An accurate behavioral model for single-photon avalanche diode statistical performance simulation

NASA Astrophysics Data System (ADS)

Xu, Yue; Zhao, Tingchen; Li, Ding

2018-01-01

An accurate behavioral model is presented to simulate important statistical performance of single-photon avalanche diodes (SPADs), such as dark count and after-pulsing noise. The derived simulation model takes into account all important generation mechanisms of the two kinds of noise. For the first time, thermal agitation, trap-assisted tunneling and band-to-band tunneling mechanisms are simultaneously incorporated in the simulation model to evaluate dark count behavior of SPADs fabricated in deep sub-micron CMOS technology. Meanwhile, a complete carrier trapping and de-trapping process is considered in afterpulsing model and a simple analytical expression is derived to estimate after-pulsing probability. In particular, the key model parameters of avalanche triggering probability and electric field dependence of excess bias voltage are extracted from Geiger-mode TCAD simulation and this behavioral simulation model doesn't include any empirical parameters. The developed SPAD model is implemented in Verilog-A behavioral hardware description language and successfully operated on commercial Cadence Spectre simulator, showing good universality and compatibility. The model simulation results are in a good accordance with the test data, validating high simulation accuracy.

Polar Ozone Loss Rates: Comparison Of Match Observations With Simulations Of 3-D Chemical Transport Model And Box Model

NASA Astrophysics Data System (ADS)

Tripathi, O. P.; Godin-Beekmann, S.; Lefevre, F.; Marchand, M.; Pazmino, A.; Hauchecorne, A.

2005-12-01

Model simulations of ozone loss rates during recent arctic and Antarctic winters are compared with the observed ozone loss rates from the match technique. Arctic winters 1994/1995, 1999/2000, 2002/2003 and the Antarctic winter 2003 were considered for the analysis. We use a high resolution chemical transport model MIMOSA-CHIM and REPROBUS box model for the calculation of ozone loss rates. Trajectory model calculations show that the ozone loss rates are dependent on the initialization fields. On the one hand when chemical fields are initialized by UCAM (University of Cambridge SLIMCAT model simulated fields) the loss rates were underestimated by a factor of two whereas on the other hand when it is initialized by UL (University of Leeds) fields the model loss rates are in a very good agreement with match loss rates at lower levels. The study shows a very good agreement between MIMOSA-CHIM simulation and match observation in 1999/2000 winter at both levels, 450 and 500 K, except slight underestimation in March at 500 K. But in January we have a very good agreement. This is also true for 1994/1995 when we consider simulated ozone loss rate in view of the ECMWF wind deficiency assuming that match observations were not made on isolated trajectories. Sensitivity tests, by changing JCl2O2 value, particle number density and heating rates, performed for the arctic winter 1999/2000 shows that we need to improve our understanding of particle number density and heating rate calculation mechanism. Burkholder JCl2O2 has improved the comparison of MIMOSA-CHIM model results with observations (Tripathi et al., 2005). In the same study the comparison results were shown to improved by changing heating rates and number density through NAT particle sedimentation.

Spatially coupled low-density parity-check error correction for holographic data storage

NASA Astrophysics Data System (ADS)

Ishii, Norihiko; Katano, Yutaro; Muroi, Tetsuhiko; Kinoshita, Nobuhiro

2017-09-01

The spatially coupled low-density parity-check (SC-LDPC) was considered for holographic data storage. The superiority of SC-LDPC was studied by simulation. The simulations show that the performance of SC-LDPC depends on the lifting number, and when the lifting number is over 100, SC-LDPC shows better error correctability compared with irregular LDPC. SC-LDPC is applied to the 5:9 modulation code, which is one of the differential codes. The error-free point is near 2.8 dB and over 10-1 can be corrected in simulation. From these simulation results, this error correction code can be applied to actual holographic data storage test equipment. Results showed that 8 × 10-2 can be corrected, furthermore it works effectively and shows good error correctability.

An Empirical Development of Parallelization Guidelines for Time-Driven Simulation

DTIC Science & Technology

1989-12-01

wives, who though not Cub fans, put on a good show during our trip, to waich some games . I would also like to recognize the help of my professors at...program parallelization. in this research effort a Ballistic Missile Defense (BMD) time driven simulation program, developed by DESE Research and...continuously, or continuously with discrete changes superimposed. The distinguishing feature of these simulations is the interaction between discretely

RFI in hybrid loops - Simulation and experimental results.

NASA Technical Reports Server (NTRS)

Ziemer, R. E.; Nelson, D. R.; Raghavan, H. R.

1972-01-01

A digital simulation of an imperfect second-order hybrid phase-locked loop (HPLL) operating in radio frequency interference (RFI) is described. Its performance is characterized in terms of phase error variance and phase error probability density function (PDF). Monte-Carlo simulation is used to show that the HPLL can be superior to the conventional phase-locked loops in RFI backgrounds when minimum phase error variance is the goodness criterion. Similar experimentally obtained data are given in support of the simulation data.

Interfacing VPSC with finite element codes. Demonstration of irradiation growth simulation in a cladding tube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patra, Anirban; Tome, Carlos

This Milestone report shows good progress in interfacing VPSC with the FE codes ABAQUS and MOOSE, to perform component-level simulations of irradiation-induced deformation in Zirconium alloys. In this preliminary application, we have performed an irradiation growth simulation in the quarter geometry of a cladding tube. We have benchmarked VPSC-ABAQUS and VPSC-MOOSE predictions with VPSC-SA predictions to verify the accuracy of the VPSCFE interface. Predictions from the FE simulations are in general agreement with VPSC-SA simulations and also with experimental trends.

HERMES: Hadamard Encoding and Reconstruction of MEGA-Edited Spectroscopy

PubMed Central

Chan, Kimberly L.; Puts, Nicolaas A. J.; Schär, Michael; Barker, Peter B.; Edden, Richard A. E.

2017-01-01

Purpose To investigate a novel Hadamard-encoded spectral editing scheme and evaluate its performance in simultaneously quantifying N-acetyl aspartate (NAA) and N-acetyl aspartyl glutamate (NAAG) at 3 Tesla. Methods Editing pulses applied according to a Hadamard encoding scheme allow the simultaneous acquisition of multiple metabolites. The method, called HERMES (Hadamard Encoding and Reconstruction of MEGA-Edited Spectroscopy), was optimized to detect NAA and NAAG simultaneously using density-matrix simulations and validated in phantoms at 3T. In vivo data were acquired in the centrum semiovale of 12 normal subjects. The NAA:NAAG concentration ratio was determined by modeling in vivo data using simulated basis functions. Simulations were also performed for potentially coedited molecules with signals within the detected NAA/NAAG region. Results Simulations and phantom experiments show excellent segregation of NAA and NAAG signals into the intended spectra, with minimal crosstalk. Multiplet patterns show good agreement between simulations and phantom and in vivo data. In vivo measurements show that the relative peak intensities of the NAA and NAAG spectra are consistent with a NAA:NAAG concentration ratio of 4.22:1 in good agreement with literature. Simulations indicate some coediting of aspartate and glutathione near the detected region (editing efficiency: 4.5% and 78.2%, respectively, for the NAAG reconstruction and 5.1% and 19.5%, respectively, for the NAA reconstruction). Conclusion The simultaneous and separable detection of two otherwise overlapping metabolites using HERMES is possible at 3T. PMID:27089868

Simulating secondary waterflooding in heterogeneous rocks with variable wettability using an image-based, multiscale pore network model

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Van Hoorebeke, Luc; Cnudde, Veerle

2016-09-01

The two-phase flow properties of natural rocks depend strongly on their pore structure and wettability, both of which are often heterogeneous throughout the rock. To better understand and predict these properties, image-based models are being developed. Resulting simulations are however problematic in several important classes of rocks with broad pore-size distributions. We present a new multiscale pore network model to simulate secondary waterflooding in these rocks, which may undergo wettability alteration after primary drainage. This novel approach permits to include the effect of microporosity on the imbibition sequence without the need to describe each individual micropore. Instead, we show that fluid transport through unresolved pores can be taken into account in an upscaled fashion, by the inclusion of symbolic links between macropores, resulting in strongly decreased computational demands. Rules to describe the behavior of these links in the quasistatic invasion sequence are derived from percolation theory. The model is validated by comparison to a fully detailed network representation, which takes each separate micropore into account. Strongly and weakly water-and oil-wet simulations show good results, as do mixed-wettability scenarios with different pore-scale wettability distributions. We also show simulations on a network extracted from a micro-CT scan of Estaillades limestone, which yields good agreement with water-wet and mixed-wet experimental results.

A True Metasurface Antenna.

PubMed

El Badawe, Mohamed; Almoneef, Thamer S; Ramahi, Omar M

2016-01-13

We present a true metasurface antenna based on electrically-small resonators. The resonators are placed on a flat surface and connected to one feed point using corporate feed. Unlike conventional array antennas where the distance between adjacent antennas is half wavelength to reduce mutual coupling between adjacent antennas, here the distance between the radiating elements is electrically very small to affect good impedance matching of each resonator to its feed. A metasurface antenna measuring 1.2λ × 1.2λ and designed to operate at 3 GHz achieved a gain of 12 dBi. A prototype was fabricated and tested showing good agreement between numerical simulations and experimental results. Through numerical simulation, we show that the metasurface antenna has the ability to provide beam steering by phasing all the resonators appropriately.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, R.; Harrison, D. E. Jr.

A variable time step integration algorithm for carrying out molecular dynamics simulations of atomic collision cascades is proposed which evaluates the interaction forces only once per time step. The algorithm is tested on some model problems which have exact solutions and is compared against other common methods. These comparisons show that the method has good stability and accuracy. Applications to Ar/sup +/ bombardment of Cu and Si show good accuracy and improved speed to the original method (D. E. Harrison, W. L. Gay, and H. M. Effron, J. Math. Phys. /bold 10/, 1179 (1969)).

Model of wealth and goods dynamics in a closed market

NASA Astrophysics Data System (ADS)

Ausloos, Marcel; Peķalski, Andrzej

2007-01-01

A simple computer simulation model of a closed market on a fixed network with free flow of goods and money is introduced. The model contains only two variables: the amount of goods and money beside the size of the system. An initially flat distribution of both variables is presupposed. We show that under completely random rules, i.e. through the choice of interacting agent pairs on the network and of the exchange rules that the market stabilizes in time and shows diversification of money and goods. We also indicate that the difference between poor and rich agents increases for small markets, as well as for systems in which money is steadily deduced from the market through taxation. It is also found that the price of goods decreases when taxes are introduced, likely due to the less availability of money.

Estimation of open water evaporation using land-based meteorological data

NASA Astrophysics Data System (ADS)

Li, Fawen; Zhao, Yong

2017-10-01

Water surface evaporation is an important process in the hydrologic and energy cycles. Accurate simulation of water evaporation is important for the evaluation of water resources. In this paper, using meteorological data from the Aixinzhuang reservoir, the main factors affecting water surface evaporation were determined by the principal component analysis method. To illustrate the influence of these factors on water surface evaporation, the paper first adopted the Dalton model to simulate water surface evaporation. The results showed that the simulation precision was poor for the peak value zone. To improve the model simulation's precision, a modified Dalton model considering relative humidity was proposed. The results show that the 10-day average relative error is 17.2%, assessed as qualified; the monthly average relative error is 12.5%, assessed as qualified; and the yearly average relative error is 3.4%, assessed as excellent. To validate its applicability, the meteorological data of Kuancheng station in the Luan River basin were selected to test the modified model. The results show that the 10-day average relative error is 15.4%, assessed as qualified; the monthly average relative error is 13.3%, assessed as qualified; and the yearly average relative error is 6.0%, assessed as good. These results showed that the modified model had good applicability and versatility. The research results can provide technical support for the calculation of water surface evaporation in northern China or similar regions.

Multi-dimensional free-electron laser simulation codes : a comparison study.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biedron, S. G.; Chae, Y. C.; Dejus, R. J.

A self-amplified spontaneous emission (SASE) free-electron laser (FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL.

Multi-Dimensional Free-Electron Laser Simulation Codes: A Comparison Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nuhn, Heinz-Dieter

A self-amplified spontaneous emission (SASE) free-electron laser (FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL.

Optical and infrared properties of glancing angle-deposited nanostructured tungsten films.

PubMed

Ungaro, Craig; Shah, Ankit; Kravchenko, Ivan; Hensley, Dale K; Gray, Stephen K; Gupta, Mool C

2015-02-15

Nanotextured tungsten thin films were obtained on a stainless steel (SS) substrate using the glancing-angle-deposition (GLAD) method. It was found that the optical absorption and thermal emittance of the SS substrate can be controlled by varying the parameters used during deposition. Finite-difference time-domain (FDTD) simulations were used to predict the optical absorption and infrared (IR) reflectance spectra of the fabricated samples, and good agreement was found between simulated and measured data. FDTD simulations were also used to predict the effect of changes in the height and periodicity of the nanotextures. These simulations show that good control over the absorption can be achieved by altering the height and periodicity of the nanostructure. These nanostructures were shown to be temperature stable up to 500°C with the addition of a protective HfO2 layer. Applications for this structure are explored, including a promising application for solar thermal energy systems.

Tropospheric ozone in the western Pacific Rim: Analysis of satellite and surface-based observations along with comprehensive 3-D model simulations

NASA Technical Reports Server (NTRS)

Young, Sun-Woo; Carmichael, Gregory R.

1994-01-01

Tropospheric ozone production and transport in mid-latitude eastern Asia is studied. Data analysis of surface-based ozone measurements in Japan and satellite-based tropospheric column measurements of the entire western Pacific Rim are combined with results from three-dimensional model simulations to investigate the diurnal, seasonal and long-term variations of ozone in this region. Surface ozone measurements from Japan show distinct seasonal variation with a spring peak and summer minimum. Satellite studies of the entire tropospheric column of ozone show high concentrations in both the spring and summer seasons. Finally, preliminary model simulation studies show good agreement with observed values.

[Kinetic model and simulation of the adsorption-biofilm theory for the process of biopurifying VOC waste gases].

PubMed

Sun, Peishi; Huang, Bing; Huang, Ruohua; Yang, Ping

2002-05-01

For the process of biopurifying waste gas containing VOC in low concentration by using a biological trickling filter, the related kinetic model and simulation of the new Adsorption-Biofilm theory were investigated in this study. By using the lab test data and the industrial test data, the results of contrast and validation indicated that the model had a good applicability for describing the practical bio-purification process of VOC waste gas. In the simulation study for the affection of main factor, such as the concentration of toluene in inlet gas, the gas flow and the height of biofilm-packing, a good pertinence was showed between calculated data and test dada, the interrelation coefficients were in 0.80-0.97.

Lattice Thermal Conductivity of Ultra High Temperature Ceramics ZrB2 and HfB2 from Atomistic Simulations

NASA Technical Reports Server (NTRS)

Lawson, John W.; Murray, Daw S.; Bauschlicher, Charles W., Jr.

2011-01-01

Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB2 and HfB2 for a range of temperatures. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations which can be identified with mixed metal-Boron optical phonon modes. Agreement with available experimental data is good.

Long-range temporal correlations in the Kardar-Parisi-Zhang growth: numerical simulations

NASA Astrophysics Data System (ADS)

Song, Tianshu; Xia, Hui

2016-11-01

To analyze long-range temporal correlations in surface growth, we study numerically the (1  +  1)-dimensional Kardar-Parisi-Zhang (KPZ) equation driven by temporally correlated noise, and obtain the scaling exponents based on two different numerical methods. Our simulations show that the numerical results are in good agreement with the dynamic renormalization group (DRG) predictions, and are also consistent with the simulation results of the ballistic deposition (BD) model.

Numerical simulation of cavitating flows in shipbuilding

NASA Astrophysics Data System (ADS)

Bagaev, D.; Yegorov, S.; Lobachev, M.; Rudnichenko, A.; Taranov, A.

2018-05-01

The paper presents validation of numerical simulations of cavitating flows around different marine objects carried out at the Krylov State Research Centre (KSRC). Preliminary validation was done with reference to international test objects. The main part of the paper contains results of solving practical problems of ship propulsion design. The validation of numerical simulations by comparison with experimental data shows a good accuracy of the supercomputer technologies existing at Krylov State Research Centre for both hydrodynamic and cavitation characteristics prediction.

Simulation and experimental analysis of nanoindentation and mechanical properties of amorphous NiAl alloys.

PubMed

Wang, Chih-Hao; Fang, Te-Hua; Cheng, Po-Chien; Chiang, Chia-Chin; Chao, Kuan-Chi

2015-06-01

This paper used numerical and experimental methods to investigate the mechanical properties of amorphous NiAl alloys during the nanoindentation process. A simulation was performed using the many-body tight-binding potential method. Temperature, plastic deformation, elastic recovery, and hardness were evaluated. The experimental method was based on nanoindentation measurements, allowing a precise prediction of Young's modulus and hardness values for comparison with the simulation results. The indentation simulation results showed a significant increase of NiAl hardness and elastic recovery with increasing Ni content. Furthermore, the results showed that hardness and Young's modulus increase with increasing Ni content. The simulation results are in good agreement with the experimental results. Adhesion test of amorphous NiAl alloys at room temperature is also described in this study.

Optimization of submerged depth of surface aerators for a carrousel oxidation ditch based on large eddy simulation with Smagorinsky model.

PubMed

Wei, Wenli; Bai, Yu; Liu, Yuling

2016-01-01

This paper is concerned with the simulation and experimental study of hydraulic characteristics in a pilot Carrousel oxidation ditch for the optimization of submerged depth ratio of surface aerators. The simulation was based on the large eddy simulation with the Smagorinsky model, and the velocity was monitored in the ditches with an acoustic Doppler velocimeter method. Comparisons of the simulated velocities and experimental ones show a good agreement, which validates that the accuracy of this simulation is good. The best submerged depth ratio of 2/3 for surface aerators was obtained according to the analysis of the flow field structure, the ratio of gas and liquid in the bottom layer of a ditch, the average velocity of mixture and the flow region with a velocity easily causing sludge deposition under the four operation conditions with submerged depth ratios of 1/3, 1/2, 2/3 and 3/4 for surface aerators. The research result can provide a reference for the design of Carrousel oxidation ditches.

An Effective Construction Method of Modular Manipulator 3D Virtual Simulation Platform

NASA Astrophysics Data System (ADS)

Li, Xianhua; Lv, Lei; Sheng, Rui; Sun, Qing; Zhang, Leigang

2018-06-01

This work discusses about a fast and efficient method of constructing an open 3D manipulator virtual simulation platform which make it easier for teachers and students to learn about positive and inverse kinematics of a robot manipulator. The method was carried out using MATLAB. In which, the Robotics Toolbox, MATLAB GUI and 3D animation with the help of modelling using SolidWorks, were fully applied to produce a good visualization of the system. The advantages of using quickly build is its powerful function of the input and output and its ability to simulate a 3D manipulator realistically. In this article, a Schunk six DOF modular manipulator was constructed by the author's research group to be used as example. The implementation steps of this method was detailed described, and thereafter, a high-level open and realistic visualization manipulator 3D virtual simulation platform was achieved. With the graphs obtained from simulation, the test results show that the manipulator 3D virtual simulation platform can be constructed quickly with good usability and high maneuverability, and it can meet the needs of scientific research and teaching.

Wind Energy System Time-domain (WEST) analyzers using hybrid simulation techniques

NASA Technical Reports Server (NTRS)

Hoffman, J. A.

1979-01-01

Two stand-alone analyzers constructed for real time simulation of the complex dynamic characteristics of horizontal-axis wind energy systems are described. Mathematical models for an aeroelastic rotor, including nonlinear aerodynamic and elastic loads, are implemented with high speed digital and analog circuitry. Models for elastic supports, a power train, a control system, and a rotor gimbal system are also included. Limited correlation efforts show good comparisons between results produced by the analyzers and results produced by a large digital simulation. The digital simulation results correlate well with test data.

Real-time visual simulation of APT system based on RTW and Vega

NASA Astrophysics Data System (ADS)

Xiong, Shuai; Fu, Chengyu; Tang, Tao

2012-10-01

The Matlab/Simulink simulation model of APT (acquisition, pointing and tracking) system is analyzed and established. Then the model's C code which can be used for real-time simulation is generated by RTW (Real-Time Workshop). Practical experiments show, the simulation result of running the C code is the same as running the Simulink model directly in the Matlab environment. MultiGen-Vega is a real-time 3D scene simulation software system. With it and OpenGL, the APT scene simulation platform is developed and used to render and display the virtual scenes of the APT system. To add some necessary graphics effects to the virtual scenes real-time, GLSL (OpenGL Shading Language) shaders are used based on programmable GPU. By calling the C code, the scene simulation platform can adjust the system parameters on-line and get APT system's real-time simulation data to drive the scenes. Practical application shows that this visual simulation platform has high efficiency, low charge and good simulation effect.

Advances in snow cover distributed modelling via ensemble simulations and assimilation of satellite data

NASA Astrophysics Data System (ADS)

Revuelto, J.; Dumont, M.; Tuzet, F.; Vionnet, V.; Lafaysse, M.; Lecourt, G.; Vernay, M.; Morin, S.; Cosme, E.; Six, D.; Rabatel, A.

2017-12-01

Nowadays snowpack models show a good capability in simulating the evolution of snow in mountain areas. However singular deviations of meteorological forcing and shortcomings in the modelling of snow physical processes, when accumulated on time along a snow season, could produce large deviations from real snowpack state. The evaluation of these deviations is usually assessed with on-site observations from automatic weather stations. Nevertheless the location of these stations could strongly influence the results of these evaluations since local topography may have a marked influence on snowpack evolution. Despite the evaluation of snowpack models with automatic weather stations usually reveal good results, there exist a lack of large scale evaluations of simulations results on heterogeneous alpine terrain subjected to local topographic effects.This work firstly presents a complete evaluation of the detailed snowpack model Crocus over an extended mountain area, the Arve upper catchment (western European Alps). This catchment has a wide elevation range with a large area above 2000m a.s.l. and/or glaciated. The evaluation compares results obtained with distributed and semi-distributed simulations (the latter nowadays used on the operational forecasting). Daily observations of the snow covered area from MODIS satellite sensor, seasonal glacier surface mass balance evolution measured in more than 65 locations and the galciers annual equilibrium line altitude from Landsat/Spot/Aster satellites, have been used for model evaluation. Additionally the latest advances in producing ensemble snowpack simulations for assimilating satellite reflectance data over extended areas will be presented. These advances comprises the generation of an ensemble of downscaled high-resolution meteorological forcing from meso-scale meteorological models and the application of a particle filter scheme for assimilating satellite observations. Despite the results are prefatory, they show a good potential improving snowpack forecasting capabilities.

Methods of sound simulation and applications in flight simulators

NASA Technical Reports Server (NTRS)

Gaertner, K. P.

1980-01-01

An overview of methods for electronically synthesizing sounds is presented. A given amount of hardware and computer capacity places an upper limit on the degree and fidelity of realism of sound simulation which is attainable. Good sound realism for aircraft simulators can be especially expensive because of the complexity of flight sounds and their changing patterns through time. Nevertheless, the flight simulator developed at the Research Institute for Human Engineering, West Germany, shows that it is possible to design an inexpensive sound simulator with the required acoustic properties using analog computer elements. The characteristics of the sub-sound elements produced by this sound simulator for take-off, cruise and approach are discussed.

Simulation of energy- efficient building prototype using different insulating materials

NASA Astrophysics Data System (ADS)

Ouhaibi, Salma; Belouaggadia, Naoual; Lbibb, Rachid; Ezzine, Mohammed

2018-05-01

The objective of this work is to analyze the energetic efficiency of an individual building including an area of 130 m2 multi-zone, located in the region of FEZ which is characterized by a very hot and dry climate in summer and a quite cold one in winter, by incorporating insulating materials. This study was performed using TRNSYS V16 simulation software during a typical year of the FEZ region. Our simulation consists in developing a comparative study of two types of polystyrene and silica-aerogel insulation materials, in order to determine the best thermal performance. The results show that the thermal insulation of the building envelope is among the most effective solutions that give a significant reduction in energy requirements. Similarly, the use of silica-aerogels gives a good thermal performance, and therefore a good energy gain.

Ground-to-Flight Handling Qualities Comparisons for a High Performance Airplane

NASA Technical Reports Server (NTRS)

Brandon, Jay M.; Glaab, Louis J.; Brown, Philip W.; Phillips, Michael R.

1995-01-01

A flight test program was conducted in conjunction with a ground-based piloted simulation study to enable a comparison of handling qualities ratings for a variety of maneuvers between flight and simulation of a modern high performance airplane. Specific objectives included an evaluation of pilot-induced oscillation (PIO) tendencies and a determination of maneuver types which result in either good or poor ground-to-flight pilot handling qualities ratings. A General Dynamics F-16XL aircraft was used for the flight evaluations, and the NASA Langley Differential Maneuvering Simulator was employed for the ground based evaluations. Two NASA research pilots evaluated both the airplane and simulator characteristics using tasks developed in the simulator. Simulator and flight tests were all conducted within approximately a one month time frame. Maneuvers included numerous fine tracking evaluations at various angles of attack, load factors and speed ranges, gross acquisitions involving longitudinal and lateral maneuvering, roll angle captures, and an ILS task with a sidestep to landing. Overall results showed generally good correlation between ground and flight for PIO tendencies and general handling qualities comments. Differences in pilot technique used in simulator evaluations and effects of airplane accelerations and motions are illustrated.

Coupled attenuation and multiscale damage model for composite structures

NASA Astrophysics Data System (ADS)

Moncada, Albert M.; Chattopadhyay, Aditi; Bednarcyk, Brett; Arnold, Steven M.

2011-04-01

Composite materials are widely used in many applications for their high strength, low weight, and tailorability for specific applications. However, the development of robust and reliable methodologies to detect micro level damage in composite structures has been challenging. For composite materials, attenuation of ultrasonic waves propagating through the media can be used to determine damage within the material. Currently available numerical solutions for attenuation induce arbitrary damage, such as fiber-matrix debonding or inclusions, to show variations between healthy and damaged states. This paper addresses this issue by integrating a micromechanics analysis to simulate damage in the form of a fiber-matrix crack and an analytical model for calculating the attenuation of the waves when they pass through the damaged region. The hybrid analysis is validated by comparison with experimental stress-strain curves and piezoelectric sensing results for attenuation measurement. The results showed good agreement between the experimental stress-strain curves and the results from the micromechanics analysis. Wave propagation analysis also showed good correlation between simulation and experiment for the tested frequency range.

Face, Content, and Construct Validations of Endoscopic Needle Injection Simulator for Transurethral Bulking Agent in Treatment of Stress Urinary Incontinence.

PubMed

Farhan, Bilal; Soltani, Tandis; Do, Rebecca; Perez, Claudia; Choi, Hanul; Ghoniem, Gamal

2018-05-02

Endoscopic injection of urethral bulking agents is an office procedure that is used to treat stress urinary incontinence secondary to internal sphincteric deficiency. Validation studies important part of simulator evaluation and is considered important step to establish the effectiveness of simulation-based training. The endoscopic needle injection (ENI) simulator has not been formally validated, although it has been used widely at University of California, Irvine. We aimed to assess the face, content, and construct validity of the UC, Irvine ENI simulator. Dissected female porcine bladders were mounted in a modified Hysteroscopy Diagnostic Trainer. Using routine endoscopic equipment for this procedure with video monitoring, 6 urologists (experts group) and 6 urology trainee (novice group) completed urethral bulking agents injections on a total of 12 bladders using ENI simulator. Face and content validities were assessed by using structured quantitative survey which rating the realism. Construct validity was assessed by comparing the performance, time of the procedure, and the occlusive (anatomical and functional) evaluations between the experts and novices. Trainees also completed a postprocedure feedback survey. Effective injections were evaluated by measuring the retrograde urethral opening pressure, visual cystoscopic coaptation, and postprocedure gross anatomic examination. All 12 participants felt the simulator was a good training tool and should be used as essential part of urology training (face validity). ENI simulator showed good face and content validity with average score varies between the experts and the novices was 3.9/5 and 3.8/5, respectively. Content validity evaluation showed that most aspects of the simulator were adequately realistic (mean Likert scores 3.9-3.8/5). However, the bladder does not bleed, and sometimes thin. Experts significantly outperformed novices (p < 001) across all measure of performance therefore establishing construct validity. The ENI simulator shows face, content and construct validities, although few aspects of simulator were not very realistic (e.g., bleeding).This study provides a base for the future formal validation for this simulator and for continuing use of this simulator in endourology training. Copyright © 2018 Association of Program Directors in Surgery. Published by Elsevier Inc. All rights reserved.

Research on pressure tactile sensing technology based on fiber Bragg grating array

NASA Astrophysics Data System (ADS)

Song, Jinxue; Jiang, Qi; Huang, Yuanyang; Li, Yibin; Jia, Yuxi; Rong, Xuewen; Song, Rui; Liu, Hongbin

2015-09-01

A pressure tactile sensor based on the fiber Bragg grating (FBG) array is introduced in this paper, and the numerical simulation of its elastic body was implemented by finite element software (ANSYS). On the basis of simulation, fiber Bragg grating strings were implanted in flexible silicone to realize the sensor fabrication process, and a testing system was built. A series of calibration tests were done via the high precision universal press machine. The tactile sensor array perceived external pressure, which is demodulated by the fiber grating demodulation instrument, and three-dimension pictures were programmed to display visually the position and size. At the same time, a dynamic contact experiment of the sensor was conducted for simulating robot encountering other objects in the unknown environment. The experimental results show that the sensor has good linearity, repeatability, and has the good effect of dynamic response, and its pressure sensitivity was 0.03 nm/N. In addition, the sensor also has advantages of anti-electromagnetic interference, good flexibility, simple structure, low cost and so on, which is expected to be used in the wearable artificial skin in the future.

Development and characterization of a new oral dapsone nanoemulsion system: permeability and in silico bioavailability studies

PubMed Central

Monteiro, Lidiane M; Lione, Viviane F; do Carmo, Flavia A; do Amaral, Lilian H; da Silva, Julianna H; Nasciutti, Luiz E; Rodrigues, Carlos R; Castro, Helena C; de Sousa, Valeria P; Cabral, Lucio M

2012-01-01

Background Dapsone is described as being active against Mycobacterium leprae, hence its role in the treatment of leprosy and related pathologies. Despite its therapeutic potential, the low solubility of dapsone in water results in low bioavailability and high microbial resistance. Nanoemulsions are pharmaceutical delivery systems derived from micellar solutions with a good capacity for improving absorption. The aim of this work was to develop and compare the permeability of a series of dapsone nanoemulsions in Caco-2 cell culture against that of effective permeability in the human body simulated using Gastroplus™ software. Methods and results The release profiles of the dapsone nanoemulsions using different combinations of surfactants and cosolvent showed a higher dissolution rate in simulated gastric and enteric fluid than did the dispersed dapsone powder. The drug release kinetics were consistent with a Higuchi model. Conclusion This comparison of dapsone permeability in Caco-2 cells with effective permeability in the human body simulated by Gastroplus showed a good correlation and indicates potential improvement in the biodisponibility of dapsone using this new system. PMID:23055729

Development and characterization of a new oral dapsone nanoemulsion system: permeability and in silico bioavailability studies.

PubMed

Monteiro, Lidiane M; Lione, Viviane F; do Carmo, Flavia A; do Amaral, Lilian H; da Silva, Julianna H; Nasciutti, Luiz E; Rodrigues, Carlos R; Castro, Helena C; de Sousa, Valeria P; Cabral, Lucio M

2012-01-01

Dapsone is described as being active against Mycobacterium leprae, hence its role in the treatment of leprosy and related pathologies. Despite its therapeutic potential, the low solubility of dapsone in water results in low bioavailability and high microbial resistance. Nanoemulsions are pharmaceutical delivery systems derived from micellar solutions with a good capacity for improving absorption. The aim of this work was to develop and compare the permeability of a series of dapsone nanoemulsions in Caco-2 cell culture against that of effective permeability in the human body simulated using Gastroplus™ software. The release profiles of the dapsone nanoemulsions using different combinations of surfactants and cosolvent showed a higher dissolution rate in simulated gastric and enteric fluid than did the dispersed dapsone powder. The drug release kinetics were consistent with a Higuchi model. This comparison of dapsone permeability in Caco-2 cells with effective permeability in the human body simulated by Gastroplus showed a good correlation and indicates potential improvement in the biodisponibility of dapsone using this new system.

Cochlear Modeling Using Time-Averaged Lagrangian" Method:. Comparison with VBM, PST, and ZC Measurements

NASA Astrophysics Data System (ADS)

Yoon, Y.; Kim, N.; Puria, S.; Steele, C. R.

2009-02-01

In this work, basilar membrane velocity (VBM), scala tympani intracochlear pressure (PST), and cochlear input impedances (Zc) for gerbil and chinchilla are implemented using a three-dimensional hydro-dynamic cochlear model using 1) time-averaged Lagrangian, 2) push-pull mechanism in active case, and 3) the complex anatomy of cochlear scalae by micro computed tomography (μCT) scanning and 3-D reconstructions of gerbil and chinchilla temporal bones. The objective of this work is to compare the calculations and the physiological measurements of gerbil and chinchilla cochlear such as VBM (Ren and Nuttall [1]), PST (Olson [2]), and ZC (Decraemer et al. [3], Songer and Rosowski [4], Ruggero et al. [5]) with present model. A WKB asymptotic method combined with Fourier series expansions is used to provide an efficient simulation. VBM and PST simulation results for the gerbil cochlea show good agreement both in the magnitude and the phase for the physiological measurements without larger phase excursion. ZC simulation from the gerbil and chinchilla model show reasonably good agreement with measurement.

A scaled-ionic-charge simulation model that reproduces enhanced and suppressed water diffusion in aqueous salt solutions.

PubMed

Kann, Z R; Skinner, J L

2014-09-14

Non-polarizable models for ions and water quantitatively and qualitatively misrepresent the salt concentration dependence of water diffusion in electrolyte solutions. In particular, experiment shows that the water diffusion coefficient increases in the presence of salts of low charge density (e.g., CsI), whereas the results of simulations with non-polarizable models show a decrease of the water diffusion coefficient in all alkali halide solutions. We present a simple charge-scaling method based on the ratio of the solvent dielectric constants from simulation and experiment. Using an ion model that was developed independently of a solvent, i.e., in the crystalline solid, this method improves the water diffusion trends across a range of water models. When used with a good-quality water model, e.g., TIP4P/2005 or E3B, this method recovers the qualitative behaviour of the water diffusion trends. The model and method used were also shown to give good results for other structural and dynamic properties including solution density, radial distribution functions, and ion diffusion coefficients.

Low-Density Nozzle Flow by the Direct Simulation Monte Carlo and Continuum Methods

NASA Technical Reports Server (NTRS)

Chung, Chang-Hong; Kim, Sku C.; Stubbs, Robert M.; Dewitt, Kenneth J.

1994-01-01

Two different approaches, the direct simulation Monte Carlo (DSMC) method based on molecular gasdynamics, and a finite-volume approximation of the Navier-Stokes equations, which are based on continuum gasdynamics, are employed in the analysis of a low-density gas flow in a small converging-diverging nozzle. The fluid experiences various kinds of flow regimes including continuum, slip, transition, and free-molecular. Results from the two numerical methods are compared with Rothe's experimental data, in which density and rotational temperature variations along the centerline and at various locations inside a low-density nozzle were measured by the electron-beam fluorescence technique. The continuum approach showed good agreement with the experimental data as far as density is concerned. The results from the DSMC method showed good agreement with the experimental data, both in the density and the rotational temperature. It is also shown that the simulation parameters, such as the gas/surface interaction model, the energy exchange model between rotational and translational modes, and the viscosity-temperature exponent, have substantial effects on the results of the DSMC method.

Langasite surface acoustic wave gas sensors: modeling and verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng Zheng,; Greve, D. W.; Oppenheim, I. J.

2013-03-01

We report finite element simulations of the effect of conductive sensing layers on the surface wave velocity of langasite substrates. The simulations include both the mechanical and electrical influences of the conducting sensing layer. We show that three-dimensional simulations are necessary because of the out-of-plane displacements of the commonly used (0, 138.5, 26.7) Euler angle. Measurements of the transducer input admittance in reflective delay-line devices yield a value for the electromechanical coupling coefficient that is in good agreement with the three-dimensional simulations on bare langasite substrate. The input admittance measurements also show evidence of excitation of an additional wave modemore » and excess loss due to the finger resistance. The results of these simulations and measurements will be useful in the design of surface acoustic wave gas sensors.« less

Texas cracking performance prediction, simulation, and binder recommendation.

DOT National Transportation Integrated Search

2014-10-01

Recent studies show some mixes with softer binders used outside of Texas (e.g., Minnesotas Cold Weather Road Research Facility mixes) have both good rutting and cracking performance. However, the current binder performance grading (PG) system fail...

Non-periodic high-index contrast gratings reflector with large-angle beam forming ability

NASA Astrophysics Data System (ADS)

Fang, Wenjing; Huang, Yongqing; Duan, Xiaofeng; Fei, Jiarui; Ren, Xiaomin; Mao, Min

2016-05-01

A non-periodic high-index contrast gratings (HCGs) reflector on SOI wafer with large-angle beam forming ability has been proposed and fabricated. The proposed reflector was designed using rigorous coupled-wave analysis (RCWA) and finite-element-method (FEM). A deflection angle of 17.35° and high reflectivity of 92.31% are achieved under transverse magnetic (TM) polarized light in numerical simulation. Experimental results show that the reflected power peaked at 17.2° under a 1550 nm incident light, which is in good accordance with the simulation results. Moreover, the reflected power spectrum was also measured. Under different incident wavelengths around 1550 nm, reflected powers all peaked at 17.2°. The results show that the proposed non-periodic HCGs reflector has a good reflection and beam forming ability in a wavelength range as wide as 40 nm around 1550 nm.

Direct simulations of chemically reacting turbulent mixing layers, part 2

NASA Technical Reports Server (NTRS)

Metcalfe, Ralph W.; Mcmurtry, Patrick A.; Jou, Wen-Huei; Riley, James J.; Givi, Peyman

1988-01-01

The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques.

Optical and infrared properties of glancing angle-deposited nanostructured tungsten films

DOE PAGES

Ungaro, Craig; Shah, Ankit; Kravchenko, Ivan; ...

2015-02-06

For this study, nanotextured tungsten thin films were obtained on a stainless steel (SS) substrate using the glancing-angle-deposition (GLAD) method. It was found that the optical absorption and thermal emittance of the SS substrate can be controlled by varying the parameters used during deposition. Finite-difference time-domain (FDTD) simulations were used to predict the optical absorption and infrared (IR) reflectance spectra of the fabricated samples, and good agreement was found between simulated and measured data. FDTD simulations were also used to predict the effect of changes in the height and periodicity of the nanotextures. These simulations show that good control overmore » the absorption can be achieved by altering the height and periodicity of the nanostructure. These nanostructures were shown to be temperature stable up to 500°C with the addition of a protective HfO 2 layer. Finally, applications for this structure are explored, including a promising application for solar thermal energy systems.« less

Trajectory control of robot manipulators with closed-kinematic chain mechanism

NASA Technical Reports Server (NTRS)

Nguyen, Charles C.; Pooran, Farhad J.; Premack, Timothy

1987-01-01

The problem of Cartesian trajectory control of a closed-kinematic chain mechanism robot manipulator, recently built at CAIR to study the assembly of NASA hardware for the future Space Station, is considered. The study is performed by both computer simulation and experimentation for tracking of three different paths: a straight line, a sinusoid, and a circle. Linearization and pole placement methods are employed to design controller gains. Results show that the controllers are robust and there are good agreements between simulation and experimentation. The results also show excellent tracking quality and small overshoots.

Characterization of a long-focal-length polycapillary optic for high-energy x-rays

NASA Astrophysics Data System (ADS)

Cari, Padiyar; Suparmi, -; Padiyar, Sushil D.; Gibson, Walter M.; MacDonald, Carolyn A.; Alexander, Cheryl D.; Joy, Marshall K.; Russell, Christine H.; Chen, Zewu

2000-11-01

Polycapillary fibers and a prototype collector for high energy x rays with a 2 m focal length have been fabricated and characterized. Measurements of a prototype collector, performed in collimating mode, show that the optic has high transmission, good uniformity, and small exit divergence. The transmission as a function of energy was analyzed using an extended single fiber geometrical optic simulation and the result shows that the simulation fits the data fairly well. Scatter transmission and contrast enhancement were measured in focusing mode using a parallel beam input.

Powder metallurgical low-modulus Ti-Mg alloys for biomedical applications.

PubMed

Liu, Yong; Li, Kaiyang; Luo, Tao; Song, Min; Wu, Hong; Xiao, Jian; Tan, Yanni; Cheng, Ming; Chen, Bing; Niu, Xinrui; Hu, Rong; Li, Xiaohui; Tang, Huiping

2015-11-01

In this work, powder metallurgical (PM) Ti-Mg alloys were prepared using combined techniques of mechanical alloying and spark plasma sintering. The alloys mainly consist of super saturations of Mg in Ti matrix, and some laminar structured Ti- and Mg-rich phases. The PM Ti-Mg alloys contain a homogeneous mixtures of nanocrystalline Mg and Ti phases. The novel microstructures result in unconventional mechanical and biological properties. It has been shown that the PM Ti-Mg alloys have a much lower compression modulus (36-50GPa) compared to other Ti alloys, but still remain a very high compressive strength (1500-1800MPa). In addition, the PM Ti-Mg alloys show good biocompatibility and bioactivity. Mg can dissolve in the simulated body fluids, and induce the formation of the calcium phosphate layer. The compression modulus of PM Ti-Mg alloys decreases with the amount of Mg, while the bioactivity increases. Although the corrosion resistance of Ti-Mg alloys decreases with the content of Mg, the alloys still show good stability in simulated body fluid under electrochemical conditions. The indirect and direct cytotoxicity results show that PM Ti-Mg alloys have a good biocompatibility to NIH-3T3 cells. Therefore, the PM Ti-Mg alloys are promising candidates in biomedical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Convection in a Very Compressible Fluid: Comparison of Simulations With Experiments

NASA Technical Reports Server (NTRS)

Meyer, H.; Furukawa, A.; Onuki, A.; Kogan, A. B.

2003-01-01

The time profile (Delta)T(t) of the temperature difference, measured across a very compressible fluid layer of supercritical He-3 after the start of a heat flow, shows a damped oscillatory behavior before steady state convection is reached. The results for (Delta)T(t) obtained from numerical simulations and from laboratory experiments are compared over a temperature range where the compressibility varies by a factor of approx. = 40. First the steady-state convective heat current j(sup conv) as a function of the Rayleigh number R(alpha) is presented, and the agreement is found to be good. Second, the shape of the time profile and two characteristic times in the transient part of (Delta)T(t) from simulations and experiments are compared, namely: 1) t(sub osc), the oscillatory period and 2) t(sub p), the time of the first peak after starting the heat flow. These times, scaled by the diffusive time tau(sub D) versus R(alpha), are presented. The agreement is good for t(sup osc)/tau(sub D), where the results collapse on a single curve showing a powerlaw behavior. The simulation hence confirms the universal scaling behavior found experimentally. However for t(sub p)/tau(sub D), where the experimental data also collapse on a single curve, the simulation results show systematic departures from such a behavior. A possible reason for some of the disagreements, both in the time profile and in t(sub p) is discussed. In the Appendix a third characteristic time, t(sub m), between the first peak and the first oscillation minimum is plotted and a comparison between the results of experiments and simulations is made.

Quantifying the Effect of Polymer Blending through Molecular Modelling of Cyanurate Polymers

PubMed Central

Crawford, Alasdair O.; Hamerton, Ian; Cavalli, Gabriel; Howlin, Brendan J.

2012-01-01

Modification of polymer properties by blending is a common practice in the polymer industry. We report here a study of blends of cyanurate polymers by molecular modelling that shows that the final experimentally determined properties can be predicted from first principles modelling to a good degree of accuracy. There is always a compromise between simulation length, accuracy and speed of prediction. A comparison of simulation times shows that 125ps of molecular dynamics simulation at each temperature provides the optimum compromise for models of this size with current technology. This study opens up the possibility of computer aided design of polymer blends with desired physical and mechanical properties. PMID:22970230

Full Core TREAT Kinetics Demonstration Using Rattlesnake/BISON Coupling Within MAMMOTH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortensi, Javier; DeHart, Mark D.; Gleicher, Frederick N.

2015-08-01

This report summarizes key aspects of research in evaluation of modeling needs for TREAT transient simulation. Using a measured TREAT critical measurement and a transient for a small, experimentally simplified core, Rattlesnake and MAMMOTH simulations are performed building from simple infinite media to a full core model. Cross sections processing methods are evaluated, various homogenization approaches are assessed and the neutronic behavior of the core studied to determine key modeling aspects. The simulation of the minimum critical core with the diffusion solver shows very good agreement with the reference Monte Carlo simulation and the experiment. The full core transient simulationmore » with thermal feedback shows a significantly lower power peak compared to the documented experimental measurement, which is not unexpected in the early stages of model development.« less

Numerical simulation of miscible viscous fingering with viscosity change in a displacing fluid by chemical reaction

NASA Astrophysics Data System (ADS)

Omori, Keiichiro; Nagatsu, Yuichiro

2017-11-01

Viscous fingering (VF) with viscosity changes by chemical reactions in case of miscible systems have been investigated both experimentally and theoretically in the recent years. Nagatsu et al. investigated experimentally miscible VF in which viscosity of the displaced fluid or the displacing one is changed by fast chemical reaction They showed that VF was more dense by the viscosity increase whereas less dense by the viscosity increase regardless of whether the viscosity change occurs in the displaced fluid or displacing one. From a theoretical viewpoint, numerical simulation performed on the reactive VF where viscosity of the displaced fluid is changed by instantaneously fast chemical reaction. The results had a good agreement with those in the corresponding experiment. In this work, we have conducted numerical simulation on such reactive VF where viscosity of the displacing fluid is changed. We have found the results have a good agreement with the corresponding experimental ones.

A finite element model of a six-year-old child for simulating pedestrian accidents.

PubMed

Meng, Yunzhu; Pak, Wansoo; Guleyupoglu, Berkan; Koya, Bharath; Gayzik, F Scott; Untaroiu, Costin D

2017-01-01

Child pedestrian protection deserves more attention in vehicle safety design since they are the most vulnerable road users who face the highest mortality rate. Pediatric Finite Element (FE) models could be used to simulate and understand the pedestrian injury mechanisms during crashes in order to mitigate them. Thus, the objective of the study was to develop a computationally efficient (simplified) six-year-old (6YO-PS) pedestrian FE model and validate it based on the latest published pediatric data. The 6YO-PS FE model was developed by morphing the existing GHBMC adult pedestrian model. Retrospective scan data were used to locally adjust the geometry as needed for accuracy. Component test simulations focused only the lower extremities and pelvis, which are the first body regions impacted during pedestrian accidents. Three-point bending test simulations were performed on the femur and tibia with adult material properties and then updated using child material properties. Pelvis impact and knee bending tests were also simulated. Finally, a series of pediatric Car-to-Pedestrian Collision (CPC) were simulated with pre-impact velocities ranging from 20km/h up to 60km/h. The bone models assigned pediatric material properties showed lower stiffness and a good match in terms of fracture force to the test data (less than 6% error). The pelvis impact force predicted by the child model showed a similar trend with test data. The whole pedestrian model was stable during CPC simulations and predicted common pedestrian injuries. Overall, the 6YO-PS FE model developed in this study showed good biofidelity at component level (lower extremity and pelvis) and stability in CPC simulations. While more validations would improve it, the current model could be used to investigate the lower limb injury mechanisms and in the prediction of the impact parameters as specified in regulatory testing protocols. Copyright © 2016 Elsevier Ltd. All rights reserved.

Imaging performance of a LaBr3-based PET scanner

PubMed Central

Daube-Witherspoon, M E; Surti, S; Perkins, A; Kyba, C C M; Wiener, R; Werner, M E; Kulp, R; Karp, J S

2010-01-01

A prototype time-of-flight (TOF) PET scanner based on cerium-doped lanthanum bromide [LaBr3 (5% Ce)] has been developed. LaBr3 has high light output, excellent energy resolution, and fast timing properties that have been predicted to lead to good image quality. Intrinsic performance measurements of spatial resolution, sensitivity, and scatter fraction demonstrate good conventional PET performance; the results agree with previous simulation studies. Phantom measurements show the excellent image quality achievable with the prototype system. Phantom measurements and corresponding simulations show a faster and more uniform convergence rate, as well as more uniform quantification, for TOF reconstruction of the data, which have 375-ps intrinsic timing resolution, compared to non-TOF images. Measurements and simulations of a hot and cold sphere phantom show that the 7% energy resolution helps to mitigate residual errors in the scatter estimate because a high energy threshold (>480 keV) can be used to restrict the amount of scatter accepted without a loss of true events. Preliminary results with incorporation of a model of detector blurring in the iterative reconstruction algorithm show improved contrast recovery but also point out the importance of an accurate resolution model of the tails of LaBr3’s point spread function. The LaBr3 TOF-PET scanner has demonstrated the impact of superior timing and energy resolutions on image quality. PMID:19949259

An integrated algorithm for hypersonic fluid-thermal-structural numerical simulation

NASA Astrophysics Data System (ADS)

Li, Jia-Wei; Wang, Jiang-Feng

2018-05-01

In this paper, a fluid-structural-thermal integrated method is presented based on finite volume method. A unified integral equations system is developed as the control equations for physical process of aero-heating and structural heat transfer. The whole physical field is discretized by using an up-wind finite volume method. To demonstrate its capability, the numerical simulation of Mach 6.47 flow over stainless steel cylinder shows a good agreement with measured values, and this method dynamically simulates the objective physical processes. Thus, the integrated algorithm proves to be efficient and reliable.

RCWA and FDTD modeling of light emission from internally structured OLEDs.

PubMed

Callens, Michiel Koen; Marsman, Herman; Penninck, Lieven; Peeters, Patrick; de Groot, Harry; ter Meulen, Jan Matthijs; Neyts, Kristiaan

2014-05-05

We report on the fabrication and simulation of a green OLED with an Internal Light Extraction (ILE) layer. The optical behavior of these devices is simulated using both Rigorous Coupled Wave Analysis (RCWA) and Finite Difference Time-Domain (FDTD) methods. Results obtained using these two different techniques show excellent agreement and predict the experimental results with good precision. By verifying the validity of both simulation methods on the internal light extraction structure we pave the way to optimization of ILE layers using either of these methods.

Display aids for remote control of untethered undersea vehicles

NASA Technical Reports Server (NTRS)

Verplank, W. L.

1978-01-01

A predictor display superimposed on slow-scan video or sonar data is proposed as a method to allow better remote manual control of an untethered submersible. Simulation experiments show good control under circumstances which otherwise make control practically impossible.

Simulating the IPOD, East Asian summer monsoon, and their relationships in CMIP5

NASA Astrophysics Data System (ADS)

Yu, Miao; Li, Jianping; Zheng, Fei; Wang, Xiaofan; Zheng, Jiayu

2018-03-01

This paper evaluates the simulation performance of the 37 coupled models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) with respect to the East Asian summer monsoon (EASM) and the Indo-Pacific warm pool and North Pacific Ocean dipole (IPOD) and also the interrelationships between them. The results show that the majority of the models are unable to accurately simulate the interannual variability and long-term trends of the EASM, and their simulations of the temporal and spatial variations of the IPOD are also limited. Further analysis showed that the correlation coefficients between the simulated and observed EASM index (EASMI) is proportional to those between the simulated and observed IPOD index (IPODI); that is, if the models have skills to simulate one of them then they will likely generate good simulations of another. Based on the above relationship, this paper proposes a conditional multi-model ensemble method (CMME) that eliminates those models without capability to simulate the IPOD and EASM when calculating the multi-model ensemble (MME). The analysis shows that, compared with the MME, this CMME method can significantly improve the simulations of the spatial and temporal variations of both the IPOD and EASM as well as their interrelationship, suggesting the potential for the CMME approach to be used in place of the MME method.

Results from flight and simulator studies of a Mach 3 cruise longitudinal autopilot

NASA Technical Reports Server (NTRS)

Gilyard, G. B.; Smith, J. W.

1978-01-01

At Mach numbers of approximately 3.0 and altitudes greater than 21,300 meters, the original altitude and Mach hold modes of the YF-12 autopilot produced aircraft excursions that were erratic or divergent, or both. Flight data analysis and simulator studies showed that the sensitivity of the static pressure port to angle of attack had a detrimental effect on the performance of the altitude and Mach hold modes. Good altitude hold performance was obtained when a high passed pitch rate feedback was added to compensate for angle of attack sensitivity and the altitude error and integral altitude gains were reduced. Good Mach hold performance was obtained when the angle of attack sensitivity was removed; however, the ride qualities remained poor.

Wave optics simulation of atmospheric turbulence and reflective speckle effects in carbon dioxide lidar

NASA Astrophysics Data System (ADS)

Nelson, Douglas Harold

Laser speckle can influence lidar measurements from a diffuse hard target. Atmospheric optical turbulence will also affect the lidar return signal. This investigation develops a numerical simulation that models the propagation of a lidar beam and accounts for both reflective speckle and atmospheric turbulence effects. The simulation, previously utilized to simulate the effects of atmospheric optical turbulence alone, is based on implementing a Huygens-Fresnel approximation to laser propagation. A series of phase screens, with the appropriate atmospheric statistical characteristics, is used to simulate the effect of atmospheric optical turbulence. A single random phase screen is used to simulate scattering of the entire beam from a rough surface. These investigations compare the output of the numerical model with separate CO2 lidar measurements of atmospheric turbulence and reflective speckle. This work also compares the output of the model with separate analytical predictions for atmospheric turbulence and reflective speckle. Good agreement is found between the model and the experimental data. Good agreement is also found with analytical predictions. Additionally, results of simulation of the combined effects on a finite aperture lidar system show agreement with experimental observations of increasing RMS noise with increasing turbulence level and the behavior of the experimental integrated intensity probability distribution. Simulation studies are included that demonstrate the usefulness of the model, examine its limitations and provide greater insight into the process of combined atmospheric optical turbulence and reflective speckle. One highlight of these studies is examination of the limitations of the simulation that shows, in general, precision increases with increasing grid size. The study of the backscatter intensity enhancement predicted by analytical theory show it to behave as a multi-path effect, like scintillation, with the highest contributions from atmospheric optical turbulence weighted at the middle of the propagation path. Aperture geometry also affects the signal-to-noise ratio with thin annular apertures exhibiting lower RMS noise than circular apertures of the same active area. The simulation is capable of studying a variety of lidar schemes including varying atmospheric optical turbulence along the propagation path as well as diverse transmitter and receiver geometries.

Three dimensional nonlinear simulations of edge localized modes on the EAST tokamak using BOUT++ code

NASA Astrophysics Data System (ADS)

Liu, Z. X.; Xu, X. Q.; Gao, X.; Xia, T. Y.; Joseph, I.; Meyer, W. H.; Liu, S. C.; Xu, G. S.; Shao, L. M.; Ding, S. Y.; Li, G. Q.; Li, J. G.

2014-09-01

Experimental measurements of edge localized modes (ELMs) observed on the EAST experiment are compared to linear and nonlinear theoretical simulations of peeling-ballooning modes using the BOUT++ code. Simulations predict that the dominant toroidal mode number of the ELM instability becomes larger for lower current, which is consistent with the mode structure captured with visible light using an optical CCD camera. The poloidal mode number of the simulated pressure perturbation shows good agreement with the filamentary structure observed by the camera. The nonlinear simulation is also consistent with the experimentally measured energy loss during an ELM crash and with the radial speed of ELM effluxes measured using a gas puffing imaging diagnostic.

Radiation and ionization energy loss simulation for the GDH sum rule experiment in Hall-A at Jefferson Lab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Xin -Hu; Ye, Yun -Xiu; Chen, Jian -Ping

2015-07-17

The radiation and ionization energy loss are presented for single arm Monte Carlo simulation for the GDH sum rule experiment in Hall-A at Jefferson Lab. Radiation and ionization energy loss are discussed formore » $$^{12}C$$ elastic scattering simulation. The relative momentum ratio $$\\frac{\\Delta p}{p}$$ and $$^{12}C$$ elastic cross section are compared without and with radiation energy loss and a reasonable shape is obtained by the simulation. The total energy loss distribution is obtained, showing a Landau shape for $$^{12}C$$ elastic scattering. This simulation work will give good support for radiation correction analysis of the GDH sum rule experiment.« less

Ion velocity distribution functions in argon and helium discharges: detailed comparison of numerical simulation results and experimental data

NASA Astrophysics Data System (ADS)

Wang, Huihui; Sukhomlinov, Vladimir S.; Kaganovich, Igor D.; Mustafaev, Alexander S.

2017-02-01

Using the Monte Carlo collision method, we have performed simulations of ion velocity distribution functions (IVDF) taking into account both elastic collisions and charge exchange collisions of ions with atoms in uniform electric fields for argon and helium background gases. The simulation results are verified by comparison with the experiment data of the ion mobilities and the ion transverse diffusion coefficients in argon and helium. The recently published experimental data for the first seven coefficients of the Legendre polynomial expansion of the ion energy and angular distribution functions are used to validate simulation results for IVDF. Good agreement between measured and simulated IVDFs shows that the developed simulation model can be used for accurate calculations of IVDFs.

The effects of simulated fog and motion on simulator sickness in a driving simulator and the duration of after-effects.

PubMed

Dziuda, Lukasz; Biernacki, Marcin P; Baran, Paulina M; Truszczyński, Olaf E

2014-05-01

In the study, we checked: 1) how the simulator test conditions affect the severity of simulator sickness symptoms; 2) how the severity of simulator sickness symptoms changes over time; and 3) whether the conditions of the simulator test affect the severity of these symptoms in different ways, depending on the time that has elapsed since the performance of the task in the simulator. We studied 12 men aged 24-33 years (M = 28.8, SD = 3.26) using a truck simulator. The SSQ questionnaire was used to assess the severity of the symptoms of simulator sickness. Each of the subjects performed three 30-minute tasks running along the same route in a driving simulator. Each of these tasks was carried out in a different simulator configuration: A) fixed base platform with poor visibility; B) fixed base platform with good visibility; and C) motion base platform with good visibility. The measurement of the severity of the simulator sickness symptoms took place in five consecutive intervals. The results of the analysis showed that the simulator test conditions affect in different ways the severity of the simulator sickness symptoms, depending on the time which has elapsed since performing the task on the simulator. The simulator sickness symptoms persisted at the highest level for the test conditions involving the motion base platform. Also, when performing the tasks on the motion base platform, the severity of the simulator sickness symptoms varied depending on the time that had elapsed since performing the task. Specifically, the addition of motion to the simulation increased the oculomotor and disorientation symptoms reported as well as the duration of the after-effects. Copyright © 2013 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Adsorption of 1-naphthyl methyl carbamate in water by utilizing a surface molecularly imprinted polymer

NASA Astrophysics Data System (ADS)

So, Juhyok; Pang, Cholho; Dong, Hongxing; Jang, Paeksan; U, Juhyok; Ri, Kumchol; Yun, Cholyong

2018-05-01

Surface molecularly imprinting polymer (SMIP) was utilized in the removal of a residual pesticide (carbaryl (CBL)) in water and simulated fruit juice. Being the crosslinking agent, ethylene glycol dimethacrylate (EGDMA) was copolymerized with the monomer, methacrylic acid (MAA) and CBL as the template molecules on the surface of the silica gel particles to produce the SMIP adsorbents. The SMIP adsorbents showed good selectivity and good adsorption capacity for CBL in the competitive adsorptions with two structurally related carbamate pesticides. The effect of the pretreatment solvents on the adsorption capacity of the SMIP adsorbent was investigated with the results of the numerical simulations. The adsorption isotherms and the adsorption kinetics were well described by the Freundlich equilibrium model and the pseudo-second-order kinetic model, respectively. Scatchard plot analysis revealed that there were two classes of binding sites populated in the SMIP adsorbents. In addition, the good selective adsorption of CBL by the SMIP adsorbent in a simulated fruit juice containing vitamin C and fructose indicated the great potential of the SMIP adsorbents to remove residual pesticide in food industry and processing industry for agricultural products.

Spectral simulations of an axisymmetric force-free pulsar magnetosphere

NASA Astrophysics Data System (ADS)

Cao, Gang; Zhang, Li; Sun, Sineng

2016-02-01

A pseudo-spectral method with an absorbing outer boundary is used to solve a set of time-dependent force-free equations. In this method, both electric and magnetic fields are expanded in terms of the vector spherical harmonic (VSH) functions in spherical geometry and the divergence-free state of the magnetic field is enforced analytically by a projection method. Our simulations show that the Deutsch vacuum solution and the Michel monopole solution can be reproduced well by our pseudo-spectral code. Further, the method is used to present a time-dependent simulation of the force-free pulsar magnetosphere for an aligned rotator. The simulations show that the current sheet in the equatorial plane can be resolved well and the spin-down luminosity obtained in the steady state is in good agreement with the value given by Spitkovsky.

Cosmic Reionization on Computers: Properties of the Post-reionization IGM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gnedin, Nickolay Y.; Becker, George D.; Fan, Xiaohui

Here, we present a comparison between several observational tests of the post-reionization IGM and the numerical simulations of reionization completed under the Cosmic Reionization On Computers (CROC) project. The CROC simulations match the gap distribution reasonably well, and also provide a good match for the distribution of peak heights, but there is a notable lack of wide peaks in the simulated spectra and the flux PDFs are poorly matched in the narrow redshift interval 5.5 < z < 5.7, with the match at other redshifts being significantly better, albeit not exact. Both discrepancies are related: simulations show more opacity thanmore » the data.« less

Cosmic Reionization on Computers: Properties of the Post-reionization IGM

DOE PAGES

Gnedin, Nickolay Y.; Becker, George D.; Fan, Xiaohui

2017-05-19

Here, we present a comparison between several observational tests of the post-reionization IGM and the numerical simulations of reionization completed under the Cosmic Reionization On Computers (CROC) project. The CROC simulations match the gap distribution reasonably well, and also provide a good match for the distribution of peak heights, but there is a notable lack of wide peaks in the simulated spectra and the flux PDFs are poorly matched in the narrow redshift interval 5.5 < z < 5.7, with the match at other redshifts being significantly better, albeit not exact. Both discrepancies are related: simulations show more opacity thanmore » the data.« less

Concurrent design of an RTP chamber and advanced control system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spence, P.; Schaper, C.; Kermani, A.

1995-12-31

A concurrent-engineering approach is applied to the development of an axisymmetric rapid-thermal-processing (RTP) reactor and its associated temperature controller. Using a detailed finite-element thermal model as a surrogate for actual hardware, the authors have developed and tested a multi-input multi-output (MIMO) controller. Closed-loop simulations are performed by linking the control algorithm with the finite-element code. Simulations show that good temperature uniformity is maintained on the wafer during both steady and transient conditions. A numerical study shows the effect of ramp rate, feedback gain, sensor placement, and wafer-emissivity patterns on system performance.

Finite element model of the temperature increase in excised porcine cadaver iris during direct illumination by femtosecond laser pulses

PubMed Central

Sun, Hui; Kurtz, Ronald M.

2012-01-01

Abstract. In order to model the thermal effect of laser exposure of the iris during laser corneal surgery, we simulated the temperature increase in porcine cadaver iris. The simulation data for the 60 kHz FS60 Laser showed that the temperature increased up to 1.23°C and 2.45°C (at laser pulse energy 1 and 2 µJ, respectively) by the 24 second procedure time. Calculated temperature profiles show good agreement with data obtained from ex vivo experiments using porcine cadaver iris. Simulation results of different types of femtosecond lasers indicate that the Laser in situ keratomileusis procedure does not present a safety hazard to the iris. PMID:22894525

Normalization of time-series satellite reflectance data to a standard sun-target-sensor geometry using a semi-empirical model

NASA Astrophysics Data System (ADS)

Zhao, Yongguang; Li, Chuanrong; Ma, Lingling; Tang, Lingli; Wang, Ning; Zhou, Chuncheng; Qian, Yonggang

2017-10-01

Time series of satellite reflectance data have been widely used to characterize environmental phenomena, describe trends in vegetation dynamics and study climate change. However, several sensors with wide spatial coverage and high observation frequency are usually designed to have large field of view (FOV), which cause variations in the sun-targetsensor geometry in time-series reflectance data. In this study, on the basis of semiempirical kernel-driven BRDF model, a new semi-empirical model was proposed to normalize the sun-target-sensor geometry of remote sensing image. To evaluate the proposed model, bidirectional reflectance under different canopy growth conditions simulated by Discrete Anisotropic Radiative Transfer (DART) model were used. The semi-empirical model was first fitted by using all simulated bidirectional reflectance. Experimental result showed a good fit between the bidirectional reflectance estimated by the proposed model and the simulated value. Then, MODIS time-series reflectance data was normalized to a common sun-target-sensor geometry by the proposed model. The experimental results showed the proposed model yielded good fits between the observed and estimated values. The noise-like fluctuations in time-series reflectance data was also reduced after the sun-target-sensor normalization process.

Experiments and FEM simulations of fracture behaviors for ADC12 aluminum alloy under impact load

NASA Astrophysics Data System (ADS)

Hu, Yumei; Xiao, Yue; Jin, Xiaoqing; Zheng, Haoran; Zhou, Yinge; Shao, Jinhua

2016-11-01

Using the combination of experiment and simulation, the fracture behavior of the brittle metal named ADC12 aluminum alloy was studied. Five typical experiments were carried out on this material, with responding data collected on different stress states and dynamic strain rates. Fractographs revealed that the morphologies of fractured specimen under several rates showed different results, indicating that the fracture was predominantly a brittle one in nature. Simulations of the fracture processes of those specimens were conducted by Finite Element Method, whilst consistency was observed between simulations and experiments. In simulation, the Johnson- Cook model was chosen to describe the damage development and to predict the failure using parameters determined from those experimental data. Subsequently, an ADC12 engine mount bracket crashing simulation was conducted and the results indicated good agreement with the experiments. The accordance showed that our research can provide an accurate description for the deforming and fracture processes of the studied alloy.

Simulation of the toxicokinetics of trichloroethylene, methylene chloride, styrene and n-hexane by a toxicokinetics/toxicodynamics model using experimental data.

PubMed

Nakayama, Yumiko; Kishida, Fumio; Nakatsuka, Iwao; Matsuo, Masatoshi

2005-01-01

The toxicokinetics/toxicodynamics (TKTD) model simulates the toxicokinetics of a chemical based on physiological data such as blood flow, tissue partition coefficients and metabolism. In this study, Andersen and Clewell's TKTD model was used with seven compartments and ten differential equations for calculating chemical balances in the compartments (Andersen and Clewell 1996, Workshop on physiologically-based pharmacokinetic/pharmacodynamic modeling and risk assessment, Aug. 5-16 at Colorado State University, U.S.A) . Using this model, the authors attempted to simulate the behavior of four chemicals: trichloroethylene, methylene chloride, styrene and n-hexane, and the results were evaluated. Simulations of the behavior of trichloroethylene taken in via inhalation and oral exposure routes were also done. The differences between simulations and measurements are due to the differences between the absorption rates of the exposure routes. By changing the absorption rates, the simulation showed agreement with the measured values. The simulations of the other three chemicals showed good results. Thus, this model is useful for simulating the behavior of chemicals for preliminary toxicity assessment.

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun

Here, an entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace’s law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results.more » Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.« less

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

NASA Astrophysics Data System (ADS)

Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun; Derome, Dominique; Carmeliet, Jan

2018-03-01

An entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace's law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results. Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

DOE PAGES

Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun; ...

2018-03-22

Here, an entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace’s law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results.more » Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.« less

3-D velocity structure model for long-period ground motion simulation of the hypothetical Nankai Earthquake

NASA Astrophysics Data System (ADS)

Kagawa, T.; Petukhin, A.; Koketsu, K.; Miyake, H.; Murotani, S.; Tsurugi, M.

2010-12-01

Three dimensional velocity structure model of southwest Japan is provided to simulate long-period ground motions due to the hypothetical subduction earthquakes. The model is constructed from numerous physical explorations conducted in land and offshore areas and observational study of natural earthquakes. Any available information is involved to explain crustal structure and sedimentary structure. Figure 1 shows an example of cross section with P wave velocities. The model has been revised through numbers of simulations of small to middle earthquakes as to have good agreement with observed arrival times, amplitudes, and also waveforms including surface waves. Figure 2 shows a comparison between Observed (dash line) and simulated (solid line) waveforms. Low velocity layers have added on seismological basement to reproduce observed records. The thickness of the layer has been adjusted through iterative analysis. The final result is found to have good agreement with the results from other physical explorations; e.g. gravity anomaly. We are planning to make long-period (about 2 to 10 sec or longer) simulations of ground motion due to the hypothetical Nankai Earthquake with the 3-D velocity structure model. As the first step, we will simulate the observed ground motions of the latest event occurred in 1946 to check the source model and newly developed velocity structure model. This project is partly supported by Integrated Research Project for Long-Period Ground Motion Hazard Maps by Ministry of Education, Culture, Sports, Science and Technology (MEXT). The ground motion data used in this study were provided by National Research Institute for Earth Science and Disaster Prevention Disaster (NIED). Figure 1 An example of cross section with P wave velocities Figure 2 Observed (dash line) and simulated (solid line) waveforms due to a small earthquake

Monte Carlo Simulation of X-Ray Spectra in Mammography and Contrast-Enhanced Digital Mammography Using the Code PENELOPE

NASA Astrophysics Data System (ADS)

Cunha, Diego M.; Tomal, Alessandra; Poletti, Martin E.

2013-04-01

In this work, the Monte Carlo (MC) code PENELOPE was employed for simulation of x-ray spectra in mammography and contrast-enhanced digital mammography (CEDM). Spectra for Mo, Rh and W anodes were obtained for tube potentials between 24-36 kV, for mammography, and between 45-49 kV, for CEDM. The spectra obtained from the simulations were analytically filtered to correspond to the anode/filter combinations usually employed in each technique (Mo/Mo, Rh/Rh and W/Rh for mammography and Mo/Cu, Rh/Cu and W/Cu for CEDM). For the Mo/Mo combination, the simulated spectra were compared with those obtained experimentally, and for spectra for the W anode, with experimental data from the literature, through comparison of distribution shape, average energies, half-value layers (HVL) and transmission curves. For all combinations evaluated, the simulated spectra were also compared with those provided by different models from the literature. Results showed that the code PENELOPE provides mammographic x-ray spectra in good agreement with those experimentally measured and those from the literature. The differences in the values of HVL ranged between 2-7%, for anode/filter combinations and tube potentials employed in mammography, and they were less than 5% for those employed in CEDM. The transmission curves for the spectra obtained also showed good agreement compared to those computed from reference spectra, with average relative differences less than 12% for mammography and CEDM. These results show that the code PENELOPE can be a useful tool to generate x-ray spectra for studies in mammography and CEDM, and also for evaluation of new x-ray tube designs and new anode materials.

A quasi two-dimensional model for sound attenuation by the sonic crystals.

PubMed

Gupta, A; Lim, K M; Chew, C H

2012-10-01

Sound propagation in the sonic crystal (SC) along the symmetry direction is modeled by sound propagation through a variable cross-sectional area waveguide. A one-dimensional (1D) model based on the Webster horn equation is used to obtain sound attenuation through the SC. This model is compared with two-dimensional (2D) finite element simulation and experiment. The 1D model prediction of frequency band for sound attenuation is found to be shifted by around 500 Hz with respect to the finite element simulation. The reason for this shift is due to the assumption involved in the 1D model. A quasi 2D model is developed for sound propagation through the waveguide. Sound pressure profiles from the quasi 2D model are compared with the finite element simulation and the 1D model. The result shows significant improvement over the 1D model and is in good agreement with the 2D finite element simulation. Finally, sound attenuation through the SC is computed based on the quasi 2D model and is found to be in good agreement with the finite element simulation. The quasi 2D model provides an improved method to calculate sound attenuation through the SC.

Land cover change or land-use intensification: simulating land system change with a global-scale land change model.

PubMed

van Asselen, Sanneke; Verburg, Peter H

2013-12-01

Land-use change is both a cause and consequence of many biophysical and socioeconomic changes. The CLUMondo model provides an innovative approach for global land-use change modeling to support integrated assessments. Demands for goods and services are, in the model, supplied by a variety of land systems that are characterized by their land cover mosaic, the agricultural management intensity, and livestock. Land system changes are simulated by the model, driven by regional demand for goods and influenced by local factors that either constrain or promote land system conversion. A characteristic of the new model is the endogenous simulation of intensification of agricultural management versus expansion of arable land, and urban versus rural settlements expansion based on land availability in the neighborhood of the location. Model results for the OECD Environmental Outlook scenario show that allocation of increased agricultural production by either management intensification or area expansion varies both among and within world regions, providing useful insight into the land sparing versus land sharing debate. The land system approach allows the inclusion of different types of demand for goods and services from the land system as a driving factor of land system change. Simulation results are compared to observed changes over the 1970-2000 period and projections of other global and regional land change models. © 2013 John Wiley & Sons Ltd.

Crystal morphology optimization of thiamine hydrochloride in solvent system: Experimental and molecular dynamics simulation studies

NASA Astrophysics Data System (ADS)

Yang, Yang; Han, Dandan; Du, Shichao; Wu, Songgu; Gong, Junbo

2018-01-01

Thiamine hydrochloride (THCL) was produced in methanol accompanied with agglomeration in industry, the plate like morphology of THCL in methanol was not deserve to have a good quality. Selecting a suitable solvent should be considered because solvent could be one of the essential factors to impact morphology. Methanol and methanol/ethyl acetate solvent (0.2 vol fraction of methanol) was selected as the solvent system in reactive crystallization of THCL. The experiment results show the THCL crystal morphology in methanol/ethyl acetate solvent system was granular and more regular than that in methanol. In order to explicate the different crystal morphology in different solvents, molecular dynamics (MD) simulation was introduced to simulate crystal morphology in different solvents. The attachment energy (AE) model was employed to investigate the morphology of THCL under vacuum conditions, methanol and methanol/ethyl acetate solvent conditions, respectively. The simulation crystal morphology was in a good agreement with that of experimented. The particle of THCL in methanol/ethyl acetate solvent has less tendency to agglomeration, and then it is favorable to the downstream process, such as filtration, storage and transportation.

Identifying a key physical factor sensitive to the performance of Madden-Julian oscillation simulation in climate models

NASA Astrophysics Data System (ADS)

Kim, Go-Un; Seo, Kyong-Hwan

2018-01-01

A key physical factor in regulating the performance of Madden-Julian oscillation (MJO) simulation is examined by using 26 climate model simulations from the World Meteorological Organization's Working Group for Numerical Experimentation/Global Energy and Water Cycle Experiment Atmospheric System Study (WGNE and MJO-Task Force/GASS) global model comparison project. For this, intraseasonal moisture budget equation is analyzed and a simple, efficient physical quantity is developed. The result shows that MJO skill is most sensitive to vertically integrated intraseasonal zonal wind convergence (ZC). In particular, a specific threshold value of the strength of the ZC can be used as distinguishing between good and poor models. An additional finding is that good models exhibit the correct simultaneous convection and large-scale circulation phase relationship. In poor models, however, the peak circulation response appears 3 days after peak rainfall, suggesting unfavorable coupling between convection and circulation. For an improving simulation of the MJO in climate models, we propose that this delay of circulation in response to convection needs to be corrected in the cumulus parameterization scheme.

Development of an advanced pitch active control system for a wide body jet aircraft

NASA Technical Reports Server (NTRS)

Guinn, Wiley A.; Rising, Jerry J.; Davis, Walt J.

1984-01-01

An advanced PACS control law was developed for a commercial wide-body transport (Lockheed L-1011) by using modern control theory. Validity of the control law was demonstrated by piloted flight simulation tests on the NASA Langley visual motion simulator. The PACS design objective was to develop a PACS that would provide good flying qualities to negative 10 percent static stability margins that were equivalent to those of the baseline aircraft at a 15 percent static stability margin which is normal for the L-1011. Also, the PACS was to compensate for high-Mach/high-g instabilities that degrade flying qualities during upset recoveries and maneuvers. The piloted flight simulation tests showed that the PACS met the design objectives. The simulation demonstrated good flying qualities to negative 20 percent static stability margins for hold, cruise and high-speed flight conditions. Analysis and wind tunnel tests performed on other Lockheed programs indicate that the PACS could be used on an advanced transport configuration to provide a 4 percent fuel savings which results from reduced trim drag by flying at negative static stability margins.

Cosmology with the cosmic web

NASA Astrophysics Data System (ADS)

Forero-Romero, J. E.

2017-07-01

This talk summarizes different algorithms that can be used to trace the cosmic web both in simulations and observations. We present different applications in galaxy formation and cosmology. To finalize, we show how the Dark Energy Spectroscopic Instrument (DESI) could be a good place to apply these techniques.

Variable Entry Biased Paracentric Hemispherical Deflector: Experimental results on energy resolution for different entry positions

NASA Astrophysics Data System (ADS)

Dogan, Mevlut; Ulu, Melike; Gennerakis, Giannis; Zouros, Theo J. M.

2014-04-01

A new hemispherical deflector analyzer (HDA) which is designed for electron energy analysis in atomic collisions has been constructed and tested. Using the crossed beam technique at the electron spectrometer, test measurements were performed for electron beam (200 eV) - Helium atoms interactions. These first experimental results show that the paracentric entries give almost twice as good resolution as that for the conventional entry. Supporting simulations of the entire lens+HDA spectrometer are found in relatively good agreement with experiment.

New beam monitoring tool for radiobiology experiments at the cyclotron ARRONAX.

PubMed

Schwob, L; Koumeir, C; Servagent, N; Cherel, M; Guertin, A; Haddad, F; Métivier, V; Michel, N; Poirier, F; Rahmani, A; Varmenot, N

2015-09-01

The ARRONAX cyclotron is able to deliver alpha particles at 68 MeV. In the frame of radiological research, a new method is studied to infer in situ the deposited dose: it is based on the online measurement of the bremsstrahlung (>1 keV) produced by the interaction of the incident particle with the medium. Experiments are made using bombarded poly(methyl methacrylate) (PMMA)-equivalent water targets in order to characterise this continuous X-ray spectrum. The intensity of the bremsstrahlung spectrum allows for the beam monitoring. A simulation code of the bremsstrahlung has been built, and a good agreement is found with the experimental spectra. With this simulation, it is possible to predict the sensibility of this method: it varies with the target thickness, showing a good sensibility for thin target (<1000 µm) and saturation for thicker ones. Bremsstrahlung spectrum also shows a sensibility on the target's chemical composition. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Designing Process Improvement of Finished Good On Time Release and Performance Indicator Tool in Milk Industry Using Business Process Reengineering Method

NASA Astrophysics Data System (ADS)

Dachyar, M.; Christy, E.

2014-04-01

To maintain position as a major milk producer, the Indonesian milk industry should do some business development with the purpose of increasing customer service level. One strategy is to create on time release conditions for finished goods which will be distributed to customers and distributors. To achieve this condition, management information systems of finished goods on time release needs to be improved. The focus of this research is to conduct business process improvement using Business Process Reengineering (BPR). The deliverable key of this study is a comprehensive business strategy which is the solution of the root problems. To achieve the goal, evaluation, reengineering, and improvement of the ERP system are conducted. To visualize the predicted implementation, a simulation model is built by Oracle BPM. The output of this simulation showed that the proposed solution could effectively reduce the process lead time and increase the number of quality releases.

A new design of an S/X dual band circular slot antenna for radar applications.

PubMed

Ghnimi, Said; Wali, Rawia; Gharsallh, Ali; Razban, Tchanguiz

2013-01-01

A novel design of dual-band slot antenna with a circular patch for radar applications is presented and studied. It is fed by a micro-strip line and built on a FR-4 substrate with a whole size of 18 x 30 mm2. A dual band printed antenna is created by introducing slots on the radiating element. By this, two bandwidth, covering C and X band, are achieved. In order to obtain a good fundamental antenna design, the initial studies were carried out theoretically, using CST Microwave Studio simulation software. In this case, the frequency range at return loss < 10 dB is 5.24 - 6.16 GHz for low frequency and is 7.9 -11.7 GHz for high frequency. In addition, the proposed antenna has good radiation characteristics and stable gains over the whole operating bands. A prototype of antenna is fabricated and tested. Experimental data show good agreement between simulated and measured results.

Artefacts in intracavitary temperature measurements during regional hyperthermia.

PubMed

Kok, H P; Van den Berg, C A T; Van Haaren, P M A; Crezee, J

2007-09-07

For adequate hyperthermia treatments, reliable temperature information during treatment is essential. During regional hyperthermia, temperature information is preferably obtained non-invasively from intracavitary or intraluminal measurements to avoid implant risks for the patient. However, for intracavitary or intraluminal thermometry optimal tissue contact is less natural as for invasive thermometry. In this study, the reliability of intraluminal/intracavitary measurements was examined in phantom experiments and in a numerical model for various extents of thermal contact between thermometry and the surroundings. Both thermocouple probes and fibre optic probes were investigated. Temperature rises after a 30 s power pulse of the 70 MHz AMC-4 hyperthermia system were measured in a tissue-equivalent phantom using a multisensor thermocouple probe placed centrally in a hollow tube. The tube was filled with (1) air, (2) distilled water or (3) saline solution that mimics the properties of tissue, simulating situations with (1) bad thermal contact and no power dissipation in the tube, (2) good thermal contact but no power dissipation or (3) good thermal contact and tissue representative power dissipation. For numerical simulations, a cylindrical symmetric model of a thermocouple probe or a fibre optic probe in a cavity was developed. The cavity was modelled as air, distilled water or saline solution. A generalised E-Field distribution was assumed, resulting in a power deposition. With this power deposition, the temperature rise after a 30 s power pulse was calculated. When thermal contact was bad (1), both phantom measurements and simulations with a thermocouple probe showed very high temperature rises (>0.5 degrees C), which are artefacts due to self-heating of the thermocouple probe, since no power is dissipated in air. Simulations with a fibre optic probe showed almost no temperature rise when the cavity was filled with air. When thermal contact was good, but no power was dissipated in the tube (2), artefacts due to self-heating were not significant and the observed temperature rises were very low ( approximately 0-0.1 degrees C). For the situation, with tissue representative power dissipation (3), a temperature rise of approximately 0.23 degrees C was observed for both measurements and simulations. A clinical example of a regional hyperthermia treatment of a patient with a cervix uteri carcinoma showed that the artefacts observed in the case of bad thermal contact also affect the steady-state temperature measurements. Good tissue contact must be assured for reliable intraluminal or intracavitary measurements.

Kinetics of transient electroluminescence in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Shukla, Manju; Kumar, Pankaj; Chand, Suresh; Brahme, Nameeta; Kher, R. S.; Khokhar, M. S. K.

2008-08-01

Mathematical simulation on the rise and decay kinetics of transient electroluminescence (EL) in organic light emitting diodes (OLEDs) is presented. The transient EL is studied with respect to a step voltage pulse. While rising, for lower values of time, the EL intensity shows a quadratic dependence on (t - tdel), where tdel is the time delay observed in the onset of EL, and finally attains saturation at a sufficiently large time. When the applied voltage is switched off, the initial EL decay shows an exponential dependence on (t - tdec), where tdec is the time when the voltage is switched off. The simulated results are compared with the transient EL performance of a bilayer OLED based on small molecular bis(2-methyl 8-hydroxyquinoline)(triphenyl siloxy) aluminium (SAlq). Transient EL studies have been carried out at different voltage pulse amplitudes. The simulated results show good agreement with experimental data. Using these simulated results the lifetime of the excitons in SAlq has also been calculated.

Deformation effect simulation and optimization for double front axle steering mechanism

NASA Astrophysics Data System (ADS)

Wu, Jungang; Zhang, Siqin; Yang, Qinglong

2013-03-01

This paper research on tire wear problem of heavy vehicles with Double Front Axle Steering Mechanism from the flexible effect of Steering Mechanism, and proposes a structural optimization method which use both traditional static structural theory and dynamic structure theory - Equivalent Static Load (ESL) method to optimize key parts. The good simulated and test results show this method has high engineering practice and reference value for tire wear problem of Double Front Axle Steering Mechanism design.

SWAT use of gridded observations for simulating runoff - a Vietnam river basin study

NASA Astrophysics Data System (ADS)

Vu, M. T.; Raghavan, S. V.; Liong, S. Y.

2012-08-01

Many research studies that focus on basin hydrology have applied the SWAT model using station data to simulate runoff. But over regions lacking robust station data, there is a problem of applying the model to study the hydrological responses. For some countries and remote areas, the rainfall data availability might be a constraint due to many different reasons such as lacking of technology, war time and financial limitation that lead to difficulty in constructing the runoff data. To overcome such a limitation, this research study uses some of the available globally gridded high resolution precipitation datasets to simulate runoff. Five popular gridded observation precipitation datasets: (1) Asian Precipitation Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources (APHRODITE), (2) Tropical Rainfall Measuring Mission (TRMM), (3) Precipitation Estimation from Remote Sensing Information using Artificial Neural Network (PERSIANN), (4) Global Precipitation Climatology Project (GPCP), (5) a modified version of Global Historical Climatology Network (GHCN2) and one reanalysis dataset, National Centers for Environment Prediction/National Center for Atmospheric Research (NCEP/NCAR) are used to simulate runoff over the Dak Bla river (a small tributary of the Mekong River) in Vietnam. Wherever possible, available station data are also used for comparison. Bilinear interpolation of these gridded datasets is used to input the precipitation data at the closest grid points to the station locations. Sensitivity Analysis and Auto-calibration are performed for the SWAT model. The Nash-Sutcliffe Efficiency (NSE) and Coefficient of Determination (R2) indices are used to benchmark the model performance. Results indicate that the APHRODITE dataset performed very well on a daily scale simulation of discharge having a good NSE of 0.54 and R2 of 0.55, when compared to the discharge simulation using station data (0.68 and 0.71). The GPCP proved to be the next best dataset that was applied to the runoff modelling, with NSE and R2 of 0.46 and 0.51, respectively. The PERSIANN and TRMM rainfall data driven runoff did not show good agreement compared to the station data as both the NSE and R2 indices showed a low value of 0.3. GHCN2 and NCEP also did not show good correlations. The varied results by using these datasets indicate that although the gauge based and satellite-gauge merged products use some ground truth data, the different interpolation techniques and merging algorithms could also be a source of uncertainties. This entails a good understanding of the response of the hydrological model to different datasets and a quantification of the uncertainties in these datasets. Such a methodology is also useful for planning on Rainfall-runoff and even reservoir/river management both at rural and urban scales.

Axisymmetric Plume Simulations with NASA's DSMC Analysis Code

NASA Technical Reports Server (NTRS)

Stewart, B. D.; Lumpkin, F. E., III

2012-01-01

A comparison of axisymmetric Direct Simulation Monte Carlo (DSMC) Analysis Code (DAC) results to analytic and Computational Fluid Dynamics (CFD) solutions in the near continuum regime and to 3D DAC solutions in the rarefied regime for expansion plumes into a vacuum is performed to investigate the validity of the newest DAC axisymmetric implementation. This new implementation, based on the standard DSMC axisymmetric approach where the representative molecules are allowed to move in all three dimensions but are rotated back to the plane of symmetry by the end of the move step, has been fully integrated into the 3D-based DAC code and therefore retains all of DAC s features, such as being able to compute flow over complex geometries and to model chemistry. Axisymmetric DAC results for a spherically symmetric isentropic expansion are in very good agreement with a source flow analytic solution in the continuum regime and show departure from equilibrium downstream of the estimated breakdown location. Axisymmetric density contours also compare favorably against CFD results for the R1E thruster while temperature contours depart from equilibrium very rapidly away from the estimated breakdown surface. Finally, axisymmetric and 3D DAC results are in very good agreement over the entire plume region and, as expected, this new axisymmetric implementation shows a significant reduction in computer resources required to achieve accurate simulations for this problem over the 3D simulations.

Determining team cognition from delay analysis using cross recurrence plot.

PubMed

Hajari, Nasim; Cheng, Irene; Bin Zheng; Basu, Anup

2016-08-01

Team cognition is an important factor in evaluating and determining team performance. Forming a team with good shared cognition is even more crucial for laparoscopic surgery applications. In this study, we analyzed the eye tracking data of two surgeons during a laparoscopic simulation operation, then performed Cross Recurrence Analysis (CRA) on the recorded data to study the delay behaviour for good performer and poor performer teams. Dual eye tracking data for twenty two dyad teams were recorded during a laparoscopic task and then the teams were divided into good performer and poor performer teams based on the task times. Eventually we studied the delay between two team members for good and poor performer teams. The results indicated that the good performer teams show a smaller delay comparing to poor performer teams. This study is compatible with gaze overlap analysis between team members and therefore it is a good evidence of shared cognition between team members.

Relativistic weak lensing from a fully non-linear cosmological density field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, D.B.; Bruni, M.; Wands, D., E-mail: thomas.daniel@ucy.ac.cy, E-mail: marco.bruni@port.ac.uk, E-mail: david.wands@port.ac.uk

2015-09-01

In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- andmore » B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.« less

Hard-sphere-like dynamics in highly concentrated alpha-crystallin suspensions

DOE PAGES

Vodnala, Preeti; Karunaratne, Nuwan; Lurio, Laurence; ...

2018-02-02

The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray photon correlation spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.

Hard-sphere-like dynamics in highly concentrated alpha-crystallin suspensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vodnala, Preeti; Karunaratne, Nuwan; Lurio, Laurence

The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray photon correlation spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.

Three axis electronic flight motion simulator real time control system design and implementation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Zhiyuan; Miao, Zhonghua, E-mail: zhonghua-miao@163.com; Wang, Xiaohua

2014-12-15

A three axis electronic flight motion simulator is reported in this paper including the modelling, the controller design as well as the hardware implementation. This flight motion simulator could be used for inertial navigation test and high precision inertial navigation system with good dynamic and static performances. A real time control system is designed, several control system implementation problems were solved including time unification with parallel port interrupt, high speed finding-zero method of rotary inductosyn, zero-crossing management with continuous rotary, etc. Tests were carried out to show the effectiveness of the proposed real time control system.

Hard-sphere-like dynamics in highly concentrated alpha-crystallin suspensions

NASA Astrophysics Data System (ADS)

Vodnala, Preeti; Karunaratne, Nuwan; Lurio, Laurence; Thurston, George M.; Vega, Michael; Gaillard, Elizabeth; Narayanan, Suresh; Sandy, Alec; Zhang, Qingteng; Dufresne, Eric M.; Foffi, Giuseppe; Grybos, Pawel; Kmon, Piotr; Maj, Piotr; Szczygiel, Robert

2018-02-01

The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray photon correlation spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f (q ,τ ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.

Three axis electronic flight motion simulator real time control system design and implementation.

PubMed

Gao, Zhiyuan; Miao, Zhonghua; Wang, Xuyong; Wang, Xiaohua

2014-12-01

A three axis electronic flight motion simulator is reported in this paper including the modelling, the controller design as well as the hardware implementation. This flight motion simulator could be used for inertial navigation test and high precision inertial navigation system with good dynamic and static performances. A real time control system is designed, several control system implementation problems were solved including time unification with parallel port interrupt, high speed finding-zero method of rotary inductosyn, zero-crossing management with continuous rotary, etc. Tests were carried out to show the effectiveness of the proposed real time control system.

The Application of Voltage Transformer Simulator in Electrical Test Training

NASA Astrophysics Data System (ADS)

Li, Nan; Zhang, Jun; Chai, Ziqi; Wang, Jingpeng; Yang, Baowei

2018-02-01

The voltage transformer test is an important means to monitor its operating state. The accuracy and reliability of the test data is directly related to the test skill level of the operator. However, the risk of test instruments damage, equipment being tested damage and electric shock in operator is caused by improper operation when training the transformer test. In this paper, a simulation device of voltage transformer is set up, and a simulation model is built for the most common 500kV capacitor voltage transformer (CVT), the simulation model can realize several test items of CVT by combing with teaching guidance platform, simulation instrument, complete set of system software and auxiliary equipment in Changchun. Many successful applications show that the simulation device has good practical value and wide application prospect.

Wargame Simulation Theory and Evaluation Method for Emergency Evacuation of Residents from Urban Waterlogging Disaster Area

PubMed Central

Chen, Peng; Zhang, Jiquan; Sun, Yingyue; Liu, Xiaojing

2016-01-01

Urban waterlogging seriously threatens the safety of urban residents and properties. Wargame simulation research on resident emergency evacuation from waterlogged areas can determine the effectiveness of emergency response plans for high risk events at low cost. Based on wargame theory and emergency evacuation plans, we used a wargame exercise method, incorporating qualitative and quantitative aspects, to build an urban waterlogging disaster emergency shelter using a wargame exercise and evaluation model. The simulation was empirically tested in Daoli District of Harbin. The results showed that the wargame simulation scored 96.40 points, evaluated as good. From the simulation results, wargame simulation of urban waterlogging emergency procedures for disaster response can improve the flexibility and capacity for command, management and decision-making in emergency management departments. PMID:28009805

Design of orbital debris shields for oblique hypervelocity impact

NASA Technical Reports Server (NTRS)

Fahrenthold, Eric P.

1994-01-01

A new impact debris propagation code was written to link CTH simulations of space debris shield perforation to the Lagrangian finite element code DYNA3D, for space structure wall impact simulations. This software (DC3D) simulates debris cloud evolution using a nonlinear elastic-plastic deformable particle dynamics model, and renders computationally tractable the supercomputer simulation of oblique impacts on Whipple shield protected structures. Comparison of three dimensional, oblique impact simulations with experimental data shows good agreement over a range of velocities of interest in the design of orbital debris shielding. Source code developed during this research is provided on the enclosed floppy disk. An abstract based on the work described was submitted to the 1994 Hypervelocity Impact Symposium.

Turbulence detection in a stenosed artery bifurcation by numerical simulation of pulsatile blood flow using the low-Reynolds number turbulence model.

PubMed

Ghalichi, Farzan; Deng, Xiaoyan

2003-01-01

The pulsatile blood flow in a partially blocked artery is significantly altered as the flow regime changes through the cardiac cycle. This paper reports on the application of a low-Reynolds turbulence model for computation of physiological pulsatile flow in a healthy and stenosed carotid artery bifurcation. The human carotid artery was chosen since it has received much attention because atherosclerotic lesions are frequently observed. The Wilcox low-Re k-omega turbulence model was used for the simulation since it has proven to be more accurate in describing transition from laminar to turbulent flow. Using the FIDAP finite element code a validation showed very good agreement between experimental and numerical results for a steady laminar to turbulent flow transition as reported in a previous publication by the same authors. Since no experimental or numerical results were available in the literature for a pulsatile and turbulent flow regime, a comparison between laminar and low-Re turbulent calculations was made to further validate the turbulence model. The results of this study showed a very good agreement for velocity profiles and wall shear stress values for this imposed pulsatile laminar flow regime. To explore further the medical aspect, the calculations showed that even in a healthy or non-stenosed artery, small instabilities could be found at least for a portion of the pulse cycle and in different sections. The 40% and 55% diameter reduction stenoses did not significantly change the turbulence characteristics. Further results showed that the presence of 75% stenoses changed the flow properties from laminar to turbulent flow for a good portion of the cardiac pulse. A full 3D simulation with this low-Re-turbulence model, coupled with Doppler ultrasound, can play a significant role in assessing the degree of stenosis for cardiac patients with mild conditions.

Wide-angle x-ray scattering and solid-state nuclear magnetic resonance data combined to test models for cellulose microfibrils in mung bean cell walls.

PubMed

Newman, Roger H; Hill, Stefan J; Harris, Philip J

2013-12-01

A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-β-glucan chains in cellulose microfibrils. Computer-simulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24- and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette.

Full Ka Band Waveguide-to-Microstrip Inline Transition Design

NASA Astrophysics Data System (ADS)

Li, Jianxing; Li, Lei; Qiao, Yu; Chen, Juan; Chen, Jianzhong; Zhang, Anxue

2018-05-01

In this paper, a compact and broadband inline waveguide-to-microstrip transition is proposed to cover the full Ka band. The transition can be segmented from the electric point of view into three building blocks, comprising a microstrip line to rectangular coaxial line, a wedged rectangular coaxial line to ridged waveguide, and a final tapered ridged waveguide impedance transformer to standard waveguide. Both good electrical performance and simple modular assembly without any soldering have been simultaneously obtained. The validation of the design concept has been conducted by numerical simulations and experimental measurements. The experimental results of a fabricated back-to-back transition prototype coincide with the simulated results. It shows that the proposed transition achieves good return loss of lower than 15.5 dB and low insertion loss with a fluctuation between 0.23 to 0.60 dB across the entire Ka band. Details of design considerations and operation mechanism as well as simulation and measurement results are presented.

Computer-based simulation of the Bielschowsky head-tilt test using the SEE++ software system.

PubMed

Kaltofen, Thomas; Buchberger, Michael; Priglinger, Siegfried

2008-01-01

Latest measurements of the vestibulo-ocular reflex (VOR) allowed the integration of the simulation of the Bielschowsky head-tilt test (BHTT) into the SEE++ software system. SEE++ realizes a biomechanical model of the human eye in order to simulate eye motility disorders and strabismus surgeries. With the addition of the BHTT it can now also be used for differential-diagnostic simulations of complex disorders (e.g., superior oblique palsies). In order to simulate the BHTT in SEE++, the user can freely choose the desired head-tilt angle from -45 degrees to +45 degrees. The chosen angle is shown in the 3D view with a human body model and is also used in the calculation of the Hess-Lancaster test. The integration of the BHTT offers an additional improvement of the possibilities for simulating eye motility disorders. Moreover, SEE++ allows the creation of a video of the "virtual patient" while tilting the head from one side to the other, which shows dynamic changes in the simulated Hess-diagrams. Comparisons of simulation results with patient-measured data showed a good correlation between the simulated and the measured data. Further comparisons with patient data are planned.

Three-dimensional microstructure simulation of Ni-based superalloy investment castings

NASA Astrophysics Data System (ADS)

Pan, Dong; Xu, Qingyan; Liu, Baicheng

2011-05-01

An integrated macro and micro multi-scale model for the three-dimensional microstructure simulation of Ni-based superalloy investment castings was developed, and applied to industrial castings to investigate grain evolution during solidification. A ray tracing method was used to deal with the complex heat radiation transfer. The microstructure evolution was simulated based on the Modified Cellular Automaton method, which was coupled with three-dimensional nested macro and micro grids. Experiments for Ni-based superalloy turbine wheel investment casting were carried out, which showed a good correspondence with the simulated results. It is indicated that the proposed model is able to predict the microstructure of the casting precisely, which provides a tool for the optimizing process.

Quadrature Moments Method for the Simulation of Turbulent Reactive Flows

NASA Technical Reports Server (NTRS)

Raman, Venkatramanan; Pitsch, Heinz; Fox, Rodney O.

2003-01-01

A sub-filter model for reactive flows, namely the DQMOM model, was formulated for Large Eddy Simulation (LES) using the filtered mass density function. Transport equations required to determine the location and size of the delta-peaks were then formulated for a 2-peak decomposition of the FDF. The DQMOM scheme was implemented in an existing structured-grid LES solver. Simulations of scalar shear layer using an experimental configuration showed that the first and second moments of both reactive and inert scalars are in good agreement with a conventional Lagrangian scheme that evolves the same FDF. Comparisons with LES simulations performed using laminar chemistry assumption for the reactive scalar show that the new method provides vast improvements at minimal computational cost. Currently, the DQMOM model is being implemented for use with the progress variable/mixture fraction model of Pierce. Comparisons with experimental results and LES simulations using a single-environment for the progress-variable are planned. Future studies will aim at understanding the effect of increase in environments on predictions.

The cost of conservative synchronization in parallel discrete event simulations

NASA Technical Reports Server (NTRS)

Nicol, David M.

1990-01-01

The performance of a synchronous conservative parallel discrete-event simulation protocol is analyzed. The class of simulation models considered is oriented around a physical domain and possesses a limited ability to predict future behavior. A stochastic model is used to show that as the volume of simulation activity in the model increases relative to a fixed architecture, the complexity of the average per-event overhead due to synchronization, event list manipulation, lookahead calculations, and processor idle time approach the complexity of the average per-event overhead of a serial simulation. The method is therefore within a constant factor of optimal. The analysis demonstrates that on large problems--those for which parallel processing is ideally suited--there is often enough parallel workload so that processors are not usually idle. The viability of the method is also demonstrated empirically, showing how good performance is achieved on large problems using a thirty-two node Intel iPSC/2 distributed memory multiprocessor.

Evaluating the Credibility of Transport Processes in the Global Modeling Initiative 3D Model Simulations of Ozone Recovery

NASA Technical Reports Server (NTRS)

Strahan, Susan E.; Douglass, Anne R.

2003-01-01

The Global Modeling Initiative has integrated two 35-year simulations of an ozone recovery scenario with an offline chemistry and transport model using two different meteorological inputs. Physically based diagnostics, derived from satellite and aircraft data sets, are described and then used to evaluate the realism of temperature and transport processes in the simulations. Processes evaluated include barrier formation in the subtropics and polar regions, and extratropical wave-driven transport. Some diagnostics are especially relevant to simulation of lower stratospheric ozone, but most are applicable to any stratospheric simulation. The temperature evaluation, which is relevant to gas phase chemical reactions, showed that both sets of meteorological fields have near climatological values at all latitudes and seasons at 30 hPa and below. Both simulations showed weakness in upper stratospheric wave driving. The simulation using input from a general circulation model (GMI(sub GCM)) showed a very good residual circulation in the tropics and northern hemisphere. The simulation with input from a data assimilation system (GMI(sub DAS)) performed better in the midlatitudes than at high latitudes. Neither simulation forms a realistic barrier at the vortex edge, leading to uncertainty in the fate of ozone-depleted vortex air. Overall, tracer transport in the offline GMI(sub GCM) has greater fidelity throughout the stratosphere than the GMI(sub DAS).

∆ E /∆ E Measurements of Energetic Ions Using CVD Diamond Detectors

DOE PAGES

Alghamdi, Ahmed; Heilbronn, Lawrence; Castellanos, Luis A.; ...

2018-06-20

Experimental and computational results of a Δ E /Δ E diamond detection system are presented. The Δ E /Δ E detection system was evaluated using energetic proton and iron beams striking thick polyethylene targets at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). The measured data for diamond sensor A show good agreement with the Geant4 simulation. In addition, simulations have demonstrated the ability to identify hydrogen isotopes using a diamond detection system.

∆ E /∆ E Measurements of Energetic Ions Using CVD Diamond Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alghamdi, Ahmed; Heilbronn, Lawrence; Castellanos, Luis A.

Experimental and computational results of a Δ E /Δ E diamond detection system are presented. The Δ E /Δ E detection system was evaluated using energetic proton and iron beams striking thick polyethylene targets at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). The measured data for diamond sensor A show good agreement with the Geant4 simulation. In addition, simulations have demonstrated the ability to identify hydrogen isotopes using a diamond detection system.

Orientation influence on grain size-effects in ultrafine-grained magnesium

DOE PAGES

Fan, Haidong; Aubry, Sylvie; Arsenlis, A.; ...

2014-11-08

The mechanical behavior of ultrafine-grained magnesium was studied by discrete dislocation dynamics (DDD) simulations. Our results show basal slip yields a strong size effect, while prismatic and pyramidal slips produce a weak one. We developed a new size-strength model that considers dislocation transmission across grain boundaries. Good agreement between this model, current DDD simulations and previous experiments is observed. These results reveal that the grain size effect depends on 3 factors: Peierls stress, dislocation source strength and grain boundary strength.

EFFECTS OF LASER RADIATION ON MATTER: Simulation of photon acceleration upon irradiation of a mylar target by femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Andreev, Stepan N.; Rukhadze, Anri A.; Tarakanov, V. P.; Yakutov, B. P.

2010-01-01

Acceleration of protons is simulated by the particle-in-cell (PIC) method upon irradiation of mylar targets of different thicknesses by femtosecond plane-polarised pulsed laser radiation and at different angles of radiation incidence on the target. The comparison of the results of calculations with the experimental data obtained in recent experiments shows their good agreement. The optimal angle of incidence (458) at which the proton energy achieves its absolute maximum is obtained.

Development of New Transferable Coarse-Grained Models of Hydrocarbons.

PubMed

An, Yaxin; Bejagam, Karteek K; Deshmukh, Sanket A

2018-06-21

We have utilized an approach that integrates molecular dynamics (MD) simulations with particle swarm optimization (PSO) to accelerate the development of coarse-grained (CG) models of hydrocarbons. Specifically, we have developed new transferable CG beads, which can be used to model the hydrocarbons (C5 to C17) and reproduce their experimental properties with good accuracy. Firstly, the PSO method was used to develop the CG beads of the decane model represented with 2:1 (2-2-2-2-2) mapping scheme. This was followed by the development of the nonane model described with hybrid 2-2-3-2, and 3:1 (3-3-3) mapping schemes. The force-field (FF) parameters for these three CG models were optimized to reproduce four experimentally observed properties including density, enthalpy of vaporization, surface tension, and self-diffusion coefficient at 300 K. The CG MD simulations conducted with these new CG models of decane and nonane, at different timesteps, for various system sizes, and at a range of different temperatures, were able to predict their density, enthalpy of vaporization, surface tension, self-diffusion coefficient, expansibility, and isothermal compressibility with a good accuracy. Moreover, comparison of structural features obtained from the CG MD simulations and the CG beads of mapped all-atom (AA) trajectories of decane and nonane showed very good agreement. To test the chemical transferability of these models, we have constructed the models for hydrocarbons ranging from pentane to heptadecane, by using different combination of the CG beads of decane and nonane. The properties of pentane to heptadecane predicted by these new CG models showed an excellent agreement with the experimental data.

Development of Viscoelastic Multi-Body Simulation and Impact Response Analysis of a Ballasted Railway Track under Cyclic Loading

PubMed Central

Nishiura, Daisuke; Sakaguchi, Hide; Aikawa, Akira

2017-01-01

Simulation of a large number of deformable bodies is often difficult because complex high-level modeling is required to address both multi-body contact and viscoelastic deformation. This necessitates the combined use of a discrete element method (DEM) and a finite element method (FEM). In this study, a quadruple discrete element method (QDEM) was developed for dynamic analysis of viscoelastic materials using a simpler algorithm compared to the standard FEM. QDEM easily incorporates the contact algorithm used in DEM. As the first step toward multi-body simulation, the fundamental performance of QDEM was investigated for viscoelastic analysis. The amplitude and frequency of cantilever elastic vibration were nearly equal to those obtained by the standard FEM. A comparison of creep recovery tests with an analytical solution showed good agreement between them. In addition, good correlation between the attenuation degree and the real physical viscosity was confirmed for viscoelastic vibration analysis. Therefore, the high accuracy of QDEM in the fundamental analysis of infinitesimal viscoelastic deformations was verified. Finally, the impact response of a ballast and sleeper under cyclic loading on a railway track was analyzed using QDEM as an application of deformable multi-body dynamics. The results showed that the vibration of the ballasted track was qualitatively in good agreement with the actual measurements. Moreover, the ballast layer with high friction reduced the ballasted track deterioration. This study suggests that QDEM, as an alternative to DEM and FEM, can provide deeper insights into the contact dynamics of a large number of deformable bodies. PMID:28772974

Development of Viscoelastic Multi-Body Simulation and Impact Response Analysis of a Ballasted Railway Track under Cyclic Loading.

PubMed

Nishiura, Daisuke; Sakaguchi, Hide; Aikawa, Akira

2017-06-03

Simulation of a large number of deformable bodies is often difficult because complex high-level modeling is required to address both multi-body contact and viscoelastic deformation. This necessitates the combined use of a discrete element method (DEM) and a finite element method (FEM). In this study, a quadruple discrete element method (QDEM) was developed for dynamic analysis of viscoelastic materials using a simpler algorithm compared to the standard FEM. QDEM easily incorporates the contact algorithm used in DEM. As the first step toward multi-body simulation, the fundamental performance of QDEM was investigated for viscoelastic analysis. The amplitude and frequency of cantilever elastic vibration were nearly equal to those obtained by the standard FEM. A comparison of creep recovery tests with an analytical solution showed good agreement between them. In addition, good correlation between the attenuation degree and the real physical viscosity was confirmed for viscoelastic vibration analysis. Therefore, the high accuracy of QDEM in the fundamental analysis of infinitesimal viscoelastic deformations was verified. Finally, the impact response of a ballast and sleeper under cyclic loading on a railway track was analyzed using QDEM as an application of deformable multi-body dynamics. The results showed that the vibration of the ballasted track was qualitatively in good agreement with the actual measurements. Moreover, the ballast layer with high friction reduced the ballasted track deterioration. This study suggests that QDEM, as an alternative to DEM and FEM, can provide deeper insights into the contact dynamics of a large number of deformable bodies.

An integrated assessment modeling framework for uncertainty studies in global and regional climate change: the MIT IGSM-CAM (version 1.0)

NASA Astrophysics Data System (ADS)

Monier, E.; Scott, J. R.; Sokolov, A. P.; Forest, C. E.; Schlosser, C. A.

2013-12-01

This paper describes a computationally efficient framework for uncertainty studies in global and regional climate change. In this framework, the Massachusetts Institute of Technology (MIT) Integrated Global System Model (IGSM), an integrated assessment model that couples an Earth system model of intermediate complexity to a human activity model, is linked to the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM). Since the MIT IGSM-CAM framework (version 1.0) incorporates a human activity model, it is possible to analyze uncertainties in emissions resulting from both uncertainties in the underlying socio-economic characteristics of the economic model and in the choice of climate-related policies. Another major feature is the flexibility to vary key climate parameters controlling the climate system response to changes in greenhouse gases and aerosols concentrations, e.g., climate sensitivity, ocean heat uptake rate, and strength of the aerosol forcing. The IGSM-CAM is not only able to realistically simulate the present-day mean climate and the observed trends at the global and continental scale, but it also simulates ENSO variability with realistic time scales, seasonality and patterns of SST anomalies, albeit with stronger magnitudes than observed. The IGSM-CAM shares the same general strengths and limitations as the Coupled Model Intercomparison Project Phase 3 (CMIP3) models in simulating present-day annual mean surface temperature and precipitation. Over land, the IGSM-CAM shows similar biases to the NCAR Community Climate System Model (CCSM) version 3, which shares the same atmospheric model. This study also presents 21st century simulations based on two emissions scenarios (unconstrained scenario and stabilization scenario at 660 ppm CO2-equivalent) similar to, respectively, the Representative Concentration Pathways RCP8.5 and RCP4.5 scenarios, and three sets of climate parameters. Results of the simulations with the chosen climate parameters provide a good approximation for the median, and the 5th and 95th percentiles of the probability distribution of 21st century changes in global mean surface air temperature from previous work with the IGSM. Because the IGSM-CAM framework only considers one particular climate model, it cannot be used to assess the structural modeling uncertainty arising from differences in the parameterization suites of climate models. However, comparison of the IGSM-CAM projections with simulations of 31 CMIP5 models under the RCP4.5 and RCP8.5 scenarios show that the range of warming at the continental scale shows very good agreement between the two ensemble simulations, except over Antarctica, where the IGSM-CAM overestimates the warming. This demonstrates that by sampling the climate system response, the IGSM-CAM, even though it relies on one single climate model, can essentially reproduce the range of future continental warming simulated by more than 30 different models. Precipitation changes projected in the IGSM-CAM simulations and the CMIP5 multi-model ensemble both display a large uncertainty at the continental scale. The two ensemble simulations show good agreement over Asia and Europe. However, the ranges of precipitation changes do not overlap - but display similar size - over Africa and South America, two continents where models generally show little agreement in the sign of precipitation changes and where CCSM3 tends to be an outlier. Overall, the IGSM-CAM provides an efficient and consistent framework to explore the large uncertainty in future projections of global and regional climate change associated with uncertainty in the climate response and projected emissions.

A multimedia fate and chemical transport modeling system for pesticides: II. Model evaluation

NASA Astrophysics Data System (ADS)

Li, Rong; Scholtz, M. Trevor; Yang, Fuquan; Sloan, James J.

2011-07-01

Pesticides have adverse health effects and can be transported over long distances to contaminate sensitive ecosystems. To address problems caused by environmental pesticides we developed a multimedia multi-pollutant modeling system, and here we present an evaluation of the model by comparing modeled results against measurements. The modeled toxaphene air concentrations for two sites, in Louisiana (LA) and Michigan (MI), are in good agreement with measurements (average concentrations agree to within a factor of 2). Because the residue inventory showed no soil residues at these two sites, resulting in no emissions, the concentrations must be caused by transport; the good agreement between the modeled and measured concentrations suggests that the model simulates atmospheric transport accurately. Compared to the LA and MI sites, the measured air concentrations at two other sites having toxaphene soil residues leading to emissions, in Indiana and Arkansas, showed more pronounced seasonal variability (higher in warmer months); this pattern was also captured by the model. The model-predicted toxaphene concentration fraction on particles (0.5-5%) agrees well with measurement-based estimates (3% or 6%). There is also good agreement between modeled and measured dry (1:1) and wet (within a factor of less than 2) depositions in Lake Ontario. Additionally this study identified erroneous soil residue data around a site in Texas in a published US toxaphene residue inventory, which led to very low modeled air concentrations at this site. Except for the erroneous soil residue data around this site, the good agreement between the modeled and observed results implies that both the US and Mexican toxaphene soil residue inventories are reasonably good. This agreement also suggests that the modeling system is capable of simulating the important physical and chemical processes in the multimedia compartments.

Comparison of CFD simulations to non-rotating MEXICO blades experiment in the LTT wind tunnel of TUDelft

NASA Astrophysics Data System (ADS)

Zhang, Ye; van Zuijlen, Alexander; van Bussel, Gerard

2014-06-01

In this paper, three dimensional flow over non-rotating MEXICO blades is simulated by CFD methods. The numerical results are compared with the latest MEXICO wind turbine blades measurements obtained in the low speed low turbulence (LTT) wind tunnel of Delft University of Technology. This study aims to validate CFD codes by using these experimental data measured in well controlled conditions. In order to avoid use of wind tunnel corrections, both the blades and the wind tunnel test section are modelled in the simulations. The ability of Menter's k - ω shear stress transport (SST) turbulence model is investigated at both attached flow and massively separated flow cases. Steady state Reynolds averaged Navier Stokes (RANS) equations are solved in these computations. The pressure distribution at three measured sections are compared under the conditions of different inflow velocities and a range of angles of attack. The comparison shows that at attached flow condition, good agreement can be obtained for all three airfoil sections. Even with massively separated flow, still fairly good pressure distribution comparison can be found for the DU and NACA airfoil sections, although the RISØ section shows poor comparison. At the near stall case, considerable deviations exists on the forward half part of the upper surface for all three sections.

Longitudinal train dynamics: an overview

NASA Astrophysics Data System (ADS)

Wu, Qing; Spiryagin, Maksym; Cole, Colin

2016-12-01

This paper discusses the evolution of longitudinal train dynamics (LTD) simulations, which covers numerical solvers, vehicle connection systems, air brake systems, wagon dumper systems and locomotives, resistance forces and gravitational components, vehicle in-train instabilities, and computing schemes. A number of potential research topics are suggested, such as modelling of friction, polymer, and transition characteristics for vehicle connection simulations, studies of wagon dumping operations, proper modelling of vehicle in-train instabilities, and computing schemes for LTD simulations. Evidence shows that LTD simulations have evolved with computing capabilities. Currently, advanced component models that directly describe the working principles of the operation of air brake systems, vehicle connection systems, and traction systems are available. Parallel computing is a good solution to combine and simulate all these advanced models. Parallel computing can also be used to conduct three-dimensional long train dynamics simulations.

Study of the effect of loop inductance on the RF transmission line to cavity coupling coefficient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lal, Shankar, E-mail: shankar@rrcat.gov.in; Pant, K. K.

2016-08-15

Coupling of RF power is an important aspect in the design and development of RF accelerating structures. RF power coupling employing coupler loops has the advantage of tunability of β, the transmission line to cavity coupling coefficient. Analytical expressions available in literature for determination of size of the coupler loop using Faraday’s law of induction show reasonably good agreement with experimentally measured values of β below critical coupling (β ≤ 1) but show large deviation with experimentally measured values and predictions by simulations for higher values of β. In actual accelerator application, many RF cavities need to be over-coupled withmore » β > 1 for reasons of beam loading compensation, reduction of cavity filling time, etc. This paper discusses a modified analytical formulation by including the effect of loop inductance in the determination of loop size for any desired coupling coefficient. The analytical formulation shows good agreement with 3D simulations and with experimentally measured values. It has been successfully qualified by the design and development of power coupler loops for two 476 MHz pre-buncher RF cavities, which have successfully been conditioned at rated power levels using these coupler loops.« less

Study of the effect of loop inductance on the RF transmission line to cavity coupling coefficient

NASA Astrophysics Data System (ADS)

Lal, Shankar; Pant, K. K.

2016-08-01

Coupling of RF power is an important aspect in the design and development of RF accelerating structures. RF power coupling employing coupler loops has the advantage of tunability of β, the transmission line to cavity coupling coefficient. Analytical expressions available in literature for determination of size of the coupler loop using Faraday's law of induction show reasonably good agreement with experimentally measured values of β below critical coupling (β ≤ 1) but show large deviation with experimentally measured values and predictions by simulations for higher values of β. In actual accelerator application, many RF cavities need to be over-coupled with β > 1 for reasons of beam loading compensation, reduction of cavity filling time, etc. This paper discusses a modified analytical formulation by including the effect of loop inductance in the determination of loop size for any desired coupling coefficient. The analytical formulation shows good agreement with 3D simulations and with experimentally measured values. It has been successfully qualified by the design and development of power coupler loops for two 476 MHz pre-buncher RF cavities, which have successfully been conditioned at rated power levels using these coupler loops.

A Numerical Analysis of Heat Transfer and Effectiveness on Film Cooled Turbine Blade Tip Models

NASA Technical Reports Server (NTRS)

Ameri, A. A.; Rigby, D. L.

1999-01-01

A computational study has been performed to predict the distribution of convective heat transfer coefficient on a simulated blade tip with cooling holes. The purpose of the examination was to assess the ability of a three-dimensional Reynolds-averaged Navier-Stokes solver to predict the rate of tip heat transfer and the distribution of cooling effectiveness. To this end, the simulation of tip clearance flow with blowing of Kim and Metzger was used. The agreement of the computed effectiveness with the data was quite good. The agreement with the heat transfer coefficient was not as good but improved away from the cooling holes. Numerical flow visualization showed that the uniformity of wetting of the surface by the film cooling jet is helped by the reverse flow due to edge separation of the main flow.

Emergence of Scale-Free Leadership Structure in Social Recommender Systems

PubMed Central

Zhou, Tao; Medo, Matúš; Cimini, Giulio; Zhang, Zi-Ke; Zhang, Yi-Cheng

2011-01-01

The study of the organization of social networks is important for the understanding of opinion formation, rumor spreading, and the emergence of trends and fashion. This paper reports empirical analysis of networks extracted from four leading sites with social functionality (Delicious, Flickr, Twitter and YouTube) and shows that they all display a scale-free leadership structure. To reproduce this feature, we propose an adaptive network model driven by social recommending. Artificial agent-based simulations of this model highlight a “good get richer” mechanism where users with broad interests and good judgments are likely to become popular leaders for the others. Simulations also indicate that the studied social recommendation mechanism can gradually improve the user experience by adapting to tastes of its users. Finally we outline implications for real online resource-sharing systems. PMID:21857891

Reflection spectra of etched FBGs under the influence of axial contraction and stress-induced index change.

PubMed

Yang, Hang-Zhou; Lim, Kok-Sing; Qiao, Xue-Guang; Chong, Wu-Yi; Cheong, Yew-Ken; Lim, Weng-Hong; Lim, Wei-Sin; Ahmad, Harith

2013-06-17

We present a new theoretical model for the broadband reflection spectra of etched FBGs which includes the effects of axial contraction and stress-induced index change. The reflection spectra of the etched FBGs with several different taper profiles are simulated based on the proposed model. In our observation, decaying exponential profile produces a broadband reflection spectrum with good uniformity over the range of 1540-1560 nm. An etched FBG with similar taper profile is fabricated and the experimental result shows good agreement with the theoretical model.

Application of Improved APO Algorithm in Vulnerability Assessment and Reconstruction of Microgrid

NASA Astrophysics Data System (ADS)

Xie, Jili; Ma, Hailing

2018-01-01

Artificial Physics Optimization (APO) has good global search ability and can avoid the premature convergence phenomenon in PSO algorithm, which has good stability of fast convergence and robustness. On the basis of APO of the vector model, a reactive power optimization algorithm based on improved APO algorithm is proposed for the static structure and dynamic operation characteristics of microgrid. The simulation test is carried out through the IEEE 30-bus system and the result shows that the algorithm has better efficiency and accuracy compared with other optimization algorithms.

Fabrication and evaluation of novel rabbit model cardiovascular simulator with 3D printer

NASA Astrophysics Data System (ADS)

Jang, Min; Lee, Min-Woo; Seo, See-Yoon; Shin, Sang-Hoon

2017-03-01

Simulators allow researchers to study the hemodynamics of the cardiovascular system in a reproducible way without using complicated equations. Previous simulators focused on heart functions. However, a detailed model of the vessels is required to replicate the pulse wave of the arterial system. A computer simulation was used to simplify the arterial branch because producing every small artery is neither possible nor necessary. A 3D-printed zig was used to make a hand-made arterial tree. The simulator that was developed was evaluated by comparing its results to in-vivo data, in terms of the hemodynamic parameters (waveform, augmentation index, impedance, etc.) that were measured at three points: the ascending aorta, the thoracic aorta, and the brachiocephalic artery. The results from the simulator showed good agreement with the in-vivo data. Therefore, this simulator can be used as a research tool for the cardiovascular study of animal models, specifically rabbits.

Ionospheric Trend Over Wuhan During 1947-2017: Comparison Between Simulation and Observation

NASA Astrophysics Data System (ADS)

Yue, Xinan; Hu, Lianhuan; Wei, Yong; Wan, Weixing; Ning, Baiqi

2018-02-01

Since Roble and Dickinson (1989), who drew the community's attention about the greenhouse gas effect on the ionosphere, huge efforts have been implemented on ionospheric climate study. However, direct comparison between observations and simulations is still rare. Recently, the Wuhan ionosonde observations were digitized and standardized through unified method back to 1947. In this study, the NCAR-TIEGCM was driven by Mauna Loa Observatory observed CO2 level and International Geomagnetic Reference Field (IGRF) geomagnetic field to simulate their effects on ionospheric long-term trend over Wuhan. Only March equinox was considered in both data analysis and simulation. Simulation results show that the CO2 and geomagnetic field have comparable effect on hmF2 trend, while geomagnetic field effect is stronger than CO2 on foF2 trend over Wuhan. Both factors result in obvious but different diurnal variations of foF2/hmF2 long-term trends. The geomagnetic field effect is nonlinear versus years since the long-term variation of geomagnetic field intensity and orientation is complex. Mean value of foF2 and hmF2 trend is (-0.0021 MHz/yr, -0.106 km/yr) and (-0.0022 MHz/yr, -0.0763 km/yr) for observation and simulation, respectively. Regarding the diurnal variation of the trend, the simulation accords well with that of observation except hmF2 results around 12 UT. Overall, good agreement between observation and simulation illustrates the good quality of Wuhan ionosonde long-term data and the validity of ancient ionosphere reconstruction based on realistic indices driving simulation.

Coniferous canopy BRF simulation based on 3-D realistic scene.

PubMed

Wang, Xin-Yun; Guo, Zhi-Feng; Qin, Wen-Han; Sun, Guo-Qing

2011-09-01

It is difficulties for the computer simulation method to study radiation regime at large-scale. Simplified coniferous model was investigated in the present study. It makes the computer simulation methods such as L-systems and radiosity-graphics combined method (RGM) more powerful in remote sensing of heterogeneous coniferous forests over a large-scale region. L-systems is applied to render 3-D coniferous forest scenarios, and RGM model was used to calculate BRF (bidirectional reflectance factor) in visible and near-infrared regions. Results in this study show that in most cases both agreed well. Meanwhile at a tree and forest level, the results are also good.

Coniferous Canopy BRF Simulation Based on 3-D Realistic Scene

NASA Technical Reports Server (NTRS)

Wang, Xin-yun; Guo, Zhi-feng; Qin, Wen-han; Sun, Guo-qing

2011-01-01

It is difficulties for the computer simulation method to study radiation regime at large-scale. Simplified coniferous model was investigate d in the present study. It makes the computer simulation methods such as L-systems and radiosity-graphics combined method (RGM) more powerf ul in remote sensing of heterogeneous coniferous forests over a large -scale region. L-systems is applied to render 3-D coniferous forest scenarios: and RGM model was used to calculate BRF (bidirectional refle ctance factor) in visible and near-infrared regions. Results in this study show that in most cases both agreed well. Meanwhiie at a tree and forest level. the results are also good.

Wind energy system time-domain (WEST) analyzers

NASA Technical Reports Server (NTRS)

Dreier, M. E.; Hoffman, J. A.

1981-01-01

A portable analyzer which simulates in real time the complex nonlinear dynamics of horizontal axis wind energy systems was constructed. Math models for an aeroelastic rotor featuring nonlinear aerodynamic and inertial terms were implemented with high speed digital controllers and analog calculation. This model was combined with other math models of elastic supports, control systems, a power train and gimballed rotor kinematics. A stroboscopic display system graphically depicting distributed blade loads, motion, and other aerodynamic functions on a cathode ray tube is included. Limited correlation efforts showed good comparison between the results of this analyzer and other sophisticated digital simulations. The digital simulation results were successfully correlated with test data.

Experimental verification and simulation of negative index of refraction using Snell's law.

PubMed

Parazzoli, C G; Greegor, R B; Li, K; Koltenbah, B E C; Tanielian, M

2003-03-14

We report the results of a Snell's law experiment on a negative index of refraction material in free space from 12.6 to 13.2 GHz. Numerical simulations using Maxwell's equations solvers show good agreement with the experimental results, confirming the existence of negative index of refraction materials. The index of refraction is a function of frequency. At 12.6 GHz we measure and compute the real part of the index of refraction to be -1.05. The measurements and simulations of the electromagnetic field profiles were performed at distances of 14lambda and 28lambda from the sample; the fields were also computed at 100lambda.

Finite element simulation of thunderstorm electrodynamics in the proximity of the storm

NASA Technical Reports Server (NTRS)

Baginski, Michael Edward

1988-01-01

Observations of electric fields, Maxwell current density, and air conductivity over thunderstorms were presented. The measurements were obtained using electric field mils and conductivity probes installed on a U2 aircraft as the aircraft passed approximately directly over an active thunderstorm at an altitude of 18 to 20 km. Accurate electrical observations of this type are rare and provide important information to those involved in numerically modeling a thunderstorm. A preliminary set of computer simulations based on this data were conducted and are described. The simulations show good agreement with measurements and are used to infer the thundercloud's charging current and amount of charge exchanged per flash.

magnum.fe: A micromagnetic finite-element simulation code based on FEniCS

NASA Astrophysics Data System (ADS)

Abert, Claas; Exl, Lukas; Bruckner, Florian; Drews, André; Suess, Dieter

2013-11-01

We have developed a finite-element micromagnetic simulation code based on the FEniCS package called magnum.fe. Here we describe the numerical methods that are applied as well as their implementation with FEniCS. We apply a transformation method for the solution of the demagnetization-field problem. A semi-implicit weak formulation is used for the integration of the Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of simulation results. magnum.fe is open source and well documented. The broad feature range of the FEniCS package makes magnum.fe a good choice for the implementation of novel micromagnetic finite-element algorithms.

Improved simulation method of automotive spot weld failure with an account of the mechanical properties of spot welds

NASA Astrophysics Data System (ADS)

Wu, H.; Meng, X. M.; Fang, R.; Huang, Y. F.; Zhan, S.

2017-12-01

In this paper, the microstructure and mechanical properties of spot weld were studied, the hardness of nugget and heat affected zone (HAZ) were also tested by metallographic microscope and microhardness tester. The strength of the spot weld with the different parts' area has been characterized. According to the experiments result, CAE model of spot weld with HAZ structure was established, and simulation results of different lap-shear CAE models were analyzed. The results show that the spot weld model which contained the HAZ has good performance and more suitable for engineering application in spot weld simulation.

A Wsbnd Ne interatomic potential for simulation of neon implantation in tungsten

NASA Astrophysics Data System (ADS)

Backman, Marie; Juslin, Niklas; Huang, Guiyang; Wirth, Brian D.

2016-08-01

An interatomic pair potential for Wsbnd Ne is developed for atomistic molecular dynamics simulations of neon implantation in tungsten. The new potential predicts point defect energies and binding energies of small clusters that are in good agreement with electronic structure calculations. Molecular dynamics simulations of small neon clusters in tungsten show that trap mutation, in which an interstitial neon cluster displaces a tungsten atom from its lattice site, occurs for clusters of three or more neon atoms. However, near a free surface, trap mutation can occur at smaller sizes, including even a single neon interstitial in close proximity to a (100) or (110) surface.

Optimum Design of Anti-Siphon Device used to Prevent Cerebrospinal Fluid from Overdraining

NASA Astrophysics Data System (ADS)

Jang, Jong Yun; Lee, Chong Sun; Suh, Chang Min

The present study investigated design parameters of an anti-siphon device used with shunt valves to treat patients with hydrocephalus. Structural analyses were performed to understand roles of design variables and optimize performance of the diaphragm-type anti-siphon device (hereafter referred to as the ASD). Experiments were performed on the lab-made product and showed good agreements with the numerical simulations. Using the simulations, we were able to design a more physiological ASD which gave equal opening pressures in both supine and upright postures. Tissue encapsulization phenomenon was also simulated and the results indicated underdrainage of CSF in the upright position of the patient.

Radial density distribution of a warm dense plasma formed by underwater electrical explosion of a copper wire

NASA Astrophysics Data System (ADS)

Nitishinskiy, M.; Yanuka, D.; Virozub, A.; Krasik, Ya. E.

2017-12-01

Time- and space-resolved evolution of the density (down to 0.07 of solid state density) of a copper wire during its microsecond timescale electrical explosion in water was obtained by X-ray backlighting. In the present research, a flash X-ray source of 20 ns pulse-width and >60 keV photon energy was used. The conductivity of copper was evaluated for a temperature of 10 kK and found to be in good agreement with the data obtained in earlier experiments [DeSilva and Katsouros, Phys. Rev. E 57, 5945 (1998) and Sheftman and Krasik, Phys. Plasmas 18, 092704 (2011)] where only electrical and optical diagnostics were applied. Magneto-hydrodynamic simulation shows a good agreement between the simulated and experimental waveforms of the current and voltage and measured the radial expansion of the exploding wire. Also, the radial density distribution obtained by an inverse Abel transform analysis agrees with the results of these simulations. Thus, the validity of the equations of state for copper and the conductivity model used in the simulations was confirmed for the parameters of the exploding wire realized in the present research.

Accuracy of Estimating Solar Radiation Pressure for GEO Debris with Tumbling Effect

NASA Astrophysics Data System (ADS)

Chao, Chia-Chun George

2009-03-01

The accuracy of estimating solar radiation pressure for GEO debris is examined and demonstrated, via numerical simulations, by fitting a batch (months) of simulated position vectors. These simulated position vectors are generated from a "truth orbit" with added white noise using high-precision numerical integration tools. After the long-arc fit of the simulated observations (position vectors), one can accurately and reliably determine how close the estimated value of solar radiation pressure is to the truth. Results of this study show that the inherent accuracy in estimating the solar radiation pressure coefficient can be as good as 1% if a long-arc fit span up to 180 days is used and the satellite is not tumbling. The corresponding position prediction accuracy can be as good as, in maximum error, 1 km along in-track, 0.3 km along radial and 0.1 km along cross-track up to 30 days. Similar accuracies can be expected when the object is tumbling as long as the rate of attitude change is different from the orbit rate. Results of this study reveal an important phenomenon that the solar radiation pressure significantly affects the orbit motion when the spin rate is equal to the orbit rate.

Gas adsorption in Mg-porphyrin-based porous organic frameworks: A computational simulation by first-principles derived force field.

PubMed

Pang, Yujia; Li, Wenliang; Zhang, Jingping

2017-09-15

A novel type of porous organic frameworks, based on Mg-porphyrin, with diamond-like topology, named POF-Mgs is computationally designed, and the gas uptakes of CO 2 , H 2 , N 2 , and H 2 O in POF-Mgs are investigated by Grand canonical Monte Carlo simulations based on first-principles derived force fields (FF). The FF, which describes the interactions between POF-Mgs and gases, are fitted by dispersion corrected double-hybrid density functional theory, B2PLYP-D3. The good agreement between the obtained FF and the first-principle energies data confirms the reliability of the FF. Furthermore our simulation shows the presence of a small amount of H 2 O (≤ 0.01 kPa) does not much affect the adsorption quantity of CO 2 , but the presence of higher partial pressure of H 2 O (≥ 0.1 kPa) results in the CO 2 adsorption decrease significantly. The good performance of POF-Mgs in the simulation inspires us to design novel porous materials experimentally for gas adsorption and purification. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Numerical modeling of separated flows at moderate Reynolds numbers appropriate for turbine blades and unmanned aero vehicles

NASA Astrophysics Data System (ADS)

Castiglioni, Giacomo

Flows over airfoils and blades in rotating machinery, for unmanned and micro-aerial vehicles, wind turbines, and propellers consist of a laminar boundary layer near the leading edge that is often followed by a laminar separation bubble and transition to turbulence further downstream. Typical Reynolds averaged Navier-Stokes turbulence models are inadequate for such flows. Direct numerical simulation is the most reliable, but is also the most computationally expensive alternative. This work assesses the capability of immersed boundary methods and large eddy simulations to reduce the computational requirements for such flows and still provide high quality results. Two-dimensional and three-dimensional simulations of a laminar separation bubble on a NACA-0012 airfoil at Rec = 5x104 and at 5° of incidence have been performed with an immersed boundary code and a commercial code using body fitted grids. Several sub-grid scale models have been implemented in both codes and their performance evaluated. For the two-dimensional simulations with the immersed boundary method the results show good agreement with the direct numerical simulation benchmark data for the pressure coefficient Cp and the friction coefficient Cf, but only when using dissipative numerical schemes. There is evidence that this behavior can be attributed to the ability of dissipative schemes to damp numerical noise coming from the immersed boundary. For the three-dimensional simulations the results show a good prediction of the separation point, but an inaccurate prediction of the reattachment point unless full direct numerical simulation resolution is used. The commercial code shows good agreement with the direct numerical simulation benchmark data in both two and three-dimensional simulations, but the presence of significant, unquantified numerical dissipation prevents a conclusive assessment of the actual prediction capabilities of very coarse large eddy simulations with low order schemes in general cases. Additionally, a two-dimensional sweep of angles of attack from 0° to 5° is performed showing a qualitative prediction of the jump in lift and drag coefficients due to the appearance of the laminar separation bubble. The numerical dissipation inhibits the predictive capabilities of large eddy simulations whenever it is of the same order of magnitude or larger than the sub-grid scale dissipation. The need to estimate the numerical dissipation is most pressing for low-order methods employed by commercial computational fluid dynamics codes. Following the recent work of Schranner et al., the equations and procedure for estimating the numerical dissipation rate and the numerical viscosity in a commercial code are presented. The method allows for the computation of the numerical dissipation rate and numerical viscosity in the physical space for arbitrary sub-domains in a self-consistent way, using only information provided by the code in question. The method is first tested for a three-dimensional Taylor-Green vortex flow in a simple cubic domain and compared with benchmark results obtained using an accurate, incompressible spectral solver. Afterwards the same procedure is applied for the first time to a realistic flow configuration, specifically to the above discussed laminar separation bubble flow over a NACA 0012 airfoil. The method appears to be quite robust and its application reveals that for the code and the flow in question the numerical dissipation can be significantly larger than the viscous dissipation or the dissipation of the classical Smagorinsky sub-grid scale model, confirming the previously qualitative finding.

Nonlinear state-space modelling of the kinematics of an oscillating circular cylinder in a fluid flow

NASA Astrophysics Data System (ADS)

Decuyper, J.; De Troyer, T.; Runacres, M. C.; Tiels, K.; Schoukens, J.

2018-01-01

The flow-induced vibration of bluff bodies is an important problem of many marine, civil, or mechanical engineers. In the design phase of such structures, it is vital to obtain good predictions of the fluid forces acting on the structure. Current methods rely on computational fluid dynamic simulations (CFD), with a too high computational cost to be effectively used in the design phase or for control applications. Alternative methods use heuristic mathematical models of the fluid forces, but these lack the accuracy (they often assume the system to be linear) or flexibility to be useful over a wide operating range. In this work we show that it is possible to build an accurate, flexible and low-computational-cost mathematical model using nonlinear system identification techniques. This model is data driven: it is trained over a user-defined region of interest using data obtained from experiments or simulations, or both. Here we use a Van der Pol oscillator as well as CFD simulations of an oscillating circular cylinder to generate the training data. Then a discrete-time polynomial nonlinear state-space model is fit to the data. This model relates the oscillation of the cylinder to the force that the fluid exerts on the cylinder. The model is finally validated over a wide range of oscillation frequencies and amplitudes, both inside and outside the so-called lock-in region. We show that forces simulated by the model are in good agreement with the data obtained from CFD.

The importance of plume rise on the concentrations and atmospheric impacts of biomass burning aerosol

NASA Astrophysics Data System (ADS)

Walter, Carolin; Freitas, Saulo R.; Kottmeier, Christoph; Kraut, Isabel; Rieger, Daniel; Vogel, Heike; Vogel, Bernhard

2016-07-01

We quantified the effects of the plume rise of biomass burning aerosol and gases for the forest fires that occurred in Saskatchewan, Canada, in July 2010. For this purpose, simulations with different assumptions regarding the plume rise and the vertical distribution of the emissions were conducted. Based on comparisons with observations, applying a one-dimensional plume rise model to predict the injection layer in combination with a parametrization of the vertical distribution of the emissions outperforms approaches in which the plume heights are initially predefined. Approximately 30 % of the fires exceed the height of 2 km with a maximum height of 8.6 km. Using this plume rise model, comparisons with satellite images in the visible spectral range show a very good agreement between the simulated and observed spatial distributions of the biomass burning plume. The simulated aerosol optical depth (AOD) with data of an AERONET station is in good agreement with respect to the absolute values and the timing of the maximum. Comparison of the vertical distribution of the biomass burning aerosol with CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) retrievals also showed the best agreement when the plume rise model was applied. We found that downwelling surface short-wave radiation below the forest fire plume is reduced by up to 50 % and that the 2 m temperature is decreased by up to 6 K. In addition, we simulated a strong change in atmospheric stability within the biomass burning plume.

A Modified Johnson-Cook Model for Sheet Metal Forming at Elevated Temperatures and Its Application for Cooled Stress-Strain Curve and Spring-Back Prediction

NASA Astrophysics Data System (ADS)

Duc-Toan, Nguyen; Tien-Long, Banh; Young-Suk, Kim; Dong-Won, Jung

2011-08-01

In this study, a modified Johnson-Cook (J-C) model and an innovated method to determine (J-C) material parameters are proposed to predict more correctly stress-strain curve for tensile tests in elevated temperatures. A MATLAB tool is used to determine material parameters by fitting a curve to follow Ludwick's hardening law at various elevated temperatures. Those hardening law parameters are then utilized to determine modified (J-C) model material parameters. The modified (J-C) model shows the better prediction compared to the conventional one. As the first verification, an FEM tensile test simulation based on the isotropic hardening model for boron sheet steel at elevated temperatures was carried out via a user-material subroutine, using an explicit finite element code, and compared with the measurements. The temperature decrease of all elements due to the air cooling process was then calculated when considering the modified (J-C) model and coded to VUMAT subroutine for tensile test simulation of cooling process. The modified (J-C) model showed the good agreement between the simulation results and the corresponding experiments. The second investigation was applied for V-bending spring-back prediction of magnesium alloy sheets at elevated temperatures. Here, the combination of proposed J-C model with modified hardening law considering the unusual plastic behaviour for magnesium alloy sheet was adopted for FEM simulation of V-bending spring-back prediction and shown the good comparability with corresponding experiments.

Directed translocation of a flexible polymer through a cone-shaped nano-channel

NASA Astrophysics Data System (ADS)

Nikoofard, Narges; Khalilian, Hamidreza; Fazli, Hossein

2013-08-01

Translocation of a flexible polymer through a cone-shaped channel is studied, theoretically and using computer simulations. Our simulations show that the shape of the channel causes the polymer translocation to be a driven process. The effective driving force of entropic origin acting on the polymer is calculated as a function of the length and the apex-angle of the channel, theoretically. It is found that the translocation time is a non-monotonic function of the apex-angle of the channel. By increasing the apex-angle from zero, the translocation time shows a minimum and then a maximum. Also, it is found that regardless of the value of the apex-angle, the translocation time is a uniformly decreasing function of the channel length. The results of the theory and the simulation are in good qualitative agreement.

Flowfield analysis of helicopter rotor in hover and forward flight based on CFD

NASA Astrophysics Data System (ADS)

Zhao, Qinghe; Li, Xiaodong

2018-05-01

The helicopter rotor field is simulated in hover and forward flight based on Computational Fluid Dynamics(CFD). In hover case only one rotor is simulated with the periodic boundary condition in the rotational coordinate system and the grid is fixed. In the non-lift forward flight case, the total rotor is simulated in inertia coordinate system and the whole grid moves rigidly. The dual-time implicit scheme is applied to simulate the unsteady flowfield on the movement grids. The k – ω turbulence model is employed in order to capture the effects of turbulence. To verify the solver, the flowfield around the Caradonna-Tung rotor is computed. The comparison shows a good agreement between the numerical results and the experimental data.

Computer Simulations of Resonant Coherent Excitation of Heavy Hydrogen-Like Ions Under Planar Channeling

NASA Astrophysics Data System (ADS)

Babaev, A. A.; Pivovarov, Yu L.

2010-04-01

Resonant coherent excitation (RCE) of relativistic hydrogen-like ions is investigated by computer simulations methods. The suggested theoretical model is applied to the simulations of recent experiments on RCE of 390 MeV/u Ar17+ ions under (220) planar channeling in a Si crystal performed by T.Azuma et al at HIMAC (Tokyo). Theoretical results are in a good agreement with these experimental data and clearly show the appearance of the doublet structure of RCE peaks. The simulations are also extended to greater ion energies in order to predict the new RCE features at the future accelerator facility FAIR OSI and as an example, RCE of II GeV/u U91+ ions is considered in detail.

Equivalent circuit model of Ge/Si separate absorption charge multiplication avalanche photodiode

NASA Astrophysics Data System (ADS)

Wang, Wei; Chen, Ting; Yan, Linshu; Bao, Xiaoyuan; Xu, Yuanyuan; Wang, Guang; Wang, Guanyu; Yuan, Jun; Li, Junfeng

2018-03-01

The equivalent circuit model of Ge/Si Separate Absorption Charge Multiplication Avalanche Photodiode (SACM-APD) is proposed. Starting from the carrier rate equations in different regions of device and considering the influences of non-uniform electric field, noise, parasitic effect and some other factors, the equivalent circuit model of SACM-APD device is established, in which the steady-state and transient current voltage characteristics can be described exactly. In addition, the proposed Ge/Si SACM APD equivalent circuit model is embedded in PSpice simulator. The important characteristics of Ge/Si SACM APD such as dark current, frequency response, shot noise are simulated, the simulation results show that the simulation with the proposed model are in good agreement with the experimental results.

Comparative Study of Antenna Elements for TDRSS Enhanced Multiple Access System

NASA Technical Reports Server (NTRS)

Kory, Carol L.; Lambert, Kevin; Acosta, Roberto; Nessel, James

2006-01-01

We compare three antennas, which are candidates for the TDRSS-Continuation enhanced MA array antenna elements. Measured and simulated data show very good agreement for all antenna elements. All of the antennas meet the specifications with the exception of the SBA isolation. However, improvements can likely be made with further design efforts.

Sharing Scarce Resources: Group-Outcome Orientation, External Disaster, and Stealing in a Simulated Commons.

ERIC Educational Resources Information Center

Edney, Julian J.; Bell, Paul A.

1984-01-01

Conducted two studies in which subjects (N=216) faced the dilemma of how to harvest resources from a shared pool when faced with external catastrophies and given opportunities to steal. Results showed that tying the individual's outcome to the rest of the group is good for the group. (LLL)

Flying mirror model for interaction of a super-intense laser pulse with a thin plasma layer: Transparency and shaping of linearly polarized laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulagin, Victor V.; Cherepenin, Vladimir A.; Hur, Min Sup

2007-11-15

A self-consistent one-dimensional (1D) flying mirror model is developed for description of an interaction of an ultra-intense laser pulse with a thin plasma layer (foil). In this model, electrons of the foil can have large longitudinal displacements and relativistic longitudinal momenta. An approximate analytical solution for a transmitted field is derived. Transmittance of the foil shows not only a nonlinear dependence on the amplitude of the incident laser pulse, but also time dependence and shape dependence in the high-transparency regime. The results are compared with particle-in-cell (PIC) simulations and a good agreement is ascertained. Shaping of incident laser pulses usingmore » the flying mirror model is also considered. It can be used either for removing a prepulse or for reducing the length of a short laser pulse. The parameters of the system for effective shaping are specified. Predictions of the flying mirror model for shaping are compared with the 1D PIC simulations, showing good agreement.« less

Ab initio study of the structure and dynamics of bulk liquid Fe

NASA Astrophysics Data System (ADS)

Marqués, M.; González, L. E.; González, D. J.

2015-10-01

Several static and dynamic properties of bulk liquid Fe at a thermodynamic state near its triple point have been evaluated by ab initio molecular dynamics simulations. The calculated static structure shows very good agreement with the available experimental data, including an asymmetric second peak in the structure factor which underlines a substantial local icosahedral short-range order in the liquid. The dynamical structure reveals propagating density fluctuations, with an associated dispersion relation which closely follows the experimental data. The dynamic structure factors S (q ,ω ) show a good agreement with their experimental counterparts which have been recently measured by an inelastic x-ray scattering experiment. The dynamical processes behind the S (q ,ω ) have been analyzed by using a model with two decay channels (a fast and a slow) associated with the relaxations of the collective excitations. The recent finding of transverselike excitation modes in the IXS data is analyzed by using the present ab initio simulation results. Several transport coefficients have been evaluated and the results are compared with the available experimental data.

Adjustment and validation of a simulation tool for CSP plants based on parabolic trough technology

NASA Astrophysics Data System (ADS)

García-Barberena, Javier; Ubani, Nora

2016-05-01

The present work presents the validation process carried out for a simulation tool especially designed for the energy yield assessment of concentrating solar plants based on parabolic through (PT) technology. The validation has been carried out by comparing the model estimations with real data collected from a commercial CSP plant. In order to adjust the model parameters used for the simulation, 12 different days were selected among one-year of operational data measured at the real plant. The 12 days were simulated and the estimations compared with the measured data, focusing on the most important variables from the simulation point of view: temperatures, pressures and mass flow of the solar field, gross power, parasitic power, and net power delivered by the plant. Based on these 12 days, the key parameters for simulating the model were properly fixed and the simulation of a whole year performed. The results obtained for a complete year simulation showed very good agreement for the gross and net electric total production. The estimations for these magnitudes show a 1.47% and 2.02% BIAS respectively. The results proved that the simulation software describes with great accuracy the real operation of the power plant and correctly reproduces its transient behavior.

Simulations of the OKE Response in Simple Liquids Using a Polarizable and a Nonpolarizable Force Field.

PubMed

Polok, Kamil

2018-02-08

Recently polarizable force fields are becoming increasingly popular for molecular dynamics simulations. As the signal obtained in the optical Kerr effect (OKE) experiment is due to the polarizability dynamics of the investigated system, a study is conducted in order to compare the experimental results with those obtained with the polarizable AMOEBA force field. The comparison is made in the frequency domain; however, time domain data are also included. The selected molecular systems are the isotropic carbon tetrachloride molecule, the anisotropic chloroform, carbon disulfide and acetone molecules, and the hydrogen-bonded water and methanol molecules. Different dipole-induced-dipole (DID) method variants are used for calculation of the OKE response, showing the importance of use of the all-atom approach with preoptimized atomic polarizabilities. In order to obtain a good intermolecular to intramolecular components amplitude ratio, the isotropic polarizability in the Thole correction needs to be updated between iterations. The convergence of the spectra calculated with different DID variants is also considered, and the approach that appears to be the best gives a very good approximation after three iterations. The comparison of the experimental and simulated spectra shows a rather good agreement for the non-hydrogen-bonded molecules, although the contribution of the reorientation of anisotropic molecules is overestimated. In the case of the hydrogen-bonded molecules, the theoretical spectra are far from the experimental ones. The highly overestimated librational bands indicate excessive polarizability anisotropy introduced by the potential model. Finally, in order to verify the significance of different components of the AMOEBA model, it is gradually simplified and compared with a simple reference potential model. Removal of polarizability shows a tremendous change in the case of hydrogen-bonded liquids, whereas for the other molecules it is of minor importance. The non-hydrogen-bonded liquids are, however, more sensitive to the presence of atomic multipoles in the model.

An ab initio study of the structure and atomic transport in bulk liquid Ag and its liquid-vapor interface

NASA Astrophysics Data System (ADS)

del Rio, Beatriz G.; González, David J.; González, Luis E.

2016-10-01

Several static and dynamic properties of bulk liquid Ag at a thermodynamic state near its triple point have been calculated by means of ab initio molecular dynamics simulations. The calculated static structure shows a very good agreement with the available experimental data. The dynamical structure reveals propagating excitations whose dispersion at long wavelengths is compatible with the experimental sound velocity. Results are also reported for other transport coefficients. Additional simulations have also been performed so as to study the structure of the free liquid surface. The calculated longitudinal ionic density profile shows an oscillatory behaviour, whose properties are analyzed through macroscopic and microscopic methods. The intrinsic X-ray reflectivity of the surface is predicted to show a layering peak associated to the interlayer distance.

Review of Monte Carlo simulations for backgrounds from radioactivity

NASA Astrophysics Data System (ADS)

Selvi, Marco

2013-08-01

For all experiments dealing with the rare event searches (neutrino, dark matter, neutrino-less double-beta decay), the reduction of the radioactive background is one of the most important and difficult tasks. There are basically two types of background, electron recoils and nuclear recoils. The electron recoil background is mostly from the gamma rays through the radioactive decay. The nuclear recoil background is from neutrons from spontaneous fission, (α, n) reactions and muoninduced interactions (spallations, photo-nuclear and hadronic interaction). The external gammas and neutrons from the muons and laboratory environment, can be reduced by operating the detector at deep underground laboratories and by placing active or passive shield materials around the detector. The radioactivity of the detector materials also contributes to the background; in order to reduce it a careful screening campaign is mandatory to select highly radio-pure materials. In this review I present the status of current Monte Carlo simulations aimed to estimate and reproduce the background induced by gamma and neutron radioactivity of the materials and the shield of rare event search experiment. For the electromagnetic background a good level of agreement between the data and the MC simulation has been reached by the XENON100 and EDELWEISS experiments, using the GEANT4 toolkit. For the neutron background, a comparison between the yield of neutrons from spontaneous fission and (α, n) obtained with two dedicated softwares, SOURCES-4A and the one developed by Mei-Zhang-Hime, show a good overall agreement, with total yields within a factor 2 difference. The energy spectra from SOURCES-4A are in general smoother, while those from MZH presents sharp peaks. The neutron propagation through various materials has been studied with two MC codes, GEANT4 and MCNPX, showing a reasonably good agreement, inside 50% discrepancy.

Fast scattering simulation tool for multi-energy x-ray imaging

NASA Astrophysics Data System (ADS)

Sossin, A.; Tabary, J.; Rebuffel, V.; Létang, J. M.; Freud, N.; Verger, L.

2015-12-01

A combination of Monte Carlo (MC) and deterministic approaches was employed as a means of creating a simulation tool capable of providing energy resolved x-ray primary and scatter images within a reasonable time interval. Libraries of Sindbad, a previously developed x-ray simulation software, were used in the development. The scatter simulation capabilities of the tool were validated through simulation with the aid of GATE and through experimentation by using a spectrometric CdTe detector. A simple cylindrical phantom with cavities and an aluminum insert was used. Cross-validation with GATE showed good agreement with a global spatial error of 1.5% and a maximum scatter spectrum error of around 6%. Experimental validation also supported the accuracy of the simulations obtained from the developed software with a global spatial error of 1.8% and a maximum error of around 8.5% in the scatter spectra.

Topology for efficient information dissemination in ad-hoc networking

NASA Technical Reports Server (NTRS)

Jennings, E.; Okino, C. M.

2002-01-01

In this paper, we explore the information dissemination problem in ad-hoc wirless networks. First, we analyze the probability of successful broadcast, assuming: the nodes are uniformly distributed, the available area has a lower bould relative to the total number of nodes, and there is zero knowledge of the overall topology of the network. By showing that the probability of such events is small, we are motivated to extract good graph topologies to minimize the overall transmissions. Three algorithms are used to generate topologies of the network with guaranteed connectivity. These are the minimum radius graph, the relative neighborhood graph and the minimum spanning tree. Our simulation shows that the relative neighborhood graph has certain good graph properties, which makes it suitable for efficient information dissemination.

Fuzzy PID control algorithm based on PSO and application in BLDC motor

NASA Astrophysics Data System (ADS)

Lin, Sen; Wang, Guanglong

2017-06-01

A fuzzy PID control algorithm is studied based on improved particle swarm optimization (PSO) to perform Brushless DC (BLDC) motor control which has high accuracy, good anti-jamming capability and steady state accuracy compared with traditional PID control. The mathematical and simulation model is established for BLDC motor by simulink software, and the speed loop of the fuzzy PID controller is designed. The simulation results show that the fuzzy PID control algorithm based on PSO has higher stability, high control precision and faster dynamic response speed.

Spatial distribution of fluorescent light emitted from neon and nitrogen excited by low energy electron beams

NASA Astrophysics Data System (ADS)

Morozov, A.; Krücken, R.; Ulrich, A.; Wieser, J.

2006-11-01

Side-view intensity profiles of fluorescent light were measured for neon and nitrogen excited with 12keV electron beams at gas pressures from 250to1400hPa. The intensity profiles were compared with theoretical profiles calculated using the CASINO program which performs Monte Carlo simulations of electron scattering. It was assumed that the spatial distribution of fluorescent intensity is directly proportional to the spatial distribution of energy loss by primary electrons. The comparison shows good correlation of experimental data and the results of numeric simulations.

FIBER ORIENTATION IN INJECTION MOLDED LONG CARBON FIBER THERMOPLASTIC COMPOSITES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jin; Nguyen, Ba Nghiep; Mathur, Raj N.

2015-03-23

A set of edge-gated and center-gated plaques were injection molded with long carbon fiber-reinforced thermoplastic composites, and the fiber orientation was measured at different locations of the plaques. Autodesk Simulation Moldflow Insight (ASMI) software was used to simulate the injection molding of these plaques and to predict the fiber orientation, using the anisotropic rotary diffusion and the reduced strain closure models. The phenomenological parameters of the orientation models were carefully identified by fitting to the measured orientation data. The fiber orientation predictions show very good agreement with the experimental data.

The effect of the rigidity of perfluoropolyether surfactant on its behavior at the water/supercritical carbon dioxide interface.

PubMed

Lu, Lanyuan; Berkowitz, Max L

2005-11-24

We performed a series of molecular dynamics simulations to study the PFPE (perfluoropolyether) and PE (polyether) surfactant monolayers at the water/supercritical carbon dioxide interface. Molecular differences between fluorocarbon surfactant PFPE and its hydrocarbon analogue PE were analyzed. We observed that values of intramolecular bonded interaction parameters which are related to chain rigidity determine the monolayer surface pressure. We show that "good" and "bad" properties of PFPE/PE surfactants are connected to conformational entropy. These results are consistent with our previous micellar simulations.

Pulse fracture simulation in shale rock reservoirs: DEM and FEM-DEM approaches

NASA Astrophysics Data System (ADS)

González, José Manuel; Zárate, Francisco; Oñate, Eugenio

2018-07-01

In this paper we analyze the capabilities of two numerical techniques based on DEM and FEM-DEM approaches for the simulation of fracture in shale rock caused by a pulse of pressure. We have studied the evolution of fracture in several fracture scenarios related to the initial stress state in the soil or the pressure pulse peak. Fracture length and type of failure have been taken as reference for validating the models. The results obtained show a good approximation to FEM results from the literature.

A model for a continuous-wave iodine laser

NASA Technical Reports Server (NTRS)

Hwang, In H.; Tabibi, Bagher M.

1990-01-01

A model for a continuous-wave (CW) iodine laser has been developed and compared with the experimental results obtained from a solar-simulator-pumped CW iodine laser. The agreement between the calculated laser power output and the experimental results is generally good for various laser parameters even when the model includes only prominent rate coefficients. The flow velocity dependence of the output power shows that the CW iodine laser cannot be achieved with a flow velocity below 1 m/s for the present solar-simulator-pumped CW iodine laser system.

(Invited) Comprehensive Assessment of Oxide Memristors As Post-CMOS Memory and Logic Devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, X.; Mamaluy, D.; Cyr, E. C.

As CMOS technology approaches the end of its scaling, oxide-based memristors have become one of the leading candidates for post-CMOS memory and logic devices. In orderTo facilitate the understanding of physical switching mechanisms and accelerate experimental development of memristors, we have developed a three-dimensional fully-coupled electrical and thermal transport model, which captures all the important processes that drive memristive switching and is applicable for simulating a wide range of memristors. Moreover, the model is applied to simulate the RESET and SET switching in a 3D filamentary TaOx memristor. Extensive simulations show that the switching dynamics of the bipolar device ismore » determined by thermally-activated field-dominant processes: with Joule heating, the raised temperature enables the movement of oxygen vacancies, and the field drift dominates the overall motion of vacancies. Simulated current-voltage hysteresis and device resistance profiles as a function of time and voltage during RESET and SET switching show good agreement with experimental measurement.« less

(Invited) Comprehensive Assessment of Oxide Memristors As Post-CMOS Memory and Logic Devices

DOE PAGES

Gao, X.; Mamaluy, D.; Cyr, E. C.; ...

2016-05-10

As CMOS technology approaches the end of its scaling, oxide-based memristors have become one of the leading candidates for post-CMOS memory and logic devices. In orderTo facilitate the understanding of physical switching mechanisms and accelerate experimental development of memristors, we have developed a three-dimensional fully-coupled electrical and thermal transport model, which captures all the important processes that drive memristive switching and is applicable for simulating a wide range of memristors. Moreover, the model is applied to simulate the RESET and SET switching in a 3D filamentary TaOx memristor. Extensive simulations show that the switching dynamics of the bipolar device ismore » determined by thermally-activated field-dominant processes: with Joule heating, the raised temperature enables the movement of oxygen vacancies, and the field drift dominates the overall motion of vacancies. Simulated current-voltage hysteresis and device resistance profiles as a function of time and voltage during RESET and SET switching show good agreement with experimental measurement.« less

Temperature field simulation and phantom validation of a Two-armed Spiral Antenna for microwave thermotherapy.

PubMed

Du, Yongxing; Zhang, Lingze; Sang, Lulu; Wu, Daocheng

2016-04-29

In this paper, an Archimedean planar spiral antenna for the application of thermotherapy was designed. This type of antenna was chosen for its compact structure, flexible application and wide heating area. The temperature field generated by the use of this Two-armed Spiral Antenna in a muscle-equivalent phantom was simulated and subsequently validated by experimentation. First, the specific absorption rate (SAR) of the field was calculated using the Finite Element Method (FEM) by Ansoft's High Frequency Structure Simulation (HFSS). Then, the temperature elevation in the phantom was simulated by an explicit finite difference approximation of the bioheat equation (BHE). The temperature distribution was then validated by a phantom heating experiment. The results showed that this antenna had a good heating ability and a wide heating area. A comparison between the calculation and the measurement showed a fair agreement in the temperature elevation. The validated model could be applied for the analysis of electromagnetic-temperature distribution in phantoms during the process of antenna design or thermotherapy experimentation.

Wide-Angle X-Ray Scattering and Solid-State Nuclear Magnetic Resonance Data Combined to Test Models for Cellulose Microfibrils in Mung Bean Cell Walls1

PubMed Central

Newman, Roger H.; Hill, Stefan J.; Harris, Philip J.

2013-01-01

A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-β-glucan chains in cellulose microfibrils. Computer-simulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24- and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette. PMID:24154621

The Illustris simulation: supermassive black hole-galaxy connection beyond the bulge

NASA Astrophysics Data System (ADS)

Mutlu-Pakdil, Burçin; Seigar, Marc S.; Hewitt, Ian B.; Treuthardt, Patrick; Berrier, Joel C.; Koval, Lauren E.

2018-02-01

We study the spiral arm morphology of a sample of the local spiral galaxies in the Illustris simulation and explore the supermassive black hole-galaxy connection beyond the bulge (e.g. spiral arm pitch angle, total stellar mass, dark matter mass, and total halo mass), finding good agreement with other theoretical studies and observational constraints. It is important to study the properties of supermassive black holes and their host galaxies through both observations and simulations and compare their results in order to understand their physics and formative histories. We find that Illustris prediction for supermassive black hole mass relative to pitch angle is in rather good agreement with observations and that barred and non-barred galaxies follow similar scaling relations. Our work shows that Illustris presents very tight correlations between supermassive black hole mass and large-scale properties of the host galaxy, not only for early-type galaxies but also for low-mass, blue and star-forming galaxies. These tight relations beyond the bulge suggest that halo properties determine those of a disc galaxy and its supermassive black hole.

Penetration of rod projectiles in semi-infinite targets : a validation test for Eulerian X-FEM in ALEGRA.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Byoung Yoon; Leavy, Richard Brian; Niederhaus, John Henry J.

2013-03-01

The finite-element shock hydrodynamics code ALEGRA has recently been upgraded to include an X-FEM implementation in 2D for simulating impact, sliding, and release between materials in the Eulerian frame. For validation testing purposes, the problem of long-rod penetration in semi-infinite targets is considered in this report, at velocities of 500 to 3000 m/s. We describe testing simulations done using ALEGRA with and without the X-FEM capability, in order to verify its adequacy by showing X-FEM recovers the good results found with the standard ALEGRA formulation. The X-FEM results for depth of penetration differ from previously measured experimental data by lessmore » than 2%, and from the standard formulation results by less than 1%. They converge monotonically under mesh refinement at first order. Sensitivities to domain size and rear boundary condition are investigated and shown to be small. Aside from some simulation stability issues, X-FEM is found to produce good results for this classical impact and penetration problem.« less

Computational Aerodynamic Simulations of a Spacecraft Cabin Ventilation Fan Design

NASA Technical Reports Server (NTRS)

Tweedt, Daniel L.

2010-01-01

Quieter working environments for astronauts are needed if future long-duration space exploration missions are to be safe and productive. Ventilation and payload cooling fans are known to be dominant sources of noise, with the International Space Station being a good case in point. To address this issue cost effectively, early attention to fan design, selection, and installation has been recommended, leading to an effort by NASA to examine the potential for small-fan noise reduction by improving fan aerodynamic design. As a preliminary part of that effort, the aerodynamics of a cabin ventilation fan designed by Hamilton Sundstrand has been simulated using computational fluid dynamics codes, and the computed solutions analyzed to quantify various aspects of the fan aerodynamics and performance. Four simulations were performed at the design rotational speed: two at the design flow rate and two at off-design flow rates. Following a brief discussion of the computational codes, various aerodynamic- and performance-related quantities derived from the computed flow fields are presented along with relevant flow field details. The results show that the computed fan performance is in generally good agreement with stated design goals.

Identifying equivalent sound sources from aeroacoustic simulations using a numerical phased array

NASA Astrophysics Data System (ADS)

Pignier, Nicolas J.; O'Reilly, Ciarán J.; Boij, Susann

2017-04-01

An application of phased array methods to numerical data is presented, aimed at identifying equivalent flow sound sources from aeroacoustic simulations. Based on phased array data extracted from compressible flow simulations, sound source strengths are computed on a set of points in the source region using phased array techniques assuming monopole propagation. Two phased array techniques are used to compute the source strengths: an approach using a Moore-Penrose pseudo-inverse and a beamforming approach using dual linear programming (dual-LP) deconvolution. The first approach gives a model of correlated sources for the acoustic field generated from the flow expressed in a matrix of cross- and auto-power spectral values, whereas the second approach results in a model of uncorrelated sources expressed in a vector of auto-power spectral values. The accuracy of the equivalent source model is estimated by computing the acoustic spectrum at a far-field observer. The approach is tested first on an analytical case with known point sources. It is then applied to the example of the flow around a submerged air inlet. The far-field spectra obtained from the source models for two different flow conditions are in good agreement with the spectra obtained with a Ffowcs Williams-Hawkings integral, showing the accuracy of the source model from the observer's standpoint. Various configurations for the phased array and for the sources are used. The dual-LP beamforming approach shows better robustness to changes in the number of probes and sources than the pseudo-inverse approach. The good results obtained with this simulation case demonstrate the potential of the phased array approach as a modelling tool for aeroacoustic simulations.

Numerical simulation of tip vortices of wings in subsonic and transonic flows

NASA Technical Reports Server (NTRS)

Srinivasan, G. R.; Mccroskey, W. J.; Baeder, J. D.; Edwards, T. A.

1986-01-01

A multi block zonal algorithm which solves the thin-layer Navier-Stokes and the Euler equations is used to numerically simulate the formation and roll-up of the tip vortex in both subsonic and transonic flows. Four test cases which used small and large aspect ratio wings have been considered to examine the influence of the tip-cap shape, the tip planform and the free-stream Mach number. It appears that both the tip-planform and the tip-cap shape have some influence on the formation of the tip vortex, but its subsequent roll-up seems to be more influenced by the tip-planform shape. In general, a good definition of the formation and the roll-up of the tip vortex has been observed for all the cases considered here. Comparions of the numerical results with the limited, available experimental data show good agreement with both the surface pressures and the tip-vortex strength.

Polymer collapse in miscible good solvents is a generic phenomenon driven by preferential adsorption

PubMed Central

Mukherji, Debashish; Marques, Carlos M.; Kremer, Kurt

2014-01-01

Water and alcohol, such as methanol or ethanol, are miscible and, individually, good solvents for poly(N-isopropylacrylamide) (PNIPAm), but this polymer precipitates in water–alcohol mixtures. The intriguing behaviour of solvent mixtures that cannot dissolve a given polymer or a given protein, while the same macromolecule dissolves well in each of the cosolvents, is called cononsolvency. It is a widespread phenomenon, relevant for many formulation steps in the physicochemical and pharmaceutical industry, that is usually explained by invoking specific chemical details of the mixtures: as such, it has so far eluded any generic explanation. Here, by using a combination of simulations and theory, we present a simple and universal treatment that requires only the preferential interaction of one of the cosolvents with the polymer. The results show striking quantitative agreement with experiments and chemically specific simulations, opening a new perspective towards an operational understanding of macromolecular solubility. PMID:25216245

Element analysis and calculation of the attenuation coefficients for gold, bronze and water matrixes using MCNP, WinXCom and experimental data

NASA Astrophysics Data System (ADS)

Esfandiari, M.; Shirmardi, S. P.; Medhat, M. E.

2014-06-01

In this study, element analysis and the mass attenuation coefficient for matrixes of gold, bronze and water with various impurities and the concentrations of heavy metals (Cu, Mn, Pb and Zn) are evaluated and calculated by the MCNP simulation code for photons emitted from Barium-133, Americium-241 and sources with energies between 1 and 100 keV. The MCNP data are compared with the experimental data and WinXCom code simulated results by Medhat. The results showed that the obtained results of bronze and gold matrix are in good agreement with the other methods for energies above 40 and 60 keV, respectively. However for water matrixes with various impurities, there is a good agreement between the three methods MCNP, WinXCom and the experimental one in low and high energies.

A new bio-inspired stimulator to suppress hyper-synchronized neural firing in a cortical network.

PubMed

Amiri, Masoud; Amiri, Mahmood; Nazari, Soheila; Faez, Karim

2016-12-07

Hyper-synchronous neural oscillations are the character of several neurological diseases such as epilepsy. On the other hand, glial cells and particularly astrocytes can influence neural synchronization. Therefore, based on the recent researches, a new bio-inspired stimulator is proposed which basically is a dynamical model of the astrocyte biophysical model. The performance of the new stimulator is investigated on a large-scale, cortical network. Both excitatory and inhibitory synapses are also considered in the simulated spiking neural network. The simulation results show that the new stimulator has a good performance and is able to reduce recurrent abnormal excitability which in turn avoids the hyper-synchronous neural firing in the spiking neural network. In this way, the proposed stimulator has a demand controlled characteristic and is a good candidate for deep brain stimulation (DBS) technique to successfully suppress the neural hyper-synchronization. Copyright © 2016 Elsevier Ltd. All rights reserved.

Extended Information Ratio for Portfolio Optimization Using Simulated Annealing with Constrained Neighborhood

NASA Astrophysics Data System (ADS)

Orito, Yukiko; Yamamoto, Hisashi; Tsujimura, Yasuhiro; Kambayashi, Yasushi

The portfolio optimizations are to determine the proportion-weighted combination in the portfolio in order to achieve investment targets. This optimization is one of the multi-dimensional combinatorial optimizations and it is difficult for the portfolio constructed in the past period to keep its performance in the future period. In order to keep the good performances of portfolios, we propose the extended information ratio as an objective function, using the information ratio, beta, prime beta, or correlation coefficient in this paper. We apply the simulated annealing (SA) to optimize the portfolio employing the proposed ratio. For the SA, we make the neighbor by the operation that changes the structure of the weights in the portfolio. In the numerical experiments, we show that our portfolios keep the good performances when the market trend of the future period becomes different from that of the past period.

Atomistic simulations of carbon diffusion and segregation in liquid silicon

NASA Astrophysics Data System (ADS)

Luo, Jinping; Alateeqi, Abdullah; Liu, Lijun; Sinno, Talid

2017-12-01

The diffusivity of carbon atoms in liquid silicon and their equilibrium distribution between the silicon melt and crystal phases are key, but unfortunately not precisely known parameters for the global models of silicon solidification processes. In this study, we apply a suite of molecular simulation tools, driven by multiple empirical potential models, to compute diffusion and segregation coefficients of carbon at the silicon melting temperature. We generally find good consistency across the potential model predictions, although some exceptions are identified and discussed. We also find good agreement with the range of available experimental measurements of segregation coefficients. However, the carbon diffusion coefficients we compute are significantly lower than the values typically assumed in continuum models of impurity distribution. Overall, we show that currently available empirical potential models may be useful, at least semi-quantitatively, for studying carbon (and possibly other impurity) transport in silicon solidification, especially if a multi-model approach is taken.

Large fraction of crystal directions leads to ion channeling

NASA Astrophysics Data System (ADS)

Nordlund, K.; Djurabekova, F.; Hobler, G.

2016-12-01

It is well established that when energetic ions are moving in crystals, they may penetrate much deeper if they happen to be directed in some specific crystal directions. This `channeling' effect is utilized for instance in certain ion beam analysis methods and has been described by analytical theories and atomistic computer simulations. However, there have been very few systematic studies of channeling in directions other than the principal low-index ones. We present here a molecular dynamics-based approach to calculate ion channeling systematically over all crystal directions, providing ion `channeling maps' that easily show in which directions channeling is expected. The results show that channeling effects can be quite significant even at energies below 1 keV, and that in many cases, significant planar channeling occurs also in a wide range of crystal directions between the low-index principal ones. In all of the cases studied, a large fraction (˜20 -60 % ) of all crystal directions show channeling. A practical implication of this is that modern experiments on randomly oriented nanostructures will have a large probability of channeling. It also means that when ion irradiations are carried out on polycrystalline samples, channeling effects on the results cannot a priori be assumed to be negligible. The maps allow for easy selection of good `nonchanneling' directions in experiments or alternatively finding wide channels for beneficial uses of channeling. We implement channeling theory to also give the fraction of channeling directions in a manner directly comparable to the simulations. The comparison shows good qualitative agreement. In particular, channeling theory is very good at predicting which channels are active at a given energy. This is true down to sub-keV energies, provided the penetration depth is not too small.

Ultrasound imaging based on nonlinear pressure field properties

NASA Astrophysics Data System (ADS)

Bouakaz, Ayache; Frinking, Peter J. A.; de Jong, Nico

2000-07-01

Ultrasound image quality has experienced a significant improvement over the past years with the utilization of harmonic frequencies. This brings the need to understand the physical processes involved in the propagation of finite amplitude sound beams, and the issues for redesigning and optimizing the phased array transducers. New arrays with higher imaging performances are essential for tissue imaging and contrast imaging as well. This study presents measurements and simulations on a 4.6 MHz square transducer. The numerical scheme used solves the KZK equation in the time domain. Comparison of measured and computed data showed good agreement for low and high excitation levels. In a similar way, a numerical simulation was performed on a linear array with five elements. The simulation showed that the second harmonic beam is narrower than the fundamental with less energy in the near field. In addition, the grating lobes are significantly lower. Accordingly, selective harmonic imaging shows less near field artifacts and will lower the clutter, resulting in much cleaner images.

A Lagrangian Simulation of Subsonic Aircraft Exhaust Emissions

NASA Technical Reports Server (NTRS)

Schoeberl, M. R.; Morris, G. A.

1999-01-01

To estimate the effect of subsonic and supersonic aircraft exhaust on the stratospheric concentration of NO(y), we employ a trajectory model initialized with air parcels based on the standard release scenarios. The supersonic exhaust simulations are in good agreement with 2D and 3D model results and show a perturbation of about 1-2 ppbv of NO(y) in the stratosphere. The subsonic simulations show that subsonic emissions are almost entirely trapped below the 380 K potential temperature surface. Our subsonic results contradict results from most other models, which show exhaust products penetrating above 380 K, as summarized. The disagreement can likely be attributed to an excessive vertical diffusion in most models of the strong vertical gradient in NO(y) that forms at the boundary between the emission zone and the stratosphere above 380 K. Our results suggest that previous assessments of the impact of subsonic exhaust emission on the stratospheric region above 380 K should be considered to be an upper bound.

Simulation-based training for nurses: Systematic review and meta-analysis.

PubMed

Hegland, Pål A; Aarlie, Hege; Strømme, Hilde; Jamtvedt, Gro

2017-07-01

Simulation-based training is a widespread strategy to improve health-care quality. However, its effect on registered nurses has previously not been established in systematic reviews. The aim of this systematic review is to evaluate effect of simulation-based training on nurses' skills and knowledge. We searched CDSR, DARE, HTA, CENTRAL, CINAHL, MEDLINE, Embase, ERIC, and SveMed+ for randomised controlled trials (RCT) evaluating effect of simulation-based training among nurses. Searches were completed in December 2016. Two reviewers independently screened abstracts and full-text, extracted data, and assessed risk of bias. We compared simulation-based training to other learning strategies, high-fidelity simulation to other simulation strategies, and different organisation of simulation training. Data were analysed through meta-analysis and narrative syntheses. GRADE was used to assess the quality of evidence. Fifteen RCTs met the inclusion criteria. For the comparison of simulation-based training to other learning strategies on nurses' skills, six studies in the meta-analysis showed a significant, but small effect in favour of simulation (SMD -1.09, CI -1.72 to -0.47). There was large heterogeneity (I 2 85%). For the other comparisons, there was large between-study variation in results. The quality of evidence for all comparisons was graded as low. The effect of simulation-based training varies substantially between studies. Our meta-analysis showed a significant effect of simulation training compared to other learning strategies, but the quality of evidence was low indicating uncertainty. Other comparisons showed inconsistency in results. Based on our findings simulation training appears to be an effective strategy to improve nurses' skills, but further good-quality RCTs with adequate sample sizes are needed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Efficient Computing Budget Allocation for Finding Simplest Good Designs

PubMed Central

Jia, Qing-Shan; Zhou, Enlu; Chen, Chun-Hung

2012-01-01

In many applications some designs are easier to implement, require less training data and shorter training time, and consume less storage than the others. Such designs are called simple designs, and are usually preferred over complex ones when they all have good performance. Despite the abundant existing studies on how to find good designs in simulation-based optimization (SBO), there exist few studies on finding simplest good designs. We consider this important problem in this paper, and make the following contributions. First, we provide lower bounds for the probabilities of correctly selecting the m simplest designs with top performance, and selecting the best m such simplest good designs, respectively. Second, we develop two efficient computing budget allocation methods to find m simplest good designs and to find the best m such designs, respectively; and show their asymptotic optimalities. Third, we compare the performance of the two methods with equal allocations over 6 academic examples and a smoke detection problem in wireless sensor networks. We hope that this work brings insight to finding the simplest good designs in general. PMID:23687404

Orthogonal recursive bisection as data decomposition strategy for massively parallel cardiac simulations.

PubMed

Reumann, Matthias; Fitch, Blake G; Rayshubskiy, Aleksandr; Pitman, Michael C; Rice, John J

2011-06-01

We present the orthogonal recursive bisection algorithm that hierarchically segments the anatomical model structure into subvolumes that are distributed to cores. The anatomy is derived from the Visible Human Project, with electrophysiology based on the FitzHugh-Nagumo (FHN) and ten Tusscher (TT04) models with monodomain diffusion. Benchmark simulations with up to 16,384 and 32,768 cores on IBM Blue Gene/P and L supercomputers for both FHN and TT04 results show good load balancing with almost perfect speedup factors that are close to linear with the number of cores. Hence, strong scaling is demonstrated. With 32,768 cores, a 1000 ms simulation of full heart beat requires about 6.5 min of wall clock time for a simulation of the FHN model. For the largest machine partitions, the simulations execute at a rate of 0.548 s (BG/P) and 0.394 s (BG/L) of wall clock time per 1 ms of simulation time. To our knowledge, these simulations show strong scaling to substantially higher numbers of cores than reported previously for organ-level simulation of the heart, thus significantly reducing run times. The ability to reduce runtimes could play a critical role in enabling wider use of cardiac models in research and clinical applications.

Divertor heat flux simulations in ELMy H-mode discharges of EAST

NASA Astrophysics Data System (ADS)

Xia, T. Y.; Xu, X. Q.; Wu, Y. B.; Huang, Y. Q.; Wang, L.; Zheng, Z.; Liu, J. B.; Zang, Q.; Li, Y. Y.; Zhao, D.; EAST Team

2017-11-01

This paper presents heat flux simulations for the ELMy H-mode on the Experimental Advanced Superconducting Tokamak (EAST) using a six-field two-fluid model in BOUT++. Three EAST ELMy H-mode discharges with different plasma currents I p and geometries are studied. The trend of the scrape-off layer width λq with I p is reproduced by the simulation. The simulated width is only half of that derived from the EAST scaling law, but agrees well with the international multi-machine scaling law. Note that there is no radio-frequency (RF) heating scheme in the simulations, and RF heating can change the boundary topology and increase the flux expansion. Anomalous electron transport is found to contribute to the divertor heat fluxes. A coherent mode is found in the edge region in simulations. The frequency and poloidal wave number kθ are in the range of the edge coherent mode in EAST. The magnetic fluctuations of the mode are smaller than the electric field fluctuations. Statistical analysis of the type of turbulence shows that the turbulence transport type (blobby or turbulent) does not influence the heat flux width scaling. The two-point model differs from the simulation results but the drift-based model shows good agreement with simulations.

Comparative simulations of microjetting using atomistic and continuous approaches in the presence of viscosity and surface tension

NASA Astrophysics Data System (ADS)

Durand, O.; Jaouen, S.; Soulard, L.; Heuzé, O.; Colombet, L.

2017-10-01

We compare, at similar scales, the processes of microjetting and ejecta production from shocked roughened metal surfaces by using atomistic and continuous approaches. The atomistic approach is based on very large scale molecular dynamics (MD) simulations with systems containing up to 700 × 106 atoms. The continuous approach is based on Eulerian hydrodynamics simulations with adaptive mesh refinement; the simulations take into account the effects of viscosity and surface tension, and the equation of state is calculated from the MD simulations. The microjetting is generated by shock-loading above its fusion point a three-dimensional tin crystal with an initial sinusoidal free surface perturbation, the crystal being set in contact with a vacuum. Several samples with homothetic wavelengths and amplitudes of defect are simulated in order to investigate the influence of viscosity and surface tension of the metal. The simulations show that the hydrodynamic code reproduces with very good agreement the profiles, calculated from the MD simulations, of the ejected mass and velocity along the jet. Both codes also exhibit a similar fragmentation phenomenology of the metallic liquid sheets ejected, although the fragmentation seed is different. We show in particular, that it depends on the mesh size in the continuous approach.

A model for including thermal conduction in molecular dynamics simulations

NASA Technical Reports Server (NTRS)

Wu, Yue; Friauf, Robert J.

1989-01-01

A technique is introduced for including thermal conduction in molecular dynamics simulations for solids. A model is developed to allow energy flow between the computational cell and the bulk of the solid when periodic boundary conditions cannot be used. Thermal conduction is achieved by scaling the velocities of atoms in a transitional boundary layer. The scaling factor is obtained from the thermal diffusivity, and the results show good agreement with the solution for a continuous medium at long times. The effects of different temperature and size of the system, and of variations in strength parameter, atomic mass, and thermal diffusivity were investigated. In all cases, no significant change in simulation results has been found.

Simulation of fatigue fracture of TiNi shape memory alloy samples at cyclic loading in pseudoelastic state

NASA Astrophysics Data System (ADS)

Belyaev, Fedor S.; Volkov, Aleksandr E.; Evard, Margarita E.; Khvorov, Aleksandr A.

2018-05-01

Microstructural simulation of mechanical behavior of shape memory alloy samples at cyclic loading in the pseudoelastic state has been carried out. Evolution of the oriented and scattered deformation defects leading to damage accumulation and resulting in the fatigue fracture has been taken into account. Simulations were performed for the regime of loading imitating that for endovascular stents: preliminary straining, unloading, deformation up to some mean level of the strain and subsequent mechanical cycling at specified strain amplitude. Dependence of the fatigue life on the loading parameters (pre-strain, mean and amplitude values of strain) has been obtained. The results show a good agreement with available experimental data.

Direct numerical simulation of annular flows

NASA Astrophysics Data System (ADS)

Batchvarov, Assen; Kahouadji, Lyes; Chergui, Jalel; Juric, Damir; Shin, Seungwon; Craster, Richard V.; Matar, Omar K.

2017-11-01

Vertical counter-current two-phase flows are investigated using direct numerical simulations. The computations are carried out using Blue, a front-tracking-based CFD solver. Preliminary results show good qualitative agreement with experimental observations in terms of interfacial phenomena; these include three-dimensional, large-amplitude wave formation, the development of long ligaments, and droplet entrainment. The flooding phenomena in these counter current systems are closely investigated. The onset of flooding in our simulations is compared to existing empirical correlations such as Kutateladze-type and Wallis-type. The effect of varying tube diameter and fluid properties on the flooding phenomena is also investigated in this work. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM).

Evaluating the Credibility of Transport Processes in Simulations of Ozone Recovery using the Global Modeling Initiative Three-dimensional Model

NASA Technical Reports Server (NTRS)

Strahan, Susan E.; Douglass, Anne R.

2004-01-01

The Global Modeling Initiative (GMI) has integrated two 36-year simulations of an ozone recovery scenario with an offline chemistry and tra nsport model using two different meteorological inputs. Physically ba sed diagnostics, derived from satellite and aircraft data sets, are d escribed and then used to evaluate the realism of temperature and transport processes in the simulations. Processes evaluated include barri er formation in the subtropics and polar regions, and extratropical w ave-driven transport. Some diagnostics are especially relevant to sim ulation of lower stratospheric ozone, but most are applicable to any stratospheric simulation. The global temperature evaluation, which is relevant to gas phase chemical reactions, showed that both sets of me teorological fields have near climatological values at all latitudes and seasons at 30 hPa and below. Both simulations showed weakness in upper stratospheric wave driving. The simulation using input from a g eneral circulation model (GMI(GCM)) showed a very good residual circulation in the tropics and Northern Hemisphere. The simulation with inp ut from a data assimilation system (GMI(DAS)) performed better in the midlatitudes than it did at high latitudes. Neither simulation forms a realistic barrier at the vortex edge, leading to uncertainty in the fate of ozone-depleted vortex air. Overall, tracer transport in the offline GML(GCM) has greater fidelity throughout the stratosphere tha n it does in the GMI(DAS)

Numerical Study of Wake Vortex Interaction with the Ground Using the Terminal Area Simulation System

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Han, Jongil

1999-01-01

A sensitivity study for the in-ground effect on aircraft wake vortices has been conducted using a validated large eddy simulation model. The numerical results are compared with observed data and show good agreement for vortex decay and lateral vortex transport. The vortex decay rate is strongly influenced by the ground, but appears somewhat insensitive to ambient turbulence. In addition, the results show that the ground can affect the trajectory and descent-rate of a wake vortex pair at elevations up to about 3 b(sub o) (where b(sub o) is the initial vortex separation). However, the ground does not influence the average circulation of the vortices until the cores descend to within about 0.6 b(sub o), after which time the ground greatly enhances their rate of demise. Vortex rebound occurs in the simulations, but is more subtle than shown in previous numerical studies.

Effective Medium Ratio Obeying Wideband Left-Handed Miniaturized Meta-atoms for Multi-band Applications

NASA Astrophysics Data System (ADS)

Hossain, Mohammad Jakir; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2017-12-01

In this paper, a miniaturized wideband left-handed (LH) meta-atom based on planar modified multiple hexagonal split ring resonators was designed, simulated, fabricated and tested that can maintain a left-handed property. An analysis and comparison of the different array structures were performed that obtained better effective medium ratio (EMR) and wideband (5.54 GHz) for multi band operations in the microwave regime. Finite-difference time-domain (FDTD) method based Computer Simulation Technology was implemented to design the meta-atom. The meta-atom showed multi-band response in conjunction with wideband and LH property over the certain frequency bands in the microwave spectra. The EMR was considerably improved compared to previously reported meta-atoms. The measured results showed good agreement with the simulated results. The dimensions, S-parameters and EMR parameters of the proposed miniaturized LH meta-atom are appropriate for L-, S-, C-, X-, and Ku-band applications.

Effective Medium Ratio Obeying Wideband Left-Handed Miniaturized Meta-atoms for Multi-band Applications

NASA Astrophysics Data System (ADS)

Hossain, Mohammad Jakir; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2018-03-01

In this paper, a miniaturized wideband left-handed (LH) meta-atom based on planar modified multiple hexagonal split ring resonators was designed, simulated, fabricated and tested that can maintain a left-handed property. An analysis and comparison of the different array structures were performed that obtained better effective medium ratio (EMR) and wideband (5.54 GHz) for multi band operations in the microwave regime. Finite-difference time-domain (FDTD) method based Computer Simulation Technology was implemented to design the meta-atom. The meta-atom showed multi-band response in conjunction with wideband and LH property over the certain frequency bands in the microwave spectra. The EMR was considerably improved compared to previously reported meta-atoms. The measured results showed good agreement with the simulated results. The dimensions, S-parameters and EMR parameters of the proposed miniaturized LH meta-atom are appropriate for L-, S-, C-, X-, and Ku-band applications.

The APS SASE FEL : modeling and code comparison.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biedron, S. G.

A self-amplified spontaneous emission (SASE) free-electron laser (FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL.

Modelling of diesel engine fuelled with biodiesel using engine simulation software

NASA Astrophysics Data System (ADS)

Said, Mohd Farid Muhamad; Said, Mazlan; Aziz, Azhar Abdul

2012-06-01

This paper is about modelling of a diesel engine that operates using biodiesel fuels. The model is used to simulate or predict the performance and combustion of the engine by simplified the geometry of engine component in the software. The model is produced using one-dimensional (1D) engine simulation software called GT-Power. The fuel properties library in the software is expanded to include palm oil based biodiesel fuels. Experimental works are performed to investigate the effect of biodiesel fuels on the heat release profiles and the engine performance curves. The model is validated with experimental data and good agreement is observed. The simulation results show that combustion characteristics and engine performances differ when biodiesel fuels are used instead of no. 2 diesel fuel.

Optical modeling based on mean free path calculations for quantum dot phosphors applied to optoelectronic devices.

PubMed

Shin, Min-Ho; Kim, Hyo-Jun; Kim, Young-Joo

2017-02-20

We proposed an optical simulation model for the quantum dot (QD) nanophosphor based on the mean free path concept to understand precisely the optical performance of optoelectronic devices. A measurement methodology was also developed to get the desired optical characteristics such as the mean free path and absorption spectra for QD nanophosphors which are to be incorporated into the simulation. The simulation results for QD-based white LED and OLED displays show good agreement with the experimental values from the fabricated devices in terms of spectral power distribution, chromaticity coordinate, CCT, and CRI. The proposed simulation model and measurement methodology can be applied easily to the design of lots of optoelectronics devices using QD nanophosphors to obtain high efficiency and the desired color characteristics.

Car-to-pedestrian collision reconstruction with injury as an evaluation index.

PubMed

Weng, Yiliu; Jin, Xianlong; Zhao, Zhijie; Zhang, Xiaoyun

2010-07-01

Reconstruction of accidents is currently considered as a useful means in the analysis of accidents. By multi-body dynamics and numerical methods, and by adopting vehicle and pedestrian models, the scenario of the crash can often be simulated. When reconstructing the collisions, questions often arise regarding the criteria for the evaluation of simulation results. This paper proposes a reconstruction method for car-to-pedestrian collisions based on injuries of the pedestrians. In this method, pedestrian injury becomes a critical index in judging the correctness of the reconstruction result and guiding the simulation process. Application of this method to a real accident case is also presented in this paper. The study showed a good agreement between injuries obtained by numerical simulation and that by forensic identification. Copyright 2010 Elsevier Ltd. All rights reserved.

Improvements of the two-dimensional FDTD method for the simulation of normal- and superconducting planar waveguides using time series analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hofschen, S.; Wolff, I.

1996-08-01

Time-domain simulation results of two-dimensional (2-D) planar waveguide finite-difference time-domain (FDTD) analysis are normally analyzed using Fourier transform. The introduced method of time series analysis to extract propagation and attenuation constants reduces the desired computation time drastically. Additionally, a nonequidistant discretization together with an adequate excitation technique is used to reduce the number of spatial grid points. Therefore, it is possible to reduce the number of spatial grid points. Therefore, it is possible to simulate normal- and superconducting planar waveguide structures with very thin conductors and small dimensions, as they are used in MMIC technology. The simulation results are comparedmore » with measurements and show good agreement.« less

A Model for Simulating the Response of Aluminum Honeycomb Structure to Transverse Loading

NASA Technical Reports Server (NTRS)

Ratcliffe, James G.; Czabaj, Michael W.; Jackson, Wade C.

2012-01-01

A 1-dimensional material model was developed for simulating the transverse (thickness-direction) loading and unloading response of aluminum honeycomb structure. The model was implemented as a user-defined material subroutine (UMAT) in the commercial finite element analysis code, ABAQUS(Registered TradeMark)/Standard. The UMAT has been applied to analyses for simulating quasi-static indentation tests on aluminum honeycomb-based sandwich plates. Comparison of analysis results with data from these experiments shows overall good agreement. Specifically, analyses of quasi-static indentation tests yielded accurate global specimen responses. Predicted residual indentation was also in reasonable agreement with measured values. Overall, this simple model does not involve a significant computational burden, which makes it more tractable to simulate other damage mechanisms in the same analysis.

A molecular dynamics simulation study of chloroform

NASA Astrophysics Data System (ADS)

Tironi, Ilario G.; van Gunsteren, Wilfred F.

Three different chloroform models have been investigated using molecular dynamics computer simulation. The thermodynamic, structural and dynamic properties of the various models were investigated in detail. In particular, the potential energies, diffusion coefficients and rotational correlation times obtained for each model are compared with experiment. It is found that the theory of rotational Brownian motion fails in describing the rotational diffusion of chloroform. The force field of Dietz and Heinzinger was found to give good overall agreement with experiment. An extended investigation of this chloroform model has been performed. Values are reported for the isothermal compressibility, the thermal expansion coefficient and the constant volume heat capacity. The values agree well with experiment. The static and frequency dependent dielectric permittivity were computed from a 1·2 ns simulation conducted under reaction field boundary conditions. Considering the fact that the model is rigid with fixed partial charges, the static dielectric constant and Debye relaxation time compare well with experiment. From the same simulation the shear viscosity was computed using the off-diagonal elements of the pressure tensor, both via an Einstein type relation and via a Green-Kubo equation. The calculated viscosities show good agreement with experimental values. The excess Helmholtz energy is calculated using the thermodynamic integration technique and simulations of 50 and 80 ps. The value obtained for the excess Helmholtz energy matches the theoretical value within a few per cent.

Understanding the Central Equatorial African long-term drought using AMIP-type simulations

NASA Astrophysics Data System (ADS)

Hua, Wenjian; Zhou, Liming; Chen, Haishan; Nicholson, Sharon E.; Jiang, Yan; Raghavendra, Ajay

2018-02-01

Previous studies show that Indo-Pacific sea surface temperature (SST) variations may help to explain the observed long-term drought during April-May-June (AMJ) since the 1990s over Central equatorial Africa (CEA). However, the underlying physical mechanisms for this drought are still not clear due to observation limitations. Here we use the AMIP-type simulations with 24 ensemble members forced by observed SSTs from the ECHAM4.5 model to explore the likely physical processes that determine the rainfall variations over CEA. We not only examine the ensemble mean (EM), but also compare the "good" and "poor" ensemble members to understand the intra-ensemble variability. In general, EM and the "good" ensemble member can simulate the drought and associated reduced vertical velocity and anomalous anti-cyclonic circulation in the lower troposphere. However, the "poor" ensemble members cannot simulate the drought and associated circulation patterns. These contrasts indicate that the drought is tightly associated with the tropical Walker circulation and atmospheric teleconnection patterns. If the observational circulation patterns cannot be reproduced, the CEA drought will not be captured. Despite the large intra-ensemble spread, the model simulations indicate an essential role of SST forcing in causing the drought. These results suggest that the long-term drought may result from tropical Indo-Pacific SST variations associated with the enhanced and westward extended tropical Walker circulation.

Assessment of leaf carotenoids content with a new carotenoid index: Development and validation on experimental and model data

NASA Astrophysics Data System (ADS)

Zhou, Xianfeng; Huang, Wenjiang; Kong, Weiping; Ye, Huichun; Dong, Yingying; Casa, Raffaele

2017-05-01

Leaf carotenoids content (LCar) is an important indicator of plant physiological status. Accurate estimation of LCar provides valuable insight into early detection of stress in vegetation. With spectroscopy techniques, a semi-empirical approach based on spectral indices was extensively used for carotenoids content estimation. However, established spectral indices for carotenoids that generally rely on limited measured data, might lack predictive accuracy for carotenoids estimation in various species and at different growth stages. In this study, we propose a new carotenoid index (CARI) for LCar assessment based on a large synthetic dataset simulated from the leaf radiative transfer model PROSPECT-5, and evaluate its capability with both simulated data from PROSPECT-5 and 4SAIL and extensive experimental datasets: the ANGERS dataset and experimental data acquired in field experiments in China in 2004. Results show that CARI was the index most linearly correlated with carotenoids content at the leaf level using a synthetic dataset (R2 = 0.943, RMSE = 1.196 μg/cm2), compared with published spectral indices. Cross-validation results with CARI using ANGERS data achieved quite an accurate estimation (R2 = 0.545, RMSE = 3.413 μg/cm2), though the RBRI performed as the best index (R2 = 0.727, RMSE = 2.640 μg/cm2). CARI also showed good accuracy (R2 = 0.639, RMSE = 1.520 μg/cm2) for LCar assessment with leaf level field survey data, though PRI performed better (R2 = 0.710, RMSE = 1.369 μg/cm2). Whereas RBRI, PRI and other assessed spectral indices showed a good performance for a given dataset, overall their estimation accuracy was not consistent across all datasets used in this study. Conversely CARI was more robust showing good results in all datasets. Further assessment of LCar with simulated and measured canopy reflectance data indicated that CARI might not be very sensitive to LCar changes at low leaf area index (LAI) value, and in these conditions soil moisture influenced the LCar retrieval accuracy.

Evaluating the streamflow simulation capability of PERSIANN-CDR daily rainfall products in two river basins on the Tibetan Plateau

DOE PAGES

Liu, Xiaomang; Yang, Tiantian; Hsu, Koulin; ...

2017-01-10

On the Tibetan Plateau, the limited ground-based rainfall information owing to a harsh environment has brought great challenges to hydrological studies. Satellite-based rainfall products, which allow for a better coverage than both radar network and rain gauges on the Tibetan Plateau, can be suitable alternatives for studies on investigating the hydrological processes and climate change. In this study, a newly developed daily satellite-based precipitation product, termed Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks $-$ Climate Data Record (PERSIANN-CDR), is used as input for a hydrologic model to simulate streamflow in the upper Yellow and Yangtze River basinsmore » on the Tibetan Plateau. The results show that the simulated streamflows using PERSIANN-CDR precipitation and the Global Land Data Assimilation System (GLDAS) precipitation are closer to observation than that using limited gauge-based precipitation interpolation in the upper Yangtze River basin. The simulated streamflow using gauge-based precipitation are higher than the streamflow observation during the wet season. In the upper Yellow River basin, gauge-based precipitation, GLDAS precipitation, and PERSIANN-CDR precipitation have similar good performance in simulating streamflow. Finally, the evaluation of streamflow simulation capability in this study partly indicates that the PERSIANN-CDR rainfall product has good potential to be a reliable dataset and an alternative information source of a limited gauge network for conducting long-term hydrological and climate studies on the Tibetan Plateau.« less

In vitro digestion of curcuminoid-loaded lipid nanoparticles

NASA Astrophysics Data System (ADS)

Noack, Andreas; Oidtmann, Johannes; Kutza, Johannes; Mäder, Karsten

2012-09-01

Curcuminoid-loaded lipid nanoparticles were produced by melt homogenization. The used lipid matrices were medium chain triglycerides, trimyristin (TM), and tristearin. The mean particle size of the preparations was between 130 and 180 nm. The incorporated curcuminoids revealed a good stability over a period of 12 months. The curcuminoid-loaded lipid nanoparticles were intended for the oral delivery of curcuminoids. Therefore, the fate of the triglyceride matrix in simulated gastric and simulated intestinal media under the influence of pepsin and pancreatin, respectively, was assessed. The degradation of the triglycerides was monitored by the pH-stat method and with high performance thin layer chromatography in connection with spectrodensitometry to quantify the different lipid fractions. The TM nanoparticles were not degraded in simulated gastric fluid (SGF), but the decomposition of the triglyceride matrix was rapid in the intestinal media. The digestion process was faster in the simulated fed state medium compared to the simulated fasted state medium. Additionally, the stability of the incorporated drug was tested in the respective physiological media. The curcuminoids showed an overall good stability in the different test media. The release of the curcuminoids from the lipid nanoparticles was determined by fluorescence imaging techniques. A slow release of the drug was found in phosphate buffer. In contrast, a more distinct release of the curcuminoids was verifiable in SGF and in simulated intestinal fluids. Overall, it was considered that the transfer of the drug into the outer media was mainly triggered by the lipid degradation and not by drug release.

Evaluating the streamflow simulation capability of PERSIANN-CDR daily rainfall products in two river basins on the Tibetan Plateau

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiaomang; Yang, Tiantian; Hsu, Koulin

On the Tibetan Plateau, the limited ground-based rainfall information owing to a harsh environment has brought great challenges to hydrological studies. Satellite-based rainfall products, which allow for a better coverage than both radar network and rain gauges on the Tibetan Plateau, can be suitable alternatives for studies on investigating the hydrological processes and climate change. In this study, a newly developed daily satellite-based precipitation product, termed Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks $-$ Climate Data Record (PERSIANN-CDR), is used as input for a hydrologic model to simulate streamflow in the upper Yellow and Yangtze River basinsmore » on the Tibetan Plateau. The results show that the simulated streamflows using PERSIANN-CDR precipitation and the Global Land Data Assimilation System (GLDAS) precipitation are closer to observation than that using limited gauge-based precipitation interpolation in the upper Yangtze River basin. The simulated streamflow using gauge-based precipitation are higher than the streamflow observation during the wet season. In the upper Yellow River basin, gauge-based precipitation, GLDAS precipitation, and PERSIANN-CDR precipitation have similar good performance in simulating streamflow. Finally, the evaluation of streamflow simulation capability in this study partly indicates that the PERSIANN-CDR rainfall product has good potential to be a reliable dataset and an alternative information source of a limited gauge network for conducting long-term hydrological and climate studies on the Tibetan Plateau.« less

Extension and Validation of a Hybrid Particle-Finite Element Method for Hypervelocity Impact Simulation. Chapter 2

NASA Technical Reports Server (NTRS)

Fahrenthold, Eric P.; Shivarama, Ravishankar

2004-01-01

The hybrid particle-finite element method of Fahrenthold and Horban, developed for the simulation of hypervelocity impact problems, has been extended to include new formulations of the particle-element kinematics, additional constitutive models, and an improved numerical implementation. The extended formulation has been validated in three dimensional simulations of published impact experiments. The test cases demonstrate good agreement with experiment, good parallel speedup, and numerical convergence of the simulation results.

DSMC Simulation and Experimental Validation of Shock Interaction in Hypersonic Low Density Flow

PubMed Central

2014-01-01

Direct simulation Monte Carlo (DSMC) of shock interaction in hypersonic low density flow is developed. Three collision molecular models, including hard sphere (HS), variable hard sphere (VHS), and variable soft sphere (VSS), are employed in the DSMC study. The simulations of double-cone and Edney's type IV hypersonic shock interactions in low density flow are performed. Comparisons between DSMC and experimental data are conducted. Investigation of the double-cone hypersonic flow shows that three collision molecular models can predict the trend of pressure coefficient and the Stanton number. HS model shows the best agreement between DSMC simulation and experiment among three collision molecular models. Also, it shows that the agreement between DSMC and experiment is generally good for HS and VHS models in Edney's type IV shock interaction. However, it fails in the VSS model. Both double-cone and Edney's type IV shock interaction simulations show that the DSMC errors depend on the Knudsen number and the models employed for intermolecular interaction. With the increase in the Knudsen number, the DSMC error is decreased. The error is the smallest in HS compared with those in the VHS and VSS models. When the Knudsen number is in the level of 10−4, the DSMC errors, for pressure coefficient, the Stanton number, and the scale of interaction region, are controlled within 10%. PMID:24672360

A comparison between implicit and hybrid methods for the calculation of steady and unsteady inlet flows

NASA Technical Reports Server (NTRS)

Coakley, T. J.; Hsieh, T.

1985-01-01

Numerical simulation of steady and unsteady transonic diffuser flows using two different computer codes are discussed and compared with experimental data. The codes solve the Reynolds-averaged, compressible, Navier-Stokes equations using various turbulence models. One of the codes has been applied extensively to diffuser flows and uses the hybrid method of MacCormack. This code is relatively inefficient numerically. The second code, which was developed more recently, is fully implicit and is relatively efficient numerically. Simulations of steady flows using the implicit code are shown to be in good agreement with simulations using the hybrid code. Both simulations are in good agreement with experimental results. Simulations of unsteady flows using the two codes are in good qualitative agreement with each other, although the quantitative agreement is not as good as in the steady flow cases. The implicit code is shown to be eight times faster than the hybrid code for unsteady flow calculations and up to 32 times faster for steady flow calculations. Results of calculations using alternative turbulence models are also discussed.

The 48-Pictures Test: a two-alternative forced-choice recognition test for the detection of malingering.

PubMed

Chouinard, M J; Rouleau, I

1997-11-01

We tested the validity of the 48-Pictures Test, a 2-alternative forced-choice recognition test, in detecting exaggerated memory impairments. This test maximizes subjective difficulty, through a large number of stimuli and shows minimal objective difficulty. We compared 17 suspected malingerers to 39 patients with memory impairments (6 amnesic, 15 frontal lobe dysfunctions, 18 other etiologies), and 17 normal adults instructed to simulate malingering on three memory tests: the 48-Pictures Test, the Rey Auditory Verbal Learning Test (RAVLT), and the Rey Complex Figure Test (RCFT). On the 48-Pictures Test, the clinical groups showed good recognition performance (amnesics: 85%; frontal dysfunction: 94%; other memory impairments: 97%), whereas the two simulator groups showed a poor performance (suspected malingerers: 62% correct; volunteer simulators 68% correct). The two other tests did not show a high degree of discrimination between the clinical groups and the simulator groups, except in 2 measures: the 2 simulator groups tended to show a performance decrement from the last recall trial to immediate recognition of the RAVLT and also performed better than the clinical groups on the immediate recall of the RCFT. A discriminant analysis with the latter 2 measures and the 48-Pictures Test correctly classified 96% of the participants. These results suggest that the 48-Pictures Test is a useful tool for the detection of possible simulated memory impairment and that when combined to the RAVLT recall-recognition difference score and to the immediate recall score on the RCFT can provide strong evidence of exaggerated memory impairment.

Simulation of alnico coercivity

DOE PAGES

Ke, Liqin; Skomski, Ralph; Hoffmann, Todd D.; ...

2017-07-10

Micromagnetic simulations of alnico show substantial deviations from Stoner-Wohlfarth behavior due to the unique size and spatial distribution of the rod-like Fe-Co phase formed during spinodal decomposition in an external magnetic field. Furthemore, the maximum coercivity is limited by single-rod effects, especially deviations from ellipsoidal shape, and by interactions between the rods. In both the exchange interaction between connected rods and magnetostatic we consider the interaction between rods, and the results of our calculations show good agreement with recent experiments. Unlike systems dominated by magnetocrystalline anisotropy, coercivity in alnico is highly dependent on size, shape, and geometric distribution of themore » Fe-Co phase, all factors that can be tuned with appropriate chemistry and thermal-magnetic annealing.« less

Effect of two imidazolium derivatives of ionic liquids on the structure and activity of adenosine deaminase.

PubMed

Ajloo, Davood; Sangian, Masoomeh; Ghadamgahi, Maryam; Evini, Mina; Saboury, Ali Akbar

2013-04-01

The effect of two ionic liquids, 1-allyl 3-methyl-imidazolium (IL1) and 1-octhyl 3-methyl-imidozolium chlorides (IL2), on the structure and activity of adenosine deaminase (ADA) were described by UV-vis and fluorescence spectrophotometry in phosphate buffer and results were compared with docking and molecular dynamics (MD) simulation studies. All results showed that inhibition of activity and reduction of enzyme tertiary structure are more for octhyl than allyl derivative due to the more hydrophobic property of it. Finally structure parameters obtained from MD simulation showed that ionic liquid reduces intermolecular hydrogen bond and unfold enzyme structure. Calculation results are in good agreement with spectrophotometric studies. Copyright © 2013 Elsevier B.V. All rights reserved.

Design of 5.8 GHz Integrated Antenna on 180nm Complementary Metal Oxide Semiconductor (CMOS) Technology

NASA Astrophysics Data System (ADS)

Razak, A. H. A.; Shamsuddin, M. I. A.; Idros, M. F. M.; Halim, A. K.; Ahmad, A.; Junid, S. A. M. Al

2018-03-01

This project discusses the design and simulation performances of integrated loop antenna. Antenna is one of the main parts in any wireless radio frequency integrated circuit (RFIC). Naturally, antenna is the bulk in any RFIC design. Thus, this project aims to implement an integrated antenna on a single chip making the end product more compact. This project targets 5.8 GHz as the operating frequency of the integrated antenna for a transceiver module based on Silterra CMOS 180nm technology. The simulation of the antenna was done by using High Frequency Structure Simulator (HFSS). This software is industrial standard software that been used to simulate all electromagnetic effect including antenna simulation. This software has ability to simulate frequency at range of 100 MHz to 4 THz. The simulation set up in 3 dimension structure with driven terminal. The designed antenna has 1400um of diameter and placed on top metal layer. Loop configuration of the antenna has been chosen as the antenna design. From the configuration, it is able to make the chip more compact. The simulation shows that the antenna has single frequency band at center frequency 5.8 GHz with -48.93dB. The antenna radiation patterns shows, the antenna radiate at omnidirectional. From the simulation result, it could be concluded that the antenna have a good radiation pattern and propagation for wireless communication.

Correlation of Prediction and Actual Outcome of Three-Dimensional Simulation in Breast Augmentation Using a Cloud-Based Program.

PubMed

Vorstenbosch, Joshua; Islur, Avi

2017-06-01

Breast augmentation is among the most frequently performed cosmetic plastic surgeries. Providing patients with "realistic" 3D simulations of breast augmentation outcomes is becoming increasingly common. Until recently, such programs were costly and required significant equipment, training, and office space. New simple user-friendly cloud-based programs have been developed, but to date there remains a paucity of objective evidence comparing these 3D simulations with the post-operative outcomes. To determine the aesthetic similarity between pre-operative 3D simulation generated by Crisalix and real post-operative outcomes. A retrospective review of 20 patients receiving bilateral breast augmentation was conducted comparing 6-month post-operative outcomes with 3D simulation using Crisalix software. Similarities between post-operative and simulated images were measured by three attending plastic surgeons and ten plastic surgery residents using a series of parameters. Assessment reveals similarity between the 3D simulation and 6-month post-operative images for overall appearance, breast height, breast width, breast volume, breast projection, and nipple correction. Crisalix software generated more representative simulations for symmetric breasts than for tuberous or ptotic breasts. Comparison of overall aesthetic outcome to simulation showed that the post-operative outcome was more appealing for the symmetric and tuberous breasts and less appealing for the ptotic breasts. Our data suggest that Crisalix offers a good overall 3D simulated image of post-operative breast augmentation outcomes. Improvements to the simulation of the post-operative outcomes for ptotic and tuberous breasts would result in greater predictive capabilities of Crisalix. Collectively, Crisalix offers good predictive simulations for symmetric breasts. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors http://www.springer.com/00266 .

Simulations of 6-DOF Motion with a Cartesian Method

NASA Technical Reports Server (NTRS)

Murman, Scott M.; Aftosmis, Michael J.; Berger, Marsha J.; Kwak, Dochan (Technical Monitor)

2003-01-01

Coupled 6-DOF/CFD trajectory predictions using an automated Cartesian method are demonstrated by simulating a GBU-32/JDAM store separating from an F-18C aircraft. Numerical simulations are performed at two Mach numbers near the sonic speed, and compared with flight-test telemetry and photographic-derived data. Simulation results obtained with a sequential-static series of flow solutions are contrasted with results using a time-dependent flow solver. Both numerical methods show good agreement with the flight-test data through the first half of the simulations. The sequential-static and time-dependent methods diverge over the last half of the trajectory prediction. after the store produces peak angular rates. A cost comparison for the Cartesian method is included, in terms of absolute cost and relative to computing uncoupled 6-DOF trajectories. A detailed description of the 6-DOF method, as well as a verification of its accuracy, is provided in an appendix.

Validation of pore network simulations of ex-situ water distributions in a gas diffusion layer of proton exchange membrane fuel cells with X-ray tomographic images

NASA Astrophysics Data System (ADS)

Agaesse, Tristan; Lamibrac, Adrien; Büchi, Felix N.; Pauchet, Joel; Prat, Marc

2016-11-01

Understanding and modeling two-phase flows in the gas diffusion layer (GDL) of proton exchange membrane fuel cells are important in order to improve fuel cells performance. They are scientifically challenging because of the peculiarities of GDLs microstructures. In the present work, simulations on a pore network model are compared to X-ray tomographic images of water distributions during an ex-situ water invasion experiment. A method based on watershed segmentation was developed to extract a pore network from the 3D segmented image of the dry GDL. Pore network modeling and a full morphology model were then used to perform two-phase simulations and compared to the experimental data. The results show good agreement between experimental and simulated microscopic water distributions. Pore network extraction parameters were also benchmarked using the experimental data and results from full morphology simulations.

Contribution of land use changes to meteorological parameters in Greater Jakarta: Case 17 January 2014

NASA Astrophysics Data System (ADS)

Nuryanto, D. E.; Pawitan, H.; Hidayat, R.; Aldrian, E.

2018-05-01

The impact of land use changes on meteorological parameters during a heavy rainfall event on 17 January 2014 in Greater Jakarta (GJ) was examined using the Weather Research and Forecasting (WRF) model. This study performed two experimental simulation methods. The first WRF simulation uses default land use (CTL). The second simulation applies the experiment by changing the size of urban and built-up land use (SCE). The Global Forecast System (GFS) data is applied to provide more realistic initial and boundary conditions for the nested model domains (3 km, 1 km). The simulations were initiated at 00:00 UTC January 13, 2014 and the period of modeling was equal to six days. The air temperature and the precipitation pattern in GJ shows a good agreement between the observed and simulated data. The results show a consistent significant contribution of urban development and accompany land use changes in air temperature and precipitation. According to the model simulation, urban and built-up land contributed about 6% of heavy rainfall and about 0.2 degrees of air temperatures in the morning. Simulations indicate that new urban developments led to an intensification and expansion of the rain area. The results can support the decision-making of flooding and watershed management.

Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential

NASA Astrophysics Data System (ADS)

Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

2015-12-01

To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06016h

Good Exemplars of Natural Scene Categories Elicit Clearer Patterns than Bad Exemplars but Not Greater BOLD Activity

PubMed Central

Torralbo, Ana; Walther, Dirk B.; Chai, Barry; Caddigan, Eamon; Fei-Fei, Li; Beck, Diane M.

2013-01-01

Within the range of images that we might categorize as a “beach”, for example, some will be more representative of that category than others. Here we first confirmed that humans could categorize “good” exemplars better than “bad” exemplars of six scene categories and then explored whether brain regions previously implicated in natural scene categorization showed a similar sensitivity to how well an image exemplifies a category. In a behavioral experiment participants were more accurate and faster at categorizing good than bad exemplars of natural scenes. In an fMRI experiment participants passively viewed blocks of good or bad exemplars from the same six categories. A multi-voxel pattern classifier trained to discriminate among category blocks showed higher decoding accuracy for good than bad exemplars in the PPA, RSC and V1. This difference in decoding accuracy cannot be explained by differences in overall BOLD signal, as average BOLD activity was either equivalent or higher for bad than good scenes in these areas. These results provide further evidence that V1, RSC and the PPA not only contain information relevant for natural scene categorization, but their activity patterns mirror the fundamentally graded nature of human categories. Analysis of the image statistics of our good and bad exemplars shows that variability in low-level features and image structure is higher among bad than good exemplars. A simulation of our neuroimaging experiment suggests that such a difference in variance could account for the observed differences in decoding accuracy. These results are consistent with both low-level models of scene categorization and models that build categories around a prototype. PMID:23555588

Simulation and experimental research of 1MWe solar tower power plant in China

NASA Astrophysics Data System (ADS)

Yu, Qiang; Wang, Zhifeng; Xu, Ershu

2016-05-01

The establishment of a reliable simulation system for a solar tower power plant can greatly increase the economic and safety performance of the whole system. In this paper, a dynamic model of the 1MWe Solar Tower Power Plant at Badaling in Beijing is developed based on the "STAR-90" simulation platform, including the heliostat field, the central receiver system (water/steam), etc. The dynamic behavior of the global CSP plant can be simulated. In order to verify the validity of simulation system, a complete experimental process was synchronously simulated by repeating the same operating steps based on the simulation platform, including the locations and number of heliostats, the mass flow of the feed water, etc. According to the simulation and experimental results, some important parameters are taken out to make a deep comparison. The results show that there is good alignment between the simulations and the experimental results and that the error range can be acceptable considering the error of the models. In the end, a comprehensive and deep analysis on the error source is carried out according to the comparative results.

Comparison of Measured and Numerically Simulated Turbulence Statistics in a Convective Boundary Layer Over Complex Terrain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rai, Raj K.; Berg, Larry K.; Kosović, Branko

High resolution numerical simulation can provide insight into important physical processes that occur within the planetary boundary layer (PBL). The present work employs large eddy simulation (LES) using the Weather Forecasting and Research (WRF) model, with the LES domain nested within mesoscale simulation, to simulate real conditions in the convective PBL over an area of complex terrain. A multiple nesting approach has been used to downsize the grid spacing from 12.15 km (mesoscale) to 0.03 km (LES). A careful selection of grid spacing in the WRF Meso domain has been conducted to minimize artifacts in the WRF-LES solutions. The WRF-LESmore » results have been evaluated with in situ and remote sensing observations collected during the US Department of Energy-supported Columbia BasinWind Energy Study (CBWES). Comparison of the first- and second-order moments, turbulence spectrum, and probability density function (PDF) of wind speed shows good agreement between the simulations and data. Furthermore, the WRF-LES variables show a great deal of variability in space and time caused by the complex topography in the LES domain. The WRF-LES results show that the flow structures, such as roll vortices and convective cells, vary depending on both the location and time of day. In addition to basic studies related to boundary-layer meteorology, results from these simulations can be used in other applications, such as studying wind energy resources, atmospheric dispersion, fire weather etc.« less

Cognitive deficits are associated with poorer simulated driving in older adults with heart failure

PubMed Central

2013-01-01

Background Cognitive impairment is prevalent in older adults with heart failure (HF) and associated with reduced functional independence. HF patients appear at risk for reduced driving ability, as past work in other medical samples has shown cognitive dysfunction to be an important contributor to driving performance. The current study examined whether cognitive dysfunction was independently associated with reduced driving simulation performance in a sample of HF patients. Methods 18 persons with HF (67.72; SD = 8.56 year) completed echocardiogram and a brief neuropsychological test battery assessing global cognitive function, attention/executive function, memory and motor function. All participants then completed the Kent Multidimensional Assessment Driving Simulation (K-MADS), a driving simulator scenario with good psychometric properties. Results The sample exhibited an average Mini Mental State Examination (MMSE) score of 27.83 (SD = 2.09). Independent sample t-tests showed that HF patients performed worse than healthy adults on the driving simulation scenario. Finally, partial correlations showed worse attention/executive and motor function were independently associated with poorer driving simulation performance across several indices reflective of driving ability (i.e., centerline crossings, number of collisions, % of time over the speed limit, among others). Conclusion The current findings showed that reduced cognitive function was associated with poor simulated driving performance in older adults with HF. If replicated using behind-the-wheel testing, HF patients may be at elevated risk for unsafe driving and routine driving evaluations in this population may be warranted. PMID:24499466

GPAW - massively parallel electronic structure calculations with Python-based software.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enkovaara, J.; Romero, N.; Shende, S.

2011-01-01

Electronic structure calculations are a widely used tool in materials science and large consumer of supercomputing resources. Traditionally, the software packages for these kind of simulations have been implemented in compiled languages, where Fortran in its different versions has been the most popular choice. While dynamic, interpreted languages, such as Python, can increase the effciency of programmer, they cannot compete directly with the raw performance of compiled languages. However, by using an interpreted language together with a compiled language, it is possible to have most of the productivity enhancing features together with a good numerical performance. We have used thismore » approach in implementing an electronic structure simulation software GPAW using the combination of Python and C programming languages. While the chosen approach works well in standard workstations and Unix environments, massively parallel supercomputing systems can present some challenges in porting, debugging and profiling the software. In this paper we describe some details of the implementation and discuss the advantages and challenges of the combined Python/C approach. We show that despite the challenges it is possible to obtain good numerical performance and good parallel scalability with Python based software.« less

In Silico Evaluation of the Impacts of Quorum Sensing Inhibition (QSI) on Strain Competition and Development of QSI Resistance

NASA Astrophysics Data System (ADS)

Wei, Guopeng; Lo, Chieh; Walsh, Connor; Hiller, N. Luisa; Marculescu, Radu

2016-10-01

As understanding of bacterial regulatory systems and pathogenesis continues to increase, QSI has been a major focus of research. However, recent studies have shown that mechanisms of resistance to quorum sensing (QS) inhibitors (QSIs) exist, calling into question their clinical value. We propose a computational framework that considers bacteria genotypes relative to QS genes and QS-regulated products including private, quasi-public, and public goods according to their impacts on bacterial fitness. Our results show (1) QSI resistance spreads when QS positively regulates the expression of private or quasi-public goods. (2) Resistance to drugs targeting secreted compounds downstream of QS for a mix of private, public, and quasi-public goods also spreads. (3) Changing the micro-environment during treatment with QSIs may decrease the spread of resistance. At fundamental-level, our simulation framework allows us to directly quantify cell-cell interactions and biofilm dynamics. Practically, the model provides a valuable tool for the study of QSI-based therapies, and the simulations reveal experimental paths that may guide QSI-based therapies in a manner that avoids or decreases the spread of QSI resistance.

Monte Carlo simulation for Neptun 10 PC medical linear accelerator and calculations of output factor for electron beam

PubMed Central

Bahreyni Toossi, Mohammad Taghi; Momennezhad, Mehdi; Hashemi, Seyed Mohammad

2012-01-01

Aim Exact knowledge of dosimetric parameters is an essential pre-requisite of an effective treatment in radiotherapy. In order to fulfill this consideration, different techniques have been used, one of which is Monte Carlo simulation. Materials and methods This study used the MCNP-4Cb to simulate electron beams from Neptun 10 PC medical linear accelerator. Output factors for 6, 8 and 10 MeV electrons applied to eleven different conventional fields were both measured and calculated. Results The measurements were carried out by a Wellhofler-Scanditronix dose scanning system. Our findings revealed that output factors acquired by MCNP-4C simulation and the corresponding values obtained by direct measurements are in a very good agreement. Conclusion In general, very good consistency of simulated and measured results is a good proof that the goal of this work has been accomplished. PMID:24377010

Numerical Modeling of Flow Control in a Boundary-Layer-Ingesting Offset Inlet Diffuser at Transonic Mach Numbers

NASA Technical Reports Server (NTRS)

Allan, Brian G.; Owens, Lewis R.

2006-01-01

This paper will investigate the validation of the NASA developed, Reynolds-averaged Navier-Stokes (RANS) flow solver, OVERFLOW, for a boundary-layer-ingesting (BLI) offset (S-shaped) inlet in transonic flow with passive and active flow control devices as well as a baseline case. Numerical simulations are compared to wind tunnel results of a BLI inlet experiment conducted at the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. Comparisons of inlet flow distortion, pressure recovery, and inlet wall pressures are performed. The numerical simulations are compared to the BLI inlet data at a free-stream Mach number of 0.85 and a Reynolds number of approximately 2 million based on the fanface diameter. The numerical simulations with and without tunnel walls are performed, quantifying tunnel wall effects on the BLI inlet flow. A comparison is made between the numerical simulations and the BLI inlet experiment for the baseline and VG vane cases at various inlet mass flow rates. A comparison is also made to a BLI inlet jet configuration for varying actuator mass flow rates at a fixed inlet mass flow rate. Overall, the numerical simulations were able to predict the baseline circumferential flow distortion, DPCP avg, very well within the designed operating range of the BLI inlet. A comparison of the average total pressure recovery showed that the simulations were able to predict the trends but had a negative 0.01 offset when compared to the experimental levels. Numerical simulations of the baseline inlet flow also showed good agreement with the experimental inlet centerline surface pressures. The vane case showed that the CFD predicted the correct trends in the circumferential distortion levels for varying inlet mass flow but had a distortion level that was nearly twice as large as the experiment. Comparison to circumferential distortion measurements for a 15 deg clocked 40 probe rake indicated that the circumferential distortion levels are very sensitive to the symmetry of the flow and that a misalignment of the vanes in the experiment could have resulted in this difference. The numerical simulations of the BLI inlet with jets showed good agreement with the circumferential inlet distortion levels for a range of jet actuator mass flow ratios at a fixed inlet mass flow rate. The CFD simulations for the jet case also predicted an average total pressure recovery offset that was 0.01 lower than the experiment as was seen in the baseline. Comparisons of the flow features for the jet cases revealed that the CFD predicted a much larger vortex at the engine fan-face when compare to the experiment.

Monte Carlo simulation of particle-induced bit upsets

NASA Astrophysics Data System (ADS)

Wrobel, Frédéric; Touboul, Antoine; Vaillé, Jean-Roch; Boch, Jérôme; Saigné, Frédéric

2017-09-01

We investigate the issue of radiation-induced failures in electronic devices by developing a Monte Carlo tool called MC-Oracle. It is able to transport the particles in device, to calculate the energy deposited in the sensitive region of the device and to calculate the transient current induced by the primary particle and the secondary particles produced during nuclear reactions. We compare our simulation results with SRAM experiments irradiated with neutrons, protons and ions. The agreement is very good and shows that it is possible to predict the soft error rate (SER) for a given device in a given environment.

Propulsion system mathematical model for a lift/cruise fan V/STOL aircraft

NASA Technical Reports Server (NTRS)

Cole, G. L.; Sellers, J. F.; Tinling, B. E.

1980-01-01

A propulsion system mathematical model is documented that allows calculation of internal engine parameters during transient operation. A non-realtime digital computer simulation of the model is presented. It is used to investigate thrust response and modulation requirements as well as the impact of duty cycle on engine life and design criteria. Comparison of simulation results with steady-state cycle deck calculations showed good agreement. The model was developed for a specific 3-fan subsonic V/STOL aircraft application, but it can be adapted for use with any similar lift/cruise V/STOL configuration.

Comparison of heavy-ion- and electron-beam upset data for GaAS SRAMS. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flesner, L.D.; Zuleeg, R.; Kolasinski, W.A.

1992-07-16

We report the results of experiments designed to evaluate the extent to which focused electron-beam pulses simulate energetic ion upset phenomena in GaAs memory circuits fabricated by the McDonnell Douglas Astronautics Company. The results of two experimental methods were compared, irradiation by heavy-ion particle beams, and upset mapping using focused electron pulses. Linear energy transfer (LET) thresholds and upset cross sections are derived from the data for both methods. A comparison of results shows good agreement, indicating that for these circuits electron-beam pulse mapping is a viable simulation technique.

High-pressure melting of molybdenum.

PubMed

Belonoshko, A B; Simak, S I; Kochetov, A E; Johansson, B; Burakovsky, L; Preston, D L

2004-05-14

The melting curve of the body-centered cubic (bcc) phase of Mo has been determined for a wide pressure range using both direct ab initio molecular dynamics simulations of melting as well as a phenomenological theory of melting. These two methods show very good agreement. The simulations are based on density functional theory within the generalized gradient approximation. Our calculated equation of state of bcc Mo is in excellent agreement with experimental data. However, our melting curve is substantially higher than the one determined in diamond anvil cell experiments up to a pressure of 100 GPa. An explanation is suggested for this discrepancy.

Millimeter-Wave Wireless Power Transfer Technology for Space Applications

NASA Technical Reports Server (NTRS)

Chattopadhyay, Goutam; Manohara, Harish; Mojarradi, Mohammad M.; Vo, Tuan A.; Mojarradi, Hadi; Bae, Sam Y.; Marzwell, Neville

2008-01-01

In this paper we present a new compact, scalable, and low cost technology for efficient receiving of power using RF waves at 94 GHz. This technology employs a highly innovative array of slot antennas that is integrated on substrate composed of gold (Au), silicon (Si), and silicon dioxide (SiO2) layers. The length of the slots and spacing between them are optimized for a highly efficient beam through a 3-D electromagnetic simulation process. Antenna simulation results shows a good beam profile with very low side lobe levels and better than 93% antenna efficiency.

A numerical model for simulation of bioremediation of hydrocarbons in aquifers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Munoz, J.F.; Irarrazaval, M.J.

1998-03-01

A numerical model was developed to describe the bioremediation of hydrocarbons in ground water aquifers considering aerobic degradation. The model solves the independent transport of three solutes (oxygen, hydrocarbons, and microorganisms) in ground water flow using the method of characteristics. Interactions between the three solutes, in which oxygen and hydrocarbons are consumed by microorganisms, are represented by Monod kinetics, solved using a Runge-Kutta method. Model simulations showed good correlation as compared with results of soil column experiments. The model was used to estimate the time needed to remediate the columns, which varied from one to two years.

A neural network controller of a flotation process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durao, F.; Cortez, L.

1995-12-31

The dynamic control of a froth flotation section is simulated through a neural network feedback controller, trained in order to stabilize the concentrate metal grade and recovery by applying random step changes to the feed metal grade. The results of the application example show that this controller seems to be sufficiently robust and a good alternative to handle a non-linear process.

Regardless-of-Speed Superconducting LSM Controlled-Repulsive MAGLEV Vehicle

NASA Technical Reports Server (NTRS)

Yoshida, Kinjiro; Egashira, Tatsuya; Hirai, Ryuichi

1996-01-01

This paper proposes a new repulsive Maglev vehicle which a superconducting linear synchronous motor (LSM) can levitate and propel simultaneously, independently of the vehicle speeds. The combined levitation and propulsion control is carried out by controlling mechanical-load angle and armature-current. Dynamic simulations show successful operations with good ride-quality by using a compact control method proposed here.

Study of the effect of short ranged ordering on the magnetism in FeCr alloys

NASA Astrophysics Data System (ADS)

Jena, Ambika Prasad; Sanyal, Biplab; Mookerjee, Abhijit

2014-01-01

For the study of magnetism in systems where the local environment plays an important role, we propose a marriage between the Monte Carlo simulation and Zunger's special quasi-random structures. We apply this technique on disordered FeCr alloys and show that our estimates of the transition temperature is in good agreement with earlier experiments.

Continuum simulation of the discharge of the granular silo: a validation test for the μ(I) visco-plastic flow law.

PubMed

Staron, L; Lagrée, P-Y; Popinet, S

2014-01-01

Using a continuum Navier-Stokes solver with the μ(I) flow law implemented to model the viscous behavior, and the discrete Contact Dynamics algorithm, the discharge of granular silos is simulated in two dimensions from the early stages of the discharge until complete release of the material. In both cases, the Beverloo scaling is recovered. We first do not attempt a quantitative comparison, but focus on the qualitative behavior of velocity and pressure at different locations in the flow. A good agreement for the velocity is obtained in the regions of rapid flows, while areas of slow creep are not entirely captured by the continuum model. The pressure field shows a general good agreement, while bulk deformations are found to be similar in both approaches. The influence of the parameters of the μ(I) flow law is systematically investigated, showing the importance of the dependence on the inertial number I to achieve quantitative agreement between continuum and discrete discharge. However, potential problems involving the systems size, the configuration and "non-local" effects, are suggested. Yet the general ability of the continuum model to reproduce qualitatively the granular behavior is found to be very encouraging.

Flexible and conformable broadband metamaterial absorber with wide-angle and polarization stability for radar application

NASA Astrophysics Data System (ADS)

Chen, Huijie; Yang, Xiaoqing; Wu, Shiyue; Zhang, Di; Xiao, Hui; Huang, Kama; Zhu, Zhanxia; Yuan, Jianping

2018-01-01

In this work, a type of flexible, broadband electromagnetic microwave absorber is designed, fabricated and experimentally characterized. The absorber is composed of lumped resistors loaded frequency selective surface which is mounted on flexible substrate using silicone rubber and in turn backed by copper film. The simulated results show that an effective absorption (over 90%) bandwidth spans from 7.6 to 18.3 GHz, which covers both X (8-12 GHz) and Ku (12-18 GHz) bands, namely a 82.6% fraction bandwidth. And the bandwidth performs a good absorption response by varying the incident angle up to 60° for both TE and TM polarization. Moreover, the flexibility of the substrate enables the absorber conformably to bend and attach to cylinders of various radius without breakdown of the absorber. The designed structure has been fabricated and measured for both planar and conformable cases, and absorption responses show a good agreement of the broadband absorption feature with the simulated ones. This work has demonstrated specifically that proposed structure provides polarization-insensitive, wide-angle, flexible and conformable wideband absorption, which extends the absorber’s application to practical radar cross section reductions for radars and warships.

Shear wave velocity imaging using transient electrode perturbation: phantom and ex vivo validation.

PubMed

DeWall, Ryan J; Varghese, Tomy; Madsen, Ernest L

2011-03-01

This paper presents a new shear wave velocity imaging technique to monitor radio-frequency and microwave ablation procedures, coined electrode vibration elastography. A piezoelectric actuator attached to an ablation needle is transiently vibrated to generate shear waves that are tracked at high frame rates. The time-to-peak algorithm is used to reconstruct the shear wave velocity and thereby the shear modulus variations. The feasibility of electrode vibration elastography is demonstrated using finite element models and ultrasound simulations, tissue-mimicking phantoms simulating fully (phantom 1) and partially ablated (phantom 2) regions, and an ex vivo bovine liver ablation experiment. In phantom experiments, good boundary delineation was observed. Shear wave velocity estimates were within 7% of mechanical measurements in phantom 1 and within 17% in phantom 2. Good boundary delineation was also demonstrated in the ex vivo experiment. The shear wave velocity estimates inside the ablated region were higher than mechanical testing estimates, but estimates in the untreated tissue were within 20% of mechanical measurements. A comparison of electrode vibration elastography and electrode displacement elastography showed the complementary information that they can provide. Electrode vibration elastography shows promise as an imaging modality that provides ablation boundary delineation and quantitative information during ablation procedures.

Compact planar monopole antenna for wearable wireless applications

NASA Astrophysics Data System (ADS)

Andriamiharivolamena, Tsitoha; Lemaître-Auger, Pierre; Tedjini, Smail; Tirard, Franck

2015-11-01

We report in this paper the design and the realization of a compact wearable monopole antenna directly placed over an Artificial Magnetic Conductor (AMC), which is located directly on the body. The major contribution is that there is no space between the monopole and the AMC, or between the AMC and the body. Simulation results and measurements are in good agreement and show that the antenna's performances are as good as the best ones reported so far in the literature, while having a smaller volume. The antenna operates at 1.92 GHz with a bandwidth of 8%. The reflection coefficient of the antenna is - 35 dB. The measurement of the antenna gain provides a value of 4.3 dBi with a half-power beamwidth of 70° and a front-to-back radiation ratio of 15.8 dB. Measurement and simulation results also show that the AMC isolates well the monopole from the body: the localized Specific Absorption Rate (SAR) value calculated with 1 g of tissue is 0.34 W/kg with an injected power of 1 W. The antenna with the AMC is well adapted for wearable applications.

Mutual Amide Prodrug of Etodolac-glucosamine: Synthesis, Characterization and Pharmacological Screening

PubMed Central

Pandey, Preeti; Pandey, S.; Dubey, Shaifali

2013-01-01

Etodolac, a nonsteroidal antiinflammatory drug, widely used in arthritis is associated with gastric ulceration and irritation due to presence of free carboxylic group. The current investigation reports synthesis of mutual amide prodrug of etodolac by masking free carboxylic group with glucosamine, a nutritional supplement for treatment of arthritis. Confirmation and characterization of the structure of the synthesized prodrug done by elemental and spectroscopy analysis, melting point, determination of migration parameters (Rf, RM, and Rt) by using thin layer chromatography and high performance liquid chromatography, respectively. Partition coefficient and solubility study confirms its lipophilic character so can be suitable candidate for controlled release delivery. In vitro hydrolytic studies of prodrug confirms good rate of hydrolysis in blood plasma, fecal matter, and simulated intestinal fluid while stable in gastric simulated fluid. In vivo pharmacological screening performed on animals. Prodrug with respect to etodolac shows good analgesic, antiinflammatory, and antiarthritic activity. The prodrug was assessed for their probable damaging effects by ulcerogeniticity and histopathological analysis. The histopathological studies showed less ulceration in the gastric region when treated with prodrug, thereby proving the prodrug to be better in action as compared to etodolac and are advantageous in having less gastrointestinal side effects. PMID:24302794

A novel hybrid algorithm for the design of the phase diffractive optical elements for beam shaping

NASA Astrophysics Data System (ADS)

Jiang, Wenbo; Wang, Jun; Dong, Xiucheng

2013-02-01

In this paper, a novel hybrid algorithm for the design of a phase diffractive optical elements (PDOE) is proposed. It combines the genetic algorithm (GA) with the transformable scale BFGS (Broyden, Fletcher, Goldfarb, Shanno) algorithm, the penalty function was used in the cost function definition. The novel hybrid algorithm has the global merits of the genetic algorithm as well as the local improvement capabilities of the transformable scale BFGS algorithm. We designed the PDOE using the conventional simulated annealing algorithm and the novel hybrid algorithm. To compare the performance of two algorithms, three indexes of the diffractive efficiency, uniformity error and the signal-to-noise ratio are considered in numerical simulation. The results show that the novel hybrid algorithm has good convergence property and good stability. As an application example, the PDOE was used for the Gaussian beam shaping; high diffractive efficiency, low uniformity error and high signal-to-noise were obtained. The PDOE can be used for high quality beam shaping such as inertial confinement fusion (ICF), excimer laser lithography, fiber coupling laser diode array, laser welding, etc. It shows wide application value.

Hybrid thermal link-wise artificial compressibility method

NASA Astrophysics Data System (ADS)

Obrecht, Christian; Kuznik, Frédéric

2015-10-01

Thermal flow prediction is a subject of interest from a scientific and engineering points of view. Our motivation is to develop an accurate, easy to implement and highly scalable method for convective flows simulation. To this end, we present an extension to the link-wise artificial compressibility method (LW-ACM) for thermal simulation of weakly compressible flows. The novel hybrid formulation uses second-order finite difference operators of the energy equation based on the same stencils as the LW-ACM. For validation purposes, the differentially heated cubic cavity was simulated. The simulations remained stable for Rayleigh numbers up to Ra =108. The Nusselt numbers at isothermal walls and dynamics quantities are in good agreement with reference values from the literature. Our results show that the hybrid thermal LW-ACM is an effective and easy-to-use solution to solve convective flows.

Modeling and simulation of a 2-DOF bidirectional electrothermal microactuator

NASA Astrophysics Data System (ADS)

Topaloglu, N.; Elbuken, C.; Nieva, P. M.; Yavuz, M.; Huissoon, J. P.

2008-03-01

In this paper we present the modeling and simulation of a 2 degree-of-freedom (DOF) bidirectional electrothermal actuator. The four arm microactuator was designed to move in both the horizontal and vertical axes. By tailoring the geometrical parameters of the design, the in-plane and out-of-plane motions were decoupled, resulting in enhanced mobility in both directions. The motion of the actuator was modeled analytically using an electro-thermo-mechanical analysis. To validate the analytical model, finite element simulations were performed using ANSYS. The microactuators were fabricated using PolyMUMPS process and experimental results show good agreement with both the analytical model and the simulations. We demonstrated that the 2-DOF bidirectional electrothermal actuator can achieve 3.7 μm in-plane and 13.3 μm out-of-plane deflections with an input voltage of 10 V.

Investigation of neutron interactions with Ge detectors

NASA Astrophysics Data System (ADS)

Baginova, Miloslava; Vojtyla, Pavol; Povinec, Pavel P.

2018-07-01

Interactions of neutrons with a high-purity germanium detector were studied experimentally and by simulations using the GEANT4 tool. Elastic and inelastic scattering of fast neutrons as well as neutron capture on Ge nuclei were observed. Peaks induced by inelastic scattering of neutrons on 70Ge, 72Ge, 73Ge, 74Ge and 76Ge were well visible in the γ-ray spectra. In addition, peaks due to inelastic scattering of neutrons on copper and lead nuclei, including the well-known peak of 208Pb at 2614.51 keV, were detected. The GEANT4 simulations showed that the simulated spectrum was in a good agreement with the experimental one. Differences between the simulated and the measured spectra were due to the high γ-ray intensity of the used neutron source, physics implemented in GEANT4 and contamination of the neutron source.

Evaluation of a subject-specific, torque-driven computer simulation model of one-handed tennis backhand groundstrokes.

PubMed

Kentel, Behzat B; King, Mark A; Mitchell, Sean R

2011-11-01

A torque-driven, subject-specific 3-D computer simulation model of the impact phase of one-handed tennis backhand strokes was evaluated by comparing performance and simulation results. Backhand strokes of an elite subject were recorded on an artificial tennis court. Over the 50-ms period after impact, good agreement was found with an overall RMS difference of 3.3° between matching simulation and performance in terms of joint and racket angles. Consistent with previous experimental research, the evaluation process showed that grip tightness and ball impact location are important factors that affect postimpact racket and arm kinematics. Associated with these factors, the model can be used for a better understanding of the eccentric contraction of the wrist extensors during one-handed backhand ground strokes, a hypothesized mechanism of tennis elbow.

Accurate Mapping of Multilevel Rydberg Atoms on Interacting Spin-1 /2 Particles for the Quantum Simulation of Ising Models

NASA Astrophysics Data System (ADS)

de Léséleuc, Sylvain; Weber, Sebastian; Lienhard, Vincent; Barredo, Daniel; Büchler, Hans Peter; Lahaye, Thierry; Browaeys, Antoine

2018-03-01

We study a system of atoms that are laser driven to n D3 /2 Rydberg states and assess how accurately they can be mapped onto spin-1 /2 particles for the quantum simulation of anisotropic Ising magnets. Using nonperturbative calculations of the pair potentials between two atoms in the presence of electric and magnetic fields, we emphasize the importance of a careful selection of experimental parameters in order to maintain the Rydberg blockade and avoid excitation of unwanted Rydberg states. We benchmark these theoretical observations against experiments using two atoms. Finally, we show that in these conditions, the experimental dynamics observed after a quench is in good agreement with numerical simulations of spin-1 /2 Ising models in systems with up to 49 spins, for which numerical simulations become intractable.

Electron backscattering simulation in Geant4

NASA Astrophysics Data System (ADS)

Dondero, Paolo; Mantero, Alfonso; Ivanchencko, Vladimir; Lotti, Simone; Mineo, Teresa; Fioretti, Valentina

2018-06-01

The backscattering of electrons is a key phenomenon in several physics applications which range from medical therapy to space including AREMBES, the new ESA simulation framework for radiation background effects. The importance of properly reproducing this complex interaction has grown considerably in the last years and the Geant4 Monte Carlo simulation toolkit, recently upgraded to the version 10.3, is able to comply with the AREMBES requirements in a wide energy range. In this study a validation of the electron Geant4 backscattering models is performed with respect to several experimental data. In addition a selection of the most recent validation results on the electron scattering processes is also presented. Results of our analysis show a good agreement between simulations and data from several experiments, confirming the Geant4 electron backscattering models to be robust and reliable up to a few tens of electronvolts.

A method to reproduce alpha-particle spectra measured with semiconductor detectors.

PubMed

Timón, A Fernández; Vargas, M Jurado; Sánchez, A Martín

2010-01-01

A method is proposed to reproduce alpha-particle spectra measured with silicon detectors, combining analytical and computer simulation techniques. The procedure includes the use of the Monte Carlo method to simulate the tracks of alpha-particles within the source and in the detector entrance window. The alpha-particle spectrum is finally obtained by the convolution of this simulated distribution and the theoretical distributions representing the contributions of the alpha-particle spectrometer to the spectrum. Experimental spectra from (233)U and (241)Am sources were compared with the predictions given by the proposed procedure, showing good agreement. The proposed method can be an important aid for the analysis and deconvolution of complex alpha-particle spectra. Copyright 2009 Elsevier Ltd. All rights reserved.

A scale model wind tunnel study of dispersion in the Cleveland area. Laboratory simulation of lake breeze effects on diffusion from ground level emissions

NASA Technical Reports Server (NTRS)

Hoydysh, W. G.

1974-01-01

A wind tunnel simulation of the diffusion patterns in a sea breeze was attempted. The results indicate that the low level onshore flow was well simulated for neutral, stable, unstable, and elevated inversion conditions. Velocity, turbulence, shear stress, and temperature data were taken, and the spread of emissions from ground level sources was investigated. Comparison is made with theoretical predictions by E. Inoue and with the open, homogeneous plane field results of Pasquill. Agreement with the predictions by Inoue is good, and the comparison with Pasquill's results shows that the wind tunnel flows are shifted two categories towards more stable. The discrepancy may be explained as a matter of averaging time.

The one-dimensional minesweeper game: What are your chances of winning?

NASA Astrophysics Data System (ADS)

Rodríguez-Achach, M.; Coronel-Brizio, H. F.; Hernández-Montoya, A. R.; Huerta-Quintanilla, R.; Canto-Lugo, E.

2016-04-01

Minesweeper is a famous computer game consisting usually in a two-dimensional lattice, where cells can be empty or mined and gamers are required to locate the mines without dying. Even if minesweeper seems to be a very simple system, it has some complex and interesting properties as NP-completeness. In this paper and for the one-dimensional case, given a lattice of n cells and m mines, we calculate the winning probability. By numerical simulations this probability is also estimated. We also find out by mean of these simulations that there exists a critical density of mines that minimize the probability of winning the game. Analytical results and simulations are compared showing a very good agreement.

Parallel Dynamics Simulation Using a Krylov-Schwarz Linear Solution Scheme

DOE PAGES

Abhyankar, Shrirang; Constantinescu, Emil M.; Smith, Barry F.; ...

2016-11-07

Fast dynamics simulation of large-scale power systems is a computational challenge because of the need to solve a large set of stiff, nonlinear differential-algebraic equations at every time step. The main bottleneck in dynamic simulations is the solution of a linear system during each nonlinear iteration of Newton’s method. In this paper, we present a parallel Krylov- Schwarz linear solution scheme that uses the Krylov subspacebased iterative linear solver GMRES with an overlapping restricted additive Schwarz preconditioner. As a result, performance tests of the proposed Krylov-Schwarz scheme for several large test cases ranging from 2,000 to 20,000 buses, including amore » real utility network, show good scalability on different computing architectures.« less

Simulation of the temperature increase in human cadaver retina during direct illumination by 150-kHz femtosecond laser pulses

PubMed Central

Sun, Hui; Hosszufalusi, Nora; Mikula, Eric R.; Juhasz, Tibor

2011-01-01

We have developed a two-dimensional computer model to predict the temperature increase of the retina during femtosecond corneal laser flap cutting. Simulating a typical clinical setting for 150-kHz iFS advanced femtosecond laser (0.8- to 1-μJ laser pulse energy and 15-s procedure time at a laser wavelength of 1053 nm), the temperature increase is 0.2°C. Calculated temperature profiles show good agreement with data obtained from ex vivo experiments using human cadaver retina. Simulation results obtained for different commercial femtosecond lasers indicate that during the laser in situ keratomileusis procedure the temperature increase of the retina is insufficient to induce damage. PMID:22029369

Simulation of Surface Pressure Induced by Vortex/Body Interaction

NASA Astrophysics Data System (ADS)

He, M.; Islam, M.; Veitch, B.; Bose, N.; Colbourne, M. B.; Liu, P.

When a strong vortical wake impacts a structure, the pressure on the impacted surface sees large variations in its amplitude. This pressure fluctuation is one of the main sources causing severe structural vibration and hydrodynamic noise. Economical and effective prediction methods of the fluctuating pressure are required by engineers in many fields. This paper presents a wake impingement model (WIM) that has been incorporated into a panel method code, Propella, and its applications in simulations of a podded propeller wake impacting on a strut. Simulated strut surface pressure distributions and variations are compared with experimental data in terms of time-averaged components and phase-averaged components. The pressure comparisons show that the calculated results are in a good agreement with experimental data.

Parallel Dynamics Simulation Using a Krylov-Schwarz Linear Solution Scheme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abhyankar, Shrirang; Constantinescu, Emil M.; Smith, Barry F.

Fast dynamics simulation of large-scale power systems is a computational challenge because of the need to solve a large set of stiff, nonlinear differential-algebraic equations at every time step. The main bottleneck in dynamic simulations is the solution of a linear system during each nonlinear iteration of Newton’s method. In this paper, we present a parallel Krylov- Schwarz linear solution scheme that uses the Krylov subspacebased iterative linear solver GMRES with an overlapping restricted additive Schwarz preconditioner. As a result, performance tests of the proposed Krylov-Schwarz scheme for several large test cases ranging from 2,000 to 20,000 buses, including amore » real utility network, show good scalability on different computing architectures.« less

Supernova spectra below strong circumstellar interaction

NASA Astrophysics Data System (ADS)

Leloudas, G.; Hsiao, E. Y.; Johansson, J.; Maeda, K.; Moriya, T. J.; Nordin, J.; Petrushevska, T.; Silverman, J. M.; Sollerman, J.; Stritzinger, M. D.; Taddia, F.; Xu, D.

2015-02-01

We construct spectra of supernovae (SNe) interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum, and an emission-line spectrum. In a Monte Carlo simulation we vary a large number of parameters, such as the SN type, brightness and phase, the strength of the CSM interaction, the extinction, and the signal to noise ratio (S/N) of the observed spectrum. We generate more than 800 spectra, distribute them to ten different human classifiers, and study how the different simulation parameters affect the appearance of the spectra and their classification. The SNe IIn showing some structure over the continuum were characterized as "SNe IInS" to allow for a better quantification. We demonstrate that the flux ratio of the underlying SN to the continuum fV is the single most important parameter determining whether a spectrum can be classified correctly. Other parameters, such as extinction, S/N, and the width and strength of the emission lines, do not play a significant role. Thermonuclear SNe get progressively classified as Ia-CSM, IInS, and IIn as fV decreases. The transition between Ia-CSM and IInS occurs at fV ~ 0.2-0.3. It is therefore possible to determine that SNe Ia-CSM are found at the (un-extincted) magnitude range -19.5 >M> -21.6, in very good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The literature sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does not support that this association can be attributed to a luminosity bias (91T-like being brighter than normal events). We therefore conclude that this association has real physical origins and we propose that 91T-like explosions result from single degenerate progenitors that are responsible for the CSM. Despite the spectroscopic similarities between SNe Ibc and SNe Ia, the number of misclassifications between these types was very small in our simulation and mostly at low S/N. Combined with the SN luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Hα profiles vary with fV. SNe IIn fainter than M = -17.2 are unable to mask SNe IIP brighter than M = -15. A more advanced simulation, including radiative transfer, shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement with real data.

Microstructure simulation of rapidly solidified ASP30 high-speed steel particles by gas atomization

NASA Astrophysics Data System (ADS)

Ma, Jie; Wang, Bo; Yang, Zhi-liang; Wu, Guang-xin; Zhang, Jie-yu; Zhao, Shun-li

2016-03-01

In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element (CAFE) model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions (UDFs) to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also investigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy (SEM). The experimental results showed that four major types of microstructures were formed: dendritic, equiaxed, mixed, and multi-droplet microstructures. The simulated results and the available experimental data are in good agreement.

3D simulation of friction stir welding based on movable cellular automaton method

NASA Astrophysics Data System (ADS)

Eremina, Galina M.

2017-12-01

The paper is devoted to a 3D computer simulation of the peculiarities of material flow taking place in friction stir welding (FSW). The simulation was performed by the movable cellular automaton (MCA) method, which is a representative of particle methods in mechanics. Commonly, the flow of material in FSW is simulated based on computational fluid mechanics, assuming the material as continuum and ignoring its structure. The MCA method considers a material as an ensemble of bonded particles. The rupture of interparticle bonds and the formation of new bonds enable simulations of crack nucleation and healing as well as mas mixing and microwelding. The simulation results showed that using pins of simple shape (cylinder, cone, and pyramid) without a shoulder results in small displacements of plasticized material in workpiece thickness directions. Nevertheless, the optimal ratio of longitudinal velocity to rotational speed makes it possible to transport the welded material around the pin several times and to produce a joint of good quality.

Shot Peening Numerical Simulation of Aircraft Aluminum Alloy Structure

NASA Astrophysics Data System (ADS)

Liu, Yong; Lv, Sheng-Li; Zhang, Wei

2018-03-01

After shot peening, the 7050 aluminum alloy has good anti-fatigue and anti-stress corrosion properties. In the shot peening process, the pellet collides with target material randomly, and generated residual stress distribution on the target material surface, which has great significance to improve material property. In this paper, a simplified numerical simulation model of shot peening was established. The influence of pellet collision velocity, pellet collision position and pellet collision time interval on the residual stress of shot peening was studied, which is simulated by the ANSYS/LS-DYNA software. The analysis results show that different velocity, different positions and different time intervals have great influence on the residual stress after shot peening. Comparing with the numerical simulation results based on Kriging model, the accuracy of the simulation results in this paper was verified. This study provides a reference for the optimization of the shot peening process, and makes an effective exploration for the precise shot peening numerical simulation.

A simplified DEM-CFD approach for pebble bed reactor simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y.; Ji, W.

In pebble bed reactors (PBR's), the pebble flow and the coolant flow are coupled with each other through coolant-pebble interactions. Approaches with different fidelities have been proposed to simulate similar phenomena. Coupled Discrete Element Method-Computational Fluid Dynamics (DEM-CFD) approaches are widely studied and applied in these problems due to its good balance between efficiency and accuracy. In this work, based on the symmetry of the PBR geometry, a simplified 3D-DEM/2D-CFD approach is proposed to speed up the DEM-CFD simulation without significant loss of accuracy. Pebble flow is simulated by a full 3-D DEM, while the coolant flow field is calculatedmore » with a 2-D CFD simulation by averaging variables along the annular direction in the cylindrical geometry. Results show that this simplification can greatly enhance the efficiency for cylindrical core, which enables further inclusion of other physics such as thermal and neutronic effect in the multi-physics simulations for PBR's. (authors)« less

Non-stationary Return Levels of CMIP5 Multi-model Temperature Extremes

DOE PAGES

Cheng, L.; Phillips, T. J.; AghaKouchak, A.

2015-05-01

The objective of this study is to evaluate to what extent the CMIP5 climate model simulations of the climate of the twentieth century can represent observed warm monthly temperature extremes under a changing environment. The biases and spatial patterns of 2-, 10-, 25-, 50- and 100-year return levels of the annual maxima of monthly mean temperature (hereafter, annual temperature maxima) from CMIP5 simulations are compared with those of Climatic Research Unit (CRU) observational data considered under a non-stationary assumption. The results show that CMIP5 climate models collectively underestimate the mean annual maxima over arid and semi-arid regions that are mostmore » subject to severe heat waves and droughts. Furthermore, the results indicate that most climate models tend to underestimate the historical annual temperature maxima over the United States and Greenland, while generally disagreeing in their simulations over cold regions. Return level analysis shows that with respect to the spatial patterns of the annual temperature maxima, there are good agreements between the CRU observations and most CMIP5 simulations. However, the magnitudes of the simulated annual temperature maxima differ substantially across individual models. Discrepancies are generally larger over higher latitudes and cold regions.« less

Moving-window dynamic optimization: design of stimulation profiles for walking.

PubMed

Dosen, Strahinja; Popović, Dejan B

2009-05-01

The overall goal of the research is to improve control for electrical stimulation-based assistance of walking in hemiplegic individuals. We present the simulation for generating offline input (sensors)-output (intensity of muscle stimulation) representation of walking that serves in synthesizing a rule-base for control of electrical stimulation for restoration of walking. The simulation uses new algorithm termed moving-window dynamic optimization (MWDO). The optimization criterion was to minimize the sum of the squares of tracking errors from desired trajectories with the penalty function on the total muscle efforts. The MWDO was developed in the MATLAB environment and tested using target trajectories characteristic for slow-to-normal walking recorded in healthy individual and a model with the parameters characterizing the potential hemiplegic user. The outputs of the simulation are piecewise constant intensities of electrical stimulation and trajectories generated when the calculated stimulation is applied to the model. We demonstrated the importance of this simulation by showing the outputs for healthy and hemiplegic individuals, using the same target trajectories. Results of the simulation show that the MWDO is an efficient tool for analyzing achievable trajectories and for determining the stimulation profiles that need to be delivered for good tracking.

A Progressive Damage Model for unidirectional Fibre Reinforced Composites with Application to Impact and Penetration Simulation

NASA Astrophysics Data System (ADS)

Kerschbaum, M.; Hopmann, C.

2016-06-01

The computationally efficient simulation of the progressive damage behaviour of continuous fibre reinforced plastics is still a challenging task with currently available computer aided engineering methods. This paper presents an original approach for an energy based continuum damage model which accounts for stress-/strain nonlinearities, transverse and shear stress interaction phenomena, quasi-plastic shear strain components, strain rate effects, regularised damage evolution and consideration of load reversal effects. The physically based modelling approach enables experimental determination of all parameters on ply level to avoid expensive inverse analysis procedures. The modelling strategy, implementation and verification of this model using commercially available explicit finite element software are detailed. The model is then applied to simulate the impact and penetration of carbon fibre reinforced cross-ply specimens with variation of the impact speed. The simulation results show that the presented approach enables a good representation of the force-/displacement curves and especially well agreement with the experimentally observed fracture patterns. In addition, the mesh dependency of the results were assessed for one impact case showing only very little change of the simulation results which emphasises the general applicability of the presented method.

High-Alpha Research Vehicle Lateral-Directional Control Law Description, Analyses, and Simulation Results

NASA Technical Reports Server (NTRS)

Davidson, John B.; Murphy, Patrick C.; Lallman, Frederick J.; Hoffler, Keith D.; Bacon, Barton J.

1998-01-01

This report contains a description of a lateral-directional control law designed for the NASA High-Alpha Research Vehicle (HARV). The HARV is a F/A-18 aircraft modified to include a research flight computer, spin chute, and thrust-vectoring in the pitch and yaw axes. Two separate design tools, CRAFT and Pseudo Controls, were integrated to synthesize the lateral-directional control law. This report contains a description of the lateral-directional control law, analyses, and nonlinear simulation (batch and piloted) results. Linear analysis results include closed-loop eigenvalues, stability margins, robustness to changes in various plant parameters, and servo-elastic frequency responses. Step time responses from nonlinear batch simulation are presented and compared to design guidelines. Piloted simulation task scenarios, task guidelines, and pilot subjective ratings for the various maneuvers are discussed. Linear analysis shows that the control law meets the stability margin guidelines and is robust to stability and control parameter changes. Nonlinear batch simulation analysis shows the control law exhibits good performance and meets most of the design guidelines over the entire range of angle-of-attack. This control law (designated NASA-1A) was flight tested during the Summer of 1994 at NASA Dryden Flight Research Center.

Geophysical and botanical monitoring of simulated graves in a tropical rainforest, Colombia, South America

NASA Astrophysics Data System (ADS)

Molina, Carlos Martin; Pringle, Jamie K.; Saumett, Miguel; Evans, Gethin T.

2016-12-01

In most Latin American countries there are significant numbers of missing people and forced disappearances, currently 80,000 only in Colombia. Successful detection of shallow buried human remains by forensic search teams is currently difficult in varying terrain and climates. Within this research we built four simulated clandestine burial styles in tropical rainforests, as this is a common scenario and depositional environment encountered in Latin America, to gain knowledge of optimum forensic geophysics detection techniques. The results of geophysically monitoring these burials using ground penetrating radar, magnetic susceptibility, bulk ground conductivity and electrical resistivity are presented from one to forty three weeks post-burial. Radar survey results with both the 250 MHz and 500 MHz frequency antennae showed good detection of modern simulated burials on 2D profiles and horizontal time slices but poor detection on the other simulated graves. Magnetic susceptibility, bulk ground conductivity and electrical resistivity results were generally poor at detecting the simulated targets. Observations of botanical variations on the test site show rapid regrowth of Malvaceae and Petiveria alliacea vegetation over all burials that are common in these forests, which can make detection more difficult.

Pharmacophore modeling, molecular docking, and molecular dynamics simulation approaches for identifying new lead compounds for inhibiting aldose reductase 2.

PubMed

Sakkiah, Sugunadevi; Thangapandian, Sundarapandian; Lee, Keun Woo

2012-07-01

Aldose reductase 2 (ALR2), which catalyzes the reduction of glucose to sorbitol using NADP as a cofactor, has been implicated in the etiology of secondary complications of diabetes. A pharmacophore model, Hypo1, was built based on 26 compounds with known ALR2-inhibiting activity values. Hypo1 contains important chemical features required for an ALR2 inhibitor, and demonstrates good predictive ability by having a high correlation coefficient (0.95) as well as the highest cost difference (128.44) and the lowest RMS deviation (1.02) among the ten pharmacophore models examined. Hypo1 was further validated by Fisher's randomization method (95%), test set (r = 0.91), and the decoy set shows the goodness of fit (0.70). Furthermore, during virtual screening, Hypo1 was used as a 3D query to screen the NCI database, and the hit leads were sorted by applying Lipinski's rule of five and ADME properties. The best-fitting leads were subjected to docking to identify a suitable orientation at the ALR2 active site. The molecule that showed the strongest interactions with the critical amino acids was used in molecular dynamics simulations to calculate its binding affinity to the candidate molecules. Thus, Hypo1 describes the key structure-activity relationship along with the estimated activities of ALR2 inhibitors. The hit molecules were searched against PubChem to find similar molecules with new scaffolds. Finally, four molecules were found to satisfy all of the chemical features and the geometric constraints of Hypo1, as well as to show good dock scores, PLPs and PMFs. Thus, we believe that Hypo1 facilitates the selection of novel scaffolds for ALR2, allowing new classes of ALR2 inhibitors to be designed.

Development of a reactive-dispersive plume model

NASA Astrophysics Data System (ADS)

Kim, Hyun S.; Kim, Yong H.; Song, Chul H.

2017-04-01

A reactive-dispersive plume model (RDPM) was developed in this study. The RDPM can consider two main components of large-scale point source plume: i) turbulent dispersion and ii) photochemical reactions. In order to evaluate the simulation performance of newly developed RDPM, the comparisons between the model-predicted and observed mixing ratios were made using the TexAQS II 2006 (Texas Air Quality Study II 2006) power-plant experiment data. Statistical analyses show good correlation (0.61≤R≤0.92), and good agreement with the Index of Agreement (0.70≤R≤0.95). The chemical NOx lifetimes for two power-plant plumes (Monticello and Welsh power plants) were also estimated.

Application of distributed optical fiber sensing technologies to the monitoring of leakage and abnormal disturbance of oil pipeline

NASA Astrophysics Data System (ADS)

Yang, Xiaojun; Zhu, Xiaofei; Deng, Chi; Li, Junyi; Liu, Cheng; Yu, Wenpeng; Luo, Hui

2017-10-01

To improve the level of management and monitoring of leakage and abnormal disturbance of long distance oil pipeline, the distributed optical fiber temperature and vibration sensing system is employed to test the feasibility for the healthy monitoring of a domestic oil pipeline. The simulating leakage and abnormal disturbance affairs of oil pipeline are performed in the experiment. It is demonstrated that the leakage and abnormal disturbance affairs of oil pipeline can be monitored and located accurately with the distributed optical fiber sensing system, which exhibits good performance in the sensitivity, reliability, operation and maintenance etc., and shows good market application prospect.

Characterization of the Body-to-Body Propagation Channel for Subjects during Sports Activities.

PubMed

Mohamed, Marshed; Cheffena, Michael; Moldsvor, Arild

2018-02-18

Body-to-body wireless networks (BBWNs) have great potential to find applications in team sports activities among others. However, successful design of such systems requires great understanding of the communication channel as the movement of the body components causes time-varying shadowing and fading effects. In this study, we present results of the measurement campaign of BBWN during running and cycling activities. Among others, the results indicated the presence of good and bad states with each state following a specific distribution for the considered propagation scenarios. This motivated the development of two-state semi-Markov model, for simulation of the communication channels. The simulation model was validated using the available measurement data in terms of first and second order statistics and have shown good agreement. The first order statistics obtained from the simulation model as well as the measured results were then used to analyze the performance of the BBWNs channels under running and cycling activities in terms of capacity and outage probability. Cycling channels showed better performance than running, having higher channel capacity and lower outage probability, regardless of the speed of the subjects involved in the measurement campaign.

Investigations of FAK inhibitors: a combination of 3D-QSAR, docking, and molecular dynamics simulations studies.

PubMed

Cheng, Peng; Li, Jiaojiao; Wang, Juan; Zhang, Xiaoyun; Zhai, Honglin

2018-05-01

Focal adhesion kinase (FAK) is one kind of tyrosine kinases that modulates integrin and growth factor signaling pathways, which is a promising therapeutic target because of involving in cancer cell migration, proliferation, and survival. To investigate the mechanism between FAK and triazinic inhibitors and design high activity inhibitors, a molecular modeling integrated with 3D-QSAR, molecular docking, molecular dynamics simulations, and binding free energy calculations was performed. The optimum CoMFA and CoMSIA models showed good reliability and satisfactory predictability (with Q 2  = 0.663, R 2  = 0.987, [Formula: see text] = 0.921 and Q 2  = 0.670, R 2  = 0.981, [Formula: see text] = 0.953). Its contour maps could provide structural features to improve inhibitory activity. Furthermore, a good consistency between contour maps, docking, and molecular dynamics simulations strongly demonstrates that the molecular modeling is reliable. Based on it, we designed several new compounds and their inhibitory activities were validated by the molecular models. We expect our studies could bring new ideas to promote the development of novel inhibitors with higher inhibitory activity for FAK.

The natural oscillation of two types of ENSO events based on analyses of CMIP5 model control runs

NASA Astrophysics Data System (ADS)

Xu, Kang; Su, Jingzhi; Zhu, Congwen

2014-07-01

The eastern- and central-Pacific El Niño-Southern Oscillation (EP- and CP-ENSO) have been found to be dominant in the tropical Pacific Ocean, and are characterized by interannual and decadal oscillation, respectively. In the present study, we defined the EP- and CP-ENSO modes by singular value decomposition (SVD) between SST and sea level pressure (SLP) anomalous fields. We evaluated the natural features of these two types of ENSO modes as simulated by the pre-industrial control runs of 20 models involved in phase five of the Coupled Model Intercomparison Project (CMIP5). The results suggested that all the models show good skill in simulating the SST and SLP anomaly dipolar structures for the EP-ENSO mode, but only 12 exhibit good performance in simulating the tripolar CP-ENSO modes. Wavelet analysis suggested that the ensemble principal components in these 12 models exhibit an interannual and multi-decadal oscillation related to the EP- and CP-ENSO, respectively. Since there are no changes in external forcing in the pre-industrial control runs, such a result implies that the decadal oscillation of CP-ENSO is possibly a result of natural climate variability rather than external forcing.

Environmental Flow for Sungai Johor Estuary

NASA Astrophysics Data System (ADS)

Adilah, A. Kadir; Zulkifli, Yusop; Zainura, Z. Noor; Bakhiah, Baharim N.

2018-03-01

Sungai Johor estuary is a vital water body in the south of Johor and greatly affects the water quality in the Johor Straits. In the development of the hydrodynamic and water quality models for Sungai Johor estuary, the Environmental Fluid Dynamics Code (EFDC) model was selected. In this application, the EFDC hydrodynamic model was configured to simulate time varying surface elevation, velocity, salinity, and water temperature. The EFDC water quality model was configured to simulate dissolved oxygen (DO), dissolved organic carbon (DOC), chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N), nitrate nitrogen (NO3-N), phosphate (PO4), and Chlorophyll a. The hydrodynamic and water quality model calibration was performed utilizing a set of site specific data acquired in January 2008. The simulated water temperature, salinity and DO showed good and fairly good agreement with observations. The calculated correlation coefficients between computed and observed temperature and salinity were lower compared with the water level. Sensitivity analysis was performed on hydrodynamic and water quality models input parameters to quantify their impact on modeling results such as water surface elevation, salinity and dissolved oxygen concentration. It is anticipated and recommended that the development of this model be continued to synthesize additional field data into the modeling process.

Contribution of cosmic ray particles to radiation environment at high mountain altitude: Comparison of Monte Carlo simulations with experimental data.

PubMed

Mishev, A L

2016-03-01

A numerical model for assessment of the effective dose due to secondary cosmic ray particles of galactic origin at high mountain altitude of about 3000 m above the sea level is presented. The model is based on a newly numerically computed effective dose yield function considering realistic propagation of cosmic rays in the Earth magnetosphere and atmosphere. The yield function is computed using a full Monte Carlo simulation of the atmospheric cascade induced by primary protons and α- particles and subsequent conversion of secondary particle fluence (neutrons, protons, gammas, electrons, positrons, muons and charged pions) to effective dose. A lookup table of the newly computed effective dose yield function is provided. The model is compared with several measurements. The comparison of model simulations with measured spectral energy distributions of secondary cosmic ray neutrons at high mountain altitude shows good consistency. Results from measurements of radiation environment at high mountain station--Basic Environmental Observatory Moussala (42.11 N, 23.35 E, 2925 m a.s.l.) are also shown, specifically the contribution of secondary cosmic ray neutrons. A good agreement with the model is demonstrated. Copyright © 2015 Elsevier Ltd. All rights reserved.

Simulation of Degraded Properties of 2D plain Woven C/SiC Composites under Preloading Oxidation Atmosphere

NASA Astrophysics Data System (ADS)

Chen, Xihui; Sun, Zhigang; Sun, Jianfen; Song, Yingdong

2017-12-01

In this paper, a numerical model which incorporates the oxidation damage model and the finite element model of 2D plain woven composites is presented for simulation of the oxidation behaviors of 2D plain woven C/SiC composite under preloading oxidation atmosphere. The equal proportional reduction method is firstly proposed to calculate the residual moduli and strength of unidirectional C/SiC composite. The multi-scale method is developed to simulate the residual elastic moduli and strength of 2D plain woven C/SiC composite. The multi-scale method is able to accurately predict the residual elastic modulus and strength of the composite. Besides, the simulated residual elastic moduli and strength of 2D plain woven C/SiC composites under preloading oxidation atmosphere show good agreements with experimental results. Furthermore, the preload, oxidation time, temperature and fiber volume fractions of the composite are investigated to show their influences upon the residual elastic modulus and strength of 2D plain woven C/SiC composites.

Geometric integrator for simulations in the canonical ensemble

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tapias, Diego, E-mail: diego.tapias@nucleares.unam.mx; Sanders, David P., E-mail: dpsanders@ciencias.unam.mx; Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139

2016-08-28

We introduce a geometric integrator for molecular dynamics simulations of physical systems in the canonical ensemble that preserves the invariant distribution in equations arising from the density dynamics algorithm, with any possible type of thermostat. Our integrator thus constitutes a unified framework that allows the study and comparison of different thermostats and of their influence on the equilibrium and non-equilibrium (thermo-)dynamic properties of a system. To show the validity and the generality of the integrator, we implement it with a second-order, time-reversible method and apply it to the simulation of a Lennard-Jones system with three different thermostats, obtaining good conservationmore » of the geometrical properties and recovering the expected thermodynamic results. Moreover, to show the advantage of our geometric integrator over a non-geometric one, we compare the results with those obtained by using the non-geometric Gear integrator, which is frequently used to perform simulations in the canonical ensemble. The non-geometric integrator induces a drift in the invariant quantity, while our integrator has no such drift, thus ensuring that the system is effectively sampling the correct ensemble.« less

Comparative simulations of microjetting using atomistic and continuous approaches in presence of viscosity and surface tension

NASA Astrophysics Data System (ADS)

Durand, Olivier; Soulard, Laurent; Jaouen, Stephane; Heuze, Olivier; Colombet, Laurent; Cieren, Emmanuel

2017-06-01

We compare, at similar scales, the processes of microjetting and ejecta production from shocked roughened metal surfaces by using atomistic and continuous approaches. The atomistic approach is based on very large scale molecular dynamics (MD) simulations. The continuous approach is based on Eulerian hydrodynamics simulations with adaptive mesh refinement; the simulations take into account the effects of viscosity and surface tension, and they use an equation of state calculated from the MD simulations. The microjetting is generated by shock-loading above its fusion point a three-dimensional tin crystal with an initial sinusoidal free surface perturbation, the crystal being set in contact with a vacuum. Several samples with homothetic wavelengths and amplitudes of defect are simulated in order to investigate the influence of the viscosity and surface tension of the metal. The simulations show that the hydrodynamic code reproduces with a very good agreement the distributions, calculated from the MD simulations, of the ejected mass and velocity along the jet. Both codes exhibit also a similar phenomenology of fragmentation of the metallic liquid sheets ejected.

Structure and dynamics of aqueous solutions from PBE-based first-principles molecular dynamics simulations.

PubMed

Pham, Tuan Anh; Ogitsu, Tadashi; Lau, Edmond Y; Schwegler, Eric

2016-10-21

Establishing an accurate and predictive computational framework for the description of complex aqueous solutions is an ongoing challenge for density functional theory based first-principles molecular dynamics (FPMD) simulations. In this context, important advances have been made in recent years, including the development of sophisticated exchange-correlation functionals. On the other hand, simulations based on simple generalized gradient approximation (GGA) functionals remain an active field, particularly in the study of complex aqueous solutions due to a good balance between the accuracy, computational expense, and the applicability to a wide range of systems. Such simulations are often performed at elevated temperatures to artificially "correct" for GGA inaccuracies in the description of liquid water; however, a detailed understanding of how the choice of temperature affects the structure and dynamics of other components, such as solvated ions, is largely unknown. To address this question, we carried out a series of FPMD simulations at temperatures ranging from 300 to 460 K for liquid water and three representative aqueous solutions containing solvated Na + , K + , and Cl - ions. We show that simulations at 390-400 K with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional yield water structure and dynamics in good agreement with experiments at ambient conditions. Simultaneously, this computational setup provides ion solvation structures and ion effects on water dynamics consistent with experiments. Our results suggest that an elevated temperature around 390-400 K with the PBE functional can be used for the description of structural and dynamical properties of liquid water and complex solutions with solvated ions at ambient conditions.

Trace Gases and Aerosols Simulated Over the Indian Domain: Evaluation of the Model Wrf-Chem

NASA Astrophysics Data System (ADS)

Michael, M.; Yadav, A.; Tripathi, S. N.; Venkataraman, C.; Kanawade, V. P.

2012-12-01

As the anthropogenic emissions from the Asian countries contribute substantially to the global aerosol loading, the study of the distribution of trace gases and aerosols over this region has received increasing attention in recent years. In the present work, the aerosol properties over the Indian domain during the pre-monsoon season has been addressed. The "online" meteorological and chemical transport Weather Research and Forecasting-Chemistry (WRF-Chem) model has been implemented over Indian subcontinent for three consecutive summers in 2008, 2009 and 2010.The initial and boundary conditions are obtained from NCAR reanalysis data. The global emission inventories (REanalysis of the TROpospheric chemical composition (RETRO) and Emissions Database for Global Atmospheric Research (EDGAR)) have been used and are projected for the period of study using the method provided in Ohara et al. (2007). The emission rates of sulfur dioxide, black carbon, organic carbon and PM2.5 available in the global inventory are replaced with the high resolution emission inventory developed over India for the present study. The model simulates meteorological parameters, trace gases and particulate matter. Simulated mixing ratios of trace gases (Ozone, carbon monoxide, nitrogen oxides, and SO2) are compared with ground based as well as satellite observations over India with specific focus on Indo-Gangetic Plain. Simulated aerosol optical depth are in good agreement with those observed by Aerosol Robotic Network (AERONET). The vertical profiles of extinction coefficient have been compared with the Micro Pulse Lidar Network (MPLnet) data. The simulated mass concentration of BC shows very good agreement with those observed at a few ground stations. The vertical profiles of BC have also been compared with aircraft observations carried out during summer of 2008 and 2009, resulting in good agreement. This study shows that WRF-Chem model captures many important features of the observations and therefore can be used for understanding and forecasting regional weather patterns over Indian subcontinent. Acknowledgements: The author MM was supported by the DST-Fast Track fellowship. References: Ohara, T., H. Akimoto, J. Kurokawa, N. Horii, K. Yamaji, X. Yan, and T. Hayasaka, An Asian emission inventory of anthropogenic emission sources for the period 1980-2020, Atmos. Chem. Phys., 7, 4419, doi:10.5194/acp744192007, 2007.

Modeling the TTL at Continental Scale for a Wet Season: An Evaluation of the BRAMS Mesoscale Model Using TRO-Pico Campaign, and Measurements From Airborne and Spaceborne Sensors

NASA Astrophysics Data System (ADS)

Behera, Abhinna K.; Rivière, Emmanuel D.; Marécal, Virginie; Rysman, Jean-François; Chantal, Claud; Sèze, Geneviève; Amarouche, Nadir; Ghysels, Mélanie; Khaykin, Sergey M.; Pommereau, Jean-Pierre; Held, Gerhard; Burgalat, Jérémie; Durry, Georges

2018-03-01

In order to better understand the water vapor (WV) intrusion into the tropical stratosphere, a mesoscale simulation of the tropical tropopause layer using the BRAMS (Brazilian version of Regional Atmospheric Modeling System (RAMS)) model is evaluated for a wet season. This simulation with a horizontal grid point resolution of 20 km × 20 km cannot resolve the stratospheric overshooting convection (SOC). Its ability to reproduce other key parameters playing a role in the stratospheric WV abundance is investigated using the balloon-borne TRO-Pico campaign measurements, the upper-air soundings over Brazil, and the satellite observations by Aura Microwave Limb Sounder, Microwave Humidity Sounder, and Geostationary Operational Environmental Satellite 12. The BRAMS exhibits a good ability in simulating temperature, cold-point, WV variability around the tropopause. However, the simulation is typically observed to be warmer by ˜2.0°C and wetter by ˜0.4 ppmv at the hygropause, which can be partly affiliated with the grid boundary nudging of the model by European Centre for Medium-Range Weather Forecasts operational analyses. The modeled cloud tops show a good correlation (maximum cross-correlation of ˜0.7) with Geostationary Operational Environmental Satellite 12. Furthermore, the overshooting cells detected by Microwave Humidity Sounder are observed at the locations, where 75% of the modeled cloud tops are higher than 11 km. Finally, the modeled inertia-gravity wave periodicity and wavelength are comparable with those deduced from the radio sounding measurements during TRO-Pico campaign. The good behavior of BRAMS confirms the SOC contribution in the WV abundance, and variability is of lesser importance than the large-scale processes. This simulation can be used as a reference run for upscaling the impact of SOC at a continental scale for future studies.

Comparison of projection skills of deterministic ensemble methods using pseudo-simulation data generated from multivariate Gaussian distribution

NASA Astrophysics Data System (ADS)

Oh, Seok-Geun; Suh, Myoung-Seok

2017-07-01

The projection skills of five ensemble methods were analyzed according to simulation skills, training period, and ensemble members, using 198 sets of pseudo-simulation data (PSD) produced by random number generation assuming the simulated temperature of regional climate models. The PSD sets were classified into 18 categories according to the relative magnitude of bias, variance ratio, and correlation coefficient, where each category had 11 sets (including 1 truth set) with 50 samples. The ensemble methods used were as follows: equal weighted averaging without bias correction (EWA_NBC), EWA with bias correction (EWA_WBC), weighted ensemble averaging based on root mean square errors and correlation (WEA_RAC), WEA based on the Taylor score (WEA_Tay), and multivariate linear regression (Mul_Reg). The projection skills of the ensemble methods improved generally as compared with the best member for each category. However, their projection skills are significantly affected by the simulation skills of the ensemble member. The weighted ensemble methods showed better projection skills than non-weighted methods, in particular, for the PSD categories having systematic biases and various correlation coefficients. The EWA_NBC showed considerably lower projection skills than the other methods, in particular, for the PSD categories with systematic biases. Although Mul_Reg showed relatively good skills, it showed strong sensitivity to the PSD categories, training periods, and number of members. On the other hand, the WEA_Tay and WEA_RAC showed relatively superior skills in both the accuracy and reliability for all the sensitivity experiments. This indicates that WEA_Tay and WEA_RAC are applicable even for simulation data with systematic biases, a short training period, and a small number of ensemble members.

Direct Lagrangian tracking simulations of particles in vertically-developing atmospheric clouds

NASA Astrophysics Data System (ADS)

Onishi, Ryo; Kunishima, Yuichi

2017-11-01

We have been developing the Lagrangian Cloud Simulator (LCS), which follows the so-called Euler-Lagrangian framework, where flow motion and scalar transportations (i.e., temperature and humidity) are computed with the Euler method and particle motion with the Lagrangian method. The LCS simulation considers the hydrodynamic interaction between approaching particles for robust collision detection. This leads to reliable simulations of collision growth of cloud droplets. Recently the activation process, in which aerosol particles become tiny liquid droplets, has been implemented in the LCS. The present LCS can therefore consider the whole warm-rain precipitation processes -activation, condensation, collision and drop precipitation. In this talk, after briefly introducing the LCS, we will show kinematic simulations using the LCS for quasi-one dimensional domain, i.e., vertically elongated 3D domain. They are compared with one-dimensional kinematic simulations using a spectral-bin cloud microphysics scheme, which is based on the Euler method. The comparisons show fairly good agreement with small discrepancies, the source of which will be presented. The Lagrangian statistics, obtained for the first time for the vertical domain, will be the center of discussion. This research was supported by MEXT as ``Exploratory Challenge on Post-K computer'' (Frontiers of Basic Science: Challenging the Limits).

COMSOL-Based Modeling and Simulation of SnO2/rGO Gas Sensor for Detection of NO2.

PubMed

Yaghouti Niyat, Farshad; Shahrokh Abadi, M H

2018-02-01

Despite SIESTA and COMSOL being increasingly used for the simulation of the sensing mechanism in the gas sensors, there are no modeling and simulation reports in literature for detection of NO 2 based rGO/SnO 2 sensors. In the present study, we model, simulate, and characterize an NO 2 based rGO/SnO 2 gas sensor using COMSOL by solving the Poisson's equations under associated boundary conditions of mass, heat and electrical transitions. To perform the simulation, we use an exposure model for presenting the required NO 2 , a heat transfer model to obtain a reaction temperature, and an electrical model to characterize the sensor's response in the presence of the gas. We characterize the sensor's response in the presence of different concentrations of NO 2 at different working temperatures and compare the results with the experimental data, reported by Zhang et al. The results from the simulated sensor show a good agreement with the real sensor with some inconsistencies due to differences between the practical conditions in the real chamber and applied conditions to the analytical equations. The results also show that the method can be used to define and predict the behavior of the rGO-based gas sensors before undergoing the fabrication process.

Combining Monte Carlo methods with coherent wave optics for the simulation of phase-sensitive X-ray imaging

PubMed Central

Peter, Silvia; Modregger, Peter; Fix, Michael K.; Volken, Werner; Frei, Daniel; Manser, Peter; Stampanoni, Marco

2014-01-01

Phase-sensitive X-ray imaging shows a high sensitivity towards electron density variations, making it well suited for imaging of soft tissue matter. However, there are still open questions about the details of the image formation process. Here, a framework for numerical simulations of phase-sensitive X-ray imaging is presented, which takes both particle- and wave-like properties of X-rays into consideration. A split approach is presented where we combine a Monte Carlo method (MC) based sample part with a wave optics simulation based propagation part, leading to a framework that takes both particle- and wave-like properties into account. The framework can be adapted to different phase-sensitive imaging methods and has been validated through comparisons with experiments for grating interferometry and propagation-based imaging. The validation of the framework shows that the combination of wave optics and MC has been successfully implemented and yields good agreement between measurements and simulations. This demonstrates that the physical processes relevant for developing a deeper understanding of scattering in the context of phase-sensitive imaging are modelled in a sufficiently accurate manner. The framework can be used for the simulation of phase-sensitive X-ray imaging, for instance for the simulation of grating interferometry or propagation-based imaging. PMID:24763652

Simulation of therapeutic electron beam tracking through a non-uniform magnetic field using finite element method

PubMed Central

Tahmasebibirgani, Mohammad Javad; Maskani, Reza; Behrooz, Mohammad Ali; Zabihzadeh, Mansour; Shahbazian, Hojatollah; Fatahiasl, Jafar; Chegeni, Nahid

2017-01-01

Introduction In radiotherapy, megaelectron volt (MeV) electrons are employed for treatment of superficial cancers. Magnetic fields can be used for deflection and deformation of the electron flow. A magnetic field is composed of non-uniform permanent magnets. The primary electrons are not mono-energetic and completely parallel. Calculation of electron beam deflection requires using complex mathematical methods. In this study, a device was made to apply a magnetic field to an electron beam and the path of electrons was simulated in the magnetic field using finite element method. Methods A mini-applicator equipped with two neodymium permanent magnets was designed that enables tuning the distance between magnets. This device was placed in a standard applicator of Varian 2100 CD linear accelerator. The mini-applicator was simulated in CST Studio finite element software. Deflection angle and displacement of the electron beam was calculated after passing through the magnetic field. By determining a 2 to 5cm distance between two poles, various intensities of transverse magnetic field was created. The accelerator head was turned so that the deflected electrons became vertical to the water surface. To measure the displacement of the electron beam, EBT2 GafChromic films were employed. After being exposed, the films were scanned using HP G3010 reflection scanner and their optical density was extracted using programming in MATLAB environment. Displacement of the electron beam was compared with results of simulation after applying the magnetic field. Results Simulation results of the magnetic field showed good agreement with measured values. Maximum deflection angle for a 12 MeV beam was 32.9° and minimum deflection for 15 MeV was 12.1°. Measurement with the film showed precision of simulation in predicting the amount of displacement in the electron beam. Conclusion A magnetic mini-applicator was made and simulated using finite element method. Deflection angle and displacement of electron beam were calculated. With the method used in this study, a good prediction of the path of high-energy electrons was made before they entered the body. PMID:28607652

[Simulation for balanced effect of soil and water resources on cultivated land in Naoli River Basin, Northeast China under the RCPs climate scene].

PubMed

Zhou, Hao; Lei, Guo Ping; Yang, Xue Xin; Zhao, Yu Hui; Zhang, Ji Xin

2018-04-01

Under the scenarios of climate change, balancing the land and water resources is one of the key problems needed to be solved in land development. To reveal the water dynamics of the cultivated land in Naoli River Basin, we simulated the future scenarios by using the future land use simulation model based on Landsat Satellite images, the DEM data and the meteorological data. Results showed that the growth rate of cultivated land gradually decreased. It showed different changing characteristics in different time periods, which led to different balancing effect between land and water resources. In 1990, the water dynamics of the cultivated land resources was in good state, At the same time, the adjustment of crops structure caused the paddy fields increased dramatically. During 2002 to 2014, the cultivated land that in moderate and serious moisture shortage state increased slightly, the water deficit was deteriorating to a certain degree, and maintained sound development of water profit and loss situation gradually. By comparing the simulation accuracy with different spatial resolutions and time scales, we selected 200 m as the spatial resolution of the simulation, and simulated the land use status in 2038. The simulation results showed that the cultivated land's water profit and loss degree in the river basin showed significant polarization characteristic, in that the water profit and loss degree of the cultivated land would be further intensified, the area with the higher grades of moisture profit and loss degree would distribute more centralized, and partially high evaluated grades for the moisture shortage would expand. It is needed to develop the cultivated land irrigation schemes and adjust the cultivated land in Naoli River Basin to balance soil and water resources.

Impact Analyses and Tests of Metal Cask Considering Aircraft Engine Crash - 12308

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sanghoon; Choi, Woo-Seok; Kim, Ki-Young

2012-07-01

The structural integrity of a dual purpose metal cask currently under development by the Korea Radioactive Waste Management Cooperation (KRMC) is evaluated through analyses and tests under a high-speed missile impact considering the targeted aircraft crash conditions. The impact conditions were carefully chosen through a survey on accident cases and recommendations from the literature. The missile impact velocity was set at 150 m/s, and two impact orientations were considered. A simplified missile simulating a commercial aircraft engine is designed from an impact load history curve provided in the literature. In the analyses, the focus is on the evaluation of themore » containment boundary integrity of the metal cask. The analyses results are compared with the results of tests using a 1/3 scale model. The results show very good agreements, and the procedure and methodology adopted in the structural analyses are validated. While the integrity of the cask is maintained in one evaluation where the missile impacts the top side of the free standing cask, the containment boundary is breached in another case in which the missile impacts the center of the cask lid in a perpendicular orientation. A safety assessment using a numerical simulation of an aircraft engine crash into spent nuclear fuel storage systems is performed. A commercially available explicit finite element code is utilized for the dynamic simulation, and the strain rate effect is included in the modeling of the materials used in the target system and missile. The simulation results show very good agreement with the test results. It is noted that this is the first test considering an aircraft crash in Korea. (authors)« less

Fast analytical scatter estimation using graphics processing units.

PubMed

Ingleby, Harry; Lippuner, Jonas; Rickey, Daniel W; Li, Yue; Elbakri, Idris

2015-01-01

To develop a fast patient-specific analytical estimator of first-order Compton and Rayleigh scatter in cone-beam computed tomography, implemented using graphics processing units. The authors developed an analytical estimator for first-order Compton and Rayleigh scatter in a cone-beam computed tomography geometry. The estimator was coded using NVIDIA's CUDA environment for execution on an NVIDIA graphics processing unit. Performance of the analytical estimator was validated by comparison with high-count Monte Carlo simulations for two different numerical phantoms. Monoenergetic analytical simulations were compared with monoenergetic and polyenergetic Monte Carlo simulations. Analytical and Monte Carlo scatter estimates were compared both qualitatively, from visual inspection of images and profiles, and quantitatively, using a scaled root-mean-square difference metric. Reconstruction of simulated cone-beam projection data of an anthropomorphic breast phantom illustrated the potential of this method as a component of a scatter correction algorithm. The monoenergetic analytical and Monte Carlo scatter estimates showed very good agreement. The monoenergetic analytical estimates showed good agreement for Compton single scatter and reasonable agreement for Rayleigh single scatter when compared with polyenergetic Monte Carlo estimates. For a voxelized phantom with dimensions 128 × 128 × 128 voxels and a detector with 256 × 256 pixels, the analytical estimator required 669 seconds for a single projection, using a single NVIDIA 9800 GX2 video card. Accounting for first order scatter in cone-beam image reconstruction improves the contrast to noise ratio of the reconstructed images. The analytical scatter estimator, implemented using graphics processing units, provides rapid and accurate estimates of single scatter and with further acceleration and a method to account for multiple scatter may be useful for practical scatter correction schemes.

Modeling the energy balance in Marseille: Sensitivity to roughness length parameterizations and thermal admittance

NASA Astrophysics Data System (ADS)

Demuzere, M.; De Ridder, K.; van Lipzig, N. P. M.

2008-08-01

During the ESCOMPTE campaign (Experience sur Site pour COntraindre les Modeles de Pollution atmospherique et de Transport d'Emissions), a 4-day intensive observation period was selected to evaluate the Advanced Regional Prediction System (ARPS), a nonhydrostatic meteorological mesoscale model that was optimized with a parameterization for thermal roughness length to better represent urban surfaces. The evaluation shows that the ARPS model is able to correctly reproduce temperature, wind speed, and direction for one urban and two rural measurements stations. Furthermore, simulated heat fluxes show good agreement compared to the observations, although simulated sensible heat fluxes were initially too low for the urban stations. In order to improve the latter, different roughness length parameterization schemes were tested, combined with various thermal admittance values. This sensitivity study showed that the Zilitinkevich scheme combined with and intermediate value of thermal admittance performs best.

An ab initio study of the structure and dynamics of bulk liquid Cd and its liquid-vapor interface.

PubMed

Calderín, L; González, L E; González, D J

2013-02-13

Several static and dynamic properties of bulk liquid Cd at a thermodynamic state near its triple point have been calculated by means of ab initio molecular dynamics simulations. The calculated static structure shows a very good agreement with the available experimental data. The dynamical structure reveals collective density excitations with an associated dispersion relation which points to a small positive dispersion. Results are also reported for several transport coefficients. Additional simulations have also been performed at a slightly higher temperature in order to study the structure of the free liquid surface. The ionic density profile shows an oscillatory behavior with two different wavelengths, as the spacing between the outer and first inner layer is different from that between the other inner layers. The calculated reflectivity shows a marked maximum whose origin is related to the surface layering, along with a shoulder located at a much smaller wavevector transfer.

Direct current dielectric barrier assistant discharge to get homogeneous plasma in capacitive coupled discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Yinchang, E-mail: ycdu@mail.ustc.edu.cn; Max-Planck Institute for Extraterrestrial Physics, D-85748 Garching; Li, Yangfang

In this paper, we propose a method to get more homogeneous plasma in the geometrically asymmetric capacitive coupled plasma (CCP) discharge. The dielectric barrier discharge (DBD) is used for the auxiliary discharge system to improve the homogeneity of the geometrically asymmetric CCP discharge. The single Langmuir probe measurement shows that the DBD can increase the electron density in the low density volume, where the DBD electrodes are mounted, when the pressure is higher than 5 Pa. By this manner, we are able to improve the homogeneity of the plasma production and increase the overall density in the target volume. At last,more » the finite element simulation results show that the DC bias, applied to the DBD electrodes, can increase the homogeneity of the electron density in the CCP discharge. The simulation results show a good agreement with the experiment results.« less

Effect of moisture on disintegration kinetics during anaerobic digestion of complex organic substrates.

PubMed

Liotta, Flavia; d'Antonio, Giuseppe; Esposito, Giovanni; Fabbricino, Massimiliano; Frunzo, Luigi; van Hullebusch, Eric D; Lens, Piet N L; Pirozzi, Francesco

2014-01-01

The role of the moisture content and particle size (PS) on the disintegration of complex organic matter during the wet anaerobic digestion (AD) process was investigated. A range of total solids (TS) from 5% to 11.3% and PS from 0.25 to 15 mm was evaluated using carrot waste as model complex organic matter. The experimental results showed that the methane production rate decreased with higher TS and PS. A modified version of the AD model no.1 for complex organic substrates was used to model the experimental data. The simulations showed a decrease of the disintegration rate constants with increasing TS and PS. The results of the biomethanation tests were used to calibrate and validate the applied model. In particular, the values of the disintegration constant for various TS and PS were determined. The simulations showed good agreement between the numerical and observed data.

Numerical simulation of offset-drain amorphous oxide-based thin-film transistors

NASA Astrophysics Data System (ADS)

Jeong, Jaewook

2016-11-01

In this study, we analyzed the electrical characteristics of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with an offset-drain structure by technology computer aided design (TCAD) simulation. When operating in a linear region, an enhancement-type TFT shows poor field-effect mobility because most conduction electrons are trapped in acceptor-like defects in an offset region when the offset length (L off) exceeds 0.5 µm, whereas a depletion-type TFT shows superior field-effect mobility owing to the high free electron density in the offset region compared with the trapped electron density. When operating in the saturation region, both types of TFTs show good field-effect mobility comparable to that of a reference TFT with a large gate overlap. The underlying physics of the depletion and enhancement types of offset-drain TFTs are systematically analyzed.

Nanostructure Formation by controlled dewetting on patterned substrates: A combined theoretical, modeling and experimental study.

PubMed

Lu, Liang-Xing; Wang, Ying-Min; Srinivasan, Bharathi Madurai; Asbahi, Mohamed; Yang, Joel K W; Zhang, Yong-Wei

2016-09-01

We perform systematic two-dimensional energetic analysis to study the stability of various nanostructures formed by dewetting solid films deposited on patterned substrates. Our analytical results show that by controlling system parameters such as the substrate surface pattern, film thickness and wetting angle, a variety of equilibrium nanostructures can be obtained. Phase diagrams are presented to show the complex relations between these system parameters and various nanostructure morphologies. We further carry out both phase field simulations and dewetting experiments to validate the analytically derived phase diagrams. Good agreements between the results from our energetic analyses and those from our phase field simulations and experiments verify our analysis. Hence, the phase diagrams presented here provide guidelines for using solid-state dewetting as a tool to achieve various nanostructures.

Large-Eddy Simulation of the Base Flow of a Cylindrical Space Vehicle Configuration

NASA Astrophysics Data System (ADS)

Meiß, J.-H.; Schröder, W.

2009-01-01

A Large-Eddy Simulation (LES) is performed out to in- vestigate high Reynolds number base flow of an axisymmetric rocket-like configuration having an underex- panded nozzle flow. The subsonic base region of low pressure levels is characterized and bounded by the interaction of the freestream of Mach 5.3 and the wide plume of the hot exhaust jet of Mach 3.8. An analysis of the base flow shows that the system of base area vortices determines the highly time-dependent pressure distribution and causes an upstream convection of hot exhaust gas. A comparison of the results with experiments conducted at the German Aerospace Center (DLR) Cologne shows good agreement. The investigation is part of the German RESPACE Pro- gram, which focuses on Key Technologies for Reusable Space Systems.

Docking simulations suggest that all-trans retinoic acid could bind to retinoid X receptors.

PubMed

Tsuji, Motonori; Shudo, Koichi; Kagechika, Hiroyuki

2015-10-01

Retinoid X receptors (RXRs) are ligand-controlled transcription factors which heterodimerize with other nuclear receptors to regulate gene transcriptions associated with crucial biological events. 9-cis retinoic acid (9cRA), which transactivates RXRs, is believed to be an endogenous RXR ligand. All-trans retinoic acid (ATRA) is a natural ligand for retinoic acid receptors (RARs), which heterodimerize with RXRs. Although the concentration of 9cRA in tissues is very low, ATRA is relatively abundant and some reports show that ATRA activates RXRs. We computationally studied the possibility of ATRA binding to RXRs using two different docking methods with our developed programs to assess the binding affinities of naturally occurring retinoids. The simulations showed good correlations to the reported binding affinities of these molecules for RXRs and RARs.

Applying Multivariate Discrete Distributions to Genetically Informative Count Data.

PubMed

Kirkpatrick, Robert M; Neale, Michael C

2016-03-01

We present a novel method of conducting biometric analysis of twin data when the phenotypes are integer-valued counts, which often show an L-shaped distribution. Monte Carlo simulation is used to compare five likelihood-based approaches to modeling: our multivariate discrete method, when its distributional assumptions are correct, when they are incorrect, and three other methods in common use. With data simulated from a skewed discrete distribution, recovery of twin correlations and proportions of additive genetic and common environment variance was generally poor for the Normal, Lognormal and Ordinal models, but good for the two discrete models. Sex-separate applications to substance-use data from twins in the Minnesota Twin Family Study showed superior performance of two discrete models. The new methods are implemented using R and OpenMx and are freely available.

Cavitation-induced fragmentation of an acoustically-levitated droplet

NASA Astrophysics Data System (ADS)

Gonzalez Avila, Silvestre Roberto; Ohl, Claus-Dieter

2015-12-01

In this paper we investigate the initial sequence of events that lead to the fragmentation of a millimetre sized water droplets when interacting with a focused ns-laser pulse. The experimental results show complex processes that result from the reflection of an initial shock wave from plasma generation with the soft boundary of the levitating droplet; furthermore, when the reflected waves from the walls of the droplet refocus they leave behind a trail of microbubbles that later act as cavitation inception regions. Numerical simulations of a shock wave impacting and reflecting from a soft boundary are also reported; the simulated results show that the lowest pressure inside the droplet occurs at the equatorial plane. The results of the numerical model display good agreement with the experimental results both in time and in space.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barbante, Paolo; Frezzotti, Aldo; Gibelli, Livio

The unsteady evaporation of a thin planar liquid film is studied by molecular dynamics simulations of Lennard-Jones fluid. The obtained results are compared with the predictions of a diffuse interface model in which capillary Korteweg contributions are added to hydrodynamic equations, in order to obtain a unified description of the liquid bulk, liquid-vapor interface and vapor region. Particular care has been taken in constructing a diffuse interface model matching the thermodynamic and transport properties of the Lennard-Jones fluid. The comparison of diffuse interface model and molecular dynamics results shows that, although good agreement is obtained in equilibrium conditions, remarkable deviationsmore » of diffuse interface model predictions from the reference molecular dynamics results are observed in the simulation of liquid film evaporation. It is also observed that molecular dynamics results are in good agreement with preliminary results obtained from a composite model which describes the liquid film by a standard hydrodynamic model and the vapor by the Boltzmann equation. The two mathematical model models are connected by kinetic boundary conditions assuming unit evaporation coefficient.« less

Strain-rate dependence of ramp-wave evolution and strength in tantalum

DOE PAGES

Lane, J. Matthew D.; Foiles, Stephen M.; Lim, Hojun; ...

2016-08-25

We have conducted molecular dynamics (MD) simulations of quasi-isentropic ramp-wave compression to very high pressures over a range of strain rates from 10 11 down to 10 8 1/s. Using scaling methods, we collapse wave profiles from various strain rates to a master profile curve, which shows deviations when material response is strain-rate dependent. Thus, we can show with precision where, and how, strain-rate dependence affects the ramp wave. We find that strain rate affects the stress-strain material response most dramatically at strains below 20%, and that above 30% strain the material response is largely independent of strain rate. Wemore » show good overall agreement with experimental stress-strain curves up to approximately 30% strain, above which simulated response is somewhat too stiff. We postulate that this could be due to our interatomic potential or to differences in grain structure and/or size between simulation and experiment. Strength is directly measured from per-atom stress tensor and shows significantly enhanced elastic response at the highest strain rates. As a result, this enhanced elastic response is less pronounced at higher pressures and at lower strain rates.« less

Reciprocity and the Tragedies of Maintaining and Providing the Commons.

PubMed

Gächter, Simon; Kölle, Felix; Quercia, Simone

2017-09-01

Social cooperation often requires collectively beneficial but individually costly restraint to maintain a public good1-4, or it needs costly generosity to create one1,5. Status quo effects6 predict that maintaining a public good is easier than providing a new one. Here we show experimentally and with simulations that even under identical incentives, low levels of cooperation (the 'tragedy of the commons'2) are systematically more likely in Maintenance than Provision. Across three series of experiments, we find that strong and weak positive reciprocity, known to be fundamental tendencies underpinning human cooperation7-10, are substantially diminished under Maintenance compared to Provision. As we show in a fourth experiment, the opposite holds for negative reciprocity ('punishment'). Our findings suggest that incentives to avoid the 'tragedy of the commons' need to contend with dilemma-specific reciprocity.

Recognition of an obstacle in a flow using artificial neural networks.

PubMed

Carrillo, Mauricio; Que, Ulices; González, José A; López, Carlos

2017-08-01

In this work a series of artificial neural networks (ANNs) has been developed with the capacity to estimate the size and location of an obstacle obstructing the flow in a pipe. The ANNs learn the size and location of the obstacle by reading the profiles of the dynamic pressure q or the x component of the velocity v_{x} of the fluid at a certain distance from the obstacle. Data to train the ANN were generated using numerical simulations with a two-dimensional lattice Boltzmann code. We analyzed various cases varying both the diameter and the position of the obstacle on the y axis, obtaining good estimations using the R^{2} coefficient for the cases under study. Although the ANN showed problems with the classification of very small obstacles, the general results show a very good capacity for prediction.

Variation in the Helical Structure of Native Collagen

DTIC Science & Technology

2014-02-24

unsampled molecular transform of the sample (non-crystalline diffraction arising from the helical symmetry), these patterns also contain Bragg peaks...tissues may be treated as analogous to that from a single macromolecular crystal. Except that it arises from many fibrils within the sample , giving rise...density maps, constructed from experimentally determined phases and observed amplitudes, showed good agreement. The observed diffraction and the simulated

The lattice Boltzmann method and the problem of turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Djenidi, L.

2015-03-10

This paper reports a brief review of numerical simulations of homogeneous isotopic turbulence (HIT) using the lattice Boltzmann method (LBM). The LBM results shows that the details of HIT are well captured and in agreement with existing data. This clearly indicates that the LBM is as good as current Navier-Stokes solvers and is very much adequate for investigating the problem of turbulence.

Low-Cost Simulation to Teach Anesthetists' Non-Technical Skills in Rwanda.

PubMed

Skelton, Teresa; Nshimyumuremyi, Isaac; Mukwesi, Christian; Whynot, Sara; Zolpys, Lauren; Livingston, Patricia

2016-08-01

Safe anesthesia care is challenging in developing countries where there are shortages of personnel, drugs, equipment, and training. Anesthetists' Non-technical Skills (ANTS)-task management, team working, situation awareness, and decision making-are difficult to practice well in this context. Cesarean delivery is the most common surgical procedure in sub-Saharan Africa. This pilot study investigates whether a low-cost simulation model, with good psychological fidelity, can be used effectively to teach ANTS during cesarean delivery in Rwanda. Study participants were anesthesia providers working in a tertiary referral hospital in Rwanda. Baseline observations were conducted for 20 anesthesia providers during cesarean delivery using the established ANTS framework. After the first observation set was complete, participants were randomly assigned to either simulation intervention or control groups. The simulation intervention group underwent ANTS training using low-cost high psychological fidelity simulation with debriefing. No training was offered to the control group. Postintervention observations were then conducted in the same manner as the baseline observations. The primary outcome was the overall ANTS score (maximum, 16). The median (range) ANTS score of the simulation group was 13.5 (11-16). The ANTS score of the control group was 8 (8-9), with a statistically significant difference (P = .002). Simulation participants showed statistically significant improvement in subcategories and in the overall ANTS score compared with ANTS score before simulation exposure. Rwandan anesthesia providers show improvement in ANTS practice during cesarean delivery after 1 teaching session using a low-cost high psychological fidelity simulation model with debriefing.

Physical Scaffolding Accelerates the Evolution of Robot Behavior.

PubMed

Buckingham, David; Bongard, Josh

2017-01-01

In some evolutionary robotics experiments, evolved robots are transferred from simulation to reality, while sensor/motor data flows back from reality to improve the next transferral. We envision a generalization of this approach: a simulation-to-reality pipeline. In this pipeline, increasingly embodied agents flow up through a sequence of increasingly physically realistic simulators, while data flows back down to improve the next transferral between neighboring simulators; physical reality is the last link in this chain. As a first proof of concept, we introduce a two-link chain: A fast yet low-fidelity ( lo-fi) simulator hosts minimally embodied agents, which gradually evolve controllers and morphologies to colonize a slow yet high-fidelity ( hi-fi) simulator. The agents are thus physically scaffolded. We show here that, given the same computational budget, these physically scaffolded robots reach higher performance in the hi-fi simulator than do robots that only evolve in the hi-fi simulator, but only for a sufficiently difficult task. These results suggest that a simulation-to-reality pipeline may strike a good balance between accelerating evolution in simulation while anchoring the results in reality, free the investigator from having to prespecify the robot's morphology, and pave the way to scalable, automated, robot-generating systems.

KC-135 wing and winglet flight pressure distributions, loads, and wing deflection results with some wind tunnel comparisons

NASA Technical Reports Server (NTRS)

Montoya, L. C.; Jacobs, P.; Flechner, S.; Sims, R.

1982-01-01

A full-scale winglet flight test on a KC-135 airplane with an upper winglet was conducted. Data were taken at Mach numbers from 0.70 to 0.82 at altitudes from 34,000 feet to 39,000 feet at stabilized flight conditions for wing/winglet configurations of basic wing tip, 15/-4 deg, 15/-2 deg, and 0/-4 deg winglet cant/incidence. An analysis of selected pressure distribution and data showed that with the basic wing tip, the flight and wind tunnel wing pressure distribution data showed good agreement. With winglets installed, the effects on the wing pressure distribution were mainly near the tip. Also, the flight and wind tunnel winglet pressure distributions had some significant differences primarily due to the oilcanning in flight. However, in general, the agreement was good. For the winglet cant and incidence configuration presented, the incidence had the largest effect on the winglet pressure distributions. The incremental flight wing deflection data showed that the semispan wind tunnel model did a reasonable job of simulating the aeroelastic effects at the wing tip. The flight loads data showed good agreement with predictions at the design point and also substantiated the predicted structural penalty (load increase) of the 15 deg cant/-2 deg incidence winglet configuration.

Characterizing Flow and Suspended Sediment Trends in the Sacramento River Basin, CA Using Hydrologic Simulation Program - FORTRAN (HSPF)

NASA Astrophysics Data System (ADS)

Stern, M. A.; Flint, L. E.; Flint, A. L.; Wright, S. A.; Minear, J. T.

2014-12-01

A watershed model of the Sacramento River Basin, CA was developed to simulate streamflow and suspended sediment transport to the San Francisco Bay Delta (SFBD) for fifty years (1958-2008) using the Hydrological Simulation Program - FORTRAN (HSPF). To compensate for the large model domain and sparse data, rigorous meteorological development and characterization of hydraulic geometry were employed to spatially distribute climate and hydrologic processes in unmeasured locations. Parameterization techniques sought to include known spatial information for tributaries such as soil information and slope, and then parameters were scaled up or down during calibration to retain the spatial characteristics of the land surface in un-gaged areas. Accuracy was assessed by comparing model calibration to measured streamflow. Calibration and validation of the Sacramento River ranged from "good" to "very good" performance based upon a "goodness-of-fit" statistical guideline. Model calibration to measured sediment loads were underestimated on average by 39% for the Sacramento River, and model calibration to suspended sediment concentrations were underestimated on average by 22% for the Sacramento River. Sediment loads showed a slight decreasing trend from 1958-2008 and was significant (p < 0.0025) in the lower 50% of stream flows. Hypothetical climate change scenarios were developed using the Climate Assessment Tool (CAT). Several wet and dry scenarios coupled with temperature increases were imposed on the historical base conditions to evaluate sensitivity of streamflow and sediment on potential changes in climate. Wet scenarios showed an increase of 9.7 - 17.5% in streamflow, a 7.6 - 17.5% increase in runoff, and a 30 - 93% increase in sediment loads. The dry scenarios showed a roughly 5% decrease in flow and runoff, and a 16 - 18% decrease in sediment loads. The base hydrology was most sensitive to a temperature increase of 1.5 degrees Celsius and an increase in storm intensity and frequency. The complete calibrated HSPF model will use future climate scenarios to make projections of potential hydrologic and sediment trends to the SFBD from 2000-2100.

SU-F-T-619: Dose Evaluation of Specific Patient Plans Based On Monte Carlo Algorithm for a CyberKnife Stereotactic Radiosurgery System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piao, J; PLA 302 Hospital, Beijing; Xu, S

2016-06-15

Purpose: This study will use Monte Carlo to simulate the Cyberknife system, and intend to develop the third-party tool to evaluate the dose verification of specific patient plans in TPS. Methods: By simulating the treatment head using the BEAMnrc and DOSXYZnrc software, the comparison between the calculated and measured data will be done to determine the beam parameters. The dose distribution calculated in the Raytracing, Monte Carlo algorithms of TPS (Multiplan Ver4.0.2) and in-house Monte Carlo simulation method for 30 patient plans, which included 10 head, lung and liver cases in each, were analyzed. The γ analysis with the combinedmore » 3mm/3% criteria would be introduced to quantitatively evaluate the difference of the accuracy between three algorithms. Results: More than 90% of the global error points were less than 2% for the comparison of the PDD and OAR curves after determining the mean energy and FWHM.The relative ideal Monte Carlo beam model had been established. Based on the quantitative evaluation of dose accuracy for three algorithms, the results of γ analysis shows that the passing rates (84.88±9.67% for head,98.83±1.05% for liver,98.26±1.87% for lung) of PTV in 30 plans between Monte Carlo simulation and TPS Monte Carlo algorithms were good. And the passing rates (95.93±3.12%,99.84±0.33% in each) of PTV in head and liver plans between Monte Carlo simulation and TPS Ray-tracing algorithms were also good. But the difference of DVHs in lung plans between Monte Carlo simulation and Ray-tracing algorithms was obvious, and the passing rate (51.263±38.964%) of γ criteria was not good. It is feasible that Monte Carlo simulation was used for verifying the dose distribution of patient plans. Conclusion: Monte Carlo simulation algorithm developed in the CyberKnife system of this study can be used as a reference tool for the third-party tool, which plays an important role in dose verification of patient plans. This work was supported in part by the grant from Chinese Natural Science Foundation (Grant No. 11275105). Thanks for the support from Accuray Corp.« less

Experiment and simulation of a LiFePO4 battery pack with a passive thermal management system using composite phase change material and graphite sheets

NASA Astrophysics Data System (ADS)

Lin, Chunjing; Xu, Sichuan; Chang, Guofeng; Liu, Jinling

2015-02-01

A passive thermal management system (TMS) for LiFePO4 battery modules using phase change material (PCM) as the heat dissipation source to control battery temperature rise is developed. Expanded graphite matrix and graphite sheets are applied to compensate low thermal conductivity of PCM and improve temperature uniformity of the batteries. Constant current discharge and mixed charge-discharge duties were applied on battery modules with and without PCM on a battery thermal characteristics test platform. Experimental results show that PCM cooling significantly reduces the battery temperature rise during short-time intense use. It is also found that temperature uniformity across the module deteriorates with the increasing of both discharge time and current rates. The maximum temperature differences at the end of 1C and 2C-rate discharges are both less than 5 °C, indicating a good performance in battery thermal uniformity of the passive TMS. Experiments on warm-keeping performance show that the passive TMS can effectively keep the battery within its optimum operating temperature for a long time during cold weather uses. A three dimensional numerical model of the battery pack with the passive TMS was conducted using ANSYS Fluent. Temperature profiles with respect to discharging time reveal that simulation shows good agreement with experiment at 1C-discharge rate.

Numerical Analysis of a Flexible Dual Loop Coil and its Experimental Validation for pre-Clinical Magnetic Resonance Imaging of Rodents at 7 T

NASA Astrophysics Data System (ADS)

Solis-Najera, S.; Vazquez, F.; Hernandez, R.; Marrufo, O.; Rodriguez, A. O.

2016-12-01

A surface radio frequency coil was developed for small animal image acquisition in a pre-clinical magnetic resonance imaging system at 7 T. A flexible coil composed of two circular loops was developed to closely cover the object to be imaged. Electromagnetic numerical simulations were performed to evaluate its performance before the coil construction. An analytical expression of the mutual inductance for the two circular loops as a function of the separation between them was derived and used to validate the simulations. The RF coil is composed of two circular loops with a 5 cm external diameter and was tuned to 300 MHz and 50 Ohms matched. The angle between the loops was varied and the Q factor was obtained from the S11 simulations for each angle. B1 homogeneity was also evaluated using the electromagnetic simulations. The coil prototype was designed and built considering the numerical simulation results. To show the feasibility of the coil and its performance, saline-solution phantom images were acquired. A correlation of the simulations and imaging experimental results was conducted showing a concordance of 0.88 for the B1 field. The best coil performance was obtained at the 90° aperture angle. A more realistic phantom was also built using a formaldehyde-fixed rat phantom for ex vivo imaging experiments. All images showed a good image quality revealing clearly defined anatomical details of an ex vivo rat.

Pyrazolo[3,4-d]pyrimidines as novel inhibitors of O-acetyl-L-serine sulfhydrylase of Entamoeba histolytica: an in silico study.

PubMed

Yadava, Umesh; Shukla, Bindesh Kumar; Roychoudhury, Mihir; Kumar, Devesh

2015-04-01

Amoebiasis, a worldwide explosive epidemic, caused by the gastrointestinal anaerobic protozoan parasite Entamoeba histolytica, infects the large intestine and, in advance stages, liver, kidney, brain and lung. Metronidazole (MNZ)-the first line medicament against amoebiasis-is potentially carcinogenic to humans and shows significant side-effects. Pyrazolo[3,4-d]pyrimidine compounds have been reported to demonstrate antiamoebic activity. In silico molecular docking simulations on nine pyrazolo[3,4-d]pyrimidine molecules without linkers (molecules 1-9) and nine pyrazolo[3,4-d]pyrimidine molecules with a trimethylene linker (molecules 10-18) along with the reference drug metronidazole (MNZ) were conducted using the modules of the programs Glide-SP, Glide-XP and Autodock with O-acetyl-L-serine sulfhydrylase (OASS) enzyme-a promising target for inhibiting the growth of Entamoeba histolytica. Docking simulations using Glide-SP demonstrate good agreement with reported biological activities of molecules 1-9 and indicate that molecules 2 and 4 may act as potential high affinity inhibitors. Trimethylene linker molecules show improved binding affinities among which molecules 15 and 16 supersede. MD simulations on the best docked poses of molecules 2, 4, 15, 16 and MNZ were carried out for 20 ns using DESMOND. It was observed that the docking complexes of molecules 4, 15 and MNZ remain stable in aqueous conditions and do not undergo noticeable fluctuations during the course of the dynamics. Relative binding free energy calculations of the ligands with the enzyme were executed on the best docked poses using the molecular mechanics generalized Born surface area (MM-GBSA) approach, which show good agreement with the reported biological activities.

Preferential attachment in multiple trade networks

NASA Astrophysics Data System (ADS)

Foschi, Rachele; Riccaboni, Massimo; Schiavo, Stefano

2014-08-01

In this paper we develop a model for the evolution of multiple networks which is able to replicate the concentrated and sparse nature of world trade data. Our model is an extension of the preferential attachment growth model to the case of multiple networks. Countries trade a variety of goods of different complexity. Every country progressively evolves from trading less sophisticated to high-tech goods. The probabilities of capturing more trade opportunities at a given level of complexity and of starting to trade more complex goods are both proportional to the number of existing trade links. We provide a set of theoretical predictions and simulative results. A calibration exercise shows that our model replicates the same concentration level of world trade as well as the sparsity pattern of the trade matrix. We also discuss a set of numerical solutions to deal with large multiple networks.

Numerical Modeling of Flow Control in a Boundary-Layer-Ingesting Offset Inlet Diffuser at Transonic Mach Numbers

NASA Technical Reports Server (NTRS)

Allan Brian G.; Owens, Lewis, R.

2006-01-01

This paper will investigate the validation of a NASA developed, Reynolds-averaged Navier-Stokes (RANS) flow solver, OVERFLOW, for a boundary-layer-ingesting (BLI) offset (S-shaped) inlet in transonic flow with passive and active flow control devices as well as the baseline case. Numerical simulations are compared to wind tunnel results of a BLI inlet conducted at the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. Comparisons of inlet flow distortion, pressure recovery, and inlet wall pressures are performed. The numerical simulations are compared to the BLI inlet data at a freestream Mach number of 0.85 and a Reynolds number of approximately 2 million based on the length of the fan-face diameter. The numerical simulations with and without wind tunnel walls are performed, quantifying effects of the tunnel walls on the BLI inlet flow measurements. The wind tunnel test evaluated several different combinations of jet locations and mass flow rates as well as a vortex generator (VG) vane case. The numerical simulations will be performed on a single jet configuration for varying actuator mass flow rates at a fix inlet mass flow condition. Validation of the numerical simulations for the VG vane case will also be performed for varying inlet mass flow rates. Overall, the numerical simulations were able to predict the baseline circumferential flow distortion, DPCPavg, very well for comparisons made within the designed operating range of the BLI inlet. However the CFD simulations did predict a total pressure recovery that was 0.01 lower than the experiment. Numerical simulations of the baseline inlet flow also showed good agreement with the experimental inlet centerline surface pressures. The vane case showed that the CFD predicted the correct trends in the circumferential distortion for varying inlet mass flow but had a distortion level that was nearly twice as large as the experiment. Comparison to circumferential distortion measurements for a 15 deg clocked 40 probe rake indicated that the circumferential distortion levels are very sensitive to the symmetry of the flow and that a miss alignment of the vanes in the experiment could have resulted in this difference. The numerical simulations of the BLI inlet with jets showed good agreement with the circumferential inlet distortion levels for a range of jet actuator mass flow ratios at a fixed inlet mass flow rate. The CFD simulations for the jet case also predicted an average total pressure recovery that was 0.01 lower than the experiment as was seen in the baseline. Comparison of the flow features the jet case revealed that the CFD predicted a much larger vortex at the engine fan-face when compare to the experiment.

Oil flow at the scroll compressor discharge: visualization and CFD simulation

NASA Astrophysics Data System (ADS)

Xu, Jiu; Hrnjak, Pega

2017-08-01

Oil is important to the compressor but has other side effect on the refrigeration system performance. Discharge valves located in the compressor plenum are the gateway for the oil when leaving the compressor and circulate in the system. The space in between: the compressor discharge plenum has the potential to separate the oil mist and reduce the oil circulation ratio (OCR) in the system. In order to provide information for building incorporated separation feature for the oil flow near the compressor discharge, video processing method is used to quantify the oil droplets movement and distribution. Also, CFD discrete phase model gives the numerical approach to study the oil flow inside compressor plenum. Oil droplet size distributions are given by visualization and simulation and the results show a good agreement. The mass balance and spatial distribution are also discussed and compared with experimental results. The verification shows that discrete phase model has the potential to simulate the oil droplet flow inside the compressor.

Numerical analysis of azimuthal rotating spokes in a crossed-field discharge plasma

NASA Astrophysics Data System (ADS)

Kawashima, R.; Hara, K.; Komurasaki, K.

2018-03-01

Low-frequency rotating spokes are obtained in a cross-field discharge plasma using two-dimensional numerical simulations. A particle-fluid hybrid model is used to model the plasma flow in a configuration similar to a Hall thruster. It has been reported that the drift-diffusion approximation for an electron fluid results in an ill-conditioned matrix when solving for the potential because of the differences in the electron mobilities across the magnetic field and in the direction of the E × B drift. In this paper, we employ a hyperbolic approach that enables stable calculation, namely, better iterative convergence of the electron fluid model. Our simulation results show a coherent rotating structure propagating in the E × B direction with a phase velocity of 2500 m s‑1, which agrees with experimental data. The phase velocity obtained from the numerical simulations shows good agreement with that predicted by the dispersion relation of the gradient drift instability.

Effective height of chimney for biomass cook stove simulated by computational fluid dynamics

NASA Astrophysics Data System (ADS)

Faisal; Setiawan, A.; Wusnah; Khairil; Luthfi

2018-02-01

This paper presents the results of numerical modelling of temperature distribution and flow pattern in a biomass cooking stove using CFD simulation. The biomass stove has been designed to suite the household cooking process. The stove consists of two pots. The first is the main pot located on the top of the combustion chamber where the heat from the combustion process is directly received. The second pot absorbs the heat from the exhaust gas. A chimney installed at the end of the stove releases the exhaust gas to the ambient air. During the tests, the height of chimney was varied to find the highest temperatures at both pots. Results showed that the height of the chimney at the highest temperatures of the pots is 1.65 m. This chimney height was validated by developing a model for computational fluid dynamics. Both experimental and simulations results show a good agreement and help in tune-fining the design of biomass cooking stove.

Multifractal vector fields and stochastic Clifford algebra.

PubMed

Schertzer, Daniel; Tchiguirinskaia, Ioulia

2015-12-01

In the mid 1980s, the development of multifractal concepts and techniques was an important breakthrough for complex system analysis and simulation, in particular, in turbulence and hydrology. Multifractals indeed aimed to track and simulate the scaling singularities of the underlying equations instead of relying on numerical, scale truncated simulations or on simplified conceptual models. However, this development has been rather limited to deal with scalar fields, whereas most of the fields of interest are vector-valued or even manifold-valued. We show in this paper that the combination of stable Lévy processes with Clifford algebra is a good candidate to bridge up the present gap between theory and applications. We show that it indeed defines a convenient framework to generate multifractal vector fields, possibly multifractal manifold-valued fields, based on a few fundamental and complementary properties of Lévy processes and Clifford algebra. In particular, the vector structure of these algebra is much more tractable than the manifold structure of symmetry groups while the Lévy stability grants a given statistical universality.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schertzer, Daniel, E-mail: Daniel.Schertzer@enpc.fr; Tchiguirinskaia, Ioulia, E-mail: Ioulia.Tchiguirinskaia@enpc.fr

In the mid 1980s, the development of multifractal concepts and techniques was an important breakthrough for complex system analysis and simulation, in particular, in turbulence and hydrology. Multifractals indeed aimed to track and simulate the scaling singularities of the underlying equations instead of relying on numerical, scale truncated simulations or on simplified conceptual models. However, this development has been rather limited to deal with scalar fields, whereas most of the fields of interest are vector-valued or even manifold-valued. We show in this paper that the combination of stable Lévy processes with Clifford algebra is a good candidate to bridge upmore » the present gap between theory and applications. We show that it indeed defines a convenient framework to generate multifractal vector fields, possibly multifractal manifold-valued fields, based on a few fundamental and complementary properties of Lévy processes and Clifford algebra. In particular, the vector structure of these algebra is much more tractable than the manifold structure of symmetry groups while the Lévy stability grants a given statistical universality.« less

Spatial Release From Masking in Simulated Cochlear Implant Users With and Without Access to Low-Frequency Acoustic Hearing

PubMed Central

Dietz, Mathias; Hohmann, Volker; Jürgens, Tim

2015-01-01

For normal-hearing listeners, speech intelligibility improves if speech and noise are spatially separated. While this spatial release from masking has already been quantified in normal-hearing listeners in many studies, it is less clear how spatial release from masking changes in cochlear implant listeners with and without access to low-frequency acoustic hearing. Spatial release from masking depends on differences in access to speech cues due to hearing status and hearing device. To investigate the influence of these factors on speech intelligibility, the present study measured speech reception thresholds in spatially separated speech and noise for 10 different listener types. A vocoder was used to simulate cochlear implant processing and low-frequency filtering was used to simulate residual low-frequency hearing. These forms of processing were combined to simulate cochlear implant listening, listening based on low-frequency residual hearing, and combinations thereof. Simulated cochlear implant users with additional low-frequency acoustic hearing showed better speech intelligibility in noise than simulated cochlear implant users without acoustic hearing and had access to more spatial speech cues (e.g., higher binaural squelch). Cochlear implant listener types showed higher spatial release from masking with bilateral access to low-frequency acoustic hearing than without. A binaural speech intelligibility model with normal binaural processing showed overall good agreement with measured speech reception thresholds, spatial release from masking, and spatial speech cues. This indicates that differences in speech cues available to listener types are sufficient to explain the changes of spatial release from masking across these simulated listener types. PMID:26721918

Implementation of the vortex force formalism in the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system for inner shelf and surf zone applications

USGS Publications Warehouse

Kumar, Nirnimesh; Voulgaris, George; Warner, John C.; Olabarrieta, Maitane

2012-01-01

Model results from the planar beach case show good agreement with depth-averaged analytical solutions and with theoretical flow structures. Simulation results for the DUCK' 94 experiment agree closely with measured profiles of cross-shore and longshore velocity data from and . Diagnostic simulations showed that the nonlinear processes of wave roller generation and wave-induced mixing are important for the accurate simulation of surf zone flows. It is further recommended that a more realistic approach for determining the contribution of wave rollers and breaking induced turbulent mixing can be formulated using non-dimensional parameters which are functions of local wave parameters and the beach slope. Dominant terms in the cross-shore momentum balance are found to be the quasi-static pressure gradient and breaking acceleration. In the alongshore direction, bottom stress, breaking acceleration, horizontal advection and horizontal vortex forces dominate the momentum balance. The simulation results for the bar/rip channel morphology case clearly show the ability of the modeling system to reproduce horizontal and vertical circulation patterns similar to those found in laboratory studies and to numerical simulations using the radiation stress representation. The vortex force term is found to be more important at locations where strong flow vorticity interacts with the wave-induced Stokes flow field. Outside the surf zone, the three-dimensional model simulations of wave-induced flows for non-breaking waves closely agree with flow observations from MVCO, with the vertical structure of the simulated flow varying as a function of the vertical viscosity as demonstrated by Lentz et al. (2008).

Dynamics of Protonated Peptide Ion Collisions with Organic Surfaces: Consonance of Simulation and Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pratihar, Subha; Barnes, George L.; Laskin, Julia

In this Perspective mass spectrometry experiments and chemical dynamics simulations are described which have explored the atomistic dynamics of protonated peptide ions, peptide-H+, colliding with organic surfaces. These studies have investigated surface-induced dissociation (SID) for which peptide-H+ fragments upon collision with the surface, peptide-H+ physisorption on the surface, soft landing (SL), and peptide-H+ reaction with the surface, reactive landing (RL). The simulations include QM+MM and QM/MM direct dynamics. For collisions with self-assembled monolayer (SAM) surfaces there is quite good agreement between experiment and simulation in the efficiency of energy transfer to the peptide-H+ ion’s internal degrees of freedom. Both themore » experiments and simulations show two mechanisms for peptide-H+ fragmentation, i.e. shattering and statistical, RRKM dynamics. Mechanisms for SL are probed in simulations of collisions of protonated dialanine with a perfluorinated SAM surface. RL has been studied experimentally for a number of peptide-H+ + surface systems, and qualitative agreement between simulation and experiment is found for two similar systems.« less

Optimization of tissue physical parameters for accurate temperature estimation from finite-element simulation of radiofrequency ablation.

PubMed

Subramanian, Swetha; Mast, T Douglas

2015-10-07

Computational finite element models are commonly used for the simulation of radiofrequency ablation (RFA) treatments. However, the accuracy of these simulations is limited by the lack of precise knowledge of tissue parameters. In this technical note, an inverse solver based on the unscented Kalman filter (UKF) is proposed to optimize values for specific heat, thermal conductivity, and electrical conductivity resulting in accurately simulated temperature elevations. A total of 15 RFA treatments were performed on ex vivo bovine liver tissue. For each RFA treatment, 15 finite-element simulations were performed using a set of deterministically chosen tissue parameters to estimate the mean and variance of the resulting tissue ablation. The UKF was implemented as an inverse solver to recover the specific heat, thermal conductivity, and electrical conductivity corresponding to the measured area of the ablated tissue region, as determined from gross tissue histology. These tissue parameters were then employed in the finite element model to simulate the position- and time-dependent tissue temperature. Results show good agreement between simulated and measured temperature.

Monitoring, analyzing and simulating of spatial-temporal changes of landscape pattern over mining area

NASA Astrophysics Data System (ADS)

Liu, Pei; Han, Ruimei; Wang, Shuangting

2014-11-01

According to the merits of remotely sensed data in depicting regional land cover and Land changes, multi- objective information processing is employed to remote sensing images to analyze and simulate land cover in mining areas. In this paper, multi-temporal remotely sensed data were selected to monitor the pattern, distri- bution and trend of LUCC and predict its impacts on ecological environment and human settlement in mining area. The monitor, analysis and simulation of LUCC in this coal mining areas are divided into five steps. The are information integration of optical and SAR data, LULC types extraction with SVM classifier, LULC trends simulation with CA Markov model, landscape temporal changes monitoring and analysis with confusion matrixes and landscape indices. The results demonstrate that the improved data fusion algorithm could make full use of information extracted from optical and SAR data; SVM classifier has an efficient and stable ability to obtain land cover maps, which could provide a good basis for both land cover change analysis and trend simulation; CA Markov model is able to predict LULC trends with good performance, and it is an effective way to integrate remotely sensed data with spatial-temporal model for analysis of land use / cover change and corresponding environmental impacts in mining area. Confusion matrixes are combined with landscape indices to evaluation and analysis show that, there was a sustained downward trend in agricultural land and bare land, but a continues growth trend tendency in water body, forest and other lands, and building area showing a wave like change, first increased and then decreased; mining landscape has undergone a from small to large and large to small process of fragmentation, agricultural land is the strongest influenced landscape type in this area, and human activities are the primary cause, so the problem should be pay more attentions by government and other organizations.

Using growth and arrest of Richtmyer-Meshkov instabilities and Lagrangian simulations to study high-rate material strength

NASA Astrophysics Data System (ADS)

Prime, M. B.; Vaughan, D. E.; Preston, D. L.; Buttler, W. T.; Chen, S. R.; Oró, D. M.; Pack, C.

2014-05-01

Experiments applying a supported shock through mating surfaces (Atwood number = 1) with geometrical perturbations have been proposed for studying strength at strain rates up to 107/s using Richtmyer-Meshkov (RM) instabilities. Buttler et al. recently reported experimental results for RM instability growth in copper but with an unsupported shock applied by high explosives and the geometrical perturbations on the opposite free surface (Atwood number = -1). This novel configuration allowed detailed experimental observation of the instability growth and arrest. We present results and interpretation from numerical simulations of the Buttler RM instability experiments. Highly-resolved, two-dimensional simulations were performed using a Lagrangian hydrocode and the Preston-Tonks-Wallace (PTW) strength model. The model predictions show good agreement with the data. The numerical simulations are used to examine various assumptions previously made in an analytical model and to estimate the sensitivity of such experiments to material strength.

Model and particle-in-cell simulation of ion energy distribution in collisionless sheath

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Zhuwen, E-mail: zzwwdxy@gznc.edu.cn; Key Laboratory of Photoelectron Materials Design and Simulation in Guizhou Province, Guiyang 550018; Scientific Research Innovation Team in Plasma and Functional Thin Film Materials in Guizhou Province, Guiyang 550018

2015-06-15

In this paper, we propose a self-consistent theoretical model, which is described by the ion energy distributions (IEDs) in collisionless sheaths, and the analytical results for different combined dc/radio frequency (rf) capacitive coupled plasma discharge cases, including sheath voltage errors analysis, are compared with the results of numerical simulations using a one-dimensional plane-parallel particle-in-cell (PIC) simulation. The IEDs in collisionless sheaths are performed on combination of dc/rf voltage sources electrodes discharge using argon as the process gas. The incident ions on the grounded electrode are separated, according to their different radio frequencies, and dc voltages on a separated electrode, themore » IEDs, and widths of energy in sheath and the plasma sheath thickness are discussed. The IEDs, the IED widths, and sheath voltages by the theoretical model are investigated and show good agreement with PIC simulations.« less

Unsteady hydraulic simulation of the cavitating part load vortex rope in Francis turbines

NASA Astrophysics Data System (ADS)

Brammer, J.; Segoufin, C.; Duparchy, F.; Lowys, P. Y.; Favrel, A.; Avellan, F.

2017-04-01

For Francis turbines at part load operation a helical vortex rope is formed due to the swirling nature of the flow exiting the runner. This vortex creates pressure fluctuations which can lead to power swings, and the unsteady loading can lead to fatigue damage of the runner. In the case that the vortex rope cavitates there is the additional risk that hydro-acoustic resonance can occur. It is therefore important to be able to accurately simulate this phenomenon to address these issues. In this paper an unsteady, multi-phase CFD model was used to simulate two part-load operating points, for two different cavitation conditions. The simulation results were validated with test-rig data, and showed very good agreement. These results also served as an input for FEA calculations and fatigue analysis, which are presented in a separate study.

Internal structure of a vortex breakdown

NASA Technical Reports Server (NTRS)

Nakamura, Y.; Leonard, A.; Spalart, P. R.

1986-01-01

An axisymmetric vortex breakdown was well simulated by the vortex filament method. The agreement with the experiment was qualitatively good. In particular, the structure in the interior of the vortex breakdown was ensured to a great degree by the present simulation. The second breakdown, or spiral type, which occurs downstream of the first axisymmetric breakdown, was simulated more similarly to the experiment than before. It shows a kink of the vortex filaments and strong three-dimensionality. Furthermore, a relatively low velocity region was observed near the second breakdown. It was also found that it takes some time for this physical phenomenon to attain its final stage. The comparison with the experiment is getting better as time goes on. In this paper, emphasis is placed on the comparison of the simulated results with the experiment. The present results help to make clear the mechanism of a vortex breakdown.

Glass Formation of n-Butanol: Coarse-grained Molecular Dynamics Simulations Using Gay-Berne Potential Model

NASA Astrophysics Data System (ADS)

Xie, Gui-long; Zhang, Yong-hong; Huang, Shi-ping

2012-04-01

Using coarse-grained molecular dynamics simulations based on Gay-Berne potential model, we have simulated the cooling process of liquid n-butanol. A new set of GB parameters are obtained by fitting the results of density functional theory calculations. The simulations are carried out in the range of 290-50 K with temperature decrements of 10 K. The cooling characteristics are determined on the basis of the variations of the density, the potential energy and orientational order parameter with temperature, whose slopes all show discontinuity. Both the radial distribution function curves and the second-rank orientational correlation function curves exhibit splitting in the second peak. Using the discontinuous change of these thermodynamic and structure properties, we obtain the glass transition at an estimate of temperature Tg=120±10 K, which is in good agreement with experimental results 110±1 K.

Flowing gas, non-nuclear experiments on the gas core reactor

NASA Technical Reports Server (NTRS)

Kunze, J. F.; Suckling, D. H.; Copper, C. G.

1972-01-01

Flow tests were conducted on models of the gas core (cavity) reactor. Variations in cavity wall and injection configurations were aimed at establishing flow patterns that give a maximum of the nuclear criticality eigenvalue. Correlation with the nuclear effect was made using multigroup diffusion theory normalized by previous benchmark critical experiments. Air was used to simulate the hydrogen propellant in the flow tests, and smoked air, argon, or freon to simulate the central nuclear fuel gas. All tests were run in the down-firing direction so that gravitational effects simulated the acceleration effect of a rocket. Results show that acceptable flow patterns with high volume fraction for the simulated nuclear fuel gas and high flow rate ratios of propellant to fuel can be obtained. Using a point injector for the fuel, good flow patterns are obtained by directing the outer gas at high velocity along the cavity wall, using louvered or oblique-angle-honeycomb injection schemes.

Statistical validation of predictive TRANSP simulations of baseline discharges in preparation for extrapolation to JET D-T

NASA Astrophysics Data System (ADS)

Kim, Hyun-Tae; Romanelli, M.; Yuan, X.; Kaye, S.; Sips, A. C. C.; Frassinetti, L.; Buchanan, J.; Contributors, JET

2017-06-01

This paper presents for the first time a statistical validation of predictive TRANSP simulations of plasma temperature using two transport models, GLF23 and TGLF, over a database of 80 baseline H-mode discharges in JET-ILW. While the accuracy of the predicted T e with TRANSP-GLF23 is affected by plasma collisionality, the dependency of predictions on collisionality is less significant when using TRANSP-TGLF, indicating that the latter model has a broader applicability across plasma regimes. TRANSP-TGLF also shows a good matching of predicted T i with experimental measurements allowing for a more accurate prediction of the neutron yields. The impact of input data and assumptions prescribed in the simulations are also investigated in this paper. The statistical validation and the assessment of uncertainty level in predictive TRANSP simulations for JET-ILW-DD will constitute the basis for the extrapolation to JET-ILW-DT experiments.

Numerical Simulation and Experimental Casting of Nickel-Based Single-Crystal Superalloys by HRS and LMC Directional Solidification Processes

NASA Astrophysics Data System (ADS)

Yan, Xuewei; Wang, Run'nan; Xu, Qingyan; Liu, Baicheng

2017-04-01

Mathematical models for dynamic heat radiation and convection boundary in directional solidification processes are established to simulate the temperature fields. Cellular automaton (CA) method and Kurz-Giovanola-Trivedi (KGT) growth model are used to describe nucleation and growth. Primary dendritic arm spacing (PDAS) and secondary dendritic arm spacing (SDAS) are calculated by the Ma-Sham (MS) and Furer-Wunderlin (FW) models respectively. The mushy zone shape is investigated based on the temperature fields, for both high-rate solidification (HRS) and liquid metal cooling (LMC) processes. The evolution of the microstructure and crystallographic orientation are analyzed by simulation and electron back-scattered diffraction (EBSD) technique, respectively. Comparison of the simulation results from PDAS and SDAS with experimental results reveals a good agreement with each other. The results show that LMC process can provide both dendritic refinement and superior performance for castings due to the increased cooling rate and thermal gradient.

Particle-in-cell simulations of anomalous transport in a Penning discharge

NASA Astrophysics Data System (ADS)

Carlsson, Johan; Kaganovich, Igor; Powis, Andrew; Raitses, Yevgeny; Romadanov, Ivan; Smolyakov, Andrei

2018-06-01

Electrostatic particle-in-cell simulations of a Penning discharge are performed in order to investigate azimuthally asymmetric, spoke-like structures previously observed in experiments. Two-dimensional simulations show that for Penning-discharge conditions, a persistent nonlinear spoke-like structure forms readily and rotates in the direction of E × B and electron diamagnetic drifts. The azimuthal velocity is within about a factor of 2 of the ion acoustic speed. The spoke frequency follows the experimentally observed scaling with ion mass, which indicates the importance of ion inertia in spoke formation. The spoke provides enhanced (anomalous) radial electron transport, and the effective cross-field conductivity is several times larger than the classical (collisional) value. The level of anomalous current obtained in the simulations is in good agreement with the experimental data. The rotating spoke channels most of the radial current, observable by an edge probe as short pulses.

A mesoscopic simulation on distributions of red blood cells in a bifurcating channel

NASA Astrophysics Data System (ADS)

Inoue, Yasuhiro; Takagi, Shu; Matsumoto, Yoichiro

2004-11-01

Transports of red blood cells (RBCs) or particles in bifurcated channels have been attracting renewed interest since the advent of concepts of MEMS for sorting, analyzing, and removing cells or particles from sample medium. In this talk, we present a result on a transport of red blood cells (RBCs) in a bifurcating channel studied by using a mesoscale simulation technique of immiscible droplets, where RBCs have been modeled as immiscible droplets. The distribution of RBCs is represented by the fractional RBC flux into two daughters as a function of volumetric flow ratio between the daughters. The data obtained in our simulations are examined with a theoretical prediction, in which, we assume an exponential distribution for positions of RBCs in the mother channel. The theoretical predictions show a good agreement with simulation results. A non-uniform distribution of RBCs in the mother channel affects disproportional separation of RBC flux at a bifurcation.

A New Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuit for Active Matrix Organic Light Emitting Diode

NASA Astrophysics Data System (ADS)

Ching-Lin Fan,; Yi-Yan Lin,; Jyu-Yu Chang,; Bo-Jhang Sun,; Yan-Wei Liu,

2010-06-01

This study presents one novel compensation pixel design and driving method for active matrix organic light-emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage feed-back method and the simulation results are proposed and verified by SPICE simulator. The measurement and simulation of LTPS TFT characteristics demonstrate the good fitting result. The proposed circuit consists of four TFTs and two capacitors with an additional signal line. The error rates of OLED anode voltage variation are below 0.3% under the threshold voltage deviation of driving TFT (Δ VTH = ± 0.33 V). The simulation results show that the pixel design can improve the display image non-uniformity by compensating the threshold voltage deviation of driving TFT and the degradation of OLED threshold voltage at the same time.

A New Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuit for Active Matrix Organic Light Emitting Diode

NASA Astrophysics Data System (ADS)

Fan, Ching-Lin; Lin, Yi-Yan; Chang, Jyu-Yu; Sun, Bo-Jhang; Liu, Yan-Wei

2010-06-01

This study presents one novel compensation pixel design and driving method for active matrix organic light-emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage feed-back method and the simulation results are proposed and verified by SPICE simulator. The measurement and simulation of LTPS TFT characteristics demonstrate the good fitting result. The proposed circuit consists of four TFTs and two capacitors with an additional signal line. The error rates of OLED anode voltage variation are below 0.3% under the threshold voltage deviation of driving TFT (ΔVTH = ±0.33 V). The simulation results show that the pixel design can improve the display image non-uniformity by compensating the threshold voltage deviation of driving TFT and the degradation of OLED threshold voltage at the same time.

Simulation of dilute polymeric fluids in a three-dimensional contraction using a multiscale FENE model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griebel, M., E-mail: griebel@ins.uni-bonn.de, E-mail: ruettgers@ins.uni-bonn.de; Rüttgers, A., E-mail: griebel@ins.uni-bonn.de, E-mail: ruettgers@ins.uni-bonn.de

The multiscale FENE model is applied to a 3D square-square contraction flow problem. For this purpose, the stochastic Brownian configuration field method (BCF) has been coupled with our fully parallelized three-dimensional Navier-Stokes solver NaSt3DGPF. The robustness of the BCF method enables the numerical simulation of high Deborah number flows for which most macroscopic methods suffer from stability issues. The results of our simulations are compared with that of experimental measurements from literature and show a very good agreement. In particular, flow phenomena such as a strong vortex enhancement, streamline divergence and a flow inversion for highly elastic flows are reproduced.more » Due to their computational complexity, our simulations require massively parallel computations. Using a domain decomposition approach with MPI, the implementation achieves excellent scale-up results for up to 128 processors.« less

Improved staff procedure skills lead to improved managment skills: an observational study in an educational setting.

PubMed

Rüter, Anders; Vikstrom, Tore

2009-01-01

Good staff procedure skills in a management group during incidents and disasters are believed to be a prerequisite for good management of the situation. However, this has not been demonstrated scientifically. Templates for evaluation results from performance indicators during simulation exercises have previously been tested. The aim of this study was to demonstrate the possibility that these indicators can be used as a tool for studying the relationship between good management skills and good staff procedure skills. Good and structured work (staff procedure skills) in a hospital management group during simulation exercises in disaster medicine is related to good and timely decisions (good management skills). Results from 29 consecutive simulation exercises in which staff procedure skills and management skills were evaluated using quantitative measurements were included. The statistical analysis method used was simple linear regression with staff procedure skills as the response variable and management skills as the predictor variable. An overall significant relationship was identified between staff procedure skills and management skills (p(2)0.05). This study suggests that there is a relationship between staff procedure skills and management skills in the educational setting used. Future studies are needed to demonstrate if this also can be observed during actual incidents.

Virtual goods recommendations in virtual worlds.

PubMed

Chen, Kuan-Yu; Liao, Hsiu-Yu; Chen, Jyun-Hung; Liu, Duen-Ren

2015-01-01

Virtual worlds (VWs) are computer-simulated environments which allow users to create their own virtual character as an avatar. With the rapidly growing user volume in VWs, platform providers launch virtual goods in haste and stampede users to increase sales revenue. However, the rapidity of development incurs virtual unrelated items which will be difficult to remarket. It not only wastes virtual global companies' intelligence resources, but also makes it difficult for users to find suitable virtual goods fit for their virtual home in daily virtual life. In the VWs, users decorate their houses, visit others' homes, create families, host parties, and so forth. Users establish their social life circles through these activities. This research proposes a novel virtual goods recommendation method based on these social interactions. The contact strength and contact influence result from interactions with social neighbors and influence users' buying intention. Our research highlights the importance of social interactions in virtual goods recommendation. The experiment's data were retrieved from an online VW platform, and the results show that the proposed method, considering social interactions and social life circle, has better performance than existing recommendation methods.

Studies on questions of design and construction of chain scraper conveyors. [mining operations

NASA Technical Reports Server (NTRS)

Guder, H.

1980-01-01

The basic behavior of mining crushed goods in chain scraper conveyors was examined using a special test stand. The characteristics resistance lines of the upper end-piece were determined for conveyor idle as a function of the determinative crushed good characteristics (granular structure, moisture content, type of goods) on the size of the conveyor load, on the conveyor construction and on the stopped time of the conveyor. Crushed goods with a narrow granular profile and sphere-like grains caused about 35% greater resistance than fine coal and raw coal with broad granular profile. For goods containing water more than 10% by weight, the solids friction retreated in favor of flow friction. The coefficient of resistance decreased considerably in the range of lower speeds and then increased with increasing conveyor speed. The conveyance of sandstone ore required about 280% greater specific drive than the conveyance of raw coal. Resistance coefficients for coal and raw coal showed no dependence on the design of the conveyor. Start-up of loaded conveyors after longer stop times was simulated and the specific break-loose force was determined.

Virtual Goods Recommendations in Virtual Worlds

PubMed Central

Chen, Kuan-Yu; Liao, Hsiu-Yu; Chen, Jyun-Hung; Liu, Duen-Ren

2015-01-01

Virtual worlds (VWs) are computer-simulated environments which allow users to create their own virtual character as an avatar. With the rapidly growing user volume in VWs, platform providers launch virtual goods in haste and stampede users to increase sales revenue. However, the rapidity of development incurs virtual unrelated items which will be difficult to remarket. It not only wastes virtual global companies' intelligence resources, but also makes it difficult for users to find suitable virtual goods fit for their virtual home in daily virtual life. In the VWs, users decorate their houses, visit others' homes, create families, host parties, and so forth. Users establish their social life circles through these activities. This research proposes a novel virtual goods recommendation method based on these social interactions. The contact strength and contact influence result from interactions with social neighbors and influence users' buying intention. Our research highlights the importance of social interactions in virtual goods recommendation. The experiment's data were retrieved from an online VW platform, and the results show that the proposed method, considering social interactions and social life circle, has better performance than existing recommendation methods. PMID:25834837

Prediction models for clustered data: comparison of a random intercept and standard regression model

PubMed Central

2013-01-01

Background When study data are clustered, standard regression analysis is considered inappropriate and analytical techniques for clustered data need to be used. For prediction research in which the interest of predictor effects is on the patient level, random effect regression models are probably preferred over standard regression analysis. It is well known that the random effect parameter estimates and the standard logistic regression parameter estimates are different. Here, we compared random effect and standard logistic regression models for their ability to provide accurate predictions. Methods Using an empirical study on 1642 surgical patients at risk of postoperative nausea and vomiting, who were treated by one of 19 anesthesiologists (clusters), we developed prognostic models either with standard or random intercept logistic regression. External validity of these models was assessed in new patients from other anesthesiologists. We supported our results with simulation studies using intra-class correlation coefficients (ICC) of 5%, 15%, or 30%. Standard performance measures and measures adapted for the clustered data structure were estimated. Results The model developed with random effect analysis showed better discrimination than the standard approach, if the cluster effects were used for risk prediction (standard c-index of 0.69 versus 0.66). In the external validation set, both models showed similar discrimination (standard c-index 0.68 versus 0.67). The simulation study confirmed these results. For datasets with a high ICC (≥15%), model calibration was only adequate in external subjects, if the used performance measure assumed the same data structure as the model development method: standard calibration measures showed good calibration for the standard developed model, calibration measures adapting the clustered data structure showed good calibration for the prediction model with random intercept. Conclusion The models with random intercept discriminate better than the standard model only if the cluster effect is used for predictions. The prediction model with random intercept had good calibration within clusters. PMID:23414436

Prediction models for clustered data: comparison of a random intercept and standard regression model.

PubMed

Bouwmeester, Walter; Twisk, Jos W R; Kappen, Teus H; van Klei, Wilton A; Moons, Karel G M; Vergouwe, Yvonne

2013-02-15

When study data are clustered, standard regression analysis is considered inappropriate and analytical techniques for clustered data need to be used. For prediction research in which the interest of predictor effects is on the patient level, random effect regression models are probably preferred over standard regression analysis. It is well known that the random effect parameter estimates and the standard logistic regression parameter estimates are different. Here, we compared random effect and standard logistic regression models for their ability to provide accurate predictions. Using an empirical study on 1642 surgical patients at risk of postoperative nausea and vomiting, who were treated by one of 19 anesthesiologists (clusters), we developed prognostic models either with standard or random intercept logistic regression. External validity of these models was assessed in new patients from other anesthesiologists. We supported our results with simulation studies using intra-class correlation coefficients (ICC) of 5%, 15%, or 30%. Standard performance measures and measures adapted for the clustered data structure were estimated. The model developed with random effect analysis showed better discrimination than the standard approach, if the cluster effects were used for risk prediction (standard c-index of 0.69 versus 0.66). In the external validation set, both models showed similar discrimination (standard c-index 0.68 versus 0.67). The simulation study confirmed these results. For datasets with a high ICC (≥15%), model calibration was only adequate in external subjects, if the used performance measure assumed the same data structure as the model development method: standard calibration measures showed good calibration for the standard developed model, calibration measures adapting the clustered data structure showed good calibration for the prediction model with random intercept. The models with random intercept discriminate better than the standard model only if the cluster effect is used for predictions. The prediction model with random intercept had good calibration within clusters.

Improved modeling of GaN HEMTs for predicting thermal and trapping-induced-kink effects

NASA Astrophysics Data System (ADS)

Jarndal, Anwar; Ghannouchi, Fadhel M.

2016-09-01

In this paper, an improved modeling approach has been developed and validated for GaN high electron mobility transistors (HEMTs). The proposed analytical model accurately simulates the drain current and its inherent trapping and thermal effects. Genetic-algorithm-based procedure is developed to automatically find the fitting parameters of the model. The developed modeling technique is implemented on a packaged GaN-on-Si HEMT and validated by DC and small-/large-signal RF measurements. The model is also employed for designing and realizing a switch-mode inverse class-F power amplifier. The amplifier simulations showed a very good agreement with RF large-signal measurements.

Development of fire shutters based on numerical optimizations

NASA Astrophysics Data System (ADS)

Novak, Ondrej; Kulhavy, Petr; Martinec, Tomas; Petru, Michal; Srb, Pavel

2018-06-01

This article deals with a prototype concept, real experiment and numerical simulation of a layered industrial fire shutter, based on some new insulating composite materials. The real fire shutter has been developed and optimized in laboratory and subsequently tested in the certified test room. A simulation of whole concept has been carried out as the non-premixed combustion process in the commercial final volume sw Pyrosim. Model of the combustion based on a stoichiometric defined mixture of gas and the tested layered samples showed good conformity with experimental results - i.e. thermal distribution inside and heat release rate that has gone through the sample.

Phase diagram of two-dimensional hard rods from fundamental mixed measure density functional theory

NASA Astrophysics Data System (ADS)

Wittmann, René; Sitta, Christoph E.; Smallenburg, Frank; Löwen, Hartmut

2017-10-01

A density functional theory for the bulk phase diagram of two-dimensional orientable hard rods is proposed and tested against Monte Carlo computer simulation data. In detail, an explicit density functional is derived from fundamental mixed measure theory and freely minimized numerically for hard discorectangles. The phase diagram, which involves stable isotropic, nematic, smectic, and crystalline phases, is obtained and shows good agreement with the simulation data. Our functional is valid for a multicomponent mixture of hard particles with arbitrary convex shapes and provides a reliable starting point to explore various inhomogeneous situations of two-dimensional hard rods and their Brownian dynamics.

Experimental evaluation of joint designs for a space-shuttle orbiter ablative leading edge

NASA Technical Reports Server (NTRS)

Tompkins, S. S.; Kabana, W. P.

1975-01-01

The thermal performance of two types of ablative leading-edge joints for a space-shuttle orbiter were tested and evaluated. Chordwise joints between ablative leading-edge segments, and spanwise joints between ablative leading-edge segments and reusable surface insulation tiles were exposed to simulated shuttle heating environments. The data show that the thermal performance of models with chordwise joints to be as good as jointless models in simulated ascent-heating and orbital cold-soak environments. The suggestion is made for additional work on the joint seals, and, in particular, on the effects of heat-induced seal-material surface irregularities on the local flow.

RELATIVISTIC CYCLOTRON INSTABILITY IN ANISOTROPIC PLASMAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

López, Rodrigo A.; Moya, Pablo S.; Muñoz, Víctor

2016-11-20

A sufficiently large temperature anisotropy can sometimes drive various types of electromagnetic plasma micro-instabilities, which can play an important role in the dynamics of relativistic pair plasmas in space, astrophysics, and laboratory environments. Here, we provide a detailed description of the cyclotron instability of parallel propagating electromagnetic waves in relativistic pair plasmas on the basis of a relativistic anisotropic distribution function. Using plasma kinetic theory and particle-in-cell simulations, we study the influence of the relativistic temperature and the temperature anisotropy on the collective and noncollective modes of these plasmas. Growth rates and dispersion curves from the linear theory show amore » good agreement with simulations results.« less

Energy consumption analysis of the Venus Deep Space Station (DSS-13)

NASA Technical Reports Server (NTRS)

Hayes, N. V.

1983-01-01

This report continues the energy consumption analysis and verification study of the tracking stations of the Goldstone Deep Space Communications Complex, and presents an audit of the Venus Deep Space Station (DSS 13). Due to the non-continuous radioastronomy research and development operations at the station, estimations of energy usage were employed in the energy consumption simulation of both the 9-meter and 26-meter antenna buildings. A 17.9% decrease in station energy consumption was experienced over the 1979-1981 years under study. A comparison of the ECP computer simulations and the station's main watt-hour meter readings showed good agreement.

Analysis and modeling of subgrid scalar mixing using numerical data

NASA Technical Reports Server (NTRS)

Girimaji, Sharath S.; Zhou, YE

1995-01-01

Direct numerical simulations (DNS) of passive scalar mixing in isotropic turbulence is used to study, analyze and, subsequently, model the role of small (subgrid) scales in the mixing process. In particular, we attempt to model the dissipation of the large scale (supergrid) scalar fluctuations caused by the subgrid scales by decomposing it into two parts: (1) the effect due to the interaction among the subgrid scales; and (2) the effect due to interaction between the supergrid and the subgrid scales. Model comparisons with DNS data show good agreement. This model is expected to be useful in the large eddy simulations of scalar mixing and reaction.

Frequency comb generation in a continuously pumped optical parametric oscillator

NASA Astrophysics Data System (ADS)

Mosca, S.; Parisi, M.; Ricciardi, I.; Leo, F.; Hansson, T.; Erkintalo, M.; Maddaloni, P.; De Natale, P.; Wabnitz, S.; De Rosa, M.

2018-02-01

We demonstrate optical frequency comb generation in a continuously pumped optical parametric oscillator, in the parametric region around half of the pump frequency. We also model the dynamics of such quadratic combs using a single time-domain mean-field equation, and obtain simulation results that are in good agreement with experimentally observed spectra. Moreover, we numerically investigate the coherence properties of simulated combs, showing the existence of correlated and phase-locked combs. Our work could pave the way for a new class of frequency comb sources, which may enable straightforward access to new spectral regions and stimulate novel applications of frequency combs.

Direct magnetocaloric characterization and simulation of thermomagnetic cycles

NASA Astrophysics Data System (ADS)

Porcari, G.; Buzzi, M.; Cugini, F.; Pellicelli, R.; Pernechele, C.; Caron, L.; Brück, E.; Solzi, M.

2013-07-01

An experimental setup for the direct measurement of the magnetocaloric effect capable of simulating high frequency magnetothermal cycles on laboratory-scale samples is described. The study of the magnetocaloric properties of working materials under operative conditions is fundamental for the development of innovative devices. Frequency and time dependent characterization can provide essential information on intrinsic features such as magnetic field induced fatigue in materials undergoing first order magnetic phase transitions. A full characterization of the adiabatic temperature change performed for a sample of Gadolinium across its Curie transition shows the good agreement between our results and literature data and in-field differential scanning calorimetry.

A precise mass function in the excursion set approach

NASA Astrophysics Data System (ADS)

Del Popolo, Antonino

2017-04-01

In the present paper, using previous results from Del Popolo papers, we show how the mass function evolution can be obtained in the framework of a spherical collapse model, which has been modified to take account of dynamical friction, the cosmological constant, and angular momentum which proto-structures acquire through tidal interaction with neighbouring ones. We found an improved barrier which is in excellent agreement with simulations. The quoted barrier is used to calculated the mass function. In the case of the ΛCDM paradigm, our mass function is in good agreement (within some %) with the mass function of Klypin's Bolshoi simulation for the virial mass range 5 × 109 - 5 × 1014h-1M⊙, and 0 ≾ z ≿ 10. Similar agreement is obtained with Tinker's mass function, and Castorina's simulations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Akihiro; Maeda, Keiichi; Shigeyama, Toshikazu

A two-dimensional special relativistic radiation-hydrodynamics code is developed and applied to numerical simulations of supernova shock breakout in bipolar explosions of a blue supergiant. Our calculations successfully simulate the dynamical evolution of a blast wave in the star and its emergence from the surface. Results of the model with spherical energy deposition show a good agreement with previous simulations. Furthermore, we calculate several models with bipolar energy deposition and compare their results with the spherically symmetric model. The bolometric light curves of the shock breakout emission are calculated by a ray-tracing method. Our radiation-hydrodynamic models indicate that the early partmore » of the shock breakout emission can be used to probe the geometry of the blast wave produced as a result of the gravitational collapse of the iron core.« less

Thermography During Thermal Test of the Gaia Deployable Sunshield Assembly Qualification Model in the ESTEC Large Space Simulator

NASA Astrophysics Data System (ADS)

Simpson, R.; Broussely, M.; Edwards, G.; Robinson, D.; Cozzani, A.; Casarosa, G.

2012-07-01

The National Physical Laboratory (NPL) and The European Space Research and Technology Centre (ESTEC) have performed for the first time successful surface temperature measurements using infrared thermal imaging in the ESTEC Large Space Simulator (LSS) under vacuum and with the Sun Simulator (SUSI) switched on during thermal qualification tests of the GAIA Deployable Sunshield Assembly (DSA). The thermal imager temperature measurements, with radiosity model corrections, show good agreement with thermocouple readings on well characterised regions of the spacecraft. In addition, the thermal imaging measurements identified potentially misleading thermocouple temperature readings and provided qualitative real-time observations of the thermal and spatial evolution of surface structure changes and heat dissipation during hot test loadings, which may yield additional thermal and physical measurement information through further research.

Simulation of heat and mass transfer in turbulent channel flow using the spectral-element method: effect of spatial resolution

NASA Astrophysics Data System (ADS)

Ryzhenkov, V.; Ivashchenko, V.; Vinuesa, R.; Mullyadzhanov, R.

2016-10-01

We use the open-source code nek5000 to assess the accuracy of high-order spectral element large-eddy simulations (LES) of a turbulent channel flow depending on the spatial resolution compared to the direct numerical simulation (DNS). The Reynolds number Re = 6800 is considered based on the bulk velocity and half-width of the channel. The filtered governing equations are closed with the dynamic Smagorinsky model for subgrid stresses and heat flux. The results show very good agreement between LES and DNS for time-averaged velocity and temperature profiles and their fluctuations. Even the coarse LES grid which contains around 30 times less points than the DNS one provided predictions of the friction velocity within 2.0% accuracy interval.

Study of the heat transfer in solids using infrared photothermal radiometry and simulation by COMSOL Multiphysics.

PubMed

Suarez, V; Hernández Wong, J; Nogal, U; Calderón, A; Rojas-Trigos, J B; Juárez, A G; Marín, E

2014-01-01

It is reported the study of the heat transfer through a homogeneous and isotropic solid exited by square periodic light beam on its front surface. For this, we use the Infrared Photothermal Radiometry in order to obtain the evolution of the temperature difference on the rear surface of three samples, silicon, copper and wood, as a function of the exposure time. Also, we solved the heat transport equation for this problem with the boundary conditions congruent with the physical situation, by means of numerical simulation based in finite element analysis. Our results show a good agreement between the experimental and numerical simulated results, which demonstrate the utility of this methodology for the study of the thermal response of solids. Copyright © 2013 Elsevier Ltd. All rights reserved.

Lumped-parameters equivalent circuit for condenser microphones modeling.

PubMed

Esteves, Josué; Rufer, Libor; Ekeom, Didace; Basrour, Skandar

2017-10-01

This work presents a lumped parameters equivalent model of condenser microphone based on analogies between acoustic, mechanical, fluidic, and electrical domains. Parameters of the model were determined mainly through analytical relations and/or finite element method (FEM) simulations. Special attention was paid to the air gap modeling and to the use of proper boundary condition. Corresponding lumped-parameters were obtained as results of FEM simulations. Because of its simplicity, the model allows a fast simulation and is readily usable for microphone design. This work shows the validation of the equivalent circuit on three real cases of capacitive microphones, including both traditional and Micro-Electro-Mechanical Systems structures. In all cases, it has been demonstrated that the sensitivity and other related data obtained from the equivalent circuit are in very good agreement with available measurement data.

Real-time target tracking of soft tissues in 3D ultrasound images based on robust visual information and mechanical simulation.

PubMed

Royer, Lucas; Krupa, Alexandre; Dardenne, Guillaume; Le Bras, Anthony; Marchand, Eric; Marchal, Maud

2017-01-01

In this paper, we present a real-time approach that allows tracking deformable structures in 3D ultrasound sequences. Our method consists in obtaining the target displacements by combining robust dense motion estimation and mechanical model simulation. We perform evaluation of our method through simulated data, phantom data, and real-data. Results demonstrate that this novel approach has the advantage of providing correct motion estimation regarding different ultrasound shortcomings including speckle noise, large shadows and ultrasound gain variation. Furthermore, we show the good performance of our method with respect to state-of-the-art techniques by testing on the 3D databases provided by MICCAI CLUST'14 and CLUST'15 challenges. Copyright © 2016 Elsevier B.V. All rights reserved.

The diagnosis and treatment of donovanosis (granuloma inguinale).

PubMed Central

Richens, J

1991-01-01

Donovanosis is a predominantly tropical cause of genital ulcer occurring chiefly in small endemic foci in all continents except Europe. Diagnosis requires the careful collection, staining and examination of smears or biopsies of characteristic genital and, occasionally, extragenital lesions for demonstration of the pathognomonic Donovan bodies (Calymmatobacterium granulomatis) within histiocytes. Successful isolation of C. granulomatis has rarely proved feasible, the last report being in 1962. Donovanosis has a characteristic histopathological picture which occasionally simulates epithelioma. The antibiotics reported as showing good activity in donovanosis are those with good activity against gram negative bacilli and whose lipid solubility ensures good intracellular penetration. They include streptomycin, chloramphenicol, erythromycin, lincomycin, cotrimoxazole and the tetracyclines. More recently, good results have been reported with norfloxacin and thiamphenicol. The treatment of donovanosis in pregnant women and patients with AIDS poses special problems. Complications of donovanosis such as elephantiasis, stricture and pelvic abscess may require surgery. Contacts should be traced for examination but only treated if lesions are found. Images PMID:1774048

Dilemma of dilemmas: how collective and individual perspectives can clarify the size dilemma in voluntary linear public goods dilemmas.

PubMed

Shank, Daniel B; Kashima, Yoshihisa; Saber, Saam; Gale, Thomas; Kirley, Michael

2015-01-01

Empirical findings on public goods dilemmas indicate an unresolved dilemma: that increasing size-the number of people in the dilemma-sometimes increases, decreases, or does not influence cooperation. We clarify this dilemma by first classifying public goods dilemma properties that specify individual outcomes as individual properties (e.g., Marginal Per Capita Return) and group outcomes as group properties (e.g., public good multiplier), mathematically showing how only one set of properties can remain constant as the dilemma size increases. Underpinning decision-making regarding individual and group properties, we propose that individuals are motivated by both individual and group preferences based on a theory of collective rationality. We use Van Lange's integrated model of social value orientations to operationalize these preferences as an amalgamation of outcomes for self, outcomes for others, and equality of outcomes. Based on this model, we then predict how the public good's benefit and size, combined with controlling individual versus group properties, produce different levels of cooperation in public goods dilemmas. A two (low vs. high benefit) by three (2-person baseline vs. 5-person holding constant individual properties vs. 5-person holding constant group properties) factorial experiment (group n = 99; participant n = 390) confirms our hypotheses. The results indicate that when holding constant group properties, size decreases cooperation. Yet when holding constant individual properties, size increases cooperation when benefit is low and does not affect cooperation when benefit is high. Using agent-based simulations of individual and group preferences vis-à-vis the integrative model, we fit a weighted simulation model to the empirical data. This fitted model is sufficient to reproduce the empirical results, but only when both individual (self-interest) and group (other-interest and equality) preference are included. Our research contributes to understanding how people's motivations and behaviors within public goods dilemmas interact with the properties of the dilemma to lead to collective outcomes.

Dilemma of Dilemmas: How Collective and Individual Perspectives Can Clarify the Size Dilemma in Voluntary Linear Public Goods Dilemmas

PubMed Central

Shank, Daniel B.; Kashima, Yoshihisa; Saber, Saam; Gale, Thomas; Kirley, Michael

2015-01-01

Empirical findings on public goods dilemmas indicate an unresolved dilemma: that increasing size—the number of people in the dilemma—sometimes increases, decreases, or does not influence cooperation. We clarify this dilemma by first classifying public goods dilemma properties that specify individual outcomes as individual properties (e.g., Marginal Per Capita Return) and group outcomes as group properties (e.g., public good multiplier), mathematically showing how only one set of properties can remain constant as the dilemma size increases. Underpinning decision-making regarding individual and group properties, we propose that individuals are motivated by both individual and group preferences based on a theory of collective rationality. We use Van Lange's integrated model of social value orientations to operationalize these preferences as an amalgamation of outcomes for self, outcomes for others, and equality of outcomes. Based on this model, we then predict how the public good's benefit and size, combined with controlling individual versus group properties, produce different levels of cooperation in public goods dilemmas. A two (low vs. high benefit) by three (2-person baseline vs. 5-person holding constant individual properties vs. 5-person holding constant group properties) factorial experiment (group n = 99; participant n = 390) confirms our hypotheses. The results indicate that when holding constant group properties, size decreases cooperation. Yet when holding constant individual properties, size increases cooperation when benefit is low and does not affect cooperation when benefit is high. Using agent-based simulations of individual and group preferences vis-à-vis the integrative model, we fit a weighted simulation model to the empirical data. This fitted model is sufficient to reproduce the empirical results, but only when both individual (self-interest) and group (other-interest and equality) preference are included. Our research contributes to understanding how people's motivations and behaviors within public goods dilemmas interact with the properties of the dilemma to lead to collective outcomes. PMID:25799355

MEMS-based wide-bandwidth electromagnetic energy harvester with electroplated nickel structure

NASA Astrophysics Data System (ADS)

Sun, Shi; Dai, Xuhan; Sun, Yunna; Xiang, Xiaojian; Ding, Guifu; Zhao, Xiaolin

2017-11-01

A novel nickel-based nonlinear electromagnetic energy harvester has been designed, fabricated, and characterized in this work. Electroplated nickel is very suitable for a stretching-based mechanism to broaden the bandwidth due to its good process and mechanical properties. A strong hardening nonlinearity is induced due to the large deformation of the thin nickel based guided-beam structure. Combining the merits of both the mechanical properties and guided-beam structure, the energy harvester shows good bandwidth performance. It is found that increasing the thickness of the central platform could guarantee nonlinearity. Static and dynamic models of the energy harvester are simulated and validated. Test results show that the energy harvester has good repeatability without any destruction under a large deformation condition. At the acceleration of 0.5 g, comparative large bandwidths of 129 and 59 Hz are obtained for displacement and RMS output voltage, respectively. Power output of 3.4 µW and normalized power density of 125.92 µW cm-3 g-2 are achieved with the load resistance of 38 Ω.

THE CENTRAL SLOPE OF DARK MATTER CORES IN DWARF GALAXIES: SIMULATIONS VERSUS THINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oh, Se-Heon; De Blok, W. J. G.; Brook, Chris

2011-07-15

We make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming a {Lambda}CDM cosmology and the observed dwarf galaxies sample from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope {alpha} of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating, and most importantly, physically motivated gas outflows driven by supernovae, form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to thatmore » inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called cusp/core problem in the {Lambda}CDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than cold dark matter rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes {alpha} of the simulated galaxies' DM density profiles is {approx}-0.4 {+-} 0.1, which shows good agreement with {alpha} = -0.29 {+-} 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with {alpha} {approx}-1.0 to -1.5 predicted by DM-only simulations shallower and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.« less

Advanced EMT and Phasor-Domain Hybrid Simulation with Simulation Mode Switching Capability for Transmission and Distribution Systems

DOE PAGES

Huang, Qiuhua; Vittal, Vijay

2018-05-09

Conventional electromagnetic transient (EMT) and phasor-domain hybrid simulation approaches presently exist for trans-mission system level studies. Their simulation efficiency is generally constrained by the EMT simulation. With an increasing number of distributed energy resources and non-conventional loads being installed in distribution systems, it is imperative to extend the hybrid simulation application to include distribution systems and integrated transmission and distribution systems. Meanwhile, it is equally important to improve the simulation efficiency as the modeling scope and complexity of the detailed system in the EMT simulation increases. To meet both requirements, this paper introduces an advanced EMT and phasor-domain hybrid simulationmore » approach. This approach has two main features: 1) a comprehensive phasor-domain modeling framework which supports positive-sequence, three-sequence, three-phase and mixed three-sequence/three-phase representations and 2) a robust and flexible simulation mode switching scheme. The developed scheme enables simulation switching from hybrid simulation mode back to pure phasor-domain dynamic simulation mode to achieve significantly improved simulation efficiency. The proposed method has been tested on integrated transmission and distribution systems. In conclusion, the results show that with the developed simulation switching feature, the total computational time is significantly reduced compared to running the hybrid simulation for the whole simulation period, while maintaining good simulation accuracy.« less

Advanced EMT and Phasor-Domain Hybrid Simulation with Simulation Mode Switching Capability for Transmission and Distribution Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Qiuhua; Vittal, Vijay

Conventional electromagnetic transient (EMT) and phasor-domain hybrid simulation approaches presently exist for trans-mission system level studies. Their simulation efficiency is generally constrained by the EMT simulation. With an increasing number of distributed energy resources and non-conventional loads being installed in distribution systems, it is imperative to extend the hybrid simulation application to include distribution systems and integrated transmission and distribution systems. Meanwhile, it is equally important to improve the simulation efficiency as the modeling scope and complexity of the detailed system in the EMT simulation increases. To meet both requirements, this paper introduces an advanced EMT and phasor-domain hybrid simulationmore » approach. This approach has two main features: 1) a comprehensive phasor-domain modeling framework which supports positive-sequence, three-sequence, three-phase and mixed three-sequence/three-phase representations and 2) a robust and flexible simulation mode switching scheme. The developed scheme enables simulation switching from hybrid simulation mode back to pure phasor-domain dynamic simulation mode to achieve significantly improved simulation efficiency. The proposed method has been tested on integrated transmission and distribution systems. In conclusion, the results show that with the developed simulation switching feature, the total computational time is significantly reduced compared to running the hybrid simulation for the whole simulation period, while maintaining good simulation accuracy.« less

Titan's organic chemistry: Results of simulation experiments

NASA Technical Reports Server (NTRS)

Sagan, Carl; Thompson, W. Reid; Khare, Bishun N.

1992-01-01

Recent low pressure continuous low plasma discharge simulations of the auroral electron driven organic chemistry in Titan's mesosphere are reviewed. These simulations yielded results in good accord with Voyager observations of gas phase organic species. Optical constants of the brownish solid tholins produced in similar experiments are in good accord with Voyager observations of the Titan haze. Titan tholins are rich in prebiotic organic constituents; the Huygens entry probe may shed light on some of the processes that led to the origin of life on Earth.

Phenylethanoid Glycoside Profiles and Antioxidant Activities of Osmanthus fragrans Lour. Flowers by UPLC/PDA/MS and Simulated Digestion Model.

PubMed

Jiang, Yirong; Mao, Shuqin; Huang, Weisu; Lu, Baiyi; Cai, Zengxuan; Zhou, Fei; Li, Maiquan; Lou, Tiantian; Zhao, Yajing

2016-03-30

Variations of phenylethanoid glycoside profiles and antioxidant activities in Osmanthus fragrans flowers through the digestive tract were evaluated by a simulated digestion model and UPLC/PDA/MS. Major phenylethanoid glycosides and phenolic acids, namely, salidroside, acteoside, isoacteoside, chlorogenic acid, and caffeic acid, were identified in four cultivars of O. fragrans flowers, and the concentration of acteoside was the highest, being up to 71.79 mg/g dry weight. After simulated digestion, total phenylethanoid glycoside contents and antioxidant activities were significantly decreased. Acteoside was identified as decomposing into caffeic acid, whereas salidroside was found to be stable during simulated digestion. According to Pearson's correlation analysis, acteoside contents showed good correlations with antioxidant activities during simulated digestion (R(2) = 0.994, P < 0.01). In conclusion, acteoside was the major contributor to the antioxidant activity of O. fragrans flowers, and salidroside was considered as the major antioxidant compound of O. fragrans flowers in vivo.

Simulations of a binary-sized mixture of inelastic grains in rapid shear flow.

PubMed

Clelland, R; Hrenya, C M

2002-03-01

In an effort to explore the rapid flow behavior associated with a binary-sized mixture of grains and to assess the predictive ability of the existing theory for such systems, molecular-dynamic simulations have been carried out. The system under consideration is composed of inelastic, smooth, hard disks engaged in rapid shear flow. The simulations indicate that nondimensional stresses decrease with an increase in d(L)/d(S) (ratio of large particle diameter to small particle diameter) or a decrease in nu(L)/nu(S) (area fraction ratio), as is also predicted by the kinetic theory of Willits and Arnarson [Phys. Fluids 11, 3116 (1999)]. Furthermore, the level of quantitative agreement between the theoretical stress predictions and simulation data is good over the entire range of parameters investigated. Nonetheless, the molecular-dynamic simulations also show that the assumption of an equipartition of energy rapidly deteriorates as the coefficient of restitution is decreased. The magnitude of this energy difference is found to increase with the difference in particle sizes.

[Adaptability of APSIM model in Southwestern China: A case study of winter wheat in Chongqing City].

PubMed

Dai, Tong; Wang, Jing; He, Di; Zhang, Jian-ping; Wang, Na

2015-04-01

Field experimental data of winter wheat and parallel daily meteorological data at four typical stations in Chongqing City were used to calibrate and validate APSIM-wheat model and determine the genetic parameters for 12 varieties of winter wheat. The results showed that there was a good agreement between the simulated and observed growth periods from sowing to emergence, flowering and maturity of wheat. Root mean squared errors (RMSEs) between simulated and observed emergence, flowering and maturity were 0-3, 1-8, and 0-8 d, respectively. Normalized root mean squared errors (NRMSEs) between simulated and observed above-ground biomass for 12 study varieties were less than 30%. NRMSE between simulated and observed yields for 10 varieties out of 12 study varieties were less than 30%. APSIM-wheat model performed well in simulating phenology, aboveground biomass and yield of winter wheat in Chongqing City, which could provide a foundational support for assessing the impact of climate change on wheat production in the study area based on the model.

The Axial Velocity Distribution of a Polyethylene Strand During Extrusion: Simulation and Comparison with Measurements

NASA Astrophysics Data System (ADS)

Schneider, Christian; Schwetz, Martin; Münstedt, Helmut; Kaschta, Joachim

2004-09-01

The velocity distribution along the axis of a low-density polyethylene (LDPE) melt strand extruded through an axisymmetric capillary and drawn by various forces is simulated using an integral constitutive equation with a PSM damping function (Papanastasiou, Scriven, Macosko, Journal of Rheology, 27: 381 410, 1983). The simulations are performed for different drawdown forces of the strand. The numerical results are compared with experimental data obtained by velocity measurements using the laser-Doppler velocimetry. The strand is drawn by rotating wheels as used in a Rheotens™ testing device. At drawdown forces greater than zero the investigations show that the strand velocity does not increase linearly with increasing distance from the die exit. Instead, it is observed that the acceleration of the strand increases monotonically. Except in the next vicinity of the die exit there is a good agreement between simulation and experiment. However, near to the die the simulation predicts a higher strand velocity.

Surface Dimming by the 2013 Rim Fire Simulated by a Sectional Aerosol Model

NASA Technical Reports Server (NTRS)

Yu, Pengfei; Toon, Owen B.; Bardeen, Charles G; Bucholtz, Anthony; Rosenlof, Karen; Saide, Pablo E.; Da Silva, Arlindo M.; Ziemba, Luke D.; Thornhill, Kenneth L.; Jimenez, Jose-Luis;

Surface dimming by the 2013 Rim Fire simulated by a sectional aerosol model.

PubMed

Yu, Pengfei; Toon, Owen B; Bardeen, Charles G; Bucholtz, Anthony; Rosenlof, Karen H; Saide, Pablo E; Da Silva, Arlindo; Ziemba, Luke D; Thornhill, Kenneth L; Jimenez, Jose-Luis; Campuzano-Jost, Pedro; Schwarz, Joshua P; Perring, Anne E; Froyd, Karl D; Wagner, N L; Mills, Michael J; Reid, Jeffrey S

2016-06-27

The Rim Fire of 2013, the third largest area burned by fire recorded in California history, is simulated by a climate model coupled with a size-resolved aerosol model. Modeled aerosol mass, number, and particle size distribution are within variability of data obtained from multiple-airborne in situ measurements. Simulations suggest that Rim Fire smoke may block 4-6% of sunlight energy reaching the surface, with a dimming efficiency around 120-150 W m -2 per unit aerosol optical depth in the midvisible at 13:00-15:00 local time. Underestimation of simulated smoke single scattering albedo at midvisible by 0.04 suggests that the model overestimates either the particle size or the absorption due to black carbon. This study shows that exceptional events like the 2013 Rim Fire can be simulated by a climate model with 1° resolution with overall good skill, although that resolution is still not sufficient to resolve the smoke peak near the source region.

Tempting food words activate eating simulations

PubMed Central

Papies, Esther K.

2013-01-01

This study shows that tempting food words activate simulations of eating the food, including simulations of the taste and texture of the food, simulations of eating situations, and simulations of hedonic enjoyment. In a feature listing task, participants generated features that are typically true of four tempting foods (e.g., chips) and four neutral foods (e.g., rice). The resulting features were coded as features of eating simulations if they referred to the taste, texture, and temperature of the food (e.g., “crunchy”; “sticky”), to situations of eating the food (e.g., “movie”; “good for Wok dishes”), and to the hedonic experience when eating the food (e.g., “tasty”). Based on the grounded cognition perspective, it was predicted that tempting foods are more likely to be represented in terms of actually eating them, so that participants would list more features referring to eating simulations for tempting than for neutral foods. Confirming this hypothesis, results showed that eating simulation features constituted 53% of the features for tempting food, and 26% of the features for neutral food. Visual features, in contrast, were mentioned more often for neutral foods (45%) than for tempting foods (19%). Exploratory analyses revealed that the proportion of eating simulation features for tempting foods was positively correlated with perceived attractiveness of the foods, and negatively with participants’ dieting concerns, suggesting that eating simulations may depend on individuals’ goals with regard to eating. These findings are discussed with regard to their implications for understanding the processes guiding eating behavior, and for interventions designed to reduce the consumption of attractive, unhealthy food. PMID:24298263

First Lunar Wake Passage of ARTEMIS: Discrimination of Wake Effects and Solar Wind Fluctuations by 3D Hybrid Simulations

NASA Technical Reports Server (NTRS)

Wiehle, S.; Plaschke, F.; Motschmann, U.; Glassmeier, K. H.; Auster, H. U.; Angelopoulos, V.; Mueller, J.; Kriegel, H.; Georgescu, E.; Halekas, J.;

Preparation and characterisation of a novel hydrogel based on Auricularia polytricha β-glucan and its bio-release property for vitamin B12 delivery.

PubMed

Zhu, Kai; Chen, Xiaoyuan; Yu, Da; He, Yue; Song, Guanglei

2018-05-01

This study investigates a novel hydrogel synthesis method and its bio-release property. This hydrogel, with a three-dimensional network structure based on Auricularia polytricha β-glucan, was characterised by means of Fourier transform infrared spectroscopy, 1 H NMR and scanning electron microscopy. Vitamin B 12 (VB 12 , cobalamin) as a hydrophilic functional food component was entrapped into these hydrogels. The in vitro release profile of VB 12 was established in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The results showed that the hydrogel had medium pore size from 30 to 300 µm, and the swelling ratio increased with the degree of substitution. The hydrogel demonstrated good stability in SGF and bio-release capability in SIF for VB 12 . The accumulated release rate is about 80% in SIF and below 20% in SGF, which indicated the significant different release property in stomach and intestine. The Auricularia polytricha β-glucan-based hydrogel has a good swelling ratio, pepsin stability and pancrelipase-catalysed biodegradation property. The bio-release rate is significantly different in SIF and SGF, which indicated that this hydrogel could be a good intestinal target carrier of VB 12 . © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Modeling the Lyα Forest in Collisionless Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sorini, Daniele; Oñorbe, José; Lukić, Zarija

2016-08-11

Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present in this paper "Iteratively Matched Statistics" (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) andmore » the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%–80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. Finally, in addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic "mock" skies for Lyα forest surveys.« less

MODELING THE Ly α FOREST IN COLLISIONLESS SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sorini, Daniele; Oñorbe, José; Hennawi, Joseph F.

2016-08-20

Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Ly α forest with collisionless N -body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and themore » power spectrum of the real-space Ly α forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N -body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Ly α forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%–80%), especially for N -body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Ly α forest surveys.« less

Three-dimensional variable-density flow simulation of a coastal aquifer in southern Oahu, Hawaii, USA

USGS Publications Warehouse

Gingerich, S.B.; Voss, C.I.

2005-01-01

Three-dimensional modeling of groundwater flow and solute transport in the Pearl Harbor aquifer, southern Oahu, Hawaii, shows that the readjustment of the freshwater-saltwater transition zone takes a long time following changes in pumping, irrigation, or recharge in the aquifer system. It takes about 50-years for the transition zone to move 90% of the distance to its new steady position. Further, the Ghyben-Herzberg estimate of the freshwater/saltwater interface depth occurred between the 10 and 50% simulated seawater concentration contours in a complex manner during 100-years of the pumping history of the aquifer. Thus, it is not a good predictor of the depth of potable water. Pre-development recharge was used to simulate the 1880 freshwater-lens configuration. Historical pumpage and recharge distributions were used and the resulting freshwater-lens size and position were simulated through 1980. Simulations show that the transition zone moved upward and landward during the period simulated. Previous groundwater flow models for Oahu have been limited to areal models that simulate a sharp interface between freshwater and saltwater or solute-transport models that simulate a vertical aquifer section. The present model is based on the US Geological Survey's three-dimensional solute transport (3D SUTRA) computer code. Using several new tools for pre- and post-processing of model input and results have allowed easy model construction and unprecedented visualization of the freshwater lens and underlying transition zone in Hawaii's most developed aquifer. ?? Springer-Verlag 2005.

A Performance Comparison on the Probability Plot Correlation Coefficient Test using Several Plotting Positions for GEV Distribution.

NASA Astrophysics Data System (ADS)

Ahn, Hyunjun; Jung, Younghun; Om, Ju-Seong; Heo, Jun-Haeng

2014-05-01

It is very important to select the probability distribution in Statistical hydrology. Goodness of fit test is a statistical method that selects an appropriate probability model for a given data. The probability plot correlation coefficient (PPCC) test as one of the goodness of fit tests was originally developed for normal distribution. Since then, this test has been widely applied to other probability models. The PPCC test is known as one of the best goodness of fit test because it shows higher rejection powers among them. In this study, we focus on the PPCC tests for the GEV distribution which is widely used in the world. For the GEV model, several plotting position formulas are suggested. However, the PPCC statistics are derived only for the plotting position formulas (Goel and De, In-na and Nguyen, and Kim et al.) in which the skewness coefficient (or shape parameter) are included. And then the regression equations are derived as a function of the shape parameter and sample size for a given significance level. In addition, the rejection powers of these formulas are compared using Monte-Carlo simulation. Keywords: Goodness-of-fit test, Probability plot correlation coefficient test, Plotting position, Monte-Carlo Simulation ACKNOWLEDGEMENTS This research was supported by a grant 'Establishing Active Disaster Management System of Flood Control Structures by using 3D BIM Technique' [NEMA-12-NH-57] from the Natural Hazard Mitigation Research Group, National Emergency Management Agency of Korea.

Proceedings of Tunnel Detection Symposium on Subsurface Exploration Technology (4th) held in Golden, Colorado on 26 - 29 Apr 1993

DTIC Science & Technology

1993-04-29

characteristics such as intuition, telepathy , ESP, PSI, subconscious creativity and the likz. "Don’t do it Ruskey," they told me, "give them nuts and bolts." Nuts...basic shape of the homogeneous media response ( i.e. the primary wave). The synthetic waveforms 72 show good conformance with the field data. The minor...as a fracture halo surrounding the tunnel which is unaccounted for in the simulation. Figure 5 shows a suite of synthetic waveforms for an air tilled

Computer Simulation of the Alonso Household Location Model in the Microeconomics Course

ERIC Educational Resources Information Center

Bolton, Roger E.

2005-01-01

Computer simulation of the Alonso household location model can enrich the intermediate microeconomics course. The model includes decisions on location, land space, and other goods and is a valuable complement to the usual textbook model of household consumption. It has three decision variables, one of which is a "bad," and one good's price is a…

Model predictions of latitude-dependent ozone depletion due to aerospace vehicle operations

NASA Technical Reports Server (NTRS)

Borucki, W. J.; Whitten, R. C.; Watson, V. R.; Riegel, C. A.; Maples, A. L.; Capone, L. A.

1976-01-01

Results are presented from a two-dimensional model of the stratosphere that simulates the seasonal movement of ozone by both wind and eddy transport, and contains all the chemistry known to be important. The calculated reductions in ozone due to NO2 injection from a fleet of supersonic transports are compared with the zonally averaged results of a three-dimensional model for a similar episode of injection. The agreement is good in the northern hemisphere, but is not as good in the southern hemisphere. Both sets of calculations show a strong corridor effect in that the predicted ozone depletions are largest to the north of the flight corridor for aircraft operating in the northern hemisphere.

Radial Basis Function Neural Network Application to Power System Restoration Studies

PubMed Central

Sadeghkhani, Iman; Ketabi, Abbas; Feuillet, Rene

2012-01-01

One of the most important issues in power system restoration is overvoltages caused by transformer switching. These overvoltages might damage some equipment and delay power system restoration. This paper presents a radial basis function neural network (RBFNN) to study transformer switching overvoltages. To achieve good generalization capability for developed RBFNN, equivalent parameters of the network are added to RBFNN inputs. The developed RBFNN is trained with the worst-case scenario of switching angle and remanent flux and tested for typical cases. The simulated results for a partial of 39-bus New England test system show that the proposed technique can estimate the peak values and duration of switching overvoltages with good accuracy. PMID:22792093

Research on control strategy based on fuzzy PR for grid-connected inverter

NASA Astrophysics Data System (ADS)

Zhang, Qian; Guan, Weiguo; Miao, Wen

2018-04-01

In the traditional PI controller, there is static error in tracking ac signals. To solve the problem, the control strategy of a fuzzy PR and the grid voltage feed-forward is proposed. The fuzzy PR controller is to eliminate the static error of the system. It also adjusts parameters of PR controller in real time, which avoids the defect of fixed parameter fixed. The grid voltage feed-forward control can ensure the quality of current and improve the system's anti-interference ability when the grid voltage is distorted. Finally, the simulation results show that the system can output grid current with good quality and also has good dynamic and steady state performance.

Study on zigzag maneuver characteristics of V-U very large crude oil (VLCC) tankers

NASA Astrophysics Data System (ADS)

Jaswar, Maimun, A.; Wahid, M. A.; Priyanto, A.; Zamani, Pauzi, Saman

2012-06-01

The Department of Marine Technology at the Faculty of Mechanical Engineering, University Teknologi Malaysia has recently developed an Ship Maneuverability tool which intends to upgrade student's level understanding the application of fluid dynamic on interaction between hull, propeller, and rudder during maneuvering. This paper discusses zigzag maneuver for conventional Very Large Crude Oil (VLCC) ships with the same principal dimensions but different stern flame shape. 10/10 zigzag maneuver characteristics of U and V types of VLCC ships are investigated. Simulation results for U-type show a good agreement with the experimental data, but V-type not good agreement with experimental one. Further study on zigzag maneuver characteristics are required.

Analysis of Artificial Neural Network in Erosion Modeling: A Case Study of Serang Watershed

NASA Astrophysics Data System (ADS)

Arif, N.; Danoedoro, P.; Hartono

2017-12-01

Erosion modeling is an important measuring tool for both land users and decision makers to evaluate land cultivation and thus it is necessary to have a model to represent the actual reality. Erosion models are a complex model because of uncertainty data with different sources and processing procedures. Artificial neural networks can be relied on for complex and non-linear data processing such as erosion data. The main difficulty in artificial neural network training is the determination of the value of each network input parameters, i.e. hidden layer, momentum, learning rate, momentum, and RMS. This study tested the capability of artificial neural network application in the prediction of erosion risk with some input parameters through multiple simulations to get good classification results. The model was implemented in Serang Watershed, Kulonprogo, Yogyakarta which is one of the critical potential watersheds in Indonesia. The simulation results showed the number of iterations that gave a significant effect on the accuracy compared to other parameters. A small number of iterations can produce good accuracy if the combination of other parameters was right. In this case, one hidden layer was sufficient to produce good accuracy. The highest training accuracy achieved in this study was 99.32%, occurred in ANN 14 simulation with combination of network input parameters of 1 HL; LR 0.01; M 0.5; RMS 0.0001, and the number of iterations of 15000. The ANN training accuracy was not influenced by the number of channels, namely input dataset (erosion factors) as well as data dimensions, rather it was determined by changes in network parameters.

Signal recognition and parameter estimation of BPSK-LFM combined modulation

NASA Astrophysics Data System (ADS)

Long, Chao; Zhang, Lin; Liu, Yu

2015-07-01

Intra-pulse analysis plays an important role in electronic warfare. Intra-pulse feature abstraction focuses on primary parameters such as instantaneous frequency, modulation, and symbol rate. In this paper, automatic modulation recognition and feature extraction for combined BPSK-LFM modulation signals based on decision theoretic approach is studied. The simulation results show good recognition effect and high estimation precision, and the system is easy to be realized.

Modeling of air pollution from the power plant ash dumps

NASA Astrophysics Data System (ADS)

Aleksic, Nenad M.; Balać, Nedeljko

A simple model of air pollution from power plant ash dumps is presented, with emission rates calculated from the Bagnold formula and transport simulated by the ATDL type model. Moisture effects are accounted for by assumption that there is no pollution on rain days. Annual mean daily sedimentation rates, calculated for the area around the 'Nikola Tesla' power plants near Belgrade for 1987, show reasonably good agreement with observations.

Shear Wave Velocity Imaging Using Transient Electrode Perturbation: Phantom and ex vivo Validation

PubMed Central

Varghese, Tomy; Madsen, Ernest L.

2011-01-01

This paper presents a new shear wave velocity imaging technique to monitor radio-frequency and microwave ablation procedures, coined electrode vibration elastography. A piezoelectric actuator attached to an ablation needle is transiently vibrated to generate shear waves that are tracked at high frame rates. The time-to-peak algorithm is used to reconstruct the shear wave velocity and thereby the shear modulus variations. The feasibility of electrode vibration elastography is demonstrated using finite element models and ultrasound simulations, tissue-mimicking phantoms simulating fully (phantom 1) and partially ablated (phantom 2) regions, and an ex vivo bovine liver ablation experiment. In phantom experiments, good boundary delineation was observed. Shear wave velocity estimates were within 7% of mechanical measurements in phantom 1 and within 17% in phantom 2. Good boundary delineation was also demonstrated in the ex vivo experiment. The shear wave velocity estimates inside the ablated region were higher than mechanical testing estimates, but estimates in the untreated tissue were within 20% of mechanical measurements. A comparison of electrode vibration elastography and electrode displacement elastography showed the complementary information that they can provide. Electrode vibration elastography shows promise as an imaging modality that provides ablation boundary delineation and quantitative information during ablation procedures. PMID:21075719

Structure and dynamics of aqueous solutions from PBE-based first-principles molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Tuan Anh; Ogitsu, Tadashi; Lau, Edmond Y.

Establishing an accurate and predictive computational framework for the description of complex aqueous solutions is an ongoing challenge for density functional theory based first-principles molecular dynamics (FPMD) simulations. In this context, important advances have been made in recent years, including the development of sophisticated exchange-correlation functionals. On the other hand, simulations based on simple generalized gradient approximation (GGA) functionals remain an active field, particularly in the study of complex aqueous solutions due to a good balance between the accuracy, computational expense, and the applicability to a wide range of systems. In such simulations we often perform them at elevated temperaturesmore » to artificially “correct” for GGA inaccuracies in the description of liquid water; however, a detailed understanding of how the choice of temperature affects the structure and dynamics of other components, such as solvated ions, is largely unknown. In order to address this question, we carried out a series of FPMD simulations at temperatures ranging from 300 to 460 K for liquid water and three representative aqueous solutions containing solvated Na +, K +, and Cl - ions. We show that simulations at 390–400 K with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional yield water structure and dynamics in good agreement with experiments at ambient conditions. Simultaneously, this computational setup provides ion solvation structures and ion effects on water dynamics consistent with experiments. These results suggest that an elevated temperature around 390–400 K with the PBE functional can be used for the description of structural and dynamical properties of liquid water and complex solutions with solvated ions at ambient conditions.« less

Structure and dynamics of aqueous solutions from PBE-based first-principles molecular dynamics simulations

DOE PAGES

Pham, Tuan Anh; Ogitsu, Tadashi; Lau, Edmond Y.; ...

2016-10-17

Establishing an accurate and predictive computational framework for the description of complex aqueous solutions is an ongoing challenge for density functional theory based first-principles molecular dynamics (FPMD) simulations. In this context, important advances have been made in recent years, including the development of sophisticated exchange-correlation functionals. On the other hand, simulations based on simple generalized gradient approximation (GGA) functionals remain an active field, particularly in the study of complex aqueous solutions due to a good balance between the accuracy, computational expense, and the applicability to a wide range of systems. In such simulations we often perform them at elevated temperaturesmore » to artificially “correct” for GGA inaccuracies in the description of liquid water; however, a detailed understanding of how the choice of temperature affects the structure and dynamics of other components, such as solvated ions, is largely unknown. In order to address this question, we carried out a series of FPMD simulations at temperatures ranging from 300 to 460 K for liquid water and three representative aqueous solutions containing solvated Na +, K +, and Cl - ions. We show that simulations at 390–400 K with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional yield water structure and dynamics in good agreement with experiments at ambient conditions. Simultaneously, this computational setup provides ion solvation structures and ion effects on water dynamics consistent with experiments. These results suggest that an elevated temperature around 390–400 K with the PBE functional can be used for the description of structural and dynamical properties of liquid water and complex solutions with solvated ions at ambient conditions.« less

Nanostructure Formation by controlled dewetting on patterned substrates: A combined theoretical, modeling and experimental study

PubMed Central

Lu, Liang-Xing; Wang, Ying-Min; Srinivasan, Bharathi Madurai; Asbahi, Mohamed; Yang, Joel K. W.; Zhang, Yong-Wei

2016-01-01

We perform systematic two-dimensional energetic analysis to study the stability of various nanostructures formed by dewetting solid films deposited on patterned substrates. Our analytical results show that by controlling system parameters such as the substrate surface pattern, film thickness and wetting angle, a variety of equilibrium nanostructures can be obtained. Phase diagrams are presented to show the complex relations between these system parameters and various nanostructure morphologies. We further carry out both phase field simulations and dewetting experiments to validate the analytically derived phase diagrams. Good agreements between the results from our energetic analyses and those from our phase field simulations and experiments verify our analysis. Hence, the phase diagrams presented here provide guidelines for using solid-state dewetting as a tool to achieve various nanostructures. PMID:27580943

Pseudochemotaxis in inhomogeneous active Brownian systems

NASA Astrophysics Data System (ADS)

Vuijk, Hidde D.; Sharma, Abhinav; Mondal, Debasish; Sommer, Jens-Uwe; Merlitz, Holger

2018-04-01

We study dynamical properties of confined, self-propelled Brownian particles in an inhomogeneous activity profile. Using Brownian dynamics simulations, we calculate the probability to reach a fixed target and the mean first passage time to the target of an active particle. We show that both these quantities are strongly influenced by the inhomogeneous activity. When the activity is distributed such that high-activity zone is located between the target and the starting location, the target finding probability is increased and the passage time is decreased in comparison to a uniformly active system. Moreover, for a continuously distributed profile, the activity gradient results in a drift of active particle up the gradient bearing resemblance to chemotaxis. Integrating out the orientational degrees of freedom, we derive an approximate Fokker-Planck equation and show that the theoretical predictions are in very good agreement with the Brownian dynamics simulations.

Numerical simulation of terrain-induced mesoscale circulation in the Chiang Mai area, Thailand

NASA Astrophysics Data System (ADS)

Sathitkunarat, Surachai; Wongwises, Prungchan; Pan-Aram, Rudklao; Zhang, Meigen

2008-11-01

The regional atmospheric modeling system (RAMS) was applied to Chiang Mai province, a mountainous area in Thailand, to study terrain-induced mesoscale circulations. Eight cases in wet and dry seasons under different weather conditions were analyzed to show thermal and dynamic impacts on local circulations. This is the first study of RAMS in Thailand especially investigating the effect of mountainous area on the simulated meteorological data. Analysis of model results indicates that the model can reproduce major features of local circulation and diurnal variations in temperatures. For evaluating the model performance, model results were compared with observed wind speed, wind direction, and temperature monitored at a meteorological tower. Comparison shows that the modeled values are generally in good agreement with observations and that the model captured many of the observed features.

Effect of damping on the laser induced ultrafast switching in rare earth-transition metal alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oniciuc, Eugen; Stoleriu, Laurentiu; Cimpoesu, Dorin

2014-06-02

In this paper, we present simulations of thermally induced magnetic switching in ferrimagnetic systems performed with a Landau-Lifshitz-Bloch (LLB) equation for damping constant in a wide range of values. We have systematically studied the GdFeCo ferrimagnet with various concentrations of Gd and compared for some values of parameters the LLB results with atomistic simulations. The agreement is remarkably good, which shows that the dynamics described by the ferrimagnetic LLB is a reasonable approximation of this complex physical phenomenon. As an important element, we show that the LLB is able to also describe the intermediate formation of a ferromagnetic state whichmore » seems to be essential to understand laser induced ultrafast switching. The study reveals the fundamental role of damping during the switching process.« less

Carotid DSA based CFD simulation in assessing the patient with asymptomatic carotid stenosis: a preliminary study.

PubMed

Zhang, Dong; Xu, Pengcheng; Qiao, Hongyu; Liu, Xin; Luo, Liangping; Huang, Wenhua; Zhang, Heye; Shi, Changzheng

2018-03-12

Cerebrovascular events are frequently associated with hemodynamic disturbance caused by internal carotid artery (ICA) stenosis. It is challenging to determine the ischemia-related carotid stenosis during the intervention only using digital subtracted angiography (DSA). Inspired by the performance of well-established FFRct technique in hemodynamic assessment of significant coronary stenosis, we introduced a pressure-based carotid arterial functional assessment (CAFA) index generated from computational fluid dynamic (CFD) simulation in DSA data, and investigated its feasibility in the assessment of hemodynamic disturbance preliminarily using pressure-wired measurement and arterial spin labeling (ASL) MRI as references. The cerebral multi-delay multi-parametric ASL-MRI and carotid DSA including trans-stenotic pressure-wired measurement were implemented on a 65-year-old man with asymptomatic unilateral (left) ICA stenosis. A CFD simulation using simplified boundary condition was performed in DSA data to calculate the CAFA index. The cerebral blood flow (CBF) and arterial transit time (ATT) of ICA territories were acquired. CFD simulation showed good correlation (r = 0.839, P = 0.001) with slight systematic overestimation (mean difference - 0.007, standard deviation 0.017) compared with pressure-wired measurement. No significant difference was observed between them (P = 0.09). Though the narrowing degree of in the involved ICA was about 70%, the simulated and measured CAFA (0.942/0.937) revealed a functionally nonsignificant stenosis which was also verified by a compensatory final CBF (fronto-temporal/fronto-parietal region: 51.58/45.62 ml/100 g/min) and slightly prolonged ATT (1.23/1.4 s) in the involved territories, together with a normal left-right percentage difference (2.1-8.85%). The DSA based CFD simulation showed good consistence with invasive approach and could be used as a cost-saving and efficient way to study the relationship between hemodynamic disorder caused by ICA stenosis and subsequent perfusion variations in brain. Further research should focus on the role of noninvasive pressure-based CAFA in screening asymptomatic ischemia-causing carotid stenosis.

Reciprocity and the Tragedies of Maintaining and Providing the Commons

PubMed Central

Gächter, Simon; Kölle, Felix; Quercia, Simone

2017-01-01

Social cooperation often requires collectively beneficial but individually costly restraint to maintain a public good1–4, or it needs costly generosity to create one1,5. Status quo effects6 predict that maintaining a public good is easier than providing a new one. Here we show experimentally and with simulations that even under identical incentives, low levels of cooperation (the ‘tragedy of the commons’2) are systematically more likely in Maintenance than Provision. Across three series of experiments, we find that strong and weak positive reciprocity, known to be fundamental tendencies underpinning human cooperation7–10, are substantially diminished under Maintenance compared to Provision. As we show in a fourth experiment, the opposite holds for negative reciprocity (‘punishment’). Our findings suggest that incentives to avoid the ‘tragedy of the commons’ need to contend with dilemma-specific reciprocity. PMID:28944297

Finite element modeling of mitral leaflet tissue using a layered shell approximation

PubMed Central

Ratcliffe, Mark B.; Guccione, Julius M.

2012-01-01

The current study presents a finite element model of mitral leaflet tissue, which incorporates the anisotropic material response and approximates the layered structure. First, continuum mechanics and the theory of layered composites are used to develop an analytical representation of membrane stress in the leaflet material. This is done with an existing anisotropic constitutive law from literature. Then, the concept is implemented in a finite element (FE) model by overlapping and merging two layers of transversely isotropic membrane elements in LS-DYNA, which homogenizes the response. The FE model is then used to simulate various biaxial extension tests and out-of-plane pressure loading. Both the analytical and FE model show good agreement with experimental biaxial extension data, and show good mutual agreement. This confirms that the layered composite approximation presented in the current study is able to capture the exponential stiffening seen in both the circumferential and radial directions of mitral leaflets. PMID:22971896

Two-dimensional wavelet transform for reliability-guided phase unwrapping in optical fringe pattern analysis.

PubMed

Li, Sikun; Wang, Xiangzhao; Su, Xianyu; Tang, Feng

2012-04-20

This paper theoretically discusses modulus of two-dimensional (2D) wavelet transform (WT) coefficients, calculated by using two frequently used 2D daughter wavelet definitions, in an optical fringe pattern analysis. The discussion shows that neither is good enough to represent the reliability of the phase data. The differences between the two frequently used 2D daughter wavelet definitions in the performance of 2D WT also are discussed. We propose a new 2D daughter wavelet definition for reliability-guided phase unwrapping of optical fringe pattern. The modulus of the advanced 2D WT coefficients, obtained by using a daughter wavelet under this new daughter wavelet definition, includes not only modulation information but also local frequency information of the deformed fringe pattern. Therefore, it can be treated as a good parameter that represents the reliability of the retrieved phase data. Computer simulation and experimentation show the validity of the proposed method.

Modeling Selection and Extinction Mechanisms of Biological Systems

NASA Astrophysics Data System (ADS)

Amirjanov, Adil

In this paper, the behavior of a genetic algorithm is modeled to enhance its applicability as a modeling tool of biological systems. A new description model for selection mechanism is introduced which operates on a portion of individuals of population. The extinction and recolonization mechanism is modeled, and solving the dynamics analytically shows that the genetic drift in the population with extinction/recolonization is doubled. The mathematical analysis of the interaction between selection and extinction/recolonization processes is carried out to assess the dynamics of motion of the macroscopic statistical properties of population. Computer simulations confirm that the theoretical predictions of described models are in good approximations. A mathematical model of GA dynamics was also examined, which describes the anti-predator vigilance in an animal group with respect to a known analytical solution of the problem, and showed a good agreement between them to find the evolutionarily stable strategies.

Genetically modified haloes: towards controlled experiments in ΛCDM galaxy formation

NASA Astrophysics Data System (ADS)

Roth, Nina; Pontzen, Andrew; Peiris, Hiranya V.

2016-01-01

We propose a method to generate `genetically modified' (GM) initial conditions for high-resolution simulations of galaxy formation in a cosmological context. Building on the Hoffman-Ribak algorithm, we start from a reference simulation with fully random initial conditions, then make controlled changes to specific properties of a single halo (such as its mass and merger history). The algorithm demonstrably makes minimal changes to other properties of the halo and its environment, allowing us to isolate the impact of a given modification. As a significant improvement over previous work, we are able to calculate the abundance of the resulting objects relative to the reference simulation. Our approach can be applied to a wide range of cosmic structures and epochs; here we study two problems as a proof of concept. First, we investigate the change in density profile and concentration as the collapse times of three individual haloes are varied at fixed final mass, showing good agreement with previous statistical studies using large simulation suites. Secondly, we modify the z = 0 mass of haloes to show that our theoretical abundance calculations correctly recover the halo mass function. The results demonstrate that the technique is robust, opening the way to controlled experiments in galaxy formation using hydrodynamic zoom simulations.

Driving performance in a power wheelchair simulator.

PubMed

Archambault, Philippe S; Tremblay, Stéphanie; Cachecho, Sarah; Routhier, François; Boissy, Patrick

2012-05-01

A power wheelchair simulator can allow users to safely experience various driving tasks. For such training to be efficient, it is important that driving performance be equivalent to that in a real wheelchair. This study aimed at comparing driving performance in a real and in a simulated environment. Two groups of healthy young adults performed different driving tasks, either in a real power wheelchair or in a simulator. Smoothness of joystick control as well as the time necessary to complete each task were recorded and compared between the two groups. Driving strategies were analysed from video recordings. The sense of presence, of really being in the virtual environment, was assessed through a questionnaire. Smoothness of joystick control was the same in the real and virtual groups. Task completion time was higher in the simulator for the more difficult tasks. Both groups showed similar strategies and difficulties. The simulator generated a good sense of presence, which is important for motivation. Performance was very similar for power wheelchair driving in the simulator or in real life. Thus, the simulator could potentially be used to complement training of individuals who require a power wheelchair and use a regular joystick. [Box: see text].

Solving optimization problems by the public goods game

NASA Astrophysics Data System (ADS)

Javarone, Marco Alberto

2017-09-01

We introduce a method based on the Public Goods Game for solving optimization tasks. In particular, we focus on the Traveling Salesman Problem, i.e. a NP-hard problem whose search space exponentially grows increasing the number of cities. The proposed method considers a population whose agents are provided with a random solution to the given problem. In doing so, agents interact by playing the Public Goods Game using the fitness of their solution as currency of the game. Notably, agents with better solutions provide higher contributions, while those with lower ones tend to imitate the solution of richer agents for increasing their fitness. Numerical simulations show that the proposed method allows to compute exact solutions, and suboptimal ones, in the considered search spaces. As result, beyond to propose a new heuristic for combinatorial optimization problems, our work aims to highlight the potentiality of evolutionary game theory beyond its current horizons.

3D Fiber Orientation Simulation for Plastic Injection Molding

NASA Astrophysics Data System (ADS)

Lin, Baojiu; Jin, Xiaoshi; Zheng, Rong; Costa, Franco S.; Fan, Zhiliang

2004-06-01

Glass fiber reinforced polymer is widely used in the products made using injection molding processing. The distribution of fiber orientation inside plastic parts has direct effects on quality of molded parts. Using computer simulation to predict fiber orientation distribution is one of most efficient ways to assist engineers to do warpage analysis and to find a good design solution to produce high quality plastic parts. Fiber orientation simulation software based on 2-1/2D (midplane /Dual domain mesh) techniques has been used in industry for a decade. However, the 2-1/2D technique is based on the planar Hele-Shaw approximation and it is not suitable when the geometry has complex three-dimensional features which cannot be well approximated by 2D shells. Recently, a full 3D simulation software for fiber orientation has been developed and integrated into Moldflow Plastics Insight 3D simulation software. The theory for this new 3D fiber orientation calculation module is described in this paper. Several examples are also presented to show the benefit in using 3D fiber orientation simulation.

On the first crossing distributions in fractional Brownian motion and the mass function of dark matter haloes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiotelis, Nicos; Popolo, Antonino Del, E-mail: adelpopolo@oact.inaf.it, E-mail: hiotelis@ipta.demokritos.gr

We construct an integral equation for the first crossing distributions for fractional Brownian motion in the case of a constant barrier and we present an exact analytical solution. Additionally we present first crossing distributions derived by simulating paths from fractional Brownian motion. We compare the results of the analytical solutions with both those of simulations and those of some approximated solutions which have been used in the literature. Finally, we present multiplicity functions for dark matter structures resulting from our analytical approach and we compare with those resulting from N-body simulations. We show that the results of analytical solutions aremore » in good agreement with those of path simulations but differ significantly from those derived from approximated solutions. Additionally, multiplicity functions derived from fractional Brownian motion are poor fits of the those which result from N-body simulations. We also present comparisons with other models which are exist in the literature and we discuss different ways of improving the agreement between analytical results and N-body simulations.« less

Face aging effect simulation model based on multilayer representation and shearlet transform

NASA Astrophysics Data System (ADS)

Li, Yuancheng; Li, Yan

2017-09-01

In order to extract detailed facial features, we build a face aging effect simulation model based on multilayer representation and shearlet transform. The face is divided into three layers: the global layer of the face, the local features layer, and texture layer, which separately establishes the aging model. First, the training samples are classified according to different age groups, and we use active appearance model (AAM) at the global level to obtain facial features. The regression equations of shape and texture with age are obtained by fitting the support vector machine regression, which is based on the radial basis function. We use AAM to simulate the aging of facial organs. Then, for the texture detail layer, we acquire the significant high-frequency characteristic components of the face by using the multiscale shearlet transform. Finally, we get the last simulated aging images of the human face by the fusion algorithm. Experiments are carried out on the FG-NET dataset, and the experimental results show that the simulated face images have less differences from the original image and have a good face aging simulation effect.

RANS Simulation (Rotating Reference Frame Model [RRF]) of Single Full Scale DOE RM1 MHK Turbine

DOE Data Explorer

Javaherchi, Teymour; Stelzenmuller, Nick; Aliseda, Alberto

2013-04-10

Attached are the .cas and .dat files for the Reynolds Averaged Navier-Stokes (RANS) simulation of a single full scale DOE RM1 turbine implemented in ANSYS FLUENT CFD-package. In this case study taking advantage of the symmetry of the DOE RM1 geometry, only half of the geometry is modeled using (Single) Rotating Reference Frame model [RRF]. In this model RANS equations, coupled with k-\\omega turbulence closure model, are solved in the rotating reference frame. The actual geometry of the turbine blade is included and the turbulent boundary layer along the blade span is simulated using wall-function approach. The rotation of the blade is modeled by applying periodic boundary condition to sets of plane of symmetry. This case study simulates the performance and flow field in both the near and far wake of the device at the desired operating conditions. The results of these simulations showed good agreement to the only publicly available numerical simulation of the device done in the NREL. Please see the attached paper.

Accelerating Monte Carlo simulations of photon transport in a voxelized geometry using a massively parallel graphics processing unit.

PubMed

Badal, Andreu; Badano, Aldo

2009-11-01

It is a known fact that Monte Carlo simulations of radiation transport are computationally intensive and may require long computing times. The authors introduce a new paradigm for the acceleration of Monte Carlo simulations: The use of a graphics processing unit (GPU) as the main computing device instead of a central processing unit (CPU). A GPU-based Monte Carlo code that simulates photon transport in a voxelized geometry with the accurate physics models from PENELOPE has been developed using the CUDATM programming model (NVIDIA Corporation, Santa Clara, CA). An outline of the new code and a sample x-ray imaging simulation with an anthropomorphic phantom are presented. A remarkable 27-fold speed up factor was obtained using a GPU compared to a single core CPU. The reported results show that GPUs are currently a good alternative to CPUs for the simulation of radiation transport. Since the performance of GPUs is currently increasing at a faster pace than that of CPUs, the advantages of GPU-based software are likely to be more pronounced in the future.

Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

NASA Astrophysics Data System (ADS)

Salhi, Mohammed Adnan; Kazemipour, Alireza; Gentille, Gennaro; Spirito, Marco; Kleine-Ostmann, Thomas; Schrader, Thorsten

2016-09-01

We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003™ substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.

PSO-Assisted Development of New Transferable Coarse-Grained Water Models.

PubMed

Bejagam, Karteek K; Singh, Samrendra; An, Yaxin; Berry, Carter; Deshmukh, Sanket A

2018-02-15

We have employed two-to-one mapping scheme to develop three coarse-grained (CG) water models, namely, 1-, 2-, and 3-site CG models. Here, for the first time, particle swarm optimization (PSO) and gradient descent methods were coupled to optimize the force-field parameters of the CG models to reproduce the density, self-diffusion coefficient, and dielectric constant of real water at 300 K. The CG MD simulations of these new models conducted with various timesteps, for different system sizes, and at a range of different temperatures are able to predict the density, self-diffusion coefficient, dielectric constant, surface tension, heat of vaporization, hydration free energy, and isothermal compressibility of real water with excellent accuracy. The 1-site model is ∼3 and ∼4.5 times computationally more efficient than 2- and 3-site models, respectively. To utilize the speed of 1-site model and electrostatic interactions offered by 2- and 3-site models, CG MD simulations of 1:1 combination of 1- and 2-/3-site models were performed at 300 K. These mixture simulations could also predict the properties of real water with good accuracy. Two new CG models of benzene, consisting of beads with and without partial charges, were developed. All three water models showed good capacity to solvate these benzene models.

Multi-objective Calibration of DHSVM Based on Hydrologic Key Elements in Jinhua River Basin, East China

NASA Astrophysics Data System (ADS)

Pan, S.; Liu, L.; Xu, Y. P.

2017-12-01

Abstract: In physically based distributed hydrological model, large number of parameters, representing spatial heterogeneity of watershed and various processes in hydrologic cycle, are involved. For lack of calibration module in Distributed Hydrology Soil Vegetation Model, this study developed a multi-objective calibration module using Epsilon-Dominance Non-Dominated Sorted Genetic Algorithm II (ɛ-NSGAII) and based on parallel computing of Linux cluster for DHSVM (ɛP-DHSVM). In this study, two hydrologic key elements (i.e., runoff and evapotranspiration) are used as objectives in multi-objective calibration of model. MODIS evapotranspiration obtained by SEBAL is adopted to fill the gap of lack of observation for evapotranspiration. The results show that good performance of runoff simulation in single objective calibration cannot ensure good simulation performance of other hydrologic key elements. Self-developed ɛP-DHSVM model can make multi-objective calibration more efficiently and effectively. The running speed can be increased by more than 20-30 times via applying ɛP-DHSVM. In addition, runoff and evapotranspiration can be simulated very well simultaneously by ɛP-DHSVM, with superior values for two efficiency coefficients (0.74 for NS of runoff and 0.79 for NS of evapotranspiration, -10.5% and -8.6% for PBIAS of runoff and evapotranspiration respectively).

Broadband Polarization Conversion Metasurface Based on Metal Cut-Wire Structure for Radar Cross Section Reduction.

PubMed

Yang, Jia Ji; Cheng, Yong Zhi; Ge, Chen Chen; Gong, Rong Zhou

2018-04-19

A class of linear polarization conversion coding metasurfaces (MSs) based on a metal cut-wire structure is proposed, which can be applied to the reduction properties of radar cross section (RCS). We firstly present a hypothesis based on the principle of planar array theory, and then verify the RCS reduction characteristics using linear polarization conversion coding MSs by simulations and experiments. The simulated results show that in the frequency range of 6⁻14 GHz, the linear polarization conversion ratio reaches a maximum value of 90%, which is in good agreement with the theoretical predictions. For normal incident x - and y -polarized waves, RCS reduction of designed coding MSs 01/01 and 01/10 is essentially more than 10 dB in the above-mentioned frequency range. We prepare and measure the 01/10 coding MS sample, and find that the experimental results in terms of reflectance and RCS reduction are in good agreement with the simulated ones under normal incidence. In addition, under oblique incidence, RCS reduction is suppressed as the angle of incidence increases, but still exhibits RCS reduction effects in a certain frequency range. The designed MS is expected to have valuable potential in applications for stealth field technology.

Static and moving solid/gas interface modeling in a hybrid rocket engine

NASA Astrophysics Data System (ADS)

Mangeot, Alexandre; William-Louis, Mame; Gillard, Philippe

2018-07-01

A numerical model was developed with CFD-ACE software to study the working condition of an oxygen-nitrogen/polyethylene hybrid rocket combustor. As a first approach, a simplified numerical model is presented. It includes a compressible transient gas phase in which a two-step combustion mechanism is implemented coupled to a radiative model. The solid phase from the fuel grain is a semi-opaque material with its degradation process modeled by an Arrhenius type law. Two versions of the model were tested. The first considers the solid/gas interface with a static grid while the second uses grid deformation during the computation to follow the asymmetrical regression. The numerical results are obtained with two different regression kinetics originating from ThermoGravimetry Analysis and test bench results. In each case, the fuel surface temperature is retrieved within a range of 5% error. However, good results are only found using kinetics from the test bench. The regression rate is found within 0.03 mm s-1 and average combustor pressure and its variation over time have the same intensity than the measurements conducted on the test bench. The simulation that uses grid deformation to follow the regression shows a good stability over a 10 s simulated time simulation.

[Learning in clinical simulation: observational study on satisfaction perceived by students of nursing].

PubMed

Rubbi, Ivan; Ferri, Paola; Andreina, Giulia; Cremonini, Valeria

2016-01-01

Simulation in the context of the educational workshop is becoming an important learning method, as it allows to play realistic clinical-care situations. These vocational training activities promote the development of cognitive, affective and psychomotor skills in a pedagogical context safe and risk-free, but need to be accounted for using by valid and reliable instruments. To inspect the level of satisfaction of the students of a Degree in Nursing in northern Italy about static and high-fidelity exercises with simulators and clinical cases. A prospective observational study has been conducted involving a non-probabili- stic sample of 51 third-year students throughout the academic year 2013/14. The data collection instrument consists of three questionnaires Student Satisfaction and Self-confidence in Learning Scale, Educational Practices Questionnaire, Simulation Design Scale and 3 questions on overall satisfaction. Statistical analysis was performed with SPSS 20.0 and Office 2003 Excel. The response rate of 89.5% is obtained. The Cronbach Alfa showed a good internal reliability (α = .982). The students were generally satisfied with the activities carried out in the teaching laboratory, showing more enthusiasm for the simulation with static mannequins (71%) and with high-fidelity simulators (60%), activities for which they have experienced a significant involvement and active learning. The teaching with clinical cases scored a lesser degree of satisfaction (38%) and for this method it was found the largest number of elements of weakness.

Numerical Simulation of Dry Granular Flow Impacting a Rigid Wall Using the Discrete Element Method

PubMed Central

Wu, Fengyuan; Fan, Yunyun; Liang, Li; Wang, Chao

2016-01-01

This paper presents a clump model based on Discrete Element Method. The clump model was more close to the real particle than a spherical particle. Numerical simulations of several tests of dry granular flow impacting a rigid wall flowing in an inclined chute have been achieved. Five clump models with different sphericity have been used in the simulations. By comparing the simulation results with the experimental results of normal force on the rigid wall, a clump model with better sphericity was selected to complete the following numerical simulation analysis and discussion. The calculation results of normal force showed good agreement with the experimental results, which verify the effectiveness of the clump model. Then, total normal force and bending moment of the rigid wall and motion process of the granular flow were further analyzed. Finally, comparison analysis of the numerical simulations using the clump model with different grain composition was obtained. By observing normal force on the rigid wall and distribution of particle size at the front of the rigid wall at the final state, the effect of grain composition on the force of the rigid wall has been revealed. It mainly showed that, with the increase of the particle size, the peak force at the retaining wall also increase. The result can provide a basis for the research of relevant disaster and the design of protective structures. PMID:27513661

High energy density physics effects predicted in simulations of the CERN HiRadMat beam-target interaction experiments

NASA Astrophysics Data System (ADS)

Tahir, N. A.; Burkart, F.; Schmidt, R.; Shutov, A.; Wollmann, D.; Piriz, A. R.

2016-12-01

Experiments have been done at the CERN HiRadMat (High Radiation to Materials) facility in which large cylindrical copper targets were irradiated with 440 GeV proton beam generated by the Super Proton Synchrotron (SPS). The primary purpose of these experiments was to confirm the existence of hydrodynamic tunneling of ultra-relativistic protons and their hadronic shower in solid materials, that was predicted by previous numerical simulations. The experimental measurements have shown very good agreement with the simulation results. This provides confidence in our simulations of the interaction of the 7 TeV LHC (Large Hadron Collider) protons and the 50 TeV Future Circular Collider (FCC) protons with solid materials, respectively. This work is important from the machine protection point of view. The numerical simulations have also shown that in the HiRadMat experiments, a significant part of thetarget material is be converted into different phases of High Energy Density (HED) matter, including two-phase solid-liquid mixture, expanded as well as compressed hot liquid phases, two-phase liquid-gas mixture and gaseous state. The HiRadMat facility is therefore a unique ion beam facility worldwide that is currently available for studying the thermophysical properties of HED matter. In the present paper we discuss the numerical simulation results and present a comparison with the experimental measurements.

A beam hardening and dispersion correction for x-ray dark-field radiography.

PubMed

Pelzer, Georg; Anton, Gisela; Horn, Florian; Rieger, Jens; Ritter, André; Wandner, Johannes; Weber, Thomas; Michel, Thilo

2016-06-01

X-ray dark-field imaging promises information on the small angle scattering properties even of large samples. However, the dark-field image is correlated with the object's attenuation and phase-shift if a polychromatic x-ray spectrum is used. A method to remove part of these correlations is proposed. The experimental setup for image acquisition was modeled in a wave-field simulation to quantify the dark-field signals originating solely from a material's attenuation and phase-shift. A calibration matrix was simulated for ICRU46 breast tissue. Using the simulated data, a dark-field image of a human mastectomy sample was corrected for the finger print of attenuation- and phase-image. Comparing the simulated, attenuation-based dark-field values to a phantom measurement, a good agreement was found. Applying the proposed method to mammographic dark-field data, a reduction of the dark-field background and anatomical noise was achieved. The contrast between microcalcifications and their surrounding background was increased. The authors show that the influence of and dispersion can be quantified by simulation and, thus, measured image data can be corrected. The simulation allows to determine the corresponding dark-field artifacts for a wide range of setup parameters, like tube-voltage and filtration. The application of the proposed method to mammographic dark-field data shows an increase in contrast compared to the original image, which might simplify a further image-based diagnosis.

Validation and Simulation of Ares I Scale Model Acoustic Test - 2 - Simulations at 5 Foot Elevation for Evaluation of Launch Mount Effects

NASA Technical Reports Server (NTRS)

Strutzenberg, Louise L.; Putman, Gabriel C.

2011-01-01

The Ares I Scale Model Acoustics Test (ASMAT) is a series of live-fire tests of scaled rocket motors meant to simulate the conditions of the Ares I launch configuration. These tests have provided a well documented set of high fidelity measurements useful for validation including data taken over a range of test conditions and containing phenomena like Ignition Over-Pressure and water suppression of acoustics. Expanding from initial simulations of the ASMAT setup in a held down configuration, simulations have been performed using the Loci/CHEM computational fluid dynamics software for ASMAT tests of the vehicle at 5 ft. elevation (100 ft. real vehicle elevation) with worst case drift in the direction of the launch tower. These tests have been performed without water suppression and have compared the acoustic emissions for launch structures with and without launch mounts. In addition, simulation results have also been compared to acoustic and imagery data collected from similar live-fire tests to assess the accuracy of the simulations. Simulations have shown a marked change in the pattern of emissions after removal of the launch mount with a reduction in the overall acoustic environment experienced by the vehicle and the formation of highly directed acoustic waves moving across the platform deck. Comparisons of simulation results to live-fire test data showed good amplitude and temporal correlation and imagery comparisons over the visible and infrared wavelengths showed qualitative capture of all plume and pressure wave evolution features.

Mapping the Protein Fold Universe Using the CamTube Force Field in Molecular Dynamics Simulations.

PubMed

Kukic, Predrag; Kannan, Arvind; Dijkstra, Maurits J J; Abeln, Sanne; Camilloni, Carlo; Vendruscolo, Michele

2015-10-01

It has been recently shown that the coarse-graining of the structures of polypeptide chains as self-avoiding tubes can provide an effective representation of the conformational space of proteins. In order to fully exploit the opportunities offered by such a 'tube model' approach, we present here a strategy to combine it with molecular dynamics simulations. This strategy is based on the incorporation of the 'CamTube' force field into the Gromacs molecular dynamics package. By considering the case of a 60-residue polyvaline chain, we show that CamTube molecular dynamics simulations can comprehensively explore the conformational space of proteins. We obtain this result by a 20 μs metadynamics simulation of the polyvaline chain that recapitulates the currently known protein fold universe. We further show that, if residue-specific interaction potentials are added to the CamTube force field, it is possible to fold a protein into a topology close to that of its native state. These results illustrate how the CamTube force field can be used to explore efficiently the universe of protein folds with good accuracy and very limited computational cost.

Vacuum simulation and characterization for the Linac4 H- source

NASA Astrophysics Data System (ADS)

Pasquino, C.; Chiggiato, P.; Michet, A.; Hansen, J.; Lettry, J.

2013-02-01

At CERN, the 160 MeV H- Linac4 will soon replace the 50 MeV proton Linac2. In the H- source two major sources of gas are identified. The first is the pulsed injection at about 0.1 mbar in the plasma chamber. The second is the constant H2 injection up to 10-5 mbar in the LEBT for beam space charge compensation. In addition, the outgassing of materials exposed to vacuum can play an important role in contamination control and global gas balance. To evaluate the time dependent partial pressure profiles in the H- ion source and the RFQ, electrical network - vacuum analogy and test particle Monte Carlo simulation have been used. The simulation outcome indicates that the pressure requirements are in the reach of the proposed vacuum pumping system. Preliminary results show good agreement between the experimental and the simulated pressure profiles; a calibration campaign is in progress to fully benchmark the implemented calculations. Systematic outgassing rate measurements are on-going for critical components in the ion source and RFQ. Amongst them those for the Cu-coated SmCo magnet located in the vacuum system of the biased electron dump electrode, show results lower to stainless steel at room temperature.

Multi-scale sensitivity analysis of pile installation using DEM

NASA Astrophysics Data System (ADS)

Esposito, Ricardo Gurevitz; Velloso, Raquel Quadros; , Eurípedes do Amaral Vargas, Jr.; Danziger, Bernadete Ragoni

2017-12-01

The disturbances experienced by the soil due to the pile installation and dynamic soil-structure interaction still present major challenges to foundation engineers. These phenomena exhibit complex behaviors, difficult to measure in physical tests and to reproduce in numerical models. Due to the simplified approach used by the discrete element method (DEM) to simulate large deformations and nonlinear stress-dilatancy behavior of granular soils, the DEM consists of an excellent tool to investigate these processes. This study presents a sensitivity analysis of the effects of introducing a single pile using the PFC2D software developed by Itasca Co. The different scales investigated in these simulations include point and shaft resistance, alterations in porosity and stress fields and particles displacement. Several simulations were conducted in order to investigate the effects of different numerical approaches showing indications that the method of installation and particle rotation could influence greatly in the conditions around the numerical pile. Minor effects were also noted due to change in penetration velocity and pile-soil friction. The difference in behavior of a moving and a stationary pile shows good qualitative agreement with previous experimental results indicating the necessity of realizing a force equilibrium process prior to any load-test to be simulated.

Mapping the Protein Fold Universe Using the CamTube Force Field in Molecular Dynamics Simulations

PubMed Central

Dijkstra, Maurits J. J.; Abeln, Sanne; Camilloni, Carlo; Vendruscolo, Michele

2015-01-01

It has been recently shown that the coarse-graining of the structures of polypeptide chains as self-avoiding tubes can provide an effective representation of the conformational space of proteins. In order to fully exploit the opportunities offered by such a ‘tube model’ approach, we present here a strategy to combine it with molecular dynamics simulations. This strategy is based on the incorporation of the ‘CamTube’ force field into the Gromacs molecular dynamics package. By considering the case of a 60-residue polyvaline chain, we show that CamTube molecular dynamics simulations can comprehensively explore the conformational space of proteins. We obtain this result by a 20 μs metadynamics simulation of the polyvaline chain that recapitulates the currently known protein fold universe. We further show that, if residue-specific interaction potentials are added to the CamTube force field, it is possible to fold a protein into a topology close to that of its native state. These results illustrate how the CamTube force field can be used to explore efficiently the universe of protein folds with good accuracy and very limited computational cost. PMID:26505754

Modeling universal dynamics of cell spreading on elastic substrates.

PubMed

Fan, Houfu; Li, Shaofan

2015-11-01

A three-dimensional (3D) multiscale moving contact line model is combined with a soft matter cell model to study the universal dynamics of cell spreading over elastic substrates. We have studied both the early stage and the late stage cell spreading by taking into account the actin tension effect. In this work, the cell is modeled as an active nematic droplet, and the substrate is modeled as a St. Venant Kirchhoff elastic medium. A complete 3D simulation of cell spreading has been carried out. The simulation results show that the spreading area versus spreading time at different stages obeys specific power laws, which is in good agreement with experimental data and theoretical prediction reported in the literature. Moreover, the simulation results show that the substrate elasticity may affect force dipole distribution inside the cell. The advantage of this approach is that it combines the hydrodynamics of actin retrograde flow with moving contact line model so that it can naturally include actin tension effect resulting from actin polymerization and actomyosin contraction, and thus it might be capable of simulating complex cellular scale phenomenon, such as cell spreading or even crawling.

Heat Transfer Model for Hot Air Balloons

NASA Astrophysics Data System (ADS)

Llado-Gambin, Adriana

A heat transfer model and analysis for hot air balloons is presented in this work, backed with a flow simulation using SolidWorks. The objective is to understand the major heat losses in the balloon and to identify the parameters that affect most its flight performance. Results show that more than 70% of the heat losses are due to the emitted radiation from the balloon envelope and that convection losses represent around 20% of the total. A simulated heating source is also included in the modeling based on typical thermal input from a balloon propane burner. The burner duty cycle to keep a constant altitude can vary from 10% to 28% depending on the atmospheric conditions, and the ambient temperature is the parameter that most affects the total thermal input needed. The simulation and analysis also predict that the gas temperature inside the balloon decreases at a rate of -0.25 K/s when there is no burner activity, and it increases at a rate of +1 K/s when the balloon pilot operates the burner. The results were compared to actual flight data and they show very good agreement indicating that the major physical processes responsible for balloon performance aloft are accurately captured in the simulation.

Comparative study on the performance of power and bandwidth efficient modulations in LMSS under fading and interference

NASA Technical Reports Server (NTRS)

Liu, Jian; Kim, Junghwan; Kwatra, S. C.; Stevens, Grady H.

1991-01-01

Aspects of error performance of various power and bandwidth efficient modulations for the land mobile satellite systems (LMSS) were investigated under multipath fading and interferences by using Monte-Carlo simulation. A differential detection for 16QAM (quadrature amplitude modulation) was proposed to cope with Ricean fading and Doppler shift. Computer simulation results show that the performance of 16QAM with differential detection is as good as that of 16PSK with coherent detection and 3 dB better than that of 16PSK with differential detection, although it degrades by about 4.5 dB as compared to 16QAM with coherent detection under an additive white Gaussian noise (AWGN) channel. For the nonlinear channels, 16QAM with modified signal constellations is introduced and analyzed. The simulation results show that the modified 16QAM exhibits a gain of 2.5 dB over 16PSK under traveling-wave tube nonlinearity, and about 4 dB gain over 16PSK at the bit error rate of 10 exp -5 under AWGN. Computer simulation results for modified 16 QAM under cochannel interference and adjacent-channel interference are also presented.

Multi-scale sensitivity analysis of pile installation using DEM

NASA Astrophysics Data System (ADS)

Esposito, Ricardo Gurevitz; Velloso, Raquel Quadros; , Eurípedes do Amaral Vargas, Jr.; Danziger, Bernadete Ragoni

2018-07-01

The disturbances experienced by the soil due to the pile installation and dynamic soil-structure interaction still present major challenges to foundation engineers. These phenomena exhibit complex behaviors, difficult to measure in physical tests and to reproduce in numerical models. Due to the simplified approach used by the discrete element method (DEM) to simulate large deformations and nonlinear stress-dilatancy behavior of granular soils, the DEM consists of an excellent tool to investigate these processes. This study presents a sensitivity analysis of the effects of introducing a single pile using the PFC2D software developed by Itasca Co. The different scales investigated in these simulations include point and shaft resistance, alterations in porosity and stress fields and particles displacement. Several simulations were conducted in order to investigate the effects of different numerical approaches showing indications that the method of installation and particle rotation could influence greatly in the conditions around the numerical pile. Minor effects were also noted due to change in penetration velocity and pile-soil friction. The difference in behavior of a moving and a stationary pile shows good qualitative agreement with previous experimental results indicating the necessity of realizing a force equilibrium process prior to any load-test to be simulated.

Formation of well-mixed warm water column in central Bohai Sea during summer: Role of high-frequency atmospheric forcing

NASA Astrophysics Data System (ADS)

Ma, Weiwei; Wan, Xiuquan; Wang, Zhankun; Liu, Yulong; Wan, Kai

2017-12-01

The influence of high-frequency atmospheric forcing on the formation of a well-mixed summer warm water column in the central Bohai Sea is investigated comparing model simulations driven by daily surface forcing and those using monthly forcing data. In the absence of high-frequency atmospheric forcing, numerical simulations have repeatedly failed to reproduce this vertically uniform column of warm water measured over the past 35 years. However, high-frequency surface forcing is found to strongly influence the structure and distribution of the well-mixed warm water column, and simulations are in good agreement with observations. Results show that high frequency forcing enhances vertical mixing over the central bank, intensifies downward heat transport, and homogenizes the water column to form the Bohai central warm column. Evidence presented shows that high frequency forcing plays a dominant role in the formation of the well-mixed warm water column in summer, even without the effects of tidal and surface wave mixing. The present study thus provides a practical and rational way of further improving the performance of oceanic simulations in the Bohai Sea and can be used to adjust parameterization schemes of ocean models.

Organ radiation exposure with EOS: GATE simulations versus TLD measurements

NASA Astrophysics Data System (ADS)

Clavel, A. H.; Thevenard-Berger, P.; Verdun, F. R.; Létang, J. M.; Darbon, A.

2016-03-01

EOS® is an innovative X-ray imaging system allowing the acquisition of two simultaneous images of a patient in the standing position, during the vertical scan of two orthogonal fan beams. This study aimed to compute organs radiation exposure to a patient, in the particular geometry of this system. Two different positions of the patient in the machine were studied, corresponding to postero-anterior plus left lateral projections (PA-LLAT) and antero-posterior plus right lateral projections (AP-RLAT). To achieve this goal, a Monte-Carlo simulation was developed based on a GATE environment. To model the physical properties of the patient, a computational phantom was produced based on computed tomography scan data of an anthropomorphic phantom. The simulations provided several organs doses, which were compared to previously published dose results measured with Thermo Luminescent Detectors (TLD) in the same conditions and with the same phantom. The simulation results showed a good agreement with measured doses at the TLD locations, for both AP-RLAT and PA-LLAT projections. This study also showed that the organ dose assessed only from a sample of locations, rather than considering the whole organ, introduced significant bias, depending on organs and projections.

Study of intermolecular contacts in the proline-rich homeodomain (PRH)-DNA complex using molecular dynamics simulations.

PubMed

Jalili, Seifollah; Karami, Leila

2012-03-01

The proline-rich homeodomain (PRH)-DNA complex consists of a protein with 60 residues and a 13-base-pair DNA. The PRH protein is a transcription factor that plays a key role in the regulation of gene expression. PRH is a significant member of the Q50 class of homeodomain proteins. The homeodomain section of PRH is essential for binding to DNA and mediates sequence-specific DNA binding. Three 20-ns molecular dynamics (MD) simulations (free protein, free DNA and protein-DNA complex) in explicit solvent water were performed to elucidate the intermolecular contacts in the PRH-DNA complex and the role of dynamics of water molecules forming water-mediated contacts. The simulation provides a detailed explanation of the trajectory of hydration water molecules. The simulations show that some water molecules in the protein-DNA interface exchange with bulk waters. The simulation identifies that most of the contacts consisted of direct interactions between the protein and DNA including specific and non-specific contacts, but several water-mediated polar contacts were also observed. The specific interaction between Gln50 and C18 and water-mediated hydrogen bond between Gln50 and T7 were found to be present during almost the entire time of the simulation. These results show good consistency with experimental and previous computational studies. Structural properties such as root-mean-square deviations (RMSD), root-mean-square fluctuations (RMSF) and secondary structure were also analyzed as a function of time. Analyses of the trajectories showed that the dynamic fluctuations of both the protein and the DNA were lowered by the complex formation.

Simulation Models for Socioeconomic Inequalities in Health: A Systematic Review

PubMed Central

Speybroeck, Niko; Van Malderen, Carine; Harper, Sam; Müller, Birgit; Devleesschauwer, Brecht

2013-01-01

Background: The emergence and evolution of socioeconomic inequalities in health involves multiple factors interacting with each other at different levels. Simulation models are suitable for studying such complex and dynamic systems and have the ability to test the impact of policy interventions in silico. Objective: To explore how simulation models were used in the field of socioeconomic inequalities in health. Methods: An electronic search of studies assessing socioeconomic inequalities in health using a simulation model was conducted. Characteristics of the simulation models were extracted and distinct simulation approaches were identified. As an illustration, a simple agent-based model of the emergence of socioeconomic differences in alcohol abuse was developed. Results: We found 61 studies published between 1989 and 2013. Ten different simulation approaches were identified. The agent-based model illustration showed that multilevel, reciprocal and indirect effects of social determinants on health can be modeled flexibly. Discussion and Conclusions: Based on the review, we discuss the utility of using simulation models for studying health inequalities, and refer to good modeling practices for developing such models. The review and the simulation model example suggest that the use of simulation models may enhance the understanding and debate about existing and new socioeconomic inequalities of health frameworks. PMID:24192788

Introducing CGOLS: The Cholla Galactic Outflow Simulation Suite

NASA Astrophysics Data System (ADS)

Schneider, Evan E.; Robertson, Brant E.

2018-06-01

We present the Cholla Galactic OutfLow Simulations (CGOLS) suite, a set of extremely high resolution global simulations of isolated disk galaxies designed to clarify the nature of multiphase structure in galactic winds. Using the GPU-based code Cholla, we achieve unprecedented resolution in these simulations, modeling galaxies over a 20 kpc region at a constant resolution of 5 pc. The simulations include a feedback model designed to test the effects of different mass- and energy-loading factors on galactic outflows over kiloparsec scales. In addition to describing the simulation methodology in detail, we also present the results from an adiabatic simulation that tests the frequently adopted analytic galactic wind model of Chevalier & Clegg. Our results indicate that the Chevalier & Clegg model is a good fit to nuclear starburst winds in the nonradiative region of parameter space. Finally, we investigate the role of resolution and convergence in large-scale simulations of multiphase galactic winds. While our largest-scale simulations show convergence of observable features like soft X-ray emission, our tests demonstrate that simulations of this kind with resolutions greater than 10 pc are not yet converged, confirming the need for extreme resolution in order to study the structure of winds and their effects on the circumgalactic medium.

Materials processing in a centrifuge - Numerical modeling of macrogravity effects

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Downey, J. P.; Jones, J. C.; Curreri, P. A.

1992-01-01

The fluid mechanics associated with crystal growth processes on a centrifuge is investigated. A simple scaling analysis is used to examine the relative magnitudes of the forces acting on the system and good agreement is obtained with previous studies. A two-dimensional model of crystal growth on a centrifuge is proposed and calculations are undertaken to help in understanding the fundamental transport processes within the crystal growth cell. Results from three-dimensional calculations of actual centrifuge-based crystal growth systems are presented both for the thermodynamically stable and unstable configurations. The calculations show the existence of flow bifurcations in certain configurations but not in all instances. The numerical simulations also show that the centrifugal force is the dominant stabilizing force on fluid convection in the stable configuration. The stabilizing influence of the Coriolis force is found to be only secondary in nature. No significant impact of gravity gradient is found in the calculations. Simulations of unstable configurations show that the Coriolis force has a stabilizing influence on fluid motion by delaying the onset of unsteady convection. Detailed flow and thermal field characteristics are presented for all the different cases that are simulated.

Characterization and Simulation of a New Design Parallel-Plate Ionization Chamber for CT Dosimetry at Calibration Laboratories

NASA Astrophysics Data System (ADS)

Perini, Ana P.; Neves, Lucio P.; Maia, Ana F.; Caldas, Linda V. E.

2013-12-01

In this work, a new extended-length parallel-plate ionization chamber was tested in the standard radiation qualities for computed tomography established according to the half-value layers defined at the IEC 61267 standard, at the Calibration Laboratory of the Instituto de Pesquisas Energéticas e Nucleares (IPEN). The experimental characterization was made following the IEC 61674 standard recommendations. The experimental results obtained with the ionization chamber studied in this work were compared to those obtained with a commercial pencil ionization chamber, showing a good agreement. With the use of the PENELOPE Monte Carlo code, simulations were undertaken to evaluate the influence of the cables, insulator, PMMA body, collecting electrode, guard ring, screws, as well as different materials and geometrical arrangements, on the energy deposited on the ionization chamber sensitive volume. The maximum influence observed was 13.3% for the collecting electrode, and regarding the use of different materials and design, the substitutions showed that the original project presented the most suitable configuration. The experimental and simulated results obtained in this work show that this ionization chamber has appropriate characteristics to be used at calibration laboratories, for dosimetry in standard computed tomography and diagnostic radiology quality beams.

Analytical modeling and numerical simulation of the short-wave infrared electron-injection detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Movassaghi, Yashar; Fathipour, Morteza; Fathipour, Vala

2016-03-21

This paper describes comprehensive analytical and simulation models for the design and optimization of the electron-injection based detectors. The electron-injection detectors evaluated here operate in the short-wave infrared range and utilize a type-II band alignment in InP/GaAsSb/InGaAs material system. The unique geometry of detectors along with an inherent negative-feedback mechanism in the device allows for achieving high internal avalanche-free amplifications without any excess noise. Physics-based closed-form analytical models are derived for the detector rise time and dark current. Our optical gain model takes into account the drop in the optical gain at high optical power levels. Furthermore, numerical simulation studiesmore » of the electrical characteristics of the device show good agreement with our analytical models as well experimental data. Performance comparison between devices with different injector sizes shows that enhancement in the gain and speed is anticipated by reducing the injector size. Sensitivity analysis for the key detector parameters shows the relative importance of each parameter. The results of this study may provide useful information and guidelines for development of future electron-injection based detectors as well as other heterojunction photodetectors.« less

A numerical study on combustion process in a small compression ignition engine run dual-fuel mode (diesel-biogas)

NASA Astrophysics Data System (ADS)

Ambarita, H.; Widodo, T. I.; Nasution, D. M.

2017-01-01

In order to reduce the consumption of fossil fuel of a compression ignition (CI) engines which is usually used in transportation and heavy machineries, it can be operated in dual-fuel mode (diesel-biogas). However, the literature reviews show that the thermal efficiency is lower due to incomplete combustion process. In order to increase the efficiency, the combustion process in the combustion chamber need to be explored. Here, a commercial CFD code is used to explore the combustion process of a small CI engine run on dual fuel mode (diesel-biogas). The turbulent governing equations are solved based on finite volume method. A simulation of compression and expansions strokes at an engine speed and load of 1000 rpm and 2500W, respectively has been carried out. The pressure and temperature distributions and streamlines are plotted. The simulation results show that at engine power of 732.27 Watt the thermal efficiency is 9.05%. The experiment and simulation results show a good agreement. The method developed in this study can be used to investigate the combustion process of CI engine run on dual-fuel mode.

Structural properties of atactic polystyrene adsorbed onto solid surfaces.

PubMed

Tatek, Yergou B; Tsige, Mesfin

2011-11-07

In the present work, we are studying the local conformation of chains in a thin film of polystyrene adsorbed on a solid substrate by using atomistically detailed simulations. The simulations are carried out by using the readily available and massively parallel molecular dynamics code known as LAMMPS. In particular, a special emphasis is given to the density and orientation of side chains (which consist of phenyl groups and methylene units) at solid/polymer and polymer/vacuum interfaces. Three types of substrates were used in our study: α-quartz, graphite, and amorphous silica. Our investigation was restricted to atactic polystyrene. Our results show that the density and structural properties of side chains depend on the type of surface. An excess of phenyl rings is observed near the α-quartz substrate while the film adsorbed on graphite is depleted in C(6)H(5). Moreover, the orientation of the rings and methylene units on the substrate/film interface show a strong dependence on the type of the substrate, while the rings at the film/vacuum interface show a marked tendency to point outward, away from the film. The results we obtained are in a large part in good agreement with previous experimental and simulation results.

Precise predictions of H2O line shapes over a wide pressure range using simulations corrected by a single measurement

NASA Astrophysics Data System (ADS)

Ngo, N. H.; Nguyen, H. T.; Tran, H.

2018-03-01

In this work, we show that precise predictions of the shapes of H2O rovibrational lines broadened by N2, over a wide pressure range, can be made using simulations corrected by a single measurement. For that, we use the partially-correlated speed-dependent Keilson-Storer (pcsdKS) model whose parameters are deduced from molecular dynamics simulations and semi-classical calculations. This model takes into account the collision-induced velocity-changes effects, the speed dependences of the collisional line width and shift as well as the correlation between velocity and internal-state changes. For each considered transition, the model is corrected by using a parameter deduced from its broadening coefficient measured for a single pressure. The corrected-pcsdKS model is then used to simulate spectra for a wide pressure range. Direct comparisons of the corrected-pcsdKS calculated and measured spectra of 5 rovibrational lines of H2O for various pressures, from 0.1 to 1.2 atm, show very good agreements. Their maximum differences are in most cases well below 1%, much smaller than residuals obtained when fitting the measurements with the Voigt line shape. This shows that the present procedure can be used to predict H2O line shapes for various pressure conditions and thus the simulated spectra can be used to deduce the refined line-shape parameters to complete spectroscopic databases, in the absence of relevant experimental values.

Impact of land cover data on the simulation of urban heat island for Berlin using WRF coupled with bulk approach of Noah-LSM

NASA Astrophysics Data System (ADS)

Li, Huidong; Wolter, Michael; Wang, Xun; Sodoudi, Sahar

2017-09-01

Urban-rural difference of land cover is the key determinant of urban heat island (UHI). In order to evaluate the impact of land cover data on the simulation of UHI, a comparative study between up-to-date CORINE land cover (CLC) and Urban Atlas (UA) with fine resolution (100 and 10 m) and old US Geological Survey (USGS) data with coarse resolution (30 s) was conducted using the Weather Research and Forecasting model (WRF) coupled with bulk approach of Noah-LSM for Berlin. The comparison between old data and new data partly reveals the effect of urbanization on UHI and the historical evolution of UHI, while the comparison between different resolution data reveals the impact of resolution of land cover on the simulation of UHI. Given the high heterogeneity of urban surface and the fine-resolution land cover data, the mosaic approach was implemented in this study to calculate the sub-grid variability in land cover compositions. Results showed that the simulations using UA and CLC data perform better than that using USGS data for both air and land surface temperatures. USGS-based simulation underestimates the temperature, especially in rural areas. The longitudinal variations of both temperature and land surface temperature show good agreement with urban fraction for all the three simulations. To better study the comprehensive characteristic of UHI over Berlin, the UHI curves (UHIC) are developed for all the three simulations based on the relationship between temperature and urban fraction. CLC- and UA-based simulations show smoother UHICs than USGS-based simulation. The simulation with old USGS data obviously underestimates the extent of UHI, while the up-to-date CLC and UA data better reflect the real urbanization and simulate the spatial distribution of UHI more accurately. However, the intensity of UHI simulated by CLC and UA data is not higher than that simulated by USGS data. The simulated air temperature is not dominated by the land cover as much as the land surface temperature, as air temperature is also affected by air advection.

Ocean Color and Evidence of Chlorophyll Signature in the TOMS Minimum Reflectivity Data

NASA Technical Reports Server (NTRS)

Ahmad, Z.; Herman, J. R.; Bhartia, P. K.

2003-01-01

Analysis of the TOMS minimum reflectivity data for 380 nm channel (R380) show regions of high reflectivity values (approx. 7 to 8%) over Sargasso Sea in the Northern Atlantic, anti-cyclonic region in the Southern Atlantic, and a large part of the ocean in the Southern Pacific, and low values (5 approx. 6 %) over the rest of the open ocean. Through radiative transfer simulations we show that these features are highly correlated with the distribution of chlorophyll in the ocean. Theoretical minimum reflectivity values derived with the help of CZCS chlorophyll concentration data as input into a vector ocean-atmosphere radiative transfer code developed by Ahmad and Fraser show very good agreement with TOMS minimum reflectivity data for the winter season of year 1980. For the summer season of year 1980, good qualitative agreement is observed in the equatorial and northern hemisphere but not as good in the southern hemisphere. Also, for cloud-free conditions, we find a very strong correlation between R340 minus R380 values and the chlorophyll concentration in the ocean. Results on the possible effects of absorbing and non-absorbing aerosols on the TOMS minimum reflectivity will also be presented. The results also imply that ocean color will affect the aerosol retrieval over oceans unless corrected.

Monte Carlo simulation of non-invasive glucose measurement based on FMCW LIDAR

NASA Astrophysics Data System (ADS)

Xiong, Bing; Wei, Wenxiong; Liu, Nan; He, Jian-Jun

2010-11-01

Continuous non-invasive glucose monitoring is a powerful tool for the treatment and management of diabetes. A glucose measurement method, with the potential advantage of miniaturizability with no moving parts, based on the frequency modulated continuous wave (FMCW) LIDAR technology is proposed and investigated. The system mainly consists of an integrated near-infrared tunable semiconductor laser and a detector, using heterodyne technology to convert the signal from time-domain to frequency-domain. To investigate the feasibility of the method, Monte Carlo simulations have been performed on tissue phantoms with optical parameters similar to those of human interstitial fluid. The simulation showed that the sensitivity of the FMCW LIDAR system to glucose concentration can reach 0.2mM. Our analysis suggests that the FMCW LIDAR technique has good potential for noninvasive blood glucose monitoring.

Direct Numerical Simulation of Acoustic Noise Generation from the Nozzle Wall of a Hypersonic Wind Tunnel

NASA Technical Reports Server (NTRS)

Huang, Junji; Duan, Lian; Choudhari, Meelan M.

2017-01-01

The acoustic radiation from the turbulent boundary layer on the nozzle wall of a Mach 6 Ludwieg Tube is simulated using Direct Numerical Simulations (DNS), with the flow conditions falling within the operational range of the Mach 6 Hypersonic Ludwieg Tube, Braunschweig (HLB). The mean and turbulence statistics of the nozzle-wall boundary layer show good agreement with those predicted by Pate's correlation and Reynolds Averaged Navier-Stokes (RANS) computations. The rms pressure fluctuation P'(rms)/T(w) plateaus in the freestream core of the nozzle. The intensity of the freestream noise within the nozzle is approximately 20% higher than that radiated from a single at pate with a similar freestream Mach number, potentially because of the contributions to the acoustic radiation from multiple azimuthal segments of the nozzle wall.

Flood Simulation based on ArcGIS in the Ungauged Area from Fugu to Wubao of the middle Yellow River

NASA Astrophysics Data System (ADS)

Jin, Shuangyan; Yan, Yiqi; Jiang, Xinhui

2017-12-01

The Qingliangsigou and Jialuhe in the middle Yellow River are selected as the typical tributaries, history flood data in 1980-2013 and Horton infiltration capacity curve are used to calculate the stable infiltration rate and establish the model of runoff yield and concentration, the parameters are calibrated and applied in the ungauged area from Fugu to Wubao. The study area is divided into 20 units based on ArcGIS, Muskingum method parameters in each unit are calibrated, and typical floods of ungauged area from Fugu to Wubao are simulated. The results show that the simulation effects are good: the average error of peak time is about -0.4h, the error of peak discharge is in the forecasting allowable range, and the deterministic coefficient is 0.66.

Dynamical analysis of surface-insulated planar wire array Z-pinches

NASA Astrophysics Data System (ADS)

Li, Yang; Sheng, Liang; Hei, Dongwei; Li, Xingwen; Zhang, Jinhai; Li, Mo; Qiu, Aici

2018-05-01

The ablation and implosion dynamics of planar wire array Z-pinches with and without surface insulation are compared and discussed in this paper. This paper first presents a phenomenological model named the ablation and cascade snowplow implosion (ACSI) model, which accounts for the ablation and implosion phases of a planar wire array Z-pinch in a single simulation. The comparison between experimental data and simulation results shows that the ACSI model could give a fairly good description about the dynamical characteristics of planar wire array Z-pinches. Surface insulation introduces notable differences in the ablation phase of planar wire array Z-pinches. The ablation phase is divided into two stages: insulation layer ablation and tungsten wire ablation. The two-stage ablation process of insulated wires is simulated in the ACSI model by updating the formulas describing the ablation process.

Simulation of the early startup period of high-temperature heat pipes from the frozen state by a rarefied vapor self-diffusion model

NASA Technical Reports Server (NTRS)

Cao, Y.; Faghri, A.

1993-01-01

The heat pipe startup process is described physically and is divided into five periods for convenience of analysis. The literature survey revealed that none of the previous attempts to simulate the heat pipe startup process numerically were successful, since the rarefied vapor flow in the heat pipe was not considered. Therefore, a rarefied vapor self-diffusion model is proposed, and the early startup periods, in which the rarefied vapor flow is dominant within the heat pipe, are first simulated numerically. The numerical results show that large vapor density gradients existed along the heat pipe length, and the vapor flow reaches supersonic velocities when the density is extremely low. The numerical results are compared with the experimental data of the early startup period with good agreement.

An efficient hybrid method for stochastic reaction-diffusion biochemical systems with delay

NASA Astrophysics Data System (ADS)

Sayyidmousavi, Alireza; Ilie, Silvana

2017-12-01

Many chemical reactions, such as gene transcription and translation in living cells, need a certain time to finish once they are initiated. Simulating stochastic models of reaction-diffusion systems with delay can be computationally expensive. In the present paper, a novel hybrid algorithm is proposed to accelerate the stochastic simulation of delayed reaction-diffusion systems. The delayed reactions may be of consuming or non-consuming delay type. The algorithm is designed for moderately stiff systems in which the events can be partitioned into slow and fast subsets according to their propensities. The proposed algorithm is applied to three benchmark problems and the results are compared with those of the delayed Inhomogeneous Stochastic Simulation Algorithm. The numerical results show that the new hybrid algorithm achieves considerable speed-up in the run time and very good accuracy.

CFD Approaches for Simulation of Wing-Body Stage Separation

NASA Technical Reports Server (NTRS)

Buning, Pieter G.; Gomez, Reynaldo J.; Scallion, William I.

2004-01-01

A collection of computational fluid dynamics tools and techniques are being developed and tested for application to stage separation and abort simulation for next-generation launch vehicles. In this work, an overset grid Navier-Stokes flow solver has been enhanced and demonstrated on a matrix of proximity cases and on a dynamic separation simulation of a belly-to-belly wing-body configuration. Steady cases show excellent agreement between Navier-Stokes results, Cartesian grid Euler solutions, and wind tunnel data at Mach 3. Good agreement has been obtained between Navier-Stokes, Euler, and wind tunnel results at Mach 6. An analysis of a dynamic separation at Mach 3 demonstrates that unsteady aerodynamic effects are not important for this scenario. Results provide an illustration of the relative applicability of Euler and Navier-Stokes methods to these types of problems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakosi, Jozsef; Christon, Mark A.; Francois, Marianne M.

This report describes the work carried out for completion of the Thermal Hydraulics Methods (THM) Level 3 Milestone THM.CFD.P5.05 for the Consortium for Advanced Simulation of Light Water Reactors (CASL). A series body-fitted computational meshes have been generated by Numeca's Hexpress/Hybrid, a.k.a. 'Spider', meshing technology for the V5H 3x3 and 5x5 rod bundle geometry used to compute the fluid dynamics of grid-to-rod fretting (GTRF). Spider is easy to use, fast, and automatically generates high-quality meshes for extremely complex geometries, required for the GTRF problem. Hydra-TH has been used to carry out large-eddy simulations on both 3x3 and 5x5 geometries, usingmore » different mesh resolutions. The results analyzed show good agreement with Star-CCM+ simulations and experimental data.« less

Calibration and simulation of two large wastewater treatment plants operated for nutrient removal.

PubMed

Ferrer, J; Morenilla, J J; Bouzas, A; García-Usach, F

2004-01-01

Control and optimisation of plant processes has become a priority for WWTP managers. The calibration and verification of a mathematical model provides an important tool for the investigation of advanced control strategies that may assist in the design or optimization of WWTPs. This paper describes the calibration of the ASM2d model for two full scale biological nitrogen and phosphorus removal plants in order to characterize the biological process and to upgrade the plants' performance. Results from simulation showed a good correspondence with experimental data demonstrating that the model and the calibrated parameters were able to predict the behaviour of both WWTPs. Once the calibration and simulation process was finished, a study for each WWTP was done with the aim of improving its performance. Modifications focused on reactor configuration and operation strategies were proposed.

Numerical simulations of the flow in the HYPULSE expansion tube

NASA Technical Reports Server (NTRS)

Wilson, Gregory J.; Sussman, Myles A.; Bakos, Robert J.

1995-01-01

Axisymmetric numerical simulations with finite-rate chemistry are presented for two operating conditions in the HYPULSE expansion tube. The operating gas for these two cases is nitrogen and the computations are compared to experimental data. One test condition is at a total enthalpy of 15.2 MJ/Kg and a relatively low static pressure of 2 kPa. This case is characterized by a laminar boundary layer and significant chemical nonequilibrium in the acceleration gas. The second test condition is at a total enthalpy of 10.2 MJ/Kg and a static pressure of 38 kPa and is characterized by a turbulent boundary layer. For both cases, the time-varying test gas pressure predicted by the simulations is in good agreement with experimental data. The computations are also found to be in good agreement with Mirels' correlations for shock tube flow. It is shown that the nonuniformity of the test gas observed in the HYPULSE expansion tube is strongly linked to the boundary layer thickness. The turbulent flow investigated has a larger boundary layer and greater test gas nonuniformity. In order to investigate possibilities of improving expansion tube flow quality by reducing the boundary layer thickness, parametric studies showing the effect of density and turbulent transition point on the test conditions are also presented. Although an increase in the expansion tube operating pressure level would reduce the boundary layer thickness, the simulations indicate that the reduction would be less than what is predicted by flat plate boundary layer correlations.

The 3D pore structure and fluid dynamics simulation of macroporous monoliths: High permeability due to alternating channel width.

PubMed

Jungreuthmayer, Christian; Steppert, Petra; Sekot, Gerhard; Zankel, Armin; Reingruber, Herbert; Zanghellini, Jürgen; Jungbauer, Alois

2015-12-18

Polymethacrylate-based monoliths have excellent flow properties. Flow in the wide channel interconnected with narrow channels is theoretically assumed to account for favorable permeability. Monoliths were cut into 898 slices in 50nm distances and visualized by serial block face scanning electron microscopy (SBEM). A 3D structure was reconstructed and used for the calculation of flow profiles within the monolith and for calculation of pressure drop and permeability by computational fluid dynamics (CFD). The calculated and measured permeabilities showed good agreement. Small channels clearly flowed into wide and wide into small channels in a repetitive manner which supported the hypothesis describing the favorable flow properties of these materials. This alternating property is also reflected in the streamline velocity which fluctuated. These findings were corroborated by artificial monoliths which were composed of regular (interconnected) cells where narrow cells followed wide cells. In the real monolith and the artificial monoliths with interconnected flow channels similar velocity fluctuations could be observed. A two phase flow simulation showed a lateral velocity component, which may contribute to the transport of molecules to the monolith wall. Our study showed that the interconnection of small and wide pores is responsible for the excellent pressure flow properties. This study is also a guide for further design of continuous porous materials to achieve good flow properties. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Peregrine soliton generation and breakup in standard telecommunications fiber.

PubMed

Hammani, Kamal; Kibler, Bertrand; Finot, Christophe; Morin, Philippe; Fatome, Julien; Dudley, John M; Millot, Guy

2011-01-15

We present experimental and numerical results showing the generation and breakup of the Peregrine soliton in standard telecommunications fiber. The impact of nonideal initial conditions is studied through direct cutback measurements of the longitudinal evolution of the emerging soliton dynamics and is shown to be associated with the splitting of the Peregrine soliton into two subpulses, with each subpulse itself exhibiting Peregrine soliton characteristics. Experimental results are in good agreement with simulations.

Electron heat transport measured in a stochastic magnetic field.

PubMed

Biewer, T M; Forest, C B; Anderson, J K; Fiksel, G; Hudson, B; Prager, S C; Sarff, J S; Wright, J C; Brower, D L; Ding, W X; Terry, S D

2003-07-25

New profile measurements have allowed the electron thermal diffusivity profile to be estimated from power balance in the Madison Symmetric Torus where magnetic islands overlap and field lines are stochastic. The measurements show that (1) the electron energy transport is conductive not convective, (2) the measured thermal diffusivities are in good agreement with numerical simulations of stochastic transport, and (3) transport is greatly reduced near the reversal surface where magnetic diffusion is small.

Distributions of neutron yields and doses around a water phantom bombarded with 290-MeV/nucleon and 430-MeV/nucleon carbon ions

NASA Astrophysics Data System (ADS)

Satoh, D.; Kajimoto, T.; Shigyo, N.; Itashiki, Y.; Imabayashi, Y.; Koba, Y.; Matsufuji, N.; Sanami, T.; Nakao, N.; Uozumi, Y.

2016-11-01

Double-differential neutron yields from a water phantom bombarded with 290-MeV/nucleon and 430-MeV/nucleon carbon ions were measured at emission angles of 15°, 30°, 45°, 60°, 75°, and 90°, and angular distributions of neutron yields and doses around the phantom were obtained. The experimental data were compared with results of the Monte-Carlo simulation code PHITS. The PHITS results showed good agreement with the measured data. On the basis of the PHITS simulation, we estimated the angular distributions of neutron yields and doses from 0° to 180° including thermal neutrons.

Induced movement of the magnetic beads and DNA-based dumbbell in a micro fluidic channel

NASA Astrophysics Data System (ADS)

Babić, B.; Ghai, R.; Dimitrov, K.

2007-12-01

We have explored controlled movement of magnetic beads and a dumbbell structure composed of DNA, a magnetic and a non-magnetic bead in a micro fluidic channel. Movement of the beads and dumbbells is simulated assuming that a net force is described as a superposition between the magnetic and hydrodynamic drag forces. Trajectories of beads and dumbbells are observed with optical light microscopy. The experimentally measured data show a good agreement with the simulations. This dynamical approach offers the prospect to stretch the DNA within the dumbbell and investigate its conformational changes. Further on, we demonstrate that short sonication can reduce multiple attachments of DNA to the beads.

System Wide Joint Position Sensor Fault Tolerance in Robot Systems Using Cartesian Accelerometers

NASA Technical Reports Server (NTRS)

Aldridge, Hal A.; Juang, Jer-Nan

1997-01-01

Joint position sensors are necessary for most robot control systems. A single position sensor failure in a normal robot system can greatly degrade performance. This paper presents a method to obtain position information from Cartesian accelerometers without integration. Depending on the number and location of the accelerometers. the proposed system can tolerate the loss of multiple position sensors. A solution technique suitable for real-time implementation is presented. Simulations were conducted using 5 triaxial accelerometers to recover from the loss of up to 4 joint position sensors on a 7 degree of freedom robot moving in general three dimensional space. The simulations show good estimation performance using non-ideal accelerometer measurements.

Optimization of the parameters for obtaining zirconia-alumina coatings, made by flame spraying from results of numerical simulation

NASA Astrophysics Data System (ADS)

Ferrer, M.; Vargas, F.; Peña, G.

2017-12-01

The K-Sommerfeld values (K) and the melting percentage (% F) obtained by numerical simulation using the Jets et Poudres software were used to find the projection parameters of zirconia-alumina coatings by thermal spraying flame, in order to obtain coatings with good morphological and structural properties to be used as thermal insulation. The experimental results show the relationship between the Sommerfeld parameter and the porosity of the zirconia-alumina coatings. It is found that the lowest porosity is obtained when the K-Sommerfeld value is close to 45 with an oxidant flame, on the contrary, when superoxidant flames are used K values are close 52, which improve wear resistance.

Optimal design of DC-based polarization beam splitter in lithium niobate on insulator

NASA Astrophysics Data System (ADS)

Gong, Zisu; Yin, Rui; Ji, Wei; Wang, Junbao; Wu, Chonghao; Li, Xiao; Zhang, Shicheng

2017-08-01

We propose a DC-based polarization beam splitter (PBS) in lithium niobate on insulator (LNOI). Utilizing the high birefringence property of Lithium Niobate (LiNbO3, LN), the device is achieved by simple structure in a short length. With the use of beam propagation method (BPM), the simulation results show that the device has a good performance for the separation of TE and TM polarizations with a high extinction ratio (about 35 dB). The simulated fabrication tolerance for the variation of the waveguide width is about 100 nm and the bandwidth is about 65 nm when the extinction ratio is higher than 10 dB.

Time-Accurate Simulations and Acoustic Analysis of Slat Free-Shear Layer

NASA Technical Reports Server (NTRS)

Khorrami, Mehdi R.; Singer, Bart A.; Berkman, Mert E.

2001-01-01

A detailed computational aeroacoustic analysis of a high-lift flow field is performed. Time-accurate Reynolds Averaged Navier-Stokes (RANS) computations simulate the free shear layer that originates from the slat cusp. Both unforced and forced cases are studied. Preliminary results show that the shear layer is a good amplifier of disturbances in the low to mid-frequency range. The Ffowcs-Williams and Hawkings equation is solved to determine the acoustic field using the unsteady flow data from the RANS calculations. The noise radiated from the excited shear layer has a spectral shape qualitatively similar to that obtained from measurements in a corresponding experimental study of the high-lift system.

Large-eddy simulation of a backward facing step flow using a least-squares spectral element method

NASA Technical Reports Server (NTRS)

Chan, Daniel C.; Mittal, Rajat

1996-01-01

We report preliminary results obtained from the large eddy simulation of a backward facing step at a Reynolds number of 5100. The numerical platform is based on a high order Legendre spectral element spatial discretization and a least squares time integration scheme. A non-reflective outflow boundary condition is in place to minimize the effect of downstream influence. Smagorinsky model with Van Driest near wall damping is used for sub-grid scale modeling. Comparisons of mean velocity profiles and wall pressure show good agreement with benchmark data. More studies are needed to evaluate the sensitivity of this method on numerical parameters before it is applied to complex engineering problems.

The vibrational spectrum of the hydrated alanine-leucine peptide in the amide region from IR experiments and first principles calculations

NASA Astrophysics Data System (ADS)

Hassan, Irtaza; Donati, Luca; Stensitzki, Till; Keller, Bettina G.; Heyne, Karsten; Imhof, Petra

2018-04-01

We have combined infrared (IR) experiments with molecular dynamics (MD) simulations in solution at finite temperature to analyse the vibrational signature of the small floppy peptide Alanine-Leucine. IR spectra computed from first-principles MD simulations exhibit no distinct differences between conformational clusters of α -helix or β -sheet-like folds with different orientations of the bulky leucine side chain. All computed spectra show two prominent bands, in good agreement with the experiment, that are assigned to the stretch vibrations of the carbonyl and carboxyl group, respectively. Variations in band widths and exact maxima are likely due to small fluctuations in the backbone torsion angles.

Comparison of long-term numerical simulations at the Ketzin pilot site using the Schlumberger ECLIPSE and LBNL TOUGH2 simulators

NASA Astrophysics Data System (ADS)

Kempka, T.; Norden, B.; Tillner, E.; Nakaten, B.; Kühn, M.

2012-04-01

Geological modelling and dynamic flow simulations were conducted at the Ketzin pilot site showing a good agreement of history matched geological models with CO2 arrival times in both observation wells and timely development of reservoir pressure determined in the injection well. Recently, a re-evaluation of the seismic 3D data enabled a refinement of the structural site model and the implementation of the fault system present at the top of the Ketzin anticline. The updated geological model (model size: 5 km x 5 km) shows a horizontal discretization of 5 x 5 m and consists of three vertical zones, with the finest discretization at the top (0.5 m). According to the revised seismic analysis, the facies modelling to simulate the channel and floodplain facies distribution at Ketzin was updated. Using a sequential Gaussian simulator for the distribution of total and effective porosities and an empiric porosity-permeability relationship based on site and literature data available, the structural model was parameterized. Based on this revised reservoir model of the Stuttgart formation, numerical simulations using the TOUGH2-MP/ECO2N and Schlumberger Information Services (SIS) ECLIPSE 100 black-oil simulators were undertaken in order to evaluate the long-term (up to 10,000 years) migration of the injected CO2 (about 57,000 t at the end of 2011) and the development of reservoir pressure over time. The simulation results enabled us to quantitatively compare both reservoir simulators based on current operational data considering the long-term effects of CO2 storage including CO2 dissolution in the formation fluid. While the integration of the static geological model developed in the SIS Petrel modelling package into the ECLIPSE simulator is relatively flawless, a work-flow allowing for the export of Petrel models into the TOUGH2-MP input file format had to be implemented within the scope of this study. The challenge in this task was mainly determined by the presence of a complex faulted system in the revised reservoir model demanding for an integrated concept to deal with connections between the elements aligned to faults in the TOUGH2-MP simulator. Furthermore, we developed a methodology to visualize and compare the TOUGH2-MP simulation results with those of the Eclipse simulator using the Petrel software package. The long-term simulation results of both simulators are generally in good agreement. Spatial and timely migration of the CO2 plume as well as residual gas saturation are almost identical for both simulators, even though a time-dependent approach of CO2 dissolution in the formation fluid was chosen in the ECLIPSE simulator. Our results confirmed that a scientific open-source simulator as the TOUGH2-MP software package is capable to provide the same accuracy as the industrial standard simulator ECLIPSE 100. However, the computational time and additional efforts to implement a suitable workflow for using the TOUGH2-MP simulator are significantly higher, while the open-source concept of TOUGH2 provides more flexibility regarding process adaptation.

Chemical potential in active systems: predicting phase equilibrium from bulk equations of state?

NASA Astrophysics Data System (ADS)

Paliwal, Siddharth; Rodenburg, Jeroen; van Roij, René; Dijkstra, Marjolein

2018-01-01

We derive a microscopic expression for a quantity μ that plays the role of chemical potential of active Brownian particles (ABPs) in a steady state in the absence of vortices. We show that μ consists of (i) an intrinsic chemical potential similar to passive systems, which depends on density and self-propulsion speed, but not on the external potential, (ii) the external potential, and (iii) a newly derived one-body swim potential due to the activity of the particles. Our simulations on ABPs show good agreement with our Fokker-Planck calculations, and confirm that μ (z) is spatially constant for several inhomogeneous active fluids in their steady states in a planar geometry. Finally, we show that phase coexistence of ABPs with a planar interface satisfies not only mechanical but also diffusive equilibrium. The coexistence can be well-described by equating the bulk chemical potential and bulk pressure obtained from bulk simulations for systems with low activity but requires explicit evaluation of the interfacial contributions at high activity.

Evaluation of nonequilibrium boundary conditions for hypersonic rarefied gas flows

NASA Astrophysics Data System (ADS)

Le, N. T. P.; Greenshields, Ch. J.; Reese, J. M.

2012-01-01

A new Computational Fluid Dynamics (CFD) solver for high-speed viscous §ows in the OpenFOAM code is validated against published experimental data and Direct Simulation Monte Carlo (DSMC) results. The laminar §at plate and circular cylinder cases are studied for Mach numbers, Ma, ranging from 6 to 12.7, and with argon and nitrogen as working gases. Simulation results for the laminar §at plate cases show that the combination of accommodation coefficient values σu = 0.7 and σT = 1.0 in the Maxwell/Smoluchowski conditions, and the coefficient values A1 = 1.5 and A2 = 1.0 in the second-order velocity slip condition, give best agreement with experimental data of surface pressure. The values σu = 0.7 and σT = 1.0 also give good agreement with DSMC data of surface pressure at the stagnation point in the circular cylinder case at Kn = 0.25. The Langmuir surface adsorption condition is also tested for the laminar §at plate case, but initial results were not as good as the Maxwell/Smoluchowski boundary conditions.

Effects of non-adiabatic walls on shock/boundary-layer interaction using direct numerical simulations

NASA Astrophysics Data System (ADS)

Volpiani, Pedro S.; Bernardini, Matteo; Larsson, Johan

2017-11-01

The influence of wall thermal conditions on the properties of an impinging shock wave interacting with a turbulent supersonic boundary layer is a research topic that still remains underexplored. In the present study, direct numerical simulations (DNS) are employed to investigate the flow properties of a shock wave interacting with a turbulent boundary layer at free-stream Mach number M∞ = 2.28 with distinct wall thermal conditions and shock strengths. Instantaneous and mean flow fields, wall quantities and the low-frequency unsteadiness are analyzed. While heating contributes to increase the extent of the interaction zone, wall cooling turns out to be a good candidate for flow control. The distribution of the Stanton number shows a good agreement with prior experimental studies and confirms the strong heat transfer and complex pattern within the interaction region. Numerical results indicate that the changes in the interaction length are mainly linked to the incoming boundary layer as suggested in previous studies (Souverein et al., 2013 and Jaunet et al., 2014). This work was supported by the Air Force Office of Scientific Research, Grant FA95501610385.

Microstructure Evolution and Flow Stress Model of a 20Mn5 Hollow Steel Ingot during Hot Compression.

PubMed

Liu, Min; Ma, Qing-Xian; Luo, Jian-Bin

2018-03-21

20Mn5 steel is widely used in the manufacture of heavy hydro-generator shaft due to its good performance of strength, toughness and wear resistance. However, the hot deformation and recrystallization behaviors of 20Mn5 steel compressed under high temperature were not studied. In this study, the hot compression experiments under temperatures of 850-1200 °C and strain rates of 0.01/s-1/s are conducted using Gleeble thermal and mechanical simulation machine. And the flow stress curves and microstructure after hot compression are obtained. Effects of temperature and strain rate on microstructure are analyzed. Based on the classical stress-dislocation relation and the kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of 20Mn5 steel. Comparisons between experimental flow stress and predicted flow stress show that the predicted flow stress values are in good agreement with the experimental flow stress values, which indicates that the proposed constitutive model is reliable and can be used for numerical simulation of hot forging of 20Mn5 hollow steel ingot.

Studies of concentration and temperature dependences of precipitation kinetics in iron-copper alloys using kinetic Monte Carlo and stochastic statistical simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khromov, K. Yu.; Vaks, V. G., E-mail: vaks@mbslab.kiae.ru; Zhuravlev, I. A.

2013-02-15

The previously developed ab initio model and the kinetic Monte Carlo method (KMCM) are used to simulate precipitation in a number of iron-copper alloys with different copper concentrations x and temperatures T. The same simulations are also made using an improved version of the previously suggested stochastic statistical method (SSM). The results obtained enable us to make a number of general conclusions about the dependences of the decomposition kinetics in Fe-Cu alloys on x and T. We also show that the SSM usually describes the precipitation kinetics in good agreement with the KMCM, and using the SSM in conjunction withmore » the KMCM allows extending the KMC simulations to the longer evolution times. The results of simulations seem to agree with available experimental data for Fe-Cu alloys within statistical errors of simulations and the scatter of experimental results. Comparison of simulation results with experiments for some multicomponent Fe-Cu-based alloys allows making certain conclusions about the influence of alloying elements in these alloys on the precipitation kinetics at different stages of evolution.« less

[Dosimetric evaluation of eye lense shieldings in computed tomography examination--measurements and Monte Carlo simulations].

PubMed

Wulff, Jorg; Keil, Boris; Auvanis, Diyala; Heverhagen, Johannes T; Klose, Klaus Jochen; Zink, Klemens

2008-01-01

The present study aims at the investigation of eye lens shielding of different composition for the use in computed tomography examinations. Measurements with thermo-luminescent dosimeters and a simple cylindrical waterfilled phantom were performed as well as Monte Carlo simulations with an equivalent geometry. Besides conventional shielding made of Bismuth coated latex, a new shielding with a mixture of metallic components was analyzed. This new material leads to an increased dose reduction compared to the Bismuth shielding. Measured and Monte Carlo simulated dose reductions are in good agreement and amount to 34% for the Bismuth shielding and 46% for the new material. For simulations the EGSnrc code system was used and a new application CTDOSPP was developed for the simulation of the computed tomography examination. The investigations show that a satisfying agreement between simulation and measurement with the chosen geometries of this study could only be achieved, when transport of secondary electrons was accounted for in the simulation. The amount of scattered radiation due to the protector by fluorescent photons was analyzed and is larger for the new material due to the smaller atomic number of the metallic components.

MicroHH 1.0: a computational fluid dynamics code for direct numerical simulation and large-eddy simulation of atmospheric boundary layer flows

NASA Astrophysics Data System (ADS)

van Heerwaarden, Chiel C.; van Stratum, Bart J. H.; Heus, Thijs; Gibbs, Jeremy A.; Fedorovich, Evgeni; Mellado, Juan Pedro

2017-08-01

This paper describes MicroHH 1.0, a new and open-source (www.microhh.org) computational fluid dynamics code for the simulation of turbulent flows in the atmosphere. It is primarily made for direct numerical simulation but also supports large-eddy simulation (LES). The paper covers the description of the governing equations, their numerical implementation, and the parameterizations included in the code. Furthermore, the paper presents the validation of the dynamical core in the form of convergence and conservation tests, and comparison of simulations of channel flows and slope flows against well-established test cases. The full numerical model, including the associated parameterizations for LES, has been tested for a set of cases under stable and unstable conditions, under the Boussinesq and anelastic approximations, and with dry and moist convection under stationary and time-varying boundary conditions. The paper presents performance tests showing good scaling from 256 to 32 768 processes. The graphical processing unit (GPU)-enabled version of the code can reach a speedup of more than an order of magnitude for simulations that fit in the memory of a single GPU.

Accelerated molecular dynamics simulations of protein folding.

PubMed

Miao, Yinglong; Feixas, Ferran; Eun, Changsun; McCammon, J Andrew

2015-07-30

Folding of four fast-folding proteins, including chignolin, Trp-cage, villin headpiece and WW domain, was simulated via accelerated molecular dynamics (aMD). In comparison with hundred-of-microsecond timescale conventional molecular dynamics (cMD) simulations performed on the Anton supercomputer, aMD captured complete folding of the four proteins in significantly shorter simulation time. The folded protein conformations were found within 0.2-2.1 Å of the native NMR or X-ray crystal structures. Free energy profiles calculated through improved reweighting of the aMD simulations using cumulant expansion to the second-order are in good agreement with those obtained from cMD simulations. This allows us to identify distinct conformational states (e.g., unfolded and intermediate) other than the native structure and the protein folding energy barriers. Detailed analysis of protein secondary structures and local key residue interactions provided important insights into the protein folding pathways. Furthermore, the selections of force fields and aMD simulation parameters are discussed in detail. Our work shows usefulness and accuracy of aMD in studying protein folding, providing basic references in using aMD in future protein-folding studies. © 2015 Wiley Periodicals, Inc.

Dynamic Hybrid Simulation of the Lunar Wake During ARTEMIS Crossing

NASA Astrophysics Data System (ADS)

Wiehle, S.; Plaschke, F.; Angelopoulos, V.; Auster, H.; Glassmeier, K.; Kriegel, H.; Motschmann, U. M.; Mueller, J.

2010-12-01

The interaction of the highly dynamic solar wind with the Moon is simulated with the A.I.K.E.F. (Adaptive Ion Kinetic Electron Fluid) code for the ARTEMIS P1 flyby on February 13, 2010. The A.I.K.E.F. hybrid plasma simulation code is the improved version of the Braunschweig code. It is able to automatically increase simulation grid resolution in areas of interest during runtime, which greatly increases resolution as well as performance. As the Moon has no intrinsic magnetic field and no ionosphere, the solar wind particles are absorbed at its surface, resulting in the formation of the lunar wake at the nightside. The solar wind magnetic field is basically convected through the Moon and the wake is slowly filled up with solar wind particles. However, this interaction is strongly influenced by the highly dynamic solar wind during the flyby. This is considered by a dynamic variation of the upstream conditions in the simulation using OMNI solar wind measurement data. By this method, a very good agreement between simulation and observations is achieved. The simulations show that the stationary structure of the lunar wake constitutes a tableau vivant in space representing the well-known Friedrichs diagram for MHD waves.

MCNPX simulation of proton dose distribution in homogeneous and CT phantoms

NASA Astrophysics Data System (ADS)

Lee, C. C.; Lee, Y. J.; Tung, C. J.; Cheng, H. W.; Chao, T. C.

2014-02-01

A dose simulation system was constructed based on the MCNPX Monte Carlo package to simulate proton dose distribution in homogeneous and CT phantoms. Conversion from Hounsfield unit of a patient CT image set to material information necessary for Monte Carlo simulation is based on Schneider's approach. In order to validate this simulation system, inter-comparison of depth dose distributions among those obtained from the MCNPX, GEANT4 and FLUKA codes for a 160 MeV monoenergetic proton beam incident normally on the surface of a homogeneous water phantom was performed. For dose validation within the CT phantom, direct comparison with measurement is infeasible. Instead, this study took the approach to indirectly compare the 50% ranges (R50%) along the central axis by our system to the NIST CSDA ranges for beams with 160 and 115 MeV energies. Comparison result within the homogeneous phantom shows good agreement. Differences of simulated R50% among the three codes are less than 1 mm. For results within the CT phantom, the MCNPX simulated water equivalent Req,50% are compatible with the CSDA water equivalent ranges from the NIST database with differences of 0.7 and 4.1 mm for 160 and 115 MeV beams, respectively.

FT-IR and Raman spectra, DFT and SQMFF calculations for geometrical interpretation and vibrational analysis of 3-nitro-p-toluic acid

NASA Astrophysics Data System (ADS)

Nataraj, A.; Balachandran, V.; Karthick, T.

2012-08-01

The Fourier transform infrared (FT-IR) and FT-Raman of 3-nitro-p-toluic acid (NTA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been investigated with the help of ab initio and density functional theory (DFT) methods. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The optimized geometric bond lengths and bond angles obtained by computation show good agreement with experimental data of the relative compound. The computed dimer parameters also show good agreement with experimental data. The first hyperpolarizability (β0) of this noval molecular system and related properties (β, α0, and Δα) of NTA are calculated using B3LYP/6-311++G(d,p) method on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* antibonding orbital and second order delocalization energies E(2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The calculated HOMO and LUMO energies also show that charge transfer occurs within the molecule. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.

Impact of Biomass Burning Aerosols on Cloud Formation in Coastal Regions

NASA Astrophysics Data System (ADS)

Nair, U. S.; Wu, Y.; Reid, J. S.

2017-12-01

In the tropics, shallow and deep convective cloud structures organize in hierarchy of spatial scales ranging from meso-gamma (2-20 km) to planetary scales (40,000km). At the lower end of the spectrum is shallow convection over the open ocean, whose upscale growth is dependent upon mesoscale convergence triggers. In this context, cloud systems associated with land breezes that propagate long distances into open ocean areas are important. We utilized numerical model simulations to examine the impact of biomass burning on such cloud systems in the maritime continent, specifically along the coastal regions of Sarawak. Numerical model simulations conducted using the Weather Research and Forecasting Chemistry (WRF-Chem) model show spatial patterns of smoke that show good agreement to satellite observations. Analysis of model simulations show that, during daytime the horizontal convective rolls (HCRs) that form over land play an important role in organizing transport of smoke in the coastal regions. Alternating patterns of low and high smoke concentrations that are well correlated to the wavelengths of HCRs are found in both the simulations and satellite observations. During night time, smoke transport is modulated by the land breeze circulation and a band of enhanced smoke concentration is found along the land breeze front. Biomass burning aerosols are ingested by the convective clouds that form along the land breeze and leads to changes in total water path, cloud structure and precipitation formation.

Combining simulated patients and simulators: pilot study of hybrid simulation in teaching cardiac auscultation.

PubMed

Friederichs, Hendrik; Weissenstein, Anne; Ligges, Sandra; Möller, David; Becker, Jan C; Marschall, Bernhard

2014-12-01

Auscultation torsos are widely used to teach position-dependent heart sounds and murmurs. To provide a more realistic teaching experience, both whole body auscultation mannequins and torsos have been used in clinical examination skills training at the Medical Faculty of the University of Muenster since the winter term of 2008-2009. This training has since been extended by simulated patients, which are normal, healthy subjects who have undergone attachment of the electronic components of the auscultation mannequins to their chests to mimic pathophysiological conditions ("hybrid models"). The acceptance of this new learning method was examined in the present pilot study. In total, 143 students in their second preclinical year who were participating in auscultation training were randomized into an intervention group (hybrid models) and a control group (auscultation mannequins). One hundred forty-two (99.3%) of these students completed a self-assessment Likert-scale questionnaire regarding different teaching approaches (where 1 = "very poor" to 100 = "very good"). The questionnaire focused on the "value of learning" of different teaching approaches. Direct comparison showed that students evaluated the hybrid models to be significantly more effective than the auscultation mannequins (median: 83 vs. 64, P < 0.001). The cardiac auscultation training was generally assessed positively (median: 88). Additionally, verbal feedback was obtained from simulated patients and tutors (trained students who had successfully passed the course a few semesters earlier). Personal feedback showed high satisfaction from student tutors and simulated patients. Hybrid simulators for teaching cardiac auscultation elucidated positive responses from students, tutors, and simulated patients. Copyright © 2014 The American Physiological Society.

A CellML simulation compiler and code generator using ODE solving schemes

PubMed Central

2012-01-01

Models written in description languages such as CellML are becoming a popular solution to the handling of complex cellular physiological models in biological function simulations. However, in order to fully simulate a model, boundary conditions and ordinary differential equation (ODE) solving schemes have to be combined with it. Though boundary conditions can be described in CellML, it is difficult to explicitly specify ODE solving schemes using existing tools. In this study, we define an ODE solving scheme description language-based on XML and propose a code generation system for biological function simulations. In the proposed system, biological simulation programs using various ODE solving schemes can be easily generated. We designed a two-stage approach where the system generates the equation set associating the physiological model variable values at a certain time t with values at t + Δt in the first stage. The second stage generates the simulation code for the model. This approach enables the flexible construction of code generation modules that can support complex sets of formulas. We evaluate the relationship between models and their calculation accuracies by simulating complex biological models using various ODE solving schemes. Using the FHN model simulation, results showed good qualitative and quantitative correspondence with the theoretical predictions. Results for the Luo-Rudy 1991 model showed that only first order precision was achieved. In addition, running the generated code in parallel on a GPU made it possible to speed up the calculation time by a factor of 50. The CellML Compiler source code is available for download at http://sourceforge.net/projects/cellmlcompiler. PMID:23083065

Simulation of earthquake ground motions in the eastern United States using deterministic physics‐based and site‐based stochastic approaches

USGS Publications Warehouse

Rezaeian, Sanaz; Hartzell, Stephen; Sun, Xiaodan; Mendoza, Carlos

2017-01-01

Earthquake ground‐motion recordings are scarce in the central and eastern United States (CEUS) for large‐magnitude events and at close distances. We use two different simulation approaches, a deterministic physics‐based method and a site‐based stochastic method, to simulate ground motions over a wide range of magnitudes. Drawing on previous results for the modeling of recordings from the 2011 Mw 5.8 Mineral, Virginia, earthquake and using the 2001 Mw 7.6 Bhuj, India, earthquake as a tectonic analog for a large magnitude CEUS event, we are able to calibrate the two simulation methods over this magnitude range. Both models show a good fit to the Mineral and Bhuj observations from 0.1 to 10 Hz. Model parameters are then adjusted to obtain simulations for Mw 6.5, 7.0, and 7.6 events in the CEUS. Our simulations are compared with the 2014 U.S. Geological Survey weighted combination of existing ground‐motion prediction equations in the CEUS. The physics‐based simulations show comparable response spectral amplitudes and a fairly similar attenuation with distance. The site‐based stochastic simulations suggest a slightly faster attenuation of the response spectral amplitudes with distance for larger magnitude events and, as a result, slightly lower amplitudes at distances greater than 200 km. Both models are plausible alternatives and, given the few available data points in the CEUS, can be used to represent the epistemic uncertainty in modeling of postulated CEUS large‐magnitude events.

Computational Aerodynamic Simulations of an 840 ft/sec Tip Speed Advanced Ducted Propulsor Fan System Model for Acoustic Methods Assessment and Development

NASA Technical Reports Server (NTRS)

Tweedt, Daniel L.

2014-01-01

Computational Aerodynamic simulations of an 840 ft/sec tip speed, Advanced Ducted Propulsor fan system were performed at five different operating points on the fan operating line, in order to provide detailed internal flow field information for use with fan acoustic prediction methods presently being developed, assessed and validated. The fan system is a sub-scale, lownoise research fan/nacelle model that has undergone extensive experimental testing in the 9- by 15- foot Low Speed Wind Tunnel at the NASA Glenn Research Center, resulting in quality, detailed aerodynamic and acoustic measurement data. Details of the fan geometry, the computational fluid dynamics methods, the computational grids, and various computational parameters relevant to the numerical simulations are discussed. Flow field results for three of the five operating conditions simulated are presented in order to provide a representative look at the computed solutions. Each of the five fan aerodynamic simulations involved the entire fan system, excluding a long core duct section downstream of the core inlet guide vane. As a result, only fan rotational speed and system bypass ratio, set by specifying static pressure downstream of the core inlet guide vane row, were adjusted in order to set the fan operating point, leading to operating points that lie on a fan operating line and making mass flow rate a fully dependent parameter. The resulting mass flow rates are in good agreement with measurement values. The computed blade row flow fields for all five fan operating points are, in general, aerodynamically healthy. Rotor blade and fan exit guide vane flow characteristics are good, including incidence and deviation angles, chordwise static pressure distributions, blade surface boundary layers, secondary flow structures, and blade wakes. Examination of the computed flow fields reveals no excessive boundary layer separations or related secondary-flow problems. A few spanwise comparisons between computational and measurement data in the bypass duct show that they are in good agreement, thus providing a partial validation of the computational results.

From Simulation to Real Robots with Predictable Results: Methods and Examples

NASA Astrophysics Data System (ADS)

Balakirsky, S.; Carpin, S.; Dimitoglou, G.; Balaguer, B.

From a theoretical perspective, one may easily argue (as we will in this chapter) that simulation accelerates the algorithm development cycle. However, in practice many in the robotics development community share the sentiment that “Simulation is doomed to succeed” (Brooks, R., Matarić, M., Robot Learning, Kluwer Academic Press, Hingham, MA, 1993, p. 209). This comes in large part from the fact that many simulation systems are brittle; they do a fair-to-good job of simulating the expected, and fail to simulate the unexpected. It is the authors' belief that a simulation system is only as good as its models, and that deficiencies in these models lead to the majority of these failures. This chapter will attempt to address these deficiencies by presenting a systematic methodology with examples for the development of both simulated mobility models and sensor models for use with one of today's leading simulation engines. Techniques for using simulation for algorithm development leading to real-robot implementation will be presented, as well as opportunities for involvement in international robotics competitions based on these techniques.

Progress in the development of an H{sup −} ion source for cyclotrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Etoh, H., E-mail: Hrh-Etoh@shi.co.jp; Aoki, Y.; Mitsubori, H.

2015-04-08

A multi-cusp DC H{sup −} ion source has been developed for cyclotrons in medical use. Beam optics of the H{sup −} ion beam is studied using a 2D beam trajectory code. The simulation results are compared with the experimental results obtained in the Mark I source, which has produced up to 16 mA H{sup −} ion beams. The optimum extraction voltages show good agreement between the calculation and the experimental results. A new ion source, Mark II source, is designed to achieve the next goal of producing an H{sup −} beam of 20 mA. The magnetic field configurations and the plasma electrodemore » design are optimized for Cs-seeded operation. Primary electron trajectory simulation shows that primary electrons are confined well and the magnetic filter prevents the primary electrons from entering into the extraction region.« less

Computational Analysis on Performance of Thermal Energy Storage (TES) Diffuser

NASA Astrophysics Data System (ADS)

Adib, M. A. H. M.; Adnan, F.; Ismail, A. R.; Kardigama, K.; Salaam, H. A.; Ahmad, Z.; Johari, N. H.; Anuar, Z.; Azmi, N. S. N.

2012-09-01

Application of thermal energy storage (TES) system reduces cost and energy consumption. The performance of the overall operation is affected by diffuser design. In this study, computational analysis is used to determine the thermocline thickness. Three dimensional simulations with different tank height-to-diameter ratio (HD), diffuser opening and the effect of difference number of diffuser holes are investigated. Medium HD tanks simulations with double ring octagonal diffuser show good thermocline behavior and clear distinction between warm and cold water. The result show, the best performance of thermocline thickness during 50% time charging occur in medium tank with height-to-diameter ratio of 4.0 and double ring octagonal diffuser with 48 holes (9mm opening ~ 60%) acceptable compared to diffuser with 6mm ~ 40% and 12mm ~ 80% opening. The conclusion is computational analysis method are very useful in the study on performance of thermal energy storage (TES).

Investigation of Electric and Self-Generated Magnetic Fields in Implosion Experiments on OMEGA

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.; Nilson, P. M.; Goncharov, V. N.; Li, C. K.; Zylstra, A. B.; Petrasso, R. D.

2013-10-01

Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA laser were investigated using proton radiography. The experiments use plastic-shell targets with various surface defects (glue spot, wire, and stalk mount) to seed perturbations and generate localized electromagnetic fields at the ablation surface and in the plasma corona surrounding the targets. Proton radiographs show features from these perturbations and quasi-spherical multiple shell structures around the capsules at earlier times of implosions (up to ~700 ps for a 1-ns laser pulse) indicating the development of the fields. Two-dimensional magnetohydrodynamic simulations of these experiments predict the growth of magnetic fields up to several MG. The simulated distributions of electromagnetic fields were used to produce proton images, which show good agreement with experimental radiographs. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Monte Carlo derivation of filtered tungsten anode X-ray spectra for dose computation in digital mammography.

PubMed

Paixão, Lucas; Oliveira, Bruno Beraldo; Viloria, Carolina; de Oliveira, Marcio Alves; Teixeira, Maria Helena Araújo; Nogueira, Maria do Socorro

2015-01-01

Derive filtered tungsten X-ray spectra used in digital mammography systems by means of Monte Carlo simulations. Filtered spectra for rhodium filter were obtained for tube potentials between 26 and 32 kV. The half-value layer (HVL) of simulated filtered spectra were compared with those obtained experimentally with a solid state detector Unfors model 8202031-H Xi R/F & MAM Detector Platinum and 8201023-C Xi Base unit Platinum Plus w mAs in a Hologic Selenia Dimensions system using a direct radiography mode. Calculated HVL values showed good agreement as compared with those obtained experimentally. The greatest relative difference between the Monte Carlo calculated HVL values and experimental HVL values was 4%. The results show that the filtered tungsten anode X-ray spectra and the EGSnrc Monte Carlo code can be used for mean glandular dose determination in mammography.

Cooperative Monocular-Based SLAM for Multi-UAV Systems in GPS-Denied Environments †

PubMed Central

Guerra, Edmundo

2018-01-01

This work presents a cooperative monocular-based SLAM approach for multi-UAV systems that can operate in GPS-denied environments. The main contribution of the work is to show that, using visual information obtained from monocular cameras mounted onboard aerial vehicles flying in formation, the observability properties of the whole system are improved. This fact is especially notorious when compared with other related visual SLAM configurations. In order to improve the observability properties, some measurements of the relative distance between the UAVs are included in the system. These relative distances are also obtained from visual information. The proposed approach is theoretically validated by means of a nonlinear observability analysis. Furthermore, an extensive set of computer simulations is presented in order to validate the proposed approach. The numerical simulation results show that the proposed system is able to provide a good position and orientation estimation of the aerial vehicles flying in formation. PMID:29701722