scholarly journals Advection on Cut-Cell Grids for an Idealized Mountain of Constant Slope

2017 ◽  
Vol 145 (5) ◽  
pp. 1765-1777 ◽  
Author(s):  
J. Steppeler ◽  
J. B. Klemp
Keyword(s):  
Velocity Field ◽  
Test Problem ◽  
Piecewise Linear ◽  
Real Data ◽  
Basis Functions ◽  
Rectangular Grid ◽  
The Past ◽  
Cut Cell ◽  
Straight Line ◽  
Constant Slope

Abstract Cut cells use regular or nearly regular polygonal cells to describe fields. For a given orography, some cells may be completely under the mountain, some completely above the mountain, and some are partially filled with air. While there are reports indicating considerably improved simulations with cut cells, inaccuracies may arise with some approximations, producing noise in fields near the surface. This behavior may depend strongly on the approximations made for the advection terms near the surface. This paper investigates the accuracy of advection for numerical schemes for a nondivergent flow near a mountain surface. The schemes use C-grid staggering with densities located at cell centers or on the corners of cells. Also, a nonconserving scheme is considered, which was used in the past with real-data cut-cell simulations. Since the cut cells near the surface create an irregular resolution, the accuracy and order of some approximations may break down near the surface. The objective of this paper is to find schemes having the same accuracy for advection near the surface as in the interior of the domain. As a test problem, uniform advection by a nondivergent velocity field is used with a 45° slope mountain (represented as a straight line) on a rectangular grid. Along the surface a sequence of triangular and pentagonal cells of quite different sizes are generated. Some schemes being discussed for cut cells lead to inaccurate and noisy solutions for this perfectly smooth mountain. A scheme using piecewise linear basis functions in a C grid with density points at the cell corners avoids these inaccuracies.

Experience

2021 ◽  
Vol 13 (1) ◽  
pp. 1-16
Author(s):  
Michela Fazzolari ◽  
Francesco Buccafurri ◽  
Gianluca Lax ◽  
Marinella Petrocchi
Keyword(s):  
Relative Frequency ◽  
Service Providers ◽  
Real Data ◽  
Online Reviews ◽  
Purchase Decision ◽  
The Past ◽  
Supervised Classifiers ◽  
Relative Frequency Distribution ◽  
Opinion Spam ◽  
Fake Reviews

Over the past few years, online reviews have become very important, since they can influence the purchase decision of consumers and the reputation of businesses. Therefore, the practice of writing fake reviews can have severe consequences on customers and service providers. Various approaches have been proposed for detecting opinion spam in online reviews, especially based on supervised classifiers. In this contribution, we start from a set of effective features used for classifying opinion spam and we re-engineered them by considering the Cumulative Relative Frequency Distribution of each feature. By an experimental evaluation carried out on real data from Yelp.com, we show that the use of the distributional features is able to improve the performances of classifiers.

scholarly journals Open Data Release and Privacy Concerns: Complexity in Mitigating Vulnerability with Controlled Perturbation

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Shah Imran Alam ◽  
Ihtiram Raza Khan ◽  
Syed Imtiyaz Hassan ◽  
Farheen Siddiqui ◽  
M. Afshar Alam ◽  
...  
Keyword(s):  
Data Quality ◽  
Open Data ◽  
Real Data ◽  
Privacy Concerns ◽  
The Past ◽  
Privacy Laws ◽  
Data Quality Assessment ◽  
Anonymized Data ◽  
Evaluation Parameters ◽  
Technology Domain

The benefits of open data were realised worldwide since the past decades, and the efforts to move more data under the license of open data intensified. There was a steep rise of open data in government repositories. In our study, we point out that privacy is one of the consistent and leading barriers among others. Strong privacy laws restrict data owners from opening the data freely. In this paper, we attempted to study the applied solutions and to the best of our knowledge, we found that anonymity-preserving algorithms did a substantial job to protect privacy in the release of the structured microdata. Such anonymity-preserving algorithms argue and compete in objectivethat not only could the released anonymized data preserve privacy but also the anonymized data preserve the required level of quality. K-anonymity algorithm was the foundation of many of its successor algorithms of all privacy-preserving algorithms. l-diversity claims to add another dimension of privacy protection. Both these algorithms used together are known to provide a good balance between privacy and quality control of the dataset as a whole entity. In this research, we have used the K-anonymity algorithm and compared the results with the addon of l-diversity. We discussed the gap and reported the benefits and loss with various combinations of K and l values, taken in combination with released data quality from an analyst’s perspective. We first used dummy fictitious data to explain the general expectations and then concluded the contrast in the findings with the real data from the food technology domain. The work contradicts the general assumptions with a specific set of evaluation parameters for data quality assessment. Additionally, it is intended to argue in favour of pushing for research contributions in the field of anonymity preservation and intensify the effort for major trends of research, considering its importance and potential to benefit people.

scholarly journals Intracluster Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 597-604 ◽  
Author(s):  
John J. Feldmeier
Keyword(s):  
Velocity Field ◽  
Stellar Population ◽  
Planetary Nebulae ◽  
Line Of Sight ◽  
Galaxy Groups ◽  
The Past ◽  
Star Production ◽  
Intracluster Light ◽  
Lower Luminosity

We review the progress of research on intracluster planetary nebulae (IPN). In the past five years, hundreds of IPN candidates have been detected in the Virgo and Fornax galaxy clusters and searches are also underway in poorer galaxy groups. From the observations to date, and applying the known properties of extragalactic planetary nebulae, the intracluster light in Virgo and Fornax: 1) is significant, at least 20% of the total cluster stellar luminosity, 2) is elongated in Virgo along our line of sight, and 3) may derive from lower-luminosity galaxies, consistent with some models of intracluster star production. A fraction of IPN candidates are not true IPN, but emission-line sources of very large observed equivalent width (≥ 200 Å). The most likely source for these contaminating objects are Lyman-α galaxies at z ≈ 3.1. Follow-up spectroscopy of the IPN candidates will be crucial to discriminate against high red-shift galaxies and to derive the velocity field of the intracluster stellar population.

scholarly journals On the mixing properties of piecewise expanding maps under composition with permutations, II: Maps of non-constant orientation

2016 ◽  
Vol 16 (03) ◽  
pp. 1660013 ◽  
Author(s):  
Nigel P. Byott ◽  
Congping Lin ◽  
Yiwei Zhang
Keyword(s):  
Piecewise Linear ◽  
Unit Interval ◽  
Interval Exchange ◽  
Expanding Maps ◽  
Mixing Properties ◽  
Linear Maps ◽  
Piecewise Linear Maps ◽  
Fold Map ◽  
Constant Slope ◽  
Piecewise Expanding Maps

For an integer [Formula: see text], let [Formula: see text] be the partition of the unit interval [Formula: see text] into [Formula: see text] equal subintervals, and let [Formula: see text] be the class of piecewise linear maps on [Formula: see text] with constant slope [Formula: see text] on each element of [Formula: see text]. We investigate the effect on mixing properties when [Formula: see text] is composed with the interval exchange map given by a permutation [Formula: see text] interchanging the [Formula: see text] subintervals of [Formula: see text]. This extends the work in a previous paper [N. P. Byott, M. Holland and Y. Zhang, DCDS 33 (2013) 3365–3390], where we considered only the “stretch-and-fold” map [Formula: see text].

Prediction of Thermal Displacements in Finite Element Tool Models

2001 ◽  
Author(s):  
Jörg Aßmus ◽  
Niels Wessel ◽  
Jürgen Kurths ◽  
Frank Weidermann ◽  
Jan Konvicka ◽  
...  
Keyword(s):  
Finite Element ◽  
Stable Process ◽  
Real Data ◽  
Thermal Displacement ◽  
Thermally Induced ◽  
The Past ◽  
Alternating Conditional Expectation ◽  
Thermal Displacements ◽  
Displacement Based ◽  
Ace Algorithm

Abstract Precision and productivity are very important criteria for the evaluation of modular tool systems and require a thermally stable process with tolerances in the micrometer range. During the past decades there has been an increasing interest in compensating thermally induced errors. In this paper we investigate wheather a prediction of thermal displacement based on a nonlinear regression analysis is possible, namely using the alternating conditional expectation algorithm (ACE) introduced by Breiman and Friedman, 1985. The data we are analyzing were generated by two different finite element spindle models of modular tool systems. As the main result we find that the ACE-algorithm is a powerful tool to model the relation between temperatures and displacements. It could also be a promising approach to handle well-known hysteresis effects. Limitations of this study are the model restricted results, next our findings have to be validated on real data.

Clusters Of Polyhedra In Architecture

1996 ◽  
Vol 11 (1-2) ◽  
pp. 97-101
Author(s):  
J. Francois Gabriel
Keyword(s):  
Good Reason ◽  
Modern Technology ◽  
Rectangular Grid ◽  
Connected Network ◽  
Advantages And Disadvantages ◽  
Truncated Octahedron ◽  
The Past ◽  
Building Systems ◽  
Visual Order ◽  
Do So

Conventional structural and building systems could not in the past bring into existence medium-rise buildings based on polyhedra. Modern technology makes it now possible to conceive and erect such buildings. One good reason to do so is that clusters of polyhedra can satisfy an essential need of architecture: the need for visual order. Too many contemporary buildings rely on a simplistic rectangular grid. The effect is, indeed, orderly, but it is also usually boring and non-hierarchical. The configuration selected here is the 12-connected network considered as a habitable three-way, multi-layer space frame. It is presented along with two variations. One is an infinite structure of three polyhedra also derived from the 12-connected network, the truncated octahedron, the cuboctahedron and the truncated tetrahedron. The other configuration is the honeycomb pattern resulting from the absorption of tetrahedron by adjacent octahedra, to which I have given the name Hexmod. Similarities and differences are identified and advantages and disadvantages of the three patterns are examined. Finally, combinations between patterns are introduced.

scholarly journals How well do we know the rotation curve of our Galaxy?

1985 ◽  
Vol 106 ◽  
pp. 107-108
Author(s):  
Paris Pişmiş
Keyword(s):  
Velocity Field ◽  
Rotation Curve ◽  
Spiral Galaxies ◽  
Spiral Structure ◽  
Smooth Curve ◽  
Velocity Fields ◽  
Rotation Curves ◽  
The Past ◽  
Different Populations ◽  
The Waves

The existence of variations from a smooth curve, in the form of waves, in the rotation curves of galaxies was pointed out earlier, and an interpretation was proposed based on the argument that the waves were the manifestation of the coexistence of different populations in a galaxy (see for example PişLmiş 1965, 1974). Observations in the past few years have shown that “undulations” in the rotation curve of spiral galaxies are rather common phenomena; maxima and minima occur roughly at arm and interarm regions, respectively. The velocity fields of the majority of the 23 galaxies compiled by Bosma (1978) exhibit well-defined waves. In particular the velocity field in the 21-cm HI line of M81 by Visser shows clearly the correlation of the waves with the spiral structure.

scholarly journals Limit Cycles Bifurcating from the Periodic Orbits of a Discontinuous Piecewise Linear Differentiable Center with Two Zones

2015 ◽  
Vol 25 (11) ◽  
pp. 1550144 ◽  
Author(s):  
Jaume Llibre ◽  
Douglas D. Novaes ◽  
Marco A. Teixeira
Keyword(s):  
Equilibrium Point ◽  
Periodic Solutions ◽  
Periodic Orbits ◽  
Limit Cycles ◽  
Homoclinic Orbit ◽  
Piecewise Linear ◽  
Differential Systems ◽  
Linear Differential Systems ◽  
Straight Line ◽  
Linear Differential

We study a class of discontinuous piecewise linear differential systems with two zones separated by the straight line x = 0. In x > 0, we have a linear saddle with its equilibrium point living in x > 0, and in x < 0 we have a linear differential center. Let p be the equilibrium point of this linear center, when p lives in x < 0, we say that it is real, and when p lives in x > 0 we say that it is virtual. We assume that this discontinuous piecewise linear differential system formed by the center and the saddle has a center q surrounded by periodic orbits ending in a homoclinic orbit of the saddle, independent if p is real, virtual or p is in x = 0. Note that q = p if p is real or p is in x = 0. We perturb these three classes of systems, according to the position of p, inside the class of all discontinuous piecewise linear differential systems with two zones separated by x = 0. Let N be the maximum number of limit cycles which can bifurcate from the periodic solutions of the center q with these perturbations. Our main results show that N = 2 when p is on x = 0, and N ≥ 2 when p is a real or virtual center. Furthermore, when p is a real center we found an example satisfying N ≥ 3.

Runway foreign object detection using RGB

2015 ◽  
Vol 119 (1212) ◽  
pp. 229-243
Author(s):  
W. Chen
Keyword(s):  
Background Subtraction ◽  
Detection Probability ◽  
Real Data ◽  
Background Model ◽  
Clutter Suppression ◽  
Foreign Object ◽  
Detection Scheme ◽  
The Past ◽  
Innovative Techniques ◽  
Better Than

AbstractThis paper presents an improved algorithm for foreign object debris (FOD) detection on the runway with several innovative techniques. The detection scheme incorporates four steps of geometric adjustment, background subtraction, clutter suppression and camouflage elimination. After geometric adjustment, the background model is built for each pixel with a set of RGB colour values taken in the past at the same location or in the neighborhood in the step of background subtraction. The background model samples are substituted randomly with an unfixed update period. Furthermore, the steps of clutter suppression and camouflage elimination are added to modify the segmentation map after background subtraction in order to increase the detection probability and decrease the false alarm rate. The overall algorithm is applied to the test data and real data on the runway. The results show that the RGB-based algorithm performs better than the classical gray-based techniques.

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