Topography Analysis of Random Anisotropic Gaussian Rough Surfaces

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Deepak K. Prajapati ◽  
Mayank Tiwari
Keyword(s):  
Standard Deviation ◽  
Rough Surface ◽  
Correlation Length ◽  
Rough Surfaces ◽  
Spectral Moments ◽  
Statistical Characterization ◽  
Wear Process ◽  
Increase With Increase ◽  
Bandwidth Parameter ◽  
Significant Difference

Engineered surfaces (ground and similarly structured rough surfaces) show anisotropic characteristics and their topography parameters are direction dependent. Statistical characterization of these surfaces is still complex because of directional nature of surfaces. In this technical brief, an attempt is made to simulate anisotropic surfaces through use of topography parameters (three-dimensional (3D) surface parameters). First, 3D anisotropic random Gaussian rough surface is generated numerically with fast Fourier transform (FFT). Numerically generated anisotropic random Gaussian rough surface shows statistical properties (texture direction, texture ratio) similar to ground and similarly directional anisotropic rough surfaces. For numerically generated anisotropic Gaussian rough surface, important 3D roughness parameters are determined. Sayles and Thomas' (1976, “Thermal Conductance of Rough Elastic Contact,” Appl. Energy, 2(4), pp. 249–267.) theoretical model for directional anisotropic rough surface is adopted here for calculating the summit parameters, i.e., equivalent bandwidth parameter, mean summit curvature, skewness of summit height, standard deviation of summit height, and equivalent spectral moments. This work demonstrates the variation of spectral moments in both across and parallel to the lay directions with pattern ratio (γ=βx/βy). Correlation length (βx) is fixed 10μm and correlation length (βy) is varied from 100 to 10 μm. Variation of summit parameters with pattern ratio is also discussed in detail. Results shows that mean summit curvature and skewness of summit heights increase with increase in pattern ratio, whereas standard deviation of summit heights and equivalent bandwidth parameter (αe) decreases with pattern ratio. A significant difference is found in “Abbott-Firestone” parameters when calculated in both perpendicular and parallel to lay directions. Effect of these parameters on wear process is discussed in brief.

Combining and Contacting of Two Rough Surfaces with Asymmetric Distribution of Asperity Heights

2004 ◽  
Vol 126 (2) ◽  
pp. 225-232 ◽  
Author(s):  
Ning Yu ◽  
Andreas A. Polycarpou
Keyword(s):  
Standard Deviation ◽  
Weibull Distribution ◽  
Rough Surface ◽  
Rough Surfaces ◽  
Asymmetric Distribution ◽  
Magnetic Storage ◽  
Roughness Parameters ◽  
Practical Applications ◽  
Practical Engineering ◽  
Contour Plots

The statistical approach of describing rough surfaces is extended to include the contact of two rough surfaces in which their distribution of asperity heights can either be symmetric or asymmetric, and the asymmetry is modeled using the normalized Weibull distribution. In considering the contact between two rough surfaces, as in most practical applications, the contact can be approximated by an equivalent rough surface in contact with a smooth plane. The roughness parameters of the equivalent surface are obtained using the spectral moment method, and its validity is verified using realistic surface roughness measurements. This paper presents a method to obtain the equivalent rough surface with a Weibull distribution of asperity heights, in which the standard deviation and skewness parameters of asperity heights of the actual contacting surfaces are preserved. The advantages of this method are demonstrated via direct comparisons with a previously proposed method as well as with exact numerical simulation of the contact parameters of several different actual surfaces from magnetic storage and MEMS applications. For practical engineering applications, where the roughness parameters of each individual surface are known, contour plots for the skewness value of the equivalent rough surface are provided for practical ranges of combinations of standard deviation ratios and skewness values. As expected when the roughness of one of the contacting surfaces dominates, the skewness is solely determined by the rougher surface.

The Effect of Determining Topography Parameters on Analyzing Elastic Contact Between Isotropic Rough Surfaces

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Gorakh Pawar ◽  
Pawel Pawlus ◽  
Izhak Etsion ◽  
Bart Raeymaekers
Keyword(s):  
Rough Surface ◽  
Cross Sections ◽  
Nearest Neighbor ◽  
Rough Surfaces ◽  
Sampling Interval ◽  
Elastic Contact ◽  
Spectral Moments ◽  
Identification Scheme ◽  
Contact Parameters ◽  
Identification Model

The elastic contact between two computer generated isotropic rough surfaces is studied. First the surface topography parameters including the asperity density, mean summit radius, and standard deviation of asperity heights of the equivalent rough surface are determined using an 8-nearest neighbor summit identification scheme. Second, many cross sections of the equivalent rough surface are traced and their individual topography parameters are determined from their corresponding spectral moments. The topography parameters are also obtained from the average spectral moments of all cross sections. The asperity density is found to be the main difference between the summit identification scheme and the spectral moments method. The contact parameters such as the number of contacting asperities, real area of contact, and contact load for any given separation between the equivalent rough surface and a rigid flat are calculated by summing the contributions of all the contacting asperities using the summit identification model. These contact parameters are also obtained with the Greenwood-Williamson (GW) model using the topography parameters from each individual cross section and from the average spectral moments of all cross sections. Three different surfaces and three different sampling intervals were used to study how the method to determine topography parameters affects the resulting contact parameters. The contact parameters are found to vary significantly based on the method used to determine the topography parameters, and as a function of the autocorrelation length of the surface, as well as the sampling interval. Using a summit identification model or the GW model based on topography parameters obtained from a summit identification scheme is perhaps the most reliable approach.

HISTÓRICO DO COMPRIMENTO TOTAL DE TAMBAQUI (Colossoma macropomum, CHARACIFORMES: CHARACIDAE, CUVIER, 1818) DESEMBARCADO NO MERCADO DE TEFÉ, AMAZONAS, BRASIL, COM NOVE RECOMENDAÇÕES PARA O MANEJO PESQUEIRO DA ESPÉCIE

2008 ◽  
Vol 2 (1) ◽  
pp. 27-34 ◽  
Author(s):  
Jorge Iván Sánchez-Botero ◽  
Danielle Sequeira Garcez ◽  
Wesllen Chaves Cortezão
Keyword(s):  
Sustainable Development ◽  
Standard Deviation ◽  
Environmental Protection ◽  
Fisheries Management ◽  
Historical Data ◽  
Colossoma Macropomum ◽  
Pressure Diffusion ◽  
Significant Difference ◽  
Efficient Mechanisms ◽  
Solimões River

This study evaluates the total length of tambaqui (Colossoma macropomum ) captured in the middle Solimões river and traded during seven years (1993, 1997 and 2000 to 2005) in the Tefé market, Amazon, Brazil. The Mamirauá Institute of Sustainable Development obtained measurements of the total lengths from 42207 individuals. The length average was 45.23 ± 6.29 cm (minim um of 13 cm and maximum of 105.5 cm ) and the mode was 45 cm . From the total tambaquis, 92.86% were smaller than 55 cm and 7.14% measured 58.24 ± 5.41 cm on average. Medium and standard deviation of the lengths recorded in all years showed sizes below the established by the environmental federal agency. The Kruskal Wallis test showed that there is no significant difference between the abundances and medium sizes of the captures during all months of the year. The historical data of the tambaqui fisheries for the middle Solimões region indicate that individuals of this species have been constantly captured at sizes below the minim um length of reproduction. Nine recommendations for tambaquis fisheries management in the region related to more efficient mechanisms of inspection, auto-ecology studies of the species, environmental protection, reduction of fishery pressure, diffusion and educational cam paigns that aim to correct exploitation of this resource are presented in this manuscript.

PENGARUH PENDIDIKAN KESEHATAN REPRODUKSI PADA PEER GROUP (TEMAN SEBAYA) TERHADAP PENGETAHUAN DAN PERSEPSI REMAJA TENTANG PENDEWASAAN USIA PERKAWINAN DI SMA NEGERI 1 KECAMATAN NAMORAMBE KAB. DELI SERDANG 2018

2020 ◽  
Vol 1 (2) ◽  
pp. 56-66
Author(s):  
Irma Linda
Keyword(s):  
Standard Deviation ◽  
Health Education ◽  
Reproductive Health ◽  
Peer Group ◽  
Peer Groups ◽  
A Value ◽  
Significant Difference ◽  
Reproductive Health Education ◽  
The Mean ◽  
Adolescent Perceptions

Background: Early marriages are at high risk of marital failure, poor family quality, young pregnancies at risk of maternal death, and the risk of being mentally ill to foster marriage and be responsible parents. Objective: To determine the effect of reproductive health education on peer groups (peers) on the knowledge and perceptions of adolescents about marriage age maturity. Method: This research uses the Quasi experimental method with One group pre and post test design, conducted from May to September 2018. The statistical analysis used in this study is a paired T test with a confidence level of 95% (α = 0, 05). Results: There is an average difference in the mean value of adolescent knowledge between the first and second measurements is 0.50 with a standard deviation of 1.922. The mean difference in mean scores of adolescent perceptions between the first and second measurements was 4.42 with a standard deviation of 9.611. Conclusion: There is a significant difference between adolescent knowledge on the pretest and posttest measurements with a value of P = 0.002, and there is a significant difference between adolescent perceptions on the pretest and posttest measurements with a value of p = 0.001. Increasing the number of facilities and facilities related to reproductive health education by peer groups (peers) in adolescents is carried out on an ongoing basis at school, in collaboration with local health workers as prevention of risky pregnancy.

INVESTIGATION OF ATTITUDES OF STUDENTS STUDYING AT THE FACULTY OF SPORT SCIENCES FIRAT UNIVERSITY TOWARDS SPORT TOURISM

2021 ◽  
Vol 0 (39) ◽  
pp. 0-0
Author(s):  
Barış Utku ÖZDEMİR ◽  
Ali Serdar YÜCEL
Keyword(s):  
Standard Deviation ◽  
Attitude Scale ◽  
Education Level ◽  
Sport Tourism ◽  
Significance Level ◽  
Significant Difference ◽  
Sports Tourism ◽  
Package Program ◽  
Students Attitudes ◽  
Course Variables

Aim: This research was conducted to examine the attitudes of students studying at Fırat University Faculty of Sport Sciences towards sport tourism. Methods: 1091 students participated in the study. In order to examine the students' attitudes towards sports tourism, the attitude scale towards sports tourism (STYTÖ) developed by Kardaş and Sadık (2018) was used. The data obtained were evaluated in the SPSS 22.0 package program. Frequency, mean, standard deviation, one-wayAnova, independent t-test were used to analyze the data. The significance level of the statistics made was accepted as p <.05. Conclusion: As a result of the study, it was determined that the students' attitudes towards sports tourism were at a positive level and there were signifi-cant differences in terms of some variables (age, class, mother and father education level, branch, department, etc.) according to the sub-dimensions of the scale. It was deter-mined that there was no significant difference in terms of gender, marital status and sports tourism course variables. It is predicted that this research will provide an advantage in determining the attitudes of university students who receive sports education towards sports tourism and evaluating the issue in the sectoral field.

Reduced Rough-Surface Parametrization for Use With the Discrete-Element Model

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Stephen T. McClain ◽  
Jason M. Brown
Keyword(s):  
Heat Transfer ◽  
Rough Surface ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Roughness Element ◽  
Three Dimensional ◽  
Element Model ◽  
Discrete Element ◽  
Diameter Distribution ◽  
Discrete Element Model

The discrete-element model for flows over rough surfaces was recently modified to predict drag and heat transfer for flow over randomly rough surfaces. However, the current form of the discrete-element model requires a blockage fraction and a roughness-element diameter distribution as a function of height to predict the drag and heat transfer of flow over a randomly rough surface. The requirement for a roughness-element diameter distribution at each height from the reference elevation has hindered the usefulness of the discrete-element model and inhibited its incorporation into a computational fluid dynamics (CFD) solver. To incorporate the discrete-element model into a CFD solver and to enable the discrete-element model to become a more useful engineering tool, the randomly rough surface characterization must be simplified. Methods for determining characteristic diameters for drag and heat transfer using complete three-dimensional surface measurements are presented. Drag and heat transfer predictions made using the model simplifications are compared to predictions made using the complete surface characterization and to experimental measurements for two randomly rough surfaces. Methods to use statistical surface information, as opposed to the complete three-dimensional surface measurements, to evaluate the characteristic dimensions of the roughness are also explored.

Comparative Analysis of the Exposure and Surgical Freedom of the Endoscopic Extended Minipterional Craniotomy and the Transorbital Endoscopic Approach to the Anterior and Middle Cranial Fossae

2018 ◽  
Vol 17 (2) ◽  
pp. 174-181 ◽  
Author(s):  
Raywat Noiphithak ◽  
Juan C Yanez-Siller ◽  
Juan M Revuelta Barbero ◽  
Raymond I Cho ◽  
Bradley A Otto ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Standard Deviation ◽  
Minimally Invasive ◽  
Vertical Axis ◽  
Endoscopic Approach ◽  
Extended Version ◽  
Specific Approach ◽  
Significant Difference ◽  
Surgical Application ◽  
The Mean

AbstractBACKGROUNDNumerous minimally invasive approaches to the skull base have been successively developed. Knowledge of the surgical nuances of a specific approach may facilitate approach selection. This study sought to compare the nuances of an extended version of the minipterional craniotomy (EMPT) with those of the transorbital endoscopic approach (TOEA) to the anterior and middle cranial fossae (ACF and MCF, respectively).OBJECTIVETo quantitatively analyze and compare the area of exposure and surgical freedom between EMPT and TOEA to the ACF and MCF.METHODSEMPT and TOEA were carried out in 5 latex-injected cadaveric heads, bilaterally (10 sides). For each approach, the area of exposure, surgical freedom, and angle of attack were obtained with neuronavigation and statistically compared.RESULTSNo significant difference was found between the mean area of exposure of EMPT and TOEA at the ACF and MCF (P = .709 and .317, respectively). The mean exposure area at the ACF was of 13.4 ± 2.6 cm2 (mean ± standard deviation) and 13.0 ± 1.9 cm2 for EMPT and TOEA, respectively. Except for the crista galli, EMPT afforded a larger area of surgical freedom at all targets. EMPT also achieved significantly greater attack angles in vertical axis except to the crista galli. The horizontal attack angles to all targets were similar between approaches.CONCLUSIONEMPT and TOEA offer a comparable area of exposure at the ACF and MCF in the cadaver; however, the instrument maneuverability afforded by EMPT is superior. Further studies are necessary to better define their precise surgical application.

Self-Concepts of Preschool Girls in a Preballet Program

1993 ◽  
Vol 77 (1) ◽  
pp. 104-106
Author(s):  
Anne E. Kozlowski
Keyword(s):  
Preschool Children ◽  
Standard Deviation ◽  
Normative Data ◽  
T Test ◽  
The Self ◽  
Self Concept ◽  
Significant Difference ◽  
One Year

The self-concepts of 10 5-yr.-old girls enrolled in a preballet program at a ballet school in Tulsa, Oklahoma for over one year were measured using the Purdue Self-concept Scale for Preschool Children. Their scores were compared against the scale's normative data for girls of similar age. A one-sample two-tailed t test showed girls' mean was 1 standard deviation above the normative population's mean, a significant difference. Preballet education may be an effective tool for enhancing self-concept, although selective factors may contribute also.

scholarly journals Circadian variation of fatigue in both patients with paralytic poliomyelitis and post-polio syndrome

2013 ◽  
Vol 71 (7) ◽  
pp. 442-445 ◽  
Author(s):  
Celiana Figueiredo Viana ◽  
Márcia Pradella-Hallinan ◽  
Abrahão Augusto Juviniano Quadros ◽  
Luis Fabiano Marin ◽  
Acary Souza Bulle Oliveira
Keyword(s):  
Standard Deviation ◽  
Sleep Disturbances ◽  
Circadian Variation ◽  
Progressive Increase ◽  
Paralytic Poliomyelitis ◽  
Poor Sleep ◽  
Poor Sleep Quality ◽  
Significant Difference ◽  
Sleep Parameters

ObjectiveIt was to evaluate the degree of fatigue in patients with paralytic poliomyelitis (PP) and with post-polio syndrome (PPS), and correlate it with parameters of sleep and the circadian cycle.MethodsThirty patients, 17 female (56.7%), participated in the study: they answered the Revised Piper Fatigue Scale and performed a nocturnal polysomnographic study. Eleven had PP (mean age±standard deviation of 47.9±6.4 years), and 19 had PPS (mean age±standard deviation of 46.4±5.6 years).ResultsOur study showed that fatigue was worse in the afternoon in the PP Group and had a progressive increase throughout the day in the PPS Group. We also observed compromised quality of sleep in both groups, but no statically significant difference was found in the sleep parameters measured by polysomnography.ConclusionFatigue has a well-defined circadian variation, especially in PPS Group. Poor sleep quality is associated with fatigue and, therefore, sleep disturbances should be evaluated and treated in this group of PPS.

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