Pairs Of Points Research Articles

RIGA: Rotation-Invariant and Globally-Aware Descriptors for Point Cloud Registration.

Successful point cloud registration relies on accurate correspondences established upon powerful descriptors. However, existing neural descriptors either leverage a rotation-variant backbone whose performance declines under large rotations, or encode local geometry that is less distinctive. To address this issue, we introduce RIGA to learn descriptors that are Rotation-Invariant by design and Globally-Aware. From the Point Pair Features (PPFs) of sparse local regions, rotation-invariant local geometry is encoded into geometric descriptors. Global awareness of 3D structures and geometric context is subsequently incorporated, both in a rotation-invariant fashion. More specifically, 3D structures of the whole frame are first represented by our global PPF signatures, from which structural descriptors are learned to help geometric descriptors sense the 3D world beyond local regions. Geometric context from the whole scene is then globally aggregated into descriptors. Finally, the description of sparse regions is interpolated to dense point descriptors, from which correspondences are extracted for registration. To validate our approach, we conduct extensive experiments on both object- and scene-level data. With large rotations, RIGA surpasses the state-of-the-art methods by a margin of 8 ° in terms of the Relative Rotation Error on ModelNet40 and improves the Feature Matching Recall by at least 5 percentage points on 3DLoMatch.

Type-2 Fuzzy Metric Spaces

In this paper, an attempt is made to define a Type-2 fuzzy metric on a nonempty set [Formula: see text] by allowing it to take fuzzy numbers as values of distance of a pair of points under a membership grade which is also a fuzzy number. Its type-1 counterpart is a fuzzy metric mostly similar to those defined by Kramosil and Michalek[Formula: see text] and also by George and Veeramani.6 It is shown that the topology induced by this fuzzy metric is Hausdorff in nature. In this type of fuzzy metric space, Banach’s fixed point theorem and Edelstein’s fixed point theorems are extended. Finally decomposition theorems for this fuzzy metric are proved from which a justification of type-2 behavior of this fuzzy metric can also be interpreted.

The alternating simultaneous Halpern–Lions–Wittmann–Bauschke algorithm for finding the best approximation pair for two disjoint intersections of convex sets

Given two nonempty and disjoint intersections of closed and convex subsets, we look for a best approximation pair relative to them, i.e., a pair of points, one in each intersection, attaining the minimum distance between the disjoint intersections. We propose an iterative process based on projections onto the subsets which generate the intersections. The process is inspired by the Halpern–Lions–Wittmann–Bauschke algorithm and the classical alternating process of Cheney and Goldstein, and its advantage is that there is no need to project onto the intersections themselves, a task which can be rather demanding. We prove that under certain conditions the two interlaced subsequences converge to a best approximation pair. These conditions hold, in particular, when the space is Euclidean and the subsets which generate the intersections are compact and strictly convex. Our result extends the one of Aharoni, Censor and Jiang [“Finding a best approximation pair of points for two polyhedra”, Computational Optimization and Applications 71 (2018), 509–23] who considered the case of finite-dimensional polyhedra.

On a new variant of cyclic (noncyclic) condensing operators with existence of optimal solutions to an FDE

Abstract The paper is designed to highlight the presence of an optimal solution to a differential system comprising fractional order derivatives, precisely the ψ-Caputo derivative, under the prescribed initial constraints. This is attained through a new variant of cyclic (noncyclic) condensing operators incorporating a pair of maps. The altered notion facilitates in evolving best proximity point (pair) results as well as coupled best proximity point results with supportive corollaries.

Anisotropy and compaction gradient assessment on rammed earth specimens through sonic tomography approach

Rammed earth is a traditional construction technique that has recently gained attention because of its benefits from an ecological perspective. The conservation of the existing valuable cultural heritage sites and the quality control of new constructions built with this material require the development and application of practical inspection techniques. This paper explores the application of sonic tests and sonic tomography as practical tools for monitoring the state of conservation of existing structures and the identification of heterogeneities or damaged areas. Two groups of 6 rammed earth specimens were manufactured and tested. The manufacturing process of each group allowed the application of compression loads and the identification of the Sonic Wave Propagation Velocities along directions parallel and perpendicular to the compaction forces during manufacturing. The SWPV were identified for the different paths between 9 measuring points located at two opposite sides of the specimens, leading to up to 6 different planes for each specimen. The SWPV are identified by identifying the Time-of-Flight of the elastic wave between each pair of excitation and receiver points. A discretized coloured map of the SWPV distribution for each plane defined by the measurement points array is obtained by the application of an algorithm already developed by the authors to obtain tomographic images for other materials and applications. The SWPV are identified after 2 different increasing values of a uniform compressive load is applied to each specimen. The results show that the analysis of the SWPV and tomographic images is sensitive to heterogeneities, such as compaction gradients from the manufacturing process, and also to the accumulated damage in the solid. The paper demonstrates that the proposed technique can be potentially used for a qualitative inspection of the state of conservation of specific rammed earth constructions.

A Kinematic Synthesis Methodology for P-Drivable Spatial Single Degree-of-Freedom Mechanisms to Avoid Singularities

Abstract For a single degree-of-freedom spatial mechanism, a reference frame attached to any of its links produces a continuous motion of this frame. Given the progression of this frame from the start through the end of the mechanism’s motion, this paper seeks to identify specific points relative to this moving reference frame. The points of interest are those that can be coupled with a second point determined in the fixed frame to act as the end joint locations for a spherical–prismatic–spherical (SPS) driving chain. If the selection of the point pair is made such that the change in distance between them as the mechanism moves is strictly monotonic, then the SPS chain they define is potentially capable of driving the mechanism over the desired range of motion. This motion is referred to as locally P-drivable because a global solution is not ensured by the process proposed herein. This synthesis process can avoid singularities encountered by actuating the mechanism at one of its original joints. The proposed approach enables the dimensional synthesis of a single degree-of-freedom mechanism to focus on creating circuit-defect-free solutions without concern for potential singular positions. The actuating chain can then be determined as a separate step in the synthesis process. This paper also considers motions that are not P-drivable and the specialization to planar systems with the synthesis of a P-drivable revolute–prismatic–revolute (RPR) chain.

Detection of maize stem diameter by using RGB-D cameras' depth information under selected field condition.

Stem diameter is a critical phenotypic parameter for maize, integral to yield prediction and lodging resistance assessment. Traditionally, the quantification of this parameter through manual measurement has been the norm, notwithstanding its tedious and laborious nature. To address these challenges, this study introduces a non-invasive field-based system utilizing depth information from RGB-D cameras to measure maize stem diameter. This technology offers a practical solution for conducting rapid and non-destructive phenotyping. Firstly, RGB images, depth images, and 3D point clouds of maize stems were captured using an RGB-D camera, and precise alignment between the RGB and depth images was achieved. Subsequently, the contours of maize stems were delineated using 2D image processing techniques, followed by the extraction of the stem's skeletal structure employing a thinning-based skeletonization algorithm. Furthermore, within the areas of interest on the maize stems, horizontal lines were constructed using points on the skeletal structure, resulting in 2D pixel coordinates at the intersections of these horizontal lines with the maize stem contours. Subsequently, a back-projection transformation from 2D pixel coordinates to 3D world coordinates was achieved by combining the depth data with the camera's intrinsic parameters. The 3D world coordinates were then precisely mapped onto the 3D point cloud using rigid transformation techniques. Finally, the maize stem diameter was sensed and determined by calculating the Euclidean distance between pairs of 3D world coordinate points. The method demonstrated a Mean Absolute Percentage Error (MAPE) of 3.01%, a Mean Absolute Error (MAE) of 0.75mm, a Root Mean Square Error (RMSE) of 1.07mm, and a coefficient of determination (R²) of 0.96, ensuring accurate measurement of maize stem diameter. This research not only provides a new method of precise and efficient crop phenotypic analysis but also offers theoretical knowledge for the advancement of precision agriculture.

Predicting the Time-Dependent Toxicities of Binary Mixtures of Five Antibiotics to Vibrio qinghaiensis sp.-Q67 Based on the QSAR Model.

Antibiotics may be exposed in a mixed state in natural environments. The toxicity of antibiotic mixtures exhibits time-dependent characteristics, and data on the time-dependent toxicity of antibiotic mixtures is also relatively lacking. In this study, the toxicities of 45 binary mixtures composed of five antibiotics were investigated against Vibrio qinghaiensis sp.-Q67 (Q67) at multiple exposure times (4, 6, 8, 10, and 12 h). Quantitative structure-activity relationship (QSAR) models were developed for predicting the time-dependent toxicities of 45 binary mixtures. The results showed that the best QSAR models presented coefficient of determination (R 2) of (0.818-0.913) and explained variance in prediction leave-one-out (Q 2 LOO) of (0.781-0.894) and predictive ability (Q 2 F1, Q 2 F2, Q 2 F3 > 0.682, concordance correlation coefficient > 0.859). The R 2 values of QSAR models outperformed the R 2 (0.628-0.810) of the conventional concentration addition models and the R 2 (0.654-0.792) of the independent action models. Furthermore, the QSAR models showed higher R 2 and Q 2 LOO values at 4 h compared to other exposure times. Specifically, the model at the 30% effective concentration (EC30) had R 2 of 0.902 and Q 2 LOO of 0.883, while the model at the 50% effective concentration (EC50) had R 2 of 0.913 and Q 2 LOO of 0.894. The CATS2D_04_DP descriptor was found to be the most dominant and negatively correlated factor influencing the toxicity of mixed antibiotics against Q67 in the nine QSAR models developed over five exposure times. The reduction in the number of DP pharmacophore point pairs with a topological distance of 4 in the represented molecules is the primary cause for the rise in the time-dependent toxicity of the antibiotics against Q67.

Fitting Distances by Tree Metrics Minimizing the Total Error within a Constant Factor

We consider the numerical taxonomy problem of fitting a positive distance function \({\mathcal {D}:{S\choose 2}\rightarrow \mathbb {R}_{\gt 0}}\) by a tree metric. We want a tree T with positive edge weights and including S among the vertices so that their distances in T match those in \(\mathcal {D}\) . A nice application is in evolutionary biology where the tree T aims to approximate thebranching process leading to the observed distances in \(\mathcal {D}\) [Cavalli-Sforza and Edwards 1967]. We consider the total error, that is, the sum of distance errors over all pairs of points. We present a deterministic polynomial time algorithm minimizing the total error within a constant factor. We can do this both for general trees and for the special case of ultrametrics with a root having the same distance to all vertices in S . The problems are APX-hard, so a constant factor is the best we can hope for in polynomial time. The best previous approximation factor was O ((log n )(log log n )) by Ailon and Charikar [2005], who wrote “determining whether an O (1) approximation can be obtained is a fascinating question.”

In-plane elastic waves in piezoelectric metamaterials with Parity–Time symmetry

The propagation of in-plane waves in piezoelectric metamaterials involves the coupling of longitudinal (i.e. quasi–pressure), transverse (i.e. quasi–shear) and electric potential waves, which can result in different exotic phenomena. In this study, the stiffness matrix method is used to analyze the dispersion relation, which contains anomalous propagation characteristics. With the coupling of electric potential, the frequency spectrum of in–plane wave shows new characteristics. The exceptional point caused by non–Hermitian operator that does not exist before also appears when the vertical wave number is imaginary. The oblique incidence of the in–plane wave at the interface between a homogeneous medium and phononic crystal can excite multiple refraction modes which include the negative refraction. The normal mode decomposition is developed to study the in-plane incidence of piezoelectric metamaterial and then the averaged Poynting vector is applied to obtain the refraction angle. Moreover, the defect layer is introduced into the phononic crystals to study the transmission coefficients with two different symmetrical arrangements. When the balanced gain and loss are considered in the metamaterial, the Parity–Time symmetry appears and brings in pairs of exceptional points to achieve complete transmission with unidirectional zero reflection.

TransPose: 6D object pose estimation with geometry-aware Transformer

Efficient and accurate estimation of objects’ pose is essential in numerous practical applications. Due to the depth data contains abundant geometric information, some existing methods devote to extract features from 3D point cloud. However, these depth-based methods focus on extracting the point cloud local features and consider less about the global information. How to extract and utilize the local and global geometry features in depth information is crucial to achieve accurate predictions. To this end, we propose TransPose, a novel 6D pose framework that exploits Transformer Encoder with geometry-aware module to develop better learning of point cloud feature representations. To better extract local geometry features, we finely design the graph convolution network-based feature extractor that first uniformly sample point cloud and extract point pair features of point cloud. To further improve robustness to occlusion, we adopt Transformer to perform the propagation of global information, making each local feature obtains global information. Moreover, we introduce geometry-aware module in Transformer Encoder, which to form an effective constrain for point cloud feature learning and makes the global information exchange more tightly coupled with point cloud tasks. Extensive experiments indicate the effectiveness of TransPose, our pose estimation pipeline achieves competitive results on three benchmark datasets.

Comparison of the Effects of Sevoflurane and Desflurane on Endothelial Glycocalyx in Patients Undergoing Laparoscopic Hysterectomy: A Randomized, Double-Blind Trial.

Various enzymes, reactive oxygen species, inflammatory conditions, and major surgeries cause endothelial glycocalyx breakdown. Inhalation of anaesthetic agents may have protective effects on the endothelium. This study compared syndecan-1 and heparan sulfate levels to evaluate the effects of sevoflurane and desflurane on the endothelial glycocalyx. This prospective randomized, double-blind study included 46 patients undergoing laparoscopic hysterectomy. The participants were allocated into sevoflurane and desflurane groups. Subsequently, blood samples were drawn at three time points: before anaesthesia induction for a baseline value (T0), after pneumoperitoneum (T1), and after extubation (T2). Heparan sulfate and syndecan-1 levels were measured. There was no statistical difference between the sevoflurane and desflurane groups in terms of heparan sulfate and syndecan-1 levels at any time point. A significant difference was found only in the desflurane group in the intragroup comparisons of the measurements of heparan sulfate levels (χ2=29.826, P < 0.001). Matched pairs of the time points in the desflurane group showed that P=0.036 (Z=-2.099) for T1-T0, P < 0.001 (Z=-3.924) for T2-T0, and P < 0.001 (Z=-4.197) for T2-T1. The change in percentage between T2 and T1 of heparan sulfate in the desflurane group was found to be statistically significant (P=0.034). The damage caused by surgical stress on the endothelial glycocalyx can be reduced by both desflurane and sevoflurane. The protective effect of desflurane is more prominent than that of sevoflurane.

Models of Klein Surface Obstruction Graphs

The task of researching the structure of graphs of given connectivity, which are obstructions for a given surface of non-oriented kind, and building their models, from which obstruction graphs are formed by removing or compressing a set of edges, is considered. The issue of edge coverage of an obstruction graph of a given kind with a minimum number of quasi-stars with centers – planar graphs that have given sets of points and all edges are significant with respect to the reachability number 2 on the Euclidean plane and has reachability on the projective plane or Klein surface, is considered. K4, K2,3 or a degenerate graph. The task of researching the structure of graphs of undirected kind was considered [4–6]. In [7], the set of minors for the projective plane was compressed to 12 basic minors using the method of relative components, and a set of 62 minors of the Klein surface was constructed. To do this, we considered all non-isomorphic minimal embeddings of each of the basic minors and found the set of all different pairs of vertices that are reachable on the projective plane during the operations of removing or compressing an arbitrary edge of this graph to a point, then a pair of non-adjacent graph vertices was attached to the selected pair of points. In [8], the number of 2-connected obstruction graphs for the Klein surface was calculated, part of the diagrams of these graphs is given in [10]. Note that the following definition of the cell distance is similar to that in [11].Our approach, as a continuation of [9], will consist in finding the edge covering of an obstruction graph of a given kind by the minimum number of subgraphs of the covering from the number of quasi-stars with centers - graphs with essential edges relative to the number of reachability or nonorientable genus during compression to a point or removal operations edges relative to a given set of points with reachability number 2 relative to the Euclidean plane and reachable on projective planes or Klein surfaces, for example, these are subsets of the set of points of graphs K4, K2,3, K5\e, Kr, r &gt;= 2, or graph-obstructions of the projective plane. We also found the necessary conditions for constructing obstruction graphs for the Klein surface by identifying pairs of center points and hanging vertices of three quasi-stars, thus we have the basis of an algorithm for constructing a larger number of obstruction graphs for the Klein surface. Hypothetically, a graph-obstruction of a given nonorientable genus has the form of a cylindrical surface with n, n &gt;= 2, disks-bases and a side part, which can have common sets of points on the boundaries and on which are embedded, at least in part, the graph-centers of quasi-stars having a given set of reachability points 2 on the Euclidean plane, and on the side surface there are hanging edges that intersect on the plane and are inserted without crossing with the help of Mobius strips glued to the side surface. At the same time, the edges will have at least two nesting options in the side part of the cylindrical surface, but no more than the number of glued Mobius strips, thanks to which each hanging edge will nest on the Mobius strip, either with only one edge or with two adjacent edges. We have found the necessary conditions for constructing models of obstruction graphs for the Klein surface by identifying pairs of centers and hanging vertices of three quasi-stars, thus we have the basis of an algorithm for constructing a larger number of obstruction graphs for the Klein surface. The main result: statements 1, 2, 3 and the algorithm for constructing models of 3-connected graph-obstructions of the Klein surface. Keywords: φ-transformation of graphs, nonorientable surface, prototypes of graph-obstruction.

Detection and Imaging of Corrosion Defects in Steel Structures Based on Ultrasonic Digital Image Processing

Corrosion is one of the critical factors leading to the failure of steel structures. Ultrasonic C-scans are widely used to identify corrosion damage. Limited by the range of C-scans, multiple C-scans are usually required to cover the whole component. Thus, stitching multiple C-scans into a panoramic image of the area under detection is necessary for interpreting non-destructive testing (NDT) data. In this paper, an image mosaic method for ultrasonic C-scan based on scale invariant feature transform (SIFT) is proposed. Firstly, to improve the success rate of registration, the difference in the probe starting position in two scans is used to filter the matching pairs of feature points obtained by SIFT. Secondly, dynamic programming methods are used to search for the optimal seam path. Finally, the pixels in the overlapping area are fused by fade-in and fade-out fusion along the seam line. The improved method has a higher success rate of registration and lower image distortion than the conventional method in the mosaic of ultrasonic C-scan images. Experimental results show that the proposed method can stitch multiple C-scan images of a testing block containing artificial defects into a panorama image effectively.

Rules of acupoint selection in treatment of inflammatory bowel disease with acupuncture-moxibustion based on complex network analysis.

To analyze the rules of acupoint selection and compatibility of acupuncture and moxibustion in treatment of inflammatory bowel disease (IBD) based on complex network technology and provide the reliable evidences for acupoint selection in treatment of this disease with acupuncture and moxibustion. The clinical studies on acupuncture-moxibustion treatment of IBD were searched from the databases including CNKI, Wanfang, VIP, PubMed and Embase. The studies were screened and the acupoint prescriptions were extracted to set up the database of acupuncture-moxibustion treatment for IBD. Using Microsoft Excel 2021 software, the use times of acupoint, the use frequency (%) of acupoint, meridian tropism and the use of special point were imported. With SPSS Modeler 18.0 software adopted, the association rules were analyzed on the acupoint prescriptions. The acupoint co-occurrence network diagram, k-core network diagram, and community analysis diagram were drawn by Gephi 0.9.5 software. A total of 156 studies were included, composed of 175 acupoint prescriptions, 75 acupoints, with 1 378 use times in total and around 8 acupoints in one prescription. Regarding the top use frequency, Tianshu (ST25), Zusanli (ST36), Guanyuan (CV4), Zhongwan (CV12) and Pishu (BL20) were listed. The top meridians involved were the foot-yangming stomach meridian, the foot-taiyang bladder meridian and the Conception Vessel. The front-mu point had been used with the highest frequency among the special points. ST36 and ST25 were a pair of points with the highest frequency in treatment. The k-core hierarchical analysis was adopted to optimize acupoint prescriptions, and 22 core acupoints were obtained, i.e. ST25, ST36, CV4, CV12, BL20, Dachangshu (BL25), Shangjuxu (ST37), Shenshu (BL23), Qihai (CV6), Sanyinjiao (SP6), Mingmen (GV4), Xingjian (LR2), Yinlingquan (SP9), Neiting (ST44), Taichong (LR3), Xiajuxu (ST39), Shuifen (CV9), Shenque (CV8), Ganshu (BL18), Weishu (BL21), Hegu (LI4) and Quchi(LI11), which were classified into three core acupoint groups by community analysis. Through complex network analysis, it is found that the local acupoints on the chest and abdomen are generally selected in treatment with acupuncture-moxibustion for IBD, the combination of the nearby and distal points is considered simulta-neously, and the acupoint prescription is modified according to syndrome/pattern differentiation；and among special points, the front-mu point is widely used in treatment. All of these rules provide the ideas for the acupoint selection of acupuncture-moxibustion in treatment of IBD.

Approximation Scheme for Weighted Metric Clustering via Sherali-Adams

Motivated by applications to classification problems on metric data, we study Weighted Metric Clustering problem: given a metric d over n points and a k x k symmetric matrix A with non-negative entries, the goal is to find a k-partition of these points into clusters C1,...,Ck, while minimizing the sum of A[i,j] * d(u,v) over all pairs of clusters Ci and Cj and all pairs of points u from Ci and v from Cj. Specific choices of A lead to Weighted Metric Clustering capturing well-studied graph partitioning problems in metric spaces, such as Min-Uncut, Min-k-Sum, Min-k-Cut, and more. Our main result is that Weighted Metric Clustering admits a polynomial-time approximation scheme (PTAS). Our algorithm handles all the above problems using the Sherali-Adams linear programming relaxation. This subsumes several prior works, unifies many of the techniques for various metric clustering objectives, and yields a PTAS for several new problems, including metric clustering on manifolds and a new family of hierarchical clustering objectives. Our experiments on the hierarchical clustering objective show that it better captures the ground-truth structural information compared to the popular Dasgupta's objective.

PosDiffNet: Positional Neural Diffusion for Point Cloud Registration in a Large Field of View with Perturbations

Point cloud registration is a crucial technique in 3D computer vision with a wide range of applications. However, this task can be challenging, particularly in large fields of view with dynamic objects, environmental noise, or other perturbations. To address this challenge, we propose a model called PosDiffNet. Our approach performs hierarchical registration based on window-level, patch-level, and point-level correspondence. We leverage a graph neural partial differential equation (PDE) based on Beltrami flow to obtain high-dimensional features and position embeddings for point clouds. We incorporate position embeddings into a Transformer module based on a neural ordinary differential equation (ODE) to efficiently represent patches within points. We employ the multi-level correspondence derived from the high feature similarity scores to facilitate alignment between point clouds. Subsequently, we use registration methods such as SVD-based algorithms to predict the transformation using corresponding point pairs. We evaluate PosDiffNet on several 3D point cloud datasets, verifying that it achieves state-of-the-art (SOTA) performance for point cloud registration in large fields of view with perturbations. The implementation code of experiments is available at https://github.com/AI-IT-AVs/PosDiffNet.

Revisiting the lung cancer screening eligibility criteria to promote equity for Black individuals

BackgroundEarly detection using low-dose computed tomography reduces lung-cancer-specific mortality by 20% among high-risk individuals. Blacks are less likely than Whites to meet lung cancer screening (LCS) criteria under both the former and the updated United States Preventive Services Task Force (USPSTF) guidelines. The purpose of this study was to assess racial disparities in LCS eligibility and to propose tailored eligibility criteria for Blacks to enable equitable screening rate between Whites and Blacks. MethodsData for this study were obtained from the Behavioral Risk Factor Surveillance System (2017–2021). 101,552 subjects were included in the final analysis. By employing a systematic approach, we sought cut-off points at which Blacks were equally likely as Whites to be eligible for LCS. We evaluated the minimum age and smoking pack-years for Blacks while we retained the 2021 USPSTF criteria for Whites. The final decision was based on the minimum Wald’s Chi-square statistics. ResultsThe model we employed identified cut-off points at which Blacks were equally likely as Whites to be eligible for LCS. Retaining the 2021 USPSTF criteria for Whites, the model discovered a new pair of points for Blacks by reducing the minimum age to 43 years and decreasing the cumulative number of cigarettes smoked to 15 pack-years. Based on these cut-off points, we created tailored criteria for Blacks. Under the tailored criteria, Blacks (OR: 1.00; 95 %CI: 0.88–1.14) had the same odds of eligibility for LCS as Whites. The odds of eligibility for LCS by sex under the tailored criteria did not differ significantly for Black men (OR: 1.02; 95 %CI: 0.85–1.24) and Black women (OR: 0.95; 95 %CI: 0.81–1.12) compared to their respective White counterparts. ConclusionsThese tailored criteria for Blacks eliminate the disparities between Blacks and Whites in LCS eligibility. Future studies should test the sensitivity and specificity of these tailored criteria.

Enhancing Reliability in Wind Turbine Power Curve Estimation

Accurate power curve modeling is essential to continuously evaluate the performance of a wind turbine (WT). In this work, we characterize the wind power curves using SCADA data acquired at a frequency of 5 min in a wind farm (WF) consisting of five WTs. Regarding the non-parametric methods, we select artificial neural networks (ANNs) to make curve estimations. Given that, we have the curves provided by the manufacturer of the WTs given by some very precisely measured pair of wind speed and power points. We can evaluate the difference between the manufacturer characterization and the ones estimated with the data provided by the SCADA system. Before the estimation, we propose a method of filtering the anomalies based on the characteristics provided by the manufacturer. We use three-quarters of the available data for curve estimation and one-quarter for the test. One WT suffered a break in the test part, so we can check how the test estimates reflect this problem in its wind-power curve compared to the estimations obtained in the WTs that worked adequately.

Comparative evaluation of the dimensional accuracy of two commercially available extended pour alginates and a conventional alginate impression material at various time intervals – An in vitro study

Because of its acceptable accuracy, affordable price, accessible availability, and simplicity of handling, alginate impression materials continue to be a crucial component of dental practice despite many developments.The purpose of this study was to evaluate and compare the dimensional accuracy of two commercially available extended pour alginates (Cavex ColorChange and Algeniux) and a conventional alginate impression material (Zelgan) at different time intervals. On a maxillary model (Columbia Dentoform, Long Island City, N.Y.) the canines and the first molars were replaced with metal dies. This was selected as the master model. A ‘+’ mark was inscribed on these metal dies to serve as a reference for measurements. A self-cure acrylic resin custom tray was fabricated such that it was positioned over the model in the same spatial relationship with equal amount of space between the tray and model every time an impression was made. A total of 180 impressions were made of the master model, 15 impressions with each material at four different time intervals; immediate, 30 minutes, 48 hours (2 days) and 120 hours (5 days) to obtain gypsum cast. Manufacturer recommended water/powder ratios and storage conditions were followed in the process. Following the designated storage time interval, the casts were poured in minimum expansion Type IV dental stone. Measurements were done with a coordinate measuring machine after 7 days when the casts were completely dry. To evaluate and compare the dimensional accuracy of materials across various time points, for each group, the mean and standard deviation were estimated and subjected to statistical analysis. Two Way Repeated Measure Analysis of Variance (ANOVA) was performed to determine if the dimensions differed significantly across groups with time. The pair wise analysis for materials and time points was performed using Tukey’s post-hoc test. The p value was taken as significant when less than 0.05.Across different time points, a minimum % change was observed at immediate time point, which gradually increased at 30 minutes and at 48 hour, but at 120 hour the % change was maximum for all dimensions. Among three groups, Cavex ColorChange material showed minimum % change across time points, whereas Zelgan group showed maximum % change across all dimensions. All the paired differences were statistically insignificant (p &amp;#62; 0.05) for Algeniux and Cavex ColorChange group. But for Zelgan group, the difference between all the pairs of time points were statistically significant (p &amp;#60; 0.05), except for the pair immediate vs. 30 minutes. These results suggest that Zelgan material showed significant changes after 30 min for all the dimensions.: The results revealed that both the extended pour alginates Cavex ColorChange and Algeniux produced dimensionally accurate casts at all time intervals while the conventional alginate, Zelgan was accurate only at immediate and 30-minute time interval. It was also observed that, among the 4-time intervals investigated, most accurate casts were obtained when the impressions were poured immediately.