Implicit Parameters Research Articles

Analysis of multidimensional difference-of-Gaussians filters in terms of directly observable parameters

The difference-of-Gaussians (DOG) filter is a widely used model for the receptive field of neurons in the retina and lateral geniculate nucleus (LGN) and is a potential model in general for responses modulated by an excitatory center with an inhibitory surrounding region. A DOG filter is defined by three standard parameters: the center and surround sigmas (which define the variance of the radially symmetric Gaussians) and the balance (which defines the linear combination of the two Gaussians). These parameters are not directly observable and are typically determined by nonlinear parameter estimation methods applied to the frequency response function. DOG filters show both low-pass (optimal response at zero frequency) and bandpass (optimal response at a nonzero frequency) behavior. This paper reformulates the DOG filter in terms of a directly observable parameter, the zero-crossing radius, and two new (but not directly observable) parameters. In the two-dimensional parameter space, the exact region corresponding to bandpass behavior is determined. A detailed description of the frequency response characteristics of the DOG filter is obtained. It is also found that the directly observable optimal frequency and optimal gain (the ratio of the response at optimal frequency to the response at zero frequency) provide an alternate coordinate system for the bandpass region. Altogether, the DOG filter and its three standard implicit parameters can be determined by three directly observable values. The two-dimensional bandpass region is a potential tool for the analysis of populations of DOG filters (for example, populations of neurons in the retina or LGN), because the clustering of points in this parameter space may indicate an underlying organizational principle. This paper concentrates on circular Gaussians, but the results generalize to multidimensional radially symmetric Gaussians and are given as an appendix.

Stability and consistency of nonhydrostatic free‐surface models using the semi‐implicit θ‐method

SUMMARYThe θ‐method is a popular semi‐implicit finite‐difference method for simulating free‐surface flows. Problem stiffness, arising because of the presence of both fast and slow timescale processes, is easily handled by the θ‐method. In most ocean, coastal, and estuary modeling applications, stiffness is caused by fast surface gravity wave timescales imposed on slower timescales of baroclinic variability. The method is well known to be unconditionally stable for shallow water (hydrostatic) models when , where θ is the implicitness parameter. In this paper, we demonstrate that the method is also unconditionally stable for nonhydrostatic models, when for both pressure projection and pressure correction methods. However, the methods result in artificial damping of the barotropic mode. In addition to investigating stability, we also estimate the form of artificial damping induced by both the free surface and nonhydrostatic pressure solution methods. Finally, this analysis may be used to estimate the damping or growth associated with a particular wavenumber and the overall order of accuracy of the discretization. Copyright © 2012 John Wiley & Sons, Ltd.

A generalised framework for dispute derivations in assumption-based argumentation

Assumption-based argumentation is a general-purpose argumentation framework with well-understood theoretical foundations and viable computational mechanisms (in the form of dispute derivations), as well as several applications. However, the existing computational mechanisms have several limitations, hindering their deployment in practice: (i) they are defined in terms of implicit parameters, that nonetheless need to be instantiated at implementation time; (ii) they are variations (for computing different semantics) of one another, but still require different implementation efforts; (iii) they reduce the problem of computing arguments to the problem of computing assumptions supporting these arguments, even though applications of argumentation require a justification of claims in terms of explicit arguments and attacks between them.In this context, the contribution of this paper is two-fold. Firstly, we provide a unified view of the existing (GB-, AB- and IB-)dispute derivations (for computation under the grounded, admissible and ideal semantics, respectively), by obtaining them as special instances of a single notion of X-dispute derivations that, in addition, renders explicit the implicit parameters in the original dispute derivations. Thus, X-dispute derivations address issues (i) and (ii). Secondly, we define structured X-dispute derivations, extending X-dispute derivations by computing explicitly the underlying arguments and attacks, in addition to assumptions. Thus, structured X-dispute derivations also address issue (iii). We prove soundness and completeness results for appropriate instances of (structured) X-dispute derivations, w.r.t. the grounded, admissible and ideal semantics, thus laying the necessary theoretical foundations for deployability thereof.

Determination of Parameters in Compound Fill Sphere Model for Haptic Interaction

The compound Fill Sphere Model (cFSM), which is an extension of common Fill Sphere Model, is widely used in real-time haptic interaction with deformable body. Comparing with finite element based model, the simplicity and efficiency are advantages of cFSM. However, determining implicit parameters of cFSM is a difficult task since a vivid deformation should be attained during haptic interaction. In this paper, to improve the simulation precision, parameter matrices of the cFSM are identified through an analytical method for the first time to our best knowledge. After deriving parameter matrices by linearization, the stiffness matrix, damp matrix and mass matrix of the cFSM are obtained by minimizing errors between stiffness matrix of the Finite Element Model (FEM). In order to evaluate the performance of derived parameters, comparative experiment has been conducted between the cFSM and FEM. Additionally, based on the derived parameters, a real-time haptic interactive scenario is constructed to validate the performance of deformation simulation.

Stage-specific family structure models: implicit parameter restrictions and Bayesian model comparison with an application to prosocial behavior

The two most frequently used specifications in stage-specific family structure analyses of young adult outcomes-state × stage and event × stage-impose restrictions on the parameters of the underlying model of child development. The restrictions imposed by the state specification have substantive a priori disadvantages, implying that use of the state specification requires justification by a specification test. Because the state and event specifications are non-nested, a classical approach to specification testing runs into practical problems. We demonstrate the advantages of a Bayesian approach to the specification testing problem using two applications to young adult prosocial behavior-charitable giving and volunteering. Substantive results are that family structure transitions during adolescence are negatively associated with subsequent giving, and transitions during middle childhood are positively associated with subsequent volunteering. There are other substantive results that would have been missed had we not realized that the state and event specifications impose restrictions on the underlying model and had we not made specification testing a prerequisite for substantive analysis.

A ground motion selection algorithm based on the generalized conditional intensity measure approach

An algorithm is presented for the selection of ground motions for use in seismic response analysis. The algorithm is based on the use of random realizations from the conditional multivariate distribution of ground motion intensity measures, IM|IMj, obtained from the generalized conditional intensity measure (GCIM) approach. The algorithm can be applied to the selection of both as-recorded amplitude-scaled and synthetic/simulated ground motions. A key feature is that the generality of the GCIM methodology allows for ground motion selection based on only explicit measures of the ground motions themselves, as represented by the various IM’s considered, rather than implicit causal parameters (e.g., source magnitude, source-to-site distance) which are presently used in other contemporary ground motion selection procedures. Several examples are used to illustrate the salient features of the algorithm, including: the effect of intensity measures considered; and the properties of ground motions selected for multiple exceedance probabilities. The flexibility of the proposed algorithm coupled with the GCIM methodology allows for objective and consistent ground motion selection as a natural extension of seismic hazard analysis.

Phase diagram of the toric code model in a parallel magnetic field

Ground-state phase diagram of the toric code model in a parallel magnetic field has three distinct phases: topological, charge-condensed, and vortex-condensed states. To study it we consider an implicit local order parameter characterizing the transition between the topological and charge-condensed phases, and sample it using continuous-time Monte Carlo simulations. The corresponding second-order transition line is obtained by finite-size scaling analysis of this order parameter. Symmetry breaking between charges and vortices along the first-order transition line is also observed, and our numerical result shows that the end point of the first-order transition line is located at $h_x^{(c)}=h_z^{(c)}=0.418(2)$.

NONLOCAL GRADIENT-DEPENDENT CONSTITUTIVE MODEL FOR SIMULATING LOCALIZED DAMAGE AND FRACTURE OF VISCOPLASTIC SOLIDS UNDER HIGH-ENERGY IMPACTS

Understanding the constraints and limitations of various potential hull structure materials and armor is paramount in design considerations of future civil and military vehicles. Developing and applying theoretical and computational models that guide the development of design criteria and fabrication processes of high-impact/ballistic-resistant materials are essential. Therefore, performing accurate computational modeling and simulation of the ballistic response of vehicles made of high-performance materials under impact/blast loading conditions is invaluable. However, as soon as material failure dominates a deformation process, the material increasingly displays strain softening (localization) and the finite-element computations are affected considerably by the mesh size and alignment and gives non-physical descriptions of the damaged regions and failure of solids. This study is concerned with the development and numerical implementation of a novel coupled thermo-hypo-elasto, thermo-visco-plastic, and thermo-visco-damage constitutive model within the laws of thermodynamics in which implicit and explicit intrinsic material length-scale parameters are incorporated through the nonlocal gradient-dependent viscoplasticity and viscodamage constitutive equations. In this current model, the Laplacian of the effective viscoplastic strain rate and its coef cient, which introduces a missing length-scale parameter, enter the constitutive equations beside the local effective viscoplastic strain. It is shown through simulating plugging fracture in ballistic penetration of high-strength steel circular plates by hardened blunt-nose cylindrical steel projectiles that the Laplacian coefficient parameter plays the role of a localization limiter during the penetration and perforation processes allowing one to obtain meaningful values for the ballistic limit velocity (or perforation resistance) independent of the finite-element mesh density. For the corresponding local model, on the other hand, the ballistic limit continuously decreases as the mesh density increases and does not converge even for the finest mesh.

LIS: Localization based on an intelligent distributed fuzzy system applied to a WSN

The localization of the sensor nodes is a fundamental problem in wireless sensor networks. There are a lot of different kinds of solutions in the literature. Some of them use external devices like GPS, while others use special hardware or implicit parameters in wireless communications. In applications like wildlife localization in a natural environment, where the power available and the weight are big restrictions, the use of hungry energy devices like GPS or hardware that add extra weight like mobile directional antenna is not a good solution. Due to these reasons it would be better to use the localization’s implicit characteristics in communications, such as connectivity, number of hops or RSSI. The measurement related to these parameters are currently integrated in most radio devices. These measurement techniques are based on the beacons’ transmissions between the devices. In the current study, a novel tracking distributed method, called LIS, for localization of the sensor nodes using moving devices in a network of static nodes, which have no additional hardware requirements is proposed. The position is obtained with the combination of two algorithms; one based on a local node using a fuzzy system to obtain a partial solution and the other based on a centralized method which merges all the partial solutions. The centralized algorithm is based on the calculation of the centroid of the partial solutions. Advantages of using fuzzy system versus the classical Centroid Localization (CL) algorithm without fuzzy preprocessing are compared with an ad hoc simulator made for testing localization algorithms. With this simulator, it is demonstrated that the proposed method obtains less localization errors and better accuracy than the centroid algorithm.

A pure embedding of attribute grammars

Attribute grammars are a powerful specification paradigm for many language processing tasks, particularly semantic analysis of programming languages. Recent attribute grammar systems use dynamic scheduling algorithms to evaluate attributes on demand. In this paper, we show how to remove the need for a generator, by embedding a dynamic approach in a modern, object-oriented and functional programming language. The result is a small, lightweight attribute grammar library that is part of our larger Kiama language processing library. Kiama’s attribute grammar library supports a range of advanced features including cached, uncached, higher order, parameterised and circular attributes. Forwarding is available to modularise higher order attributes and decorators abstract away from the details of attribute value propagation. Kiama also implements new techniques for dynamic extension and variation of attribute equations. We use the Scala programming language because of its support for domain-specific notations and emphasis on scalability. Unlike generators with specialised notation, Kiama attribute grammars use standard Scala notations such as pattern-matching functions for equations, traits and mixins for composition and implicit parameters for forwarding. A benchmarking exercise shows that our approach is practical for realistic language processing.

A New Model of Bundle Adjustment Used in Camera Calibration

The calibration of the internal and external parameters of each camera is a crucial step for free-form surface measurement based on stereo vision. The nonlinear optimization method of bundle adjustment is usually used in the camera calibration. The model of bundle adjustment can be derived from the nonlinear collinearity equations which contains the nonlinear distortions of camera lens. As the internal parameters of camera, the distortion parameters are implied in the projective transformation matrix, and difficult to be explicitly expressed by an equation. But the establishment of the model of bundle adjustment needs to calculate the first-order partial derivative of each parameter. At present, there is no effective method to decompose the implicit parameters which are taken as a whole in the expansion of first-order partial derivative. The existing bundle adjustment models are not comprehensive and easy to cause ill-conditioned matrix problems. In this paper, we discuss the methods of the nonlinear camera lens distortion correction, establish a new lens distortion expression, and propose a new model of bundle adjustment based on the new distortion expression. Experiments results indicate that the new bundle adjustment model can obtain high camera calibration accuracy, and avoid the ill-conditioned matrix problems.

The spatial limitations of current neutral models of biodiversity.

The unified neutral theory of biodiversity and biogeography is increasingly accepted as an informative null model of community composition and dynamics. It has successfully produced macro-ecological patterns such as species-area relationships and species abundance distributions. However, the models employed make many unrealistic auxiliary assumptions. For example, the popular spatially implicit version assumes a local plot exchanging migrants with a large panmictic regional source pool. This simple structure allows rigorous testing of its fit to data. In contrast, spatially explicit models assume that offspring disperse only limited distances from their parents, but one cannot as yet test the significance of their fit to data. Here we compare the spatially explicit and the spatially implicit model, fitting the most-used implicit model (with two levels, local and regional) to data simulated by the most-used spatially explicit model (where offspring are distributed about their parent on a grid according to either a radially symmetric Gaussian or a ‘fat-tailed’ distribution). Based on these fits, we express spatially implicit parameters in terms of spatially explicit parameters. This suggests how we may obtain estimates of spatially explicit parameters from spatially implicit ones. The relationship between these parameters, however, makes no intuitive sense. Furthermore, the spatially implicit model usually fits observed species-abundance distributions better than those calculated from the spatially explicit model's simulated data. Current spatially explicit neutral models therefore have limited descriptive power. However, our results suggest that a fatter tail of the dispersal kernel seems to improve the fit, suggesting that dispersal kernels with even fatter tails should be studied in future. We conclude that more advanced spatially explicit models and tools to analyze them need to be developed.

Type classes as objects and implicits

Type classes were originally developed in Haskell as a disciplined alternative to ad-hoc polymorphism. Type classes have been shown to provide a type-safe solution to important challenges in software engineering and programming languages such as, for example, retroactive extension of programs. They are also recognized as a good mechanism for concept-based generic programming and, more recently, have evolved into a mechanism for type-level computation. This paper presents a lightweight approach to type classes in object-oriented (OO) languages with generics using the CONCEPT pattern and implicits (a type-directed implicit parameter passing mechanism). This paper also shows how Scala's type system conspires with implicits to enable, and even surpass, many common extensions of the Haskell type class system, making Scala ideally suited for generic programming in the large.

Deformation of coke-furnace heating walls under the action of nonsteady forces and temperatures

The hierarchical model of Dinas ceramic based on defining relations with a minimum of implicit parameters permits assessment of the viability of Dinas structures and prediction of the creep and long-term strength of the heating walls in coke furnaces. However, prediction of the cyclic creep is also required, on account of the cyclic variation in the heating-wall temperature and the load (the coking pressure). The prediction of the creep curves at hazardous points of the heating walls is considered, in the light of the simultaneous variation in stress and temperature during coke-battery operation.

Mnemonics: type-safe bytecode generation at run time

Mnemonics is a Scala library for generating method bodies in JVM bytecode at run time. Mnemonics supports a large subset of the JVM instructions, for which the static typing of the generator guarantees the well-formedness of the generated bytecode. The library exploits a number of advanced features of Scala's type system (type inference with bounded polymorphism, implicit parameters, and reflection) to guarantee that the compiler only accepts legal combinations of instructions at compile time. Additional instructions are supported at the price of a check at run time of the generator. In either case, bytecode verification of generated code is guaranteed to succeed.

Multiparameter Receiver Operating Characteristic Analysis for Signal Detection and Classification

Receiver operating characteristic (ROC) analysis is a widely used evaluation tool in signal processing and communications, and medical diagnosis for performance analysis. It utilizes 2-D curves plotted by detection rate ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> ) against false alarm rate ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> ) to assess effectiveness of a detector, sensor/device for detection. However, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> are actually dependent parameters resulting from a more crucial but implicit parameter hidden in the ROC curves, threshold ¿ , which is determined by the cost of implementing a detector or sensor/device, except only the case that when the Bayes theory is used for detection, ¿ is completely determined by the Bayes cost. This paper extends the traditional ROC analysis for single-signal detection to detection and classification of multiple signals. It also explores relationships among the three parameters, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> , and ¿ , and further develops a new concept of multiparameter ROC analysis, which uses 3-D ROC curves plotted by three parameters, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> , and ¿, to evaluate effectiveness of detection performance based on interrelationship among <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> , and ¿, rather then only <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> used by 2-D ROC analysis. As a result of a 3-D ROC curve, three 2-D ROC curves can be also derived: the conventional 2-D ROC curve plotted by <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> versus <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> and two new 2-D ROC curves plotted based on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> versus ¿ and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> versus ¿. In order to demonstrate the utility of 3-D ROC analysis, four applications are considered: hyperspectral target detection, medical diagnosis, chemical/biological agent detection, and biometric recognition.

Monitoring interstitial m‐THPC‐PDT in vivo using fluorescence and reflectance spectroscopy

In order to understand the mechanisms of photodynamic therapy (PDT) it is important to monitor parameters during illumination that yield information on deposited PDT dose. The aim of this study is to investigate the possibility of monitoring implicit parameters, such as photobleaching, in addition to monitoring explicit parameters (fluence (rate), oxygenation, photosensitizer concentration) directly or indirectly. These parameters are monitored during PDT without interrupting the therapeutic illumination. Rats were injected with 0.3 mg kg(-1) m-THPC. Sixteen hours after administration the abdominal muscle in rats was irradiated for 1,500 seconds using clinically relevant fluence rates of 50, 100, and 250 mW cm(-1) of diffuser length at 652 nm. In addition to the linear diffuser for delivering treatment light, isotropic fiber-optic probes and fiber-optic probes for differential path-length spectroscopy (DPS) were placed on both sides of the muscle to monitor tissue physiological parameters, fluence rate, and fluorescence. The m-THPC treatment groups show a decrease in fluence rate throughout PDT of 16%, 19%, and 27% for the 50, 100, and 250 mW cm(-1) groups, respectively. Both during and post-PDT differences in vascular response between treatment groups and animals within the same treatment group are observed. Furthermore we show fluence rate dependent bleaching of m-THPC up to a measured fluence rate of 100 mW cm(-1). The data presented in this study show the possibility of simultaneously monitoring fluence (rate), fluorescence, hemoglobin oxygen saturation, and blood volume during PDT without interruptions to the therapeutic illumination. Differences in saturation profiles between animals and treatment groups indicate differences in vascular response during illumination. Furthermore, the relationship between fluence rate and m-THPC fluorescence photobleaching is complex in an interstitial environment.

Predicting dinas creep at the operating temperatures of coke-furnace walls

A hierarchical model of Dinas refractory with a minimum number of implicit parameters permits estimation of the performance and long-term strength of the heating walls in coke furnaces, as established in [1]. In the present work, the hierarchical model is used to predict the creep of Dinas refractory at 1273, 1373, 1473, and 1573 K. In this approach to creep prediction, the short-term creep curves are measured at 1573 K, while predictions are given for 1273,1373, and 1473 K.

Long-term strength of coke-furnace heating walls

A hierarchical model of material with a minimum number of implicit parameters has previously been proposed. This model permits calculation of the long-term strength of the heating walls in coke furnaces, as well as assessment of their condition. As an example, three long-term strength curves are presented for Dinas brick at 1273, 1323, and 1373 K. These curves are based on the equation of state and the kinetic equations containing the minimum number of implicit parameters.

1513 MEMSウェットエッチング特性の陰的パラメータ表現によるプロセスシミュレーション(OS15.電子デバイス・電子材料と計算力学(4),オーガナイズドセッション)

This paper describes a new wet etching simulation that considers physical phenomenon such as flow, diffusion and chemical reaction. A partial differential equation with implicit parameterization of etching properties is presented, which is solvable by commercial software. Three implicit parameters associated with flow, diffusion and chemical reaction are determined through experiment by test device so that the simulation fits the experimental result. For automatic parameter identification, an error function was proposed considering position of etching front at the final target time, average of etching rate and shape of etching front. The central composite design algorithm was adopted with quadratic interpolation and minimum least square approximation to reduce the computational cost. Once the parameters are determined, the etching simulation of real MEMS device is practically carried out.