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1
Kwon, O., und F. E. Ames. „A Velocity and Length Scale Approach to k–ε Modeling“. Journal of Heat Transfer 118, Nr. 4 (01.11.1996): 857–63. http://dx.doi.org/10.1115/1.2822581.
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This paper describes a velocity and length scale approach to low-Reynolds-number k–ε modeling, which formulates the eddy viscosity on the normal component of turbulence and a length scale. The normal component of turbulence is modeled based on the dissipation and distance from the wall and is bounded by the isotropic condition. The model accounts for the anisotropy of the dissipation and the reduced length of mixing in the near wall region. The kinetic energy and dissipation rate were computed from the k and ε transport equations of Durbin (1993). The model was tested for a wide range of turbulent flows and proved to be superior to other k–ε based models.
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Liu, Yujiong, und Pinhas Ben-Tzvi. „Dynamic Modeling, Analysis, and Design Synthesis of a Reduced Complexity Quadruped with a Serpentine Robotic Tail“. Integrative and Comparative Biology 61, Nr. 2 (17.05.2021): 464–77. http://dx.doi.org/10.1093/icb/icab083.
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Synopsis Serpentine tail structures are widely observed in the animal kingdom and are thought to help animals to handle various motion tasks. Developing serpentine robotic tails and using them on legged robots has been an attractive idea for robotics. This article presents the theoretical analysis for such a robotic system that consists of a reduced complexity quadruped and a serpentine robotic tail. Dynamic model and motion controller are formulated first. Simulations are then conducted to analyze the tail’s performance on the airborne righting and maneuvering tasks of the quadruped. Using the established simulation environment, systematic analyses on critical design parameters, namely, the tail mounting point, tail length, torso center of mass (COM) location, tail–torso mass ratio, and the power consumption distribution, are performed. The results show that the tail length and the mass ratio influence the maneuvering angle the most while the COM location affects the landing stability the most. Based on these design guidelines, for the current robot design, the optimal tail parameters are determined as a length of two times as long as the torso length and a weight of 0.09 times as heavy as the torso weight.
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Chowdhury, Md Arman, Ahmad Rahmzadeh, Saber Moradi und M. Shahria Alam. „Feasibility of using reduced length superelastic shape memory alloy strands in post-tensioned steel beam–column connections“. Journal of Intelligent Material Systems and Structures 30, Nr. 2 (12.11.2018): 283–307. http://dx.doi.org/10.1177/1045389x18806393.
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Driven by a need to reduce repair costs and downtime in structures following a major earthquake, self-centering systems have been introduced. Post-tensioned high strength steel strands have shown promising results in providing self-centering capability in steel frames, where the beams are compressed to columns. This study aims at investigating the feasibility of using reduced length of steel and shape memory alloy strands in steel beam–column connections. Through finite element modeling, the study first evaluates the effect of using short-length regular post-tensioned strands in steel connections. The results show higher strength, stiffness, and energy dissipation capacity for connections with shorter length regular post-tensioned strands. The moment capacity and energy absorption capacity of a post-tensioned beam–column connection with one-third strand length were 105% and 114% higher than those of with full-length strands, respectively. However, residual drifts increased from 4 to 39 mm. To avoid loss in the re-centering capability of such connections due to yielding/failing of post-tensioned steel strands, the application of shape memory alloy and hybrid strands are proposed. The results show that shorter length shape memory alloy strands are effective in regaining self-centering and dissipating higher amount of energy compared to the full-length steel strands.
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Xu, Shi Xian, Yu Zhang, Meng Lan Duan und Bing Dai. „Three-Dimensional Modeling of Single-Lap Joints with Variable Interfacial Crack Length “. Key Engineering Materials 665 (September 2015): 161–64. http://dx.doi.org/10.4028/www.scientific.net/kem.665.161.
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This paper investigated the performance of single-lap joints with interfacial crack through the finite element method. The finite element method was validated by the G-R solutions at first. And then the influence of geometric parameter of the joint as well as the length of the interfacial crack were discussed. Results showed that the presence of a spew fillet can reduced the stress intensity factors (SIF).The relationship of the crack length ratio and SIF, adhesive thickness ratio and SIF were built.
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Yilmaz, Ibrahim, Ece Ayli und Selin Aradag. „Investigation of the Effects of Length to Depth Ratio on Open Supersonic Cavities Using CFD and Proper Orthogonal Decomposition“. Scientific World Journal 2013 (2013): 1–12. http://dx.doi.org/10.1155/2013/810175.
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Simulations of supersonic turbulent flow over an open rectangular cavity are performed to observe the effects of length to depth ratio (L/D) of the cavity on the flow structure. Two-dimensional compressible time-dependent Reynolds-averaged Navier-Stokes equations with k-ωturbulence model are solved. A reduced order modeling approach, Proper Orthogonal Decomposition (POD) method, is used to further analyze the flow. Results are obtained for cavities with severalL/Dratios at a Mach number of 1.5. Mostly, sound pressure levels (SPL) are used for comparison. After a reduced order modeling approach, the number of modes necessary to represent the systems is observed for each case. The necessary minimum number of modes to define the system increases as the flow becomes more complex with the increase in theL/Dratio. This study provides a basis for the control of flow over supersonic open cavities by providing a reduced order model for flow control, and it also gives an insight to cavity flow physics by comparing several simulation results with different length to depth ratios.
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Anderson, L. S., und R. S. Anderson. „Modeling debris-covered glaciers: extension due to steady debris input“. Cryosphere Discussions 9, Nr. 6 (23.11.2015): 6423–70. http://dx.doi.org/10.5194/tcd-9-6423-2015.
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Abstract. Debris-covered glaciers are common in rapidly-eroding alpine landscapes. When thicker than a few centimeters, surface debris suppresses melt rates. If continuous debris cover is present, mass balance gradients can be reduced leading to increases in glacier length. In order to quantify feedbacks in the debris-glacier-climate system, we developed a 2-D long-valley numerical glacier model that includes englacial and supraglacial advection. We ran 120 simulations in which a steady state debris-free glacier responds to a step increase of surface debris deposition. Simulated glaciers advance to steady states in which ice accumulation equals ice ablation, and debris input equals debris loss from the glacier. Our model and parameter selections produce two-fold increases in glacier length. Debris flux onto the glacier and the relationship between debris thickness and melt rate strongly control glacier length. Debris deposited near the equilibrium-line altitude, where ice discharge is high, results in the greatest glacier extension when other debris related variables are held constant. Continuous debris cover reduces ice discharge gradients, ice thickness gradients, and velocity gradients relative to initial debris-free glaciers. Debris-forced glacier extension decreases the ratio of accumulation zone to total glacier area (AAR). The model reproduces first-order relationships between debris cover, AARs, and glacier surface velocities from glaciers in High Asia. We provide a quantitative, theoretical foundation to interpret the effect of debris cover on the moraine record, and to assess the effects of climate change on debris-covered glaciers.
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Anderson, Leif S., und Robert S. Anderson. „Modeling debris-covered glaciers: response to steady debris deposition“. Cryosphere 10, Nr. 3 (26.05.2016): 1105–24. http://dx.doi.org/10.5194/tc-10-1105-2016.
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Abstract. Debris-covered glaciers are common in rapidly eroding alpine landscapes. When thicker than a few centimeters, surface debris suppresses melt rates. If continuous debris cover is present, ablation rates can be significantly reduced leading to increases in glacier length. In order to quantify feedbacks in the debris–glacier–climate system, we developed a 2-D long-valley numerical glacier model that includes englacial and supraglacial debris advection. We ran 120 simulations on a linear bed profile in which a hypothetical steady state debris-free glacier responds to a step increase of surface debris deposition. Simulated glaciers advance to steady states in which ice accumulation equals ice ablation, and debris input equals debris loss from the glacier terminus. Our model and parameter selections can produce 2-fold increases in glacier length. Debris flux onto the glacier and the relationship between debris thickness and melt rate strongly control glacier length. Debris deposited near the equilibrium-line altitude, where ice discharge is high, results in the greatest glacier extension when other debris-related variables are held constant. Debris deposited near the equilibrium-line altitude re-emerges high in the ablation zone and therefore impacts melt rate over a greater fraction of the glacier surface. Continuous debris cover reduces ice discharge gradients, ice thickness gradients, and velocity gradients relative to initial debris-free glaciers. Debris-forced glacier extension decreases the ratio of accumulation zone to total glacier area (AAR). Our simulations reproduce the "general trends" between debris cover, AARs, and glacier surface velocity patterns from modern debris-covered glaciers. We provide a quantitative, theoretical foundation to interpret the effect of debris cover on the moraine record, and to assess the effects of climate change on debris-covered glaciers.
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Mehr, E. H., und H. R. Saba. „Ductility Evaluation of Steel Structures with Reduced Beam Sections and Post-Tensioned Cables Using the Finite Element Method“. Engineering, Technology & Applied Science Research 7, Nr. 6 (18.12.2017): 2236–39. http://dx.doi.org/10.48084/etasr.1568.
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Given the importance of structure strengthening, this research introduces a particular type of steel structure in which the reduced beam section and post-tensioned cables were used for creating centralized property and preventing the formation of plastic hinges in the beam and columns. After introducing the system, ABAQUS modeling results are compared with a reliable laboratory sample to check its accuracy. Good convergence was seen which shows the modeling accuracy. The results of the model’s nonlinear static analysis revealed that the above steel structure has higher ductility when compared to conventional steel structures. Also, the results showed that with the rising of height, span length and early post-tensioned power of the cables we can increase the ductility of the structure.
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Cheng, Fang-Yi, Chin-Fang Lin, Yu-Tzu Wang, Jeng-Lin Tsai, Ben-Jei Tsuang und Ching-Ho Lin. „Impact of Effective Roughness Length on Mesoscale Meteorological Simulations over Heterogeneous Land Surfaces in Taiwan“. Atmosphere 10, Nr. 12 (12.12.2019): 805. http://dx.doi.org/10.3390/atmos10120805.
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The Weather Research and Forecasting (WRF) modeling system obtains the aerodynamic roughness length (z0) from a land use (LU) lookup table. The effective aerodynamic roughness length (z0eff) was estimated for the island of Taiwan by considering the individual roughness lengths (z0i) of the underlying LU types within a modeling grid box. Two z0eff datasets were prepared: one using the z0i from the default LU lookup table and the other using the observed z0i for three LU types (urban, dry cropland and pasture, and irrigated cropland and pasture). The spatial variability of the z0eff distribution was higher than that of the LU table-based z0 distribution. Three WRF sensitivity experiments were performed: (1) dominant LU table-based z0 (namely, S1), (2) z0eff estimated from the default z0i (namely, S2), and (3) z0eff estimated from the observed z0i (namely, S3). Comparisons of the thermal field, temperature, and surface sensible and latent heat fluxes revealed no significant differences among the three simulations. The wind field overestimation and surface momentum flux underestimation in S1 were reduced in S2 and S3, and these improvements were more prominent over areas with highly heterogeneous land surface conditions.
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Zhou, Beibei, Xiaopeng Chen, Lijun Su, Hujun Li, Quanjiu Wang und Wanghai Tao. „Evaluation and modeling of factors influencing the depth of mixing layer in which soil solute releasing from soil to surface runoff“. Canadian Journal of Soil Science 101, Nr. 3 (01.09.2021): 415–29. http://dx.doi.org/10.1139/cjss-2020-0141.
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The depth of mixing layer is one of the important parameters which cannot be assigned a constant value affected by many factors in the slope runoff. The objective of this study was to investigate the effect of slope length and underground biomass on slope runoff, solute transport processes, as well as mixing layer depth. In this study, the experimental plots with the four slope lengths (5, 10, 15, and 20 m) and a width of 2 m were built on the slope with the gradient of 20°. In addition, the plots with the millet or wheat planting were built on the slope. The change of runoff and solute transport was analyzed through simulated rainfall experiments and then to estimate mixing layer depth. The results showed that the runoff rate decreased and more runoff seeped into the slope soil with increasing slope length. Increasing underground biomass also promoted greater rainfall infiltration into the soil. The increase in slope length increased the concentration of solute in runoff, but more underground biomass reduced the nutrients transported with runoff. The effective mixing depth increased with an increase in slope length, but effective mixing depth decreased with increased underground biomass. The modified expression of the equivalent mixing model under different slope lengths and underground biomass could accurately describe the solute transfer process in runoff when compared with complete mixing model and incomplete mixing model based on exponential functions. This research provided a reference for improving the application of mixing layer models in the slope management.
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Karami Moghadam, Mehdi, Ata Amini, Marlinda Abdul Malek, Thamer Mohammad und Hasan Hoseini. „Physical Modeling of Ski-Jump Spillway to Evaluate Dynamic Pressure“. Water 11, Nr. 8 (15.08.2019): 1687. http://dx.doi.org/10.3390/w11081687.
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The effects of changes in the angle of pool impact plate, plunging depth, and discharge upon the dynamic pressure caused by ski-jump buckets were investigated in the laboratory. Four impact plate angles and four plunging depths were used. Discharges of 67, 86, 161, and 184 L/s were chosen. For any discharge, plunging depth and impact plate angle were regulated, and dynamic pressures were measured by a transducer. The results showed that with the increase in the ratio of drop length of the jet to its break-up length (H/Lb), and with an increase in the impact plate angle, the mean dynamic pressure coefficient decreased. An inspection of the plunging depth (Y) ratio to the initial thickness of the jet (Bj) revealed that when Y/Bj > 3, the plunging depth of the downstream pool reduced dynamic pressure. At the angle of 60°, the dynamic pressure coefficient due to increasing in plunging depth varied from 34% to 95%.
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Bina, Rasoul, und Mahdi Mojahedi. „Static Deflection, Pull-in Instability and Oscillatory Behavior of the Electrostatically Actuated Microresonator with a Distributed Proof Mass Considering Non-Classical Theory“. International Journal of Applied Mechanics 09, Nr. 02 (März 2017): 1750023. http://dx.doi.org/10.1142/s1758825117500235.
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In this paper, the static and vibration responses of a microresonator by considering distributed proof mass are investigated based on the modified couple stress theory (MCST). The microresonator has a proof mass placed on the end of micro-cantilever beam and the proof mass actuated by electrostatic actuation. Due to the large length of proof mass compared to beam length, the proof mass is considered as a lengthy mass in the modeling. Hence, the resultant force and moment acting on the proof mass can be calculated by integrating the density of the electrostatic force along the mass length. Considering the length effects of the proof mass, MCST and electrostatic actuation, the equation of dynamic motion is derived using the extended Hamilton principle. Using a model approximation, i.e., Galerkin decomposition method, the governing equations of static and oscillatory motions are reduced and the resultant equation is solved by analytical (multiple scale method) and numerical methods. The result shows that the developed model, that includes distributed proof mass and size dependency effects, improves the results of pull-in instability voltage, natural frequency and amplitude of vibration.
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Jankoski, Radoslav, Ulrich Römer und Sebastian Schöps. „Modeling of spatial uncertainties in the magnetic reluctivity“. COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 36, Nr. 4 (03.07.2017): 1151–67. http://dx.doi.org/10.1108/compel-10-2016-0438.
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Purpose The purpose of this paper is to present a computationally efficient approach for the stochastic modeling of an inhomogeneous reluctivity of magnetic materials. These materials can be part of electrical machines such as a single-phase transformer (a benchmark example that is considered in this paper). The approach is based on the Karhunen–Loève expansion (KLE). The stochastic model is further used to study the statistics of the self-inductance of the primary coil as a quantity of interest (QoI). Design/methodology/approach The computation of the KLE requires solving a generalized eigenvalue problem with dense matrices. The eigenvalues and the eigenfunction are computed by using the Lanczos method that needs only matrix vector multiplications. The complexity of performing matrix vector multiplications with dense matrices is reduced by using hierarchical matrices. Findings The suggested approach is used to study the impact of the spatial variability in the magnetic reluctivity on the QoI. The statistics of this parameter are influenced by the correlation lengths of the random reluctivity. Both, the mean value and the standard deviation increase as the correlation length of the random reluctivity increases. Originality/value The KLE, computed by using hierarchical matrices, is used for uncertainty quantification of low frequency electrical machines as a computationally efficient approach in terms of memory requirement, as well as computation time.
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Bustillo, Andres, Luis N. López de Lacalle, Asier Fernández-Valdivielso und Pedro Santos. „Data-mining modeling for the prediction of wear on forming-taps in the threading of steel components“. Journal of Computational Design and Engineering 3, Nr. 4 (30.06.2016): 337–48. http://dx.doi.org/10.1016/j.jcde.2016.06.002.
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Abstract An experimental approach is presented for the measurement of wear that is common in the threading of cold-forged steel. In this work, the first objective is to measure wear on various types of roll taps manufactured to tapping holes in microalloyed HR45 steel. Different geometries and levels of wear are tested and measured. Taking their geometry as the critical factor, the types of forming tap with the least wear and the best performance are identified. Abrasive wear was observed on the forming lobes. A higher number of lobes in the chamber zone and around the nominal diameter meant a more uniform load distribution and a more gradual forming process. A second objective is to identify the most accurate data-mining technique for the prediction of form-tap wear. Different data-mining techniques are tested to select the most accurate one: from standard versions such as Multilayer Perceptrons, Support Vector Machines and Regression Trees to the most recent ones such as Rotation Forest ensembles and Iterated Bagging ensembles. The best results were obtained with ensembles of Rotation Forest with unpruned Regression Trees as base regressors that reduced the RMS error of the best-tested baseline technique for the lower length output by 33%, and Additive Regression with unpruned M5P as base regressors that reduced the RMS errors of the linear fit for the upper and total lengths by 25% and 39%, respectively. However, the lower length was statistically more difficult to model in Additive Regression than in Rotation Forest. Rotation Forest with unpruned Regression Trees as base regressors therefore appeared to be the most suitable regressor for the modeling of this industrial problem. Highlights Analysis of the shape and geometry of the best roll taps for cold forged Steel, concluding useful features. Study of influence of metal forming in the close area to thread made by roll tapping. Careful study of worn areas on forming edges. A new study about a not very well-known threading process. A data mining approach for the best modelling of experimental results.
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PROVATAS, NIKOLAS, MICHAEL GREENWOOD, BADRINARAYAN ATHREYA, NIGEL GOLDENFELD und JONATHAN DANTZIG. „MULTISCALE MODELING OF SOLIDIFICATION: PHASE-FIELD METHODS TO ADAPTIVE MESH REFINEMENT“. International Journal of Modern Physics B 19, Nr. 31 (20.12.2005): 4525–65. http://dx.doi.org/10.1142/s0217979205032917.
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We review the use of phase field methods in solidification modeling, describing their fundamental connection to the physics of phase transformations. The inherent challenges associated with simulating phase field models across multiple length and time scales are discussed, as well as how these challenges have been addressed in recent years. Specifically, we discuss new asymptotic analysis methods that enable phase field equations to emulate the sharp interface limit even in the case of quite diffuse phase-field interfaces, an aspect that greatly reduces computation times. We then review recent dynamic adaptive mesh refinement algorithms that have enabled a dramatic increase in the scale of microstructures that can be simulated using phase-field models, at significantly reduced simulation times. Combined with new methods of asymptotic analysis, the adaptive mesh approach provides a truly multi-scale capability for simulating solidification microstructures from nanometers up to centimeters. Finally, we present recent results on 2D and 3D dendritic growth and dendritic spacing selection, which have been made using phase-field models solved with adaptive mesh refinement.
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Lu, Xin, und Gui Li Wang. „Influence of Fusible Interlining on Draping Modeling Ability of Fabrics“. Applied Mechanics and Materials 685 (Oktober 2014): 72–75. http://dx.doi.org/10.4028/www.scientific.net/amm.685.72.
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In the design of modern garment, fabrics have a remarkable influence on the garment styles and modeling. This paper, taking the flare skirt as an example, discusses the draping ability of six kinds of different fabric slitting under the conditions of bare chip and adhesive through the experiment. The study shows that the whole modeling of the skirt pieces after adhesion with fusible interlining, will show the changes of the reduced drapability and the reduced angular line numbers and the formed wave’s position dot will move downward. The length of wave will be shortened, the overall width will be widened and the drapability will be worse. The morphology of the bottom wing will have obvious change, that is the bottom wing will become larger and the wave depth of bottom wing become larger. The wave arrangement of the skirt pieces after adhesion takes on the asymmetry condition and the pleating effect of the bottom wing will become worse. In the pattern design of apparel, the effect of the fusible interlining on the fabrics draping modeling should be taken into consideration, which can complete accurately the transformation of style-structure-process and thus serve well with the apparels industrialized production.
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Sorrel, Miguel A., Francisco J. Abad, Julio Olea, Jimmy de la Torre und Juan Ramón Barrada. „Inferential Item-Fit Evaluation in Cognitive Diagnosis Modeling“. Applied Psychological Measurement 41, Nr. 8 (19.05.2017): 614–31. http://dx.doi.org/10.1177/0146621617707510.
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Research related to the fit evaluation at the item level involving cognitive diagnosis models (CDMs) has been scarce. According to the parsimony principle, balancing goodness of fit against model complexity is necessary. General CDMs require a larger sample size to be estimated reliably, and can lead to worse attribute classification accuracy than the appropriate reduced models when the sample size is small and the item quality is poor, which is typically the case in many empirical applications. The main purpose of this study was to systematically examine the statistical properties of four inferential item-fit statistics: [Formula: see text], the likelihood ratio (LR) test, the Wald (W) test, and the Lagrange multiplier (LM) test. To evaluate the performance of the statistics, a comprehensive set of factors, namely, sample size, correlational structure, test length, item quality, and generating model, is systematically manipulated using Monte Carlo methods. Results show that the [Formula: see text] statistic has unacceptable power. Type I error and power comparisons favor LR and W tests over the LM test. However, all the statistics are highly affected by the item quality. With a few exceptions, their performance is only acceptable when the item quality is high. In some cases, this effect can be ameliorated by an increase in sample size and test length. This implies that using the above statistics to assess item fit in practical settings when the item quality is low remains a challenge.
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Shi, Xiong, und Jun Chen. „Numerical Simulation Based on CFD for the Movement Field of the Hydraulic Poppet Valve“. Advanced Materials Research 466-467 (Februar 2012): 1266–70. http://dx.doi.org/10.4028/www.scientific.net/amr.466-467.1266.
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Based on the physical numerical modeling of the hydraulic poppet valve, the inside flow field was simulated by numerical method of the dynamic mesh technology of Fluent. The analysis results indicate that the intake rate and flux are reduced by minishing the poppet. And the eddy section’ s length of the intake and the concave corner of the valve core is gradually minished and disappeared at last.
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Khalid, N., N. I. M. Nor, W. M. W. Norhaimi, Zaliman Sauli und Vithyacharan Retnasamy. „Design and Analysis on Symmetric MEMS Inductor“. Applied Mechanics and Materials 815 (November 2015): 364–68. http://dx.doi.org/10.4028/www.scientific.net/amm.815.364.
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This paper presents the design and analysis of new proposed topology micro-electro-mechanical system (MEMS) inductor. This new symmetric MEMS inductor is designed to reduce the total length of the conductor strip and hence reduce the resistance of the metal tracks. This results significant increases in the quality (Q) factor of the inductor. In this paper, the MEMS inductor is designed using CoventorWare®, which is powerful software for MEMS computer aided design (CAD), modeling and simulation. Results indicate that new symmetric inductor topology has thehighest Q-factor and it hasbeenimproved bytwo times compared to circular inductor. The analysis revealed that area of the symmetric inductor has reduced by37.5% compared to the circular inductor. Result has proved that the reduction of length of the conductor strip has reduced the resistance of the metal tracks and results in a high Q-factor inductor.
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Jiang, Hongxiang, Changlong Du, Songyong Liu und Liping Wang. „Theoretical Modeling of Rock Breakage by Hydraulic and Mechanical Tool“. Mathematical Problems in Engineering 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/895835.
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Rock breakage by coupled mechanical and hydraulic action has been developed over the past several decades, but theoretical study on rock fragmentation by mechanical tool with water pressure assistance was still lacking. The theoretical model of rock breakage by mechanical tool was developed based on the rock fracture mechanics and the solution of Boussinesq’s problem, and it could explain the process of rock fragmentation as well as predicating the peak reacting force. The theoretical model of rock breakage by coupled mechanical and hydraulic action was developed according to the superposition principle of intensity factors at the crack tip, and the reacting force of mechanical tool assisted by hydraulic action could be reduced obviously if the crack with a critical length could be produced by mechanical or hydraulic impact. The experimental results indicated that the peak reacting force could be reduced about 15% assisted by medium water pressure, and quick reduction of reacting force after peak value decreased the specific energy consumption of rock fragmentation by mechanical tool. The crack formation by mechanical or hydraulic impact was the prerequisite to improvement of the ability of combined breakage.
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Ouakad, Hassen M., und Mohammad I. Younis. „Modeling and Simulations of Collapse Instabilities of Microbeams due to Capillary Forces“. Mathematical Problems in Engineering 2009 (2009): 1–16. http://dx.doi.org/10.1155/2009/871902.
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We present modeling and analysis for the static behavior and collapse instabilities of doubly-clamped and cantilever microbeams subjected to capillary forces. These forces can be as a result of a volume of liquid trapped underneath the microbeam during the rinsing and drying process in fabrication. The model considers the microbeam as a continuous medium, the capillary force as a nonlinear function of displacement, and accounts for the mid-plane stretching and geometric nonlinearities. The capillary force is assumed to be distributed over a specific length underneath the microbeam. The Galerkin procedure is used to derive a reduced-order model consisting of a set of nonlinear algebraic and differential equations that describe the microbeams static and dynamic behaviors. We study the collapse instability, which brings the microbeam from its unstuck configuration to touch the substrate and gets stuck in the so-called pinned configuration. We calculate the pull-in length that distinguishes the free from the pinned configurations as a function of the beam thickness and gap width for both microbeams. Comparisons are made with analytical results reported in the literature based on the Ritz method for linear and nonlinear beam models. The instability problem, which brings the microbeam from a pinned to adhered configuration is also investigated. For this case, we use a shooting technique to solve the boundary-value problem governing the deflection of the microbeams. The critical microbeam length for this second instability is also calculated.
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Zhang, Chun-Lu, und Liang Yang. „Modeling of Supercritical CO2 Flow Through Short Tube Orifices“. Journal of Fluids Engineering 127, Nr. 6 (11.07.2005): 1194–98. http://dx.doi.org/10.1115/1.2060738.
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The transcritical cycle of carbon dioxide (CO2) is a promising alternative approach to heat pumps and automobile air conditioners. As an expansion device, the short tube orifice in a transcritical CO2 system usually receives supercritical fluid at the entrance and discharges a two-phase mixture at the exit. In this work, a two-fluid model (TFM) is developed for modeling the flow characteristics of supercritical CO2 through the short tube orifice. The deviations between the TFM predictions and the measured mass flow rates are within ±20%. Meanwhile, the TFM predicts reasonable pressure, temperature, and velocity distributions along the tube length. The small values of interphase temperature difference and velocity slip indicate that the nonequilibrium characteristics of the two-phase flow of CO2 in the short tube orifice are not significant. Consequently, the homogeneous equilibrium model reduced from the TFM gives a good prediction of the mass flow rate as well.
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SEDIGHI, HAMID M., A. KOOCHI und M. ABADYAN. „MODELING THE SIZE DEPENDENT STATIC AND DYNAMIC PULL-IN INSTABILITY OF CANTILEVER NANOACTUATOR BASED ON STRAIN GRADIENT THEORY“. International Journal of Applied Mechanics 06, Nr. 05 (Oktober 2014): 1450055. http://dx.doi.org/10.1142/s1758825114500550.
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It is well-established that mechanical behavior of nanoscale systems is size dependent. In this paper, strain gradient elasticity theory is used for mathematical modeling of size dependent electromechanical instability of cantilever nanoactuator. The nanoactuator is modeled using Euler–Bernoulli beam theory and equation of motion is derived using Hamilton's principle. In order to solve the nonlinear governing equation, reduced order method (ROM) is employed. The dynamic pull-in instability of the nanoactuator is investigated through plotting the time history and phase portrait of the system. Static and dynamic pull-in voltage of nanoactuator as a function of dimensionless length scale parameters is determined. The obtained results show that when thickness of the nanoactuator is comparable with the intrinsic material length scales, size effect can substantially influence the pull-in behavior of the system.
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Li, Yuanyuan, und Dietmar Bauer. „Modeling I(2) Processes Using Vector Autoregressions Where the Lag Length Increases with the Sample Size“. Econometrics 8, Nr. 3 (17.09.2020): 38. http://dx.doi.org/10.3390/econometrics8030038.
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In this paper the theory on the estimation of vector autoregressive (VAR) models for I(2) processes is extended to the case of long VAR approximation of more general processes. Hereby the order of the autoregression is allowed to tend to infinity at a certain rate depending on the sample size. We deal with unrestricted OLS estimators (in the model formulated in levels as well as in vector error correction form) as well as with two stage estimation (2SI2) in the vector error correction model (VECM) formulation. Our main results are analogous to the I(1) case: We show that the long VAR approximation leads to consistent estimates of the long and short run dynamics. Furthermore, tests on the autoregressive coefficients follow standard asymptotics. The pseudo likelihood ratio tests on the cointegrating ranks (using the Gaussian likelihood) used in the 2SI2 algorithm show under the null hypothesis the same distributions as in the case of data generating processes following finite order VARs. The same holds true for the asymptotic distribution of the long run dynamics both in the unrestricted VECM estimation and the reduced rank regression in the 2SI2 algorithm. Building on these results we show that if the data is generated by an invertible VARMA process, the VAR approximation can be used in order to derive a consistent initial estimator for subsequent pseudo likelihood optimization in the VARMA model.
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Sun, Shanhui, Meihua Zhou, Wei Lu und Afshin Davarpanah. „Application of Symmetry Law in Numerical Modeling of Hydraulic Fracturing by Finite Element Method“. Symmetry 12, Nr. 7 (06.07.2020): 1122. http://dx.doi.org/10.3390/sym12071122.
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In this paper, influential parameters on the hydraulic fracturing processes in porous media were investigated. Besides, the simultaneous stimulation of solids, fluids and fractures geomechanical equations were numerically analyzed as a developed 3D model. To do this, the Abacus software was used as a multi-objective program to solve the physical-mechanical symmetry law governing equations, according to the finite element method. Two different layers, A (3104–2984 m) and B (4216–4326 m), are considered in the model. According to the result of this study, the maximum fracture opening length in the connection of the wall surface is 10 and 9 mm for layer B and layer A, respectively. Moreover, the internal fracture fluid pressure for layer B and layer A is 65 and 53 Mpa. It is indicated that fracture fluid pressure reduced with the increase in fracture propagation length. Consequently, the results of this study would be of benefit for petroleum industries to consider several crucial geomechanical characteristics in hydraulic fractures simultaneously as a developed numerical model for different formation layers to compare a comprehensive analysis between each layer.
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Siddaiah, Nalluri, D. V. Rama Koti Reddy, Y. Bhavani Sankar, R. Anil Kumar und Hossein Pakdast. „Modeling and Simulation of Triple Coupled Cantilever Sensor for Mass Sensing Applications“. International Journal of Electrical and Computer Engineering (IJECE) 5, Nr. 3 (01.06.2015): 403. http://dx.doi.org/10.11591/ijece.v5i3.pp403-408.
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Cantilever sensors have been the growing attention in last decades and their use as a mass detector. This work presents design, modeling and analysis of Triple coupled cantilever(TCC) sensor using MEMS simulation software Comsol Multiphysics with critical dimensions of 100μm length,20μm width and 2μm thickness. Simulations were performed based on finite element modeling techniques, where different resonant frequencies were observed for different modes of operation. It is also observed that the resonant frequency of the sensor decreases as some mass is applied on one particular cantilever. The various parameters greatly affecting the performance of TCC such as resonant frequency, dimensions, material and pressure or force applied on it.we also observed that while adding some mass on any one lateral cantilever, the resonant frequency of that respective mode reduced.
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Diamond, Joel M., Christopher A. Call und Nora Devoe. „Effects of targeted cattle grazing on fire behavior of cheatgrass-dominated rangeland in the northern Great Basin, USA“. International Journal of Wildland Fire 18, Nr. 8 (2009): 944. http://dx.doi.org/10.1071/wf08075.
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We evaluated the effectiveness of using targeted, or prescribed, cattle grazing to reduce the flame length and rate of spread of fires on cheatgrass (Bromus tectorum)-dominated rangeland in northern Nevada. Cattle removed 80–90% of B. tectorum biomass during the boot (phenological) stage in grazed plots in May 2005. Grazed and ungrazed plots were burned in October 2005 to assess fire behavior characteristics. Targeted grazing reduced B. tectorum biomass and cover, which resulted in reductions in flame length and rate of spread. When the grazing treatments were repeated on the same plots in May 2006, B. tectorum biomass and cover were reduced to the point that fires did not carry in the grazed plots in October 2006. Fuel characteristics of the 2005 burns were used to parameterize dry-climate grass models in BEHAVE Plus, and simulation modeling indicates that targeted grazing in spring (May) will reduce the potential for catastrophic fires during the peak fire season (July–August) in the northern Great Basin.
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Wang, Yanfei, Yaxin Ning und Yibo Wang. „Fractional Time Derivative Seismic Wave Equation Modeling for Natural Gas Hydrate“. Energies 13, Nr. 22 (12.11.2020): 5901. http://dx.doi.org/10.3390/en13225901.
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Simulation of the seismic wave propagation in natural gas hydrate (NGH) is of great importance. To finely portray the propagation of seismic wave in NGH, attenuation properties of the earth’s medium which causes reduced amplitude and dispersion need to be considered. The traditional viscoacoustic wave equations described by integer-order derivatives can only nearly describe the seismic attenuation. Differently, the fractional time derivative seismic wave-equation, which was rigorously derived from the Kjartansson’s constant-Q model, could be used to accurately describe the attenuation behavior in realistic media. We propose a new fractional finite-difference method, which is more accurate and faster with the short memory length. Numerical experiments are performed to show the feasibility of the proposed simulation scheme for NGH, which will be useful for next stage of seismic imaging of NGH.
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Danos, Nicole, Natalie C. Holt, Gregory S. Sawicki und Emanuel Azizi. „Modeling age-related changes in muscle-tendon dynamics during cyclical contractions in the rat gastrocnemius“. Journal of Applied Physiology 121, Nr. 4 (01.10.2016): 1004–12. http://dx.doi.org/10.1152/japplphysiol.00396.2016.
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Efficient muscle-tendon performance during cyclical tasks is dependent on both active and passive mechanical tissue properties. Here we examine whether age-related changes in the properties of muscle-tendon units (MTUs) compromise their ability to do work and utilize elastic energy storage. We empirically quantified passive and active properties of the medial gastrocnemius muscle and material properties of the Achilles tendon in young (∼6 mo) and old (∼32 mo) rats. We then used these properties in computer simulations of a Hill-type muscle model operating in series with a Hookean spring. The modeled MTU was driven through sinusoidal length changes and activated at a phase that optimized muscle-tendon tuning to assess the relative contributions of active and passive elements to the force and work in each cycle. In physiologically realistic simulations where young and old MTUs started at similar passive forces and developed similar active forces, the capacity of old MTUs to store elastic energy and produce positive work was compromised. These results suggest that the observed increase in the metabolic cost of locomotion with aging may be in part due to the recruitment of additional muscles to compensate for the reduced work at the primary MTU. Furthermore, the age-related increases in passive stiffness coupled with a reduced active force capacity in the muscle can lead to shifts in the force-length and force-velocity operating range that may significantly impact mechanical and metabolic performance. Our study emphasizes the importance of the interplay between muscle and tendon mechanical properties in shaping MTU performance during cyclical contractions.
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Song, Binjie, Jianhai Yue und Zhunqing Hu. „Modeling and simulation for low-frequency vibration energy harvesting based on piezoelectric unimorph cantilever beam“. MATEC Web of Conferences 208 (2018): 04003. http://dx.doi.org/10.1051/matecconf/201820804003.
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In order to solve the problem of sustainable energy supply for low-power electronic products used in low-frequency vibration environment, the mathematic model was established based on the theory of piezoelectricity and Euler-Bernoulli beam. Also, the effects of different parameters of PZT unimorph beams such as the length, width, and tip mass on generating capacity were studied by FEM. The results show that the energy harvester with PZT unimorph beam and tip mass is suitable for low-frequency vibration environment. Increasing the length or reducing the width of the beam can significantly lower the first-order modal frequency of energy harvester when other conditions remain the same. Within certain range, the first-order modal frequency of the beam also gradually reduced as the tip mass increasing. When the size of the PZT unimorph beam is 60x60x0.33mm, the tip mass is 8.92g and an exciting force of 0.01N is applied to it along z axis, an output of 8.1V can be obtained. Meanwhile, the PZT unimorph beam is under the first vibration mode and the resonant frequency is 16.296Hz.
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Kumar, K. Senthil, Saptarsi Ghosh, Anup Sarkar, S. Bhattacharya und Subir Kumar Sarkar. „Analytical Modeling for Short Channel SOI-MOSFET and to Study its Performance“. Applied Mechanics and Materials 110-116 (Oktober 2011): 5150–54. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.5150.
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With the emergence of mobile computing and communication, low power device design and implementation have got a significant role to play in VLSI circuit design. Conventional silicon (bulk CMOS) technology couldn‘t overcome the fundamental physical limitations belonging to sub-micro or nanometer region which leads to alternative device technology like Silicon-on-Insulator (SOI) technology. In a fully-depleted FDSOI structure the electrostatic coupling of channel with source/drain and substrate through the buried layer (BL) is reduced. This allows in turn to reduce the minimal channel length of transistors or to relax the requirements on Si film thickness. A generalized compact threshold voltage model for SOI-MOSFET is developed by solving 2-D Poisson‘s equation in the channel region and analytical expressions are also developed for the same. The performance of the device is evaluated after incorporating the short channel effects. It is observed that in SOI, presence of the oxide layer resists the short channel effects and reduces device anomalies such as substrate leakage by a great factor than bulk-MOS. The threshold voltage and current drive make SOI the ultimate candidate for low power application. Thus SOI-MOSFET technology could very well be the solution for further ultra scale integration of devices and improvised performance.
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Inoue, Tomohiro, und Takashi Miyatake. „3D simulation of near-field strong ground motion based on dynamic modeling“. Bulletin of the Seismological Society of America 88, Nr. 6 (01.12.1998): 1445–56. http://dx.doi.org/10.1785/bssa0880061445.
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Abstract We simulate the strong ground motion generated from the earthquake rupture process on a shallow strike-slip fault using a 3D finite-difference method. The faulting process is modeled using a crack model with fixed rupture velocity. The variability of peak ground velocity patterns, correlated with fault location and source parameters such as stress drop or rupture velocity, is investigated. Our findings suggest that these patterns are strongly affected by rupture directivity and the uppermost depth of the fault or that of the asperity. When a fault breaks the ground surface, the peak ground velocity and the peak ground acceleration show a narrow region of strong motion. When a fault is buried under the ground, the high peak ground velocity zone of the fault-parallel component is apart from the fault trace by a distance comparable to the fault depth. On the other hand, the fault-normal peak ground velocity is a maximum along the fault trace. The fault length (or asperity length) is not so effective for peak ground velocities. The effect of heterogeneity in stress drop and rupture velocity on strong ground motion is also investigated. When stress drop is not uniform but increases linearly with depth from zero at the uppermost depth, the peak ground velocity is reduced. These results help better predict the strong ground motion generated from a potential fault.
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Safin, Ruslan R., Ruslan R. Khasanshin, Regina V. Salimgaraeva und Elena A. Beliakova. „Heat Treatment of Crushed Wood in Rotary Drum Dryers“. Key Engineering Materials 743 (Juli 2017): 378–82. http://dx.doi.org/10.4028/www.scientific.net/kem.743.378.
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The developed mathematical description of heat treatment of the crushed wood in rotary drum dryers, and also the results of the mathematical description of the studied process is presented in the article. The results of mathematical modeling have shown that with increase in the diameter of a drum by 3 times its length can be reduced almost by 7 times due to the increase in the relative stay time of particles in flight. It provides the best interaction of particles with the heat carrier. Increase in speed of rotation of the drum twice also allows reducing its length almost by 3 times, but at the same time energy consumption increases and crushing of raw wood materials is observed. It was established that the practical speed of the heat carrier is 0.75-2.6 m/s, which limits the drum length to no more than 8-10 meters.
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ROY, KAUSHIK, SAIBAL MUKHOPADHYAY und HAMID MAHMOODI-MEIMAND. „LEAKAGE CURRENT IN DEEP-SUBMICRON CMOS CIRCUITS“. Journal of Circuits, Systems and Computers 11, Nr. 06 (Dezember 2002): 575–600. http://dx.doi.org/10.1142/s021812660200063x.
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The high leakage current in deep submicron regimes is becoming a significant contributor to the power dissipation of CMOS circuits as the threshold voltage, channel length, and gate oxide thickness are reduced. Consequently, the identification and modeling of different leakage components is very important for the estimation and reduction of leakage power, especially in the low power applications. This paper explores the various transistor intrinsic leakage mechanisms including the weak inversion, the drain-induced barrier lowering, the gate-induced drain leakage, and the gate oxide tunneling.
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Hakhamaneshi, Manouchehr, Bruce L. Kutter, Mark Moore und Casey Champion. „Validation of ASCE 41-13 Modeling Parameters and Acceptance Criteria for Rocking Shallow Foundations“. Earthquake Spectra 32, Nr. 2 (Mai 2016): 1121–40. http://dx.doi.org/10.1193/121914eqs216m.
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The standard ASCE 41-13 Seismic Evaluation and Retrofit of Existing Buildings includes new provisions for linear and non-linear modeling parameters and acceptance criteria for rocking shallow foundations. The new modeling parameters and acceptance criteria were largely based on model tests on rectangular rocking foundations with a limited range of footing length to width ratio (L/B). New model test results are presented, including a systematic variation of L/B and also non-rectangular (I-shaped) footings. This new data along with previously published results are presented to validate the trilinear modeling parameters and acceptance criteria of ASCE 41-13. This paper investigates the effects of footing shape on the residual settlement, residual uplift, rocking stiffness, and re-centering. Overall, the new data supports the provisions of ASCE 41-13; however, the acceptance limits for rocking rotation of I-shaped footings could be reduced to produce performance consistent with the acceptance limits for rectangular footings.
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Wood, Katherine A., Charlie F. Rowlands, Wasay Mohiuddin Shaikh Qureshi, Huw B. Thomas, Weronika A. Buczek, Tracy A. Briggs, Simon J. Hubbard, Kathryn E Hentges, William G. Newman und Raymond T. O’Keefe. „Disease modeling of core pre-mRNA splicing factor haploinsufficiency“. Human Molecular Genetics 28, Nr. 22 (13.07.2019): 3704–23. http://dx.doi.org/10.1093/hmg/ddz169.
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Abstract The craniofacial disorder mandibulofacial dysostosis Guion-Almeida type is caused by haploinsufficiency of the U5 snRNP gene EFTUD2/SNU114. However, it is unclear how reduced expression of this core pre-mRNA splicing factor leads to craniofacial defects. Here we use a CRISPR-Cas9 nickase strategy to generate a human EFTUD2-knockdown cell line and show that reduced expression of EFTUD2 leads to diminished proliferative ability of these cells, increased sensitivity to endoplasmic reticulum (ER) stress and the mis-expression of several genes involved in the ER stress response. RNA-Seq analysis of the EFTUD2-knockdown cell line revealed transcriptome-wide changes in gene expression, with an enrichment for genes associated with processes involved in craniofacial development. Additionally, our RNA-Seq data identified widespread mis-splicing in EFTUD2-knockdown cells. Analysis of the functional and physical characteristics of mis-spliced pre-mRNAs highlighted conserved properties, including length and splice site strengths, of retained introns and skipped exons in our disease model. We also identified enriched processes associated with the affected genes, including cell death, cell and organ morphology and embryonic development. Together, these data support a model in which EFTUD2 haploinsufficiency leads to the mis-splicing of a distinct subset of pre-mRNAs with a widespread effect on gene expression, including altering the expression of ER stress response genes and genes involved in the development of the craniofacial region. The increased burden of unfolded proteins in the ER resulting from mis-splicing would exceed the capacity of the defective ER stress response, inducing apoptosis in cranial neural crest cells that would result in craniofacial abnormalities during development.
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Zahed, Fatemeh, Amir Etemad-Shahidi und Ebrahim Jabbari. „Modeling of salinity intrusion under different hydrological conditions in the Arvand River Estuary“. Canadian Journal of Civil Engineering 35, Nr. 12 (Dezember 2008): 1476–80. http://dx.doi.org/10.1139/l08-087.
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Arvand River Estuary is the most important inland water body of Iran and its discharge has been reduced in the last decades due to construction of several dams. Hence, a two-dimensional laterally averaged time dependent hydrodynamic and water quality model called CE-QUAL-W2 was applied to this estuary to assess the impacts of river discharge reduction. The model was first implemented with three different closure schemes for parameterization of vertical transport of mass and momentum. It was found that the W2N scheme performs better than the other schemes in predicting the vertical salinity structure. The model was then used for prediction of salinity intrusion in different hydrological conditions and a simple equation was obtained for estimation of the intrusion length as a function of upstream freshwater discharge.
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Wang, Bo, Yan Huang und Yi Chao Yuan. „Modeling Spray Formed by Spring Nozzle Using Volume-of-Fluid Method“. Advanced Materials Research 354-355 (Oktober 2011): 499–503. http://dx.doi.org/10.4028/www.scientific.net/amr.354-355.499.
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Spring nozzles are widely used in deaerators. The spray issued from a spring nozzle was studied numerically with an adapted volume of fluid method combined with a continuous surface force model to capture the gas–liquid interface dynamics. The present analysis focuses on the formation of a water film and the generation of droplets near the spring nozzle outlet. The numerical simulation results show that the water film breaks up to droplets at the location 20~25cm from the nozzle exit vertically. The vortical structures are formed due to the interaction between the liquid film and the surrounding air, which leads to air recirculation and water film instability. When the inlet water velocity decreases from 5.33m/s to 4.1m/s, it results in a slightly reduced spray angle. But the vertical break up length is not obviously influenced. The water sheet disintegration is probably at the transition state between Rayleigh and first wind-induced breakup regimes.
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Ho, Y. H., und B. Lakshminarayana. „Computational Modeling of Three-Dimensional Endwall Flow Through a Turbine Rotor Cascade With Strong Secondary Flows“. Journal of Turbomachinery 118, Nr. 2 (01.04.1996): 250–61. http://dx.doi.org/10.1115/1.2836634.
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A steady, three-dimensional Navier–Stokes solver that utilizes a pressure-based technique for incompressible flows is used to simulate the three-dimensional flow field in a turbine cascade. A new feature of the numerical scheme is the implementation of a second-order plus fourth-order artificial dissipation formulation, which provides a precise control of the numerical dissipation. A low-Reynolds-number form of a two-equation turbulence model is used to account for the turbulence effects. Comparison between the numerical predictions and the experimental data indicates that the numerical model is able to capture most of the complex flow phenomena in the endwall region of a turbine cascade, except the high gradient region in the secondary vortex core. The effects of inlet turbulence intensity and turbulence length scale on secondary vortices, total pressure loss, and turbulence kinetic energy inside the passage are presented and interpreted. It is found that higher turbulence intensity energizes the vortical motions and tends to move the passage vortex away from the endwall. With a larger turbulence length scale, the secondary flow inside the passage is reduced. However, the total pressure loss increases due to higher turbulence kinetic energy production.
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Pushkarev, S., A. Plaksin, A. Sycheva und P. Harlanova. „Geometric Modeling of Stress Visualization Tools Based on the Functional-Voxel Method“. Geometry & Graphics 8, Nr. 3 (24.11.2020): 36–43. http://dx.doi.org/10.12737/2308-4898-2020-36-43.
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One of the approaches to the construction of graphic images of the stress state for the force vector applied to a point is considered in this work. Has been proposed a geometric model for a continuous medium, formed by a bunch of projection planes for each point of the examined object’s space. This permits to obtain a model for a volume vector in the form of a distributed decomposition into stress components at each point specified by a bunch of projection planes.
The building a model for a volume vector, defined as a set of specified laws of direction and length, in the context of modeling stress from an applied force vector to a selected point, is based on strength of materials’ classical laws for calculation the stress state values at an inclined section. Such approach allows use a voxel graphic structure for computer representation of the simulated stress, rather than a finite element mesh. In such a case, there is no obtained result’s error dependence on the spatial position of the mesh nodal points, which is often a problem in FEM calculations.
The resulting functional-voxel computer model of the volume stress vector is a structural unit for modeling the distributed load on areas of complex configuration. In this case, the elementary summation of such vectors allows any uneven distribution of the load relative to each point on the specified area.
The considered approach works well with geometric models initially represented analytically in the form of a function space (for example, models obtained by the R-functional modelling – RFM-method), and reduced to functional-voxel computer models.
A method for deformation modeling based on obtained stresses by means of local transformations of the function space, describing the investigated geometric object, is demonstrated.
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Ford, Jennifer Lynn, Joanne Balmer Green und Michael H. Green. „Addition of Vitamin A Intake Data during Compartmental Modeling of Retinol Kinetics in Theoretical Humans Leads to Accurate Prediction of Vitamin A Total Body Stores and Kinetic Parameters in Studies of Reasonable Duration“. Journal of Nutrition 149, Nr. 11 (12.06.2019): 2065–72. http://dx.doi.org/10.1093/jn/nxz112.
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ABSTRACT Background Mathematical modeling of theoretical data has been used to validate experimental protocols and methods in several fields. Objectives We hypothesized that adding dietary vitamin A intake data as an input during compartmental modeling of retinol kinetics would lead to accurate prediction of vitamin A total body stores (TBS) at 2 specified study lengths and would reduce study duration required to accurately define the system. Methods We generated reference values for state variables (including TBS and intake) and kinetic parameters for 12 theoretical individuals (4 each of children, younger adults, and older adults) based on modeling plasma retinol tracer data for 365 d. We compared TBS predictions using data to 28 d (children) or 56 d (adults) without and with intake included in the model to reference values for each subject. Then, by truncating data sets from 365 d, we determined the shortest study duration required to accurately define the system without and with inclusion of vitamin A intake. Results Reference values for TBS ranged from 30 to 3023 µmol. Study durations of 28 and 56 d were sufficient to accurately predict TBS for 6 of the 12 subjects without intake; adding intake resulted in accurate predictions of TBS for all individuals. When intake was not included as a modeling input, durations of 35–310 d were required to define the system; inclusion of intake data substantially reduced the time required to 10–42 d. Conclusions Inclusion of vitamin A intake as additional data input when modeling vitamin A kinetics allows investigators to accurately predict TBS and define the vitamin A system in studies of reasonable length (4 wk in children and 8 wk in adults). Because it is generally possible to obtain estimates/measures of intake, including such data increases confidence in model predictions while also making studies more feasible.
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Grieve, Catherine M., James A. Poss, Peter J. Shouse und Christy T. Carter. „Modeling Growth of Matthiola incana in Response to Saline Wastewaters Differing in Nitrogen Level“. HortScience 43, Nr. 6 (Oktober 2008): 1787–93. http://dx.doi.org/10.21273/hortsci.43.6.1787.
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The capture and reuse of nutrient-rich greenhouse effluents may be an environmentally sound option for floriculture production, which would conserve fresh water resources and reduce off-site pollution of surface and groundwaters. This study was initiated in 24 outdoor lysimeters to determine effects of salinity and varying concentrations of nitrogen on the growth, yield, and ion relations of stock [Matthiola incana (L.) R. Br.] cultivar Cheerful White. The experiment was a 4 × 4 factorial, partially replicated design with four irrigation water salinities (2, 5, 8, and 11 dS·m−1) and four nitrate concentrations (2.5, 3.6, 5.4, and 7.1 mmol·L−1; N = 35, 50, 75, and 100 ppm). Ammonium nitrogen was included in the nutrient solutions. Stem lengths were measured three times weekly. Measurements at final harvest were stem and inflorescence lengths, stem and floret diameters, number of axillary buds and florets, and shoot and root fresh weights. Time course of stem elongation was quantified as a function of thermal time with a phasic growth model. Salinity significantly delayed initiation of the exponential growth phase, shortened its duration, and reduced the rate of plant development. The overall effect was to delay time to harvest of marketable stems. Although length of the flowering stems decreased with increasing salinity, marketable stems (≈60 cm) were produced in all treatments. Mineral ion relations in the plant tissues were influenced significantly, but independently, by both salinity and nitrogen. Leaf sodium, magnesium, and chlorine concentrations increased with increasing salinity; calcium and potassium decreased. In response to increasing external nitrogen, both potassium and chlorine decreased; sodium increased, whereas calcium and magnesium were unaffected. We conclude that in closed-loop irrigation systems, the nitrogen requirements for stock are low and that growers could minimize costs and limit off-site pollution by reducing nitrogen inputs.
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Kong, Song-Charng, Yong Sun und Rolf D. Rietz. „Modeling Diesel Spray Flame Liftoff, Sooting Tendency, and NOx Emissions Using Detailed Chemistry With Phenomenological Soot Model“. Journal of Engineering for Gas Turbines and Power 129, Nr. 1 (15.12.2005): 245–51. http://dx.doi.org/10.1115/1.2181596.
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A detailed chemistry-based CFD model was developed to simulate the diesel spray combustion and emission process. A reaction mechanism of n-heptane is coupled with a reduced NOx mechanism to simulate diesel fuel oxidation and NOx formation. The soot emission process is simulated by a phenomenological soot model that uses a competing formation and oxidation rate formulation. The model is applied to predict the diesel spray lift-off length and its sooting tendency under high temperature and pressure conditions with good agreement with experiments of Sandia. Various nozzle diameters and chamber conditions were investigated. The model successfully predicts that the sooting tendency is reduced as the nozzle diameter is reduced and/or the initial chamber gas temperature is decreased, as observed by the experiments. The model is also applied to simulate diesel engine combustion under premixed charge compression ignition (PCCI) conditions. Trends of heat release rate, NOx, and soot emissions with respect to EGR levels and start-of-injection timings are also well predicted. Both experiments and models reveal that soot emissions peak when the start of injection (SOI) occurs close to TDC. The model indicates that low soot emission at early SOI is due to better oxidation while low soot emission at late SOI is due to less formation. Since NOx emissions decrease monotonically with injection retardation, a late injection scheme can be utilized for simultaneous soot and NOx reduction for the engine conditions investigated in this study.
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Ma, Yuanyuan, Bjørn Olav Hogstad, Matthias Pätzold und Pedro M. Crespo. „Statistical Modeling, Simulation, and Experimental Verification of Wideband Indoor Mobile Radio Channels“. Wireless Communications and Mobile Computing 2018 (2018): 1–13. http://dx.doi.org/10.1155/2018/8271765.
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This paper focuses on the modeling, simulation, and experimental verification of wideband single-input single-output (SISO) mobile fading channels for indoor propagation environments. The indoor reference channel model is derived from a geometrical rectangle scattering model, which consists of an infinite number of scatterers. It is assumed that the scatterers are exponentially distributed over the two-dimensional (2D) horizontal plane of a rectangular room. Analytical expressions are derived for the probability density function (PDF) of the angle of arrival (AOA), the PDF of the propagation path length, the power delay profile (PDP), and the frequency correlation function (FCF). An efficient sum-of-cisoids (SOC) channel simulator is derived from the nonrealizable reference model by employing the SOC principle. It is shown that the SOC channel simulator approximates closely the reference model with respect to the FCF. The SOC channel simulator enables the performance evaluation of wideband indoor wireless communication systems with reduced realization expenditure. Moreover, the rationality and usefulness of the derived indoor channel model is confirmed by various measurements at 2.4, 5, and 60 GHz.
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Hou, Ya Li, und Wei Ping Mao. „Analysis of Static and Dynamic Stiffness for Coupled Double-Rotor Spindle System of High Speed Grinder“. Key Engineering Materials 522 (August 2012): 278–82. http://dx.doi.org/10.4028/www.scientific.net/kem.522.278.
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This study was focused on the theoretical modeling and numerical investigation about the dynamic and static stiffness of coupled double-rotor spindle system of high speed grinder. The moment balance and the transition matrix, the state vector, field matrix of spindle system of high speed grinder were analyzed and deduced. The theoretical models about dynamic and static stiffness were established using the transfer matrix method. The numerical results showed that increased rigidity of front bearing significantly increased static and dynamic rigidity of spindle end and the rigidity of front bearing increased, dynamic rigidity increased more significantly than static rigidity. Furthermore, it can be conclued that increased overhang length reduced dynamic and static rigidity of spindle end at an increasingly slower rate and the span of bearing increased, static and dynamic rigidities of spindle end were reduced
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Aleksandrov, Samuil R., Timo T. Overboom und Elena A. Lomonova. „2D Hybrid Steady-State Magnetic Field Model for Linear Induction Motors“. Mathematical and Computational Applications 24, Nr. 3 (25.07.2019): 74. http://dx.doi.org/10.3390/mca24030074.
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This paper presents a 2D hybrid steady-state magnetic field model, capable of accurately modeling the electromagnetic behavior in a linear induction motor, including primary slotting, finite yoke length, and longitudinal end-effects by primary motion. This model integrates a complex harmonic modeling technique with a discretized magnetic equivalent circuit model. The Fourier model is applied to regions with homogeneous material properties, e.g., air regions and the track of the motor, while the magnetic equivalent circuit (MEC) approach is used for the regions containing non-homogeneous material properties, e.g., the primary of the linear induction motor (LIM). By only meshing the domains containing highly-permeable materials, the computational effort is reduced in comparison with the finite element method (FEM). The model is applied to a double-layer single-sided LIM, and the resulting thrust and normal forces show an excellent agreement with respect to finite element analysis and measurement data.
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Choi, Hwan, Tishya Anne Leong Wren und Katherine Muterspaugh Steele. „Gastrocnemius operating length with ankle foot orthoses in cerebral palsy“. Prosthetics and Orthotics International 41, Nr. 3 (09.09.2016): 274–85. http://dx.doi.org/10.1177/0309364616665731.
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Background:Many individuals with cerebral palsy wear ankle foot orthoses during daily life. Orthoses influence joint motion, but how they impact muscle remains unclear. In particular, the gastrocnemius is commonly stiff in cerebral palsy. Understanding whether orthoses stretch or shorten this muscle during daily life may inform orthosis design and rehabilitation.Objectives:This study investigated the impact of different ankle foot orthoses on gastrocnemius operating length during walking in children with cerebral palsy.Study design:Case series, within subject comparison of gastrocnemius operating length while walking barefoot and with two types of ankle foot orthoses.Methods:We performed gait analyses for 11 children with cerebral palsy. Each child was fit with two types of orthoses: a dynamic ankle foot orthosis (Cascade dynamic ankle foot orthosis) and an adjustable dynamic response ankle foot orthosis (Ultraflex ankle foot orthosis). Musculoskeletal modeling was used to quantify gastrocnemius musculotendon operating length and velocity with each orthosis.Results:Walking with ankle foot orthoses could stretch the gastrocnemius more than barefoot walking for some individuals; however, there was significant variability between participants and orthoses. At least one type of orthosis stretched the gastrocnemius during walking for 4/6 and 3/5 of the Gross Motor Functional Classification System Level I and III participants, respectively. AFOs also reduced peak gastrocnemius lengthening velocity compared to barefoot walking for some participants, with greater reductions among the Gross Motor Functional Classification System Level III participants. Changes in gastrocnemius operating length and lengthening velocity were related to changes in ankle and knee kinematics during gait.Conclusion:Ankle foot orthoses impact gastrocnemius operating length during walking and, with proper design, may assist with stretching tight muscles in daily life.Clinical relevanceDetermining whether ankle foot orthoses stretch tight muscles can inform future orthotic design and potentially provide a platform for integrating therapy into daily life. However, stretching tight muscles must be balanced with other goals of orthoses such as improving gait and preventing bone deformities.
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Fernandez-Gamiz, Unai, Macarena Gomez-Mármol und Tomas Chacón-Rebollo. „Computational Modeling of Gurney Flaps and Microtabs by POD Method“. Energies 11, Nr. 8 (11.08.2018): 2091. http://dx.doi.org/10.3390/en11082091.
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Gurney flaps (GFs) and microtabs (MTs) are two of the most frequently used passive flow control devices on wind turbines. They are small tabs situated close to the airfoil trailing edge and normal to the surface. A study to find the most favorable dimension and position to improve the aerodynamic performance of an airfoil is presented herein. Firstly, a parametric study of a GF on a S810 airfoil and an MT on a DU91(2)250 airfoil was carried out. To that end, 2D computational fluid dynamic simulations were performed at Re = 106 based on the airfoil chord length and using RANS equations. The GF and MT design parameters resulting from the computational fluid dynamics (CFD) simulations allowed the sizing of these passive flow control devices based on the airfoil’s aerodynamic performance. In both types of flow control devices, the results showed an increase in the lift-to-drag ratio for all angles of attack studied in the current work. Secondly, from the data obtained by means of CFD simulations, a regular function using the proper orthogonal decomposition (POD) was used to build a reduced order method. In both flow control cases (GFs and MTs), the recursive POD method was able to accurately and very quickly reproduce the computational results with very low computational cost.
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Razmi, A. M., R. Bakhtyar, B. Firoozabadi und D. A. Barry. „Experiments and numerical modeling of baffle configuration effects on the performance of sedimentation tanks“. Canadian Journal of Civil Engineering 40, Nr. 2 (Februar 2013): 140–50. http://dx.doi.org/10.1139/cjce-2012-0176.
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The hydraulic efficiency of sedimentation basins is reduced by short-circuiting, circulation zones and bottom particle-laden jets. Baffles are used to improve the sediment tank performance. In this study, laboratory experiments were used to examine the hydrodynamics of several baffle configurations. An accompanying numerical analysis was performed based on the 2-D Reynolds-averaged Navier–Stokes equations along with the k-ε turbulence closure model. The numerical model was supplemented with the volume-of-fluid technique, and the advection–diffusion equation to simulate the dynamics of particle-laden flow. Model predictions compared well with the experimental data. An empirical function was constructed to indicate the location and amount of sediment collected in the tank. Hydraulic performance was determined for given baffle locations and heights. The results revealed that, for the laboratory setup, a baffle half way along its length decreases its performance, while a baffle much closer to its inlet and with height 25∼30% of water depth improves efficiency.
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Watcharakitchakorn, Orrathai, und Rardchawadee Silapunt. „Design and Modeling of the Photonic Crystal Waveguide Structure for Heat-Assisted Magnetic Recording“. Advances in Materials Science and Engineering 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/8097841.
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The application of the photonic crystal (PC) waveguide (WG) as the light delivery system in the heat-assisted magnetic recording (HAMR) system is demonstrated. The structure consists of a 90° bending PC waveguide and a ridge dielectric waveguide taper coupler. Three-dimensional (3D) models of structures are built and simulated in order to determine light coupling and transmission efficiencies. Geometric parameters including the taper length (LTP), coupler inlet width (WFW), and PC waveguide width (WWG) are investigated. The initial simulation shows that the transmission efficiency of over 90% can be achieved with the coupler integrated with the straight PC waveguide. However, the overall transmission efficiency is substantially reduced to 53.8% when the coupler is attached to the 90° bending PC waveguide. Our analysis shows that the wave mode matching and light decay rate in the waveguide cavity are significant contributing factors. The transmission efficiency increases to around 60.8% after some modification of the bending region.