Near Point Research Articles

Some results of geodetic referring of the radio telescope and SLR stations to GPS markers in the Crimean geodynamical test area Simeiz-Katsyveli

Positions of space-geodetic instruments are calculated in the International Terrestrial Reference Frame (ITRF2000) by referring the instrument reference points to the local geodetic network and GPS markers. The eccentricities of the SLR stations CrAO and CLO and the permanent GPS station CrAO with respect to the reference point of the radio telescope RT-22 are determined. The local relative deformations of the Earth’s surface are presented as shifts of the instrument reference points with respect to the nearest points of the local geodetic network and with respect to each other.

SPATCLUS: An R package for arbitrarily shaped multiple spatial cluster detection for case event data

This paper describes an R package, named SPATCLUS that implements a method recently proposed for spatial cluster detection of case event data. This method is based on a data transformation. This transformation is achieved by the definition of a trajectory, which allows to attribute to each point a selection order and the distance to its nearest neighbour. The nearest point is searched among the points which have not yet been selected in the trajectory. Due to the trajectory effects, the distance is weighted by the expected distance under the uniform distribution hypothesis. Potential clusters are located by using multiple structural change models and a dynamic programming algorithm. The double maximum test allows to select the best model. The significativity of potential clusters is determined by Monte Carlo simulations. This method makes it possible the detection of multiple clusters of any shape.

Interpolating methods for solar radiation in Uganda

Existing literature lacks information on evaluation of interpolation methods for the estimation of solar radiation in the East African region. It follows that this study investigates the performance of five interpolations in Uganda which include: Nearest Point, Moving Average, Moving Surface, Trend Surface and Ordinary Kriging. Results have shown that the Moving Average linear decrease is the most appropriate for interpolation of solar radiation in Uganda and subsequent drawing of solar maps. The corresponding normalized mean bias error and root mean square error is 0.035 and 0.078, respectively. The worst performing is the Nearest Point interpolation with normalized mean bias error and root mean square error of 0.084 and 0.149, respectively.

WE-D-ValB-09: Deformable Image Registration with Auto-Mapped Control Volumes

Purpose: Conventional deformable registration treats all image volume equally and the calculations are “brute‐force” in nature. In reality, some regions can be mapped between the moving and fixed images with high confidence. In this work we investigate a strategy of using a priori knowledge about the system to reduce the dimensionality of the deformable image registration.Method and Materials: We propose a two‐stage deformable image registration algorithm that incorporates prior knowledge into the system through auto‐mapping of control volumes. In the first stage, a set of control volumes is selected on the fixed image. Each control volume is mapped on to the moving image using a rigid transformation. Control volumes are placed on distinct features for robust auto‐mapping. In the second stage, a BSpline grid is defined over the moving image. For each control volume, the nearest point on the grid is located based on the Euclidean distance. An upper bound that is dependent on the displacement of the control volume in the auto‐mapping is imposed on the corresponding grid point. The BSpline deformable transformation is determined for registration of the two images subject to the bounds on the displacements of the grid points as described. The utility of the new method is demonstrated by clinical case studies. Results: The algorithm was applied to register phases of 4D‐CT images for mapping lung and liver deformations. Experimental results show that the algorithm is fast, robust and practical with a registration accuracy of ∼2mm. Conclusions: We have developed a deformable registration mechanism that incorporates a priori system knowledge to improve the performance of registration. The algorithm is based on the BSpline deformable transform with displacement constraints based on auto‐mapped control volumes. The algorithm has been found to be practical for registration of phases of 4D‐CT images of lung and liver.

Testing the performance of a 2D nearest point algorithm with genetic algorithm generated Gaussian distributions

Genetic algorithms have successfully been used in automatic software testing. Particularly programming errors and inputs that conflict with time constraints can be found. In this paper, the idea of genetic algorithm based software testing is broadened to algorithm performance testing. It is shown how the best and worst case performance of the algorithms can be found effectively. This information can be further utilized when comparing and improving algorithms. In this paper, the proposed test method is introduced and the advantages of using genetic algorithms are discussed. Furthermore, the proposed method is applied to a 2D nearest point algorithm, which is tested by optimizing the parameters of 2D Gaussian distributions using genetic algorithms in order to find the best and worst case distributions and the corresponding performances.

Stroke-based modeling and haptic skill display for Chinese calligraphy simulation system

The goal of this paper is to study haptic skill representation and display in a Chinese calligraphy training system. The challenge is to model haptic skill during the writing of different strokes in Chinese characters and to achieve haptic rendering with high fidelity and stability. The planning of the writing process is organized at three levels: task, representation and device level to describe the haptic handwriting skill. State transition graph (STG) is proposed to describe switches between tasks during the handwriting. Chinese characters are modeled using 39 typical strokes, which are further grouped into basic and compound strokes. The compound stroke is considered to be sequential combination of the basic strokes. Straight and curve strokes are modeled using line segment and the Bezier curve, respectively. Information from STG is used for real-time collision detection and haptic rendering. Ambiguity of the collision detection at stroke-corner points is prevented using active stroke combined with local nearest point computation. A modified virtual fixture method is developed for haptic rendering. The approach is tested on a prototype training system using Phantom desktop. Initial experiments suggest that the proposed modeling and rendering method is effective.

運動残効による視覚系疲労の評価方法の検討

In order to develop the effective evaluation system for the fatigue of operator's visual system in long term operation, the experiments were carried out utilizing perceptual time duration of motion aftereffect (MAE), critical flicker frequency (CFF) and the near point (NP) measurement. The MAE was measured using rotated spiral figure displayed on a CRT screen. To generate visual fatigue, a signal detection task in randomly displayed alphabets was used. After the task, MAE duration, CFF and NP were increased. It is supposed that the visual fatigue generated by the experimental task affects motion processing system of visual cortex. Results suggest that the MAE can be an effective tool for visual fatigue evaluation.

Proximinality in geodesic spaces

LetXbe a complete CAT(0)space with the geodesic extension property and Alexandrov curvature bounded below. It is shown that ifCis a closed subset ofX,then the set of points ofXwhich have a unique nearest point inCisGδand of the second Baire category inX.If, in addition,Cis bounded, then the set of points ofXwhich have a unique farthest point inCis dense inX.A proximity result for set-valued mappings is also included.

Use of GIS and remotely sensed data for a priori identification of reference areas for Great Lakes coastal ecosystems

Identification of reference conditions for ecological assessments of coastal ecosystems poses a challenging problem in highly modified landscapes. A method is described for characterizing disturbance in coastal ecosystems using remotely sensed land classification and other publicly available GIS data. Within ecoregions bordering the US Great Lakes coast, aquatic habitats bordering the shoreline were classified into five ecological types: high‐energy shoreline, embayments, open‐coast, river‐influenced and protected wetlands. Degree of anthropogenic disturbance in contributing areas to these ecosystems was assessed using a watershed approach for wetland types or a moving window approach for high‐energy shorelines. Anthropogenic stress variables included proportions of agricultural or residential land use, information on population and road density, and distance from the nearest point source. Polygons (wetlands) or pixels (high‐energy shoreline) were categorized as ‘reference’ if the magnitude of the most severe stressor, based on its cumulative frequency distribution within that ecoregion, placed it within the lowest 20th percentile. For shorelines, adjacent ‘reference’ pixels were agglomerated into polygons and a final ranking of polygons containing at least 2 km of shoreline was used to identify candidate reference areas. A subset of these sites is currently being sampled for fish, macroinvertebrates and physical habitat attributes. This a priori approach to reference area identification will allow managers to identify biological correlates of reference conditions, providing a benchmark for bioassessment and restoration efforts in coastal regions.

Effects of short-term VDT usage on visual functions

To evaluate the effects of short-term VDT usage on visual functions. Visual function of the video display terminal (VDT) operators before and after 1 hour VDT usage were assessed. These included refraction, amplitude of accommodation, near point of convergence, AC/A, phorias, fusional convergence and divergence, tear film break time (BUT) and aberrations. And the same situation was compared was the non-VDT usage. In comparison with pre-VDT use, amplitude of accommodation, BUT were significantly decreased (P < 0.05), near point of convergence, near lateral exophoria were significantly increased after VDT use (P < 0.05). Total, high order, 4th and 5th order aberrations were significantly greater after VDT use (P < 0.05). Short-term VDT work does have a significantly greater temporarily effect on visual function, tear film quality and visual quality.

Unusual Offshore Occurrence of an American Alligator

An American Alligator (Alligator mississippiensis Daudin) was observed and photographed in the Gulf of Mexico on 4 May 2004, some 56 km south of Marsh Island, LA (approximately 63 km from the nearest point on mainland Louisiana). Alligators generally avoid saltwater and we are unaware of prior documentation of an alligator occurring this distance offshore.

An almost distribution-independent incremental Delaunay triangulation algorithm

This paper presents a new incremental insertion algorithm for constructing a Delaunay triangulation. Firstly, the nearest point is found in order to speed up the location of a triangle containing a currently inserted point. A hash table and 1–3 deterministic skip lists, combined with a walking strategy, are used for this task. The obtained algorithm is compared with the most popular Delaunay triangulation algorithms. The algorithm has the following attractive features: it is fast and practically independent of the distribution of input points, it is not memory demanding, and it is numerically stable and easy to implement.

REEVALUATION OF RADIATION DOSE AROUND THE JCO SITE FROM THE CRITICALITY ACCIDENT IN TOKAI-MURA

Based on the monitoring data periodically taken during the JCO criticality accident in Tokai-mura, neutron and gamma-ray doses were evaluated at 13 points around the site boundary ranging from 73 to 540 m from the conversion building where the criticality took place. Radiation doses obtained by the present study were compared with the dose-distance curves developed through the works of the Nuclear Safety Commission Investigation Committee. The latter values are larger by 30 to 120% than the former at the 6 nearest points within 150 m from the conversion building, while they agree well at the points beyond 250 m. It is suggested that the shielding effects by the surrounding buildings around the conversion building contributed to the difference of estimated doses near the JCO boundary. To reconstruct the radiation environment realistically at the residential area near the JCO facilities, it is necessary to employ radiation transport calculations with three-dimensional models of the configuration around the conversion building. Radiation doses evaluated in the present study can be used to check the validity of such calculations based on the three-dimensional model.

Some results on nearest points in normed linear spaces

We will focus on some results that we hope to give an algorithm for constructing the best approximations in some types of normed linear spaces. Also some results on best approximation will be obtained.

Investigation of the spatial distribution of second-order nonlinearity in thermally poled optical fibers

The spatial distribution of second-order nonlinearity in thermally poled optical fibers was characterized by second-harmonic microscopy. The second-order nonlinearity was found to be confined to a thin layer close to the anode surface and progressed further into the silica as the poling time increased. Position uncertainty of the anode metal wire was observed to have an effect, as the nonlinear layers were found not always symmetrically located around the nearest points between the anode and cathode. Optical microscopy results were obtained on etched poled fiber cross-sections and compared with those from second-harmonic microscopy.

The geometric structure of Chebyshev sets in ℓ∞(n)

A subset M of a normed linear space X is called a Chebyshev set if each x ∈ X has a unique nearest point in M. We characterize Chebyshev sets in l∞(n) in geometric terms and study the approximative properties of sections of Chebyshev sets, suns, and strict suns in l∞(n) by coordinate subspaces.

Implicit iteration process of nonexpansive non‐self‐mappings

Suppose C is a nonempty closed convex subset of real Hilbert space H. Let T : C → H be a nonexpansive non‐self‐mapping and P is the nearest point projection of H onto C. In this paper, we study the convergence of the sequences {xn}, {yn}, {zn} satisfying xn = (1 − αn)u + αnT[(1 − βn)xn + βnTxn], yn = (1 − αn)u + αnPT[(1 − βn)yn + βnPTyn], and zn = P[(1 − αn)u + αnTP[(1 − βn)zn + βnTzn]], where {αn}⊆(0, 1), 0 ≤ βn ≤ β &lt; 1 and αn → 1 as n → ∞. Our results extend and improve the recent ones announced by Xu and Yin, and many others.

Approximately unbiased tests of regions using multistep-multiscale bootstrap resampling

Approximately unbiased tests based on bootstrap probabilities are considered for the exponential family of distributions with unknown expectation parameter vector, where the null hypothesis is represented as an arbitrary-shaped region with smooth boundaries. This problem has been discussed previously in Efron and Tibshirani [Ann. Statist. 26 (1998) 1687-1718], and a corrected p-value with second-order asymptotic accuracy is calculated by the two-level bootstrap of Efron, Halloran and Holmes [Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 13429-13434] based on the ABC bias correction of Efron [J. Amer. Statist. Assoc. 82 (1987) 171-185]. Our argument is an extension of their asymptotic theory, where the geometry, such as the signed distance and the curvature of the boundary, plays an important role. We give another calculation of the corrected p-value without finding the ``nearest point'' on the boundary to the observation, which is required in the two-level bootstrap and is an implementational burden in complicated problems. The key idea is to alter the sample size of the replicated dataset from that of the observed dataset. The frequency of the replicates falling in the region is counted for several sample sizes, and then the p-value is calculated by looking at the change in the frequencies along the changing sample sizes. This is the multiscale bootstrap of Shimodaira [Systematic Biology 51 (2002) 492-508], which is third-order accurate for the multivariate normal model. Here we introduce a newly devised multistep-multiscale bootstrap, calculating a third-order accurate p-value for the exponential family of distributions.

On the size of the set of points where the metric projection exists

In this paper we answer in the negative a question due to J. P. R. Christensen about almost everywhere existence of nearest points using a decomposition of l2 due to J. Matousek and E. Matouskova. We also formulate a similar question about almost everywhere existence of farthest points and answer it in the negative.

Forecasting method study on chaotic load series with high embedded dimension

The current chaos forecasting methods, which apply Euclidean distance to determine the nearest points in state space to forecast chaos time series with high dimensions, are not so effective. In this paper, one new idea based on incidence degree instead of Euclidean distance is firstly put forward to determine the nearest point in phase space. In the mean time, the method is developed to improve the character of the full Lyapunov exponential spectrum in reconstruction space with high dimensions. The test result of short-term load forecasting series shows that the precision of load forecasting is greatly improved by means of the new method when the embedded dimension is high compared with the method used recently.