Two-pass Method Research Articles

Efficient Mesh Segmentation base on Region Growing and Merging

To effectively use scanned meshes obtained by 3D laser scanner or X-ray CT scanning systems in engineering applications, such as inspection and CAD model reconstruction, we need to segment meshes and extract desirable regions and their approximating surfaces. Surfaces of engineering objects are commonly represented by a set of analytic surfaces, such as planes, cylinders, spheres, cones. Therefore, the mesh surface of them needs to be approximated by a set of analytic surfaces. In this paper we propose an efficient mesh segmentation algorithm based on region growing and region merging. Our algorithm first robustly and accurately estimates mesh principal curvatures using the two-pass estimation method. Then it fast extracts regions and their approximating analytic surfaces based on region growing even if regions are smoothly blended. Finally it efficiently merges initial set of regions of large and complex scanned meshes under the user specified tolerances using region merging. We demonstrate the efficiency and accuracy of our algorithm with scanned meshes acquired from real engineering objects by X-ray CT scanning systems.

An Efficient Scan Tree Design for Compact Test Pattern Set

Tree-based scan path architectures have recently been suggested for reducing test application time or test data volume in today's high-density very large scale integrated circuits. However, these techniques strongly rely on the existence of a large number of compatible sets of flip-flops under the given test set and therefore may not be suitable for a highly compact test set generated by an efficient automatic test pattern generator tool. Tree-based architectures also suffer from loss of fault coverage while achieving a significant reduction ratio for test time or data. In this paper, to circumvent this problem, a new two-pass hybrid method is proposed to design an efficient scan tree architecture based on approximate compatibility. The method is particularly suitable for a highly compact test set having fewer don't cares and low compatibility. Finally, to reduce the volume of scan-out data, test responses shifted out from the leaf nodes of the scan tree are compacted by a space compactor, which is designed specially for the proposed scan tree architecture. The compactor uses an XOR tree, and its overhead is low. The design thus offers a solution to both test data and response compaction. Experimental results on various benchmark circuits demonstrate that the proposed algorithm outperforms the earlier methods in reducing test application time significantly without degrading fault coverage.

English

Passive millimeter wave (PMMW) imaging systems have attracted an increasing interestover the past years due to their superior poor-weather performance compared with visible andIR systems. In passive imaging, the spatial information acquired is strictly band-limited. A majordrawback to PMMW images is their poor angular resolution. Also, another problem of single-channel PMMW imaging systems is the slow response time due to the lack of thermal sensitivity.The imager could operate at TV (television) rates using a number of parallel channels which mayreduce the extent of this problem. In multi-channel, differences between the responses of individualchannels can introduce noise into the image, which can obscure details of interest. The proposednoise-removal technique is a two-pass combined method of two techniques. One technique isfor removing the DC component in the frequency domain and the other one is statistical filteringbased on homogeneous region in the image (spatial) domain, followed by high-boost filteringby 3×3 mask for enhancement the image. High quality images are presented to demonstrate thepotential of this technique.

Web Delay Analysis and Reduction By Using Load Balancing of a DNS-Based Web Server Cluster

Based on our survey of recent articles, there is little research being conducted into quantitative analysis of the load balancing of Web server clusters. In this paper, we propose a quantitative analysis for DNS-based server clusters. We also propose a two-pass load-balancing method for determining the load balance area of these clusters. The first pass uses the lookup table instead of a complicated computation for obtaining the load balancing of the Web service requests. The second pass also utilizes a lookup table by a precomputed Hessian matrix to obtain the load balancing. In addition, we compare the relative performance of dispatcher-based and DNS-based server clusters using queuing theory, analysis, and simulation, and we compare the measurement results using benchmarks. To increase the simulation performance we have designed a simulation module to promptly locate the load balancing, with a potential improvement of 36.58% over the average system response time.

Characterization of the growth mechanism of YIG crystal fibers using the laser heated pedestal growth method

Yttrium iron garnet (YIG, Y 3Fe 5O 12) single-crystal fibers were grown by the laser heated pedestal growth (LHPG) method. Different compositions, with various Y 2O 3 and Fe 2O 3 ratios seeds were used. The microstructure and the compositional variation of the obtained crystals show that YIG single-crystal fibers could be directly grown at the stable freezing interface when the melt had a composition of 78–87 mol% Fe 2O 3. When the seed's Fe 2O 3 concentration was below 78 mol%, the yttrium orthoferrite (YFeO 3) would crystallize out until the composition of the melt increased along the liquidus curve until it needed a concentration of 78 mol% Fe 2O 3 or higher, whereupon YIG started to crystallize from the liquid. With the LHPG method, however, when Fe-rich ceramic rod used as a seed was employed to grow YIG crystal, the crystallographic orientation was indefinite. Therefore, YIG single-crystal fibers with the desired crystallographic orientation could only be obtained using a two-pass method. During the forward pass, YIG single crystal could be directly grown using a Fe-rich solvent, while during the backward pass, the crystallographic orientation of the grown crystal would be the same as that of the YIG seed.

Behavior of a movable electrode in piezo-response mode of an atomic force microscope

The objective of this work was to understand the effect of the movable electrode (the tip of an atomic force microscope) on a piezoelectric-induced (PEI) image. Local polarization is induced on a lead zirconate titanate (PZT) thin film using an atomic force microscope (AFM), by applying dc voltage between the movable electrode and the Pt bottom electrode. The polarized PZT film is then characterized by the AFM using a two-pass method, in which both the topography and PEI image are obtained. The surface morphology is recorded in the first pass under contact mode with a fixed setpoint. A PEI image is obtained in the second pass in piezo-response mode. In this mode, the sample surface is scanned by applying ac voltage between the AFM tip and the Pt bottom electrode at sample displacement. PEI images of various sample displacement, corresponding to different stress exerted by the tip on the sample surface, are obtained and analyzed using force–sample displacement curves. It is found that PEI images can be detected if the tip adheres to the sample. The asymmetry of the A cos θ signal is improved as the force changes from repulsive to attractive.

A partitioned state estimator for external network modeling

This paper presents a partitioned state estimation (SE) method for real-time external network modeling. The method utilizes an unreduced model of the external network and it is based on the SE approach. Since the external network model must not contaminate the internal system state and power mismatches at boundary buses should be minimal, the boundary measurements (tie-line flows and boundary injections) should be critical. Any type of real-time measurements (power flows and injections) can be used. The entire system state is computed by a two-pass method based on measurement model partitioning. The method is based on the fast decoupled model and it can be easily implemented by modifying an existing SE program. Partitioned observability and bad data processing schemes have been developed for the internal and external networks. The external system model can be dynamically updated when changes on topological or analog measurements happen. The method is tested on the IEEE 14-bus system and a 2040-bus system. Contingency analysis is performed and the results are compared with those of load flow (LF) studies which consider the same contingencies.

A Partitioned State Estimator for External Network Modeling

This paper presents a partitioned state estimation (SE) method for real-time external network modeling. The method utilizes an unreduced model of the external network and it is based on the SE approach. Since the external network model must not contaminate the internal system state and power mismatches at boundary buses should be minimal, the boundary measurements (tie-line flows and boundary injections) should be critical. Any type of real-time measurements (power flows and injections) can be used. The entire system state is computed by a two-pass method based on measurement model partitioning. The method is based on the fast decoupled model and it can be easily implemented by modifying an existing SE program. Partitioned observability and bad data processing schemes have been developed for the internal and external networks. The external system model can be dynamically updated when changes on topological or analog measurements happen. The method is tested on the IEEE 14-bus system and a 2040-bus system. Contingency analysis is performed and the results are compared with those of load flow (LF) studies which consider the same contingencies.

Effect of crosslinking reactions and order of mixing on properties of compatibilized PBT/ABS blends

The low-temperature notched Izod impact strength of poly(butylene terephthalate), PBT, blends with acrylonitrile–butadiene–styrene terpolymers, ABS, can be improved by incorporating methyl methacrylate, glycidyl methacrylate, ethyl acrylate terpolymers, MGE, as a reactive compatibilizer. However, fracture properties depend on the order of mixing of the blend components. When all components of compatibilized blends are melt mixed together in a single-pass extrusion, the low-temperature toughness is improved; however, the room-temperature impact strength is reduced relative to uncompatibilized blends. Using a two-pass extrusion method where PBT and MGE are melt mixed together in a first extrusion prior to incorporating ABS in a second extrusion, the room-temperature impact strength is superior to that of blends prepared by the single-pass method. When a two-pass method is used where ABS and MGE are combined prior to extrusion with PBT, the impact properties at all temperatures are inferior to those of uncompatibilized blends. Evidence is presented which suggests that residual acids present in emulsion-made ABS material may cause a crosslinking reaction involving the epoxide functionality of MGE terpolymers resulting in a deleterious effect on the ABS mechanical properties and its blends with PBT. By changing the order of mixing, the sequence of chemical reactions which occur can be controlled to optimize blend properties.

A study of the growth mechanism of bismuth silicon oxide during LHPG method

Single-crystal fibers of Bi 12SiO 20 were grown by a laser-heated pedestal growth (LHPG) method. The thermal radiative emissions during the growth were monitored by a thermal imaging radiometer with a 5 μm bandpass filter. The variation in thermal emissions in the 5 μm spectrum during the growth process reflects the interior structure of re-crystallized Bi 12SiO 20. When a crystal fiber was grown upward from a sintered powder rod, bubbles oscillate in the upper floating zone and may be caught within the grown crystal, which may cause the inclusions, color fragments, voids or other defects inside the grown crystal. When we grew a crystal downward to minimize the effects of the bubbles, the defects were reduced, but could still be observed inside the crystal. In order to solve this problem, we used a two-pass method that is during the first pass, we grew downward to obtain an almost bubble-free polycrystalline rod. In the second pass, we grew the single-crystal fiber upward using the polycrystal source rod obtained in the first pass. The grown fiber has uniform luster and higher transmissivity.

Deformation of the 1995 North Sakhalin earthquake detected by JERS-1/SAR interferometry

We present a map of the coseismic displacement field resulting from the North Sakhalin, Russia, May 28, 1995, earthquake. Raw radar signal data from the JERS-1 synthetic aperture radar instrument acquired in 28 April, 11 June, 25 July, and 7 September 1995 are used to generate a high-resolution, wide area map of the displacements by the two-pass differential interferometry method. The interferogram shows that an area of 60 km (EW) by 80 km (NS) experienced crustal deformations. The slip mechanism with fine structure is inverted using the displacement field of the SAR interferogram. This inversion of the SAR interferogram shows, 1) the rupture area extends to the south of the southernmost rupture trace on the surface, 2) slip varies from one to seven meters from the south to the northern part on the fault plane. A theoretical fringe pattern from the model of the earthquake motion matches the observations closely. We generate a full scene digital elevation model (DEM) by JERS-1 SAR interferometry and synthesize a four-pass interferogram. Comparison of the differential interferometry between the four-pass and two-pass interferograms shows that they are very similar and the both methods are reliable to show surface displacements using JERS-1 SAR. Correlation study of the Sakhalin interferograms indicates that low surface temperatures, below the freezing point, reduced the correlation probably because a freeze would alter the dielectric constant of the surface. In these Sakhalin interferograms, we find few spurious fringes due to the usual heterogeneous distribution of weather-related atmospheric and surface conditions, probably because of the low temperatures. We also present a map of the postseismic displacement field with the SAR interferometry.

Parallel interconnection through a multimode optical fiber with a tandem arrangement of two photorefractive crystals

We propose a new method for one-way multipixel image transmission through a multimode optical fiber (MOF). The method is based on the two-pass method, in which a light field bearing an image makes a round trip through a MOF. One-way multipixel image transmission can be realized even through a long and/or winding MOF in which the fiber modes are strongly scrambled with a tandem arrangement of two photorefractive crystals to generate a precise phase-conjugated wave. In this study, images of two pixels (2-bit data) are transmitted through a 100-m MOF more than 20 times for one recording of holograms onto a photorefractive Bi12SiO20 crystal. We also show that a reference beam with a distorted wave front can be utilized, which is transmitted by another MOF instead of a single-mode optical fiber.

Keyword/non-keyword classification in isolated word speech recognition

A two-pass classification system and method that post-processes HMM scores with additional confidence scores to derive a value that may be applied to a threshold on which a keyword verses non-keyword determination may be based. The first stage comprises Generalized Probabilistic Descent (GPD) analysis which uses feature vectors of the spoken words and the HMM segmentation information (developed by the HMM detector during processing) as inputs to develop a first set of confidence scores through a linear combination (a weighted sum) of the feature vectors of the speech. The second stage comprises a linear discrimination method that combines the HMM scores and the confidence scores from the GPD stage with a weighted sum to derive a second confidence score. The output of the second stage may then be compared to a predetermined threshold to determine whether the spoken word or words include a keyword.

A general two-pass method integrating specular and diffuse reflection

We analyse some recent approaches to the global illumination problem by introducing the corresponding reflection operators , and we demonstrate the advantages of a two-pass method. A generalization of the system introduced by Wallace et al. at Siggraph '87 to integrate diffuse as well as specular effects is presented. It is based on the calculation of extended form-factors , which allows arbitrary geometries to be used in the scene description, as well as refraction effects. We also present a new sampling method for the calculation of form-factors, which is an alternative to the hemi-cube technique introduced by Cohen and Greenberg for radiosity calculations. This method is particularly well suited to the extended form-factors calculation. The problem of interactive display of the picture being created is also addressed by using hardware-assisted projections and image composition to recreate a complete specular view of the scene.

Determining object motion in a sequence of stereo images

The motion of a three-dimensional object is determined from a sequence of stereo images by extracting three-dimensional features, establishing correspondences between these features, and finally, computing the rigid motion parameters. Three-dimensional features are extracted from the depth map of a scene. A two-pass relaxation method is developed for matching features extracted from successive depth maps. In each iteration, geometrical relationships between a feature and its neighbors in one map are compared to those between a candidate in the other map and its neighbors to update the matching probability of the candidate. The comparison of the geometrical relationship is based on the principle of conservation of distance and angle between features during rigid motion. The use of three-dimensional features allows one to find the rotation and translation components of motion separately via solving linear equations. Experimental results using several sets of real data are presented to illustrate results and difficulties.

Design and analysis of dynamic Huffman codes

A new one-pass algorithm for constructing dynamic Huffman codes is introduced and analyzed. We also analyze the one-pass algorithm due to Faller, Gallager, and Knuth. In each algorithm, both the sender and the receiver maintain equivalent dynamically varying Huffman trees, and the coding is done in real time. We show that the number of bits used by the new algorithm to encode a message containing t letters is < t bits more than that used by the conventional two-pass Huffman scheme, independent of the alphabet size. This is best possible in the worst case, for any one-pass Huffman method. Tight upper and lower bounds are derived. Empirical tests show that the encodings produced by the new algorithm are shorter than those of the other one-pass algorithm and, except for long messages, are shorter than those of the two-pass method. The new algorithm is well suited for on-line encoding/decoding in data networks and for tile compression.

On the Concept of Varying Influence Radii for a Successive Corrections Objective Analysis

There has been a long-standing concept by those who use successive corrections objective analysis that the way to obtain the most accurate objective analysis is first, to analyze for the long wavelengths and then to build in details of the shorter wavelengths by successively decreasing the influence of the more distant observations upon the interpolated values. Using the Barnes method. we compared the filter characteristics for families of response curves that pass through a common point at a reference wavelength. It was found that the filter cutoff is a maximum if the filter parameters that determine the influence of observations are unchanged for both the initial and correction passes. This information was used to define and test the following hypothesis. If accuracy is defined by how well the method retains desired Wavelengths and removes undesired wavelengths, then the Barnes method gives the most accurate analyses if the filter parameters on the initial and correction passes are the same. This hypothesis does not follow the usual conceptual approach to successive corrections analysis. Theoretical filter response characteristics of the Barnes method were compared for filter parameters set to retrieve the long wavelengths and then build in the short wavelengths with the method for filter parameters set to retrieve the short wavelengths and then build in the long wavelengths. The theoretical results and results from analyses of regularly spaced data show that the customary method of first analyzing for the long wavelengths and then building in the shorter wavelengths is not necessary for the stride correction pass version of the Barnes method. Use of the same filter parameters for initial and correction passes improved the analyses from a fraction of a percent for long wavelengths to about ten percent for short but resolvable wavelengths. However, the more sparsely and irregularly distributed the data, the less the results are in accord with the predictions of theory. Use of the same filter parameters gave better overall fit to the wavelengths shorter than eight times the minimum resolvable wave and slightly degraded fit to the longer wavelengths. Therefore, in the application of the Barnes method to irregularly spaced data, successively decreasing the influence of the more distant observations is still advisable if longer wavelengths are present in the held of data. It also was found that no single selection of filter parameters for the two-pass method gives the best analysis for all wavelengths. A three-pass hybrid method is shown to reduce this problem.

Pairing heaps

The pairing heap has recently been introduced as a new data structure for priority queues. Pairing heaps are extremely simple to implement and seem to be very efficient in practice, but they are difficult to analyze theoretically, and open problems remain. It has been conjectured that they achieve the same amortized time bounds as Fibonacci heaps, namely, O (log n ) time for delete and delete_min and O(1) for all other operations, where n is the size of the priority queue at the time of the operation. We provide empirical evidence that supports this conjecture. The most promising algorithm in our simulations is a new variant of the twopass method, called auxiliary twopass. We prove that, assuming no decrease_key operations are performed, it achieves the same amortized time bounds as Fibonacci heaps.