the accessibility and fairness of accommodations. While many states have…

  6. Against the accommodation of subjective healthcare provider beliefs in medicine: counteracting supporters of conscientious objector accommodation arguments.

    PubMed

    Smalling, Ricardo; Schuklenk, Udo

    2017-04-01

    We respond in this paper to various counter arguments advanced against our stance on conscientious objection accommodation. Contra Maclure and Dumont, we show that it is impossible to develop reliable tests for conscientious objectors' claims with regard to the reasonableness of the ideological basis of their convictions, and, indeed, with regard to whether they actually hold they views they claim to hold. We demonstrate furthermore that, within the Canadian legal context, the refusal to accommodate conscientious objectors would not constitute undue hardship for such objectors. We reject concerns that refusing to accommodate conscientious objectors would limit the equality of opportunity for budding professionals holding particular ideological positions. We also clarify various misrepresentations of our views by respondents Symons, Glick and Jotkowitz, and Lyus. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

  7. The rate of change of vergence-accommodation conflict affects visual discomfort.

    PubMed

    Kim, Joohwan; Kane, David; Banks, Martin S

    2014-12-01

    Stereoscopic (S3D) displays create conflicts between the distance to which the eyes must converge and the distance to which the eyes must accommodate. Such conflicts require the viewer to overcome the normal coupling between vergence and accommodation, and this effort appears to cause viewer discomfort. Vergence-accommodation coupling is driven by the phasic components of the underlying control systems, and those components respond to relatively fast changes in vergence and accommodative stimuli. Given the relationship between phasic changes and vergence-accommodation coupling, we examined how the rate of change in the vergence-accommodation conflict affects viewer discomfort. We used a stereoscopic display that allows independent manipulation of the stimuli to vergence and accommodation. We presented stimuli that simulate natural viewing (i.e., vergence and accommodative stimuli changed together) and stimuli that simulate S3D viewing (i.e., vergence stimulus changes but accommodative stimulus remains fixed). The changes occurred at 0.01, 0.05, or 0.25 Hz. The lowest rate is too slow to stimulate the phasic components while the highest rate is well within the phasic range. The results were consistent with our expectation: somewhat greater discomfort was experienced when stimulus distance changed rapidly, particularly in S3D viewing when the vergence stimulus changed but the accommodative stimulus did not. These results may help in the generation of guidelines for the creation and viewing of stereo content with acceptable viewer comfort.

  8. The Rate of Change of Vergence-Accommodation Conflict Affects Visual Discomfort

    PubMed Central

    Kane, David; Banks, Martin S.

    2014-01-01

    Stereoscopic (S3D) displays create conflicts between the distance to which the eyes must converge and the distance to which the eyes must accommodate. Such conflicts require the viewer to overcome the normal coupling between vergence and accommodation, and this effort appears to cause viewer discomfort. Vergence-accommodation coupling is driven by the phasic components of the underlying control systems, and those components respond to relatively fast changes in vergence and accommodative stimuli. Given the relationship between phasic changes and vergence-accommodation coupling, we examined how the rate of change in the vergence-accommodation conflict affects viewer discomfort. We used a stereoscopic display that allows independent manipulation of the stimuli to vergence and accommodation. We presented stimuli that simulate natural viewing (i.e., vergence and accommodative stimuli changed together) and stimuli that simulate S3D viewing (i.e., vergence stimulus changes but accommodative stimulus remains fixed). The changes occurred at 0.01, 0.05, or 0.25Hz. The lowest rate is too slow to stimulate the phasic components while the highest rate is well within the phasic range. The results were consistent with our expectation: somewhat greater discomfort was experienced when stimulus distance changed rapidly, particularly in S3D viewing when the vergence stimulus changed but the accommodative stimulus did not. These results may help in the generation of guidelines for the creation and viewing of stereo content with acceptable viewer comfort. PMID:25448713

  9. The impact of testing accommodations on MCAT scores: descriptive results.

    PubMed

    Julian, Ellen R; Ingersoll, Deborah J; Etienne, Patricia M; Hilger, Anthony E

    2004-04-01

    Medical College Admission Test (MCAT) examinees with disabilities who receive accommodations receive flagged scores indicating nonstandard administration. This report compares MCAT examinees who received accommodations and their performances with standard examinees. Aggregate history records of all 1994-2000 MCAT examinees were identified as flagged (2,401) or standard (297,880), then further sorted by race/ethnicity (broadly identified as underrepresented minority and non-URM, at the time of testing) and gender. Those with flagged scores were also classified by disability (LD = learning disability, ADHD = attention deficit hyperactivity disorder, LD/ADHD = learning disability and attention deficit hyperactivity disorder, and Other = other disability) and type of accommodation. Mean MCAT scores were calculated for all groups. A group of 866 examinees took the MCAT first as a standard administration and subsequently with accommodations. In a separate analysis, their two sets of scores were compared. Less than 1% of examinees (2,401) had accommodations; of these, 55% were LD, 17% ADHD, 5% LD/ADHD, and 23% Other. Extended time was the most frequently provided accommodation. Mean flagged scores slightly exceeded mean standard scores on all MCAT sections. Examinees who retook the MCAT with accommodations after a standard administration increased their scores by six points, quadrupling the average gain Standard-Standard retest cohort from another study. The small but statistically significant different higher flagged scores may reflect either appropriate compensation or overly generous accommodations. Extended time had a positive impact on the scores of those who retested with this accommodation. The validity the flagged MCAT in predicting success in medical school is not known, and further investigation is underway.

  10. A meta-analysis of family accommodation and OCD symptom severity.

    PubMed

    Wu, Monica S; McGuire, Joseph F; Martino, Charitie; Phares, Vicky; Selles, Robert R; Storch, Eric A

    2016-04-01

    Family accommodation in obsessive-compulsive disorder (OCD) is characterized by myriad behaviors, such as modifying family routines, facilitating avoidance, and engaging in compulsions to reduce obsessional distress. It has been linked to various deleterious outcomes including increased functional impairment and poorer treatment response for OCD. Although extant literature suggests a linear relationship between family accommodation and OCD symptom severity, the magnitude and statistical significance of this association has been inconsistent across studies, indicating that moderators may be influencing this relationship. The present study examined this relationship using meta-analytic techniques, and investigated sample-dependent (age, gender, comorbid anxiety/mood disorders) and methodological (administration method and number of items used in family accommodation measure, informant type, sample size, publication year) moderators. Forty-one studies were included in the present meta-analysis, and the overall effect size (ES) for the correlation between family accommodation and OCD symptom severity was moderate (r=.42). Moderator analyses revealed that the number of items on the family accommodation scale moderated the ES. No other sample-dependent or methodological characteristics emerged as moderators. In addition to being the first systematic examination of family accommodation moderators, these results highlight the moderate relationship between family accommodation and OCD severity that is influenced by measurement scales. Findings may be used to guide clinical care and inform future investigations by providing a more nuanced understanding of family accommodation in OCD. Copyright © 2016 Elsevier Ltd. All rights reserved.

  11. Computational dynamics of soft machines

    NASA Astrophysics Data System (ADS)

    Hu, Haiyan; Tian, Qiang; Liu, Cheng

    2017-06-01

    Soft machine refers to a kind of mechanical system made of soft materials to complete sophisticated missions, such as handling a fragile object and crawling along a narrow tunnel corner, under low cost control and actuation. Hence, soft machines have raised great challenges to computational dynamics. In this review article, recent studies of the authors on the dynamic modeling, numerical simulation, and experimental validation of soft machines are summarized in the framework of multibody system dynamics. The dynamic modeling approaches are presented first for the geometric nonlinearities of coupled overall motions and large deformations of a soft component, the physical nonlinearities of a soft component made of hyperelastic or elastoplastic materials, and the frictional contacts/impacts of soft components, respectively. Then the computation approach is outlined for the dynamic simulation of soft machines governed by a set of differential-algebraic equations of very high dimensions, with an emphasis on the efficient computations of the nonlinear elastic force vector of finite elements. The validations of the proposed approaches are given via three case studies, including the locomotion of a soft quadrupedal robot, the spinning deployment of a solar sail of a spacecraft, and the deployment of a mesh reflector of a satellite antenna, as well as the corresponding experimental studies. Finally, some remarks are made for future studies.

  12. Spacelab payload accommodation handbook. Main volume

    NASA Technical Reports Server (NTRS)

    1978-01-01

    The main characteristics of the Spacelab system are described to enable individual experimenters or payload planning groups to determine how their payload equipment can be accommodated by Spacelab. Spacelab/experiment interfaces, Spacelab payload support systems and requirements that the experiments have to comply with are described to allow experiment design and development. The basic operational aspects are outlined as far as they have an impact on experiment design. The relationship of the Spacelab Payload Accommodation Handbook to Space Transportation System documentation is outlined. Data concerning the space shuttle system are briefly described.

  13. An Accommodations Model for the Secondary Inclusive Classroom

    ERIC Educational Resources Information Center

    Scanlon, David; Baker, Diana

    2012-01-01

    Despite expectations for accommodations in inclusive classrooms, little guidance for effective practice is available. Most accommodations policies and evidence-based practices address assessments. High school regular and special educators collaborated in focus groups to articulate a model based on their practices and perceptions of best practice.…

  14. Religious Observance Accommodation in Ontario Universities. Discussion Paper.

    ERIC Educational Resources Information Center

    Reed, Carole Ann

    This paper highlights the religious accommodations that Ontario (Canada) universities have undertaken to create an inclusive, supportive learning community for all students, faculty, and staff. It outlines the demographic changes and public policy surrounding religious accommodation issues in Canada and in Ontario in particular, focusing on the…

  15. Experimental Validation of a Coupled Fluid-Multibody Dynamics Model for Tanker Trucks

    DTIC Science & Technology

    2007-11-08

    order to accurately predict the dynamic response of tanker trucks, the model must accurately account for the following effects : • Incompressible...computational code which uses a time- accurate explicit solution procedure is used to solve both the solid and fluid equations of motion. Many commercial...position vector, τ is the deviatoric stress tensor, D is the rate of deformation tensor, f r is the body force vector, r is the artificial

  16. Computational methods and software systems for dynamics and control of large space structures

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Felippa, C. A.; Farhat, C.; Pramono, E.

    1990-01-01

    This final report on computational methods and software systems for dynamics and control of large space structures covers progress to date, projected developments in the final months of the grant, and conclusions. Pertinent reports and papers that have not appeared in scientific journals (or have not yet appeared in final form) are enclosed. The grant has supported research in two key areas of crucial importance to the computer-based simulation of large space structure. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area, as reported here, involves massively parallel computers.

  17. Quick and Easy Adaptations and Accommodations for Early Childhood Students

    ERIC Educational Resources Information Center

    Breitfelder, Leisa M.

    2008-01-01

    Research-based information is used to support the idea of the use of adaptations and accommodations for early childhood students who have varying disabilities. Multiple adaptations and accommodations are outlined. A step-by-step plan is provided on how to make specific adaptations and accommodations to fit the specific needs of early childhood…

  18. Dynamic modelling and experimental validation of three wheeled tilting vehicles

    NASA Astrophysics Data System (ADS)

    Amati, Nicola; Festini, Andrea; Pelizza, Luigi; Tonoli, Andrea

    2011-06-01

    The present paper describes the study of the stability in the straight running of a three-wheeled tilting vehicle for urban and sub-urban mobility. The analysis was carried out by developing a multibody model in the Matlab/SimulinkSimMechanics environment. An Adams-Motorcycle model and an equivalent analytical model were developed for the cross-validation and for highlighting the similarities with the lateral dynamics of motorcycles. Field tests were carried out to validate the model and identify some critical parameters, such as the damping on the steering system. The stability analysis demonstrates that the lateral dynamic motions are characterised by vibration modes that are similar to that of a motorcycle. Additionally, it shows that the wobble mode is significantly affected by the castor trail, whereas it is only slightly affected by the dynamics of the front suspension. For the present case study, the frame compliance also has no influence on the weave and wobble.

  19. Thermodynamics of mixtures of patchy and spherical colloids of different sizes: A multi-body association theory with complete reference fluid information.

    PubMed

    Bansal, Artee; Valiya Parambathu, Arjun; Asthagiri, D; Cox, Kenneth R; Chapman, Walter G

    2017-04-28

    We present a theory to predict the structure and thermodynamics of mixtures of colloids of different diameters, building on our earlier work [A. Bansal et al., J. Chem. Phys. 145, 074904 (2016)] that considered mixtures with all particles constrained to have the same size. The patchy, solvent particles have short-range directional interactions, while the solute particles have short-range isotropic interactions. The hard-sphere mixture without any association site forms the reference fluid. An important ingredient within the multi-body association theory is the description of clustering of the reference solvent around the reference solute. Here we account for the physical, multi-body clusters of the reference solvent around the reference solute in terms of occupancy statistics in a defined observation volume. These occupancy probabilities are obtained from enhanced sampling simulations, but we also present statistical mechanical models to estimate these probabilities with limited simulation data. Relative to an approach that describes only up to three-body correlations in the reference, incorporating the complete reference information better predicts the bonding state and thermodynamics of the physical solute for a wide range of system conditions. Importantly, analysis of the residual chemical potential of the infinitely dilute solute from molecular simulation and theory shows that whereas the chemical potential is somewhat insensitive to the description of the structure of the reference fluid, the energetic and entropic contributions are not, with the results from the complete reference approach being in better agreement with particle simulations.

  20. Structure and thermodynamics of a mixture of patchy and spherical colloids: A multi-body association theory with complete reference fluid information

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bansal, Artee; Asthagiri, D.; Cox, Kenneth R.

    A mixture of solvent particles with short-range, directional interactions and solute particles with short-range, isotropic interactions that can bond multiple times is of fundamental interest in understanding liquids and colloidal mixtures. Because of multi-body correlations, predicting the structure and thermodynamics of such systems remains a challenge. Earlier Marshall and Chapman [J. Chem. Phys. 139, 104904 (2013)] developed a theory wherein association effects due to interactions multiply the partition function for clustering of particles in a reference hard-sphere system. The multi-body effects are incorporated in the clustering process, which in their work was obtained in the absence of the bulk medium.more » The bulk solvent effects were then modeled approximately within a second order perturbation approach. However, their approach is inadequate at high densities and for large association strengths. Based on the idea that the clustering of solvent in a defined coordination volume around the solute is related to occupancy statistics in that defined coordination volume, we develop an approach to incorporate the complete information about hard-sphere clustering in a bulk solvent at the density of interest. The occupancy probabilities are obtained from enhanced sampling simulations but we also develop a concise parametric form to model these probabilities using the quasichemical theory of solutions. We show that incorporating the complete reference information results in an approach that can predict the bonding state and thermodynamics of the colloidal solute for a wide range of system conditions.« less

  1. Thermodynamics of mixtures of patchy and spherical colloids of different sizes: A multi-body association theory with complete reference fluid information

    NASA Astrophysics Data System (ADS)

    Bansal, Artee; Valiya Parambathu, Arjun; Asthagiri, D.; Cox, Kenneth R.; Chapman, Walter G.

    2017-04-01

    We present a theory to predict the structure and thermodynamics of mixtures of colloids of different diameters, building on our earlier work [A. Bansal et al., J. Chem. Phys. 145, 074904 (2016)] that considered mixtures with all particles constrained to have the same size. The patchy, solvent particles have short-range directional interactions, while the solute particles have short-range isotropic interactions. The hard-sphere mixture without any association site forms the reference fluid. An important ingredient within the multi-body association theory is the description of clustering of the reference solvent around the reference solute. Here we account for the physical, multi-body clusters of the reference solvent around the reference solute in terms of occupancy statistics in a defined observation volume. These occupancy probabilities are obtained from enhanced sampling simulations, but we also present statistical mechanical models to estimate these probabilities with limited simulation data. Relative to an approach that describes only up to three-body correlations in the reference, incorporating the complete reference information better predicts the bonding state and thermodynamics of the physical solute for a wide range of system conditions. Importantly, analysis of the residual chemical potential of the infinitely dilute solute from molecular simulation and theory shows that whereas the chemical potential is somewhat insensitive to the description of the structure of the reference fluid, the energetic and entropic contributions are not, with the results from the complete reference approach being in better agreement with particle simulations.

  2. Accommodative Behavior of Young Eyes Wearing Multifocal Contact Lenses.

    PubMed

    Altoaimi, Basal H; Almutairi, Meznah S; Kollbaum, Pete S; Bradley, Arthur

    2018-05-01

    The effectiveness of multifocal contact lenses (MFCLs) at slowing myopia progression may hinge on the accommodative behavior of young eyes fit with these presbyopic style lenses. Can they remove hyperopic defocus? Convergence accommodation as well as pupil size and the zonal geometry are likely to contribute to the final accommodative responses. The aim of this study was to examine the accommodation behavior of young adult eyes wearing MFCLs and the effectiveness of these MFCLs at removing foveal hyperopic defocus when viewing near targets binocularly. Using a high-resolution Shack-Hartmann aberrometer, accommodation and pupil behavior of eight young adults (27.25 ± 2.05 years) were measured while subjects fixated a 20/40 character positioned between 2 m and 20 cm (0.50 to 5.00 diopters [D]) in 0.25-D steps. Refractive states were measured while viewing binocularly and monocularly with single-vision and both center-distance and center-near +2.00 D add MFCLs. Refractive state was defined using three criteria: the dioptric power that would (1) minimize the root mean square wavefront error, (2) focus the pupil center, and (3) provide the peak image quality. Refractive state pupil maps reveal the complex optics that exist in eyes wearing MFCLs. Reduced accommodative gain beyond the far point of the near add revealed that young subjects used the added plus power to help focus near targets. During accommodation to stimuli closer than the far point generated by the add power, a midperipheral region of the pupil was approximately focused, resulting in the smallest accommodative errors for the minimum root mean square-defined measures of refractive state. Paraxial images were always hyperopically or myopically defocused in eyes viewing binocularly with center-distance or center-near MFCLs, respectively. Because of zone geometry in the concentric MFCLs tested, the highly aberrated transition zone between the distance and near optics contributed a significant proportion and

  3. The effect of proximity on open-loop accommodation responses measured with pinholes.

    PubMed

    Morrison, K A; Seidel, D; Strang, N C; Gray, L S

    2010-07-01

    Open-loop accommodation levels were measured in 41 healthy, young subjects using a Shin-Nippon SRW-5000 autorefractor in the three viewing conditions: a small physical pinhole pupil (SP), an optically projected pinhole in Maxwellian view (MV) and in the dark (DF). The target viewed through the pinholes was a high-contrast letter presented at 0 D vergence in a +5 D Badal lens system. Overall, results showed that SP open-loop accommodation levels were significantly higher than MV and DF levels. Subjects could be divided into two distinct subgroups according to their response behaviour: responders to the proximal effect of the small physical pinhole (SP accommodation > MV accommodation) and non-responders to the proximal effect of the small physical pinhole (SP accommodation approximately MV accommodation). Correlation analysis demonstrated that open-loop accommodation for both pinhole conditions was correlated with DF for the responders, while for the non-responders SP and MV accommodation were correlated, but were not related to DF accommodation. This suggests that under open-loop conditions some individuals' accommodation levels are mainly affected by proximal and cognitive factors (responders) while others are guided primarily by the presence of the more distal target (non-responders). In conclusion, MV reduces the proximal effect of the physical pinhole and produces open-loop accommodation responses which are more consistent than SP and DF responses.

  4. Convergence and Accommodation Development Is Preprogrammed in Premature Infants.

    PubMed

    Horwood, Anna M; Toor, Sonia S; Riddell, Patricia M

    2015-08-01

    This study investigated whether vergence and accommodation development in preterm infants is preprogrammed or is driven by experience. Thirty-two healthy infants, born at mean 34 weeks gestation (range, 31.2-36 weeks), were compared with 45 healthy full-term infants (mean 40.0 weeks) over a 6-month period, starting at 4 to 6 weeks postnatally. Simultaneous accommodation and convergence to a detailed target were measured using a Plusoptix PowerRefII infrared photorefractor as a target moved between 0.33 and 2 m. Stimulus/response gains and responses at 0.33 and 2 m were compared by both corrected (gestational) age and chronological (postnatal) age. When compared by their corrected age, preterm and full-term infants showed few significant differences in vergence and accommodation responses after 6 to 7 weeks of age. However, when compared by chronological age, preterm infants' responses were more variable, with significantly reduced vergence gains, reduced vergence response at 0.33 m, reduced accommodation gain, and increased accommodation at 2 m compared to full-term infants between 8 and 13 weeks after birth. When matched by corrected age, vergence and accommodation in preterm infants show few differences from full-term infants' responses. Maturation appears preprogrammed and is not advanced by visual experience. Longer periods of immature visual responses might leave preterm infants more at risk of development of oculomotor deficits such as strabismus.

  5. Parental accommodation of child anxiety and related symptoms: Range, impact, and correlates

    PubMed Central

    Thompson-Hollands, Johanna; Kerns, Caroline E.; Pincus, Donna B.; Comer, Jonathan S.

    2014-01-01

    Parental accommodation—i.e., changes in parents’ behavior in attempts to prevent or reduce child distress—has been most studied in relation to OCD. Although recent work suggests parents of children with non-OCD anxiety diagnoses also engage in accommodation, little is known about the specific forms, correlates, and associated interference of such accommodation. The present study examined the range and associated interference of parental accommodation behaviors using the newly developed Family Accommodation Checklist and Interference Scale (FACLIS) in a sample of the parents of 71 clinic-referred children with anxiety disorders (NMothers = 68; NFathers= 51). The FACLIS demonstrated good reliability and validity. Ninety-seven percent of mothers and 88% of fathers reported engaging in at least one type of accommodation in the previous two weeks, with parents reporting an average of roughly 4 interfering parental accommodation behaviors. Greater parental accommodation and associated interference were associated with higher maternal distress. Among the anxiety disorders, accommodation was most strongly associated with generalized and separation anxiety disorder, as well as specific phobias. Findings (a) offer psychometric support for the FACLIS as a reliable and valid tool for the assessment of accommodation range and impact, and (b) help clarify the considerable scope and interference associated with parental accommodation of childhood anxiety. PMID:25261837

  6. Evaluating Computer-Based Test Accommodations for English Learners

    ERIC Educational Resources Information Center

    Roohr, Katrina Crotts; Sireci, Stephen G.

    2017-01-01

    Test accommodations for English learners (ELs) are intended to reduce the language barrier and level the playing field, allowing ELs to better demonstrate their true proficiencies. Computer-based accommodations for ELs show promising results for leveling that field while also providing us with additional data to more closely investigate the…

  7. Disability disclosure and workplace accommodations among youth with disabilities.

    PubMed

    Lindsay, Sally; Cagliostro, Elaine; Leck, Joanne; Shen, Winny; Stinson, Jennifer

    2018-03-20

    Many youths with disabilities find it challenging to disclose their medical condition and request workplace accommodations. Our objective was to explore when and how young people with disabilities disclose their condition and request workplace accommodations. We conducted 17 in-depth interviews (11 females, six males) with youth with disabilities aged 15-34 (mean age 26). We analyzed our data using an interpretive, qualitative, and thematic approach. Our results showed the timing of when youth disclosed their disability to their employer depended on disability type and severity, comfort level, type of job, and industry. Youth's strategies and reasons for disclosure included advocating for their needs, being knowledgeable about workplace rights, and accommodation solutions. Facilitators for disclosure included job preparation, self-confidence, and self-advocacy skills, and having an inclusive work environment. Challenges to disability disclosure included the fear of stigma and discrimination, lack of employer's knowledge about disability and accommodations, negative past experiences of disclosing, and not disclosing on your own terms. Our findings highlight that youth encounter several challenges and barriers to disclosing their condition and requesting workplace accommodations. The timing and process for disclosing is complex and further work is needed to help support youth with disclosing their condition. Implications for rehabilitation Clinicians, educators, and employers should emphasize the importance of mentoring and leadership programs to give youth the confidence and self-advocacy skills needed to disclose and ask for accommodations in the workplace. Clinicians should advocate for the inclusion of youth with disabilities in the workforce and educate employers on the importance of doing so. Youth with disabilities need more opportunities for employment training and particularly how to disclose their disability and request workplace accommodations.

  8. Prediction of accommodative optical response in prepresbyopic patients using ultrasound biomicroscopy

    PubMed Central

    Ramasubramanian, Viswanathan; Glasser, Adrian

    2015-01-01

    PURPOSE To determine whether relatively low-resolution ultrasound biomicroscopy (UBM) can predict the accommodative optical response in prepresbyopic eyes as well as in a previous study of young phakic subjects, despite lower accommodative amplitudes. SETTING College of Optometry, University of Houston, Houston, USA. DESIGN Observational cross-sectional study. METHODS Static accommodative optical response was measured with infrared photorefraction and an autorefractor (WR-5100K) in subjects aged 36 to 46 years. A 35 MHz UBM device (Vumax, Sonomed Escalon) was used to image the left eye, while the right eye viewed accommodative stimuli. Custom-developed Matlab image-analysis software was used to perform automated analysis of UBM images to measure the ocular biometry parameters. The accommodative optical response was predicted from biometry parameters using linear regression, 95% confidence intervals (CIs), and 95% prediction intervals. RESULTS The study evaluated 25 subjects. Per-diopter (D) accommodative changes in anterior chamber depth (ACD), lens thickness, anterior and posterior lens radii of curvature, and anterior segment length were similar to previous values from young subjects. The standard deviations (SDs) of accommodative optical response predicted from linear regressions for UBM-measured biometry parameters were ACD, 0.15 D; lens thickness, 0.25 D; anterior lens radii of curvature, 0.09 D; posterior lens radii of curvature, 0.37 D; and anterior segment length, 0.42 D. CONCLUSIONS Ultrasound biomicroscopy parameters can, on average, predict accommodative optical response with SDs of less than 0.55 D using linear regressions and 95% CIs. Ultrasound biomicroscopy can be used to visualize and quantify accommodative biometric changes and predict accommodative optical response in prepresbyopic eyes. PMID:26049831

  9. A Daily Diary Study of Posttraumatic Stress Symptoms and Romantic Partner Accommodation

    PubMed Central

    Campbell, Sarah B.; Renshaw, Keith D.; Kashdan, Todd B.; Curby, Timothy W.; Carter, Sarah P.

    2017-01-01

    Little is known about the role of romantic partner symptom accommodation in PTSD symptom maintenance. To explore the bidirectional associations of posttraumatic stress disorder (PTSD) symptoms and romantic partner symptom accommodation over time, military servicemen (n = 64) with symptoms of PTSD and their co-habiting heterosexual civilian romantic partners (n = 64) completed a 2-week daily diary study. Cross-lagged, autoregressive models assessed the stability of men’s PTSD symptoms and partners’ accommodation, as well as the prospective associations of earlier PTSD symptoms with later accommodation and vice versa. Analyses used Bayesian estimation to provide point estimates (b) and Credible Intervals (CIs). In all models, PTSD symptoms (total and individual clusters) were highly stable (b = 0.91; CI: 0.88–0.95), and accommodation was moderately stable (b = 0.48; CI: 0.40–0.54). In all models, earlier PTSD symptoms (total and clusters) were significantly, positively associated with later accommodation (b = 0.04; CI: 0.02–0.07). In contrast, earlier accommodation was significantly associated only with later situational avoidance (b = 0.02; CI: 0.00–0.07). Thus, PTSD symptoms may lead to subsequent accommodating behaviors in romantic partners, but partner accommodation seems to contribute only to survivors’ future situational avoidance symptoms. The findings reinforce the notion that PTSD symptoms have an impact on relationship behaviors, and that accommodation from partners may sustain avoidant behaviors in particular. Clinicians should attend to romantic partners’ accommodating behaviors when working with survivors. PMID:28270332

  10. Testing Accommodations: Theory and Research to Inform Practice

    ERIC Educational Resources Information Center

    Kettler, Ryan J.

    2012-01-01

    This article presents a framework for practitioners in education and psychology to select accommodations based on student profiles and testing demands. A brief history of testing accommodations policy in the US and a definition of terms provide context for the discussion. A review of theory and empirical findings related to testing accommodations…

  11. Layout of personnel accommodations for the SOFIA

    NASA Astrophysics Data System (ADS)

    Daughters, David M.; Bruich, J. G.; Arceneaux, Gregory P.; Zirretta, Jason; Caton, William B.

    2000-06-01

    The NASA Stratospheric Observatory for Infrared Astronomy (SOFIA) Observatory is based upon a refurbished and heavily modified Boeing 747 SP aircraft. The Observatory, which provides accommodations for the Deutsches Zentrum Fur Luftund Raumfahrt 2.5 m telescope, science investigator teams, scientific instruments, mission crew and support systems. The US contractor team has removed most of the aircraft original furnishings and designed a new Layout of Personnel Accommodations (LOPA) tailored to SOFIA's needs.

  12. Space station dynamic modeling, disturbance accommodation, and adaptive control

    NASA Technical Reports Server (NTRS)

    Wang, S. J.; Ih, C. H.; Lin, Y. H.; Metter, E.

    1985-01-01

    Dynamic models for two space station configurations were derived. Space shuttle docking disturbances and their effects on the station and solar panels are quantified. It is shown that hard shuttle docking can cause solar panel buckling. Soft docking and berthing can substantially reduce structural loads at the expense of large shuttle and station attitude excursions. It is found predocking shuttle momentum reduction is necessary to achieve safe and routine operations. A direct model reference adaptive control is synthesized and evaluated for the station model parameter errors and plant dynamics truncations. The rigid body and the flexible modes are treated. It is shown that convergence of the adaptive algorithm can be achieved in 100 seconds with reasonable performance even during shuttle hard docking operations in which station mass and inertia are instantaneously changed by more than 100%.

  13. Space Station accommodation of attached payloads

    NASA Technical Reports Server (NTRS)

    Browning, Ronald K.; Gervin, Janette C.

    1987-01-01

    The Attached Payload Accommodation Equipment (APAE), which provides the structure to attach payloads to the Space Station truss assembly, to access Space Station resources, and to orient payloads relative to specified targets, is described. The main subelements of the APAE include a station interface adapter, payload interface adapter, subsystem support module, contamination monitoring system, payload pointing system, and attitude determination system. These components can be combined to provide accommodations for small single payloads, small multiple payloads, large self-supported payloads, carrier-mounted payloads, and articulated payloads. The discussion also covers the power, thermal, and data/communications subsystems and operations.

  14. Guidelines for Providing Accommodations Using CASAS Assessment for Learners with Disabilities

    ERIC Educational Resources Information Center

    CASAS - Comprehensive Adult Student Assessment Systems (NJ1), 2005

    2005-01-01

    These guidelines address methods for administering Comprehensive Adult Student Assessment System (CASAS) assessments using accommodations for learners with documented disabilities. The suggested accommodations for disability categories include provisions for: (1) Accommodations in test administration procedures; and (2) Use of appropriate CASAS…

  15. Accommodative performance for chromatic displays.

    PubMed

    Lovasik, J V; Kergoat, H

    1988-01-01

    Over the past few years, video display units (VDUs) have been incorporated into many varieties of workplaces and occupational demands. The success of electro-optical displays in facilitating and improving job performance has spawned interest in extracting further advantage from VDUs by incorporating colour coding into such communication systems. However, concerns have been raised about the effect of chromatic stimuli on the visual comfort and task efficiency, because of the chromatic aberration inherent in the optics of the human eye. In this study, we used a computer aided laser speckle optometer system to measure the accommodative responses to brightness-matched chromatic letters displayed on a high-resolution RGB monitor. Twenty, visually normal, paid volunteers in a 22-35 year age category served as subjects. Stimuli were 14, 21, 28 minutes of arc letters presented in a 'monochromatic' (white, red, green or blue, on a black background) or 'multichromatic' (blue-red, blue-green, red-green, foreground-background combinations) mode at 40 and 80 cm viewing distances. The results demonstrated that while the accommodative responses were strongly influenced by the foreground-background colour combination, the group-averaged dioptric difference across colours was relatively small. Further, accommodative responses were not guided in any systematic fashion by the size of letters presented for fixation. Implications of these findings for display designs are discussed.

  16. The Measures Contribution Researches on Renewable Energy Accommodation Based on Production Simulation

    NASA Astrophysics Data System (ADS)

    Zhe, MI; Jinfang, Zhang; Jun, Liu

    2018-06-01

    This paper presents the impacts of load, source and grid factors on renewable energy accommodation in the northern region of China. Renewable energy curtailment reasons and key measures to improve accommodations are also discussed. The production simulation method is utilized to analysis renewable energy accommodation and the Shapely value method is introduced to calculate the accommodation contribution rate of different factors. The result shows that the amount of renewable energy accommodation is 389 TWh in northern region of China by the year 2020. The contribution rate of load, source and grid factors to renewable energy accommodation are 39%, 35.8% and 25.1%, respectively.

  17. [Electrostimulation and magnetic therapy in the treatment of accommodation cramp and in the prevention of progressive myopia in children and adolescents].

    PubMed

    Riabtseva, A A; Gerasimenko, M Iu; Savina, M M; Filatova, E V

    2002-01-01

    The paper presents a procedure and results of use of electrostimulation, magnetic therapy, and electrophoresis during treatment for accommodation cramp and in the prevention of myopia in children and adolescents. Data that characterize the dynamics and stability of achieved results are given.

  18. Subjective vs Objective Accommodative Amplitude: Preschool to Presbyopia

    PubMed Central

    Anderson, Heather A.; Stuebing, Karla K.

    2014-01-01

    Purpose This study compared subjective and objective accommodative amplitudes to characterize changes from preschool to presbyopia. Methods Monocular accommodative amplitude was measured with three techniques in random order (subjective push-up, objective minus lens stimulated, and objective proximal stimulated) on 236 subjects 3–64 years using a 1.5mm letter. Subjective push-up amplitudes were the dioptric distance at which the target first blurred along a near-point rod. Objective minus lens stimulated amplitudes were the greatest accommodative response obtained by Grand Seiko autorefraction as subjects viewed the stimulus at 33cm through increasing minus lens powers. Objective proximal stimulated amplitudes were the greatest accommodative response obtained by Grand Seiko autorefraction as subjects viewed the stimulus at increasing proximity from 40cm up to 3.33cm. Results In comparison with subjective push-up amplitudes, objective amplitudes were lower at all ages, with the most dramatic difference occurring in the 3–5 year group (subjective push-up = 16.00 ± 4.98D versus objective proximal stimulated = 7.94 ± 2.37D and objective lens stimulated = 6.20 ± 1.99D). Objective proximal and lens stimulated amplitudes were largest in the 6–10 year group (8.81 ± 1.24D and 8.05 ± 1.82D, respectively) and gradually decreased until the fourth decade of life when a rapid decline to presbyopia occurred. There was a significant linear relationship between objective techniques (y = 0.74 + 0.96x, R2 = 0.85, p<0.001) with greater amplitudes measured for the proximal stimulated technique (mean difference = 0.55D). Conclusions Objective measurements of accommodation demonstrate that accommodative amplitude is substantially less than that measured by the subjective push-up technique, particularly in young children. These findings have important clinical implications for the management of uncorrected hyperopia. PMID:25602235

  19. Caffeine intake is associated with pupil dilation and enhanced accommodation

    PubMed Central

    Abokyi, S; Owusu-Mensah, J; Osei, K A

    2017-01-01

    Purpose It is purported that caffeine, an autonomic stimulant, affects visual performance. This study sought to assess whether caffeine intake was associated with changes in pupil size and/or amplitude of accommodation. Patients and methods A double-masked, crossover study was conducted in 50 healthy subjects of age range 19 to 25 years. Subjects were randomized to treatments such that subjects consumed either 250 mg caffeine drink or vehicle on separate days. Amplitude of accommodation was measured by the push-up technique, and pupil size using a millimeter ruler fixed to a slit lamp biomicroscope in dim illumination (5 lux). Amplitude of accommodation and pupil size were taken at baseline, and at 30, 60 and 90 min time points post treatment. Repeated measures one-way ANOVA and paired t-test were used in analyzing data. Results Amplitude of accommodation and pupil size after caffeine intake were significantly greater than vehicle (P<0.001) at each time point. Consumption of the caffeine beverage was associated with significant increases in amplitude of accommodation and pupil size with time (P<0.001). Amplitude of accommodation rose from 12.4 (±2.2 D) at baseline to 15.8(±2.6 D) at 90 min. Similarly, pupil size increased from 3.4 (±0.4 mm) at baseline to 4.5 (±0.72 mm) at 90 min. Consumption of vehicle was not associated with increase in amplitude of accommodation or pupil size with time. Conclusion Pupil size and accommodation are affected after ingestion of caffeine. This study suggests caffeine may have some influence on visual functions. PMID:27983733

  20. Measuring Changes in Ciliary Muscle Thickness with Accommodation in Young Adults

    PubMed Central

    Lossing, Laura Ashley; Sinnott, Loraine T.; Kao, Chiu-Yen; Richdale, Kathryn; Bailey, Melissa D.

    2012-01-01

    Purpose To develop a measurement protocol for changes in the shape and size of the ciliary muscle with accommodation using the Zeiss Visante™ Anterior Segment Optical Coherence Tomographer (AS-OCT) and to determine the test-retest repeatability of these measurements. Methods Subjects were 25 adults ages 23–28 years. The ciliary muscle was imaged at two visits with the Visante™ while accommodative response was monitored during imaging using the PowerRefractor. Ciliary muscle thickness was measured at 1 mm (CMT1), 2 mm (CMT2), and 3 mm (CMT3) posterior to the scleral spur and at the point of maximal thickness (CMTMAX). Thickness was measured at these locations while subjects viewed a target at distance and at a 4.00-D accommodative stimulus. Outcome measures were the change in thickness between distance and the 4.00-D stimulus and the change in thickness per diopter of accommodative response (PowerRefractor). Finally, the repeatability measurements between visit 1 and visit 2 were determined with a Bland-Altman analysis. Results The statistically significant modeled changes in ciliary muscle thickness were as follows: CMTMAX = 69.2 μm (4.00-D stimulus) and 18.1 μm (per diopter of accommodation); CMT1 = 45.2 μm (4.00-D stimulus) and 12.3 μm (per diopter of accommodation); and CMT3 = −45.9 μm (4.00-D stimulus) and −12.0 μm (per diopter of accommodation); p < 0.0001 for all. Conclusions The combination of the Visante™ and the PowerRefractor is a feasible tool for measuring thickening of ciliary muscle at more anterior locations and thinning at more posterior locations during accommodation. We noted a wide range of accommodative responses during the time of image capture in this study indicating that the most accurate estimates of the change in ciliary muscle dimensions with accommodation may be obtained by using accommodative response rather than stimulus values and by using measurements taken simultaneously with image capture. PMID:22504328