Aerothermal modeling. Executive summary
NASA Technical Reports Server (NTRS)
Kenworthy, M. K.; Correa, S. M.; Burrus, D. L.
1983-01-01
One of the significant ways in which the performance level of aircraft turbine engines has been improved is by the use of advanced materials and cooling concepts that allow a significant increase in turbine inlet temperature level, with attendant thermodynamic cycle benefits. Further cycle improvements have been achieved with higher pressure ratio compressors. The higher turbine inlet temperatures and compressor pressure ratios with corresponding higher temperature cooling air has created a very hostile environment for the hot section components. To provide the technology needed to reduce the hot section maintenance costs, NASA has initiated the Hot Section Technology (HOST) program. One key element of this overall program is the Aerothermal Modeling Program. The overall objective of his program is to evolve and validate improved analysis methods for use in the design of aircraft turbine engine combustors. The use of such combustor analysis capabilities can be expected to provide significant improvement in the life and durability characteristics of both combustor and turbine components.
Aerothermal modeling program, phase 1
NASA Technical Reports Server (NTRS)
Srinivasan, R.; Reynolds, R.; Ball, I.; Berry, R.; Johnson, K.; Mongia, H.
1983-01-01
Aerothermal submodels used in analytical combustor models are analyzed. The models described include turbulence and scalar transport, gaseous full combustion, spray evaporation/combustion, soot formation and oxidation, and radiation. The computational scheme is discussed in relation to boundary conditions and convergence criteria. Also presented is the data base for benchmark quality test cases and an analysis of simple flows.
Aerothermal modeling program, phase 1
NASA Technical Reports Server (NTRS)
Sturgess, G. J.
1983-01-01
The physical modeling embodied in the computational fluid dynamics codes is discussed. The objectives were to identify shortcomings in the models and to provide a program plan to improve the quantitative accuracy. The physical models studied were for: turbulent mass and momentum transport, heat release, liquid fuel spray, and gaseous radiation. The approach adopted was to test the models against appropriate benchmark-quality test cases from experiments in the literature for the constituent flows that together make up the combustor real flow.
Aerothermal modeling program, phase 1
NASA Technical Reports Server (NTRS)
Srinivasan, R.; Reynolds, R.; Ball, I.; Berry, R.; Johnson, K.; Mongia, H.
1983-01-01
The combustor performance submodels for complex flows are evaluated. The benchmark test cases for complex nonswirling flows are identified and analyzed. The introduction of swirl into the flow creates much faster mixing, caused by radial pressure gradients and increase in turbulence generation. These phenomena are more difficult to predict than the effects due to geometrical streamline curvatures, like the curved duct, and sudden expansion. Flow fields with swirl, both confined and unconfined are studied. The role of the dilution zone to achieve the turbine inlet radial profile plays an important part, therefore temperature field measurements were made in several idealized dilution zone configurations.
NASA Astrophysics Data System (ADS)
Xu, Bo; Li, Lin; Zhu, Ying
2014-11-01
Researches on hypersonic vehicles have been a hotspot in the field of aerospace because of the pursuits for higher speed by human being. Infrared imaging guidance is playing a very important role in modern warfare. When an Infrared Ray(IR) imaging guided missile is flying in the air at high speed, its optical dome suffers from serious aero-optic effects because of air flow. The turbulence around the dome and the thermal effects of the optical window would cause disturbance to the wavefront from the target. Therefore, detected images will be biased, dithered and blurred, and the capabilities of the seeker for detecting, tracking and recognizing are weakened. In this paper, methods for thermal and structural analysis with Heat Transfer and Elastic Mechanics are introduced. By studying the aero-thermal effects and aero-thermal radiation effects of the optical window, a 3D analysis model of the optical window is established by using finite element method. The direct coupling analysis is employed as a solving strategy. The variation regularity of the temperature field is obtained. For light with different incident angles, the influence on the ray propagation caused by window deformation is analyzed with theoretical calculation and optical/thermal/structural integrated analysis method respectively.
Aerothermal modeling, phase 1. Volume 1: Model assessment
NASA Technical Reports Server (NTRS)
Kenworthy, M. J.; Correa, S. M.; Burrus, D. L.
1983-01-01
Phase 1 was conducted as part of the overall NASA Hot Section Technology (HOST) Program. The purpose of this effort was to determine the predictive accuracy of and the deficiencies within the various analytical modules comprising the overall combustor aerothermal model used at General Electric, as well as to formulate recommendations for improvement where needed. This effort involved the assembly of a benchmark quality data base from selected available literature, and from General Electric engine and combustor component test data. This data base was supplemented with additional definitive data obtained from an experimental test program conducted as part of the Phase 1 effort. Using selections from this data base, assessment studies were conducted to evaluate the various modules. Assessment of the internal flow module was conducted using 2-D parabolic and ellipitic, as well as 3-D elliptic internal flow calculations of definitive test data selected from the assembled data base. The 2-D assessment provided methodical examination of the mathematical techniques and the physical submodules, while the 3-D assessment focused on usefulness as a design tool. Calculations of combustor linear metal temperatures, pressure loss performance, and airflow distribution were performed using aerothermal modules which were in general use for many years at General Electric. The results of these assessment provided for the identification of deficiencies within the modules. The deficiencies were addressed in some detail providing a foundation on which to formulate a prioritized list of recommendations for improvement.
A Review of Aerothermal Modeling for Mars Entry Missions
NASA Technical Reports Server (NTRS)
Wright, Michael J; Tang, Chun Y.; Edquist, Karl T.; Hollis, Brian R.; Krasa, Paul
2009-01-01
The current status of aerothermal analysis for Mars entry missions is reviewed. The aeroheating environment of all Mars missions to date has been dominated by convective heating. Two primary uncertainties in our ability to predict forebody convective heating are turbulence on a blunt lifting cone and surface catalysis in a predominantly CO2 environment. Future missions, particularly crewed vehicles, will encounter additional heating from shock-layer radiation due to a combination of larger size and faster entry velocity. Localized heating due to penetrations or other singularities on the aeroshell must also be taken into account. The physical models employed to predict these phenomena are reviewed, and key uncertainties or deficiencies inherent in these models are explored. Capabilities of existing ground test facilities to support aeroheating validation are also summarized. Engineering flight data from the Viking and Pathfinder missions, which may be useful for aerothermal model validation, are discussed, and an argument is presented for obtaining additional flight data. Examples are taken from past, present, and future Mars entry missions, including the twin Mars Exploration Rovers and the Mars Science Laboratory, scheduled for launch by NASA in 2011.
Assessment, development and application of combustor aerothermal models
NASA Technical Reports Server (NTRS)
Holdeman, J. D.; Mongia, H. C.; Mularz, E. J.
1988-01-01
The gas turbine combustion system design and development effort is an engineering exercise to obtain an acceptable solution to the conflicting design trade-offs between combustion efficiency, gaseous emissions, smoke, ignition, restart, lean blowout, burner exit temperature quality, structural durability, and life cycle cost. For many years, these combustor design trade-offs have been carried out with the help of fundamental reasoning and extensive component and bench testing, backed by empirical and experience correlations. Recent advances in the capability of computational fluid dynamics codes have led to their application to complex 3-D flows such as those in the gas turbine combustor. A number of U.S. Government and industry sponsored programs have made significant contributions to the formulation, development, and verification of an analytical combustor design methodology which will better define the aerothermal loads in a combustor, and be a valuable tool for design of future combustion systems. The contributions made by NASA Hot Section Technology (HOST) sponsored Aerothermal Modeling and supporting programs are described.
Methodology for the Assessment of 3D Conduction Effects in an Aerothermal Wind Tunnel Test
NASA Technical Reports Server (NTRS)
Oliver, Anthony Brandon
2010-01-01
This slide presentation reviews a method for the assessment of three-dimensional conduction effects during test in a Aerothermal Wind Tunnel. The test objectives were to duplicate and extend tests that were performed during the 1960's on thermal conduction on proturberance on a flat plate. Slides review the 1D versus 3D conduction data reduction error, the analysis process, CFD-based analysis, loose coupling method that simulates a wind tunnel test run, verification of the CFD solution, Grid convergence, Mach number trend, size trends, and a Sumary of the CFD conduction analysis. Other slides show comparisons to pretest CFD at Mach 1.5 and 2.16 and the geometries of the models and grids.
Flow interaction experiment. Volume 1: Aerothermal modeling, phase 2
NASA Technical Reports Server (NTRS)
Nikjooy, M.; Mongia, H. C.; Sullivan, J. P.; Murthy, S. N. B.
1993-01-01
An experimental and computational study is reported for the flow of a turbulent jet discharging into a rectangular enclosure. The experimental configurations consisting of primary jets only, annular jets only, and a combination of annular and primary jets are investigated to provide a better understanding of the flow field in an annular combustor. A laser Doppler velocimeter is used to measure mean velocity and Reynolds stress components. Major features of the flow field include recirculation, primary and annular jet interaction, and high turbulence. A significant result from this study is the effect the primary jets have on the flow field. The primary jets are seen to create statistically larger recirculation zones and higher turbulence levels. In addition, a technique called marker nephelometry is used to provide mean concentration values in the model combustor. Computations are performed using three levels of turbulence closures, namely k-epsilon model, algebraic second moment (ASM), and differential second moment (DSM) closure. Two different numerical schemes are applied. One is the lower-order power-law differencing scheme (PLDS) and the other is the higher-order flux-spline differencing scheme (FSDS). A comparison is made of the performance of these schemes. The numerical results are compared with experimental data. For the cases considered in this study, the FSDS is more accurate than the PLDS. For a prescribed accuracy, the flux-spline scheme requires a far fewer number of grid points. Thus, it has the potential for providing a numerical error-free solution, especially for three-dimensional flows, without requiring an excessively fine grid. Although qualitatively good comparison with data was obtained, the deficiencies regarding the modeled dissipation rate (epsilon) equation, pressure-strain correlation model, and the inlet epsilon profile and other critical closure issues need to be resolved before one can achieve the degree of accuracy required to
Flow interaction experiment. Volume 2: Aerothermal modeling, phase 2
NASA Technical Reports Server (NTRS)
Nikjooy, M.; Mongia, H. C.; Sullivan, J. P.; Murthy, S. N. B.
1993-01-01
An experimental and computational study is reported for the flow of a turbulent jet discharging into a rectangular enclosure. The experimental configurations consisting of primary jets only, annular jets only, and a combination of annular and primary jets are investigated to provide a better understanding of the flow field in an annular combustor. A laser Doppler velocimeter is used to measure mean velocity and Reynolds stress components. Major features of the flow field include recirculation, primary and annular jet interaction, and high turbulence. A significant result from this study is the effect the primary jets have on the flow field. The primary jets are seen to create statistically larger recirculation zones and higher turbulence levels. In addition, a technique called marker nephelometry is used to provide mean concentration values in the model combustor. Computations are performed using three levels of turbulence closures, namely k-epsilon model, algebraic second moment (ASM), and differential second moment (DSM) closure. Two different numerical schemes are applied. One is the lower-order power-law differencing scheme (PLDS) and the other is the higher-order flux-spline differencing scheme (FSDS). A comparison is made of the performance of these schemes. The numerical results are compared with experimental data. For the cases considered in this study, the FSDS is more accurate than the PLDS. For a prescribed accuracy, the flux-spline scheme requires a far fewer number of grid points. Thus, it has the potential for providing a numerical error-free solution, especially for three-dimensional flows, without requiring an excessively fine grid. Although qualitatively good comparison with data was obtained, the deficiencies regarding the modeled dissipation rate (epsilon) equation, pressure-strain correlation model, and the inlet epsilon profile and other critical closure issues need to be resolved before one can achieve the degree of accuracy required to
Aerothermal Considerations for Entry, Descent, and Landing
NASA Technical Reports Server (NTRS)
Tang, Chun
2015-01-01
Aerothermal modeling is inherently entwined with TPS design. Aerothermal, radiation, and TPS material response are coupled so it's important to check modeling assumptions. Validation of numerical models using ground and flight tests is important to quantify uncertainties. A margin policy based on statistical methods may provide greater insight in the key drivers and overall reliability of the design
Transient aero-thermal simulations for TMT
NASA Astrophysics Data System (ADS)
Vogiatzis, Konstantinos
2014-08-01
Aero-thermal simulations are an integral part of the design process for the Thirty Meter Telescope (TMT). These simulations utilize Computational Solid-Fluid Dynamics (CSFD) to estimate wind jitter and blur, dome and mirror seeing, telescope pointing error due to thermal drift, and to predict thermal effects on performance of components such as the primary mirror segments. Design guidance obtained from these simulations is provided to the Telescope, Enclosure, Facilities and Adaptive Optics groups. Computational advances allow for model enhancements and inclusion of phenomena not previously resolved, such as transient effects on wind loading and thermal seeing due to vent operation while observing or long exposure effects, with potentially different flow patterns corresponding to the beginning and end of observation. Accurate knowledge of the Observatory aero-thermal environment will result in developing reliable look-up tables for effective open loop correction of key active optics system elements, and cost efficient operation of the Observatory.
Advanced Models for Prediction of High Altitude Aero-Thermal Loads of a Space Re-entry Vehicle
NASA Astrophysics Data System (ADS)
Votta, R.; Schettino, A.; Bonfiglioli, A.
2011-05-01
The analysis of the rarefaction effects in predicting the main aero-thermal loads of a Space re-entry vehicle is presented. It is well known that the Navier-Stokes equations fail in rarefied regimes and other approaches must be used. In the present paper different configurations have been simulated by using the Direct Simulation Monte Carlo method. Moreover, slip flow boundary conditions have been implemented in a Navier-Stokes code in order to extend the validity of the continuum approach to the transitional flow regime. Finally, bridging formulas for high altitude aerodynamics of winged bodies have been used. Firstly, two simple geometries have been analysed, specifically designed to study the phenomenon of shock wave boundary layer interaction: a hollow cylinder flare, for which some experiments are available; and a blunt-nosed flat plate/flap model designed and tested at the Italian Aerospace Research Centre. The other configurations taken into account are, respectively, an experimental winged re-entry vehicle and a capsule, for which global aerodynamic coefficients and local wall heating have been determined with different approaches. The Navier-Stokes code with slip flow boundary conditions has shown good predicting capabilities compared with experiments in the hollow cylinder flare case; however, for the winged vehicle and capsule cases, the CFD results are not fully satisfactory and the Monte Carlo method remains the most reliable approach, together with the bridging formula, that provides good results for the aerodynamic coefficients.
NASA Technical Reports Server (NTRS)
Tang, Chun; Muppidi, Suman; Bose, Deepak; Van Norman, John W.; Tanimoto, Rebekah; Clark, Ian
2015-01-01
NASA's Low Density Supersonic Decelerator Program is developing new technologies that will enable the landing of heavier payloads in low density environments, such as Mars. A recent flight experiment conducted high above the Hawaiian Islands has demonstrated the performance of several decelerator technologies. In particular, the deployment of the Robotic class Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) was highly successful, and valuable data were collected during the test flight. This paper outlines the Computational Fluid Dynamics (CFD) analysis used to estimate the aerodynamic and aerothermal characteristics of the SIAD-R. Pre-flight and post-flight predictions are compared with the flight data, and a very good agreement in aerodynamic force and moment coefficients is observed between the CFD solutions and the reconstructed flight data.
Aerothermal tests of quilted dome models on a flat plate at a Mach number of 6.5
NASA Technical Reports Server (NTRS)
Glass, Christopher E.; Hunt, L. Roane
1988-01-01
Aerothermal tests were conducted in the NASA Langley 8 Foot High Temperature Tunnel (8'HTT) at a Mach number of 6.5 on simulated arrays of thermally bowed metallic thermal protection system (TPS) tiles at an angle of attack of 5 deg. Detailed surface pressures and heating rates were obtained for arrays aligned with the flow and skewed 45 deg diagonally to the flow with nominal bowed heights of 0.1, 0.2, and 0.4 inch submerged in both laminar and turbulent boundary layers. Aerothermal tests were made at a nominal total temperature of 3300 R, a total pressure of 400 psia, a total enthalpy of 950 Btu/lbm, a dynamic pressure of 2.7 psi, and a unit Reynolds number of 400,000 per foot. The experimental results form a data base that can be used to help protect aerothermal load increases from bowed arrays of TPS tiles.
Application of CFD to aerothermal heating problems
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.
1986-01-01
Numerical solutions of the compressible Navier-Stokes equations by an Alternating Direction Implicit scheme, applied to two experimental investigations at NASA Langley Research Center are presented. The first is cooling by injection of a gas jet through the nose of an ogive-cone, and the second is the aerothermal environment in the gap formed by the wing and elevon section of a test model of the Space Shuttle. The simulations demonstrate that accurate pressure calculations are easily obtained on a coarse grid, witih convergence being obtained after the residual reduces by four orders of magnitude. However, accurate heating rates require a fine grid solution, with convergence requiring at least a reduction of six orders of magnitude in the residual. The effect of artificial dissipation on numerical results is also assessed.
Application of CFD to aerothermal heating problems
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.
1986-01-01
Numerical solutions of the compressible Navier-Stokes equations by an alternating direction implicit scheme, applied to two experimental investigations are presented. The first is cooling by injection of a gas jet through the nose of an ogive-cone, and the second is the aerothermal environment in the gap formed by the wing and elevon section of a test model of the space shuttle. The simulations demonstrate that accurate pressure calculations are easily obtained on a coarse grid, while convergence is obtained after the residual reduces by four orders of magnitude. Accurate heating rates, however, require a fine grid solution, with convergence requiring at least a reduction of six orders of magnitude in the residual. The effect of artificial dissipation on numerical results is also assessed.
Computation and modeling of aero-thermal fields in turbine cascades and strongly curved ducts
NASA Technical Reports Server (NTRS)
Luo, J.; Lakshminarayana, B.
1994-01-01
Advanced turbulence models are crucial for accurate prediction of rocket engine flows, due to existence of very large extra strain rates, such as strong streamline curvature. Numerical simulation of the turbulent flow in a strongly curved turn-around duct (TAD) has been carried out with a Reynolds stress model (RSM), an algebraic Reynolds stress model (ARSM) and a kappa-epsilon model. the RSM model and the ARSM model are found to capture the turbulence damping due to the convex curvature, but underpredict the turbulence enhancement caused by the concave curvature. To capture the concave curvature effects, it is necessary to modify the epsilon-equation. The modification of episilon-equation suggested by Launder, et.al, provides the correct trend, but over-corrects the curvature effects. A comparative study of two modes of transition in gas turbine, the by-pass transition and the separation-induced transition, has been carried out with several low-Reynolds-number (LRN) kappa-epsilon models. Effects of blade surface pressure gradient, freestream turbulence and Reynolds number on the blade boundary layer development, and particularly the inception of transition are examined in detail. The present study indicates that the turbine blade transition, in the presence of high freestream turbulence, is predicted well with LRN kappa-epsilon models employed.
LSST summit enclosure-facility design optimization using aero-thermal modeling
NASA Astrophysics Data System (ADS)
Sebag, J.; Vogiatzis, K.; Barr, J.; Neill, D.
2012-09-01
This paper describes Computational Fluid Dynamic (CFD) analyses combined with thermal analyses for modeling the effects of passive ventilation, enclosure-building configuration and topography on the optical performance of the Large Synoptic Survey Telescope (LSST). The primary purpose of the analyses was to evaluate the seeing contribution of the major enclosure-facility elements and to select the features to be adopted in the baseline design from among various configurations being explored by the LSST project and the contracted architectural design team. In addition, one of several simulations for different telescope orientations is presented including various wind-telescope relative azimuth angles. Using a post-processing analysis, the effects of turbulence and thermal variations within the airflow around the buildings and inside the telescope-enclosure configuration were determined, and the optical performance due to the thermal seeing along the optical path was calculated.
Fuel injector: Air swirl characterization aerothermal modeling, phase 2, volume 1
NASA Technical Reports Server (NTRS)
Nikjooy, M.; Mongia, H. C.; Mcdonell, V. G.; Samuelsen, G. S.
1993-01-01
A well integrated experimental/analytical investigation was conducted to provide benchmark quality relevant to a prefilming type airblast fuel nozzle and its interaction with the combustor dome air swirler. The experimental investigation included a systematic study of both single-phase flows that involved single and twin co-axial jets with and without swirl. A two-component Phase Doppler Particle Analyzer (PDPA) was used to document the interaction of single and co-axial air jets with glass beads that simulate nonevaporating spray and simultaneously avoid the complexities associated with fuel atomization processes and attendant issues about the specification of relevant boundary conditions. The interaction of jets with methanol spray produced by practical airblast nozzle was also documented in the spatial domain of practical interest. Model assessment activities included the use of three turbulence models (k-epsilon, algebraic second moment (ASM), and differential second moment (DSM)) for the carrier phase, deterministic or stochastic Lagrangian treatment of the dispersed phase, and advanced numerical schemes. Although qualitatively good comparison with data was obtained for most of the cases investigated, the model deficiencies in regard to modeled dissipation rate transport equation, single length scale, pressure-strain correlation, and other critical closure issues need to be resolved before one can achieve the degree of accuracy required to analytically design combustion systems.
Fuel Injector: Air swirl characterization aerothermal modeling, phase 2, volume 2
NASA Technical Reports Server (NTRS)
Nikjooy, M.; Mongia, H. C.; Mcdonell, V. G.; Samuelson, G. S.
1993-01-01
A well integrated experimental/analytical investigation was conducted to provide benchmark quality data relevant to prefilming type airblast fuel nozzle and its interaction with combustor dome air swirler. The experimental investigation included a systematic study of both single-phase flows that involved single and twin co-axial jets with and without swirl. A two-component Phase Doppler Particle Analyzer (PDPA) equipment was used to document the interaction of single and co-axial air jets with glass beads that simulate nonevaporating spray and simultaneously avoid the complexities associated with fuel atomization processes and attendant issues about the specification of relevant boundary conditions. The interaction of jets with methanol spray produced by practical airblast nozzle was also documented in the spatial domain of practical interest. Model assessment activities included the use of three turbulence models (k-epsilon, algebraic second moment (ASM) and differential second moment (DSM)) for the carrier phase, deterministic or stochastic Lagrangian treatment of the dispersed phase, and advanced numerical schemes. Although qualitatively good comparison with data was obtained for most of the cases investigated, the model deficiencies in regard to modeled dissipation rate transport equation, single length scale, pressure-strain correlation, and other critical closure issues need to be resolved before one can achieve the degree of accuracy required to analytically design combustion systems.
EFT-1 Heatshield Aerothermal Environment Reconstruction
NASA Technical Reports Server (NTRS)
Oliver, A. Brandon; Amar, Adam J.; Droba, Justin; Lessard, Victor; Mahzari, Milad
2016-01-01
The EFT-1 Avcoat heatshield was instrumented with 34 plugs containing multiple thermocouples in-depth with an objective being to measure the flight aerothermal environment. This paper presents a discussion of the instrumentation and the techniques used to reconstruct the heating environment from the measured in-depth temperatures. The inverse heat transfer problem algorithms, models and assumptions will be outlined, and available results will be presented.
Aerothermal Effects of Cavities and Protuberances for High-Speed Sample Return Capsules
NASA Technical Reports Server (NTRS)
Olynick, David; Kontinos, Dean; Arnold, James O. (Technical Monitor)
1998-01-01
Extraterrestrial sample return is a growing component of solar system exploration. Currently, four missions, Stardust, 1 Muses-C, 2 Genesis, and Mars Sample Return, are under development that employ sample return as a prime component of the mission architecture. Respectively, these missions will return samples from the tail of a comet, an asteroid, the solar wind, and, Mars. An important component of these missions and the focus of this paper is the design of the sample return capsule (SRC). The purpose of the SRC is to safely return to Earth any gathered samples for terrestrial analysis. The two major design constraints for any SRC are as follows: 1) it must be able to survive a high-speed Earth entry (11 km/s to as a high as 15 km/s), 2) the mass of the SRC must be as small as possible. Because the SRC mass is carried from Earth to the sample sight and back, the SRC mass is a strong driver in the mission mass budget. Further, for the Mars Sample Return Capsule, planetary protection is another constraint. For this capsule, the probability of planetary contamination at Earth due to an SRC failure at entry must be minimal. For an SRC, a possible failure mechanism is severe local heating as a result of cavities and or protuberances in the SRC forebody heatshield. For example, the Apollo Command Module had a number of cavities and protuberances as part of the baseline designs Wind-tunnel tests of models containing small cavities and protuberances showed severe local heating augmentations in the vicinity of these surface discontinuities.4-5 As another example, the Genesis SRC forebody heat-shield contains penetrations (cavities) to mount the vehicle to the carrier bus. It is expected that these penetrations will also experience a severe local heating environment. A concern is that the large thermal gradients may produce sufficient thermal stress to cause local mechanical failure of the heatshield. Penetrations to the forebody heat-shield can also result from damage at
NASA Technical Reports Server (NTRS)
Sawyer, J. W.
1977-01-01
A flightweight, metallic thermal protection system (TPS) applicable to reentry and hypersonic vehicles was subjected to multiple cycles of both radiant and aerothermal heating in order to evaluate its aerothermal performance and structural integrity. Good structural integrity and thermal performance were demonstrated by the TPS under both a radiant and aerothermal heating environment typical of a shuttle entry. The shingle-slip joints effectively allowed for thermal expansion of the panel without allowing any appreciable hot gas flow into the TPS cavity. The TPS also demonstrated good structural ruggedness.
Aero-Thermal Calibration of the NASA Glenn Icing Research Tunnel (2012 Test)
NASA Technical Reports Server (NTRS)
Pastor-Barsi, Christine M.; Arrington, E. Allen; VanZante, Judith Foss
2012-01-01
A major modification of the refrigeration plant and heat exchanger at the NASA Glenn Icing Research Tunnel (IRT) occurred in autumn of 2011. It is standard practice at NASA Glenn to perform a full aero-thermal calibration of the test section of a wind tunnel facility upon completion of major modifications. This paper will discuss the tools and techniques used to complete an aero-thermal calibration of the IRT and the results that were acquired. The goal of this test entry was to complete a flow quality survey and aero-thermal calibration measurements in the test section of the IRT. Test hardware that was used includes the 2D Resistive Temperature Detector (RTD) array, 9-ft pressure survey rake, hot wire survey rake, and the quick check survey rake. This test hardware provides a map of the velocity, Mach number, total and static pressure, total temperature, flow angle and turbulence intensity. The data acquired were then reduced to examine pressure, temperature, velocity, flow angle, and turbulence intensity. Reduced data has been evaluated to assess how the facility meets flow quality goals. No icing conditions were tested as part of the aero-thermal calibration. However, the effects of the spray bar air injections on the flow quality and aero-thermal calibration measurements were examined as part of this calibration.
Spacecraft Orbital Debris Reentry: Aerothermal Analysis
NASA Technical Reports Server (NTRS)
Rochelle, Wm. C.; Kinsey, Robin E.; Reid, Ethan A.; Reynolds, Robert C.; Johnson, Nicholas L.
1997-01-01
In the past 40 years, thousands of objects have been placed in Earth orbit and are being tracked. Space hardware reentry survivability must be evaluated to assess risks to human life and property on the ground. The objective of this paper is to present results of a study to determine altitude of demise (burn-up) or survivability of reentering objects. Two NASA/JSC computer codes - Object Reentry Survival Analysis Tool (ORSAT) and Miniature ORSAT (MORSAT) were used to determine trajectories, aerodynamic aerothermal environment, and thermal response of selected spacecraft components. The methodology of the two codes is presented, along with results of a parametric study of reentering objects modeled as spheres and cylinders. Parameters varied included mass, diameter, wall thickness, ballistic coefficient, length, type of material, and mode of tumbling/spinning. Two fragments of a spent Delta second stage undergoing orbital decay, stainless steel cylindrical propellant tank and titanium pressurization sphere, were evaluated with ORSAT and found to survive entry, as did the actual objects. Also, orbital decay reentry predictions of the Japanese Advanced Earth Observing Satellite (ADEOS) aluminum and nickel box-type components and the Russian COSMOS 954 satellite beryllium cylinders were made with MORSAT. These objects were also shown to survive reentry.
Aerothermal Heating Predictions for Mars Microprobe
NASA Technical Reports Server (NTRS)
Mitcheltree, R. A.; DiFulvio, M.; Horvath, T. J.; Braun, R. D.
1998-01-01
A combination of computational predictions and experimental measurements of the aerothermal heating expected on the two Mars Microprobes during their entry to Mars are presented. The maximum, non-ablating, heating rate at the vehicle's stagnation point (at alpha = 0 degrees) is predicted for an undershoot trajectory to be 194 Watts per square centimeters with associated stagnation point pressure of 0.064 atm. Maximum stagnation point pressure occurs later during the undershoot trajectory and is 0.094 atm. From computations at seven overshoot-trajectory points, the maximum heat load expected at the stagnation point is near 8800 Joules per square centimeter. Heat rates and heat loads on the vehicle's afterbody are much lower than the forebody. At zero degree angle-of-attack, heating over much of the hemi-spherical afterbody is predicted to be less than 2 percent of the stagnation point value. Good qualitative agreement is demonstrated for forebody and afterbody heating between CFD calculations at Mars entry conditions and experimental thermographic phosphor measurements from the Langley 20-Inch Mach 6 Air Tunnel. A novel approach which incorporates six degree-of-freedom trajectory simulations to perform a statistical estimate of the effect of angle-of-attack, and other off-nominal conditions, on heating is included.
Aerothermal analysis of a wing-elevon cove with variable leakage
NASA Technical Reports Server (NTRS)
Hunt, R. L.
1980-01-01
A mathematical model of the heating associated with leakage within the space shuttle orbiter wing elevon cove was used to analyze the aerothermal response of the structure. The analysis was applied to wind tunnel results and to shuttle entry conditions. A parametric study described the mechanism by which the energy of the ingested mass is distributed as a function of the Reynolds number, wall conductivity, surface emissivity, and cove height and length. The rate at which energy was transferred into the cove interior was primarily determined by the combined effects of the convection, wall capacitance, and internal radiation terms. Correlation with wind tunnel results indicated that the cold wall convective heating rates, wall temperature, and gas temperature of the cove were predicted by the analytical model for short exposure times. Predicted transient thermal response of the elevon cove subjected to shuttle entry conditions indicated that the allowable leak area at the cove seal was 20 percent less than that previously indicated by experiment.
NASA Technical Reports Server (NTRS)
Avery, D. E.
1984-01-01
A flight-weight, metallic thermal protection system (TPS) model applicable to Earth-entry and hypersonic-cruise vehicles was subjected to multiple cycles of both radiant and aerothermal heating in order to evaluate its aerothermal performance, structural integrity, and damage tolerance. The TPS was designed for a maximum operating temperature of 2060 R and featured a shingled, corrugation-stiffened corrugated-skin heat shield of Rene 41, a nickel-base alloy. The model was subjected to 10 radiant heating tests and to 3 radiant preheat/aerothermal tests. Under radiant-heating conditions with a maximum surface temperature of 2050 R, the TPS performed as designed and limited the primary structure away from the support ribs to temperatures below 780 R. During the first attempt at aerothermal exposure, a failure in the panel-holder test fixture severely damaged the model. However, two radiant preheat/aerothermal tests were made with the damaged model to test its damage tolerance. During these tests, the damaged area did not enlarge; however, the rapidly increasing structural temperature measuring during these tests indicates that had the damaged area been exposed to aerodynamic heating for the entire trajectory, an aluminum burn-through would have occurred.
Statistical Methods for Rapid Aerothermal Analysis and Design Technology
NASA Technical Reports Server (NTRS)
Morgan, Carolyn; DePriest, Douglas; Thompson, Richard (Technical Monitor)
2002-01-01
The cost and safety goals for NASA's next generation of reusable launch vehicle (RLV) will require that rapid high-fidelity aerothermodynamic design tools be used early in the design cycle. To meet these requirements, it is desirable to establish statistical models that quantify and improve the accuracy, extend the applicability, and enable combined analyses using existing prediction tools. The research work was focused on establishing the suitable mathematical/statistical models for these purposes. It is anticipated that the resulting models can be incorporated into a software tool to provide rapid, variable-fidelity, aerothermal environments to predict heating along an arbitrary trajectory. This work will support development of an integrated design tool to perform automated thermal protection system (TPS) sizing and material selection.
Aerothermal Test of Metallic TPS for X-33 Reusable Launch Vehicle
NASA Technical Reports Server (NTRS)
Sawyer, James Wayne; Hodge, Jefferson; Moore, Brad
1998-01-01
An array of metallic Thermal Protection System (TPS) panels including the seals developed for the windward surface of the X-33 vehicle is being tested in the Eight Foot High Temperature Tunnel at the NASA Langley Research Center. These tests are the first aerothermal tests of an X-33 TPS array and will be used to validate the TPS for the X-33 flight program. Specifically, the tests will be used to evaluate the structural and thermal performance of the TPS, the effectiveness of the high temperature seals between adjacent tiles and the durability of the TPS under realistic aerothermal flight conditions. The effect of varying step heights, damage to the seals between adjacent panels, and the use of secondary seals will also be investigated during the test program. The metallic TPS developed for the windward surface of the X-33 and the test program in the Eight Foot High Temperature Tunnel is presented and discussed.
Atlas F entry aerothermic study
NASA Technical Reports Server (NTRS)
1972-01-01
The feasibility of obtaining heat transfer data on an expended Atlas F booster launch vehicle was investigated in the altitude range of 300,000 to 200,000 feet during entry conditions, with a velocity in the range of 20,000 to 25,000 feet per second, and through a range of vehicle attitudes of plus or minus 90 degrees. These data are desired for correlation with turbulent heat transfer and boundary layer transition data obtained from wind tunnel test facilities. The data would also be valuable in assessing rarified gas and surface catalicity effects in a real gas environment.
Adaptive computational methods for aerothermal heating analysis
NASA Technical Reports Server (NTRS)
Price, John M.; Oden, J. Tinsley
1988-01-01
The development of adaptive gridding techniques for finite-element analysis of fluid dynamics equations is described. The developmental work was done with the Euler equations with concentration on shock and inviscid flow field capturing. Ultimately this methodology is to be applied to a viscous analysis for the purpose of predicting accurate aerothermal loads on complex shapes subjected to high speed flow environments. The development of local error estimate strategies as a basis for refinement strategies is discussed, as well as the refinement strategies themselves. The application of the strategies to triangular elements and a finite-element flux-corrected-transport numerical scheme are presented. The implementation of these strategies in the GIM/PAGE code for 2-D and 3-D applications is documented and demonstrated.
Performance of Conformable Ablators in Aerothermal Environments
NASA Technical Reports Server (NTRS)
Thornton, J.; Fan, W.; Skokova, K.; Stackpoole, M.; Beck, R.; Chavez-Garcia, J.
2012-01-01
Conformable Phenolic Impregnated Carbon Ablator, a cousin of Phenolic Impregnated Carbon Ablator (PICA), was developed at NASA Ames Research Center as a lightweight thermal protection system under the Fundamental Aeronautics Program. PICA is made using a brittle carbon substrate, which has a very low strain to failure. Conformable PICA is made using a flexible carbon substrate, a felt in this case. The flexible felt significantly increases the strain to failure of the ablator. PICA is limited by its thermal mechanical properties. Future NASA missions will require heatshields that are more fracture resistant than PICA and, as a result, NASA Ames is working to improve PICAs performance by developing conformable PICA to meet these needs. Research efforts include tailoring the chemistry of conformable PICA with varying amounts of additives to enhance mechanical properties and testing them in aerothermal environments. This poster shows the performance of conformable PICA variants in arc jets tests. Some mechanical and thermal properties will also be presented.
Aerodynamic and Aerothermal TPS Instrumentation Reference Guide
NASA Technical Reports Server (NTRS)
Woollard, Bryce A.; Braun, Robert D.; Bose, Deepack
2016-01-01
The hypersonic regime of planetary entry combines the most severe environments that an entry vehicle will encounter with the greatest amount of uncertainty as to the events unfolding during that time period. This combination generally leads to conservatism in the design of an entry vehicle, specifically that of the thermal protection system (TPS). Each planetary entry provides a valuable aerodynamic and aerothermal testing opportunity; the utilization of this opportunity is paramount in better understanding how a specific entry vehicle responds to the demands of the hypersonic entry environment. Previous efforts have been made to instrument entry vehicles in order to collect data during the entry period and reconstruct the corresponding vehicle response. The purpose of this paper is to cumulatively document past TPS instrumentation designs for applicable planetary missions, as well as to list pertinent results and any explainable shortcomings.
Shuttle Return-to-Flight IH-108 Aerothermal Test at CUBRC - Flow Field Calibration and CFD
NASA Technical Reports Server (NTRS)
Lau, Kei Y.; Holden, Michael
2010-01-01
This paper discusses one specific aspect of the Shuttle Retrun-To-Flight IH-108 Aerothermal Test at CUBRC, the test flow field calibration. It showed the versatility of the CUBRC LENS II wind tunnel for an aerothermal test with unique and demanding requirements. CFD analyses were used effectively to extend the test range at the low end of the Mach range. It demonstrated how ground test facility and CFD synergy can be utilitzed iteratively to enhance the confidence in the fedility of both tools. It addressed the lingering concerns of the aerothermal community on use of inpulse facility and CFD analysis. At the conclusion of the test program, members from the NASA Marshall (MSFC), CUBRC and USA (United Space Alliance) Consultants (The Grey Beards) were asked to independently verify the flight scaling data generated by Boeing for flight certification of the re-designed external tank (ET) components. The blind test comparison showed very good results. A more comprehensive discussion of the topics in this paper can be found in Chapter 6 of Reference [1]. The overall aspect of the test program has been discussed in an AIAA paper by Tim Wadhams [2]. The Shuttle Ascent Stack performance and related issues discussed in the Report [1] are not included in this paper. No ITAR data is included in this paper.
Shuttle Return-to-Flight IH-108 Aerothermal Test at CUBRC - Flow Field Calibration and CFD
NASA Technical Reports Server (NTRS)
Lau, Kei Y.; Holden, M. S.
2011-01-01
This paper discusses one specific aspect of the Shuttle Retrun-To-Flight IH-108 Aerothermal Test at Calspan-University of Buffalo Research Center (CUBRC), the test flow field calibration. It showed the versatility of the CUBRC Large Energy National Shock Tunnel (LENS) II wind tunnel for an aerothermal test with unique and demanding requirements. CFD analyses were used effectively to extend the test range at the low end of the Mach range. It demonstrated how ground test facility and CFD synergy can be utilitzed iteratively to enhance the confidence in the fedility of both tools. It addressed the lingering concerns of the aerothermal community on use of inpulse facility and CFD analysis. At the conclusion of the test program, members from the NASA Marshall (MSFC), CUBRC and USA (United Space Alliance) Consultants (The Grey Beards) were asked to independently verify the flight scaling data generated by Boeing for flight certification of the re-designed external tank (ET) components. The blind test comparison showed very good results.
NASA Technical Reports Server (NTRS)
Albertson, Cindy W.
1987-01-01
A model to be used in the flow studies and curved Thermal Protection System (TPS) evaluations was tested in the Langley 8 Foot High-Temperature Tunnel at a nominal Mach number of 6.8. The purpose of the study was to define the surface pressure and heating rates at high angles of attack (in support of curved metallic TPS studies) and to determine the conditions for which the model would be suitable as a test bed for aerothermal load studies. The present study was conducted at a nominal total temperature of 2400 and 3300 R, dynamic pressures from 2.3 to 10.9 psia, and free-stream Reynolds numbers from 4000,000 to 1,700,000/ft. The measurements consisted primarily of surface pressure and cold-wall (530 R) heating rates. Qualitative comparisons between predictions and data show that for this configuration, aerothermal tests should be limited to angles of attack between 10 and -10 degrees. Outside this range, the effects of free-stream flow nonuniformity appear in the data, as a result of the long length of the model. However, for TPS testing, this is not a concern and tests can be performed at angles of attack ranging from 20 to -20 degrees. Laminar and naturally turbulent boundary layers are available over limited ranges of conditions.
A database of aerothermal measurements in hypersonic flow for CFD validation
NASA Technical Reports Server (NTRS)
Holden, M. S.; Moselle, J. R.
1992-01-01
This paper presents an experimental database selected and compiled from aerothermal measurements obtained on basic model configurations on which fundamental flow phenomena could be most easily examined. The experimental studies were conducted in hypersonic flows in 48-inch, 96-inch, and 6-foot shock tunnels. A special computer program was constructed to provide easy access to the measurements in the database as well as the means to plot the measurements and compare them with imported data. The database contains tabulations of model configurations, freestream conditions, and measurements of heat transfer, pressure, and skin friction for each of the studies selected for inclusion. The first segment contains measurements in laminar flow emphasizing shock-wave boundary-layer interaction. In the second segment, measurements in transitional flows over flat plates and cones are given. The third segment comprises measurements in regions of shock-wave/turbulent-boundary-layer interactions. Studies of the effects of surface roughness of nosetips and conical afterbodies are presented in the fourth segment of the database. Detailed measurements in regions of shock/shock boundary layer interaction are contained in the fifth segment. Measurements in regions of wall jet and transpiration cooling are presented in the final two segments.
Evaluation of aerothermal modeling computer programs
NASA Technical Reports Server (NTRS)
Hsieh, K. C.; Yu, S. T.
1987-01-01
Various computer programs based upon the SIMPLE or SIMPLER algorithm were studied and compared for numerical accuracy, efficiency, and grid dependency. Four two-dimensional and one three-dimensional code originally developed by a number of research groups were considered. In general, the accuracy and computational efficieny of these TEACH type programs were improved by modifying the differencing schemes and their solvers. A brief description of each program is given. Error reduction, spline flux and second upwind differencing programs are covered.
NASA Astrophysics Data System (ADS)
Gomez-Garcia, Fabrisio; Santiago, Sergio; Luque, Salvador; Romero, Manuel; Gonzalez-Aguilar, Jose
2016-05-01
This paper describes a new modular laboratory-scale experimental facility that was designed to conduct detailed aerothermal characterizations of volumetric absorbers for use in concentrating solar power plants. Absorbers are generally considered to be the element with the highest potential for efficiency gains in solar thermal energy systems. The configu-ration of volumetric absorbers enables concentrated solar radiation to penetrate deep into their solid structure, where it is progressively absorbed, prior to being transferred by convection to a working fluid flowing through the structure. Current design trends towards higher absorber outlet temperatures have led to the use of complex intricate geometries in novel ceramic and metallic elements to maximize the temperature deep inside the structure (thus reducing thermal emission losses at the front surface and increasing efficiency). Although numerical models simulate the conjugate heat transfer mechanisms along volumetric absorbers, they lack, in many cases, the accuracy that is required for precise aerothermal validations. The present work aims to aid this objective by the design, development, commissioning and operation of a new experimental facility which consists of a 7 kWe (1.2 kWth) high flux solar simulator, a radiation homogenizer, inlet and outlet collector modules and a working section that can accommodate volumetric absorbers up to 80 mm × 80 mm in cross-sectional area. Experimental measurements conducted in the facility include absorber solid temperature distributions along its depth, inlet and outlet air temperatures, air mass flow rate and pressure drop, incident radiative heat flux, and overall thermal efficiency. In addition, two windows allow for the direct visualization of the front and rear absorber surfaces, thus enabling full-coverage surface temperature measurements by thermal imaging cameras. This paper presents the results from the aerothermal characterization of a siliconized silicon
Aerothermal Test of Thermal Protection Systems for X-33 Reusable Launch Vehicle
NASA Technical Reports Server (NTRS)
Sawyer, James Wayne; Hodge, Jefferson; Moore, Brad; Snyder, Kevin
1999-01-01
An array of metallic Thermal Protection System (TPS) panels developed for the windward surface of the X-33 vehicle was tested in the 8-Foot High Temperature Tunnel at the NASA Langley Research Center. These tests were the first aerothermal tests of an X-33 TPS array and the test results will be used to validate the TPS for the X-33 flight program. Specifically, the tests evaluated the structural and thermal performance of the TPS, the effectiveness of the high temperature seals between adjacent panels and the durability of the TPS under realistic aerothermal flight conditions. The effect of varying panel-to-panel step heights, intentional damage to the seals between adjacent panels, and the use of secondary seals were also investigated during the test program. The metallic TPS developed for the windward surface of the X-33, the blanket TPS developed to protect the leeward surfaces of the X-33, and the test program in the 8-Foot High Temperature Tunnel are presented and discussed.
Orbital flight test shuttle external tank aerothermal flight evaluation, volume 2
NASA Technical Reports Server (NTRS)
Praharaj, Sarat C.; Engel, Carl D.; Warmbrod, John D.
1986-01-01
This 3-volume report discusses the evaluation of aerothermal flight measurements made on the orbital flight test Space Shuttle External Tanks (ETs). Six ETs were instrumented to measure various quantities during flight; including heat transfer, pressure, and structural temperature. The flight data was reduced and analyzed against math models established from an extensive wind tunnel data base and empirical heat-transfer relationships. This analysis has supported the validity of the current aeroheating methodology and existing data base; and, has also identified some problem areas which require methodology modifications. Volume 1 is the Executive Summary. This is volume 2, containing Appendix A (Aerothermal Comparisons), and Appendix B (Flight-Derived h sub i/h sub u vs. M sub inf. Plots). Volume 3 contains Appendix C (Comparison of Interference Factors between OFT Flight, Prediction and 1H-97A Data), Appendix D (Freestream Stanton Number and Reynolds Number Correlation for Flight and Tunnel Data), and Appendix E (Flight-Derived h sub i/h sub u Tables).
Orbital flight test shuttle external tank aerothermal flight evaluation, volume 3
NASA Technical Reports Server (NTRS)
Praharaj, Sarat C.; Engel, Carl D.; Warmbrod, John D.
1986-01-01
This 3-volume report discusses the evaluation of aerothermal flight measurements made on the orbital flight test Space Shuttle External Tanks (ETs). Six ETs were instrumented to measure various quantities during flight; including heat transfer, pressure, and structural temperature. The flight data was reduced and analyzed against math models established from an extensive wind tunnel data base and empirical heat-transfer relationships. This analysis has supported the validity of the current aeroheating methodology and existing data base; and, has also identified some problem areas which require methodology modifications. Volume 1 is the Executive Summary. Volume 2 contains Appendix A (Aerothermal Comparisons), and Appendix B (Flight-Derived h sub 1/h sub u vs. M sub inf. Plots). This is Volume 3, containing Appendix C (Comparison of Interference Factors between OFT Flight, Prediction and 1H-97A Data), Appendix D (Freestream Stanton Number and Reynolds Number Correlation for Flight and Tunnel Data), and Appendix E (Flight-Derived h sub i/h sub u Tables).
Studies of aerothermal loads generated in regions of shock/shock interaction in hypersonic flow
NASA Technical Reports Server (NTRS)
Holden, Michael S.; Moselle, John R.; Lee, Jinho
1991-01-01
Experimental studies were conducted to examine the aerothermal characteristics of shock/shock/boundary layer interaction regions generated by single and multiple incident shocks. The presented experimental studies were conducted over a Mach number range from 6 to 19 for a range of Reynolds numbers to obtain both laminar and turbulent interaction regions. Detailed heat transfer and pressure measurements were made for a range of interaction types and incident shock strengths over a transverse cylinder, with emphasis on the 3 and 4 type interaction regions. The measurements were compared with the simple Edney, Keyes, and Hains models for a range of interaction configurations and freestream conditions. The complex flowfields and aerothermal loads generated by multiple-shock impingement, while not generating as large peak loads, provide important test cases for code prediction. The detailed heat transfer and pressure measurements proved a good basis for evaluating the accuracy of simple prediction methods and detailed numerical solutions for laminar and transitional regions or shock/shock interactions.
Note: thermal imaging enhancement algorithm for gas turbine aerothermal characterization.
Beer, S K; Lawson, S A
2013-08-01
An algorithm was developed to convert radiation intensity images acquired using a black and white CCD camera to thermal images without requiring knowledge of incident background radiation. This unique infrared (IR) thermography method was developed to determine aerothermal characteristics of advanced cooling concepts for gas turbine cooling application. Compared to IR imaging systems traditionally used for gas turbine temperature monitoring, the system developed for the current study is relatively inexpensive and does not require calibration with surface mounted thermocouples.
Note: thermal imaging enhancement algorithm for gas turbine aerothermal characterization.
Beer, S K; Lawson, S A
2013-08-01
An algorithm was developed to convert radiation intensity images acquired using a black and white CCD camera to thermal images without requiring knowledge of incident background radiation. This unique infrared (IR) thermography method was developed to determine aerothermal characteristics of advanced cooling concepts for gas turbine cooling application. Compared to IR imaging systems traditionally used for gas turbine temperature monitoring, the system developed for the current study is relatively inexpensive and does not require calibration with surface mounted thermocouples. PMID:24007128
NASA Technical Reports Server (NTRS)
Kolodziej, Paul
1997-01-01
Small radius leading edges and nosetips were utilized to minimize wave drag in early hypervelocity vehicle concepts until further analysis demonstrated that extreme aerothermodynamic heating would cause severe ablation or blunting of the available thermal protection system materials. Recent studies indicate that ultrahigh temperature ceramic (UHTC) materials are shape stable at temperatures approaching 3033 K and will be available for use as sharp UHTC leading edge components in the near future. Aerothermal performance constraints for sharp components made from these materials are presented in this work to demonstrate the effects of convective blocking, surface catalycity, surface emissivity, and rarefied flow effects on steady state operation at altitudes from sea level to 90 km. These components are capable of steady state operation at velocities up to 7.9 km/s at attitudes near 90 km.
External tank aerothermal design criteria verification
NASA Technical Reports Server (NTRS)
Praharaj, Sarat C.; Saladino, Anthony J.
1991-01-01
If a Space Shuttle Main Engine (SSME) fails during the initial 160 seconds of the Shuttle flight, a return-to-launch-site maneuver will be implemented. The period of concern for this task is the pitch-around maneuver when the vehicle is flying backward. The intent of this report is to identify and define the flowfield at the most critical locations from an environment perspective. The solution procedure used to predict the plume heating rates involves both computational analysis and engineering modeling.
Aero-Thermal Calibration of the NASA Glenn Icing Research Tunnel (2012 Tests)
NASA Technical Reports Server (NTRS)
Pastor-Barsi, Christine; Allen, Arrington E.
2013-01-01
A full aero-thermal calibration of the NASA Glenn Icing Research Tunnel (IRT) was completed in 2012 following the major modifications to the facility that included replacement of the refrigeration plant and heat exchanger. The calibration test provided data used to fully document the aero-thermal flow quality in the IRT test section and to construct calibration curves for the operation of the IRT.
Performance of Conformable Phenolic Impregnated Carbon Ablator in Aerothermal Environments
NASA Technical Reports Server (NTRS)
Thornton, Jeremy; Fan, Wendy; Stackpoole, Mairead; Kao, David; Skokova, Kristina; Chavez-Garcia, Jose
2012-01-01
Conformable Phenolic Impregnated Carbon Ablator, a cousin of Phenolic Impregnated Carbon Ablator (PICA), was developed at NASA Ames Research Center as a lightweight thermal protection system under the Fundamental Aeronautics Program. PICA is made using a brittle carbon substrate, which has a very low strain to failure. Conformable PICA is made using a flexible carbon substrate, a felt in this case. The flexible felt significantly increases the strain to failure of the ablator. PICA is limited by its thermal mechanical properties. Future NASA missions will require heatshields that are more fracture resistant than PICA and, as a result, NASA Ames is working to improve PICA's performance by developing conformable PICA to meet these needs. Research efforts include tailoring the chemistry of conformable PICA with varying amounts of additives to enhance mechanical properties and testing them in aerothermal environments. This poster shows the performance of conformable PICA variants in arc jets tests. Some mechanical and thermal properties will also be presented.
Exploration Flight Test 1 Afterbody Aerothermal Environment Reconstruction
NASA Technical Reports Server (NTRS)
Hyatt, Andrew J.; Oliver, Brandon; Amar, Adam; Lessard, Victor
2016-01-01
The Exploration Flight Test 1 vehicle included roughly 100 near surface thermocouples on the after body of the vehicle. The temperature traces at each of these instruments have been used to perform inverse environment reconstruction to determine the aerothermal environment experienced during re-entry of the vehicle. This paper provides an overview of the reconstructed environments and identifies critical aspects of the environment. These critical aspects include transition and reaction control system jet influence. A blind test of the process and reconstruction tool was also performed to build confidence in the reconstructed environments. Finally, an uncertainty quantification analysis was also performed to identify the impact of each of the uncertainties on the reconstructed environments.
NASA Astrophysics Data System (ADS)
Errera, M.-P.; Duchaine, F.
2016-05-01
This paper tests the performance of coupling coefficients of a Dirichlet-Robin transmission procedure in the context of steady conjugate heat transfer (CHT). Particular emphasis is put on the optimal coefficients highlighted recently in a theoretical study based on a normal mode stability analysis. This work can be seen as the logical continuation of that study in order to assess the relevance of the coefficients provided by the model problem in a realistic aerothermal computation. First, the numerical and physical CHT modeling methodologies are presented. Then, the optimal procedure applied to a Dirichlet-Robin algorithm (one-coefficient method) is briefly described. In order to gauge the ability of this model to predict the stability and convergence properties of a realistic case, it is compared on a heated cylinder in a flowfield test case. A series of five coupling coefficients and three Fourier numbers are considered. These parameters are introduced into the model problem as data to compute the amplification factor and the stability limits. The stability and convergence properties predicted by the model problem are then compared to those obtained in the CHT computation. This comparison shows an excellent overall agreement. Moreover, for all the Fourier numbers considered, the numerical solution is stable and oscillation-free when the optimal coefficient of the model problem is used. This would suggest that the one-dimensional normal mode analysis can provide relevant coefficients directly applicable to real CHT problems.
NASA Astrophysics Data System (ADS)
Hudson, Douglas J.; Torres, Manuel; Dougherty, Catherine; Rajendran, Natesan; Thompson, Rhoe A.
2003-09-01
The Air Force Research Laboratory (AFRL) Aerothermal Targets Analysis Program (ATAP) is a user-friendly, engineering-level computational tool that features integrated aerodynamics, six-degree-of-freedom (6-DoF) trajectory/motion, convective and radiative heat transfer, and thermal/material response to provide an optimal blend of accuracy and speed for design and analysis applications. ATAP is sponsored by the Kinetic Kill Vehicle Hardware-in-the-Loop Simulator (KHILS) facility at Eglin AFB, where it is used with the CHAMP (Composite Hardbody and Missile Plume) technique for rapid infrared (IR) signature and imagery predictions. ATAP capabilities include an integrated 1-D conduction model for up to 5 in-depth material layers (with options for gaps/voids with radiative heat transfer), fin modeling, several surface ablation modeling options, a materials library with over 250 materials, options for user-defined materials, selectable/definable atmosphere and earth models, multiple trajectory options, and an array of aerodynamic prediction methods. All major code modeling features have been validated with ground-test data from wind tunnels, shock tubes, and ballistics ranges, and flight-test data for both U.S. and foreign strategic and theater systems. Numerous applications include the design and analysis of interceptors, booster and shroud configurations, window environments, tactical missiles, and reentry vehicles.
NASA Technical Reports Server (NTRS)
Bruce, Walter E., III; Mesick, Nathaniel J.; Ferlemann, Paul G.; Siemers, Paul M., III; DelCorso, Joseph A.; Hughes, Stephen J.; Tobin, Steven A.; Kardell, Matthew P.
2012-01-01
Flexible TPS development involves ground testing and analysis necessary to characterize performance of the FTPS candidates prior to flight testing. This paper provides an overview of the analysis and ground testing efforts performed over the last year at the NASA Langley Research Center and in the Boeing Large-Core Arc Tunnel (LCAT). In the LCAT test series, material layups were subjected to aerothermal loads commensurate with peak re-entry conditions enveloping a range of HIAD mission trajectories. The FTPS layups were tested over a heat flux range from 20 to 50 W/cm with associated surface pressures of 3 to 8 kPa. To support the testing effort a significant redesign of the existing shear (wedge) model holder from previous testing efforts was undertaken to develop a new test technique for supporting and evaluating the FTPS in the high-temperature, arc jet flow. Since the FTPS test samples typically experience a geometry change during testing, computational fluid dynamic (CFD) models of the arc jet flow field and test model were developed to support the testing effort. The CFD results were used to help determine the test conditions experienced by the test samples as the surface geometry changes. This paper includes an overview of the Boeing LCAT facility, the general approach for testing FTPS, CFD analysis methodology and results, model holder design and test methodology, and selected thermal results of several FTPS layups.
Engineering Aerothermal Analysis for X-34 Thermal Protection System Design
NASA Technical Reports Server (NTRS)
Wurster, Kathryn E.; Riley, Christopher J.; Zoby, E. Vincent
1998-01-01
Design of the thermal protection system for any hypersonic flight vehicle requires determination of both the peak temperatures over the surface and the heating-rate history along the flight profile. In this paper, the process used to generate the aerothermal environments required for the X-34 Testbed Technology Demonstrator thermal protection system design is described as it has evolved from a relatively simplistic approach based on engineering methods applied to critical areas to one of detailed analyses over the entire vehicle. A brief description of the trajectory development leading to the selection of the thermal protection system design trajectory is included. Comparisons of engineering heating predictions with wind-tunnel test data and with results obtained using a Navier-Stokes flowfield code and an inviscid/boundary layer method are shown. Good agreement is demonstrated among all these methods for both the ground-test condition and the peak heating flight condition. Finally, the detailed analysis using engineering methods to interpolate the surface-heating-rate results from the inviscid/boundary layer method to predict the required thermal environments is described and results presented.
Engineering Aerothermal Analysis for X-34 Thermal Protection System Design
NASA Technical Reports Server (NTRS)
Wurster, Kathryn E.; Riley, Christopher J.; Zoby, E. Vincent
1998-01-01
Design of the thermal protection system for any hypersonic flight vehicle requires determination of both the peak temperatures over the surface and the heating-rate history along the flight profile. In this paper, the process used to generate the aerothermal environments required for the X-34 Testbed Technology Demonstrator thermal protection system design is described as it has evolved from a relatively simplistic approach based on engineering methods applied to critical areas to one of detailed analyses over the entire vehicle. A brief description of the trajectory development leading to the selection of the thermal protection system design trajectory is included. Comparisons of engineering heating predictions with wind-tunnel test data and with results obtained using a Navier- Stokes flowfield code and an inviscid/boundary layer method are shown. Good agreement is demonstrated among all these methods for both the ground-test condition and the peak heating flight condition. Finally, the detailed analysis using engineering methods to interpolate the surface-heating-rate results from the inviscid/boundary layer method to predict the required thermal environments is described and results presented.
Aero-thermal analysis of lifting body configurations in hypersonic flow
NASA Astrophysics Data System (ADS)
Kumar, Sachin; Mahulikar, Shripad P.
2016-09-01
The aero-thermal analysis of a hypersonic vehicle is of fundamental interest for designing its thermal protection system. The aero-thermal environment predictions over several critical regions of the hypothesized lifting body vehicle, including the stagnation region of the nose-cap, cylindrically swept leading edges, fuselage-upper, and fuselage-lower surfaces, are discussed. The drag (Λ=70°) and temperature (Λ=80°) minimized sweepback angles are considered in the configuration design of the two hypothesized lifting body shape hypersonic vehicles. The main aim of the present study is to analyze and compare the aero-thermal characteristics of these two lifting body configurations at same heat capacity. Accordingly, a Computational Fluid Dynamics simulation has been carried out at Mach number (M∞=7), H=35 km altitude with zero Angle of Attack. Finally, the material selection for thermal protection system based on these predictions and current methodology is described.
Aero-Thermal Calibration of the NASA Glenn Icing Research Tunnel (2004 and 2005 Tests)
NASA Technical Reports Server (NTRS)
Arrington, E. Allen; Pastor, Christine M.; Gonsalez, Jose C.; Curry, Monroe R., III
2010-01-01
A full aero-thermal calibration of the NASA Glenn Icing Research Tunnel was completed in 2004 following the replacement of the inlet guide vanes upstream of the tunnel drive system and improvement to the facility total temperature instrumentation. This calibration test provided data used to fully document the aero-thermal flow quality in the IRT test section and to construct calibration curves for the operation of the IRT. The 2004 test was also the first to use the 2-D RTD array, an improved total temperature calibration measurement platform.
Aero-thermal Calibration of the NASA Glenn Icing Research Tunnel (2000 Tests)
NASA Technical Reports Server (NTRS)
Gonsalez, Jose C.; Arrington, E. Allen; Curry, Monroe R., III
2001-01-01
Aerothermal calibration measurements and flow quality surveys were made in the test section of the Icing Research Tunnel at the NASA Glenn Research Center. These surveys were made following major facility modifications including widening of the heat exchanger tunnel section, replacement of the heat exchanger, installation of new turning vanes, and installation of new fan exit guide vanes. Standard practice at NASA Glenn requires that test section calibration and flow quality surveys be performed following such major facility modifications. A single horizontally oriented rake was used to survey the flow field at several vertical positions within a single cross-sectional plane of the test section. These surveys provided a detailed mapping of the total and static pressure, total temperature, Mach number, velocity, flow angle and turbulence intensity. Data were acquired over the entire velocity and total temperature range of the facility. No icing conditions were tested; however, the effects of air sprayed through the water injecting spray bars were assessed. All data indicate good flow quality. Mach number standard deviations were less than 0.0017, flow angle standard deviations were between 0.3 deg and 0.8 deg, total temperature standard deviations were between 0.5 and 1.8 F for subfreezing conditions, axial turbulence intensities varied between 0.3 and 1.0 percent, and transverse turbulence intensities varied between 0.3 and 1.5 percent. Measurement uncertainties were also quantified.
Aerothermal environment induced by mismatch at the SSME main combustion chamber-nozzle joint
NASA Technical Reports Server (NTRS)
Mcconnaughey, H. V.; O'Farrell, J. M.; Olive, T. A.; Brown, G. B.; Holt, J. B.
1990-01-01
The computational study reported here is motivated by a Space Shuttle main engine hardware problem detected in post-flight and post-test inspections. Of interest are the potential for hot gas ingestion into the joint (G15) at the main combustion chamber-to-nozzle interface and the effect of particular goemetric nonuniformities on that gas ingestion. The flowfield in the G15 region involves supersonic flow past a rounded forward facing step preceded by a deep narrow cavity. This paper describes the physical problem associated with joint G15 and computational investigations of the G15 aerothermal environment. The associated flowfield was simulated in two and three space dimensions using the United Solutions Algorithm (USA) computational fluid dynamics code series. A benchmark calculation of experimentally measured supersonic flow over of a square cavity was performed to demonstrate the accuracy of the USA code in analyzing flows similar to the G15 computational flowfield. The G15 results demonstrate the mechanism for hot gas ingestion into the joint and reveal the sensitivity to salient geometric nonuniformities.
A Risk-Based Approach for Aerothermal/TPS Analysis and Testing
NASA Technical Reports Server (NTRS)
Wright, Michael J.; Grinstead, Jay H.; Bose, Deepak
2007-01-01
The current status of aerothermal and thermal protection system modeling for civilian entry missions is reviewed. For most such missions, the accuracy of our simulations is limited not by the tools and processes currently employed, but rather by reducible deficiencies in the underlying physical models. Improving the accuracy of and reducing the uncertainties in these models will enable a greater understanding of the system level impacts of a particular thermal protection system and of the system operation and risk over the operational life of the system. A strategic plan will be laid out by which key modeling deficiencies can be identified via mission-specific gap analysis. Once these gaps have been identified, the driving component uncertainties are determined via sensitivity analyses. A Monte-Carlo based methodology is presented for physics-based probabilistic uncertainty analysis of aerothermodynamics and thermal protection system material response modeling. These data are then used to advocate for and plan focused testing aimed at reducing key uncertainties. The results of these tests are used to validate or modify existing physical models. Concurrently, a testing methodology is outlined for thermal protection materials. The proposed approach is based on using the results of uncertainty/sensitivity analyses discussed above to tailor ground testing so as to best identify and quantify system performance and risk drivers. A key component of this testing is understanding the relationship between the test and flight environments. No existing ground test facility can simultaneously replicate all aspects of the flight environment, and therefore good models for traceability to flight are critical to ensure a low risk, high reliability thermal protection system design. Finally, the role of flight testing in the overall thermal protection system development strategy is discussed.
NASA Technical Reports Server (NTRS)
Martinez, Edward R.; Weber, Carissa Tudryn; Oishi, Tomo; Santos, Jose; Mach, Joseph
2011-01-01
The Sheathed Miniature Aerothermal Reentry Thermocouple is a micro-miniature thermocouple for high temperature measurement in extreme environments. It is available for use in Thermal Protection System materials for ground testing and flight. This paper discusses the heritage, and design of the instrument. Experimental and analytical methods used to verify its performance and limitations are described.
Aerothermal modeling, phase 1. Volume 2: Experimental data
NASA Technical Reports Server (NTRS)
Kenworthy, M. J.; Correa, S. M.; Burrus, D. L.
1983-01-01
The experimental test effort is discussed. The test data are presented. The compilation is divided into sets representing each of the 18 experimental configurations tested. A detailed description of each configuration, and plots of the temperature difference ratio parameter or pattern factor parameter calculated from the test data are also provided.
Aerothermal Protuberance Heating Design and Test Configurations for Ascent Vehicle Design
NASA Technical Reports Server (NTRS)
Martin, Charles E.; Neumann, Richard D.; Freeman, Delma
2010-01-01
A series of tests were conducted to evaluate protuberance heating for the purposes of vehicle design and modification. These tests represent a state of the art approach to both testing and instrumentation for defining aerothermal protuberance effects on the protuberance and surrounding areas. The testing was performed with a number of wind tunnel entries beginning with the proof of concept "pathfinder" test in the Test Section 1 (TS1) tunnel in the Langley Unitary Plan Wind Tunnel (UPWT). The TS1 section (see Figures 1a and 1b) is a lower Mach number tunnel and the Test Section 2 (TS2) has overlapping and higher Mach number capability as showin in Figure 1c. The pathfinder concept was proven and testing proceeded for a series of protuberance tests using an existing splitter aluminum protuberance mounting plate, Macor protuberances, thin film gages, total temperature and pressure gages, Kulite pressure transducers, Infra-Red camera imaging, LASER velocimetry evaluations and the UPWT data collection system. A boundary layer rake was used to identify the boundary layer profile at the protuberance locations for testing and helped protuberance design. This paper discusses the techniques and instrumentation used during the protuberance heating tests performed in the UPWT in TS1 and TS2. Runs of the protuberances were made Mach numbers of 1.5, 2.16, 2.65, and 3.51. The data set generated from this testing is for ascent protuberance effects and is termed Protuberance Heating Ascent Data (PHAD) and this testing may be termed PHAD-1 to distinguish it from future testing of this type.
NASA Technical Reports Server (NTRS)
Bey, K. S.; Thornton, E. A.; Dechaumphai, P.; Ramakrishnan, R.
1985-01-01
Recent progress in the development of finite element methodology for the prediction of aerothermal loads is described. Two dimensional, inviscid computations are presented, but emphasis is placed on development of an approach extendable to three dimensional viscous flows. Research progress is described for: (1) utilization of a commerically available program to construct flow solution domains and display computational results, (2) development of an explicit Taylor-Galerkin solution algorithm, (3) closed form evaluation of finite element matrices, (4) vector computer programming strategies, and (5) validation of solutions. Two test problems of interest to NASA Langley aerothermal research are studied. Comparisons of finite element solutions for Mach 6 flow with other solution methods and experimental data validate fundamental capabilities of the approach for analyzing high speed inviscid compressible flows.
NASA Astrophysics Data System (ADS)
Ostoich, Christopher Mark
Future high-speed air vehicles will be lightweight, flexible, and reusable. Ve- hicles fitting this description are subject to severe thermal and fluid dynamic loading from multiple sources such as aerothermal heating, propulsion sys- tem exhaust, and high dynamic pressures. The combination of low-margin design requirements and extreme environmental conditions emphasizes the occurrence of fluid-thermal-structural coupling. Numerous attempts to field such vehicles have been unsuccessful over the past half-century due par- tially to the inability of traditional design and analysis practices to predict the structural response in this flight regime. In this thesis, a high-fidelity computational approach is used to examine the fluid-structural response of aerospace structures in high-speed flows. The method is applied to two cases: one involving a fluid-thermal interaction problem in a hypersonic flow and the other a fluid-structure interaction study involving a turbulent boundary layer and a compliant panel. The coupled fluid-thermal investigation features a nominally rigid alu- minum spherical dome fixed to a ceramic panel holder placed in a Mach 6.59 laminar boundary layer. The problem was originally studied by Glass and Hunt in a 1988 wind tunnel experiment in the NASA Langley 8-Foot High Temperature Tunnel and is motivated by thermally bowed body panels designed for the National Aerospace Plane. In this work, the compressible Navier-Stokes equations for a thermally perfect gas and the transient heat equation in the structure are solved simultaneously using two high-fidelity solvers coupled at the solid-fluid interface. Predicted surface heat fluxes are within 10% of the measured values in the dome interior with greater differ- ences found near the dome edges where uncertainties concerning the exper- imental model's construction likely influence the thermal dynamics. On the flat panel holder, the local surface heat fluxes approach those on the wind- ward dome face
Inverse Heat Conduction Methods in the CHAR Code for Aerothermal Flight Data Reconstruction
NASA Technical Reports Server (NTRS)
Oliver, A. Brandon; Amar, Adam J.
2016-01-01
Reconstruction of flight aerothermal environments often requires the solution of an inverse heat transfer problem, which is an ill-posed problem of determining boundary conditions from discrete measurements in the interior of the domain. This paper will present the algorithms implemented in the CHAR code for use in reconstruction of EFT-1 flight data and future testing activities. Implementation details will be discussed, and alternative hybrid-methods that are permitted by the implementation will be described. Results will be presented for a number of problems.
Inverse Heat Conduction Methods in the CHAR Code for Aerothermal Flight Data Reconstruction
NASA Technical Reports Server (NTRS)
Oliver, A Brandon; Amar, Adam J.
2016-01-01
Reconstruction of flight aerothermal environments often requires the solution of an inverse heat transfer problem, which is an ill-posed problem of specifying boundary conditions from discrete measurements in the interior of the domain. This paper will present the algorithms implemented in the CHAR code for use in reconstruction of EFT-1 flight data and future testing activities. Implementation nuances will be discussed, and alternative hybrid-methods that are permitted by the implementation will be described. Results will be presented for a number of one-dimensional and multi-dimensional problems
Generation of an Aerothermal Data Base for the X33 Spacecraft
NASA Technical Reports Server (NTRS)
Roberts, Cathy; Huynh, Loc
1998-01-01
The X-33 experimental program is a cooperative program between industry and NASA, managed by Lockheed-Martin Skunk Works to develop an experimental vehicle to demonstrate new technologies for a single-stage-to-orbit, fully reusable launch vehicle (RLV). One of the new technologies to be demonstrated is an advanced Thermal Protection System (TPS) being designed by BF Goodrich (formerly Rohr, Inc.) with support from NASA. The calculation of an aerothermal database is crucial to identifying the critical design environment data for the TPS. The NASA Ames X-33 team has generated such a database using Computational Fluid Dynamics (CFD) analyses, engineering analysis methods and various programs to compare and interpolate the results from the CFD and the engineering analyses. This database, along with a program used to query the database, is used extensively by several X-33 team members to help them in designing the X-33. This paper will describe the methods used to generate this database, the program used to query the database, and will show some of the aerothermal analysis results for the X-33 aircraft.
Static and aerothermal tests of a superalloy honeycomb prepackaged thermal protection system
NASA Technical Reports Server (NTRS)
Gorton, Mark P.; Shideler, John L.; Webb, Granville L.
1993-01-01
A reusable metallic thermal protection system has been developed for vehicles with maximum surface temperatures of up to 2000 F. An array of two 12- by 12-in. panels was subjected to radiant heating tests that simulated Space Shuttle entry temperature and pressure histories. Results indicate that this thermal protection system, with a mass of 2.201 lbm/ft(exp 2), can successfully prevent typical aluminum primary structure of an entry vehicle like the Space Shuttle from exceeding temperatures greater than 350 F at a location on the vehicle where the maximum surface temperature is 1900 F. A flat array of 20 panels was exposed to aerothermal flow conditions, at a Mach number of 6.75. The panels were installed in a worst-case orientation with the gaps between panels parallel to the flow. Results from the aerothermal tests indicated that convective heating occurred from hot gas flow in the gaps between the panels. Proposed design changes to prevent gap heating occurred from hot gas flow in the gaps between the panels. Proposed design changes to prevent gap heating include orienting panels so that gaps are not parallel to the flow and using a packaged, compressible gap-filler material between panels to block hot gas flow in the gaps.
Statistical Methods for Rapid Aerothermal Analysis and Design Technology: Validation
NASA Technical Reports Server (NTRS)
DePriest, Douglas; Morgan, Carolyn
2003-01-01
The cost and safety goals for NASA s next generation of reusable launch vehicle (RLV) will require that rapid high-fidelity aerothermodynamic design tools be used early in the design cycle. To meet these requirements, it is desirable to identify adequate statistical models that quantify and improve the accuracy, extend the applicability, and enable combined analyses using existing prediction tools. The initial research work focused on establishing suitable candidate models for these purposes. The second phase is focused on assessing the performance of these models to accurately predict the heat rate for a given candidate data set. This validation work compared models and methods that may be useful in predicting the heat rate.
Aerothermal Testing for Project Orion Crew Exploration Vehicle
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Lillard, Randolph P.; Kirk, Benjamin S.; Fischer-Cassady, Amy
2009-01-01
The Project Orion Crew Exploration Vehicle aerothermodynamic experimentation strategy, as it relates to flight database development, is reviewed. Experimental data has been obtained to both validate the computational predictions utilized as part of the database and support the development of engineering models for issues not adequately addressed with computations. An outline is provided of the working groups formed to address the key deficiencies in data and knowledge for blunt reentry vehicles. The facilities utilized to address these deficiencies are reviewed, along with some of the important results obtained thus far. For smooth wall comparisons of computational convective heating predictions against experimental data from several facilities, confidence was gained with the use of algebraic turbulence model solutions as part of the database. For cavities and protuberances, experimental data is being used for screening various designs, plus providing support to the development of engineering models. With the reaction-control system testing, experimental data were acquired on the surface in combination with off-body flow visualization of the jet plumes and interactions. These results are being compared against predictions for improved understanding of aftbody thermal environments and uncertainties.
Several problems posed by aerothermal calculations in machines
NASA Astrophysics Data System (ADS)
Dutoya, Denis
Problems encountered in the quantitative prediction of high-temperature aerodynamic flows are discussed, with emphasis placed on problems relating to spatial scale and time scale. It is suggested that the discretization networks employed should be adapted to the configuration under consideration, that special attention be given to the stability of the calculated states, and that the validity of the physical models employed should be verified for each new flow type studied. The MATILDA code is used to solve the Navier-Stokes equations for the example of a diesel engine cylinder.
Grid Generation Issues and CFD Simulation Accuracy for the X33 Aerothermal Simulations
NASA Technical Reports Server (NTRS)
Polsky, Susan; Papadopoulos, Periklis; Davies, Carol; Loomis, Mark; Prabhu, Dinesh; Langhoff, Stephen R. (Technical Monitor)
1997-01-01
Grid generation issues relating to the simulation of the X33 aerothermal environment using the GASP code are explored. Required grid densities and normal grid stretching are discussed with regards to predicting the fluid dynamic and heating environments with the desired accuracy. The generation of volume grids is explored and includes discussions of structured grid generation packages such as GRIDGEN, GRIDPRO and HYPGEN. Volume grid manipulation techniques for obtaining desired outer boundary and grid clustering using the OUTBOUND code are examined. The generation of the surface grid with the required surface grid with the required surface grid topology is also discussed. Utilizing grids without singular axes is explored as a method of avoiding numerical difficulties at the singular line.
NASA Technical Reports Server (NTRS)
White, Todd Richard; Mahazari, Milad; Bose, Deepak; Santos, Jose Antonio
2013-01-01
The Mars Science Laboratory successfully landed on the Martian surface on August 5th, 2012. The rover was protected from the extreme heating environments of atmospheric entry by an ablative heatshield. This Phenolic Impregnated Carbon Ablator heatshield was instrumented with a suite of embedded thermocouples, isotherm sensors, and pressure transducers. The sensors monitored the in-depth ablator response, as well as the surface pressure at discrete locations throughout the hypersonic deceleration. This paper presents a comparison of the flight data with post-entry estimates. An assessment of the aerothermal environments, as well as the in-depth response of the heatshield material is made, and conclusions regarding the overall performance of the ablator at the suite locations are presented.
NASA Technical Reports Server (NTRS)
Ko, William L.; Gong, Leslie
2000-01-01
To visually record the initial free flight event of the Hyper-X research flight vehicle immediately after separation from the Pegasus(registered) booster rocket, a video camera was mounted on the bulkhead of the adapter through which Hyper-X rides on Pegasus. The video camera was shielded by a protecting camera window made of heat-resistant quartz material. When Hyper-X separates from Pegasus, this camera window will be suddenly exposed to Mach 7 stagnation thermal shock and dynamic pressure loading (aerothermal loading). To examine the structural integrity, thermoelastic analysis was performed, and the stress distributions in the camera windows were calculated. The critical stress point where the tensile stress reaches a maximum value for each camera window was identified, and the maximum tensile stress level at that critical point was found to be considerably lower than the tensile failure stress of the camera window material.
Development of a Tool to Recreate the Mars Science Laboratory Aerothermal Environment
NASA Technical Reports Server (NTRS)
Beerman, A. F.; Lewis, M. J.; Santos, J. A.; White, T. R.
2010-01-01
The Mars Science Laboratory will enter the Martian atmosphere in 2012 with multiple char depth sensors and in-depth thermocouples in its heatshield. The aerothermal environment experienced by MSL may be computationally recreated using the data from the sensors and a material response program, such as the Fully Implicit Ablation and Thermal (FIAT) response program, through the matching of the char depth and thermocouple predictions of the material response program to the sensor data. A tool, CHanging Inputs from the Environment of FIAT (CHIEF), was developed to iteratively change different environmental conditions such that FIAT predictions match within certain criteria applied to an external data set. The computational environment is changed by iterating on the enthalpy, pressure, or heat transfer coefficient at certain times in the trajectory. CHIEF was initially compared against arc-jet test data from the development of the MSL heatshield and then against simulated sensor data derived from design trajectories for MSL. CHIEF was able to match char depth and in-depth thermocouple temperatures within the bounds placed upon it for these cases. Further refinement of CHIEF to compare multiple time points and assign convergence criteria may improve accuracy.
NASA Technical Reports Server (NTRS)
Karki, K. C.; Mongia, H. C.; Patankar, Suhas V.; Runchal, A. K.
1987-01-01
The objective of this effort is to develop improved numerical schemes for predicting combustor flow fields. Various candidate numerical schemes were evaluated, and promising schemes were selected for detailed assessment. The criteria for evaluation included accuracy, computational efficiency, stability, and ease of extension to multidimensions. The candidate schemes were assessed against a variety of simple one- and two-dimensional problems. These results led to the selection of the following schemes for further evaluation: flux spline schemes (linear and cubic) and controlled numerical diffusion with internal feedback (CONDIF). The incorporation of the flux spline scheme and direct solution strategy in a computer program for three-dimensional flows is in progress.
Improved numerical methods for turbulent viscous flows aerothermal modeling program, phase 2
NASA Technical Reports Server (NTRS)
Karki, K. C.; Patankar, S. V.; Runchal, A. K.; Mongia, H. C.
1988-01-01
The details of a study to develop accurate and efficient numerical schemes to predict complex flows are described. In this program, several discretization schemes were evaluated using simple test cases. This assessment led to the selection of three schemes for an in-depth evaluation based on two-dimensional flows. The scheme with the superior overall performance was incorporated in a computer program for three-dimensional flows. To improve the computational efficiency, the selected discretization scheme was combined with a direct solution approach in which the fluid flow equations are solved simultaneously rather than sequentially.
Leakage effects in car underhood aerothermal management: temperature and heat flux analysis
NASA Astrophysics Data System (ADS)
Khaled, Mahmoud; Habchi, Charbel; Harambat, Fabien; Elmarakbi, Ahmed; Peerhossaini, Hassan
2014-10-01
Air leakage from the engine compartment of a vehicle comes mainly from the junctions of the vehicle hood and the front end grill, the vehicle wings, the optical and the windshield. The present paper studies the thermal impact of these air leakage zones on the components of the vehicle engine compartment through temperature and heat-flux measurements. The front wheels of the test vehicle are positioned on a dynamometer and driven by the vehicle engine. The engine compartment is instrumented with almost 100 surface and air thermocouples and 20 fluxmeters of normal gradients. Measurements were made for three different thermal operating points. Five leak-sealing configurations are studied.
Hypersonic aerothermal characteristics of a manned low finenes ratio shuttle booster
NASA Technical Reports Server (NTRS)
Bernot, P. T.; Throckmorton, D. A.
1972-01-01
An investigation of a winged booster model having canards and an ascent configuration comprised of the booster mounted in tandem with an orbiter model has been conducted at Mach 10.2 in the continuous flow hypersonic tunnel. Longitudinal and lateral directional force characteristics were obtained over angle of attack ranges of -12 deg to 60 deg for the booster and -11 deg to 11 deg for the ascent configuration. Interference heating effects on the booster using the phase-change coating technique were determined at 0 deg angle of attack. Some oil flow photographs of the isolated booster and orbiter and ascent configuration are also presented.
Direct and system effects of water ingestion into jet engine compresors
NASA Technical Reports Server (NTRS)
Murthy, S. N. B.; Ehresman, C. M.; Haykin, T.
1986-01-01
Water ingestion into aircraft-installed jet engines can arise both during take-off and flight through rain storms, resulting in engine operation with nearly saturated air-water droplet mixture flow. Each of the components of the engine and the system as a whole are affected by water ingestion, aero-thermally and mechanically. The greatest effects arise probably in turbo-machinery. Experimental and model-based results (of relevance to 'immediate' aerothermal changes) in compressors have been obtained to show the effects of film formation on material surfaces, centrifugal redistribution of water droplets, and interphase heat and mass transfer. Changes in the compressor performance affect the operation of the other components including the control and hence the system. The effects on the engine as a whole are obtained through engine simulation with specified water ingestion. The interest is in thrust, specific fuel consumption, surge margin and rotational speeds. Finally two significant aspects of performance changes, scalability and controllability, are discussed in terms of characteristic scales and functional relations.
Bohn, D.E.; Kusterer, K.A.
2000-04-01
A leading edge cooling configuration is investigated numerically by application of a three-dimensional conjugate fluid flow and heat transfer solver, CHT-flow. The code has been developed at the Institute of Steam and Gas Turbines, Aachen University of Technology. It works on the basis of an implicit finite volume method combined with a multi-block technique. The cooling configuration is an axial turbine blade cascade with leading edge ejection through two rows of cooling holes. The rows are located in the vicinity of the stagnation line, one row on the suction side, the other row is on the pressure side. the cooling holes have a radial ejection angle of 45 degrees. This configuration has been investigated experimentally by other authors and the results have been documented as a test case for numerical calculations of ejection flow phenomena. The numerical investigations focus on the aerothermal mixing process in the cooling jets and the impact on the temperature distribution on the blade surface. The radial ejection angles lead to a fully three-dimensional and asymmetric jet flow field. Within a secondary flow analysis, the cooling fluid jets are investigated in detail. The secondary flow fields include asymmetric kidney vortex systems with one dominating vortex on the back side of the jets. The numerical and experimental data show a respectable agreement concerning the vortex development.
Numerical simulation of aerothermal loads in hypersonic engine inlets due to shock impingement
NASA Technical Reports Server (NTRS)
Ramakrishnan, R.
1992-01-01
The effect of shock impingement on an axial corner simulating the inlet of a hypersonic vehicle engine is modeled using a finite-difference procedure. A three-dimensional dynamic grid adaptation procedure is utilized to move the grids to regions with strong flow gradients. The adaptation procedure uses a grid relocation stencil that is valid at both the interior and boundary points of the finite-difference grid. A linear combination of spatial derivatives of specific flow variables, calculated with finite-element interpolation functions, are used as adaptation measures. This computational procedure is used to study laminar and turbulent Mach 6 flows in the axial corner. The description of flow physics and qualitative measures of heat transfer distributions on cowl and strut surfaces obtained from the analysis are compared with experimental observations. Conclusions are drawn regarding the capability of the numerical scheme for enhanced modeling of high-speed compressible flows.
Analysis of Aerothermal Heating Over Reusable Single-Stage to Orbit Vehicles
NASA Technical Reports Server (NTRS)
Chen, Y. K.; Henline, William D.; Rasky, Daniel J. (Technical Monitor)
1995-01-01
Using the General Aerodynamic Simulation Program (GASP) with finite-rate surface catalysis and radiative equilibrium surface temperature conditions, a computational study has been conducted to predict three-dimensional aero-convective heating over the proposed reusable single-stage to orbit vehicles. The solutions for three basic classes of usable single-stage-to-orbit vehicles, including wing body, lifting body and vertical lander, are presented and compared to provide information for vehicle design. The free stream conditions used in this study occur at an altitude of 57.5 km, ambient density of 4.129e-4 kg/cubic m, and velocity of 4,849 m/s. The convective heating over the vehicle surface in both laminar and turbulent flow regimes were computed. The Baldwin-Lomax algebraic model with a modified van Driest damping factor was applied in the turbulent flow calculations. A bifurcation model which guarantees the conservation of mass diffusive fluxes was adopted to account for the multi-species mass diffusion. The effects of turbulence and surface catalysis on the surface heating are discussed in detail The solutions indicate the degree of oxygen dissociation over the leeward side is sensitive to the shape of vehicle body. Predicted convective heating over the entire surface of lifting body is strongly affected by the presence of surface catalysis. For wing body and vertical lander, the surface catalysis effect does not appear to be important in the far downstream region, and turbulence is the dominant effect on the heating prediction in this region.
NASA Astrophysics Data System (ADS)
MacLean, M.; Holden, M.
2009-01-01
The effect of gas/surface interaction in making CFD predictions of convective heating has been considered with application to ground tests performed in high enthalpy shock tunnels where additional heating augmentation attributable to surface recombination has been observed for nitrogen, air and carbon dioxide flows. For test articles constructed of stainless steel and aluminum, measurements have been made with several types of heat transfer instrumentation including thin- film, calorimeter, and coaxial thermocouple sensors. These experiments have been modeled by computations made with the high quality, chemically reacting, Navier- Stokes solver, DPLR and the heating results compared. Some typical cases considered include results on an axisymmetric sphere-cone, axisymmetric spherical capsule, spherical capsule at angle of attack, and two- dimensional cylinder. In nitrogen flows, cases considered show a recombination probability on the order of 10-3, which agrees with published data. In many cases in air and CO2, measurements exceeding the predicted level of convective heating have been observed which are consistent with approximately complete recombination (to O2/N2 or CO2) on the surface of the model (sometimes called a super-catalytic wall). It has been recognized that the conclusion that this behavior is tied to an excessively high degree of catalytic efficiency is dependent on the current understanding of the freestream and shock-layer state of the gas.
NASA Technical Reports Server (NTRS)
Nowak, R. J.; Albertson, C. W.; Hunt, L. R.
1984-01-01
The effects of free-stream unit Reynolds number, angle of attack, and nose shape on the aerothermal environment of a 3-ft basediameter, 12.5 deg half-angle cone were investigated in the Langley 8-foot high temperature tunnel at Mach 6.7. The average total temperature was 3300 R, the freestream unit Reynolds number ranged from 400,000 to 1,400,000 per foot, and the angle of attack ranged from 0 deg to 10 deg. Three nose configurations were tested on the cone: a 3-in-radius tip, a 1-in-radius tip on an ogive frustum, and a sharp tip on an ogive frustum. Surface-pressure and cold-wall heating-rate distributions were obtained for laminar, transitional temperature in the shock layer were obtained. The location of the start of transition moved forward both on windward and leeward sides with increasing free-stream Reynolds numbers, increasing angle of attack, and decreasing nose bluntness.
NASA Technical Reports Server (NTRS)
Tiwari, S. N.; Subramanian, S. V.
1981-01-01
The influence of nonequilibrium radiative energy transfer and the effect of probe configuration changes on the flow phenomena around a Jovian entry body are investigated. The radiating shock layer flow is assumed to be axisymmetric, viscous, laminar and in chemical equilibrium. The radiative transfer equations are derived under nonequilibrium conditions which include multilevel energy transitions. The equilibrium radiative transfer analysis is performed with an existing nongray radiation model which accounts for molecular band, atomic line, and continuum transitions. The nonequilibrium results are obtained with and without ablation injection in the shock layer. The nonequilibrium results are found to be greatly influenced by the temperature distribution in the shock layer. In the absence of ablative products, the convective and radiative heating to the entry body are reduced under nonequilibrium conditions. The influence of nonequilibrium is found to be greater at higher entry altitudes. With coupled ablation and carbon phenolic injection, 16 chemical species are used in the ablation layer for radiation absorption. Equilibrium and nonequilibrium results are compared under peak heating conditions.
Hribar-Lee, Barbara; Vlachy, Vojko; Dill, Ken A
2009-03-11
A two dimensional model of water, so-called Mercedes-Benz model, was used to study effects of the size of hydrophobic solute on the insertion thermodynamics in electrolyte solutions. The model was examined by the constant pressure Monte Carlo computer simulation. The results were compared with the experimental data for noble gasses and methane in water and electrolyte solution. The influence of different ions at infinite dilution on the free energy of transfer was explored. Qualitative agreement with the experimental results was obtained. The mechanism of Hofmeister effects was proposed.
Hribar-Lee, Barbara; Vlachy, Vojko; Dill, Ken A.
2009-01-01
A two dimensional model of water, so-called Mercedes-Benz model, was used to study effects of the size of hydrophobic solute on the insertion thermodynamics in electrolyte solutions. The model was examined by the constant pressure Monte Carlo computer simulation. The results were compared with the experimental data for noble gasses and methane in water and electrolyte solution. The influence of different ions at infinite dilution on the free energy of transfer was explored. Qualitative agreement with the experimental results was obtained. The mechanism of Hofmeister effects was proposed. PMID:20161468
Hribar-Lee, Barbara; Vlachy, Vojko; Dill, Ken A
2009-03-11
A two dimensional model of water, so-called Mercedes-Benz model, was used to study effects of the size of hydrophobic solute on the insertion thermodynamics in electrolyte solutions. The model was examined by the constant pressure Monte Carlo computer simulation. The results were compared with the experimental data for noble gasses and methane in water and electrolyte solution. The influence of different ions at infinite dilution on the free energy of transfer was explored. Qualitative agreement with the experimental results was obtained. The mechanism of Hofmeister effects was proposed. PMID:20161468
NASA Astrophysics Data System (ADS)
Beniaiche, Ahmed; Ghenaiet, Adel; Facchini, Bruno
2016-05-01
The aero-thermal behavior of the flow field inside 30:1 scaled model reproducing an innovative smooth trailing edge of shaped wedge discharge duct with one row of enlarged pedestals have been investigated in order to determine the effect of rotation, inlet velocity and blowing conditions effects, for Re = 20,000 and 40,000 and Ro = 0-0.23. Two configurations are presented: with and without open tip configurations. Thermo-chromic liquid crystals technique is used to ensure a local measurement of the heat transfer coefficient on the blade suction side under stationary and rotation conditions. Results are reported in terms of detailed 2D HTC maps on the suction side surface as well as the averaged Nusselt number inside the pedestal ducts. Two correlations are proposed, for both closed and open tip configurations, based on the Re, Pr, Ro and a new non-dimensional parameter based on the position along the radial distance, to assess a reliable estimation of the averaged Nusselt number at the inter-pedestal region. A good agreement is found between prediction and experimental data with about ±10 to ±12 % of uncertainty, for the simple form correlation, and about ±16 % using a complex form. The obtained results help to predict the flow field visualization and the evaluation of the aero-thermal performance of the studied blade cooling system during the design step.
NASA Technical Reports Server (NTRS)
Woods, W. C.; Arrington, J. P.
1972-01-01
Comparisons between flow visualization systems using electron-beam fluorescence, schlieren, and shadowgraph techniques illustrate the advantages associated with the electron beam. Specific applications of this method as an aid in defining the origin of erosion on a heat-transfer model are cited. Results of combined electron-beam oil-flow studies on configurations illustrate that the simultaneous definition of the external flow field and its surface flow can be obtained. Comparisons between the electron-beam oil-flow visualization method and phase-change coating heat-transfer tests on a shuttle ascent configuration indicate the complementary nature of these two testing techniques. Potential methods for improving the electron-beam technique are included.
Aero-thermal simulations of the TMT Laser Guide Star Facility
NASA Astrophysics Data System (ADS)
Vogiatzis, Konstantinos; Boyer, Corinne; Wei, Kai; Tang, Jinlong; Ellerbroek, Brent
2014-08-01
The Laser Guide Star Facility (LGSF) system of the Thirty Meter Telescope (TMT) will generate the artificial laser guide stars required by the TMT Adaptive Optics (AO) systems. The LGSF uses multiple sodium lasers to generate and project several asterisms from a laser launch telescope located behind the TMT secondary mirror. The laser beams are transported from a location below the primary mirror to the launch telescope using conventional optics to relay the beams along the telescope structure. The beams and relay optics are enclosed into hermetic ducts for safety reasons and to protect the optics against the environment. A Computational Solid Fluid Dynamics (CSFD) model of the LGSF ducts has been developed. It resolves the duct thickness, laser beam transfer lenses, mirrors and their framework for most of the laser beam path that is subject to significant temperature gradients and/or large vertical change. It also resolves the air inside the duct and its thermal interaction with the aforementioned components through conjugate heat transfer. The thermal interaction of the laser beam with the optics is also captured. The model provides guidance to the LGSF design team and a first estimate of the laser beam stability performance and requirement compliance. As the telescope structure design has evolved in the recent years, a new optical path has been proposed for the LGSF. Both the original and the new optical paths are compared against optical, mechanical and other telescope performance related criteria. The optical performance criteria include a first order analysis of the optical turbulence generated within the ducts. In this study simulations of the thermal environment within the ducts of the two candidate paths are performed and conclusions are drawn.
Ecotoxicological effects extrapolation models
Suter, G.W. II
1996-09-01
One of the central problems of ecological risk assessment is modeling the relationship between test endpoints (numerical summaries of the results of toxicity tests) and assessment endpoints (formal expressions of the properties of the environment that are to be protected). For example, one may wish to estimate the reduction in species richness of fishes in a stream reach exposed to an effluent and have only a fathead minnow 96 hr LC50 as an effects metric. The problem is to extrapolate from what is known (the fathead minnow LC50) to what matters to the decision maker, the loss of fish species. Models used for this purpose may be termed Effects Extrapolation Models (EEMs) or Activity-Activity Relationships (AARs), by analogy to Structure-Activity Relationships (SARs). These models have been previously reviewed in Ch. 7 and 9 of and by an OECD workshop. This paper updates those reviews and attempts to further clarify the issues involved in the development and use of EEMs. Although there is some overlap, this paper does not repeat those reviews and the reader is referred to the previous reviews for a more complete historical perspective, and for treatment of additional extrapolation issues.
NASA Technical Reports Server (NTRS)
Tiwari, S. N.; Subramanian, S. V.
1980-01-01
Radiative transfer equations are derived under nonequilibrium conditions which include multilevel energy transitions. The nonequalibrium results, obtained with and without ablation injection in the shock layer, are found to be greatly influenced by the temperature distribution in the shock layer. In the absence of ablative products, the convective and radiative heating to the entry body are reduced significantly under nonequilibrium conditions. The influence of nonequilibrium is found to be greater at higher entry altitudes. With coupled ablation and carbon phenolic injection, 16 chemical species are used in the ablation layer for radiation absorption. Equilibrium and nonequilibrium results are compared under peak heating conditions. A 45 degree sphere cone, a 35 degree hyperboloid, and a 45 degree ellipsoid were used to study probe shape change. Results indicate that the shock layer flow field and heat transfer to the body are influenced significantly by the probe shape change. The effect of shape change on radiative heating of the afterbodies is found to be considerably larger for the sphere cone and ellipsoid than for the hyperboloid.
Development of a Multi-Disciplinary Aerothermostructural Model Applicable to Hypersonic Flight
NASA Technical Reports Server (NTRS)
Kostyk, Chris; Risch, Tim
2013-01-01
The harsh and complex hypersonic flight environment has driven design and analysis improvements for many years. One of the defining characteristics of hypersonic flight is the coupled, multi-disciplinary nature of the dominant physics. In an effect to examine some of the multi-disciplinary problems associated with hypersonic flight engineers at the NASA Dryden Flight Research Center developed a non-linear 6 degrees-of-freedom, full vehicle simulation that includes the necessary model capabilities: aerothermal heating, ablation, and thermal stress solutions. Development of the tool and results for some investigations will be presented. Requirements and improvements for future work will also be reviewed. The results of the work emphasize the need for a coupled, multi-disciplinary analysis to provide accurate
Astroinfect Effect - Revised Model
NASA Astrophysics Data System (ADS)
Arkhipov, A. V.
Space activities lead to a lasting pollution of the Solar System. Light pressure, gravitational interaction with the planets, collisions and explosions (similar to spontaneous explosions of Earth satellite) of artefacts in the outer parts of the planetary system can lead to effective, inevitable spontaneous leakage of interplanetary trash into the interstellar medium, even in the absence of interstellar flights. If there are alien artefacts between the stars, some of them are likely to fall down to Earth at times [1,2]. They could be non-sterile, so sporadic interstellar panspermia is possible [3]. The minimum pollution threshold for such panspermia was estimated [2] for 2 m-microartefacts at the level of Galactic cosmic radiation of 4 x 10-7 rad/s [4]. However, C. Mileikowsky showed that, if the X-rays are taken into consideration, the interstellar dose rate is ~3 x 10- 5 rad/s [5]. At this high dose rate the microartefacts must be sterilised at the distances >0.1 pc from the planetary system, hence they cannot be an effective agent of interstellar panspermia. Sufficient protection of microbial spores is possible inside macroartefacts. Therefore, the panspermia model and the corresponding minimum pollution threshold must be re-examined.
ERIC Educational Resources Information Center
Eichinger, John
2005-01-01
Models are crucial to science teaching and learning, yet they can create unforeseen and overlooked challenges for students and teachers. For example, consider the time-tested clay volcano that relies on a vinegar and-baking-soda mixture for its "eruption." Based on a classroom demonstration of that geologic model, elementary students may interpret…
NASA Technical Reports Server (NTRS)
Wadhams, T.P.; MacLean, M.; Holden, M.S.; Cassady, A.M.
2009-01-01
An experimental program has been completed by CUBRC exploring laminar, transitional, and turbulent flows over a 7.0% scale model of the Project ORION CEV geometry. This program was executed primarily to answer questions concerning the increase in heat transfer on the windward, or "hot shoulder" of the CEV heat shield from laminar to turbulent flow. To answer these questions CUBRC constructed and instrumented a 14.0 inch diameter Project ORION CEV model and ran a range of Reynolds numbers based on diameter from 1.0 to over 40 million at a Mach number of 8.0. These Reynolds numbers were selected to cover laminar to turbulent heating data on the "hot shoulder". Data obtained during these runs will be used to guide design decisions as they apply to heat shield thickness and extent. Several experiments at higher enthalpies were achieved to obtain data for code validation with real gas effects and transition. CUBRC also performed computation studies of these experiments to aid in the data reduction process and study turbulence modeling.
NASA Technical Reports Server (NTRS)
Vemaganti, Gururaja R.
1994-01-01
This report presents computations for the Type 4 shock-shock interference flow under laminar and turbulent conditions using unstructured grids. Mesh adaptation was accomplished by remeshing, refinement, and mesh movement. Two two-equation turbulence models were used to analyze turbulent flows. The mean flow governing equations and the turbulence governing equations are solved in a coupled manner. The solution algorithm and the details pertaining to its implementation on unstructured grids are described. Computations were performed at two different freestream Reynolds numbers at a freestream Mach number of 11. Effects of the variation in the impinging shock location are studied. The comparison of the results in terms of wall heat flux and wall pressure distributions is presented.
Multilevel Modeling with Correlated Effects
ERIC Educational Resources Information Center
Kim, Jee-Seon; Frees, Edward W.
2007-01-01
When there exist omitted effects, measurement error, and/or simultaneity in multilevel models, explanatory variables may be correlated with random components, and standard estimation methods do not provide consistent estimates of model parameters. This paper introduces estimators that are consistent under such conditions. By employing generalized…
The Compass Rose Effectiveness Model
ERIC Educational Resources Information Center
Spiers, Cynthia E.; Kiel, Dorothy; Hohenrink, Brad
2008-01-01
The effectiveness model focuses the institution on mission achievement through assessment and improvement planning. Eleven mission criteria, measured by key performance indicators, are aligned with the accountability interest of internal and external stakeholders. A Web-based performance assessment application supports the model, documenting the…
Size Effect in Continuum Modeling
Lu, Wei-Yang; James W. Foulk; Huestis, Edwin M.; Connelly, Kevin; Song, Bo; Yang, Nancy Y. C.
2008-09-01
The mechanical properties of some materials (Cu, Ni, Ag, etc.) have been shown to develop strong dependence on the geometric dimensions, resulting in a size effect. Several theories have been proposed to model size effects, but have been based on very few experiments conducted at appropriate scales. Some experimental results implied that size effects are caused by increasing strain gradients and have been used to confirm many strain gradient theories. On the other hand, some recent experiments show that a size effect exists in the absence of strain gradients. This report describes a brief analytical and experimental study trying to clarify the material and experimental issues surrounding the most influential size-effect experiments by Fleck et al (1994). This effort is to understand size effects intended to further develop predictive models.
Test model designs for advanced refractory ceramic materials
NASA Technical Reports Server (NTRS)
Tran, Huy Kim
1993-01-01
The next generation of space vehicles will be subjected to severe aerothermal loads and will require an improved thermal protection system (TPS) and other advanced vehicle components. In order to ensure the satisfactory performance system (TPS) and other advanced vehicle materials and components, testing is to be performed in environments similar to space flight. The design and fabrication of the test models should be fairly simple but still accomplish test objectives. In the Advanced Refractory Ceramic Materials test series, the models and model holders will need to withstand the required heat fluxes of 340 to 817 W/sq cm or surface temperatures in the range of 2700 K to 3000 K. The model holders should provide one dimensional (1-D) heat transfer to the samples and the appropriate flow field without compromising the primary test objectives. The optical properties such as the effective emissivity, catalytic efficiency coefficients, thermal properties, and mass loss measurements are also taken into consideration in the design process. Therefore, it is the intent of this paper to demonstrate the design schemes for different models and model holders that would accommodate these test requirements and ensure the safe operation in a typical arc jet facility.
Modeling Incoherent Electron Cloud Effects
Fischer, W.; Benedetto, E.; Rumolo, G.; Schulte, D.; Tomas, R.; Zimmermann, Frank; Franchetti, G.; Ohmi, Kazuhito; Sonnad, K.G.; Vay, Jean-Luc; Pivi, M.T.F.; Raubenheimer, Tor O.; /SLAC
2008-01-24
Incoherent electron effects could seriously limit the beam lifetime in proton or ion storage rings, such as LHC, SPS, or RHIC, or blow up the vertical emittance of positron beams, e.g., at the B factories or in linear-collider damping rings. Different approaches to modeling these effects each have their own merits and drawbacks. We describe several simulation codes which simplify the descriptions of the beam-electron interaction and of the accelerator structure in various different ways, and present results for a toy model of the SPS. In addition, we present evidence that for positron beams the interplay of incoherent electron-cloud effects and synchrotron radiation can lead to a significant increase in vertical equilibrium emittance. The magnitude of a few incoherent e{sup +}e{sup -} scattering processes is also estimated. Options for future code development are reviewed.
Modeling Incoherent Electron Cloud Effects
Vay, Jean-Luc; Benedetto, E.; Fischer, W.; Franchetti, G.; Ohmi, K.; Schulte, D.; Sonnad, K.; Tomas, R.; Vay, J.-L.; Zimmermann, F.; Rumolo, G.; Pivi, M.; Raubenheimer, T.
2007-06-18
Incoherent electron effects could seriously limit the beam lifetime in proton or ion storage rings, such as LHC, SPS, or RHIC, or blow up the vertical emittance of positron beams, e.g., at the B factories or in linear-collider damping rings. Different approaches to modeling these effects each have their own merits and drawbacks. We describe several simulation codes which simplify the descriptions of the beam-electron interaction and of the accelerator structure in various different ways, and present results for a toy model of the SPS. In addition, we present evidence that for positron beams the interplay of incoherent electron-cloud effects and synchrotron radiation can lead to a significant increase in vertical equilibrium emittance. The magnitude of a few incoherent e+e- scattering processes is also estimated. Options for future code development are reviewed.
Orion MPCV Continuum RCS Heating Augmentation Model Development
NASA Technical Reports Server (NTRS)
Hyatt, Andrew J.; White, Molly E.
2014-01-01
The reaction control system jets of the Orion Multi Purpose Crew Vehicle can have a significant impact on the magnitude and distribution of the surface heat flux on the leeside of the aft-body, when they are fired. Changes in surface heating are expressed in terms of augmentation factor over the baseline smooth body heating. Wind tunnel tests revealed heating augmentation factors as high as 13.0, 7.6, 2.8, and 5.8 for the roll, pitch down, pitch up, and yaw jets respectively. Heating augmentation factor models, based almost exclusively on data from a series of wind tunnel tests have been developed, for the purposes of thermal protection system design. The wind tunnel tests investigated several potential jet-to-freestream similarity parameters, and heating augmentation factors derived from the data showed correlation with the jet-to-freestream momentum ratio. However, this correlation was not utilized in the developed models. Instead augmentation factors were held constant throughout the potential trajectory space. This simplification was driven by the fact that ground to flight traceability and sting effects are not well understood. Given the sensitivity of the reaction control system jet heating augmentation to configuration, geometry, and orientation the focus in the present paper is on the methodology used to develop the models and the lessons learned from the data. The models that are outlined in the present work are specific to the aerothermal database used to design the thermal protection system for the Exploration Flight Test 1 vehicle.
Mathematical model for gyroscope effects
NASA Astrophysics Data System (ADS)
Usubamatov, Ryspek
2015-05-01
Gyroscope effects are used in many engineering calculations of rotating parts, and a gyroscope is the basic unit of numerous devices and instruments used in aviation, space, marine and other industries. The primary attribute of a gyroscope is a spinning rotor that persists in maintaining its plane of rotation, creating gyroscope effects. Numerous publications represent the gyroscope theory using mathematical models based on the law of kinetic energy conservation and the rate of change in angular momentum of a spinning rotor. Gyroscope theory still attracts many researchers who continue to discover new properties of gyroscopic devices. In reality, gyroscope effects are more complex and known mathematical models do not accurately reflect the actual motions. Analysis of forces acting on a gyroscope shows that four dynamic components act simultaneously: the centrifugal, inertial and Coriolis forces and the rate of change in angular momentum of the spinning rotor. The spinning rotor generates a rotating plane of centrifugal and Coriols forces that resist the twisting of the spinning rotor with external torque applied. The forced inclination of the spinning rotor generates inertial forces, resulting in precession torque of a gyroscope. The rate of change of the angular momentum creates resisting and precession torques which are not primary one in gyroscope effects. The new mathematical model for the gyroscope motions under the action of the external torque applied can be as base for new gyroscope theory. At the request of the author of the paper, this corrigendum was issued on 24 May 2016 to correct an incomplete Table 1 and errors in Eq. (47) and Eq. (48).
Better models are more effectively connected models
NASA Astrophysics Data System (ADS)
Nunes, João Pedro; Bielders, Charles; Darboux, Frederic; Fiener, Peter; Finger, David; Turnbull-Lloyd, Laura; Wainwright, John
2016-04-01
The concept of hydrologic and geomorphologic connectivity describes the processes and pathways which link sources (e.g. rainfall, snow and ice melt, springs, eroded areas and barren lands) to accumulation areas (e.g. foot slopes, streams, aquifers, reservoirs), and the spatial variations thereof. There are many examples of hydrological and sediment connectivity on a watershed scale; in consequence, a process-based understanding of connectivity is crucial to help managers understand their systems and adopt adequate measures for flood prevention, pollution mitigation and soil protection, among others. Modelling is often used as a tool to understand and predict fluxes within a catchment by complementing observations with model results. Catchment models should therefore be able to reproduce the linkages, and thus the connectivity of water and sediment fluxes within the systems under simulation. In modelling, a high level of spatial and temporal detail is desirable to ensure taking into account a maximum number of components, which then enables connectivity to emerge from the simulated structures and functions. However, computational constraints and, in many cases, lack of data prevent the representation of all relevant processes and spatial/temporal variability in most models. In most cases, therefore, the level of detail selected for modelling is too coarse to represent the system in a way in which connectivity can emerge; a problem which can be circumvented by representing fine-scale structures and processes within coarser scale models using a variety of approaches. This poster focuses on the results of ongoing discussions on modelling connectivity held during several workshops within COST Action Connecteur. It assesses the current state of the art of incorporating the concept of connectivity in hydrological and sediment models, as well as the attitudes of modellers towards this issue. The discussion will focus on the different approaches through which connectivity
Mechanical effects in cookoff modeling
Gross, R.J.; Baer, M.R.; Hobbs, M.L.
1994-07-01
Complete cookoff modeling of energetic material in confined geometries must couple thermal, chemical and mechanical effects. In the past, modeling has focused on the prediction of the onset of combustion behavior based only on thermal-chemistry effects with little or no regard to the mechanical behavior of the energetic material. In this paper, an analysis tool is outlined which couples thermal, chemical, and mechanical behavior for one-dimensional Geometries comprised of multi-materials. A reactive heat flow code, XCHEM, and a quasistatic mechanics code, SANTOS, have been completely coupled using, a reactive, elastic-plastic constitutive model describing pressurization of the energetic material. This new Thermally Reactive Elastic-plastic explosive code, TREX, was developed to assess the coupling, of mechanics with thermal chemistry making multidimensional cookoff analysis possible. In this study, TREX is applied to confined and unconfined systems. The confined systems simulate One-Dimensional Time to explosion (ODTX) experiments in both spherical and cylindrical configurations. The spherical ODTX system is a 1.27 cm diameter sphere of TATB confined by aluminum exposed to a constant external temperature. The cylindrical ODTX system is an aluminum tube filled with HMX, NC, and inert exposed to a constant temperature bath. Finally. an unconfined system consisting of a hollow steel cylinder filled with a propellant composed of Al, RMX, and NC, representative of a rocket motor, is considered. This model system is subjected to transient internal and external radiative/convective boundary conditions representative of 5 minutes exposure to a fire. The confined systems show significant pressure prior to ignition, and the unconfined system shows extrusion of the propellent suggesting that the energetic material becomes more shock sensitive.
Model of neutrino effective masses
Dinh Nguyen Dinh; Nguyen Thi Hong Van; Nguyen Anh Ky; Phi Quang Van
2006-10-01
It is shown that an effective (nonrenormalizable) coupling of lepton multiplets to scalar triplets in the 331 model with sterile/exotic neutrinos, can be a good way for generating neutrino masses of different types. The method is simple and avoids radiative/loop calculations which, sometimes, are long and complicated. Basing on some astrophysical arguments it is also stated that the scale of SU(3){sub L} symmetry breaking is at TeV scale, in agreement with earlier investigations. Or equivalently, starting from this symmetry breaking scale we could have sterile/exotic neutrinos with mass of a few keV's which could be used to explain several astrophysical and cosmological puzzles, such as the dark matter, the fast motion of the observed pulsars, the re-ionization of the Universe, etc.
The critical role of aerodynamic heating effects in the design of hypersonic vehicles
NASA Technical Reports Server (NTRS)
Wieting, Allan R.
1989-01-01
Hypersonic vehicles operate in a hostile aerothermal environment, which has a significant impact on their aerothermostructural performance. Significant coupling occurs between the aerodynamic flow field, structural heat transfer, and structural response, creating a multidisciplinary interaction. The critical role of aerodynamic heating effects in the design of hypersonic vehicles is identified with an example of high localized heating on an engine-cowl leading edge. Recent advances is integrated fluid-thermal-structural finite-element analyses are presented.
Random Effects Diagonal Metric Multidimensional Scaling Models.
ERIC Educational Resources Information Center
Clarkson, Douglas B.; Gonzalez, Richard
2001-01-01
Defines a random effects diagonal metric multidimensional scaling model, gives its computational algorithms, describes researchers' experiences with these algorithms, and provides an illustration of the use of the model and algorithms. (Author/SLD)
Random-effects models for longitudinal data
Laird, N.M.; Ware, J.H.
1982-12-01
Models for the analysis of longitudinal data must recognize the relationship between serial observations on the same unit. Multivariate models with general covariance structure are often difficult to apply to highly unbalanced data, whereas two-stage random-effects models can be used easily. In two-stage models, the probability distributions for the response vectors of different individuals belong to a single family, but some random-effects parameters vary across individuals, with a distribution specified at the second stage. A general family of models is discussed, which includes both growth models and repeated-measures models as special cases. A unified approach to fitting these models, based on a combination of empirical Bayes and maximum likelihood estimation of model parameters and using the EM algorithm, is discussed. Two examples are taken from a current epidemiological study of the health effects of air pollution.
ERIC Educational Resources Information Center
Huang, Hung-Yu; Wang, Wen-Chung
2014-01-01
The DINA (deterministic input, noisy, and gate) model has been widely used in cognitive diagnosis tests and in the process of test development. The outcomes known as slip and guess are included in the DINA model function representing the responses to the items. This study aimed to extend the DINA model by using the random-effect approach to allow…
NASA Astrophysics Data System (ADS)
Prisbell, A.; Marichalar, J.; Lumpkin, F.; LeBeau, G.
2011-05-01
Plume impingement effects on the Orion Crew Service Module (CSM) were analyzed for various dual Reaction Control System (RCS) engine firings and various configurations of the solar arrays. The study was performed using a decoupled computational fluid dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) approach. This approach included a single jet plume solution for the R1E RCS engine computed with the General Aerodynamic Simulation Program (GASP) CFD code. The CFD solution was used to create an inflow surface for the DSMC solution based on the Bird continuum breakdown parameter. The DSMC solution was then used to model the dual RCS plume impingement effects on the entire CSM geometry with deployed solar arrays. However, because the continuum breakdown parameter of 0.05 could not be achieved due to geometrical constraints and because high resolution in the plume shock interaction region is desired, a focused DSMC simulation modeling only the plumes and the shock interaction region was performed. This high resolution intermediate solution was then used as the inflow to the larger DSMC solution to obtain plume impingement heating, forces, and moments on the CSM and the solar arrays for a total of 21 cases that were analyzed. The results of these simulations were used to populate the Orion CSM Aerothermal Database.
NASA Technical Reports Server (NTRS)
Prisbell, Andrew; Marichalar, J.; Lumpkin, F.; LeBeau, G.
2010-01-01
Plume impingement effects on the Orion Crew Service Module (CSM) were analyzed for various dual Reaction Control System (RCS) engine firings and various configurations of the solar arrays. The study was performed using a decoupled computational fluid dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) approach. This approach included a single jet plume solution for the R1E RCS engine computed with the General Aerodynamic Simulation Program (GASP) CFD code. The CFD solution was used to create an inflow surface for the DSMC solution based on the Bird continuum breakdown parameter. The DSMC solution was then used to model the dual RCS plume impingement effects on the entire CSM geometry with deployed solar arrays. However, because the continuum breakdown parameter of 0.5 could not be achieved due to geometrical constraints and because high resolution in the plume shock interaction region is desired, a focused DSMC simulation modeling only the plumes and the shock interaction region was performed. This high resolution intermediate solution was then used as the inflow to the larger DSMC solution to obtain plume impingement heating, forces, and moments on the CSM and the solar arrays for a total of 21 cases that were analyzed. The results of these simulations were used to populate the Orion CSM Aerothermal Database.
Effect of modeling on sexual imagery.
Sachs, D H; Duffy, K G
1976-07-01
Social learning theory was used to examine the effects of a model's sexual imagery on the observer's sexual imagery. In the guise of a creative writing experiment, male and female college students were asked to listen to a tape recording of a same- or opposite-sex model relating a story in response to a sample TAT card. The story described a man and a woman in a physical sex encounter (high sex), a romantic date (medium sex), or a casual study date (low sex). The sample TAT picture and model's story were omitted in the control groups. All subjects wrote stories in response to two other TAT cards. These stories were scored for sexual imagery by a male and a female judge who were blind to experimental conditions and who used a standard sexual imagery scoring manual. The following prediction were based on social learning theory: There would be greater sexual imagery in the stories of subjects who heard the high sex model than in the stories of those who heard the medium or low sex model or no model. Past research implied the prediction that the modeling effects would be greater for males than for females in the high sex model condition and greater for females than for males in the medium sex model condition. The results were analyzed using two factorial analyses of variance. There was greater sexual imagery by subjects who heard the high sex model than by those who heard the low sex model or model. The sexual imagery by subjects who heard the medium sex model was intermediate between that by those who heard the high sex model and that by those who heard the low sex model. The modeling effect was greater in males. The results also confirmed the prediction that sexual imagery would be greater for males in the high sex model condition but did not confirm the prediction that sexual imagery would be greater for females in the medium sex model condition.
Scientists' internal models of the greenhouse effect
NASA Astrophysics Data System (ADS)
Libarkin, J. C.; Miller, H.; Thomas, S. R.
2013-12-01
A prior study utilized exploratory factor analysis to identify models underlying drawings of the greenhouse effect made by entering university freshmen. This analysis identified four archetype models of the greenhouse effect that appear within the college enrolling population. The current study collected drawings made by 144 geoscientists, from undergraduate geoscience majors through professionals. These participants scored highly on a standardized assessment of climate change understanding and expressed confidence in their understanding; many also indicated that they teach climate change in their courses. Although geoscientists held slightly more sophisticated greenhouse effect models than entering freshmen, very few held complete, explanatory models. As with freshmen, many scientists (44%) depict greenhouse gases in a layer in the atmosphere; 52% of participants depicted this or another layer as a physical barrier to escaping energy. In addition, 32% of participants indicated that incoming light from the Sun remains unchanged at Earth's surface, in alignment with a common model held by students. Finally, 3-20% of scientists depicted physical greenhouses, ozone, or holes in the atmosphere, all of which correspond to non-explanatory models commonly seen within students and represented in popular literature. For many scientists, incomplete models of the greenhouse effect are clearly enough to allow for reasoning about climate change. These data suggest that: 1) better representations about interdisciplinary concepts, such as the greenhouse effect, are needed for both scientist and public understanding; and 2) the scientific community needs to carefully consider how much understanding of a model is needed before necessary reasoning can occur.
Effective roughness in meso-scale modeling.
NASA Astrophysics Data System (ADS)
Nielsen, Joakim R.
2010-05-01
Effective roughness in meso-scale modeling. J.R. Nielsen, E. Dellwik, A. Hahmann, A. Sogachev, C.B. Hasager, Wind Energy Division, Risø DTU National Laboratory, Denmark Accurate estimation of effective roughness lengths for use in meso-scale models in heterogeneous terrain requires assessment of highly non-linear processes. These non-linear effects are often neglected in meso-scale modeling where, typically, a simple logarithmic average or a dominant vegetation type provide crude estimates of the aggregated aerodynamical roughness length in each grid cell. Although the parameterizations are computationally efficient, improvements are needed since some regional-scale sensitivity studies indicate that grid cell roughnesses strongly influence model predictions (i.e. Hasager and Jensen, 1999). Effective roughness parameterizations can be provided through the use of microscale flow models, which simulate the he local scale effect of orography and roughness changes. Results from two linearized micro-scale models and a k-ω model (Sogachev and Panferov, 2006) are presented for an idealized terrain with roughness changes. Furthermore, sensitivity experiments are performed within the meso-scale model WRF (Weather Research and Forecasting) using the standard Community Noah Land Surface model. The same experiment will be performed with a new modified version with multi-physics options (Niu et al.,submitted 2009). The analysis is carried out using different roughness aggregation techniques in WRF and the influence on scalar fluxes such as temperature, humidity and CO2 is investigated. Based on the WRF sensitivity analysis and the results of micro-scale modeling, the potential improvement of using micro-scale models for parameterization of sub-grid scale variability is evaluated.
Effect of Spray Cone Angle on Flame Stability in an Annular Gas Turbine Combustor
NASA Astrophysics Data System (ADS)
Mishra, R. K.; Kumar, S. Kishore; Chandel, Sunil
2016-04-01
Effect of fuel spray cone angle in an aerogas turbine combustor has been studied using computational fluid dynamics (CFD) and full-scale combustor testing. For CFD analysis, a 22.5° sector of an annular combustor is modeled and the governing equations are solved using the eddy dissipation combustion model in ANSYS CFX computational package. The analysis has been carried out at 125 kPa and 303 K inlet conditions for spray cone angles from 60° to 140°. The lean blowout limits are established by studying the behavior of combustion zone during transient engine operation from an initial steady-state condition. The computational study has been followed by testing the practical full-scale annular combustor in an aerothermal test facility. The experimental result is in a good agreement with the computational predictions. The lean blowout fuel-air ratio increases as the spray cone angle is decreased at constant operating pressure and temperature. At higher spray cone angle, the flame and high-temperature zone moves upstream close to atomizer face and a uniform flame is sustained over a wide region causing better flame stability.
Instructional Models Effective in Distance Education.
ERIC Educational Resources Information Center
Jackman, Diane H.; Swan, Michael K.
The purpose of this study was to identify which instructional models based on the framework of Joyce, Weil, and Showers, could be used effectively in distance education over the Interactive Video Network (IVN) system in North Dakota. Instructional models have been organized into families such as Information Processing, Social, Personal, and…
Effects of Self-Modelling on Stuttering
ERIC Educational Resources Information Center
Webber, Margaret J.; Packman, Ann; Onslow, Mark
2004-01-01
Background: The paper reports on a laboratory investigation of the effects of self-modelling on stuttering rate in adolescents and adults. Self-modelling refers to a therapeutic or training method, usually involving videotape, that uses exposure to oneself performing selected error-free behaviours as the conduit for promoting behaviour change.…
The Mixed Effects Trend Vector Model
ERIC Educational Resources Information Center
de Rooij, Mark; Schouteden, Martijn
2012-01-01
Maximum likelihood estimation of mixed effect baseline category logit models for multinomial longitudinal data can be prohibitive due to the integral dimension of the random effects distribution. We propose to use multidimensional unfolding methodology to reduce the dimensionality of the problem. As a by-product, readily interpretable graphical…
Optical Hall effect-model description: tutorial.
Schubert, Mathias; Kühne, Philipp; Darakchieva, Vanya; Hofmann, Tino
2016-08-01
The optical Hall effect is a physical phenomenon that describes the occurrence of magnetic-field-induced dielectric displacement at optical wavelengths, transverse and longitudinal to the incident electric field, and analogous to the static electrical Hall effect. The electrical Hall effect and certain cases of the optical Hall effect observations can be explained by extensions of the classic Drude model for the transport of electrons in metals. The optical Hall effect is most useful for characterization of electrical properties in semiconductors. Among many advantages, while the optical Hall effect dispenses with the need of electrical contacts, electrical material properties such as effective mass and mobility parameters, including their anisotropy as well as carrier type and density, can be determined from the optical Hall effect. Measurement of the optical Hall effect can be performed within the concept of generalized ellipsometry at an oblique angle of incidence. In this paper, we review and discuss physical model equations, which can be used to calculate the optical Hall effect in single- and multiple-layered structures of semiconductor materials. We define the optical Hall effect dielectric function tensor, demonstrate diagonalization approaches, and show requirements for the optical Hall effect tensor from energy conservation. We discuss both continuum and quantum approaches, and we provide a brief description of the generalized ellipsometry concept, the Mueller matrix calculus, and a 4×4 matrix algebra to calculate data accessible by experiment. In a follow-up paper, we will discuss strategies and approaches for experimental data acquisition and analysis.
Optical Hall effect-model description: tutorial.
Schubert, Mathias; Kühne, Philipp; Darakchieva, Vanya; Hofmann, Tino
2016-08-01
The optical Hall effect is a physical phenomenon that describes the occurrence of magnetic-field-induced dielectric displacement at optical wavelengths, transverse and longitudinal to the incident electric field, and analogous to the static electrical Hall effect. The electrical Hall effect and certain cases of the optical Hall effect observations can be explained by extensions of the classic Drude model for the transport of electrons in metals. The optical Hall effect is most useful for characterization of electrical properties in semiconductors. Among many advantages, while the optical Hall effect dispenses with the need of electrical contacts, electrical material properties such as effective mass and mobility parameters, including their anisotropy as well as carrier type and density, can be determined from the optical Hall effect. Measurement of the optical Hall effect can be performed within the concept of generalized ellipsometry at an oblique angle of incidence. In this paper, we review and discuss physical model equations, which can be used to calculate the optical Hall effect in single- and multiple-layered structures of semiconductor materials. We define the optical Hall effect dielectric function tensor, demonstrate diagonalization approaches, and show requirements for the optical Hall effect tensor from energy conservation. We discuss both continuum and quantum approaches, and we provide a brief description of the generalized ellipsometry concept, the Mueller matrix calculus, and a 4×4 matrix algebra to calculate data accessible by experiment. In a follow-up paper, we will discuss strategies and approaches for experimental data acquisition and analysis. PMID:27505654
Thermal Effects Modeling Developed for Smart Structures
NASA Technical Reports Server (NTRS)
Lee, Ho-Jun
1998-01-01
Applying smart materials in aeropropulsion systems may improve the performance of aircraft engines through a variety of vibration, noise, and shape-control applications. To facilitate the experimental characterization of these smart structures, researchers have been focusing on developing analytical models to account for the coupled mechanical, electrical, and thermal response of these materials. One focus of current research efforts has been directed toward incorporating a comprehensive thermal analysis modeling capability. Typically, temperature affects the behavior of smart materials by three distinct mechanisms: Induction of thermal strains because of coefficient of thermal expansion mismatch 1. Pyroelectric effects on the piezoelectric elements; 2. Temperature-dependent changes in material properties; and 3. Previous analytical models only investigated the first two thermal effects mechanisms. However, since the material properties of piezoelectric materials generally vary greatly with temperature (see the graph), incorporating temperature-dependent material properties will significantly affect the structural deflections, sensory voltages, and stresses. Thus, the current analytical model captures thermal effects arising from all three mechanisms through thermopiezoelectric constitutive equations. These constitutive equations were incorporated into a layerwise laminate theory with the inherent capability to model both the active and sensory response of smart structures in thermal environments. Corresponding finite element equations were formulated and implemented for both the beam and plate elements to provide a comprehensive thermal effects modeling capability.
Modeling of microstructural effects on electromigration failure
Ceric, H.; Orio, R. L. de; Zisser, W.; Selberherr, S.
2014-06-19
Current electromigration models used for simulation and analysis of interconnect reliability lack the appropriate description of metal microstructure and consequently have a very limited predictive capability. Therefore, the main objective of our work was obtaining more sophisticated electromigration tools. The problem is addressed through a combination of different levels of atomistic modeling and already available, continuum level macroscopic models. A novel method for an ab initio calculation of the effective valence for electromigration is presented and its application on the analysis of EM behavior is demonstrated. Additionally, a simple analytical model for the early electromigration lifetime is obtained. We have shown that its application provides a reasonable estimate for the early electromigration failures including the effect of microstructure. A simulation study is also applied on electromigration failure in tin solder bumps, where it contributed the understanding of the role of tin crystal anisotropy in the degradation mechanism of solder bumps.
ANSYS Modeling of Hydrostatic Stress Effects
NASA Technical Reports Server (NTRS)
Allen, Phillip A.
1999-01-01
Classical metal plasticity theory assumes that hydrostatic pressure has no effect on the yield and postyield behavior of metals. Plasticity textbooks, from the earliest to the most modem, infer that there is no hydrostatic effect on the yielding of metals, and even modem finite element programs direct the user to assume the same. The object of this study is to use the von Mises and Drucker-Prager failure theory constitutive models in the finite element program ANSYS to see how well they model conditions of varying hydrostatic pressure. Data is presented for notched round bar (NRB) and "L" shaped tensile specimens. Similar results from finite element models in ABAQUS are shown for comparison. It is shown that when dealing with geometries having a high hydrostatic stress influence, constitutive models that have a functional dependence on hydrostatic stress are more accurate in predicting material behavior than those that are independent of hydrostatic stress.
A model of the Earth's Dole effect
NASA Astrophysics Data System (ADS)
Hoffmann, Georg; Cuntz, Matthias; Weber, Christine; Ciais, Philippe; Friedlingstein, Pierre; Heimann, Martin; Jouzel, Jean; Kaduk, JöRg; Maier-Reimer, Ernst; Seibt, Ulrike; Six, Katharina
2004-03-01
The Earth's Dole effect describes the isotopic 18O/16O-enrichment of atmospheric oxygen with respect to ocean water, amounting under today's conditions to 23.5‰. We have developed a model of the Earth's Dole effect by combining the results of three-dimensional models of the oceanic and terrestrial carbon and oxygen cycles with results of atmospheric general circulation models (AGCMs) with built-in water isotope diagnostics. We obtain a range from 22.4‰ to 23.3‰ for the isotopic enrichment of atmospheric oxygen. We estimate a stronger contribution to the global Dole effect by the terrestrial relative to the marine biosphere in contrast to previous studies. This is primarily caused by a modeled high leaf water enrichment of 5-6‰. Leaf water enrichment rises by ˜1‰ to 6-7‰ when we use it to fit the observed 23.5‰ of the global Dole effect. The present model is designed to be utilized in forthcoming paleo studies allowing a quantitative analysis of long-term observations from polar ice cores.
Modeling socioeconomic status effects on language development.
Thomas, Michael S C; Forrester, Neil A; Ronald, Angelica
2013-12-01
Socioeconomic status (SES) is an important environmental predictor of language and cognitive development, but the causal pathways by which it operates are unclear. We used a computational model of development to explore the adequacy of manipulations of environmental information to simulate SES effects in English past-tense acquisition, in a data set provided by Bishop (2005). To our knowledge, this is the first application of computational models of development to SES. The simulations addressed 3 new challenges: (a) to combine models of development and individual differences in a single framework, (b) to expand modeling to the population level, and (c) to implement both environmental and genetic/intrinsic sources of individual differences. The model succeeded in capturing the qualitative patterns of regularity effects in both population performance and the predictive power of SES that were observed in the empirical data. The model suggested that the empirical data are best captured by relatively wider variation in learning abilities and relatively narrow variation in (and good quality of) environmental information. There were shortcomings in the model's quantitative fit, which are discussed. The model made several novel predictions, with respect to the influence of SES on delay versus giftedness, the change of SES effects over development, and the influence of SES on children of different ability levels (gene-environment interactions). The first of these predictions was that SES should reliably predict gifted performance in children but not delayed performance, and the prediction was supported by the Bishop data set. Finally, the model demonstrated limits on the inferences that can be drawn about developmental mechanisms on the basis of data from individual differences.
Lensing effects in inhomogeneous cosmological models
Ghassemi, Sima; Khoeini-Moghaddam, Salomeh; Mansouri, Reza
2009-05-15
Concepts developed in the gravitational lensing techniques such as shear, convergence, tangential, and radial arcs maybe used to see how tenable inhomogeneous models proposed to explain the acceleration of the universe models are. We study the widely discussed Lemaitre-Tolman-Bondi (LTB) cosmological models. It turns out that for the observer sitting at origin of a global LTB solution the shear vanishes as in the Friedmann-Robertson-Walker models, while the value of convergence is different, which may lead to observable cosmological effects. We also consider Swiss-cheese models proposed recently based on LTB with an observer sitting in the Friedmann-Robertson-Walker part. It turns out that they have different behavior as far as the formation of radial and tangential arcs are concerned.
Dynamic hysteresis modeling including skin effect using diffusion equation model
NASA Astrophysics Data System (ADS)
Hamada, Souad; Louai, Fatima Zohra; Nait-Said, Nasreddine; Benabou, Abdelkader
2016-07-01
An improved dynamic hysteresis model is proposed for the prediction of hysteresis loop of electrical steel up to mean frequencies, taking into account the skin effect. In previous works, the analytical solution of the diffusion equation for low frequency (DELF) was coupled with the inverse static Jiles-Atherton (JA) model in order to represent the hysteresis behavior for a lamination. In the present paper, this approach is improved to ensure the reproducibility of measured hysteresis loops at mean frequency. The results of simulation are compared with the experimental ones. The selected results for frequencies 50 Hz, 100 Hz, 200 Hz and 400 Hz are presented and discussed.
ERIC Educational Resources Information Center
Ker, H. W.
2014-01-01
Multilevel data are very common in educational research. Hierarchical linear models/linear mixed-effects models (HLMs/LMEs) are often utilized to analyze multilevel data nowadays. This paper discusses the problems of utilizing ordinary regressions for modeling multilevel educational data, compare the data analytic results from three regression…
IPEM: An Integrated Planning, Effectiveness Model.
ERIC Educational Resources Information Center
Donsky, Aaron P.
1995-01-01
Proposes a Florida community college's integrated planning approach comprised of three key elements: strategic planning, operational planning, and effectiveness measures. This model, which uses the institutional mission statement as the initiating point, is an efficient and meaningful way to relate an institution's purpose, goals, and outcome…
COMSOL modelling of the acoustoelastic effect
NASA Astrophysics Data System (ADS)
Watson, N. J.; Hazlehurst, T.; Povey, M. J. W.; Drennan, A.; Seaman, P.
2015-01-01
Many structural components are subjected to either constant or temporal mechanical loads, such as a suspension bridge bolts and rail tracks. Methods are required to accurately and efficiently measure the stresses experienced by these components to ensure they can continue to operate in an effective and safe manner. Acoustic techniques can be used to monitor the stress in a solid material via the acoustoelastic effect. This is the stress dependence of the acoustic velocity in an elastic media. This work develops a multiphysics computational model to study the acoustoelastic effect in a three point bending system. A simple linear relationship was utilised to represent the stress effect on the acoustic velocity. The simulation results were compared with experimental results and the same general trend was observed. An increase in applied load resulted in a greater difference between the time of flight of two transducers at the top and bottom of a component and perpendicular to the applied load. However, there were quantitative differences between the model and the experiment. The model was used to investigate different ultrasound transducer location and operating frequency, highlighting the benefit of modelling tools for the design of acoustic equipment.
Designing Effective Learning Environments: Cognitive Apprenticeship Models.
ERIC Educational Resources Information Center
Berryman, Sue E.
1991-01-01
Using cognitive science as the knowledge base for the discussion, this paper reviews why many school learning situations are ineffective and introduces cognitive apprenticeship models that suggest what effective learning situations might look like. Five wrong assumptions about learning are examined: (1) people transfer learning from one situation…
Modeling Socioeconomic Status Effects on Language Development
ERIC Educational Resources Information Center
Thomas, Michael S. C.; Forrester, Neil A.; Ronald, Angelica
2013-01-01
Socioeconomic status (SES) is an important environmental predictor of language and cognitive development, but the causal pathways by which it operates are unclear. We used a computational model of development to explore the adequacy of manipulations of environmental information to simulate SES effects in English past-tense acquisition, in a data…
Holden, M.S.; Bergman, R.; Harvey, J.; Duryea, G.; Moselle, J.
1988-12-02
The first of these 2 studies examined the detailed structure of the hypersonic boundary layer over a large cone/flare configuration. Emphasis was on development and use of instrumentation with which to obtain flow-field measurements of the mean and fluctuating properties of the attached and separated shear layers. Development and use of holographic interferometry and electron-beam techniques in the high Mach number and Reynolds number environment developed in the shock tunnel are described. In the second study, detailed measurements of heat transfer, pressure, and skin friction were made on a unique 'blowing and roughness' model constructed to simulate the aerothermal phenomena associated with a rough ablating maneuverable reentry vehicle. In this study emphasis was placed on development and use of unique heat transfer and skin-friction instrumentation to obtain measurements of the combined effects of blowing and roughness and to understand how such effects influence boundary-layer separation in regions of shock wave/boundary layer interaction. Each focused around providing information with which to construct and evaluate the modeling required in time-averaged Navier-Stokes equations to predict the structure of compressible hypersonic boundary layers in regions of strong pressure gradient, shock-wave/boundary-layer interaction and flow separation over smooth, rough, and ablating surfaces.
Radiative effects in the standard model extension
NASA Astrophysics Data System (ADS)
Zhukovsky, V. Ch.; Lobanov, A. E.; Murchikova, E. M.
2006-03-01
The possibility of radiative effects induced by the Lorentz and CPT noninvariant interaction term for fermions in the standard model extension is investigated. In particular, electron-positron photo production and photon emission by electrons and positrons are studied. The rates of these processes are calculated in the Furry picture. It is demonstrated that the rates obtained in the framework of the model adopted strongly depend on the polarization states of the particles involved. As a result, ultrarelativistic particles produced should occupy states with a preferred spin orientation, i.e., photons have the sign of polarization opposite to the sign of the effective potential, while charged particles are preferably in the state with the helicity coinciding with the sign of the effective potential. This leads to evident spatial asymmetries which may have certain consequences observable at high energy accelerators, and in astrophysical and cosmological studies.
Modeling psychiatric disorders for developing effective treatments
Kaiser, Tobias; Feng, Guoping
2016-01-01
The recent advance in identifying risk genes has provided an unprecedented opportunity for developing animal models for psychiatric disease research with the goal of attaining translational utility to ultimately develop novel treatments. However, at this early stage, successful translation has yet to be achieved. Here, we review recent advances in modeling psychiatric disease, discuss utility and limitations of animal models, and emphasize the importance of shifting from behavioral analysis to identifying neurophysiological defects, which are likely more conserved across species and thus increase translatability. Looking forward, we envision that preclinical research will align with clinical research to build a common framework of comparable neurobiological abnormalities and form subgroups of patients based on similar pathophysiology. Experimental neuroscience can then use animal models to discover mechanisms underlying distinct abnormalities and develop strategies for effective treatments. PMID:26340119
Biologically based multistage modeling of radiation effects
William Hazelton; Suresh Moolgavkar; E. Georg Luebeck
2005-08-30
This past year we have made substantial progress in modeling the contribution of homeostatic regulation to low-dose radiation effects and carcinogenesis. We have worked to refine and apply our multistage carcinogenesis models to explicitly incorporate cell cycle states, simple and complex damage, checkpoint delay, slow and fast repair, differentiation, and apoptosis to study the effects of low-dose ionizing radiation in mouse intestinal crypts, as well as in other tissues. We have one paper accepted for publication in ''Advances in Space Research'', and another manuscript in preparation describing this work. I also wrote a chapter describing our combined cell-cycle and multistage carcinogenesis model that will be published in a book on stochastic carcinogenesis models edited by Wei-Yuan Tan. In addition, we organized and held a workshop on ''Biologically Based Modeling of Human Health Effects of Low dose Ionizing Radiation'', July 28-29, 2005 at Fred Hutchinson Cancer Research Center in Seattle, Washington. We had over 20 participants, including Mary Helen Barcellos-Hoff as keynote speaker, talks by most of the low-dose modelers in the DOE low-dose program, experimentalists including Les Redpath (and Mary Helen), Noelle Metting from DOE, and Tony Brooks. It appears that homeostatic regulation may be central to understanding low-dose radiation phenomena. The primary effects of ionizing radiation (IR) are cell killing, delayed cell cycling, and induction of mutations. However, homeostatic regulation causes cells that are killed or damaged by IR to eventually be replaced. Cells with an initiating mutation may have a replacement advantage, leading to clonal expansion of these initiated cells. Thus we have focused particularly on modeling effects that disturb homeostatic regulation as early steps in the carcinogenic process. There are two primary considerations that support our focus on homeostatic regulation. First, a number of epidemiologic studies using multistage
On effective resolution in ocean models
NASA Astrophysics Data System (ADS)
Soufflet, Yves; Marchesiello, Patrick; Lemarié, Florian; Jouanno, Julien; Capet, Xavier; Debreu, Laurent; Benshila, Rachid
2016-02-01
The increase of model resolution naturally leads to the representation of a wider energy spectrum. As a result, in recent years, the understanding of oceanic submesoscale dynamics has significantly improved. However, dissipation in submesoscale models remains dominated by numerical constraints rather than physical ones. Effective resolution is limited by the numerical dissipation range, which is a function of the model numerical filters (assuming that dispersive numerical modes are efficiently removed). We present a Baroclinic jet test case set in a zonally reentrant channel that provides a controllable test of a model capacity at resolving submesoscale dynamics. We compare simulations from two models, ROMS and NEMO, at different mesh sizes (from 20 to 2 km). Through a spectral decomposition of kinetic energy and its budget terms, we identify the characteristics of numerical dissipation and effective resolution. It shows that numerical dissipation appears in different parts of a model, especially in spatial advection-diffusion schemes for momentum equations (KE dissipation) and tracer equations (APE dissipation) and in the time stepping algorithms. Effective resolution, defined by scale-selective dissipation, is inadequate to qualify traditional ocean models with low-order spatial and temporal filters, even at high grid resolution. High-order methods are better suited to the concept and probably unavoidable. Fourth-order filters are suited only for grid resolutions less than a few kilometers and momentum advection schemes of even higher-order may be justified. The upgrade of time stepping algorithms (from filtered Leapfrog), a cumbersome task in a model, appears critical from our results, not just as a matter of model solution quality but also of computational efficiency (extended stability range of predictor-corrector schemes). Effective resolution is also shaken by the need for non scale-selective barotropic mode filters and requires carefully addressing the
Modeling of the Yarkovsky and YORP effects
NASA Astrophysics Data System (ADS)
Rozitis, B.
2014-07-01
The Yarkovsky and YORP effects are now widely regarded to be fundamental mechanisms, in addition to collisions and gravitational forces, which drive the dynamical and physical evolution of small asteroids in the Solar System [1]. They are caused by the net force and torque resulting from the asymmetric reflection and thermal re-radiation of sunlight from an asteroid's surface. The net force (Yarkovsky effect) causes the asteroid's orbit to drift outwards or inwards depending on whether the asteroid is a prograde or retrograde rotator. The first direct measurement of Yarkovsky orbital drift was achieved by sensitive radar-ranging on the near-Earth asteroid (NEA) (6489) Golevka in 2003 [2]. The net torque (YORP effect) changes the asteroid's rotation rate and the direction of its spin axis. It can cause an asteroid to spin faster or slower depending on the shape asymmetry, and the first direct measurement of the YORP rotational acceleration was achieved by lightcurve observations on NEA (54509) YORP in 2007 [3]. Since these first direct detections, the Yarkovsky orbital drift has been detected in several tens of NEAs [4,5], and the YORP rotational acceleration has been detected in four more NEAs [6--9]. Indirect evidence of the action of these two effects has also been seen in the populations of NEAs [10], small main-belt asteroids [11], and asteroid families [12]. Modeling of these effects allows further insights into the properties of detected asteroids to be gained, such as the bulk density, obliquity, and surface thermal properties. Recently, high-precision astrometric observations of the Yarkovsky orbital drift of PHA (101955) Bennu were combined with suitable models informed by thermal-infrared observations to derive a bulk density with an uncertainty comparable to that of in-situ spacecraft investigations [13]. Also, the recent YORP effect detection in (25143) Itokawa was combined with a model utilizing the highly detailed Hayabusa-derived shape model to infer
Effects of anethole in nociception experimental models.
Ritter, Alessandra Mileni Versuti; Ames, Franciele Queiroz; Otani, Fernando; de Oliveira, Rubia Maria Weffort; Cuman, Roberto Kenji Nakamura; Bersani-Amado, Ciomar Aparecida
2014-01-01
This study investigated the antinociceptive activity of anethole (anethole 1-methoxy-4-benzene (1-propenyl)), major compound of the essential oil of star anise (Illicium verum), in different experimental models of nociception. The animals were pretreated with anethole (62.5, 125, 250, and 500 mg/kg) one hour before the experiments. To eliminate a possible sedative effect of anethole, the open field test was conducted. Anethole (62.5, 125, 250, and 500 mg/kg) showed an antinociceptive effect in the writhing model induced by acetic acid, in the second phase of the formalin test (125 and 250 mg/kg) in the test of glutamate (62.5, 125, and 250 mg/kg), and expresses pain induced by ACF (250 mg/kg). In contrast, anethole was not able to increase the latency time on the hot plate and decrease the number of flinches during the initial phase of the formalin test in any of the doses tested. It was also demonstrated that anethole has no association with sedative effects. Therefore, these data showed that anethole, at all used doses, has no sedative effect and has an antinociceptive effect. This effect may be due to a decrease in the production/release of inflammatory mediators. PMID:25506382
Effects of Anethole in Nociception Experimental Models
Ritter, Alessandra Mileni Versuti; Ames, Franciele Queiroz; Otani, Fernando; de Oliveira, Rubia Maria Weffort; Cuman, Roberto Kenji Nakamura; Bersani-Amado, Ciomar Aparecida
2014-01-01
This study investigated the antinociceptive activity of anethole (anethole 1-methoxy-4-benzene (1-propenyl)), major compound of the essential oil of star anise (Illicium verum), in different experimental models of nociception. The animals were pretreated with anethole (62.5, 125, 250, and 500 mg/kg) one hour before the experiments. To eliminate a possible sedative effect of anethole, the open field test was conducted. Anethole (62.5, 125, 250, and 500 mg/kg) showed an antinociceptive effect in the writhing model induced by acetic acid, in the second phase of the formalin test (125 and 250 mg/kg) in the test of glutamate (62.5, 125, and 250 mg/kg), and expresses pain induced by ACF (250 mg/kg). In contrast, anethole was not able to increase the latency time on the hot plate and decrease the number of flinches during the initial phase of the formalin test in any of the doses tested. It was also demonstrated that anethole has no association with sedative effects. Therefore, these data showed that anethole, at all used doses, has no sedative effect and has an antinociceptive effect. This effect may be due to a decrease in the production/release of inflammatory mediators. PMID:25506382
Hysteresis modeling in graphene field effect transistors
Winters, M.; Rorsman, N.; Sveinbjörnsson, E. Ö.
2015-02-21
Graphene field effect transistors with an Al{sub 2}O{sub 3} gate dielectric are fabricated on H-intercalated bilayer graphene grown on semi-insulating 4H-SiC by chemical vapour deposition. DC measurements of the gate voltage v{sub g} versus the drain current i{sub d} reveal a severe hysteresis of clockwise orientation. A capacitive model is used to derive the relationship between the applied gate voltage and the Fermi energy. The electron transport equations are then used to calculate the drain current for a given applied gate voltage. The hysteresis in measured data is then modeled via a modified Preisach kernel.
Gravitational effects in models of grand unification
NASA Astrophysics Data System (ADS)
Reeb, David
Grand unified theories constitute an attractive idea bringing further coherence into our understanding of the fundamental forces of Nature beyond the well-accepted Standard Model. This dissertation contains a systematic study of the unification of gauge couplings associated with these forces in the presence of one or several effective dimension-5 operators cHG munuGmunu/4MPl, which are induced into the grand unified theory through gravitational interactions at the Planck scale. These operators alter the usually assumed condition for gauge coupling unification and can, depending on the Higgs content H of the theory and on its vacuum expectation value, lead to grand unification in models other than commonly believed and at scales Mx significantly different than naively expected. After presenting a general framework to treat such effects, we compute, for the case of SU(5) and SO(10) unification groups, the associated group theory constants necessary for the study of concrete models. We investigate the size of these effects in non-supersymmetric unification models and find that there exist regions of natural Wilson coefficients c in parameter space that achieve successful unification of the gauge couplings, while easily satisfying the bounds on the unification scale coming from the non-observation of proton decay. Both of these requirements are widely assumed to be violated in non-supersymmetric models of grand unification, but, as we show, can be fulfilled due to the effects coming from gravitational dimension-5 operators. A comparison to supersymmetric unification models shows that their parameter space for successful grand unification is no more natural than the one for the non-supersymmetric models. The main conclusion of this dissertation is that fairly minimal unification models are possible, i.e., with small unification groups and without supersymmetric particles. Whereas the observation of proton decay seems to be the only possible evidence for grand
Effect on Prediction when Modeling Covariates in Bayesian Nonparametric Models.
Cruz-Marcelo, Alejandro; Rosner, Gary L; Müller, Peter; Stewart, Clinton F
2013-04-01
In biomedical research, it is often of interest to characterize biologic processes giving rise to observations and to make predictions of future observations. Bayesian nonparametric methods provide a means for carrying out Bayesian inference making as few assumptions about restrictive parametric models as possible. There are several proposals in the literature for extending Bayesian nonparametric models to include dependence on covariates. Limited attention, however, has been directed to the following two aspects. In this article, we examine the effect on fitting and predictive performance of incorporating covariates in a class of Bayesian nonparametric models by one of two primary ways: either in the weights or in the locations of a discrete random probability measure. We show that different strategies for incorporating continuous covariates in Bayesian nonparametric models can result in big differences when used for prediction, even though they lead to otherwise similar posterior inferences. When one needs the predictive density, as in optimal design, and this density is a mixture, it is better to make the weights depend on the covariates. We demonstrate these points via a simulated data example and in an application in which one wants to determine the optimal dose of an anticancer drug used in pediatric oncology. PMID:23687472
Modeling of the Yarkovsky and YORP effects
NASA Astrophysics Data System (ADS)
Rozitis, B.
2014-07-01
The Yarkovsky and YORP effects are now widely regarded to be fundamental mechanisms, in addition to collisions and gravitational forces, which drive the dynamical and physical evolution of small asteroids in the Solar System [1]. They are caused by the net force and torque resulting from the asymmetric reflection and thermal re-radiation of sunlight from an asteroid's surface. The net force (Yarkovsky effect) causes the asteroid's orbit to drift outwards or inwards depending on whether the asteroid is a prograde or retrograde rotator. The first direct measurement of Yarkovsky orbital drift was achieved by sensitive radar-ranging on the near-Earth asteroid (NEA) (6489) Golevka in 2003 [2]. The net torque (YORP effect) changes the asteroid's rotation rate and the direction of its spin axis. It can cause an asteroid to spin faster or slower depending on the shape asymmetry, and the first direct measurement of the YORP rotational acceleration was achieved by lightcurve observations on NEA (54509) YORP in 2007 [3]. Since these first direct detections, the Yarkovsky orbital drift has been detected in several tens of NEAs [4,5], and the YORP rotational acceleration has been detected in four more NEAs [6--9]. Indirect evidence of the action of these two effects has also been seen in the populations of NEAs [10], small main-belt asteroids [11], and asteroid families [12]. Modeling of these effects allows further insights into the properties of detected asteroids to be gained, such as the bulk density, obliquity, and surface thermal properties. Recently, high-precision astrometric observations of the Yarkovsky orbital drift of PHA (101955) Bennu were combined with suitable models informed by thermal-infrared observations to derive a bulk density with an uncertainty comparable to that of in-situ spacecraft investigations [13]. Also, the recent YORP effect detection in (25143) Itokawa was combined with a model utilizing the highly detailed Hayabusa-derived shape model to infer
Models for impurity effects in tokamaks
Hogan, J.T.
1980-03-01
Models for impurity effects in tokamaks are described with an emphasis on the relationship between attainment of high ..beta.. and impurity problems. We briefly describe the status of attempts to employ neutral beam heating to achieve high ..beta.. in tokamaks and propose a qualitative model for the mechanism by which heavy metal impurities may be produced in the startup phase of the discharge. We then describe paradoxes in impurity diffusion theory and discuss possible resolutions in terms of the effects of large-scale islands and sawtooth oscillations. Finally, we examine the prospects for the Zakharov-Shafranov catastrophe (long time scale disintegration of FCT equilibria) in the context of present and near-term experimental capability.
Gyrofluid turbulence models with kinetic effects
Dorland, W.; Hammett, G.W.
1992-12-01
Nonlinear gyrofluid equations are derived by taking moments of the nonlinear, electrostatic gyrokinetic equation. The principal model presented includes evolution equations for the guiding center n, u[parallel], T[parallel], and T[perpendicular] along with an equation expressing the quasineutrality constraint. Additional evolution equations for higher moments are derived which may be used if greater accuracy is desired. The moment hierarchy is closed with a Landau-damping model which is equivalent to a multi-pole approximation to the plasma dispersion function, extended to include finite Larmor radius effects. In particular, new dissipative, nonlinear terms are found which model the perpendicular phase-mixing of the distribution function along contours of constant electrostatic potential. These FLR phase-mixing'' terms introduce a hyperviscosity-like damping [proportional to] k[sub [perpendicular
Joint Non-kinetic Effects Model (JNEM)
NASA Technical Reports Server (NTRS)
Chamberlain, Robert G.; Metivier, Timothy
2006-01-01
This slide presentation reviews the development of the Joint Non-kinetic Effects Model (JNEM), which is tool to support Battle Command Training that links simulation-generated non-kinetic events and outcomes to Training Audience Command and Staff decisions. JNEM helps create the operating environment for the following population groups (P-groups): (1) Local Civilians on the Battlefield, (2) Inter-Governmental Organizations (3) Non-Governmental Organizations (4) Contractors on the battlefield.
Chiral susceptibility in an effective interaction model
Min He; Yu Jiang; Sun Weimin; Zong Hongshi
2008-04-01
A closed integral expression for the chiral susceptibility at finite temperature is derived. The corresponding disconnected part, which proves to be of major physical relevance and free from the additive quadratic ultraviolet divergence, is identified. Then a calculation based on an effective model gluon propagator is conducted within the framework of the Dyson-Schwinger equations for two flavors in the chiral limit. A narrow, divergent peak is observed as temperature varies, and its implications are discussed.
GLOBAL REFERENCE ATMOSPHERIC MODELS FOR AEROASSIST APPLICATIONS
NASA Technical Reports Server (NTRS)
Duvall, Aleta; Justus, C. G.; Keller, Vernon W.
2005-01-01
Aeroassist is a broad category of advanced transportation technology encompassing aerocapture, aerobraking, aeroentry, precision landing, hazard detection and avoidance, and aerogravity assist. The eight destinations in the Solar System with sufficient atmosphere to enable aeroassist technology are Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Saturn's moon Titan. Engineering-level atmospheric models for five of these targets - Earth, Mars, Titan, Neptune, and Venus - have been developed at NASA's Marshall Space Flight Center. These models are useful as tools in mission planning and systems analysis studies associated with aeroassist applications. The series of models is collectively named the Global Reference Atmospheric Model or GRAM series. An important capability of all the models in the GRAM series is their ability to simulate quasi-random perturbations for Monte Carlo analysis in developing guidance, navigation and control algorithms, for aerothermal design, and for other applications sensitive to atmospheric variability. Recent example applications are discussed.
Atomic Models for Motional Stark Effects Diagnostics
Gu, M F; Holcomb, C; Jayakuma, J; Allen, S; Pablant, N A; Burrell, K
2007-07-26
We present detailed atomic physics models for motional Stark effects (MSE) diagnostic on magnetic fusion devices. Excitation and ionization cross sections of the hydrogen or deuterium beam traveling in a magnetic field in collisions with electrons, ions, and neutral gas are calculated in the first Born approximation. The density matrices and polarization states of individual Stark-Zeeman components of the Balmer {alpha} line are obtained for both beam into plasma and beam into gas models. A detailed comparison of the model calculations and the MSE polarimetry and spectral intensity measurements obtained at the DIII-D tokamak is carried out. Although our beam into gas models provide a qualitative explanation for the larger {pi}/{sigma} intensity ratios and represent significant improvements over the statistical population models, empirical adjustment factors ranging from 1.0-2.0 must still be applied to individual line intensities to bring the calculations into full agreement with the observations. Nevertheless, we demonstrate that beam into gas measurements can be used successfully as calibration procedures for measuring the magnetic pitch angle through {pi}/{sigma} intensity ratios. The analyses of the filter-scan polarization spectra from the DIII-D MSE polarimetry system indicate unknown channel and time dependent light contaminations in the beam into gas measurements. Such contaminations may be the main reason for the failure of beam into gas calibration on MSE polarimetry systems.
Thermal Response Modeling System for a Mars Sample Return Vehicle
NASA Technical Reports Server (NTRS)
Chen, Y.-K.; Miles, Frank S.; Arnold, Jim (Technical Monitor)
2001-01-01
A multi-dimensional, coupled thermal response modeling system for analysis of hypersonic entry vehicles is presented. The system consists of a high fidelity Navier-Stokes equation solver (GIANTS), a two-dimensional implicit thermal response, pyrolysis and ablation program (TITAN), and a commercial finite-element thermal and mechanical analysis code (MARC). The simulations performed by this integrated system include hypersonic flowfield, fluid and solid interaction, ablation, shape change, pyrolysis gas eneration and flow, and thermal response of heatshield and structure. The thermal response of the heatshield is simulated using TITAN, and that of the underlying structural is simulated using MARC. The ablating heatshield is treated as an outer boundary condition of the structure, and continuity conditions of temperature and heat flux are imposed at the interface between TITAN and MARC. Aerothermal environments with fluid and solid interaction are predicted by coupling TITAN and GIANTS through surface energy balance equations. With this integrated system, the aerothermal environments for an entry vehicle and the thermal response of the entire vehicle can be obtained simultaneously. Representative computations for a flat-faced arc-jet test model and a proposed Mars sample return capsule are presented and discussed.
Thermal Response Modeling System for a Mars Sample Return Vehicle
NASA Technical Reports Server (NTRS)
Chen, Y.-K.; Milos, F. S.
2002-01-01
A multi-dimensional, coupled thermal response modeling system for analysis of hypersonic entry vehicles is presented. The system consists of a high fidelity Navier-Stokes equation solver (GIANTS), a two-dimensional implicit thermal response, pyrolysis and ablation program (TITAN), and a commercial finite element thermal and mechanical analysis code (MARC). The simulations performed by this integrated system include hypersonic flowfield, fluid and solid interaction, ablation, shape change, pyrolysis gas generation and flow, and thermal response of heatshield and structure. The thermal response of the heatshield is simulated using TITAN, and that of the underlying structural is simulated using MARC. The ablating heatshield is treated as an outer boundary condition of the structure, and continuity conditions of temperature and heat flux are imposed at the interface between TITAN and MARC. Aerothermal environments with fluid and solid interaction are predicted by coupling TITAN and GIANTS through surface energy balance equations. With this integrated system, the aerothermal environments for an entry vehicle and the thermal response of the entire vehicle can be obtained simultaneously. Representative computations for a flat-faced arc-jet test model and a proposed Mars sample return capsule are presented and discussed.
Radiative Effects in the Standard Model Extension
NASA Astrophysics Data System (ADS)
Zhukovsky, V. Ch.; Lobanov, A. E.; Murchikova, E. M.
2006-10-01
The possibility of radiative effects that are due to interaction of fermions with the constant axial-vector background in the standard model extension is investigated. Electron-positron photo-production and photon emission by electrons and positrons were studied. The rates of these processes were calculated in the Furry picture. It was demonstrated that the rates obtained strongly depend on the polarization states of the particles involved. In consequence of this fact ultra-relativistic particles should occupy states with a preferred spin orientation, i.e., photons have the sign of polarization opposite to the sign of the effective potential, while charged particle are preferably in the state with the helicity coinciding with the sign of the effective potential. This leads to evident spatial asymmetries.
Effective action for noncommutative Bianchi I model
Rosenbaum, M.; Vergara, J. D.; Minzoni, A. A.
2013-06-12
Quantum Mechanics, as a mini-superspace of Field Theory has been assumed to provide physically relevant information on quantum processes in Field Theory. In the case of Quantum Gravity this would imply using Cosmological models to investigate quantum processes at distances of the order of the Planck scale. However because of the Stone-von Neuman Theorem, it is well known that quantization of Cosmological models by the Wheeler-DeWitt procedure in the context of a Heisenberg-Weyl group with piecewise continuous parameters leads irremediably to a volume singularity. In order to avoid this information catastrophe it has been suggested recently the need to introduce in an effective theory of the quantization some form of reticulation in 3-space. On the other hand, since in the geometry of the General Relativistic formulation of Gravitation space can not be visualized as some underlying static manifold in which the physical system evolves, it would be interesting to investigate whether the effective reticulation which removes the singularity in such simple cosmologies as the Bianchi models has a dynamical origin manifested by a noncommutativity of the generators of the Heisenberg-Weyl algebra, as would be expected from an operational point of view at the Planck length scale.
Electromagnetohydrodynamic Modeling of Lorentz Effect Imaging
Pourtaheri, Navid; Truong, Trong-Kha; Henriquez, Craig S.
2013-01-01
Lorentz Effect Imaging (LEI) is an MRI technique that has been proposed for direct imaging of neuronal activity. While promising results have been obtained in phantoms and in the human median nerve in vivo, its contrast mechanism is still not fully understood. In this paper, computational model simulations were used to investigate how electromagnetohydrodynamics (EMHD) may explain the LEI contrast. Three computational models of an electrolyte-filled phantom subject to an applied current dipole, synchronized to oscillating magnetic field gradients of an LEI protocol, were developed to determine the velocity and displacement of water molecules as well as the resulting signal loss in an MR image. The simulated images were compared to images from previous LEI phantom experiments with identical properties for different stimulus current amplitudes and polarities. The first model, which evaluated ion trajectories based on Stokes flow using different mobility values, did not generate an appreciable signal loss due to an insufficient number of water molecules associated with the ion hydration shells. The second model, which computed particle drift based on the Lorentz force of charged particles in free space, was able to approximate the magnitude, but not the distribution of signal loss observed in the experimental images. The third model, which computed EMHD based on the Lorentz force and Navier-Stokes equations for flow of a conducting fluid, provided results consistent with both the magnitude and distribution of signal loss seen in the LEI experiments. Our EMHD model further yields information on electrical potential, velocity, displacement, and pressure, which are not readily available in an experiment, thereby providing a robust means to study and optimize LEI for imaging neuronal activity in the human cortex. PMID:24056273
Empirical Treatment Effectiveness Models for Binary Outcomes.
Dalton, Jarrod E; Dawson, Neal V; Sessler, Daniel I; Schold, Jesse D; Love, Thomas E; Kattan, Michael W
2016-01-01
Randomized trials provide strong evidence regarding efficacy of interventions but are limited in their capacity to address potential heterogeneity in effectiveness within broad clinical populations. For example, a treatment that on average is superior may be distinctly worse in certain patients. We propose a technique for using large electronic health registries to develop and validate decision models that measure-for distinct combinations of covariate values-the difference in predicted outcomes among 2 alternative treatments. We demonstrate the methodology in a prototype analysis of in-hospital mortality under alternative revascularization treatments. First, we developed prediction models for a binary outcome of interest for each treatment. Decision criteria were then defined based on the treatment-specific model predictions. Patients were then classified as receiving concordant or discordant care (in relation to the model recommendation), and the association between discordance and outcomes was evaluated. We then present alternative decision criteria and validation methodologies, as well as sensitivity analyses that investigate 1) the imbalance between treatments on observed covariates and 2) the aggregate impact of unobserved covariates. Our methodology supplements population-average clinical trial results by modeling heterogeneity in outcomes according to specific covariate values. It thus allows for assessment of current practice, from which cogent hypotheses for improved care can be derived. Newly emerging large population registries will allow for accurate predictions of outcome risk under competing treatments, as complex functions of predictor variables. Whether or not the models might be used to inform decision making depends on the extent to which important predictors are available. Further work is needed to understand the strengths and limitations of this approach, particularly in relation to those based on randomized trials. PMID:25852080
Cost effectiveness of recycling: A systems model
Tonjes, David J.; Mallikarjun, Sreekanth
2013-11-15
Highlights: • Curbside collection of recyclables reduces overall system costs over a range of conditions. • When avoided costs for recyclables are large, even high collection costs are supported. • When avoided costs for recyclables are not great, there are reduced opportunities for savings. • For common waste compositions, maximizing curbside recyclables collection always saves money. - Abstract: Financial analytical models of waste management systems have often found that recycling costs exceed direct benefits, and in order to economically justify recycling activities, externalities such as household expenses or environmental impacts must be invoked. Certain more empirically based studies have also found that recycling is more expensive than disposal. Other work, both through models and surveys, have found differently. Here we present an empirical systems model, largely drawn from a suburban Long Island municipality. The model accounts for changes in distribution of effort as recycling tonnages displace disposal tonnages, and the seven different cases examined all show that curbside collection programs that manage up to between 31% and 37% of the waste stream should result in overall system savings. These savings accrue partially because of assumed cost differences in tip fees for recyclables and disposed wastes, and also because recycling can result in a more efficient, cost-effective collection program. These results imply that increases in recycling are justifiable due to cost-savings alone, not on more difficult to measure factors that may not impact program budgets.
Cost effectiveness of recycling: a systems model.
Tonjes, David J; Mallikarjun, Sreekanth
2013-11-01
Financial analytical models of waste management systems have often found that recycling costs exceed direct benefits, and in order to economically justify recycling activities, externalities such as household expenses or environmental impacts must be invoked. Certain more empirically based studies have also found that recycling is more expensive than disposal. Other work, both through models and surveys, have found differently. Here we present an empirical systems model, largely drawn from a suburban Long Island municipality. The model accounts for changes in distribution of effort as recycling tonnages displace disposal tonnages, and the seven different cases examined all show that curbside collection programs that manage up to between 31% and 37% of the waste stream should result in overall system savings. These savings accrue partially because of assumed cost differences in tip fees for recyclables and disposed wastes, and also because recycling can result in a more efficient, cost-effective collection program. These results imply that increases in recycling are justifiable due to cost-savings alone, not on more difficult to measure factors that may not impact program budgets.
Nuclear EMC effect in a statistical model
NASA Astrophysics Data System (ADS)
Zhang, Yunhua; Shao, Lijing; Ma, Bo-Qiang
2009-09-01
A simple statistical model in terms of light-front kinematic variables is used to explain the nuclear EMC effect in the range x∈[0.2,0.7], which was constructed by us previously to calculate the parton distribution functions (PDFs) of the nucleon. Here, we treat the temperature T as a parameter of the atomic number A, and get reasonable results in agreement with the experimental data. Our results show that the larger A, the lower T thus the bigger volume V, and these features are consistent with other models. Moreover, we give the predictions of the quark distribution ratios, i.e., q(x)/q(x), q(x)/q(x), and s(x)/s(x), and also the gluon ratio g(x)/g(x) for iron as an example. The predictions are different from those by other models, thus experiments aiming at measuring the parton ratios of anti-quarks, strange quarks, and gluons can provide a discrimination of different models.
Modeling terahertz heating effects on water.
Kristensen, Torben T L; Withayachumnankul, Withawat; Jepsen, Peter U; Abbott, Derek
2010-03-01
We apply Kirchhoff's heat equation to model the influence of a CW terahertz beam on a sample of water, which is assumed to be static. We develop a generalized model, which easily can be applied to other liquids and solids by changing the material constants. If the terahertz light source is focused down to a spot with a diameter of 0.5 mm, we find that the steady-state temperature increase per milliwatt of transmitted power is 1.8?C/mW. A quantum cascade laser can produce a CW beam in the order of several milliwatts and this motivates the need to estimate the effect of beam power on the sample temperature. For THz time domain systems, we indicate how to use our model as a worst-case approximation based on the beam average power. It turns out that THz pulses created from photoconductive antennas give a negligible increase in temperature. As biotissue contains a high water content, this leads to a discussion of worst-case predictions for THz heating of the human body in order to motivate future detailed study. An open source Matlab implementation of our model is freely available for use at www.eleceng.adelaide.edu.au/thz. PMID:20389486
Instruction manual, Optical Effects Module, Model OEM
NASA Technical Reports Server (NTRS)
1975-01-01
The Optical Effects Module Model OEM-1, a laboratory prototype instrument designed for the automated measurement of radiation transmission and scattering through optical samples, is described. The system comprises two main components: the Optical Effects Module Enclosure (OEME) and the Optical Effects Module Electronic Controller and Processor (OEMCP). The OEM is designed for operation in the near UV at approximately 2540A, corresponding to the most intense spectral line activated by the mercury discharge lamp used for illumination. The radiation from this source is detected in transmission and reflection through a number of selectable samples. The basic objective of this operation is to monitor in real time the accretion of possible contamination on the surface of these samples. The optical samples are exposed outside of the OEME proper to define exposure conditions and to separate exposure and measurement environments. Changes in the transmissivity of the sample are attributable to surface contamination or to bulk effects due to radiation. Surface contamination will increase radiation scattering due to Rayleigh-Gans effect or to other phenomena, depending on the characteristics size of the particulate contaminants. Thus, also scattering from the samples becomes a part of the measurement program.
Modeling the effects of reflective roofing
Gartland, L.M.; Konopacki, S.J.; Akbari, H.
1996-08-01
Roofing materials which are highly reflective to sunlight are currently being developed. Reflective roofing is an effective summertime energy saver in warm and sunny climates. It has been demonstrated to save up to 40% of the energy needed to cool a building during the summer months. Buildings without air conditioning can reduce their indoor temperatures and improve occupant comfort during the summer if highly reflective roofing materials are used. But there are questions about the tradeoff between summer energy savings and extra wintertime energy use due to reduced heat collection by the roof. These questions are being answered by simulating buildings in various climates using the DOE-2 program (version 2.1E). Unfortunately, DOE-2 does not accurately model radiative, convective and conductive processes in the roof-attic. Radiative heat transfer from the underside of a reflective roof is much smaller than that of a roof which absorbs heat from sunlight, and must be accounted for in the building energy model. Convection correlations for the attic and the roof surface must be fine tuned. An equation to model the insulation`s conductivity dependence on temperature must also be added. A function was written to incorporate the attic heat transfer processes into the DOE-2 building energy simulation. This function adds radiative, convective and conductive equations to the energy balance of the roof. Results of the enhanced DOE-2 model were compared to measured data collected from a school bungalow in a Sacramento Municipal Utility District monitoring project, with particular attention paid to the year-round energy effects.
NASA Technical Reports Server (NTRS)
1994-01-01
This model of the Boeing A/FX (Advanced Attack/Fighter) Aircraft was photographed between test runs in NASA Langley Research Center's 16-Foot Transonic Tunnel. Testing was conducted to determine the effects of the jet exhaust on the aerodynamic characteristics of the aircraft afterbody. The A/FX program was a Navy effort to obtain a next-generation replacement for the A-6 and F/A-18. The A/FX program evolved into the current multi-service JSF (Joint Strike Fighter) program.
An antenna model for the Purcell effect
Krasnok, Alexander E.; Slobozhanyuk, Alexey P.; Simovski, Constantin R.; Tretyakov, Sergei A.; Poddubny, Alexander N.; Miroshnichenko, Andrey E.; Kivshar, Yuri S.; Belov, Pavel A.
2015-01-01
The Purcell effect is defined as a modification of the spontaneous emission rate of a quantum emitter at the presence of a resonant cavity. However, a change of the emission rate of an emitter caused by an environment has a classical counterpart. Any small antenna tuned to a resonance can be described as an oscillator with radiative losses, and the effect of the environment on its radiation can be modeled and measured in terms of the antenna radiation resistance, similar to a quantum emitter. We exploit this analogue behavior to develop a general approach for calculating the Purcell factors of different systems and various frequency ranges including both electric and magnetic Purcell factors. Our approach is illustrated by a general equivalent scheme, and it allows resenting the Purcell factor through the continuous radiation of a small antenna at the presence of an electromagnetic environment. PMID:26256529
An antenna model for the Purcell effect.
Krasnok, Alexander E; Slobozhanyuk, Alexey P; Simovski, Constantin R; Tretyakov, Sergei A; Poddubny, Alexander N; Miroshnichenko, Andrey E; Kivshar, Yuri S; Belov, Pavel A
2015-01-01
The Purcell effect is defined as a modification of the spontaneous emission rate of a quantum emitter at the presence of a resonant cavity. However, a change of the emission rate of an emitter caused by an environment has a classical counterpart. Any small antenna tuned to a resonance can be described as an oscillator with radiative losses, and the effect of the environment on its radiation can be modeled and measured in terms of the antenna radiation resistance, similar to a quantum emitter. We exploit this analogue behavior to develop a general approach for calculating the Purcell factors of different systems and various frequency ranges including both electric and magnetic Purcell factors. Our approach is illustrated by a general equivalent scheme, and it allows resenting the Purcell factor through the continuous radiation of a small antenna at the presence of an electromagnetic environment. PMID:26256529
Experimental Models on Effects of Psychostimulants.
Kõks, Sulev
2015-01-01
Psychostimulants are a diverse group of substances that cause an increase in psychomotor activity at least in part through their actions on catecholaminergic systems including the dopaminergic mesolimbic pathways. Animal models used to study addiction are based on the psychomotor stimulant theory of addiction. The basics of this theory are that the reinforcing effects and the addition liabilities of the drugs can be predicted from their ability to induce psychomotor activation. This approach focuses on the ability of the drugs to directly control the animal's behavior and to induce psychomotor stimulation, and is consistent with the behavioral definition of addiction and behavioral sensitization. Animal experiments have the advantage over clinical studies of lower variation and fewer confounding effects. PMID:26070755
Experimental Models on Effects of Psychostimulants.
Kõks, Sulev
2015-01-01
Psychostimulants are a diverse group of substances that cause an increase in psychomotor activity at least in part through their actions on catecholaminergic systems including the dopaminergic mesolimbic pathways. Animal models used to study addiction are based on the psychomotor stimulant theory of addiction. The basics of this theory are that the reinforcing effects and the addition liabilities of the drugs can be predicted from their ability to induce psychomotor activation. This approach focuses on the ability of the drugs to directly control the animal's behavior and to induce psychomotor stimulation, and is consistent with the behavioral definition of addiction and behavioral sensitization. Animal experiments have the advantage over clinical studies of lower variation and fewer confounding effects.
Cavitation erosion - scale effect and model investigations
NASA Astrophysics Data System (ADS)
Geiger, F.; Rutschmann, P.
2015-12-01
The experimental works presented in here contribute to the clarification of erosive effects of hydrodynamic cavitation. Comprehensive cavitation erosion test series were conducted for transient cloud cavitation in the shear layer of prismatic bodies. The erosion pattern and erosion rates were determined with a mineral based volume loss technique and with a metal based pit count system competitively. The results clarified the underlying scale effects and revealed a strong non-linear material dependency, which indicated significantly different damage processes for both material types. Furthermore, the size and dynamics of the cavitation clouds have been assessed by optical detection. The fluctuations of the cloud sizes showed a maximum value for those cavitation numbers related to maximum erosive aggressiveness. The finding suggests the suitability of a model approach which relates the erosion process to cavitation cloud dynamics. An enhanced experimental setup is projected to further clarify these issues.
NASA Technical Reports Server (NTRS)
Olsen, G. C.; Smith, R. E.
1984-01-01
Attention is given to hypersonic laminar flow over a quilted surface configuration that simulates an array of Space Shuttle Thermal Protection System panels bowed in a spherical shape as a result of thermal gradients through the panel thickness. Pressure and heating loads to the surface are determined. The flow field over the configuration was mathematically modeled by means of time-dependent, three-dimensional conservation of mass, momentum, and energy equations. A boundary mapping technique was then used to obtain a rectangular, parallelepiped computational domain, and an explicit MacCormack (1972) explicit time-split predictor-corrector finite difference algorithm was used to obtain steady state solutions. Total integrated heating loads vary linearly with bowed height when this value does not exceed the local boundary layer thickness.
Gyrofluid turbulence models with kinetic effects
Dorland, W.; Hammett, G.W.
1992-12-01
Nonlinear gyrofluid equations are derived by taking moments of the nonlinear, electrostatic gyrokinetic equation. The principal model presented includes evolution equations for the guiding center n, u{parallel}, T{parallel}, and T{perpendicular} along with an equation expressing the quasineutrality constraint. Additional evolution equations for higher moments are derived which may be used if greater accuracy is desired. The moment hierarchy is closed with a Landau-damping model which is equivalent to a multi-pole approximation to the plasma dispersion function, extended to include finite Larmor radius effects. In particular, new dissipative, nonlinear terms are found which model the perpendicular phase-mixing of the distribution function along contours of constant electrostatic potential. These ``FLR phase-mixing`` terms introduce a hyperviscosity-like damping {proportional_to} k{sub {perpendicular}}{sup 2}{vert_bar}{Phi}{sub {rvec k}}{rvec k} {times}{rvec k}{prime}{vert_bar} which should provide a physics-based damping mechanism at high k{perpendicular}{rho} which is potentially as important as the usual polarization drift nonlinearity. The moments are taken in guiding center space to pick up the correct nonlinear FLR terms and the gyroaveraging of the shear. The equations are solved with a nonlinear, three dimensional initial value code. Linear results are presented, showing excellent agreement with linear gyrokinetic theory.
Modeling nuclear volume isotope effects in crystals.
Schauble, Edwin A
2013-10-29
Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from (119)Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium.
Modeling nuclear volume isotope effects in crystals
Schauble, Edwin A.
2013-01-01
Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac–Hartree–Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor–crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium
Modeling nuclear volume isotope effects in crystals
NASA Astrophysics Data System (ADS)
Schauble, Edwin A.
2013-10-01
Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium.
Simple model of the slingshot effect
NASA Astrophysics Data System (ADS)
Fiore, Gaetano; De Nicola, Sergio
2016-07-01
We present a detailed quantitative description of the recently proposed "slingshot effect." Namely, we determine a broad range of conditions under which the impact of a very short and intense laser pulse normally onto a low-density plasma (or matter locally completely ionized into a plasma by the pulse) causes the expulsion of a bunch of surface electrons in the direction opposite to the one of propagation of the pulse, and the detailed, ready-for-experiments features of the expelled electrons (energy spectrum, collimation, etc). The effect is due to the combined actions of the ponderomotive force and the huge longitudinal field arising from charge separation. Our predictions are based on estimating 3D corrections to a simple, yet powerful plane 2-fluid magnetohydrodynamic (MHD) model where the equations to be solved are reduced to a system of Hamilton equations in one dimension (or a collection of) which become autonomous after the pulse has overcome the electrons. Experimental tests seem to be at hand. If confirmed by the latter, the effect would provide a new extraction and acceleration mechanism for electrons, alternative to traditional radio-frequency-based or Laser-Wake-Field ones.
Modeling Instruction: An Effective Model for Science Education
ERIC Educational Resources Information Center
Jackson, Jane; Dukerich, Larry; Hestenes, David
2008-01-01
The authors describe a Modeling Instruction program that places an emphasis on the construction and application of conceptual models of physical phenomena as a central aspect of learning and doing science. (Contains 1 table.)
A Field-Effect Transistor (FET) model for ASAP
NASA Technical Reports Server (NTRS)
Ming, L.
1965-01-01
The derivation of the circuitry of a field effect transistor (FET) model, the procedure for adapting the model to automated statistical analysis program (ASAP), and the results of applying ASAP on this model are described.
ERIC Educational Resources Information Center
Macho, Siegfried; Ledermann, Thomas
2011-01-01
The phantom model approach for estimating, testing, and comparing specific effects within structural equation models (SEMs) is presented. The rationale underlying this novel method consists in representing the specific effect to be assessed as a total effect within a separate latent variable model, the phantom model that is added to the main…
Optimal Scaling of Interaction Effects in Generalized Linear Models
ERIC Educational Resources Information Center
van Rosmalen, Joost; Koning, Alex J.; Groenen, Patrick J. F.
2009-01-01
Multiplicative interaction models, such as Goodman's (1981) RC(M) association models, can be a useful tool for analyzing the content of interaction effects. However, most models for interaction effects are suitable only for data sets with two or three predictor variables. Here, we discuss an optimal scaling model for analyzing the content of…
An Integrated Model of Training Evaluation and Effectiveness
ERIC Educational Resources Information Center
Alvarez, Kaye; Salas, Eduardo; Garofano, Christina M.
2004-01-01
A decade of training evaluation and training effectiveness research was reviewed to construct an integrated model of training evaluation and effectiveness. This model integrates four prior evaluation models and results of 10 years of training effectiveness research. It is the first to be constructed using a set of strict criteria and to…
A Model for Measuring Effectiveness of an Online Course
ERIC Educational Resources Information Center
Mashaw, Bijan
2012-01-01
As a result of this research, a quantitative model and a procedure have been developed to create an online mentoring effectiveness index (EI). To develop the model, mentoring and teaching effectiveness are defined, and then the constructs and factors of effectiveness are identified. The model's construction is based on the theory that…
Space Environments and Effects: Trapped Proton Model
NASA Technical Reports Server (NTRS)
Huston, S. L.; Kauffman, W. (Technical Monitor)
2002-01-01
An improved model of the Earth's trapped proton environment has been developed. This model, designated Trapped Proton Model version 1 (TPM-1), determines the omnidirectional flux of protons with energy between 1 and 100 MeV throughout near-Earth space. The model also incorporates a true solar cycle dependence. The model consists of several data files and computer software to read them. There are three versions of the mo'del: a FORTRAN-Callable library, a stand-alone model, and a Web-based model.
Modelling the biologic effect of ions with the Local Effect Model
NASA Astrophysics Data System (ADS)
Friedrich, Thomas; Elsässer, Thilo; Durante, Marco; Scholz, Michael
In many cases in radiobiological experiments as well as in ion beam therapy the Local Effect Model (LEM) has proven to be capable to describe the biologic effect of ion irradiation based on the response to X-rays. During the last years, the LEM has been extended to include important processes such as the diffusion of free radicals or the biologic effect enhancement due to clustered lesions of the DNA in a more mechanistic fashion. In its current status the predictive power of the LEM covers a wide range of ions with good quantitative precision. Hence there is potential to also apply the LEM to problems in radiation protection. In this talk, the development stages of the LEM are illustrated. Emphasis is put on the most recent version of the LEM, where spatial distributions of DNA lesions are considered. Applicability, limits and strategies for an advanced model testing are discussed. Finally, planned extensions and applications of the LEM are presented.
Aerothermal analysis for the Mars Reconnaissance Orbiter.
Gallis, Michail A.; Hermina, Wahid L.; Chapel, James D.; Johnson, Mark A.
2004-06-01
The force on and the heat flux to the NASA Mars Reconnaissance Orbiter (MRO) during drag passes are analyzed. Aerobraking takes place in the higher/rarefied levels of the Martian atmosphere, where traditional continuum flui d dynamics methods cannot be applied. Therefore, molecular gas dynamics simulations such as the Direct Simulation Monte Carlo Method are used to calculate these flow fields and provide heating and aerodynamic predictions for the vehicles. The heating and aerodynamic predictions calculated for the MRO include the heat transfer coefficient (C{sub h}), calculated for a number of angles of attack and the drag coefficient (C{sub D}) calculated for a number of altitudes and velocities. Bridging relations are sought that are applicable over the range of conditions of interest. A sensitivity analysis of the results to the chemical reaction rates, surface accommodation and temperature is also performed.
Modeling Distributions of Immediate Memory Effects: No Strategies Needed?
ERIC Educational Resources Information Center
Beaman, C. Philip; Neath, Ian; Surprenant, Aimee M.
2008-01-01
Many models of immediate memory predict the presence or absence of various effects, but none have been tested to see whether they predict an appropriate distribution of effect sizes. The authors show that the feature model (J. S. Nairne, 1990) produces appropriate distributions of effect sizes for both the phonological confusion effect and the…
A random effects epidemic-type aftershock sequence model
Lin, Feng-Chang
2013-01-01
We consider an extension of the temporal epidemic-type aftershock sequence (ETAS) model with random effects as a special case of a well-known doubly stochastic self-exciting point process. The new model arises from a deterministic function that is randomly scaled by a nonnegative random variable, which is unobservable but assumed to follow either positive stable or one-parameter gamma distribution with unit mean. Both random effects models are of interest although the one-parameter gamma random effects model is more popular when modeling associated survival times. Our estimation is based on the maximum likelihood approach with marginalized intensity. The methods are shown to perform well in simulation experiments. When applied to an earthquake sequence on the east coast of Taiwan, the extended model with positive stable random effects provides a better model fit, compared to the original ETAS model and the extended model with one-parameter gamma random effects. PMID:24039322
A random effects epidemic-type aftershock sequence model.
Lin, Feng-Chang
2011-04-01
We consider an extension of the temporal epidemic-type aftershock sequence (ETAS) model with random effects as a special case of a well-known doubly stochastic self-exciting point process. The new model arises from a deterministic function that is randomly scaled by a nonnegative random variable, which is unobservable but assumed to follow either positive stable or one-parameter gamma distribution with unit mean. Both random effects models are of interest although the one-parameter gamma random effects model is more popular when modeling associated survival times. Our estimation is based on the maximum likelihood approach with marginalized intensity. The methods are shown to perform well in simulation experiments. When applied to an earthquake sequence on the east coast of Taiwan, the extended model with positive stable random effects provides a better model fit, compared to the original ETAS model and the extended model with one-parameter gamma random effects.
A synapse memristor model with forgetting effect
NASA Astrophysics Data System (ADS)
Chen, Ling; Li, Chuandong; Huang, Tingwen; Chen, Yiran; Wen, Shiping; Qi, Jiangtao
2013-12-01
In this Letter we improved the ion diffusion term proposed in literature [13] and redesigned the previous model as a dynamical model with two more internal state variables ‘forgetting rate’ and ‘retention’ besides the original variable ‘conductance’. The new model can not only describe the basic memory ability of memristor but also be able to capture the new finding forgetting behavior in memristor. And different from the previous model, the transition from short term memory to long term memory is also defined by the new model. Besides, the new model is better matched with the physical memristor (Pd/WOx/W) than the previous one.
Effective Stimuli for Constructing Reliable Neuron Models
Druckmann, Shaul; Berger, Thomas K.; Schürmann, Felix; Hill, Sean; Markram, Henry; Segev, Idan
2011-01-01
The rich dynamical nature of neurons poses major conceptual and technical challenges for unraveling their nonlinear membrane properties. Traditionally, various current waveforms have been injected at the soma to probe neuron dynamics, but the rationale for selecting specific stimuli has never been rigorously justified. The present experimental and theoretical study proposes a novel framework, inspired by learning theory, for objectively selecting the stimuli that best unravel the neuron's dynamics. The efficacy of stimuli is assessed in terms of their ability to constrain the parameter space of biophysically detailed conductance-based models that faithfully replicate the neuron's dynamics as attested by their ability to generalize well to the neuron's response to novel experimental stimuli. We used this framework to evaluate a variety of stimuli in different types of cortical neurons, ages and animals. Despite their simplicity, a set of stimuli consisting of step and ramp current pulses outperforms synaptic-like noisy stimuli in revealing the dynamics of these neurons. The general framework that we propose paves a new way for defining, evaluating and standardizing effective electrical probing of neurons and will thus lay the foundation for a much deeper understanding of the electrical nature of these highly sophisticated and non-linear devices and of the neuronal networks that they compose. PMID:21876663
Irradiation effects on polymer-model compounds
NASA Astrophysics Data System (ADS)
Seguchi, Tadao; Katsumura, Yosuke; Hayashi, Nariyuki; Hayakawa, Naohiro; Tamura, Naoyuki; Tabata, Yoneho
Irradiation effects on n-paraffins and squalane, used as models of polymers, were investigated by product analysis. Four n-paraffins, C 20H 42, C 21H 44, C 23H 48 and C 24H 50, and squalane (C 30H 62) were γ-irradiated under vacuum in liquid, crystalline and glassy states. The evolved gases were analyzed by gas chromatography and changes in molecular weight were analyzed by liquid chromatography and mass spectroscopy. G-values for crosslinking of n-paraffins were 1.2 for crystalline states (at 25°C) and 1.7 for liquid states (at 55°C), and showed no difference between odd and even carbon numbers. The G-value of liquid squalane was 1.7; it was 1.3 for the glassy state at low temperature (-77°C). Double bonds were common in the crosslinked products, especially after liquid-phase irradiation. The probability of chain scission was estimated as being negligible, though a small number of chain-scission products (which were products of scission at chain-ends or side chains) were observed by gas analysis.
NASA Technical Reports Server (NTRS)
Reinarts, Thomas R.; Crain, William K.; Stuckey, C. Irvin; Palko, Richard L.
1998-01-01
The purpose of the work is to demonstrate that the flat test panel substrate temperatures are consistent with analysis predictions for MCC-1 applied to a aluminum substrate. The testing was performed in an aerothermal facility on samples of three different thicknesses of MCC-1 on an aluminum substrate. The results of the test were compared with a Transient Thermal model. The key assumptions of the Transient Thermal model were: (1) a one-dimensional heat transfer; (2) a constant ablation recession rate (determined from pre and post-test measurements); (3) ablation temperature of 540 degrees F; (4) Char left behind the ablation front; and (5) temperature jump correction for incident heat transfer coefficient. Two methods were used to model the heating of bare MCC-1: (1) Directly input surface temperature as a function of time; and (2) Aerothermal heating using calibration plate data and subtracting the radiation losses to tunnel walls. The results are presented as graphs. This article is presented in Viewgraph format.
Plume-Free Stream Interaction Heating Effects During Orion Crew Module Reentry
NASA Technical Reports Server (NTRS)
Marichalar, J.; Lumpkin, F.; Boyles, K.
2012-01-01
During reentry of the Orion Crew Module (CM), vehicle attitude control will be performed by firing reaction control system (RCS) thrusters. Simulation of RCS plumes and their interaction with the oncoming flow has been difficult for the analysis community due to the large scarf angles of the RCS thrusters and the unsteady nature of the Orion capsule backshell environments. The model for the aerothermal database has thus relied on wind tunnel test data to capture the heating effects of thruster plume interactions with the freestream. These data are only valid for the continuum flow regime of the reentry trajectory. A Direct Simulation Monte Carlo (DSMC) analysis was performed to study the vehicle heating effects that result from the RCS thruster plume interaction with the oncoming freestream flow at high altitudes during Orion CM reentry. The study was performed with the DSMC Analysis Code (DAC). The inflow boundary conditions for the jets were obtained from Data Parallel Line Relaxation (DPLR) computational fluid dynamics (CFD) solutions. Simulations were performed for the roll, yaw, pitch-up and pitch-down jets at altitudes of 105 km, 125 km and 160 km as well as vacuum conditions. For comparison purposes (see Figure 1), the freestream conditions were based on previous DAC simulations performed without active RCS to populate the aerodynamic database for the Orion CM. Other inputs to the analysis included a constant Orbital reentry velocity of 7.5 km/s and angle of attack of 160 degrees. The results of the study showed that the interaction effects decrease quickly with increasing altitude. Also, jets with highly scarfed nozzles cause more severe heating compared to the nozzles with lower scarf angles. The difficulty of performing these simulations was based on the maximum number density and the ratio of number densities between the freestream and the plume for each simulation. The lowest altitude solutions required a substantial amount of computational resources
Modifications in Children's Cognitive Styles: Some Effects of Peer Modeling.
ERIC Educational Resources Information Center
Cohen, Stewart; Przybycien, Collette A.
An extension of previous attempts at modifying children's cognitive styles is discussed. Specifically, the present study employed sociometric peer models in order to ascertain whether: (1) impulsivity is modifiable through observation of salient models, and (2) sociometrically selected peer models are more effective than unselected models in the…
ERIC Educational Resources Information Center
Ashraf, Giti; Kadir, Suhaida bte Abd
2012-01-01
Organizational effectiveness is the main concern of all higher education institutes. Over the years there have been many different models of effectiveness along with the criteria for measuring organizational effectiveness. In this paper, four main models of organizational effectiveness namely the goal approach, the system resource approach, the…
Effective cost modeling for service line planning.
Scott, Michael; Stephen, Robert
2010-05-01
Healthcare executives have struggled to have accurate, timely information about cost and resources to model and monitor service line performance. Process-based cost modeling has been used successfully in other industries, but is relatively new in health care. Understanding costs and resources at process and patient levels can make the difference between a service line having a positive or negative margin. PMID:20446426
NASA Technical Reports Server (NTRS)
Bose, Deepak
2012-01-01
The design of entry vehicles requires predictions of aerothermal environment during the hypersonic phase of their flight trajectories. These predictions are made using computational fluid dynamics (CFD) codes that often rely on physics and chemistry models of nonequilibrium processes. The primary processes of interest are gas phase chemistry, internal energy relaxation, electronic excitation, nonequilibrium emission and absorption of radiation, and gas-surface interaction leading to surface recession and catalytic recombination. NASAs Hypersonics Project is advancing the state-of-the-art in modeling of nonequilibrium phenomena by making detailed spectroscopic measurements in shock tube and arcjets, using ab-initio quantum mechanical techniques develop fundamental chemistry and spectroscopic databases, making fundamental measurements of finite-rate gas surface interactions, implementing of detailed mechanisms in the state-of-the-art CFD codes, The development of new models is based on validation with relevant experiments. We will present the latest developments and a roadmap for the technical areas mentioned above
Shadowing effect modeling and compensation for EUV lithography
NASA Astrophysics Data System (ADS)
Song, Hua; Zavyalova, Lena; Su, Irene; Shiely, James; Schmoeller, Thomas
2011-04-01
Extreme ultraviolet (EUV) lithography is one of the leading technologies for 16nm and smaller node device patterning. One patterning issue intrinsic to EUV lithography is the shadowing effect due to oblique illumination at the mask and mask absorber thickness. This effect can cause CD errors up to a few nanometers, consequently needs to be accounted for in OPC modeling and compensated accordingly in mask synthesis. Because of the dependence on the reticle field coordinates, shadowing effect is very different from the traditional optical and resist effects. It poses challenges to modeling, compensation, and verification that were not encountered in tradition optical lithography mask synthesis. In this paper, we present a systematic approach for shadowing effect modeling and model-based shadowing compensation. Edge based shadowing effect calculation with reticle and scan information is presented. Model calibration and mask synthesis flows are described. Numerical experiments are performed to demonstrate the effectiveness of the approach.
Simulation Model Development for Icing Effects Flight Training
NASA Technical Reports Server (NTRS)
Barnhart, Billy P.; Dickes, Edward G.; Gingras, David R.; Ratvasky, Thomas P.
2003-01-01
A high-fidelity simulation model for icing effects flight training was developed from wind tunnel data for the DeHavilland DHC-6 Twin Otter aircraft. First, a flight model of the un-iced airplane was developed and then modifications were generated to model the icing conditions. The models were validated against data records from the NASA Twin Otter Icing Research flight test program with only minimal refinements being required. The goals of this program were to demonstrate the effectiveness of such a simulator for training pilots to recognize and recover from icing situations and to establish a process for modeling icing effects to be used for future training devices.
ERIC Educational Resources Information Center
Tsai, Chia-Ching; Chang, Chih-Hsiang
2007-01-01
This study investigates the effect of advertising with physically attractive models on male and female adolescents. The findings suggest that highly attractive models are less effective than those who are normally attractive. Implications of social comparison are discussed.
Analysis of dispersal effects in metapopulation models.
Ruiz-Herrera, Alfonso
2016-02-01
The interplay between local dynamics and dispersal rates in discrete metapopulation models for homogeneous landscapes is studied. We introduce an approach based on scalar dynamics to study global attraction of equilibria and periodic orbits. This approach applies for any number of patches, dispersal rates, or landscape structure. The existence of chaos in metapopulation models is also discussed. We analyze issues such as sensitive dependence on the initial conditions or short/intermediate/long term behaviours of chaotic orbits. PMID:26032652
Random effects and shrinkage estimation in capture-recapture models
Royle, J. Andrew; Link, W.A.
2002-01-01
We discuss the analysis of random effects in capture-recapture models, and outline Bayesian and frequentists approaches to their analysis. Under a normal model, random effects estimators derived from Bayesian or frequentist considerations have a common form as shrinkage estimators. We discuss some of the difficulties of analysing random effects using traditional methods, and argue that a Bayesian formulation provides a rigorous framework for dealing with these difficulties. In capture-recapture models, random effects may provide a parsimonious compromise between constant and completely time-dependent models for the parameters (e.g. survival probability). We consider application of random effects to band-recovery models, although the principles apply to more general situations, such as Cormack-Jolly-Seber models. We illustrate these ideas using a commonly analysed band recovery data set.
Modeling the effects of ozone on soybean growth and yield.
Kobayashi, K; Miller, J E; Flagler, R B; Heck, W W
1990-01-01
A simple mechanistic model was developed based on an existing growth model in order to address the mechanisms of the effects of ozone on growth and yield of soybean [Glycine max. (L.) Merr. 'Davis'] and interacting effects of other environmental stresses. The model simulates daily growth of soybean plants using environmental data including shortwave radiation, temperature, precipitation, irrigation and ozone concentration. Leaf growth, dry matter accumulation, water budget, nitrogen input and seed growth linked to senescence and abscission of leaves are described in the model. The effects of ozone are modeled as reduced photosynthate production and accelerated senescence. The model was applied to the open-top chamber experiments in which soybean plants were exposed to ozone under two levels of soil moisture regimes. After calibrating the model to the growth data and seed yield, goodness-of-fit of the model was tested. The model fitted well for top dry weight in the vegetative growth phase and also at maturity. The effect of ozone on seen yield was also described satisfactorily by the model. The simulation showed apparent interaction between the effect of ozone and soil moisture stress on the seed yield. The model revealed that further work is needed concerning the effect of ozone on the senescence process and the consequences of alteration of canopy microclimate by the open-top chambers.
Modeling the effects of ozone on soybean growth and yield.
Kobayashi, K; Miller, J E; Flagler, R B; Heck, W W
1990-01-01
A simple mechanistic model was developed based on an existing growth model in order to address the mechanisms of the effects of ozone on growth and yield of soybean [Glycine max. (L.) Merr. 'Davis'] and interacting effects of other environmental stresses. The model simulates daily growth of soybean plants using environmental data including shortwave radiation, temperature, precipitation, irrigation and ozone concentration. Leaf growth, dry matter accumulation, water budget, nitrogen input and seed growth linked to senescence and abscission of leaves are described in the model. The effects of ozone are modeled as reduced photosynthate production and accelerated senescence. The model was applied to the open-top chamber experiments in which soybean plants were exposed to ozone under two levels of soil moisture regimes. After calibrating the model to the growth data and seed yield, goodness-of-fit of the model was tested. The model fitted well for top dry weight in the vegetative growth phase and also at maturity. The effect of ozone on seen yield was also described satisfactorily by the model. The simulation showed apparent interaction between the effect of ozone and soil moisture stress on the seed yield. The model revealed that further work is needed concerning the effect of ozone on the senescence process and the consequences of alteration of canopy microclimate by the open-top chambers. PMID:15092277
Model for Effective Contraceptive Counseling on Campus.
ERIC Educational Resources Information Center
Bachmann, Gloria A.
1981-01-01
A study compared the effective v ineffective use of contraceptives at a major university by comparing college women who had experienced birth control failure with those who had not. Factors related to a woman's use of a contraceptive device include: satisfaction with its aesthetic properties; trust in its effectiveness; a feeling of comfort…
Effective Interactions from No Core Shell Model
Dikmen, E.; Lisetskiy, A. F.; Barrett, B. R.; Navratil, P.; Vary, J. P.
2008-11-11
We construct the many-body effective Hamiltonian for pf-shell by carrying out 2({Dirac_h}/2{pi}){omega}. NCSM calculations at the 2-body cluster level. We demonstrate how the effective Hamiltonian derived from realistic nucleon-nucleon (NN) potentials for the 2({Dirac_h}/2{pi}){omega} NCSM space should be modified to properly account for the many-body correlations produced by truncating to the major pf-shell. We obtain two-body effective interactions for the pf-shell by using direct projection and use them to reproduce the results of large scale NCSM for other light Ca isotopes.
Coriolis effects and motion sickness modelling.
Bles, W
1998-11-15
Coriolis effects are notorious in relation to disorientation and motion sickness in aircrew. A review is provided of experimental data on these Coriolis effects, including the modulatory effects of adding visual or somatosensory rotatory motion information. A vector analysis of the consequences of head movements during somatosensory, visual and/or vestibular rotatory motion stimulation revealed that the more the sensed angular velocity vector after the head movements is aligned with the gravitoinertial force vector, the less nauseating effects are experienced. It is demonstrated that this is a special case of the subjective vertical conflict theory on motion sickness that assumes that motion sickness may be provoked if a discrepancy is detected between the subjective vertical and the sensed vertical as determined on the basis of incoming sensory information.
IPEM: An Integrated Planning, Effectiveness Model.
ERIC Educational Resources Information Center
Donsky, Aaron P.
While historically higher education has utilized many different planning paradigms and elements, two concepts (strategic planning and operational planning) can be presented as the major planning concepts into which the various paradigms can be placed. Starting in fall 1991, Seminole Community College developed a planning model which integrated…
A Mixed Effects Randomized Item Response Model
ERIC Educational Resources Information Center
Fox, J.-P.; Wyrick, Cheryl
2008-01-01
The randomized response technique ensures that individual item responses, denoted as true item responses, are randomized before observing them and so-called randomized item responses are observed. A relationship is specified between randomized item response data and true item response data. True item response data are modeled with a (non)linear…
Modeling quantum gravity effects in inflation
NASA Astrophysics Data System (ADS)
Martinec, Emil J.; Moore, Wynton E.
2014-07-01
Cosmological models in 1+1 dimensions are an ideal setting for investigating the quantum structure of inflationary dynamics — gravity is renormalizable, while there is room for spatial structure not present in the minisuperspace approximation. We use this fortuitous convergence to investigate the mechanism of slow-roll eternal inflation. A variant of 1+1 Liouville gravity coupled to matter is shown to model precisely the scalar sector of cosmological perturbations in 3+1 dimensions. A particular example of quintessence in 1+1d is argued on the one hand to exhibit slow-roll eternal inflation according to standard criteria; on the other hand, a field redefinition relates the model to pure de Sitter gravity coupled to a free scalar matter field with no potential. This and other examples show that the standard logic leading to slow-roll eternal inflation is not invariant under field redefinitions, thus raising concerns regarding its validity. Aspects of the quantization of Liouville gravity as a model of quantum de Sitter space are also discussed.
SCID: Model for Effective Instructional Development.
ERIC Educational Resources Information Center
Norton, Robert E.
The Systematic Curriculum and Instructional Development (SCID) model provides a tested procedure for developing high-quality, low-cost competency-based education and tech prep curriculum and instructional materials. It consists of 5 phases--analysis, design, development, implementation, and evaluation--and 23 components. The analysis phase…
Mesoscale modelling of PBX. Binder effects.
NASA Astrophysics Data System (ADS)
Milne, Alec; Dunnett, Jim; Bourne, Neil
2007-06-01
In earlier work we have studied aspects of shock to detonation transition and detonation structure in polymer bonded explosives on the scale of the largest grains (the mesoscale) to augment continuum models for these processes. Building blocks have been unreacted Hugoniots of mixtures, mapping from experiment (2D micrographs and 3D tomography) for accurate initial conditions and details of cavity collapse mechanisms as hot spots for ignition. Recently we have applied continuum mixture theory (multi-phase modelling) to dirty binder (the mixture of explosive crystal fines and binder that surrounds the large grains) and validated it for the unreacted Hugoniot of a range of UK explosives. In this paper we build on all of this work and report our progress in using continuum mixture theory to model the reactive behaviour of dirty binder. We begin by considering the binder on its own and then use this continuum mixture mode in conjunction with mesoscale representations of PBX. We consider PBX9501 and a UK PBX as examples. We identify the numerical modelling issues that have arisen, our current approaches and our plans for further development and testing.
Evaluating Differential Effects Using Regression Interactions and Regression Mixture Models
ERIC Educational Resources Information Center
Van Horn, M. Lee; Jaki, Thomas; Masyn, Katherine; Howe, George; Feaster, Daniel J.; Lamont, Andrea E.; George, Melissa R. W.; Kim, Minjung
2015-01-01
Research increasingly emphasizes understanding differential effects. This article focuses on understanding regression mixture models, which are relatively new statistical methods for assessing differential effects by comparing results to using an interactive term in linear regression. The research questions which each model answers, their…
A Model for Effectively Assessing Student Learning Outcomes
ERIC Educational Resources Information Center
Ohia, Uche O.
2011-01-01
This paper describes a model proven to be effective for assessing and documenting evidence of student learning outcomes. Specifically, it will share a model, F.A.M.O.U.S. Copyright ©2008, which is an acronym exemplifying six effective steps for complying with institutional accountability and eternal assessment requirements proscribed by the…
Effects of Modeling and Desensitation in Reducing Dentist Phobia
ERIC Educational Resources Information Center
Shaw, David W.; Thoresen, Carl E.
1974-01-01
Many persons avoid dentists and dental work. The present study explored the effects of systematic desensitization and social-modeling treatments with placebo and assessment control groups. Modeling was more effective than desensitization as shown by the number of subjects who went to a dentist. (Author)
Institutional Effectiveness: A Model for Planning, Assessment & Validation.
ERIC Educational Resources Information Center
Truckee Meadows Community Coll., Sparks, NV.
The report presents Truckee Meadows Community College's (Colorado) model for assessing institutional effectiveness and validating the College's mission and vision, and the strategic plan for carrying out the institutional effectiveness model. It also outlines strategic goals for the years 1999-2001. From the system-wide directive that education…
Observational Learning and the Effects of Model-Observer Similarity.
ERIC Educational Resources Information Center
Braaksma, Martine A. H.; Rijlaarsdam, Gert; van den Bergh, Huub
2002-01-01
This study examined the effects of similarity in competence between model and observer on the effectiveness of observational learning in argumentative writing. Results are consistent with the similarity hypothesis: weak learners learn more from focusing their observations on weak models, whereas better learners learn more from focusing on good…
Mixed-Effects Modeling with Crossed Random Effects for Subjects and Items
ERIC Educational Resources Information Center
Baayen, R. H.; Davidson, D. J.; Bates, D. M.
2008-01-01
This paper provides an introduction to mixed-effects models for the analysis of repeated measurement data with subjects and items as crossed random effects. A worked-out example of how to use recent software for mixed-effects modeling is provided. Simulation studies illustrate the advantages offered by mixed-effects analyses compared to…
Effective Reading and Writing Instruction: A Focus on Modeling
ERIC Educational Resources Information Center
Regan, Kelley; Berkeley, Sheri
2012-01-01
When providing effective reading and writing instruction, teachers need to provide explicit modeling. Modeling is particularly important when teaching students to use cognitive learning strategies. Examples of how teachers can provide specific, explicit, and flexible instructional modeling is presented in the context of two evidence-based…
A Cost Effectiveness Model for Comparing Various Circulation Systems
ERIC Educational Resources Information Center
Burgess, Thomas K.
1973-01-01
Two models for circulation systems (manual and automated) costing are presented. Validation tests for the model assumptions are devised and explained. Use of the models for cost effectiveness comparison and for cost prediction are discussed and examples are given showing their application. (10 references) (Author/SJ)
Seventh Grade Students' Mental Models of the Greenhouse Effect
ERIC Educational Resources Information Center
Shepardson, Daniel P.; Choi, Soyoung; Niyogi, Dev; Charusombat, Umarporn
2011-01-01
This constructivist study investigates 225 student drawings and explanations from three different schools in the midwest in the US, to identify seventh grade students' mental models of the greenhouse effect. Five distinct mental models were derived from an inductive analysis of the content of the students' drawings and explanations: Model 1, a…
The Effect of Sample Size on Latent Growth Models.
ERIC Educational Resources Information Center
Hamilton, Jennifer; Gagne, Phillip E.; Hancock, Gregory R.
A Monte Carlo simulation approach was taken to investigate the effect of sample size on a variety of latent growth models. A fully balanced experimental design was implemented, with samples drawn from multivariate normal populations specified to represent 12 unique growth models. The models varied factorially by crossing number of time points,…
Effects of Modeling and Reinforcement on Adult Chronic Schizophrenics
ERIC Educational Resources Information Center
Olson, R. Paul
1971-01-01
This study confirmed two general predictions: (1) the model contributes to new learning; and (2) neither the model nor reinforcement of the model adds significantly to motivation, beyond the effect that can be attributed to reinforcement of the subject himself. (Author/CG)
Assumptions of Value-Added Models for Estimating School Effects
ERIC Educational Resources Information Center
Reardon, Sean F.; Raudenbush, Stephen W.
2009-01-01
The ability of school (or teacher) value-added models to provide unbiased estimates of school (or teacher) effects rests on a set of assumptions. In this article, we identify six assumptions that are required so that the estimands of such models are well defined and the models are able to recover the desired parameters from observable data. These…
Highly physical penumbra solar radiation pressure modeling with atmospheric effects
NASA Astrophysics Data System (ADS)
Robertson, Robert; Flury, Jakob; Bandikova, Tamara; Schilling, Manuel
2015-10-01
We present a new method for highly physical solar radiation pressure (SRP) modeling in Earth's penumbra. The fundamental geometry and approach mirrors past work, where the solar radiation field is modeled using a number of light rays, rather than treating the Sun as a single point source. However, we aim to clarify this approach, simplify its implementation, and model previously overlooked factors. The complex geometries involved in modeling penumbra solar radiation fields are described in a more intuitive and complete way to simplify implementation. Atmospheric effects are tabulated to significantly reduce computational cost. We present new, more efficient and accurate approaches to modeling atmospheric effects which allow us to consider the high spatial and temporal variability in lower atmospheric conditions. Modeled penumbra SRP accelerations for the Gravity Recovery and Climate Experiment (GRACE) satellites are compared to the sub-nm/s2 precision GRACE accelerometer data. Comparisons to accelerometer data and a traditional penumbra SRP model illustrate the improved accuracy which our methods provide. Sensitivity analyses illustrate the significance of various atmospheric parameters and modeled effects on penumbra SRP. While this model is more complex than a traditional penumbra SRP model, we demonstrate its utility and propose that a highly physical model which considers atmospheric effects should be the basis for any simplified approach to penumbra SRP modeling.
A Gompertzian model with random effects to cervical cancer growth
Mazlan, Mazma Syahidatul Ayuni; Rosli, Norhayati
2015-05-15
In this paper, a Gompertzian model with random effects is introduced to describe the cervical cancer growth. The parameters values of the mathematical model are estimated via maximum likehood estimation. We apply 4-stage Runge-Kutta (SRK4) for solving the stochastic model numerically. The efficiency of mathematical model is measured by comparing the simulated result and the clinical data of the cervical cancer growth. Low values of root mean-square error (RMSE) of Gompertzian model with random effect indicate good fits.
A Gompertzian model with random effects to cervical cancer growth
NASA Astrophysics Data System (ADS)
Mazlan, Mazma Syahidatul Ayuni; Rosli, Norhayati
2015-05-01
In this paper, a Gompertzian model with random effects is introduced to describe the cervical cancer growth. The parameters values of the mathematical model are estimated via maximum likehood estimation. We apply 4-stage Runge-Kutta (SRK4) for solving the stochastic model numerically. The efficiency of mathematical model is measured by comparing the simulated result and the clinical data of the cervical cancer growth. Low values of root mean-square error (RMSE) of Gompertzian model with random effect indicate good fits.
NASA Astrophysics Data System (ADS)
Beniaiche, Ahmed; Ghenaiet, Adel; Carcasci, Carlo; Facchini, Bruno
2016-05-01
This paper presents a numerical validation of the aero-thermal study of a 30:1 scaled model reproducing an innovative trailing edge with one row of enlarged pedestals under stationary and rotating conditions. A CFD analysis was performed by means of commercial ANSYS-Fluent modeling the isothermal air flow and using k-ω SST turbulence model and an isothermal air flow for both static and rotating conditions (Ro up to 0.23). The used numerical model is validated first by comparing the numerical velocity profiles distribution results to those obtained experimentally by means of PIV technique for Re = 20,000 and Ro = 0-0.23. The second validation is based on the comparison of the numerical results of the 2D HTC maps over the heated plate to those of TLC experimental data, for a smooth surface for a Reynolds number = 20,000 and 40,000 and Ro = 0-0.23. Two-tip conditions were considered: open tip and closed tip conditions. Results of the average Nusselt number inside the pedestal ducts region are presented too. The obtained results help to predict the flow field visualization and the evaluation of the aero-thermal performance of the studied blade cooling system during the design step.
The media effect in Axelrod's model explained
NASA Astrophysics Data System (ADS)
Peres, L. R.; Fontanari, J. F.
2011-11-01
We revisit the problem of introducing an external global field —the mass media— in Axelrod's model of social dynamics, where in addition to their nearest neighbors, the agents can interact with a virtual neighbor whose cultural features are fixed from the outset. The finding that this apparently homogenizing field actually increases the cultural diversity has been considered a puzzle since the phenomenon was first reported more than a decade ago. Here we offer a simple explanation for it, which is based on the pedestrian observation that Axelrod's model exhibits more cultural diversity, i.e., more distinct cultural domains, when the agents are allowed to interact solely with the media field than when they can interact with their neighbors as well. In this perspective, it is the local homogenizing interactions that work towards making the absorbing configurations less fragmented as compared with the extreme situation in which the agents interact with the media only.
Modeling Effective Dosages in Hormetic Dose-Response Studies
Belz, Regina G.; Piepho, Hans-Peter
2012-01-01
Background Two hormetic modifications of a monotonically decreasing log-logistic dose-response function are most often used to model stimulatory effects of low dosages of a toxicant in plant biology. As just one of these empirical models is yet properly parameterized to allow inference about quantities of interest, this study contributes the parameterized functions for the second hormetic model and compares the estimates of effective dosages between both models based on 23 hormetic data sets. Based on this, the impact on effective dosage estimations was evaluated, especially in case of a substantially inferior fit by one of the two models. Methodology/Principal Findings The data sets evaluated described the hormetic responses of four different test plant species exposed to 15 different chemical stressors in two different experimental dose-response test designs. Out of the 23 data sets, one could not be described by any of the two models, 14 could be better described by one of the two models, and eight could be equally described by both models. In cases of misspecification by any of the two models, the differences between effective dosages estimates (0–1768%) greatly exceeded the differences observed when both models provided a satisfactory fit (0–26%). This suggests that the conclusions drawn depending on the model used may diverge considerably when using an improper hormetic model especially regarding effective dosages quantifying hormesis. Conclusions/Significance The study showed that hormetic dose responses can take on many shapes and that this diversity can not be captured by a single model without risking considerable misinterpretation. However, the two empirical models considered in this paper together provide a powerful means to model, prove, and now also to quantify a wide range of hormetic responses by reparameterization. Despite this, they should not be applied uncritically, but after statistical and graphical assessment of their adequacy. PMID
Models of Effective Migrant Education Programs.
ERIC Educational Resources Information Center
Mattera, Gloria
Intended to encourage both migrant and non-migrant educators to explore the possibilities of adopting and/or adapting the cited programs or appropriate components into their own units, this volume updates the 1974 description of some of the many programs that have proven effective in serving migrant students. Chapter I summarizes seven programs…
Effective UV radiation from model calculations and measurements
NASA Technical Reports Server (NTRS)
Feister, Uwe; Grewe, Rolf
1994-01-01
Model calculations have been made to simulate the effect of atmospheric ozone and geographical as well as meteorological parameters on solar UV radiation reaching the ground. Total ozone values as measured by Dobson spectrophotometer and Brewer spectrometer as well as turbidity were used as input to the model calculation. The performance of the model was tested by spectroradiometric measurements of solar global UV radiation at Potsdam. There are small differences that can be explained by the uncertainty of the measurements, by the uncertainty of input data to the model and by the uncertainty of the radiative transfer algorithms of the model itself. Some effects of solar radiation to the biosphere and to air chemistry are discussed. Model calculations and spectroradiometric measurements can be used to study variations of the effective radiation in space in space time. The comparability of action spectra and their uncertainties are also addressed.
Simple effective thickness model for circular brush seals
NASA Astrophysics Data System (ADS)
Dowler, Constance A.; Chupp, Raymond E.; Holle, Glenn F.
1992-07-01
Brush seals are being investigated as replacements for some of the labyrinth seals in gas turbine engines. A relatively simple flow model approach has been presented to generalize brush seal leakage throughout the range of test and application environments. The model uses a single parameter, effective brush thickness, to correlate flow through the seal. A revision to the flow model is presented in this paper to account for seal curvature, which is especially important for smaller diameter brush seals. The revised model has been applied to leakage flow data from five sources. The results demonstrate the utility of the flow model approach in correlating the performance of brush seals having different design geometries. The revised model is shown to effectively account for the effect of seal curvature.
Indirect aerosol effect increases CMIP5 models projected Arctic warming
Chylek, Petr; Vogelsang, Timothy J.; Klett, James D.; Hengartner, Nicholas; Higdon, Dave; Lesins, Glen; Dubey, Manvendra K.
2016-02-20
Phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models’ projections of the 2014–2100 Arctic warming under radiative forcing from representative concentration pathway 4.5 (RCP4.5) vary from 0.9° to 6.7°C. Climate models with or without a full indirect aerosol effect are both equally successful in reproducing the observed (1900–2014) Arctic warming and its trends. However, the 2014–2100 Arctic warming and the warming trends projected by models that include a full indirect aerosol effect (denoted here as AA models) are significantly higher (mean projected Arctic warming is about 1.5°C higher) than those projected by models without a full indirect aerosolmore » effect (denoted here as NAA models). The suggestion is that, within models including full indirect aerosol effects, those projecting stronger future changes are not necessarily distinguishable historically because any stronger past warming may have been partially offset by stronger historical aerosol cooling. In conclusion, the CMIP5 models that include a full indirect aerosol effect follow an inverse radiative forcing to equilibrium climate sensitivity relationship, while models without it do not.« less
Improving Institutional Effectiveness: Description and Application of an Implementation Model
ERIC Educational Resources Information Center
Sheldon, Michael R.; Golub, Andrew J.; Langevin, John R.; St. Ours, Paulette A.; Swartzlander, Barbara J.
2008-01-01
The higher education literature continues to highlight difficulties with efforts to implement and sustain institutional effectiveness activities. This article describes an implementation effectiveness model from the field of organizational management and applies it to the implementation of institutional effectiveness initiatives in higher…
Effects of quasiperiodic forcing in epidemic models
NASA Astrophysics Data System (ADS)
Bilal, Shakir; Singh, Brajendra K.; Prasad, Awadhesh; Michael, Edwin
2016-09-01
We study changes in the bifurcations of seasonally driven compartmental epidemic models, where the transmission rate is modulated temporally. In the presence of periodic modulation of the transmission rate, the dynamics varies from periodic to chaotic. The route to chaos is typically through period doubling bifurcation. There are coexisting attractors for some sets of parameters. However in the presence of quasiperiodic modulation, tori are created in place of periodic orbits and chaos appears via finite torus doublings. Strange nonchaotic attractors (SNAs) are created at the boundary of chaotic and torus dynamics. Multistability is found to be reduced as a function of quasiperiodic modulation strength. It is argued that occurrence of SNAs gives an opportunity of asymptotic predictability of epidemic growth even when the underlying dynamics is strange.
Modeling hurricane effects on mangrove ecosystems
Doyle, Thomas W.
1997-01-01
Mangrove ecosystems are at their most northern limit along the coastline of Florida and in isolated areas of the gulf coast in Louisiana and Texas. Mangroves are marine-based forests that have adapted to colonize and persist in salty intertidal waters. Three species of mangrove trees are common to the United States, black mangrove (Avicennia germinans), white mangrove (Laguncularia racemosa), and red mangrove (Rhizophora mangle). Mangroves are highly productive ecosystems and provide valuable habitat for fisheries and shorebirds. They are susceptible to lightning and hurricane disturbance, both of which occur frequently in south Florida. Climate change studies predict that, while these storms may not become more frequent, they may become more intense with warming sea temperatures. Sea-level rise alone has the potential for increasing the severity of storm surge, particularly in areas where coastal habitats and barrier shorelines are rapidly deteriorating. Given this possibility, U.S. Geological Survey researchers modeled the impact of hurricanes on south Florida mangrove communities.
Modelling the effect of temperature on unsaturated soil behaviour
NASA Astrophysics Data System (ADS)
Dumont, Matthieu; Taibi, Said; Fleureau, Jean-Marie; Abou Bekr, Nabil; Saouab, Abdelghani
2010-12-01
A simple thermohydromechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way.
Effective Strategies to Communicate Modeling with Project Regulators and Stakeholders
NASA Astrophysics Data System (ADS)
Arola, C.; Moser, K.; Bratton, W.
2008-12-01
Modeling is commonly used to support environmental project decision making. A notable example of the role of groundwater flow, fate, and transport modeling is to support the CERCLA remedial investigation and feasibility study (RI/FS) process. Modeling within an RI/FS is often used to evaluate new sampling locations, or to support evaluation of potential groundwater remedial technologies. Modeling used in these efforts ranges from simple to complex, and often must fit within a variety of state and federal regulations. Project stakeholder understanding and familiarity with model tools and application ranges broadly. Effective communication of the purpose, expected outcomes, strengths, limitations, and uncertainties of modeling efforts with regulators and project stakeholders is critical to successfully support project needs. Effective communication begins prior to the implementation of modeling efforts and should continue throughout the lifecycle of the modeling project. Communication efforts should include regular project workshops to keep stakeholders apprised of modeling progress. Regular communication throughout the modeling lifecycle provides a more technically and cost effective final product due to consideration of stakeholder concerns throughout the modeling effort through information exchange and negotiation, rather than at the end of the project, when it is often too late in the process or too expensive to change course and meet project milestones.
Modeling Randomness in Judging Rating Scales with a Random-Effects Rating Scale Model
ERIC Educational Resources Information Center
Wang, Wen-Chung; Wilson, Mark; Shih, Ching-Lin
2006-01-01
This study presents the random-effects rating scale model (RE-RSM) which takes into account randomness in the thresholds over persons by treating them as random-effects and adding a random variable for each threshold in the rating scale model (RSM) (Andrich, 1978). The RE-RSM turns out to be a special case of the multidimensional random…
Technical note: Equivalent genomic models with a residual polygenic effect.
Liu, Z; Goddard, M E; Hayes, B J; Reinhardt, F; Reents, R
2016-03-01
Routine genomic evaluations in animal breeding are usually based on either a BLUP with genomic relationship matrix (GBLUP) or single nucleotide polymorphism (SNP) BLUP model. For a multi-step genomic evaluation, these 2 alternative genomic models were proven to give equivalent predictions for genomic reference animals. The model equivalence was verified also for young genotyped animals without phenotypes. Due to incomplete linkage disequilibrium of SNP markers to genes or causal mutations responsible for genetic inheritance of quantitative traits, SNP markers cannot explain all the genetic variance. A residual polygenic effect is normally fitted in the genomic model to account for the incomplete linkage disequilibrium. In this study, we start by showing the proof that the multi-step GBLUP and SNP BLUP models are equivalent for the reference animals, when they have a residual polygenic effect included. Second, the equivalence of both multi-step genomic models with a residual polygenic effect was also verified for young genotyped animals without phenotypes. Additionally, we derived formulas to convert genomic estimated breeding values of the GBLUP model to its components, direct genomic values and residual polygenic effect. Third, we made a proof that the equivalence of these 2 genomic models with a residual polygenic effect holds also for single-step genomic evaluation. Both the single-step GBLUP and SNP BLUP models lead to equal prediction for genotyped animals with phenotypes (e.g., reference animals), as well as for (young) genotyped animals without phenotypes. Finally, these 2 single-step genomic models with a residual polygenic effect were proven to be equivalent for estimation of SNP effects, too. PMID:26723117
Technical note: Equivalent genomic models with a residual polygenic effect.
Liu, Z; Goddard, M E; Hayes, B J; Reinhardt, F; Reents, R
2016-03-01
Routine genomic evaluations in animal breeding are usually based on either a BLUP with genomic relationship matrix (GBLUP) or single nucleotide polymorphism (SNP) BLUP model. For a multi-step genomic evaluation, these 2 alternative genomic models were proven to give equivalent predictions for genomic reference animals. The model equivalence was verified also for young genotyped animals without phenotypes. Due to incomplete linkage disequilibrium of SNP markers to genes or causal mutations responsible for genetic inheritance of quantitative traits, SNP markers cannot explain all the genetic variance. A residual polygenic effect is normally fitted in the genomic model to account for the incomplete linkage disequilibrium. In this study, we start by showing the proof that the multi-step GBLUP and SNP BLUP models are equivalent for the reference animals, when they have a residual polygenic effect included. Second, the equivalence of both multi-step genomic models with a residual polygenic effect was also verified for young genotyped animals without phenotypes. Additionally, we derived formulas to convert genomic estimated breeding values of the GBLUP model to its components, direct genomic values and residual polygenic effect. Third, we made a proof that the equivalence of these 2 genomic models with a residual polygenic effect holds also for single-step genomic evaluation. Both the single-step GBLUP and SNP BLUP models lead to equal prediction for genotyped animals with phenotypes (e.g., reference animals), as well as for (young) genotyped animals without phenotypes. Finally, these 2 single-step genomic models with a residual polygenic effect were proven to be equivalent for estimation of SNP effects, too.
Updating nuclear effects in theater models. Final report
Youngreen, M.A.
1988-11-01
Large-scale, low-resolution simulation models frequently group nuclear weapons effects against area targets into a few aggregated state vectors. This can create serious inaccuracies in the treatment of multiple-burst and other time-dependent effects. This paper presents improved techniques for updating nuclear weapon effects against area targets, allowing the analyst to model the processes of delay injury (damage), recovery (repair) over time, and the effects of subsequent nuclear bursts. The approach here is to store the effects in a state vector of coefficients for a piecewise Pareto distribution. Examples illustrating the benefits of this approach are provided. This procedure will be implemented in the US Army Concepts Analysis Agency IWFORCEM theater model, but is applicable to any low-resolution simulation that includes nuclear effects representation.
A multiscale gradient-dependent plasticity model for size effects
NASA Astrophysics Data System (ADS)
Lyu, Hao; Taheri-Nassaj, Nasrin; Zbib, Hussein M.
2016-06-01
The mechanical behaviour of polycrystalline material is closely correlated to grain size. In this study, we investigate the size-dependent phenomenon in multi-phase steels using a continuum dislocation dynamic model coupled with viscoplastic self-consistent model. We developed a dislocation-based strain gradient plasticity model and a stress gradient plasticity model, as well as a combined model, resulting in a theory that can predict size effect over a wide range of length scales. Results show that strain gradient plasticity and stress gradient plasticity are complementary rather than competing theories. The stress gradient model is dominant at the initial strain stage, and is much more effective for predicting yield strength than the strain gradient model. For larger deformations, the strain gradient model is dominant and more effective for predicting size-dependent hardening. The numerical results are compared with experimental data and it is found that they have the same trend for the yield stress. Furthermore, the effect of dislocation density at different strain stages is investigated, and the findings show that the Hall-Petch relation holds for the initial strain stage and breaks down for higher strain levels. Finally, a power law to describe the size effect and the transition zone between the strain gradient and stress gradient dominated regions is developed.
Modeling the effects of annual influenza vaccination
Smith, D.J.; Ackley, D.H.; Forrest, S.; Perelson, A.S.
1998-12-31
Although influenza vaccine efficacy is 70--90% in young healthy first-time vaccinees, the efficacy in repeat vaccinees has varied considerably. In some studies, vaccine efficacy in repeat vaccinees was higher than in first-time vaccinees, whereas in other studies vaccine efficacy in repeat vaccinees was significantly lower than in first-time vaccinees and sometimes no higher than in unvaccinated controls. It is known that the closeness of the antigenic match between the vaccine strain and the epidemic virus is important for vaccine effectiveness. In this study the authors show that the antigenic differences between a first vaccine strain and a second vaccine strain, and between the first vaccine strain and the epidemic strain, might account for the observed variation in attack rate among two-time vaccinees.
Modeling individual effects in the Cormack-Jolly-Seber Model: A state-space formulation
Royle, J. Andrew
2008-01-01
In population and evolutionary biology, there exists considerable interest in individual heterogeneity in parameters of demographic models for open populations. However, flexible and practical solutions to the development of such models have proven to be elusive. In this article, I provide a state-space formulation of open population capture-recapture models with individual effects. The state-space formulation provides a generic and flexible framework for modeling and inference in models with individual effects, and it yields a practical means of estimation in these complex problems via contemporary methods of Markov chain Monte Carlo. A straightforward implementation can be achieved in the software package WinBUGS. I provide an analysis of a simple model with constant parameter detection and survival probability parameters. A second example is based on data from a 7-year study of European dippers, in which a model with year and individual effects is fitted.
Gompertzian stochastic model with delay effect to cervical cancer growth
Mazlan, Mazma Syahidatul Ayuni binti; Rosli, Norhayati binti; Bahar, Arifah
2015-02-03
In this paper, a Gompertzian stochastic model with time delay is introduced to describe the cervical cancer growth. The parameters values of the mathematical model are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic model numerically. The efficiency of mathematical model is measured by comparing the simulated result and the clinical data of cervical cancer growth. Low values of Mean-Square Error (MSE) of Gompertzian stochastic model with delay effect indicate good fits.
Gompertzian stochastic model with delay effect to cervical cancer growth
NASA Astrophysics Data System (ADS)
Mazlan, Mazma Syahidatul Ayuni binti; Rosli, Norhayati binti; Bahar, Arifah
2015-02-01
In this paper, a Gompertzian stochastic model with time delay is introduced to describe the cervical cancer growth. The parameters values of the mathematical model are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic model numerically. The efficiency of mathematical model is measured by comparing the simulated result and the clinical data of cervical cancer growth. Low values of Mean-Square Error (MSE) of Gompertzian stochastic model with delay effect indicate good fits.
Pharmacodynamic effects in the cardiovascular system: the modeller's view.
Fink, Martin; Noble, Denis
2010-03-01
Cardiovascular disease, and the cardiovascular side effects of drugs, are essentially multifactorial problems involving interactions between many proteins, dependent on highly organized cell, tissue and organ structures. This is one reason why the side effects of drugs are often unanticipated. It is impossible to unravel such problems without using a systems approach, i.e. focussing on processes, not just molecular components. This inevitably involves modelling as the interactions require quantitative analysis. Modelling is a tool of analysis aimed at understanding, first, and predicting, eventually. We illustrate these principles using modelling of the heart. Models of the cardiac myocyte have benefited from several decades of interaction between experimentation and simulation. They are now sufficiently detailed to have been of use in the development of new drug compounds like ranolazine and ivabradine. With the help of cardiac modelling, we have also been able to unravel the mechanisms underlying the beneficial effect of sodium calcium exchange block for long QT syndrome (LQTS) 2 and LQTS3 patients. Detailed models of the interaction between ion channels and blocking agents provide the basis for modelling drug action from basic principles and predict changes in the inhomogeneous tissue of the heart. We demonstrate that mathematical models are beneficial for unravelling the complex interactions of pharmacodynamics in the heart. Embedding these detailed biophysical cellular scale models into anatomically correct models of the ventricle geometry will enable reconstructions of Torsades de Pointes arrhythmias and of fibrillation, providing a mechanism for linking detailed cellular scale experimental data to clinical applications.
Modelling the effect of conjugate vaccines in pneumococcal disease: cohort or population models?
Standaert, Baudouin; Demarteau, Nadia; Talbird, Sandra; Mauskopf, Josephine
2010-11-19
Cohort and population models estimate vaccine impact on disease events, and yield different estimates in countries with different demographic compositions. We compared administration of the new 10-valent pneumococcal Haemophilus influenzae-protein D conjugate vaccine (PHiD-CV) with no vaccination in two countries, the United Kingdom (UK) and Mexico, using two modelling strategies: a cohort model and a population model. The cohort model followed a birth cohort over a lifetime, beginning 10 years after initiation of the vaccine program, when vaccine efficacy steady state had been reached. The population model examined the country-specific population over 1 year, also beginning 10 years after initiation of the vaccine program. Both models included the same age-specific disease rates of meningitis, bacteraemia, pneumonia, and otitis media. The output variables were the numbers of specific events, with and without indirect vaccine effects. Without indirect effects, the cohort and population models produced similar results for both countries (deviation of <20% difference per output measure for most outcomes). The difference between the model types was much greater when indirect vaccine effects were included, especially in Mexico (up to 120% difference). Cohort and population modelling methods produce different results depending on the disease, the intervention, the demographic composition, and the time horizon evaluated. Results from the two model types provide different information about the impact of interventions on events: accumulated vaccine benefit for an individual in a cohort model; vaccine benefit for a whole population at a specific time point in a population model.
Effective stress model for partially and fully saturated rocks
Dey, T.N.
1989-01-01
An effective stress model which calculates the pressure-volume (P-V) and deviatoric stress response of partially and fully saturated rocks is described here. The model includes pore pressure effects on pore crushing and shear strength as well as effects of shear enhanced void collapse and shear caused dilatancy. The model can directly use tabular data for the P-V behavior of the rock solids and the water, and for the drained pore crushing behavior and shear strength, which simplifies model fitting. Phase transitions in the solids and vaporization of the water are also allowed. Use of the model is illustrated by an example of wave propagation in limestone. 6 refs., 4 figs.
Water's hydrogen bonds in the hydrophobic effect: a simple model.
Xu, Huafeng; Dill, Ken A
2005-12-15
We propose a simple analytical model to account for water's hydrogen bonds in the hydrophobic effect. It is based on computing a mean-field partition function for a water molecule in the first solvation shell around a solute molecule. The model treats the orientational restrictions from hydrogen bonding, and utilizes quantities that can be obtained from bulk water simulations. We illustrate the principles in a 2-dimensional Mercedes-Benz-like model. Our model gives good predictions for the heat capacity of hydrophobic solvation, reproduces the solvation energies and entropies at different temperatures with only one fitting parameter, and accounts for the solute size dependence of the hydrophobic effect. Our model supports the view that water's hydrogen bonding propensity determines the temperature dependence of the hydrophobic effect. It explains the puzzling experimental observation that dissolving a nonpolar solute in hot water has positive entropy.
Homogenization limit for a multiband effective mass model in heterostructures
Morandi, O.
2014-06-15
We study the homogenization limit of a multiband model that describes the quantum mechanical motion of an electron in a quasi-periodic crystal. In this approach, the distance among the atoms that constitute the material (lattice parameter) is considered a small quantity. Our model include the description of materials with variable chemical composition, intergrowth compounds, and heterostructures. We derive the effective multiband evolution system in the framework of the kp approach. We study the well posedness of the mathematical problem. We compare the effective mass model with the standard kp models for uniform and non-uniforms crystals. We show that in the limit of vanishing lattice parameter, the particle density obtained by the effective mass model, converges to the exact probability density of the particle.
Water's hydrogen bonds in the hydrophobic effect: a simple model.
Xu, Huafeng; Dill, Ken A
2005-12-15
We propose a simple analytical model to account for water's hydrogen bonds in the hydrophobic effect. It is based on computing a mean-field partition function for a water molecule in the first solvation shell around a solute molecule. The model treats the orientational restrictions from hydrogen bonding, and utilizes quantities that can be obtained from bulk water simulations. We illustrate the principles in a 2-dimensional Mercedes-Benz-like model. Our model gives good predictions for the heat capacity of hydrophobic solvation, reproduces the solvation energies and entropies at different temperatures with only one fitting parameter, and accounts for the solute size dependence of the hydrophobic effect. Our model supports the view that water's hydrogen bonding propensity determines the temperature dependence of the hydrophobic effect. It explains the puzzling experimental observation that dissolving a nonpolar solute in hot water has positive entropy. PMID:16375338
Organizational effectiveness: toward an integrated model for schools of nursing.
Baker, C M; Reising, D L; Johnson, D R; Stewart, R L; Baker, S D
1997-01-01
Assessing the quality of academic institutions involves much more than the opinions of peers or experts. Examination of the organizational effectiveness of schools of nursing has been neglected. Current emphasis on assessing educational outcomes has diverted attention from the construct, organizational effectiveness, and more comprehensive theory-driven approaches to evaluation. This review of the organizational effectiveness literature focuses on the major assessment models: goal attainment, human relations, open systems, internal processes, culture, and life cycle. Attention is given to the influence of organizational maturation on an integrated model of organizational effectiveness. Selected macrolevel studies of schools of nursing are examined, and an agenda for nursing research is proposed.
Mechanisms and models of effective thermal conductivities of nanofluids.
Yu, W.; France, D. M.; Singh, D.; Timofeeva, E. V.; Smith, D. S.; Routbort, J. L.; Univ. of Illinois
2010-08-01
The physical mechanisms and mathematical models of the effective thermal conductivities of nanofluids have long been of interest to the nanofluid research community because the effective thermal conductivities of nanofluids cannot generally be fully explained and predicted by classical effective medium theories. This review article summarizes considerable progress made on this topic. Specifically, the physical mechanisms and mathematical models of the effective thermal conductivities of nanofluids are reviewed, the potential contributions of those physical mechanisms are evaluated, and the comparisons of the theoretical predictions and experimental data are presented along with opportunities for future research.
Seismic model of Mars: Effects of hydration
NASA Astrophysics Data System (ADS)
Zharkov, V. N.; Gudkova, T. V.
2014-12-01
The arguments according to which the Martian minerals are assumed to contain large amount of water in the mantle minerals are given. As for the Earth, these minerals may constitute about 60 wt% of the Martian mantle, and can be considered as main components in their zones. In the mantle of the Earth the molecular concentration of Fe is about 10%, and for the mantle of Mars - about 20%. Taking into account twofold increase of Fe in Martian silicates in comparison with the terrestrial minerals, we have extrapolated the available partial experimental data of the hydration effect on the compressional and shear velocities of seismic waves in forsterite (olivine) and its high pressure phases - wadsleyite and ringwoodite for Martian conditions. The presence of water in the mantle of Mars may lead to the noticeable widening of the olivine-wadsleite phase transition zone, thus the determination of the olivine-wadsleite phase transition width by seismological methods could get a direct indication on the presence of water in the mantle of Mars. To find out real estimates of water content in the mantle of Mars is a task for the future seismic missions. The results of this article are important for InSight mission that will land a geophysical station on Mars in 2016.
Evaluating differential effects using regression interactions and regression mixture models
Van Horn, M. Lee; Jaki, Thomas; Masyn, Katherine; Howe, George; Feaster, Daniel J.; Lamont, Andrea E.; George, Melissa R. W.; Kim, Minjung
2015-01-01
Research increasingly emphasizes understanding differential effects. This paper focuses on understanding regression mixture models, a relatively new statistical methods for assessing differential effects by comparing results to using an interactive term in linear regression. The research questions which each model answers, their formulation, and their assumptions are compared using Monte Carlo simulations and real data analysis. The capabilities of regression mixture models are described and specific issues to be addressed when conducting regression mixtures are proposed. The paper aims to clarify the role that regression mixtures can take in the estimation of differential effects and increase awareness of the benefits and potential pitfalls of this approach. Regression mixture models are shown to be a potentially effective exploratory method for finding differential effects when these effects can be defined by a small number of classes of respondents who share a typical relationship between a predictor and an outcome. It is also shown that the comparison between regression mixture models and interactions becomes substantially more complex as the number of classes increases. It is argued that regression interactions are well suited for direct tests of specific hypotheses about differential effects and regression mixtures provide a useful approach for exploring effect heterogeneity given adequate samples and study design. PMID:26556903
Micromagnetic model for biaxial stress effects on magnetic properties
NASA Astrophysics Data System (ADS)
Sablik, M. J.; Riley, L. A.; Burkhardt, G. L.; Kwun, H.; Cannell, P. Y.; Watts, K. T.; Langman, R. A.
1994-04-01
A micromagnetic formulation has been developed for modeling the effect of biaxial stress on magnetoelastic processes in polycrystalline steels. The formulation uses a modified version of the Kashiwaya model for the effect of biaxial stress on magnetic properties and combines it with the Schneider-Cannell-Watts model for magnetoelastic processes in steels. In particular, the model involves use of an effective stress equal to one of the deviatoric (i.e. distortional) normal stress components, depending on whether the field is parallel to a tensile or compressive axis or to the third axis perpendicular to the plane of biaxial stress. Computer results are compared to experimental results on the effects of biaxial stress on magnetic properties in mild steel and in SAE-4130 steel. Good qualitative agreement is found in almost all cases, in that in going from one biaxial stress case to the next, the same kinds of changes are seen magnetically.
Effective field model of roughness in magnetic nano-structures
Lepadatu, Serban
2015-12-28
An effective field model is introduced here within the micromagnetics formulation, to study roughness in magnetic structures, by considering sub-exchange length roughness levels as a perturbation on a smooth structure. This allows the roughness contribution to be separated, which is found to give rise to an effective configurational anisotropy for both edge and surface roughness, and accurately model its effects with fine control over the roughness depth without the explicit need to refine the computational cell size to accommodate the roughness profile. The model is validated by comparisons with directly roughened structures for a series of magnetization switching and domain wall velocity simulations and found to be in excellent agreement for roughness levels up to the exchange length. The model is further applied to vortex domain wall velocity simulations with surface roughness, which is shown to significantly modify domain wall movement and result in dynamic pinning and stochastic creep effects.
Cranking the Chiral Soliton Bag Model:. Gluonic Effects
NASA Astrophysics Data System (ADS)
Stern, Jacqueline; Bourenane, Mohamed; Clément, Gérard
The nucleon-delta mass difference is computed in the chiral soliton bag model with soft confinement of gluons by the cranking method. The resulting value of the effective strong fine structure constant is αs≃0.7.
Fluid-Gravity Model for the Chiral Magnetic Effect
Kalaydzhyan, Tigran; Kirsch, Ingo
2011-05-27
We consider the STU model as a gravity dual of a strongly coupled plasma with multiple anomalous U(1) currents. In the bulk we add additional background gauge fields to include the effects of external electric and magnetic fields on the plasma. Reducing the number of chemical potentials in the STU model to two and interpreting them as quark and chiral chemical potential, we obtain a holographic description of the chiral magnetic and chiral vortical effects (CME and CVE) in relativistic heavy-ion collisions. These effects formally appear as first-order transport coefficients in the electromagnetic current. We compute these coefficients from our model using fluid-gravity duality. We also find analogous effects in the axial-vector current. Finally, we briefly discuss a variant of our model, in which the CME/CVE is realized in the late-time dynamics of an expanding plasma.
Fluid-gravity model for the chiral magnetic effect.
Kalaydzhyan, Tigran; Kirsch, Ingo
2011-05-27
We consider the STU model as a gravity dual of a strongly coupled plasma with multiple anomalous U(1) currents. In the bulk we add additional background gauge fields to include the effects of external electric and magnetic fields on the plasma. Reducing the number of chemical potentials in the STU model to two and interpreting them as quark and chiral chemical potential, we obtain a holographic description of the chiral magnetic and chiral vortical effects (CME and CVE) in relativistic heavy-ion collisions. These effects formally appear as first-order transport coefficients in the electromagnetic current. We compute these coefficients from our model using fluid-gravity duality. We also find analogous effects in the axial-vector current. Finally, we briefly discuss a variant of our model, in which the CME/CVE is realized in the late-time dynamics of an expanding plasma. PMID:21699286
Effects of distributed database modeling on evaluation of transaction rollbacks
NASA Technical Reports Server (NTRS)
Mukkamala, Ravi
1991-01-01
Data distribution, degree of data replication, and transaction access patterns are key factors in determining the performance of distributed database systems. In order to simplify the evaluation of performance measures, database designers and researchers tend to make simplistic assumptions about the system. The effect is studied of modeling assumptions on the evaluation of one such measure, the number of transaction rollbacks, in a partitioned distributed database system. Six probabilistic models and expressions are developed for the numbers of rollbacks under each of these models. Essentially, the models differ in terms of the available system information. The analytical results so obtained are compared to results from simulation. From here, it is concluded that most of the probabilistic models yield overly conservative estimates of the number of rollbacks. The effect of transaction commutativity on system throughout is also grossly undermined when such models are employed.
Effects of yaw and pitch motion on model attitude measurements
NASA Technical Reports Server (NTRS)
Tcheng, Ping; Tripp, John S.; Finley, Tom D.
1995-01-01
This report presents a theoretical analysis of the dynamic effects of angular motion in yaw and pitch on model attitude measurements in which inertial sensors were used during wind tunnel tests. A technique is developed to reduce the error caused by these effects. The analysis shows that a 20-to-1 reduction in model attitude measurement error caused by angular motion is possible with this technique.
EFFECTS OF VIDEO MODELING ON TREATMENT INTEGRITY OF BEHAVIORAL INTERVENTIONS
DiGennaro-Reed, Florence D; Codding, Robin; Catania, Cynthia N; Maguire, Helena
2010-01-01
We examined the effects of individualized video modeling on the accurate implementation of behavioral interventions using a multiple baseline design across 3 teachers. During video modeling, treatment integrity improved above baseline levels; however, teacher performance remained variable. The addition of verbal performance feedback increased treatment integrity to 100% for all participants, and performance was maintained 1 week later. Teachers found video modeling to be more socially acceptable with performance feedback than alone, but rated both positively. PMID:21119903
Effects of Scenario Planning on Participant Mental Models
ERIC Educational Resources Information Center
Glick, Margaret B.; Chermack, Thomas J.; Luckel, Henry; Gauck, Brian Q.
2012-01-01
Purpose: The purpose of this paper is to assess the effects of scenario planning on participant mental model styles. Design/methodology/approach: The scenario planning literature is consistent with claims that scenario planning can change individual mental models. These claims are supported by anecdotal evidence and stories from the practical…
Consequences of Unmodeled Nonlinear Effects in Multilevel Models
ERIC Educational Resources Information Center
Bauer, Daniel J.; Cai, Li
2009-01-01
Applications of multilevel models have increased markedly during the past decade. In incorporating lower-level predictors into multilevel models, a key interest is often whether or not a given predictor requires a random slope, that is, whether the effect of the predictor varies over upper-level units. If the variance of a random slope…
Estimation of Spatial Dynamic Nonparametric Durbin Models with Fixed Effects
ERIC Educational Resources Information Center
Qian, Minghui; Hu, Ridong; Chen, Jianwei
2016-01-01
Spatial panel data models have been widely studied and applied in both scientific and social science disciplines, especially in the analysis of spatial influence. In this paper, we consider the spatial dynamic nonparametric Durbin model (SDNDM) with fixed effects, which takes the nonlinear factors into account base on the spatial dynamic panel…
Making Assessment Easier with the Organizational Effectiveness Model
ERIC Educational Resources Information Center
Heilman, Savannah C.; Kennedy-Phillips, Lance
2011-01-01
The Organizational Effectiveness Model was originally developed by Lance Kennedy-Phillips and Ellen Meents-DeCaigny at DePaul University and has been adapted to address the needs of The Ohio State University. The model's purpose is to help organizations measure progress toward mission fulfillment and goal achievement. It cascades, with each step…
Personal Coaching: Reflection on a Model for Effective Learning
ERIC Educational Resources Information Center
Griffiths, Kerryn
2015-01-01
The article "Personal Coaching: A Model for Effective Learning" (Griffiths, 2006) appeared in the "Journal of Learning Design" Volume 1, Issue 2 in 2006. Almost ten years on, Kerryn Griffiths reflects upon her original article. Specifically, Griffiths looks back at the combined coaching-learning model she suggested in her…
The Effect of Math Modeling on Student's Emerging Understanding
ERIC Educational Resources Information Center
Sokolowski, Andrzej
2015-01-01
This study investigated the effects of applying mathematical modeling on revising students' preconception of the process of optimizing area enclosed by a string of a fixed length. A group of 28 high school pre-calculus students were immersed in modeling activity that included direct measurements, data collecting, and formulating algebraic…
Effects of Video Modeling on Treatment Integrity of Behavioral Interventions
ERIC Educational Resources Information Center
DiGennaro-Reed, Florence D.; Codding, Robin; Catania, Cynthia N.; Maguire, Helena
2010-01-01
We examined the effects of individualized video modeling on the accurate implementation of behavioral interventions using a multiple baseline design across 3 teachers. During video modeling, treatment integrity improved above baseline levels; however, teacher performance remained variable. The addition of verbal performance feedback increased…
NASA Astrophysics Data System (ADS)
Elshall, A. S.; Ye, M.; Niu, G. Y.; Barron-Gafford, G.
2014-12-01
A Bayesian framework is developed to quantify predictive uncertainty in environmental modeling caused by uncertainty in modeling scenarios, model structures, model parameters, and data. An example of using the framework to quantify model uncertainty is presented to simulate soil microbial respiration pulses in response to episodic rainfall pulses (the "Birch effect"). A total of five models are developed; they evolve from an existing four-carbon (C) pool model to models with additional C pools and recently developed models with explicit representations of soil moisture controls on C degradation and microbial uptake rates. Markov chain Monte Carlo (MCMC) methods with generalized likelihood function (not Gaussian) are used to estimate posterior parameter distributions of the models, and the posterior parameter samples are used to evaluate probabilities of the models. The models with explicit representations of soil moisture controls outperform the other models. The models with additional C pools for accumulation of degraded C in the dry zone of the soil pore space result in a higher probability of reproducing the observed Birch pulses. A cross-validation is conducted to explore predictive performance of model averaging and of individual models. The Bayesian framework is mathematically general and can be applied to a wide range of environmental problems.
The effect of model structure and data in modeling land conditions in disturbed complex ecosystems.
Fang, Shoufan; Gertner, George Z; Anderson, Alan B
2007-10-01
Off-road vehicles increase soil erosion by reducing vegetation cover and other types of ground cover, and by changing the structure of soil. The investigation of the relationship between disturbance from off-road vehicles and the intensity of the activities that involve use of vehicles is essential for water and soil conservation and facility management. Models have been developed in a previous study to predict disturbance caused by off-road vehicles. However, the effect of data on model quality and model performance, and the appropriate structure of models have not been previously investigated. In order to improve the quality and performance of disturbance models, this study was designed to investigate the effects of model structure and data. The experiment considered and tested: (1) two measures of disturbance based on the Vegetation Cover Factor (C Factor) of the Revised Universal Soil Loss Equation (RUSLE) and Disturbance Intensity; (2) model structure using two modeling approaches; and (3) three subsets of data. The adjusted R-square and residuals from validation data are used to represent model quality and performance, respectively. Analysis of variance (ANOVA) is used to identify factors which have significant effects on model quality and performance. The results of the ANOVA show that subsets of data have significant effects on both model quality and performance for both measures of disturbance. The ANOVA also detected that the C Factor models have higher quality and performance than the Disturbance models. Although modeling approaches are not a significant factor based on the ANOVA tests, models containing interaction terms can increase the adjusted R-squares for nearly all tested conditions and the maximum improvement can reach 31%.
Predictive modeling of nanomaterial exposure effects in biological systems
Liu, Xiong; Tang, Kaizhi; Harper, Stacey; Harper, Bryan; Steevens, Jeffery A; Xu, Roger
2013-01-01
Background Predictive modeling of the biological effects of nanomaterials is critical for industry and policymakers to assess the potential hazards resulting from the application of engineered nanomaterials. Methods We generated an experimental dataset on the toxic effects experienced by embryonic zebrafish due to exposure to nanomaterials. Several nanomaterials were studied, such as metal nanoparticles, dendrimer, metal oxide, and polymeric materials. The embryonic zebrafish metric (EZ Metric) was used as a screening-level measurement representative of adverse effects. Using the dataset, we developed a data mining approach to model the toxic endpoints and the overall biological impact of nanomaterials. Data mining techniques, such as numerical prediction, can assist analysts in developing risk assessment models for nanomaterials. Results We found several important attributes that contribute to the 24 hours post-fertilization (hpf) mortality, such as dosage concentration, shell composition, and surface charge. These findings concur with previous studies on nanomaterial toxicity using embryonic zebrafish. We conducted case studies on modeling the overall effect/impact of nanomaterials and the specific toxic endpoints such as mortality, delayed development, and morphological malformations. The results show that we can achieve high prediction accuracy for certain biological effects, such as 24 hpf mortality, 120 hpf mortality, and 120 hpf heart malformation. The results also show that the weighting scheme for individual biological effects has a significant influence on modeling the overall impact of nanomaterials. Sample prediction models can be found at http://neiminer.i-a-i.com/nei_models. Conclusion The EZ Metric-based data mining approach has been shown to have predictive power. The results provide valuable insights into the modeling and understanding of nanomaterial exposure effects. PMID:24098077
Modeling of dynamic effects of a low power laser beam
NASA Technical Reports Server (NTRS)
Lawrence, George N.; Scholl, Marija S.; Khatib, AL
1988-01-01
Methods of modeling some of the dynamic effects involved in laser beam propagation through the atmosphere are addressed with emphasis on the development of simple but accurate models which are readily implemented in a physical optics code. A space relay system with a ground based laser facility is considered as an example. The modeling of such characteristic phenomena as laser output distribution, flat and curved mirrors, diffraction propagation, atmospheric effects (aberration and wind shear), adaptive mirrors, jitter, and time integration of power on target, is discussed.
Modeling the Effect of Temperature on Ozone-Related Mortality.
Modeling the Effect of Temperature on Ozone-Related Mortality. Wilson, Ander, Reich, Brian J, Neas, Lucas M., Rappold, Ana G. Background: Previous studies show ozone and temperature are associated with increased mortality; however, the joint effect is not well explored. Underst...
Understanding the Effectiveness of Online Peer Assessment: A Path Model
ERIC Educational Resources Information Center
Lu, Jingyan; Zhang, Zhidong
2012-01-01
Peer assessment has been implemented in schools as both a learning tool and an assessment tool. Earlier studies have explored the effectiveness of peer assessment from different perspectives, such as domain knowledge and skills, peer assessment skills, and attitude changes. However, there is no holistic model describing the effects of cognitive…
School Processes Mediate School Compositional Effects: Model Specification and Estimation
ERIC Educational Resources Information Center
Liu, Hongqiang; Van Damme, Jan; Gielen, Sarah; Van Den Noortgate, Wim
2015-01-01
School composition effects have been consistently verified, but few studies ever attempted to study how school composition affects school achievement. Based on prior research findings, we employed multilevel mediation modeling to examine whether school processes mediate the effect of school composition upon school outcomes based on the data of 28…
Assessing Mediational Models: Testing and Interval Estimation for Indirect Effects
ERIC Educational Resources Information Center
Biesanz, Jeremy C.; Falk, Carl F.; Savalei, Victoria
2010-01-01
Theoretical models specifying indirect or mediated effects are common in the social sciences. An indirect effect exists when an independent variable's influence on the dependent variable is mediated through an intervening variable. Classic approaches to assessing such mediational hypotheses (Baron & Kenny, 1986; Sobel, 1982) have in recent years…
Electronic Model of a Ferroelectric Field Effect Transistor
NASA Technical Reports Server (NTRS)
MacLeod, Todd C.; Ho, Fat Duen; Russell, Larry (Technical Monitor)
2001-01-01
A pair of electronic models has been developed of a Ferroelectric Field Effect transistor. These models can be used in standard electrical circuit simulation programs to simulate the main characteristics of the FFET. The models use the Schmitt trigger circuit as a basis for their design. One model uses bipolar junction transistors and one uses MOSFET's. Each model has the main characteristics of the FFET, which are the current hysterisis with different gate voltages and decay of the drain current when the gate voltage is off. The drain current from each model has similar values to an actual FFET that was measured experimentally. T'he input and o Output resistance in the models are also similar to that of the FFET. The models are valid for all frequencies below RF levels. No attempt was made to model the high frequency characteristics of the FFET. Each model can be used to design circuits using FFET's with standard electrical simulation packages. These circuits can be used in designing non-volatile memory circuits and logic circuits and is compatible with all SPICE based circuit analysis programs. The models consist of only standard electrical components, such as BJT's, MOSFET's, diodes, resistors, and capacitors. Each model is compared to the experimental data measured from an actual FFET.
Modeling of Turbulence Effects on Liquid Jet Atomization and Breakup
NASA Technical Reports Server (NTRS)
Trinh, Huu P.; Chen, C. P.
2005-01-01
Recent experimental investigations and physical modeling studies have indicated that turbulence behaviors within a liquid jet have considerable effects on the atomization process. This study aims to model the turbulence effect in the atomization process of a cylindrical liquid jet. Two widely used models, the Kelvin-Helmholtz (KH) instability of Reitz (blob model) and the Taylor-Analogy-Breakup (TAB) secondary droplet breakup by O Rourke et al, are further extended to include turbulence effects. In the primary breakup model, the level of the turbulence effect on the liquid breakup depends on the characteristic scales and the initial flow conditions. For the secondary breakup, an additional turbulence force acted on parent drops is modeled and integrated into the TAB governing equation. The drop size formed from this breakup regime is estimated based on the energy balance before and after the breakup occurrence. This paper describes theoretical development of the current models, called "T-blob" and "T-TAB", for primary and secondary breakup respectivety. Several assessment studies are also presented in this paper.
Modelling the effect of fluctuating herbicide concentrations on algae growth.
Copin, Pierre-Jean; Coutu, Sylvain; Chèvre, Nathalie
2015-03-01
Herbicide concentrations fluctuate widely in watercourses after crop applications and rain events. The level of concentrations in pulses can exceed the water chronic quality criteria. In the present study, we proposed modelling the effects of successive pulse exposure on algae. The deterministic model proposed is based on two parameters: (i) the typical growth rate of the algae, obtained by monitoring growth rates of several successive batch cultures in growth media, characterizing both the growth of the control and during the recovery periods; (ii) the growth rate of the algae exposed to pulses, determined from a dose-response curve obtained with a standard toxicity test. We focused on the herbicide isoproturon and on the freshwater alga Scenedesmus vacuolatus, and we validated the model prediction based on effect measured during five sequential pulse exposures in laboratory. The comparison between the laboratory and the modelled effects illustrated that the results yielded were consistent, making the model suitable for effect prediction of the herbicide photosystem II inhibitor isoproturon on the alga S. vacuolatus. More generally, modelling showed that both pulse duration and level of concentration play a crucial role. The application of the model to a real case demonstrated that both the highest peaks and the low peaks with a long duration affect principally the cell density inhibition of the alga S. vacuolatus. It is therefore essential to detect these characteristic pulses when monitoring of herbicide concentrations are conducted in rivers. PMID:25499055
Inclusion of Dominance Effects in the Multivariate GBLUP Model.
dos Santos, Jhonathan Pedroso Rigal; Vasconcellos, Renato Coelho de Castro; Pires, Luiz Paulo Miranda; Balestre, Marcio; Von Pinho, Renzo Garcia
2016-01-01
New proposals for models and applications of prediction processes with data on molecular markers may help reduce the financial costs of and identify superior genotypes in maize breeding programs. Studies evaluating Genomic Best Linear Unbiased Prediction (GBLUP) models including dominance effects have not been performed in the univariate and multivariate context in the data analysis of this crop. A single cross hybrid construction procedure was performed in this study using phenotypic data and actual molecular markers of 4,091 maize lines from the public database Panzea. A total of 400 simple hybrids resulting from this process were analyzed using the univariate and multivariate GBLUP model considering only additive effects additive plus dominance effects. Historic heritability scenarios of five traits and other genetic architecture settings were used to compare models, evaluating the predictive ability and estimation of variance components. Marginal differences were detected between the multivariate and univariate models. The main explanation for the small discrepancy between models is the low- to moderate-magnitude correlations between the traits studied and moderate heritabilities. These conditions do not favor the advantages of multivariate analysis. The inclusion of dominance effects in the models was an efficient strategy to improve the predictive ability and estimation quality of variance components. PMID:27074056
A Layered Decision Model for Cost-Effective System Security
Wei, Huaqiang; Alves-Foss, James; Soule, Terry; Pforsich, Hugh; Zhang, Du; Frincke, Deborah A.
2008-10-01
System security involves decisions in at least three areas: identification of well-defined security policies, selection of cost-effective defence strategies, and implementation of real-time defence tactics. Although choices made in each of these areas affect the others, existing decision models typically handle these three decision areas in isolation. There is no comprehensive tool that can integrate them to provide a single efficient model for safeguarding a network. In addition, there is no clear way to determine which particular combinations of defence decisions result in cost-effective solutions. To address these problems, this paper introduces a Layered Decision Model (LDM) for use in deciding how to address defence decisions based on their cost-effectiveness. To validate the LDM and illustrate how it is used, we used simulation to test model rationality and applied the LDM to the design of system security for an e-commercial business case.
Probability-summation model of multiple laser-exposure effects.
Menendez, A R; Cheney, F E; Zuclich, J A; Crump, P
1993-11-01
A probability-summation model is introduced to provide quantitative criteria for discriminating independent from interactive effects of multiple laser exposures on biological tissue. Data that differ statistically from predictions of the probability-summation model indicate the action of sensitizing (synergistic/positive) or desensitizing (hardening/negative) biophysical interactions. Interactions are indicated when response probabilities vary with changes in the spatial or temporal separation of exposures. In the absence of interactions, probability-summation parsimoniously accounts for "cumulative" effects. Data analyzed using the probability-summation model show instances of both sensitization and desensitization of retinal tissue by laser exposures. Other results are shown to be consistent with probability-summation. The relevance of the probability-summation model to previous laser-bioeffects studies, models, and safety standards is discussed and an appeal is made for improved empirical estimates of response probabilities for single exposures.
Systematic effects in CALOR simulation code to model experimental configurations
Job, P.K.; Proudfoot, J. ); Handler, T. . Dept. of Physics and Astronomy); Gabriel, T.A. )
1991-03-27
CALOR89 code system is being used to simulate test beam results and the design parameters of several calorimeter configurations. It has been bench-marked against the ZEUS, D{theta} and HELIOS data. This study identifies the systematic effects in CALOR simulation to model the experimental configurations. Five major systematic effects are identified. These are the choice of high energy nuclear collision model, material composition, scintillator saturation, shower integration time, and the shower containment. Quantitative estimates of these systematic effects are presented. 23 refs., 6 figs., 7 tabs.
A Simple Model of Global Aerosol Indirect Effects
NASA Technical Reports Server (NTRS)
Ghan, Steven J.; Smith, Steven J.; Wang, Minghuai; Zhang, Kai; Pringle, Kirsty; Carslaw, Kenneth; Pierce, Jeffrey; Bauer, Susanne; Adams, Peter
2013-01-01
Most estimates of the global mean indirect effect of anthropogenic aerosol on the Earth's energy balance are from simulations by global models of the aerosol lifecycle coupled with global models of clouds and the hydrologic cycle. Extremely simple models have been developed for integrated assessment models, but lack the flexibility to distinguish between primary and secondary sources of aerosol. Here a simple but more physically based model expresses the aerosol indirect effect (AIE) using analytic representations of cloud and aerosol distributions and processes. Although the simple model is able to produce estimates of AIEs that are comparable to those from some global aerosol models using the same global mean aerosol properties, the estimates by the simple model are sensitive to preindustrial cloud condensation nuclei concentration, preindustrial accumulation mode radius, width of the accumulation mode, size of primary particles, cloud thickness, primary and secondary anthropogenic emissions, the fraction of the secondary anthropogenic emissions that accumulates on the coarse mode, the fraction of the secondary mass that forms new particles, and the sensitivity of liquid water path to droplet number concentration. Estimates of present-day AIEs as low as 5 W/sq m and as high as 0.3 W/sq m are obtained for plausible sets of parameter values. Estimates are surprisingly linear in emissions. The estimates depend on parameter values in ways that are consistent with results from detailed global aerosol-climate simulation models, which adds to understanding of the dependence on AIE uncertainty on uncertainty in parameter values.
Therapeutic effects of progesterone in animal models of neurological disorders.
De Nicola, Alejandro F; Coronel, Florencia; Garay, Laura I; Gargiulo-Monachelli, Gisella; Gonzalez Deniselle, Maria Claudia; Gonzalez, Susana L; Labombarda, Florencia; Meyer, Maria; Guennoun, Rachida; Schumacher, Michael
2013-12-01
Substantial evidence supports that progesterone exerts many functions in the central and peripheral nervous system unrelated to its classical role in reproduction. In this review we first discussed progesterone effects following binding to the classical intracellular progesterone receptors A and B and several forms of membrane progesterone receptors, the modulation of intracellular signalling cascades and the interaction of progesterone reduced metabolites with neurotransmitter receptors. We next described our results involving animal models of human neuropathologies to elucidate the protective roles of progesterone. We described: (a) the protective and promyelinating effects of progesterone in experimental spinal cord injury; (b) the progesterone protective effects exerted upon motoneurons in the degenerating spinal cord of Wobbler mouse model of amyotropic lateral sclerosis; (c) the protective and anti-inflammatory effects of progesterone in the murine experimental autoimmune encephalomyelitis model of multiple sclerosis and after lysolecithin demyelination; (d) the progesterone prevention of nociception and neuropathic pain which follow spinal cord injury; and (e) the protective effect of progesterone in experimental ischemic stroke. Whenever available, the molecular mechanisms involved in these progesterone effects were examined. The multiplicity of progesterone beneficial effects has opened new venues of research for neurological disorders. In this way, results obtained in animal models could provide the basis for novel therapeutic strategies and pre-clinical studies.
Physics-Based Reactive Burn Model: Grain Size Effects
NASA Astrophysics Data System (ADS)
Lu, X.; Hamate, Y.; Horie, Y.
2007-12-01
We have been developing a physics-based reactive burn (PBRB) model, which was formulated based on the concept of a statistical hot spot cell. In the model, essential thermomechanics and physiochemical features are explicitly modeled. In this paper, we have extended the statistical hot spot model to explicitly describe the ignition and growth of hot spots. In particular, grain size effects are explicitly delineated through introduction of grain size-dependent, thickness of the hot-region, energy deposition criterion, and specific surface area. Besides the linear relationships between the run distance to detonation and the critical diameter with respect to the reciprocal specific surface area of heterogeneous explosives (HE), which is based on the original model and discussed in a parallel paper of this meeting, parametric studies have shown that the extended PBRB model can predict a non-monotonic variation of shock sensitivity with grain size, as observed by Moulard et al.
Modeling free convective gravitational effects in chemical vapor deposition
NASA Technical Reports Server (NTRS)
Stinespring, C. D.; Annen, K. D.
1987-01-01
In this paper, a combined fluid-mechanics, mass-transport, and chemistry model describing CVD in an open-tube atmospheric-pressure flow reactor is developed. The model allows gas-phase reactions to proceed to equilibrium and accounts for finite reaction rates at the surface of the deposition substrate. This model is a useful intermediate step toward a model employing fully rate-limited chemistry. The model is used to predict the effects of free convection on flow patterns, temperature and species-concentration profiles, and local deposition rates for silicon deposited by silane pyrolysis. These results are discussed in terms of implications for CVD of silicon and other compounds, microgravity studies, and techniques for testing and validating the model.
Identification of dynamical biological systems based on random effects models.
Batista, Levy; Bastogne, Thierry; Djermoune, El-Hadi
2015-01-01
System identification is a data-driven modeling approach more and more used in biology and biomedicine. In this application context, each assay is always repeated to estimate the response variability. The inference of the modeling conclusions to the whole population requires to account for the inter-individual variability within the modeling procedure. One solution consists in using random effects models but up to now no similar approach exists in the field of dynamical system identification. In this article, we propose a new solution based on an ARX (Auto Regressive model with eXternal inputs) structure using the EM (Expectation-Maximisation) algorithm for the estimation of the model parameters. Simulations show the relevance of this solution compared with a classical procedure of system identification repeated for each subject. PMID:26736981
Effective microscopic models for sympathetic cooling of atomic gases
NASA Astrophysics Data System (ADS)
Onofrio, Roberto; Sundaram, Bala
2015-09-01
Thermalization of a system in the presence of a heat bath has been the subject of many theoretical investigations especially in the framework of solid-state physics. In this setting, the presence of a large bandwidth for the frequency distribution of the harmonic oscillators schematizing the heat bath is crucial, as emphasized in the Caldeira-Leggett model. By contrast, ultracold gases in atomic traps oscillate at well-defined frequencies and therefore seem to lie outside the Caldeira-Leggett paradigm. We introduce interaction Hamiltonians which allow us to adapt the model to an atomic physics framework. The intrinsic nonlinearity of these models differentiates them from the original Caldeira-Leggett model and calls for a nontrivial stability analysis to determine effective ranges for the model parameters. These models allow for molecular-dynamics simulations of mixtures of ultracold gases, which is of current relevance for optimizing sympathetic cooling in degenerate Bose-Fermi mixtures.
Three-dimensional effects for radio frequency antenna modeling
NASA Astrophysics Data System (ADS)
Carter, M. D.; Batchelor, D. B.; Stallings, D. C.
Electromagnetic field calculations for radio frequency (RF) antennas in two dimensions (2-D) neglect finite antenna length effects as well as the feeders leading to the main current strap. The 2-D calculations predict that the return currents in the sidewalls of the antenna structure depend strongly on the plasma parameters, but this prediction is suspect because of experimental evidence. To study the validity of the 2-D approximation, the Multiple Antenna Implementation System (MAntIS) has been used to perform three-dimensional (3-D) modeling of the power spectrum, plasma loading, and inductance for a relevant loop antenna design. Effects on antenna performance caused by feeders to the main current strap and conducting sidewalls are considered. The modeling shows that the feeders affect the launched power spectrum in an indirect way by forcing the driven RF current to return in the antenna structure rather than the plasma, as in the 2-D model. It has also been found that poloidal dependencies in the plasma impedance matrix can reduce the loading predicted from that predicted in the 2-D model. For some plasma parameters, the combined 3-D effects can lead to a reduction in the predicted loading by as much as a factor of 2 from that given by the 2-D model, even with end-effect corrections for the 2-D model.
Three-dimensional effects for radio frequency antenna modeling
NASA Astrophysics Data System (ADS)
Carter, M. D.; Batchelor, D. B.; Stallings, D. C.
1994-10-01
Electromagnetic field calculations for radio frequency (rf) antennas in two dimensions (2-D) neglect finite antenna length effects as well as the feeders leading to the main current strap. The 2-D calculations predict that the return currents in the sidewalls of the antenna structure depend strongly on the plasma parameters, but this prediction is suspect because of experimental evidence. To study the validity of the 2-D approximation, the Multiple Antenna Implementation System (MAntIS) has been used to perform three-dimensional (3-D) modeling of the power spectrum, plasma loading, and inductance for a relevant loop antenna design. Effects on antenna performance caused by feeders to the main current strap and conducting sidewalls are considered. The modeling shows that the feeders affect the launched power spectrum in an indirect way by forcing the driven rf current to return in the antenna structure rather than the plasma, as in the 2-D model. It has also been found that poloidal dependencies in the plasma impedance matrix can reduce the loading predicted from that predicted in the 2-D model. For some plasma parameters, the combined 3-D effects can lead to a reduction in the predicted loading by as much as a factor of 2 from that given by the 2-D model, even with end-effect corrections for the 2-D model.
A sonic boom propagation model including mean flow atmospheric effects
NASA Astrophysics Data System (ADS)
Salamone, Joe; Sparrow, Victor W.
2012-09-01
This paper presents a time domain formulation of nonlinear lossy propagation in onedimension that also includes the effects of non-collinear mean flow in the acoustic medium. The model equation utilized is an augmented Burgers equation that includes the effects of nonlinearity, geometric spreading, atmospheric stratification, and also absorption and dispersion due to thermoviscous and molecular relaxation effects. All elements of the propagation are implemented in the time domain and the effects of non-collinear mean flow are accounted for in each term of the model equation. Previous authors have presented methods limited to showing the effects of wind on ray tracing and/or using an effective speed of sound in their model equation. The present work includes the effects of mean flow for all terms included in the augmented Burgers equation with all of the calculations performed in the time-domain. The capability to include the effects of mean flow in the acoustic medium allows one to make predictions more representative of real-world atmospheric conditions. Examples are presented for nonlinear propagation of N-waves and shaped sonic booms. [Work supported by Gulfstream Aerospace Corporation.
Modeling the Effects of Stress: An Approach to Training
NASA Technical Reports Server (NTRS)
Cuper, Taryn
2010-01-01
Stress is an integral element of the operational conditions experienced by combat medics. The effects of stress can compromise the performance of combat medics who must reach and treat their comrades under often threatening circumstances. Examples of these effects include tunnel vision, loss of motor control, and diminished hearing, which can result in an inability to perceive further danger, satisfactorily treat the casualty, and communicate with others. While many training programs strive to recreate this stress to aid in the experiential learning process, stress inducement may not always be feasible or desired. In addition, live simulations are not always a practical, convenient, and repeatable method of training. Instead, presenting situational training on a personal computer is proposed as an effective training platform in which the effects of stress can be addressed in a different way. We explore the cognitive and motor effects of stress, as well as the benefits of training for mitigating these effects in real life. While many training applications focus on inducing stress in order to "condition" the stress response, the author explores the possibilities of modeling stress to produce a similar effect. Can presenting modeled effects of stress help prepare or inoculate soldiers for stressful situations in which they must perform at a high level? This paper investigates feasibility of modeling stress and describes the preliminary design considerations of a combat medic training system that utilizes this method of battlefield preparation.
An Atmospheric Variability Model for Venus Aerobraking Missions
NASA Technical Reports Server (NTRS)
Tolson, Robert T.; Prince, Jill L. H.; Konopliv, Alexander A.
2013-01-01
Aerobraking has proven to be an enabling technology for planetary missions to Mars and has been proposed to enable low cost missions to Venus. Aerobraking saves a significant amount of propulsion fuel mass by exploiting atmospheric drag to reduce the eccentricity of the initial orbit. The solar arrays have been used as the primary drag surface and only minor modifications have been made in the vehicle design to accommodate the relatively modest aerothermal loads. However, if atmospheric density is highly variable from orbit to orbit, the mission must either accept higher aerothermal risk, a slower pace for aerobraking, or a tighter corridor likely with increased propulsive cost. Hence, knowledge of atmospheric variability is of great interest for the design of aerobraking missions. The first planetary aerobraking was at Venus during the Magellan mission. After the primary Magellan science mission was completed, aerobraking was used to provide a more circular orbit to enhance gravity field recovery. Magellan aerobraking took place between local solar times of 1100 and 1800 hrs, and it was found that the Venusian atmospheric density during the aerobraking phase had less than 10% 1 sigma orbit to orbit variability. On the other hand, at some latitudes and seasons, Martian variability can be as high as 40% 1 sigmaFrom both the MGN and PVO mission it was known that the atmosphere, above aerobraking altitudes, showed greater variability at night, but this variability was never quantified in a systematic manner. This paper proposes a model for atmospheric variability that can be used for aerobraking mission design until more complete data sets become available.
ERIC Educational Resources Information Center
Grossman, Ellin
1980-01-01
After 15 lessons on clay modeling skills, modeled and drawn human figures by 41 nursery school children were compared to those by control children on formal elements, structure, and detail. The instructional experience significantly improved subjects' clay figure work. No significant sex effect or skill transfer to drawing was found. (SJL)
Simulation Model of A Ferroelectric Field Effect Transistor
NASA Technical Reports Server (NTRS)
MacLeod, Todd C.; Ho, Fat Duen; Russell, Larry W. (Technical Monitor)
2002-01-01
An electronic simulation model has been developed of a ferroelectric field effect transistor (FFET). This model can be used in standard electrical circuit simulation programs to simulate the main characteristics of the FFET. The model uses a previously developed algorithm that incorporates partial polarization as a basis for the design. The model has the main characteristics of the FFET, which are the current hysterisis with different gate voltages and decay of the drain current when the gate voltage is off. The drain current has values matching actual FFET's, which were measured experimentally. The input and output resistance in the model is similar to that of the FFET. The model is valid for all frequencies below RF levels. A variety of different ferroelectric material characteristics can be modeled. The model can be used to design circuits using FFET'S with standard electrical simulation packages. The circuit can be used in designing non-volatile memory circuits and logic circuits and is compatible with all SPICE based circuit analysis programs. The model is a drop in library that integrates seamlessly into a SPICE simulation. A comparison is made between the model and experimental data measured from an actual FFET.
Integrating Multiscale Modeling with Drug Effects for Cancer Treatment
Li, Xiangfang L.; Oduola, Wasiu O.; Qian, Lijun; Dougherty, Edward R.
2015-01-01
In this paper, we review multiscale modeling for cancer treatment with the incorporation of drug effects from an applied system’s pharmacology perspective. Both the classical pharmacology and systems biology are inherently quantitative; however, systems biology focuses more on networks and multi factorial controls over biological processes rather than on drugs and targets in isolation, whereas systems pharmacology has a strong focus on studying drugs with regard to the pharmacokinetic (PK) and pharmacodynamic (PD) relations accompanying drug interactions with multiscale physiology as well as the prediction of dosage-exposure responses and economic potentials of drugs. Thus, it requires multiscale methods to address the need for integrating models from the molecular levels to the cellular, tissue, and organism levels. It is a common belief that tumorigenesis and tumor growth can be best understood and tackled by employing and integrating a multifaceted approach that includes in vivo and in vitro experiments, in silico models, multiscale tumor modeling, continuous/discrete modeling, agent-based modeling, and multiscale modeling with PK/PD drug effect inputs. We provide an example application of multiscale modeling employing stochastic hybrid system for a colon cancer cell line HCT-116 with the application of Lapatinib drug. It is observed that the simulation results are similar to those observed from the setup of the wet-lab experiments at the Translational Genomics Research Institute. PMID:26792977
Modeling of Turbulence Effects on Liquid Jet Atomization and Breakup
NASA Technical Reports Server (NTRS)
Trinh, Huu; Chen, C. P.
2004-01-01
Recent experimental investigations and physical modeling studies have indicated that turbulence behaviors within a liquid jet have considerable effects on the atomization process. For certain flow regimes, it has been observed that the liquid jet surface is highly turbulent. This turbulence characteristic plays a key role on the breakup of the liquid jet near to the injector exit. Other experiments also showed that the breakup length of the liquid core is sharply shortened as the liquid jet is changed from the laminar to the turbulent flow conditions. In the numerical and physical modeling arena, most of commonly used atomization models do not include the turbulence effect. Limited attempts have been made in modeling the turbulence phenomena on the liquid jet disintegration. The subject correlation and models treat the turbulence either as an only source or a primary driver in the breakup process. This study aims to model the turbulence effect in the atomization process of a cylindrical liquid jet. In the course of this study, two widely used models, Reitz's primary atomization (blob) and Taylor-Analogy-Break (TAB) secondary droplet breakup by O Rourke et al. are examined. Additional terms are derived and implemented appropriately into these two models to account for the turbulence effect on the atomization process. Since this enhancement effort is based on a framework of the two existing atomization models, it is appropriate to denote the two present models as T-blob and T-TAB for the primary and secondary atomization predictions, respectively. In the primary breakup model, the level of the turbulence effect on the liquid breakup depends on the characteristic time scales and the initial flow conditions. This treatment offers a balance of contributions of individual physical phenomena on the liquid breakup process. For the secondary breakup, an addition turbulence force acted on parent drops is modeled and integrated into the TAB governing equation. The drop size
A Bayesian nonlinear mixed-effects disease progression model
Kim, Seongho; Jang, Hyejeong; Wu, Dongfeng; Abrams, Judith
2016-01-01
A nonlinear mixed-effects approach is developed for disease progression models that incorporate variation in age in a Bayesian framework. We further generalize the probability model for sensitivity to depend on age at diagnosis, time spent in the preclinical state and sojourn time. The developed models are then applied to the Johns Hopkins Lung Project data and the Health Insurance Plan for Greater New York data using Bayesian Markov chain Monte Carlo and are compared with the estimation method that does not consider random-effects from age. Using the developed models, we obtain not only age-specific individual-level distributions, but also population-level distributions of sensitivity, sojourn time and transition probability. PMID:26798562
Chern-Simons potential in models of Casimir effect
Pis'mak, Yury M.; Pis'mak, Daria Yu.
2014-07-23
In the model constructed in the framework of the proposed by Symanzik approach for description of interaction of a macroscopic material body with quantum fields the interaction of thin material film with photon field is presented by the Chern-Simons potential. All the effects of this interaction with can by described in the framework of one model. In this way, the Casimir energy for two parallel infinite planes and sphere, the Casimir-Polder potential, and characteristics of other physical phenomena have been calculated for non-ideal conducting material of film. The specific of regularization and renormalization procedures used by calculations and the physical meaning of obtained results are discussed. In the limit of infinite coupling constant one obtains the known results of models with boundary conditions. By finite value of coupling constants the model predicts unusual effects which could be important for micro-mechanics, nano-photonics, constructing of new materials.
Effects of anticipatory driving in a traffic flow model
NASA Astrophysics Data System (ADS)
Eissfeldt, N.; Wagner, P.
2003-05-01
Anticipation in traffic means that drivers estimate their leaders' velocities for future timesteps. In the article a specific stochastic car-following model with non-unique flow-density relation is investigated with respect to anticipatory driving. It is realized by next-nearest-neighbour interaction which leads to large flows and short temporal headways. The underlying mechanism that causes these effects is explained by the headways of the cars which organize in an alternating structure with a short headway following a long one, thereby producing a strong anti-correlation in the gaps or in the headways of subsequent cars. For the investigated model the corresponding time headway distributions display the short headways observed in reality. Even though these effects are discussed for a specific model, the mechanism described is in general present in any traffic flow models that work with anticipation.
Semianalytical quantum model for graphene field-effect transistors
Pugnaghi, Claudio; Grassi, Roberto Gnudi, Antonio; Di Lecce, Valerio; Gnani, Elena; Reggiani, Susanna; Baccarani, Giorgio
2014-09-21
We develop a semianalytical model for monolayer graphene field-effect transistors in the ballistic limit. Two types of devices are considered: in the first device, the source and drain regions are doped by charge transfer with Schottky contacts, while, in the second device, the source and drain regions are doped electrostatically by a back gate. The model captures two important effects that influence the operation of both devices: (i) the finite density of states in the source and drain regions, which limits the number of states available for transport and can be responsible for negative output differential resistance effects, and (ii) quantum tunneling across the potential steps at the source-channel and drain-channel interfaces. By comparison with a self-consistent non-equilibrium Green's function solver, we show that our model provides very accurate results for both types of devices, in the bias region of quasi-saturation as well as in that of negative differential resistance.
Stochastic effects in a seasonally forced epidemic model
NASA Astrophysics Data System (ADS)
Rozhnova, G.; Nunes, A.
2010-10-01
The interplay of seasonality, the system’s nonlinearities and intrinsic stochasticity, is studied for a seasonally forced susceptible-exposed-infective-recovered stochastic model. The model is explored in the parameter region that corresponds to childhood infectious diseases such as measles. The power spectrum of the stochastic fluctuations around the attractors of the deterministic system that describes the model in the thermodynamic limit is computed analytically and validated by stochastic simulations for large system sizes. Size effects are studied through additional simulations. Other effects such as switching between coexisting attractors induced by stochasticity often mentioned in the literature as playing an important role in the dynamics of childhood infectious diseases are also investigated. The main conclusion is that stochastic amplification, rather than these effects, is the key ingredient to understand the observed incidence patterns.
Memory efficient atmospheric effects modeling for infrared scene generators
NASA Astrophysics Data System (ADS)
Kavak, Çaǧlar; Özsaraç, Seçkin
2015-05-01
The infrared (IR) energy radiated from any source passes through the atmosphere before reaching the sensor. As a result, the total signature captured by the IR sensor is significantly modified by the atmospheric effects. The dominant physical quantities that constitute the mentioned atmospheric effects are the atmospheric transmittance and the atmospheric path radiance. The incoming IR radiation is attenuated by the transmittance and path radiance is added on top of the attenuated radiation. In IR scene simulations OpenGL is widely used for rendering purposes. In the literature there are studies, which model the atmospheric effects in an IR band using OpenGLs exponential fog model as suggested by Beers law. In the standard pipeline of OpenGL, the related fog model needs single equivalent OpenGL variables for the transmittance and path radiance, which actually depend on both the distance between the source and the sensor and also on the wavelength of interest. However, in the conditions where the range dependency cannot be modeled as an exponential function, it is not accurate to replace the atmospheric quantities with a single parameter. The introduction of OpenGL Shading Language (GLSL) has enabled the developers to use the GPU more flexible. In this paper, a novel method is proposed for the atmospheric effects modeling using the least squares estimation with polynomial fitting by programmable OpenGL shader programs built with GLSL. In this context, a radiative transfer model code is used to obtain the transmittance and path radiance data. Then, polynomial fits are computed for the range dependency of these variables. Hence, the atmospheric effects model data that will be uploaded in the GPU memory is significantly reduced. Moreover, the error because of fitting is negligible as long as narrow IR bands are used.
A toy model for quantum spin Hall effect
NASA Astrophysics Data System (ADS)
Owerre, S. A.; Nsofini, J.
2015-09-01
In this communication, we investigate a toy model of three-dimensional topological insulator surface, coupled homogeneously to a fictitious pseudospin-1/2 particle. We show that this toy model captures the interesting features of topological insulator surface states, which include topological quantum phase transition and quantum spin Hall effect. We further incorporate an out-of-plane magnetic field and obtain the Landau levels.
Modelling and predicting the biological effects of nanomaterials.
Winkler, D A; Burden, F R; Yan, B; Weissleder, R; Tassa, C; Shaw, S; Epa, V C
2014-01-01
The commercial applications of nanoparticles are growing rapidly, but we know relatively little about how nanoparticles interact with biological systems. Their value--but also their risk--is related to their nanophase properties being markedly different to those of the same material in bulk. Experiments to determine how nanoparticles are taken up, distributed, modified, and elicit any adverse effects are essential. However, cost and time considerations mean that predictive models would also be extremely valuable, particularly assisting regulators to minimize health and environmental risks. We used novel sparse machine learning methods that employ Bayesian neural networks to model three nanoparticle data sets using both linear and nonlinear machine learning methods. The first data comprised iron oxide nanoparticles decorated with 108 different molecules tested against five cell lines, HUVEC, pancreatic cancer, and three macrophage or macrophage-like lines. The second data set comprised 52 nanoparticles with various core compositions, coatings, and surface attachments. The nanoparticles were characterized using four descriptors (size, relaxivities, and zeta potential), and their biological effects on four cells lines assessed using four biological assays per cell line and four concentrations per assay. The third data set involved the biological responses to gold nanoparticles functionalized by 80 different small molecules. Nonspecific binding and binding to AChE were the biological endpoints modelled. The biological effects of nanoparticles were modelled using molecular descriptors for the molecules that decorated the nanoparticle surface. Models with good statistical quality were constructed for most biological endpoints. These proof-of-concept models show that modelling biological effects of nanomaterials is possible using modern modelling methods.
Guidance for modeling causes and effects in environmental problem solving
Armour, Carl L.; Williamson, Samuel C.
1988-01-01
Environmental problems are difficult to solve because their causes and effects are not easily understood. When attempts are made to analyze causes and effects, the principal challenge is organization of information into a framework that is logical, technically defensible, and easy to understand and communicate. When decisionmakers attempt to solve complex problems before an adequate cause and effect analysis is performed there are serious risks. These risks include: greater reliance on subjective reasoning, lessened chance for scoping an effective problem solving approach, impaired recognition of the need for supplemental information to attain understanding, increased chance for making unsound decisions, and lessened chance for gaining approval and financial support for a program/ Cause and effect relationships can be modeled. This type of modeling has been applied to various environmental problems, including cumulative impact assessment (Dames and Moore 1981; Meehan and Weber 1985; Williamson et al. 1987; Raley et al. 1988) and evaluation of effects of quarrying (Sheate 1986). This guidance for field users was written because of the current interest in documenting cause-effect logic as a part of ecological problem solving. Principal literature sources relating to the modeling approach are: Riggs and Inouye (1975a, b), Erickson (1981), and United States Office of Personnel Management (1986).
“Serial” effects in parallel models of reading
Chang, Ya-Ning; Furber, Steve; Welbourne, Stephen
2012-01-01
There is now considerable evidence showing that the time to read a word out loud is influenced by an interaction between orthographic length and lexicality. Given that length effects are interpreted by advocates of dual-route models as evidence of serial processing this would seem to pose a serious challenge to models of single word reading which postulate a common parallel processing mechanism for reading both words and nonwords (Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001; Rastle, Havelka, Wydell, Coltheart, & Besner, 2009). However, an alternative explanation of these data is that visual processes outside the scope of existing parallel models are responsible for generating the word-length related phenomena (Seidenberg & Plaut, 1998). Here we demonstrate that a parallel model of single word reading can account for the differential word-length effects found in the naming latencies of words and nonwords, provided that it includes a mapping from visual to orthographic representations, and that the nature of those orthographic representations are not preconstrained. The model can also simulate other supposedly “serial” effects. The overall findings were consistent with the view that visual processing contributes substantially to the word-length effects in normal reading and provided evidence to support the single-route theory which assumes words and nonwords are processed in parallel by a common mechanism. PMID:22343366
Postural effects on intracranial pressure: modeling and clinical evaluation.
Qvarlander, Sara; Sundström, Nina; Malm, Jan; Eklund, Anders
2013-11-01
The physiological effect of posture on intracranial pressure (ICP) is not well described. This study defined and evaluated three mathematical models describing the postural effects on ICP, designed to predict ICP at different head-up tilt angles from the supine ICP value. Model I was based on a hydrostatic indifference point for the cerebrospinal fluid (CSF) system, i.e., the existence of a point in the system where pressure is independent of body position. Models II and III were based on Davson's equation for CSF absorption, which relates ICP to venous pressure, and postulated that gravitational effects within the venous system are transferred to the CSF system. Model II assumed a fully communicating venous system, and model III assumed that collapse of the jugular veins at higher tilt angles creates two separate hydrostatic compartments. Evaluation of the models was based on ICP measurements at seven tilt angles (0-71°) in 27 normal pressure hydrocephalus patients. ICP decreased with tilt angle (ANOVA: P < 0.01). The reduction was well predicted by model III (ANOVA lack-of-fit: P = 0.65), which showed excellent fit against measured ICP. Neither model I nor II adequately described the reduction in ICP (ANOVA lack-of-fit: P < 0.01). Postural changes in ICP could not be predicted based on the currently accepted theory of a hydrostatic indifference point for the CSF system, but a new model combining Davson's equation for CSF absorption and hydrostatic gradients in a collapsible venous system performed well and can be useful in future research on gravity and CSF physiology.
Clinical Trials: Spline Modeling is Wonderful for Nonlinear Effects.
Cleophas, Ton J
2016-01-01
Traditionally, nonlinear relationships like the smooth shapes of airplanes, boats, and motor cars were constructed from scale models using stretched thin wooden strips, otherwise called splines. In the past decades, mechanical spline methods have been replaced with their mathematical counterparts. The objective of the study was to study whether spline modeling can adequately assess the relationships between exposure and outcome variables in a clinical trial and also to study whether it can detect patterns in a trial that are relevant but go unobserved with simpler regression models. A clinical trial assessing the effect of quantity of care on quality of care was used as an example. Spline curves consistent of 4 or 5 cubic functions were applied. SPSS statistical software was used for analysis. The spline curves of our data outperformed the traditional curves because (1) unlike the traditional curves, they did not miss the top quality of care given in either subgroup, (2) unlike the traditional curves, they, rightly, did not produce sinusoidal patterns, and (3) unlike the traditional curves, they provided a virtually 100% match of the original values. We conclude that (1) spline modeling can adequately assess the relationships between exposure and outcome variables in a clinical trial; (2) spline modeling can detect patterns in a trial that are relevant but may go unobserved with simpler regression models; (3) in clinical research, spline modeling has great potential given the presence of many nonlinear effects in this field of research and given its sophisticated mathematical refinement to fit any nonlinear effect in the mostly accurate way; and (4) spline modeling should enable to improve making predictions from clinical research for the benefit of health decisions and health care. We hope that this brief introduction to spline modeling will stimulate clinical investigators to start using this wonderful method.
Attractive Casimir effect in an infrared modified gluon bag model
Oxman, L.E.; Amaral, R.L.P.G.
2005-12-15
In this work, we are motivated by previous attempts to derive the vacuum contribution to the bag energy in terms of familiar Casimir energy calculations for spherical geometries. A simple infrared modified model is introduced which allows studying the effects of the analytic structure as well as the geometry in a clear manner. In this context, we show that if a class of infrared vanishing effective gluon propagators is considered, then the renormalized vacuum energy for a spherical bag is attractive, as required by the bag model to adjust hadron spectroscopy.
Thermoacoustic resonance effect and circuit modelling of biological tissue
NASA Astrophysics Data System (ADS)
Gao, Fei; Zheng, Yuanjin; Feng, Xiaohua; Ohl, Claus-Dieter
2013-02-01
In this letter, thermoacoustic resonance effect is predicted from theoretical analysis with series resistor-inductor-capacitor resonance circuit model and then observed experimentally using muscle tissue illuminated by multi-pulse microwave source. Through model fitting, the circuit parameters are extracted to characterize quantitatively the resonant response of the tissue. Coherent demodulation is applied to obtain the enhanced signal-to-noise ratio and spatial information by treating tissue as a communication channel. This physical phenomenon shows significantly higher sensitivity than conventional single microwave pulse induced thermoacoustic effect, enabling the potential design of low-power thermoacoustic imaging device for portable and on-site diagnosis.
Modelling of the Peltier effect in magnetic multilayers
NASA Astrophysics Data System (ADS)
Juarez-Acosta, Isaac; Olivares-Robles, Miguel A.; Bosu, Subrojati; Sakuraba, Yuya; Kubota, Takahide; Takahashi, Saburo; Takanashi, Koki; Bauer, Gerrit E. W.
2016-02-01
We model the charge, spin, and heat currents in ferromagnetic metal|normal metal|normal metal trilayer structures in the two current model, taking into account bulk and interface thermoelectric properties as well as Joule heating. The results include the temperature distribution as well as resistance-current curves that reproduce the observed shifted parabolic characteristics. Thin tunneling barriers can enhance the apparent Peltier cooling. The model agrees with the experimental results for wide multilayer pillars, but the giant effects observed for diameters ≲100 nm are still under discussion.
Effect of attenuation models on communication system design
NASA Technical Reports Server (NTRS)
Shimabukuro, Fred I.
1995-01-01
The atmosphere has a significant impact on the design of a global communication system operating at 20 GHz. The system under consideration has a total atmospheric link attenuation budget that is less than 6 dB. For this relatively small link margin, rain, cloud, and molecular attenuation have to be taken into account. For an assessment of system performance on a global basis, attenuation models are utilized. There is concern whether current models can adequately describe the atmospheric effects such that a system planner can properly allocate his resources for superior overall system performance. The atmospheric attenuation as predicted by models will be examined.
Organizational effectiveness. Primary care and the congruence model.
Eiser, A R; Eiser, B J
1996-10-01
The congruence model is a framework used to analyze organizational strengths and weaknesses and pinpoint specific areas for improving effectiveness. This article provides an overview of organizations as open systems, with examples in the primary care arena. It explains and applies the congruence model in the context of primary care issues and functions, including methods by which the model can be used to diagnose organizational problems and generate solutions. Changes needed in primary care due to the managed care environment, and areas of potential problems and sensitivities requiring organizational changes to meet market and regulatory demands now placed on PCOs are examined.
Analog model for quantum gravity effects: phonons in random fluids.
Krein, G; Menezes, G; Svaiter, N F
2010-09-24
We describe an analog model for quantum gravity effects in condensed matter physics. The situation discussed is that of phonons propagating in a fluid with a random velocity wave equation. We consider that there are random fluctuations in the reciprocal of the bulk modulus of the system and study free phonons in the presence of Gaussian colored noise with zero mean. We show that, in this model, after performing the random averages over the noise function a free conventional scalar quantum field theory describing free phonons becomes a self-interacting model.
Coherent Effects in Microwave Backscattering Models for Forest Canopies
NASA Technical Reports Server (NTRS)
Saatchi, Sasan; McDonald, Kyle
1995-01-01
In modeling forest canopies, several scattering mechanisms are taken into account: 1) volume scattering, 2) surface-volume interaction, and 3) surface scattering from forest floor. Depending on the structural and dielectric characteristics of forest canopies, the relative contribution of each mechanism in the total backscatter signal of an imaging radar can vary. In this paper, two commonly used first order discrete scattering models, Distorted Born Approximation (DBA) and Radiative Transfer (RT) are used to simulate the backscattered power received by polarimetric radars at P-, L-, and C-bands over coniferous and deciduous forests. The difference between the two models resides on the coherent effect in the surface-volume interaction terms.
The effect of model uncertainty on cooperation in sensorimotor interactions
Grau-Moya, J.; Hez, E.; Pezzulo, G.; Braun, D. A.
2013-01-01
Decision-makers have been shown to rely on probabilistic models for perception and action. However, these models can be incorrect or partially wrong in which case the decision-maker has to cope with model uncertainty. Model uncertainty has recently also been shown to be an important determinant of sensorimotor behaviour in humans that can lead to risk-sensitive deviations from Bayes optimal behaviour towards worst-case or best-case outcomes. Here, we investigate the effect of model uncertainty on cooperation in sensorimotor interactions similar to the stag-hunt game, where players develop models about the other player and decide between a pay-off-dominant cooperative solution and a risk-dominant, non-cooperative solution. In simulations, we show that players who allow for optimistic deviations from their opponent model are much more likely to converge to cooperative outcomes. We also implemented this agent model in a virtual reality environment, and let human subjects play against a virtual player. In this game, subjects' pay-offs were experienced as forces opposing their movements. During the experiment, we manipulated the risk sensitivity of the computer player and observed human responses. We found not only that humans adaptively changed their level of cooperation depending on the risk sensitivity of the computer player but also that their initial play exhibited characteristic risk-sensitive biases. Our results suggest that model uncertainty is an important determinant of cooperation in two-player sensorimotor interactions. PMID:23945266
Multivariate longitudinal data analysis with mixed effects hidden Markov models.
Raffa, Jesse D; Dubin, Joel A
2015-09-01
Multiple longitudinal responses are often collected as a means to capture relevant features of the true outcome of interest, which is often hidden and not directly measurable. We outline an approach which models these multivariate longitudinal responses as generated from a hidden disease process. We propose a class of models which uses a hidden Markov model with separate but correlated random effects between multiple longitudinal responses. This approach was motivated by a smoking cessation clinical trial, where a bivariate longitudinal response involving both a continuous and a binomial response was collected for each participant to monitor smoking behavior. A Bayesian method using Markov chain Monte Carlo is used. Comparison of separate univariate response models to the bivariate response models was undertaken. Our methods are demonstrated on the smoking cessation clinical trial dataset, and properties of our approach are examined through extensive simulation studies. PMID:25761965
Modeling of Metal-Ferroelectric-Semiconductor Field Effect Transistors
NASA Technical Reports Server (NTRS)
Duen Ho, Fat; Macleod, Todd C.
1998-01-01
The characteristics for a MFSFET (metal-ferroelectric-semiconductor field effect transistor) is very different than a conventional MOSFET and must be modeled differently. The drain current has a hysteresis shape with respect to the gate voltage. The position along the hysteresis curve is dependent on the last positive or negative polling of the ferroelectric material. The drain current also has a logarithmic decay after the last polling. A model has been developed to describe the MFSFET drain current for both gate voltage on and gate voltage off conditions. This model takes into account the hysteresis nature of the MFSFET and the time dependent decay. The model is based on the shape of the Fermi-Dirac function which has been modified to describe the MFSFET's drain current. This is different from the model proposed by Chen et. al. and that by Wu.
Improved Estimation of Human Lipoprotein Kinetics with Mixed Effects Models
Berglund, Martin; Adiels, Martin; Taskinen, Marja-Riitta; Borén, Jan; Wennberg, Bernt
2015-01-01
Context Mathematical models may help the analysis of biological systems by providing estimates of otherwise un-measurable quantities such as concentrations and fluxes. The variability in such systems makes it difficult to translate individual characteristics to group behavior. Mixed effects models offer a tool to simultaneously assess individual and population behavior from experimental data. Lipoproteins and plasma lipids are key mediators for cardiovascular disease in metabolic disorders such as diabetes mellitus type 2. By the use of mathematical models and tracer experiments fluxes and production rates of lipoproteins may be estimated. Results We developed a mixed effects model to study lipoprotein kinetics in a data set of 15 healthy individuals and 15 patients with type 2 diabetes. We compare the traditional and the mixed effects approach in terms of group estimates at various sample and data set sizes. Conclusion We conclude that the mixed effects approach provided better estimates using the full data set as well as with both sparse and truncated data sets. Sample size estimates showed that to compare lipoprotein secretion the mixed effects approach needed almost half the sample size as the traditional method. PMID:26422201
Estimating anatomical trajectories with Bayesian mixed-effects modeling
Ziegler, G.; Penny, W.D.; Ridgway, G.R.; Ourselin, S.; Friston, K.J.
2015-01-01
We introduce a mass-univariate framework for the analysis of whole-brain structural trajectories using longitudinal Voxel-Based Morphometry data and Bayesian inference. Our approach to developmental and aging longitudinal studies characterizes heterogeneous structural growth/decline between and within groups. In particular, we propose a probabilistic generative model that parameterizes individual and ensemble average changes in brain structure using linear mixed-effects models of age and subject-specific covariates. Model inversion uses Expectation Maximization (EM), while voxelwise (empirical) priors on the size of individual differences are estimated from the data. Bayesian inference on individual and group trajectories is realized using Posterior Probability Maps (PPM). In addition to parameter inference, the framework affords comparisons of models with varying combinations of model order for fixed and random effects using model evidence. We validate the model in simulations and real MRI data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) project. We further demonstrate how subject specific characteristics contribute to individual differences in longitudinal volume changes in healthy subjects, Mild Cognitive Impairment (MCI), and Alzheimer's Disease (AD). PMID:26190405
Estimation of effective connectivity via data-driven neural modeling
Freestone, Dean R.; Karoly, Philippa J.; Nešić, Dragan; Aram, Parham; Cook, Mark J.; Grayden, David B.
2014-01-01
This research introduces a new method for functional brain imaging via a process of model inversion. By estimating parameters of a computational model, we are able to track effective connectivity and mean membrane potential dynamics that cannot be directly measured using electrophysiological measurements alone. The ability to track the hidden aspects of neurophysiology will have a profound impact on the way we understand and treat epilepsy. For example, under the assumption the model captures the key features of the cortical circuits of interest, the framework will provide insights into seizure initiation and termination on a patient-specific basis. It will enable investigation into the effect a particular drug has on specific neural populations and connectivity structures using minimally invasive measurements. The method is based on approximating brain networks using an interconnected neural population model. The neural population model is based on a neural mass model that describes the functional activity of the brain, capturing the mesoscopic biophysics and anatomical structure. The model is made subject-specific by estimating the strength of intra-cortical connections within a region and inter-cortical connections between regions using a novel Kalman filtering method. We demonstrate through simulation how the framework can be used to track the mechanisms involved in seizure initiation and termination. PMID:25506315
Estimating anatomical trajectories with Bayesian mixed-effects modeling.
Ziegler, G; Penny, W D; Ridgway, G R; Ourselin, S; Friston, K J
2015-11-01
We introduce a mass-univariate framework for the analysis of whole-brain structural trajectories using longitudinal Voxel-Based Morphometry data and Bayesian inference. Our approach to developmental and aging longitudinal studies characterizes heterogeneous structural growth/decline between and within groups. In particular, we propose a probabilistic generative model that parameterizes individual and ensemble average changes in brain structure using linear mixed-effects models of age and subject-specific covariates. Model inversion uses Expectation Maximization (EM), while voxelwise (empirical) priors on the size of individual differences are estimated from the data. Bayesian inference on individual and group trajectories is realized using Posterior Probability Maps (PPM). In addition to parameter inference, the framework affords comparisons of models with varying combinations of model order for fixed and random effects using model evidence. We validate the model in simulations and real MRI data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) project. We further demonstrate how subject specific characteristics contribute to individual differences in longitudinal volume changes in healthy subjects, Mild Cognitive Impairment (MCI), and Alzheimer's Disease (AD).
Estimating anatomical trajectories with Bayesian mixed-effects modeling.
Ziegler, G; Penny, W D; Ridgway, G R; Ourselin, S; Friston, K J
2015-11-01
We introduce a mass-univariate framework for the analysis of whole-brain structural trajectories using longitudinal Voxel-Based Morphometry data and Bayesian inference. Our approach to developmental and aging longitudinal studies characterizes heterogeneous structural growth/decline between and within groups. In particular, we propose a probabilistic generative model that parameterizes individual and ensemble average changes in brain structure using linear mixed-effects models of age and subject-specific covariates. Model inversion uses Expectation Maximization (EM), while voxelwise (empirical) priors on the size of individual differences are estimated from the data. Bayesian inference on individual and group trajectories is realized using Posterior Probability Maps (PPM). In addition to parameter inference, the framework affords comparisons of models with varying combinations of model order for fixed and random effects using model evidence. We validate the model in simulations and real MRI data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) project. We further demonstrate how subject specific characteristics contribute to individual differences in longitudinal volume changes in healthy subjects, Mild Cognitive Impairment (MCI), and Alzheimer's Disease (AD). PMID:26190405
A Composite Model of Quarks with the `Effective Supersymmetry'
NASA Astrophysics Data System (ADS)
Okada, N.
1998-04-01
We present a composite model of quarks with `effective supersymmetry'. The model is based on the gauge group (SU(2)S × SU(2)M) × (SU(2)U × SU(2)C × SU(2)T) × SU(5)SM , where SU(5)SM is the standard model gauge group. In the dynamical supersymmetry breaking sector based on the gauge group SU(2)S × SU(2)M , supersymmetry is dynamically broken. The preon sector is constructed by the model proposed by Nelson and Strassler. The fermion mass hierarchy among the up-type quarks originates from the SU(2)U × SU(2)C × SU(2)T gauge dynamics. The supersymmetry breaking is mediated to the minimal supersymmetric standard model sector by the `preon' superfields which compose the quarks in the first two generations. To obtain an experimentally acceptable mass spectrum, the scalar quarks in the first two generations need masses of order 10 TeV, while the other superpartners need masses less than 1 TeV. Therefore, the mass spectrum in our model is one example of the `effective supersymmetry' model proposed by Cohen, Kaplan and Nelson.
Modeling of the effective permittivity of insulating presspaper
NASA Astrophysics Data System (ADS)
Huang, Jianwen; Zhou, Yuanxiang; Dong, Longyu; Huang, Meng; Zhou, Zhongliu; Liu, Rui
2016-07-01
Effective permittivity model of insulating presspaper is built on the basis of the microstructure of the material. Due to the essentially layered structure in z-direction of presspaper, air voids inside the mixture can be treated as right prismatic inclusions. Analytical formula for the prediction of the effective permittivity of insulating presspaper is derived. Interestingly, the derived formula equals to the mixing equation applied for dielectrics in series. Numerical simulation was used to validate the analytical results by considering the air voids as cubical inclusions. Results show a good agreement between the analytically and numerically calculated effective permittivity values. Furthermore, dielectric permittivity results of commercial kraft paper and laboratory-made presspaper at 50 Hz were measured and compared with modeled data. It turns out that the deduced results give a good accuracy for the effective permittivity determination.
Multi-agent Reinforcement Learning Model for Effective Action Selection
NASA Astrophysics Data System (ADS)
Youk, Sang Jo; Lee, Bong Keun
Reinforcement learning is a sub area of machine learning concerned with how an agent ought to take actions in an environment so as to maximize some notion of long-term reward. In the case of multi-agent, especially, which state space and action space gets very enormous in compared to single agent, so it needs to take most effective measure available select the action strategy for effective reinforcement learning. This paper proposes a multi-agent reinforcement learning model based on fuzzy inference system in order to improve learning collect speed and select an effective action in multi-agent. This paper verifies an effective action select strategy through evaluation tests based on Robocop Keep away which is one of useful test-beds for multi-agent. Our proposed model can apply to evaluate efficiency of the various intelligent multi-agents and also can apply to strategy and tactics of robot soccer system.
Modelling the effects of sanitary policies on European vulture conservation.
Margalida, Antoni; Colomer, Ma Àngels
2012-01-01
Biodiversity losses are increasing as a consequence of negative anthropogenic effects on ecosystem dynamics. However, the magnitude and complexity of these effects may still be greatly underestimated. Most Old World vultures have experienced rapid population declines in recent years. In Europe, their immediate conservation depends on changes in health regulations affecting the availability of food provided by domestic carcasses. Information is lacking on the effects of a hypothetical food shortage on the population dynamics of vultures, and is necessary to assess the potential impacts of policy decisions on future changes in biodiversity and ecosystem services. A novel computational model (P-systems) was used to model these effects, forecasting a rapid decline in the Eurasian griffon vulture (Gyps fulvus). By contrast, vulture species with greater plasticity in their dietary range appeared less sensitive to declining food availability. This study extends our understanding of vulture ecosystem services, which have social and economic implications.
Modelling the effects of sanitary policies on European vulture conservation
NASA Astrophysics Data System (ADS)
Margalida, Antoni; Colomer, M.^{A.} Àngels
2012-10-01
Biodiversity losses are increasing as a consequence of negative anthropogenic effects on ecosystem dynamics. However, the magnitude and complexity of these effects may still be greatly underestimated. Most Old World vultures have experienced rapid population declines in recent years. In Europe, their immediate conservation depends on changes in health regulations affecting the availability of food provided by domestic carcasses. Information is lacking on the effects of a hypothetical food shortage on the population dynamics of vultures, and is necessary to assess the potential impacts of policy decisions on future changes in biodiversity and ecosystem services. A novel computational model (P-systems) was used to model these effects, forecasting a rapid decline in the Eurasian griffon vulture (Gyps fulvus). By contrast, vulture species with greater plasticity in their dietary range appeared less sensitive to declining food availability. This study extends our understanding of vulture ecosystem services, which have social and economic implications.
Modelling the effects of sanitary policies on European vulture conservation
Margalida, Antoni; Colomer, Ma Àngels
2012-01-01
Biodiversity losses are increasing as a consequence of negative anthropogenic effects on ecosystem dynamics. However, the magnitude and complexity of these effects may still be greatly underestimated. Most Old World vultures have experienced rapid population declines in recent years. In Europe, their immediate conservation depends on changes in health regulations affecting the availability of food provided by domestic carcasses. Information is lacking on the effects of a hypothetical food shortage on the population dynamics of vultures, and is necessary to assess the potential impacts of policy decisions on future changes in biodiversity and ecosystem services. A novel computational model (P-systems) was used to model these effects, forecasting a rapid decline in the Eurasian griffon vulture (Gyps fulvus). By contrast, vulture species with greater plasticity in their dietary range appeared less sensitive to declining food availability. This study extends our understanding of vulture ecosystem services, which have social and economic implications. PMID:23082243
Modeling the effect of comprehensive interventions on Ebola virus transmission
NASA Astrophysics Data System (ADS)
Shen, Mingwang; Xiao, Yanni; Rong, Libin
2015-10-01
Since the re-emergence of Ebola in West Africa in 2014, comprehensive and stringent interventions have been implemented to decelerate the spread of the disease. The effectiveness of interventions still remains unclear. In this paper, we develop an epidemiological model that includes various controlling measures to systematically evaluate their effects on the disease transmission dynamics. By fitting the model to reported cumulative cases and deaths in Guinea, Sierra Leone and Liberia until March 22, 2015, we estimate the basic reproduction number in these countries as 1.2552, 1.6093 and 1.7994, respectively. Model analysis shows that there exists a threshold of the effectiveness of isolation, below which increasing the fraction of latent individuals diagnosed prior to symptoms onset or shortening the duration between symptoms onset and isolation may lead to more Ebola infection. This challenges an existing view. Media coverage plays a substantial role in reducing the final epidemic size. The response to reported cumulative infected cases and deaths may have a different effect on the epidemic spread in different countries. Among all the interventions, we find that shortening the duration between death and burial and improving the effectiveness of isolation are two effective interventions for controlling the outbreak of Ebola virus infection.
Sublethal toxicant effects with dynamic energy budget theory: model formulation.
Muller, Erik B; Nisbet, Roger M; Berkley, Heather A
2010-01-01
We develop and test a general modeling framework to describe the sublethal effects of pollutants by adding toxicity modules to an established dynamic energy budget (DEB) model. The DEB model describes the rates of energy acquisition and expenditure by individual organisms; the toxicity modules describe how toxicants affect these rates by changing the value of one or more DEB parameters, notably the parameters quantifying the rates of feeding and maintenance. We investigate four toxicity modules that assume: (1) effects on feeding only; (2) effects on maintenance only; (3) effects on feeding and maintenance with similar values for the toxicity parameters; and (4) effects on feeding and maintenance with different values for the toxicity parameters. We test the toxicity modules by fitting each to published data on feeding, respiration, growth and reproduction. Among the pollutants tested are metals (mercury and copper) and various organic compounds (chlorophenols, toluene, polycyclic aromatic hydrocarbons, tetradifon and pyridine); organisms include mussels, oysters, earthworms, water fleas and zebrafish. In most cases, the data sets could be adequately described with any of the toxicity modules, and no single module gave superior fits to all data sets. We therefore propose that for many applications, it is reasonable to use the most general and parameter sparse module, i.e. module 3 that assumes similar effects on feeding and maintenance, as a default. For one example (water fleas), we use parameter estimates to calculate the impact of food availability and toxicant levels on the long term population growth rate. PMID:19633955
Modeling the effect of comprehensive interventions on Ebola virus transmission
Shen, Mingwang; Xiao, Yanni; Rong, Libin
2015-01-01
Since the re-emergence of Ebola in West Africa in 2014, comprehensive and stringent interventions have been implemented to decelerate the spread of the disease. The effectiveness of interventions still remains unclear. In this paper, we develop an epidemiological model that includes various controlling measures to systematically evaluate their effects on the disease transmission dynamics. By fitting the model to reported cumulative cases and deaths in Guinea, Sierra Leone and Liberia until March 22, 2015, we estimate the basic reproduction number in these countries as 1.2552, 1.6093 and 1.7994, respectively. Model analysis shows that there exists a threshold of the effectiveness of isolation, below which increasing the fraction of latent individuals diagnosed prior to symptoms onset or shortening the duration between symptoms onset and isolation may lead to more Ebola infection. This challenges an existing view. Media coverage plays a substantial role in reducing the final epidemic size. The response to reported cumulative infected cases and deaths may have a different effect on the epidemic spread in different countries. Among all the interventions, we find that shortening the duration between death and burial and improving the effectiveness of isolation are two effective interventions for controlling the outbreak of Ebola virus infection. PMID:26515898
Three-dimensional effects for radio frequency antenna modeling
NASA Astrophysics Data System (ADS)
Carter, M. D.; Batchelor, D. B.; Stallings, D. C.
1993-09-01
Electromagnetic field calculations for radio frequency (RF) antennas in two dimensions (2-D) neglect finite antenna length effects as well as the feeders leading to the main current strap. Comparisons with experiments indicate that these 2-D calculations can overestimate the loading of the antenna and fail to give the correct reactive behavior. To study the validity of the 2-D approximation, the Multiple Antenna Implementation System (MAntIS) has been used to perform 3-D modeling of the power spectrum, plasma loading, and inductance for a relevant loop antenna design. Effects on antenna performance caused by feeders to the main current strap, conducting sidewalls, and finite phase velocity are considered. The plasma impedance matrix for the loading calculation is generated by use of the ORION-1D code. The 3-D model is benchmarked with the 2-D model in the 2-D limit. For finite-length antennas, inductance calculations are found to be in much more reasonable agreement with experiments for 3-D modeling than for the 2-D estimates. The modeling shows that the feeders affect the launched power spectrum in an indirect way by forcing the driven RF current to return in the antenna sidewalls rather than in the plasma as in the 2-D model. Thus, the feeders have much more influence than the plasma on the currents that return in the sidewall. It has also been found that poloidal dependencies in the plasma impedance matrix can reduce the loading from that predicted in the 2-D model. For some plasma parameters, the combined 3-D effects can lead to a reduction in the predicted loading by as much as a factor of 2 from that given by the 2-D model.
Modeling the effects of conservation practices on stream health.
Einheuser, Matthew D; Nejadhashemi, A Pouyan; Sowa, Scott P; Wang, Lizhu; Hamaamin, Yaseen A; Woznicki, Sean A
2012-10-01
Anthropogenic activities such as agricultural practices can have large effects on the ecological components and overall health of stream ecosystems. Therefore, having a better understanding of those effects and relationships allows for better design of mitigating strategies. The objectives of this study were to identify influential stream variables that correlate with macroinvertebrate indices using biophysical and statistical models. The models developed were later used to evaluate the impact of three agricultural management practices on stream integrity. Our study began with the development of a high-resolution watershed model for the Saginaw River watershed in Michigan for generating in-stream water quality and quantity data at stream reaches with biological sampling data. These in-stream data were then used to explain macroinvertebrate measures of stream health including family index of biological integrity (FamilyIBI), Hilsenhoff biotic index (HBI), and the number of Ephemeroptera, Plecoptera , and Trichoptera taxa (EPTtaxa). Two methods (stepwise linear regression and adaptive neuro-fuzzy inference systems (ANFIS)) were evaluated for developing predictive models for macroinvertebrate measures. The ANFIS method performed the best on average and the final models displayed the highest R(2) and lowest mean squared error (MSE) for FamilyIBI (R(2)=0.50, MSE=29.80), HBI (R(2)=0.57, MSE=0.20), and EPTtaxa (R(2)=0.54, MSE=6.60). Results suggest that nutrient concentrations have the strongest influence on all three macroinvertebrate measures. Consistently, average annual organic nitrogen showed the most significant association with EPTtaxa and HBI. Meanwhile, the best model for FamilyIBI included average annual ammonium and average seasonal organic phosphorus. The ANFIS models were then used in conjunction with the Soil and Water Assessment Tool to forecast and assess the potential effects of different best management practices (no-till, residual management, and native
Three-dimensional effects for radio frequency antenna modeling
Carter, M.D.; Batchelor, D.B.; Stallings, D.C.
1993-09-01
Electromagnetic field calculations for radio frequency (rf) antennas in two dimensions (2-D) neglect finite antenna length effects as well as the feeders leading to the main current strap. Comparisons with experiments indicate that these 2-D calculations can overestimate the loading of the antenna and fail to give the correct reactive behavior. To study the validity of the 2-D approximation, the Multiple Antenna Implementation System (MAntIS) has been used to perform 3-D modeling of the power spectrum, plasma loading, and inductance for a relevant loop antenna design. Effects on antenna performance caused by feeders to the main current strap, conducting sidewalls, and finite phase velocity are considered. The plasma impedance matrix for the loading calculation is generated by use of the ORION-1D code. The 3-D model is benchmarked with the 2-D model in the 2-D limit. For finite-length antennas, inductance calculations are found to be in much more reasonable agreement with experiments for 3-D modeling than for the 2-D estimates. The modeling shows that the feeders affect the launched power spectrum in an indirect way by forcing the driven rf current to return in the antenna sidewalls rather than in the plasma as in the 2-D model. Thus, the feeders have much more influence than the plasma on the currents that return in the sidewall. It has also been found that poloidal dependencies in the plasma impedance matrix can reduce the loading from that predicted in the 2-D model. For some plasma parameters, the combined 3-D effects can lead to a reduction in the predicted loading by as much as a factor of 2 from that given by the 2-D model.
Effects of linking a soil-water-balance model with a groundwater-flow model.
Stanton, Jennifer S; Ryter, Derek W; Peterson, Steven M
2013-01-01
A previously published regional groundwater-flow model in north-central Nebraska was sequentially linked with the recently developed soil-water-balance (SWB) model to analyze effects to groundwater-flow model parameters and calibration results. The linked models provided a more detailed spatial and temporal distribution of simulated recharge based on hydrologic processes, improvement of simulated groundwater-level changes and base flows at specific sites in agricultural areas, and a physically based assessment of the relative magnitude of recharge for grassland, nonirrigated cropland, and irrigated cropland areas. Root-mean-squared (RMS) differences between the simulated and estimated or measured target values for the previously published model and linked models were relatively similar and did not improve for all types of calibration targets. However, without any adjustment to the SWB-generated recharge, the RMS difference between simulated and estimated base-flow target values for the groundwater-flow model was slightly smaller than for the previously published model, possibly indicating that the volume of recharge simulated by the SWB code was closer to actual hydrogeologic conditions than the previously published model provided. Groundwater-level and base-flow hydrographs showed that temporal patterns of simulated groundwater levels and base flows were more accurate for the linked models than for the previously published model at several sites, particularly in agricultural areas.
Effects of linking a soil-water-balance model with a groundwater-flow model
Stanton, Jennifer S.; Ryter, Derek W.; Peterson, Steven M.
2013-01-01
A previously published regional groundwater-flow model in north-central Nebraska was sequentially linked with the recently developed soil-water-balance (SWB) model to analyze effects to groundwater-flow model parameters and calibration results. The linked models provided a more detailed spatial and temporal distribution of simulated recharge based on hydrologic processes, improvement of simulated groundwater-level changes and base flows at specific sites in agricultural areas, and a physically based assessment of the relative magnitude of recharge for grassland, nonirrigated cropland, and irrigated cropland areas. Root-mean-squared (RMS) differences between the simulated and estimated or measured target values for the previously published model and linked models were relatively similar and did not improve for all types of calibration targets. However, without any adjustment to the SWB-generated recharge, the RMS difference between simulated and estimated base-flow target values for the groundwater-flow model was slightly smaller than for the previously published model, possibly indicating that the volume of recharge simulated by the SWB code was closer to actual hydrogeologic conditions than the previously published model provided. Groundwater-level and base-flow hydrographs showed that temporal patterns of simulated groundwater levels and base flows were more accurate for the linked models than for the previously published model at several sites, particularly in agricultural areas.
High-resolution DEM Effects on Geophysical Flow Models
NASA Astrophysics Data System (ADS)
Williams, M. R.; Bursik, M. I.; Stefanescu, R. E. R.; Patra, A. K.
2014-12-01
Geophysical mass flow models are numerical models that approximate pyroclastic flow events and can be used to assess the volcanic hazards certain areas may face. One such model, TITAN2D, approximates granular-flow physics based on a depth-averaged analytical model using inputs of basal and internal friction, material volume at a coordinate point, and a GIS in the form of a digital elevation model (DEM). The volume of modeled material propagates over the DEM in a way that is governed by the slope and curvature of the DEM surface and the basal and internal friction angles. Results from TITAN2D are highly dependent upon the inputs to the model. Here we focus on a single input: the DEM, which can vary in resolution. High resolution DEMs are advantageous in that they contain more surface details than lower-resolution models, presumably allowing modeled flows to propagate in a way more true to the real surface. However, very high resolution DEMs can create undesirable artifacts in the slope and curvature that corrupt flow calculations. With high-resolution DEMs becoming more widely available and preferable for use, determining the point at which high resolution data is less advantageous compared to lower resolution data becomes important. We find that in cases of high resolution, integer-valued DEMs, very high-resolution is detrimental to good model outputs when moderate-to-low (<10-15°) slope angles are involved. At these slope angles, multiple adjacent DEM cell elevation values are equal due to the need for the DEM to approximate the low slope with a limited set of integer values for elevation. The first derivative of the elevation surface thus becomes zero. In these cases, flow propagation is inhibited by these spurious zero-slope conditions. Here we present evidence for this "terracing effect" from 1) a mathematically defined simulated elevation model, to demonstrate the terracing effects of integer valued data, and 2) a real-world DEM where terracing must be
Modeling of Turbulence Effect on Liquid Jet Atomization
NASA Technical Reports Server (NTRS)
Trinh, H. P.
2007-01-01
Recent studies indicate that turbulence behaviors within a liquid jet have considerable effect on the atomization process. Such turbulent flow phenomena are encountered in most practical applications of common liquid spray devices. This research aims to model the effects of turbulence occurring inside a cylindrical liquid jet to its atomization process. The two widely used atomization models Kelvin-Helmholtz (KH) instability of Reitz and the Taylor analogy breakup (TAB) of O'Rourke and Amsden portraying primary liquid jet disintegration and secondary droplet breakup, respectively, are examined. Additional terms are formulated and appropriately implemented into these two models to account for the turbulence effect. Results for the flow conditions examined in this study indicate that the turbulence terms are significant in comparison with other terms in the models. In the primary breakup regime, the turbulent liquid jet tends to break up into large drops while its intact core is slightly shorter than those without turbulence. In contrast, the secondary droplet breakup with the inside liquid turbulence consideration produces smaller drops. Computational results indicate that the proposed models provide predictions that agree reasonably well with available measured data.
Demographic Toxicokinetic-Toxicodynamic Modeling of Lethal Effects.
Gergs, André; Gabsi, Faten; Zenker, Armin; Preuss, Thomas G
2016-06-01
The aquatic effect assessment of chemicals is largely based on standardized measures of toxicity determined in short-term laboratory tests which are designed to reduce variability. For this purpose, uniform individuals of a species are kept under environmental and chemical exposure conditions which are as constant as possible. In nature, exposure often appears to be pulsed, effects might last longer than a few days, sensitivity might vary among different sized organisms and populations are usually size or age structured and are subject to demographic processes. To overcome this discrepancy, we tested toxicokinetic-toxicodynamic models of different complexities, including body size scaling approaches, for their ability to represent lethal effects observed for Daphnia magna exposed to triphenyltin. The consequences of the different toxicokinetic and toxicodynamic assumptions for population level responses to pulsed exposure are tested by means of an individual based model and are evaluated by confronting model predictions with population data for various pulsed exposure scenarios. We provide an example where increased model complexity reduces the uncertainty in model outputs. Furthermore, our results emphasize the importance of considering population demography in toxicokinetics and toxicodynamics for understanding and predicting potential chemical impacts at higher levels of biological organization. PMID:27158745
How to use the Standard Model effective field theory
NASA Astrophysics Data System (ADS)
Henning, Brian; Lu, Xiaochuan; Murayama, Hitoshi
2016-01-01
We present a practical three-step procedure of using the Standard Model effective field theory (SM EFT) to connect ultraviolet (UV) models of new physics with weak scale precision observables. With this procedure, one can interpret precision measurements as constraints on a given UV model. We give a detailed explanation for calculating the effective action up to one-loop order in a manifestly gauge covariant fashion. This covariant derivative expansion method dramatically simplifies the process of matching a UV model with the SM EFT, and also makes available a universal formalism that is easy to use for a variety of UV models. A few general aspects of RG running effects and choosing operator bases are discussed. Finally, we provide mapping results between the bosonic sector of the SM EFT and a complete set of precision electroweak and Higgs observables to which present and near future experiments are sensitive. Many results and tools which should prove useful to those wishing to use the SM EFT are detailed in several appendices.
Neurobehavioral effects of liraglutide and sitagliptin in experimental models.
Kamble, Mayur; Gupta, Rachna; Rehan, Harmeet S; Gupta, Lalit K
2016-03-01
Glucagon-like peptide (GLP-1) receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors are two currently approved therapies for type 2 diabetes mellitus (T2DM). Present study evaluated the effect of liraglutide (a long-acting GLP-1 agonist) and sitagliptin (a DPP-4 inhibitor) on nociception, anxiety, depression-like behavior and cognition in rats or mice. Nociception was assessed using tail-flick test; anxiety-behavior in open-field test and elevated plus maze (EPM) test while depression-like behavior was evaluated in forced swim test (FST) and tail-suspension test (TST). Cognition was assessed in EPM and Morris water maze (MWM) following memory deficit induced by pentylenetetrazole (PTZ) or scopolamine. In tail-flick test sitagliptin (6 mg/kg) produced transient nociceptive effect. Liraglutide (200 µg/kg) reduced peripheral square crossings by rats in open field test as well as reduced closed arm entries in the EPM, indicating a decline in exploratory behavior. In FST and TST models for depression, the duration of immobility with sitagliptin (6 mg/kg) was reduced significantly in comparison to control group suggesting its antidepressant effect. Liraglutide did not show any antidepressant action. In EPM test for cognition, liraglutide and sitagliptin ameliorated the increase in transfer latency caused by PTZ in a dose-dependent manner. In MWM liraglutide and sitagliptin prevented the scopolamine-induced increase of the escape latency. This study shows that sitagliptin has mild antinociceptive effect and anti-depressant effect in the animal models of depression while liraglutide did not have such an effect. Liraglutide showed anxiogenic effects in the animal models. Both liraglutide and sitagliptin produced cognitive improvement in the animal models. PMID:26849938
A Nonlinear Mixed Effects Model for Latent Variables
ERIC Educational Resources Information Center
Harring, Jeffrey R.
2009-01-01
The nonlinear mixed effects model for continuous repeated measures data has become an increasingly popular and versatile tool for investigating nonlinear longitudinal change in observed variables. In practice, for each individual subject, multiple measurements are obtained on a single response variable over time or condition. This structure can be…
Effects of question formats on causal judgments and model evaluation
Smithson, Michael
2015-01-01
Evaluation of causal reasoning models depends on how well the subjects’ causal beliefs are assessed. Elicitation of causal beliefs is determined by the experimental questions put to subjects. We examined the impact of question formats commonly used in causal reasoning research on participant’s responses. The results of our experiment (Study 1) demonstrate that both the mean and homogeneity of the responses can be substantially influenced by the type of question (structure induction versus strength estimation versus prediction). Study 2A demonstrates that subjects’ responses to a question requiring them to predict the effect of a candidate cause can be significantly lower and more heterogeneous than their responses to a question asking them to diagnose a cause when given an effect. Study 2B suggests that diagnostic reasoning can strongly benefit from cues relating to temporal precedence of the cause in the question. Finally, we evaluated 16 variations of recent computational models and found the model fitting was substantially influenced by the type of questions. Our results show that future research in causal reasoning should place a high priority on disentangling the effects of question formats from the effects of experimental manipulations, because that will enable comparisons between models of causal reasoning uncontaminated by method artifact. PMID:25954225
Evidence of Effective Early Numeracy Models. CEELO FastFacts
ERIC Educational Resources Information Center
Schilder, D.
2014-01-01
In this "Fast Facts," a state requested information on supporting districts' use of effective models and approaches to improve children's early literacy and numeracy outcomes. In response, Center on Enhancing Early Learning Outcomes (CEELO) staff reviewed key research including information from the What Works Clearinghouse obtained by…
Facilitative Orthographic Neighborhood Effects: The SERIOL Model Account
ERIC Educational Resources Information Center
Whitney, Carol; Lavidor, Michal
2005-01-01
A large orthographic neighborhood (N) facilitates lexical decision for central and left visual field/right hemisphere (LVF/RH) presentation, but not for right visual field/left hemisphere (RVF/LH) presentation. Based on the SERIOL model of letter-position encoding, this asymmetric N effect is explained by differential activation patterns at the…
A Conceptual Model for Effective Distance Learning in Higher Education
ERIC Educational Resources Information Center
Farajollahi, Mehran; Zare, Hosein; Hormozi, Mahmood; Sarmadi, Mohammad Reza; Zarifsanaee, Nahid
2010-01-01
The present research aims at presenting a conceptual model for effective distance learning in higher education. Findings of this research shows that an understanding of the technological capabilities and learning theories especially constructive theory and independent learning theory and communicative and interaction theory in Distance learning is…
Effects of Modeling Versus Instructions on Sensitivity to Reinforcement Schedules
ERIC Educational Resources Information Center
Neef, Nancy A.; Marckel, Julie; Ferreri, Summer; Jung, Sunhwa; Nist, Lindsay; Armstrong, Nancy
2004-01-01
This study examined the effects of modeling versus instructions on the choices of 3 typically developing children and 3 children with attention deficit hyperactivity disorder (ADHD) whose academic responding showed insensitivity to reinforcement schedules. During baseline, students chose between successively presented pairs of mathematics problems…
Numbers and Space: A Computational Model of the SNARC Effect
ERIC Educational Resources Information Center
Gevers, Wim; Verguts, Tom; Reynvoet, Bert; Caessens, Bernie; Fias, Wim
2006-01-01
The SNARC (spatial numerical associations of response codes) effect reflects the tendency to respond faster with the left hand to relatively small numbers and with the right hand to relatively large numbers (S. Dehaene, S. Bossini, & P. Giraux, 1993). Using computational modeling, the present article aims to provide a framework for conceptualizing…
Maximizing the Effectiveness of Leadership Inservice Education: An Operational Model.
ERIC Educational Resources Information Center
Sommerville, Joseph C.
This paper includes a functional model for upgrading the effectiveness of inservice training for school administrators. It is based on the writer's contention that most inservice programs for administrators do not relate to the leadership concerns of each participant, skills developed in those programs often are not applied to the participant's…
Effects of question formats on causal judgments and model evaluation.
Shou, Yiyun; Smithson, Michael
2015-01-01
Evaluation of causal reasoning models depends on how well the subjects' causal beliefs are assessed. Elicitation of causal beliefs is determined by the experimental questions put to subjects. We examined the impact of question formats commonly used in causal reasoning research on participant's responses. The results of our experiment (Study 1) demonstrate that both the mean and homogeneity of the responses can be substantially influenced by the type of question (structure induction versus strength estimation versus prediction). Study 2A demonstrates that subjects' responses to a question requiring them to predict the effect of a candidate cause can be significantly lower and more heterogeneous than their responses to a question asking them to diagnose a cause when given an effect. Study 2B suggests that diagnostic reasoning can strongly benefit from cues relating to temporal precedence of the cause in the question. Finally, we evaluated 16 variations of recent computational models and found the model fitting was substantially influenced by the type of questions. Our results show that future research in causal reasoning should place a high priority on disentangling the effects of question formats from the effects of experimental manipulations, because that will enable comparisons between models of causal reasoning uncontaminated by method artifact.
Performance of Random Effects Model Estimators under Complex Sampling Designs
ERIC Educational Resources Information Center
Jia, Yue; Stokes, Lynne; Harris, Ian; Wang, Yan
2011-01-01
In this article, we consider estimation of parameters of random effects models from samples collected via complex multistage designs. Incorporation of sampling weights is one way to reduce estimation bias due to unequal probabilities of selection. Several weighting methods have been proposed in the literature for estimating the parameters of…
The Coriolis Effect: A Model for Student Involvement
ERIC Educational Resources Information Center
Exline, Joseph D.
1977-01-01
Lists materials and procedures for constructing a model that demonstrates certain aspects of the Coriolis effect. Materials include an electric drill motor, voltage control, toy dart gun and darts, wood blocks of varying dimensions. Includes description of an experiment illustrating relationship between speed of rotation and amount of apparent…
An Integrated Model for Effective Knowledge Management in Chinese Organizations
ERIC Educational Resources Information Center
An, Xiaomi; Deng, Hepu; Wang, Yiwen; Chao, Lemen
2013-01-01
Purpose: The purpose of this paper is to provide organizations in the Chinese cultural context with a conceptual model for an integrated adoption of existing knowledge management (KM) methods and to improve the effectiveness of their KM activities. Design/methodology/approaches: A comparative analysis is conducted between China and the western…
A Computer Model of the Cardiovascular System for Effective Learning.
ERIC Educational Resources Information Center
Rothe, Carl F.
1979-01-01
Described is a physiological model which solves a set of interacting, possibly nonlinear, differential equations through numerical integration on a digital computer. Sample printouts are supplied and explained for effects on the components of a cardiovascular system when exercise, hemorrhage, and cardiac failure occur. (CS)
The Random-Effect Generalized Rating Scale Model
ERIC Educational Resources Information Center
Wang, Wen-Chung; Wu, Shiu-Lien
2011-01-01
Rating scale items have been widely used in educational and psychological tests. These items require people to make subjective judgments, and these subjective judgments usually involve randomness. To account for this randomness, Wang, Wilson, and Shih proposed the random-effect rating scale model in which the threshold parameters are treated as…
Key Elements of Effective Teaching in the Direct Teaching Model.
ERIC Educational Resources Information Center
Bruning, Roger H.
Summaries and outlines are presented of key elements in effective teaching identified in research studies by Kounin (1970), Brophy (1973), Brophy and Evertson (1976), Stallings (1974; l975), Berliner (1979), and Good and Grouws (1979). These elements are synthesized in a direct teaching model that delineates the characteristics of effective…
Order Effects in Belief Updating: The Belief-Adjustment Model.
ERIC Educational Resources Information Center
Hogarth, Robin M.; Einhorn, Hillel J.
1992-01-01
A theory of the updating of beliefs over time is presented that explicitly accounts for order-effect phenomena as arising from the interaction of information-processing strategies and task characteristics. The belief-adjustment model is supported by 5 experiments involving 192 adult subjects. (SLD)
The Theoretical Basis of the Effective School Improvement Model (ESI)
ERIC Educational Resources Information Center
Scheerens, Jaap; Demeuse, Marc
2005-01-01
This article describes the process of theoretical reflection that preceded the development and empirical verification of a model of "effective school improvement". The focus is on basic mechanisms that could be seen as underlying "getting things in motion" and change in education systems. Four mechanisms are distinguished: synoptic rational…
Modeling Health Insurance Expansions: Effects of Alternate Approaches
ERIC Educational Resources Information Center
Remler, Dahlia K.; Zivin, Joshua Graff; Glied, Sherry A.
2004-01-01
Estimates of the costs and consequences of many types of public policy proposals play an important role in the development and adoption of particular policy programs. Estimates of the same, or similar, policies that employ different modeling approaches can yield widely divergent results. Such divergence often undermines effective policymaking.…
Conceptual Models and Theory-Embedded Principles on Effective Schooling.
ERIC Educational Resources Information Center
Scheerens, Jaap
1997-01-01
Reviews models and theories on effective schooling. Discusses four rationality-based organization theories and a fifth perspective, chaos theory, as applied to organizational functioning. Discusses theory-embedded principles flowing from these theories: proactive structuring, fit, market mechanisms, cybernetics, and self-organization. The…
Effects of Cueing and Modeling Variables in Teacher Training Systems.
ERIC Educational Resources Information Center
Orme, Michael E. J.
Theoretical considerations suggest that the differential effectiveness of teaching models and associated feedback procedures stems from their distinctive cueing properties. This led to the development of three treatment conditions which may be labeled "rating" (rehearsal of key discriminations), "observation" vicarious reinforcement), and "direct…
Developing a More Effective Recruitment and Retention Model.
ERIC Educational Resources Information Center
Janke, Walter; Kelly, Gary
The purpose of a project was to develop a model for more effective recruitment and retention of people of color in the Associate Degree Interior Design and Diploma Interior Design Assistant Program at Milwaukee Area Technical College (MATC), Wisconsin. During Activity One, individuals in MATC's Student Development and High School Relations…
Defining Teacher Effectiveness on a Continuum: A Rasch Model Approach.
ERIC Educational Resources Information Center
Burry, Judith A.; Shaw, Dale
The Rasch rating scale model was used to provide diagnostic information about a teacher effectiveness instrument, the Inventory of Myself as a Professional (IMP). Two forms of the instrument, a self-report form to be completed by the teacher and an observation form to be completed by a supervisor or administrator contained the same thirty-six…
The effect of nonstationarity on models inferred from neural data
NASA Astrophysics Data System (ADS)
Tyrcha, Joanna; Roudi, Yasser; Marsili, Matteo; Hertz, John
2013-03-01
Neurons subject to a common nonstationary input may exhibit a correlated firing behavior. Correlations in the statistics of neural spike trains also arise as the effect of interaction between neurons. Here we show that these two situations can be distinguished with machine learning techniques, provided that the data are rich enough. In order to do this, we study the problem of inferring a kinetic Ising model, stationary or nonstationary, from the available data. We apply the inference procedure to two data sets: one from salamander retinal ganglion cells and the other from a realistic computational cortical network model. We show that many aspects of the concerted activity of the salamander retinal neurons can be traced simply to the external input. A model of non-interacting neurons subject to a nonstationary external field outperforms a model with stationary input with couplings between neurons, even accounting for the differences in the number of model parameters. When couplings are added to the nonstationary model, for the retinal data, little is gained: the inferred couplings are generally not significant. Likewise, the distribution of the sizes of sets of neurons that spike simultaneously and the frequency of spike patterns as a function of their rank (Zipf plots) are well explained by an independent-neuron model with time-dependent external input, and adding connections to such a model does not offer significant improvement. For the cortical model data, robust couplings, well correlated with the real connections, can be inferred using the nonstationary model. Adding connections to this model slightly improves the agreement with the data for the probability of synchronous spikes but hardly affects the Zipf plot.
Modeling Hysteresis Effect in Three-Phase Relative Permeability
NASA Astrophysics Data System (ADS)
Kianinejad, A.; Chen, X.; DiCarlo, D. A.
2014-12-01
Simulation and fluid flow prediction of many petroleum enhanced oil recovery methods as well as environmental processes such as carbon dioxide (CO2) geological storage requires accurate modeling and determination of relative permeability under different saturation histories. Based on this critical need, there has been several different three-phase relative permeability models developed to predict the hysteresis effects in relative permeability, most of which requiring many different parameters which introduce extreme complexity to the models for practical purposes. In this work, we experimentally measured three-phase, water/oil/gas, relative permeability in a 1-m long water-wet sand pack, under several different flow histories. We measured the in-situ saturations along the sand pack using a CT scanner. We then determined the relative permeabilities directly from the measured in-situ saturations, using unsteady-state method. Based on our results, good estimation of residual saturations yields in excellent three-phase relative permeability estimations by just using the simple, standard relative permeability models such as, Saturation Weighted Interpolation (SWI), Corey's and Stones. Our results show that, the key parameter to model the hysteresis in three-phase relative permeability (effect of saturation history) is the residual saturations. Once the residual saturations were correctly determined for each specific saturation path, the standard relative permeability models can predict the three-phase relative permeabilities perfectly.
Effects of subgrid-scale modeling on wind turbines flows
NASA Astrophysics Data System (ADS)
Ciri, Umberto; Salvetti, Maria Vittoria; Leonardi, Stefano
2015-11-01
The increased demand for wind energy had led to a continuous increase in the size of wind turbines and, consequently, of wind farms. A potential drawback of such large clusters lies in the decrease in the efficiency due to the wake interference. Large-Eddy Simulations (LES) coupled with blade models have shown the capability of resolving the unsteady nature of wind turbine wakes. In LES, subgrid-scale (SGS) models are needed to introduce the effect of the turbulence small scales not resolved by the computational grid. Many LES of wind farms employ the classic Smagorinsky model, despite it suffers from some major drawbacks, e.g. (i) the presence of an input tuning parameter and (ii) the wrong behaviour near solid walls. In the present work an analysis of the effects of various SGS models is carried out for LES in which the turbine tower and nacelle are directly simulated with the Immersed Boundaries method. Particular attention is dedicated to the region of separated flow behind the tower where the impact of the SGS models is expected to be important. We focus herein on non-dynamic eddy-viscosity models, which have proven to have a correct behaviour near solid walls. A priori and a posteriori tests are performed for a configuration reproducing an experiment conducted at NTNU. The work is partially supported by the NSF PIRE Award IIA 1243482. TACC is acknowledged for providing computational time.
Compact model for switching characteristics of graphene field effect transistor
NASA Astrophysics Data System (ADS)
Sreenath, R.; Bala Tripura Sundari, B.
2016-04-01
The scaling of CMOS transistors has resulted in intensified short channel effects, indicating that CMOS has reached its physical limits. Alternate non silicon based materials namely carbon based graphene, carbon nanotubes are being explored for usability as channel and interconnect material due to their established higher mobility and robustness. This paper presents a drift-diffusion based circuit simulatable Verilog-A compact model of graphene field effect transistor (GFET) for channel length of 100nm.The focus is on the development of simulatable device model in Verilog A based on intrinsic parameters and obtain the current, high cutoff frequency and use the model into circuit level simulations to realize an inverter and a 3-stage ring oscillator using Synopsys HSPICE. The applications are so chosen that their switching characteristics enable the determination of the RF frequency ranges of operation that the model can achieve when used in digital applications and also to compare its performance with existing CMOS model. The GFET's switching characteristics and power consumption were found to be better than similarly sized CMOS operating at same range of voltages. The basic frequency of operation in the circuit is of significant importance so as to use the model in other applications at RF and in future for millimeter wave applications. The frequency of operation at circuit level is found to be 1.1GHz at 100nm which is far higher than the existing frequency of 245 MHz reported at 500nm using AlN.
Transmission Model of Hepatitis B Virus with the Migration Effect
Khan, Muhammad Altaf; Islam, Saeed; Arif, Muhammad; ul Haq, Zahoor
2013-01-01
Hepatitis B is a globally infectious disease. Mathematical modeling of HBV transmission is an interesting research area. In this paper, we present characteristics of HBV virus transmission in the form of a mathematical model. We analyzed the effect of immigrants in the model to study the effect of immigrants for the host population. We added the following flow parameters: “the transmission between migrated and exposed class” and “the transmission between migrated and acute class.” With these new features, we obtained a compartment model of six differential equations. First, we find the basic threshold quantity Ro and then find the local asymptotic stability of disease-free equilibrium and endemic equilibrium. Furthermore, we find the global stability of the disease-free and endemic equilibria. Previous similar publications have not added the kind of information about the numerical results of the model. In our case, from numerical simulation, a detailed discussion of the parameters and their numerical results is presented. We claim that with these assumptions and by adding the migrated class, the model informs policy for governments, to be aware of the immigrants and subject them to tests about the disease status. Immigrants for short visits and students should be subjected to tests to reduce the number of immigrants with disease. PMID:23984318
Three-dimensional Model of Tissue and Heavy Ions Effects
NASA Technical Reports Server (NTRS)
Ponomarev, Artem L.; Sundaresan, Alamelu; Huff, Janice L.; Cucinotta, Francis A.
2007-01-01
A three-dimensional tissue model was incorporated into a new Monte Carlo algorithm that simulates passage of heavy ions in a tissue box . The tissue box was given as a realistic model of tissue based on confocal microscopy images. The action of heavy ions on the cellular matrix for 2- or 3-dimensional cases was simulated. Cells were modeled as a cell culture monolayer in one example, where the data were taken directly from microscopy (2-d cell matrix), and as a multi-layer obtained from confocal microscopy (3-d case). Image segmentation was used to identify cells with precise areas/volumes in an irradiated cell culture monolayer, and slices of tissue with many cell layers. The cells were then inserted into the model box of the simulated physical space pixel by pixel. In the case of modeled tissues (3-d), the tissue box had periodic boundary conditions imposed, which extrapolates the technique to macroscopic volumes of tissue. For the real tissue (3-d), specific spatial patterns for cell apoptosis and necrosis are expected. The cell patterns were modeled based on action cross sections for apoptosis and necrosis estimated from current experimental data. A spatial correlation function indicating a higher spatial concentration of damaged cells from heavy ions relative to the low-LET radiation cell damage pattern is presented. The spatial correlation effects among necrotic cells can help studying microlesions in organs, and probable effects of directionality of heavy ion radiation on epithelium and endothelium.
GENERALIZED PARTIALLY LINEAR MIXED-EFFECTS MODELS INCORPORATING MISMEASURED COVARIATES
Liang, Hua
2009-01-01
In this article we consider a semiparametric generalized mixed-effects model, and propose combining local linear regression, and penalized quasilikelihood and local quasilikelihood techniques to estimate both population and individual parameters and nonparametric curves. The proposed estimators take into account the local correlation structure of the longitudinal data. We establish normality for the estimators of the parameter and asymptotic expansion for the estimators of the nonparametric part. For practical implementation, we propose an appropriate algorithm. We also consider the measurement error problem in covariates in our model, and suggest a strategy for adjusting the effects of measurement errors. We apply the proposed models and methods to study the relation between virologic and immunologic responses in AIDS clinical trials, in which virologic response is classified into binary variables. A dataset from an AIDS clinical study is analyzed. PMID:20160899
The generation effect and the modeling of associations in memory.
Clark, S E
1995-07-01
The search of associative memory (SAM) model of Gillund and Shiffrin (1984) was applied to data of two experiments that examined the generation effect (Slamecka & Graf, 1978). Subjects studied a list of related word pairs, in which they either read both words in the pair or generated the right- hand response term using the left-hand stimulus term plus the response word fragment as generation cues. Experiment 1 manipulated encoding condition within subjects and used an incidental learning procedure. Experiment 2 manipulated encoding condition between subjects and used an intentional learning procedure. Memory was tested with recognition, cued recall, and free recall. A higher order association model gave a better and more parsimonious fit to the results than did an item-level association model. The relationship between various versions of SAM and current accounts of the generation effect are discussed, particulary the two-factor theory of Hirshman and Bjork (1988). PMID:7666757
Modelling the effect of acoustic waves on nucleation
NASA Astrophysics Data System (ADS)
Haqshenas, S. R.; Ford, I. J.; Saffari, N.
2016-07-01
A phase transformation in a metastable phase can be affected when it is subjected to a high intensity ultrasound wave. In this study we determined the effect of oscillation in pressure and temperature on a phase transformation using the Gibbs droplet model in a generic format. The developed model is valid for both equilibrium and non-equilibrium clusters formed through a stationary or non-stationary process. We validated the underlying model by comparing the predicted kinetics of water droplet formation from the gas phase against experimental data in the absence of ultrasound. Our results demonstrated better agreement with experimental data in comparison with classical nucleation theory. Then, we determined the thermodynamics and kinetics of nucleation and the early stage of growth of clusters in an isothermal sonocrystallisation process. This new contribution shows that the effect of pressure on the kinetics of nucleation is cluster size-dependent in contrast to classical nucleation theory.
Hawking effect in dielectric media and the Hopfield model
NASA Astrophysics Data System (ADS)
Belgiorno, F.; Cacciatori, S. L.; Dalla Piazza, F.
2015-06-01
We consider the so-called Hopfield model for the electromagnetic field in a dielectric dispersive medium in a framework in which one allows a space-time dependence of microscopic parameters, aimed at a phenomenological description of a space-time varying dielectric perturbation induced by means of the Kerr effect. We discuss the analogue Hawking effect by introducing a simplified model which avoids some difficulties which characterize in the full Hopfield model, still keeping the same dispersion relation. Our main result is an analytical calculation of the spontaneous thermal emission in the single-branch case, which is provided nonperturbatively for the first time in the framework of dielectric black holes. A universal mechanism for thermality which is shared both by optical black holes and acoustic black holes is also pointed out.
Modelling the effect of acoustic waves on nucleation.
Haqshenas, S R; Ford, I J; Saffari, N
2016-07-14
A phase transformation in a metastable phase can be affected when it is subjected to a high intensity ultrasound wave. In this study we determined the effect of oscillation in pressure and temperature on a phase transformation using the Gibbs droplet model in a generic format. The developed model is valid for both equilibrium and non-equilibrium clusters formed through a stationary or non-stationary process. We validated the underlying model by comparing the predicted kinetics of water droplet formation from the gas phase against experimental data in the absence of ultrasound. Our results demonstrated better agreement with experimental data in comparison with classical nucleation theory. Then, we determined the thermodynamics and kinetics of nucleation and the early stage of growth of clusters in an isothermal sonocrystallisation process. This new contribution shows that the effect of pressure on the kinetics of nucleation is cluster size-dependent in contrast to classical nucleation theory. PMID:27421413
Rotenberg, Ken J; Carte, Laura; Speirs, Amanda
2005-01-01
Sixty-nine female undergraduates completed the restraint scale, a dieting checklist, and the Eating Attribution Style Questionnaire (EASQ). The participants were exposed either to no model, a peer model who behaviorally demonstrated dietary restraint, or a peer model who behaviorally and verbally demonstrated dietary restraint. The participants had an opportunity to consume food as part of a taste test. The findings revealed that attribution style, but not restraint or current dieting status, moderated the effects of exposure to the peer models. Females who had an internal attribution style for indulgent food consumption decreased their consumption of food as a function of the dietary restraint of the models, whereas females who had an external attribution style for indulgent food consumption increased their consumption of food as a function of the dietary restraint of the models. The latter disinhibitory effect was attributed to negative social comparison and learned helplessness. The results supported the conclusion that the effectiveness of modeling dietary restraint is dependent on the attribution style of the observers. PMID:15567113
NASA Astrophysics Data System (ADS)
Fennel, Katja; Laurent, Arnaud; Hetland, Robert; Justić, Dubravko; Ko, Dong S.; Lehrter, John; Murrell, Michael; Wang, Lixia; Yu, Liuqian; Zhang, Wenxia
2016-08-01
A large hypoxic zone forms every summer on the Texas-Louisiana Shelf in the northern Gulf of Mexico due to nutrient and freshwater inputs from the Mississippi/Atchafalaya River System. Efforts are underway to reduce the extent of hypoxic conditions through reductions in river nutrient inputs, but the response of hypoxia to such nutrient load reductions is difficult to predict because biological responses are confounded by variability in physical processes. The objective of this study is to identify the major physical model aspects that matter for hypoxia simulation and prediction. In order to do so, we compare three different circulation models (ROMS, FVCOM, and NCOM) implemented for the northern Gulf of Mexico, all coupled to the same simple oxygen model, with observations and against each other. By using a highly simplified oxygen model, we eliminate the potentially confounding effects of a full biogeochemical model and can isolate the effects of physical features. In a systematic assessment, we found that (1) model-to-model differences in bottom water temperatures result in differences in simulated hypoxia because temperature influences the uptake rate of oxygen by the sediments (an important oxygen sink in this system), (2) vertical stratification does not explain model-to-model differences in hypoxic conditions in a straightforward way, and (3) the thickness of the bottom boundary layer, which sets the thickness of the hypoxic layer in all three models, is key to determining the likelihood of a model to generate hypoxic conditions. These results imply that hypoxic area, the commonly used metric in the northern Gulf which ignores hypoxic layer thickness, is insufficient for assessing a model's ability to accurately simulate hypoxia, and that hypoxic volume needs to be considered as well.
Flombaum, Pedro; Sala, Osvaldo E; Rastetter, Edward B
2014-02-01
Resource partitioning, facilitation, and sampling effect are the three mechanisms behind the biodiversity effect, which is depicted usually as the effect of plant-species richness on aboveground net primary production. These mechanisms operate simultaneously but their relative importance and interactions are difficult to unravel experimentally. Thus, niche differentiation and facilitation have been lumped together and separated from the sampling effect. Here, we propose three hypotheses about interactions among the three mechanisms and test them using a simulation model. The model simulated water movement through soil and vegetation, and net primary production mimicking the Patagonian steppe. Using the model, we created grass and shrub monocultures and mixtures, controlled root overlap and grass water-use efficiency (WUE) to simulate gradients of biodiversity, resource partitioning and facilitation. The presence of shrubs facilitated grass growth by increasing its WUE and in turn increased the sampling effect, whereas root overlap (resource partitioning) had, on average, no effect on sampling effect. Interestingly, resource partitioning and facilitation interacted so the effect of facilitation on sampling effect decreased as resource partitioning increased. Sampling effect was enhanced by the difference between the two functional groups in their efficiency in using resources. Morphological and physiological differences make one group outperform the other; once these differences were established further differences did not enhance the sampling effect. In addition, grass WUE and root overlap positively influence the biodiversity effect but showed no interactions.
Physical model of bathymetric effects on the Antarctic circumpolar current
Boyer, D.L.; Ruirong Chen; Lijun Tao ); Davies, P.A. )
1993-02-15
Laboratory experiments were conducted to simulate some of the effects of the bathymetry of the southern ocean on the physical characteristics of the Antarctic Circumpolar Current (ACC). An idealized zonal wind stress, which varied inversely with the distance from the model Antarctic continent, was simulated in the laboratory model by a radially inward sink-source flow in a thin layer along the surface of the circular test cell. The present model, however, has the limitation of not accounting for such factors as the longitudinal variations in the wind shear and the decrease in wind stress on approaching the Antarctic continent from the north. Planetary beta effects were neglected because the topographic beta term can be shown to dominate over large portions of the model area. The neglect of beta effects is also a limitation of the model. In spite of these limitations, however, the simulations of the physical model for both the homogeneous and linearly stratified cases were shown to be in good agreement with observations of the ACC. These include well-defined strong currents along the mid-ocean ridge; strong perturbations in the vicinity of the Macquarie Ridge, Campbell Plateau, and Kerguelen Gaussberg Plateau; strong meridional transport to the east of the Drake Passage; and anomalies to the south (wave troughs) and to the north (wave ridges) of the main circumpolar current over ocean basins and mountain ridges, respectively. It was shown that the Eltanin and Udintsev fracture zones in the vicinity of 135[degrees]W are important factors in directing the ACC eastward across the Southeast Pacific Basin to the Drake Passage. The estimated volume transports through the Drake Passage based on the model results are in fair agreement with oceanic observations. Estimates of the spin-up time of the system for homogeneous and stratified cases have been provided. 28 refs., 21 figs., 1 tab.
Global dynamics of avian influenza epidemic models with psychological effect.
Liu, Sanhong; Pang, Liuyong; Ruan, Shigui; Zhang, Xinan
2015-01-01
Cross-sectional surveys conducted in Thailand and China after the outbreaks of the avian influenza A H5N1 and H7N9 viruses show a high degree of awareness of human avian influenza in both urban and rural populations, a higher level of proper hygienic practice among urban residents, and in particular a dramatically reduced number of visits to live markets in urban population after the influenza A H7N9 outbreak in China in 2013. In this paper, taking into account the psychological effect toward avian influenza in the human population, a bird-to-human transmission model in which the avian population exhibits saturation effect is constructed. The dynamical behavior of the model is studied by using the basic reproduction number. The results demonstrate that the saturation effect within avian population and the psychological effect in human population cannot change the stability of equilibria but can affect the number of infected humans if the disease is prevalent. Numerical simulations are given to support the theoretical results and sensitivity analyses of the basic reproduction number in terms of model parameters that are performed to seek for effective control measures for avian influenza.
Effective Thermal Conductivity Modeling of Sandstones: SVM Framework Analysis
NASA Astrophysics Data System (ADS)
Rostami, Alireza; Masoudi, Mohammad; Ghaderi-Ardakani, Alireza; Arabloo, Milad; Amani, Mahmood
2016-06-01
Among the most significant physical characteristics of porous media, the effective thermal conductivity (ETC) is used for estimating the thermal enhanced oil recovery process efficiency, hydrocarbon reservoir thermal design, and numerical simulation. This paper reports the implementation of an innovative least square support vector machine (LS-SVM) algorithm for the development of enhanced model capable of predicting the ETCs of dry sandstones. By means of several statistical parameters, the validity of the presented model was evaluated. The prediction of the developed model for determining the ETCs of dry sandstones was in excellent agreement with the reported data with a coefficient of determination value ({R}2) of 0.983 and an average absolute relative deviation of 0.35 %. Results from present research show that the proposed LS-SVM model is robust, reliable, and efficient in calculating the ETCs of sandstones.
Effective-field-theory model for the fractional quantum Hall effect
NASA Technical Reports Server (NTRS)
Zhang, S. C.; Hansson, T. H.; Kivelson, S.
1989-01-01
Starting directly from the microscopic Hamiltonian, a field-theory model is derived for the fractional quantum Hall effect. By considering an approximate coarse-grained version of the same model, a Landau-Ginzburg theory similar to that of Girvin (1986) is constructed. The partition function of the model exhibits cusps as a function of density. It is shown that the collective density fluctuations are massive.
Examples of Mixed-Effects Modeling with Crossed Random Effects and with Binomial Data
ERIC Educational Resources Information Center
Quene, Hugo; van den Bergh, Huub
2008-01-01
Psycholinguistic data are often analyzed with repeated-measures analyses of variance (ANOVA), but this paper argues that mixed-effects (multilevel) models provide a better alternative method. First, models are discussed in which the two random factors of participants and items are crossed, and not nested. Traditional ANOVAs are compared against…
Effects of Tidal Modulation in Heterogeneous Models of Slow Slip
NASA Astrophysics Data System (ADS)
Skarbek, R. M.; Rempel, A. W.; Thomas, A.
2014-12-01
Since their discovery, numerous models have been put forward to explain the occurance of slow slip and associated tremor. These models invoke a wide array of causal mechanisms and are all successful in reproducing the first-order behavior of slow-slip events. Discriminating amongst the various proposed models requires looking at second-order effects of slow slip and tremor. Here, we consider the effects of tidal modulation on slow slip in subduction zones. A great deal of observational evidence has established that slow-slip and associated tremor are modulated by the small stress perturbations associated with tides and teleseismic events. Recent modeling studies that have examined the influence of tidal stresses (<10 kPa) have focused either on the effects of tidally induced changes in shear stress, or on changes in shear and normal stress that coincide. However, along the Cascadia margin, the relative phase of the tidally induced fault-normal and shear stresses depends on position along the plate boundary fault, and can vary from being in phase, to completely out of phase. We report on the predictions of models designed to examine the sensitivity of slow-slip in subduction zones to the phase shift γ between tidally induced normal and shear stress perturbations. We consider both simple spring-slider and 1-D elastodynamic models that are designed to mimic the effects of geologic heterogeneity by allowing for variations in the rate-and-state frictional parameters. For a given slow-slip event, spring-slider results indicate that the phase lag γv between the peak slip rate and the tidally induced shear stress perturbation depends on both the phase shift γ, and the perturbation amplitude. Models parameterized for Cascadia are capable of producing phase lags γv within the range (15◦ to 30◦) of those reported by Royer et al. (JGR, 2014). Additionally, our models predict that the correlation between tidally induced shear stress perturbations and resultant slip also
Circuit models and SPICE macro-models for quantum Hall effect devices
NASA Astrophysics Data System (ADS)
Ortolano, Massimo; Callegaro, Luca
2015-08-01
Precise electrical measurement technology based on the quantum Hall effect is one of the pillars of modern quantum electrical metrology. Electrical networks including one or more QHE elements can be used as quantum resistance and impedance standards. The analysis of these networks allows metrologists to evaluate the effect of the inevitable parasitic parameters on their performance as standards. This paper presents a concise review of the various circuit models for QHE elements proposed in the literature, and the development of a new model. This last model is particularly suited to be employed with the analogue electronic circuit simulator SPICE. The SPICE macro-model and examples of SPICE simulations, validated by comparison with the corresponding analytical solution and/or experimental data, are provided.
Modeling age-of-onset: Cox model with latent major gene effects
Li, H.; Thompson, E.A.
1994-09-01
Analysis of age-of-onset is a key factor in the segregation and linkage analysis of complex genetic traits, but is complicated by the censoring of unaffected individuals. Most previous work has used parametric distributional assumptions, but it is hard to characterize the distribution of age-of-onset by a single distribution. Other approaches discretize age-of-onset and use logistic regression to model incidence; this approach does not use the information fully. Frailty models have been used for age-of-oset in the biostatistics literature, but these models do not lend themselves to modeling the correlations due to genetic effects which segregate within a family. Here, we propose use of the Cox model with latent major gene effects; conditional on the major genotypes, Cox`s proportional hazards model is used for age-of-onset for each individual. This is a semiparametric model; we do not specify the baseline hazard function. Likelihood analysis of such models is restricted by the difficulty in evaluating of maximizing the likelihood, especially when data are available for some of the members of an extended pedigree. Markov chain Monte Carlo permits genotypic configurations to be realized from the posterior distributions given a current model and the observed data. Hence methods for likelihood analysis can be developed: Monte Carlo EM is used for estimation of the parameters and their variance-covariance matrix. Markers and observed covariates are easily incorporated into this analysis. We present the model, methods for likelihood analysis and the results of a simulation study. The results are comparable with those based on a Cox model with known genotypic dependence in a pedigree. An early-onset Alzheimer`s pedigree and some breast cancer pedigrees have been used as real data examples. Some possible extensions are also discussed.
Shiyko, Mariya P.; Burkhalter, Jack; Li, Runze; Park, Bernard J.
2014-01-01
Objective The goal of this paper is to introduce to social and behavioral scientists the generalized time-varying effect model (TVEM), a semi-parametric approach for investigating time-varying effects of a treatment. The method is best suited for data collected intensively over time, e.g., experience sampling or ecological momentary assessment, and addresses questions pertaining to effects of treatment changing dynamically with time. Thus, of interest is the description of timing, magnitude, and (non-linear) pattern of the effect. Method Our presentation focuses on practical aspects of the model. A step-by step demonstration is presented in the context of an empirical study designed to evaluate effects of surgical treatment on quality of life among early stage lung cancer patients during post-hospitalization recovery (N = 59, 61% female, Mean age = 66.1). Frequency and level of distress associated with physical symptoms were assessed twice daily over a two-week period, providing a total of 1,544 momentary assessments. Results Traditional analyses (ANCOVA, repeated-measures ANCOVA, and multilevel modeling) yielded findings of no group differences. In contrast, generalized TVEM identified a pattern of the effect that varied in time and magnitude. Group differences manifested after day four. Conclusions Generalized TVEM is a flexible statistical approach that offers insight into the complexity of treatment effects and allows modeling of non-normal outcomes. The practical demonstration, shared syntax, and availability of a free set of macros aim to encourage researchers to apply TVEM to complex data and stimulate important scientific discoveries. PMID:24364799
A simple mechanistic model to interpret the effects of narcotics.
Baas, J; Spurgeon, D; Broerse, M
2015-01-01
In this research we will show the advantages of using a time-independent dose metric in a mechanistic model to evaluate toxic effects for different narcotic compounds on different species. We will show how different already existing QSARs can be combined within a mechanistic framework to 1) make predictions of lethal thresholds; 2) show some limitations in the use of existing QSARs; 3) show how a mechanistic framework solves some conceptual problems in current approaches and 4) show how such a framework can be used to be of aid in an experimental setup in predicting the outcome of a survival experiment. The approach we chose is based on the simplest mechanistic model available, a scaled one-compartment model to describe uptake and elimination and hazard model to link the exposure to effects on survival. Within this theoretical framework a prediction for an internal threshold for effects on survival of 3 mmol/kg bw can be made, which should be similar for different species and independent of the partitioning characteristics of the toxicant. To demonstrate this, a threshold for 51 different species was derived, which indeed appeared to lie in a relatively small range, typically between 1 and 10 mmol/kg bw.
Modeling electron emission and surface effects from diamond cathodes
Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.
2015-02-05
We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transversemore » electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. In this study, using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.« less
Modeling electron emission and surface effects from diamond cathodes
Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.
2015-02-05
We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. In this study, using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.
New calculations in Dirac gaugino models: operators, expansions, and effects
NASA Astrophysics Data System (ADS)
Carpenter, Linda M.; Goodman, Jessica
2015-07-01
In this work we calculate important one loop SUSY-breaking parameters in models with Dirac gauginos, which are implied by the existence of heavy messenger fields. We find that these SUSY-breaking effects are all related by a small number of parameters, thus the general theory is tightly predictive. In order to make the most accurate analyses of one loop effects, we introduce calculations using an expansion in SUSY breaking messenger mass, rather than relying on postulating the forms of effective operators. We use this expansion to calculate one loop contributions to gaugino masses, non-holomorphic SM adjoint masses, new A-like and B-like terms, and linear terms. We also test the Higgs potential in such models, and calculate one loop contributions to the Higgs mass in certain limits of R-symmetric models, finding a very large contribution in many regions of the [InlineMediaObject not available: see fulltext.], where Higgs fields couple to standard model adjoint fields.
Numerical modeling of ductile tearing effects on cleavage fracture toughness
Dodds, R.H. Jr.; Tang, M.; Anderson, T.L.
1994-05-01
Experimental studies demonstrate a significant effect of specimen size, a/W ratio and prior ductile tearing on cleavage fracture toughness values (J{sub c}) measured in the ductile-to-brittle transition region of ferritic materials. In the lower-transition region, cleavage fracture often occurs under conditions of large-scale yielding but without prior ductile crack extension. The increased toughness develops when plastic zones formed at the crack tip interact with nearby specimen surfaces which relaxes crack-tip constraint (stress triaxiality). In the mid-to-upper transition region, small amounts of ductile crack extension (often < 1-2 mm) routinely precede termination of the J-{Delta}a curve by brittle fracture. Large-scale yielding, coupled with small amounts of ductile tearing, magnifies the impact of small variations in microscale material properties on the macroscopic fracture toughness which contributes to the large amount scatter observed in measured J{sub c}-values. Previous work by the authors described a micromechanics fracture model to correct measured J{sub c}-values for the mechanistic effects of large-scale yielding. This new work extends the model to also include the influence of ductile crack extension prior to cleavage. The paper explores development of the new model, provides necessary graphs and procedures for its application and demonstrates the effects of the model on fracture data sets for two pressure vessel steels (A533B and A515).
A model to evaluate quality and effectiveness of disease management.
Lemmens, K M M; Nieboer, A P; van Schayck, C P; Asin, J D; Huijsman, R
2008-12-01
Disease management has emerged as a new strategy to enhance quality of care for patients suffering from chronic conditions, and to control healthcare costs. So far, however, the effects of this strategy remain unclear. Although current models define the concept of disease management, they do not provide a systematic development or an explanatory theory of how disease management affects the outcomes of care. The objective of this paper is to present a framework for valid evaluation of disease-management initiatives. The evaluation model is built on two pillars of disease management: patient-related and professional-directed interventions. The effectiveness of these interventions is thought to be affected by the organisational design of the healthcare system. Disease management requires a multifaceted approach; hence disease-management programme evaluations should focus on the effects of multiple interventions, namely patient-related, professional-directed and organisational interventions. The framework has been built upon the conceptualisation of these disease-management interventions. Analysis of the underlying mechanisms of these interventions revealed that learning and behavioural theories support the core assumptions of disease management. The evaluation model can be used to identify the components of disease-management programmes and the mechanisms behind them, making valid comparison feasible. In addition, this model links the programme interventions to indicators that can be used to evaluate the disease-management programme. Consistent use of this framework will enable comparisons among disease-management programmes and outcomes in evaluation research.
Modeling electron emission and surface effects from diamond cathodes
Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.
2015-02-07
We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass, and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. Using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.
Boron doped simulated graphene field effect transistor model
NASA Astrophysics Data System (ADS)
Sharma, Preetika; Kaur, Inderpreet; Gupta, Shuchi; Singh, Sukhbir
2016-05-01
Graphene based electronic devices due to its unique properties has transformed electronics. A Graphene Field Effect Transistor (GNRFET) model is simulated in Virtual Nano Lab (VNL) and the calculations are based on density functional theory (DFT). Simulations were performed on this pristine GNRFET model and the transmission spectrum was observed. The graph obtained showed a uniform energy gap of +1 to -1eV and the highest transmission peak at -1.75 eV. To this pristine model of GNRFET, doping was introduced and its effect was seen on the Fermi level obtained in the transmission spectrum. Boron as a dopant was used which showed variations in both the transmission peaks and the energy gap. In this model, first the single boron was substituted in place of carbon and Fermi level showed an energy gap of 1.5 to -0.5eV with the highest transmission peak at -1.3 eV. In another variation in the model, two carbon atoms were replaced by two boron atoms and Fermi level shifted from 2 to 0.25eV. In this observation, the highest transmission peak was observed at -1(approx.). The use of nanoelectronic devices have opened many areas of applications as GFET is an excellent building block for electronic circuits, and is being used in applications such as high-performance frequency doublers and mixers, digital modulators, phase detectors, optoelectronics and spintronics.
Effective equations of cosmological models in (loop) quantum gravity
NASA Astrophysics Data System (ADS)
Simpson, David
This dissertation focuses on the properties of several differing models within quantum cosmology. Specifically, by using the method of effective equations, we explore: a linear discrete Schrodinger model, a non-linear discrete Schrodinger model, factor ordering ambiguities in the Hamiltonian constraint (with a focus on large-volume behavior), and the use of the electric vector potential as deparameterized time. In the linear and non-linear Schrodinger models, we arrive at a new possibility for studying inhomogeneous quantum cosmology (where the non-linearities are interpreted as non-local deviations from the spatial average) that allows for a variety of dynamics and raises a number of questions for future research. We then turn our focus to the general effects of factor ordering ambiguities and their possible role in large-volume collapse of a k = 0 isotropic quantum cosmology with a free, massless scalar field. With the additional inclusion of holonomy and inverse-triad corrections, the choice in factor ordering of the Hamiltonian constraint is quite relevant; however, with our assumptions, we do not see any significant departure from classical large-volume behavior. The final model discussed is formulated with the electric vector potential as the global internal time in a Wheeler-DeWitt setting sourced by radiation. While further analysis is required to make a definitive statement on the impact that the choice of deparameterization makes, we find that the specific form of quantum state can affect early-universe dynamics and even lead to new possibilities.
Modelling of single bubble-dynamics and thermal effects
NASA Astrophysics Data System (ADS)
Papoulias, D.; Gavaises, M.
2015-12-01
This paper evaluates the solution effects of different Rayleigh-Plesset models (R-P) for simulating the growth/collapse dynamics and thermal behaviour of homogeneous gas bubbles. The flow inputs used for the discrete cavitation bubble calculations are obtained from Reynolds-averaged Navier-Stokes simulations (RANS), performed in high-pressure nozzle holes. Parametric 1-D results are presented for the classical thermal R-P equation [1] as well as for refined models which incorporated compressibility corrections and thermal effects [2, 3]. The thermal bubble model is coupled with the energy equation, which provides the temperature of the bubble as a function of conduction/convection and radiation heat-transfer mechanisms. For approximating gas pressure variations a high-order virial equation of state (EOS) was used, based on Helmholtz free energy principle [4]. The coded thermal R-P model was validated against experimental measurements [5] and model predictions [6] reported in single-bubble sonoluminescence (SBSL).
Modeling the Effects of Morphine on Simian Immunodeficiency Virus Dynamics
Vaidya, Naveen K.; Ribeiro, Ruy M.; Perelson, Alan S.; Kumar, Anil
2016-01-01
Complications of HIV-1 infection in individuals who utilize drugs of abuse is a significant problem, because these drugs have been associated with higher virus replication and accelerated disease progression as well as severe neuropathogenesis. To gain further insight it is important to quantify the effects of drugs of abuse on HIV-1 infection dynamics. Here, we develop a mathematical model that incorporates experimentally observed effects of morphine on inducing HIV-1 co-receptor expression. For comparison we also considered viral dynamic models with cytolytic or noncytolytic effector cell responses. Based on the small sample size Akaike information criterion, these models were inferior to the new model based on changes in co-receptor expression. The model with morphine affecting co-receptor expression agrees well with the experimental data from simian immunodeficiency virus infections in morphine-addicted macaques. Our results show that morphine promotes a target cell subpopulation switch from a lower level of susceptibility to a state that is about 2-orders of magnitude higher in susceptibility to SIV infection. As a result, the proportion of target cells with higher susceptibility remains extremely high in morphine conditioning. Such a morphine-induced population switch not only has adverse effects on the replication rate, but also results in a higher steady state viral load and larger CD4 count drops. Moreover, morphine conditioning may pose extra obstacles to controlling viral load during antiretroviral therapy, such as pre-exposure prophylaxis and post infection treatments. This study provides, for the first time, a viral dynamics model, viral dynamics parameters, and related analytical and simulation results for SIV dynamics under drugs of abuse. PMID:27668463
Modelling the effect of telegraph noise in the SIRS epidemic model using Markovian switching
NASA Astrophysics Data System (ADS)
Greenhalgh, D.; Liang, Y.; Mao, X.
2016-11-01
We discuss the effect of introducing telegraph noise, which is an example of an environmental noise, into the susceptible-infectious-recovered-susceptible (SIRS) model by examining the model using a finite-state Markov Chain (MC). First we start with a two-state MC and show that there exists a unique nonnegative solution and establish the conditions for extinction and persistence. We then explain how the results can be generalised to a finite-state MC. The results for the SIR (Susceptible-Infectious-Removed) model with Markovian Switching (MS) are a special case. Numerical simulations are produced to confirm our theoretical results.
Modeling Grade IV Gas Emboli using a Limited Failure Population Model with Random Effects
NASA Astrophysics Data System (ADS)
Thompson, Laura A.; Conkin, Johnny; Chhikara, Raj S.; Powell, Michael R.
2002-05-01
Venous gas emboli (VGE) (gas bubbles in venous blood) are associated with an increased risk of decompression sickness (DCS) in hypobaric environments. A high grade of VGE can be a precursor to serious DCS. In this paper, we model time to Grade IV VGE considering a subset of individuals assumed to be immune from experiencing VGE. Our data contain monitoring test results from subjects undergoing up to 13 denitrogenation test procedures prior to exposure to a hypobaric environment. The onset time of Grade IV VGE is recorded as contained within certain time intervals. We fit a parametric (lognormal) mixture survival model to the interval-and right-censored data to account for the possibility of a subset of "cured" individuals who are immune to the event. Our model contains random subject effects to account for correlations between repeated measurements on a single individual. Model assessments and cross-validation indicate that this limited failure population mixture model is an improvement over a model that does not account for the potential of a fraction of cured individuals. We also evaluated some alternative mixture models. Predictions from the best fitted mixture model indicate that the actual process is reasonably approximated by a limited failure population model.
Modeling Grade IV Gas Emboli using a Limited Failure Population Model with Random Effects
NASA Technical Reports Server (NTRS)
Thompson, Laura A.; Conkin, Johnny; Chhikara, Raj S.; Powell, Michael R.
2002-01-01
Venous gas emboli (VGE) (gas bubbles in venous blood) are associated with an increased risk of decompression sickness (DCS) in hypobaric environments. A high grade of VGE can be a precursor to serious DCS. In this paper, we model time to Grade IV VGE considering a subset of individuals assumed to be immune from experiencing VGE. Our data contain monitoring test results from subjects undergoing up to 13 denitrogenation test procedures prior to exposure to a hypobaric environment. The onset time of Grade IV VGE is recorded as contained within certain time intervals. We fit a parametric (lognormal) mixture survival model to the interval-and right-censored data to account for the possibility of a subset of "cured" individuals who are immune to the event. Our model contains random subject effects to account for correlations between repeated measurements on a single individual. Model assessments and cross-validation indicate that this limited failure population mixture model is an improvement over a model that does not account for the potential of a fraction of cured individuals. We also evaluated some alternative mixture models. Predictions from the best fitted mixture model indicate that the actual process is reasonably approximated by a limited failure population model.
Modeling Refuge Effect of Submerged Macrophytes in Lake System.
Lv, Dongyu; Fan, Meng; Kang, Yun; Blanco, Krystal
2016-04-01
This paper considers a significant problem in biological control of algae issue in ecological environment. A four-dimensional dynamic model is carefully formulated to characterize the interactions among phytoplankton, submerged macrophyte, zooplankton, and general fish class in a lake ecosystem. The predation relationship is modeled by Beddington-DeAngelis functional responses derived from the classical Holling time budget arguments. Qualitative analyses of the global dynamics show that the system can generate very rich dynamics with potentially 10 different equilibria and several bistable scenarios. We perform analysis on the existence and local stability of equilibria and explore the refuge effect of macrophyte on the zooplankton with numerical simulations on aquatic ecosystems. We also discuss effective methods of biological control used to restrain the increase of phytoplankton. Our study shows the proposed model could have rich and complex dynamics including but not limited to bistable and chaotic phenomenon. Numerical simulation results demonstrate that both the refuge constant and the density of the macrophytes are two key factors where refuge effects take place. In addition, the intraspecific competition between the macrophyte and the phytoplankton can also affect the macrophyte's refuge effect. Our analytical and simulation results suggest that macrophytes provide structure and shelter against predation for zooplankton such that it could restore the zooplankton population, and that planting macrophyte properly might achieve the purpose of controlling algae growth. PMID:27055658
Modeling the prediction of business intelligence system effectiveness.
Weng, Sung-Shun; Yang, Ming-Hsien; Koo, Tian-Lih; Hsiao, Pei-I
2016-01-01
Although business intelligence (BI) technologies are continually evolving, the capability to apply BI technologies has become an indispensable resource for enterprises running in today's complex, uncertain and dynamic business environment. This study performed pioneering work by constructing models and rules for the prediction of business intelligence system effectiveness (BISE) in relation to the implementation of BI solutions. For enterprises, effectively managing critical attributes that determine BISE to develop prediction models with a set of rules for self-evaluation of the effectiveness of BI solutions is necessary to improve BI implementation and ensure its success. The main study findings identified the critical prediction indicators of BISE that are important to forecasting BI performance and highlighted five classification and prediction rules of BISE derived from decision tree structures, as well as a refined regression prediction model with four critical prediction indicators constructed by logistic regression analysis that can enable enterprises to improve BISE while effectively managing BI solution implementation and catering to academics to whom theory is important. PMID:27376005
Infrared lens thermal effect: equivalent focal shift and calculating model
NASA Astrophysics Data System (ADS)
Zhang, Cheng-shuo; Shi, Zelin; Feng, Bin; Xu, Bao-shu
2014-11-01
It's well-know that the focal shift of infrared lens is the major factor in degeneration of imaging quality when temperature change. In order to figure out the connection between temperature change and focal shift, partial differential equations of thermal effect on light path are obtained by raytrace method, to begin with. The approximately solution of the PDEs show that focal shift is proportional to temperature change. And a formula to compute the proportional factor is given. In order to understand infrared lens thermal effect deeply, we use defocus by image plane shift at constant temperature to equivalently represent thermal effect on infrared lens. So equivalent focal shift (EFS) is defined and its calculating model is proposed at last. In order to verify EFS and its calculating model, Physical experimental platform including a motorized linear stage with built-in controller, blackbody, target, collimator, IR detector, computer and other devices is developed. The experimental results indicate that EFS make the image plane shift at constant temperature have the same influence on infrared lens as thermal effect and its calculating model is correct.
Modeling the prediction of business intelligence system effectiveness.
Weng, Sung-Shun; Yang, Ming-Hsien; Koo, Tian-Lih; Hsiao, Pei-I
2016-01-01
Although business intelligence (BI) technologies are continually evolving, the capability to apply BI technologies has become an indispensable resource for enterprises running in today's complex, uncertain and dynamic business environment. This study performed pioneering work by constructing models and rules for the prediction of business intelligence system effectiveness (BISE) in relation to the implementation of BI solutions. For enterprises, effectively managing critical attributes that determine BISE to develop prediction models with a set of rules for self-evaluation of the effectiveness of BI solutions is necessary to improve BI implementation and ensure its success. The main study findings identified the critical prediction indicators of BISE that are important to forecasting BI performance and highlighted five classification and prediction rules of BISE derived from decision tree structures, as well as a refined regression prediction model with four critical prediction indicators constructed by logistic regression analysis that can enable enterprises to improve BISE while effectively managing BI solution implementation and catering to academics to whom theory is important.
Deep donor model for the persistent photoconductivity effect
Hjalmarson, H.P.; Drummond, T.J.
1986-03-10
It is proposed that a persistent photoconductivity (PPC) effect is universally produced by deep donors. The general requirements of a class of models which explains the PPC effect in semiconductors are discussed. In particular, donor dopants such as Si and Te in Ga/sub 1-x/Al/sub x/As with xapprox.0.3 are conjectured to be deep and responsible for the PPC effect attributed to DX centers consisting of donor-vacancy pairs. It is shown that the Si donor has properties which explain the known data attributed to the DX center; these data include (1) the slow capture rate at low temperatures, (2) the thermally activated capture rate at high temperatures, and (3) the shape of the photoexcitation cross section. However, in contrast with the DX-center model, the deep donor model does not require a high trapped vacancy concentration ((V)approx.10/sup 18/ cm/sup -3/) to explain the PPC effect in highly doped semiconductors.
Modeling and analysis of cosmetic treatment effects on human skin
NASA Astrophysics Data System (ADS)
Lunderstaedt, Reinhart A.; Hopermann, Hermann; Hillemann, Thomas
2000-10-01
In view of treatment effects of cosmetics, quality management becomes more and more important. Due to the efficiency reasons it is desirable to quantify these effects and predict them as a function of time. For this, a mathematical model of the skin's surface (epidermis) is needed. Such a model cannot be worked out purely analytically. It can only be derived with the help of measurement data. The signals of interest as output of different measurement devices consist of two parts: noise of high (spatial) frequencies (stochastic signal) and periodic functions (deterministic signal) of low (spatial) frequencies. Both parts can be separated by correlation analysis. The paper introduces in addition to the Fourier Transform (FT) with the Wavelet Transform (WT), a brand new, highly sophisticated method with excellent properties for both modeling the skin's surface as well as evaluating treatment effects. Its main physical advantage is (in comparison to the FT) that local irregularities in the measurement signal (e.g. by scars) remain at their place and are not represented as mean square values as it is the case when applying the FT. The method has just now been installed in industry and will there be used in connection with a new in vivo measurement device for quality control of cosmetic products. As texture parameter for an integral description of the human skin the fractal dimension D is used which is appropriate for classification of different skin regions and treatment effects as well.
Linear mixed-effects modeling approach to FMRI group analysis
Chen, Gang; Saad, Ziad S.; Britton, Jennifer C.; Pine, Daniel S.; Cox, Robert W.
2013-01-01
Conventional group analysis is usually performed with Student-type t-test, regression, or standard AN(C)OVA in which the variance–covariance matrix is presumed to have a simple structure. Some correction approaches are adopted when assumptions about the covariance structure is violated. However, as experiments are designed with different degrees of sophistication, these traditional methods can become cumbersome, or even be unable to handle the situation at hand. For example, most current FMRI software packages have difficulty analyzing the following scenarios at group level: (1) taking within-subject variability into account when there are effect estimates from multiple runs or sessions; (2) continuous explanatory variables (covariates) modeling in the presence of a within-subject (repeated measures) factor, multiple subject-grouping (between-subjects) factors, or the mixture of both; (3) subject-specific adjustments in covariate modeling; (4) group analysis with estimation of hemodynamic response (HDR) function by multiple basis functions; (5) various cases of missing data in longitudinal studies; and (6) group studies involving family members or twins. Here we present a linear mixed-effects modeling (LME) methodology that extends the conventional group analysis approach to analyze many complicated cases, including the six prototypes delineated above, whose analyses would be otherwise either difficult or unfeasible under traditional frameworks such as AN(C)OVA and general linear model (GLM). In addition, the strength of the LME framework lies in its flexibility to model and estimate the variance–covariance structures for both random effects and residuals. The intraclass correlation (ICC) values can be easily obtained with an LME model with crossed random effects, even at the presence of confounding fixed effects. The simulations of one prototypical scenario indicate that the LME modeling keeps a balance between the control for false positives and the
Effective dark energy models and dark energy models with bounce in frames of F( T) gravity
NASA Astrophysics Data System (ADS)
Astashenok, Artyom V.
2014-05-01
Various cosmological models in frames of F( T) gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with ΛCDM model. The dynamics of universe governed by F( T) gravity can mimics ΛCDM evolution in past but declines from it in a future. We also construct some dark energy models with the "real" (non-effective) equation-of-state parameter w such that w≤-1. It is showed that in F( T) gravity the Universe filled phantom field not necessarily ends its existence in singularity. There are two possible mechanisms permitting the final singularity. Firstly due to the nonlinear dependence between energy density and H 2 ( H is the Hubble parameter) the universe can expands not so fast as in the general relativity and in fact Little Rip regime take place instead Big Rip. We also considered the models with possible bounce in future. In these models the universe expansion can mimics the dynamics with future singularity but due to bounce in future universe begin contracts.
Elements of effective palliative care models: a rapid review
2014-01-01
Background Population ageing, changes to the profiles of life-limiting illnesses and evolving societal attitudes prompt a critical evaluation of models of palliative care. We set out to identify evidence-based models of palliative care to inform policy reform in Australia. Method A rapid review of electronic databases and the grey literature was undertaken over an eight week period in April-June 2012. We included policy documents and comparative studies from countries within the Organisation for Economic Co-operation and Development (OECD) published in English since 2001. Meta-analysis was planned where >1 study met criteria; otherwise, synthesis was narrative using methods described by Popay et al. (2006). Results Of 1,959 peer-reviewed articles, 23 reported systematic reviews, 9 additional RCTs and 34 non-randomised comparative studies. Variation in the content of models, contexts in which these were implemented and lack of detailed reporting meant that elements of models constituted a more meaningful unit of analysis than models themselves. Case management was the element most consistently reported in models for which comparative studies provided evidence for effectiveness. Essential attributes of population-based palliative care models identified by policy and addressed by more than one element were communication and coordination between providers (including primary care), skill enhancement, and capacity to respond rapidly to individuals’ changing needs and preferences over time. Conclusion Models of palliative care should integrate specialist expertise with primary and community care services and enable transitions across settings, including residential aged care. The increasing complexity of care needs, services, interventions and contextual drivers warrants future research aimed at elucidating the interactions between different components and the roles played by patient, provider and health system factors. The findings of this review are limited by its
A multifluid mix model with material strength effects
Chang, C. H.; Scannapieco, A. J.
2012-04-23
We present a new multifluid mix model. Its features include material strength effects and pressure and temperature nonequilibrium between mixing materials. It is applicable to both interpenetration and demixing of immiscible fluids and diffusion of miscible fluids. The presented model exhibits the appropriate smooth transition in mathematical form as the mixture evolves from multiphase to molecular mixing, extending its applicability to the intermediate stages in which both types of mixing are present. Virtual mass force and momentum exchange have been generalized for heterogeneous multimaterial mixtures. The compression work has been extended so that the resulting species energy equations are consistent with the pressure force and material strength.
Finite driving rate and anisotropy effects in landslide modeling
Piegari, E.; Cataudella, V.; Di Maio, R.; Milano, L.; Nicodemi, M.
2006-02-15
In order to characterize landslide frequency-size distributions and individuate hazard scenarios and their possible precursors, we investigate a cellular automaton where the effects of a finite driving rate and the anisotropy are taken into account. The model is able to reproduce observed features of landslide events, such as power-law distributions, as experimentally reported. We analyze the key role of the driving rate and show that, as it is increased, a crossover from power-law to non-power-law behaviors occurs. Finally, a systematic investigation of the model on varying its anisotropy factors is performed and the full diagram of its dynamical behaviors is presented.
A model for bouncing droplets: effects of obstacles and confinements
NASA Astrophysics Data System (ADS)
Kasimov, Aslan; Faria, Luiz
2015-11-01
We propose a simple model for particle-wave interactions that captures many aspects of experiments with droplets bouncing on a vibrating bath. The model results from shallow water, small viscosity, and linear approximation to free surface hydrodynamics. The droplet motion is governed by an equation with a force that depends on the wave slope. We study a droplet motion in a wave guide, a droplet passing through a single/double slits, and other interactions that are known experimentally to exhibit quantum effects.
ERIC Educational Resources Information Center
Fortney, Patrick M.
1992-01-01
By keeping abreast of the latest research in the field, music educators can better understand how practicing helps students to use practice methods that are the most effective. The purpose of this study was to determine the relative effectiveness of modeling and silent analysis on the performance ability of advanced elementary school…
Global model for the lithospheric strength and effective elastic thickness
NASA Astrophysics Data System (ADS)
Tesauro, Magdala; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.
2013-08-01
Global distribution of the strength and effective elastic thickness (Te) of the lithosphere are estimated using physical parameters from recent crustal and lithospheric models. For the Te estimation we apply a new approach, which provides a possibility to take into account variations of Young modulus (E) within the lithosphere. In view of the large uncertainties affecting strength estimates, we evaluate global strength and Te distributions for possible end-member 'hard' (HRM) and a 'soft' (SRM) rheology models of the continental crust. Temperature within the lithosphere has been estimated using a recent tomography model of Ritsema et al. (2011), which has much higher horizontal resolution than previous global models. Most of the strength is localized in the crust for the HRM and in the mantle for the SRM. These results contribute to the long debates on applicability of the "crème brulée" or "jelly-sandwich" model for the lithosphere structure. Changing from the SRM to HRM turns most of the continental areas from the totally decoupled mode to the fully coupled mode of the lithospheric layers. However, in the areas characterized by a high thermal regime and thick crust, the layers remain decoupled even for the HRM. At the same time, for the inner part of the cratons the lithospheric layers are coupled in both models. Therefore, rheological variations lead to large changes in the integrated strength and Te distribution in the regions characterized by intermediate thermal conditions. In these areas temperature uncertainties have a greater effect, since this parameter principally determines rheological behavior. Comparison of the Te estimates for both models with those determined from the flexural loading and spectral analysis shows that the 'hard' rheology is likely applicable for cratonic areas, whereas the 'soft' rheology is more representative for young orogens.
A Model for Effective Professional Development of Formal Science Educators
NASA Astrophysics Data System (ADS)
Bleacher, L.; Jones, A. P.; Farrell, W. M.
2015-12-01
The Lunar Workshops for Educators (LWE) series was developed by the Lunar Reconnaissance Orbiter (LRO) education team in 2010 to provide professional development on lunar science and exploration concepts for grades 6-9 science teachers. Over 300 educators have been trained to date. The LWE model incorporates best practices from pedagogical research of science education, thoughtful integration of scientists and engineer subject matter experts for both content presentations and informal networking with educators, access to NASA-unique facilities, hands-on and data-rich activities aligned with education standards, exposure to the practice of science, tools for addressing common misconceptions, follow-up with participants, and extensive evaluation. Evaluation of the LWE model via pre- and post-assessments, daily workshop surveys, and follow-up surveys at 6-month and 1-year intervals indicate that the LWE are extremely effective in increasing educators' content knowledge, confidence in incorporating content into the classroom, understanding of the practice of science, and ability to address common student misconceptions. In order to address the efficacy of the LWE model for other science content areas, the Dynamic Response of Environments at Asteroids, the Moon, and moons of Mars (DREAM2) education team, funded by NASA's Solar System Exploration Research Virtual Institute, developed and ran a pilot workshop called Dream2Explore at NASA's Goddard Space Flight Center in June, 2015. Dream2Explore utilized the LWE model, but incorporated content related to the science and exploration of asteroids and the moons of Mars. Evaluation results indicate that the LWE model was effectively used for educator professional development on non-lunar content. We will present more detail on the LWE model, evaluation results from the Dream2Explore pilot workshop, and suggestions for the application of the model with other science content for robust educator professional development.
A Model for Effective Professional Development of Formal Science Educators
NASA Technical Reports Server (NTRS)
Bleacher, L. V.; Jones, A. J. P.; Farrell, W. M.
2015-01-01
The Lunar Workshops for Educators (LWE) series was developed by the Lunar Reconnaissance Orbiter (LRO) education team in 2010 to provide professional development on lunar science and exploration concepts for grades 6-9 science teachers. Over 300 educators have been trained to date. The LWE model incorporates best practices from pedagogical research of science education, thoughtful integration of scientists and engineer subject matter experts for both content presentations and informal networking with educators, access to NASA-unique facilities, hands-on and data-rich activities aligned with education standards, exposure to the practice of science, tools for addressing common misconceptions, follow-up with participants, and extensive evaluation. Evaluation of the LWE model via pre- and post-assessments, daily workshop surveys, and follow-up surveys at 6-month and 1-year intervals indicate that the LWE are extremely effective in increasing educators' content knowledge, confidence in incorporating content into the classroom, understanding of the practice of science, and ability to address common student misconceptions. In order to address the efficacy of the LWE model for other science content areas, the Dynamic Response of Environments at Asteroids, the Moon, and moons of Mars (DREAM2) education team, funded by NASA's Solar System Exploration Research Virtual Institute, developed and ran a pilot workshop called Dream2Explore at NASA's Goddard Space Flight Center in June, 2015. Dream2Explore utilized the LWE model, but incorporated content related to the science and exploration of asteroids and the moons of Mars. Evaluation results indicate that the LWE model was effectively used for educator professional development on non-lunar content. We will present more detail on the LWE model, evaluation results from the Dream2Explore pilot workshop, and suggestions for the application of the model with other science content for robust educator professional development.
Development and validation of a tokamak skin effect transformer model
NASA Astrophysics Data System (ADS)
Romero, J. A.; Moret, J.-M.; Coda, S.; Felici, F.; Garrido, I.
2012-02-01
A lumped parameter, state space model for a tokamak transformer including the slow flux penetration in the plasma (skin effect transformer model) is presented. The model does not require detailed or explicit information about plasma profiles or geometry. Instead, this information is lumped in system variables, parameters and inputs. The model has an exact mathematical structure built from energy and flux conservation theorems, predicting the evolution and non-linear interaction of plasma current and internal inductance as functions of the primary coil currents, plasma resistance, non-inductive current drive and the loop voltage at a specific location inside the plasma (equilibrium loop voltage). Loop voltage profile in the plasma is substituted by a three-point discretization, and ordinary differential equations are used to predict the equilibrium loop voltage as a function of the boundary and resistive loop voltages. This provides a model for equilibrium loop voltage evolution, which is reminiscent of the skin effect. The order and parameters of this differential equation are determined empirically using system identification techniques. Fast plasma current modulation experiments with random binary signals have been conducted in the TCV tokamak to generate the required data for the analysis. Plasma current was modulated under ohmic conditions between 200 and 300 kA with 30 ms rise time, several times faster than its time constant L/R ≈ 200 ms. A second-order linear differential equation for equilibrium loop voltage is sufficient to describe the plasma current and internal inductance modulation with 70% and 38% fit parameters, respectively. The model explains the most salient features of the plasma current transients, such as the inverse correlation between plasma current ramp rates and internal inductance changes, without requiring detailed or explicit information about resistivity profiles. This proves that a lumped parameter modelling approach can be used to
Effects of modeling versus instructions on sensitivity to reinforcement schedules.
Neef, Nancy A; Marckel, Julie; Ferreri, Summer; Jung, Sunhwa; Nist, Lindsay; Armstrong, Nancy
2004-01-01
This study examined the effects of modeling versus instructions on the choices of 3 typically developing children and 3 children with attention deficit hyperactivity disorder (ADHD) whose academic responding showed insensitivity to reinforcement schedules. During baseline, students chose between successively presented pairs of mathematics problems associated with different variable-interval schedules of reinforcement. After responding proved insensitive to the schedules, sessions were preceded by either instructions or modeling, counterbalanced across students in a multiple baseline design across subjects. During the instruction condition, students were told how to distribute responding to earn the most reinforcers. During the modeling condition, students observed the experimenter performing the task while describing her distribution of responding to obtain the most reinforcers. Once responding approximated obtained reinforcement under either condition, the schedules of reinforcement were changed, and neither instruction nor modeling was provided. Both instruction and modeling interventions quickly produced patterns of response allocation that approximated obtained rates of reinforcement, but responding established with modeling was more sensitive to subsequent changes in the reinforcement schedules than responding established with instructions. Results were similar for students with and without ADHD.
Coherent Effects in Microwave Backscattering Models for Forrest Canopies
NASA Technical Reports Server (NTRS)
Saatchi, Sasan S.; McDonald, Kyle C.
1997-01-01
In modeling forest canopies, several scattering mechanisms are taken into account: (1) volume scattering; (2) surface-volume interaction; and (3) surface scattering from forest floor. Depending on the structural and dielectric characteristics of forest canopies, the relative contribution of each mechanism in the total backscatter signal of an imaging radar can vary. In this paper, two commonly used first-order discrete scattering models, distorted born approximation (DBA) and radiative transfer (RT) are used to simulate the backscattered power received by polarimetric radars at P-, L-, and C-bands over coniferous and deciduous forests. The difference between the two models resides on the coherent effect in the surface-volume interaction terms. To demonstrate this point, the models are first compared based on their underlying theoretical assumptions and then according to simulation results over coniferous and deciduous forests. It is shown that by using the same scattering functions for various components of trees (i.e., leaf, branch, stem), the radiative transfer and distorted Born models are equivalent, except in low frequencies, where surface-volume interaction terms may become important, and the coherent contribution may be significant. In this case, the difference between the two models can reach up to 3 dB in both co-polarized and cross-polarized channels, which can influence the performance of retrieval algorithms.
Effects of modeling versus instructions on sensitivity to reinforcement schedules.
Neef, Nancy A; Marckel, Julie; Ferreri, Summer; Jung, Sunhwa; Nist, Lindsay; Armstrong, Nancy
2004-01-01
This study examined the effects of modeling versus instructions on the choices of 3 typically developing children and 3 children with attention deficit hyperactivity disorder (ADHD) whose academic responding showed insensitivity to reinforcement schedules. During baseline, students chose between successively presented pairs of mathematics problems associated with different variable-interval schedules of reinforcement. After responding proved insensitive to the schedules, sessions were preceded by either instructions or modeling, counterbalanced across students in a multiple baseline design across subjects. During the instruction condition, students were told how to distribute responding to earn the most reinforcers. During the modeling condition, students observed the experimenter performing the task while describing her distribution of responding to obtain the most reinforcers. Once responding approximated obtained reinforcement under either condition, the schedules of reinforcement were changed, and neither instruction nor modeling was provided. Both instruction and modeling interventions quickly produced patterns of response allocation that approximated obtained rates of reinforcement, but responding established with modeling was more sensitive to subsequent changes in the reinforcement schedules than responding established with instructions. Results were similar for students with and without ADHD. PMID:15529886
Modeling of Air Attenuation Effects on Gamma Detection at Altitude
R. S. Detwiler
2002-10-01
This paper focuses on modeling the detection capabilities of NaI sensor systems at high altitudes for ground sources. The modeling was done with the Monte Carlo N-Transport (MCNP) code developed at Los Alamos National Laboratory. The specific systems modeled were the fixed wing and helicopter aircraft sensor systems, assets of the U. S. Department of Energy's National Nuclear Security Administration Nevada Operations Office (NNSA/NV) Aerial Measuring System (AMS). In previous (2001) modeling, Sodium Iodine (NaI) detector responses were simulated for both point and distributed surface sources as a function of gamma energy and altitude. For point sources, photo-peak efficiencies were calculated for a zero radial distance and an offset equal to the altitude. For distributed sources approximating an infinite plane, gross count efficiencies were calculated and normalized to a uniform surface deposition of 1 {micro}Ci/m{sup 2}. To validate the calculations, benchmark measurements were made for simple source-detector configurations. The 2002 continuation of the modeling presented here includes checking models against available data, and modifications to allow more effective and accurate directional biasing of ground point and distributed sources. Fixed-wing data results will be shown for two point sources as a function of altitude.
Effective parameterizations of three nonwetting phase relative permeability models
NASA Astrophysics Data System (ADS)
Yang, Zhenlei; Mohanty, Binayak P.
2015-08-01
Describing convective nonwetting phase flow in unsaturated porous media requires knowledge of the nonwetting phase relative permeability. This study was conducted to formulate and derive a generalized expression for the nonwetting phase relative permeability via combining with the Kosugi water retention function. This generalized formulation is then used to flexibly investigate the Burdine, Mualem, and Alexander and Skaggs models' prediction accuracy for relative nonwetting phase permeability. The model and data comparison results show that these three permeability models, if used in their original form, but applied to the nonwetting phase, could not predict the experimental data well. The optimum pore tortuosity and connectivity value is thus obtained for the improved prediction of relative nonwetting phase permeability. As a result, the effective parameterization of (α,β,η) parameters in the modified Burdine, modified Mualem, and modified Alexander and Skaggs permeability models were found to be (2.5, 2, 1), (2, 1, 2), and (2.5, 1, 1), respectively. These three suggested models display the highest accuracy among the nine relative permeability models investigated in this study. However, the corresponding discontinuous nonwetting phase and the liquid film flow should be accounted for in future for the improved prediction of nonwetting phase relative permeability at very high and very low water saturation range, respectively.
Mathematical modeling the radiation effects on humoral immunity
NASA Astrophysics Data System (ADS)
Smirnova, O. A.
A mathematical model of humoral immune response in nonirradiated and irradiated mammals is developed. It is based on conventional theories and experimental facts in this field. The model is a system of nonlinear differential equations which describe the dynamics of concentrations of antibody and antigen molecules, immunocompetent B lymphocytes, and the rest blood lymphocytes, as well as the bone-marrow lymphocyte precursors. The interaction of antigen molecules with antibodies and with antibody-like receptors on immunocompetent cells is also incorporated. The model quantitatively reproduces the dynamics of the humoral immune response to the T-independent antigen (capsular antigen of plague microbe) in nonirradiated mammals (CBA mice). It describes the peculiarities of the humoral immune response in CBA mice exposed to acute radiation before or after introducing antigen. The model predicts an adaptation of humoral immune system to low dose rate chronic irradiation in the result of which the intensity of immune response relaxes to a new, lower than normal, stable level. The mechanisms of this phenomenon are revealed. The results obtained show that the developed model, after the appropriate identification, can be used to predict the effects of acute and low-level long-term irradiation on the system of humoral immunity in humans. Employment of the mathematical model identified in the proper way should be important in estimating the radiation risk for cosmonauts and astronauts on long space missions such as a voyage to Mars or a lunar colony.
A Time-Varying Effect Model for Intensive Longitudinal Data
Tan, Xianming; Shiyko, Mariya P.; Li, Runze; Li, Yuelin; Dierker, Lisa
2011-01-01
Understanding temporal change in human behavior and psychological processes is a central issue in the behavioral sciences. With technological advances, intensive longitudinal data (ILD) are increasingly generated by studies of human behavior that repeatedly administer assessments over time. ILD offer unique opportunities to describe temporal behavioral changes in detail and identify related environmental and psychosocial antecedents and consequences. Traditional analytical approaches impose strong parametric assumptions about the nature of change in the relationship between time-varying covariates and outcomes of interest. This paper introduces time-varying effect models (TVEM) that explicitly model changes in the association between ILD covariates and ILD outcomes over time in a flexible manner. In this article, we describes unique research questions that the TVEM addresses, outline the model-estimation procedure, share a SAS macro for implementing the model, demonstrate model utility with a simulated example, and illustrate model applications in ILD collected as part of a smoking-cessation study to explore the relationship between smoking urges and self-efficacy during the course of the pre- and post- cessation period. PMID:22103434
Optics of an opal modeled with a stratified effective index and the effect of the interface
NASA Astrophysics Data System (ADS)
Maurin, Isabelle; Moufarej, Elias; Laliotis, Athanasios; Bloch, Daniel
2015-08-01
Reflection and transmission for an artificial opal are described through a model of stratified medium based upon a one-dimensional variation of an effective index. The model is notably applicable to a Langmuir-Blodgett type disordered opal. Light scattering is accounted for by a phenomenological absorption. The interface region between the opal and the substrate -or the vacuum- induces a periodicity break in the photonic crystal arrangement, which exhibits a prominent influence on the reflection, notably away from the Bragg reflection peak. Experimental results are compared to our model. The model is extendable to inverse opals, stacked cylinders, or irradiation by evanescent waves
Subduction zone guided waves: 3D modelling and attenuation effects
NASA Astrophysics Data System (ADS)
Garth, T.; Rietbrock, A.
2013-12-01
Waveform modelling is an important tool for understanding complex seismic structures such as subduction zone waveguides. These structures are often simplified to 2D structures for modelling purposes to reduce computational costs. In the case of subduction zone waveguide affects, 2D models have shown that dispersed arrivals are caused by a low velocity waveguide, inferred to be subducted oceanic crust and/or hydrated outer rise normal faults. However, due to the 2D modelling limitations the inferred seismic properties such as velocity contrast and waveguide thickness are still debated. Here we test these limitations with full 3D waveform modelling. For waveguide effects to be observable the waveform must be accurately modelled to relatively high frequencies (> 2 Hz). This requires a small grid spacing due to the high seismic velocities present in subduction zones. A large area must be modelled as well due to the long propagation distances (400 - 600 km) of waves interacting with subduction zone waveguides. The combination of the large model area and small grid spacing required means that these simulations require a large amount of computational resources, only available at high performance computational centres like the UK National super computer HECTOR (used in this study). To minimize the cost of modelling for such a large area, the width of the model area perpendicular to the subduction trench (the y-direction) is made as small as possible. This reduces the overall volume of the 3D model domain. Therefore the wave field is simulated in a model ';corridor' of the subduction zone velocity structure. This introduces new potential sources of error particularly from grazing wave side reflections in the y-direction. Various dampening methods are explored to reduce these grazing side reflections, including perfectly matched layers (PML) and more traditional exponential dampening layers. Defining a corridor model allows waveguide affects to be modelled up to at least 2
NASA Astrophysics Data System (ADS)
Den, M.; Horiuchi, R.; Fujita, S.; Tanaka, T.
2011-12-01
Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Tanaka and Fujita reproduced substorm evolution process by numerical simulation with the global MHD code [1]. In the MHD framework, the dissipation model is introduced for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dissipation model employed there, gave a large effect for the dipolarization, central phenomenon in the substorm development process, though that viscosity was assumed to be a constant parameter. It is well known that magnetic reconnection is controlled by microscopic kinetic mechanism. Frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow [2, 3]. Horiuchi and his collaborators showed that reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics [2]. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. In this paper, we perform substorm simulation by using the global MHD code developed by Tanaka [3] with this effective resistivity instead of the empirical resistivity model. We obtain the AE indices from simulation data, in which substorm onset can be seen clearly, and investigate the relationship between the substorm development and the effective resistivity model. [1] T. Tanaka, A, Nakamizo, A. Yoshikawa, S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, and K. K. Hashimoto, J. Geophys. Res. 115 (2010) A05220,doi:10.1029/2009JA014676. [2] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. 8 (2001), pp. 3251-3257. [3] A. Ishizawa, and R. Horiuchi, Phys. Rev. Lett., Vol. 95, 045003 (2005). [4
Leverage Effect in Financial Markets: The Retarded Volatility Model
NASA Astrophysics Data System (ADS)
Bouchaud, Jean-Philippe; Matacz, Andrew; Potters, Marc
2001-11-01
We investigate quantitatively the so-called ``leverage effect,'' which corresponds to a negative correlation between past returns and future volatility. For individual stocks this correlation is moderate and decays over 50 days, while for stock indices it is much stronger but decays faster. For individual stocks the magnitude of this correlation has a universal value that can be rationalized in terms of a new ``retarded'' model which interpolates between a purely additive and a purely multiplicative stochastic process. For stock indices a specific amplification phenomenon seems to be necessary to account for the observed amplitude of the effect.
Quantification of memory effects in the spin-boson model
NASA Astrophysics Data System (ADS)
Clos, Govinda; Breuer, Heinz-Peter
2012-07-01
Employing a recently proposed measure for quantum non-Markovianity, we carry out a systematic study of the size of memory effects in the spin-boson model for a large region of temperature and frequency cutoff parameters. The dynamics of the open system is described utilizing a second-order time-convolutionless master equation without the Markov or rotating wave approximations. While the dynamics is found to be strongly non-Markovian for low temperatures and cutoffs, in general, we observe a special regime favoring Markovian behavior. This effect is explained as resulting from a resonance between the system's transition frequency and the frequencies of the dominant environmental modes. We further demonstrate that the corresponding Redfield equation is capable of reproducing the characteristic features of the non-Markovian quantum behavior of the model.
A Computational Model for Biomechanical Effects of Arterial Compliance Mismatch.
He, Fan; Hua, Lu; Gao, Li-Jian
2015-01-01
Background. Compliance mismatch is a negative factor and it needs to be considered in arterial bypass grafting. Objective. A computational model was employed to investigate the effects of arterial compliance mismatch on blood flow, wall stress, and deformation. Methods. The unsteady blood flow was assumed to be laminar, Newtonian, viscous, and incompressible. The vessel wall was assumed to be linear elastic, isotropic, and incompressible. The fluid-wall interaction scheme was constructed using the finite element method. Results. The results show that there are identical wall shear stress waveforms, wall stress, and strain waveforms at different locations. The comparison of the results demonstrates that wall shear stresses and wall strains are higher while wall stresses are lower at the more compliant section. The differences promote the probability of intimal thickening at some locations. Conclusions. The model is effective and gives satisfactory results. It could be extended to all kinds of arteries with complicated geometrical and material factors. PMID:27019580
Applying learning theories and instructional design models for effective instruction.
Khalil, Mohammed K; Elkhider, Ihsan A
2016-06-01
Faculty members in higher education are involved in many instructional design activities without formal training in learning theories and the science of instruction. Learning theories provide the foundation for the selection of instructional strategies and allow for reliable prediction of their effectiveness. To achieve effective learning outcomes, the science of instruction and instructional design models are used to guide the development of instructional design strategies that elicit appropriate cognitive processes. Here, the major learning theories are discussed and selected examples of instructional design models are explained. The main objective of this article is to present the science of learning and instruction as theoretical evidence for the design and delivery of instructional materials. In addition, this article provides a practical framework for implementing those theories in the classroom and laboratory.
Computational effects of inlet representation on powered hypersonic, airbreathing models
NASA Technical Reports Server (NTRS)
Huebner, Lawrence D.; Tatum, Kenneth E.
1993-01-01
Computational results are presented to illustrate the powered aftbody effects of representing the scramjet inlet on a generic hypersonic vehicle with a fairing, to divert the external flow, as compared to an operating flow-through scramjet inlet. This study is pertinent to the ground testing of hypersonic, airbreathing models employing scramjet exhaust flow simulation in typical small-scale hypersonic wind tunnels. The comparison of aftbody effects due to inlet representation is well-suited for computational study, since small model size typically precludes the ability to ingest flow into the inlet and perform exhaust simulation at the same time. Two-dimensional analysis indicates that, although flowfield differences exist for the two types of inlet representations, little, if any, difference in surface aftbody characteristics is caused by fairing over the inlet.
Modeling Correlation Effects in Nickelates with Slave Particles
NASA Astrophysics Data System (ADS)
Georgescu, Alexandru Bogdan; Ismail-Beigi, Sohrab
Nickelate interfaces display interesting electronic properties including orbital ordering similar to that of cuprate superconductors and thickness dependent metal-insulator transitions. One-particle band theory calculations do not include dynamic localized correlation effects on the nickel sites and thus often incorrectly predict metallic systems or incorrect ARPES spectra. Building on two previous successful slave-particle treatments of local correlations, we present a generalized slave-particle method that includes prior models and allows us to produce new intermediate models. The computational efficiency of these slave-boson methods means that one can readily study correlation effects in complex heterostructures. We show some predictions of these methods for the electronic structure of bulk and thin film nickelates. Work supported by NSF Grant MRSEC DMR-1119826.
Effects of distribution of infection rate on epidemic models.
Lachiany, Menachem; Louzoun, Yoram
2016-08-01
A goal of many epidemic models is to compute the outcome of the epidemics from the observed infected early dynamics. However, often, the total number of infected individuals at the end of the epidemics is much lower than predicted from the early dynamics. This discrepancy is argued to result from human intervention or nonlinear dynamics not incorporated in standard models. We show that when variability in infection rates is included in standard susciptible-infected-susceptible (SIS) and susceptible-infected-recovered (SIR) models the total number of infected individuals in the late dynamics can be orders lower than predicted from the early dynamics. This discrepancy holds for SIS and SIR models, where the assumption that all individuals have the same sensitivity is eliminated. In contrast with network models, fixed partnerships are not assumed. We derive a moment closure scheme capturing the distribution of sensitivities. We find that the shape of the sensitivity distribution does not affect R_{0} or the number of infected individuals in the early phases of the epidemics. However, a wide distribution of sensitivities reduces the total number of removed individuals in the SIR model and the steady-state infected fraction in the SIS model. The difference between the early and late dynamics implies that in order to extrapolate the expected effect of the epidemics from the initial phase of the epidemics, the rate of change in the average infectivity should be computed. These results are supported by a comparison of the theoretical model to the Ebola epidemics and by numerical simulation. PMID:27627337
Effects of distribution of infection rate on epidemic models
NASA Astrophysics Data System (ADS)
Lachiany, Menachem; Louzoun, Yoram
2016-08-01
A goal of many epidemic models is to compute the outcome of the epidemics from the observed infected early dynamics. However, often, the total number of infected individuals at the end of the epidemics is much lower than predicted from the early dynamics. This discrepancy is argued to result from human intervention or nonlinear dynamics not incorporated in standard models. We show that when variability in infection rates is included in standard susciptible-infected-susceptible (SIS ) and susceptible-infected-recovered (SIR ) models the total number of infected individuals in the late dynamics can be orders lower than predicted from the early dynamics. This discrepancy holds for SIS and SIR models, where the assumption that all individuals have the same sensitivity is eliminated. In contrast with network models, fixed partnerships are not assumed. We derive a moment closure scheme capturing the distribution of sensitivities. We find that the shape of the sensitivity distribution does not affect R0 or the number of infected individuals in the early phases of the epidemics. However, a wide distribution of sensitivities reduces the total number of removed individuals in the SIR model and the steady-state infected fraction in the SIS model. The difference between the early and late dynamics implies that in order to extrapolate the expected effect of the epidemics from the initial phase of the epidemics, the rate of change in the average infectivity should be computed. These results are supported by a comparison of the theoretical model to the Ebola epidemics and by numerical simulation.
Effects of model layer simplification using composite hydraulic properties
Kuniansky, Eve L.; Sepulveda, Nicasio; Elango, Lakshmanan
2011-01-01
Groundwater provides much of the fresh drinking water to more than 1.5 billion people in the world (Clarke et al., 1996) and in the United States more that 50 percent of citizens rely on groundwater for drinking water (Solley et al., 1998). As aquifer systems are developed for water supply, the hydrologic system is changed. Water pumped from the aquifer system initially can come from some combination of inducing more recharge, water permanently removed from storage, and decreased groundwater discharge. Once a new equilibrium is achieved, all of the pumpage must come from induced recharge and decreased discharge (Alley et al., 1999). Further development of groundwater resources may result in reductions of surface water runoff and base flows. Competing demands for groundwater resources require good management. Adequate data to characterize the aquifers and confining units of the system, like hydrologic boundaries, groundwater levels, streamflow, and groundwater pumping and climatic data for recharge estimation are to be collected in order to quantify the effects of groundwater withdrawals on wetlands, streams, and lakes. Once collected, three-dimensional (3D) groundwater flow models can be developed and calibrated and used as a tool for groundwater management. The main hydraulic parameters that comprise a regional or subregional model of an aquifer system are the hydraulic conductivity and storage properties of the aquifers and confining units (hydrogeologic units) that confine the system. Many 3D groundwater flow models used to help assess groundwater/surface-water interactions require calculating ?effective? or composite hydraulic properties of multilayered lithologic units within a hydrogeologic unit. The calculation of composite hydraulic properties stems from the need to characterize groundwater flow using coarse model layering in order to reduce simulation times while still representing the flow through the system accurately. The accuracy of flow models with
Modeling propagation effects from explosions in western China and India
Bradley, C.R.; Jones, E.M.
1998-12-31
The authors report on the results of finite-difference simulations of regional seismic wave propagation from a 1995 explosion at the Chinese test site at Lop Nor and from the recent Indian test. These simulations provide insight into variations in explosion seismograms recorded for these events. Previous modeling efforts by App et al., 1996, and Jones et al., 1998, have shown that many features in seismograms from explosions and earthquakes received at various stations surrounding Lop Nor can be reproduced with simple descriptions of the geologic structure along each path. However, differences in detail between simulations and the earthquake-like seismograms recorded at Station TLY in the Baikal Rift for the Lop Nor explosion have motivated further study of propagation effects. Differences between the TLY data and the simulations indicate that the use of homogeneous materials within the basins, crust, and mantle is too simplistic to capture some of the important features of the observed seismograms. Current efforts involve simulations in which 1-D and 2-D lithosphere models are merged to mimic gradients and 2-D structure, features which produce Rayleigh-wave dispersion and an improved agreement in group velocity curves. Source models have been modified to include a component of tectonic release during the Lop Nor explosion. The recent nuclear tests in India have been modeled in a similar fashion. The propagation path crosses the Moho step beneath the southern edge of the Tibetan Plateau before being received at station NIL. Similarly, the path from Lop Nor to NIL crosses a Moho step beneath the northern edge of the Tibetan Plateau and, in both cases, the effect of a step when combined with surface basin attenuation effectively block the Lg phase. Simulations show that both attenuation and crustal thickening are important when modeling propagation near the Tibetan Plateau.
Kinetic modeling of Nernst effect in magnetized hohlraums.
Joglekar, A S; Ridgers, C P; Kingham, R J; Thomas, A G R
2016-04-01
We present nanosecond time-scale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's law, including Nernst advection of magnetic fields. In addition to showing the prevalence of nonlocal behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in flux would suggest. Nonlocality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling.
The effect of model uncertainty on some optimal routing problems
NASA Technical Reports Server (NTRS)
Mohanty, Bibhu; Cassandras, Christos G.
1991-01-01
The effect of model uncertainties on optimal routing in a system of parallel queues is examined. The uncertainty arises in modeling the service time distribution for the customers (jobs, packets) to be served. For a Poisson arrival process and Bernoulli routing, the optimal mean system delay generally depends on the variance of this distribution. However, as the input traffic load approaches the system capacity the optimal routing assignment and corresponding mean system delay are shown to converge to a variance-invariant point. The implications of these results are examined in the context of gradient-based routing algorithms. An example of a model-independent algorithm using online gradient estimation is also included.
Kinetic modeling of Nernst effect in magnetized hohlraums.
Joglekar, A S; Ridgers, C P; Kingham, R J; Thomas, A G R
2016-04-01
We present nanosecond time-scale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's law, including Nernst advection of magnetic fields. In addition to showing the prevalence of nonlocal behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in flux would suggest. Nonlocality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling. PMID:27176417
Calculations of multiquark functions in effective models of strong interaction
Jafarov, R. G.; Rochev, V. E.
2013-09-15
In this paper we present our results of the investigation of multiquark equations in the Nambu-Jona-Lasinio model with chiral symmetry of SU(2) group in the mean-field expansion. To formulate the mean-field expansion we have used an iteration scheme of solution of the Schwinger-Dyson equations with the fermion bilocal source. We have considered the equations for Green functions of the Nambu-Jona-Lasinio model up to third step for this iteration scheme. To calculate the high-order corrections to the mean-field approximation, we propose the method of the Legendre transformation with respect to the bilocal source, which allows effectively to take into account the symmetry constraints related with the chiral Ward identity. We discuss also the problem of calculating the multiquark functions in the mean-field expansion for Nambu-Jona-Lasinio-type models with other types of the multifermion sources.
Support System Effects on the NASA Common Research Model
NASA Technical Reports Server (NTRS)
Rivers, S. Melissa B.; Hunter, Craig A.
2012-01-01
An experimental investigation of the NASA Common Research Model was conducted in the NASA Langley National Transonic Facility and NASA Ames 11-Foot Transonic Wind Tunnel Facility for use in the Drag Prediction Workshop. As data from the experimental investigations was collected, a large difference in moment values was seen between the experimental and the computational data from the 4th Drag Prediction Workshop. This difference led to the present work. In this study, a computational assessment has been undertaken to investigate model support system interference effects on the Common Research Model. The configurations computed during this investigation were the wing/body/tail=0deg without the support system and the wing/body/tail=0deg with the support system. The results from this investigation confirm that the addition of the support system to the computational cases does shift the pitching moment in the direction of the experimental results.
Physical models for the normal YORP and diurnal Yarkovsky effects
NASA Astrophysics Data System (ADS)
Golubov, O.; Kravets, Y.; Krugly, Yu. N.; Scheeres, D. J.
2016-06-01
We propose an analytic model for the normal Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) and diurnal Yarkovsky effects experienced by a convex asteroid. Both the YORP torque and the Yarkovsky force are expressed as integrals of a universal function over the surface of an asteroid. Although in general this function can only be calculated numerically from the solution of the heat conductivity equation, approximate solutions can be obtained in quadratures for important limiting cases. We consider three such simplified models: Rubincam's approximation (zero heat conductivity), low thermal inertia limit (including the next order correction and thus valid for small heat conductivity), and high thermal inertia limit (valid for large heat conductivity). All three simplified models are compared with the exact solution.
Kinetic modeling of Nernst effect in magnetized hohlraums
NASA Astrophysics Data System (ADS)
Joglekar, A. S.; Ridgers, C. P.; Kingham, R. J.; Thomas, A. G. R.
2016-04-01
We present nanosecond time-scale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's law, including Nernst advection of magnetic fields. In addition to showing the prevalence of nonlocal behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in flux would suggest. Nonlocality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling.
Effective-one-body modeling of precessing black hole binaries
NASA Astrophysics Data System (ADS)
Taracchini, Andrea; Babak, Stanislav; Buonanno, Alessandra
2016-03-01
Merging black hole binaries with generic spins that undergo precessional motion emit complicated gravitational-wave signals. We discuss how such waveforms can be accurately modeled within an effective-one-body approach by (i) exploiting the simplicity of the signals in a frame that corotates with the orbital plane of the binary and (ii) relying on an accurate model of nonprecessing black hole binaries. The model is validated by extensive comparisons to 70 numerical relativity simulations of precessing black hole binaries and can generate inspiral-merger-ringdown waveforms for mass ratios up to 100 and any spin configuration. This work is an essential tool for studying and characterizing candidate gravitational-wave events in science runs of advanced LIGO.
Treatment of cloud radiative effects in general circulation models
Wang, W.C.; Dudek, M.P.; Liang, X.Z.; Ding, M.
1996-04-01
We participate in the Atmospheric Radiation Measurement (ARM) program with two objectives: (1) to improve the general circulation model (GCM) cloud/radiation treatment with a focus on cloud verticle overlapping and layer cloud optical properties, and (2) to study the effects of cloud/radiation-climate interaction on GCM climate simulations. This report summarizes the project progress since the Fourth ARM Science Team meeting February 28-March 4, 1994, in Charleston, South Carolina.
Modeling elephant-mediated cascading effects of water point closure.
Hilbers, Jelle P; Van Langevelde, Frank; Prins, Herbert H T; Grant, C C; Peel, Mike J S; Coughenour, Michael B; De Knegt, Henrik J; Slotow, Rob; Smit, Izak P J; Kiker, Greg A; De Boer, Willem F
2015-03-01
Wildlife management to reduce the impact of wildlife on their habitat can be done in several ways, among which removing animals (by either culling or translocation) is most often used. There are, however, alternative ways to control wildlife densities, such as opening or closing water points. The effects of these alternatives are poorly studied. In this paper, we focus on manipulating large herbivores through the closure of water points (WPs). Removal of artificial WPs has been suggested in order to change the distribution of African elephants, which occur in high densities in national parks in Southern Africa and are thought to have a destructive effect on the vegetation. Here, we modeled the long-term effects of different scenarios of WP closure on the spatial distribution of elephants, and consequential effects on the vegetation and other herbivores in Kruger National Park, South Africa. Using a dynamic ecosystem model, SAVANNA, scenarios were evaluated that varied in availability of artificial WPs; levels of natural water; and elephant densities. Our modeling results showed that elephants can indirectly negatively affect the distributions of meso-mixed feeders, meso-browsers, and some meso-grazers under wet conditions. The closure of artificial WPs hardly had any effect during these natural wet conditions. Under dry conditions, the spatial distribution of both elephant bulls and cows changed when the availability of artificial water was severely reduced in the model. These changes in spatial distribution triggered changes in the spatial availability of woody biomass over the simulation period of 80 years, and this led to changes in the rest of the herbivore community, resulting in increased densities of all herbivores, except for giraffe and steenbok, in areas close to rivers. The spatial distributions of elephant bulls and cows showed to be less affected by the closure of WPs than most of the other herbivore species. Our study contributes to ecologically
Modeling elephant-mediated cascading effects of water point closure.
Hilbers, Jelle P; Van Langevelde, Frank; Prins, Herbert H T; Grant, C C; Peel, Mike J S; Coughenour, Michael B; De Knegt, Henrik J; Slotow, Rob; Smit, Izak P J; Kiker, Greg A; De Boer, Willem F
2015-03-01
Wildlife management to reduce the impact of wildlife on their habitat can be done in several ways, among which removing animals (by either culling or translocation) is most often used. There are, however, alternative ways to control wildlife densities, such as opening or closing water points. The effects of these alternatives are poorly studied. In this paper, we focus on manipulating large herbivores through the closure of water points (WPs). Removal of artificial WPs has been suggested in order to change the distribution of African elephants, which occur in high densities in national parks in Southern Africa and are thought to have a destructive effect on the vegetation. Here, we modeled the long-term effects of different scenarios of WP closure on the spatial distribution of elephants, and consequential effects on the vegetation and other herbivores in Kruger National Park, South Africa. Using a dynamic ecosystem model, SAVANNA, scenarios were evaluated that varied in availability of artificial WPs; levels of natural water; and elephant densities. Our modeling results showed that elephants can indirectly negatively affect the distributions of meso-mixed feeders, meso-browsers, and some meso-grazers under wet conditions. The closure of artificial WPs hardly had any effect during these natural wet conditions. Under dry conditions, the spatial distribution of both elephant bulls and cows changed when the availability of artificial water was severely reduced in the model. These changes in spatial distribution triggered changes in the spatial availability of woody biomass over the simulation period of 80 years, and this led to changes in the rest of the herbivore community, resulting in increased densities of all herbivores, except for giraffe and steenbok, in areas close to rivers. The spatial distributions of elephant bulls and cows showed to be less affected by the closure of WPs than most of the other herbivore species. Our study contributes to ecologically
Colored noise and memory effects on formal spiking neuron models.
da Silva, L A; Vilela, R D
2015-06-01
Simplified neuronal models capture the essence of the electrical activity of a generic neuron, besides being more interesting from the computational point of view when compared to higher-dimensional models such as the Hodgkin-Huxley one. In this work, we propose a generalized resonate-and-fire model described by a generalized Langevin equation that takes into account memory effects and colored noise. We perform a comprehensive numerical analysis to study the dynamics and the point process statistics of the proposed model, highlighting interesting new features such as (i) nonmonotonic behavior (emergence of peak structures, enhanced by the choice of colored noise characteristic time scale) of the coefficient of variation (CV) as a function of memory characteristic time scale, (ii) colored noise-induced shift in the CV, and (iii) emergence and suppression of multimodality in the interspike interval (ISI) distribution due to memory-induced subthreshold oscillations. Moreover, in the noise-induced spike regime, we study how memory and colored noise affect the coherence resonance (CR) phenomenon. We found that for sufficiently long memory, not only is CR suppressed but also the minimum of the CV-versus-noise intensity curve that characterizes the presence of CR may be replaced by a maximum. The aforementioned features allow to interpret the interplay between memory and colored noise as an effective control mechanism to neuronal variability. Since both variability and nontrivial temporal patterns in the ISI distribution are ubiquitous in biological cells, we hope the present model can be useful in modeling real aspects of neurons.
Colored noise and memory effects on formal spiking neuron models
NASA Astrophysics Data System (ADS)
da Silva, L. A.; Vilela, R. D.
2015-06-01
Simplified neuronal models capture the essence of the electrical activity of a generic neuron, besides being more interesting from the computational point of view when compared to higher-dimensional models such as the Hodgkin-Huxley one. In this work, we propose a generalized resonate-and-fire model described by a generalized Langevin equation that takes into account memory effects and colored noise. We perform a comprehensive numerical analysis to study the dynamics and the point process statistics of the proposed model, highlighting interesting new features such as (i) nonmonotonic behavior (emergence of peak structures, enhanced by the choice of colored noise characteristic time scale) of the coefficient of variation (CV) as a function of memory characteristic time scale, (ii) colored noise-induced shift in the CV, and (iii) emergence and suppression of multimodality in the interspike interval (ISI) distribution due to memory-induced subthreshold oscillations. Moreover, in the noise-induced spike regime, we study how memory and colored noise affect the coherence resonance (CR) phenomenon. We found that for sufficiently long memory, not only is CR suppressed but also the minimum of the CV-versus-noise intensity curve that characterizes the presence of CR may be replaced by a maximum. The aforementioned features allow to interpret the interplay between memory and colored noise as an effective control mechanism to neuronal variability. Since both variability and nontrivial temporal patterns in the ISI distribution are ubiquitous in biological cells, we hope the present model can be useful in modeling real aspects of neurons.
Optimizing replacement of dairy cows: modeling the effects of diseases.
Gröhn, Y T; Rajala-Schultz, P J; Allore, H G; DeLorenzo, M A; Hertl, J A; Galligan, D T
2003-09-30
We modified an existing dairy management decision model by including economically important dairy cattle diseases, and illustrated how their inclusion changed culling recommendations. Nine common diseases having treatment and veterinary costs, and affecting milk yield, fertility and survival, were considered important in the culling decision process. A sequence of stages was established during which diseases were considered significant: mastitis and lameness, any time during lactation; dystocia, milk fever and retained placenta, 0-4 days of lactation; displaced abomasum, 5-30 days; ketosis and metritis, 5-60 days; and cystic ovaries, 61-120 days. Some diseases were risk factors for others. Baseline incidences and disease effects were obtained from the literature. The effects of various disease combinations on milk yield, fertility, survival and economics were estimated. Adding diseases into the model did not increase voluntary or total culling rate. However, diseased animals were recommended for culling much more than healthy cows, regardless of parity or production level. Cows in the highest production level were not recommended for culling even if they contracted a disease. The annuity per cow decreased and herdlife increased when diseases were in the model. Higher replacement cost also increased herdlife and decreased when diseases were in the model. Higher replacement cost also increased herdlife and decreased the annuity and voluntary culling rate.
Modelling the effect of severe storms in coastal pollution
NASA Astrophysics Data System (ADS)
Grau, A.; Bolea, Y.; Guerra, E.
2009-09-01
Modelling and simulation of real events can be very useful to prevent environmental disasters, but these disasters can affect the health and life of human beings; then such tools become definitively necessary for governmental authorities to avoid population risk. In this wok we present a mathematical model that combines the effect of Mediterranean storms together with the effect of wastewater emissary dissolutions at the sea. The emissary model corresponds to a Catalan wastewater plant, the Besos plant in Barcelona. This plant throws the wastewater to the Mediterranean Sea with a 3-km pipe emissary, after a bacteriologically polluted secondary treatment. This polluted water is dissoluted in the salty water, provoking the death of all bacteria agents before they reach the coast. But in difficult conditions under violent storms, with strong East winds, the bacteriological polluted dissolution reaches the shore before the bacteria die and, therefore, a severe coastal pollution is produced. Its consequence can incur in a public health problem and the different governmental agencies activate great alarms to avoid population hazard. Storms modelling permits to evaluate the risk of coastal pollution predicting the wastewater dissolution path and velocity. Several simulations are presented under different storm conditions, making this tool very useful for the environmental protection agencies in the Catalan government.
Modeling the effects of transcranial magnetic stimulation on cortical circuits.
Esser, Steve K; Hill, Sean L; Tononi, Giulio
2005-07-01
Transcranial magnetic stimulation (TMS) is commonly used to activate or inactivate specific cortical areas in a noninvasive manner. Because of technical constraints, the precise effects of TMS on cortical circuits are difficult to assess experimentally. Here, this issue is investigated by constructing a detailed model of a portion of the thalamocortical system and examining the effects of the simulated delivery of a TMS pulse. The model, which incorporates a large number of physiological and anatomical constraints, includes 33,000 spiking neurons arranged in a 3-layered motor cortex and over 5 million intra- and interlayer synaptic connections. The model was validated by reproducing several results from the experimental literature. These include the frequency, timing, dose response, and pharmacological modulation of epidurally recorded responses to TMS (the so-called I-waves), as well as paired-pulse response curves consistent with data from several experimental studies. The modeled responses to simulated TMS pulses in different experimental paradigms provide a detailed, self-consistent account of the neural and synaptic activities evoked by TMS within prototypical cortical circuits. PMID:15788519
Modeling the effects of contrast enhancement on target acquisition performance
NASA Astrophysics Data System (ADS)
Du Bosq, Todd W.; Fanning, Jonathan D.
2008-04-01
Contrast enhancement and dynamic range compression are currently being used to improve the performance of infrared imagers by increasing the contrast between the target and the scene content, by better utilizing the available gray levels either globally or locally. This paper assesses the range-performance effects of various contrast enhancement algorithms for target identification with well contrasted vehicles. Human perception experiments were performed to determine field performance using contrast enhancement on the U.S. Army RDECOM CERDEC NVESD standard military eight target set using an un-cooled LWIR camera. The experiments compare the identification performance of observers viewing linearly scaled images and various contrast enhancement processed images. Contrast enhancement is modeled in the US Army thermal target acquisition model (NVThermIP) by changing the scene contrast temperature. The model predicts improved performance based on any improved target contrast, regardless of feature saturation or enhancement. To account for the equivalent blur associated with each contrast enhancement algorithm, an additional effective MTF was calculated and added to the model. The measured results are compared with the predicted performance based on the target task difficulty metric used in NVThermIP.
The Effect of Random Voids in the Modified Gurson Model
NASA Astrophysics Data System (ADS)
Fei, Huiyang; Yazzie, Kyle; Chawla, Nikhilesh; Jiang, Hanqing
2012-02-01
The porous plasticity model (usually referred to as the Gurson-Tvergaard-Needleman model or modified Gurson model) has been widely used in the study of microvoid-induced ductile fracture. In this paper, we studied the effects of random voids on the porous plasticity model. Finite-element simulations were conducted to study a copper/tin/copper joint bar under uniaxial tension using the commercial finite-element package ABAQUS. A randomly distributed initial void volume fraction with different types of distribution was introduced, and the effects of this randomness on the crack path and macroscopic stress-strain behavior were studied. It was found that consideration of the random voids is able to capture more detailed and localized deformation features, such as different crack paths and different ultimate tensile strengths, and meanwhile does not change the macroscopic stress-strain behavior. It seems that the random voids are able to qualitatively explain the scattered observations in experiments while keeping the macroscopic measurements consistent.
Physiological and psychophysical modeling of the precedence effect.
Xia, Jing; Brughera, Andrew; Colburn, H Steven; Shinn-Cunningham, Barbara
2010-09-01
Many past studies of sound localization explored the precedence effect (PE), in which a pair of brief, temporally close sounds from different directions is perceived as coming from a location near that of the first-arriving sound. Here, a computational model of low-frequency inferior colliculus (IC) neurons accounts for both physiological and psychophysical responses to PE click stimuli. In the model, IC neurons have physiologically plausible inputs, receiving excitation from the ipsilateral medial superior olive (MSO) and long-lasting inhibition from both ipsilateral and contralateral MSOs, relayed through the dorsal nucleus of the lateral lemniscus. In this model, physiological suppression of the lagging response depends on the inter-stimulus delay (ISD) between the lead and lag as well as their relative locations. Psychophysical predictions are generated from a population of model neurons. At all ISDs, predicted lead localization is good. At short ISDs, the estimated location of the lag is near that of the lead, consistent with subjects perceiving both lead and lag from the lead location. As ISD increases, the estimated lag location moves closer to the true lag location, consistent with listeners' perception of two sounds from separate locations. Together, these simulations suggest that location-dependent suppression in IC neurons can explain the behavioral phenomenon known as the precedence effect.
Modeling of radiation effects on nuclear waste package materials
Simonson, S.A.
1988-09-01
A methodology is developed for the assessment of radiation effects on nuclear waste package materials. An assessment of the current status of understanding with regard to waste package materials and their behavior in radiation environments is presented. The methodology is used to make prediction as to the chemically induced changes in the groundwater surrounding nuclear waste packages in a repository in tuff. The predictions indicate that mechanisms not currently being pursued by the Department of Energy may be a factor in the long-term performance of nuclear waste packages. The methodology embodies a physical model of the effects of radiation on aqueous solutions. Coupled to the physical model is a method for analyzing the complex nature of the physical model using adjoint sensitivity analysis. The sensitivity aid in both the physical understanding of the processes involved as well as aiding in eliminating portions of the model that have no bearing on the desired results. A computer implementation of the methodology is provided. 128 refs.
The Effects of Implementing TopModel Concepts in the Noah Model
NASA Technical Reports Server (NTRS)
Peters-Lidard, C. D.; Houser, Paul R. (Technical Monitor)
2002-01-01
Topographic effects on runoff generation have been documented observationally (e.g., Dunne and Black, 1970) and are the subject of the physically based rainfall-runoff model TOPMODEL (Beven and Kirkby, 1979; Beven, 1986a;b) and its extensions, which incorporate variable soil transmissivity effects (Sivapalan et al, 1987, Wood et al., 1988; 1990). These effects have been shown to exert significant control over the spatial distribution of runoff, soil moisture and evapotranspiration, and by extension, the latent and sensible heat fluxes
Linear effects models of signaling pathways from combinatorial perturbation data
Szczurek, Ewa; Beerenwinkel, Niko
2016-01-01
Motivation: Perturbations constitute the central means to study signaling pathways. Interrupting components of the pathway and analyzing observed effects of those interruptions can give insight into unknown connections within the signaling pathway itself, as well as the link from the pathway to the effects. Different pathway components may have different individual contributions to the measured perturbation effects, such as gene expression changes. Those effects will be observed in combination when the pathway components are perturbed. Extant approaches focus either on the reconstruction of pathway structure or on resolving how the pathway components control the downstream effects. Results: Here, we propose a linear effects model, which can be applied to solve both these problems from combinatorial perturbation data. We use simulated data to demonstrate the accuracy of learning the pathway structure as well as estimation of the individual contributions of pathway components to the perturbation effects. The practical utility of our approach is illustrated by an application to perturbations of the mitogen-activated protein kinase pathway in Saccharomyces cerevisiae. Availability and Implementation: lem is available as a R package at http://www.mimuw.edu.pl/∼szczurek/lem. Contact: szczurek@mimuw.edu.pl; niko.beerenwinkel@bsse.ethz.ch Supplementary information: Supplementary data are available at Bioinformatics online. PMID:27307630
Quantifying and Modeling Birth Order Effects in Autism
Turner, Tychele; Pihur, Vasyl; Chakravarti, Aravinda
2011-01-01
Autism is a complex genetic disorder with multiple etiologies whose molecular genetic basis is not fully understood. Although a number of rare mutations and dosage abnormalities are specific to autism, these explain no more than 10% of all cases. The high heritability of autism and low recurrence risk suggests multifactorial inheritance from numerous loci but other factors also intervene to modulate risk. In this study, we examine the effect of birth rank on disease risk which is not expected for purely hereditary genetic models. We analyzed the data from three publicly available autism family collections in the USA for potential birth order effects and studied the statistical properties of three tests to show that adequate power to detect these effects exist. We detect statistically significant, yet varying, patterns of birth order effects across these collections. In multiplex families, we identify V-shaped effects where middle births are at high risk; in simplex families, we demonstrate linear effects where risk increases with each additional birth. Moreover, the birth order effect is gender-dependent in the simplex collection. It is currently unknown whether these patterns arise from ascertainment biases or biological factors. Nevertheless, further investigation of parental age-dependent risks yields patterns similar to those observed and could potentially explain part of the increased risk. A search for genes considering these patterns is likely to increase statistical power and uncover novel molecular etiologies. PMID:22039484
On effective temperature in network models of collective behavior.
Porfiri, Maurizio; Ariel, Gil
2016-04-01
Collective behavior of self-propelled units is studied analytically within the Vectorial Network Model (VNM), a mean-field approximation of the well-known Vicsek model. We propose a dynamical systems framework to study the stochastic dynamics of the VNM in the presence of general additive noise. We establish that a single parameter, which is a linear function of the circular mean of the noise, controls the macroscopic phase of the system-ordered or disordered. By establishing a fluctuation-dissipation relation, we posit that this parameter can be regarded as an effective temperature of collective behavior. The exact critical temperature is obtained analytically for systems with small connectivity, equivalent to low-density ensembles of self-propelled units. Numerical simulations are conducted to demonstrate the applicability of this new notion of effective temperature to the Vicsek model. The identification of an effective temperature of collective behavior is an important step toward understanding order-disorder phase transitions, informing consistent coarse-graining techniques and explaining the physics underlying the emergence of collective phenomena. PMID:27131488
Modeling variable blowing effects in the turbulent hypersonic boundary layer
NASA Technical Reports Server (NTRS)
Vanosdol, John G.
1992-01-01
Studies of the effects of variable blowing in turbulent hypersonic boundary layers are presented. Numerical calculations of the skin friction and surface heat transfer rates are compared to the experimental measurements of Holden (1990) for a slender cone at zero angle of attack in steady flows at Mach numbers of 11 and 13. An analysis of the transpiration feed system of the cone model was performed and showed that the blowing rate could be variable along the cone surface. This effect is confirmed by internal pressure measurements which were taken inside the cone model. The blowing rates are recalibrated using the internal gauge readings and used as the wall boundary condition for a compressible turbulent boundary layer calculation using the low Reynolds number k-epsilon model of Chien (1982). At low blowing rates, the boundary layer calculations indicate that a situation where both the effects of suction and blowing are present within the same flow. The results show excellent qualitative prediction of the experimental data.
Underwater drag-reducing effect of superhydrophobic submarine model.
Zhang, Songsong; Ouyang, Xiao; Li, Jie; Gao, Shan; Han, Shihui; Liu, Lianhe; Wei, Hao
2015-01-01
To address the debates on whether superhydrophobic coatings can reduce fluid drag for underwater motions, we have achieved an underwater drag-reducing effect of large superhydrophobic submarine models with a feature size of 3.5 cm × 3.7 cm × 33.0 cm through sailing experiments of submarine models, modified with and without superhydrophobic surface under similar power supply and experimental conditions. The drag reduction rate reached as high as 15%. The fabrication of superhydrophobic coatings on a large area of submarine model surfaces was realized by immobilizing hydrophobic copper particles onto a precross-linked polydimethylsiloxane (PDMS) surface. The pre-cross-linking time was optimized at 20 min to obtain good superhydrophobicity for the underwater drag reduction effect by investigating the effect of pre-cross-linking on surface wettability and water adhesive property. We do believe that superhydrophobic coatings may provide a promising application in the field of drag-reducing of vehicle motions on or under the water surface. PMID:25496725
Effective tight-binding model for transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Ho, Yen-Hung; Cazalilla, Miguel; Ochoa, Hector
For transition metal dichalcogenides, various band models have been developed to describe the novel subband features. In this work, we propose a new effective minimum-band model by preforming a canonical transformation on the full-band Hamiltonian. We found that, depending on the form of transformation, both the Γ- and K-valley electrons can be well captured, including the frequency and band effective mass. And, for the full-band parameters used, starting from Wannier function basis set leads to a better result than from Slater-Koster basis set. A close inspection of the transformation projection also enables us to extract the modification on the site energy, as well as the orbital hopping between several nearest neighboring atoms. Instead of pure empirical fitting, our effective models preserve rich orbital physics inside, which is shown to be versatile in studying a variety of fundamental physical properties. Ministry of Science and Technology of Taiwan (NSC 102-2112-M-007-024-MY5).
Underwater drag-reducing effect of superhydrophobic submarine model.
Zhang, Songsong; Ouyang, Xiao; Li, Jie; Gao, Shan; Han, Shihui; Liu, Lianhe; Wei, Hao
2015-01-01
To address the debates on whether superhydrophobic coatings can reduce fluid drag for underwater motions, we have achieved an underwater drag-reducing effect of large superhydrophobic submarine models with a feature size of 3.5 cm × 3.7 cm × 33.0 cm through sailing experiments of submarine models, modified with and without superhydrophobic surface under similar power supply and experimental conditions. The drag reduction rate reached as high as 15%. The fabrication of superhydrophobic coatings on a large area of submarine model surfaces was realized by immobilizing hydrophobic copper particles onto a precross-linked polydimethylsiloxane (PDMS) surface. The pre-cross-linking time was optimized at 20 min to obtain good superhydrophobicity for the underwater drag reduction effect by investigating the effect of pre-cross-linking on surface wettability and water adhesive property. We do believe that superhydrophobic coatings may provide a promising application in the field of drag-reducing of vehicle motions on or under the water surface.
On effective temperature in network models of collective behavior.
Porfiri, Maurizio; Ariel, Gil
2016-04-01
Collective behavior of self-propelled units is studied analytically within the Vectorial Network Model (VNM), a mean-field approximation of the well-known Vicsek model. We propose a dynamical systems framework to study the stochastic dynamics of the VNM in the presence of general additive noise. We establish that a single parameter, which is a linear function of the circular mean of the noise, controls the macroscopic phase of the system-ordered or disordered. By establishing a fluctuation-dissipation relation, we posit that this parameter can be regarded as an effective temperature of collective behavior. The exact critical temperature is obtained analytically for systems with small connectivity, equivalent to low-density ensembles of self-propelled units. Numerical simulations are conducted to demonstrate the applicability of this new notion of effective temperature to the Vicsek model. The identification of an effective temperature of collective behavior is an important step toward understanding order-disorder phase transitions, informing consistent coarse-graining techniques and explaining the physics underlying the emergence of collective phenomena.
On effective temperature in network models of collective behavior
NASA Astrophysics Data System (ADS)
Porfiri, Maurizio; Ariel, Gil
2016-04-01
Collective behavior of self-propelled units is studied analytically within the Vectorial Network Model (VNM), a mean-field approximation of the well-known Vicsek model. We propose a dynamical systems framework to study the stochastic dynamics of the VNM in the presence of general additive noise. We establish that a single parameter, which is a linear function of the circular mean of the noise, controls the macroscopic phase of the system—ordered or disordered. By establishing a fluctuation-dissipation relation, we posit that this parameter can be regarded as an effective temperature of collective behavior. The exact critical temperature is obtained analytically for systems with small connectivity, equivalent to low-density ensembles of self-propelled units. Numerical simulations are conducted to demonstrate the applicability of this new notion of effective temperature to the Vicsek model. The identification of an effective temperature of collective behavior is an important step toward understanding order-disorder phase transitions, informing consistent coarse-graining techniques and explaining the physics underlying the emergence of collective phenomena.
Budic, Lara; Didenko, Gregor; Dormann, Carsten F
2016-01-01
In species distribution analyses, environmental predictors and distribution data for large spatial extents are often available in long-lat format, such as degree raster grids. Long-lat projections suffer from unequal cell sizes, as a degree of longitude decreases in length from approximately 110 km at the equator to 0 km at the poles. Here we investigate whether long-lat and equal-area projections yield similar model parameter estimates, or result in a consistent bias. We analyzed the environmental effects on the distribution of 12 ungulate species with a northern distribution, as models for these species should display the strongest effect of projectional distortion. Additionally we choose four species with entirely continental distributions to investigate the effect of incomplete cell coverage at the coast. We expected that including model weights proportional to the actual cell area should compensate for the observed bias in model coefficients, and similarly that using land coverage of a cell should decrease bias in species with coastal distribution. As anticipated, model coefficients were different between long-lat and equal-area projections. Having progressively smaller and a higher number of cells with increasing latitude influenced the importance of parameters in models, increased the sample size for the northernmost parts of species ranges, and reduced the subcell variability of those areas. However, this bias could be largely removed by weighting long-lat cells by the area they cover, and marginally by correcting for land coverage. Overall we found little effect of using long-lat rather than equal-area projections in our analysis. The fitted relationship between environmental parameters and occurrence probability differed only very little between the two projection types. We still recommend using equal-area projections to avoid possible bias. More importantly, our results suggest that the cell area and the proportion of a cell covered by land should be
Budic, Lara; Didenko, Gregor; Dormann, Carsten F
2016-01-01
In species distribution analyses, environmental predictors and distribution data for large spatial extents are often available in long-lat format, such as degree raster grids. Long-lat projections suffer from unequal cell sizes, as a degree of longitude decreases in length from approximately 110 km at the equator to 0 km at the poles. Here we investigate whether long-lat and equal-area projections yield similar model parameter estimates, or result in a consistent bias. We analyzed the environmental effects on the distribution of 12 ungulate species with a northern distribution, as models for these species should display the strongest effect of projectional distortion. Additionally we choose four species with entirely continental distributions to investigate the effect of incomplete cell coverage at the coast. We expected that including model weights proportional to the actual cell area should compensate for the observed bias in model coefficients, and similarly that using land coverage of a cell should decrease bias in species with coastal distribution. As anticipated, model coefficients were different between long-lat and equal-area projections. Having progressively smaller and a higher number of cells with increasing latitude influenced the importance of parameters in models, increased the sample size for the northernmost parts of species ranges, and reduced the subcell variability of those areas. However, this bias could be largely removed by weighting long-lat cells by the area they cover, and marginally by correcting for land coverage. Overall we found little effect of using long-lat rather than equal-area projections in our analysis. The fitted relationship between environmental parameters and occurrence probability differed only very little between the two projection types. We still recommend using equal-area projections to avoid possible bias. More importantly, our results suggest that the cell area and the proportion of a cell covered by land should be
Modeling Tree Shade Effect on Urban Ground Surface Temperature.
Napoli, Marco; Massetti, Luciano; Brandani, Giada; Petralli, Martina; Orlandini, Simone
2016-01-01
There is growing interest in the role that urban forests can play as urban microclimate modifiers. Tree shade and evapotranspiration affect energy fluxes and mitigate microclimate conditions, with beneficial effects on human health and outdoor comfort. The aim of this study was to investigate surface temperature () variability under the shade of different tree species and to test the capability in predicting of a proposed heat transfer model. Surface temperature data on asphalt and grass under different shading conditions were collected in the Cascine park, Florence, Italy, and were used to test the performance of a one-dimensional heat transfer model integrated with a routine for estimating the effect of plant canopies on surface heat transfer. Shading effects of 10 tree species commonly used in Italian urban settings were determined by considering the infrared radiation and the tree canopy leaf area index (LAI). The results indicate that, on asphalt, was negatively related to the LAI of trees ( reduction ranging from 13.8 to 22.8°C). On grass, this relationship was weaker probably because of the combined effect of shade and grass evapotranspiration on ( reduction ranged from 6.9 to 9.4°C). A sensitivity analysis confirmed that other factors linked to soil water content play an important role in reduction of grassed areas. Our findings suggest that the energy balance model can be effectively used to estimate of the urban pavement under different shading conditions and can be applied to the analysis of microclimate conditions of urban green spaces. PMID:26828170
Physics-Based Reactive Burn Model: Grain size effects and binder effects
NASA Astrophysics Data System (ADS)
Lu, Xia; Hamate, Yuichio; Horie, Yasuyuki
2007-06-01
We have been developing a physics-based reactive burn (PBRB) model aiming at expanding predictive capability. The PBRB model was formulated based on the concept of a statistical hot spot cell. In the model, thermomechanics and physiochemical features are explicitly modeled. In this paper, we have extended the statistical hot spot model to explicitly describe the ignition and growth of hot spots. In particular, grain size effects are explicitly delineated through introduction of a size-dependent thickness of the hot-region thickness, a size-dependent energy deposition criterion, and a specific surface area. Besides the linear relationships between the run distance to detonation and critical diameter with the reciprocal specific surface area of HE, as discussed in a parallel paper in this meeting, parametric studies have also shown that the PBRB can predict a non-monotonous variation of shock sensitivity with grain size, as observed by Moulard et al. The purpose of this work is to extend the model to include the effects of explosive binders explicitly. As a first step we investigate the thermomechanical effects of a binder by using direct mesoscale simulations. The results will be used in the extending the PBRB model to include binder thermomechanics explicitly.
Modelling effects of internalized antibody: a simple comparative study
2014-01-01
Background The modelling framework is proposed to study protection properties of antibodies to neutralize the effects of the plant toxin (ricin). The present study extends our previous work by including (i) the model of intracellular transport of toxin to the Endoplasmic Reticulum and (ii) the model of the internalised antibodies (when antibody is delivered directly into the cytosol). Method Simulation of the receptor-toxin-antibody interaction is implemented by solving the systems of PDEs (advection-diffusion models) or ODEs (rate models) for the underlying transport coupled with mass-action kinetics. Results As the main application of the enhanced framework we present a comparative study of two kinds (external and internalised) of antibodies. This comparison is based on calculation of the non-dimensional protection factor using the same set of parameters (geometry, binding constants, initial concentrations of species, and total initial amount of the antibody). Conclusion This research will provide a framework for consistent evaluation and comparison of different types of antibodies for toxicological applications. PMID:24521456
Effective Models for Scientists Engaging in Meaningful Education and Outreach
NASA Astrophysics Data System (ADS)
Noel-Storr, Jacob; InsightSTEM SILC Partnership Team
2016-10-01
We present a central paradigm, extending the model of "Teacher-Scientist" partnerships towards a new philosophy of "Scientist-Instructor-Learner-Communicator" Partnerships. In this paradigm modes of, and expertise in, communication, and the learners themselves, are held is as high status as the experts and teachers in the learning setting.We present three distinctive models that rest on this paradigm in different educational settings. First a model in which scientists and teachers work together with a communications-related specialist to design and develop new science exploration tools for the classroom, and gather feedback from learners. Secondly, we present a model which involves an ongoing joint professional development program helping scientists and teachers to be co-communicators of knowledge exploration to their specific audience of learners. And thirdly a model in which scientists remotely support classroom research based on online data, while the teachers and their students learn to become effective communicators of their genuine scientific results.This work was funded in part by the American Association for the Advancement of Science, and by NASA awards NNX16AC68A and NNX16AJ21G. All opinions are those of the authors.
Occultation Modeling for Radiation Obstruction Effects on Spacecraft Systems
NASA Technical Reports Server (NTRS)
de Carufel, Guy; Li, Zu Qun; Harvey, Jason; Crues, Edwin Z.; Bielski, Paul
2016-01-01
A geometric occultation model has been developed to determine line-of-sight obstruction of radiation sources expected for different NASA space exploration mission designs. Example applications includes fidelity improvements for surface lighting conditions, radiation pressure, thermal and power subsystem modeling. The model makes use of geometric two dimensional shape primitives to most effectively model space vehicles. A set of these primitives is used to represent three dimensional obstructing objects as a two dimensional outline from the perspective of an observing point of interest. Radiation sources, such as the Sun or a Moon's albedo is represented as a collection of points, each of which is assigned a flux value to represent a section of the radiation source. Planetary bodies, such as a Martian moon, is represented as a collection of triangular facets which are distributed in spherical height fields for optimization. These design aspects and the overall model architecture will be presented. Specific uses to be presented includes a study of the lighting condition on Phobos for a possible future surface mission, and computing the incident flux on a spacecraft's solar panels and radiators from direct and reflected solar radiation subject to self-shadowing or shadowing by third bodies.
Combined analysis of effective Higgs portal dark matter models
NASA Astrophysics Data System (ADS)
Beniwal, Ankit; Rajec, Filip; Savage, Christopher; Scott, Pat; Weniger, Christoph; White, Martin; Williams, Anthony G.
2016-06-01
We combine and extend the analyses of effective scalar, vector, Majorana and Dirac fermion Higgs portal models of dark matter (DM), in which DM couples to the Standard Model (SM) Higgs boson via an operator of the form ODMH†H . For the fermion models, we take an admixture of scalar ψ ¯ψ and pseudoscalar ψ ¯ i γ5ψ interaction terms. For each model, we apply constraints on the parameter space based on the Planck measured DM relic density and the LHC limits on the Higgs invisible branching ratio. For the first time, we perform a consistent study of the indirect detection prospects for these models based on the WMAP7/Planck observations of the cosmic microwave background, a combined analysis of 15 dwarf spheroidal galaxies by Fermi-LAT and the upcoming Cherenkov Telescope Array (CTA). We also perform a correct treatment of the momentum-dependent direct search cross section that arises from the pseudoscalar interaction term in the fermionic DM theories. We find, in line with previous studies, that current and future direct search experiments such as LUX and XENON1T can exclude much of the parameter space, and we demonstrate that a joint observation in both indirect and direct searches is possible for high mass weakly interacting massive particles. In the case of a pure pseudoscalar interaction of a fermionic DM candidate, future gamma-ray searches are the only class of experiment capable of probing the high mass range of the theory.
Neuroprotective effects of VCP modulators in mouse models of glaucoma.
Nakano, Noriko; Ikeda, Hanako Ohashi; Hasegawa, Tomoko; Muraoka, Yuki; Iwai, Sachiko; Tsuruyama, Tatsuaki; Nakano, Masaki; Fuchigami, Tomohiro; Shudo, Toshiyuki; Kakizuka, Akira; Yoshimura, Nagahisa
2016-04-01
Glaucoma is a major cause of adult blindness due to gradual death of retinal ganglion cells. Currently, no therapeutics are available for the protection of these cells from the cell death. We have recently succeeded in synthesizing novel compounds, KUSs (Kyoto University Substances), which can reduce cellular ATP consumption by specifically inhibiting the ATPase activities of VCP, a major ATPase in the cell, and we have shown that KUSs could mitigate the disease progression of rd10, a mouse model of retinitis pigmentosa, without any apparent side effects. Here we show that KUSs (e.g. KUS121 and KUS187) can prevent antimycin- and oligomycin-induced ATP depletion, endoplasmic reticulum (ER) stress, and cell death in neuronally differentiated PC12 cells. Furthermore, KUSs manifest significant efficacies on several mouse models of glaucoma. KUS administration prevented or mitigated ER stress and subsequent apoptotic cell death of retinal ganglion cells in an acute injury mouse model of retinal ganglion cell loss, which was induced with N-methyl-D-aspartate. In a mouse model of glaucoma with high intraocular pressure, KUSs prevented the typical glaucoma pathologies, i.e. enlargement of optic disc cupping and thinning of the retinal nerve fiber layer. KUSs also preserved visual functions in GLAST knockout mice, a mouse model for chronic retinal ganglion cell loss. We propose "ATP maintenance" via inhibition of ATPase activities of VCP as a promising new neuroprotective strategy for currently incurable eye diseases, such as glaucoma. PMID:27441270
Compressibility effects in the Miami isopycnic coordinate ocean model
NASA Astrophysics Data System (ADS)
Sun, Shan
Potential density referenced to sea level pressure (sigmasb0) has shown its usefulness as vertical coordinate in ocean models in many ways, but there are problems with sigmasb0 (potential density referenced to sea level) coordinates in the deep ocean: sigmasb0(z) can be multivalued, leading to coordinate folding, and sigmasb0 surfaces can deviate from the so-called neutral surfaces, which are the surfaces along which turbulent lateral mixing takes place in a stratified medium. The reason for both of these problems is that most isopycnal models regard seawater as uniformly compressible. However, the effect of water temperature on compressibility cannot be ignored. In this study a two-pronged approach is taken to improve the model accuracy. First, since the effects of compressibility variation are proportional to the difference between the local and the reference pressure, we replace the model's traditional sigmasb0 coordinate by sigmasb2 (potential density referenced to 2000 dbar). This step eliminates many of the coordinate folding problems associated with sigmasb0 and generally reduces the difference between coordinate and neutrally buoyant surfaces. Second, we split the compressibility coefficient into a pressure- and a temperature-dependent part and, recognizing that the former is dynamically passive, retain only the effect of the latter in the governing equations. This is accomplished by introducing a new variable called "active density"-the density with the pressure-related compressibility removed. Therefore, sigmasb2 is adopted as vertical coordinate, but active density is used to express the seawater density within the layers. The above changes are applied in a near-global, 16-layer, 2sp° x 2sp°cos (lat.) Miami Isopycnic Coordinate Ocean Model (MICOM). The model is driven by observed atmospheric conditions. MICOM modified in this fashion produces realistic meridional mass and associated heat fluxes in the three major ocean basins. A realistic formation
Spatial effects in real networks: Measures, null models, and applications
NASA Astrophysics Data System (ADS)
Ruzzenenti, Franco; Picciolo, Francesco; Basosi, Riccardo; Garlaschelli, Diego
2012-12-01
Spatially embedded networks are shaped by a combination of purely topological (space-independent) and space-dependent formation rules. While it is quite easy to artificially generate networks where the relative importance of these two factors can be varied arbitrarily, it is much more difficult to disentangle these two architectural effects in real networks. Here we propose a solution to this problem, by introducing global and local measures of spatial effects that, through a comparison with adequate null models, effectively filter out the spurious contribution of nonspatial constraints. Our filtering allows us to consistently compare different embedded networks or different historical snapshots of the same network. As a challenging application we analyze the World Trade Web, whose topology is known to depend on geographic distances but is also strongly determined by nonspatial constraints (degree sequence or gross domestic product). Remarkably, we are able to detect weak but significant spatial effects both locally and globally in the network, showing that our method succeeds in retrieving spatial information even when nonspatial factors dominate. We finally relate our results to the economic literature on gravity models and trade globalization.
Unified modeling of turbulence effects on sound propagation.
Cheinet, Sylvain; Ehrhardt, Loic; Juvé, Daniel; Blanc-Benon, Philippe
2012-10-01
Many aspects of outdoor sound propagation depend on the scattering effects induced by atmospheric turbulence. Standard analytical and numerical assessments of these effects make an a priori distinction between the scattering effects at large versus small angles. The present study evaluates the ability of a numerical model in overcoming this distinction. The model solves a set of two coupled equations for the sound pressure and vector acoustic velocity, with the finite-difference time domain approach. It is first introduced and evaluated. The numerical predictions are compared to well-known analytical solutions in the case of two-dimensional plane wave propagation through turbulence. They are found to agree in the investigated scenarios. Hence, the finite-difference, time domain solution of the two coupled equations provides a unified, versatile numerical approach to investigating the effects of atmospheric turbulence on sound propagation. The comparison also provides original insights on the applicability and limitations of various methods used to investigate sound propagation through turbulence.
Microscopic models for the study of taxpayer audit effects
NASA Astrophysics Data System (ADS)
Bertotti, Maria Letizia; Modanese, Giovanni
2016-03-01
A microscopic dynamic model is here constructed and analyzed, describing the evolution of the income distribution in the presence of taxation and redistribution in a society in which also tax evasion and auditing processes occur. The focus is on effects of enforcement regimes, characterized by different choices of the audited taxpayer fraction and of the penalties imposed to noncompliant individuals. A complex systems perspective is adopted: society is considered as a system composed by a large number of heterogeneous individuals. These are divided into income classes and may as well have different tax evasion behaviors. The variation in time of the number of individuals in each class is described by a system of nonlinear differential equations of the kinetic discretized Boltzmann type involving transition probabilities. A priori, one could think that audits and fines should have a positive effect on the reduction of economic inequality and correspondingly of the Gini index G. According to our model, however, such effect is rather small. In contrast, the effect on the increase of the tax revenue may be significant.
Coarse-grained DNA modeling: Hybridization and ionic effects
NASA Astrophysics Data System (ADS)
Hinckley, Daniel M.
Deoxyribonucleic acid (DNA) is a biopolymer of enormous significance in living systems. The utility of DNA in such systems is derived from the programmable nature of DNA and its unique mechanical properties. Recently, material scientists have harnessed these properties in order to create systems that spontaneous self-assemble on the nanoscale. Both biologists and material scientists are hindered by an incomplete understanding of the physical interactions that together govern DNA's behavior. Computer simulations, especially those at the coarse-grained (CG) level, can potentially complete this understanding by resolving details indiscernible with current experimental techniques. In this thesis, we advance the state-of-the-art of DNA CG simulations by first reviewing the relevant theory and the evolution of CG DNA models since their inception. Then we present 3SPN.2, an improved CG model for DNA that should provide new insights into biological and nanotechnological systems which incorporate DNA. We perform forward flux sampling simulations in order to examine the effect of sequence, oligomer length, and ionic strength on DNA oligomer hybridization. Due to the limitations inherent in continuum treatments of electrostatic interactions in biological systems, we generate a CG model of biological ions for use with 3SPN.2 and other CG models. Lastly, we illustrate the potential of 3SPN.2 and CG ions by using the models in simulations of viral capsid packaging experiments. The models and results described in this thesis will be useful in future modeling efforts that seek to identify the fundamental physics that govern behavior such as nucleosome positioning, DNA hybridization, and DNA nanoassembly.
Smith, Alastair C; Monaghan, Padraic; Huettig, Falk
2014-12-01
Learning to read and write requires an individual to connect additional orthographic representations to pre-existing mappings between phonological and semantic representations of words. Past empirical results suggest that the process of learning to read and write (at least in alphabetic languages) elicits changes in the language processing system, by either increasing the cognitive efficiency of mapping between representations associated with a word, or by changing the granularity of phonological processing of spoken language, or through a combination of both. Behavioural effects of literacy have typically been assessed in offline explicit tasks that have addressed only phonological processing. However, a recent eye tracking study compared high and low literate participants on effects of phonology and semantics in processing measured implicitly using eye movements. High literates' eye movements were more affected by phonological overlap in online speech than low literates, with only subtle differences observed in semantics. We determined whether these effects were due to cognitive efficiency and/or granularity of speech processing in a multimodal model of speech processing - the amodal shared resource model (ASR, Smith, Monaghan, & Huettig, 2013a,b). We found that cognitive efficiency in the model had only a marginal effect on semantic processing and did not affect performance for phonological processing, whereas fine-grained versus coarse-grained phonological representations in the model simulated the high/low literacy effects on phonological processing, suggesting that literacy has a focused effect in changing the grain-size of phonological mappings. PMID:25171049
Land surface modeling of energy-balance components: Model validation and scaling effects
NASA Astrophysics Data System (ADS)
Sridhar, Venkataramana Rao
Scope and method of study. Appropriate quantification of surface energy balance components that influence land-atmosphere exchange phenomena is important for improved weather prediction. The issue of scale interaction has emerged as one of the crucial challenges for the parameterization of general circulation models (GCMs) due to the strong interconnection between land and atmospheric processes. The objective of this study was to examine the effects of different spatial scales of input data on modeled net radiation, latent, sensible and ground heat fluxes and hence to understand the resolution needed for the realistic modeling of large-area land and atmospheric interactions. This study employed the NOAH- OSU (Oregon State University) Land Surface Model (LSM), which is a popular model used in a coupled fashion with the NCEP operational Eta and PSU/MM5 mesoscale models. Since the model requires downwelling longwave radiation as one of its inputs, a simple estimation procedure was developed and tested using nine Oklahoma Atmospheric Surface-Layer Instrumentation System (OASIS) sites. Then the full LSM was tested using seven OASIS sites with diverse soils, vegetation and climate. Finally, at three different spatial scales, model simulations were performed for the most homogeneous and the most heterogeneous areas of the Southern Great Plains 1997 study region. Findings and conclusions. The newly developed scheme for the estimation of downwelling longwave radiation performed very well during both daytime and nighttime as well as under clear and cloudy sky conditions. Two methods of green vegetation fraction showed some differences in the estimates of latent and sensible heat fluxes. LSM validation using OASIS measurements at individual sites showed that the seven- site mean of modeled net radiation had a slight positive bias. It appeared that the model assigned most of this excess energy to latent heat flux. In the scaling study for the heterogeneous region, simulation
Modeling misregistration and related effects on multispectral classification
NASA Technical Reports Server (NTRS)
Billingsley, F. C.
1981-01-01
The effects of misregistration on the multispectral classification accuracy when the scene registration accuracy is relaxed from 0.3 to 0.5 pixel are investigated. Noise, class separability, spatial transient response, and field size are considered simultaneously with misregistration in their effects on accuracy. Any noise due to the scene, sensor, or to the analog/digital conversion, causes a finite fraction of the measurements to fall outside of the classification limits, even within nominally uniform fields. Misregistration causes field borders in a given band or set of bands to be closer than expected to a given pixel, causing additional pixels to be misclassified due to the mixture of materials in the pixel. Simplified first order models of the various effects are presented, and are used to estimate the performance to be expected.
The antidepressant-like effects of paeoniflorin in mouse models
QIU, FENGMEI; ZHONG, XIAOMING; MAO, QINGQIU; HUANG, ZHEN
2013-01-01
Peony is often used in Chinese herbal medicine for the treatment of depression-like disorders. Our previous studies have demonstrated that the total glycosides of peony exert antidepressant-like effects in animal models. Paeoniflorin is the main active glycoside of peony. The aim of this study was to evaluate the antidepressant-like effects of paeoniflorin in mice, as well as its active mechanisms. The results revealed that intraperitoneally injected paeoniflorin significantly reduced the duration of immobility in forced swimming and tail suspension tests. The doses that affected the immobility response did not affect locomotor activity. Furthermore, paeoniflorin antagonized reserpine-induced ptosis, akinesia and hypothermia. Paeoniflorin also significantly increased the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus. These results suggest that the upregulation of serotonergic systems may be an important mechanism for the antidepressant-like effects of paeoniflorin in mice. PMID:23599734