Properties Of Model Research Articles

A new model of job design: Initial evidence and implications for future research

AbstractClegg and Spencer's (2007) model of job design synthesizes and extends recent conceptions of the job design process by incorporating variables such as knowledge, motivation, and trust into a cyclical and dynamic system. The objective of this study was to examine the sequential organization of variables that comprise the model, as a basis from which to justify further investigations of the model's dynamic properties. Data were collected via questionnaires from 432 participants in two work organizations. Results obtained from structural equation modeling are broadly supportive of the proposed relationships between the variables. Implications of this initial study for future research and practice are discussed. © 2011 Wiley Periodicals, Inc.

Evidence-based modeling of network discharge dynamics during periodic pacing to control epileptiform activity

Deep brain stimulation (DBS) is a promising therapeutic approach for epilepsy treatment. Recently, research has focused on the implementation of stimulation protocols that would adapt to the patients need (adaptive stimulation) and deliver electrical stimuli only when it is most useful. A formal mathematical description of the effects of electrical stimulation on neuronal networks is a prerequisite for the development of adaptive DBS algorithms. Using tools from non-linear dynamic analysis, we describe an evidence-based, mathematical modeling approach that (1) accurately simulates epileptiform activity at time-scales of single and multiple ictal discharges, (2) simulates modulation of neural dynamics during epileptiform activity in response to fixed, low-frequency electrical stimulation, (3) defines a mapping from real-world observations to model state, and (4) defines a mapping from model state to real-world observations. We validate the real-world utility of the model's properties by statistical comparison between the number, duration, and interval of ictal-like discharges observed in vitro and those simulated in silica under conditions of repeated stimuli at fixed-frequency. These validation results confirm that the evidence-based modeling approach captures robust, informative features of neural network dynamics of in vitro epileptiform activity under periodic pacing and support its use for further implementation of adaptive DBS protocols for epilepsy treatment.

An emergency order allocation model based on multi‐provider in two‐echelon logistics service supply chain

PurposeOn one side, the purpose of this paper is to numerically analyze the emergency order allocation mechanism and help managers to understand the relationship between the emergency coefficient, uncertainty and emergency cost in two‐echelon logistics service supply chain. On the other side, the purpose of this paper is to help managers understand how to deal with the problem of order allocation in the two‐echelon logistics service supply chain better in the case of emergency.Design/methodology/approachThe paper presents a multi‐objective planning model for emergency order allocation and then uses numerical methods with LINGO 8.0 software to identify the model's properties. The application of the order allocation model is then presented by means of a case study.FindingsWith the augment of uncertainty, the general cost of logistics service integrator (LSI) is increasing, while the total satisfaction of all functional logistics service providers (FLSPs) is decreasing, as well as the capacity reliability; at the same time the emergency cost coefficient is closely correlative with the satisfaction and general penalty intensity of FLSPs; finally, the larger the emergency cost coefficient is, the more satisfaction of FLSPs, but the capacity reliability goes up first and down later.Research limitations/implicationsManagement should note that it is not better when emergency cost coefficient is bigger. The general satisfaction degree of FLSP increases with the augment of emergency cost coefficient, but there is an upper limit of the value, i.e. it will not increase indefinitely with the augment of emergency cost coefficient. This paper also has some limitations. The optional emergency cost coefficient only adopted a group of data to analyze while the trend of the reliability of logistics capacity needs to be further discussed. In addition, the algorithm of emergency order allocation model in the case of multi‐objective remains to be solved.Practical implicationsUnder emergency conditions, LSIs can adopt this kind of model to manage their FLSPs to obtain the higher logistics performance. But LSIs should be careful selecting emergency cost coefficient. In accordance with different degrees of emergency logistics demand, LSIs can determine reasonable emergency cost coefficient, but not the bigger, the better, on the premise that LSIs acquire maximum capacity guarantee degree and overall satisfaction degree of FLSPs. FLSPs can make contract bargaining of reasonable emergency coefficient with LSIs to make both sides get the best returns and realize the benefit balance.Originality/valueMany studies have emphasized the capacity allocation of manufactures, order allocation of manufacturing supply chain and scheduling model of emergency resources without monographic study of supply chain order allocation of logistics service. Because the satisfaction degree of FLSPs the cost of integrators needs to be considered in the process of order allocation, and the inventory cost of capacity does not exist, it is different from the issue of capacity allocation planning of manufacture supply chain. Meanwhile, the match of different kinds of logistics service capacity must be considered for the reason of the integrated feature of logistics service. Additionally, cost is not the most important decision objective because of the characteristics of demand uncertainty and weak economy. Accordingly, this paper considers these issues.

Social network dynamics of face-to-face interactions

The recent availability of data describing social networks is changing our understanding of the "microscopic structure" of a social tie. A social tie indeed is an aggregated outcome of many social interactions such as face-to-face conversations or phone calls. Analysis of data on face-to-face interactions shows that such events, as many other human activities, are bursty, with very heterogeneous durations. In this paper we present a model for social interactions at short time scales, aimed at describing contexts such as conference venues in which individuals interact in small groups. We present a detailed analytical and numerical study of the model's dynamical properties, and show that it reproduces important features of empirical data. The model allows for many generalizations toward an increasingly realistic description of social interactions. In particular, in this paper we investigate the case where the agents have intrinsic heterogeneities in their social behavior, or where dynamic variations of the local number of individuals are included. Finally we propose this model as a very flexible framework to investigate how dynamical processes unfold in social networks.

Experimental and numerical study on a laminar fluid–structure interaction reference test case

With the rapid development of numerical codes for fluid–structure interaction computations, the demand for validation test cases increases. In this paper we present a comparison between numerical and experimental results for such a fluid–structure interaction reference test case. The investigated structural model consists of an aluminum front cylinder with an attached thin metal plate and a rear mass at the trailing edge. All the structure is free to rotate around the axle mounted in the center of the front cylinder. The model's geometry and mechanical properties are chosen in such a way as to attain a self-exciting periodical swiveling movement when exposed to a uniform laminar flow. Reproducibility of the coupled fluid–structure motion is the key criterion for the selection of the model in order to permit an accurate reconstruction of the results in the time-phase space. The Reynolds number of the tests varies up to 270 and within that range the structure undergoes large deformations and shows a strong nonlinear behavior. It also presents two different self-excitation mechanisms depending on the flow velocity. Hence, challenging tasks arise for both the numerical solution algorithm and the experimental measurements. To account for the two different excitation mechanisms observed on increasing the speed of the flow, results for two different velocities are considered: the first at 1.07 m/s (Re=140) and the second at 1.45 m/s (Re=195). The comparisons presented in this paper are carried out on the basis of the time trace of the front body angle, trailing edge coordinates, structure deformation and the time-phase resolved flow velocity field. They reveal very good agreement in some of the fluid–structure interaction modes whereas in others deficiencies are observed that need to be analyzed in more detail.

Cold quarks in medium: An equation of state

We derive a compact, semi-algebraic expression for the cold quark matter equation of state (EoS) in a covariant model that exhibits coincident deconfinement and chiral symmetry restoring transitions in-medium. Along the way we obtain algebraic expressions for: the number- and scalar-density distributions in both the confining Nambu and deconfined Wigner phases; and the vacuum-pressure difference between these phases, which defines a bag constant. The confining interaction materially alters the distribution functions from those of a Fermi gas and consequently has a significant impact on the model's thermodynamic properties, which is apparent in the EoS.

A MODEL OF MAGNETIC BRAKING OF SOLAR ROTATION THAT SATISFIES OBSERVATIONAL CONSTRAINTS

The model of magnetic braking of solar rotation considered by Charbonneau & MacGregor has been modified so that it is able to reproduce for the first time the rotational evolution of both the fastest and slowest rotators among solar-type stars in open clusters of different ages, without coming into conflict with other observational constraints, such as the time evolution of the atmospheric Li abundance in solar twins and the thinness of the solar tachocline. This new model assumes that rotation-driven turbulent diffusion, which is thought to amplify the viscosity and magnetic diffusivity in stellar radiative zones, is strongly anisotropic with the horizontal components of the transport coefficients strongly dominating over those in the vertical direction. Also taken into account is the poloidal field decay that helps to confine the width of the tachocline at the solar age. The model's properties are investigated by numerically solving the azimuthal components of the coupled momentum and magnetic induction equations in two dimensions using a finite element method.

Asymptotic properties of a supposedly regular (Dirac-Born-Infeld) modification of general relativity

We apply the dynamical systems tools to study the asymptotic properties of a cosmological model based on a non-linear modification of General Relativity in which the standard Einstein-Hilbert action is replaced by one of Dirac-Born-Infeld type. It is shown that the dynamics of this model is extremely rich: there are found equilibrium points in the phase space that can be associated with matter-dominated, matter-curvature scaling, de Sitter, and even phantom-like solutions. Depending on the value of the overall parameters the dynamics in phase space can show multi-attractor structure into the future (multiple future attractors may co-exist). This is a consequence of bifurcations in control parameter space, showing strong dependence of the model's dynamical properties on the free parameters. Contrary to what is expected from non-linear modifications of general relativity of this kind, removal of the initial spacetime singularity is not a generic feature of the corresponding cosmological model. Instead, the starting point of the cosmic dynamics — the past attractor in the phase space — is a state of infinitely large value of the Hubble rate squared, usually associated with the big bang singularity.

A New Semi-Explicit Solvation Model: Fast Physics for Better Results

Computational physicists, chemists, and biologists have a critical need for better models of water and aqueous solutions. We present an exciting new solvation model called Semi-Explicit Assembly, which combines the speed of the fastest continuum models available with the strong physical basis and discrete water treatment afforded by explicit solvent simulations. We base our model on several simple physical properties of water as a solvent, collected directly from explicit solvent simulations for individual atomic solutes. As a first test and application of our method, we compute solvation free energies based on dispersion and electrostatics. Our approach, which is purely physical and involves no fitting of parameters to data sets, executes as fast as the popular Generalized Born solvation model, but with substantially improved accuracy in prediction of experimental solvation free energies. Also, the structure of our model means that improvements in simulation forcefields will improve our results as well. All of this comes without any artificial parameter adjustments; our model's properties are the same as those used directly in molecular dynamics. Our model's energetic accuracy and detailed structural information have wide-ranging implications for molecular modeling research.

A coloured Petri net analysis of the Transaction Internet Protocol

The Transaction Internet Protocol (TIP) aims at facilitating e-commerce by enforcing atomicity guarantees in transactions distributed between several autonomous transaction processing systems. In this work, the authors explore a holiday booking scenario in which a customer is protected by the TIP such as to prevent ending up with a hotel reservation without the requested flight reservation i.e. enclosed in the same holiday package. In fact, TIP defines an approach that makes the commit processing independent of the communication protocol used, but there are a number of potential pitfalls that make it useful to provide a formal approach to reason about the behavioural properties of TIP. The authors propose a coloured Petri net model that allows interactive simulation and verification of correctness properties within the CPN-tools modelling environment. Representative results for the generated reachability graph, providing an insight into the model's structural properties are shown at the end of this paper. The model can be used in the CPN-tools environment for model checking tasks, where the properties of interest can be expressed in graph exploration or temporal logic-based state space queries.

Business Cycles in the Equilibrium Model of Labor Market Search and Self-Insurance

The author introduces risk-averse preferences, labor-leisure choice, capital, individual productivity shocks, and market incompleteness to the standard Mortensen-Pissarides model of search and matching and explore the model's cyclical properties. There are four main findings. First and foremost, the baseline model can generate the observed large volatility of unemployment and vacancies with a realistic replacement ratio of the unemployment insurance benefits of 64 percent. Second, labor-leisure choice plays a crucial role in generating the large volatilities; additional utility from leisure when unemployed makes the value of unemployment close to the value of employment, which is crucial in generating a strong amplification, even with the moderate replacement ratio. Besides, it contributes to the amplification through an adjustment in the intensive margin of labor supply. Third, the borrowing constraint or uninsured individual productivity shocks do not significantly affect the cyclical properties of unemployment and vacancies: Most workers are well insured only with self-insurance. Fourth, the model better replicates the business cycle properties of the U.S. economy, thanks to the co-existence of adjustments in the intensive and extensive margins of labor supply and the stronger amplification.

Business Cycles in the Equilibrium Model of Labor Market Search and Self-Insurance

The author introduces risk-averse preferences, labor-leisure choice, capital, individual productivity shocks, and market incompleteness to the standard Mortensen-Pissarides model of search and matching and explore the model's cyclical properties. There are four main findings. First and foremost, the baseline model can generate the observed large volatility of unemployment and vacancies with a realistic replacement ratio of the unemployment insurance benefits of 64 percent. Second, labor-leisure choice plays a crucial role in generating the large volatilities; additional utility from leisure when unemployed makes the value of unemployment close to the value of employment, which is crucial in generating a strong amplification, even with the moderate replacement ratio. Besides, it contributes to the amplification through an adjustment in the intensive margin of labor supply. Third, the borrowing constraint or uninsured individual productivity shocks do not significantly affect the cyclical properties of unemployment and vacancies: Most workers are well insured only with self-insurance. Fourth, the model better replicates the business cycle properties of the U.S. economy, thanks to the co-existence of adjustments in the intensive and extensive margins of labor supply and the stronger amplification.

Engineless Unmanned Aerial Vehicle Propulsion by Dynamic Soaring

Dynamic soaring is a flight technique which extracts energy from wind gradients with the potential to power small unmanned aerial vehicles in maritime applications. Wind gradients of the required magnitude naturally occur at the air-sea interface due to friction between the waves and the moving air. Suitability of dynamic soaring as a means of propulsion requires clarification of the achievable flight performance and the likelihood of favorable winds. Optimal trajectories for minimal and maximal wind conditions are generated as well as trajectories for optimal cross-country travel. The flight model's differential flatness property is used to simplify the optimization problem. The likelihood of favorable winds is predicted based on long term weather statistics and knowledge of the minimal and maximal permissible wind strengths. Comparison of the likelihood of favorable winds for the wandering albatross and an unmanned aerial vehicle of similar size shows that the ability to fly close to the surface is a key factor governing dynamic soaring performance.

A new bidirectional heteroassociative memory encompassing correlational, competitive and topological properties

In this paper, we present a new recurrent bidirectional model that encompasses correlational, competitive and topological model properties. The simultaneous use of many classes of network behaviors allows for the unsupervised learning/categorization of perceptual patterns (through input compression) and the concurrent encoding of proximities in a multidimensional space. All of these operations are achieved within a common learning operation, and using a single set of defining properties. It is shown that the model can learn categories by developing prototype representations strictly from exposition to specific exemplars. Moreover, because the model is recurrent, it can reconstruct perfect outputs from incomplete and noisy patterns. Empirical exploration of the model's properties and performance shows that its ability for adequate clustering stems from: (1) properly distributing connection weights, and (2) producing a weight space with a low dispersion level (or higher density). In addition, since the model uses a sparse representation (k-winners), the size of topological neighborhood can be fixed, and no longer requires a decrease through time as was the case with classic self-organizing feature maps. Since the model's learning and transmission parameters are independent from learning trials, the model can develop stable fixed points in a constrained topological architecture, while being flexible enough to learn novel patterns.

Random Acyclic Networks

Directed acyclic graphs make up a fundamental class of networks that includes citation networks, food webs, and family trees, among others. Here we define a random graph model for directed acyclic graphs and give solutions for a number of the model's properties, including connection probabilities and component sizes, as well as a fast algorithm for simulating the model on a computer. We compare the predictions of the model to a real-world network of citations between physics papers and find surprisingly good agreement, suggesting that the structure of the real network may be quite well described by the random graph.

Network Traffic Flow Evolution Model Considering OD Demand Mutation

Abstract Considering such a fact that the traffic demand freshly entering a network does not have perfect information about traffic condition and then might choose travel routes randomly, we propose an improved network traffic flow evolution model in this article. The model's properties and fixed points are investigated. The fixed points of the model, which are different from traditional user equilibrium state or part user equilibrium state, can better formulate the result of traffic flow assignment in realization. Simulation results obtained from a grid network show that the model can be used to approximately model the process of realizing user equilibrium state, the network flow can indeed evolve to one or more fixed points, and the initial values of all available path flows can be zero.

A Half-Size Singularity Test Matrix for Fast and Reliable Passivity Assessment of Rational Models

One major difficulty in the rational modeling of linear systems is that the obtained model can be nonpassive, thereby leading to unstable simulations. The model's passivity properties are usually assessed by computing the eigenvalues of a Hamiltonian matrix, which is derived from the model parameters. The purely imaginary eigenvalues represent crossover frequencies where the model's conductance matrix is singular, allowing to pinpoint frequency intervals of passivity violations. Unfortunately, the eigenvalue computation time can be excessive for large models. Also, the test applies only to symmetrical models, and the testing is made difficult by numerical noise in the extracted eigenvalues. In this paper a new (non-Hamiltonian) half-size singularity test matrix is derived for use with admittance parameter state-space models, which overcomes these shortcomings. It gives a computational speedup by a factor of eight; it is applicable to both symmetric and unsymmetrical models; and it produces noiseless eigenvalues for reliable passivity assessment.

OpenAD/F

The Open/ADF tool allows the evaluation of derivatives of functions defined by a Fortran program. The derivative evaluation is performed by a Fortran code resulting from the analysis and transformation of the original program that defines the function of interest. Open/ADF has been designed with a particular emphasis on modularity, flexibility, and the use of open source components. While the code transformation follows the basic principles of automatic differentiation, the tool implements new algorithmic approaches at various levels, for example, for basic block preaccumulation and call graph reversal. Unlike most other automatic differentiation tools, Open/ADF uses components provided by the Open/AD framework, which supports a comparatively easy extension of the code transformations in a language-independent fashion. It uses code analysis results implemented in the OpenAnalysis component. The interface to the language-independent transformation engine is an XML-based format, specified through an XML schema. The implemented transformation algorithms allow efficient derivative computations using locally optimized cross-country sequences of vertex, edge, and face elimination steps. Specifically, for the generation of adjoint codes, Open/ADF supports various code reversal schemes with hierarchical checkpointing at the subroutine level. As an example from geophysical fluid dynamics, a nonlinear time-dependent scalable, yet simple, barotropic ocean model is considered. OpenAD/F's reverse mode is applied to compute sensitivities of some of the model's transport properties with respect to gridded fields such as bottom topography as independent (control) variables.

Surface structure and structural point defects of liquid and amorphous aluminosilicatenanoparticles

The surface structure of liquid and amorphous aluminosilicate nanoparticles of compositionAl2O3·2SiO2 has been investigated in a model of different sizes ranging from 2.0 to 5.0 nm withthe Born–Mayer type pair potential under non-periodic boundary conditions.Models have been obtained by cooling from the melts at a constant density of2.6 g cm−3 via molecular dynamics (MD) simulation. The surface structure has been investigated viathe coordination number, bond-angle distributions and structural point defects.Calculations show that surface effects on surface static and thermodynamic properties ofmodels are significant according to the change in the number of Al atoms in the surfacelayers. Evolution of the local environment of oxygen in the surface shell of nanoparticlesupon cooling from the melt toward the glassy state was also found and discussed.In addition, the nanosize dependence of the glass transition temperature waspresented.

A Model of Computation for Bit-Level Concurrent Computing and Programming: APEC

A concurrent model of computation and a language based on the model for bit-level operation are useful for developing asynchronous and concurrent programs compositionally, which frequently use bit-level operations. Some examples are programs for video games, hardware emulation (including virtual machines), and signal processing. However, few models and languages are optimized and oriented to bit-level concurrent computation. We previously developed a visual programming language called A-BITS for bit-level concurrent programming. The language is based on a dataflow-like model that computes using processes that provide serial bit-level operations and FIFO buffers connected to them. It can express bit-level computation naturally and develop compositionally. We then devised a concurrent computation model called APEC (Asynchronous Program Elements Connection) for bit-level concurrent computation. This model enables precise and formal expression of the process of computation, and a notion of primitive program elements for controlling and operating can be expressed synthetically. Specifically, the model is based on a notion of uniform primitive processes, called primitives, that have three terminals and four ordered rules at most, as well as on bidirectional communication using vehicles called carriers. A new notion is that a carrier moving between two terminals can briefly express some kinds of computation such as synchronization and bidirectional communication. The model's properties make it most applicable to bit-level computation compositionally, since the uniform computation elements are enough to develop components that have practical functionality. Through future application of the model, our research may enable further research on a base model of fine-grain parallel computer architecture, since the model is suitable for expressing massive concurrency by a network of primitives.