Littérature scientifique sur le sujet « Quasi-independent tests »
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Articles de revues sur le sujet "Quasi-independent tests"
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Santosa, Farah Heniati, Habib Ratu Perwira Negara, Indrawati, Samsul Bahri et Samsuriadi. « Komparasi Kemampuan Penalaran matematis mahasiswa ditinjau dari Gaya Kognitif ». Jurnal Pemikiran dan Penelitian Pendidikan Matematika (JP3M) 2, no 2 (20 janvier 2020) : 142–53. http://dx.doi.org/10.36765/jp3m.v2i2.68.
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This study aims to obtain a picture of the achievement of mathematical reasoning abilities of students who obtain PBL learning in terms of cognitive fields dependent and field independent. This research is a quasi-experiment involving 97 first semester students. Analysis of the study used one way ANAVA. The research instruments were cognitive style tests and mathematical reasoning abilities tests. The results of the study concluded that there are differences in students' mathematical reasoning abilities that have field dependent and field independent cognitive styles, that is, students with independent field cognitive styles have better mathematical reasoning abilities compared to students with field dependent cognitive styles.
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Melati, Inaya Sari, Kerry Lee, Nina Farliana et Raeni Raeni. « Reducing Personal Business Failure Trauma for Students in Entrepreneurship Classes ». International Journal of Adult Education and Technology 11, no 3 (juillet 2020) : 36–48. http://dx.doi.org/10.4018/ijaet.2020070103.
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This Indonesian quasi-experimental study investigated the effectiveness of a 60-day entrepreneurial programme designed to reduce the trauma of business failure experienced by students when undertaking entrepreneurial projects. Data from pre-and post- questionnaires and journals were analysed using independent T-Tests and paired T-Tests. The results showed that there was a significant reduction in the trauma of business failure in participants after participation in the programme.
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Sun, Tao, Aoxin Liu, Chao Ge, Ying Yuan et Haifu Wang. « Mechanical Properties, Constitutive Behaviors and Failure Criteria of Al-PTFE-W Reactive Materials with Broad Density ». Materials 15, no 15 (26 juillet 2022) : 5167. http://dx.doi.org/10.3390/ma15155167.
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Quasi-static tension tests, quasi-static compression tests and dynamic compression tests were conducted to investigate the mechanical properties, constitutive behaviors and failure criteria of aluminum-polytetrafluoroethylene-tungsten (Al-PTFE-W) reactive materials with W content from 20% to 80%. The analysis of the quasi-static test results indicated that the strength of the materials may be independent of the stress state and W content. However, the compression plasticity of the materials is significantly superior to its tension plasticity. W content has no obvious influence on the compression plasticity, while tension plasticity is extremely sensitive to W content. Dynamic compression test results demonstrated the strain rate strengthening effect and the thermal softening effect of the materials, yet the dynamic compression strengths and the strain rate sensitivities of the materials with different W content show no obvious difference. Based on the experimental results and numerical iteration, the Johnson–Cook constitutive (A, B, n, C and m) and failure parameters (D1~D5) were well determined. The research results will be useful for the numerical studies, design and application of reactive materials.
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Izah, Inayatul, Muhammad Assegaf Baalwi et Achmad Wahyudi. « PENGARUH MODEL BALANCED LITERACY TERHADAP HASIL BELAJAR BAHASA INDONESIA PESERTA DIDIK KELAS III SDN SIDOKLUMPUK SIDOARJO ». Jurnal Muassis Pendidikan Dasar 1, no 3 (25 octobre 2022) : 227–36. http://dx.doi.org/10.55732/jmpd.v1i3.34.
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This research was conducted at SDN Sidoklumpuk Sidoarjo. The purpose of this study was to determine the effect of the Balanced Literacy model on Indonesian language learning outcomes for third-grade students at SDN Sidoklumpuk Sidoarjo. This research includes quantitative research where the data generated is in the form of numbers. The research data were calculated using SPSS software version 16. This type of research is quasi-experimental research (quasi-experimental) with a Nonequivalent Control Group Design. Data collection techniques used in this study were interviews and tests. The data analysis technique used a validity test, reliability test, normality test, homogeneity test, and different test t-tests (independent sample test). The results of the study stated that from the results of testing the research hypothesis, there was an effect of the Balanced Literacy Model on Indonesian language learning outcomes in third-grade students at SDN Sidoklumpuk Sidoarjo. This is evidenced by the value on the different t-tests (independent sample test) which shows that sig 0.006 0.05 then Ho is rejected or Ha is accepted. So it can be concluded that the hypothesis Ha states there is an effect of the Balanced Literacy Model on the learning outcomes of Indonesian class III students
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Poniatowski, Kelly. « Assessing Flipped Versus Traditional Classrooms : Is Flipping Really Better ? » Journalism & ; Mass Communication Educator 74, no 4 (29 mars 2019) : 422–37. http://dx.doi.org/10.1177/1077695819835037.
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Using a quasi-experiment, this research looks at grades and student satisfaction over the course of six semesters in a college-level writing class. Three of the classes were taught traditionally, and the other three classes utilized the flipped classroom concept. All classes were taught by the same instructor. Using independent samples t tests, results indicate that students received higher grades and had more satisfaction in the traditional classroom.
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Foreman, Cameron, Sherilyn Wright, Alec Edgington, Mario Berta et Florian J. Curchod. « Practical randomness amplification and privatisation with implementations on quantum computers ». Quantum 7 (30 mars 2023) : 969. http://dx.doi.org/10.22331/q-2023-03-30-969.
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We present an end-to-end and practical randomness amplification and privatisation protocol based on Bell tests. This allows the building of device-independent random number generators which output (near-)perfectly unbiased and private numbers, even if using an uncharacterised quantum device potentially built by an adversary. Our generation rates are linear in the repetition rate of the quantum device and the classical randomness post-processing has quasi-linear complexity – making it efficient on a standard personal laptop. The statistical analysis is also tailored for real-world quantum devices. Our protocol is then showcased on several different quantum computers. Although not purposely built for the task, we show that quantum computers can run faithful Bell tests by adding minimal assumptions. In this semi-device-independent manner, our protocol generates (near-)perfectly unbiased and private random numbers on today's quantum computers.
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Kharomah, Desy Nursinta Al, et Muhammad Abduh. « The impact of the MathMagic learning method on students’ mathematics cognitive learning outcomes ». Jurnal Elemen 9, no 1 (2 janvier 2023) : 120–31. http://dx.doi.org/10.29408/jel.v9i1.6838.
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Low cognitive learning outcomes of students can hinder student learning processes. This obstacle occurs because the learning method has yet to facilitate student learning trajectories resulting in low cognitive mathematics learning outcomes for students. The purpose of this research was to determine the impact of the MathMagic learning method on the mathematics cognitive learning outcomes of the students. The method used in this research was a quasi-experimental research design with a nonequivalent control group design. Data collection was done by test technique of students' cognitive learning outcomes. Data analysis techniques in this study used instrument tests in the form of validity and reliability tests, prerequisite tests in the form of normality tests and homogeneity tests, and hypothesis tests in the form of independent sample t-tests. The results show that the MathMagic learning method influenced students' cognitive learning outcomes in mathematics, especially in adding fractions with different denominators. This MathMagic learning method effectively improves understanding of the basic addition of fractions with unlike denominators.
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Banowo, Agus Sri, et Yance Hidayat. « Pengaruh Edukasi Gizi terhadap Praktik Pemberian Makan Pada Baduta Stunting di Kabupaten Bengkulu Utara ». Jurnal Ilmiah Universitas Batanghari Jambi 21, no 2 (4 juillet 2021) : 765. http://dx.doi.org/10.33087/jiubj.v21i2.1539.
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Stunting is a less chronic nutritional problem. The practice of feeding is one of the factors that contribute to stunting, so there is a need for nutrition education regarding the practice of providing food. This study aims to discuss nutrition education interventions on the practice of feeding mothers who have stunting. The study design used a quasi-experimental design with a pre-posttest design of two groups. The research location was Kerkap health centre as an intervention and Air Lais health centre as a control with a sample of 40 people each. The test used in this study paired-sample t-test and independent t-test. The different tests' results depend on the average meal management between the control groups and comparison with p values of 0,000 and 0.168, and independent tests between the intervention group and the control group of 0,000. Nutrition education is a particular program to improve the practice of family feeding of stunting children.
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Angendari, Made Diah, I. Made Candiasa, I. Wayan Sukra Warpala et Ketut Agustini. « effect of using animation video media through problem-based learning settings on learning outcomes for making fashion patterns ». International journal of health sciences 6, no 3 (8 novembre 2022) : 1607–22. http://dx.doi.org/10.53730/ijhs.v6n3.13605.
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This study aims to determine the effect of using animated video media through problem-based learning settings on learning outcomes to make fashion patterns. The type of research used is a quasi-experimental design with a non-equivalent control group design. Variables consist of independent variables and dependent variables. The independent variables are the use of animated video media with problem-based learning model settings and the use of PowerPoint media with problem-based learning model settings. The dependent variable is the result of learning to make fashion patterns. The population of this study was all students of class X Fashion Design for the 2021/2022 academic year in Buleleng Regency, which consisted of 34 people at SMK Negeri 2 Singaraja and SMK Negeri 1 Seririt. The sampling technique uses saturated sampling that is using the entire population. Data were collected by using multiple choice and rubric test techniques. The multiple-choice test instrument has been tested with item validity tests, reliability tests, item difficulty tests, and different power tests. The skill assessment rubric is tested with expert validation. Prerequisites for data analysis in the form of a homogeneity test and normality test. While the analysis of hypothesis testing was carried out using the t-test.
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Liang, Shixue, Xiaodan Ren et Jie Li. « A mesh-size-objective modeling of quasi-brittle material using micro-cell informed damage law ». International Journal of Damage Mechanics 27, no 6 (9 juin 2017) : 913–36. http://dx.doi.org/10.1177/1056789517713335.
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A multi-scale approach for mesh size independent finite element analysis of quasi-brittle material is proposed in this article. The homogenization based multi-scale damage representation is first introduced in obtaining the damage law from micro-cell simulation with consideration of microscopic crack propagation. The key idea to remedy the mesh size sensitivity in the 2D macroscopic finite element analysis is to introduce a damage law directly from the micro-cell simulation, where the micro-cell size should be identical to the macroscopic mesh size. The micro-cells with different sizes are generated and the corresponding simulations are presented in the numerical tests to obtain the micro-cell dependent damage law. The mesh independent finite element analysis results of the notched beam and the double-edge notched specimen affirm the strategy of correcting the mesh sensitivity.
Thèses sur le sujet "Quasi-independent tests"
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Li, Jin-Jie, et 李晉杰. « Quasi-Independent Test under Semi-Competing Risks Data ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/87852939098049994128.
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碩士國立中正大學
統計科學所
97
This thesis focuses on the quasi-independent test between nonterminal event and terminal event under semi-competing risks data (Fine et al. (2001)). On semi-competing risks data, a nonterminal event may be censored by a terminal event. We consider the two test statistics provided by Ghosh(2006) and Wang(2003) to test the quasi-independence. Further, we discuss the relation between the two test statistics. When we choose the corresponding weight function for the two statistics, respectively, we find they are equiralent. For the estimation of variance, we provide an estimation for small sample, which is different form the variance estimation suggested by literatures. When the data follows Archimedean copula (AC) model, we provide an appropriate weight function to make the test statistics more powerful. For the general situations, we also provide a common method to choose the weight function. We will use simulation studies to examine our inference. Finally, we will discuss a real data to test the quasi-independence
Chapitres de livres sur le sujet "Quasi-independent tests"
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Kumar, M., et P. N. Bajeel. « Introduction to System Reliability Evaluation through Bayesian Approach ». Dans Mathematical Concepts and Applications in Mechanical Engineering and Mechatronics, 130–53. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1639-2.ch007.
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Consider a parallel system with independent components. Assume that lifetime of i-th component follows exponential distribution with unknown parameter. We assume each , is distinct and the priori information can be modeled by quasi-density function given by , where is a predefined upper bound. A Bayesian estimator for , based on type-I censoring is used to get an estimate of system reliability. Optimal reliability test plan is designed, and an optimization problem is formulated satisfying usual probability requirements. Several numerical examples are considered to illustrate the Bayesian approach of obtaining optimal reliability test plan for a parallel system.
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Gezgin, Deniz Mertkan. « The Effect of Mobile Learning Approach on University Students' Academic Success for Database Management Systems Course ». Dans Mobile Devices in Education, 68–86. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-1757-4.ch005.
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This article investigates the effect of mobile learning support on students' academic success on a database management systems (DBMS) course. The research was carried out with 36 students attending a state university in Turkey. In this study, a mixed method was used, which includes both quantitative and qualitative data collection techniques. For the quantitative data, the study was conducted in accordance with the pre-test and post-test-based two group quasi-experimental model. For the qualitative data, the descriptive analysis technique was used. The independent sample t-test and paired simple t-test were employed in the analysis phase. According to the findings, mobile learning positively affected students' academic achievement on the DBMS course, in that the students supported by mobile learning were more successful than students supported only by face-to-face training method. Finally, it is seen that the students have emphasized themes of motivation, 1-1 access, and an interest in terms of the effect of m-learning approach on academic success.
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Faria, Liliana. « PORTFOLIO AS A STRATEGY TO IMPROVE CAREER ADAPTABILITY RESOURCES ». Dans Advances in Education and Educational Trends Series, 15–25. inScience Press, 2021. http://dx.doi.org/10.36315/2021ead02.
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This study aimed to determine whether the levels of career adaptability resources could be increased through the use of a portfolio writing strategy. Based on a mixed methods approach, the study used the design quasi-experimental, with two independent groups and with repeated measures, together with a focus group. Forty students (17 from the experimental group; 23 from the control group) in university-work transition completed the Portuguese version of the Career Adaptation Scale. The pre-test survey was administered at the beginning of the semester of the curricular unit of personal and professional development project (PPDP) in both groups. This was followed, in the experimental group, by a fourteen-week portfolio writing intervention, under the PPDP. In the control group, the PPDP followed the traditional expository teaching methodology. After completing the intervention procedure, post-test research was conducted byboth groups. Five students from the experimental group also participated in a focus group of feedback on the writing of portfolios under the PPDP. The results revealedthat writing the portfolios contributed to a career adaptability resources increase as well as for the confidence, self-knowledge and knowledge of the market opportunities of these students. The use of portfolios in the PPDP unit course is recommended.
Actes de conférences sur le sujet "Quasi-independent tests"
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Shivaswamy, Shashishekar, Jianmin Li et Hamid M. Lankarani. « Impact Analysis of Plates Using Quasi-Static Approach ». Dans ASME 1994 Design Technical Conferences collocated with the ASME 1994 International Computers in Engineering Conference and Exhibition and the ASME 1994 8th Annual Database Symposium. American Society of Mechanical Engineers, 1994. http://dx.doi.org/10.1115/detc1994-0089.
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Abstract Impact calculations suffer from several practical limitations which limit their application to establishing the approximate magnitude of the various phenomena involved. The transient force deformation response of a body subjected to impact can be explained accurately using stress wave propagation theory. As this approach is very complicated, a simpler quasi-static approach with non-linear force deformation Hertz relations can be employed for impact analysis. However, these relations can not explain the energy absorption and permanent deformations encountered during the impact. This necessitates independent non-linear force-deformation relations for compression and restitution phases of impact. In the present paper, impact tests conducted on Aluminum and Steel plates have been reported. The impact response of the system was compared with the various theoretical quasi-static force models. Considering the assumptions made in the quasi-static force models, the experimental results matched very well with the theoretical results. Non-linear force-deformation model with independent relations for compression and restitution phases was found to be the best approach to analyze impact problems. The value of the index in the non-linear force-deformation relations was found to be approximately 1.71 and 1.78 for Aluminum and Steel respectively. The values of impact parameters for a given material were found to depend on impact velocity.
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Hasegawa, Kunio, Katsumasa Miyazaki et Koichi Saito. « Plastic Collapse Loads for Flat Plates With Dissimilar Non-Aligned Through-Wall Cracks ». Dans ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57841.
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When multiple flaws are offset flaws, alignment rules are used to determine whether the flaws should be treated as non-aligned or as coplanar. The alignment rules are provided in fitness-for-service codes, and the rules are based on comparison of flaw dimensions. Quasi-static tensile tests were performed on Type 304 stainless steel flat plate specimens with two dissimilar through-wall offset flaws at ambient temperature. It can be seen that, in the experiments, plastic collapse loads were independent of non-alignment dimensions, when the counterpart flaw lengths are smaller enough compared with the main flaw lengths.
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McNeill, Scot, Paul Angehr, Dan Kluk, Tomokazu Saruhashi, Ikuo Sawada, Masanori Kyo, Eigo Miyazaki et Yasuyuki Yamazaki. « A Method for Determining Quasi-Static and Dynamic Riser Inclination Using Collocated Accelerometers and Angular Rate Sensors ». Dans ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24035.
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A method is described for determining quasi-static and dynamic riser angles using measured data typically found in a riser fatigue monitoring system, specifically acceleration and angular rate data. Quasi-static riser inclination and orientation of the inclination plane are determined from the low frequency triaxial accelerations, containing measurement of the gravitational body force. Components of the gravitational body force along the accelerometer axes vary slowly with the riser quasi-static response. The slowly varying Euler angles are determined from the components of gravity along the three axes. Dynamic riser inclination along and transverse to the quasi-static inclination plane are determined by integration of the angular rates, followed by transformation into a coordinate system aligned with the quasi-static inclination plane. The quasi-static and dynamic inclination angles are combined to arrive at the time trace of riser inclination angles. Following implementation of the method in Matlab®, the procedure was validated and the program verified using laboratory test data. A double-gimbaled platform was constructed, on which were mounted a triaxial accelerometer, biaxial angular rate and biaxial inclinometer (reference sensor). A battery of static and dynamic tests was carried out on the platform. Machinists’ levels and angle gauges were used to set the inclination in the various tests. The angles derived from the acceleration and angular rate data were compared to those of the reference inclinometer. Angle estimates were shown to match the reference angles with negligible error. The method was then implemented into the real-time Riser Fatigue Monitoring System (RFMS) aboard the Chikyu drillship. The algorithm was run using data from an emergency disconnect event that occurred in November, 2012. Quasi-static riser inclination angles were quite large due to high currents near the sea surface. Dynamic riser inclination angles proved to be significant due to Vortex Induced Vibration of the lower portion of the riser that immediately followed the disconnect event. It is important to note that the method uses data that is typically already included in real-time riser monitoring systems. Therefore only a software update is required to provide real-time riser angle information. If the method is built into data processing routines for real-time riser monitoring systems, the need for additional instrumentation, such as inclinometers near flex joints, may be circumvented. On the other hand, if inclinometers already exist, the method serves as an independent source of riser angle information at several locations on the riser. The method can also be used to calculate riser and Blow out Preventer (BOP) stack angles from data recorded using stand-alone, battery-powered loggers.
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Kim, Jin Weon, Myung Rak Choi, Sang Bong Lee et Yun Jae Kim. « J-R Fracture Toughness of Nuclear Piping Materials Under Excessive Seismic Loading Condition ». Dans ASME 2016 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/pvp2016-63456.
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This study investigated the loading rate effect on the fracture resistance under cyclic loading conditions to clearly understand the fracture behavior of piping materials under excessive seismic conditions. J-R fracture toughness tests were conducted under monotonic and cyclic loading conditions at various displacement rates at room temperature (RT) and the operating temperature of nuclear power plants (NPPs), i.e., 316°C. SA508 Gr. 1a lo w-alloy steel (LAS) and SA312 TP316 stainless steel (SS) piping materials were used for the tests. The fracture resistance under a reversible cyclic load was considerably lower than that under monotonic load regardless of test temperature, material, and loading rate. Under both cyclic and monotonic loading conditions, the fracture behavior of SA312 TP316 SS was independent of the loading rate at both RT and 316°C. For SA508 Gr. 1a LAS, the loading rate effect on the fracture behavior was appreciable at 316°C under both cyclic and monotonic loading conditions. However, the loading rate effect diminished when the cyclic load ratio (R) was −1. Thus, it was recognized that the fracture behavior of piping materials, including seismic loading characteristics, can be evaluated when tested under a cyclic load of R = −1 at a quasi-static loading rate.
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Díaz, Diana, Diana Díaz, Nancy Villegas et Nancy Villegas. « CANONICAL CORRELATION AMONG LARGE SCALE OSCILLATIONS, TEMPERATURE AND PRECIPITATION IN COASTAL REGIONS OF COLOMBIA ». Dans Managing risks to coastal regions and communities in a changing world. Academus Publishing, 2017. http://dx.doi.org/10.31519/conferencearticle_5b1b93a05a4f25.66586448.
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This study examines relationships between available surface meteorology variables and climatic oscillations by using canonical correlation analysis (CCA). Canonical loadings and cross loadings from CCA are evaluated for meteorological stations located over coastal regions of Colombia. The tests, used for these studies, consider the temperature, the precipitation data, three of the main oscillations – the Ocean Niño Index (ONI), North Atlantic Oscillation (NAO), and the Quasi-biennial oscillation (QBO). The results show the power of the statistical method used to identify associations on the data set with an acceptable level of confidence using multivariate approach. The analysis reveals relations mostly between the variables and the ENSO for all cases and a discrete connection with the NAO and QBO. To add climate indices to the group of independent variables increased the variance rates between 5 and 7%.
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Díaz, Diana, Diana Díaz, Nancy Villegas et Nancy Villegas. « CANONICAL CORRELATION AMONG LARGE SCALE OSCILLATIONS, TEMPERATURE AND PRECIPITATION IN COASTAL REGIONS OF COLOMBIA ». Dans Managing risks to coastal regions and communities in a changing world. Academus Publishing, 2017. http://dx.doi.org/10.21610/conferencearticle_58b4316f0ce3f.
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This study examines relationships between available surface meteorology variables and climatic oscillations by using canonical correlation analysis (CCA). Canonical loadings and cross loadings from CCA are evaluated for meteorological stations located over coastal regions of Colombia. The tests, used for these studies, consider the temperature, the precipitation data, three of the main oscillations – the Ocean Niño Index (ONI), North Atlantic Oscillation (NAO), and the Quasi-biennial oscillation (QBO). The results show the power of the statistical method used to identify associations on the data set with an acceptable level of confidence using multivariate approach. The analysis reveals relations mostly between the variables and the ENSO for all cases and a discrete connection with the NAO and QBO. To add climate indices to the group of independent variables increased the variance rates between 5 and 7%.
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Su, X. M., et C. T. Sun. « A Plane Strain Core Model for Crack Growth in Ductile Materials ». Dans ASME 1996 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/imece1996-0631.
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Abstract It is shown in the present paper that neither plane stress nor plane strain model can accurately simulate ductile fracture tests on ungrooved specimens. Three dimensional effects on the stress distribution at the crack tip must be considered. A moving plane strain core model is thus used in the simulation. For the moving plane strain core model, the deformation in a small region surrounding the crack tip is assumed to be in a state of plane strain and that of the rest of the specimen is in plane stress. With the plane strain core model, it is found that stresses at the crack tip remain constant during steady quasi-static crack growth for ungrooved specimens. For the specimens simulated, the stress at a critical distance from crack tip is independent of specimen size.
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Morscheck, Luke A., et John J. Roller. « Stress Testing of a New North American Passenger Locomotive Truck Frame in Accordance With International Union of Railways (UIC) Code ». Dans 2013 Joint Rail Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/jrc2013-2426.
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MotivePower Incorporated (MPI) a Wabtec company and CTLGroup have completed stress testing of a new two-axle passenger locomotive truck (bogie) frame for use in North America. Testing was performed in accordance with International Union of Railways (UIC) Code 615-4 – Bogie Frame Structural Strength Tests [1]. Static testing was performed to simulate exceptional, main in-service and particular in-service loads. A three-phase dynamic fatigue test of 10 million cycles was also performed. Factors for quasi-static, dynamic and track twist (warp) loads were increased from those recommended by the UIC Code for normal operating conditions on European railways to represent North American track conditions. Significant engineering thought was invested in fixture design, with each load application and reaction point receiving careful consideration. Static testing required ten different servo-controlled loading systems to simulate independent or superimposed vertical, lateral and/or longitudinal forces. The applied loads represented tractive effort, braking effort, curving, vehicle lateral dynamics, vehicle vertical dynamics and track twist. Fatigue testing required four different servo-controlled loading systems utilizing synchronized force functions to simulate alternating quasi-static and dynamic load sequences. The apparatus also included provisions for measuring vertical reactions at each primary spring pocket. Vertical reaction loads were measured by instrumented pedestals using a full Wheatstone bridge configuration to cancel out longitudinal and lateral load effects. Prior to testing, the prototype truck frame was instrumented with 133 strain gages installed at selected points of interest. Stress values discerned from the measured strains conformed to the allowable stress criteria and compared well with those predicted by finite element analysis. Measured force reactions also showed strong correlation with predicted values. No indications of cracks were discovered during periodic non-destructive inspections. In conclusion, the UIC Code 615-4 test protocol was utilized to successfully demonstrate the strength and durability of a new two-axle passenger locomotive truck frame.
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Zhu, Juner, Yong Xia, Gongyao Gu et Qing Zhou. « Extension of Non-Associated Hill48 Model for Characterizing Dynamic Mechanical Behavior of a Typical High-Strength Steel Sheet ». Dans ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36985.
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Sheet metals usually exhibit a certain degree of plastic anisotropy because of the rolling effect. To characterize the anisotropic behavior in simulations related to large deformation, strain-rate independent phenomenological models are frequently used in quasi-static conditions. Two functions are generally included in such a model, i.e. the yield function and the plastic potential. The former limits the stress state within the yield surface while the latter determines the direction of the plastic strain increment. Traditional plasticity models mostly assume associated flow rule, in which the two functions mentioned above are identical. With the enhanced demand of accuracy, the forms of the associated models become too complex with more and more parameters to achieve an easy calibration procedure. Alternatively, in the past decade the non-associated models were increasingly used for sheet metals. Separate functions for the two aspects of plasticity lead to efficient characterization and convenient calibration. In numerical study of dynamic loading cases, how to characterize strain-rate dependence of plasticity is an important issue. Some visco-plastic models were developed to take the rate effect into account, e.g. Johnson-Cook and Cowper-Symonds models, where the isotropic J2 flow theory was commonly used. However, when the material is severely anisotropic, this approach is very likely to be insufficient, and a model including both anisotropy and rate dependence would be needed. Extending a non-associated anisotropic model to be rate-dependent is a promising approach which has not been published in open literature to the best knowledge of the authors. Objective of the present study is to develop an applicable model for characterizing dynamic mechanical behavior of a typical high-strength steel sheet. Two steps are performed. The material is investigated under quasi-static loading firstly. Tensile test results show an obvious anisotropy which cannot be described by traditional associated models. So the non-associated Hill48 model is chosen and calibrated. Accuracy of the model is verified by a quasi-static punching test. Thereafter the dynamic material properties are obtained by conducting tensile tests at quite a few strain-rate levels covering 0.0004–1200s−1. To characterize the positive strain-rate effect in strength, the non-associated Hill48 model is extended to be visco-plastic after checking two rate-dependence formulations in existing isotropic models. With implementing the extended model into a user subroutine of ABAQUS/explicit, simulations of the dynamic tension tests are run and compared to the real experiments. A good agreement between the simulated and the experimental result is achieved using the VUMAT.
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Li, Mingzhe, et Weiyi Lu. « Experimental Investigation on Liquid Infiltration Speed in Liquid Nanofoam ». Dans ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-66252.
Texte intégralRésumé :
Liquid nanofoam (LN) as a novel material for energy absorption applications exhibits superior properties, including high energy absorption efficiency, ultra-fast energy dissipation, light weight and small size, over existing options. It is a liquid suspension of nanoporous particles, whose nanopore surface is non-wettable to the liquid molecules. Past studies on LN have focused on quasi-static responses, and the actual system performance under dynamic loadings has remained unclear. In this study, the mechanical behavior of two types of LN samples at various strain rates and the liquid flow speed in the nanopores have been experimentally investigated. The quasi-static behavior of LN is rigorously characterized by an Instron 5982 universal tester, from which we find that large amount of energy is dissipated into heat due to the effective excess solid-liquid interfacial tension, and confirm that the energy absorption efficiency of the LN is determined by the liquid infiltration pressure and the total deformability. The dynamic behavior of the LN is investigated by impacting it with a lab-customized drop tower apparatus at intermediate strain rates (around 102 s−1), from which the measured strain-stress curves are highly hysteretic. By comparing with the quasi-static sorption isotherm curve, we show that the liquid infiltration pressure as well as the total deformability of the LN sample in liquid marble form is not affected by the increased strain rate. This suggests that the dynamic behavior of LN can be characterized by quasi-static compressive tests. In the dynamic tests, the ultra-fast energy dissipation rate of LN indicates that the real liquid flow speed in nanopores is much higher than that predicted by the continuum theory. The flow speed can be directly measured from the strain rate by considering the total surface area of the nanoporous particles exposed to the liquid phase. The flow speed is related to the external remote pressure and the 3D porous structure of nanoporous particles. We have examined for the first time the dynamic behaviors of LN, and demonstrated the energy absorption capacity of LN can be activated at desired pressure range by virtue of the strain rate-independent liquid infiltration behavior. This is the first experimental approach to characterize the liquid flow speed in nano-environment. These findings provide strong evidence supporting the potential application of LNs to mitigate energy in blunt impact scenarios such as head to head and head to shoulder collisions in sports, traffic accidents and ballistic impact.