Limited Number Of Directions Research Articles

The nociceptive withdrawal response of the tail in the spinalized rat employs a hybrid categorical-continuous spatial mapping strategy.

Complexity in movement planning, arising from diverse temporal and spatial sources, places a computational burden on the central nervous system. However, the efficacy with which humans can perform natural, highly trained movements suggests that they have evolved effective behavioral strategies that simplify the computational burden. The specific aim of our research was to use three-dimensional high-speed video to determine whether the tail nociceptive withdrawal response (NWR) to noxious heat stimuli delivered at locations that varied both circumferentially and rostral-caudally on the tail depended on the location of the stimulus in spinalized rats. In particular, we sought to determine whether the movement strategy was categorical (limited number of directions) or continuous (any variation in stimulus location results in a variation in response direction). In spinalized rats, localized, noxious heat stimuli were delivered at eight locations circumferentially around the tail and at five rostral-caudal levels. Our results demonstrate that at all rostral-caudal levels, response movement direction was bimodal regardless of circumferential stimulus location-either ~ 64° left or right of ventral. However, in spite of tight clustering, movement direction varied significantly but weakly according to circumferential location, in that responses to stimuli were more lateral for lateral stimulus locations. In contrast, changes in stimulus level strongly affected movement direction, in that a localized bend response closely matched the level of the stimulus. Together, our results demonstrate, based on movement analysis in spinalized rats, that the NWR employs a hybrid categorical-continuous strategy that may minimize the harmful consequences of noxious stimuli.

Single Image Superresolution via Directional Group Sparsity and Directional Features.

Single image superresolution (SR) aims to construct a high-resolution version from a single low-resolution (LR) image. The SR reconstruction is challenging because of the missing details in the given LR image. Thus, it is critical to explore and exploit effective prior knowledge for boosting the reconstruction performance. In this paper, we propose a novel SR method by exploiting both the directional group sparsity of the image gradients and the directional features in similarity weight estimation. The proposed SR approach is based on two observations: 1) most of the sharp edges are oriented in a limited number of directions and 2) an image pixel can be estimated by the weighted averaging of its neighbors. In consideration of these observations, we apply the curvelet transform to extract directional features which are then used for region selection and weight estimation. A combined total variation regularizer is presented which assumes that the gradients in natural images have a straightforward group sparsity structure. In addition, a directional nonlocal means regularization term takes pixel values and directional information into account to suppress unwanted artifacts. By assembling the designed regularization terms, we solve the SR problem of an energy function with minimal reconstruction error by applying a framework of templates for first-order conic solvers. The thorough quantitative and qualitative results in terms of peak signal-to-noise ratio, structural similarity, information fidelity criterion, and preference matrix demonstrate that the proposed approach achieves higher quality SR reconstruction than the state-of-the-art algorithms.

Solving Multicolor Discrete Tomography Problems by Using Prior Knowledge

Discrete tomography deals with the reconstruction of discrete sets with given projections relative to a limited number of directions, modeling the situation where a material is studied through x-rays and we desire to reconstruct an image representing the scanned object. In many cases it would be interesting to consider the projections to be related to more than one distinguishable type of cell, called atoms or colors, as in the case of a scan involving materials of different densities, as a bone and a muscle. Unfortunately the general n-color problem with n > 1 is NP-complete, but in this paper we show how several polynomial reconstruction algorithms can be defined by assuming some prior knowledge on the set to be rebuilt. In detail, we study the cases where the union of the colors form a set without switches, a convex polyomino or a convex 8-connected set. We describe some efficient reconstruction algorithms and in a case we give a sufficient condition for uniqueness.

Effects of excitation angle and coupled heave–surge–sway motion on fluid sloshing in a three-dimensional tank

Sloshing waves in moving tanks is an important engineering problem, and most studies of this phenomenon have focused on tanks that are excited by forcing motion in a limited number of directions and with fixed excitation frequencies throughout the forcing. In practice, the excitation comprises multiple degree of freedom motion that potentially couples surge, sway, heave, pitch, roll, and yaw motions. In the present study, a time-independent finite difference method is used to simulate fluid sloshing in three-dimensional tanks filled to an arbitrary depth for various excitation frequencies and multiple degree of freedom motion. The numerical scheme developed here was verified by rigorous benchmark tests. The coupled motions of surge and sway are simulated for various excitation angles, frequencies and water depths. Five kinds of sloshing waves found under coupled surge–sway motions: diagonal, single-directional, square-like, swirling, and irregular waves. The effect of excitation angle on the frequency responses of different sloshing waves is analyzed and discussed in the present study. Further, the components of horizontal force of various sloshing waves are also presented. The coupled effect of surge, sway and heave motions is also discussed, and the results show that unstable sloshing occurs when the excitation frequency of the heave motion is twice the fundamental natural frequency. Moreover, the effects of heave motion on the different types of sloshing waves are explored. It is found that heave motion causes all of the sloshing waves to change type.

Motion Processing Streams in Drosophila Are Behaviorally Specialized

Motion vision is an ancient faculty, critical to many animals in a range of ethological contexts, the underlying algorithms of which provide central insights into neural computation. However, how motion cues guide behavior is poorly understood, as the neural circuits that implement these computations are largely unknown in any organism. We develop a systematic, forward genetic approach using high-throughput, quantitative behavioral analyses to identify the neural substrates of motion vision in Drosophila in an unbiased fashion. We then delimit the behavioral contributions of both known and novel circuit elements. Contrary to expectation from previous studies, we find that orienting responses to motion are shaped by at least two neural pathways. These pathways are sensitive to different visual features, diverge immediately postsynaptic to photoreceptors, and are coupled to distinct behavioral outputs. Thus, behavioral responses to complex stimuli can rely on surprising neural specialization from even the earliest sensory processing stages.

Dendrimer-Coated Nanoparticles

CHEMISTRY Most polymers are synthesized by adding units to one end of a growing chain, but other architectures can be created by adding several monomer units at sites around a growing core. Dendrimers are the most ordered type of these polymers, in which each round of synthesis (or “generation”) geometrically increases the number of units added. A relatively open structure after one or two generations is converted to an almost spherical structure after about five generations. Gopidas et al. adapted a synthesis route for gold nanoparticles that assembles dendrimer “wedges” (which grow out in a limited number of directions) into a spherical structure. Polyaryl ether wedges that are linked initially via disulfide bonds react with a stabilized solution of HAuCl4 and sodium borohydride. A gold core about 2 to 3 nm in diameter forms. For low-generation number wedges (less than three), this spherical core gives the final structure more dendrimer-like properties. The fifth-generation wedges, however, still retain some openness that allows access to the gold core from solution.— PDS J. Am. Chem. Soc. 10.1021/ja029544m (2003).

Reduction of False Scattering of the Discrete Ordinates Method

A novel method, the Double Rays Method (DRM), is proposed to capture the discontinuous nature of the radiation intensity, in order to reduce false scattering of the discrete ordinates method (DOM). Numerical tests demonstrate that the DRM successfully removes false scattering in all the two-dimensional test problems discussed in this paper. The effect of false scattering on the computational results in two-dimensional situations is investigated with the DRM. False scattering plays a double role: when the boundary emits radiation in a limited number of directions, or when the irradiation comes from a limited number of directions, it produces a smeared intensity field and radiative heat flux distribution, and thus must be removed. In the case of diffuse boundary, however, false scattering plays a useful role and thus should be retained.

Effectiveness of pentran ™'s unique numerics for simulation of the Kobayashi benchmarks

In this paper, we use the PENTRAN (Parallel Environment Neutral-particle TRANsport), 3-D parallel Sn code to solve three 3-D benchmark problems. Each of the problems contains three regions: source, void, and shield. Two shield materials, zero (pure absorber) and 50% scattering ratios, are tested. This combination of a discontinuous source, void, and low scattering shield is highly problematic for the Sn method that uses a limited number of directions. In this paper, we demonstrate that the unique numerical formulations and features of PENTRAN provide the capability of obtaining relatively accurate solutions for such situations. For the pure absorber cases, we obtain maximum differences from the analytical solutions of < 40%, 24%, and 20% for the problems 1 to 3, respectively. For the 50% scattering cases, these differences reduce to <20% for all problems. In most cases, the maximum error occurs at large distances from the source. We have demonstrated that in order to obtain these solutions, it is necessary to use three important features of PENTRAN, including variable meshing, Taylor Projection Mesh Coupling (TPMC), and the adaptive differencing strategy with the DTW and EDW differencing schemes.

Applications of Profile Analysis for Micro-Crystalline Properties From Total Pattern Fitting

The characterization of finely divided and structurally imperfect solids is required in the study of many classes of materials, e.g. ceramics, catalysts, decomposition products. Diffraction line broadening is influenced by the microstructure of the solid and is a valuable technique for a unique characterization of a material in terms of size and morphology of crystallites (a region over which diffraction is coherent) and imperfections (microstrains, d- spacing fluctuations, stacking faults, etc). The extraction of these features has traditionally been based on the study of individual diffraction lines, which restricts the analysis to a limited number of directions of diffraction vectors. The complexity of most powder patterns has been a serious impediment to the widespread use of the procedure for detailed microstructural characterization. The advent of fitting techniques, with the use of structural information (Rietveld method) and without structure model (pattern decomposition method) have extended the frontiers of diffraction line profile analyses. In the Rietveld method it has been recommended to have a prior knowledge of the origin and lattice direction dependences of the imperfection effect before embarking in the modelling of line broadening through the pattern. This modelling can be carried out with pattern decomposition methods, which provide individual diffraction lines for a subsequent study of microstructural properties. Several aspects of this technique, performances, limitations and practical problems are reviewed and discussed. Applications to oxides with high specific surface-area are used to illustrate the detailed microstructural information contained in a powder diffraction pattern.

The Fn method for the one-angle radiative transfer equation applied to plant canopies

Solutions of the radiative transfer equation describing photon interactions with vegetation canopies are important in remote sensing since they provide the canopy reflectance distribution required in the interpretation of satellite-acquired information. Although the most widely used transport models such as the moments formulations collapse the photon directional information into a limited number of directions (usually two or four), the more sophisticated methods such as discrete ordinates can, in principle, employ an unlimited number of discrete directions. These discrete methods, however, also contain spatial discretization error and lack testing against more accurate Numerical formulations for specific vegetation canopy scattering kernels. In this article, we consider a semianalytical approach to the solution of the one-angle radiative transfer equation in slab geometry called the F n method. This method has a its basis two integral equations specifying the intensities exiting the vegetation canopy boundaries. The solution is then obtained through an expansion in a set of basis functions with expansion coefficients to be determined. These coefficients are obtained from a collocation procedure resulting in a set of algebraic equations solved by matrix inversion. The advantage of this method is that only discretization in the angular variable is required, thus avoiding spatial truncation error entirely. The paper begins by considering a canopy where all the leaves are oriented at the same angle. Lambertian scattering will be assumed with unequal leaf reflectance and transmittance. This simple model contains all the difficulties of the more complex model incorporating a general leaf angle distribution which is to be considered in the latter part of the presentation. A sensitivity analysis is performed including variation of the numerical and model parameters. In addition, discrete ordinates calculations as well as field measurements are compared to the F n results.

Position Index in VCP Calculations

Position Index (P), the spatial sensitivity factor used in the determination of the index of sensation for a source, is not unambiguously defined for all directions in the visual field. The working definition is a set of curves indicating contours of constant position index. Numerical values have been tabulated for the standard room tables of visual comfort probability (VCP) and serve as a precise definition for a limited number of directions in the visual field. It is desirable to define the position index by a functional relation over the entire field of view. Here, four analytic representations are considered in terms of spatial coverage, errors with respect to known representations, simplicity, and the like.