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Sample records for reactivity feedback model

  1. Control Rod Driveline Reactivity Feedback Model for Liquid Metal Reactors

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young-Min; Jeong, Hae-Yong; Chang, Won-Pyo; Cho, Chung-Ho; Lee, Yong-Bum

    2008-01-15

    The thermal expansion of the control rod drivelines (CRDL) is one important passive mitigator under all unprotected accident conditions in the metal and oxide cores. When the CRDL are washed by hot sodium in the coolant outlet plenum, the CRDL thermally expands and causes the control rods to be inserted further down into the active core region, providing a negative reactivity feedback. Since the control rods are attached to the top of the vessel head and the core attaches to the bottom of the reactor vessel (RV), the expansion of the vessel wall as it heats will either lower the core or raise the control rods supports. This contrary thermal expansion of the reactor vessel wall pulls the control rods out of the core somewhat, providing a positive reactivity feedback. However this is not a safety factor early in a transient because its time constant is relatively large. The total elongated length is calculated by subtracting the vessel expansion from the CRDL expansion to determine the net control rod expansion into the core. The system-wide safety analysis code SSC-K includes the CRDL/RV reactivity feedback model in which control rod and vessel expansions are calculated using single-nod temperatures for the vessel and CRDL masses. The KALIMER design has the upper internal structures (UIS) in which the CRDLs are positioned outside the structure where they are exposed to the mixed sodium temperature exiting the core. A new method to determine the CRDL expansion is suggested. Two dimensional hot pool thermal hydraulic model (HP2D) originally developed for the analysis of the stratification phenomena in the hot pool is utilized for a detailed heat transfer between the CRDL mass and the hot pool coolant. However, the reactor vessel wall temperature is still calculated by a simple lumped model.

  2. New Fuel Pin Axial Expansion Reactivity Feedback Model in MARS-LMR

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Chiwoong; Ha, Kwiseok [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    In this study, the sensitivity tests are conducted. In the case of the UTOP event, a sensitivity test for the reactivity insertion amount and rate were conducted. This analysis can give a requirement for margin of control rod stop system (CRSS). For example, the CRSS in the PRISM designed based on the 0.4 $ reactivity insertion, which is analyzed with safety analysis of UTOP event. Moreover, the sensitivity tests for weighting factor in the core radial expansion reactivity feedback model were also carried out for all ATWS events. Currently, the reactivity feedback model for the PGSFR is not validated yet. However, the reactivity feedback models in the MARS-LMR are validating with various plant-based data including EBR-II SHRT. The ATWS events for the PGSFR classified in the design extended condition including UTOP, ULOF, and ULOHS are analyzed with MARS-LMR. In this study, the sensitivity tests for reactivity insertion amount and rate in the UTOP event are conducted. The reactivity insertion amount is obviously an influential parameter. The reactivity insertion amount can give a requirement for design of the CRSS, therefore, this sensitivity result is very important to the CRSS. In addition, sensitivity tests for the weighting factor in the radial expansion reactivity model are carried out. The weighting factor for a grid plate, W{sub GP}, which means contribution of feedback in the grid plate is changed for all unprotected events. The grid plate expansion is governed by a core inlet temperature. As the W{sub GP} is increased, the power in the UTOP and the ULOF is increased, however, the power in the ULOHS is decreased. The higher power during transient means lower reactivity feedback and smaller expansion. Thus, the core outlet temperature rise is dominant in the UTOP and ULOF events, however, the core inlet temperature rise is dominant in the ULOHS. Therefore, the grid plate expansion in the ULOHS is predominant. These analysis results will give better

  3. A simple reactivity feedback model accounting for radial core expansion effects in the liquid metal fast reactor

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young Min; Lee, Yong Bum; Chang, Won Pyo; Haha, Do Hee [KAERI, Taejon (Korea, Republic of)

    2002-10-01

    The radial core expansion due to the structure temperature rise is one of major negative reactivity insertion mechanisms in metallic fueled reactor. Thermal expansion is a result of both the laws of nature and the particular core design and it causes negative reactivity feedback by the combination of increased core volume captures and increased core surface leakage. The simple radial core expansion reactivity feedback model developed for the SSC-K code was evaluated by the code-to-code comparison analysis. From the comparison results, it can be stated that the radial core expansion reactivity feedback model employed into the SSC-K code may be reasonably accurate in the UTOP analysis.

  4. Experimental study of the effect of void reactivity feedback on the behavior of the scaled model boiling water reactor

    Science.gov (United States)

    Meftah, Khaled

    A Scaled Model Boiling Water Reactor (SMBWR) model uses low pressure (i.e., 0.095 MPa) water in a heated channel 0.5 meters in length with four electrically heated fuel simulator rods. The axial void profile in the channel is measured using conductivity probes and the power to the heaters is modulated according to the void fraction to simulate void reactivity feedback. The steam from the heated channel is passed through a valve that reduces the pressure to 0.012 MPa where the steam is condensed in conditions similar to those found in a conventional BWR condenser. The feedwater flow rate, heater power, and instrumentation in the facility are controlled and monitored through a Quadra 950 computer running LabVIEW software. The void fraction signals are analyzed to identify the different flow regimes and determine the vapor velocity in the SMBWR channel using features of the probability density function and power spectral density. The void coefficient of reactivity is modified in the BWR scale model through the LabVIEW interface and the effect on the behavior of the channel is directly observed. The system response is reported for abrupt stepwise pressure changes and abrupt stepwise power changes. The response is typical of that expected for a BWR. The void reactivity feedback effect is also examined by analyzing the frequency response of the channel void fraction at steady state.

  5. Reactivity feedback coefficients Pakistan research reactor-1 using PRIDE code

    Energy Technology Data Exchange (ETDEWEB)

    Mansoor, Ali; Ahmed, Siraj-ul-Islam; Khan, Rustam [Pakistan Institute of Engineering and Applied Sciences, Islamabad (Pakistan). Dept. of Nuclear Engineering; Inam-ul-Haq [Comsats Institute of Information Technology, Islamabad (Pakistan). Dept. of Physics

    2017-05-15

    Results of the analyses performed for fuel, moderator and void's temperature feedback reactivity coefficients for the first high power core configuration of Pakistan Research Reactor - 1 (PARR-1) are summarized. For this purpose, a validated three dimensional model of PARR-1 core was developed and confirmed against the reference results for reactivity calculations. The ''Program for Reactor In-Core Analysis using Diffusion Equation'' (PRIDE) code was used for development of global (3-dimensional) model in conjunction with WIMSD4 for lattice cell modeling. Values for isothermal fuel, moderator and void's temperature feedback reactivity coefficients have been calculated. Additionally, flux profiles for the five energy groups were also generated.

  6. Characteristics of a reactor with power reactivity feedback

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The point-reactor model with power reactivity feedback becomes a nonlinear system. Its dynamic characteristic shows great complexity. According to the mathematic definition of stability in differential equa-tion qualitative theory, the model of a reactor with power reactivity feedback is judged unstable. The equilib-rium point is a saddle-node point. A portion of the trajectory in the neighborhood of the equilibrium point is parabolic fan curve, and the other is hyperbolic fan curve. Based on phase locus near the equilibrium point, it is pointed out that the model is still stable within physical limits. The difference between stabilities in the mathematical sense and in the physical sense is indicated.

  7. Spatial distribution effect of feedback reactivity in TRACY experiments. Evaluation of the first power peak characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Obara, Toru; Sekimoto, Hiroshi [Tokyo Inst. of Technology, Research Lab. for Nuclear Reactors, Tokyo (Japan); Nakajima, Ken; Miyoshi, Yoshinori [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2001-06-01

    To investigate the spatial effect of feedback reactivity in TRACY experiments, evaluations of the first power peak characteristics using the one-point reactor approximation model and a space dependent kinetics code, PCTAC, were conducted. Analyses for a core with uniform temperature distribution using the temperature feedback reactivity multiplied by a weight of 1.5 gave the same results as those for a core with space dependent power distribution. Neutronic calculations for spatial effect of temperature and space dependent kinetics analyses showed that the spatial effect of the temperature feedback reactivity at the peak power was dominated by the power distribution without feedback, and this resulted in a weight of 1.5. (author)

  8. Telling perfectionists about their perfectionism: Effects of providing feedback on emotional reactivity and psychological symptoms.

    Science.gov (United States)

    Aldea, Mirela A; Rice, Kenneth G; Gormley, Barbara; Rojas, Ariz

    2010-12-01

    A randomized, controlled clinical trial was conducted to determine the efficacy of receiving feedback in a sample of maladaptive perfectionists. A total of 60 young adults were randomly assigned to a feedback intervention or control group. Hierarchical Linear Modeling was utilized to analyze the effects of perfectionism over time, as well as the effects of treatment condition on the relationship between perfectionism and outcomes. Measures of interest included emotional reactivity, self-esteem, and psychological distress. Findings revealed that providing feedback to maladaptive perfectionists reduced self-reported global symptomatic distress as well as emotional reactivity. The results are discussed in light of treatment implications, especially with regard to the manner in which perfectionists respond to therapeutic interventions. Overall, study findings suggest that a brief, low-cost feedback intervention is effective at decreasing psychological distress in maladaptive perfectionists and may serve as a beneficial precursor to individual therapy or counseling.

  9. Models of AGN feedback

    CERN Document Server

    Combes, F

    2014-01-01

    The physical processes responsible of sweeping up the surrounding gas in the host galaxy of an AGN, and able in some circumstances to expel it from the galaxy, are not yet well known. The various mechanisms are briefly reviewed: quasar or radio modes, either momentum-conserving outflows, energy-conserving outflows, or intermediate. They are confronted to observations, to know whether they can explain the M-sigma relation, quench the star formation or whether they can also provide some positive feedback and how the black hole accretion history is related to that of star formation.

  10. Investigation of Reactivity Feedback Mechanism of Axial and Radial Expansion Effect of Metal-Fueled Sodium-Cooled Fast Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Seong, Seung-Hwan; Choi, Chi-Woong; Jeong, Tae-Kyung; Ha, Gi-Seok [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-05-15

    The major inherent reactivity feedback models for a ceramic fuel used in a conventional light water reactor are Doppler feedback and moderator feedback. The metal fuel has these two reactivity feedback mechanisms previously mentioned. In addition, the metal fuel has two more reactivity feedback models related to the thermal expansion phenomena of the metal fuel. Since the metal fuel has a good capability to expand according to the temperature changes of the core, two more feedback mechanisms exist. These additional two feedback mechanism are important to the inherent safety of metal fuel and can make metal-fueled SFR safer than oxide-fueled SFR. These phenomena have already been applied to safety analysis on design extended condition. In this study, the effect of these characteristics on power control capability was examined through a simple load change operation. The axial expansion mechanism is induced from the change of the fuel temperature according to the change of the power level of PGSFR. When the power increases, the fuel temperatures in the metal fuel will increase and then the reactivity will decrease due to the axial elongation of the metal fuel. To evaluate the expansion effect, 2 cases were simulated with the same scenario by using MMS-LMR code developed at KAERI. The first simulation was to analyze the change of the reactor power according to the change of BOP power without the reactivity feedback model of the axial and radial expansion of the core during the power transient event. That is to say, the core had only two reactivity feedback mechanism of Doppler and coolant temperature.

  11. Probabilistic models for feedback systems.

    Energy Technology Data Exchange (ETDEWEB)

    Grace, Matthew D.; Boggs, Paul T.

    2011-02-01

    In previous work, we developed a Bayesian-based methodology to analyze the reliability of hierarchical systems. The output of the procedure is a statistical distribution of the reliability, thus allowing many questions to be answered. The principal advantage of the approach is that along with an estimate of the reliability, we also can provide statements of confidence in the results. The model is quite general in that it allows general representations of all of the distributions involved, it incorporates prior knowledge into the models, it allows errors in the 'engineered' nodes of a system to be determined by the data, and leads to the ability to determine optimal testing strategies. In this report, we provide the preliminary steps necessary to extend this approach to systems with feedback. Feedback is an essential component of 'complexity' and provides interesting challenges in modeling the time-dependent action of a feedback loop. We provide a mechanism for doing this and analyze a simple case. We then consider some extensions to more interesting examples with local control affecting the entire system. Finally, a discussion of the status of the research is also included.

  12. Testing of an Integrated Reactor Core Simulator and Power Conversion System with Simulated Reactivity Feedback

    Science.gov (United States)

    Bragg-Sitton, Shannon M.; Hervol, David S.; Godfroy, Thomas J.

    2010-01-01

    A Direct Drive Gas-Cooled (DDG) reactor core simulator has been coupled to a Brayton Power Conversion Unit (BPCU) for integrated system testing at NASA Glenn Research Center (GRC) in Cleveland, Ohio. This is a closed-cycle system that incorporates an electrically heated reactor core module, turboalternator, recuperator, and gas cooler. Nuclear fuel elements in the gas-cooled reactor design are replaced with electric resistance heaters to simulate the heat from nuclear fuel in the corresponding fast spectrum nuclear reactor. The thermodynamic transient behavior of the integrated system was the focus of this test series. In order to better mimic the integrated response of the nuclear-fueled system, a simulated reactivity feedback control loop was implemented. Core power was controlled by a point kinetics model in which the reactivity feedback was based on core temperature measurements; the neutron generation time and the temperature feedback coefficient are provided as model inputs. These dynamic system response tests demonstrate the overall capability of a non-nuclear test facility in assessing system integration issues and characterizing integrated system response times and response characteristics.

  13. Electrocortical reactivity to social feedback in youth: A pilot study of the Island Getaway task

    Directory of Open Access Journals (Sweden)

    Autumn Kujawa

    2014-10-01

    Full Text Available Peer relationships become a major concern in adolescence, yet event-related potential (ERP measures of reactivity to social feedback in adolescence are limited. In this pilot study, we tested a novel task to elicit reactivity to social feedback in youth. Participants (10–15 years old; 57.9% male; N = 19 played a game that involved exchanging personal information with peers, voting to remove players from the game, and receiving rejection and acceptance feedback from peers. Results indicated that participants modified their voting behavior in response to peer feedback, and rejection feedback was associated with a negativity in the ERP wave compared to acceptance (i.e., the feedback negativity, FN. The FN predicted behavioral patterns, such that participants who showed greater neural reactivity to social feedback were less likely to reject co-players. Preliminary analyses suggest that the task may be a useful measure of individual differences: adolescents higher in social anxiety symptoms were less likely to reject peers and showed an enhanced FN to rejection vs. acceptance feedback, and higher depressive symptoms predicted an increased FN to rejection specifically. Results suggest that the FN elicited by social feedback may be a useful, economical neural measure of social processing across development and in clinical research.

  14. Judges in judo conform to the referee because of the reactive feedback system.

    Science.gov (United States)

    Boen, Filip; Ginis, Pieter; Smits, Tim

    2013-01-01

    This experiment tested whether the conformism observed among panels of judges in aesthetic sports also occurs among judges in judo. Similar to aesthetic sports, judo judging relies upon a form of open feedback. However, in judo, this system is reactive (i.e. two judges have to publicly 'correct' the score given by the higher-status referee), whereas it is active in aesthetic sports (i.e. judges with equal status report their score simultaneously and can use the feedback about the scores of their colleagues for evaluating later performances). In order to test whether such reactive open-feedback system leads to conformism among judges in judo, we designed an experiment in which this feedback was manipulated. Participants were 20 certified Flemish judges, who had to score two sets of 11 ambiguous video sequences that are used during formation and training of judo judges: one set with feedback about the referee's score and one set without feedback. The results revealed that when participants knew the referee's score, their scores were significantly more in line with this score than when they did not know this score. More specifically, for both sets of sequences at least 10% less deviations from the referee were observed when participants were given feedback about the score of the referee. These results suggest that preventable conformism can occur in typical judo judging, that is with reactive open feedback.

  15. Neuroticism and responsiveness to error feedback: adaptive self-regulation versus affective reactivity.

    Science.gov (United States)

    Robinson, Michael D; Moeller, Sara K; Fetterman, Adam K

    2010-10-01

    Responsiveness to negative feedback has been seen as functional by those who emphasize the value of reflecting on such feedback in self-regulating problematic behaviors. On the other hand, the very same responsiveness has been viewed as dysfunctional by its link to punishment sensitivity and reactivity. The present 4 studies, involving 203 undergraduate participants, sought to reconcile such discrepant views in the context of the trait of neuroticism. In cognitive tasks, individuals were given error feedback when they made mistakes. It was found that greater tendencies to slow down following error feedback were associated with higher levels of accuracy at low levels of neuroticism but lower levels of accuracy at high levels of neuroticism. Individual differences in neuroticism thus appear crucial in understanding whether behavioral alterations following negative feedback reflect proactive versus reactive mechanisms and processes. Implications for understanding the processing basis of neuroticism and adaptive self-regulation are discussed.

  16. How Are Feedbacks Represented in Land Models?

    Directory of Open Access Journals (Sweden)

    Yang Chen

    2016-09-01

    Full Text Available Land systems are characterised by many feedbacks that can result in complex system behaviour. We defined feedbacks as the two-way influences between the land use system and a related system (e.g., climate, soils and markets, both of which are encompassed by the land system. Land models that include feedbacks thus probably more accurately mimic how land systems respond to, e.g., policy or climate change. However, representing feedbacks in land models is a challenge. We reviewed articles incorporating feedbacks into land models and analysed each with predefined indicators. We found that (1 most modelled feedbacks couple land use systems with transport, soil and market systems, while only a few include feedbacks between land use and social systems or climate systems; (2 equation-based land use models that follow a top-down approach prevail; and (3 feedbacks’ effects on system behaviour remain relatively unexplored. We recommend that land system modellers (1 consider feedbacks between land use systems and social systems; (2 adopt (bottom-up approaches suited to incorporating spatial heterogeneity and better representing land use decision-making; and (3 pay more attention to nonlinear system behaviour and its implications for land system management and policy.

  17. Quadratic reactivity fuel cycle model

    Energy Technology Data Exchange (ETDEWEB)

    Lewins, J.D.

    1985-11-01

    For educational purposes it is highly desirable to provide simple yet realistic models for fuel cycle and fuel economy. In particular, a lumped model without recourse to detailed spatial calculations would be very helpful in providing the student with a proper understanding of the purposes of fuel cycle calculations. A teaching model for fuel cycle studies based on a lumped model assuming the summability of partial reactivities with a linear dependence of reactivity usefully illustrates fuel utilization concepts. The linear burnup model does not satisfactorily represent natural enrichment reactors. A better model, showing the trend of initial plutonium production before subsequent fuel burnup and fission product generation, is a quadratic fit. The study of M-batch cycles, reloading 1/Mth of the core at end of cycle, is now complicated by nonlinear equations. A complete account of the asymptotic cycle for any order of M-batch refueling can be given and compared with the linear model. A complete account of the transient cycle can be obtained readily in the two-batch model and this exact solution would be useful in verifying numerical marching models. It is convenient to treat the parabolic fit rho = 1 - tau/sup 2/ as a special case of the general quadratic fit rho = 1 - C/sub tau/ - (1 - C)tau/sup 2/ in suitably normalized reactivity and cycle time units. The parabolic results are given in this paper.

  18. Finite Feedback Cycling in Structural Equation Models

    Science.gov (United States)

    Hayduk, Leslie A.

    2009-01-01

    In models containing reciprocal effects, or longer causal loops, the usual effect estimates assume that any effect touching a loop initiates an infinite cycling of effects around that loop. The real world, in contrast, might permit only finite feedback cycles. I use a simple hypothetical model to demonstrate that if the world permits only a few…

  19. A Mechanistic Reliability Assessment of RVACS and Metal Fuel Inherent Reactivity Feedbacks

    Energy Technology Data Exchange (ETDEWEB)

    Grabaskas, David; Brunett, Acacia J.; Passerini, Stefano; Grelle, Austin

    2017-09-24

    GE Hitachi Nuclear Energy (GEH) and Argonne National Laboratory (Argonne) participated in a two year collaboration to modernize and update the probabilistic risk assessment (PRA) for the PRISM sodium fast reactor. At a high level, the primary outcome of the project was the development of a next-generation PRA that is intended to enable risk-informed prioritization of safety- and reliability-focused research and development. A central Argonne task during this project was a reliability assessment of passive safety systems, which included the Reactor Vessel Auxiliary Cooling System (RVACS) and the inherent reactivity feedbacks of the metal fuel core. Both systems were examined utilizing a methodology derived from the Reliability Method for Passive Safety Functions (RMPS), with an emphasis on developing success criteria based on mechanistic system modeling while also maintaining consistency with the Fuel Damage Categories (FDCs) of the mechanistic source term assessment. This paper provides an overview of the reliability analyses of both systems, including highlights of the FMEAs, the construction of best-estimate models, uncertain parameter screening and propagation, and the quantification of system failure probability. In particular, special focus is given to the methodologies to perform the analysis of uncertainty propagation and the determination of the likelihood of violating FDC limits. Additionally, important lessons learned are also reviewed, such as optimal sampling methodologies for the discovery of low likelihood failure events and strategies for the combined treatment of aleatory and epistemic uncertainties.

  20. Simple models of assortment through environmental feedback.

    Science.gov (United States)

    Pepper, John W

    2007-01-01

    Social evolution depends critically on assortment, or segregation versus even mixing, between cooperators and noncooperators. Altruistic traits, which reduce the absolute fitness of their bearers, cannot evolve without positive assortment (excess segregation). The question of how positive assortment can arise has been controversial, but most evolutionary biologists believe that common descent is the only effective general mechanism. Here I investigate another recently proposed mechanism for generating nonrandom assortment, termed environmental feedback. This requires only that two forms of a trait affect the quality of the local environment differently in such a way that all individuals are more likely to leave low-quality locales. Experiments with simple computational models confirm that environmental feedback generates significant levels of genetic similarity among non-kin within locales. The mechanism is fairly general, and can under some conditions produce levels of genetic similarity comparable to those resulting from close genealogical relationship. Environmental feedback can also generate the negative assortment necessary for the evolution of spiteful traits. Environmental feedback is expected to create positive frequency-dependent selection, which thus favor any social trait that becomes common in the population. Results from this stylized model suggest that environmental feedback could be important in the evolution of both cooperation and spite, within as well as between species.

  1. Thermal-hydraulic modeling of reactivity accidents in MTR reactors

    Directory of Open Access Journals (Sweden)

    Khater Hany

    2006-01-01

    Full Text Available This paper describes the development of a dynamic model for the thermal-hydraulic analysis of MTR research reactors during a reactivity insertion accident. The model is formulated for coupling reactor kinetics with feedback reactivity and reactor core thermal-hydraulics. To represent the reactor core, two types of channels are considered, average and hot channels. The developed computer program is compiled and executed on a personal computer, using the FORTRAN language. The model is validated by safety-related benchmark calculations for MTR-TYPE reactors of IAEA 10 MW generic reactor for both slow and fast reactivity insertion transients. A good agreement is shown between the present model and the benchmark calculations. Then, the model is used for simulating the uncontrolled withdrawal of a control rod of an ETRR-2 reactor in transient with over power scram trip. The model results for ETRR-2 are analyzed and discussed.

  2. A Superbubble Feedback Model for Galaxy Simulations

    CERN Document Server

    Keller, B W; Benincasa, S M; Couchman, H M P

    2014-01-01

    We present a new stellar feedback model that reproduces superbubbles. Superbubbles from clustered young stars evolve quite differently to individual supernovae and are substantially more efficient at generating gas motions. The essential new components of the model are thermal conduction, sub-grid evaporation and a sub-grid multi-phase treatment for cases where the simulation mass resolution is insufficient to model the early stages of the superbubble. The multi-phase stage is short compared to superbubble lifetimes. Thermal conduction physically regulates the hot gas mass without requiring a free parameter. Accurately following the hot component naturally avoids overcooling. Prior approaches tend to heat too much mass, leaving the hot ISM below $10^6$ K and susceptible to rapid cooling unless ad-hoc fixes were used. The hot phase also allows feedback energy to correctly accumulate from multiple, clustered sources, including stellar winds and supernovae. We employ high-resolution simulations of a single star ...

  3. Testing AGN feedback models in galaxy evolution

    Science.gov (United States)

    Shin, Min-Su

    Galaxy formation and evolution have been one of the most challenging problems in astrophysics. A single galaxy has various components (stars, atomic and molecular gas, a supermassive black hole, and dark matter) and has interacted with its cosmic environment throughout its history. A key issue in understanding galaxy evolution is to find the dominant physical processes in the interactions between the components of a galaxy and between a galaxy and its environment. AGN feedback has been proposed as a key process to suppress late star formation in massive elliptical galaxies and as a general consequence of galaxy mergers and interactions. In this thesis, I investigate feedback effects from active galactic nuclei (AGN) using a new simulation code and data from the Sloan Digital Sky Survey. In the first chapter, I test purely mechanical AGN feedback models via a nuclear wind around the central SMBH in elliptical galaxies by comparing simulation results to four well-defined observational constraints: the mass ratio between the SMBH and its host galaxy, the lifetime of the quasar phase, the X-ray luminosity from the hot interstellar medium, and the mass fraction of young stars. Even though purely mechanical AGN feedback is commonly assumed in cosmological simulations, I find that it is inadequate, and cannot reproduce all four observational constraints simultaneously. This result suggests that both mechanical and radiative feedback modes are important physical processes. In the second chapter, I simulate the coevolution of the SMBH and its host galaxy under different environments, represented by different amounts of gas stripping. Though the connection between environment and galaxy evolution has been well-studied, environmental effects on the growth of the SMBH have not been answered yet. I find that strong gas stripping, which satellite galaxies might experience, highly suppresses SMBH mass accretion and AGN activity. Moreover, the suppression of the SMBH growth is

  4. Application of a Virtual Reactivity Feedback Control Loop in Non-Nuclear Testing of a Fast Spectrum Reactor

    Science.gov (United States)

    Bragg-Sitton, Shannon M.; Forsbacka, Matthew

    2004-01-01

    For a compact, fast-spectrum reactor, reactivity feedback is dominated by core deformation at elevated temperature. Given the use of accurate deformation measurement techniques, it is possible to simulate nuclear feedback in non-nuclear electrically heated reactor tests. Implementation of simulated reactivity feedback in response to measured deflection is being tested at the NASA Marshall Space Flight Center Early Flight Fission Test Facility (EFF-TF). During tests of the SAFE-100 reactor prototype, core deflection was monitored using a high resolution camera. "virtual" reactivity feedback was accomplished by applying the results of Monte Carlo calculations (MCNPX) to core deflection measurements; the computational analysis was used to establish the reactivity worth of van'ous core deformations. The power delivered to the SAFE-100 prototype was then dusted accordingly via kinetics calculations, The work presented in this paper will demonstrate virtual reactivity feedback as core power was increased from 1 kilowatt(sub t), to 10 kilowatts(sub t), held approximately constant at 10 kilowatts (sub t), and then allowed to decrease based on the negative thermal reactivity coefficient.

  5. A superbubble feedback model for galaxy simulations

    Science.gov (United States)

    Keller, B. W.; Wadsley, J.; Benincasa, S. M.; Couchman, H. M. P.

    2014-08-01

    We present a new stellar feedback model that reproduces superbubbles. Superbubbles from clustered young stars evolve quite differently to individual supernovae and are substantially more efficient at generating gas motions. The essential new components of the model are thermal conduction, subgrid evaporation and a subgrid multiphase treatment for cases where the simulation mass resolution is insufficient to model the early stages of the superbubble. The multiphase stage is short compared to superbubble lifetimes. Thermal conduction physically regulates the hot gas mass without requiring a free parameter. Accurately following the hot component naturally avoids overcooling. Prior approaches tend to heat too much mass, leaving the hot interstellar medium (ISM) below 106 K and susceptible to rapid cooling unless ad hoc fixes were used. The hot phase also allows feedback energy to correctly accumulate from multiple, clustered sources, including stellar winds and supernovae. We employ high-resolution simulations of a single star cluster to show the model is insensitive to numerical resolution, unresolved ISM structure and suppression of conduction by magnetic fields. We also simulate a Milky Way analogue and a dwarf galaxy. Both galaxies show regulated star formation and produce strong outflows.

  6. A Plan for the Development of the Spatial Kinetics and the Detailed Reactivity Model for a Fast Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Y. M.; Jeong, H. Y.; Lee, Y. B.; Sim, Y. S

    2005-11-15

    The reactivity feedback effect of metallic fuel is determined by the fuel burnup characteristics, the configuration of core and fuel assembly, and the complicated interaction between the fuel assembly and core internal structures. Currently, a quite simple evaluation model is frequently applied for the calculation of reactivity feedback. The simple model usually induces some over-conservatism to compensate the simplification, which is an obstacle to take advantage of the positive characteristics of metallic fuel over the oxide fuel. Therefore, to develop a detailed reactivity feedback model and to remove the over-conservatism in the existing simple model would be the foundation to strengthen the economic and operational competitiveness of a liquid metal-cooled fast reactor. In the present study, the plan for the development of the detailed reactivity feedback model and the methodology to combine the spatial kinetics code with the thermal-hydraulic code have been set up, which are two prerequisites for the evaluation of the detailed reactivity feedback effect. The proposed detailed model is expected to be developed in short-term, thus, easily implemented in the SSC-K code. The development of the spatial kinetics code and the merging it to the detailed thermal-hydraulics code would be achieved in long-term, but finally minimize the uncertainty in the reactivity feedback evaluation by including the detailed thermal-hydraulic information in the reactivity calculation.

  7. Phase Model with Feedback Control for Power Grids

    CERN Document Server

    Matsuo, Tatsuma

    2013-01-01

    A phase model with feedback control is studied as a dynamical model of power grids. As an example, we study a model network corresponding to the power grid in the Kyushu region. The standard frequency is maintained by the mutual synchronization and the feedback control. Electric failures are induced by an overload. We propose a local feedback method in which the strength of feedback control is proportional to the magnitude of generators. We find that the electric failures do not occur until the utilization ratio is close to 1 under this feedback control. We also find that the temporal response for the time-varying input power is suppressed under this feedback control. We explain the mechanisms using the corresponding global feedback method.

  8. Phase Model with Feedback Control for Power Grids

    Science.gov (United States)

    Matsuo, Tatsuma; Sakaguchi, Hidetsugu

    2013-09-01

    A phase model with feedback control is studied as a dynamical model of power grids. As an example, we study a model network corresponding to the power grid in the Kyushu region. The standard frequency is maintained by the mutual synchronization and the feedback control. Electric failures are induced by an overload. We propose a local feedback method in which the strength of feedback control is proportional to the magnitude of generators. We find that the electric failures do not occur until the utilization ratio is close to 1 under this feedback control. We also find that the temporal response for the time-varying input power is suppressed under this feedback control. We explain the mechanisms using the corresponding global feedback method.

  9. A student-centred feedback model for educators.

    Science.gov (United States)

    Rudland, Joy; Wilkinson, Tim; Wearn, Andy; Nicol, Pam; Tunny, Terry; Owen, Cathy; O'Keefe, Maree

    2013-04-01

    Effective feedback is instrumental to effective learning. Current feedback models tend to be educator driven rather than learner-centred, with the focus on how the supervisor should give feedback rather than on the role of the learner in requesting and responding to feedback. An alternative approach emphasising the theoretical principles of student-centred and self-regulated learning is offered, drawing upon the literature and also upon the experience of the authors. The proposed feedback model places the student in the centre of the feedback process, and stresses that the attainment of student learning outcomes is influenced by the students themselves. This model emphasises the attributes of the student, particularly responsiveness, receptiveness and reflection, whilst acknowledging the important role that the context and attributes of the supervisor have in influencing the quality of feedback. Educational institutions should consider strategies to encourage and enable students to maximise the many feedback opportunities available to them. As a minimum, educators should remind students about their central role in the feedback process, and support them to develop confidence in meeting this role. In addition, supervisors may need support to develop the skills to shift the balance of responsibility and support students in precipitating feedback moments. Research is also required to validate the proposed model and to determine how to support students to adopt self-regulatory learning, with feedback as a central platform. © Blackwell Publishing Ltd 2013.

  10. Modelling Reactive and Proactive Behaviour in Simulation

    CERN Document Server

    Majid, Mazlina Abdul; Aickelin, Uwe

    2010-01-01

    This research investigated the simulation model behaviour of a traditional and combined discrete event as well as agent based simulation models when modelling human reactive and proactive behaviour in human centric complex systems. A departmental store was chosen as human centric complex case study where the operation system of a fitting room in WomensWear department was investigated. We have looked at ways to determine the efficiency of new management policies for the fitting room operation through simulating the reactive and proactive behaviour of staff towards customers. Once development of the simulation models and their verification had been done, we carried out a validation experiment in the form of a sensitivity analysis. Subsequently, we executed a statistical analysis where the mixed reactive and proactive behaviour experimental results were compared with some reactive experimental results from previously published works. Generally, this case study discovered that simple proactive individual behaviou...

  11. Modeling and simulation of reactive flows

    CERN Document Server

    Bortoli, De AL; Pereira, Felipe

    2015-01-01

    Modelling and Simulation of Reactive Flows presents information on modeling and how to numerically solve reactive flows. The book offers a distinctive approach that combines diffusion flames and geochemical flow problems, providing users with a comprehensive resource that bridges the gap for scientists, engineers, and the industry. Specifically, the book looks at the basic concepts related to reaction rates, chemical kinetics, and the development of reduced kinetic mechanisms. It considers the most common methods used in practical situations, along with equations for reactive flows, and va

  12. Optimal feedback scheduling of model predictive controllers

    Institute of Scientific and Technical Information of China (English)

    Pingfang ZHOU; Jianying XIE; Xiaolong DENG

    2006-01-01

    Model predictive control (MPC) could not be reliably applied to real-time control systems because its computation time is not well defined. Implemented as anytime algorithm, MPC task allows computation time to be traded for control performance, thus obtaining the predictability in time. Optimal feedback scheduling (FS-CBS) of a set of MPC tasks is presented to maximize the global control performance subject to limited processor time. Each MPC task is assigned with a constant bandwidth server (CBS), whose reserved processor time is adjusted dynamically. The constraints in the FSCBS guarantee scheduler of the total task set and stability of each component. The FS-CBS is shown robust against the variation of execution time of MPC tasks at runtime. Simulation results illustrate its effectiveness.

  13. Dynamic behavior of the HTR-10 reactor: Dual temperature feedback model

    Directory of Open Access Journals (Sweden)

    Hosseini Seyed Ali

    2015-01-01

    Full Text Available The current work aims at presenting a simple model for PBM-type reactors' dynamic behavior analysis. The proposed model is based on point kinetics equations coupled with feedbacks from fuel and moderator temperatures. The temperature reactivity coefficients were obtained through MCNP code and via available experimental data. Parameters such as heat capacity and heat conductivity were carefully analyzed and the final system of equations was numerically solved. The obtained results, while in partial agreement with previously proposed models, suggest lower sensitivity to step reactivity insertion as compared to other reactor designs and inherent safety of the design.

  14. Delayed feedback model of axonal length sensing.

    Science.gov (United States)

    Karamched, Bhargav R; Bressloff, Paul C

    2015-05-05

    A fundamental question in cell biology is how the sizes of cells and organelles are regulated at various stages of development. Size homeostasis is particularly challenging for neurons, whose axons can extend from hundreds of microns to meters (in humans). Recently, a molecular-motor-based mechanism for axonal length sensing has been proposed, in which axonal length is encoded by the frequency of an oscillating retrograde signal. In this article, we develop a mathematical model of this length-sensing mechanism in which advection-diffusion equations for bidirectional motor transport are coupled to a chemical signaling network. We show that chemical oscillations emerge due to delayed negative feedback via a Hopf bifurcation, resulting in a frequency that is a monotonically decreasing function of axonal length. Knockdown of either kinesin or dynein causes an increase in the oscillation frequency, suggesting that the length-sensing mechanism would produce longer axons, which is consistent with experimental findings. One major prediction of the model is that fluctuations in the transport of molecular motors lead to a reduction in the reliability of the frequency-encoding mechanism for long axons. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  15. Designing and Evaluating Tutoring Feedback Strategies for Digital Learning Environments on the Basis of the Interactive Tutoring Feedback Model

    Science.gov (United States)

    Narciss, Susanne

    2013-01-01

    This paper describes the interactive tutoring feedback model (ITF-model; Narciss, 2006; 2008), and how it can be applied to the design and evaluation of feedback strategies for digital learning environments. The ITF-model conceptualizes formative tutoring feedback as a multidimensional instructional activity that aims at contributing to the…

  16. Feedback.

    Science.gov (United States)

    Richardson, Barbara K

    2004-12-01

    The emergency department provides a rich environment for diverse patient encounters, rapid clinical decision making, and opportunities to hone procedural skills. Well-prepared faculty can utilize this environment to teach residents and medical students and gain institutional recognition for their incomparable role and teamwork. Giving effective feedback is an essential skill for all teaching faculty. Feedback is ongoing appraisal of performance based on direct observation aimed at changing or sustaining a behavior. Tips from the literature and the author's experience are reviewed to provide formats for feedback, review of objectives, and elements of professionalism and how to deal with poorly performing students. Although the following examples pertain to medical student education, these techniques are applicable to the education of all adult learners, including residents and colleagues. Specific examples of redirection and reflection are offered, and pitfalls are reviewed. Suggestions for streamlining verbal and written feedback and obtaining feedback from others in a fast-paced environment are given. Ideas for further individual and group faculty development are presented.

  17. Measurements and models of reactive transport in geological media

    Science.gov (United States)

    Berkowitz, Brian; Dror, Ishai; Hansen, Scott K.; Scher, Harvey

    2016-12-01

    Reactive chemical transport plays a key role in geological media across scales, from pore scale to aquifer scale. Systems can be altered by changes in solution chemistry and a wide variety of chemical transformations, including precipitation/dissolution reactions that cause feedbacks that directly affect the flow and transport regime. The combination of these processes with advective-dispersive-diffusive transport in heterogeneous media leads to a rich spectrum of complex dynamics. The principal challenge in modeling reactive transport is to account for the subtle effects of fluctuations in the flow field and species concentrations; spatial or temporal averaging generally suppresses these effects. Moreover, it is critical to ground model conceptualizations and test model outputs against laboratory experiments and field measurements. This review emphasizes the integration of these aspects, considering carefully designed and controlled experiments at both laboratory and field scales, in the context of development and solution of reactive transport models based on continuum-scale and particle tracking approaches. We first discuss laboratory experiments and field measurements that define the scope of the phenomena and provide data for model comparison. We continue by surveying models involving advection-dispersion-reaction equation and continuous time random walk formulations. The integration of measurements and models is then examined, considering a series of case studies in different frameworks. We delineate the underlying assumptions, and strengths and weaknesses, of these analyses, and the role of probabilistic effects. We also show the key importance of quantifying the spreading and mixing of reactive species, recognizing the role of small-scale physical and chemical fluctuations that control the initiation of reactions.

  18. Reactive actuators and sensors integrated in one device: mimicking brain-muscles feedback communication

    Science.gov (United States)

    Otero, Toribio F.; Martinez, Jose G.

    2013-04-01

    Artificial muscles based on carbon derivative molecular structures are chemical (electro-chemo-mechanical) actuators. The electrochemical reaction drives the film volume variation and the actuation. The applied current controls the movement rate and the charge controls the amplitude of the displacement (Faraday' motors). Any working or surrounding variable influencing the reaction rate will be sensed by the muscle potential, or by the consumed electrical energy, evolution during actuation. Experimental results and full theoretical description of the basic reactive material and of any dual electrochemical sensing-actuator will be presented. During current flow the muscle potential and the consumed electrical energy evolution are influenced by the working variables: temperature, electrolyte concentration, driving current, film volume variation (external pressure, applied strain, hanged masses, obstacles in its way). The working muscle becomes an electrochemical sensor. Only two connecting wires contain actuating (current) and sensing (potential) signals read and controlled, at any time from the computer-generator. One device integrates several sensing and actuating tools working simultaneously mimicking muscles/brain feedback communication.

  19. Finite element modeling and feedback control of piezoelectric smart structures

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Presents the general formula derived with a smart beam structure bonded with piezoelectric material using the piezoelectricity theory, elastic mechanism and Hamilton principle for eleetromechanically coupled piezoelectric fi nite element and dynamic equations, the second order dynamic model built, and the expression of state space, and the analysis of conventional speed and position feedback and the design of optimum feedback controller for output, the fi nite element models built for a piezoelectric cantilever beam, and the feedback controller designed eventually, and concludes with simulation results that the vibration suppression obtained is very satisfactory and the algorithms proposed are very useful.

  20. Cybernetics: A Model for Feedback in the ESL Classroom.

    Science.gov (United States)

    Zamel, Vivian

    1981-01-01

    Examines cybernetics as a model which provides framework with which to view communicators and the communications in the ESL classroom because it implies the kind of feedback the learner can assimilate and act upon. (Author/BK)

  1. Feedback model to support designers of blended learning courses

    NARCIS (Netherlands)

    Hummel, Hans

    2006-01-01

    Hummel, H. G. K. (2006, December). Feedback model to support designers of blended learning courses. International Review of Open and Distance Learning [Online], 7(3). Available: http://www.irrodl.org/index.php/irrodl/article/view/379/748

  2. Feedback network models for quantum transport.

    Science.gov (United States)

    Gough, John

    2014-12-01

    Quantum feedback networks have been introduced in quantum optics as a framework for constructing arbitrary networks of quantum mechanical systems connected by unidirectional quantum optical fields, and has allowed for a system theoretic approach to open quantum optics systems. Our aim here is to establish a network theory for quantum transport systems where typically the mediating fields between systems are bidirectional. Mathematically, this leads us to study quantum feedback networks where fields arrive at ports in input-output pairs, making it a special case of the unidirectional theory where inputs and outputs are paired. However, it is conceptually important to develop this theory in the context of quantum transport theory-the resulting theory extends traditional approaches which tend to view the components in quantum transport as scatterers for the various fields, in the process allowing us to consider emission and absorption of field quanta by these components. The quantum feedback network theory is applicable to both Bose and Fermi fields, moreover, it applies to nonlinear dynamics for the component systems. We advance the general theory, but study the case of linear passive quantum components in some detail.

  3. Feedbacks, climate sensitivity, and the limits of linear models

    Science.gov (United States)

    Rugenstein, M.; Knutti, R.

    2015-12-01

    The term "feedback" is used ubiquitously in climate research, but implies varied meanings in different contexts. From a specific process that locally affects a quantity, to a formal framework that attempts to determine a global response to a forcing, researchers use this term to separate, simplify, and quantify parts of the complex Earth system. We combine large (>120 member) ensemble GCM and EMIC step forcing simulations over a broad range of forcing levels with a historical and educational perspective to organize existing ideas around feedbacks and linear forcing-feedback models. With a new method overcoming internal variability and initial condition problems we quantify the non-constancy of the climate feedback parameter. Our results suggest a strong state- and forcing-dependency of feedbacks, which is not considered appropriately in many studies. A non-constant feedback factor likely explains some of the differences in estimates of equilibrium climate sensitivity from different methods and types of data. We discuss implications for the definition of the forcing term and its various adjustments. Clarifying the value and applicability of the linear forcing feedback framework and a better quantification of feedbacks on various timescales and spatial scales remains a high priority in order to better understand past and predict future changes in the climate system.

  4. Modeling target erosion during reactive sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Strijckmans, K., E-mail: Koen.Strijckmans@ugent.be; Depla, D.

    2015-03-15

    Highlights: • The erosion of a target is simulated with the RSD2013 software during reactive magnetron sputtering. • The influence of redeposition on the target state and on the hysteresis is explained. • The racetrack formation along the hysteresis and as function of the redeposition is quantified. • Comparison of the racetrack and the sputter profile shows clear differences. - Abstract: The influence of the reactive sputter conditions on the racetrack and the sputter profile for an Al/O{sub 2} DC reactive sputter system is studied by modeling. The role of redeposition, i.e. the deposition of sputtered material back on the target, is therefore taken into account. The used model RSD2013 is capable of simulating the effect of redeposition on the target condition in a spatial resolved way. Comparison between including and excluding redeposition in the RSD2013 model shows that the in-depth oxidation profile of the target differs. Modeling shows that it is important to distinguish between the formed racetrack, i.e. the erosion depth profile, and the sputter profile. The latter defines the distribution of the sputtered atoms in the vacuum chamber. As the target condition defines the sputter yield, it does determine the racetrack and the sputter profile of the planar circular target. Both the shape of the racetrack and the sputter profile change as function of the redeposition fraction as well as function of the oxygen flow change. Clear asymmetries and narrowing are observed for the racetrack shape. Similar effects are noticed for the sputter profile but to a different extent. Based on this study, the often heard misconception that the racetrack shape defines the distribution of the sputtered atoms during reactive sputtering is proven to be wrong.

  5. Cloud and Star Formation in Disk Galaxy Models with Feedback

    CERN Document Server

    Shetty, Rahul

    2008-01-01

    We include feedback in global hydrodynamic simulations in order to study the star formation properties, and gas structure and dynamics, in models of galactic disks. We extend previous models by implementing feedback in gravitationally bound clouds: momentum is injected at a rate proportional to the star formation rate. This mechanical energy disperses cloud gas back into the surrounding ISM, truncating star formation in a given cloud, and raising the overall level of ambient turbulence. Propagating star formation can however occur as expanding shells collide, enhancing the density and triggering new cloud and star formation. By controlling the momentum injection per massive star and the specific star formation rate in dense gas, we find that the negative effects of high turbulence outweigh the positive ones, and in net feedback reduces the fraction of dense gas and thus the overall star formation rate. The properties of the large clouds that form are not, however, very sensitive to feedback, with cutoff masse...

  6. Vaccination strategies for SEIR models using feedback linearization. Preliminary results

    CERN Document Server

    De la Sen, M; Alonso-Quesada, S

    2011-01-01

    A linearization-based feedback-control strategy for a SEIR epidemic model is discussed. The vaccination objective is the asymptotically tracking of the removed-by-immunity population to the total population while achieving simultaneously the remaining population (i.e. susceptible plus infected plus infectious) to asymptotically tend to zero. The disease controlpolicy is designed based on a feedback linearization technique which provides a general method to generate families of vaccination policies with sound technical background.

  7. System and method of designing models in a feedback loop

    Energy Technology Data Exchange (ETDEWEB)

    Gosink, Luke C.; Pulsipher, Trenton C.; Sego, Landon H.

    2017-02-14

    A method and system for designing models is disclosed. The method includes selecting a plurality of models for modeling a common event of interest. The method further includes aggregating the results of the models and analyzing each model compared to the aggregate result to obtain comparative information. The method also includes providing the information back to the plurality of models to design more accurate models through a feedback loop.

  8. Transfer Function Model of Multirate Feedback Control Systems

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Based on the suitably defined multivariable version of Krancoperators and the extended input and output vectors, the multirate sampling plant is transformed to a equivalent time invariant single rate one, then the transfer function model of the multivariable multirate sampling plant is obtained. By combining this plant model with the time invariant description of the multirate controller in terms of extended vectors, the closed-loop transfer function model of the multirate feedback control system can be determinated. This transfer function model has a very simple structure, and can be used as a basis for the analysis and synthesis of the multirate sampling feedback control systems in the frequency domain.

  9. Simulating feedbacks in land use and land cover change models

    NARCIS (Netherlands)

    Verburg, P.H.

    2006-01-01

    In spite of the many advances in land use and land cover change modelling over the past decade many challenges remain. One of these challenges relates to the explicit treatment of feedback mechanisms in descriptive models of the land use system. This paper argues for model-based analysis to explore

  10. Microscale Heat Conduction Models and Doppler Feedback

    Energy Technology Data Exchange (ETDEWEB)

    Hawari, Ayman I. [North Carolina State Univ., Raleigh, NC (United States); Ougouag, Abderrafi [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-01-22

    The objective of this project is to establish an approach for providing the fundamental input that is needed to estimate the magnitude and time-dependence of the Doppler feedback mechanism in Very High Temperature reactors. This mechanism is the foremost contributor to the passive safety of gas-cooled, graphite-moderated high temperature reactors that use fuel based on Tristructural-Isotropic (TRISO) coated particles. Therefore, its correct prediction is essential to the conduct of safety analyses for these reactors. Since the effect is directly dependent on the actual temperature reached by the fuel during transients, the underlying phenomena of heat deposition, heat transfer and temperature rise must be correctly predicted. To achieve the above objective, this project will explore an approach that accounts for lattice effects as well as local temperature variations and the correct definition of temperature and related local effects.

  11. VFM:Visual Feedback Model for Robust Object Recognition

    Institute of Scientific and Technical Information of China (English)

    王冲; 黄凯奇

    2015-01-01

    Object recognition, which consists of classification and detection, has two important attributes for robustness:1) closeness: detection windows should be as close to object locations as possible, and 2) adaptiveness: object matching should be adaptive to object variations within an object class. It is difficult to satisfy both attributes using traditional methods which consider classification and detection separately; thus recent studies propose to combine them based on confidence contextualization and foreground modeling. However, these combinations neglect feature saliency and object structure, and biological evidence suggests that the feature saliency and object structure can be important in guiding the recognition from low level to high level. In fact, ob ject recognition originates in the mechanism of “what” and “where”pathways in human visual systems. More importantly, these pathways have feedback to each other and exchange useful information, which may improve closeness and adaptiveness. Inspired by the visual feedback, we propose a robust object recognition framework by designing a computational visual feedback model (VFM) between classification and detection. In the “what” feedback, the feature saliency from classification is exploited to rectify detection windows for better closeness;while in the “where” feedback, object parts from detection are used to match object structure for better adaptiveness. Experimental results show that the “what” and “where” feedback is effective to improve closeness and adaptiveness for ob ject recognition, and encouraging improvements are obtained on the challenging PASCAL VOC 2007 dataset.

  12. An Industrial Model Based Disturbance Feedback Control Scheme

    DEFF Research Database (Denmark)

    Kawai, Fukiko; Nakazawa, Chikashi; Vinther, Kasper

    2014-01-01

    This paper presents a model based disturbance feedback control scheme. Industrial process systems have been traditionally controlled by using relay and PID controller. However these controllers are affected by disturbances and model errors and these effects degrade control performance. The authors...... propose a new control method that can decrease the negative impact of disturbance and model errors. The control method is motivated by industrial practice by Fuji Electric. Simulation tests are examined with a conventional PID controller and the disturbance feedback control. The simulation results...

  13. A Biopsychosocial Model Based on Negative Feedback and Control

    Directory of Open Access Journals (Sweden)

    Timothy Andrew Carey

    2014-02-01

    Full Text Available Although the biopsychosocial model has been a popular topic of discussion for over four decades it has not had the traction in fields of research that might be expected of such an intuitively appealing idea. One reason for this might be the absence of an identified mechanism or a functional architecture that is authentically biopsychosocial. What is needed is a robust mechanism that is equally important to biochemical processes as it is to psychological and social processes. Negative feedback may be the mechanism that is required. Negative feedback has been implicated in the regulation of neurotransmitters as well as important psychological and social processes such as emotional regulation and the relationship between a psychotherapist and a client. Moreover, negative feedback is purported to also govern the activity of all other organisms as well as humans. Perceptual Control Theory (PCT describes the way in which negative feedback establishes control at increasing levels of perceptual complexity. Thus, PCT may be the first biopsychosocial model to be articulated in functional terms. In this paper we outline the working model of PCT and explain how PCT provides an embodied hierarchical neural architecture that utilises negative feedback to control physiological, psychological, and social variables. PCT has major implications for both research and practice and, importantly, provides a guide by which fields of research that are currently separated may be integrated to bring about substantial progress in understanding the way in which the brain alters, and is altered by, its behavioural and environmental context.

  14. Dense Molecular Gas: A Sensitive Probe of Stellar Feedback Models

    CERN Document Server

    Hopkins, Philip F; Murray, Norman; Quataert, Eliot

    2012-01-01

    We show that the mass fraction of GMC gas (n>100 cm^-3) in dense (n>>10^4 cm^-3) star-forming clumps, observable in dense molecular tracers (L_HCN/L_CO(1-0)), is a sensitive probe of the strength and mechanism(s) of stellar feedback. Using high-resolution galaxy-scale simulations with pc-scale resolution and explicit models for feedback from radiation pressure, photoionization heating, stellar winds, and supernovae (SNe), we make predictions for the dense molecular gas tracers as a function of GMC and galaxy properties and the efficiency of stellar feedback. In models with weak/no feedback, much of the mass in GMCs collapses into dense sub-units, predicting L_HCN/L_CO(1-0) ratios order-of-magnitude larger than observed. By contrast, models with feedback properties taken directly from stellar evolution calculations predict dense gas tracers in good agreement with observations. Changing the strength or timing of SNe tends to move systems along, rather than off, the L_HCN-L_CO relation (because SNe heat lower-de...

  15. Low Order Empirical Galerkin Models for Feedback Flow Control

    Science.gov (United States)

    Tadmor, Gilead; Noack, Bernd

    2005-11-01

    Model-based feedback control restrictions on model order and complexity stem from several generic considerations: real time computation, the ability to either measure or reliably estimate the state in real time and avoiding sensitivity to noise, uncertainty and numerical ill-conditioning are high on that list. Empirical POD Galerkin models are attractive in the sense that they are simple and (optimally) efficient, but are notoriously fragile, and commonly fail to capture transients and control effects. In this talk we review recent efforts to enhance empirical Galerkin models and make them suitable for feedback design. Enablers include `subgrid' estimation of turbulence and pressure representations, tunable models using modes from multiple operating points, and actuation models. An invariant manifold defines the model's dynamic envelope. It must be respected and can be exploited in observer and control design. These ideas are benchmarked in the cylinder wake system and validated by a systematic DNS investigation of a 3-dimensional Galerkin model of the controlled wake.

  16. An integrative model linking feedback environment and organizational citizenship behavior.

    Science.gov (United States)

    Peng, Jei-Chen; Chiu, Su-Fen

    2010-01-01

    Past empirical evidence has suggested that a positive supervisor feedback environment may enhance employees' organizational citizenship behavior (OCB). In this study, we aim to extend previous research by proposing and testing an integrative model that examines the mediating processes underlying the relationship between supervisor feedback environment and employee OCB. Data were collected from 259 subordinate-supervisor dyads across a variety of organizations in Taiwan. We used structural equation modeling to test our hypotheses. The results demonstrated that supervisor feedback environment influenced employees' OCB indirectly through (1) both positive affective-cognition and positive attitude (i.e., person-organization fit and organizational commitment), and (2) both negative affective-cognition and negative attitude (i.e., role stressors and job burnout). Theoretical and practical implications are discussed.

  17. An Emerging Model for Student Feedback: Electronic Distributed Evaluation

    Science.gov (United States)

    Brunk-Chavez, Beth; Arrigucci, Annette

    2012-01-01

    In this article we address several issues and challenges that the evaluation of writing presents individual instructors and composition programs as a whole. We present electronic distributed evaluation, or EDE, as an emerging model for feedback on student writing and describe how it was integrated into our program's course redesign. Because the…

  18. Implementing Relevance Feedback in the Bayesian Network Retrieval Model.

    Science.gov (United States)

    de Campos, Luis M.; Fernandez-Luna, Juan M.; Huete, Juan F.

    2003-01-01

    Discussion of relevance feedback in information retrieval focuses on a proposal for the Bayesian Network Retrieval Model. Bases the proposal on the propagation of partial evidences in the Bayesian network, representing new information obtained from the user's relevance judgments to compute the posterior relevance probabilities of the documents…

  19. Simultaneous exact model matching with stability by output feedback

    Science.gov (United States)

    Kiritsis, Konstadinos H.

    2017-03-01

    In this paper, is studied the problem of simultaneous exact model matching by dynamic output feedback for square and invertible linear time invariant systems. In particular, explicit necessary and sufficient conditions are established which guarantee the solvability of the problem with stability and a procedure is given for the computation of dynamic controller which solves the problem.

  20. Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges

    Science.gov (United States)

    Liu, Ningyu; Dwyer, Joseph R.

    2013-05-01

    This paper reports a modeling study of terrestrial gamma ray flashes (TGFs) produced by relativistic feedback discharges. Terrestrial gamma ray flashes are intense energetic radiation originating from the Earth's atmosphere that has been observed by spacecraft. They are produced by bremsstrahlung interactions of energetic electrons, known as runaway electrons, with air atoms. An efficient physical mechanism for producing large fluxes of the runaway electrons to make the TGFs is the relativistic feedback discharge, where seed runaway electrons are generated by positrons and X-rays, products of the discharge itself. Once the relativistic feedback discharge becomes self-sustaining, an exponentially increasing number of relativistic electron avalanches propagate through the same high-field region inside the thundercloud until the electric field is partially discharged by the ionization created by the discharge. The modeling results indicate that the durations of the TGF pulses produced by the relativistic feedback discharge vary from tens of microseconds to several milliseconds, encompassing all durations of the TGFs observed so far. In addition, when a sufficiently large potential difference is available in thunderclouds, a self-propagating discharge known as the relativistic feedback streamer can be formed, which propagates like a conventional positive streamer. For the relativistic feedback streamer, the positive feedback mechanism of runaway electron production by the positrons and X-rays plays a similar role as the photoionization for the conventional positive streamer. The simulation results of the relativistic feedback streamer show that a sequence of TGF pulses with varying durations can be produced by the streamer. The relativistic streamer may initially propagate with a pulsed manner and turn into a continuous propagation mode at a later stage. Milliseconds long TGF pulses can be produced by the feedback streamer during its continuous propagation. However

  1. The relativistic feedback discharge model of terrestrial gamma ray flashes

    Science.gov (United States)

    Dwyer, Joseph R.

    2012-02-01

    As thunderclouds charge, the large-scale fields may approach the relativistic feedback threshold, above which the production of relativistic runaway electron avalanches becomes self-sustaining through the generation of backward propagating runaway positrons and backscattered X-rays. Positive intracloud (IC) lightning may force the large-scale electric fields inside thunderclouds above the relativistic feedback threshold, causing the number of runaway electrons, and the resulting X-ray and gamma ray emission, to grow exponentially, producing very large fluxes of energetic radiation. As the flux of runaway electrons increases, ionization eventually causes the electric field to discharge, bringing the field below the relativistic feedback threshold again and reducing the flux of runaway electrons. These processes are investigated with a new model that includes the production, propagation, diffusion, and avalanche multiplication of runaway electrons; the production and propagation of X-rays and gamma rays; and the production, propagation, and annihilation of runaway positrons. In this model, referred to as the relativistic feedback discharge model, the large-scale electric fields are calculated self-consistently from the charge motion of the drifting low-energy electrons and ions, produced from the ionization of air by the runaway electrons, including two- and three-body attachment and recombination. Simulation results show that when relativistic feedback is considered, bright gamma ray flashes are a natural consequence of upward +IC lightning propagating in large-scale thundercloud fields. Furthermore, these flashes have the same time structures, including both single and multiple pulses, intensities, angular distributions, current moments, and energy spectra as terrestrial gamma ray flashes, and produce large current moments that should be observable in radio waves.

  2. Impact of reactive settler models on simulated WWTP performance

    DEFF Research Database (Denmark)

    Gernaey, Krist; Jeppsson, Ulf; Batstone, Damien J.

    2006-01-01

    Including a reactive settler model in a wastewater treatment plant model allows representation of the biological reactions taking place in the sludge blanket in the settler, something that is neglected in many simulation studies. The idea of including a reactive settler model is investigated for ...

  3. Designing and Evaluating Tutoring Feedback Strategies for digital learning environments on the basis of the Interactive Tutoring Feedback Model

    Directory of Open Access Journals (Sweden)

    Susanne Narciss

    2013-06-01

    Full Text Available This paper describes the interactive tutoring feedback model (ITF-model; Narciss, 2006; 2008, and how it can be applied to the design and evaluation of feedback strategies for digital learning environments. The ITF-model conceptualizes formative tutoring feedback as a multidimensional instructional activity that aims at contributing to the regulation of a learning process in order to help learners acquire or improve the competencies needed to master learning tasks. It integrates findings from systems theory with recommendations of prior research on interactive instruction and elaborated feedback, on task analyses, on error analyses, and on tutoring techniques. Based on this multi-dimensional view of formative tutoring feedback methodological implications for designing and investigating multiple effects of feedback under multiple individual and situational conditions are described. Furthermore, the paper outlines how the implications of the ITF-model have been applied in several studies to the design and evaluation of tutoring feedback strategies for digital learning environments (e.g., Narciss, 2004; Narciss & Huth, 2006; Narciss, Schnaubert, Andres, Eichelmann, Goguadze, & Sosnovsky, 2013.

  4. Using a reflection model for modeling the dynamic feedback path of digital hearing aids

    DEFF Research Database (Denmark)

    Ma, Guilin; Gran, Fredrik; Jacobsen, Finn;

    2010-01-01

    Feedback whistling is one of the severe problems with hearing aids, especially in dynamic situations when the users hug, pick up a telephone, etc. This paper investigates the properties of the dynamic feedback paths of digital hearing aids and proposes a model based on a reflection assumption...... gain. The method is also extended to dual-microphone hearing aids to assess the possibility of relating the two dynamic feedback paths through the reflection model. However, it is found that in a complicated acoustic environment, the relation between the two feedback paths can be very intricate...

  5. Active Learning of Classification Models with Likert-Scale Feedback.

    Science.gov (United States)

    Xue, Yanbing; Hauskrecht, Milos

    2017-01-01

    Annotation of classification data by humans can be a time-consuming and tedious process. Finding ways of reducing the annotation effort is critical for building the classification models in practice and for applying them to a variety of classification tasks. In this paper, we develop a new active learning framework that combines two strategies to reduce the annotation effort. First, it relies on label uncertainty information obtained from the human in terms of the Likert-scale feedback. Second, it uses active learning to annotate examples with the greatest expected change. We propose a Bayesian approach to calculate the expectation and an incremental SVM solver to reduce the time complexity of the solvers. We show the combination of our active learning strategy and the Likert-scale feedback can learn classification models more rapidly and with a smaller number of labeled instances than methods that rely on either Likert-scale labels or active learning alone.

  6. Assessment of RELAP5 point kinetic model against reactivity insertion transient in the IAEA 10 MW MTR research reactor

    Energy Technology Data Exchange (ETDEWEB)

    Hamidouche, T., E-mail: t.hamidouche@crna.d [Division de l' Environnement, de la Surete et des Dechets Radioactifs, Centre de Recherche Nucleaire d' Alger, 02 Boulevard Frantz Fanon, BP 399 Alger RP (Algeria); Bousbia-Salah, A. [DIMNP - University of Pisa, Via Diotisalvi 02, 56126 Pisa (Italy)

    2010-03-15

    The current study emphasizes an aspect related to the assessment of a model embedded in a computer code. The study concerns more particularly the point neutron kinetics model of the RELAP5/Mod3 code which is worldwide used. The model is assessed against positive reactivity insertion transient taking into account calculations involving thermal-hydraulic feedback as well as transients with no feedback effects. It was concluded that the RELAP5 point kinetics model provides unphysical power evolution trends due most probably to a bug during the programming process.

  7. Modeling and stability analysis of the nonlinear reactive sputtering process

    Directory of Open Access Journals (Sweden)

    György Katalin

    2011-12-01

    Full Text Available The model of the reactive sputtering process has been determined from the dynamic equilibrium of the reactive gas inside the chamber and the dynamic equilibrium of the sputtered metal atoms which form the compound with the reactive gas atoms on the surface of the substrate. The analytically obtained dynamical model is a system of nonlinear differential equations which can result in a histeresis-type input/output nonlinearity. The reactive sputtering process has been simulated by integrating these differential equations. Linearization has been applied for classical analysis of the sputtering process and control system design.

  8. Just One Thing: a novel patient feedback model.

    Science.gov (United States)

    Gharib, I; Rolland, S L; Bateman, H; Ellis, J S

    2017-05-26

    In response to the Educational Standards of the UK's General Dental Council, Newcastle University, School of Dental Sciences introduced a patient feedback card to gather and incorporate patient feedback into their undergraduate assessment framework. The cards ask for patient response to two questions about their experience, and also ask patients to identify 'Just One Thing' (JOT) the student could do to improve this. JOT cards completed during a two week period were collected to evaluate and analyse the nature of patient responses within this model. Over 90% of JOT cards scored the students as 'Excellent' with the remainder scoring the student as 'Good' or giving no response. Many of the free text comments complimented the students and also provided focused suggestions for improvement. While the overwhelming positive responses may suggest that this model for collecting feedback may not be effective at discriminating between students with varying levels of interpersonal/communication skills, the free text comments were seen to be of value in building confidence or identifying areas for improvement.

  9. Feedback Message Passing for Inference in Gaussian Graphical Models

    CERN Document Server

    Liu, Ying; Anandkumar, Animashree; Willsky, Alan S

    2011-01-01

    While loopy belief propagation (LBP) performs reasonably well for inference in some Gaussian graphical models with cycles, its performance is unsatisfactory for many others. In particular for some models LBP does not converge, and in general when it does converge, the computed variances are incorrect (except for cycle-free graphs for which belief propagation (BP) is non-iterative and exact). In this paper we propose {\\em feedback message passing} (FMP), a message-passing algorithm that makes use of a special set of vertices (called a {\\em feedback vertex set} or {\\em FVS}) whose removal results in a cycle-free graph. In FMP, standard BP is employed several times on the cycle-free subgraph excluding the FVS while a special message-passing scheme is used for the nodes in the FVS. The computational complexity of exact inference is $O(k^2n)$, where $k$ is the number of feedback nodes, and $n$ is the total number of nodes. When the size of the FVS is very large, FMP is intractable. Hence we propose {\\em approximat...

  10. Impact of reactive settler models on simulated WWTP performance.

    Science.gov (United States)

    Gernaey, K V; Jeppsson, U; Batstone, D J; Ingildsen, P

    2006-01-01

    Including a reactive settler model in a wastewater treatment plant model allows representation of the biological reactions taking place in the sludge blanket in the settler, something that is neglected in many simulation studies. The idea of including a reactive settler model is investigated for an ASM1 case study. Simulations with a whole plant model including the non-reactive Takács settler model are used as a reference, and are compared to simulation results considering two reactive settler models. The first is a return sludge model block removing oxygen and a user-defined fraction of nitrate, combined with a non-reactive Takács settler. The second is a fully reactive ASM1 Takács settler model. Simulations with the ASM1 reactive settler model predicted a 15.3% and 7.4% improvement of the simulated N removal performance, for constant (steady-state) and dynamic influent conditions respectively. The oxygen/nitrate return sludge model block predicts a 10% improvement of N removal performance under dynamic conditions, and might be the better modelling option for ASM1 plants: it is computationally more efficient and it will not overrate the importance of decay processes in the settler.

  11. Modeling mutual feedback between users and recommender systems

    CERN Document Server

    Zeng, An; Medo, Matus; Zhang, Yi-Cheng

    2015-01-01

    Recommender systems daily influence our decisions on the Internet. While considerable attention has been given to issues such as recommendation accuracy and user privacy, the long-term mutual feedback between a recommender system and the decisions of its users has been neglected so far. We propose here a model of network evolution which allows us to study the complex dynamics induced by this feedback, including the hysteresis effect which is typical for systems with non-linear dynamics. Despite the popular belief that recommendation helps users to discover new things, we find that the long-term use of recommendation can contribute to the rise of extremely popular items and thus ultimately narrow the user choice. These results are supported by measurements of the time evolution of item popularity inequality in real systems. We show that this adverse effect of recommendation can be tamed by sacrificing part of short-term recommendation accuracy.

  12. Extended nonlinear feedback model for describing episodes of high inflation

    OpenAIRE

    Szybisz, M A; Szybisz, L.

    2016-01-01

    An extension of the nonlinear feedback (NLF) formalism to describe regimes of hyper- and high-inflation in economy is proposed in the present work. In the NLF model the consumer price index (CPI) exhibits a finite time singularity of the type $1/(t_c -t)^{(1- \\beta)/\\beta}$, with $\\beta>0$, predicting a blow up of the economy at a critical time $t_c$. However, this model fails in determining $t_c$ in the case of weak hyperinflation regimes like, e.g., that occurred in Israel. To overcome this...

  13. Reactive burn models and ignition & growth concept

    Energy Technology Data Exchange (ETDEWEB)

    Menikoff, Ralph S [Los Alamos National Laboratory; Shaw, Milton S [Los Alamos National Laboratory

    2010-01-01

    Plastic-bonded explosives are heterogeneous materials. Experimentally, shock initiation is sensitive to small amounts of porosity, due to the formation of hot spots (small localized regions of high temperature). This leads to the Ignition and Growth concept, introduced by Lee and Tarver in 1980, as the basis for reactive burn models. A homogeneized burn rate needs to account for three mesoscale physical effects (i) the density of burnt hot spots, which depends on the lead shock strength; (ii) the growth of the burn fronts triggered by hot spots, which depends on the local deflagration speed; (iii) a geometric factor that accounts for the overlap of deflagration wavelets from adjacent hot spots. These effects can be combined and the burn model defined by specifying the reaction progress variable {lambda}(t) as a function of a dimensionless reaction length {tau}{sub hs}(t)/{ell}{sub hs}, rather than by xpecifying an explicit burn rate. The length scale {ell}{sub hs} is the average distance between hot spots, which is proportional to [N{sub hs}(P{sub s})]{sup -1/3}, where N{sub hs} is the number density of hot spots activated by the lead shock. The reaction length {tau}{sub hs}(t) = {line_integral}{sub 0}{sup t} D(P(t'))dt' is the distance the burn front propagates from a single hot spot, where D is the deflagration speed and t is the time since the shock arrival. A key implementation issue is how to determine the lead shock strength in conjunction with a shock capturing scheme. They have developed a robust algorithm for this purpose based on the Hugoniot jump condition for the energy. The algorithm utilizes the time dependence of density, pressure and energy within each cell. The method is independent of the numerical dissipation used for shock capturing. It is local and can be used in one or more space dimensions. The burn model has a small number of parameters which can be calibrated to fit velocity gauge data from shock initiation experiments.

  14. Reactive burn models and ignition & growth concept

    Directory of Open Access Journals (Sweden)

    Shaw M.S.

    2011-01-01

    Full Text Available Plastic-bonded explosives are heterogeneous materials. Experimentally, shock initiation is sensitive to small amounts of porosity, due to the formation of hot spots (small localized regions of high temperature. This leads to the Ignition & Growth concept, introduced by LeeTarver in 1980, as the basis for reactive burn models. A homo- genized burn rate needs to account for three meso-scale physical effects: (i the density of active hot spots or burn centers; (ii the growth of the burn fronts triggered by the burn centers; (iii a geometric factor that accounts for the overlap of deflagration wavelets from adjacent burn centers. These effects can be combined and the burn model defined by specifying the reaction progress variable λ = g(s as a function of a dimensionless reaction length s(t = rbc/ℓbc, rather than by specifying an explicit burn rate. The length scale ℓbc(Ps = [Nbc(Ps]−1/3 is the average distance between burn centers, where Nbc is the number density of burn centers activated by the lead shock. The reaction length rbc(t = ∫t0 D(P(t′dt′ is the distance the burn front propagates from a single burn center, where D(P is the deflagration speed as a function of the local pressure and t is the time since the shock arrival. A key implementation issue is how to determine the lead shock strength in conjunction with a shock capturing scheme. We have developed a robust algorithm for this purpose based on the Hugoniot jump condition for the energy. The algorithm utilizes the time dependence of density, pressure and energy within each cell. The method is independent of the numerical dissipation used for shock capturing. It is local and can be used in one or more space dimensions. The burn model has a small number of parameters which can be calibrated to fit velocity gauge data from shock initiation experiments.

  15. Reactive puff model SCICHEM: Model enhancements and performance studies

    Science.gov (United States)

    Chowdhury, B.; Karamchandani, P. K.; Sykes, R. I.; Henn, D. S.; Knipping, E.

    2015-09-01

    The SCICHEM model incorporates complete gas phase, aqueous and aerosol phase chemistry within a state-of-the-science Gaussian puff model SCIPUFF (Second-order Closure Integrated Puff). The model is a valuable tool that can be used to calculate the impacts of a single source or a small number of sources on downwind ozone and PM2.5. The model has flexible data requirements: it can be run with routine surface and upper air observations or with prognostic meteorological model outputs and source emissions are specified in a simple text format. This paper describes significant advances to the dispersion and chemistry components of the model in the latest release, SCICHEM 3.0. Some of the major advancements include modeling of skewed turbulence for convective boundary layer and updated chemistry schemes (CB05 gas phase chemical mechanism; AERO5 aerosol and aqueous modules). The results from SCICHEM 3.0 are compared with observations from a tracer study as well as aircraft measurements of reactive species in power plant plumes from two field studies. The results with the tracer experiment (Copenhagen study) show that the incorporation of skewed turbulence improves the calculation of tracer dispersion and transport. The comparisons with the Cumberland and Dolet Hills power plume measurements show good correlation between the observed and predicted concentrations of reactive gaseous species at most downwind distances from the source.

  16. Investigation of kinetics model of dc reactive sputtering

    Institute of Scientific and Technical Information of China (English)

    朱圣龙; 王福会; 吴维叓

    1996-01-01

    A novel physical sputtering kinetics model for reactive sputtering is presented.Reactive gas gettering effects and interactions among the characteristic parameters have been taken into account in the model.The data derived from the model accorded fairly well with experimental results.The relationship between the values of initial oxide coverage on the target and the ready states was depicted in the model.This relationship gives reasons for the difference of the threshold of reactive gas fluxes (Q) from the metal sputtering region to the oxide sputtering region and in reverse direction.The discontinuities in oxide coverage on the target surface (θ) versus reactive gas fluxes (Q) are referred to as the effects of reactive gas partial pressure (p) upon the forming rates of oxide on the surfaces of target (V0).The diversity of the oxygen flux threshold results from the variance of the initial values of oxide coverage on target.

  17. Modeling energy intake by adding homeostatic feedback and drug intervention.

    Science.gov (United States)

    Gennemark, Peter; Hjorth, Stephan; Gabrielsson, Johan

    2015-02-01

    Energy intake (EI) is a pivotal biomarker used in quantification approaches to metabolic disease processes such as obesity, diabetes, and growth disorders. Eating behavior is however under both short-term and long-term control. This control system manifests itself as tolerance and rebound phenomena in EI, when challenged by drug treatment or diet restriction. The paper describes a model with the capability to capture physiological counter-regulatory feedback actions triggered by energy imbalances. This feedback is general as it handles tolerance to both increases and decreases in EI, and works in both acute and chronic settings. A drug mechanism function inhibits (or stimulates) EI. The deviation of EI relative to a reference level (set-point) serves as input to a non-linear appetite control signal which in turn impacts EI in parallel to the drug intervention. Three examples demonstrate the potential usefulness of the model in both acute and chronic dosing situations. The model shifts the predicted concentration-response relationship rightwardly at lower concentrations, in contrast to models that do not handle functional adaptation. A fourth example further shows that the model may qualitatively explain differences in rate and extent of adaptation in observed EI and its concomitants in both rodents and humans.

  18. On the Permanence of a Nonautonomous Nicholson's Blowflies Model with Feedback Control and Delay

    Institute of Scientific and Technical Information of China (English)

    LAI Wei-ying

    2011-01-01

    A nonautonomous Nicholson's Blowflies model with feedback control and delay is investigated in this paper.We show that for this system,feedback control variable has no influence on the persistent property of the system.

  19. Comparing the effects of supernovae feedback models on the interstellar medium

    Science.gov (United States)

    Byrne, Lindsey; Christensen, Charlotte; Keller, Benjamin W.

    2017-01-01

    Stellar feedback affects the state of the interstellar medium and plays an important role in the formation of galaxies. However, different ways of modeling that feedback lead to different galaxy morphologies even when using the same initial conditions. We investigated the differences between two models of supernovae feedback, blastwave feedback and superbubble feedback, using a smoothed particle hydrodynamics code to simulate the formation of an isolated galaxy. The two feedback models were compared across three different models of the ISM: primordial cooling, metal-line cooling, and metal-line cooling in addition to molecular hydrogen. The simulations run with metal-line cooling indicate that superbubble feedback creates a greater amount of high-density gas than blastwave feedback does while also regulating star formation more efficiently. Galaxies produced with metal-line cooling or H2 physics created cold, dense gas, and the increased cooling efficiency was also linked to more pronounced spiral structure.

  20. Modelling atmospheric OH-reactivity in a boreal forest ecosystem

    DEFF Research Database (Denmark)

    Mogensen, D.; Smolander, S.; Sogachev, Andrey;

    2011-01-01

    We have modelled the total atmospheric OH-reactivity in a boreal forest and investigated the individual contributions from gas phase inorganic species, isoprene, monoterpenes, and methane along with other important VOCs. Daily and seasonal variation in OH-reactivity for the year 2008 was examined...... as well as the vertical OH-reactivity profile. We have used SOSA; a one dimensional vertical chemistry-transport model (Boy et al., 2011a) together with measurements from Hyytiala, SMEAR II station, Southern Finland, conducted in August 2008. Model simulations only account for similar to 30......-50% of the total measured OH sink, and in our opinion, the reason for missing OH-reactivity is due to unmeasured unknown BVOCs, and limitations in our knowledge of atmospheric chemistry including uncertainties in rate constants. Furthermore, we found that the OH-reactivity correlates with both organic...

  1. Modelling atmospheric OH-reactivity in a boreal forest ecosystem

    DEFF Research Database (Denmark)

    Mogensen, D.; Smolander, S.; Sogachev, Andrey;

    2011-01-01

    We have modelled the total atmospheric OH-reactivity in a boreal forest and investigated the individual contributions from gas phase inorganic species, isoprene, monoterpenes, and methane along with other important VOCs. Daily and seasonal variation in OH-reactivity for the year 2008 was examined...

  2. Modeling Channelization in Coastal Wetlands with Ecological Feedbacks

    Science.gov (United States)

    Hughes, Z. J.; Mahadevan, A.; Pennings, S.; FitzGerald, D.

    2014-12-01

    In coastal wetlands in Georgia and South Carolina, dendritic channel networks are actively incising headward at the rate of nearly 2 m/yr. The future geomorphic evolution of these marshes remains in question as rates of relative sea-level rise increase. Our objective is to understand the mechanisms that lead to the evolution of these channel networks through field observations and modeling. We model the geomorphological evolution of tidal creeks by viewing the wetland as a permeable medium. The porosity of the medium affects its hydraulic conductivity, which in turn is altered by erosion. Our multiphase model spontaneously generates channelization and branching networks through flow and erosion. In our field studies, we find that crabs play an active role in grazing vegetation and in the bioturbation of sediments. These effects are incorporated in our model based on field and laboratory observations of crab behavior and its effects on the marsh. We find the erosional patterns and channelization are significantly altered by the faunal feedback. Crabs enhance the growth of channels, inducing the headward erosion of creeks where flow-induced stresses are weakest. They are instrumental in generating high rates of creek extension, which channelize the marsh more effectively in response to sea-level rise. This indicates that the evolution of coastal wetlands is responding to interactions between physics and ecology and highlights the importance of the faunal contribution to these feedbacks.

  3. Mesoscale modeling of smoke radiative feedback over the Sahel region

    Science.gov (United States)

    Yang, Z.; Wang, J.; Ichoku, C. M.; Ellison, L.; Zhang, F.; Yue, Y.

    2013-12-01

    This study employs satellite observations and a fully-coupled meteorology-chemistry-aerosol model, Weather Research and Forecasting model with Chemistry (WRF-Chem) to study the smoke radative feedback on surface energy budget, boundary layer processes, and atmospheric lapse rate in February 2008 over the Sahel region. The smoke emission inventories we use come from various sources, including but not limited to the Fire Locating and Modeling of Burning Emissions (FLAMBE) developed by NRL and the Fire Energetic and Emissions Research (FEER) developed by NASA GSFC. Model performance is evaluated using numerous satellite and ground-based datasets: MODIS true color images, ground-based Aerosol Optical Depth (AOD) measurements from AERONET, MODIS AOD retrievals, and Cloud-Aerosol Lidar data with Orthogonal Polarization (CALIOP) atmospheric backscattering and extinction products. Specification of smoke injection height of 650 m in WRF-Chem yields aerosol vertical profiles that are most consistent with CALIOP observations of aerosol layer height. Statistically, 5% of the CALIPSO valid measurements of aerosols in February 2008 show aerosol layers either above the clouds or between the clouds, reinforcing the importance of the aerosol vertical distribution for quantifying aerosol impact on climate in the Sahel region. The results further show that the smoke radiative feedbacks are sensitive to assumptions of black carbon and organic carbon ratio in the particle emission inventory. Also investigated is the smoke semi-direct effect as a function of cloud fraction.

  4. Neuromechanical models for insect locomotion: Stability, maneuverability, and proprioceptive feedback

    Science.gov (United States)

    Kukillaya, R.; Proctor, J.; Holmes, P.

    2009-06-01

    We describe a hierarchy of models for legged locomotion, emphasizing relationships among feedforward (preflexive) stability, maneuverability, and reflexive feedback. We focus on a hexapedal geometry representative of insect locomotion in the ground plane that includes a neural central pattern generator circuit, nonlinear muscles, and a representative proprioceptive sensory pathway. Although these components of the model are rather complex, neglect of leg mass yields a neuromechanical system with only three degrees of freedom, and numerical simulations coupled with a Poincaré map analysis shows that the feedforward dynamics is strongly stable, apart from one relatively slow mode and a neutral mode in body yaw angle. These modes moderate high frequency perturbations, producing slow heading changes that can be corrected by a stride-to-stride steering strategy. We show that the model's response to a lateral impulsive perturbation closely matches that of a cockroach subject to a similar impulse. We also describe preliminary studies of proprioceptive leg force feedback, showing how a reflexive pathway can reinforce the preflexive stability inherent in the system.

  5. Models of reactive oxygen species in cancer

    OpenAIRE

    Lu, Weiqin; Ogasawara, Marcia A.; Huang, Peng

    2007-01-01

    Increased generation of reactive oxygen species (ROS) has been observed in cancer, degenerative diseases, and other pathological conditions. ROS can stimulate cell proliferation, promote genetic instability, and induce adaptive responses that enable cancer cells to maintain their malignant phenotypes. However, when cellular redox balance is severely disturbed, high levels of ROS may cause various damages leading to cell death. The studies of ROS effects on biological systems, their underlying...

  6. Theoretical model for ultracold molecule formation via adaptive feedback control

    CERN Document Server

    Poschinger, U; Wester, R; Weidemüller, M; Koch, C P; Kosloff, R; Poschinger, Ulrich; Salzmann, Wenzel; Wester, Roland; Weidemueller, Matthias; Koch, Christiane P.; Kosloff, Ronnie

    2006-01-01

    We investigate pump-dump photoassociation of ultracold molecules with amplitude- and phase-modulated femtosecond laser pulses. For this purpose a perturbative model for the light-matter interaction is developed and combined with a genetic algorithm for adaptive feedback control of the laser pulse shapes. The model is applied to the formation of 85Rb2 molecules in a magneto-optical trap. We find for optimized pulse shapes an improvement for the formation of ground state molecules by more than a factor of 10 compared to unshaped pulses at the same pump-dump delay time, and by 40% compared to unshaped pulses at the respective optimal pump-dump delay time. Since our model yields directly the spectral amplitudes and phases of the optimized pulses, the results are directly applicable in pulse shaping experiments.

  7. Multi-Task Collaboration CPS Modeling Based on Immune Feedback

    Directory of Open Access Journals (Sweden)

    Haiying Li

    2013-09-01

    Full Text Available In this paper, a dynamic multi-task collaboration CPS control model based on the self-adaptive immune feedback is proposed and implemented in the smart home environment. First, the internal relations between CPS and the biological immune system are explored via their basic theories. Second, CPS control mechanism is elaborated through the analysis of CPS control structure. Finally, a comprehensive strategy for support is introduced into multi-task collaboration to improve the dynamic cognitive ability. At the same time, the performance of parameters is correspondingly increased by the operator of the antibody concentration and the selective pressure. Furthermore, the model has been put into service in the smart home laboratory. The experimental results show that this model can integrate user’s needs into the environment for properly regulating the home environment.

  8. Empirical Reduced-Order Modeling for Boundary Feedback Flow Control

    Directory of Open Access Journals (Sweden)

    Seddik M. Djouadi

    2008-01-01

    Full Text Available This paper deals with the practical and theoretical implications of model reduction for aerodynamic flow-based control problems. Various aspects of model reduction are discussed that apply to partial differential equation- (PDE- based models in general. Specifically, the proper orthogonal decomposition (POD of a high dimension system as well as frequency domain identification methods are discussed for initial model construction. Projections on the POD basis give a nonlinear Galerkin model. Then, a model reduction method based on empirical balanced truncation is developed and applied to the Galerkin model. The rationale for doing so is that linear subspace approximations to exact submanifolds associated with nonlinear controllability and observability require only standard matrix manipulations utilizing simulation/experimental data. The proposed method uses a chirp signal as input to produce the output in the eigensystem realization algorithm (ERA. This method estimates the system's Markov parameters that accurately reproduce the output. Balanced truncation is used to show that model reduction is still effective on ERA produced approximated systems. The method is applied to a prototype convective flow on obstacle geometry. An H∞ feedback flow controller is designed based on the reduced model to achieve tracking and then applied to the full-order model with excellent performance.

  9. Tidal Downsizing model - IV. Destructive feedback in planets

    Science.gov (United States)

    Nayakshin, Sergei

    2016-09-01

    The role of negative feedback from a massive solid core on its massive gas envelope in the Tidal Downsizing scenario of planet formation is investigated via one-dimensional planet evolution models followed by population synthesis calculations. It is shown that cores more massive than ˜10 M⊕ release enough energy to reverse contraction of their parent gas envelopes, culminating in their destruction. This process may help to explain why observed gas giant planets are so rare, why massive cores are so ubiquitous, and why there is a sharp rollover in the core mass function above ˜20 M⊕. Additionally, the short time-scales with which these massive cores are assembled in TD may help explain formation route of Uranus, Neptune and the suspected HL Tau planets. Given the negative role of cores in assembly of gas giants in the model, an antimony is found between massive cores and gas giants: cores in survived gas giant planets are on average less massive than cores free of massive envelopes. In rare circumstances when core feedback self-regulates, extremely metal-rich gas giants, such as CoRoT-20b, a gas giant made of heavy elements by up to ˜50 per cent, can be made.

  10. Combining experimental observation and modelling in investigating feedback and emotions in repeated selection tasks

    NARCIS (Netherlands)

    Fischer, A.R.H.; Blommaert, F.J.J.; Midden, C.J.H.

    2005-01-01

    People seem to learn tasks even without formal training. This can be modelled as the outcome of a feedback system that accumulates experience. In this paper we investigate such a feedback system, following an iterative research approach. A feedback loop is specified that is detailed using contempora

  11. Combining experimental observation and modelling in investigating feedback and emotions in repeated selection tasks

    NARCIS (Netherlands)

    Fischer, A.R.H.; Blommaert, F.J.J.; Midden, C.J.H.

    2005-01-01

    People seem to learn tasks even without formal training. This can be modelled as the outcome of a feedback system that accumulates experience. In this paper we investigate such a feedback system, following an iterative research approach. A feedback loop is specified that is detailed using

  12. A synchronous paradigm for modeling stable reactive systems

    Energy Technology Data Exchange (ETDEWEB)

    Winter, V.L.

    1998-12-01

    This paper describes a modeling technique for single-agent reactive systems, that is influenced by the modeling paradigm of Parnas as well as by the synchronous paradigms of LUSTRE and ESTEREL. In this paradigm, single-agent reactive systems are modeled in a universe having a discrete clock. This discretization of time greatly reduces the temporal complexity of the model. He believes that the advantage of this reduction in temporal complexity is that the resulting model is in many ways better suited to automated software construction and analysis techniques (e.g., deductive synthesis, transformation, and verification) than models that are based on continuous representations of time.

  13. Feedbacks Between Numerical and Analytical Models in Hydrogeology

    Science.gov (United States)

    Zlotnik, V. A.; Cardenas, M. B.; Toundykov, D.; Cohn, S.

    2012-12-01

    Hydrogeology is a relatively young discipline which combines elements of Earth science and engineering. Mature fundamental disciplines (e.g., physics, chemistry, fluid mechanics) have centuries-long history of mathematical modeling even prior to discovery of Darcy's law. Thus, in hydrogeology, relatively few classic analytical models (such those by Theis, Polubarinova-Kochina, Philip, Toth, Henry, Dagan, Neuman) were developed by the early 1970's. The advent of computers and practical demands refocused mathematical models towards numerical techniques. With more diverse but less mathematically-oriented training, most hydrogeologists shifted from analytical methods to use of standardized computational software. Spatial variability in internal properties and external boundary conditions and geometry, and the added complexity of chemical and biological processes will remain major challenges for analytical modeling. Possibly, analytical techniques will play a subordinate role to numerical approaches in many applications. On the other hand, the rise of analytical element modeling of groundwater flow is a strong alternative to numerical models when data demand and computational efficiency is considered. The hallmark of analytical models - transparency and accuracy - will remain indispensable for scientific exploration of complex phenomena and for benchmarking numerical models. Therefore, there will always be feedbacks and complementarities between numerical and analytical techniques, as well as a certain ideological schism among various views to modeling. We illustrate the idea of feedbacks by reviewing evolution of Joszef Toth's analytical model of gravity driven flow systems. Toth's (1963) approach was to reduce the flow domain to a rectangle which allowed for closed-form solution of the governing equations. Succeeding numerical finite-element models by Freeze and Witherspoon (1966-1968) explored the effects of geometry and heterogeneity on regional groundwater flow

  14. Modeling for Stellar Feedback in Galaxy Formation Simulations

    Science.gov (United States)

    Núñez, Alejandro; Ostriker, Jeremiah P.; Naab, Thorsten; Oser, Ludwig; Hu, Chia-Yu; Choi, Ena

    2017-02-01

    Various heuristic approaches to model unresolved supernova (SN) feedback in galaxy formation simulations exist to reproduce the formation of spiral galaxies and the overall inefficient conversion of gas into stars. Some models, however, require resolution-dependent scalings. We present a subresolution model representing the three major phases of supernova blast wave evolution—free expansion, energy-conserving Sedov–Taylor, and momentum-conserving snowplow—with energy scalings adopted from high-resolution interstellar-medium simulations in both uniform and multiphase media. We allow for the effects of significantly enhanced SN remnant propagation in a multiphase medium with the cooling radius scaling with the hot volume fraction, {f}{hot}, as {(1-{f}{hot})}-4/5. We also include winds from young massive stars and AGB stars, Strömgren sphere gas heating by massive stars, and a mechanism that limits gas cooling that is driven by radiative recombination of dense H ii regions. We present initial tests for isolated Milky Way-like systems simulated with the Gadget-based code SPHgal with improved SPH prescription. Compared to pure thermal SN input, the model significantly suppresses star formation at early epochs, with star formation extended both in time and space in better accord with observations. Compared to models with pure thermal SN feedback, the age at which half the stellar mass is assembled increases by a factor of 2.4, and the mass-loading parameter and gas outflow rate from the galactic disk increase by a factor of 2. Simulation results are converged for a variation of two orders of magnitude in particle mass in the range (1.3–130) × 104 solar masses.

  15. The magnitude-timescale relationship of surface temperature feedbacks in climate models

    Directory of Open Access Journals (Sweden)

    A. Jarvis

    2011-07-01

    Full Text Available Because of the fundamental role feedbacks play in determining the characteristics of climate it is important we are able to specify both the magnitude and response timescale of the feedbacks we are interested in. This paper employs three different climate models driven to equilibrium with a 4 × CO2 forcing to analyze the magnitude and timescales of surface temperature feedbacks. These models are a global energy balance model, an intermediate complexity climate model and a general circulation model. Rather than split surface temperature feedback into characteristic physical processes, this paper adopts a linear systems approach to split feedback according to their time constants and corresponding feedback amplitudes. The analysis reveals that there is a dominant net negative feedback realised during the first year. However, this is partially attenuated by a spectrum of positive feedbacks for time constants in the range 10 to 1000 years. This attenuation was composed of two discrete phases which are attributed to the effects of ''diffusive – mixed layer'' and ''circulatory – deep ocean'' ocean heat equilibration processes. The diffusive equilibration was associated with time constants on the decadal timescale and accounted for approximately 75 to 80 % of the overall ocean heat equilibration feedback, whilst the circulatory feedback operated on a centennial timescale and accounted for the remaining 20 to 25 % of the response. It is important to quantify these decadal and centennial feedback processes to understand the range of climate model projections on these longer timescales.

  16. Cortical factor feedback model for cellular locomotion and cytofission.

    Directory of Open Access Journals (Sweden)

    Shin I Nishimura

    2009-03-01

    Full Text Available Eukaryotic cells can move spontaneously without being guided by external cues. For such spontaneous movements, a variety of different modes have been observed, including the amoeboid-like locomotion with protrusion of multiple pseudopods, the keratocyte-like locomotion with a widely spread lamellipodium, cell division with two daughter cells crawling in opposite directions, and fragmentations of a cell to multiple pieces. Mutagenesis studies have revealed that cells exhibit these modes depending on which genes are deficient, suggesting that seemingly different modes are the manifestation of a common mechanism to regulate cell motion. In this paper, we propose a hypothesis that the positive feedback mechanism working through the inhomogeneous distribution of regulatory proteins underlies this variety of cell locomotion and cytofission. In this hypothesis, a set of regulatory proteins, which we call cortical factors, suppress actin polymerization. These suppressing factors are diluted at the extending front and accumulated at the retracting rear of cell, which establishes a cellular polarity and enhances the cell motility, leading to the further accumulation of cortical factors at the rear. Stochastic simulation of cell movement shows that the positive feedback mechanism of cortical factors stabilizes or destabilizes modes of movement and determines the cell migration pattern. The model predicts that the pattern is selected by changing the rate of formation of the actin-filament network or the threshold to initiate the network formation.

  17. Toward Holistic Scene Understanding: Feedback Enabled Cascaded Classification Models.

    Science.gov (United States)

    Li, Congcong; Kowdle, Adarsh; Saxena, Ashutosh; Chen, Tsuhan

    2012-07-01

    Scene understanding includes many related subtasks, such as scene categorization, depth estimation, object detection, etc. Each of these subtasks is often notoriously hard, and state-of-the-art classifiers already exist for many of them. These classifiers operate on the same raw image and provide correlated outputs. It is desirable to have an algorithm that can capture such correlation without requiring any changes to the inner workings of any classifier. We propose Feedback Enabled Cascaded Classification Models (FE-CCM), that jointly optimizes all the subtasks while requiring only a "black box" interface to the original classifier for each subtask. We use a two-layer cascade of classifiers, which are repeated instantiations of the original ones, with the output of the first layer fed into the second layer as input. Our training method involves a feedback step that allows later classifiers to provide earlier classifiers information about which error modes to focus on. We show that our method significantly improves performance in all the subtasks in the domain of scene understanding, where we consider depth estimation, scene categorization, event categorization, object detection, geometric labeling, and saliency detection. Our method also improves performance in two robotic applications: an object-grasping robot and an object-finding robot.

  18. Modeling Biodegradation and Reactive Transport: Analytical and Numerical Models

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Y; Glascoe, L

    2005-06-09

    The computational modeling of the biodegradation of contaminated groundwater systems accounting for biochemical reactions coupled to contaminant transport is a valuable tool for both the field engineer/planner with limited computational resources and the expert computational researcher less constrained by time and computer power. There exists several analytical and numerical computer models that have been and are being developed to cover the practical needs put forth by users to fulfill this spectrum of computational demands. Generally, analytical models provide rapid and convenient screening tools running on very limited computational power, while numerical models can provide more detailed information with consequent requirements of greater computational time and effort. While these analytical and numerical computer models can provide accurate and adequate information to produce defensible remediation strategies, decisions based on inadequate modeling output or on over-analysis can have costly and risky consequences. In this chapter we consider both analytical and numerical modeling approaches to biodegradation and reactive transport. Both approaches are discussed and analyzed in terms of achieving bioremediation goals, recognizing that there is always a tradeoff between computational cost and the resolution of simulated systems.

  19. Extended nonlinear feedback model for describing episodes of high inflation

    Science.gov (United States)

    Szybisz, Martín A.; Szybisz, Leszek

    2017-01-01

    An extension of the nonlinear feedback (NLF) formalism to describe regimes of hyper- and high-inflation in economy is proposed in the present work. In the NLF model the consumer price index (CPI) exhibits a finite time singularity of the type 1 /(tc - t) (1 - β) / β, with β > 0, predicting a blow up of the economy at a critical time tc. However, this model fails in determining tc in the case of weak hyperinflation regimes like, e.g., that occurred in Israel. To overcome this trouble, the NLF model is extended by introducing a parameter γ, which multiplies all terms with past growth rate index (GRI). In this novel approach the solution for CPI is also analytic being proportional to the Gaussian hypergeometric function 2F1(1 / β , 1 / β , 1 + 1 / β ; z) , where z is a function of β, γ, and tc. For z → 1 this hypergeometric function diverges leading to a finite time singularity, from which a value of tc can be determined. This singularity is also present in GRI. It is shown that the interplay between parameters β and γ may produce phenomena of multiple equilibria. An analysis of the severe hyperinflation occurred in Hungary proves that the novel model is robust. When this model is used for examining data of Israel a reasonable tc is got. High-inflation regimes in Mexico and Iceland, which exhibit weaker inflations than that of Israel, are also successfully described.

  20. Chemical reactor modeling multiphase reactive flows

    CERN Document Server

    Jakobsen, Hugo A

    2014-01-01

    Chemical Reactor Modeling closes the gap between Chemical Reaction Engineering and Fluid Mechanics.  The second edition consists of two volumes: Volume 1: Fundamentals. Volume 2: Chemical Engineering Applications In volume 1 most of the fundamental theory is presented. A few numerical model simulation application examples are given to elucidate the link between theory and applications. In volume 2 the chemical reactor equipment to be modeled are described. Several engineering models are introduced and discussed. A survey of the frequently used numerical methods, algorithms and schemes is provided. A few practical engineering applications of the modeling tools are presented and discussed. The working principles of several experimental techniques employed in order to get data for model validation are outlined. The monograph is based on lectures regularly taught in the fourth and fifth years graduate courses in transport phenomena and chemical reactor modeling, and in a post graduate course in modern reactor m...

  1. Hard-sphere kinetic models for inert and reactive mixtures

    Science.gov (United States)

    Polewczak, Jacek

    2016-10-01

    I consider stochastic variants of a simple reacting sphere (SRS) kinetic model (Xystris and Dahler 1978 J. Chem. Phys. 68 387-401, Qin and Dahler 1995 J. Chem. Phys. 103 725-50, Dahler and Qin 2003 J. Chem. Phys. 118 8396-404) for dense reacting mixtures. In contrast to the line-of-center models of chemical reactive models, in the SRS kinetic model, the microscopic reversibility (detailed balance) can be easily shown to be satisfied, and thus all mathematical aspects of the model can be fully justified. In the SRS model, the molecules behave as if they were single mass points with two internal states. Collisions may alter the internal states of the molecules, and this occurs when the kinetic energy associated with the reactive motion exceeds the activation energy. Reactive and non-reactive collision events are considered to be hard sphere-like. I consider a four component mixture A, B, A *, B *, in which the chemical reactions are of the type A+B\\rightleftharpoons {{A}\\ast}+{{B}\\ast} , with A * and B * being distinct species from A and B. This work extends the joined works with George Stell to the kinetic models of dense inert and reactive mixtures. The idea of introducing smearing-type effect in the collisional process results in a new class of stochastic kinetic models for both inert and reactive mixtures. In this paper the important new mathematical properties of such systems of kinetic equations are proven. The new results for stochastic revised Enskog system for inert mixtures are also provided.

  2. The Alpine snow-albedo feedback in regional climate models

    Science.gov (United States)

    Winter, Kevin J.-P. M.; Kotlarski, Sven; Scherrer, Simon C.; Schär, Christoph

    2017-02-01

    The effect of the snow-albedo feedback (SAF) on 2m temperatures and their future changes in the European Alps is investigated in the ENSEMBLES regional climate models (RCMs) with a focus on the spring season. A total of 14 re-analysis-driven RCM experiments covering the period 1961-2000 and 10 GCM-driven transient climate change projections for 1950-2099 are analysed. A positive springtime SAF is found in all RCMs, but the range of the diagnosed SAF is large. Results are compared against an observation-based SAF estimate. For some RCMs, values very close to this estimate are found; other models show a considerable overestimation of the SAF. Net shortwave radiation has the largest influence of all components of the energy balance on the diagnosed SAF and can partly explain its spatial variability. Model deficiencies in reproducing 2m temperatures above snow and ice and associated cold temperature biases at high elevations seem to contribute to a SAF overestimation in several RCMs. The diagnosed SAF in the observational period strongly influences the estimated SAF contribution to twenty first century temperature changes in the European Alps. This contribution is subject to a clear elevation dependency that is governed by the elevation-dependent change in the number of snow days. Elevations of maximum SAF contribution range from 1500 to 2000 m in spring and are found above 2000 m in summer. Here, a SAF contribution to the total simulated temperature change between 0 and 0.5 °C until 2099 (multi-model mean in spring: 0.26 °C) or 0 and 14 % (multi-model mean in spring: 8 %) is obtained for models showing a realistic SAF. These numbers represent a well-funded but only approximate estimate of the SAF contribution to future warming, and a remaining contribution of model-specific SAF misrepresentations cannot be ruled out.

  3. Modeling of titration experiments by a reactive transport model

    Institute of Scientific and Technical Information of China (English)

    Ma Hongyun; Samper Javier; Xin Xin

    2011-01-01

    Acid mine drainage (AMD) is commonly treated by neutralization with alkaline substances. This treatment is supported by titration experiments that illustrate the buffering mechanisms and estimate the base neutralization capacity (BNC) of the AMD. Detailed explanation of titration curves requires modeling with a hydro-chemical model. In this study the titration curves of water samples from the drainage of the As Pontes mine and the corresponding dumps have been investigated and six buffers are selected by analyzing those curves. Titration curves have been simulated by a reactive transport model to discover the detailed buffering mechanisms. These simulations show seven regions involving different buffering mechanism. The BNC is primarily from buffers of dissolved Fe, Al and hydrogen sulfate. The BNC can be approximated by: BNC = 3(CFe + CAl) + 0.05Csulfate, where the units are mol/L. The BNC of the sample from the mine is 9.25 × 10-3 mol/L and that of the dumps sample is 1.28 × 10-2 mol/L.

  4. Sensory feedback in a bump attractor model of path integration.

    Science.gov (United States)

    Poll, Daniel B; Nguyen, Khanh; Kilpatrick, Zachary P

    2016-04-01

    Mammalian spatial navigation systems utilize several different sensory information channels. This information is converted into a neural code that represents the animal's current position in space by engaging place cell, grid cell, and head direction cell networks. In particular, sensory landmark (allothetic) cues can be utilized in concert with an animal's knowledge of its own velocity (idiothetic) cues to generate a more accurate representation of position than path integration provides on its own (Battaglia et al. The Journal of Neuroscience 24(19):4541-4550 (2004)). We develop a computational model that merges path integration with feedback from external sensory cues that provide a reliable representation of spatial position along an annular track. Starting with a continuous bump attractor model, we explore the impact of synaptic spatial asymmetry and heterogeneity, which disrupt the position code of the path integration process. We use asymptotic analysis to reduce the bump attractor model to a single scalar equation whose potential represents the impact of asymmetry and heterogeneity. Such imperfections cause errors to build up when the network performs path integration, but these errors can be corrected by an external control signal representing the effects of sensory cues. We demonstrate that there is an optimal strength and decay rate of the control signal when cues appear either periodically or randomly. A similar analysis is performed when errors in path integration arise from dynamic noise fluctuations. Again, there is an optimal strength and decay of discrete control that minimizes the path integration error.

  5. Effect of nonlinear void reactivity on bifurcation characteristics of a lumped-parameter model of a BWR: A study relevant to RBMK

    Energy Technology Data Exchange (ETDEWEB)

    Verma, Dinkar, E-mail: dinkar@iitk.ac.in [Nuclear Engineering and Technology Program, Indian Institute of Technology Kanpur, Kanpur 208 016 (India); Kalra, Manjeet Singh, E-mail: drmanjeet.singh@dituniversity.edu.in [DIT University, Dehradun 248 009 (India); Wahi, Pankaj, E-mail: wahi@iitk.ac.in [Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016 (India)

    2017-04-15

    Highlights: • A simplified model with nonlinear void reactivity feedback is studied. • Method of multiple scales for nonlinear analysis and oscillation characteristics. • Second order void reactivity dominates in determining system dynamics. • Opposing signs of linear and quadratic void reactivity enhances global safety. - Abstract: In the present work, the effect of nonlinear void reactivity on the dynamics of a simplified lumped-parameter model for a boiling water reactor (BWR) is investigated. A mathematical model of five differential equations comprising of neutronics and thermal-hydraulics encompassing the nonlinearities associated with both the reactivity feedbacks and the heat transfer process has been used. To this end, we have considered parameters relevant to RBMK for which the void reactivity is known to be nonlinear. A nonlinear analysis of the model exploiting the method of multiple time scales (MMTS) predicts the occurrence of the two types of Hopf bifurcation, namely subcritical and supercritical, leading to the evolution of limit cycles for a range of parameters. Numerical simulations have been performed to verify the analytical results obtained by MMTS. The study shows that the nonlinear reactivity has a significant influence on the system dynamics. A parametric study with varying nominal reactor power and operating conditions in coolant channel has also been performed which shows the effect of change in concerned parameter on the boundary between regions of sub- and super-critical Hopf bifurcations in the space constituted by the two coefficients of reactivities viz. the void and the Doppler coefficient of reactivities. In particular, we find that introduction of a negative quadratic term in the void reactivity feedback significantly increases the supercritical region and dominates in determining the system dynamics.

  6. Proprioceptive Feedback through a Neuromorphic Muscle Spindle Model

    Directory of Open Access Journals (Sweden)

    Lorenzo Vannucci

    2017-06-01

    Full Text Available Connecting biologically inspired neural simulations to physical or simulated embodiments can be useful both in robotics, for the development of a new kind of bio-inspired controllers, and in neuroscience, to test detailed brain models in complete action-perception loops. The aim of this work is to develop a fully spike-based, biologically inspired mechanism for the translation of proprioceptive feedback. The translation is achieved by implementing a computational model of neural activity of type Ia and type II afferent fibers of muscle spindles, the primary source of proprioceptive information, which, in mammals is regulated through fusimotor activation and provides necessary adjustments during voluntary muscle contractions. As such, both static and dynamic γ-motoneurons activities are taken into account in the proposed model. Information from the actual proprioceptive sensors (i.e., motor encoders is then used to simulate the spindle contraction and relaxation, and therefore drive the neural activity. To assess the feasibility of this approach, the model is implemented on the NEST spiking neural network simulator and on the SpiNNaker neuromorphic hardware platform and tested on simulated and physical robotic platforms. The results demonstrate that the model can be used in both simulated and real-time robotic applications to translate encoder values into a biologically plausible neural activity. Thus, this model provides a completely spike-based building block, suitable for neuromorphic platforms, that will enable the development of sensory-motor closed loops which could include neural simulations of areas of the central nervous system or of low-level reflexes.

  7. Quantitative Models and Analysis for Reactive Systems

    DEFF Research Database (Denmark)

    Thrane, Claus

    phones and websites. Acknowledging that now more than ever, systems come in contact with the physical world, we need to revise the way we construct models and verification algorithms, to take into account the behavior of systems in the presence of approximate, or quantitative information, provided...... by the environment in which they are embedded. This thesis studies the semantics and properties of a model-based framework for re- active systems, in which models and specifications are assumed to contain quantifiable information, such as references to time or energy. Our goal is to develop a theory of approximation......, by studying how small changes to our models affect the verification results. A key source of motivation for this work can be found in The Embedded Systems Design Challenge [HS06] posed by Thomas A. Henzinger and Joseph Sifakis. It contains a call for advances in the state-of-the-art of systems verification...

  8. Mathematical Models of Tuberculosis Reactivation and Relapse

    Directory of Open Access Journals (Sweden)

    Robert Steven Wallis

    2016-05-01

    Full Text Available The natural history of human infection with Mycobacterium tuberculosis (Mtb is highly variable, as is the response to treatment of active tuberculosis. There is presently no direct means to identify individuals in whom Mtb infection has been eradicated, whether by a bactericidal immune response or sterilizing antimicrobial chemotherapy. Mathematical models can assist in such circumstances by measuring or predicting events that cannot be directly observed. The 3 models discussed in this review illustrate instances in which mathematical models were used to identify individuals with innate resistance to Mtb infection, determine the etiology of tuberculosis in patients treated with tumor necrosis factor antagonists, and predict the risk of relapse in persons undergoing tuberculosis treatment. These examples illustrate the power of various types of mathematic models to increase knowledge and thereby inform interventions in the present global tuberculosis epidemic.

  9. Assessment of parametric uncertainty for groundwater reactive transport modeling,

    Science.gov (United States)

    Shi, Xiaoqing; Ye, Ming; Curtis, Gary P.; Miller, Geoffery L.; Meyer, Philip D.; Kohler, Matthias; Yabusaki, Steve; Wu, Jichun

    2014-01-01

    The validity of using Gaussian assumptions for model residuals in uncertainty quantification of a groundwater reactive transport model was evaluated in this study. Least squares regression methods explicitly assume Gaussian residuals, and the assumption leads to Gaussian likelihood functions, model parameters, and model predictions. While the Bayesian methods do not explicitly require the Gaussian assumption, Gaussian residuals are widely used. This paper shows that the residuals of the reactive transport model are non-Gaussian, heteroscedastic, and correlated in time; characterizing them requires using a generalized likelihood function such as the formal generalized likelihood function developed by Schoups and Vrugt (2010). For the surface complexation model considered in this study for simulating uranium reactive transport in groundwater, parametric uncertainty is quantified using the least squares regression methods and Bayesian methods with both Gaussian and formal generalized likelihood functions. While the least squares methods and Bayesian methods with Gaussian likelihood function produce similar Gaussian parameter distributions, the parameter distributions of Bayesian uncertainty quantification using the formal generalized likelihood function are non-Gaussian. In addition, predictive performance of formal generalized likelihood function is superior to that of least squares regression and Bayesian methods with Gaussian likelihood function. The Bayesian uncertainty quantification is conducted using the differential evolution adaptive metropolis (DREAM(zs)) algorithm; as a Markov chain Monte Carlo (MCMC) method, it is a robust tool for quantifying uncertainty in groundwater reactive transport models. For the surface complexation model, the regression-based local sensitivity analysis and Morris- and DREAM(ZS)-based global sensitivity analysis yield almost identical ranking of parameter importance. The uncertainty analysis may help select appropriate likelihood

  10. Quantitative Models and Analysis for Reactive Systems

    DEFF Research Database (Denmark)

    Thrane, Claus

    phones and websites. Acknowledging that now more than ever, systems come in contact with the physical world, we need to revise the way we construct models and verification algorithms, to take into account the behavior of systems in the presence of approximate, or quantitative information, provided......, allowing verification procedures to quantify judgements, on how suitable a model is for a given specification — hence mitigating the usual harsh distinction between satisfactory and non-satisfactory system designs. This information, among other things, allows us to evaluate the robustness of our framework......, by studying how small changes to our models affect the verification results. A key source of motivation for this work can be found in The Embedded Systems Design Challenge [HS06] posed by Thomas A. Henzinger and Joseph Sifakis. It contains a call for advances in the state-of-the-art of systems verification...

  11. Output feedback robust model predictive control with unmeasurable model parameters and bounded disturbance☆

    Institute of Scientific and Technical Information of China (English)

    Baocang Ding; Hongguang Pan

    2016-01-01

    The output feedback model predictive control (MPC), for a linear parameter varying (LPV) process system including unmeasurable model parameters and disturbance (all lying in known polytopes), is considered. Some previously developed tools, including the norm-bounding technique for relaxing the disturbance-related constraint handling, the dynamic output feedback law, the notion of quadratic boundedness for specifying the closed-loop stability, and the el ipsoidal state estimation error bound for guaranteeing the recursive feasibility, are merged in the control design. Some previous approaches are shown to be the special cases. An example of continuous stirred tank reactor (CSTR) is given to show the effectiveness of the proposed approaches.

  12. Parameter estimation in a stochastic model of the tubuloglomerular feedback mechanism in a rat nephron

    DEFF Research Database (Denmark)

    Ditlevsen, Susanne; Yip, Kay-Pong; Holstein-Rathlou, N.-H.

    2005-01-01

    A key parameter in the understanding of renal hemodynamics is the gain of the feedback function in the tubuloglomerular feedback mechanism. A dynamic model of autoregulation of renal blood flow and glomerular filtration rate has been extended to include a stochastic differential equations model o...

  13. A Moral Experience Feedback Loop: Modeling a System of Moral Self-Cultivation in Everyday Life

    Science.gov (United States)

    Sherblom, Stephen A.

    2015-01-01

    This "systems thinking" model illustrates a common feedback loop by which people engage the moral world and continually reshape their moral sensibility. The model highlights seven processes that collectively form this feedback loop: beginning with (1) one's current moral sensibility which shapes processes of (2) perception, (3)…

  14. A Moral Experience Feedback Loop: Modeling a System of Moral Self-Cultivation in Everyday Life

    Science.gov (United States)

    Sherblom, Stephen A.

    2015-01-01

    This "systems thinking" model illustrates a common feedback loop by which people engage the moral world and continually reshape their moral sensibility. The model highlights seven processes that collectively form this feedback loop: beginning with (1) one's current moral sensibility which shapes processes of (2) perception, (3)…

  15. Sensitivity to plant modelling uncertainties in optimal feedback control of sound radiation from a panel

    DEFF Research Database (Denmark)

    Mørkholt, Jakob

    1997-01-01

    Optimal feedback control of broadband sound radiation from a rectangular baffled panel has been investigated through computer simulations. Special emphasis has been put on the sensitivity of the optimal feedback control to uncertainties in the modelling of the system under control.A model of a re...

  16. Feedback model evaluation of high-mix product manufacturing

    Science.gov (United States)

    King, Dion; Cheng, Mingjen; Lu, Aho; Mao, Zhibiao; Liang, Curtis

    2006-03-01

    As the patterns are getting smaller, the difficulty to control a margin-tight process expands exponentially. The use of the Automated Process Control (APC), therefore, becomes a widely employed mean in photolithography process to control overlay and CD variations. The accuracy of APC is dependent upon the amount of the previous process data. However, in a foundry with high-mix products it is typical that there are not enough historic data points for accurate calculation of process parameters for a low volume product. The consequence is the high rework rate of pilot runs and test runes due to poor process parameter prediction for overlay. Several studies of the method for predicting the overlay correction have been reported. The key to build a good prediction model is to break the overlay errors down to several parts. Some are equipment or technology related errors, which are shared by all products. Others are the characteristic for certain products, for instance, mask error or special alignment marks. In the production environment the former parts are updated in real time by data feedback from processing all kinds of products. The low volume products or pilot products can share the information. Thus we can achieve a more accurate control or prediction for a new product. In this paper we provide a new model for predicting the process parameter settings of overlay for a pilot run or a product not being run on a tool for a long period of time. This new model is a Simplified Cerebellar Manipulation Arithmetic Controller (SCMAC), which is one kind of Neural Network (NN) model. We assume each part of overlay errors is a cell in SCMAC and build the whole cell table by using this assumption. The final overlay correction value is the sum of a group of cells, which is activated by one lot information. We will also present the details of the building and training of this new SCMAC model. The prediction accuracy of SCMAC in overlay parameters is also evaluated. According to

  17. Cloud feedback mechanisms and their representation in global climate models: Cloud feedback mechanisms and their representation in GCMs

    Energy Technology Data Exchange (ETDEWEB)

    Ceppi, Paulo [Department of Meteorology, University of Reading, Reading UK; Brient, Florent [Centre National de Recherches M?t?orologiques, M?t?o-France/CNRS, Toulouse France; Zelinka, Mark D. [Cloud Processes Research Group, Lawrence Livermore National Laboratory, Livermore CA USA; Hartmann, Dennis L. [Department of Atmospheric Sciences, University of Washington, Seattle WA USA

    2017-05-11

    Cloud feedback—the change in top-of-atmosphere radiative flux resulting from the cloud response to warming—constitutes by far the largest source of uncertainty in the climate response to CO2 forcing simulated by global climate models (GCMs). We review the main mechanisms for cloud feedbacks, and discuss their representation in climate models and the sources of intermodel spread. Global-mean cloud feedback in GCMs results from three main effects: (1) rising free-tropospheric clouds (a positive longwave effect); (2) decreasing tropical low cloud amount (a positive shortwave [SW] effect); (3) increasing high-latitude low cloud optical depth (a negative SW effect). These cloud responses simulated by GCMs are qualitatively supported by theory, high-resolution modeling, and observations. Rising high clouds are consistent with the fixed anvil temperature (FAT) hypothesis, whereby enhanced upper-tropospheric radiative cooling causes anvil cloud tops to remain at a nearly fixed temperature as the atmosphere warms. Tropical low cloud amount decreases are driven by a delicate balance between the effects of vertical turbulent fluxes, radiative cooling, large-scale subsidence, and lower-tropospheric stability on the boundary-layer moisture budget. High-latitude low cloud optical depth increases are dominated by phase changes in mixed-phase clouds. The causes of intermodel spread in cloud feedback are discussed, focusing particularly on the role of unresolved parameterized processes such as cloud microphysics, turbulence, and convection.

  18. Finite Element Modeling of Cutaneous Electrical Stimulation for Sensory Feedback

    Institute of Scientific and Technical Information of China (English)

    LI Si; CHAI Guo-hong; SUI Xiao-hong; LAN Ning

    2014-01-01

    It is currently difficult for the amputee to perceive environmental information such as tactile pressure on the fingertip of the present upper limb prostheses. Sensory feedback induced by cutaneous electrical stimulation can be used to transmit tactile information from hand prostheses to sensory nerve of intact upper arm, thus producing the corresponding perceptions in human brain. In order to have a deeper understanding on the distribution of stimulation current within the limb, and find a better placement of the stimulating and reference electrodes, we constructed a three-dimensional upper-limb model to systematically study the effect of electrode placement on current distribution based on finite element analysis. In these simulations, the reference electrode is positioned at four different locations around and on the axial direction of the arm. The results show that with the increase of distance between reference electrode and stimulating electrode, the current density increases in the skin layer of the upper limb. When the reference electrode is on the opposite side of stimulating electrode around the arm, the current is more concentrated in the skin layer, which is in line with recent findings in psychophysiological experiments. But better spatial selectivity could be achieved when the reference electrode is closer to the stimulating electrode around the arm, and it is more obvious in comparison with that on the axial direction. These findings will provide insights for the design of electrode array used for evoking cutaneous sensory afferents.

  19. Effective Relaying in Two-user Interference Channel with Different Models of Channel Output Feedback

    CERN Document Server

    Sahai, Achaleshwar; Yuksel, Melda; Sabharwal, Ashutosh

    2011-01-01

    In this paper, we study the impact of channel output feedback architectures on the capacity of two-user interference channel. For a two-user interference channel, a feedback link can exist between receivers and transmitters in 9 canonical architectures, ranging from only one feedback link to four-feedback links. We derive exact capacity region for the deterministic interference channel and constant-gap capacity region for the Gaussian interference channel for all but two of the 9 architectures (or models). We find that the sum-capacity in deterministic interference channel with only one feedback link, from any one receiver to its own transmitter, is identical to the interference channel with four feedback links; for the Gaussian model, the gap is bounded for all channel gains. However, one feedback link is not sufficient to achieve the whole capacity region of four feedback links. To achieve the full capacity region requires at least two feedback links. To prove the results, we derive several new outer bounds...

  20. Roles of energy conservation and climate feedback in Bjerknes compensation: a coupled modeling study

    Science.gov (United States)

    Dai, Haijin; Yang, Haijun; Yin, Jie

    2016-10-01

    The roles of energy balance and climate feedback in Bjerknes compensation (BJC) are studied through wind-perturbation experiments in a coupled climate model. Shutting down surface winds over the ocean causes significant reductions in both wind-driven and thermohaline overturning circulations, leading to a remarkable decrease in poleward ocean heat transport (OHT). The sea surface temperature (SST) responds with an increasing meridional gradient, resulting in a stronger Hadley Cell, and thus an enhanced atmosphere heat transport (AHT), compensating the OHT decrease. This is the so-called BJC. Coupled model experiments confirm that the occurrence of BJC is an intrinsic requirement of local energy conservation, and local climate feedback determines the degree of BJC, consistent with our previous theoretical results. Negative (positive or zero) local feedback results in AHT change undercompensating (overcompensating or perfectly compensating) OHT change. Using the radiative kernel technique, the general local feedback between the radiative balance at the top of the atmosphere and surface temperature can be partitioned into individual feedbacks that are related to perturbations in temperature, water vapor, surface albedo, and clouds. We find that the overcompensation in the tropics (extratropics) is mainly caused by positive feedbacks related to water vapor and clouds (surface albedo). The longwave feedbacks related to SST and atmospheric temperature are always negative and strong outside the tropics, well offsetting positive feedbacks in most regions and resulting in undercompensation. Different dominant feedbacks give different BJC scenarios at different regions, acting together to maintain the local energy balance.

  1. Roles of energy conservation and climate feedback in Bjerknes compensation: a coupled modeling study

    Science.gov (United States)

    Dai, Haijin; Yang, Haijun; Yin, Jie

    2017-09-01

    The roles of energy balance and climate feedback in Bjerknes compensation (BJC) are studied through wind-perturbation experiments in a coupled climate model. Shutting down surface winds over the ocean causes significant reductions in both wind-driven and thermohaline overturning circulations, leading to a remarkable decrease in poleward ocean heat transport (OHT). The sea surface temperature (SST) responds with an increasing meridional gradient, resulting in a stronger Hadley Cell, and thus an enhanced atmosphere heat transport (AHT), compensating the OHT decrease. This is the so-called BJC. Coupled model experiments confirm that the occurrence of BJC is an intrinsic requirement of local energy conservation, and local climate feedback determines the degree of BJC, consistent with our previous theoretical results. Negative (positive or zero) local feedback results in AHT change undercompensating (overcompensating or perfectly compensating) OHT change. Using the radiative kernel technique, the general local feedback between the radiative balance at the top of the atmosphere and surface temperature can be partitioned into individual feedbacks that are related to perturbations in temperature, water vapor, surface albedo, and clouds. We find that the overcompensation in the tropics (extratropics) is mainly caused by positive feedbacks related to water vapor and clouds (surface albedo). The longwave feedbacks related to SST and atmospheric temperature are always negative and strong outside the tropics, well offsetting positive feedbacks in most regions and resulting in undercompensation. Different dominant feedbacks give different BJC scenarios at different regions, acting together to maintain the local energy balance.

  2. ON THE PERSISTENT PROPERTY OF A DELAYED NON-AUTONOMOUS SCHOENER MODEL WITH FEEDBACK CONTROL

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    We study a delayed non-autonomous Schoener model with feedback control, which was proposed by Qiming Liu, Rui Xu and Pinghua Yang [8]. By applying a differential inequality and some analysis technique, we show that under some suitable assumptions, the feedback control variable has no influence on the persistent property of the system. Our result improves the existing ones.

  3. AN IN-SITU PERMEABLE REACTIVE BARRIER FOR THE TREATMENT OF HEXAVALENT CHROMIUM AND TRICHLOROETHYLENE IN GROUNDWATER: VOLUME 3 MULTICOMPONENT REACTIVE TRANSPORT MODELING

    Science.gov (United States)

    Reactive transport modeling has been conducted to describe the performance of the permeable reactive barrier at the Coast Guard Support Center near Elizabeth City, NC. The reactive barrier was installed to treat groundwater contaminated by hexavalent chromium and chlorinated org...

  4. Verification of three-dimensional neutron kinetics model of TRAP-KS code regarding reactivity variations

    Energy Technology Data Exchange (ETDEWEB)

    Uvakin, Maxim A.; Alekhin, Grigory V.; Bykov, Mikhail A.; Zaitsev, Sergei I. [EDO ' GIDROPRESS' , Moscow Region, Podolsk (Russian Federation)

    2016-09-15

    This work deals with TRAP-KS code verification. TRAP-KS is used for coupled neutron and thermo-hydraulic process calculations of VVER reactors. The three-dimensional neutron kinetics model enables consideration of space effects, which are produced by energy field and feedback parameters variations. This feature has to be investigated especially for asymmetrical multiplying variations of core properties, power fluctuations and strong local perturbation insertion. The presented work consists of three test definitions. First, an asymmetrical control rod (CR) ejection during power operation is defined. This process leads to fast reactivity insertion with short-time power spike. As second task xenon oscillations are considered. Here, small negative reactivity insertion leads to power decreasing and induces space oscillations of xenon concentration. In the late phase, these oscillations are suppressed by external actions. As last test, an international code comparison for a hypothetical main steam line break (V1000CT-2, task 2) was performed. This scenario is interesting for asymmetrical positive reactivity insertion by decreasing coolant temperature in the affected loop.

  5. A cloud feedback emulator (CFE, version 1.0) for an intermediate complexity model

    Science.gov (United States)

    Ullman, David J.; Schmittner, Andreas

    2017-02-01

    The dominant source of inter-model differences in comprehensive global climate models (GCMs) are cloud radiative effects on Earth's energy budget. Intermediate complexity models, while able to run more efficiently, often lack cloud feedbacks. Here, we describe and evaluate a method for applying GCM-derived shortwave and longwave cloud feedbacks from 4 × CO2 and Last Glacial Maximum experiments to the University of Victoria Earth System Climate Model. The method generally captures the spread in top-of-the-atmosphere radiative feedbacks between the original GCMs, which impacts the magnitude and spatial distribution of surface temperature changes and climate sensitivity. These results suggest that the method is suitable to incorporate multi-model cloud feedback uncertainties in ensemble simulations with a single intermediate complexity model.

  6. An analytical model for soil-atmosphere feedback

    NARCIS (Netherlands)

    Schaefli, B.; Van der Ent, R.J.; Woods, R.; Savenije, H.H.G.

    2012-01-01

    Soil-atmosphere feedback is a key for understanding the hydrological cycle and the direction of potential system changes. This paper presents an analytical framework to study the interplay between soil and atmospheric moisture, using as input only the boundary conditions at the upstream end of traje

  7. Stabilizing PID controllers for a single-link biomechanical model with position, velocity, and force feedback.

    Science.gov (United States)

    Iqbal, Kamran; Roy, Anindo

    2004-12-01

    In this paper we address the problem of PID stabilization of a single-link inverted pendulum-based biomechanical model with force feedback, two levels of position and velocity feedback, and with delays in all the feedback loops. The novelty of the proposed model lies in its physiological relevance, whereby both small and medium latency sensory feedbacks from muscle spindle (MS), and force feedback from Golgi tendon organ (GTO) are included in the formulation. The biomechanical model also includes active and passive viscoelastic feedback from Hill-type muscle model and a second-order low-pass function for muscle activation. The central nervous system (CNS) regulation of postural movement is represented by a proportional-integral-derivative (PID) controller. Padé approximation of delay terms is employed to arrive at an overall rational transfer function of the biomechanical model. The Hermite-Biehler theorem is then used to derive stability results, leading to the existence of stabilizing PID controllers. An algorithm for selection of stabilizing feedback gains is developed using the linear matrix inequality (LMI) approach.

  8. The magnitudes and timescales of global mean surface temperature feedbacks in climate models

    Directory of Open Access Journals (Sweden)

    A. Jarvis

    2011-12-01

    Full Text Available Because of the fundamental role feedbacks play in determining the response of surface temperature to perturbations in radiative forcing, it is important we understand the dynamic characteristics of these feedbacks. Rather than attribute the aggregate surface temperature feedback to particular physical processes, this paper adopts a linear systems approach to investigate the partitioning with respect to the timescale of the feedbacks regulating global mean surface temperature in climate models. The analysis reveals that there is a dominant net negative feedback realised on an annual timescale and that this is partially attenuated by a spectrum of positive feedbacks with characteristic timescales in the range 10 to 1000 yr. This attenuation was composed of two discrete phases which are attributed to the equilibration of "diffusive – mixed layer" and "circulatory – deep ocean" ocean heat uptake. The diffusive equilibration was associated with time constants on the decadal timescale and accounted for approximately 75 to 80 percent of the overall ocean heat feedback, whilst the circulatory equilibration operated on a centennial timescale and accounted for the remaining 20 to 25 percent of the response. This suggests that the dynamics of the transient ocean heat uptake feedback first discussed by Baker and Roe (2009 tends to be dominated by loss of diffusive heat uptake in climate models, rather than circulatory deep ocean heat equilibration.

  9. Modeling Routing Overhead Generated by Wireless Reactive Routing Protocols

    CERN Document Server

    Javaid, Nadeem; Javaid, Akmal; Malik, Shahzad A

    2011-01-01

    In this paper, we have modeled the routing over- head generated by three reactive routing protocols; Ad-hoc On-demand Distance Vector (AODV), Dynamic Source Routing (DSR) and DYnamic MANET On-deman (DYMO). Routing performed by reactive protocols consists of two phases; route discovery and route maintenance. Total cost paid by a protocol for efficient routing is sum of the cost paid in the form of energy consumed and time spent. These protocols majorly focus on the optimization performed by expanding ring search algorithm to control the flooding generated by the mechanism of blind flooding. So, we have modeled the energy consumed and time spent per packet both for route discovery and route maintenance. The proposed framework is evaluated in NS-2 to compare performance of the chosen routing protocols.

  10. Langevin model for reactive transport in porous media

    Science.gov (United States)

    Tartakovsky, Alexandre M.

    2010-08-01

    Existing continuum models for reactive transport in porous media tend to overestimate the extent of solute mixing and mixing-controlled reactions because the continuum models treat both the mechanical and diffusive mixings as an effective Fickian process. Recently, we have proposed a phenomenological Langevin model for flow and transport in porous media [A. M. Tartakovsky, D. M. Tartakovsky, and P. Meakin, Phys. Rev. Lett. 101, 044502 (2008)10.1103/PhysRevLett.101.044502]. In the Langevin model, the fluid flow in a porous continuum is governed by a combination of a Langevin equation and a continuity equation. Pore-scale velocity fluctuations, the source of mechanical dispersion, are represented by the white noise. The advective velocity (the solution of the Langevin flow equation) causes the mechanical dispersion of a solute. Molecular diffusion and sub-pore-scale Taylor-type dispersion are modeled by an effective stochastic advection-diffusion equation. Here, we propose a method for parameterization of the model for a synthetic porous medium, and we use the model to simulate multicomponent reactive transport in the porous medium. The detailed comparison of the results of the Langevin model with pore-scale and continuum (Darcy) simulations shows that: (1) for a wide range of Peclet numbers the Langevin model predicts the mass of reaction product more accurately than the Darcy model; (2) for small Peclet numbers predictions of both the Langevin and the Darcy models agree well with a prediction of the pore-scale model; and (3) the accuracy of the Langevin and Darcy model deteriorates with the increasing Peclet number but the accuracy of the Langevin model decreases more slowly than the accuracy of the Darcy model. These results show that the separate treatment of advective and diffusive mixing in the stochastic transport model is more accurate than the classical advection-dispersion theory, which uses a single effective diffusion coefficient (the dispersion

  11. Representing Microbial Processes in Environmental Reactive Transport Models

    Science.gov (United States)

    van Cappellen, P.

    2009-04-01

    Microorganisms play a key role in the biogeochemical functioning of the earth's surface and shallow subsurface. In the context of reactive transport modeling, a major challenge is to derive, parameterize, calibrate and verify mathematical expressions for microbially-mediated reactions in the environmental. This is best achieved by combining field observations, laboratory experiments, theoretical principles and modeling. Here, I will illustrate such an integrated approach for the case of microbial respiration processes in aquatic sediments. Important issues that will be covered include experimental design, model consistency and performance, as well as the bioenergetics and transient behavior of geomicrobial reaction systems.

  12. The Model of the IT Impact Treated as Feedback in a Production Environment Based on a Cybernetic Model

    Directory of Open Access Journals (Sweden)

    Cornelia NOVAC-UDUDEC

    2011-11-01

    Full Text Available This paper presents an approach on the assessment of the impact that Information Technology has in an based- knowledge economy. In order to achieve this goal, we proposed the use of feedback model from the production environment, considered as a cybernetic system. The impact of the IT is treated similarly to the technological and behavioral relationships between the main effects of feedbacks. We also studied different effects that feedback produces as an IT impact.

  13. Experimental Model Based Feedback Control for Flutter Suppression and Gust Load Alleviation Project

    Data.gov (United States)

    National Aeronautics and Space Administration — ZONA Technology, Inc. (ZONA) proposes an R&D effort to develop an Experimental Model Based Feedback Control (EMBFC) Framework for the flutter suppression and...

  14. Career Goal Revision in Response to Negative Feedback: Testing a Longitudinal Cross-Lagged Model.

    Science.gov (United States)

    Hu, Shi; Creed, Peter A; Hood, Michelle

    2017-02-06

    We tested a model based on goal-setting and self-regulation theories of the cross-lagged relationships among negative career-related feedback, negative affect (career-related stress), and career goal revision (downward goal revision and goal disengagement). Participants were 409 Chinese university/college students (Mage 19 years; 58% female), who completed a survey at 2 time points approximately 6 months apart. Consistent with our hypotheses, negative career-related feedback at T1 was related to more career goal disengagement and greater downward goal revision at T2. Career-related stress partially mediated the relationship between negative career-related feedback and downward goal revision. In addition, there were reverse relationships between negative career-related feedback and career-related stress, and between career-related stress and goal disengagement. These findings highlight important roles for negative career-related feedback and negative affect in young peoples' career goal pursuit. (PsycINFO Database Record

  15. Knowing and acting in the clinical workplace: trainees' perspectives on modelling and feedback.

    Science.gov (United States)

    Stegeman, J H; Schoten, E J; Terpstra, O T

    2013-10-01

    In this article we discuss clinical workplace learning using a dual approach: a theoretical one and an empirical one. Drawing on the philosophical work of Aristotle, Polanyi and Schön we posit that the 'knowing and acting' underpinning day-to-day medical practice is personal and embraces by nature a tacit dimension. Consequently, imparting and acquiring this knowledge type necessitates personal interaction between trainer and trainee. The tacit dimension particularly influences modelling and feedback. In our empirical exploration we explore these educational routes in two disparate disciplines: surgery and paediatrics. We use a longitudinal design with in-depth interviewing. Our conclusion on modelling is: modelling is a dynamic and fragmented process reflecting discipline bound characteristics and working styles. On feedback it is: 'feedback' serves as vehicle for three distinctive forms of commenting on performance, each holding a specific power of expression for learning. We propose to view clinical workplace learning as: an interactive master-apprenticeship model encompassing modelling and feedback as natural educational routes. We conceptualise modelling and feedback as 'function' of interaction (developing grounded theory). Modelling function and feedback function may serve to study these routes as didactical components of ongoing interaction between trainer and trainee rather than an educator-driven series of unrelated events.

  16. Tidal Downsizing Model. IV. Destructive feedback in planets

    CERN Document Server

    Nayakshin, Sergei

    2015-01-01

    I argue that feedback is as important to formation of planets as it is to formation of stars and galaxies. Energy released by massive solid cores puffs up pre-collapse gas giant planets, making them vulnerable to tidal disruptions by their host stars. I find that feedback is the ultimate reason for some of the most robust properties of the observed exoplanet populations: the rarity of gas giants at all separations from $\\sim 0.1$ to $\\sim 100$~AU, the abundance of $\\sim 10 M_\\oplus$ cores but dearth of planets more massive than $\\sim 20 M_\\oplus$. Feedback effects can also explain (i) rapid assembly of massive cores at large separations as needed for Uranus, Neptune and the suspected HL Tau planets; (ii) the small core in Jupiter yet large cores in Uranus and Neptune; (iii) the existence of rare "metal monster" planets such as CoRoT-20b, a gas giant made of heavy elements by up to $\\sim 50$\\%.

  17. Modelling of Magnetron Sputtering of Tungsten Oxide with Reactive Gas Pulsing

    OpenAIRE

    2007-01-01

    Reactive sputtering is one of the most commonly employed processes for the deposition of thin films. However, the range of applications is limited by inherent instabilities, which necessitates the use of a complex feedback control of reactive gas (RG) partial pressure. Recently pulsing of the RG has been suggested as a possible alternative. In this report, the concept of periodically switching the RG flow between two different values is applied to the deposition of tungsten oxide. The trends ...

  18. Modeling food matrix effects on chemical reactivity: Challenges and perspectives.

    Science.gov (United States)

    Capuano, Edoardo; Oliviero, Teresa; van Boekel, Martinus A J S

    2017-06-29

    The same chemical reaction may be different in terms of its position of the equilibrium (i.e., thermodynamics) and its kinetics when studied in different foods. The diversity in the chemical composition of food and in its structural organization at macro-, meso-, and microscopic levels, that is, the food matrix, is responsible for this difference. In this viewpoint paper, the multiple, and interconnected ways the food matrix can affect chemical reactivity are summarized. Moreover, mechanistic and empirical approaches to explain and predict the effect of food matrix on chemical reactivity are described. Mechanistic models aim to quantify the effect of food matrix based on a detailed understanding of the chemical and physical phenomena occurring in food. Their applicability is limited at the moment to very simple food systems. Empirical modeling based on machine learning combined with data-mining techniques may represent an alternative, useful option to predict the effect of the food matrix on chemical reactivity and to identify chemical and physical properties to be further tested. In such a way the mechanistic understanding of the effect of the food matrix on chemical reactions can be improved.

  19. Analysis of Feedback processes in Online Group Interaction: a methodological model

    Directory of Open Access Journals (Sweden)

    Anna Espasa

    2013-06-01

    Full Text Available The aim of this article is to present a methodological model to analyze students' group interaction to improve their essays in online learning environments, based on asynchronous and written communication. In these environments teacher and student scaffolds for discussion are essential to promote interaction. One of these scaffolds can be the feedback. Research on feedback processes has predominantly focused on feedback design rather than on how students utilize feedback to improve learning. This methodological model fills this gap contributing to analyse the implementation of the feedback processes while students discuss collaboratively in a specific case of writing assignments. A review of different methodological models was carried out to define a framework adjusted to the analysis of the relationship of written and asynchronous group interaction, and students' activity and changes incorporated into the final text. The model proposed includes the following dimensions: 1 student participation 2 nature of student learning and 3 quality of student learning. The main contribution of this article is to present the methodological model and also to ascertain the model's operativity regarding how students incorporate such feedback into their essays.

  20. An accurate halo model for fitting non-linear cosmological power spectra and baryonic feedback models

    CERN Document Server

    Mead, Alexander; Heymans, Catherine; Joudaki, Shahab; Heavens, Alan

    2015-01-01

    We present an optimised variant of the halo model, designed to produce accurate matter power spectra well into the non-linear regime for a wide range of cosmological models. To do this, we introduce physically-motivated free parameters into the halo-model formalism and fit these to data from high-resolution N-body simulations. For a variety of $\\Lambda$CDM and $w$CDM models the halo-model power is accurate to $\\simeq 5$ per cent for $k\\leq 10h\\,\\mathrm{Mpc}^{-1}$ and $z\\leq 2$. We compare our results with recent revisions of the popular HALOFIT model and show that our predictions are more accurate. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spectrum. We demonstrate this by fitting the halo model to power spectra from the OWLS hydrodynamical simulation suite via parameters that govern halo internal structure. We are able to fit all feedback models investigated at the 5 per cent level using only two free parameters, and we place limi...

  1. The Abundance of Distant and Extremely Red Galaxies: The Role of AGN Feedback in Hierarchical Models

    CERN Document Server

    Menci, N; Giallongo, E; Grazian, A; Salimbeni, S

    2006-01-01

    We investigate the effect of AGN feedback associated to the bright QSO phase onto the color distribution of galaxies from z=0 up to z=4. To this aim, we insert a blast-wave model of AGN feedback in our semi-analytic model of galaxy formation, which includes the growth of supermassive black holes and the AGN activity triggered by interactions of the host galaxies. The AGN feedback is directly related to the impulsive, luminous quasar phase. We test our model by checking the consistency of its results against i) the QSO luminosity functions from z=0 to z=4; ii) the observed local relation between the black hole mass m_{BH} and the mass of the host galaxy. At low redshift the inclusion of AGN feedback enhances the number of red bright galaxies, so that the color distribution of M_r1.5) galaxies; at 0.52.5.

  2. Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yi; Notaro, Michael; Liu, Zhengyu; Gallimore, Robert; Levis, Samuel; Kutzbach, John E.

    2008-03-31

    Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte- Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

  3. A new switching parameter varying optoelectronic delayed feedback model with computer simulation

    Science.gov (United States)

    Liu, Lingfeng; Miao, Suoxia; Cheng, Mengfan; Gao, Xiaojing

    2016-02-01

    In this paper, a new switching parameter varying optoelectronic delayed feedback model is proposed and analyzed by computer simulation. This model is switching between two parameter varying optoelectronic delayed feedback models based on chaotic pseudorandom sequences. Complexity performance results show that this model has a high complexity compared to the original model. Furthermore, this model can conceal the time delay effectively against the auto-correlation function, delayed mutual information and permutation information analysis methods, and can extent the key space, which greatly improve its security.

  4. Theoretical modeling of the dynamics of a semiconductor laser subject to double-reflector optical feedback

    Science.gov (United States)

    Bakry, A.; Abdulrhmann, S.; Ahmed, M.

    2016-06-01

    We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding the second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.

  5. Theoretical modeling of the dynamics of a semiconductor laser subject to double-reflector optical feedback

    Energy Technology Data Exchange (ETDEWEB)

    Bakry, A. [King Abdulaziz University, 80203, Department of Physics, Faculty of Science (Saudi Arabia); Abdulrhmann, S. [Jazan University, 114, Department of Physics, Faculty of Sciences (Saudi Arabia); Ahmed, M., E-mail: mostafa.farghal@mu.edu.eg [King Abdulaziz University, 80203, Department of Physics, Faculty of Science (Saudi Arabia)

    2016-06-15

    We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding the second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.

  6. The CREST reactive-burn model for explosives

    Directory of Open Access Journals (Sweden)

    Maheswaran M-A.

    2011-01-01

    Full Text Available CREST is an innovative reactive-burn model that has been developed at AWE for simulating shock initiation and detonation propagation behaviour in explosives. The model has a different basis from other reactive-burn models in that its reaction rate is independent of local flow variables behind the shock wave e.g. pressure and temperature. The foundation for CREST, based on a detailed analysis of data from particle-velocity gauge experiments, is that the reaction rate depends only on the local shock strength and the time since the shock passed. Since a measure of shock strength is the entropy of the non-reacted explosive, which remains constant behind a shock, CREST uses an entropy-dependent reaction rate. This paper will provide an overview of the CREST model and its predictive capability. In particular, it will be shown that the model can predict a wide range of experimental phenomena for both shock initiation (e.g. the effects of porosity and initial temperature on sustained-shock and thin-flyer initiation and detonation propagation (e.g. the diameter effect curve and detonation failure cones using a single set of coefficients.

  7. Impact of mineralogical heterogeneity on reactive transport modelling

    Science.gov (United States)

    Liu, Min; Shabaninejad, Mehdi; Mostaghimi, Peyman

    2017-07-01

    Impact of mineralogical heterogeneity of rocks in reactive modelling is investigated by applying a pore scale model based on the Lattice Boltzmann and Finite Volume Methods. Mass transport, chemical reaction and solid structure modification are included in the model. A two-dimensional mineral map of a sandstone rock is acquired using the imaging technique of QEMSCAN SEM with Energy-Dispersive X-ray Spectroscopy (EDS). The mineralogical heterogeneity is explored by conducting multi-mineral reaction simulations on images containing various minerals. The results are then compared with the prediction of single mineral dissolution modelling. Dissolution patterns and permeability variations of multi-mineral and single mineral reactions are presented. The errors of single mineral reaction modelling are also estimated. Numerical results show that mineralogical heterogeneity can cause significant errors in permeability prediction, if a uniform mineral distribution is assumed. The errors are smaller in high Péclet regimes than in low Péclet regimes in this sample.

  8. Unifying Model-Based and Reactive Programming within a Model-Based Executive

    Science.gov (United States)

    Williams, Brian C.; Gupta, Vineet; Norvig, Peter (Technical Monitor)

    1999-01-01

    Real-time, model-based, deduction has recently emerged as a vital component in AI's tool box for developing highly autonomous reactive systems. Yet one of the current hurdles towards developing model-based reactive systems is the number of methods simultaneously employed, and their corresponding melange of programming and modeling languages. This paper offers an important step towards unification. We introduce RMPL, a rich modeling language that combines probabilistic, constraint-based modeling with reactive programming constructs, while offering a simple semantics in terms of hidden state Markov processes. We introduce probabilistic, hierarchical constraint automata (PHCA), which allow Markov processes to be expressed in a compact representation that preserves the modularity of RMPL programs. Finally, a model-based executive, called Reactive Burton is described that exploits this compact encoding to perform efficIent simulation, belief state update and control sequence generation.

  9. Neural-networks-based feedback linearization versus model predictive control of continuous alcoholic fermentation process

    Energy Technology Data Exchange (ETDEWEB)

    Mjalli, F.S.; Al-Asheh, S. [Chemical Engineering Department, Qatar University, Doha (Qatar)

    2005-10-01

    In this work advanced nonlinear neural networks based control system design algorithms are adopted to control a mechanistic model for an ethanol fermentation process. The process model equations for such systems are highly nonlinear. A neural network strategy has been implemented in this work for capturing the dynamics of the mechanistic model for the fermentation process. The neural network achieved has been validated against the mechanistic model. Two neural network based nonlinear control strategies have also been adopted using the model identified. The performance of the feedback linearization technique was compared to neural network model predictive control in terms of stability and set point tracking capabilities. Under servo conditions, the feedback linearization algorithm gave comparable tracking and stability. The feedback linearization controller achieved the control target faster than the model predictive one but with vigorous and sudden controller moves. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

  10. Relativistic feedback models of terrestrial gamma-ray flashes and gamma-ray glows

    Science.gov (United States)

    Dwyer, J. R.

    2015-12-01

    Relativistic feedback discharges, also known as dark lightning, are capable of explaining many of the observed properties of terrestrial gamma-ray flashes (TGFs) and gamma-ray glows, both created within thunderstorms. During relativistic feedback discharges, the generation of energetic electrons is self-sustained via the production of backward propagating positrons and back-scattered x-rays, resulting in very larges fluxes of energetic radiation. In addition, ionization produces large electric currents that generate LF/VLF radio emissions and eventually discharge the electric field, terminating the gamma-ray production. In this presentation, new relativistic feedback model results will be presented and compared to recent observations.

  11. On the compensation between cloud feedback and cloud adjustment in climate models

    Science.gov (United States)

    Chung, Eui-Seok; Soden, Brian J.

    2017-04-01

    Intermodel compensation between cloud feedback and rapid cloud adjustment has important implications for the range of model-inferred climate sensitivity. Although this negative intermodel correlation exists in both realistic (e.g., coupled ocean-atmosphere models) and idealized (e.g., aqua-planet) model configurations, the compensation appears to be stronger in the latter. The cause of the compensation between feedback and adjustment, and its dependence on model configuration remain poorly understood. In this study, we examine the characteristics of the cloud feedback and adjustment in model simulations with differing complexity, and analyze the causes responsible for their compensation. We show that in all model configurations, the intermodel compensation between cloud feedback and cloud adjustment largely results from offsetting changes in marine boundary-layer clouds. The greater prevalence of these cloud types in aqua-planet models is a likely contributor to the larger correlation between feedback and adjustment in those configurations. It is also shown that differing circulation changes in the aqua-planet configuration of some models act to amplify the intermodel range and sensitivity of the cloud radiative response by about a factor of 2.

  12. Formal Requirements Modeling for Reactive Systems with Coloured Petri Nets

    DEFF Research Database (Denmark)

    Tjell, Simon

    This dissertation presents the contributions of seven publications all concerned with the application of Coloured Petri Nets (CPN) to requirements modeling for reactive systems. The publications are introduced along with relevant background material and related work, and their contributions...... interface composed of recognizable artifacts and activities. The presentation of the three publications related to Use Cases is followed by a the presentation of a publication formalizing some of the guidelines applied for structuring the CPN requirements models|namely the guidelines that make it possible...... activity. The traces are automatically recorded during execution of the model. The second publication presents a formally specified framework for automating a large part of the tasks related to integrating Problem Frames with CPN. The framework is specified in VDM++, and allows the modeler to automatically...

  13. Physicochemical model for reactive sputtering of hot target

    Science.gov (United States)

    Shapovalov, Viktor I.; Karzin, Vitaliy V.; Bondarenko, Anastasia S.

    2017-02-01

    A physicochemical model for reactive magnetron sputtering of a metal target is described in this paper. The target temperature in the model is defined as a function of the ion current density. Synthesis of the coating occurs due to the surface chemical reaction. The law of mass action, the Langmuir isotherm and the Arrhenius equation for non-isothermal conditions were used for mathematical description of the reaction. The model takes into consideration thermal electron emission and evaporation of the target surface. The system of eight algebraic equations, describing the model, was solved for the tantalum target sputtered in the oxygen environment. It was established that the hysteresis effect disappears with the increase of the ion current density.

  14. Network interactions underlying mirror feedback in stroke: A dynamic causal modeling study

    Directory of Open Access Journals (Sweden)

    Soha Saleh

    2017-01-01

    Full Text Available Mirror visual feedback (MVF is potentially a powerful tool to facilitate recovery of disordered movement and stimulate activation of under-active brain areas due to stroke. The neural mechanisms underlying MVF have therefore been a focus of recent inquiry. Although it is known that sensorimotor areas can be activated via mirror feedback, the network interactions driving this effect remain unknown. The aim of the current study was to fill this gap by using dynamic causal modeling to test the interactions between regions in the frontal and parietal lobes that may be important for modulating the activation of the ipsilesional motor cortex during mirror visual feedback of unaffected hand movement in stroke patients. Our intent was to distinguish between two theoretical neural mechanisms that might mediate ipsilateral activation in response to mirror-feedback: transfer of information between bilateral motor cortices versus recruitment of regions comprising an action observation network which in turn modulate the motor cortex. In an event-related fMRI design, fourteen chronic stroke subjects performed goal-directed finger flexion movements with their unaffected hand while observing real-time visual feedback of the corresponding (veridical or opposite (mirror hand in virtual reality. Among 30 plausible network models that were tested, the winning model revealed significant mirror feedback-based modulation of the ipsilesional motor cortex arising from the contralesional parietal cortex, in a region along the rostral extent of the intraparietal sulcus. No winning model was identified for the veridical feedback condition. We discuss our findings in the context of supporting the latter hypothesis, that mirror feedback-based activation of motor cortex may be attributed to engagement of a contralateral (contralesional action observation network. These findings may have important implications for identifying putative cortical areas, which may be targeted with

  15. Development of Sirius facility that simulates void-reactivity feedback, and regional and core-wide stability estimation of natural circulation BWR

    Energy Technology Data Exchange (ETDEWEB)

    Furuya, M.; Inada, F.; Yasuo, A. [Tokyo Electric Power Co., Inc., Central Research Institute (Japan)

    2001-07-01

    The SIRIUS facility was designed and constructed for highly accurate simulation of core-wide and regional instabilities of the BWR. A real-time simulation was performed in the digital controller for modal point kinetics of reactor neutronics and fuel-rod conduction on the basis of measured void fractions in reactor core sections of the thermal-hydraulic loop. Stability experiments were conducted for a wide range of fluid conditions, power distributions, and fuel rod thermal conductivity time constants, including the normal operating conditions of a typical natural circulation BWR. The results showed that there is a sufficiently wide stability margin under normal operating conditions, even when void-reactivity feedback is taken into account. (author)

  16. Using visual cues to enhance haptic feedback for palpation on virtual model of soft tissue.

    Science.gov (United States)

    Li, Min; Konstantinova, Jelizaveta; Secco, Emanuele L; Jiang, Allen; Liu, Hongbin; Nanayakkara, Thrishantha; Seneviratne, Lakmal D; Dasgupta, Prokar; Althoefer, Kaspar; Wurdemann, Helge A

    2015-11-01

    This paper explores methods that make use of visual cues aimed at generating actual haptic sensation to the user, namely pseudo-haptics. We propose a new pseudo-haptic feedback-based method capable of conveying 3D haptic information and combining visual haptics with force feedback to enhance the user's haptic experience. We focused on an application related to tumor identification during palpation and evaluated the proposed method in an experimental study where users interacted with a haptic device and graphical interface while exploring a virtual model of soft tissue, which represented stiffness distribution of a silicone phantom tissue with embedded hard inclusions. The performance of hard inclusion detection using force feedback only, pseudo-haptic feedback only, and the combination of the two feedbacks was compared with the direct hand touch. The combination method and direct hand touch had no significant difference in the detection results. Compared with the force feedback alone, our method increased the sensitivity by 5%, the positive predictive value by 4%, and decreased detection time by 48.7%. The proposed methodology has great potential for robot-assisted minimally invasive surgery and in all applications where remote haptic feedback is needed.

  17. New NIR Calibration Models Speed Biomass Composition and Reactivity Characterization

    Energy Technology Data Exchange (ETDEWEB)

    2015-09-01

    Obtaining accurate chemical composition and reactivity (measures of carbohydrate release and yield) information for biomass feedstocks in a timely manner is necessary for the commercialization of biofuels. This highlight describes NREL's work to use near-infrared (NIR) spectroscopy and partial least squares multivariate analysis to develop calibration models to predict the feedstock composition and the release and yield of soluble carbohydrates generated by a bench-scale dilute acid pretreatment and enzymatic hydrolysis assay. This highlight is being developed for the September 2015 Alliance S&T Board meeting.

  18. Modelling reactive transport in a phosphogypsum dump, Venezia, Italia

    Science.gov (United States)

    Calcara, Massimo; Borgia, Andrea; Cattaneo, Laura; Bartolo, Sergio; Clemente, Gianni; Glauco Amoroso, Carlo; Lo Re, Fabio; Tozzato, Elena

    2013-04-01

    We develop a reactive-transport porous media flow model for a phosphogypsum dump located on the intertidal deposits of the Venetian Lagoon: 1. we construct a complex conceptual and geologic model from field data using the GMS™ graphical user interface; 2. the geological model is mapped onto a rectangular MODFLOW grid; 3. using the TMT2 FORTRAN90 code we translate this grid into the MESH, INCON and GENER input files for the TOUGH2 series of codes; 4. we run TOUGH-REACT to model flow and reactive transport in the dump and the sediments below it. The model includes 3 different dump materials (phosphogypsum, bituminous and hazardous wastes) with the pores saturated by specific fluids. The sediments below the dump are formed by an intertidal sequence of calcareous sands and silts, in addition to clays and organic deposits, all of which are initially saturated with lagoon salty waters. The recharge rain-water dilutes the dump fluids. In turn, the percolates from the dump react with the underlying sediments and the sea water that saturates them. Simulation results have been compared with chemical sampled analyses. In fact, in spite of the simplicity of our model we are able to show how the pH becomes neutral at a short distance below the dump, a fact observed during aquifer monitoring. The spatial and temporal evolution of dissolution and precipitation reactions occur in our model much alike reality. Mobility of some elements, such as divalent iron, are reduced by specific and concurrent conditions of pH from near-neutrality to moderately high values and positive redox potential; opposite conditions favour mobility of potentially toxic metals such as Cr, As Cd and Pb. Vertical movement are predominant. Trend should be therefore heavily influenced by pH and Eh values. If conditions are favourable to mobility, concentration of these substances in the bottom strata could be high. However, simulation suggest that the sediments tend to reduce the transport potential of

  19. Observational and model evidence for positive low-level cloud feedback.

    Science.gov (United States)

    Clement, Amy C; Burgman, Robert; Norris, Joel R

    2009-07-24

    Feedbacks involving low-level clouds remain a primary cause of uncertainty in global climate model projections. This issue was addressed by examining changes in low-level clouds over the Northeast Pacific in observations and climate models. Decadal fluctuations were identified in multiple, independent cloud data sets, and changes in cloud cover appeared to be linked to changes in both local temperature structure and large-scale circulation. This observational analysis further indicated that clouds act as a positive feedback in this region on decadal time scales. The observed relationships between cloud cover and regional meteorological conditions provide a more complete way of testing the realism of the cloud simulation in current-generation climate models. The only model that passed this test simulated a reduction in cloud cover over much of the Pacific when greenhouse gases were increased, providing modeling evidence for a positive low-level cloud feedback.

  20. Maximum likelihood Bayesian model averaging and its predictive analysis for groundwater reactive transport models

    Science.gov (United States)

    Curtis, Gary P.; Lu, Dan; Ye, Ming

    2015-01-01

    While Bayesian model averaging (BMA) has been widely used in groundwater modeling, it is infrequently applied to groundwater reactive transport modeling because of multiple sources of uncertainty in the coupled hydrogeochemical processes and because of the long execution time of each model run. To resolve these problems, this study analyzed different levels of uncertainty in a hierarchical way, and used the maximum likelihood version of BMA, i.e., MLBMA, to improve the computational efficiency. This study demonstrates the applicability of MLBMA to groundwater reactive transport modeling in a synthetic case in which twenty-seven reactive transport models were designed to predict the reactive transport of hexavalent uranium (U(VI)) based on observations at a former uranium mill site near Naturita, CO. These reactive transport models contain three uncertain model components, i.e., parameterization of hydraulic conductivity, configuration of model boundary, and surface complexation reactions that simulate U(VI) adsorption. These uncertain model components were aggregated into the alternative models by integrating a hierarchical structure into MLBMA. The modeling results of the individual models and MLBMA were analyzed to investigate their predictive performance. The predictive logscore results show that MLBMA generally outperforms the best model, suggesting that using MLBMA is a sound strategy to achieve more robust model predictions relative to a single model. MLBMA works best when the alternative models are structurally distinct and have diverse model predictions. When correlation in model structure exists, two strategies were used to improve predictive performance by retaining structurally distinct models or assigning smaller prior model probabilities to correlated models. Since the synthetic models were designed using data from the Naturita site, the results of this study are expected to provide guidance for real-world modeling. Limitations of applying MLBMA to the

  1. A Tumor Growth Model with Unmolded Dynamics Based on an Online Feedback Neural Network Model

    Directory of Open Access Journals (Sweden)

    ArashPourhashemi

    2014-01-01

    Full Text Available In this study, we identify tumor growth system by an online feedback neural network model based on back-propagation method. The modeling and identification of nonlinear dynamic systems is the process of developing and improving a mathematical representation of a system using experimental data. So, it is a problem of considerable importance through the use of measured experimental data in biomedical modeling. As is obvious, in biomedical researches it is really difficult and in some cases impossible to implement research on real patient or such a system which is not possible to empirical tests. To deal with, we need sometime a model close to real system in order to forecast dynamic systems so as to perform researches on models and design controller for control of system.

  2. Computer modeling of endovascular patch welding using temperature feedback

    Energy Technology Data Exchange (ETDEWEB)

    Glinsky, M.E.; London, R.A.; Zimmerman, G.B. [Lawrence Livermore National Lab., CA (United States); Jacques, S.L. [Anderson (M.D.) Cancer Center, Houston, TX (United States); Ols, J.D. [Ols & Associates, Mountain View, CA (United States)

    1995-11-01

    A new computer program, LATIS, being developed at Lawrence Livermore National Laboratory is used to study the effect of pulsed laser irradiation with temperature feedback on endovascular patch welding. Various physical and biophysical effects are included in these simulations: laser light scattering and absorption, tissue heating and heat conduction, vascular cooling, and tissue thermal damage. The geometry of a patch being held against the inner vessel wall (500 {mu}m inner diameter) by a balloon is considered. The system is exposed to light pulsed from an optical fiber inside the balloon. The laser power is adjusted during the course of a pulse. This is done automatically in the simulation by temperature feedback. A minimum in the depth of damage into the vessel wall is found. The minimum damage zone is about the thickness of the patch material that is heated by the laser. The more ordered the tissue the thinner the minimum zone of damage. The pulse length which minimizes the zone of damage is found to be the time for energy to diffuse across the layer. The delay time between the pulses is determined by the time for the heated layer to cool down. An optimal pulse length exists which minimizes the total time needed to weld the patch to the wall while keeping the thickness of the damaged tissue to less than 100 {mu}m. For the case that is considered, a patch dyed with light absorbing ICG on the side next to the vessel (thickness of the dyed layer is 60 {mu}m), the best protocol is found to be 33-600 ms pulses applied over 1.6 min.

  3. A global hybrid coupled model based on Atmosphere-SST feedbacks

    CERN Document Server

    Cimatoribus, Andrea A; Dijkstra, Henk A

    2011-01-01

    A global hybrid coupled model is developed, with the aim of studying the effects of ocean-atmosphere feedbacks on the stability of the Atlantic meridional overturning circulation. The model includes a global ocean general circulation model and a statistical atmosphere model. The statistical atmosphere model is based on linear regressions of data from a fully coupled climate model on sea surface temperature both locally and hemispherically averaged, being the footprint of Atlantic meridional overturning variability. It provides dynamic boundary conditions to the ocean model for heat, freshwater and wind-stress. A basic but consistent representation of ocean-atmosphere feedbacks is captured in the hybrid coupled model and it is more than ten times faster than the fully coupled climate model. The hybrid coupled model reaches a steady state with a climate close to the one of the fully coupled climate model, and the two models also have a similar response (collapse) of the Atlantic meridional overturning circulati...

  4. Formativ Feedback

    DEFF Research Database (Denmark)

    Hyldahl, Kirsten Kofod

    Denne bog undersøger, hvordan lærere kan anvende feedback til at forbedre undervisningen i klasselokalet. I denne sammenhæng har John Hattie, professor ved Melbourne Universitet, udviklet en model for feedback, hvilken er baseret på synteser af meta-analyser. I 2009 udgav han bogen "Visible...

  5. Review Content Analytics for the Prediction of Learner’s Feedback with Multivariate Regression Model

    Directory of Open Access Journals (Sweden)

    T. Chellatamilan

    2015-06-01

    Full Text Available E-learning facilitates both synchronous and asynchronous learning and it plays very important role in the teaching learning process. A large group of learners are engaged in the idea exchange independently by interacting with the members present in the learning management system. In order to generate meaningful learning outcome of the individual peer learners, the feedback review is very essential to extract the conceptual content which reflect the instantaneous learner’s behavior, emotions, capabilities, interestingness and difficulties and to fits them effectively. Collecting feedback in the form of numeric scale is very tough for both the learners and facilitators while specifying the rating, but it is too easy for the learners provide feedback in the form of text messages. The key challenge for analyzers is to extract the meaningful feedback content and dynamic rating of the learner’s feedback related to various conceptual contexts. We propose a novel method using multivariate predictive model for conceptual content analytics based on e-learners reviews using standard statistical model inverse regression. Finally the analysis is used in the prediction studies and to illustrate their effectiveness against the learner’s feedback.

  6. Reactive Transport Modeling and Changes in Porosity at Reactive Interfaces in a HLW repository in Clay

    Science.gov (United States)

    Samper, J.; Mon, A.; Montenegro, L.; Naves, A.; Fernández, J.

    2016-12-01

    High-level radioactive waste disposal in a deep geological repository is based on a multibarrier concept which combines natural barriers such as the geological formation and artificial barriers such as metallic containers, bentonite and concrete buffers and sealing materials. The stability and performance of the bentonite barrier could be affected by the corrosion products at the canister-bentonite interface and the hyperalkaline conditions caused by the degradation of concrete at the bentonite-concrete interface. Additionally, the host clay formation could also be affected by the hyperalkaline plume at the concrete-clay interface. Here we present a nonisothermal reactive transport model of the long-term interactions of the compacted bentonite with the corrosion products of a carbon-steel canister and the concrete liner of the engineered barrier of a high-level radioactive waste repository in clay. This problem involves large pH changes with a hyperalkaline high-pH plume, complex mineral dissolution/precipitation patterns, cation exchange reactions and proton surface complexation. These reactions lead to large changes in porosity which can even lead to pore clogging. Model results show that magnetite, the main corrosion product, precipitates and reduces significantly the porosity of the bentonite near the canister. The degradation of the concrete liner leads to the precipitation of secondary minerals and the reduction of the porosity of the bentonite and the clay formation at their interfaces with the concrete liner. The zones affected by pore clogging at the canister-bentonite, bentonite-concrete and concrete-clay interfaces at 1 Ma are equal to 10, 25 and 25 mm thick, respectively. The results of our simulations share many of the features of the models reported by others for engineered barrier systems at similar chemical conditions, including: 1) Narrow alteration zones; and 2) Pore clogging at the canister-bentonite, bentonite-concrete and concrete

  7. Adaptive Mesh Refinement in Reactive Transport Modeling of Subsurface Environments

    Science.gov (United States)

    Molins, S.; Day, M.; Trebotich, D.; Graves, D. T.

    2015-12-01

    Adaptive mesh refinement (AMR) is a numerical technique for locally adjusting the resolution of computational grids. AMR makes it possible to superimpose levels of finer grids on the global computational grid in an adaptive manner allowing for more accurate calculations locally. AMR codes rely on the fundamental concept that the solution can be computed in different regions of the domain with different spatial resolutions. AMR codes have been applied to a wide range of problem including (but not limited to): fully compressible hydrodynamics, astrophysical flows, cosmological applications, combustion, blood flow, heat transfer in nuclear reactors, and land ice and atmospheric models for climate. In subsurface applications, in particular, reactive transport modeling, AMR may be particularly useful in accurately capturing concentration gradients (hence, reaction rates) that develop in localized areas of the simulation domain. Accurate evaluation of reaction rates is critical in many subsurface applications. In this contribution, we will discuss recent applications that bring to bear AMR capabilities on reactive transport problems from the pore scale to the flood plain scale.

  8. Modeling Reactive Transport in Coupled Groundwater-Conduit Systems

    Science.gov (United States)

    Spiessl, S. M.; Sauter, M.; Zheng, C.; Viswanathan, H. S.

    2002-05-01

    Modeling reactive transport in coupled groundwater-conduit systems requires consideration of two transport time scales in the flow and transport models. Consider for example a subsurface mine consisting of a network of highly conductive shafts, drifts or ventilation raises (i.e., conduits) within the considerably less permeable ore material (i.e., matrix). In the conduits, potential contaminants can travel much more rapidly than in the background aquifer (matrix). Since conduits cannot necessarily be regarded as a continuum, double continuum models are only of limited use for simulation of contaminant transport in such coupled groundwater-conduit systems. This study utilizes a "hybrid" flow and transport model in which contaminants can in essence be transported at a slower time scale in the matrix and at a faster time scale in the conduits. The hybrid flow model uses an approach developed by Clemens et al. (1996), which is based on the modelling of flow in a discrete pipe network, coupled to a continuum representing the low-permeability inter-conduit matrix blocks. Laminar or turbulent flow can be simulated in the different pipes depending on the flow conditions in the model domain. The three-dimensional finite-difference groundwater flow model MODFLOW (Harbaugh and McDonald, 1996) is used to simulate flow in the continuum. Contaminant transport within the matrix is simulated with a continuum approach using the three-dimensional multi-species solute transport model MT3DMS (Zheng and Wang, 1999), while that in the conduit system is simulated with a one-dimensional advective transport model. As a first step for reactive transport modeling in such systems, only equilibrium reactions among multiple species are considered by coupling the hybrid transport model to a geochemical speciation package. An idealized mine network developed by Viswanathan and Sauter (2001) is used as a test problem in this study. The numerical experiment is based on reference date collected from

  9. Regular network model for the sea ice-albedo feedback in the Arctic.

    Science.gov (United States)

    Müller-Stoffels, Marc; Wackerbauer, Renate

    2011-03-01

    The Arctic Ocean and sea ice form a feedback system that plays an important role in the global climate. The complexity of highly parameterized global circulation (climate) models makes it very difficult to assess feedback processes in climate without the concurrent use of simple models where the physics is understood. We introduce a two-dimensional energy-based regular network model to investigate feedback processes in an Arctic ice-ocean layer. The model includes the nonlinear aspect of the ice-water phase transition, a nonlinear diffusive energy transport within a heterogeneous ice-ocean lattice, and spatiotemporal atmospheric and oceanic forcing at the surfaces. First results for a horizontally homogeneous ice-ocean layer show bistability and related hysteresis between perennial ice and perennial open water for varying atmospheric heat influx. Seasonal ice cover exists as a transient phenomenon. We also find that ocean heat fluxes are more efficient than atmospheric heat fluxes to melt Arctic sea ice.

  10. Modeling Subducting Slabs: Structural Variations due to Thermal Models, Latent Heat Feedback, and Thermal Parameter

    Science.gov (United States)

    Marton, F. C.

    2001-12-01

    The thermal, mineralogical, and buoyancy structures of thermal-kinetic models of subducting slabs are highly dependent upon a number of parameters, especially if the metastable persistence of olivine in the transition zone is investigated. The choice of starting thermal model for the lithosphere, whether a cooling halfspace (HS) or plate model, can have a significant effect, resulting in metastable wedges of olivine that differ in size by up to two to three times for high values of the thermal parameter (ǎrphi). Moreover, as ǎrphi is the product of the age of the lithosphere at the trench, convergence rate, and dip angle, slabs with similar ǎrphis can show great variations in structures as these constituents change. This is especially true for old lithosphere, as the lithosphere continually cools and thickens with age for HS models, but plate models, with parameters from Parson and Sclater [1977] (PS) or Stein and Stein [1992] (GDH1), achieve a thermal steady-state and constant thickness in about 70 My. In addition, the latent heats (q) of the phase transformations of the Mg2SiO4 polymorphs can also have significant effects in the slabs. Including q feedback in models raises the temperature and reduces the extent of metastable olivine, causing the sizes of the metastable wedges to vary by factors of up to two times. The effects of the choice of thermal model, inclusion and non-inclusion of q feedback, and variations in the constituents of ǎrphi are investigated for several model slabs.

  11. The Cloud Feedback Model Intercomparison Project (CFMIP) contribution to CMIP6.

    Science.gov (United States)

    Webb, Mark J.; Andrews, Timothy; Bodas-Salcedo, Alejandro; Bony, Sandrine; Bretherton, Christopher S.; Chadwick, Robin; Chepfer, Helene; Douville, Herve; Good, Peter; Kay, Jennifer E.; Tselioudis, George

    2017-01-01

    The primary objective of CFMIP is to inform future assessments of cloud feedbacks through improved understanding of cloud-climate feedback mechanisms and better evaluation of cloud processes and cloud feedbacks in climate models. However, the CFMIP approach is also increasingly being used to understand other aspects of climate change, and so a second objective has now been introduced, to improve understanding of circulation, regional-scale precipitation, and non-linear changes. CFMIP is supporting ongoing model inter-comparison activities by coordinating a hierarchy of targeted experiments for CMIP6, along with a set of cloud-related output diagnostics. CFMIP contributes primarily to addressing the CMIP6 questions 'How does the Earth system respond to forcing?' and 'What are the origins and consequences of systematic model biases?' and supports the activities of the WCRP Grand Challenge on Clouds, Circulation and Climate Sensitivity. A compact set of Tier 1 experiments is proposed for CMIP6 to address this question: (1) what are the physical mechanisms underlying the range of cloud feedbacks and cloud adjustments predicted by climate models, and which models have the most credible cloud feedbacks? Additional Tier 2 experiments are proposed to address the following questions. (2) Are cloud feedbacks consistent for climate cooling and warming, and if not, why? (3) How do cloud-radiative effects impact the structure, the strength and the variability of the general atmospheric circulation in present and future climates? (4) How do responses in the climate system due to changes in solar forcing differ from changes due to CO2, and is the response sensitive to the sign of the forcing? (5) To what extent is regional climate change per CO2 doubling state-dependent (non-linear), and why? (6) Are climate feedbacks during the 20th century different to those acting on long-term climate change and climate sensitivity? (7) How do regional climate responses (e.g. in precipitation

  12. The Cloud Feedback Model Intercomparison Project (CFMIP) contribution to CMIP6

    Science.gov (United States)

    Webb, Mark J.; Andrews, Timothy; Bodas-Salcedo, Alejandro; Bony, Sandrine; Bretherton, Christopher S.; Chadwick, Robin; Chepfer, Hélène; Douville, Hervé; Good, Peter; Kay, Jennifer E.; Klein, Stephen A.; Marchand, Roger; Medeiros, Brian; Pier Siebesma, A.; Skinner, Christopher B.; Stevens, Bjorn; Tselioudis, George; Tsushima, Yoko; Watanabe, Masahiro

    2017-01-01

    The primary objective of CFMIP is to inform future assessments of cloud feedbacks through improved understanding of cloud-climate feedback mechanisms and better evaluation of cloud processes and cloud feedbacks in climate models. However, the CFMIP approach is also increasingly being used to understand other aspects of climate change, and so a second objective has now been introduced, to improve understanding of circulation, regional-scale precipitation, and non-linear changes. CFMIP is supporting ongoing model inter-comparison activities by coordinating a hierarchy of targeted experiments for CMIP6, along with a set of cloud-related output diagnostics. CFMIP contributes primarily to addressing the CMIP6 questions How does the Earth system respond to forcing? and What are the origins and consequences of systematic model biases? and supports the activities of the WCRP Grand Challenge on Clouds, Circulation and Climate Sensitivity.A compact set of Tier 1 experiments is proposed for CMIP6 to address this question: (1) what are the physical mechanisms underlying the range of cloud feedbacks and cloud adjustments predicted by climate models, and which models have the most credible cloud feedbacks? Additional Tier 2 experiments are proposed to address the following questions. (2) Are cloud feedbacks consistent for climate cooling and warming, and if not, why? (3) How do cloud-radiative effects impact the structure, the strength and the variability of the general atmospheric circulation in present and future climates? (4) How do responses in the climate system due to changes in solar forcing differ from changes due to CO2, and is the response sensitive to the sign of the forcing? (5) To what extent is regional climate change per CO2 doubling state-dependent (non-linear), and why? (6) Are climate feedbacks during the 20th century different to those acting on long-term climate change and climate sensitivity? (7) How do regional climate responses (e.g. in precipitation) and

  13. The Cloud Feedback Model Intercomparison Project (CFMIP) contribution to CMIP6.

    Science.gov (United States)

    Webb, Mark J.; Andrews, Timothy; Bodas-Salcedo, Alejandro; Bony, Sandrine; Bretherton, Christopher S.; Chadwick, Robin; Chepfer, Helene; Douville, Herve; Good, Peter; Kay, Jennifer E.; hide

    2017-01-01

    The primary objective of CFMIP is to inform future assessments of cloud feedbacks through improved understanding of cloud-climate feedback mechanisms and better evaluation of cloud processes and cloud feedbacks in climate models. However, the CFMIP approach is also increasingly being used to understand other aspects of climate change, and so a second objective has now been introduced, to improve understanding of circulation, regional-scale precipitation, and non-linear changes. CFMIP is supporting ongoing model inter-comparison activities by coordinating a hierarchy of targeted experiments for CMIP6, along with a set of cloud-related output diagnostics. CFMIP contributes primarily to addressing the CMIP6 questions 'How does the Earth system respond to forcing?' and 'What are the origins and consequences of systematic model biases?' and supports the activities of the WCRP Grand Challenge on Clouds, Circulation and Climate Sensitivity. A compact set of Tier 1 experiments is proposed for CMIP6 to address this question: (1) what are the physical mechanisms underlying the range of cloud feedbacks and cloud adjustments predicted by climate models, and which models have the most credible cloud feedbacks? Additional Tier 2 experiments are proposed to address the following questions. (2) Are cloud feedbacks consistent for climate cooling and warming, and if not, why? (3) How do cloud-radiative effects impact the structure, the strength and the variability of the general atmospheric circulation in present and future climates? (4) How do responses in the climate system due to changes in solar forcing differ from changes due to CO2, and is the response sensitive to the sign of the forcing? (5) To what extent is regional climate change per CO2 doubling state-dependent (non-linear), and why? (6) Are climate feedbacks during the 20th century different to those acting on long-term climate change and climate sensitivity? (7) How do regional climate responses (e.g. in precipitation

  14. A model of a flexible anguilliform swimmer driven by a central pattern generator with proprioceptive feedback

    Science.gov (United States)

    Hamlet, Christina; Tytell, Eric; Hoffman, Kathleen; Fauci, Lisa

    2015-11-01

    The swimming of a simple vertebrate, the lamprey, can shed light on how a flexible body can couple with a fluid environment to swim rapidly and efficiently. Animals use proprioceptive sensory information to sense how their bodies are bending, and then adjust the neural signals to their muscles to improve performance. We will present recent progress in the development of a computational model of a lamprey swimming in a Navier-Stokes fluid where a simple central pattern generator model, based on phase oscillators, is coupled to the evolving body dynamics of the swimmer through curvature and curvature derivative feedback. Such feedback can be positive (frequency decreasing), negative (frequency increasing), or mixed (positive to one side of the body and negative to the other, or vice versa). We will examine how the emergent swimming behavior and cost of transport depends upon these functional forms of proprioceptive feedback chosen in the model.

  15. THE EFFECTS OF MODELING AND FEEDBACK VARIABLES ON THE ACQUISITION OF A COMPLEX TEACHING STRATEGY.

    Science.gov (United States)

    ORME, MICHAEL E.J.; AND OTHERS

    THE RELATIVE EFFECTIVENESS OF SIX MODES OF TRAINING TEACHERS TO USE PROBING QUESTIONS WAS INVESTIGATED. THE MODES INVOLVED SYMBOLIC MODELING, PERCEPTUAL MODELING, OR BOTH, COUPLED WITH FEEDBACK. AFTER RATINGS OF PERTINENT BEHAVIOR IN A 5-MINUTE LESSON WERE COLLECTED AS PRETRAINING MEASURES, STANFORD TEACHER INTERNS WERE RANDOMLY DISTRIBUTED AMONG…

  16. Why do children learn to say "Broke"? A model of learning the past tense without feedback

    NARCIS (Netherlands)

    Taatgen, NA; Anderson, [No Value

    2002-01-01

    Learning the English past tense is characterized by a U-shaped learning function for the irregular verbs. Existing cognitive models often rely on a sudden increase in vocabulary, a high token-frequency of regular verbs, and complicated schemes of feedback in order to model this phenomenon. All these

  17. Ignition and Growth Reactive Flow Model for IMX-101

    Energy Technology Data Exchange (ETDEWEB)

    Tarver, Craig M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2016-02-19

    A set of Ignition and Growth (I&G) reactive flow model parameters is developed for the explosive IMX-101 containing DNAN, NQ, and NTO using the available shock initiation and detonation wave propagation experimental data. The unreacted equation of state for IMX-101 is based on experimental data from gas gun experiments by Furnish et al. and is similar to that of TNT. The product equation of state for IMX-101 is based on CHEETAH chemical equilibrium calculations and cylinder test experimental data. The IMX-101 reaction rate parameters are developed using hydrodynamic reactive flow simulations of several shock initiation and detonation experiments. One set of I&G parameters does a good job of reproducing both shock initiation and detonation experimental data. This is due to the fact that IMX-101 reacts over a relatively small pressure range from about 7 GPa to 20 GPa (C-J pressure). Advanced experiments using embedded gauges and/or laser interferometry could lead to better parameters.

  18. Biogeophysical feedbacks trigger shifts in the modelled vegetation-atmosphere system at multiple scales

    Directory of Open Access Journals (Sweden)

    S. C. Dekker

    2010-04-01

    Full Text Available Terrestrial vegetation influences climate by modifying the radiative-, momentum-, and hydrologic-balance. This paper contributes to the ongoing debate on the question whether positive biogeophysical feedbacks between vegetation and climate may lead to multiple equilibria in vegetation and climate and consequent abrupt regime shifts. Several modelling studies argue that vegetation-climate feedbacks at local to regional scales could be strong enough to establish multiple states in the climate system. An Earth Model of Intermediate Complexity, PlaSim, is used to investigate the resilience of the climate system to vegetation disturbance at regional to global scales. We hypothesize that by starting with two extreme initialisations of biomass, positive vegetation-climate feedbacks will keep the vegetation-atmosphere system within different attraction domains. Indeed, model integrations starting from different initial biomass distributions diverged to clearly distinct climate-vegetation states in terms of abiotic (precipitation and temperature and biotic (biomass variables. Moreover, we found that between these states there are several other steady states which depend on the scale of perturbation. From here global susceptibility maps were made showing regions of low and high resilience. The model results suggest that mainly the boreal and monsoon regions have low resiliences, i.e. instable biomass equilibria, with positive vegetation-climate feedbacks in which the biomass induced by a perturbation is further enforced. The perturbation did not only influence single vegetation-climate cell interactions but also caused changes in spatial patterns of atmospheric circulation due to neighbouring cells constituting in spatial vegetation-climate feedbacks. Large perturbations could trigger an abrupt shift of the system towards another steady state. Although the model setup used in our simulation is rather simple, our results stress that the coupling of

  19. To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions.

    Science.gov (United States)

    Bravo-Díaz, Carlos; Romsted, Laurence Stuart; Liu, Changyao; Losada-Barreiro, Sonia; Pastoriza-Gallego, Maria José; Gao, Xiang; Gu, Qing; Krishnan, Gunaseelan; Sánchez-Paz, Verónica; Zhang, Yongliang; Dar, Aijaz Ahmad

    2015-08-25

    Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with

  20. Physicochemical model for reactive sputtering of hot target

    Energy Technology Data Exchange (ETDEWEB)

    Shapovalov, Viktor I., E-mail: vishapovalov@mail.ru; Karzin, Vitaliy V.; Bondarenko, Anastasia S.

    2017-02-05

    A physicochemical model for reactive magnetron sputtering of a metal target is described in this paper. The target temperature in the model is defined as a function of the ion current density. Synthesis of the coating occurs due to the surface chemical reaction. The law of mass action, the Langmuir isotherm and the Arrhenius equation for non-isothermal conditions were used for mathematical description of the reaction. The model takes into consideration thermal electron emission and evaporation of the target surface. The system of eight algebraic equations, describing the model, was solved for the tantalum target sputtered in the oxygen environment. It was established that the hysteresis effect disappears with the increase of the ion current density. - Highlights: • When model is applied for a cold target, hysteresis width is proportional to the ion current density. • Two types of processes of hot target sputtering are possible, depending on the current density: with and without the hysteresis. • Sputtering process is dominant at current densities less than 50 A/m{sup 2} and evaporation can be neglected. • For current densities over 50 A/m{sup 2} the hysteresis width reaches its maximum and the role of evaporation increases.

  1. Meridional overturning circulation: stability and ocean feedbacks in a box model

    CERN Document Server

    Cimatoribus, Andrea A; Dijkstra, Henk A

    2012-01-01

    A box model of the inter-hemispheric Atlantic meridional overturning circulation is developed, including a variable pycnocline depth for the tropical and subtropical regions. The circulation is forced by winds over a periodic channel in the south and by freshwater forcing at the surface. The model is aimed at investigating the ocean feedbacks related to perturbations in freshwater forcing from the atmosphere, and to changes in freshwater transport in the ocean. These feedbacks are closely connected with the stability properties of the meridional overturning circulation, in particular in response to freshwater perturbations.

  2. State-space model identification and feedback control of unsteady aerodynamic forces

    CERN Document Server

    Brunton, Steven L; Rowley, Clarence W

    2014-01-01

    Unsteady aerodynamic models are necessary to accurately simulate forces and develop feedback controllers for wings in agile motion; however, these models are often high dimensional or incompatible with modern control techniques. Recently, reduced-order unsteady aerodynamic models have been developed for a pitching and plunging airfoil by linearizing the discretized Navier-Stokes equation with lift-force output. In this work, we extend these reduced-order models to include multiple inputs (pitch, plunge, and surge) and explicit parameterization by the pitch-axis location, inspired by Theodorsen's model. Next, we investigate the na\\"{\\i}ve application of system identification techniques to input--output data and the resulting pitfalls, such as unstable or inaccurate models. Finally, robust feedback controllers are constructed based on these low-dimensional state-space models for simulations of a rigid flat plate at Reynolds number 100. Various controllers are implemented for models linearized at base angles of ...

  3. Modeling feedbacks between a boreal forest and the planetary boundary layer

    Science.gov (United States)

    Hill, T. C.; Williams, M.; Moncrieff, J. B.

    2008-08-01

    The atmosphere and biosphere interact strongly in the planetary boundary layer. Understanding the mechanisms controlling the coupled atmosphere-biosphere system allows improved scaling between observations at the stand scale (e.g., flux towers) and those at larger scales, e.g., airborne or satellite measurements. Simulation of the joint atmosphere-biosphere system permits the study of feedbacks occurring within the coupled system. In this paper, two well-tested models, one a process-based biosphere model (SPA) and the other a planetary boundary layer model (CAPS), were coupled to allow simulation of atmosphere-biosphere feedbacks and interactions with a focus on ecological controls. As part of the validation process, the biosphere model was tested using eddy covariance, surface meteorology, and soil data collected during a 120 day period at a boreal black spruce site during the 1994 BOREAS field campaign. The coupled atmosphere-biosphere model was also validated with radiosonde data above the black spruce site, demonstrating that atmosphere and biosphere models can be coherently combined. We show that negative feedbacks at the black spruce site have strong moderating effects. The feedbacks reduce the mean impact of LAI changes on the atmospheric surface layer by 21% for latent energy, 64% for air temperature, and 44% for water mixing ratio. We show that both radiative and hydraulic limitations imposed by the vegetation structure strongly affected the interactions within the atmosphere-biosphere system, while the impact of the canopy roughness length was weak.

  4. Incorporating vegetation feedbacks in regional climate modeling over West Africa

    Science.gov (United States)

    Erfanian, A.; Wang, G.; Yu, M.; Ahmed, K. F.; Anyah, R. O.

    2015-12-01

    Despite major advancements in modeling of the climate system, incorporating vegetation dynamics into climate models is still at the initial stages making it an ongoing research topic. Only few of GCMs participating in CMIP5 simulations included the vegetation dynamics component. Consideration for vegetation dynamics is even less common in RCMs. In this study, RegCM4.3.4-CLM4-CN-DV, a regional climate model synchronously coupled with a land surface component that includes both Carbon-Nitrogen (CN) and Dynamic-Vegetation (DV) processes is used to simulate and project regional climate over West Africa. Due to its unique regional features, West Africa climate is known for being susceptible to land-atmosphere interactions, enhancing the importance of including vegetation dynamics in modeling climate over this region. In this study the model is integrated for two scenarios (present-day and future) using outputs from four GCMs participating in CMIP5 (MIROC, CESM, GFDL and CCSM4) as lateral boundary conditions, which form the basis of a multi-model ensemble. Results of model validation indicates that ensemble of all models outperforms each of individual models in simulating present-day temperature and precipitation. Therefore, the ensemble set is used to analyze the impact of including vegetation dynamics in the RCM on future projection of West Africa's climate. Results from the ensemble analysis will be presented, together with comparison among individual models.

  5. Modeling the reactivities of hydroxyl radical and ozone towards atmospheric organic chemicals using quantitative structure-reactivity relationship approaches.

    Science.gov (United States)

    Gupta, Shikha; Basant, Nikita; Mohan, Dinesh; Singh, Kunwar P

    2016-07-01

    The persistence and the removal of organic chemicals from the atmosphere are largely determined by their reactions with the OH radical and O3. Experimental determinations of the kinetic rate constants of OH and O3 with a large number of chemicals are tedious and resource intensive and development of computational approaches has widely been advocated. Recently, ensemble machine learning (EML) methods have emerged as unbiased tools to establish relationship between independent and dependent variables having a nonlinear dependence. In this study, EML-based, temperature-dependent quantitative structure-reactivity relationship (QSRR) models have been developed for predicting the kinetic rate constants for OH (kOH) and O3 (kO3) reactions with diverse chemicals. Structural diversity of chemicals was evaluated using a Tanimoto similarity index. The generalization and prediction abilities of the constructed models were established through rigorous internal and external validation performed employing statistical checks. In test data, the EML QSRR models yielded correlation (R (2)) of ≥0.91 between the measured and the predicted reactivities. The applicability domains of the constructed models were determined using methods based on descriptors range, Euclidean distance, leverage, and standardization approaches. The prediction accuracies for the higher reactivity compounds were relatively better than those of the low reactivity compounds. Proposed EML QSRR models performed well and outperformed the previous reports. The proposed QSRR models can make predictions of rate constants at different temperatures. The proposed models can be useful tools in predicting the reactivities of chemicals towards OH radical and O3 in the atmosphere.

  6. Evaluating Land-Atmosphere Moisture Feedbacks in Earth System Models With Spaceborne Observations

    Science.gov (United States)

    Levine, P. A.; Randerson, J. T.; Lawrence, D. M.; Swenson, S. C.

    2016-12-01

    We have developed a set of metrics for measuring the feedback loop between the land surface moisture state and the atmosphere globally on an interannual time scale. These metrics consider both the forcing of terrestrial water storage (TWS) on subsequent atmospheric conditions as well as the response of TWS to antecedent atmospheric conditions. We designed our metrics to take advantage of more than one decade's worth of satellite observations of TWS from the Gravity Recovery and Climate Experiment (GRACE) along with atmospheric variables from the Atmospheric Infrared Sounder (AIRS), the Global Precipitation Climatology Project (GPCP), and Clouds and the Earths Radiant Energy System (CERES). Metrics derived from spaceborne observations were used to evaluate the strength of the feedback loop in the Community Earth System Model (CESM) Large Ensemble (LENS) and in several models that contributed simulations to Phase 5 of the Coupled Model Intercomparison Project (CMIP5). We found that both forcing and response limbs of the feedback loop were generally stronger in tropical and temperate regions in CMIP5 models and even more so in LENS compared to satellite observations. Our analysis suggests that models may overestimate the strength of the feedbacks between the land surface and the atmosphere, which is consistent with previous studies conducted across different spatial and temporal scales.

  7. Thermohaline feedbacks in ocean-climate models of varying complexity

    Science.gov (United States)

    den Toom, M.

    2013-03-01

    The Atlantic Meridional Overturning Circulation (AMOC) is considered an important component of the climate system, because of its significant contribution to the heat budget of the Northern Hemisphere. Theoretical models indicate that the AMOC has non-linear dynamics, which result in a strong sensitivity to high latitude freshwater forcing. These models suggest that, as a result of the presence of multiple equilibria, the AMOC may drive large, abrupt shifts of the climate when a certain threshold is exceeded. There is no direct observational evidence that such AMOC related climate variations occur in reality, but the available data are too short and sparse to be conclusive in this case. Therefore, numerical models provide the main source of information regarding the nonlinear behavior of the AMOC. Because numerical models are necessarily incomplete, not in the least because of a lack of computational resources, their results must always be tested for robustness. This thesis presents four studies that examine how the representation of a certain unresolved process affects the behavior of the simulated AMOC The study in chapter 2 deals with the representation of horizontal mixing by mesoscale eddies. It is shown that a simple horizontal tracer mixing scheme is only a reasonable alternative to the more realistic isoneutral / Gent-McWilliams parameterization, provided that no wind forcing is imposed. In chapter 3, it is demonstrated that the use of a stability-dependent tracer diffusivity, which is commonly used to parameterize convection, leads to the occurrence of artificial multiple equilibria. In chapter 4, the representation of ocean-atmosphere interaction is considered. It is found that the sensitivity to anomalous freshwater forcing is only slightly modified if an interactive (sea surface temperature-dependent) atmosphere model is used, instead of a static atmosphere model. In chapter 5, the simulated sensitivity of the AMOC is compared between a model that

  8. The biological carbon pump in the ocean: Reviewing model representations and its feedbacks on climate perturbations.

    Science.gov (United States)

    Hülse, Dominik; Arndt, Sandra; Ridgwell, Andy; Wilson, Jamie

    2016-04-01

    The ocean-sediment system, as the biggest carbon reservoir in the Earth's carbon cycle, plays a crucial role in regulating atmospheric carbon dioxide concentrations and climate. Therefore, it is essential to constrain the importance of marine carbon cycle feedbacks on global warming and ocean acidification. Arguably, the most important single component of the ocean's carbon cycle is the so-called "biological carbon pump". It transports carbon that is fixed in the light-flooded surface layer of the ocean to the deep ocean and the surface sediment, where it is degraded/dissolved or finally buried in the deep sediments. Over the past decade, progress has been made in understanding different factors that control the efficiency of the biological carbon pump and their feedbacks on the global carbon cycle and climate (i.e. ballasting = ocean acidification feedback; temperature dependant organic matter degradation = global warming feedback; organic matter sulphurisation = anoxia/euxinia feedback). Nevertheless, many uncertainties concerning the interplay of these processes and/or their relative significance remain. In addition, current Earth System Models tend to employ empirical and static parameterisations of the biological pump. As these parametric representations are derived from a limited set of present-day observations, their ability to represent carbon cycle feedbacks under changing climate conditions is limited. The aim of my research is to combine past carbon cycling information with a spatially resolved global biogeochemical model to constrain the functioning of the biological pump and to base its mathematical representation on a more mechanistic approach. Here, I will discuss important aspects that control the efficiency of the ocean's biological carbon pump, review how these processes of first order importance are mathematically represented in existing Earth system Models of Intermediate Complexity (EMIC) and distinguish different approaches to approximate

  9. Simulation of reactive processes related to biodegradation in aquifers. 1. Structure of the three-dimensional reactive transport model

    Science.gov (United States)

    Schäfer, Dirk; Schäfer, Wolfgang; Kinzelbach, Wolfgang

    1998-05-01

    The reactive transport model TBC (transport, biochemistry, and chemistry) numerically solves the equations for reactive transport in three-dimensional saturated groundwater flow. A finite element approximation and a standard Galerkin method are used. Solute transport is coupled to microbially mediated organic carbon degradation. Microbial growth is assumed to follow Monod-type kinetics. Substrate consumption and release of metabolic products is coupled to microbial growth via yield coefficients and stoichiometric relations. Additionally, the effects of microbial activity on selected inorganic chemical species in the aquifer can be considered. TBC allows the user to specify a wide range of possible biochemical and chemical reactions in the input file. This makes TBC a powerful and flexible simulation tool. It was developed to simulate reactive processes related to in situ bioremediation, but further fields of application are laboratory column studies on redox processes coupled to organic carbon degradation, field cases of intrinsic biodegradation, and early diagenetic processes in sediments.

  10. Video Modeling by Experts with Video Feedback to Enhance Gymnastics Skills

    Science.gov (United States)

    Boyer, Eva; Miltenberger, Raymond G.; Batsche, Catherine; Fogel, Victoria

    2009-01-01

    The effects of combining video modeling by experts with video feedback were analyzed with 4 female competitive gymnasts (7 to 10 years old) in a multiple baseline design across behaviors. During the intervention, after the gymnast performed a specific gymnastics skill, she viewed a video segment showing an expert gymnast performing the same skill…

  11. Positive expectations feedback experiments and number guessing games as models of financial markets

    NARCIS (Netherlands)

    Sonnemans, J.; Tuinstra, J.

    2010-01-01

    In repeated number guessing games choices typically converge quickly to the Nash equilibrium. In positive expectations feedback experiments, however, convergence to the equilibrium price tends to be very slow, if it occurs at all. Both types of experimental designs have been suggested as modeling es

  12. Video Modeling by Experts with Video Feedback to Enhance Gymnastics Skills

    Science.gov (United States)

    Boyer, Eva; Miltenberger, Raymond G.; Batsche, Catherine; Fogel, Victoria

    2009-01-01

    The effects of combining video modeling by experts with video feedback were analyzed with 4 female competitive gymnasts (7 to 10 years old) in a multiple baseline design across behaviors. During the intervention, after the gymnast performed a specific gymnastics skill, she viewed a video segment showing an expert gymnast performing the same skill…

  13. Using a Behavior Modeling Approach to Teach Students the Art of Providing and Receiving Verbal Feedback

    Science.gov (United States)

    Maritz, Carol A.

    2008-01-01

    Using a behavior modeling approach, this study examined how students' perceived self-efficacy improved as they developed, delivered, and evaluated professional presentations. Using journal entries and a self-efficacy assessment, students' perceived self-efficacy increased as they learned to provide and receive verbal peer feedback, and to stage…

  14. Learning to Swim Using Video Modelling and Video Feedback within a Self-Management Program

    Science.gov (United States)

    Lao, So-An; Furlonger, Brett E.; Moore, Dennis W.; Busacca, Margherita

    2016-01-01

    Although many adults who cannot swim are primarily interested in learning by direct coaching there are options that have a focus on self-directed learning. As an alternative a self-management program combined with video modelling, video feedback and high quality and affordable video technology was used to assess its effectiveness to assisting an…

  15. Using a Behavior Modeling Approach to Teach Students the Art of Providing and Receiving Verbal Feedback

    Science.gov (United States)

    Maritz, Carol A.

    2008-01-01

    Using a behavior modeling approach, this study examined how students' perceived self-efficacy improved as they developed, delivered, and evaluated professional presentations. Using journal entries and a self-efficacy assessment, students' perceived self-efficacy increased as they learned to provide and receive verbal peer feedback, and to stage…

  16. A feedback-based model for CSR assessment and materiality analysis

    DEFF Research Database (Denmark)

    Calabrese, Armando; Costa, Roberta; Rosati, Francesco

    2015-01-01

    Current CSR literature offers little insight into how to engage customers and other stakeholders about their CSR expectations and perceptions. The aim of this paper is to propose a model for CSR evaluation and planning based on the classification of customer CSR feedback through the comparison of...

  17. The Bjerknes feedback in the tropical Atlantic in CMIP5 models

    NARCIS (Netherlands)

    Deppenmeier, Anna Lena; Haarsma, R.J.; Hazeleger, Wilco

    2016-01-01

    Coupled state-of-the-art general circulation models still perform relatively poorly in simulating tropical Atlantic (TA) climate. To investigate whether lack of air–sea interaction might be responsible for their biases, we investigate the Bjerknes feedback (BF) in the TA, the driver of the domina

  18. Simulator for virtual surgery using deformable organ models and force feedback system.

    Science.gov (United States)

    Suzuki, N; Hattori, A; Ezumi, T; Uchiyama, A; Kumano, T; Ikemoto, A; Adachi, Y; Takatsu, A

    1998-01-01

    This paper describes a real-time surgery planning system using virtual reality techniques. This system allows us to simulate incision of skin and organs which respond as elastic objects with surgical tools in virtual space. Inner structures such as blood vessels and lesions can be seen and manipulated in the simulation. In addition to these functions we attempted to add a feedback function that responds to the operator's hands. We developed a force feedback device to manipulate the elastic organ model based on pressure from the operator's fingers.

  19. A Computational Model of the Temporal Dynamics of Plasticity in Procedural Learning: Sensitivity to Feedback Timing

    Directory of Open Access Journals (Sweden)

    Vivian V. Valentin

    2014-07-01

    Full Text Available The evidence is now good that different memory systems mediate the learning of different types of category structures. In particular, declarative memory dominates rule-based (RB category learning and procedural memory dominates information-integration (II category learning. For example, several studies have reported that feedback timing is critical for II category learning, but not for RB category learning – results that have broad support within the memory systems literature. Specifically, II category learning has been shown to be best with feedback delays of 500ms compared to delays of 0 and 1000ms, and highly impaired with delays of 2.5 seconds or longer. In contrast, RB learning is unaffected by any feedback delay up to 10 seconds. We propose a neurobiologically detailed theory of procedural learning that is sensitive to different feedback delays. The theory assumes that procedural learning is mediated by plasticity at cortical-striatal synapses that are modified by dopamine-mediated reinforcement learning. The model captures the time-course of the biochemical events in the striatum that cause synaptic plasticity, and thereby accounts for the empirical effects of various feedback delays on II category learning.

  20. Winds and radiation in unison: a new semi-analytic feedback model for cloud dissolution

    Science.gov (United States)

    Rahner, Daniel; Pellegrini, Eric W.; Glover, Simon C. O.; Klessen, Ralf S.

    2017-10-01

    Star clusters interact with the interstellar medium (ISM) in various ways, most importantly in the destruction of molecular star-forming clouds, resulting in inefficient star formation on galactic scales. On cloud scales, ionizing radiation creates H ii regions, while stellar winds and supernovae (SNe) drive the ISM into thin shells. These shells are accelerated by the combined effect of winds, radiation pressure, and SN explosions, and slowed down by gravity. Since radiative and mechanical feedback is highly interconnected, they must be taken into account in a self-consistent and combined manner, including the coupling of radiation and matter. We present a new semi-analytic 1D feedback model for isolated massive clouds (≥105 M⊙) to calculate shell dynamics and shell structure simultaneously. It allows us to scan a large range of physical parameters (gas density, star formation efficiency, and metallicity) and to estimate escape fractions of ionizing radiation fesc, i, the minimum star formation efficiency ɛmin required to drive an outflow, and recollapse time-scales for clouds that are not destroyed by feedback. Our results show that there is no simple answer to the question of what dominates cloud dynamics, and that each feedback process significantly influences the efficiency of the others. We find that variations in natal cloud density can very easily explain differences between dense-bound and diffuse-open star clusters. We also predict, as a consequence of feedback, a 4-6 Myr age difference for massive clusters with multiple generations.

  1. Using Video Modeling with Voiceover Instruction Plus Feedback to Train Staff to Implement Direct Teaching Procedures.

    Science.gov (United States)

    Giannakakos, Antonia R; Vladescu, Jason C; Kisamore, April N; Reeve, Sharon A

    2016-06-01

    Direct teaching procedures are often an important part of early intensive behavioral intervention for consumers with autism spectrum disorder. In the present study, a video model with voiceover (VMVO) instruction plus feedback was evaluated to train three staff trainees to implement a most-to-least direct (MTL) teaching procedure. Probes for generalization were conducted with untrained direct teaching procedures (i.e., least-to-most, prompt delay) and with an actual consumer. The results indicated that VMVO plus feedback was effective in training the staff trainees to implement the MTL procedure. Although additional feedback was required for the staff trainees to show mastery of the untrained direct teaching procedures (i.e., least-to-most and prompt delay) and with an actual consumer, moderate to high levels of generalization were observed.

  2. Modelling and Studies for a Wideband Feedback System for Mitigation of Transverse Single Bunch Instabilities

    CERN Document Server

    Li, K S B; Rumolo, G; Cesaratto, J; Dusatko, J; Fox, J; Pivi, M; Pollock, K; Rivetta, C; Turgut, O

    2013-01-01

    As part of the LHC Injector Upgrade (LIU) Project [1], a wideband feedback system is under study for mitigation of coherent single bunch instabilities. This type of system may provide a generic way of shifting the instability threshold to regions that are currently inaccessible, thus, boosting the brightness of future beams. To study the effectiveness of such systems, a numerical model has been developed that constitutes a realistic feedback system including real transfer functions for pickup and kicker, realistic N-tap FIR and IIR filters as well as noise and saturation effects. Simulations of SPS cases have been performed with HEADTAIL to evaluate the feedback effectiveness in the presence of transverse mode coupling and electron clouds. Some results are presented addressing bandwidth limitations and amplifier power requirements.

  3. Thermal Modeling and Feedback Requirements for LIFE Neutronic Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Seifried, J E

    2009-07-15

    An initial study is performed to determine how temperature considerations affect LIFE neutronic simulations. Among other figures of merit, the isotopic mass accumulation, thermal power, tritium breeding, and criticality are analyzed. Possible fidelities of thermal modeling and degrees of coupling are explored. Lessons learned from switching and modifying nuclear datasets is communicated.

  4. Effect of ice-albedo feedback on global sensitivity in a one-dimensional radiative-convective climate model

    Science.gov (United States)

    Wang, W.-C.; Stone, P. H.

    1980-01-01

    The feedback between the ice albedo and temperature is included in a one-dimensional radiative-convective climate model. The effect of this feedback on global sensitivity to changes in solar constant is studied for the current climate conditions. This ice-albedo feedback amplifies global sensitivity by 26 and 39%, respectively, for assumptions of fixed cloud altitude and fixed cloud temperature. The global sensitivity is not affected significantly if the latitudinal variations of mean solar zenith angle and cloud cover are included in the global model. The differences in global sensitivity between one-dimensional radiative-convective models and energy balance models are examined. It is shown that the models are in close agreement when the same feedback mechanisms are included. The one-dimensional radiative-convective model with ice-albedo feedback included is used to compute the equilibrium ice line as a function of solar constant.

  5. Paraquat-induced reactive oxygen species inhibit neutrophil apoptosis via a p38 MAPK/NF-κB-IL-6/TNF-α positive-feedback circuit.

    Directory of Open Access Journals (Sweden)

    Xiaolong Wang

    Full Text Available Paraquat (PQ, a widely used herbicide and potent reactive oxygen species (ROS inducer, can injure multiple tissues and organs, especially the lung. However, the underlying mechanism is still poorly understood. According to previous reports, neutrophil aggregation and excessive ROS production might play pivotal pathogenetic roles. In the present study, we found that PQ could prolong neutrophil lifespan and induce ROS generation in a concentration-independent manner. Activated nuclear factor-κB (NF-κB, p38 mitogen-activated kinase (p38 MAPK, and myeloid cell leukemia sequence 1 (Mcl-1 but not Akt signaling pathways were involved in this process, as well as increasing levels of interleukin-6 (IL-6, tumor necrosis factor-α (TNF-α, and IL-1β. Furthermore, the proinflammatory mediators IL-6 and TNF-α could in turn promote ROS generation, creating a vicious cycle. The existence of such a feedback loop is supported by our finding that neutrophil apoptosis is attenuated by PQ in a concentration-independent manner and could partially explain the clinical dilemma why oxygen therapy will exacerbate PQ induced tissue injury.

  6. A dynamic model of the tubuloglomerular feedback mechanism

    DEFF Research Database (Denmark)

    Holstein-Rathlou, N H; Marsh, D J

    1990-01-01

    the model predicted a substantial phase shift of the NaCl concentration relative to the flow oscillation at the macula densa. The results are consistent with the hypothesis that the oscillations are caused by the TGF mechanism. The results further support the notion that the delays and damping caused......We have reported oscillations in proximal tubular pressure and flow and in distal tubular pressure and chloride concentration in halothane-anesthetized Sprague-Dawley rats. These variables oscillated at the same frequency in each animal, approximately 35 mHz, but were out of phase with each other...... a detailed representation of pressure and flow in the tubules based on a reduced version of the Navier-Stokes equations. The NaCl concentration at the macula densa was used as the signal to the TGF mechanism. The tubular NaCl concentration was modeled by a partial differential equation based on conservation...

  7. Analysis of feedback loops and robustness in network evolution based on Boolean models

    Directory of Open Access Journals (Sweden)

    Cho Kwang-Hyun

    2007-11-01

    Full Text Available Abstract Background Many biological networks such as protein-protein interaction networks, signaling networks, and metabolic networks have topological characteristics of a scale-free degree distribution. Preferential attachment has been considered as the most plausible evolutionary growth model to explain this topological property. Although various studies have been undertaken to investigate the structural characteristics of a network obtained using this growth model, its dynamical characteristics have received relatively less attention. Results In this paper, we focus on the robustness of a network that is acquired during its evolutionary process. Through simulations using Boolean network models, we found that preferential attachment increases the number of coupled feedback loops in the course of network evolution. Whereas, if networks evolve to have more coupled feedback loops rather than following preferential attachment, the resulting networks are more robust than those obtained through preferential attachment, although both of them have similar degree distributions. Conclusion The presented analysis demonstrates that coupled feedback loops may play an important role in network evolution to acquire robustness. The result also provides a hint as to why various biological networks have evolved to contain a number of coupled feedback loops.

  8. Modeling Discontinuous Phase Transitions in Gel Membranes: Focus on Hysteresis and Feedback Mechanisms

    Science.gov (United States)

    Kuksenok, Olga

    Feedback mechanisms are vital in a number of processes in biological systems. For example, feedback loops play an essential role during a limb development in mammals and are responsible for the asymmetric cell division to constrain the growth in plants to the specific regions. An integration of well-controlled feedback loops into the fully synthetic materials is an important step in designing a range of biomimetic functionalities. Herein, we focus on hydrogels functionalized with light-sensitive trisodium salt of copper chlorophyllin and study discontinuous phase transitions in these systems. Prior experimental studies had shown that illumination of these functionalized gels results in their heating and in discontinuous, first order phase transition upon the variation in temperature. Herein, we develop the first computational model for these gels; the framework of the model is based on the gel Lattice Spring Model, in this work we account for the gel heating under the illumination. The results of our simulations are in a good agreement with prior experimental studies. We focus on pattern development during the volume phase transitions in membranes of various thicknesses and show that one can effectively utilize light intensity to remotely control feedback loops in these systems.

  9. Modeling Alphabet Skills as Instructive Feedback Within a Phonological Awareness Intervention.

    Science.gov (United States)

    Olszewski, Arnold; Soto, Xigrid; Goldstein, Howard

    2017-08-15

    This study evaluated the efficacy of an instructive feedback strategy for modeling letter names and sounds during presentation of positive feedback within a small-group phonological awareness intervention for preschoolers. Two experiments were conducted using multiple-baseline designs across children and behaviors. Letter name and sound identification and performance on a phonological awareness fluency measure served as the primary outcome variables. Six children completed Experiment 1. A progressive time delay was added to instructive feedback to elicit a response from the 9 children in the second experiment. In the first experiment, 6 children demonstrated gains on phonological awareness but not alphabet knowledge. With the addition of progressive time delay in the second experiment, all 9 children demonstrated gains on letter name and sound identification as well as phonological awareness skills. Progressive time delay to prompt children's responses appears to bolster the effects of instructive feedback as an efficient strategy for modeling alphabet skills within a broader early literacy curriculum. Modeling alphabet skills did not detract from, and may have enhanced, phonological awareness instruction for preschoolers.

  10. A unified model for AGN feedback in cosmological simulations of structure formation

    CERN Document Server

    Sijacki, Debora; Di Matteo, Tiziana; Hernquist, Lars

    2007-01-01

    We discuss a numerical model for black hole growth and its associated feedback processes that for the first time allows cosmological simulations of structure formation to simultaneously follow the build up of the cosmic population of galaxies and active galactic nuclei. Our model assumes that seed black holes are present at early cosmic epochs at the centres of forming halos. We then track their growth from gas accretion and mergers with other black holes in the course of cosmic time. For black holes that are active, we distinguish between two distinct modes of feedback, depending on the black hole accretion rate itself. Black holes that accrete at high rates are assumed to be in a `quasar regime', where we model their feedback by thermally coupling a small fraction of their bolometric luminosity to the surrounding gas. For black holes with low accretion rates, we conjecture that most of their feedback occurs in mechanical form, where AGN-driven bubbles are injected into a gaseous environment. Using our new m...

  11. Synthetic feedback loop model for increasing microbial biofuel production using a biosensor

    Directory of Open Access Journals (Sweden)

    Mary eHarrison

    2012-10-01

    Full Text Available Current biofuel production methods use engineered bacteria to break down cellulose and convert it to biofuel. A major challenge in microbial fuel production is that increasing biofuel yields can be limited by the toxicity of the biofuel to the organism that is producing it. Previous research has demonstrated that efflux pumps are effective at increasing tolerance to various biofuels. However, when overexpressed, efflux pumps burden cells, which hinders growth and slows biofuel production. Therefore, the toxicity of the biofuel must be balanced with the toxicity of pump overexpression. We have developed a mathematical model for cell growth and biofuel production that implements a synthetic feedback loop using a biosensor to control efflux pump expression. In this way, the production rate will be maximal when the concentration of biofuel is low because the cell does not expend energy expressing efflux pumps when they are not needed. Additionally, the microbe is able to adapt to toxic conditions by triggering the expression of efflux pumps, which allow it to continue biofuel production. Sensitivity analysis indicates that the feedback sensor model is insensitive to most system parameters, but a few key parameters can influence growth and production. In comparison to systems that express efflux pumps at a constant level, the feedback sensor increases overall biofuel production by delaying pump expression until it is needed. This result is more pronounced when model parameters are variable because the system can use feedback to adjust to the actual rate of biofuel production.

  12. Modeling reactive transport with particle tracking and kernel estimators

    Science.gov (United States)

    Rahbaralam, Maryam; Fernandez-Garcia, Daniel; Sanchez-Vila, Xavier

    2015-04-01

    Groundwater reactive transport models are useful to assess and quantify the fate and transport of contaminants in subsurface media and are an essential tool for the analysis of coupled physical, chemical, and biological processes in Earth Systems. Particle Tracking Method (PTM) provides a computationally efficient and adaptable approach to solve the solute transport partial differential equation. On a molecular level, chemical reactions are the result of collisions, combinations, and/or decay of different species. For a well-mixed system, the chem- ical reactions are controlled by the classical thermodynamic rate coefficient. Each of these actions occurs with some probability that is a function of solute concentrations. PTM is based on considering that each particle actually represents a group of molecules. To properly simulate this system, an infinite number of particles is required, which is computationally unfeasible. On the other hand, a finite number of particles lead to a poor-mixed system which is limited by diffusion. Recent works have used this effect to actually model incomplete mix- ing in naturally occurring porous media. In this work, we demonstrate that this effect in most cases should be attributed to a defficient estimation of the concentrations and not to the occurrence of true incomplete mixing processes in porous media. To illustrate this, we show that a Kernel Density Estimation (KDE) of the concentrations can approach the well-mixed solution with a limited number of particles. KDEs provide weighting functions of each particle mass that expands its region of influence, hence providing a wider region for chemical reactions with time. Simulation results show that KDEs are powerful tools to improve state-of-the-art simulations of chemical reactions and indicates that incomplete mixing in diluted systems should be modeled based on alternative conceptual models and not on a limited number of particles.

  13. Impact of changes in the formulation of cloud-related processes on model biases and climate feedbacks

    NARCIS (Netherlands)

    Lacagnina, C.; Selten, F.; Siebesma, A.P.

    2014-01-01

    To test the impact of modeling uncertainties and biases on the simulation of cloud feedbacks, several configurations of the EC-Earth climate model are built altering physical parameterizations. An overview of the various radiative feedbacks diagnosed from the reference EC-Earth configuration is

  14. Mathematical Models of Feedback Systems for Control of Intra-Bunch Instabilities Driven by E-Clouds and TMCI

    CERN Document Server

    Rivetta, C H; Mastoridis, T; Pivi, M T F; Turgut, O; Höfle, W; Secondo, R; Vay, J L

    2011-01-01

    The feedback control of intrabunch instabilities driven by E-Clouds or strong head-tail coupling (TMCI) requires sufficient bandwidth to sense the vertical position and drive multiple sections of a nanosecond scale bunch. These requirements impose challenges and limits in the design and implementation of the feedback system. This paper presents models for the feedback subsystems: receiver, processing channel, amplifier and kicker, that take into account their frequency response and limits. These models are included in multiparticle simulation codes (WARP/CMAD/Head-Tail) and reduced mathematical models of the bunch dynamics to evaluate the impact of subsystem limitations in the bunch stabilization and emittance improvement. With this realistic model of the hardware, it is possible to analyze and design the feedback system. This research is crucial to evaluate the performance boundary of the feedback control system due to cost and technological limitations. These models define the impact of spurious perturbatio...

  15. A nonlinear feedback model for granular and surface charging

    Science.gov (United States)

    Shinbrot, Troy; Kozachkov, Leo; Siu, Theo

    2015-03-01

    Independent laboratories have experimentally demonstrated that identical materials brought into symmetric contact generate contact charges. Even the most basic features of this odd behavior remain to be explained. In this talk, we provide a simple, Ising-like, model that appears to account for many of the observed phenomena. We calculate the electric field acting on surface molecules in a lattice, and we show that if the molecules are polarizable, then infinitesimal random polarizations typically build exponentially rapidly in time. These polarizations self-assemble to produce surface patterns that come in two types, and we find that one of these types accounts for strong localized charging, while the other produces a weaker persistent surface charge pattern. We summarize predictions for both ideal surfaces and for defects in granular beds. This work was supported by NSF Grant DMR-1404792.

  16. UPTRANS: an incremental transport model with feedback for quick-response strategy evaluation

    CSIR Research Space (South Africa)

    Venter, C

    2009-07-01

    Full Text Available is finely divided into person type segments, each segment potentially behaving differently from the others. For instance, using three employment classes (scholars, workers, other), three income classes, and car-owning vs non-car-owning households, 18... segments of people may be considered. Trips are further disaggregated by purpose (work, education, other). FIGURE 1 UPTrans in relation to other modelling approaches 4. The model is capable of including feedback between demand and supply, enabling...

  17. Effects of noise variance model on optimal feedback design and actuator placement

    Science.gov (United States)

    Ruan, Mifang; Choudhury, Ajit K.

    1994-01-01

    In optimal placement of actuators for stochastic systems, it is commonly assumed that the actuator noise variances are not related to the feedback matrix and the actuator locations. In this paper, we will discuss the limitation of that assumption and develop a more practical noise variance model. Various properties associated with optimal actuator placement under the assumption of this noise variance model are discovered through the analytical study of a second order system.

  18. A model for improving microbial biofuel production using a synthetic feedback loop

    Energy Technology Data Exchange (ETDEWEB)

    Dunlop, Mary; Keasling, Jay; Mukhopadhyay, Aindrila

    2011-07-14

    Cells use feedback to implement a diverse range of regulatory functions. Building synthetic feedback control systems may yield insight into the roles that feedback can play in regulation since it can be introduced independently of native regulation, and alternative control architectures can be compared. We propose a model for microbial biofuel production where a synthetic control system is used to increase cell viability and biofuel yields. Although microbes can be engineered to produce biofuels, the fuels are often toxic to cell growth, creating a negative feedback loop that limits biofuel production. These toxic effects may be mitigated by expressing efflux pumps that export biofuel from the cell. We developed a model for cell growth and biofuel production and used it to compare several genetic control strategies for their ability to improve biofuel yields. We show that controlling efflux pump expression directly with a biofuel-responsive promoter is a straight forward way of improving biofuel production. In addition, a feed forward loop controller is shown to be versatile at dealing with uncertainty in biofuel production rates.

  19. Assessment of radiative feedback in climate models using satellite observations of annual flux variation.

    Science.gov (United States)

    Tsushima, Yoko; Manabe, Syukuro

    2013-05-07

    In the climate system, two types of radiative feedback are in operation. The feedback of the first kind involves the radiative damping of the vertically uniform temperature perturbation of the troposphere and Earth's surface that approximately follows the Stefan-Boltzmann law of blackbody radiation. The second kind involves the change in the vertical lapse rate of temperature, water vapor, and clouds in the troposphere and albedo of the Earth's surface. Using satellite observations of the annual variation of the outgoing flux of longwave radiation and that of reflected solar radiation at the top of the atmosphere, this study estimates the so-called "gain factor," which characterizes the strength of radiative feedback of the second kind that operates on the annually varying, global-scale perturbation of temperature at the Earth's surface. The gain factor is computed not only for all sky but also for clear sky. The gain factor of so-called "cloud radiative forcing" is then computed as the difference between the two. The gain factors thus obtained are compared with those obtained from 35 models that were used for the fourth and fifth Intergovernmental Panel on Climate Change assessment. Here, we show that the gain factors obtained from satellite observations of cloud radiative forcing are effective for identifying systematic biases of the feedback processes that control the sensitivity of simulated climate, providing useful information for validating and improving a climate model.

  20. Microbially Mediated Kinetic Sulfur Isotope Fractionation: Reactive Transport Modeling Benchmark

    Science.gov (United States)

    Wanner, C.; Druhan, J. L.; Cheng, Y.; Amos, R. T.; Steefel, C. I.; Ajo Franklin, J. B.

    2014-12-01

    Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S32O42-) over the heavier isotopologue (S34O42-). Detection of isotopic shifts have been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing uranium bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. These RTM approaches employ different mathematical formulations in the representation of kinetic sulfur isotope fractionation. In order to test the various formulations, we propose a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of four problem levels and is based on a recent laboratory column experimental study of sulfur isotope fractionation. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and dispersion are included in the problem set. To date, participating RTM codes are: CRUNCHTOPE, TOUGHREACT, MIN3P and THE GEOCHEMIST'S WORKBENCH. Preliminary results from various codes show reasonable agreement for the problem levels simulating sulfur isotope fractionation in 1D.

  1. Predictive modeling of reactive wetting and metal joining.

    Energy Technology Data Exchange (ETDEWEB)

    van Swol, Frank B.

    2013-09-01

    The performance, reproducibility and reliability of metal joints are complex functions of the detailed history of physical processes involved in their creation. Prediction and control of these processes constitutes an intrinsically challenging multi-physics problem involving heating and melting a metal alloy and reactive wetting. Understanding this process requires coupling strong molecularscale chemistry at the interface with microscopic (diffusion) and macroscopic mass transport (flow) inside the liquid followed by subsequent cooling and solidification of the new metal mixture. The final joint displays compositional heterogeneity and its resulting microstructure largely determines the success or failure of the entire component. At present there exists no computational tool at Sandia that can predict the formation and success of a braze joint, as current capabilities lack the ability to capture surface/interface reactions and their effect on interface properties. This situation precludes us from implementing a proactive strategy to deal with joining problems. Here, we describe what is needed to arrive at a predictive modeling and simulation capability for multicomponent metals with complicated phase diagrams for melting and solidification, incorporating dissolutive and composition-dependent wetting.

  2. Interpretation of cloud-climate feedback as produced by 14 atmospheric general circulation models

    Science.gov (United States)

    Cess, R. D.; Potter, G. L.; Ghan, S. J.; Blanchet, J. P.; Boer, G. J.

    1989-01-01

    Understanding the cause of differences among general circulation model projections of carbon dioxide-induced climatic change is a necessary step toward improving the models. An intercomparison of 14 atmospheric general circulation models, for which sea surface temperature perturbations were used as a surrogate climate change, showed that there was a roughly threefold variation in global climate sensitivity. Most of this variation is attributable to differences in the models' depictions of cloud-climate feedback, a result that emphasizes the need for improvements in the treatment of clouds in these models if they are ultimately to be used as climatic predictors.

  3. A computational model clarifies the roles of positive and negative feedback loops in the Drosophila circadian clock

    Science.gov (United States)

    Wang, Junwei; Zhou, Tianshou

    2010-06-01

    Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per and clk mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.

  4. Reactive surface area in geochemical models - Lessons learned from a natural analogue

    NARCIS (Netherlands)

    Koenen, M.; Wasch, L.J.

    2013-01-01

    Many uncertainties exist in geochemical modeling. Mineral reactive surface area is one of the uncertain parameters. QEMSCAN analyses are performed on sandstone samples from a Dutch CO2 natural analogue to determine reactive surface areas. Geochemical modeling is performed using QEMSCAN surface areas

  5. Coherently amplified negative feedback loop as a model for NF-kappaB oscillations

    Science.gov (United States)

    Joo, Jaewook

    2010-03-01

    The cells secrets various signaling molecules as a response to an external signal and modulate its own signaling processes. The precise role of this autocrine and/or paracrine signaling on cell information processing is mostly unknown. We will present the effect of TNF alpha autocrine signaling on NF-kappaB oscillations, using a simplified model of coherently amplified negative feedback loop. We will discuss the bifurcation diagram (i.e., dose-response curve), especially the robustness and the tenability of the period of NF-kappaB oscillations. Finally, we will compare the results from the above model with those from a previous model of time-delayed negative feedback alone.

  6. Output feedback model matching in linear impulsive systems with control feedthrough: a structural approach

    Science.gov (United States)

    Zattoni, Elena

    2017-01-01

    This paper investigates the problem of structural model matching by output feedback in linear impulsive systems with control feedthrough. Namely, given a linear impulsive plant, possibly featuring an algebraic link from the control input to the output, and given a linear impulsive model, the problem consists in finding a linear impulsive regulator that achieves exact matching between the respective forced responses of the linear impulsive plant and of the linear impulsive model, for all the admissible input functions and all the admissible sequences of jump times, by means of a dynamic feedback of the plant output. The problem solvability is characterized by a necessary and sufficient condition. The regulator synthesis is outlined through the proof of sufficiency, which is constructive.

  7. Modeling Stratospheric Constituents: Reactive Species That Regulate Ozone

    Science.gov (United States)

    Salawitch, Ross J.

    2000-01-01

    Photochemical loss of stratospheric ozone occurs primarily by catalytic cycles whose rates are limited by the concentration of OH, HO2, NO2, ClO, and/or BrO as well as the concentration of either atomic oxygen or of ozone itself. Once the concentrations of these gases are established, the photochemical loss rate of O3 depends on the rate coefficient of only a handful of key reactions. We have developed a method for testing our understanding of stratospheric ozone photochemistry by comparing measured and modeled concentrations of reactive hydrogen, nitrogen, chlorine and bromine radicals using a photochemical steady state model constrained by observed concentrations of long-lived precursors (e.g., NO(y), Cl(y), Br(y), O3, H2O, CH4) and environmental parameters such as ozone column, reflectivity, and aerosol surface area. We will show based on analyses of observations obtained by aircraft, balloon, and satellite platforms during the POLARIS campaign that our overall understanding of the processes that regulate these radical species is very good. The most notable current discrepancies are the tendency to underestimate observed NO2 by 15 to 30% for air masses that experience near continuous solar illumination over a 24 hour period and the tendency to underestimate observed OH and H02 by about 10 to 20% during midday and by much larger amounts at high solar zenith angle (SZA > 85). Possible resolutions to these discrepancies will be discussed. This study was carried out in close collaboration with many members of the POLARIS science team.

  8. Numerical Modelling of Multi-Phase Multi-Component Reactive Transport in the Earth's interior

    Science.gov (United States)

    Oliveira, Beñat; Afonso, Juan Carlos; Zlotnik, Sergio; Tilhac, Romain

    2017-04-01

    We present a conceptual and numerical approach to model processes in the Earth's interior that involve multiple phases that simultaneously interact thermally, mechanically and chemically. The approach is truly multiphase in the sense that each dynamic phase is explicitly modelled with an individual set of mass, momentum, energy and chemical mass balance equations coupled via interfacial interaction terms. It is also truly multi-component in the sense that the compositions of the system and its constituent thermodynamic phases are expressed by a full set of fundamental chemical components (e.g. SiO_2, Al_2O_3, MgO, etc) rather than proxies. In contrast to previous approaches these chemical components evolve, react with, and partition into, different phases with different physical properties according to an internally-consistent thermodynamic model. This enables a thermodynamically-consistent coupling of the governing set of balance equations. Interfacial processes such as surface tensions and/or surface energy contributions to the dynamics and energetics of the system are also taken into account. The model presented here describes the evolution of systems governed by Multi-Phase Multi-Component Reactive Transport (MPMCRT) based on Ensemble Averaging and Classical Irreversible Thermodynamics principles. This novel approach provides a flexible platform to study the dynamics and non-linear feedbacks occurring within various natural systems at different scales. This notably includes major- and trace-element transport, diffusion-controlled trace-element re-equilibration or rheological changes associated with melt generation and migration in the Earth's mantle.

  9. Evaluating Effectiveness of Modeling Motion System Feedback in the Enhanced Hess Structural Model of the Human Operator

    Science.gov (United States)

    Zaychik, Kirill; Cardullo, Frank; George, Gary; Kelly, Lon C.

    2009-01-01

    In order to use the Hess Structural Model to predict the need for certain cueing systems, George and Cardullo significantly expanded it by adding motion feedback to the model and incorporating models of the motion system dynamics, motion cueing algorithm and a vestibular system. This paper proposes a methodology to evaluate effectiveness of these innovations by performing a comparison analysis of the model performance with and without the expanded motion feedback. The proposed methodology is composed of two stages. The first stage involves fine-tuning parameters of the original Hess structural model in order to match the actual control behavior recorded during the experiments at NASA Visual Motion Simulator (VMS) facility. The parameter tuning procedure utilizes a new automated parameter identification technique, which was developed at the Man-Machine Systems Lab at SUNY Binghamton. In the second stage of the proposed methodology, an expanded motion feedback is added to the structural model. The resulting performance of the model is then compared to that of the original one. As proposed by Hess, metrics to evaluate the performance of the models include comparison against the crossover models standards imposed on the crossover frequency and phase margin of the overall man-machine system. Preliminary results indicate the advantage of having the model of the motion system and motion cueing incorporated into the model of the human operator. It is also demonstrated that the crossover frequency and the phase margin of the expanded model are well within the limits imposed by the crossover model.

  10. Application of Simulated Reactivity Feedback in Nonnuclear Testing of a Direct-Drive Gas-Cooled Reactor

    Science.gov (United States)

    Bragg-Sitton, S. M.; Webster, K. L.

    2007-01-01

    Nonnuclear testing can be a valuable tool in the development of an in-space nuclear power or propulsion system. In a nonnuclear test facility, electric heaters are used to simulate heat from nuclear fuel. Standard testing allows one to fully assess thermal, heat transfer, and stress related attributes of a given system but fails to demonstrate the dynamic response that would be present in an integrated, fueled reactor system. The integration of thermal hydraulic hardware tests with simulated neutronic response provides a bridge between electrically heated testing and full nuclear testing. By implementing a neutronic response model to simulate the dynamic response that would be expected in a fueled reactor system, one can better understand system integration issues, characterize integrated system response times and response and response characteristics, and assess potential design improvements with a relatively small fiscal investment. Initial system dynamic response testing was demonstrated on the integrated SAFE 100a heat pipe cooled, electrically heated reactor and heat exchanger hardware. This Technical Memorandum discusses the status of the planned dynamic test methodology for implementation in the direct-drive gas-cooled reactor testing and assesses the additional instrumentation needed to implement high-fidelity dynamic testing.

  11. Calculation of PDS-XADS core closed-loop transfer function by using feedback with the lumped-model

    Energy Technology Data Exchange (ETDEWEB)

    Moghassem, Alireza; Payirandeh, Ali; Abbaspour, Ali [Islamic Azad Univ., Tehran (Iran, Islamic Republic of). Nuclear Engineering Dept.

    2016-03-15

    In this paper, the PDS-XADS LBE-cooled core open-loop transfer function was calculated by considering the source importance in point-kinetic equations. For this purpose, the overall-feedback transfer function was calculated considering the lumped-model for 14-steps of subcritical levels. Following effects were considered in three steps: 1. Doppler broadening, fuel expansion, coolant density and structure expansion, 2. Delayed-reactivity and void-worth inserted to prior step, 3. Severe-accident condition, inserted to prior steps. The linear stability analysis was modeled by using the Bode diagrams, Nyquist stability criterion and Nichols chart in MATLAB for each subcritical level and six groups of delayed neutrons. For optimized subcritical level determination, a conservative severe accident was considered. According to calculation results and analysis, the PDS-XADS core is stable and in optimized subcritical level, has the higher safety margin. The results are in good agreement with SIMMER-III code and main neutronic results. The optimized subcritical level by using the lumped-model is 0.97687.

  12. The role of feedback in a hierarchical model of object perception.

    Science.gov (United States)

    Dura-Bernal, Salvador; Wennekers, Thomas; Denham, Susan L

    2011-01-01

    We present a model which stems from a well-established model of object recognition, HMAX, and show how this feedforward system can include feedback, using a recently proposed architecture which reconciles biased competition and predictive coding approaches. Simulation results show successful feedforward object recognition, including cases of occluded and illusory images. Recognition is both position and size invariant. The model also provides a functional interpretation of the role of feedback connectivity in accounting for several observed effects such as enhancement, suppression and refinement of activity in lower areas. The model can qualitatively replicate responses in early visual cortex to occluded and illusory contours; and fMRI data showing that high-level object recognition reduces activity in lower areas. A Gestalt-like mechanism based on collinearity, co-orientation and good continuation principles is proposed to explain illusory contour formation which allows the system to adapt a single high-level object prototype to illusory Kanizsa figures of different sizes, shapes and positions. Overall the model provides a biophysiologically plausible interpretation, supported by current experimental evidence, of the interaction between top-down global feedback and bottom-up local evidence in the context of hierarchical object perception.

  13. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    Science.gov (United States)

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2016-09-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since z ˜ 3, while a significant increase of the number densities of low-mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-analytic model of galaxy formation. It includes a self-consistent treatment for the timings of gas, metal and energy recycling, and for the chemical yields. We show this to be crucial to use observational measurements of the metallicity as independent and powerful constraints for the adopted feedback schemes. The observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decrease significantly with cosmic time (as suggested by parametrizations of the cosmological `FIRE' simulations). Irrespective of the feedback scheme used, our successful models always imply that up to 60-70 per cent of the baryons reside in an `ejected' reservoir and are unavailable for cooling at high redshift. The same schemes predict physical properties of model galaxies (e.g. gas content, colour, age, and metallicity) that are in much better agreement with observational data than our fiducial model. The overall fraction of passive galaxies is found to be primarily determined by internal physical processes, with environment playing a secondary role.

  14. An intercomparison between the surface heat flux feedback in five coupled models, COADS and the NCEP reanalysis

    Energy Technology Data Exchange (ETDEWEB)

    Frankignoul, C.; Kestenare, E. [Universite Pierre et Marie Curie, Institute Pierre-Simon Laplace, Laboratoire d' Oceanographie Dynamique et de Climatologie, 4 place Jussieu, 75252 Paris Cedex 05 (France); Botzet, M. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Carril, A.F. [Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy); Drange, H. [Nansen Environmental and Remote Sensing Center, Bergen (Norway); Pardaens, A. [Hadley Centre for Climate Prediction and Research, Met Office (United Kingdom); Terray, L.; Sutton, R. [Department of Meteorology, University of Reading (United Kingdom)

    2004-04-01

    The surface heat flux feedback is estimated in the Atlantic and the extra-tropical Indo-Pacific, using monthly heat flux and sea surface temperature anomaly data from control simulations with five global climate models, and it is compared to estimates derived from COADS and the NCEP reanalysis. In all data sets, the heat flux feedback is negative nearly everywhere and damps the sea surface temperature anomalies. At extra-tropical latitudes, it is strongly dominated by the turbulent fluxes. The radiative feedback can be positive or negative, depending on location and season, but it remains small, except in some models in the tropical Atlantic. The negative heat flux feedback is strong in the mid-latitude storm tracks, exceeding 40 W m{sup -2} K{sup -1} at place, but in the Northern Hemisphere it is substantially underestimated in several models. The negative feedback weakens at high latitudes, although the models do not reproduce the weak positive feedback found in NCEP in the northern North Atlantic. The main differences are found in the tropical Atlantic where the heat flux feedback is weakly negative in some models, as in the observations, and strongly negative in others where it can exceed 30 W m{sup -2} K{sup -1} at large scales, in part because of a strong contribution of the radiative fluxes, in particular during spring. A comparison between models with similar atmospheric or oceanic components suggests that the atmospheric model is primarily responsible for the heat flux feedback differences at extra-tropical latitudes. In the tropical Atlantic, the ocean behavior plays an equal role. The differences in heat flux feedback in the tropical Atlantic are reflected in the sea surface temperature anomaly persistence, which is too small in models where the heat flux damping is large. A good representation of the heat flux feedback is thus required to simulate climate variability realistically. (orig.)

  15. Testing the transtheoretical model for fruit intake: comparing web-based tailored stage-matched and stage-mismatched feedback.

    Science.gov (United States)

    de Vet, Emely; de Nooijer, Jascha; de Vries, Nanne K; Brug, Johannes

    2008-04-01

    A match-mismatch test was conducted to test the transtheoretical model applied to fruit intake. Precontemplators and contemplators were randomly assigned to receive a web-based individualized precontemplation feedback (PCF), contemplation feedback (CF) or action feedback (AF) letter promoting fruit intake. Immediately and 1 week after reading this letter, post-test measures were obtained. Fruit intake increased significantly between pre- and post-test in contemplators, but not in precontemplators. No differences between the feedback conditions were found in fruit intake, stage progression, use or credibility of the feedback in precontemplators and contemplators. In precontemplators, also no differences between the conditions were found in personal relevance of the feedback. Contemplators, however, rated AF as more personally relevant than PCF or CF. To conclude, the present study failed to show superiority of stage-matched information in the promotion of fruit intake.

  16. A global hybrid coupled model based on atmosphere-SST feedbacks

    Energy Technology Data Exchange (ETDEWEB)

    Cimatoribus, Andrea A.; Drijfhout, Sybren S. [Royal Netherlands Meteorological Institute, De Bilt (Netherlands); Dijkstra, Henk A. [Utrecht University, Institute for Marine and Atmospheric Research Utrecht, Utrecht (Netherlands)

    2012-02-15

    A global hybrid coupled model is developed, with the aim of studying the effects of ocean-atmosphere feedbacks on the stability of the Atlantic meridional overturning circulation. The model includes a global ocean general circulation model and a statistical atmosphere model. The statistical atmosphere model is based on linear regressions of data from a fully coupled climate model on sea surface temperature both locally and hemispherically averaged, being the footprint of Atlantic meridional overturning variability. It provides dynamic boundary conditions to the ocean model for heat, freshwater and wind-stress. A basic but consistent representation of ocean-atmosphere feedbacks is captured in the hybrid coupled model and it is more than 10 times faster than the fully coupled climate model. The hybrid coupled model reaches a steady state with a climate close to the one of the fully coupled climate model, and the two models also have a similar response (collapse) of the Atlantic meridional overturning circulation to a freshwater hosing applied in the northern North Atlantic. (orig.)

  17. Modeling, Analysis and Design of Feedback Operational Amplifier for Undergraduate Studies in Electrical Engineering

    Directory of Open Access Journals (Sweden)

    Han Yang

    2012-12-01

    Full Text Available The analog electronics is a challenging subject for undergraduate students in electrical engineering, due to the complex combination of many previous subjects, such as linear circuit analysis, signal and system, linear control theory and some sort of mathematics. This paper presents the modeling, analysis and design of the operational amplifier, which is used as benchmark system for analog electronics, for undergraduate studies in electrical engineering. Followed by the introduction of the operation amplifier circuit, the design of feedback network for the operational amplifier using MATLAB is presented. The bandwidth and sensitivity analysis for the feedback control loop are also discussed. In order to enhance the stability margin and dynamic characteristics of the operational amplifier, the lead compensator is designed for the feedback loop by adding capacitive component to the feedback resistive network. The presented analysis and design method of the operational amplifier by using MATLAB/SIMULINK can be highly effective to compliment the classroom teaching for circuit design courses for undergraduate studies in electrical engineering.

  18. Adjoint LMS (ALMS Algorithm Based Active Noise Control with Feedback Path Modeling

    Directory of Open Access Journals (Sweden)

    U Ramachandraiah,

    2010-12-01

    Full Text Available In active noise control (ANC systems, there exists an inherent feedback from the loudspeaker to the primary microphone. Adjoint least mean square (ALMS algorithm is known to be an alternative to the widely used filtered x LMS (FxLMS for reducing the computational complexity and memory requirements, especially in the case of multi-channel systems. Further FxLMS algorithm is based on the assumptionthat the order of the weighing filter and secondary path can be commuted which is not always true in practice. Though ALMS do not make such an assumption, neither FxLMS nor the ALMS algorithms onsider the feedback path effect that is inherent in ANC systems.We propose a feedback ANC system based on ALMS algorithm which is analogous to the system based on FxLMS. Detailed computational complexity analysis for addition and multiplication requirements ispresented and are compared with those of its counterpart to establish its usefulness. Simulation results show the convergence characteristics of the ALMS based ANC with feedback path modeling is on par with that based on FxLMS.

  19. The Meaning and Consequences of Star Formation Criteria in Galaxy Models with Resolved Stellar Feedback

    CERN Document Server

    Hopkins, Philip F; Murray, Norman

    2013-01-01

    We consider the effects of different star formation criteria on galactic scales, in high-resolution simulations with explicitly resolved GMCs and stellar feedback. We compare: (1) a self-gravity criterion (based on the local virial parameter and the assumption that self-gravitating gas collapses to high density in a free-fall time), (2) a fixed density threshold, (3) a molecular-gas law, (4) a temperature threshold, (5) a Jeans-instability requirement, (6) a criteria that cooling times be shorter than dynamical times, and (7) a convergent-flow criterion. We consider these both MW-like and high-density (starburst) galaxies. With feedback present, all models produce identical integrated star formation rates (SFRs), in agreement with the Kennicutt relation. Without feedback all produce orders-of-magnitude excessive SFRs. This is totally dependent on feedback and independent of the SF law. However, the spatial and density distribution of SF depend strongly on the SF criteria. Because cooling rates are generally f...

  20. Modeling T cell antigen discrimination based on feedback control of digital ERK responses.

    Directory of Open Access Journals (Sweden)

    2005-11-01

    Full Text Available T-lymphocyte activation displays a remarkable combination of speed, sensitivity, and discrimination in response to peptide-major histocompatibility complex (pMHC ligand engagement of clonally distributed antigen receptors (T cell receptors or TCRs. Even a few foreign pMHCs on the surface of an antigen-presenting cell trigger effective signaling within seconds, whereas 1 x 10(5-1 x 10(6 self-pMHC ligands that may differ from the foreign stimulus by only a single amino acid fail to elicit this response. No existing model accounts for this nearly absolute distinction between closely related TCR ligands while also preserving the other canonical features of T-cell responses. Here we document the unexpected highly amplified and digital nature of extracellular signal-regulated kinase (ERK activation in T cells. Based on this observation and evidence that competing positive- and negative-feedback loops contribute to TCR ligand discrimination, we constructed a new mathematical model of proximal TCR-dependent signaling. The model made clear that competition between a digital positive feedback based on ERK activity and an analog negative feedback involving SH2 domain-containing tyrosine phosphatase (SHP-1 was critical for defining a sharp ligand-discrimination threshold while preserving a rapid and sensitive response. Several nontrivial predictions of this model, including the notion that this threshold is highly sensitive to small changes in SHP-1 expression levels during cellular differentiation, were confirmed by experiment. These results combining computation and experiment reveal that ligand discrimination by T cells is controlled by the dynamics of competing feedback loops that regulate a high-gain digital amplifier, which is itself modulated during differentiation by alterations in the intracellular concentrations of key enzymes. The organization of the signaling network that we model here may be a prototypic solution to the problem of achieving

  1. Permanence of a Nicholson’s Blowflies Model with Feedback Control and Multiple Time-varying Delays

    Institute of Scientific and Technical Information of China (English)

    CHEN Xiao-ying; SHI Chun-ling

    2015-01-01

    This paper covers the dynamic behaviors for a class of Nicholson’s blowflies model with multiple time-varying delay and feedback control. By using the dierential inequality theory, a set of sucient conditions are obtained to ensure the permanence of the system. Our result shows that feedback control variables have no influence on the permanence of the system.

  2. Modeling of the jack rabbit series of experiments with a temperature based reactive burn model

    Science.gov (United States)

    Desbiens, Nicolas

    2017-01-01

    The Jack Rabbit experiments, performed by Lawrence Livermore National Laboratory, focus on detonation wave corner turning and shock desensitization. Indeed, while important for safety or charge design, the behaviour of explosives in these regimes is poorly understood. In this paper, our temperature based reactive burn model is calibrated for LX-17 and compared to the Jack Rabbit data. It is shown that our model can reproduce the corner turning and shock desensitization behaviour of four out of the five experiments.

  3. Collaborative Language Learning in Immersive Virtual Worlds: Competence-based Formative Feedback and Open Learner Modeling

    Directory of Open Access Journals (Sweden)

    Michael D. Kickmeier-Rust

    2014-06-01

    Full Text Available The uptake of information and communication technologies in the classrooms is a key trend over the past years and decades. Teachers are using Moodle courses, e-Portfolios, Google Docs, perhaps learning games or virtual worlds such as OpenSim for educational purposes. A second trend pushes towards a formatively inspired assessment and feedback, often combined with attempts of educational data mining and learning analytics. In this paper we present a role model for teaching English as a second language using OpenSim and a tool that enables teachers to perform real-time learning analytics and direct formative feedback and interventions in the virtual learning session. Also we present an approach to aggregate and store the learning information into open learner models.

  4. Review of reactive kinetic models describing reductive dechlorination of chlorinated ethenes in soil and groundwater

    DEFF Research Database (Denmark)

    Chambon, Julie Claire Claudia; Bjerg, Poul Løgstrup; Scheutz, Charlotte;

    2013-01-01

    Reductive dechlorination is a major degradation pathway of chlorinated ethenes in anaerobic subsurface environments, and reactive kinetic models describing the degradation process are needed in fate and transport models of these contaminants. However, reductive dechlorination is a complex biologi...

  5. DIAGNOSTIC FEEDBACK MODEL IN DEVELOPING SPEAKING SKILLS IN ESL LEARNERS – AN EXPERIMENTAL STUDY

    Directory of Open Access Journals (Sweden)

    V. Rajesh, J. Jaya Parveen

    2013-01-01

    Full Text Available Engineering classrooms often contain mixed-ability students with less interest in language study. These students come from different backgrounds and different mediums of instruction. Grammar translation method, communicative approach, or multimedia fail to entertain one or the other group of students in the same classroom. Diagnostic Feedback Model can be utilised for effective language teaching in such mixed-ability classrooms. With a descriptive research design, an evaluative study is conducted in VV College of Engineering, Tisaiyanvilai. 200 students and 10 teachers are involved in the study. Meetings are conducted periodically. Tasks for the pre-tests and criteria for evaluation are designed by the teachers. The pre-assessment contains items to check listening, body language, fluency, and accuracy of the students in speaking. The criteria provides 5 – 1 range of marks for each sub-skill in speaking. The students are made to speak and are evaluated by the teachers using the criteria. Based on the diagnostic feedback model, data consolidation is done by the teachers. The diagnostic feedback model provide the teachers with the strengths and areas of improvement of the students. According to the overall scores, the students are classified into Beginner / Intermediate / Proficient instead of Below Average / Average / Above Average. Activities for each group are defined uniquely, and training is conducted separately for each group. At the end of the course, post-assessments are conducted using the same criteria. In the post-assessments, the average scores of 'Beginners' have increased from 20 to 35, the average scores of 'Intermediate' students have increased from 30 to 43, and the average scores of 'Proficient' students have increased from 40 to 48. This implies that diagnostic feedback model works well in mixed ability classrooms in engineering colleges.

  6. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    OpenAIRE

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2015-01-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since $z\\sim 3$, while a significant increase of the number densities of low mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-ana...

  7. 2D photochemical modeling of Saturn's stratosphere. Part II: Feedback between composition and temperature

    Science.gov (United States)

    Hue, V.; Greathouse, T. K.; Cavalié, T.; Dobrijevic, M.; Hersant, F.

    2016-03-01

    Saturn's axial tilt of 26.7° produces seasons in a similar way as on Earth. Both the stratospheric temperature and composition are affected by this latitudinally varying insolation along Saturn's orbital path. The atmospheric thermal structure is controlled and regulated by the amount of hydrocarbons in the stratosphere, which act as absorbers and coolants from the UV to the far-IR spectral range, and this structure has an influence on the amount of hydrocarbons. We study here the feedback between the chemical composition and the thermal structure by coupling a latitudinal and seasonal photochemical model with a radiative seasonal model. Our results show that the seasonal temperature peak in the higher stratosphere, associated with the seasonal increase of insolation, is shifted earlier than the maximum insolation peak. This shift is increased with increasing latitudes and is caused by the low amount of stratospheric coolants in the spring season. At 80° in both hemispheres, the temperature peak at 10-2 mbar is seen to occur half a season (3-4 Earth years) earlier than was previously predicted by radiative seasonal models that assumed spatially and temporally uniform distribution of coolants. This shift progressively decreases with increasing pressure, up to around the 0.5 mbar pressure level where it vanishes. On the opposite, the thermal field has a small feedback on the abundance distributions. Accounting for that feedback modifies the predicted equator-to-pole temperature gradient. The meridional gradients of temperature at the mbar pressure levels are better reproduced when this feedback is accounted for. At lower pressure levels, Saturn's stratospheric thermal structure seems to depart from pure radiative seasonal equilibrium as previously suggested by Guerlet et al. (2014). Although the agreement with the absolute value of the stratospheric temperature observed by Cassini is moderate, it is a mandatory step toward a fully coupled GCM-photochemical model.

  8. Pulsive feedback control of a quarter car model forced by a road profile

    Energy Technology Data Exchange (ETDEWEB)

    Litak, G. [Department of Applied Mechanics, Technical University of Lublin, Nadbystrzycka 36, PL-20-618 Lublin (Poland)]. E-mail: g.litak@pollub.pl; Borowiec, M. [Department of Applied Mechanics, Technical University of Lublin, Nadbystrzycka 36, PL-20-618 Lublin (Poland); Ali, M. [Department of Mathematics, Faculty of Mathematical Science, University of Delhi, Delhi 110007 (India); Saha, L.M. [Zakhir Husain College, University of Delhi, Delhi 110002 (India); Friswell, M.I. [Department of Aerospace Engineering, University of Bristol, Queens Building, Bristol BS8 1TR (United Kingdom)

    2007-08-15

    We examine the strange chaotic attractor and its unstable periodic orbits for a one degree of freedom nonlinear oscillator with a non-symmetric potential that models a quarter car forced by the road profile. We propose an efficient method of chaos control that stabilizes these orbits using a pulsive feedback technique. A discrete set of pulses is able to transfer the system from one periodic state to another.

  9. Constructing wetlands: measuring and modeling feedbacks of oxidation processes between plants and clay-rich material

    Science.gov (United States)

    Saaltink, Rémon; Dekker, Stefan C.; Griffioen, Jasper; Wassen, Martin J.

    2016-04-01

    Interest is growing in using soft sediment as a building material in eco-engineering projects. Wetland construction in the Dutch lake Markermeer is an example: here the option of dredging some of the clay-rich lake-bed sediment and using it to construct 10.000 ha of wetland will soon go under construction. Natural processes will be utilized during and after construction to accelerate ecosystem development. Knowing that plants can eco-engineer their environment via positive or negative biogeochemical plant-soil feedbacks, we conducted a six-month greenhouse experiment to identify the key biogeochemical processes in the mud when Phragmites australis is used as an eco-engineering species. We applied inverse biogeochemical modeling to link observed changes in pore water composition to biogeochemical processes. Two months after transplantation we observed reduced plant growth and shriveling as well as yellowing of foliage. The N:P ratios of plant tissue were low and were affected not by hampered uptake of N but by enhanced uptake of P. Plant analyses revealed high Fe concentrations in the leaves and roots. Sulfate concentrations rose drastically in our experiment due to pyrite oxidation; as reduction of sulfate will decouple Fe-P in reducing conditions, we argue that plant-induced iron toxicity hampered plant growth, forming a negative feedback loop, while simultaneously there was a positive feedback loop, as iron toxicity promotes P mobilization as a result of reduced conditions through root death, thereby stimulating plant growth and regeneration. Given these two feedback mechanisms, we propose that when building wetlands from these mud deposits Fe-tolerant species are used rather than species that thrive in N-limited conditions. The results presented in this study demonstrate the importance of studying the biogeochemical properties of the building material and the feedback mechanisms between plant and soil prior to finalizing the design of the eco-engineering project.

  10. Modelling Plant and Soil Nitrogen Feedbacks Affecting Forest Carbon Gain at High CO2

    Science.gov (United States)

    McMurtrie, R. E.; Norby, R. J.; Franklin, O.; Pepper, D. A.

    2007-12-01

    Short-term, direct effects of elevated atmospheric CO2 concentrations on plant carbon gain are relatively well understood. There is considerable uncertainty, however, about longer-term effects, which are influenced by various plant and ecosystem feedbacks. A key feedback in terrestrial ecosystems occurs through changes in plant carbon (C) allocation patterns. For instance, if high CO2 were to increase C allocation to roots, then plants may experience positive feedback through improved plant nutrition. A second type of feedback, associated with decomposition of soil-organic matter, may reduce soil-nutrient availability at high CO2. This paper will consider mechanistic models of both feedbacks. Effects of high CO2 on plant C allocation will be investigated using a simple model of forest net primary production (NPP) that incorporates the primary mechanisms of plant carbon and nitrogen (N) balance. The model called MATE (Model Any Terrestrial Ecosystem) includes an equation for annual C balance that depends on light- saturated photosynthetic rate and therefore on [CO2], and an equation for N balance incorporating an expression for N uptake as a function of root mass. The C-N model is applied to a Free Air CO2 Exchange (FACE) experiment at Oak Ridge National Laboratory (ORNL) in Tennessee, USA, where closed-canopy, monoculture stands of the deciduous hardwood sweetgum ( Liquidambar styraciflua) have been growing at [CO2] of 375 and 550 ppm for ten years. Features of this experiment are that the annual NPP response to elevated CO2 has averaged approximately 25% over seven years, but that annual fine-root production has almost doubled on average, with especially large increases in later years of the experiment (Norby et al. 2006). The model provides a simple graphical approach for analysing effects of elevated CO2 and N supply on leaf/root/wood C allocation and productivity. It simulates increases in NPP and fine-root production at the ORNL FACE site that are consistent

  11. Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production

    Science.gov (United States)

    Whalley, Lisa K.; Stone, Daniel; Bandy, Brian; Dunmore, Rachel; Hamilton, Jacqueline F.; Hopkins, James; Lee, James D.; Lewis, Alastair C.; Heard, Dwayne E.

    2016-02-01

    Near-continuous measurements of hydroxyl radical (OH) reactivity in the urban background atmosphere of central London during the summer of 2012 are presented. OH reactivity behaviour is seen to be broadly dependent on air mass origin, with the highest reactivity and the most pronounced diurnal profile observed when air had passed over central London to the east, prior to measurement. Averaged over the entire observation period of 26 days, OH reactivity peaked at ˜ 27 s-1 in the morning, with a minimum of ˜ 15 s-1 during the afternoon. A maximum OH reactivity of 116 s-1 was recorded on one day during morning rush hour. A detailed box model using the Master Chemical Mechanism was used to calculate OH reactivity, and was constrained with an extended measurement data set of volatile organic compounds (VOCs) derived from a gas chromatography flame ionisation detector (GC-FID) and a two-dimensional GC instrument which included heavier molecular weight (up to C12) aliphatic VOCs, oxygenated VOCs and the biogenic VOCs α-pinene and limonene. Comparison was made between observed OH reactivity and modelled OH reactivity using (i) a standard suite of VOC measurements (C2-C8 hydrocarbons and a small selection of oxygenated VOCs) and (ii) a more comprehensive inventory including species up to C12. Modelled reactivities were lower than those measured (by 33 %) when only the reactivity of the standard VOC suite was considered. The difference between measured and modelled reactivity was improved, to within 15 %, if the reactivity of the higher VOCs (⩾ C9) was also considered, with the reactivity of the biogenic compounds of α-pinene and limonene and their oxidation products almost entirely responsible for this improvement. Further improvements in the model's ability to reproduce OH reactivity (to within 6 %) could be achieved if the reactivity and degradation mechanism of unassigned two-dimensional GC peaks were estimated. Neglecting the contribution of the higher VOCs (⩾ C

  12. Modelling and Feedback Control of Bistability in a Turbulent Bluff Body Wake

    Science.gov (United States)

    Brackston, Rowan; Wynn, Andrew; Garcia de La Cruz, Juan Marcos; Rigas, Georgios; Morrison, Jonathan

    2016-11-01

    The turbulent wake behind many three-dimensional bluff bodies exhibits a bistable behaviour, the properties of which has been the subject of significant recent interest. This feature of the wake is known to contribute to the pressure drag on the body and is relevant for geometries representative of many road vehicles. Furthermore, due to its high visibility from surface mounted pressure measurements, it is a feature that may be observed and controlled in real-time. In Brackston et al. we have recently demonstrated such a feedback control strategy that aims to suppress the bistable feature of the wake. Starting from a stochastic modelling approach, we identify a linearised model for this mode of the flow, obtaining parameters via a system identification. The identified model is then used to design the feedback controller, with the aim of restoring the flow to the unstable, symmetric state. The controller is implemented experimentally at Re 2 . 3 ×105 and is found to both suppress the bistability of the flow and reduce the drag on the body. Furthermore, the control system is found to have a positive energy balance, providing a key demonstration of efficient feedback control applied to a 3D bluff body wake at turbulent Reynolds numbers.

  13. Model-Based State Feedback Controller Design for a Turbocharged Diesel Engine with an EGR System

    Directory of Open Access Journals (Sweden)

    Tianpu Dong

    2015-05-01

    Full Text Available This paper describes a method for the control of transient exhaust gas recirculation (EGR systems. Firstly, a state space model of the air system is developed by simplifying a mean value model. The state space model is linearized by using linearization theory and validated by the GT-Power data with an operating point of the diesel engine. Secondly, a state feedback controller based on the intake oxygen mass fraction is designed for EGR control. Since direct measurement of the intake oxygen mass fraction is unavailable on the engine, the estimation method for intake oxygen mass fraction has been proposed in this paper. The control strategy is analyzed by using co-simulation with the Matlab/Simulink and GT-Powers software. Finally, the whole control system is experimentally validated against experimental data of a turbocharged diesel engine. The control effect of the state feedback controller compared with PID controller proved to be further verify the feasibility and advantages of the proposed state feedback controller.

  14. A Model Of Critical Peer Feedback To Facilitate Business English Writing Using Qzone Weblogs Among Chinese Undergraduates

    Directory of Open Access Journals (Sweden)

    Gao Xianwei

    2016-10-01

    Full Text Available The purpose of this study was to explore critical thinking skills in peer feedback for Business English writing in order to facilitate the quality of peer feedback and quality of Business English writing. “Critical peer feedback” was conceptualized with the integration of “critical thinking” and “peer feedback” in order to improve the quality of peer feedback. This study explored the process, content and factors of critical peer feedback through Qzone weblogs, and summarized the model of critical peer feedback. A qualitative case study was conducted with a group of six junior students majoring in Business English for one semester in a Chinese university. Three models of critical thinking including Revised Bloom’s Taxonomy, Paul-Elder Model and Reichenbach’s Six Steps Model, were transferred to the participants in the workshops. Three kinds of data including semi-structured interview transcripts, six writing assignments and artifacts of critical peer feedback, were analyzed by QSR NVivo 8. The findings revealed that the Revised Bloom’s Taxonomy is more acceptable for the beginners of critical peer feedback which provides a six-step model of critical thinking. The process of critical peer feedback in online context was summarized as four steps- “intake”, “critical thinking”, “output”, and “post-output”. Each of the four steps had several mental processes in critical peer feedback. This study may be significant for the knowledge of higher-order peer feedback to facilitate the quality of higher-level writing.

  15. A feedback-based model for CSR assessment and materiality analysis

    DEFF Research Database (Denmark)

    Calabrese, Armando; Costa, Roberta; Rosati, Francesco

    2015-01-01

    Current CSR literature offers little insight into how to engage customers and other stakeholders about their CSR expectations and perceptions. The aim of this paper is to propose a model for CSR evaluation and planning based on the classification of customer CSR feedback through the comparison...... of three aspects of CSR commitment (disclosed, perceived and expected). Although the paper is focused on customers, the model can be applied indifferently to any stakeholder group, thus providing a valuable instrument for materiality analysis and stakeholder engagement. In effect, the model allows...... identifying material CSR issues regarding all stakeholder perceptions and expectations...

  16. Effects of vegetation feedback in modeling the present-day climate over China

    Science.gov (United States)

    Shi, Y.; Wang, G.; Erfanian, A.; Yu, M.

    2016-12-01

    Abstract: Proper representation of climate-vegetation interactions is important for realistic simulations of the present climate and reliable projections of the future, and dynamic vegetation is being incorporated into more and more climate models. However, coupled vegetation-climate modeling at the regional scale is still at a very early stage. Specifically, very few studies on climate over Asia have accounted for the role of dynamic vegetation feedback. In this study, the regional climate model RegCM version 4.3.4 (RCM) coupled with the Community Land Model version 4/4.5 (CLM) including models of carbon-nitrogen dynamics (CN) and vegetation dynamics (DV) is used to simulate the present day climate over China, and the role of vegetation feedback at different time scales is investigated based on a set of simulations with different treatments of vegetation. Three simulations are conducted, each using RCM-CLM, RCM-CLM-CN, and RCM-CLM-CN-DV respectively, and all simulations are driven with reanalysis data during the period of 1989 to 2009. This presentation will document the model performance in simulating vegetation and climate, and examine the role of vegetation dynamics in climate variability at different time scales. Preliminary results indicate that, when the carbon-nitrogen dynamics and dynamic vegetation feedback are included, the spatial pattern of biases remains similar, but the magnitude of the biases become larger. Model performance in simulating other aspects of the present-day climate will be examined, and the implication of this effect will be studied.

  17. An improved car-following model with multiple preceding cars' velocity fluctuation feedback

    Science.gov (United States)

    Guo, Lantian; Zhao, Xiangmo; Yu, Shaowei; Li, Xiuhai; Shi, Zhongke

    2017-04-01

    In order to explore and evaluate the effects of velocity variation trend of multiple preceding cars used in the Cooperative Adaptive Cruise Control (CACC) strategy on the dynamic characteristic, fuel economy and emission of the corresponding traffic flow, we conduct a study as follows: firstly, with the real-time car-following (CF) data, the close relationship between multiple preceding cars' velocity fluctuation feedback and the host car's behaviors is explored, the evaluation results clearly show that multiple preceding cars' velocity fluctuation with different time window-width are highly correlated to the host car's acceleration/deceleration. Then, a microscopic traffic flow model is proposed to evaluate the effects of multiple preceding cars' velocity fluctuation feedback in the CACC strategy on the traffic flow evolution process. Finally, numerical simulations on fuel economy and exhaust emission of the traffic flow are also implemented by utilizing VT-micro model. Simulation results prove that considering multiple preceding cars' velocity fluctuation feedback in the control strategy of the CACC system can improve roadway traffic mobility, fuel economy and exhaust emission performance.

  18. Uncertainty Modeling and Robust Output Feedback Control of Nonlinear Discrete Systems: A Mathematical Programming Approach

    Directory of Open Access Journals (Sweden)

    Olav Slupphaug

    2001-01-01

    Full Text Available We present a mathematical programming approach to robust control of nonlinear systems with uncertain, possibly time-varying, parameters. The uncertain system is given by different local affine parameter dependent models in different parts of the state space. It is shown how this representation can be obtained from a nonlinear uncertain system by solving a set of continuous linear semi-infinite programming problems, and how each of these problems can be solved as a (finite series of ordinary linear programs. Additionally, the system representation includes control- and state constraints. The controller design method is derived from Lyapunov stability arguments and utilizes an affine parameter dependent quadratic Lyapunov function. The controller has a piecewise affine output feedback structure, and the design amounts to finding a feasible solution to a set of linear matrix inequalities combined with one spectral radius constraint on the product of two positive definite matrices. A local solution approach to this nonconvex feasibility problem is proposed. Complexity of the design method and some special cases such as state- feedback are discussed. Finally, an application of the results is given by proposing an on-line computationally feasible algorithm for constrained nonlinear state- feedback model predictive control with robust stability.

  19. Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4

    CERN Document Server

    Skeltved, Alexander Broberg; Carlson, Brant; Gjesteland, Thomas; Celestin, Sebastien

    2016-01-01

    This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modelling results related to the production of Terrestrial Gamma-ray Flashes (TGFs) and high-energy particle emission from thunderstorms. We will study the Relativistic Runaway Electron Avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from Runaway Electrons (REs). The Monte Carlo (MC) simulations take into account the effects of electron ionisation, electron by electron (M{\\o}ller) and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair-production, in the $250$ eV$-100$ GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback, are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio o...

  20. Examination of a perceived cost model of employees' negative feedback-seeking behavior.

    Science.gov (United States)

    Lu, Kuo-Ming; Pan, Su-Ying; Cheng, Jen-Wei

    2011-01-01

    The present study extends the feedback-seeking behavior literature by investigating how supervisor-related antecedents (i.e., supervisors' expert power, reflected appraisals of supervisors, and supervisors' emotional intelligence) influence subordinates' negative feedback-seeking behavior (NFSB) through different cost/value perceptions (i.e., expectancy value, self-presentation cost, and ego cost). Using data collected from 216 supervisor-subordinate dyads from various industries in Taiwan, we employ structural equation modeling analysis to test our hypotheses. The results show that expectancy value mediates the relationship between supervisor expert power and subordinates' NFSB. Moreover, self-presentation cost mediates the relationship between reflected appraisals of supervisors' and subordinates' NFSB. Theoretical and practical implications of this study are also discussed.

  1. How baryonic feedback processes can affect dark matter halos: a stochastic model

    Science.gov (United States)

    Freundlich, J.; El-Zant, A.; Combes, F.

    2016-12-01

    Feedback processes from stars and active galactic nuclei result in gas density fluctuations which can contribute to `heating' dark matter haloes, decrease their density at the center and hence form more realistic `cores' than the steep `cusps' predicted by cold dark matter (CDM) simulations. We present a theoretical model deriving this effect from first principles: stochastic density variations in the gas distribution perturb the gravitational potential and hence affect the halo particles. We analytically derive the velocity dispersion imparted to the CDM particles and the corresponding relaxation time, and further perform numerical simulations to show that the assumed process can indeed lead to the formation of a core in an initially cuspy halo within a timescale comparable to the derived relaxation time. This suggests that feedback-induced cusp-core transformations observed in hydrodynamic simulations of galaxy formation may be understood and parametrized in relatively simple terms.

  2. Feedback Scheduling of Model-based Networked Control Systems with Flexible Workload

    Institute of Scientific and Technical Information of China (English)

    Xian-Ming Tang; Jin-Shou Yu

    2008-01-01

    In this paper, a novel control structure called feedback scheduling of model-based networked control systems is proposed to cope with a flexible network load and resource constraints. The state update time is adjusted according to the real-time network congestion situation. State observer is used under the situation where the state of the controlled plant could not be acquired. The stability criterion of the proposed structure is proved with time-varying state update time. On the basis of the stability of the novel system structure, the compromise between the control performance and the network utilization is realized by using feedback scheduler.Examples are provided to show the advantage of the proposed control structure.

  3. Model-Based Testing of a Reactive System with Coloured Petri Nets

    DEFF Research Database (Denmark)

    Tjell, Simon

    2006-01-01

    In this paper, a reactive and nondeterministic system is tested. This is doneby applying a generic model that has been specified as a configurable Coloured PetriNet. In this way, model-based testing is possible for a wide class of reactive system atthe level of discrete events. Concurrently...... executed tasks are specified at a high levelof abstraction and test traces are collected through state space analysis of the model....

  4. Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4

    Science.gov (United States)

    Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant; Gjesteland, Thomas; Celestin, Sebastien

    2014-01-01

    This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons Nγ/Ne. We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ε). In addition, we present comparisons of GEANT4 simulations performed with a “standard” and a “low-energy” physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results. Key Points Testing the feedback mechanism with GEANT4 Validating the GEANT4 programming toolkit Study the ratio of bremsstrahlung photons to electrons at TGF source altitude PMID:26167437

  5. Detailed characterization of a Comparative Reactivity Method (CRM) instrument for ambient OH reactivity measurements: experiments vs. modeling

    Science.gov (United States)

    Michoud, Vincent; Locoge, Nadine; Dusanter, Sébastien

    2015-04-01

    The Hydroxyl radical (OH) is the main daytime oxidant in the troposphere, leading to the oxidation of Volatile Organic Compounds (VOCs) and the formation of harmful pollutants such as ozone (O3) and Secondary Organic Aerosols (SOA). While OH plays a key role in tropospheric chemistry, recent studies have highlighted that there are still uncertainties associated with the OH budget, i.e the identification of sources and sinks and the quantification of production and loss rates of this radical. It has been demonstrated that ambient measurements of the total OH loss rate (also called total OH reactivity) can be used to identify and reduce these uncertainties. In this context, the Comparative Reactivity Method (CRM), developed by Sinha et al. (ACP, 2008), is a promising technique to measure total OH reactivity in ambient air and has already been used during several field campaigns. This technique relies on monitoring competitive reactions of OH with ambient trace gases and a reference compound (pyrrole) in a sampling reactor to derive ambient OH reactivity. However, this technique requires a complex data processing chain that has yet to be carefully investigated in the laboratory. In this study, we present a detailed characterization of a CRM instrument developed at Mines Douai, France. Experiments have been performed to investigate the dependence of the CRM response on humidity, ambient NOx levels, and the pyrrole-to-OH ratio inside the sampling reactor. Box modelling of the chemistry occurring in the reactor has also been performed to assess our theoretical understanding of the CRM measurement. This work shows that the CRM response is sensitive to both humidity and NOx, which can be accounted for during data processing using parameterizations depending on the pyrrole-to-OH ratio. The agreement observed between laboratory studies and model results suggests a good understanding of the chemistry occurring in the sampling reactor and gives confidence in the CRM

  6. Audio Feedback -- Better Feedback?

    Science.gov (United States)

    Voelkel, Susanne; Mello, Luciane V.

    2014-01-01

    National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…

  7. Reactive transport modeling for Cs retention: from batch to field experiments

    Science.gov (United States)

    De Pourcq, K.; Ayora, C.; Carrera, J.; García-Gutiérrez, M.; Missana, T.; Mingarro, M.

    2012-04-01

    A Permeable Reactive Barrier has been designed to treat 137Cs polluted groundwater. In order to check both reactivity and permeability, laboratory batch and column tests combined with reactive transport modeling have been performed. The trapping mechanism is based on the sorption of cesium mainly on illite-containing clays. Batch experiments were conducted to obtain the partition coefficients (Kd) of different clay samples in solutions with different potassium concentration. A clear correlation of Kd values with potassium content was observed. The results were modeled with a cation-exchange model. The permeability of the reactive material is provided by the dispersion of the clay on a matrix of wooden shavings. Constant head tests allowed obtaining permeability values. Several column experiments with different flow rates were conducted to confirm the 137Cs retention under different conditions. A blind 1D reactive transport model based on the cation-exchange model was able to predict reasonably well the results of column experiments. The reactive transport model, validated with the column experiments, was used to investigate the performance and duration of 1m thick barrier under different scenarios (flow, clay proportion, 137Cs and K concentration). As expected, the sensitivity tests proved that the retention capacity of dissolved 137Cs in groundwater depends linearly on the amount of clay used in the filling material. As well, the operation time increases linearly when decreasing the flow rate. Finally, the concentration of potassium in inflow water has a remarkable and non-linear influence in the retention of 137Cs. Very high concentrations of potassium are the greatest threat and can lead to the unfeasibility of a permeable reactive barrier. Due to the Cs-K competition, the barrier is comparatively more efficient to treat high concentrations of 137Cs. Up to now, preliminary results from a field scale experiment have confirmed the reactivity and permeability

  8. Modeling of flow and reactive transport in IPARS

    KAUST Repository

    Wheeler, Mary Fanett

    2012-03-11

    In this work, we describe a number of efficient and locally conservative methods for subsurface flow and reactive transport that have been or are currently being implemented in the IPARS (Integrated Parallel and Accurate Reservoir Simulator). For flow problems, we consider discontinuous Galerkin (DG) methods and mortar mixed finite element methods. For transport problems, we employ discontinuous Galerkin methods and Godunov-mixed methods. For efficient treatment of reactive transport simulations, we present a number of state-of-the-art dynamic mesh adaptation strategies and implementations. Operator splitting approaches and iterative coupling techniques are also discussed. Finally, numerical examples are provided to illustrate the capability of IPARS to treat general biogeochemistry as well as the effectivity of mesh adaptations with DG for transport. © 2012 Bentham Science Publishers. All rights reserved.

  9. Modeling reactive flow and transport in natural systems

    Energy Technology Data Exchange (ETDEWEB)

    Lichtner, P.C. [Center for Nuclear Waste Regulatory Analyses, S.Antonio, TX (United States)

    1998-12-31

    A general formulation of reactive transport equations in a porous medium has been presented including homogeneous reactions of aqueous species, heterogenous reactions of minerals, and microbiological processes. The canonical form of chemical reactions was introduced and the transformation between primary or basis species derived. The use of parallel linearly-dependent reactions was discussed for incorporating different reaction rate mechanisms. It was demonstrated how the electron may be used in reactive transport equations with redox reactions formulated in terms of half-cell reactions. A single component system was investigated for both a one-dimensional porous medium and a two-dimensional geometry incorporating fracture-matrix interaction. Finally two multicomponent examples were considered using the computer code MULTIFLO of in situ leaching of copper ore and acid mine drainage.

  10. Chinese Speech Recognition Model Based on Activation of the State Feedback Neural Network

    Institute of Scientific and Technical Information of China (English)

    李先志; 孙义和

    2001-01-01

    This paper proposes a simplified novel speech recognition model, the state feedback neuralnetwork activation model (SFNNAM), which is developed based on the characteristics of Chinese speechstructure. The model assumes that the current state of speech is only a correction of the last previous state.According to the "C-V"(Consonant-Vowel) structure of the Chinese language, a speech segmentation methodis also implemented in the SFNNAM model. This model has a definite physical meaning grounded on thestructure of the Chinese language and is easily implemented in very large scale integrated circuit (VLSI). In thespeech recognition experiment, less calculations were need than in the hidden Markov models (HMM) basedalgorithm. The recognition rate for Chinese numbers was 93.5% for the first candidate and 99.5% for the firsttwo candidates.``

  11. Modelling ecogeomorphic feedbacks: investigating mechanisms of land degradation in semi-arid grassland and shrubland

    Science.gov (United States)

    Turnbull, Laura; Mueller, Eva; Tietjen, Britta; Wainwright, John

    2014-05-01

    Across vast areas of the world's drylands, land degradation is exacerbated by ecohydrological processes, which alter the structure, function and connectivity of dryland hillslopes. These processes are often interlinked through feedback mechanisms in such a way that a trigger may result in a re-organization of the affected landscape. Here, we present a spatially explicit process-based ecogeomorphic model, MAHLERAN-EcoHyD to enhance our understanding of complex linkages between abiotic and biotic drivers and processes of degradation in drylands. This ecogeomorphic modelling approach is innovative in two main ways: it couples biotic and abiotic processes, and simulates intra and inter-event dynamics, thus overcoming a key limitation of previous modelling approaches in terms of their temporal scaling, by simulating key ecogeomorphic processes at process-relevant time steps. Redistribution of water, sediment and nutrients during high-intensity rainstorms is simulated at 1-sec time steps, soil moisture and transpiration dynamics at daily time steps, and vegetation dynamics (establishment, growth, mortality) at 14-day time steps, over a high-resolution 1x1 m grid. We use this innovative modelling approach to investigate soil-vegetation feedback mechanisms within a grassland-shrubland transition zone at the Sevilleta Long Term Ecological Research site in the south-western United States. Results from three modelling experiments are presented: the first modelling experiment investigates the impact of annual variations in individual high-intensity storms to assess long-term variations in runoff, soil-moisture conditions and sediment and nutrient fluxes over two decades; the second modelling experiment assesses the impact of vegetation composition on spatial changes in surface soil texture due to soil erosion by water; and the third modelling experiment investigates how long-term changes in vegetation alter feedbacks between biotic and abiotic processes using scenarios for

  12. A model of motion transparency processing with local center-surround interactions and feedback.

    Science.gov (United States)

    Raudies, Florian; Mingolla, Ennio; Neumann, Heiko

    2011-11-01

    Motion transparency occurs when multiple coherent motions are perceived in one spatial location. Imagine, for instance, looking out of the window of a bus on a bright day, where the world outside the window is passing by and movements of passengers inside the bus are reflected in the window. The overlay of both motions at the window leads to motion transparency, which is challenging to process. Noisy and ambiguous motion signals can be reduced using a competition mechanism for all encoded motions in one spatial location. Such a competition, however, leads to the suppression of multiple peak responses that encode different motions, as only the strongest response tends to survive. As a solution, we suggest a local center-surround competition for population-encoded motion directions and speeds. Similar motions are supported, and dissimilar ones are separated, by representing them as multiple activations, which occurs in the case of motion transparency. Psychophysical findings, such as motion attraction and repulsion for motion transparency displays, can be explained by this local competition. Besides this local competition mechanism, we show that feedback signals improve the processing of motion transparency. A discrimination task for transparent versus opaque motion is simulated, where motion transparency is generated by superimposing large field motion patterns of either varying size or varying coherence of motion. The model's perceptual thresholds with and without feedback are calculated. We demonstrate that initially weak peak responses can be enhanced and stabilized through modulatory feedback signals from higher stages of processing.

  13. Star Formation in Galaxy Mergers with Realistic Models of Stellar Feedback & the Interstellar Medium

    CERN Document Server

    Hopkins, Philip F; Hernquist, Lars; Narayanan, Desika; Hayward, Christopher C; Murray, Norman

    2012-01-01

    We use simulations with realistic models for stellar feedback to study galaxy mergers. These high resolution (1 pc) simulations follow formation and destruction of individual GMCs and star clusters. The final starburst is dominated by in situ star formation, fueled by gas which flows inwards due to global torques. The resulting high gas density results in rapid star formation. The gas is self gravitating, and forms massive (~10^10 M_sun) GMCs and subsequent super-starclusters (masses up to 10^8 M_sun). However, in contrast to some recent simulations, the bulk of new stars which eventually form the central bulge are not born in superclusters which then sink to the center of the galaxy, because feedback efficiently disperses GMCs after they turn several percent of their mass into stars. Most of the mass that reaches the nucleus does so in the form of gas. The Kennicutt-Schmidt law emerges naturally as a consequence of feedback balancing gravitational collapse, independent of the small-scale star formation micro...

  14. FORCE FEEDBACK MODEL OF ELECTRO-HYDRAULIC SERVO TELE-OPERATION ROBOT BASED ON VELOCITY CONTROL

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The tele-operation robotic system which consists of an excavator as the construction robot, and two joysticks for operating the robot from a safe place are useful for performing restoration in damaged areas. In order to accomplish a precise task, the operator needs to feel a realistic sense of task force brought about from a feedback force between the fork glove of slave robot and unfamiliar environment. A novel force feedback model is proposed based on velocity control of cylinder to determine environment force acting" on fork glove. Namely, the feedback force is formed by the error of displacement of joystick with velocity and driving force of piston, and the gain is calculated by the driving force and threshold of driving force of hydraulic cylinder. Moreover, the variable gain improved algorithm is developed to overcome the defect for grasping soft object. Experimental results for fork glove freedom of robotic system are provided to demonstrate the developed algorithm is available for grasping soft object.

  15. Modeling the dynamics of Plasmodium vivax infection and hypnozoite reactivation in vivo.

    Directory of Open Access Journals (Sweden)

    Adeshina I Adekunle

    2015-03-01

    Full Text Available The dynamics of Plasmodium vivax infection is characterized by reactivation of hypnozoites at varying time intervals. The relative contribution of new P. vivax infection and reactivation of dormant liver stage hypnozoites to initiation of blood stage infection is unclear. In this study, we investigate the contribution of new inoculations of P. vivax sporozoites to primary infection versus reactivation of hypnozoites by modeling the dynamics of P. vivax infection in Thailand in patients receiving treatment for either blood stage infection alone (chloroquine, or the blood and liver stages of infection (chloroquine + primaquine. In addition, we also analysed rates of infection in a study in Papua New Guinea (PNG where patients were treated with either artesunate, or artesunate + primaquine. Our results show that up to 96% of the P. vivax infection is due to hypnozoite reactivation in individuals living in endemic areas in Thailand. Similar analysis revealed the around 70% of infections in the PNG cohort were due to hypnozoite reactivation. We show how the age of the cohort, primaquine drug failure, and seasonality may affect estimates of the ratio of primary P. vivax infection to hypnozoite reactivation. Modeling of P. vivax primary infection and hypnozoite reactivation provides important insights into infection dynamics, and suggests that 90-96% of blood stage infections arise from hypnozoite reactivation. Major differences in infection kinetics between Thailand and PNG suggest the likelihood of drug failure in PNG.

  16. MODELLING AND PARAMETER ESTIMATION IN REACTIVE CONTINUOUS MIXTURES: THE CATALYTIC CRACKING OF ALKANES. PART I

    Directory of Open Access Journals (Sweden)

    PEIXOTO F. C.

    1999-01-01

    Full Text Available Fragmentation kinetics is employed to model a continuous reactive mixture. An explicit solution is found and experimental data on the catalytic cracking of a mixture of alkanes are used for deactivation and kinetic parameter estimation.

  17. Memories reactivated under ketamine are subsequently stronger: A potential pre-clinical behavioral model of psychosis.

    Science.gov (United States)

    Honsberger, Michael J; Taylor, Jane R; Corlett, Philip R

    2015-05-01

    Sub-anesthetic doses of the NMDA antagonist ketamine have been shown to model the formation and stability of delusion in human subjects. The latter has been predicted to be due to aberrant prediction error resulting in enhanced destabilization of beliefs. To extend the scope of this model, we investigated the effect of administration of low dose systemic ketamine on memory in a rodent model of memory reconsolidation. Systemic ketamine was administered either prior to or immediately following auditory fear memory reactivation in rats. Memory strength was assessed by measuring freezing behavior 24h later. Follow up experiments were designed to investigate an effect of pre-reactivation ketamine on short-term memory (STM), closely related memories, and basolateral amygdala (BLA) specific destabilization mechanisms. Rats given pre-reactivation, but not post-reactivation, ketamine showed larger freezing responses 24h later compared to vehicle. This enhancement was not observed 3h after the memory reactivation, nor was it seen in a closely related contextual memory. Prior inhibition of a known destabilization mechanism in the BLA blocked the effect of pre-reactivation ketamine. Pre- but not post-reactivation ketamine enhances fear memory. These data together with recent data in human subjects supports a model of delusion fixity that proposes that aberrant prediction errors result in enhanced destabilization and strengthening of delusional belief. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. The Modeling and Simulation of Reactive Distillation for the Esterification Process

    Institute of Scientific and Technical Information of China (English)

    朱建华; 沈复

    2003-01-01

    In this paper,a generalized model of the reactive distillation processes was developed via rate-based approach. The homotopy-continuation method was employed to solve the complicated nonlinear model equations efficiently. The simulation on the reactive distillation processes was carried out with the profiles of stage temperature,composition and flow rate for both vapor and liquid phases obtained. Based on careful analysis of the simulation results, the pitfalls in experimental design were detected. Finally, a software package for the simulation of reactive distillation processes was developed.

  19. Reciprocal Markov Modeling of Feedback Mechanisms Between Emotion and Dietary Choice Using Experience-Sampling Data.

    Science.gov (United States)

    Lu, Ji; Pan, Junhao; Zhang, Qiang; Dubé, Laurette; Ip, Edward H

    2015-01-01

    With intensively collected longitudinal data, recent advances in the experience-sampling method (ESM) benefit social science empirical research, but also pose important methodological challenges. As traditional statistical models are not generally well equipped to analyze a system of variables that contain feedback loops, this paper proposes the utility of an extended hidden Markov model to model reciprocal the relationship between momentary emotion and eating behavior. This paper revisited an ESM data set (Lu, Huet, & Dube, 2011) that observed 160 participants' food consumption and momentary emotions 6 times per day in 10 days. Focusing on the analyses on feedback loop between mood and meal-healthiness decision, the proposed reciprocal Markov model (RMM) can accommodate both hidden ("general" emotional states: positive vs. negative state) and observed states (meal: healthier, same or less healthy than usual) without presuming independence between observations and smooth trajectories of mood or behavior changes. The results of RMM analyses illustrated the reciprocal chains of meal consumption and mood as well as the effect of contextual factors that moderate the interrelationship between eating and emotion. A simulation experiment that generated data consistent with the empirical study further demonstrated that the procedure is promising in terms of recovering the parameters.

  20. Modeling and control of non-square MIMO system using relay feedback.

    Science.gov (United States)

    Kalpana, D; Thyagarajan, T; Gokulraj, N

    2015-11-01

    This paper proposes a systematic approach for the modeling and control of non-square MIMO systems in time domain using relay feedback. Conventionally, modeling, selection of the control configuration and controller design of non-square MIMO systems are performed using input/output information of direct loop, while the output of undesired responses that bears valuable information on interaction among the loops are not considered. However, in this paper, the undesired response obtained from relay feedback test is also taken into consideration to extract the information about the interaction between the loops. The studies are performed on an Air Path Scheme of Turbocharged Diesel Engine (APSTDE) model, which is a typical non-square MIMO system, with input and output variables being 3 and 2 respectively. From the relay test response, the generalized analytical expressions are derived and these analytical expressions are used to estimate unknown system parameters and also to evaluate interaction measures. The interaction is analyzed by using Block Relative Gain (BRG) method. The model thus identified is later used to design appropriate controller to carry out closed loop studies. Closed loop simulation studies were performed for both servo and regulatory operations. Integral of Squared Error (ISE) performance criterion is employed to quantitatively evaluate performance of the proposed scheme. The usefulness of the proposed method is demonstrated on a lab-scale Two-Tank Cylindrical Interacting System (TTCIS), which is configured as a non-square system.

  1. Modeling and Output Feedback Control of Networked Control Systems with Both Time Delays; and Packet Dropouts

    Directory of Open Access Journals (Sweden)

    Li Qiu

    2013-01-01

    Full Text Available This paper is concerned with the problem of modeling and output feedback controller design for a class of discrete-time networked control systems (NCSs with time delays and packet dropouts. A Markovian jumping method is proposed to deal with random time delays and packet dropouts. Different from the previous studies on the issue, the characteristics of networked communication delays and packet dropouts can be truly reflected by the unified model; namely, both sensor-to-controller (S-C and controller-to-actuator (C-A time delays, and packet dropouts are modeled and their history behavior is described by multiple Markov chains. The resulting closed-loop system is described by a new Markovian jump linear system (MJLS with Markov delays model. Based on Lyapunov stability theory and linear matrix inequality (LMI method, sufficient conditions of the stochastic stability and output feedback controller design method for NCSs with random time delays and packet dropouts are presented. A numerical example is given to illustrate the effectiveness of the proposed method.

  2. Reciprocal Markov modeling of feedback mechanisms between emotion and dietary choice using experience sampling data

    Science.gov (United States)

    Lu, Ji; Pan, Junhao; Zhang, Qiang; Dubé, Laurette; Ip, Edward H.

    2015-01-01

    With intensively collected longitudinal data, recent advances in Experience Sampling Method (ESM) benefit social science empirical research, but also pose important methodological challenges. As traditional statistical models are not generally well-equipped to analyze a system of variables that contain feedback loops, this paper proposes the utility of an extended hidden Markov model to model reciprocal relationship between momentary emotion and eating behavior. This paper revisited an ESM data set (Lu, Huet & Dube, 2011) that observed 160 participants’ food consumption and momentary emotions six times per day in 10 days. Focusing on the analyses on feedback loop between mood and meal healthiness decision, the proposed Reciprocal Markov Model (RMM) can accommodate both hidden (“general” emotional states: positive vs. negative state) and observed states (meal: healthier, same or less healthy than usual) without presuming independence between observations and smooth trajectories of mood or behavior changes. The results of RMM analyses illustrated the reciprocal chains of meal consumption and mood as well as the effect of contextual factors that moderate the interrelationship between eating and emotion. A simulation experiment that generated data consistent to the empirical study further demonstrated that the procedure is promising in terms of recovering the parameters. PMID:26717120

  3. Sensory feedback, error correction, and remapping in a multiple oscillator model of place cell activity

    Directory of Open Access Journals (Sweden)

    Joseph D. Monaco

    2011-09-01

    Full Text Available Mammals navigate by integrating self-motion signals (‘path integration’ and occasionally fixing on familiar environmental landmarks. The rat hippocampus is a model system of spatial representation in which place cells are thought to integrate both sensory and spatial information from entorhinal cortex. The localized firing fields of hippocampal place cells and entorhinal grid cells demonstrate a phase relationship with the local theta (6–10 Hz rhythm that may be a temporal signature of path integration. However, encoding self-motion in the phase of theta oscillations requires high temporal precision and is susceptible to idiothetic noise, neuronal variability, and a changing environment. We present a model based on oscillatory interference theory, previously studied in the context of grid cells, in which transient temporal synchronization among a pool of path-integrating theta oscillators produces hippocampal-like place fields. We hypothesize that a spatiotemporally extended sensory interaction with external cues modulates feedback to the theta oscillators. We implement a form of this cue-driven feedback and show that it can retrieve fixed points in the phase code of position. A single cue can smoothly reset oscillator phases to correct for both systematic errors and continuous noise in path integration. Further, simulations in which local and global cues are rotated against each other reveal a phase-code mechanism in which conflicting cue arrangements can reproduce experimentally observed distributions of ‘partial remapping’ responses. This abstract model demonstrates that phase-code feedback can provide stability to the temporal coding of position during navigation and may contribute to the context-dependence of hippocampal spatial representations. While the anatomical substrates of these processes have not been fully characterized, our findings suggest several signatures that can be evaluated in future experiments.

  4. Feedback loops and temporal misalignment in component-based hydrologic modeling

    Science.gov (United States)

    Elag, Mostafa M.; Goodall, Jonathan L.; Castronova, Anthony M.

    2011-12-01

    In component-based modeling, a complex system is represented as a series of loosely integrated components with defined interfaces and data exchanges that allow the components to be coupled together through shared boundary conditions. Although the component-based paradigm is commonly used in software engineering, it has only recently been applied for modeling hydrologic and earth systems. As a result, research is needed to test and verify the applicability of the approach for modeling hydrologic systems. The objective of this work was therefore to investigate two aspects of using component-based software architecture for hydrologic modeling: (1) simulation of feedback loops between components that share a boundary condition and (2) data transfers between temporally misaligned model components. We investigated these topics using a simple case study where diffusion of mass is modeled across a water-sediment interface. We simulated the multimedia system using two model components, one for the water and one for the sediment, coupled using the Open Modeling Interface (OpenMI) standard. The results were compared with a more conventional numerical approach for solving the system where the domain is represented by a single multidimensional array. Results showed that the component-based approach was able to produce the same results obtained with the more conventional numerical approach. When the two components were temporally misaligned, we explored the use of different interpolation schemes to minimize mass balance error within the coupled system. The outcome of this work provides evidence that component-based modeling can be used to simulate complicated feedback loops between systems and guidance as to how different interpolation schemes minimize mass balance error introduced when components are temporally misaligned.

  5. Tree cover bistability in the MPI Earth system model due to fire-vegetation feedback

    Science.gov (United States)

    Lasslop, Gitta; Brovkin, Victor; Kloster, Silvia; Reick, Christian

    2015-04-01

    The global distribution of tree cover is mainly limited by precipitation and temperature. Within tropical ecosystems different tree cover values have been observed in regions with similar climate. Satellite data even revealed a lack of ecosystems with tree coverage around 60% and dominant tree covers of 20% and 80%. Conceptual models have been used to explain this tree cover distribution and base it on a bistability in tree cover caused by fire-vegetation interactions or competition between trees and grasses. Some ecological models also show this property of multiple stable tree covers, but it remains unclear which mechanism is the cause for this behaviour. Vegetation models used in climate simulations usually use simple approaches and were criticised to neglect such ecological theories and misrepresent tropical tree cover distribution and dynamics. Here we show that including the process based fire model SPITFIRE generated a bistability in tree cover in the land surface model JSBACH. Previous model versions showed only one stable tree cover state. Using a conceptual model we can show that a bistability can occur due to a feedback between grasses and fire. Grasses and trees are represented in the model based on plant functional types. With respect to fire the main difference between grasses and trees is the fuel characteristics. Grass fuels are smaller in size, and have a higher surface area to volume ratio. These grass fuels dry faster increasing their flammability which leads to a higher fire rate of spread. Trees are characterized by coarse fuels, which are less likely to ignite and rather suppress fire. Therefore a higher fraction of grasses promotes fire, fire kills trees and following a fire, grasses establish faster. This feedback can stabilize ecosystems with low tree cover in a low tree cover state and systems with high tree cover in a high tree cover state. In previous model versions this feedback was absent. Based on the new JSBACH model driven with

  6. THE EXISTENCE OF POSITIVE PERIODIC SOLUTIONS IN A LOGISTIC DIFFERENCE MODEL WITH A FEEDBACK CONTROL

    Institute of Scientific and Technical Information of China (English)

    刘智钢; 陈安平

    2004-01-01

    Consider the following nonautonomous delayed periodic logistic difference model with feedback control term N(k+1)=N(k)exp[r(k)-a1(k)N(k)-a2(k)N(k-τ(k))-c(k)u(k)],Δu(k)=-a(k)u(k)+b(k)N(k-τ(k)), which describes the evolution of a single species. The existence of a positive periodic solution is established by using the method of Mawhin's coincidence degree. This work has important significance in both theory and applications.

  7. Deep removal of 4,6-dimethyldibenzothiophene from model transportation diesel fuels over reactive adsorbent

    Directory of Open Access Journals (Sweden)

    Shengqiang Wang

    2012-06-01

    Full Text Available This paper presents a new reactive adsorbent used to effectively remove 4,6-dimethyldibenzothiophene (4,6-DMDBT from model transportation diesel fuels. This reactive adsorbent was composed of formaldehyde, phosphotungstic acid and mesoporous silica gel. The experiment was based on an assumed condensation reaction of 4,6-DMDBT with formaldehyde using phosphotungstic acid as catalyst in pore spaces. The effect of temperature and the amount of formaldehyde and phosphotungstic acid loaded on the substrate were investigated in a batch system. In the breakthrough experiment, three different model diesel fuels containing 1000 mg/kg 4,6-DMDBT were pumped through a fixed-bed reactor packed with reactive adsorbent at constant temperature and atmospheric pressure, respectively. The experimental results showed that sulfur-free model fuel was obtained at 80ºC despite the presence of aromatics. The sulfur capacity of regenerated reactive adsorbent was almost totally recovered.

  8. A new neural network model for the feedback stabilization of nonlinear systems

    Institute of Scientific and Technical Information of China (English)

    Mei-qin LIU; Sen-lin ZHANG; Gang-long YAN

    2008-01-01

    A new neural network model termed 'standard neural network model' (SNNM) is presented,and a state-feedback control law is then designed for the SNNM to stabilize the closed-loop system.The control design constraints are shown to be a set of linear matrix inequalities (LMIs),which can be easily solved by the MATLAB LMI Control Toolbox to determine the control law.Most recurrent neural networks (including the chaotic neural network) and nonlinear systems modeled by neural networks or Takagi and Sugeno (T-S) fuzzy models can be transformed into the SNNMs to be stabilization controllers synthesized in the framework of a unified SNNM.Finally,three numerical examples are provided to illustrate the design developed in this paper.

  9. Mechanisms and Model Diversity of Trade-Wind Shallow Cumulus Cloud Feedbacks: A Review

    Science.gov (United States)

    Vial, Jessica; Bony, Sandrine; Stevens, Bjorn; Vogel, Raphaela

    2017-07-01

    Shallow cumulus clouds in the trade-wind regions are at the heart of the long standing uncertainty in climate sensitivity estimates. In current climate models, cloud feedbacks are strongly influenced by cloud-base cloud amount in the trades. Therefore, understanding the key factors controlling cloudiness near cloud-base in shallow convective regimes has emerged as an important topic of investigation. We review physical understanding of these key controlling factors and discuss the value of the different approaches that have been developed so far, based on global and high-resolution model experimentations and process-oriented analyses across a range of models and for observations. The trade-wind cloud feedbacks appear to depend on two important aspects: (1) how cloudiness near cloud-base is controlled by the local interplay between turbulent, convective and radiative processes; (2) how these processes interact with their surrounding environment and are influenced by mesoscale organization. Our synthesis of studies that have explored these aspects suggests that the large diversity of model responses is related to fundamental differences in how the processes controlling trade cumulus operate in models, notably, whether they are parameterized or resolved. In models with parameterized convection, cloudiness near cloud-base is very sensitive to the vigor of convective mixing in response to changes in environmental conditions. This is in contrast with results from high-resolution models, which suggest that cloudiness near cloud-base is nearly invariant with warming and independent of large-scale environmental changes. Uncertainties are difficult to narrow using current observations, as the trade cumulus variability and its relation to large-scale environmental factors strongly depend on the time and/or spatial scales at which the mechanisms are evaluated. New opportunities for testing physical understanding of the factors controlling shallow cumulus cloud responses using

  10. Applying forces to elastic network models of large biomolecules using a haptic feedback device.

    Science.gov (United States)

    Stocks, M B; Laycock, S D; Hayward, S

    2011-03-01

    Elastic network models of biomolecules have proved to be relatively good at predicting global conformational changes particularly in large systems. Software that facilitates rapid and intuitive exploration of conformational change in elastic network models of large biomolecules in response to externally applied forces would therefore be of considerable use, particularly if the forces mimic those that arise in the interaction with a functional ligand. We have developed software that enables a user to apply forces to individual atoms of an elastic network model of a biomolecule through a haptic feedback device or a mouse. With a haptic feedback device the user feels the response to the applied force whilst seeing the biomolecule deform on the screen. Prior to the interactive session normal mode analysis is performed, or pre-calculated normal mode eigenvalues and eigenvectors are loaded. For large molecules this allows the memory and number of calculations to be reduced by employing the idea of the important subspace, a relatively small space of the first M lowest frequency normal mode eigenvectors within which a large proportion of the total fluctuation occurs. Using this approach it was possible to study GroEL on a standard PC as even though only 2.3% of the total number of eigenvectors could be used, they accounted for 50% of the total fluctuation. User testing has shown that the haptic version allows for much more rapid and intuitive exploration of the molecule than the mouse version.

  11. Modeling Seafloor Deformation at the TAG Hydrothermal Field: Feedbacks between Permeability and Poroelastic Fluid Flow?

    Science.gov (United States)

    Crone, T. J.; Sohn, R. A.; Barreyre, T.

    2014-12-01

    Recent measurements of ocean bottom pressure suggest that hydrothermal flow induces cm-scale periodic ground surface displacement (GSD) at the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge (Sohn et al., 2009). The pressure measurements contain spectral peaks and harmonics with periods ranging from 22 to 53 min, none of which can be attributed to oceanographic or Earth tide processes. It is hypothesized that GSD cycles in this system may result from a nonlinear feedback between pore pressure and permeability in the hydrothermal system. To test this hypothesis we have developed a poroelastic convection model representing the upper crustal section at TAG that includes a "switching" type pressure-permeability feedback in the stockwork zone of the hydrothermal system. In this zone, the permeability increases when the pressure reaches a critical high value, and decreases when it reaches a critical low value. This behavior simulates the opening and closing of cracks within the hydrothermal system, and is similar to mechanisms that have been proposed for dike propagation in magmatic systems (Buck et al., 2006). Our modeling suggests that this mechanism can generate GSD that are similar to those observed at TAG. We are currently using these models to explore the sensitivity of inflation and deflation rates to system properties such as the geometry of the stockwork zone, the temperature of fluid in the upflow zone, the elastic properties of the lithosphere, and the relationship between pore pressure and permeability.

  12. Biospheric feedback effects in a synchronously coupled model of human and Earth systems

    Science.gov (United States)

    Thornton, Peter E.; Calvin, Katherine; Jones, Andrew D.; di Vittorio, Alan V.; Bond-Lamberty, Ben; Chini, Louise; Shi, Xiaoying; Mao, Jiafu; Collins, William D.; Edmonds, Jae; Thomson, Allison; Truesdale, John; Craig, Anthony; Branstetter, Marcia L.; Hurtt, George

    2017-07-01

    Fossil fuel combustion and land-use change are the two largest contributors to industrial-era increases in atmospheric CO 2 concentration. Projections of these are thus fundamental inputs for coupled Earth system models (ESMs) used to estimate the physical and biological consequences of future climate system forcing. While historical data sets are available to inform past and current climate analyses, assessments of future climate change have relied on projections of energy and land use from energy-economic models, constrained by assumptions about future policy, land-use patterns and socio-economic development trajectories. Here we show that the climatic impacts on land ecosystems drive significant feedbacks in energy, agriculture, land use and carbon cycle projections for the twenty-first century. We find that exposure of human-appropriated land ecosystem productivity to biospheric change results in reductions of land area used for crops; increases in managed forest area and carbon stocks; decreases in global crop prices; and reduction in fossil fuel emissions for a low-mid-range forcing scenario. The feedbacks between climate-induced biospheric change and human system forcings to the climate system--demonstrated here--are handled inconsistently, or excluded altogether, in the one-way asynchronous coupling of energy-economic models to ESMs used to date.

  13. Self-tuning bistable parametric feedback oscillator: Near-optimal amplitude maximization without model information

    Science.gov (United States)

    Braun, David J.; Sutas, Andrius; Vijayakumar, Sethu

    2017-01-01

    Theory predicts that parametrically excited oscillators, tuned to operate under resonant condition, are capable of large-amplitude oscillation useful in diverse applications, such as signal amplification, communication, and analog computation. However, due to amplitude saturation caused by nonlinearity, lack of robustness to model uncertainty, and limited sensitivity to parameter modulation, these oscillators require fine-tuning and strong modulation to generate robust large-amplitude oscillation. Here we present a principle of self-tuning parametric feedback excitation that alleviates the above-mentioned limitations. This is achieved using a minimalistic control implementation that performs (i) self-tuning (slow parameter adaptation) and (ii) feedback pumping (fast parameter modulation), without sophisticated signal processing past observations. The proposed approach provides near-optimal amplitude maximization without requiring model-based control computation, previously perceived inevitable to implement optimal control principles in practical application. Experimental implementation of the theory shows that the oscillator self-tunes itself near to the onset of dynamic bifurcation to achieve extreme sensitivity to small resonant parametric perturbations. As a result, it achieves large-amplitude oscillations by capitalizing on the effect of nonlinearity, despite substantial model uncertainties and strong unforeseen external perturbations. We envision the present finding to provide an effective and robust approach to parametric excitation when it comes to real-world application.

  14. Robust State Feedback H∞Control for Dynamic Biped Robot Based on T-S Fuzzy Model

    Institute of Scientific and Technical Information of China (English)

    HUAI Chuangfeng; FANG Yuefa

    2006-01-01

    T-S fuzzy model was applied to describe nonlinear system and global fuzzy model was expressed by the form of uncertain system. Based on robust state feedback H∞control strategy, designed a global asymptotic steady fuzzy model. This control system can use the experimental input-output data pairs for the biped robot learning and walking with dynamic balance. It is proved by simulation result that robust state feedback H∞ control method based on T-S fuzzy model can effectively restrain the effect of model uncertainties and external disturbance acting on biped robot. From these works, we showed the satisfactory performance of joint tracking without any chattering.

  15. Upscaling heterogeneity in aquifer reactivity via exposure-time concept: forward model.

    Science.gov (United States)

    Seeboonruang, Uma; Ginn, Timothy R

    2006-03-20

    Reactive properties of aquifer solid phase materials play an important role in solute fate and transport in the natural subsurface on time scales ranging from years in contaminant remediation to millennia in dynamics of aqueous geochemistry. Quantitative tools for dealing with the impact of natural heterogeneity in solid phase reactivity on solute fate and transport are limited. Here we describe the use of a structural variable to keep track of solute flux exposure to reactive surfaces. With this approach, we develop a non-reactive tracer model that is useful for determining the signature of multi-scale reactive solid heterogeneity in terms of solute flux distributions at the field scale, given realizations of three-dimensional reactive site density fields. First, a governing Eulerian equation for the non-reactive tracer model is determined by an upscaling technique in which it is found that the exposure time of solution to reactive surface areas evolves via both a macroscopic velocity and a macroscopic dispersion in the artificial dimension of exposure time. Second, we focus on the Lagrangian approach in the context of a streamtube ensemble and demonstrate the use of the distribution of solute flux over the exposure time dimension in modeling two-dimensional transport of a solute undergoing simplified linear reversible reactions, in hypothetical conditions following prior laboratory experiments. The distribution of solute flux over exposure time in a given case is a signature of the impact of heterogeneous aquifer reactivity coupled with a particular physical heterogeneity, boundary conditions, and hydraulic gradient. Rigorous application of this approach in a simulation sense is limited here to linear kinetically controlled reactions.

  16. Benchmarking reactive transport models at a hillslope scale

    Science.gov (United States)

    Kalbacher, T.; He, W.; Nixdorf, E.; Jang, E.; Fleckenstein, J. H.; Kolditz, O.

    2015-12-01

    The hillslope scale is an important transition between the field scale and the catchment scale. The water flow in the unsaturated zone of a hillslope can be highly dynamic, which can lead to dynamic changes of groundwater flow or stream outflow. Additionally, interactions among host rock formation, soil properties and recharge water from precipitation or anthropogenic activities (mining, agriculture etc.) can influence the water quality of groundwater and stream in the long term. To simulate reactive transport processes at such a scale is a challenging task. On the one hand, simulation of water flow in a coupled soil-aquifer system often involves solving of highly non-linear PDEs such as Richards equation; on the other hand, one has to consider complicated biogeochemical reactions (e.g. water-rock interactions, biological degradation, redox reactions). Both aspects are computationally expensive and have high requirements on the numerical precision and stabilities of the employed code. The primary goals of this study are as follows: i) Identify the bottlenecks and quantitatively analyse their influence on simulation of biogeochemical reactions at a hillslope scale; ii) find or suggest practical strategies to deal with these bottlenecks, thus to provide detailed hints for future improvements of reactive transport simulators. To achieve these goals, the parallelized reactive transport simulator OGS#IPhreeqc has been applied to simulate two benchmark examples. The first example is about uranium leaching based on Šimůnek et al. (2012), which considers the leaching of uranium from a mill tailing and accompanied mineral dissolution/precipitation. The geochemical system is then extended to include redox reactions in the second example. Based on these examples, the numerical stability and parallel performance of the tool is analysed. ReferenceŠimůnek, J., Jacques, D., Šejna, M., van Genuchten, M. T.: The HP2 program for HYDRUS (2D/3D), A coupled code for simulating two

  17. A model for gamma-ray binaries, based on the effect of pair production feedback in shocked pulsar winds

    CERN Document Server

    Derishev, E

    2016-01-01

    We analyze the model of gamma-ray binaries, consisting of a massive star and a pulsar with ultrarelativistic wind. We consider radiation from energetic particles, accelerated at the pulsar wind termination shock, and feedback of this radiation on the wind through production of secondary electron-positron pairs. We show that the pair feedback limits the Lorentz factor of the pulsar wind and creates a population of very energetic pairs, whose radiation may be responsible for the observed gamma-ray signal.

  18. The impact of baroclinic eddy feedback on the persistence of jet variability in the two-layer model

    OpenAIRE

    Zurita-Gotor, Pablo; Blanco-Fuentes, Javier; Gerber, E. P.

    2013-01-01

    Although it is well known that the persistence of extratropical jet shifts is enhanced by a positive eddy feedback, the dynamics of this feedback is still debated. Two types of mechanisms have been proposed: barotropic mechanisms rely on changes in upper-level propagation and baroclinic mechanisms rely on the coupling between barotropic and baroclinic flow. Recent studies have suggested that barotropic models can capture key aspects of the observed jet variability but the role of baroclinic d...

  19. Coupled map car-following model and its delayed-feedback control.

    Science.gov (United States)

    Konishi, K; Kokame, H; Hirata, K

    1999-10-01

    This paper proposes a coupled map car-following traffic model, which describes a dynamical behavior of a group of road vehicles running in a single lane without overtaking. This model consists of a lead vehicle and following vehicles, which have a piecewise linear optimal velocity function. When the lead-vehicle speed is varied, we can observe a traffic jam in the group of the vehicles. We derive a condition under which the traffic jam never occurs in our model. Furthermore, in order to suppress the traffic jam, for each vehicle we use a dynamic version of decentralized delayed-feedback control proposed in [Konishi, Hirai, and Kokame, Phys. Rev. E 58, 3055 (1998)], and provide a systematic procedure for designing the controller.

  20. Modeling laser-induced periodic surface structures: Finite-difference time-domain feedback simulations

    Energy Technology Data Exchange (ETDEWEB)

    Skolski, J. Z. P., E-mail: j.z.p.skolski@utwente.nl; Vincenc Obona, J. [Materials innovation institute M2i, Faculty of Engineering Technology, Chair of Applied Laser Technology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Römer, G. R. B. E.; Huis in ' t Veld, A. J. [Faculty of Engineering Technology, Chair of Applied Laser Technology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands)

    2014-03-14

    A model predicting the formation of laser-induced periodic surface structures (LIPSSs) is presented. That is, the finite-difference time domain method is used to study the interaction of electromagnetic fields with rough surfaces. In this approach, the rough surface is modified by “ablation after each laser pulse,” according to the absorbed energy profile, in order to account for inter-pulse feedback mechanisms. LIPSSs with a periodicity significantly smaller than the laser wavelength are found to “grow” either parallel or orthogonal to the laser polarization. The change in orientation and periodicity follow from the model. LIPSSs with a periodicity larger than the wavelength of the laser radiation and complex superimposed LIPSS patterns are also predicted by the model.

  1. Modeling laser-induced periodic surface structures: Finite-difference time-domain feedback simulations

    Science.gov (United States)

    Skolski, J. Z. P.; Römer, G. R. B. E.; Vincenc Obona, J.; Huis in't Veld, A. J.

    2014-03-01

    A model predicting the formation of laser-induced periodic surface structures (LIPSSs) is presented. That is, the finite-difference time domain method is used to study the interaction of electromagnetic fields with rough surfaces. In this approach, the rough surface is modified by "ablation after each laser pulse," according to the absorbed energy profile, in order to account for inter-pulse feedback mechanisms. LIPSSs with a periodicity significantly smaller than the laser wavelength are found to "grow" either parallel or orthogonal to the laser polarization. The change in orientation and periodicity follow from the model. LIPSSs with a periodicity larger than the wavelength of the laser radiation and complex superimposed LIPSS patterns are also predicted by the model.

  2. Shallow-cumulus cloud feedback: model uncertainties and perspectives of observational constraint

    Science.gov (United States)

    Bony, Sandrine

    2017-04-01

    Shallow-cumulus clouds constitute the most prominent cloud type on Earth, and their response to changing environmental conditions is critical for climate sensitivity. Research over the last decade has pointed out the importance of the interplay between clouds, convection, turbulence and circulation in controlling this response. Unfortunately, numerical models represent this interplay in diverse ways, which translates into different shallow-cumulus cloud feedbacks in climate change. Climate models predict that the cloud-base cloud fraction is very sensitive to changes in environmental conditions, while process models suggest that it is very resilient to such changes. To understand and solve this contradiction, a field campaign named EUREC4A (Elucidating the role of clouds-circulation coupling in climate) will be organized in the lower Atlantic trades in Jan-Fev 2020. The scientific objectives of this campaign will be presented, and the experimental strategy envisioned to reach these objectives will be discussed.

  3. Real-Time Gesture-Controlled Physical Modelling Music Synthesis with Tactile Feedback

    Directory of Open Access Journals (Sweden)

    David M. Howard

    2004-06-01

    Full Text Available Electronic sound synthesis continues to offer huge potential possibilities for the creation of new musical instruments. The traditional approach is, however, seriously limited in that it incorporates only auditory feedback and it will typically make use of a sound synthesis model (e.g., additive, subtractive, wavetable, and sampling that is inherently limited and very often nonintuitive to the musician. In a direct attempt to challenge these issues, this paper describes a system that provides tactile as well as acoustic feedback, with real-time synthesis that invokes a more intuitive response from players since it is based upon mass-spring physical modelling. Virtual instruments are set up via a graphical user interface in terms of the physical properties of basic well-understood sounding objects such as strings, membranes, and solids. These can be interconnected to form complex integrated structures. Acoustic excitation can be applied at any point mass via virtual bowing, plucking, striking, specified waveform, or from any external sound source. Virtual microphones can be placed at any point masses to deliver the acoustic output. These aspects of the instrument are described along with the nature of the resulting acoustic output.

  4. Bifurcation analysis of a delay reaction-diffusion malware propagation model with feedback control

    Science.gov (United States)

    Zhu, Linhe; Zhao, Hongyong; Wang, Xiaoming

    2015-05-01

    With the rapid development of network information technology, information networks security has become a very critical issue in our work and daily life. This paper attempts to develop a delay reaction-diffusion model with a state feedback controller to describe the process of malware propagation in mobile wireless sensor networks (MWSNs). By analyzing the stability and Hopf bifurcation, we show that the state feedback method can successfully be used to control unstable steady states or periodic oscillations. Moreover, formulas for determining the properties of the bifurcating periodic oscillations are derived by applying the normal form method and center manifold theorem. Finally, we conduct extensive simulations on large-scale MWSNs to evaluate the proposed model. Numerical evidences show that the linear term of the controller is enough to delay the onset of the Hopf bifurcation and the properties of the bifurcation can be regulated to achieve some desirable behaviors by choosing the appropriate higher terms of the controller. Furthermore, we obtain that the spatial-temporal dynamic characteristics of malware propagation are closely related to the rate constant for nodes leaving the infective class for recovered class and the mobile behavior of nodes.

  5. The Cusp/Core problem: supernovae feedback versus the baryonic clumps and dynamical friction model

    CERN Document Server

    Del Popolo, A

    2015-01-01

    In the present paper, we compare the predictions of two well known mechanisms considered able to solve the cusp/core problem (a. supernova feedback; b. baryonic clumps-DM interaction) by comparing their theoretical predictions to recent observations of the inner slopes of galaxies with masses ranging from dSphs to normal spirals. We compare the $\\alpha$-$V_{\\rm rot}$ and the $\\alpha$-$M_{\\ast}$ relationships, predicted by the two models with high resolution data coming from \\cite{Adams2014}, \\cite{Simon2005}, LITTLE THINGS \\citep{Oh2014}, THINGS dwarves \\citep{Oh2011a,Oh2011b}, THINGS spirals \\citep{Oh2014}, Sculptor, Fornax and the Milky Way. The comparison of the theoretical predictions with the complete set of data shows that the two models perform similarly, while when we restrict the analysis to a smaller subsample of higher quality, we show that the method presented in this paper (baryonic clumps-DM interaction) performs better than the one based on supernova feedback. We also show that, contrarily to t...

  6. Nonlinear feedback in a six-dimensional Lorenz Model: impact of an additional heating term

    Directory of Open Access Journals (Sweden)

    B.-W. Shen

    2015-03-01

    Full Text Available In this study, a six-dimensional Lorenz model (6DLM is derived, based on a recent study using a five-dimensional (5-D Lorenz model (LM, in order to examine the impact of an additional mode and its accompanying heating term on solution stability. The new mode added to improve the representation of the steamfunction is referred to as a secondary streamfunction mode, while the two additional modes, that appear in both the 6DLM and 5DLM but not in the original LM, are referred to as secondary temperature modes. Two energy conservation relationships of the 6DLM are first derived in the dissipationless limit. The impact of three additional modes on solution stability is examined by comparing numerical solutions and ensemble Lyapunov exponents of the 6DLM and 5DLM as well as the original LM. For the onset of chaos, the critical value of the normalized Rayleigh number (rc is determined to be 41.1. The critical value is larger than that in the 3DLM (rc ~ 24.74, but slightly smaller than the one in the 5DLM (rc ~ 42.9. A stability analysis and numerical experiments obtained using generalized LMs, with or without simplifications, suggest the following: (1 negative nonlinear feedback in association with the secondary temperature modes, as first identified using the 5DLM, plays a dominant role in providing feedback for improving the solution's stability of the 6DLM, (2 the additional heating term in association with the secondary streamfunction mode may destabilize the solution, and (3 overall feedback due to the secondary streamfunction mode is much smaller than the feedback due to the secondary temperature modes; therefore, the critical Rayleigh number of the 6DLM is comparable to that of the 5DLM. The 5DLM and 6DLM collectively suggest different roles for small-scale processes (i.e., stabilization vs. destabilization, consistent with the following statement by Lorenz (1972: If the flap of a butterfly's wings can be instrumental in generating a tornado, it

  7. The Bjerknes feedback in the tropical Atlantic in CMIP5 models

    Science.gov (United States)

    Deppenmeier, Anna-Lena; Haarsma, Reindert J.; Hazeleger, Wilco

    2016-10-01

    Coupled state-of-the-art general circulation models still perform relatively poorly in simulating tropical Atlantic (TA) climate. To investigate whether lack of air-sea interaction might be responsible for their biases, we investigate the Bjerknes feedback (BF) in the TA, the driver of the dominant interannual variability in that region. First, we analyse this mechanism from reanalysis data. Then, we compare our findings to model output from the Coupled Model Intercomparison Project Phase 5. The feedback is subdivided into three components. The first one consists of the influence of eastern equatorial sea surface temperature anomalies (SST') on zonal wind stress anomalies (τ _u') in the western basin. The second component is the influence of wind stress anomalies in the western TA on eastern equatorial oceanic heat content anomalies (HC'). The third component is the local response of overlying SST' to HC' in the eastern TA. All three components are shown to be present in ERA-Interim and ORAS4 reanalysis by correlating the two variables of each component with each other. The obtained patterns are compared to the ones from model output via pattern correlation per component. While the models display errors in the annual cycles of SST, τ _u, and HC, as well as in the seasonality of the feedback, the impact of SST' on wind stress and the impact of wind stress on HC' are simulated relatively well by most of the models. This is especially the case when correcting for the error in seasonality. The third component of the BF, the impact of HC' on SST' in the eastern part of the basin, deviates from what we find in reanalysis. We find an influence of HC anomalies on overlying SSTs in the eastern equatorial TA, but it is weaker than in the reanalysis and it is not strongly confined to the equator. Longitude-depth cross sections of equatorial temperature variance and correlation between subsurface temperature anomalies and SST' in the cold tongue region show that flawed

  8. A refined sub-grid model for black hole accretion and AGN feedback in large cosmological simulations

    CERN Document Server

    Bachmann, Lisa K; Hirschmann, Michaela; Prieto, M Almudena; Remus, Rhea-Silvia

    2014-01-01

    In large scale cosmological hydrodynamic simulations simplified sub-grid models for gas accretion onto black holes and AGN feedback are commonly used. Such models typically depend on various free parameters, which are not well constrained. We present a new advanced model containing a more detailed description of AGN feedback, where those parameters reflect the results of recent observations. The model takes the dependency of these parameters on the black hole properties into account and describes a continuous transition between the feedback processes acting in the so-called radio-mode and quasar-mode. In addition, we implement a more detailed description of the accretion of gas onto black holes by distinguishing between hot and cold gas accretion. Our new implementations prevent black holes from gaining too much mass, particularly at low redshifts so that our simulations are now very successful in reproducing the observed present-day black hole mass function. Our new model also suppresses star formation in ma...

  9. Modeling the feedback between aerosol and boundary layer processes: a case study in Beijing, China.

    Science.gov (United States)

    Miao, Yucong; Liu, Shuhua; Zheng, Yijia; Wang, Shu

    2016-02-01

    Rapid development has led to frequent haze in Beijing. With mountains and sea surrounding Beijing, the pollution is found to be influenced by the mountain-plain breeze and sea-land breeze in complex ways. Meanwhile, the presence of aerosols may affect the surface energy balance and impact these boundary layer (BL) processes. The effects of BL processes on aerosol pollution and the feedback between aerosol and BL processes are not yet clearly understood. Thus, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is used to investigate the possible effects and feedbacks during a haze episode on 23 September 2011. Influenced by the onshore prevailing wind, sea-breeze, and upslope breeze, about 45% of surface particulate matter (PM)2.5 in Beijing are found to be contributed by its neighbor cities through regional transport. In the afternoon, the development of upslope breeze suppresses the growth of BL in Beijing by imposing a relatively low thermal stable layer above the BL, which exacerbates the pollution. Two kinds of feedback during the daytime are revealed as follows: (1) as the aerosols absorb and scatter the solar radiation, the surface net radiation and sensible heat flux are decreased, while BL temperature is increased, resulting in a more stable and shallower BL, which leads to a higher surface PM2.5 concentration in the morning and (2) in the afternoon, as the presence of aerosols increases the BL temperature over plains, the upslope breeze is weakened, and the boundary layer height (BLH) over Beijing is heightened, resulting in the decrease of the surface PM2.5 concentration there.

  10. OH radical reactivity in an Indiana Forest: Measurements and model comparisons

    Science.gov (United States)

    Sigler, P. S. R.; Bottorff, B.; Lew, M.; Stevens, P. S.; Leonardis, T.; Locoge, N.; Sklaveniti, S.; Dusanter, S.; Kundu, S.; Wood, E. C. D.; Gentner, D. R.

    2015-12-01

    The hydroxyl (OH) radicals plays an important role in the chemistry of the atmosphere. OH radical reactions initiate the oxidation of volatile organic compounds (VOCs) which can lead to the production of ozone and secondary organic aerosols in the atmosphere. In addition, reactions of OH radicals controls the lifetime of methane and other greenhouse gases that affect the radiative balance of the atmosphere. Previous measurements of total hydroxyl radical reactivity in forest environments have found discrepancies between measured values and those calculated from collocated measurements of biogenic VOC (BVOC) concentrations. Additional measurements of total OH reactivity together with measurements of BVOCs are needed to understand the source of this missing reactivity and to further constrain atmospheric chemistry models. Total hydroxyl radical (OH) reactivity was measured using a turbulent flow reactor were made during summer 2015 as part of the Indiana Radical, Reactivity and Ozone Production Intercomparison (IRRONIC). This campaign took place in a forested area at the Indiana Research and Teaching Preserve (IURTP) near the Bloomington campus characterized by high mixing ratios of isoprene and low mixing ratios of NOx. Measurements of a suite of VOCs and oxygenated VOCs was also conducted at the site, allowing a comparison of the observed reactivity with the expected OH reactivity from these measurements.

  11. 2D photochemical modeling of Saturn's stratosphere. Part II: Feedback between composition and temperature

    CERN Document Server

    Hue, V; Cavalié, T; Dobrijevic, M; Hersant, F

    2015-01-01

    Saturn's axial tilt produces seasons in a similar way as on Earth. Both the stratospheric temperature and composition are affected by this latitudinally varying insolation along the seasons. The thermal structure is controlled and regulated by the amount of hydrocarbons in the stratosphere, which act as absorbers and coolants from the UV to the far-IR spectral range, and this structure influences the amount of hydrocarbons. We study here the feedback between the chemical composition and the thermal structure by coupling a latitudinal and seasonal photochemical model with a radiative seasonal model. Our results show that the seasonal temperature peak in the higher stratosphere, associated with the seasonal increase of insolation, is shifted earlier than the maximum insolation peak. This shift is increased with increasing latitudes and is caused by the low amount of stratospheric coolants in the spring season. At 80$^{\\circ}$ in both hemispheres, the temperature peak at 1d-2mbar is seen to occur half a season e...

  12. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    CERN Document Server

    Tombesi, Francesco

    2016-01-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this "quasar mode" feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been dir...

  13. Optical feedback effects on terahertz quantum cascade lasers: modelling and applications

    Science.gov (United States)

    Rakić, Aleksandar D.; Lim, Yah Leng; Taimre, Thomas; Agnew, Gary; Qi, Xiaoqiong; Bertling, Karl; Han, She; Wilson, Stephen J.; Kundu, Iman; Grier, Andrew; Ikonić, Zoran; Valavanis, Alexander; Demić, Aleksandar; Keeley, James; Li, Lianhe H.; Linfield, Edmund H.; Davies, A. Giles; Harrison, Paul; Ferguson, Blake; Walker, Graeme; Prow, Tarl; Indjin, Dragan; Soyer, H. Peter

    2016-11-01

    Terahertz (THz) quantum cascade lasers (QCLs) are compact sources of radiation in the 1-5 THz range with significant potential for applications in sensing and imaging. Laser feedback interferometry (LFI) with THz QCLs is a technique utilizing the sensitivity of the QCL to the radiation reflected back into the laser cavity from an external target. We will discuss modelling techniques and explore the applications of LFI in biological tissue imaging and will show that the confocal nature of the QCL in LFI systems, with their innate capacity for depth sectioning, makes them suitable for skin diagnostics with the well-known advantages of more conventional confocal microscopes. A demonstration of discrimination of neoplasia from healthy tissue using a THz, LFI-based system in the context of melanoma is presented using a transgenic mouse model.

  14. Reactive attachment disorder--a theoretical model beyond attachment.

    Science.gov (United States)

    Minnis, Helen; Marwick, Helen; Arthur, Julie; McLaughlin, Alexis

    2006-09-01

    Despite its importance in public health, reactive attachment disorder (RAD) is an under-researched and little used clinical category. Abnormalities of social relatedness have long been documented in children who have been abused, neglected or institutionalised, but there have been more recent efforts to define these behaviours within the psychiatric nosology. There has been an implicit assumption that the central deficit in RAD is in the attachment system, but this has caused controversy and may have blocked research. We propose that RAD is better construed within the framework of intersubjectivity, which has a central role in the development of core brain and social functions and may also have had an important role in the evolution of a key human characteristic-complex social functioning. This broader framework may potentially explain apparently diverse symptoms such as indiscriminate friendliness and negative or unpredictable reunion responses. Finally, we suggest that a change of name may be useful in progressing the field, but accept that this may be difficult until there is better agreement in the clinical and scientific communities about the core features and aetiology of this disorder.

  15. Adjusting kinematics and kinetics in a feedback-controlled toe walking model

    Directory of Open Access Journals (Sweden)

    Olenšek Andrej

    2012-08-01

    Full Text Available Abstract Background In clinical gait assessment, the correct interpretation of gait kinematics and kinetics has a decisive impact on the success of the therapeutic programme. Due to the vast amount of information from which primary anomalies should be identified and separated from secondary compensatory changes, as well as the biomechanical complexity and redundancy of the human locomotion system, this task is considerably challenging and requires the attention of an experienced interdisciplinary team of experts. The ongoing research in the field of biomechanics suggests that mathematical modeling may facilitate this task. This paper explores the possibility of generating a family of toe walking gait patterns by systematically changing selected parameters of a feedback-controlled model. Methods From the selected clinical case of toe walking we identified typical toe walking characteristics and encoded them as a set of gait-oriented control objectives to be achieved in a feedback-controlled walking model. They were defined as fourth order polynomials and imposed via feedback control at the within-step control level. At the between-step control level, stance leg lengthening velocity at the end of the single support phase was adaptively adjusted after each step so as to facilitate gait velocity control. Each time the gait velocity settled at the desired value, selected intra-step gait characteristics were modified by adjusting the polynomials so as to mimic the effect of a typical therapeutical intervention - inhibitory casting. Results By systematically adjusting the set of control parameters we were able to generate a family of gait kinematic and kinetic patterns that exhibit similar principal toe walking characteristics, as they were recorded by means of an instrumented gait analysis system in the selected clinical case of toe walking. We further acknowledge that they to some extent follow similar improvement tendencies as those which one can

  16. Cloud and Circulation Feedbacks in a Near-Global Aquaplanet Cloud-Resolving Model

    Science.gov (United States)

    Narenpitak, P.; Bretherton, C. S.; Khairoutdinov, M.

    2016-12-01

    A near-global aquaplanet cloud-resolving model (CRM) is used to investigate cloud feedbacks due to three climate perturbations: a uniform 4 K increase in sea-surface temperature (SST), a quadrupling of CO2 concentration, and both combined. The CRM has a horizontal resolution of 4 km with no cumulus parameterization. It is a zonally periodic 20480 km-long tropical channel, spanning 46°S-N with rigid walls. An equatorially symmetric QOBS SST distribution is specified for the control simulation. After spin-up, 80 days are analyzed for the control and 4 K SST increase simulations, and 40 days for the simulations with quadrupled CO2. The 4 K SST increase induces a statistically significant increase in subtropical low cloud but decreases midlatitude cloud; its domain-mean shortwave cloud feedbacks are slightly positive. CO2 quadrupling causes a slight shallowing and a statistically insignificant reduction of subtropical low cloud. These results are qualitatively consistent with aquaplanet versions of some conventionally-parameterized climate models [Medeiros et al., 2015, Clim Dyn], and with a superparameterized real-geography version of the Community Atmosphere Model, Version 4 [Bretherton et al., 2014, JAMES], which uses CRMs similar to this study. The geographic structure of warming-induced low cloud changes is strongly correlated with the associated changes in estimated inversion strength (EIS). The EIS increases by 1 K in the subtropics but decreases in the midlatitudes due to poleward jet shifts. Clear-sky boundary-layer radiative cooling plays a key role in the subtropical low cloud increase, as it further destabilizes the cloud layer and produces a positive feedback, in agreement with a hypothesis from Wyant et al. [2009, JAMES]. The subtropical low cloud increase is also associated with stronger vertical velocity variance, although there is little change in the vertical profile of buoyancy flux. The zonal variance of column relative humidity is compared between

  17. Model for the feedback control system of bacterial growth. II. Growth in continuous culture.

    Science.gov (United States)

    Bleecken, S

    1989-12-07

    A mathematical model is developed that describes substrate limited bacterial growth in a continuous culture and that is based upon the conceptual framework elaborated in a previous paper for describing the feedback control system of cell growth [S. Bleecken, (1988). J. theor. Biol. 133, 37.] Central to the theory are the ideas that the limiting substrate is converted into low molecular weight building blocks of macromolecular synthesis which again are converted into biomass (RNA and protein) and that the rates of RNA and protein synthesis are controlled by the intracellular concentration of building blocks. It is shown that a continuous culture can be simulated by two interconnected feedback control systems the actuating signals of which are limiting substrate concentration and the intracellular concentration of building blocks, respectively. Three types of steady-states are found to appear in a continuous culture, besides the well-known stable steady-state of the whole culture there exist two batchlike steady-states of the biotic part of the culture which are metastable. The model is used to analyse the steady-states and their stability properties as well as the dynamic responses of biomass, RNA, protein, building block and substrate concentrations to changes in environmental conditions. Especially the inoculation of a continuous culture and the effects of step changes in dilution rate, inlet substrate concentration and growth temperature are studied in detail. Relations between the growth behaviour of a single cell and that of a continuous culture are derived. The RNA to protein ratio is introduced as a rough measure of the physiological state of cells and it is shown that a cell reacts to environmental changes with a simple pattern of basic responses in growth rate and physiological state. There are reasons to assume that the model presented is the minimal version of a structured model of bacterial growth and represents an optimum compromise between biological

  18. Cosmological evolution of supermassive black holes and AGN: a synthesis model for accretion and feedback .

    Science.gov (United States)

    Merloni, A.

    The growth of supermassive black holes (SMBH) through accretion is accompanied by the release of enormous amounts of energy which can either be radiated away, as happens in quasars, advected into the black hole, or disposed of in kinetic form through powerful jets, as is observed, for example, in radio galaxies. Here, I will present new constraints on the evolution of the SMBH mass function and Eddington ratio distribution, obtained from a study of AGN luminosity functions aimed at accounting for both radiative and kinetic energy output of AGN in a systematic way. First, I discuss how a refined Soltan argument leads to joint constraints on the mass-weighted average spin of SMBH and of the total mass density of high redshift (z˜ 5) and ``wandering'' black holes. Then, I will show how to describe the ``downsizing'' trend observed in the AGN population in terms of cosmological evolution of physical quantities (black hole mass, accretion rate, radiative and kinetic energy output). Finally, the redshift evolution of the AGN kinetic feedback will be briefly discussed and compared with the radiative output of the evolving SMBH population, thus providing a robust physical framework for phenomenological models of AGN feedback within structure formation.

  19. Modeling AGN Feedback in Cool-Core Clusters: The Balance between Heating and Cooling

    CERN Document Server

    Li, Yuan

    2014-01-01

    We study the long-term evolution of an idealized cool-core galaxy cluster under the influence of momentum-driven AGN feedback using three-dimensional high-resolution (60 pc) adaptive mesh refinement (AMR) simulations. The momentum-driven AGN feedback is modeled with a pair of (small-angle) precessing jets, and the jet power is calculated based on the accretion rate of the cold gas in the vicinity of the Supermassive Black Hole (SMBH). The ICM first cools into clumps along the propagation direction of the AGN jets. As the jet power increases, gas condensation occurs isotropically, forming spatially extended (up to a few tens kpc) structures that resemble the observed $\\rm H\\alpha$ filaments in Perseus and many other cool-core cluster. Jet heating elevates the gas entropy and cooling time, halting clump formation. The cold gas that is not accreted onto the SMBH settles into a rotating disk of $\\sim 10^{11}$ M$_{\\odot}$. The hot gas cools directly onto the cold disk while the SMBH accretes from the innermost reg...

  20. Inferring Instantaneous, Multivariate and Nonlinear Sensitivities for the Analysis of Feedback Processes in a Dynamical System: Lorenz Model Case Study

    Science.gov (United States)

    Aires, Filipe; Rossow, William B.; Hansen, James E. (Technical Monitor)

    2001-01-01

    A new approach is presented for the analysis of feedback processes in a nonlinear dynamical system by observing its variations. The new methodology consists of statistical estimates of the sensitivities between all pairs of variables in the system based on a neural network modeling of the dynamical system. The model can then be used to estimate the instantaneous, multivariate and nonlinear sensitivities, which are shown to be essential for the analysis of the feedbacks processes involved in the dynamical system. The method is described and tested on synthetic data from the low-order Lorenz circulation model where the correct sensitivities can be evaluated analytically.

  1. Coupled atmospheric, land surface, and subsurface modeling: Exploring water and energy feedbacks in three-dimensions

    Science.gov (United States)

    Davison, Jason H.; Hwang, Hyoun-Tae; Sudicky, Edward A.; Lin, John C.

    2015-12-01

    Human activities amplified by climate change pose a significant threat to the sustainability of water resources. Coupled climate-hydrologic simulations commonly predict these threats by combining shallow 1-D land surface models (LSMs) with traditional 2-D and 3-D hydrology models. However, these coupled models limit the moisture and energy-feedback dynamics to the shallow near-surface. This paper presents a novel analysis by applying an integrated variably-saturated subsurface/surface hydrology and heat transport model, HydroGeoSphere (HGS), as a land surface model (LSM). Furthermore, this article demonstrates the coupling of HGS to a simple 0-D atmospheric boundary layer (ABL) model. We then applied our coupled HGS-ABL model to three separate test cases and reproduced the strong correlation between the atmospheric energy balance to the depth of the groundwater table. From our simulations, we found that conventional LSMs may overestimate surface temperatures for extended drought periods because they underestimate the heat storage in the groundwater zone. Our final test case of the atmospheric response to drought conditions illustrated that deeper roots buffered the atmosphere better than shallow roots by maintaining higher latent heat fluxes, lower sensible heat fluxes, and lower surface and atmospheric temperatures.

  2. A Comparison of Model Reduction Approaches for Feedback Control Design of Thermal Flows in Buildings

    Science.gov (United States)

    Borggaard, Jeff; Ahuja, Sunil; Burns, John; Cliff, Eugene; Surana, Amit

    2010-11-01

    The application of distributed parameter control to spatiotemporal thermo-fluid systems requires the use of model reduction methods. The form of the optimal feedback control can inform design decisions, such as sensor and actuator selection and placement. A number of model reduction approaches for fluid systems have been put forward that are based on the proper orthogonal decomposition (POD). In this talk, we examine three approaches, the traditional POD-Galerkin model, the POD-Sensitivity model, and the Balanced-POD models. Our work is motivated by the building indoor environment control problem. Energy performance in building cooling and heating systems can be substantially improved by exploiting spatial temperature stratification and buoyancy that are prevalent in passive systems. We consider the control of airflow in a room with a passively cooled radiant ceiling and displacement ventilation provided near the room floor. For this problem, we approximate the full-order solution to compute the control gains, develop reduced-order models and associated controllers, and simulate the full-order closed-loop system for comparison with the reduced-order model-based control design.

  3. The biopsychosocial model of stress in adolescence: self-awareness of performance versus stress reactivity.

    Science.gov (United States)

    Rith-Najarian, Leslie R; McLaughlin, Katie A; Sheridan, Margaret A; Nock, Matthew K

    2014-03-01

    Extensive research among adults supports the biopsychosocial (BPS) model of challenge and threat, which describes relationships among stress appraisals, physiological stress reactivity, and performance; however, no previous studies have examined these relationships in adolescents. Perceptions of stressors as well as physiological reactivity to stress increase during adolescence, highlighting the importance of understanding the relationships among stress appraisals, physiological reactivity, and performance during this developmental period. In this study, 79 adolescent participants reported on stress appraisals before and after a Trier Social Stress Test in which they performed a speech task. Physiological stress reactivity was defined by changes in cardiac output and total peripheral resistance from a baseline rest period to the speech task, and performance on the speech was coded using an objective rating system. We observed in adolescents only two relationships found in past adult research on the BPS model variables: (1) pre-task stress appraisal predicted post-task stress appraisal and (2) performance predicted post-task stress appraisal. Physiological reactivity during the speech was unrelated to pre- and post-task stress appraisals and to performance. We conclude that the lack of association between post-task stress appraisal and physiological stress reactivity suggests that adolescents might have low self-awareness of physiological emotional arousal. Our findings further suggest that adolescent stress appraisals are based largely on their performance during stressful situations. Developmental implications of this potential lack of awareness of one's physiological and emotional state during adolescence are discussed.

  4. Solid phase studies and geochemical modelling of low-cost permeable reactive barriers

    Energy Technology Data Exchange (ETDEWEB)

    Bartzas, Georgios, E-mail: gbartzas@metal.ntua.gr [Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Zografos Campus, 15780 Athens (Greece); Komnitsas, Kostas [Department of Mineral Resources Engineering, Technical University of Crete, 73100 Chania (Greece)

    2010-11-15

    A continuous column experiment was carried out under dynamic flow conditions in order to study the efficiency of low-cost permeable reactive barriers (PRBs) to remove several inorganic contaminants from acidic solutions. A 50:50 w/w waste iron/sand mixture was used as candidate reactive media in order to activate precipitation and promote sorption and reduction-oxidation mechanisms. Solid phase studies of the exhausted reactive products after column shutdown, using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), confirmed that the principal Fe corrosion products identified in the reactive zone are amorphous iron (hydr)oxides (maghemite/magnetite and goethite), intermediate products (sulfate green rust), and amorphous metal sulfides such as amFeS and/or mackinawite. Geochemical modelling of the metal removal processes, including interactions between reactive media, heavy metal ions and sulfates, and interpretation of the ionic profiles was also carried out by using the speciation/mass transfer computer code PHREEQC-2 and the WATEQ4F database. Mineralogical characterization studies as well as geochemical modelling calculations also indicate that the effect of sulfate and silica sand on the efficiency of the reactive zone should be considered carefully during design and operation of low-cost field PRBs.

  5. A computational model clarifies the roles of positive and negative feedback loops in the Drosophila circadian clock

    Energy Technology Data Exchange (ETDEWEB)

    Wang Junwei, E-mail: wangjunweilj@yahoo.com.c [Cisco School of Informatics, Guangdong University of Foreign Studies, Guangzhou 510006 (China); Zhou Tianshou [School of Mathematics and Computational Science, Sun Yat-Sen University, Guangzhou 510275 (China)

    2010-06-14

    Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per{sup 01} and clk{sup Jrk} mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.

  6. Dynamic behaviour of reactive distillation tray columns described with a non-equilibrium cell model

    NARCIS (Netherlands)

    Baur, R.; Taylor, R.; Krishna, R.

    2001-01-01

    In this paper we develop a generic, dynamic, nonequilibrium (NEQ) cell model for reactive distillation (RD) tray columns. The features of our model are (1) the use of Maxwell–Stefan equations for describing mass transfer between fluid phases, (2) the reaction is assumed to take place in the liquid

  7. Lattice Boltzmann based multicomponent reactive transport model coupled with geochemical solver for scale simulations

    NARCIS (Netherlands)

    Patel, R.A.; Perko, J.; Jaques, D.; De Schutter, G.; Ye, G.; Van Breugel, K.

    2013-01-01

    A Lattice Boltzmann (LB) based reactive transport model intended to capture reactions and solid phase changes occurring at the pore scale is presented. The proposed approach uses LB method to compute multi component mass transport. The LB multi-component transport model is then coupled with the well

  8. Real-time fMRI brain-computer interface: Development of a "motivational feedback" subsystem for the regulation of visual cue reactivity

    Directory of Open Access Journals (Sweden)

    Moses O. Sokunbi

    2014-11-01

    Full Text Available Here we present a novel neurofeedback subsystem for the presentation of motivationally relevant visual feedback during the self-regulation of functional brain activation. Our motivational neurofeedback approach uses functional magnetic resonance imaging (fMRI signals elicited by visual cues (pictures and related to motivational processes such as craving or hunger. The visual feedback subsystem provides simultaneous feedback through these images as their size corresponds to the magnitude of fMRI signal change from a target brain area. During self-regulation of cue-evoked brain responses, decreases and increases in picture size thus provide real motivational consequences in terms of cue approach versus cue avoidance, which increases face validity of the approach in applied settings. Further, the outlined approach comprises of neurofeedback (regulation and mirror runs that allow to control for non-specific and task-unrelated effects, such as habituation or neural adaptation. The approach was implemented in the Python programming language. Pilot data from 10 volunteers showed that participants were able to successfully down-regulate individually defined target areas, demonstrating feasibility of the approach. The newly developed visual feedback subsystem can be integrated into protocols for imaging-based brain-computer interfaces (BCI and may facilitate neurofeedback research and applications into healthy and dysfunctional motivational processes, such food craving or addiction.

  9. A Review of Literature on Formative Evaluation of Teachers through Mid-Term Student Feedback and How the Reiser and Dick Instructional Planning Model Can Enhance This Feedback.

    Science.gov (United States)

    Hampton, Scott E.

    Research has shown that student mid-term feedback has significantly increased subsequent ratings of teacher effectiveness, student achievement, and student attitudes when the feedback results were accompanied by expert consultation. A gap in the literature is an instrument intended to provide specific feedback on systematic planning and delivery…

  10. Correlations in state space can cause sub-optimal adaptation of optimal feedback control models.

    Science.gov (United States)

    Aprasoff, Jonathan; Donchin, Opher

    2012-04-01

    Control of our movements is apparently facilitated by an adaptive internal model in the cerebellum. It was long thought that this internal model implemented an adaptive inverse model and generated motor commands, but recently many reject that idea in favor of a forward model hypothesis. In theory, the forward model predicts upcoming state during reaching movements so the motor cortex can generate appropriate motor commands. Recent computational models of this process rely on the optimal feedback control (OFC) framework of control theory. OFC is a powerful tool for describing motor control, it does not describe adaptation. Some assume that adaptation of the forward model alone could explain motor adaptation, but this is widely understood to be overly simplistic. However, an adaptive optimal controller is difficult to implement. A reasonable alternative is to allow forward model adaptation to 're-tune' the controller. Our simulations show that, as expected, forward model adaptation alone does not produce optimal trajectories during reaching movements perturbed by force fields. However, they also show that re-optimizing the controller from the forward model can be sub-optimal. This is because, in a system with state correlations or redundancies, accurate prediction requires different information than optimal control. We find that adding noise to the movements that matches noise found in human data is enough to overcome this problem. However, since the state space for control of real movements is far more complex than in our simple simulations, the effects of correlations on re-adaptation of the controller from the forward model cannot be overlooked.

  11. Pore scale modeling of reactive transport involved in geologic CO2 sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Qinjin [Los Alamos National Laboratory; Lichtner, Peter C [Los Alamos National Laboratory; Viswanathan, Hari S [Los Alamos National Laboratory; Abdel-fattah, Amr I [Los Alamos National Laboratory

    2009-01-01

    We apply a multi-component reactive transport lattice Boltzmann model developed in previolls studies to modeling the injection of a C02 saturated brine into various porous media structures at temperature T=25 and 80 C. The porous media are originally consisted of calcite. A chemical system consisting of Na+, Ca2+, Mg2+, H+, CO2(aq), and CI-is considered. The fluid flow, advection and diHusion of aqueous species, homogeneous reactions occurring in the bulk fluid, as weB as the dissolution of calcite and precipitation of dolomite are simulated at the pore scale. The effects of porous media structure on reactive transport are investigated. The results are compared with continuum scale modeling and the agreement and discrepancy are discussed. This work may shed some light on the fundamental physics occurring at the pore scale for reactive transport involved in geologic C02 sequestration.

  12. Evaluating the strength of the land-atmosphere moisture feedback in Earth system models using satellite observations

    Science.gov (United States)

    Levine, Paul A.; Randerson, James T.; Swenson, Sean C.; Lawrence, David M.

    2016-12-01

    The relationship between terrestrial water storage (TWS) and atmospheric processes has important implications for predictability of climatic extremes and projection of future climate change. In places where moisture availability limits evapotranspiration (ET), variability in TWS has the potential to influence surface energy fluxes and atmospheric conditions. Where atmospheric conditions, in turn, influence moisture availability, a full feedback loop exists. Here we developed a novel approach for measuring the strength of both components of this feedback loop, i.e., the forcing of the atmosphere by variability in TWS and the response of TWS to atmospheric variability, using satellite observations of TWS, precipitation, solar radiation, and vapor pressure deficit during 2002-2014. Our approach defines metrics to quantify the relationship between TWS anomalies and climate globally on a seasonal to interannual timescale. Metrics derived from the satellite data were used to evaluate the strength of the feedback loop in 38 members of the Community Earth System Model (CESM) Large Ensemble (LENS) and in six models that contributed simulations to phase 5 of the Coupled Model Intercomparison Project (CMIP5). We found that both forcing and response limbs of the feedback loop in LENS were stronger than in the satellite observations in tropical and temperate regions. Feedbacks in the selected CMIP5 models were not as strong as those found in LENS, but were still generally stronger than those estimated from the satellite measurements. Consistent with previous studies conducted across different spatial and temporal scales, our analysis suggests that models may overestimate the strength of the feedbacks between the land surface and the atmosphere. We describe several possible mechanisms that may contribute to this bias, and discuss pathways through which models may overestimate ET or overestimate the sensitivity of ET to TWS.

  13. Non-Equilibrium Zeldovich-Von Neumann-Doring Theory and Reactive Flow Modeling of Detonation

    Energy Technology Data Exchange (ETDEWEB)

    Tarver, C M; Forbes, J W; Urtiew, P A

    2002-05-02

    This paper discusses the Non-Equilibrium Zeldovich - von Neumann - Doring (NEZND) theory of self-sustaining detonation waves and the Ignition and Growth reactive flow model of shock initiation and detonation wave propagation in solid explosives. The NEZND theory identified the non-equilibrium excitation processes that precede and follow the exothermic decomposition of a large high explosive molecule into several small reaction product molecules. The thermal energy deposited by the leading shock wave must be distributed to the vibrational modes of the explosive molecule before chemical reactions can occur. The induction time for the onset of the initial endothermic reactions can be calculated using high pressure, high temperature transition state theory. Since the chemical energy is released well behind the leading shock front of a detonation wave, a physical mechanism is required for this chemical energy to reinforce the leading shock front and maintain its overall constant velocity. This mechanism is the amplification of pressure wavelets in the reaction zone by the process of de-excitation of the initially highly vibrationally excited reaction product molecules. This process leads to the development of the three-dimensional structure of detonation waves observed for all explosives. For practical predictions of shock initiation and detonation in hydrodynamic codes, phenomenological reactive flow models have been developed. The Ignition and Growth reactive flow model of shock initiation and detonation in solid explosives has been very successful in describing the overall flow measured by embedded gauges and laser interferometry. This reactive flow model uses pressure and compression dependent reaction rates, because time resolved experimental temperature data is not yet available. Since all chemical reaction rates are ultimately controlled by temperature, the next generation of reactive flow models will use temperature dependent reaction rates. Progress on a

  14. Xanthan exopolysaccharide: Acid-base reactivity related to structure and conformation. A model for understanding the reactivity of degraded and colloidal soil organic matter

    OpenAIRE

    Causse, Benjamin; HEYRAUD, Alain

    2013-01-01

    Bacterial cells and bacterial exopolysaccharides differ strongly in their respective colloidal and polymeric habits. This suggests different reactivities toward metals and protons, although recent studies point to the similarity of such substrates in terms of site density and metal complexation strength. The aim of this paper is to investigate the causes of this surprising uniqueness by studying the reactivity of a model exopolysaccharide, xanthan. NMR and molecular analysis were used to unam...

  15. Feedback control for car following model based on two-lane traffic flow

    Science.gov (United States)

    Ge, Hong-xia; Meng, Xiang-pei; Zhu, Hui-bing; Li, Zhi-Peng

    2014-08-01

    In the paper, two-lane traffic flow considering lane changing behaviors has been discussed based on the control theory, and the friction interference which is from the neighbor lane has been taken into account. By using the control method, the stability condition is derived. The feedback signals, which include vehicular information from both lanes, acting on the two-lane traffic system have been introduced into the Full Velocity Difference car-following model. In the end, simulations are conducted to examine the validity and reasonability of the control method. It is proven that lane changing behaviors can aggravate the traffic perturbation. The traffic flow congestion could be suppressed by using the control method and the simulation results are in good agreement with the theoretical analysis.

  16. Feedback control scheme of traffic jams based on the coupled map car-following model

    Science.gov (United States)

    Zhou, Tong; Sun, Di-Hua; Zhao, Min; Li, Hua-Min

    2013-09-01

    Based on the pioneering work of Konishi et al. [Phys. Rev. E (1999) 60 4000], a new feedback control scheme is presented to suppress traffic jams based on the coupled map car-following model under the open boundary condition. The effect of the safe headway on the traffic system is considered. According to the control theory, the condition under which traffic jams can be suppressed is analyzed. The results are compared with the previous results concerning congestion control. The simulations show that the suppression performance of our scheme on traffic jams is better than those of the previous schemes, although all the schemes can suppress traffic jams. The simulation results are consistent with theoretical analyses.

  17. Haptic feedback control in medical robots through fractional viscoelastic tissue model.

    Science.gov (United States)

    Kobayashi, Yo; Moreira, Pedro; Liu, Chao; Poignet, Philippe; Zemiti, Nabil; Fujie, Masakatsu G

    2011-01-01

    In this paper, we discuss the design of an adaptive control system for robot-assisted surgery with haptic feedback. Through a haptic device, the surgeon teleoperates the medical instrument in free space, fixed on a remote robot or in contact. In free space, the surgeon feels the motion of the robot. In the present paper, we evaluated the performance of the controller on viscoelastic tissue, modeled by a fractional derivative equation. In addition, we propose a novel controller using an integer formalization process that is suitable for these tissue properties. The simulation results suggested that performance, in terms of force control and telepresence, became poorer when the conventional controller, which was designed for elastic target object, was applied to the viscoelastic tissues. In contrast, the results suggested that our proposed controller maintained its performance on the viscoelastic tissues.

  18. Temperature, geometry, and bifurcations in the numerical modeling of the cardiac mechano-electric feedback

    Science.gov (United States)

    Collet, A.; Bragard, J.; Dauby, P. C.

    2017-09-01

    This article characterizes the cardiac autonomous electrical activity induced by the mechanical deformations in the cardiac tissue through the mechano-electric feedback. A simplified and qualitative model is used to describe the system and we also account for temperature effects. The analysis emphasizes a very rich dynamics for the system, with periodic solutions, alternans, chaotic behaviors, etc. The possibility of self-sustained oscillations is analyzed in detail, particularly in terms of the values of important parameters such as the dimension of the system and the importance of the stretch-activated currents. It is also shown that high temperatures notably increase the parameter ranges for which self-sustained oscillations are observed and that several attractors can appear, depending on the location of the initial excitation of the system. Finally, the instability mechanisms by which the periodic solutions are destabilized have been studied by a Floquet analysis, which has revealed period-doubling phenomena and transient intermittencies.

  19. Optimum feedback strategy for access control mechanism modelled as stochastic differential equation in computer network

    Directory of Open Access Journals (Sweden)

    Ahmed N. U.

    2004-01-01

    Full Text Available We consider optimum feedback control strategy for computer communication network, in particular, the access control mechanism. The dynamic model representing the source and the access control system is described by a system of stochastic differential equations developed in our previous works. Simulated annealing (SA was used to optimize the parameters of the control law based on neural network. This technique was found to be computationally intensive. In this paper, we have proposed to use a more powerful algorithm known as recursive random search (RRS. By using this technique, we have been able to reduce the computation time by a factor of five without compromising the optimality. This is very important for optimization of high-dimensional systems serving a large number of aggregate users. The results show that the proposed control law can improve the network performance by improving throughput, reducing multiplexor and TB losses, and relaxing, not avoiding, congestion.

  20. Modeling 3D soil and sediment distributions for assessing catchment structure and hydrological feedbacks

    Science.gov (United States)

    Maurer, Thomas; Brück, Yasemine; Hinz, Christoph; Gerke, Horst H.

    2015-04-01

    . The established initial sediment distributions provide a basis for the consecutive modelling of feedbacks between surface and subsurface water flow and changes in soil properties, e.g. by using a landscape evolution model. The results should allow conclusions about the effect of different initial structural setups on the further dynamic landscape development at catchment scale.

  1. Towards a Model of Reactive-Cracking: the Role of Reactions, Elasticity and Surface Energy Driven Flow in Poro-elastic Media

    Science.gov (United States)

    Evans, O.; Spiegelman, M. W.; Wilson, C. R.; Kelemen, P. B.

    2016-12-01

    Many critical processes can be described by reactive fluid flow in brittle media, including hydration/alteration of oceanic plates near spreading ridges, chemical weathering, and dehydration/decarbonation of subducting plates. Such hydration reactions can produce volume changes that may induce stresses large enough to drive fracture in the rock, in turn exposing new reactive surface and modifying the permeability. A better understanding of this potentially rich feedback could also be critical in the design of engineered systems for geologic carbon sequestration. To aid understanding of these processes we have developed a macroscopic continuum description of reactive fluid flow in an elastically deformable porous media. We explore the behaviour of this model by considering a simplified hydration reaction (e.g. olivine + H20 -> serpentine + brucite). In a closed system, these hydration reactions will continue to consume available fluids until the permeability reaches zero, leaving behind it a highly stressed residuum. Our model demonstrates this limiting behaviour, and that the elastic stresses generated are large enough to cause failure/fracture of the host rock. Whilst it is understood that `reactive fracture' is an important mechanism for the continued evolution of this process, it is also proposed that imbibition/surface energy driven flow may play a role. Through a simplified set of computational experiments, we investigate the relative roles of elasticity and surface energy in both a non-reactive purely poro-elastic framework, and then in the presence of reaction. We demonstrate that surface energy can drive rapid diffusion of porosity, thus allowing the reaction to propagate over larger areas. As we expect both surface energy and fracture/failure to be of importance in these processes, we plan to integrate the current model into one that allows for fracture once critical stresses are exceeded.

  2. Low order modelling for feedback control of fluid flows around complex geometries

    Science.gov (United States)

    Dellar, Oliver; Jones, Bryn; Department of Automatic Control; Systems Engineering Collaboration

    2015-11-01

    The majority of goods transportation vehicles' power is consumed in overcoming aerodynamic drag. Reduction in pressure drag via feedback control could have significant economic and environmental effects on CO2 emissions, and reduce fatigue on the body by suppressing vortex shedding. The difficulty in designing such controllers lies in obtaining models suited to modern control design methods, which are necessarily of much lesser complexity than typical Computational Fluid Dynamics (CFD) models, or models derived from immediate spatial discretisation of the Navier-Stokes equations. This work develops an approach for modelling fluid flows using frequency response data generated for individual computational node sub-systems that result from a CFD type spatial discretisation of the governing equations. Input-to-sensor frequency response data for the overall system are then computed by forming interconnections between adjacent nodes via a Redheffer Star Product operation, from which one typically observes low-order dynamics. With this data, a low-order model can be identified and used for controller design. This method avoids manipulating large matrices and is therefore computationally efficient and numerically well-conditioned. It can be readily applied to complex geometry flows.

  3. PHT3D-UZF: A reactive transport model for variably-saturated porous media

    Science.gov (United States)

    Wu, Ming Zhi; Post, Vincent E. A.; Salmon, S. Ursula; Morway, Eric; Prommer, H.

    2016-01-01

    A modified version of the MODFLOW/MT3DMS-based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably-saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D-UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated-zone flow (UZF1) package. A volume-averaged approach similar to the method used in UZF-MT3DMS was adopted. The PHREEQC-based computation of chemical processes within PHT3D-UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional-scale applications, UZF1 simulates downward-only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably-saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.

  4. Adsorbed polyelectrolyte coatings decrease Fe(0) nanoparticle reactivity with TCE in water: conceptual model and mechanisms.

    Science.gov (United States)

    Phenrat, Tanapon; Liu, Yueqiang; Tilton, Robert D; Lowry, Gregory V

    2009-03-01

    The surfaces of reactive nanoscale zerovalent iron (NZVI) particles used for in situ groundwater remediation are modified with polymers or polyelectrolytes to enhance colloidal stability and mobility in the subsurface. However, surface modification decreases NZVI reactivity. Here, the TCE dechlorination rate and reaction products are measured as a function of adsorbed polyelectrolyte mass for three commercially available polyelectrolytes used for NZVI surface modification including poly(styrene sulfonate) (PSS), carboxymethyl cellulose (CMC), and polyaspartate (PAP). The adsorbed mass, extended layer thickness, and TCE-polyelectrolyte partition coefficient are measured and used to explain the effect of adsorbed polyelectrolyte on NZVI reactivity. For all modifiers, the dechlorination rate constant decreased nonlinearly with increasing surface excess, with a maximum of a 24-fold decrease in reactivity. The TCE dechlorination pathways were not affected. Consistent with Scheutjens-Fleer theory for homopolymer adsorption, the nonlinear relationship between the dechlorination rate and the surface excess of adsorbed polyelectrolyte suggests that adsorbed polyelectrolyte decreases reactivity primarily by blocking reactive surface sites at low surface excess where they adsorb relatively flat onto the NZVI surface, and by a combination of site blocking and decreasing the aqueous TCE concentration at the NZVI surface due to partitioning of TCE to adsorbed polyelectrolytes. This explanation is also consistent with the effect of adsorbed polyelectrolyte on acetylene formation. This conceptual model should apply to other medium and high molecular weight polymeric surface modifiers on nanoparticles, and potentially to adsorbed natural organic matter.

  5. Column Testing and 1D Reactive Transport Modeling to Evaluate Uranium Plume Persistence Processes

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Raymond H. [Navarro Research and Engineering, Inc.; Morrison, Stan [Navarro Research and Engineering, Inc.; Morris, Sarah [Navarro Research and Engineering, Inc.; Tigar, Aaron [Navarro Research and Engineering, Inc.; Dam, William [U.S. Department of Energy, Office of Legacy Management; Dayvault, Jalena [U.S. Department of Energy, Office of Legacy Management

    2016-04-26

    Motivation for Study: Natural flushing of contaminants at various U.S. Department of Energy Office of Legacy Management sites is not proceeding as quickly as predicted (plume persistence) Objectives: Help determine natural flushing rates using column tests. Use 1D reactive transport modeling to better understand the major processes that are creating plume persistence Approach: Core samples from under a former mill tailings area Tailings have been removed. Column leaching using lab-prepared water similar to nearby Gunnison River water. 1D reactive transport modeling to evaluate processes

  6. Impact of the Supervisor Feedback Environment on Creative Performance: A Moderated Mediation Model

    Science.gov (United States)

    Zhang, Jian; Gong, Zhenxing; Zhang, Shuangyu; Zhao, Yujia

    2017-01-01

    Studies on the relationship between feedback and creative performance have only focused on the feedback-self and have underestimated the value of the feedback environment. Building on Self Determined Theory, the purpose of this article is to examine the relationship among feedback environment, creative personality, goal self-concordance and creative performance. Hierarchical regression analysis of a sample of 162 supervisor–employee dyads from nine industry firms. The results indicate that supervisor feedback environment is positively related to creative performance, the relationship between the supervisor feedback environment and creative performance is mediated by goal self-concordance perfectly and moderated by creative personality significantly. The mediation effort of goal self-concordance is significantly influenced by creative personality. The implication of improving employees’ creative performance is further discussed. The present study advances several perspectives of previous studies, echoes recent suggestions that organizations interested in stimulating employee creativity might profitably focus on developing work contexts that support it. PMID:28275362

  7. In silico pharmacophore modeling on known pyridinium oxime reactivators of cyclosarin (GF) inhibited AChE to Aid discovery of potential, more efficacious novel non-oxime reactivators.

    Science.gov (United States)

    Bhattacharjee, Apurba K; Musilek, Kamil; Kuca, Kamil

    2013-09-01

    Cyclohexyl methylphosphonofluoridate (cyclosarin, cyclosin, GF) is a highly toxic organophosphorus (OP) nerve agent considered as potential warfare threats and known to be resistant to conventional oxime antidotal therapy. To aid discovery of novel antidotes for GF toxicity, a three-dimensional in silico pharmacophore model for reactivation efficacy against GF intoxication is presented. The model was generated from published experimental percentage reactivation data on oximes as changes of AChE/BuChE activities in the whole blood after cyclosarin intoxication and administration. The generated pharmacophore model was found to contain a hydrogen bond donor site and two ring aromatic sites as necessary optimal features for reactivation of GF intoxication. Stereo-electronic features of oximes reported by us earlier provided guidance to develop the model and were found to be consistent with the reported structure activity data. Furthermore, from virtual screening of two commercial databases, Maybridge and ChemNavigator using map-fitting of the model led us to identify two new non-oxime compounds showing reactivation efficacy within 10-fold range of 2-PAM for DFP-inhibited AChE. Since GF is a G simulator like DFP (diisopropylfluorophosphate), the model should have the potential for discovery of novel reactivators against GF intoxication.

  8. Coupled hydrogeological and reactive transport modelling of the Simpevarp area (Sweden)

    Energy Technology Data Exchange (ETDEWEB)

    Molinero, Jorge [Amphos XXI Consulting, S.L. Pg. de Rubi, 29-31, 08197 Valldoreix, Barcelona (Spain)], E-mail: jorge.molinero@amphos21.com; Raposo, Juan R.; Galindez, Juan M. [Escola Politecnica Superior, Universidade de Santiago de Compostela, Campus Universitario s/n, 27002 Lugo (Spain); Arcos, David; Guimera, Jordi [Amphos XXI Consulting, S.L. Pg. de Rubi, 29-31, 08197 Valldoreix, Barcelona (Spain)

    2008-07-15

    The Simpevarp area is one of the alternative sites being considered for the deep geological disposal of high level radioactive waste in Sweden. In this paper, a coupled regional groundwater flow and reactive solute transport model of the Simpevarp area is presented that integrates current hydrogeological and hydrochemical data of the area. The model simulates the current hydrochemical pattern of the groundwater system in the area. To that aim, a conceptual hydrochemical model was developed in order to represent the dominant chemical processes. Groundwater flow conditions were reproduced by taking into account fluid-density-dependent groundwater flow and regional hydrogeologic boundary conditions. Reactive solute transport calculations were performed on the basis of the velocity field so obtained. The model was calibrated and sensitivity analyses were carried out in order to investigate the effects of heterogeneities of hydraulic conductivity in the subsurface medium. Results provided by the reactive transport model are in good agreement with much of the measured hydrochemical data. This paper emphasizes the appropriateness of the use of reactive solute transport models when water-rock interaction reactions are involved, and demonstrates what powerful tools they are for the interpretation of hydrogeological and hydrochemical data from site geological repository characterization programs, by providing a qualitative framework for data analysis and testing of conceptual assumptions in a process-oriented approach.

  9. Modeling Of A Reactive Distillation Column: Methyl Tertiary Butyl Ether (Mtbe Simulation Studies

    Directory of Open Access Journals (Sweden)

    Ismail Mohd Saaid Abdul Rahman Mohamed and Subhash Bhatia

    2012-10-01

    Full Text Available A process simulation stage-wise reactive distillation column model formulated from equilibrium stage theory was developed. The algorithm for solving mathematical model represented by sets of differential-algebraic equations was based on relaxation method. Numerical integration scheme based on backward differentiation formula was selected for solving the stiffness of differential-algebraic equations. Simulations were performed on a personal computer (PC Pentium processor through a developed computer program using FORTRAN90 programming language. The proposed model was validated by comparing the simulated results with the published simulation results and with the pilot plant data from the literature. The model was capable of predicting high isobutene conversion for heterogeneous system, as desirable in industrial MTBE production process. The comparisons on temperature profiles, liquid composition profile and operating conditions of reactive distillation column also showed promising results. Therefore the proposed model can be used as a tool for the development and simulation of reactive distillation column.Keywords: Modeling, simulation, reactive distillation, relaxation method, equilibrium stage, heterogeneous, MTBE

  10. The importance of spatial resolution and convective parameterisation in modelling soil moisture - precipitation feedbacks

    Science.gov (United States)

    Garcia-Carreras, Luis; Taylor, Christopher M.; Roberts, Malcolm; Marsham, John H.

    2017-04-01

    Soil moisture influences low-level temperature and humidity, which can strongly affect convective development. The location of convection in turn alters the soil moisture anomalies present on the following day, providing a feedback mechanism. Satellite observations show that in the tropics afternoon rainfall falls preferentially where the ground is drier than its surroundings. A large number of global weather and climate models, on the other hand, show a positive soil moisture - rainfall feedback, inconsistent with observations. This systematic bias will tend to exaggerate drought impacts in global atmospheric models, and points to missing fundamental processes in the models related to the coupling between the surface and convection. While the source of this error is still unclear, it has been hypothesized that the triggering of parameterisations of convection is excessively sensitive to low-level moisture, leading to convection initiating preferentially over wet soils. Here we quantify the soil-moisture - precipitation feedback sign using the same method as in Taylor et al. (Nature, 2012), which is now part of the ESMValTool model evaluation toolbox. We analyse multi-year global simulations using the Met Office Unified Model (MetUM) with different resolutions and representations of convection. Three simulations are run at 15 km grid-spacing with different representations of convection: 1. the standard operational MetUM parameterisation scheme, 2. 'convection permitting', where the parameterisations of shallow and deep convection are turned off, and 3. only the parameterisation of shallow convection is turned on. The use of the same resolution and setup, except for the representation of convection, allows us to exclude any effects from changing resolution. Additional simulations at 30, 50 and 150 km grid-spacings using the standard MetUM parameterisation of convection scheme are then used to explore the impact of resolution. All simulations show daytime

  11. Nonspecific airway reactivity in a mouse model of asthma

    Energy Technology Data Exchange (ETDEWEB)

    Collie, D.D.; Wilder, J.A.; Bice, D.E.

    1995-12-01

    Animal models are indispensable for studies requiring an intact immune system, especially for studying the pathogenic mechanisms in atopic diseases, regulation of IgE production, and related biologic effects. Mice are particularly suitable and have been used extensively for such studies because their immune system is well characterized. Further, large numbers of mutants or inbred strains of mice are available that express deficiencies of individual immunologic processes, inflammatory cells, or mediator systems. By comparing reactions in such mice with appropriate control animals, the unique roles of individual cells or mediators may be characterized more precisely in the pathogenesis of atopic respiratory diseases including asthma. However, given that asthma in humans is characterized by the presence of airway hyperresponsiveness to specific and nonspecific stimuli, it is important that animal models of this disease exhibit similar physiologic abnormalities. In the past, the size of the mouse has limited its versatility in this regard. However, recent studies indicate the feasibility of measuring pulmonary responses in living mice, thus facilitating the physiologic evaluation of putative mouse models of human asthma that have been well charcterized at the immunologic and patholigic level. Future work will provide details of the morphometry of the methacholine-induced bronchoconstriction and will further seek to determine the relationship between cigarette smoke exposure and the development of NS-AHR in the transgenic mouse model.

  12. Supervisor Feedback.

    Science.gov (United States)

    Hayman, Marilyn J.

    1981-01-01

    Investigated the effectiveness of supervisor feedback in contributing to learning counseling skills. Counselor trainees (N=64) were assigned to supervisor feedback, no supervisor feedback, or control groups for three training sessions. Results indicated counseling skills were learned best by students with no supervisor feedback but self and peer…

  13. Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows

    Energy Technology Data Exchange (ETDEWEB)

    Magnussen, B.F. [The Norwegian Univ. of Science and Technology, Trondheim (Norway)

    1997-12-31

    The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.

  14. Surrogate model approach for improving the performance of reactive transport simulations

    Science.gov (United States)

    Jatnieks, Janis; De Lucia, Marco; Sips, Mike; Dransch, Doris

    2016-04-01

    Reactive transport models can serve a large number of important geoscientific applications involving underground resources in industry and scientific research. It is common for simulation of reactive transport to consist of at least two coupled simulation models. First is a hydrodynamics simulator that is responsible for simulating the flow of groundwaters and transport of solutes. Hydrodynamics simulators are well established technology and can be very efficient. When hydrodynamics simulations are performed without coupled geochemistry, their spatial geometries can span millions of elements even when running on desktop workstations. Second is a geochemical simulation model that is coupled to the hydrodynamics simulator. Geochemical simulation models are much more computationally costly. This is a problem that makes reactive transport simulations spanning millions of spatial elements very difficult to achieve. To address this problem we propose to replace the coupled geochemical simulation model with a surrogate model. A surrogate is a statistical model created to include only the necessary subset of simulator complexity for a particular scenario. To demonstrate the viability of such an approach we tested it on a popular reactive transport benchmark problem that involves 1D Calcite transport. This is a published benchmark problem (Kolditz, 2012) for simulation models and for this reason we use it to test the surrogate model approach. To do this we tried a number of statistical models available through the caret and DiceEval packages for R, to be used as surrogate models. These were trained on randomly sampled subset of the input-output data from the geochemical simulation model used in the original reactive transport simulation. For validation we use the surrogate model to predict the simulator output using the part of sampled input data that was not used for training the statistical model. For this scenario we find that the multivariate adaptive regression splines

  15. A modeling investigation of the Arctic sea ice-atmosphere feedback

    Science.gov (United States)

    Liptak, Jessica; Strong, Courtenay

    2016-10-01

    We examine the effects of a general sea ice-atmosphere feedback (SAF) over the Barents Sea by turning it on and off in a coupled climate model. The SAF is "turned off" by forcing the atmosphere with surface turbulent and longwave heat fluxes and surface temperatures that reflect climatological sea ice cover over the Barents Sea, while allowing the sea ice and sea surface temperature (SST) to freely evolve. Suppressing the SAF reduces the variability of near-surface air temperature ( T), sea ice concentration ( I) , and SST averaged over the Barents Sea by up to 35 %, confirming the existence of a positive thermodynamically-driven SAF found in prior uncoupled modeling studies. Decreased interannual variability accounts for most of the total reduction in I, T, and SST variability, and the largest reductions in variability occur during the winter sea ice growth and spring melt seasons. In contrast to the results from the coupled model experiment, the total variances of I, T, and SST do not significantly change in response to suppressing the SAF in a simple vector autoregressive model, indicating that the SAF is nonlinear.

  16. Benchmarking a Visual-Basic based multi-component one-dimensional reactive transport modeling tool

    Science.gov (United States)

    Torlapati, Jagadish; Prabhakar Clement, T.

    2013-01-01

    We present the details of a comprehensive numerical modeling tool, RT1D, which can be used for simulating biochemical and geochemical reactive transport problems. The code can be run within the standard Microsoft EXCEL Visual Basic platform, and it does not require any additional software tools. The code can be easily adapted by others for simulating different types of laboratory-scale reactive transport experiments. We illustrate the capabilities of the tool by solving five benchmark problems with varying levels of reaction complexity. These literature-derived benchmarks are used to highlight the versatility of the code for solving a variety of practical reactive transport problems. The benchmarks are described in detail to provide a comprehensive database, which can be used by model developers to test other numerical codes. The VBA code presented in the study is a practical tool that can be used by laboratory researchers for analyzing both batch and column datasets within an EXCEL platform.

  17. A Novel Lattice Boltzmann Model For Reactive Flows with Fast Chemistry

    Institute of Scientific and Technical Information of China (English)

    CHEN Sheng; LIU Zhao-Hui; HE Zhu; ZHANG Chao; TIAN Zhi-Wei; SHI Bao-Chang; ZHENG Chu-Guang

    2006-01-01

    @@ A novel lattice Boltzmann model, in which we take the ratio of temperature difference in the temperature field to the environment one to be more than one order of magnitude than before, is developed to simulate two dimensional reactive flows with fast chemistry. Different from the hybrid scheme for reactive flows [Comput.Phys. Commun. 129 (2000)267], this scheme is strictly in a pure lattice Boltzmann style (i.e., we solve the flow, temperature, and concentration fields using the lattice Boltzmann method only). Different from the recent non-coupled lattice Boltzmann scheme [Int. J. Mod. Phys. B 17(2003) 197], the fluid density in our model is coupled directly with the temperature. Excellent agreement between the present results and other numerical data shows that this scheme is an efficient numerical method for practical reactive flows with fast chemistry.

  18. SeSBench - An initiative to benchmark reactive transport models for environmental subsurface processes

    Science.gov (United States)

    Jacques, Diederik

    2017-04-01

    As soil functions are governed by a multitude of interacting hydrological, geochemical and biological processes, simulation tools coupling mathematical models for interacting processes are needed. Coupled reactive transport models are a typical example of such coupled tools mainly focusing on hydrological and geochemical coupling (see e.g. Steefel et al., 2015). Mathematical and numerical complexity for both the tool itself or of the specific conceptual model can increase rapidly. Therefore, numerical verification of such type of models is a prerequisite for guaranteeing reliability and confidence and qualifying simulation tools and approaches for any further model application. In 2011, a first SeSBench -Subsurface Environmental Simulation Benchmarking- workshop was held in Berkeley (USA) followed by four other ones. The objective is to benchmark subsurface environmental simulation models and methods with a current focus on reactive transport processes. The final outcome was a special issue in Computational Geosciences (2015, issue 3 - Reactive transport benchmarks for subsurface environmental simulation) with a collection of 11 benchmarks. Benchmarks, proposed by the participants of the workshops, should be relevant for environmental or geo-engineering applications; the latter were mostly related to radioactive waste disposal issues - excluding benchmarks defined for pure mathematical reasons. Another important feature is the tiered approach within a benchmark with the definition of a single principle problem and different sub problems. The latter typically benchmarked individual or simplified processes (e.g. inert solute transport, simplified geochemical conceptual model) or geometries (e.g. batch or one-dimensional, homogeneous). Finally, three codes should be involved into a benchmark. The SeSBench initiative contributes to confidence building for applying reactive transport codes. Furthermore, it illustrates the use of those type of models for different

  19. On Numerical Considerations for Modeling Reactive Astrophysical Shocks

    CERN Document Server

    Papatheodore, Thomas L

    2013-01-01

    Simulating detonations in astrophysical environments is often complicated by numerical approximations to shock structure. A common prescription to ensure correct detonation speeds and associated quantities is to prohibit burning inside the numerically broadened shock (Fryxell et al. 1989). We have performed a series of simulations to verify the efficacy of this approximation and to understand how resolution and dimensionality might affect its use. Our results show that, in one dimension, prohibiting burning in the shock is important wherever the carbon burning length is not resolved, in keeping with the results of Fryxell et al. (1989). In two dimensions, we find that the prohibition of shock burning effectively inhibits the development of cellular structure for all but the most highly-resolved cases. We discuss the possible impacts this outcome may have on sub-grid models and detonation propagation in models of Type Ia supernovae, including potential impacts on observables.

  20. Reactive Aggregate Model Protecting Against Real-Time Threats

    Science.gov (United States)

    2014-09-01

    SQL server and has four tables: Accumulator, BlockState, Epoc , Signature, and Weight. Accumulator columns were RemoteIP, Test1, Test2, Test3 and Time...block occurred. The Epoc table was a pivot necessary to convert the time stamps to Epoch time format. The Signature table held values indicative of...processing unit” of the RAMPART Figure 6. model. The RAMPART database exists on a Windows SQL server and has four tables: Accumulator, BlockState, Epoc

  1. Smoothed Particle Hydrodynamics Model for Reactive Transport and Mineral Precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Tartakovsky, Alexandre M.; Scheibe, Timothy D.; Redden, George; Meakin, Paul; Fang, Yilin

    2006-06-30

    A new Lagrangian particle model based on smoothed particle hydrodynamics was used to simulate pore scale precipitation reactions. The side-by-side injection of reacting solutions into two halves of a two-dimensional granular porous medium was simulated. Precipitation on grain surfaces occurred along a narrow zone in the middle of the domain, where the reacting solutes mixed to generate a supersaturated reaction product. The numerical simulations qualitatively reproduced the behavior observed in related laboratory experiments.

  2. Modeling the surface tension of complex, reactive organic-inorganic mixtures

    Science.gov (United States)

    Schwier, A. N.; Viglione, G. A.; Li, Z.; McNeill, V. Faye

    2013-11-01

    Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as heterogeneous reactivity, ice nucleation, and cloud droplet formation. We present new experimental data for the surface tension of complex, reactive organic-inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2-6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two semi-empirical surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well described by a weighted Szyszkowski-Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling of aerosol systems because the Henning model (using data obtained from organic-inorganic systems) and Tuckermann approach provide similar modeling results and goodness-of-fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

  3. Modelling nitrite dynamics and associated feedback processes in the Benguela oxygen minimum zone

    Science.gov (United States)

    Mashifane, T. B.; Vichi, M.; Waldron, H. N.; Machu, E.; Garçonc, V.

    2016-08-01

    Understanding nitrite dynamics in oxygen minimum zones (OMZs) is a challenge as it represents an intermediary nitrogen species with a short turnover time. Nitrite is also reduced to nitrogen in OMZs, preventing its accumulation. This creates difficulties in detecting nitrite with colorimetric methods as concentrations may occur below detection limits in some regions. Nitrite concentrations are key to understanding intermediate nitrogen processes and their implication for nitrogen loss in OMZs. A coupled physical-biogeochemical model is applied in the Benguela OMZ to study nitrite dynamics and its associated feedback processes. Simulated results show occurrence of primary and secondary nitrite maxima in the Benguela shelf waters. The primary nitrite maxima in the Benguela are attributed to nitrification and nitrate assimilation as they occur in association with the nitracline. Secondary nitrite maxima accumulate in the Angola-Benguela Front (ABF) OMZ and are attributed to denitrification. The secondary nitrite maxima are consumed by anaerobic ammonium oxidation (anammox) off Walvis Bay. Nitrite maxima are restricted to the shelf off Walvis Bay and advected offshore in the ABF region. Interchanges between the poleward South Atlantic Central Water (SACW) and the equatorward, well-aerated Eastern South Atlantic Central Water (ESACW) drive the seasonality of nitrogen processes in the Benguela. Subsequent nitrite reduction in the Benguela OMZ leads to nitrous oxide production, with high concentrations occurring in the ABF region as a result of nitrification and denitrification. Off Walvis Bay, nitrous oxide production is low since nitrite is consumed by anammox. Nitrous oxide production occurs in thermocline, intermediate and deeper water masses in the ABF region. High N fluxes in the Benguela are attributed to nitrification as compared to anammox and denitrification. Results from this study demonstrate the role of intermediate nitrogen species in nitrogen feedback

  4. Cloud and circulation feedbacks in a near-global aquaplanet cloud-resolving model

    Science.gov (United States)

    Narenpitak, Pornampai; Bretherton, Christopher S.; Khairoutdinov, Marat F.

    2017-06-01

    A near-global aquaplanet cloud-resolving model (NGAqua) with fixed meridionally varying sea-surface temperature (SST) is used to investigate cloud feedbacks due to three climate perturbations: a uniform 4 K SST increase, a quadrupled-CO2 concentration, and both combined. NGAqua has a horizontal resolution of 4 km with no cumulus parameterization. Its domain is a zonally periodic 20,480 km-long tropical channel, spanning 46°S-N. It produces plausible mean distributions of clouds, rainfall, and winds. After spin-up, 80 days are analyzed for the control and increased-SST simulations, and 40 days for those with quadrupled CO2. The Intertropical Convergence Zone width and tropical cloud cover are not strongly affected by SST warming or CO2 increase, except for the expected upward shift in high clouds with warming, but both perturbations weaken the Hadley circulation. Increased SST induces a statistically significant increase in subtropical low cloud fraction and in-cloud liquid water content but decreases midlatitude cloud, yielding slightly positive domain-mean shortwave cloud feedbacks. CO2 quadrupling causes a slight shallowing and a statistically insignificant reduction of subtropical low cloud fraction. Warming-induced low cloud changes are strongly correlated with changes in estimated inversion strength, which increases modestly in the subtropics but decreases in the midlatitudes. Enhanced clear-sky boundary layer radiative cooling in the warmer climate accompanies the robust subtropical low cloud increase. The probability distribution of column relative humidity across the tropics and subtropics is compared between the control and increased-SST simulations. It shows no evidence of bimodality or increased convective aggregation in a warmer climate.

  5. Multi-scale modeling of multi-component reactive transport in geothermal aquifers

    Science.gov (United States)

    Nick, Hamidreza M.; Raoof, Amir; Wolf, Karl-Heinz; Bruhn, David

    2014-05-01

    In deep geothermal systems heat and chemical stresses can cause physical alterations, which may have a significant effect on flow and reaction rates. As a consequence it will lead to changes in permeability and porosity of the formations due to mineral precipitation and dissolution. Large-scale modeling of reactive transport in such systems is still challenging. A large area of uncertainty is the way in which the pore-scale information controlling the flow and reaction will behave at a larger scale. A possible choice is to use constitutive relationships relating, for example the permeability and porosity evolutions to the change in the pore geometry. While determining such relationships through laboratory experiments may be limited, pore-network modeling provides an alternative solution. In this work, we introduce a new workflow in which a hybrid Finite-Element Finite-Volume method [1,2] and a pore network modeling approach [3] are employed. Using the pore-scale model, relevant constitutive relations are developed. These relations are then embedded in the continuum-scale model. This approach enables us to study non-isothermal reactive transport in porous media while accounting for micro-scale features under realistic conditions. The performance and applicability of the proposed model is explored for different flow and reaction regimes. References: 1. Matthäi, S.K., et al.: Simulation of solute transport through fractured rock: a higher-order accurate finite-element finite-volume method permitting large time steps. Transport in porous media 83.2 (2010): 289-318. 2. Nick, H.M., et al.: Reactive dispersive contaminant transport in coastal aquifers: Numerical simulation of a reactive Henry problem. Journal of contaminant hydrology 145 (2012), 90-104. 3. Raoof A., et al.: PoreFlow: A Complex pore-network model for simulation of reactive transport in variably saturated porous media, Computers & Geosciences, 61, (2013), 160-174.

  6. Feedback control strategies for spatial navigation revealed by dynamic modelling of learning in the Morris water maze.

    Science.gov (United States)

    Fey, Dirk; Commins, Sean; Bullinger, Eric

    2011-04-01

    The Morris water maze is an experimental procedure in which animals learn to escape swimming in a pool using environmental cues. Despite its success in neuroscience and psychology for studying spatial learning and memory, the exact mnemonic and navigational demands of the task are not well understood. Here, we provide a mathematical model of rat swimming dynamics on a behavioural level. The model consists of a random walk, a heading change and a feedback control component in which learning is reflected in parameter changes of the feedback mechanism. The simplicity of the model renders it accessible and useful for analysis of experiments in which swimming paths are recorded. Here, we used the model to analyse an experiment in which rats were trained to find the platform with either three or one extramaze cue. Results indicate that the 3-cues group employs stronger feedback relying only on the actual visual input, whereas the 1-cue group employs weaker feedback relying to some extent on memory. Because the model parameters are linked to neurological processes, identifying different parameter values suggests the activation of different neuronal pathways.

  7. Return of target material ions leads to a reduced hysteresis in reactive high power impulse magnetron sputtering: Model

    Science.gov (United States)

    Kadlec, Stanislav; Čapek, Jiří

    2017-05-01

    A tendency to disappearing hysteresis in reactive High Power Impulse Magnetron Sputtering (HiPIMS) has been reported previously without full physical explanation. An analytical model of reactive pulsed sputtering including HiPIMS is presented. The model combines a Berg-type model of reactive sputtering with the global HiPIMS model of Christie-Vlček. Both time and area averaging is used to describe the macroscopic steady state, especially the reactive gas balance in the reactor. The most important effect in the presented model is covering of reacted parts of target by the returning ionized metal, effectively lowering the target coverage by reaction product at a given partial pressure. The return probability of ionized sputtered metal has been selected as a parameter to quantify the degree of HiPIMS effects. The model explains the reasons for reduced hysteresis in HiPIMS. The critical pumping speed was up to a factor of 7 lower in reactive HiPIMS compared to the mid-frequency magnetron sputtering. The model predicts reduced hysteresis in HiPIMS due to less negative slope of metal flux to substrates and of reactive gas sorption as functions of reactive gas partial pressure. Higher deposition rate of reactive HiPIMS compared to standard reactive sputtering is predicted for some parameter combinations. Comparison of the model with experiment exhibits good qualitative and quantitative agreement for three material combinations, namely, Ti-O2, Al-O2, and Ti-N2.

  8. A phase plane graph based model of the ovulatory cycle lacking the "positive feedback" phenomenon

    Directory of Open Access Journals (Sweden)

    Kurbel Sven

    2012-08-01

    Full Text Available Abstract When hormones during the ovulatory cycle are shown in phase plane graphs, reported FSH and estrogen values form a specific pattern that resembles the leaning “&" symbol, while LH and progesterone (Pg values form a "boomerang" shape. Graphs in this paper were made using data reported by Stricker et al. [Clin Chem Lab Med 2006;44:883–887]. These patterns were used to construct a simplistic model of the ovulatory cycle without the conventional "positive feedback" phenomenon. The model is based on few well-established relations: hypothalamic GnRH secretion is increased under estrogen exposure during two weeks that start before the ovulatory surge and lasts till lutheolysis. the pituitary GnRH receptors are so prone to downregulation through ligand binding that this must be important for their function. in several estrogen target tissue progesterone receptor (PgR expression depends on previous estrogen binding to functional estrogen receptors (ER, while Pg binding to the expressed PgRs reduces both ER and PgR expression. Some key features of the presented model are here listed: High GnRH secretion induced by the recovered estrogen exposure starts in the late follicular phase and lasts till lutheolysis. The LH and FSH surges start due to combination of accumulated pituitary GnRH receptors and increased GnRH secretion. The surges quickly end due to partial downregulation of the pituitary GnRH receptors (64% reduction of the follicular phase pituitary GnRH receptors is needed to explain the reported LH drop after the surge. A strong increase in the lutheal Pg blood level, despite modest decline in LH levels, is explained as delayed expression of pituitary PgRs. Postponed pituitary PgRs expression enforces a negative feedback loop between Pg levels and LH secretions not before the mid lutheal phase. Lutheolysis is explained as a consequence of Pg binding to hypothalamic and pituitary PgRs that reduces local ER expression. When hypothalamic

  9. Extracting the invariant model from the feedback paths of digital hearing aids

    DEFF Research Database (Denmark)

    Ma, Guilin; Gran, Fredrik; Jacobsen, Finn;

    2011-01-01

    Feedback whistling is a severe problem with hearing aids. A typical acoustical feedback path represents a wave propagation path from the receiver to the microphone and includes many complicated effects among which some are invariant or nearly invariant for all users and in all acoustical environm...

  10. Attitudes towards Online Feedback on Writing: Why Students Mistrust the Learning Potential of Models

    Science.gov (United States)

    Strobl, Carola

    2015-01-01

    This exploratory study sheds new light on students' perceptions of online feedback types for a complex writing task, summary writing from spoken input in a foreign language (L2), and investigates how these correlate with their actual learning to write. Students tend to favour clear-cut, instructivist rather than constructivist feedback, and guided…

  11. Effects of Training and Coaching with Performance Feedback on Teachers' Use of "Pyramid Model" Practices

    Science.gov (United States)

    Hemmeter, Mary Louise; Hardy, Jessica K.; Schnitz, Alana G.; Adams, Jessie Morris; Kinder, Kiersten A.

    2015-01-01

    Training and coaching with performance feedback has been effective for supporting teachers to use evidence-based instructional practices. However, coaching with performance feedback has primarily been used to support teachers to use discrete skills, and there has been little evidence of maintenance and generalization. The purpose of this study was…

  12. Mathematical model of SPOC with a time dependent reactive field

    Energy Technology Data Exchange (ETDEWEB)

    Ohtaki, Masako [Department of Physics, School of Science and Engineering, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555 (Japan)

    2006-03-21

    In general the muscle is in one of the two state possible states, relaxation or contraction. These contractions result from relative sliding of myosin and actin in the sarcomere, which is the contraction structure unit of skeletal muscle. The switching between two states is depending on the Ca2{sup +} concentrations. However another state has been detected between these two states. In the third state, that is SPontaneous Oscillatory Contraction (SPOC), sarcomere repeats contraction and extension spontaneously. Muscle fibers are composed of hundreds of sarcomeres in series and one sarcomea also is composed of hundreds of myosin. In microscopic, the force generated by actin and myosin interaction occurs stochastically. SPOC, however, is macroscopically observable and there are regular oscillations. To understand SPOC mechanism, we propose a model for SPOC based on chemical reaction including mechanical process.

  13. Mathematical model of SPOC with a time dependent reactive field

    Science.gov (United States)

    Ohtaki, Masako

    2006-03-01

    In general the muscle is in one of the two state possible states, relaxation or contraction. These contractions result from relative sliding of myosin and actin in the sarcomere, which is the contraction structure unit of skeletal muscle. The switching between two states is depending on the Ca2+ concentrations. However another state has been detected between these two states. In the third state, that is SPontaneous Oscillatory Contraction (SPOC), sarcomere repeats contraction and extension spontaneously. Muscle fibers are composed of hundreds of sarcomeres in series and one sarcomea also is composed of hundreds of myosin. In microscopic, the force generated by actin and myosin interaction occurs stochastically. SPOC, however, is macroscopically observable and there are regular oscillations. To understand SPOC mechanism, we propose a model for SPOC based on chemical reaction including mechanical process.

  14. The effect of reactive power generation modeling on voltage stability analysis

    Energy Technology Data Exchange (ETDEWEB)

    Tovar, E.; Guizar, J.G.C. [Inst. de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)

    2010-08-13

    One of the most significant concerns for power system planning and operation in many countries involves problems related to voltage instability in electrical power systems. Blackouts have been caused by voltage instability problems throughout the world during the last few decades. Several factors can contribute to long term voltage instability problems, including high active and reactive loading, operation of on load tap changer transformers, inadequate locally available reactive power resources, load characteristics at low voltage magnitudes and operation of relay protection. There is a significant need to evaluate an index which gives the operating point proximity to voltage instability. This paper examined the influence of generator voltage dependent reactive power production on system voltage stability using the minimum singular value from the Jacobian Matrix of the load flow formulation. The synchronous generator model considered voltage reactive power limits due to maximum armature current, maximum and minimum field current as well as under excitation limiters. The generation model used in this paper was included in an ordinary load flow program, and resulted from studies of a representative 62 bus Norwest control area Mexican system, which included 19 generators. Specifically, the paper discussed the generator model with particular reference to the maximum field current limit; armature current limit; minimum field current limit; and underexcitation limit. The singular value decomposition and computational results were also presented. It was concluded that as the loading of the system increases, the reactive power produced by the machines also increases, and that reactive power is delivered when the induced voltage is greater than the terminal voltage. 15 refs., 3 tabs., 2 figs.

  15. Inferential modeling and predictive feedback control in real-time motion compensation using the treatment couch during radiotherapy.

    Science.gov (United States)

    Qiu, Peng; D'Souza, Warren D; McAvoy, Thomas J; Ray Liu, K J

    2007-10-07

    Tumor motion induced by respiration presents a challenge to the reliable delivery of conformal radiation treatments. Real-time motion compensation represents the technologically most challenging clinical solution but has the potential to overcome the limitations of existing methods. The performance of a real-time couch-based motion compensation system is mainly dependent on two aspects: the ability to infer the internal anatomical position and the performance of the feedback control system. In this paper, we propose two novel methods for the two aspects respectively, and then combine the proposed methods into one system. To accurately estimate the internal tumor position, we present partial-least squares (PLS) regression to predict the position of the diaphragm using skin-based motion surrogates. Four radio-opaque markers were placed on the abdomen of patients who underwent fluoroscopic imaging of the diaphragm. The coordinates of the markers served as input variables and the position of the diaphragm served as the output variable. PLS resulted in lower prediction errors compared with standard multiple linear regression (MLR). The performance of the feedback control system depends on the system dynamics and dead time (delay between the initiation and execution of the control action). While the dynamics of the system can be inverted in a feedback control system, the dead time cannot be inverted. To overcome the dead time of the system, we propose a predictive feedback control system by incorporating forward prediction using least-mean-square (LMS) and recursive least square (RLS) filtering into the couch-based control system. Motion data were obtained using a skin-based marker. The proposed predictive feedback control system was benchmarked against pure feedback control (no forward prediction) and resulted in a significant performance gain. Finally, we combined the PLS inference model and the predictive feedback control to evaluate the overall performance of the

  16. Model-data integration for predictive assessment of groundwater reactive transport systems

    NARCIS (Netherlands)

    Carniato, L.

    2014-01-01

    Predicting the evolution of groundwater contamination is a major concern for society, in particular when investments are made to remediate the contamination. Groundwater reactive transport models are valuable tools to integrate the available measurements in a consistent framework, improving our unde

  17. A Conceptual Framework for Predicting the Toxicity of Reactive Chemicals: Modeling Soft Electrophilicity

    Science.gov (United States)

    Although the literature is replete with QSAR models developed for many toxic effects caused by reversible chemical interactions, the development of QSARs for the toxic effects of reactive chemicals lacks a consistent approach. While limitations exit, an appropriate starting-point...

  18. Coupled continuum modeling of fracture reactivation and induced seismicity during enhanced geothermal operations

    NARCIS (Netherlands)

    Wassing, B.B.T.; Wees, J.D. van; Fokker, P.A.

    2012-01-01

    We developed a coupled code to obtain a better understanding of the role of pore pressure changes in causing fracture reactivation and seismicity during EGS. We implemented constitutive models for fractures in a continuum approach, which is advantageous because of the ease of integration in existing

  19. A Conceptual Framework for Predicting the Toxicity of Reactive Chemicals: Modeling Soft Electrophilicity

    Science.gov (United States)

    Although the literature is replete with QSAR models developed for many toxic effects caused by reversible chemical interactions, the development of QSARs for the toxic effects of reactive chemicals lacks a consistent approach. While limitations exit, an appropriate starting-point...

  20. Abiotic/biotic coupling in the rhizosphere: a reactive transport modeling analysis

    Science.gov (United States)

    Lawrence, Corey R.; Steefel, Carl; Maher, Kate

    2014-01-01

    A new generation of models is needed to adequately simulate patterns of soil biogeochemical cycling in response changing global environmental drivers. For example, predicting the influence of climate change on soil organic matter storage and stability requires models capable of addressing complex biotic/abiotic interactions of rhizosphere and weathering processes. Reactive transport modeling provides a powerful framework simulating these interactions and the resulting influence on soil physical and chemical characteristics. Incorporation of organic reactions in an existing reactive transport model framework has yielded novel insights into soil weathering and development but much more work is required to adequately capture root and microbial dynamics in the rhizosphere. This endeavor provides many advantages over traditional soil biogeochemical models but also many challenges.

  1. Persistence of soil organic matter as an ecosystem property: implications for experiments, feedbacks, and modeling

    Science.gov (United States)

    Schmidt, M. W.; Torn, M. S.

    2012-12-01

    Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to land use or climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we summarize recent understanding and propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming. Numerical models of soil carbon cycling are used to attribute carbon sources and sinks, predict climate-ecosystem feedbacks, and evaluate biofuel and sequestration strategies. Current ecosystem models rest heavily on the concept of recalcitrance and most models partition plant input into pools of different turnover time solely on the basis of plant tissue chemistry. However, recent research enabled by isotopic, spectroscopic, and molecular marker tools finds little evidence that recalcitrance or selective preservation determine the long residence time of SOM. Without the assumption that recalcitrance or molecular structure control decomposition rates, the framework of these models is no longer justified. Some improvements can be made easily; in other areas, research is needed to translate recent findings into new parameters, for example, to predict the effect of organo-mineral interactions and soil depth on decomposition rates. In this presentation, we will describe a new view of soil carbon cycling that is consistent with the new generation of observations, discuss suggested improvements to soil carbon models, and explore the implications for the vulnerability of soil organic carbon.

  2. Active tilting-pad journal bearings supporting flexible rotors: Part II–The model-based feedback-controlled lubrication

    DEFF Research Database (Denmark)

    Salazar, Jorge Andrés González; Santos, Ilmar

    2017-01-01

    This is part II of a twofold paper series dealing with the design and implementation of model-based controllers meant for assisting the hybrid and developing the feedback-controlled lubrication regimes in active tilting pad journal bearings (active TPJBs). In both papers theoretical and experimen......This is part II of a twofold paper series dealing with the design and implementation of model-based controllers meant for assisting the hybrid and developing the feedback-controlled lubrication regimes in active tilting pad journal bearings (active TPJBs). In both papers theoretical...... and experimental analyses are presented with focus on the reduction of rotor lateral vibration. This part is devoted to synthesising model-based LQG optimal controllers (LQR regulator + Kalman Filter) for the feedback-controlled lubrication and is based upon the mathematical model of the rotor-bearing system...... derived in part I. Results show further suppression of resonant vibrations when using the feedback-controlled or active lubrication, overweighting the reduction already achieved with hybrid lubrication, thus improving the whole machine dynamic performance....

  3. Mobile Voting Systems for Creating Collaboration Environments and Getting Immediate Feedback: A New Curriculum Model of a University Lecture

    Science.gov (United States)

    Titova, Svetlana; Talmo, Tord

    2014-01-01

    Mobile devices can enhance learning and teaching by providing instant feedback and better diagnosis of learning problems, helping design new assessment models, enhancing learner autonomy and creating new formats of enquiry-based activities. The objective of this paper is to investigate the pedagogical impact of mobile voting tools. The authors'…

  4. Effects of two types of intra-team feedback on developing a shared mental model in Command & Control teams

    NARCIS (Netherlands)

    Rasker, P.C.; Post, W.M.; Schraagen, J.M.C.

    2000-01-01

    In two studies, the effect of two types of intra-team feedback on developing a shared mental model in Command & Control teams was investigated. A distinction is made between performance monitoring and team self-correction. Performance monitoring is the ability of team members to monitor each other's

  5. Effects of two types of intra-team feedback on developing a shared mental model in Command & Control teams

    NARCIS (Netherlands)

    Rasker, P.C.; Post, W.M.; Schraagen, J.M.C.

    2000-01-01

    In two studies, the effect of two types of intra-team feedback on developing a shared mental model in Command & Control teams was investigated. A distinction is made between performance monitoring and team self-correction. Performance monitoring is the ability of team members to monitor each other's

  6. Mobile Voting Systems for Creating Collaboration Environments and Getting Immediate Feedback: A New Curriculum Model of a University Lecture

    Science.gov (United States)

    Titova, Svetlana; Talmo, Tord

    2014-01-01

    Mobile devices can enhance learning and teaching by providing instant feedback and better diagnosis of learning problems, helping design new assessment models, enhancing learner autonomy and creating new formats of enquiry-based activities. The objective of this paper is to investigate the pedagogical impact of mobile voting tools. The authors'…

  7. Chemical modelling of Alkali Silica reaction: Influence of the reactive aggregate size distribution

    Energy Technology Data Exchange (ETDEWEB)

    Poyet, S. [CEA Saclay, DEN/DANS/DPC/SCCME/LECBA, F-91191 Gif Sur Yvette, (France); Sellier, A. [UPS, LMDC, INSA Toulouse, F-33077 Bordeaux 4, (France); Capra, B. [Oxand SA, F-77210 Avon (France); Foray, G. [Univ Lyon 1, L2MS, PETRA GC, F-69622 Villeurbanne (France); Torrenti, J.M. [IRSN, F-92262 Fontenay Aux Roses (France); Cognon, H. [EdF/DER Les Renardieres, F-77818 Moret Sur Loing (France); Bourdarot, E. [CIH Savoie Technolac, F-73373 Le Bourget du Lac (France)

    2007-07-01

    This article presents a new model which aims at predicting the expansion induced by Alkali Silica Reaction (ASR) and describing the chemical evolution of affected concretes. It is based on the description of the transport and reaction of alkalis and calcium ions within a Relative Elementary Volume (REV). It takes into account the influence of the reactive aggregate size grading on ASR, i.e. the effect of the simultaneous presence of different sized reactive aggregates within concrete. The constitutive equations are detailed and fitted using experimental results. Results from numerical simulations are presented and compared with experiments. (authors)

  8. Stability analysis in a car-following model with reaction-time delay and delayed feedback control

    Science.gov (United States)

    Jin, Yanfei; Xu, Meng

    2016-10-01

    The delayed feedback control in terms of both headway and velocity differences has been proposed to guarantee the stability of a car-following model including the reaction-time delay of drivers. Using Laplace transformation and transfer function, the stable condition is derived and appropriate choices of time delay and feedback gains are designed to stabilize traffic flow. Meanwhile, an upper bound on explicit time delay is determined with respect to the response of desired acceleration. To ensure the string stability, the explicit time delay cannot over its upper bound. Numerical simulations indicate that the proposed control method can restraint traffic congestion and improve control performance.

  9. Structural models of vanadate-dependent haloperoxidases and their reactivity

    Indian Academy of Sciences (India)

    Mannar R Maurya

    2006-11-01

    Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent haloperoxidases have been reported. On reaction with [VO(acac)2] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to give oxovanadium(V), dioxovanadium (V) or -oxobis{oxovanadium(V)} species depending upon the nature of the ligand. Anionic and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The anionic complexes [VO2(ONO)]- can also be converted in situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]+ and to peroxo complexes [VO(O2)(ONO)]-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol (H2cat) and benzohydroxamic acid (H2bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)] respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO2(ONN)] as observed by 51V NMR and electronic absorption spectroscopic studies.

  10. The Use of Models as a Form of Written Feedback to Secondary School Pupils of English

    Directory of Open Access Journals (Sweden)

    Noelia Martínez Esteban

    2010-12-01

    Full Text Available El objetivo de este estudio es investigar la relación entre atención, escritura y feedback durante la redacción individual y colaborativa de textos en inglés como lengua extranjera. Los participantes eran alumnos españoles de enseñanza secundaria con nivel de competencia intermedio-bajo que completaron una tarea de redacción en tres etapas: escritura de una narración a partir de unos dibujos (Etapa 1, comparación de los textos escritos con dos modelos escritos por hablantes nativos (etapa 2 y revisión posterior de los textos originales (etapa 3. Los resultados indican que los estudiantes repararon en errores principalmente de tipo léxico durante la escritura de la narración, pero que sólo pudieron encontrar unas pocas soluciones a esos problemas en los modelos proporcionados. Sin embargo, la comparación con los modelos les permitió, especialmente a los que trabajaban en colaboración, percatarse de un amplio número de elementos relacionados con el contenido de los dibujos y los medios lingüísticos utilizados para expresar tales contenidos, así como incorporar un número razonable de estos elementos en las revisiones posteriores. De acuerdo con estos resultados, se sugieren diversas implicaciones para la docencia y la investigación.The present study investigated how noticing is related to composing and subsequent feedback processing in individual and collaborative EFL writing. Participants were Spanish secondary school pupils at a lowintermediate proficiency level who completed a three-stage writing task that included writing a picture-based story (Stage 1, comparing their written texts with two native-speaker models (Stage 2, and attempting subsequent revisions (Stage 3. The results indicate that the students noticed mainly lexical problems at the writing stage but could only find a few solutions to those problems in the models provided. However, the comparison with the models allowed them, especially those who wrote

  11. Application of a data assimilation method via an ensemble Kalman filter to reactive urea hydrolysis transport modeling

    Energy Technology Data Exchange (ETDEWEB)

    Juxiu Tong; Bill X. Hu; Hai Huang; Luanjin Guo; Jinzhong Yang

    2014-03-01

    With growing importance of water resources in the world, remediations of anthropogenic contaminations due to reactive solute transport become even more important. A good understanding of reactive rate parameters such as kinetic parameters is the key to accurately predicting reactive solute transport processes and designing corresponding remediation schemes. For modeling reactive solute transport, it is very difficult to estimate chemical reaction rate parameters due to complex processes of chemical reactions and limited available data. To find a method to get the reactive rate parameters for the reactive urea hydrolysis transport modeling and obtain more accurate prediction for the chemical concentrations, we developed a data assimilation method based on an ensemble Kalman filter (EnKF) method to calibrate reactive rate parameters for modeling urea hydrolysis transport in a synthetic one-dimensional column at laboratory scale and to update modeling prediction. We applied a constrained EnKF method to pose constraints to the updated reactive rate parameters and the predicted solute concentrations based on their physical meanings after the data assimilation calibration. From the study results we concluded that we could efficiently improve the chemical reactive rate parameters with the data assimilation method via the EnKF, and at the same time we could improve solute concentration prediction. The more data we assimilated, the more accurate the reactive rate parameters and concentration prediction. The filter divergence problem was also solved in this study.

  12. Immune response in lung cancer mouse model mimics human anti-Hu reactivity

    Science.gov (United States)

    Kazarian, Meleeneh; Calbo, Joaquim; Proost, Natalie; Carpenter, Catherine L.; Berns, Anton; Laird-Offringa, Ite A.

    2009-01-01

    Most patients with paraneoplastic encephalomyelitis/sensory neuronopathy PEM/SN have small-cell lung cancer (SCLC) and develop antibodies against neuronal-specific Hu proteins, which are abnormally expressed in the tumor. Anti-Hu reactivity is present in ~16% of SCLC patients without PEM/SN. Here we test the hypothesis that engineered SCLC-prone mice may exhibit anti-Hu reactivity. We show that tumors from SCLC-prone mice misexpress Hu proteins, and 14% of mice harbor anti-Hu antibodies. Mice appear to show reactivity prior to clinical diagnosis of SCLC. This mouse model system will be useful to study SCLC-associated autoimmunity, its diagnostic value, and the potential protective role of oncoantigen-directed autoantibodies. PMID:19765830

  13. A process model of adolescents' triangulation into parents' marital conflict: the role of emotional reactivity.

    Science.gov (United States)

    Buehler, Cheryl; Welsh, Deborah P

    2009-04-01

    This study examined adolescents' emotional reactivity to parents' marital conflict as a mediator of the association between triangulation and adolescents' internalizing problems in a sample of 2-parent families (N = 416)[corrected]. Four waves of annual, multiple-informant data were analyzed (youth ages 11-15 years). The authors used structural equation modeling and found that triangulation was associated with increases in adolescents' internalizing problems, controlling for marital hostility and adolescent externalizing problems. There also was an indirect pathway from triangulation to internalizing problems across time through youths' emotional reactivity. Moderating analyses indicated that the 2nd half of the pathway, the association between emotional reactivity and increased internalizing problems, characterized youth with lower levels of hopefulness and attachment to parents. The findings help detail why triangulation is a risk factor for adolescents' development and which youth will profit most from interventions focused on emotional regulation.

  14. Modeling variably saturated multispecies reactive groundwater solute transport with MODFLOW-UZF and RT3D

    Science.gov (United States)

    Bailey, Ryan T.; Morway, Eric D.; Niswonger, Richard G.; Gates, Timothy K.

    2013-01-01

    A numerical model was developed that is capable of simulating multispecies reactive solute transport in variably saturated porous media. This model consists of a modified version of the reactive transport model RT3D (Reactive Transport in 3 Dimensions) that is linked to the Unsaturated-Zone Flow (UZF1) package and MODFLOW. Referred to as UZF-RT3D, the model is tested against published analytical benchmarks as well as other published contaminant transport models, including HYDRUS-1D, VS2DT, and SUTRA, and the coupled flow and transport modeling system of CATHY and TRAN3D. Comparisons in one-dimensional, two-dimensional, and three-dimensional variably saturated systems are explored. While several test cases are included to verify the correct implementation of variably saturated transport in UZF-RT3D, other cases are included to demonstrate the usefulness of the code in terms of model run-time and handling the reaction kinetics of multiple interacting species in variably saturated subsurface systems. As UZF1 relies on a kinematic-wave approximation for unsaturated flow that neglects the diffusive terms in Richards equation, UZF-RT3D can be used for large-scale aquifer systems for which the UZF1 formulation is reasonable, that is, capillary-pressure gradients can be neglected and soil parameters can be treated as homogeneous. Decreased model run-time and the ability to include site-specific chemical species and chemical reactions make UZF-RT3D an attractive model for efficient simulation of multispecies reactive transport in variably saturated large-scale subsurface systems.

  15. Galactic outflow and diffuse gas properties at z>=1 using different baryonic feedback models

    CERN Document Server

    Barai, Paramita; Murante, Giuseppe; Ragagnin, Antonio; Viel, Matteo

    2014-01-01

    We measure and quantify properties of galactic outflows and diffuse gas at $z \\geq 1$ in cosmological hydrodynamical simulations. Our novel sub-resolution model, MUPPI, implements supernova feedback using fully local gas properties, where the wind velocity and mass loading are not given as input. We find the following trends at $z = 2$ by analysing central galaxies having a stellar mass higher than $10^{9} M_{\\odot}$. The outflow velocity and mass outflow rate ($\\dot{M}_{\\rm out}$) exhibit positive correlations with galaxy mass and with the star formation rate (SFR). However, most of the relations present a large scatter. The outflow mass loading factor ($\\eta$) is between $0.2 - 10$. The comparison Effective model generates a constant outflow velocity, and a negative correlation of $\\eta$ with halo mass. The number fraction of galaxies where outflow is detected decreases at lower redshifts, but remains more than $80 \\%$ over $z = 1 - 5$. High SF activity at $z \\sim 2 - 4$ drives strong outflows, causing the ...

  16. A Feedback Control Model of Comprehensive Therapy for Treating Immunogenic Tumours

    Science.gov (United States)

    Tang, Biao; Xiao, Yanni; Tang, Sanyi; Cheke, Robert A.

    Surgery is the traditional method for treating cancers, but it often fails to cure patients for complex reasons so new therapeutic approaches that include both surgery and immunotherapy have recently been proposed. These have been shown to be effective, clinically, in inhibiting cancer cells while allowing retention of immunologic memory. This comprehensive strategy is guided by whether a population of tumour cells has or has not exceeded a threshold density. Conditions for successful control of tumours in an immune tumour system were modeled and the related dynamics were addressed. A mathematical model with state-dependent impulsive interventions is formulated to describe combinations of surgery with immunotherapy. By analyzing the properties of the Poincaré map, we examine the global dynamics of the immune tumour system with state-dependent feedback control, including the existence and stability of the semi-trivial order-1 periodic solution and the positive order-k periodic solution. The main results showed that surgery alone can only control the tumour size below a certain level while there is no immunologic memory. If comprehensive therapy involving combining surgery with immunotherapy is considered, then not only can the cancers be controlled below a certain level, but the immune system can also retain its activity. The existence of positive order-k periodic solutions implies that periodical therapy is needed to control the cancers. However, choosing the treatment frequency and the strength of the therapy remains challenging, and hence a strategy of individual-based therapy is suggested.

  17. A COMSOL-GEMS interface for modeling coupled reactive-transport geochemical processes

    Science.gov (United States)

    Azad, Vahid Jafari; Li, Chang; Verba, Circe; Ideker, Jason H.; Isgor, O. Burkan

    2016-07-01

    An interface was developed between COMSOL MultiphysicsTM finite element analysis software and (geo)chemical modeling platform, GEMS, for the reactive-transport modeling of (geo)chemical processes in variably saturated porous media. The two standalone software packages are managed from the interface that uses a non-iterative operator splitting technique to couple the transport (COMSOL) and reaction (GEMS) processes. The interface allows modeling media with complex chemistry (e.g. cement) using GEMS thermodynamic database formats. Benchmark comparisons show that the developed interface can be used to predict a variety of reactive-transport processes accurately. The full functionality of the interface was demonstrated to model transport processes, governed by extended Nernst-Plank equation, in Class H Portland cement samples in high pressure and temperature autoclaves simulating systems that are used to store captured carbon dioxide (CO2) in geological reservoirs.

  18. Distinguishing Environment and System in Coloured Petri Net Models of Reactive Systems

    DEFF Research Database (Denmark)

    Tjell, Simon

    2007-01-01

    This paper introduces and formally defines the environment-and-system-partitioned property for behavioral models of reactive systems expressed in the formal modeling language Coloured Petri Net. The purpose of the formalization is to make it possible to automatically validate any CPN model with r...... code-generation from models. A prototypical tool has been implemented for performing the structural analysis of Coloured Petri Net models and the principles of this tool is described. The aim of the paper is to make the guidelines and their formalized definitions along with a proof...

  19. Permafrost landscapes in transition - towards modeling interactions, thresholds and feedbacks related to ice-rich ground

    Science.gov (United States)

    Westermann, Sebastian; Langer, Moritz; Lee, Hanna; Berntsen, Terje; Boike, Julia; Krinner, Gerhard; Aalstad, Kristoffer; Schanke Aas, Kjetil; Peter, Maria; Heikenfeld, Max; Etzelmüller, Bernd

    2016-04-01

    Thawing of permafrost is governed by a complex interplay of different processes, of which only conductive heat transfer is taken into account in most model studies. However, heat conduction alone can not account for the dynamical evolution of many permafrost landscapes, e.g. in areas rich in ground ice shaped by thermokarst ponds and lakes. Novel process parameterizations are required to include such phenomena in future projections of permafrost thaw and hereby triggered climatic feedbacks. Recently, we have demonstrated a physically-based parameterization for thaw process in ice-rich ground in the permafrost model CryoGrid 3, which can reproduce the formation of thermokarst ponds and subsidence of the ground following thawing of ice-rich subsurface layers. Long-term simulations for different subsurface stratigraphies in the Lena River Delta, Siberia, demonstrate that the hydrological regime can both accelerate and delay permafrost thawing. If meltwater from thawed ice-rich layers can drain, the ground subsides while at the same time the formation of a talik is delayed. If the meltwater pools at the surface, a pond is formed which enhances heat transfer in the ground and leads to the formation of a talik. The PERMANOR project funded by the Norwegian Research Council until 2019 will extend this work by integrating such small-scale processes in larger-scale Earth System Models (ESMs). For this purpose, the project will explore and develop statistical approaches, in particular tiling, to represent permafrost landscape dynamics on subgrid scale. Ultimately, PERMANOR will conceptualize process understanding from in-situ studies to develop new model algorithms and pursue their implementation in a coupled ESM framework.

  20. Neural cryptography with feedback

    Science.gov (United States)

    Ruttor, Andreas; Kinzel, Wolfgang; Shacham, Lanir; Kanter, Ido

    2004-04-01

    Neural cryptography is based on a competition between attractive and repulsive stochastic forces. A feedback mechanism is added to neural cryptography which increases the repulsive forces. Using numerical simulations and an analytic approach, the probability of a successful attack is calculated for different model parameters. Scaling laws are derived which show that feedback improves the security of the system. In addition, a network with feedback generates a pseudorandom bit sequence which can be used to encrypt and decrypt a secret message.

  1. Neural cryptography with feedback.

    Science.gov (United States)

    Ruttor, Andreas; Kinzel, Wolfgang; Shacham, Lanir; Kanter, Ido

    2004-04-01

    Neural cryptography is based on a competition between attractive and repulsive stochastic forces. A feedback mechanism is added to neural cryptography which increases the repulsive forces. Using numerical simulations and an analytic approach, the probability of a successful attack is calculated for different model parameters. Scaling laws are derived which show that feedback improves the security of the system. In addition, a network with feedback generates a pseudorandom bit sequence which can be used to encrypt and decrypt a secret message.

  2. Investigating dynamics of inhibitory and feedback loops in ERK signalling using power-law models.

    Science.gov (United States)

    Vera, Julio; Rath, Oliver; Balsa-Canto, Eva; Banga, Julio R; Kolch, Walter; Wolkenhauer, Olaf

    2010-11-01

    the existence of an intense feedback-loop control of the pathway by the activated ERK that maybe responsible for the damped oscillations we saw in the fraction of activated MEK both in the experiments and simulations. In addition, the model analysis suggested that phosphorylation/deactivation of RKIP during the transient stimulation may have a significant effect on the signalling peaks of both MEK and ERK. This later result suggests that dynamic modulation of signal inhibitors during stimulation may be a regulatory mechanism in ERK signalling and other pathways.

  3. In silico pharmacophore model for tabun-inhibited acetylcholinesterase reactivators: a study of their stereoelectronic properties.

    Science.gov (United States)

    Bhattacharjee, Apurba K; Kuca, Kamil; Musilek, Kamil; Gordon, Richard K

    2010-01-01

    Organophosphorus (OP) nerve agents that inhibit acetylcholinesterase (AChE; EC 3.1.1.7) function in the nervous system, causing acute intoxication. If untreated, death can result. Inhibited AChE can be reactivated by oximes, antidotes for OP exposure. However, OP intoxication caused by the nerve agent tabun (GA) is particularly resistant to oximes, which poorly reactivate GA-inhibited AChE. In an attempt to develop a rational strategy for the discovery and design of novel reactivators with lower toxicity and increased efficacy in reactivating GA-inhibited AChE, we developed the first in silico pharmacophore model for binding affinity of GA-inhibited AChE from a set of 11 oximes. Oximes were analyzed for stereoelectronic profiles and three-dimensional quantitative structure-activity relationship pharmacophores using ab initio quantum chemical and pharmacophore generation methods. Quantum chemical methods were sequentially used from semiempirical AM1 to hierarchical ab initio calculations to determine the stereoelectronic properties of nine oximes exhibiting affinity for binding to GA-inhibited AChE in vivo. The calculated stereoelectronic properties led us to develop the in silico pharmacophore model using CATALYST methodology. Specific stereoelectronic profiles including the distance between bisquarternary nitrogen atoms of the pyridinium ring in the oximes, hydrophilicity, surface area, nucleophilicity of the oxime oxygen, and location of the molecular orbitals on the isosurfaces have important roles for potencies for reactivating GA-inhibited AChE. The in silico pharmacophore model of oxime affinity for binding to GA-inhibited AChE was found to require a hydrogen bond acceptor, a hydrogen bond donor at the two terminal regions, and an aromatic ring in the central region of the oximes. The model was found to be well-correlated (R = 0.9) with experimental oxime affinity for binding to GA-inhibited AChE. Additional stereoelectronic features relating activity with

  4. Comparison of an enhanced versus a written feedback model on the management of Medicare inpatients with venous thrombosis.

    Science.gov (United States)

    Hayes, R; Bratzler, D; Armour, B; Moore, L; Murray, C; Stevens, B R; Radford, M; Fitzgerald, D; Elward, K; Ballard, D J

    2001-03-01

    A multistate randomized study conducted under the Health Care Financing Administration's (HCFA's) Health Care Quality Improvement Program (HCQIP) offered the opportunity to compare the effect of a written feedback intervention (WFI) with that of an enhanced feedback intervention (EFI) on improving the anticoagulant management of Medicare beneficiaries who present to the hospital with venous thromboembolic disease. Twenty-nine hospitals in five states were randomly assigned to receive written hospital-specific feedback (WFI) of feedback enhanced by the participation of a trained physician, quality improvement tools, and an Anticoagulant Management of Venous Thrombosis (AMVT) project liaison (EFI). Differences in the performance of five quality indicators between baseline and remeasurement were assessed. Quality managers were interviewed to determine perceptions of project implementation. No significant differences in the change from baseline to remeasurement were found between the two intervention groups. Significant improvement in one indicator and significant decline in two indicators were found for one or both groups. Yet 59% of all quality managers perceived the AMVT project as being successful to very successful, and more EFI quality managers perceived success than did WFI managers (71% versus 40%). In the majority of EFI hospitals, physician liaisons played an important role in project implementation. Study results indicated that the addition of a physician liaison, quality improvement tools, and a project liaison did not provide incremental value to hospital-specific feedback for improving quality of care. Future studies with larger sample sizes, lengthier follow-up periods, and interventions that include more of the elements shown to affect practice behavior change are needed to identify an optimal feedback model for use by external quality management organizations.

  5. Video-based feedback combined with reflective enquiry – An interactive model for movement awareness among nursing students

    OpenAIRE

    Sofia Backåberg; Mikael Rask; Christina Gummesson; David Brunt

    2015-01-01

    The aim of this study is to describe an interactive model developed for movement awareness in a practical learning situation and to explore the use of video-based digital feedback and reflective enquiry in this model among nursing students. Sixteen students participated in individual interactive video sessions with a facilitator, who encouraged the students to reflect upon their own movements. Qualitative analysis showed that movement patterns were visualized, and that movement awareness and ...

  6. A Coupled Model of Multiphase Flow, Reactive Biogeochemical Transport, Thermal Transport and Geo-Mechanics.

    Science.gov (United States)

    Tsai, C. H.; Yeh, G. T.

    2015-12-01

    In this investigation, a coupled model of multiphase flow, reactive biogeochemical transport, thermal transport and geo-mechanics in subsurface media is presented. It iteratively solves the mass conservation equation for fluid flow, thermal transport equation for temperature, reactive biogeochemical transport equations for concentration distributions, and solid momentum equation for displacement with successive linearization algorithm. With species-based equations of state, density of a phase in the system is obtained by summing up concentrations of all species. This circumvents the problem of having to use empirical functions. Moreover, reaction rates of all species are incorporated in mass conservation equation for fluid flow. Formation enthalpy of all species is included in the law of energy conservation as a source-sink term. Finite element methods are used to discretize the governing equations. Numerical experiments are presented to examine the accuracy and robustness of the proposed model. The results demonstrate the feasibility and capability of present model in subsurface media.

  7. Biospheric feedback effects in a synchronously coupled model of human and Earth systems

    Energy Technology Data Exchange (ETDEWEB)

    Thornton, Peter E.; Calvin, Katherine; Jones, Andrew D.; Di Vittorio, Alan V.; Bond-Lamberty, Ben; Chini, Louise; Shi, Xiaoying; Mao, Jiafu; Collins, William D.; Edmonds, Jae; Thomson, Allison; Truesdale, John; Craig, Anthony; Branstetter, Marcia L.; Hurtt, George

    2017-06-12

    Fossil fuel combustion and land-use change are the first and second largest contributors to industrial-era increases in atmospheric carbon dioxide concentration, which is itself the largest driver of present-day climate change1. Projections of fossil fuel consumption and land-use change are thus fundamental inputs for coupled Earth system models (ESM) used to estimate the physical and biological consequences of future climate system forcing2,3. While empirical datasets are available to inform historical analyses4,5, assessments of future climate change have relied on projections of energy and land use based on energy economic models, constrained using historical and present-day data and forced with assumptions about future policy, land-use patterns, and socio-economic development trajectories6. Here we show that the influence of biospheric change – the integrated effect of climatic, ecological, and geochemical processes – on land ecosystems has a significant impact on energy, agriculture, and land-use projections for the 21st century. Such feedbacks have been ignored in previous ESM studies of future climate. We find that synchronous exposure of land ecosystem productivity in the economic system to biospheric change as it develops in an ESM results in a 10% reduction of land area used for crop cultivation; increased managed forest area and land carbon; a 15-20% decrease in global crop price; and a 17% reduction in fossil fuel emissions for a low-mid range forcing scenario7. These simulation results demonstrate that biospheric change can significantly alter primary human system forcings to the climate system. This synchronous two-way coupling approach removes inconsistencies in description of climate change between human and biosphere components of the coupled model, mitigating a major source of uncertainty identified in assessments of future climate projections8-10.

  8. Adaptation of cardiac structure by mechanical feedback in the environment of the cell: a model study.

    Science.gov (United States)

    Arts, T; Prinzen, F W; Snoeckx, L H; Rijcken, J M; Reneman, R S

    1994-01-01

    In the cardiac left ventricle during systole mechanical load of the myocardial fibers is distributed uniformly. A mechanism is proposed by which control of mechanical load is distributed over many individual control units acting in the environment of the cell. The mechanics of the equatorial region of the left ventricle was modeled by a thick-walled cylinder composed of 6-1500 shells of myocardial fiber material. In each shell a separate control unit was simulated. The direction of the cells was varied so that systolic fiber shortening approached a given optimum of 15%. End-diastolic sarcomere length was maintained at 2.1 microns. Regional early-systolic stretch and global contractility stimulated growth of cellular mass. If systolic shortening was more than normal the passive extracellular matrix stretched. The design of the load-controlling mechanism was derived from biological experiments showing that cellular processes are sensitive to mechanical deformation. After simulating a few hundred adaptation cycles, the macroscopic anatomical arrangement of helical pathways of the myocardial fibers formed automatically. If pump load of the ventricle was changed, wall thickness and cavity volume adapted physiologically. We propose that the cardiac anatomy may be defined and maintained by a multitude of control units for mechanical load, each acting in the cellular environment. Interestingly, feedback through fiber stress is not a compelling condition for such control. PMID:8038399

  9. Optimal Hydro-Thermal Generation Scheduling Using an Efficient Feedback Neural Network Optimization Model

    Directory of Open Access Journals (Sweden)

    V. Sharma

    2011-08-01

    Full Text Available This study demonstrates the use of a high-performance feedback neural network optimizer based on a new idea of successive approximation for finding the hourly optimal release schedules of interconnected multi-reservoir power system in such a way to minimize the overall cost of thermal generations spanned over the planning period. The main advantages of the proposed neural network optimizer over the existing neural network optimization models are that no dual variables, penalty parameters or lagrange multipliers are required. This network uses a simple structure with the least number of state variables and has better asymptotic stability. For an arbitrarily chosen initial point, the trajectory of the network converges to an optimal solution of the convex nonlinear programming problem. The proposed optimizer has been tested on a nonlinear practical system consisting of a multi-chain cascade of four linked reservoir type hydro-plants and a number of thermal units represented by a single equivalent thermal power plant and so obtained results have been validated using conventional conjugate gradient method and genetic algorithm based approach.

  10. A Physical Model of FeLoBALs: Implications for Quasar Feedback

    CERN Document Server

    Faucher-Giguere, C -A; Murray, N

    2011-01-01

    Photoionization modeling of the low-ionization broad absorption lines of certain quasars, known as FeLoBALs, has recently revealed the number density of the wind absorbers and their distance from the central supermassive black hole. From these, the feedback efficiency of the quasars can in principle be derived. The implied properties of the FeLoBALs are, however, surprising, with the thickness of the absorbers relative to their distance from the black hole, Delta R/R, as small as ~10^-5. Such absorbers are unlikely to survive the journey from the supermassive black hole to their inferred location. We show that the observed FeLoBAL properties are readily explained if they are formed in situ in radiative shocks produced when a quasar blast wave impacts a moderately dense interstellar clump along the line of sight. This physical picture differs significantly from the thin shell approximation often assumed, and implies outflow rates, kinetic luminosities and momentum fluxes that differ correspondingly, in some ca...

  11. GOBF-ARMA based model predictive control for an ideal reactive distillation column.

    Science.gov (United States)

    Seban, Lalu; Kirubakaran, V; Roy, B K; Radhakrishnan, T K

    2015-11-01

    This paper discusses the control of an ideal reactive distillation column (RDC) using model predictive control (MPC) based on a combination of deterministic generalized orthonormal basis filter (GOBF) and stochastic autoregressive moving average (ARMA) models. Reactive distillation (RD) integrates reaction and distillation in a single process resulting in process and energy integration promoting green chemistry principles. Improved selectivity of products, increased conversion, better utilization and control of reaction heat, scope for difficult separations and the avoidance of azeotropes are some of the advantages that reactive distillation offers over conventional technique of distillation column after reactor. The introduction of an in situ separation in the reaction zone leads to complex interactions between vapor-liquid equilibrium, mass transfer rates, diffusion and chemical kinetics. RD with its high order and nonlinear dynamics, and multiple steady states is a good candidate for testing and verification of new control schemes. Here a combination of GOBF-ARMA models is used to catch and represent the dynamics of the RDC. This GOBF-ARMA model is then used to design an MPC scheme for the control of product purity of RDC under different operating constraints and conditions. The performance of proposed modeling and control using GOBF-ARMA based MPC is simulated and analyzed. The proposed controller is found to perform satisfactorily for reference tracking and disturbance rejection in RDC.

  12. Exploring classroom feedback interactions around EAP writing : a data based model

    OpenAIRE

    Unlu, Zuleyha; Wharton, Sue

    2015-01-01

    This paper is based on case study research in the grounded theory tradition. In this paper we describe and theorise feedback interactions on EAP writing which were observed in classes in our institution. Working from detailed descriptions of feedback incidents and from interviews with teachers and students, we theorise a series of teacher and student actions. We argue that combinations of these actions are both reflective and constitutive of patterns of teacher-student relationships in the cl...

  13. The Analysis and Modeling of The Profitability Feedback Process – A Dynamic Model on Portugal’s National Economy

    Directory of Open Access Journals (Sweden)

    Bianca-Ioana Popescu

    2015-06-01

    Full Text Available The aim of the present paper is to underline the influence of the profitability process at macroe-conomic level will exert on real economy. Until now relevant literature has been focused on firms, banks and industries but only with the objective of comparing past profitability of the studied entity or comparison to other competitors on the market and with microfoundation calculus - profitability being calculated for a panel of firms in the studied industry. The model of the Profitability Feedback Process is capable of surprising the influences the concept of profitability will have at macroeconomic level as being considered to be one of the auto-regulation processes of a national economy. The simulations have been made on EUROSTAT’s official stats of Portugal between 2005 and 2012 annual data and the simulations have revealed robust behavior of the system in relation to the profitability and the economic context and sustain the rationality of our attempt.

  14. Anthropogenic contamination of a phreatic drinking water winning: 3-dimensional reactive transport modelling

    Science.gov (United States)

    Griffioen, J.; van der Grift, B.; Maas, D.; van den Brink, C.; Zaadnoordijk, J. W.

    2003-04-01

    Groundwater is contaminated at the regional scale by agricultural activities and atmospheric deposition. A 3-D transport model was set-up for a phreatic drinking water winning, where the groundwater composition was monitored accurately. The winning is situated at an area with unconsolidated Pleistocene deposits. The land use is nature and agriculture. Annual mass-balances were determined using a wide range of historic data. The modelling approach for the unsaturated zone was either simple box models (Cl, NO_3 and SO_4) or 1-D transport modelling using HYDRUS (Cd). The modelling approach for the saturated zone used a multiple solute version of MT3D, where denitrification associated with pyrite oxidation and sorption of Cd were included. The solute transport calculations were performed for the period 1950--2030. The results obtained for the year 2000 were used as input concentration for the period 2000--2030. A comparison between the calculated and the measured concentrations of groundwater abstracted for Cl, NO_3 and SO_4 yields the following. First, the input at the surface is rather well estimated. Second, the redox reactivity of the first two aquifers is negligible around the winning, which is confirmed by respiration experiments using anaerobically sampled aquifer sediments. The reactivity of the third aquifer, which is a marine deposit and lies at least 30 meters below surface, is considerable. The discrepancies between modelled and measured output are explained by lack of knowledge about the subsurface reactivity and/or wrong estimates of surface loading and leaching from the unsaturated zone. The patterns for other hydrogeochemical variables such as Ca, HCO_3 may further constrain this lack of knowledge. The results for Cd indicate that Cd becomes strongly retarded, despite the low reactivity of the sandy sediments. The winning is rather insensitive to Cd contamination (but the surface water drainage network is not). Two major uncertainties for input of Cd

  15. Modeling the surface tension of complex, reactive organic-inorganic mixtures

    Directory of Open Access Journals (Sweden)

    A. N. Schwier

    2013-01-01

    Full Text Available Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as cloud condensation nuclei (CCN ability. We present new experimental data for the surface tension of complex, reactive organic-inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2–6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well-described by a weighted Szyszkowski–Langmuir (S–L model which was first presented by Henning et al. (2005. Two approaches for modeling the effects of salt were tested: (1 the Tuckermann approach (an extension of the Henning model with an additional explicit salt term, and (2 a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2 for surface tension modeling because the Henning model (using data obtained from organic-inorganic systems and Tuckermann approach provide similar modeling fits and goodness of fit (χ2 values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

  16. Model evidence for low-level cloud feedback driving persistent changes in atmospheric circulation and regional hydroclimate

    Science.gov (United States)

    Burgman, Robert J.; Kirtman, Ben P.; Clement, Amy C.; Vazquez, Heather

    2017-01-01

    Recent studies suggest that low clouds in the Pacific play an important role in the observed decadal climate variability and future climate change. In this study, we implement a novel modeling experiment designed to isolate how interactions between local and remote feedbacks associated with low cloud, SSTs, and the large-scale circulation play a significant role in the observed persistence of tropical Pacific SST and associated North American drought. The modeling approach involves the incorporation of observed patterns of satellite-derived shortwave cloud radiative effect (SWCRE) into the coupled model framework and is ideally suited for examining the role of local and large-scale coupled feedbacks and ocean heat transport in Pacific decadal variability. We show that changes in SWCRE forcing in eastern subtropical Pacific alone reproduces much of the observed changes in SST and atmospheric circulation over the past 16 years, including the observed changes in precipitation over much of the Western Hemisphere.

  17. A Study of Low Cloud Climate Feedbacks Using a Generalized Higher-Order Closure Subgrid Model

    Science.gov (United States)

    Firl, Grant J.

    One of the biggest uncertainties in projections of future climate is whether and how low cloudiness will change and whether that change will feed back on the climate system. Much of the uncertainty revolves around the difference in scales between the processes that govern low cloudiness and the processes that can be resolved in climate models, a fact that relegates shallow convection to the parameterization realm with varying levels of success. A new subgrid-scale parameterization, named THOR, has been developed in an effort to improve the representation of low cloudiness via parameterization in climate models. THOR uses the higher-order closure approach to determine the statistics describing subgrid-scale processes. These statistics are used to determine a trivariate double-Gaussian PDF among vertical velocity, ice-liquid water potential temperature, and total water specific humidity. With this information, one can diagnose what portion of the grid cell is cloudy, subgrid-scale cloud water content, and subgrid-scale vertical cloud water flux. In addition, samples are drawn from the trivariate PDF in order to drive the microphysics and radiation schemes. Although schemes similar to THOR have been developed over the past decade, THOR includes several novel concepts, like the generalization of the saturation curve to include condensation over both ice and liquid substrates, the determination of the PDF parameters from the given turbulence statistics, the introduction of a stochastic parcel entrainment process for the turbulence length scale, and a sub-column approach for calculating radiative transfer using the PDF. The new model is validated by simulating five test cases spanning a wide range of boundary layer cloud types, from stratocumulus to cumulus and the transition between the two. The results are compared to an ensemble of LES models running the same cases, with particular attention paid to turbulence statistics and cloud structure. For all cloud types tested

  18. Climate-sensitive feedbacks between hillslope processes and fluvial erosion in sediment-driven incision models

    Science.gov (United States)

    Skov, Daniel S.; Egholm, David L.

    2016-04-01

    Surface erosion and sediment production seem to have accelerated globally as climate cooled in the Late Cenozoic, [Molnar, P. 2004, Herman et al 2013]. Glaciers emerged in many high mountain ranges during the Quaternary, and glaciation therefore represents a likely explanation for faster erosion in such places. Still, observations and measurements point to increases in erosion rates also in landscapes where erosion is driven mainly by fluvial processes [Lease and Ehlers (2013), Reusser (2004)]. Flume experiments and fieldwork have shown that rates of incision are to a large degree controlled by the sediment load of streams [e.g. Sklar and Dietrich (2001), Beer and Turowski (2015)]. This realization led to the formulation of sediment-flux dependent incision models [Sklar and Dietrich (2004)]. The sediment-flux dependence links incision in the channels to hillslope processes that supply sediment to the channels. The rates of weathering and soil transport on the hillslopes are processes that are likely to respond to changing temperatures, e.g. because of vegetation changes or the occurrence of frost. In this study, we perform computational landscape evolution experiments, where the coupling between fluvial incision and hillslope processes is accounted for by coupling a sediment-flux-dependent model for fluvial incision to a climate-dependent model for weathering and hillslope sediment transport. The computational experiments first of all demonstrate a strong positive feedback between channel and hillslope processes. In general, faster weathering leads to higher rates of channel incision, which further increases the weathering rates, mainly because of hillslope steepening. Slower weathering leads to the opposite result. The experiments also demonstrate, however, that the feedbacks vary significantly between different parts of a drainage network. For example, increasing hillslope sediment production may accelerate incision in the upper parts of the catchment, while at

  19. Investigating feedback mechanisms between stress and grain-size: preliminary findings from finite-element modelling

    Science.gov (United States)

    Cross, A. J.; Prior, D. J.; Ellis, S. M.

    2012-12-01

    It is widely accepted that changes in stress and grain size can induce a switch between grain-size insensitive (GSI) and sensitive (GSS) creep mechanisms. Under steady-state conditions, grains evolve to an equilibrium size in the boundary region between GSS and GSI, described by the paleopiezometer for a given material. Under these conditions, significant rheological weakening is not expected, as grain size reduction processes are balanced by grain growth processes. However, it has been shown that the stress field surrounding faults varies through the seismic cycle, with both rapid loading and unloading of stress possible in the co- and post-seismic stages. We propose that these changes in stress in the region of the brittle-ductile transition zone may be sufficient to force a deviation from the GSI-GSS boundary and thereby cause a change in grain size and creep mechanism prior to system re-equilibration. Here we present preliminary findings from numerical modelling of stress and grain size changes in response to loading of mechanical inhomogeneities. Our results are attained using a grain-size evolution (GSE) subroutine incorporated into the SULEC finite-element code developed by Susan Ellis and Susanne Buiter, which utilises an iterative approach of solving for spatial and temporal changes in differential stress, grain size and active creep mechanism. Preliminary models demonstrate that stress changes in response to the opening of a fracture in a flowing medium can be significant enough to cause a switch from GSI to GSS creep. These results are significant in the context of understanding spatial variations and feedback between stress, grain size and deformation mechanisms through the seismic cycle.

  20. Vegetation-climate feedback causes reduced precipitation in CMIP5 regional Earth system model simulation over Africa

    Science.gov (United States)

    Wu, Minchao; Smith, Benjamin; Schurgers, Guy; Lindström, Joe; Rummukainen, Markku; Samuelsson, Patrick

    2013-04-01

    Terrestrial ecosystems have been demonstrated to play a significant role within the climate system, amplifying or dampening climate change via biogeophysical and biogeochemical exchange with the atmosphere and vice versa (Cox et al. 2000; Betts et al. 2004). Africa is particularly vulnerable to climate change and studies of vegetation-climate feedback mechanisms on Africa are still limited. Our study is the first application of A coupled Earth system model at regional scale and resolution over Africa. We applied a coupled regional climate-vegetation model, RCA-GUESS (Smith et al. 2011), over the CORDEX Africa domain, forced by boundary conditions from a CanESM2 CMIP5 simulation under the RCP8.5 future climate scenario. The simulations were from 1961 to 2100 and covered the African continent at a horizontal grid spacing of 0.44°. RCA-GUESS simulates changes in the phenology, productivity, relative cover and population structure of up to eight plant function types (PFTs) in response to forcing from the climate part of the model. These vegetation changes feedback to simulated climate through dynamic adjustments in surface energy fluxes and surface properties. Changes in the net ecosystem-atmosphere carbon flux and its components net primary production (NPP), heterotrophic respiration and emissions from biomass burning were also simulated but do not feedback to climate in our model. Constant land cover was assumed. We compared simulations with and without vegetation feedback switched "on" to assess the influence of vegetation-climate feedback on simulated climate, vegetation and ecosystem carbon cycling. Both positive and negative warming feedbacks were identified in different parts of Africa. In the Sahel savannah zone near 15°N, reduced vegetation cover and productivity, and mortality caused by a deterioration of soil water conditions led to a positive warming feedback mediated by decreased evapotranspiration and increased sensible heat flux between vegetation and

  1. The Reactive-Diffusive Length of OH and Ozone in Model Organic Aerosols.

    Science.gov (United States)

    Lee, Lance; Wilson, Kevin

    2016-09-01

    A key step in the heterogeneous oxidation of atmospheric aerosols is the reaction of ozone (O3) and hydroxyl radicals (OH) at the gas-particle interface. The formation of reaction products and free radical intermediates and their spatial distribution inside the particle is a sensitive function of the length over which these oxidants diffuse prior to reaction. The reactive-diffusive length of OH and ozone at organic aerosol interfaces is determined by observing the change in the effective uptake coefficient for size-selected model aerosols comprising a reactive core and a thin nanometer-sized (0-12 nm) organic shell. The core and shell materials are selected so that they are immiscible and adopt an assumed core-shell configuration. The results indicate a reactive-diffusive length of 1.4 nm for hydroxyl (OH) radicals in squalane and 1.0 nm for ozone in squalene. Measurements for a purely diffusive system allow for an estimate for diffusion constant (1.6 × 10(-6) cm(2)/s) of ozone in squalane to be determined. The reactive-diffusive length offers a simple first order estimate of how shielding of aerosols by immiscible layers can alter estimates of oxidative lifetimes of aerosols in the atmosphere.

  2. Tuning surface reactivity by finite size effects: role of orbital symmetry in the d - band model

    Science.gov (United States)

    Snijders, Paul; Yin, Xiangshi; Cooper, Valentino; Weitering, Hanno

    Catalytic activity depends sensitively on the strength of the interactions between reactant molecules and catalyst surface: too weak and the catalyst cannot capture enough molecules to react; too strong and the reaction products do not desorb, blocking further reactions. The ability to control the binding strength of molecules to metal surfaces is thus fundamental to the design of efficient and selective catalysts. Catalyst design often relies on increasing the interaction strength on relatively non-reactive materials by introducing active sites. Here, we present a complementary approach: we exploit finite size effects in the electronic structure of ultrathin Pd(111) films grown on Ru(0001) to tune their reactivity by changing the film thickness one atom layer at a time. While bulk Pd(111) is reactive toward oxygen, we find that Pd films thinner than 6 atom layers are surprisingly inert to oxidation. This observation can be explained with the d-band model only when it is applied to the orbitals directly involved in the bonding. The insight into orbital specific contributions to surface reactivity could be useful in the design of catalysts. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

  3. Multivariate zero-inflated modeling with latent predictors: Modeling feedback behavior

    NARCIS (Netherlands)

    Fox, Gerardus J.A.

    2013-01-01

    In educational studies, the use of computer-based assessments leads to the collection of multiple outcomes to assess student performance. The student-specific outcomes are correlated and often measured in different scales, such as continuous and count outcomes. A multivariate zero-inflated model

  4. Feedforward-feedback hybrid control for magnetic shape memory alloy actuators based on the Krasnosel'skii-Pokrovskii model.

    Directory of Open Access Journals (Sweden)

    Miaolei Zhou

    Full Text Available As a new type of smart material, magnetic shape memory alloy has the advantages of a fast response frequency and outstanding strain capability in the field of microdrive and microposition actuators. The hysteresis nonlinearity in magnetic shape memory alloy actuators, however, limits system performance and further application. Here we propose a feedforward-feedback hybrid control method to improve control precision and mitigate the effects of the hysteresis nonlinearity of magnetic shape memory alloy actuators. First, hysteresis nonlinearity compensation for the magnetic shape memory alloy actuator is implemented by establishing a feedforward controller which is an inverse hysteresis model based on Krasnosel'skii-Pokrovskii operator. Secondly, the paper employs the classical Proportion Integration Differentiation feedback control with feedforward control to comprise the hybrid control system, and for further enhancing the adaptive performance of the system and improving the control accuracy, the Radial Basis Function neural network self-tuning Proportion Integration Differentiation feedback control replaces the classical Proportion Integration Differentiation feedback control. Utilizing self-learning ability of the Radial Basis Function neural network obtains Jacobian information of magnetic shape memory alloy actuator for the on-line adjustment of parameters in Proportion Integration Differentiation controller. Finally, simulation results show that the hybrid control method proposed in this paper can greatly improve the control precision of magnetic shape memory alloy actuator and the maximum tracking error is reduced from 1.1% in the open-loop system to 0.43% in the hybrid control system.

  5. Feedforward-feedback hybrid control for magnetic shape memory alloy actuators based on the Krasnosel'skii-Pokrovskii model.

    Science.gov (United States)

    Zhou, Miaolei; Zhang, Qi; Wang, Jingyuan

    2014-01-01

    As a new type of smart material, magnetic shape memory alloy has the advantages of a fast response frequency and outstanding strain capability in the field of microdrive and microposition actuators. The hysteresis nonlinearity in magnetic shape memory alloy actuators, however, limits system performance and further application. Here we propose a feedforward-feedback hybrid control method to improve control precision and mitigate the effects of the hysteresis nonlinearity of magnetic shape memory alloy actuators. First, hysteresis nonlinearity compensation for the magnetic shape memory alloy actuator is implemented by establishing a feedforward controller which is an inverse hysteresis model based on Krasnosel'skii-Pokrovskii operator. Secondly, the paper employs the classical Proportion Integration Differentiation feedback control with feedforward control to comprise the hybrid control system, and for further enhancing the adaptive performance of the system and improving the control accuracy, the Radial Basis Function neural network self-tuning Proportion Integration Differentiation feedback control replaces the classical Proportion Integration Differentiation feedback control. Utilizing self-learning ability of the Radial Basis Function neural network obtains Jacobian information of magnetic shape memory alloy actuator for the on-line adjustment of parameters in Proportion Integration Differentiation controller. Finally, simulation results show that the hybrid control method proposed in this paper can greatly improve the control precision of magnetic shape memory alloy actuator and the maximum tracking error is reduced from 1.1% in the open-loop system to 0.43% in the hybrid control system.

  6. Tuberculosis genes expressed during persistence and reactivation in the resistant rabbit model

    OpenAIRE

    Kesavan, Anup K.; Brooks, Megan; Tufariello, JoAnn; Chan, John; Manabe, Yukari C.

    2008-01-01

    As previously published, after aerosol infection with Mycobacterium tuberculosis H37Rv, New Zealand white rabbits established infection with active bacillary replication, but later contained disease to a paucibacillary state through an effective adaptive response consistent with latency. Despite the heterogeneity among outbred rabbits, the resistant response was uniform. Immunosuppression resulted in reactivation with increased lung bacillary burden. Using this rabbit model, we isolated bacil...

  7. Real catalysis on single crystalline model catalysts with in-situ reactivity measurement

    OpenAIRE

    O. Shekhah; Ranke, W.; Schlögl, R.

    2003-01-01

    The pressure and materials gap between reactivity studies in UHV and real catalysis can only be overcome by application of in-situ methods for catalyst characterization and/or activity measurements under realistic pressure and temperature conditions. As a model reaction we study the economically important catalytic dehydrogenation of ethylbenzene (EB) to styrene (St) [1]. The technical catalyst consists of potassium-promoted iron oxides. We use single crystalline epitaxial layers of Fe2O3, Fe...

  8. Using Consensus Bayesian Network to Model the Reactive Oxygen Species Regulatory Pathway

    OpenAIRE

    Liangdong Hu; Limin Wang

    2013-01-01

    Bayesian network is one of the most successful graph models for representing the reactive oxygen species regulatory pathway. With the increasing number of microarray measurements, it is possible to construct the bayesian network from microarray data directly. Although large numbers of bayesian network learning algorithms have been developed, when applying them to learn bayesian networks from microarray data, the accuracies are low due to that the databases they used to learn bayesian networks...

  9. A New Model for Reactive Wetting of Metal/Ceramic System

    Institute of Scientific and Technical Information of China (English)

    Fusheng Pan; Jian Chen; Tianmo Liu; Jing Zhang

    2000-01-01

    @@ A new model has been suggested for illustrating the effects of interfacial reactions on the wettability of metal / ceramic system. It is shown that both the free energy change released by the reaction (△Gr) and the change in the nature of interfaces (△δr) are the important factors affecting reactive wetting of metal / ceramic system, but sometimes either of them will become the decisive one.

  10. Safe motion planning for mobile agents: A model of reactive planning for multiple mobile agents

    Energy Technology Data Exchange (ETDEWEB)

    Fujimura, Kikuo.

    1990-01-01

    The problem of motion planning for multiple mobile agents is studied. Each planning agent independently plans its own action based on its map which contains a limited information about the environment. In an environment where more than one mobile agent interacts, the motions of the robots are uncertain and dynamic. A model for reactive agents is described and simulation results are presented to show their behavior patterns. 18 refs., 2 figs.

  11. Modelling and parameter estimation in reactive continuous mixtures: the catalytic cracking of alkanes - part II

    Directory of Open Access Journals (Sweden)

    F. C. PEIXOTO

    1999-09-01

    Full Text Available Fragmentation kinetics is employed to model a continuous reactive mixture of alkanes under catalytic cracking conditions. Standard moment analysis techniques are employed, and a dynamic system for the time evolution of moments of the mixture's dimensionless concentration distribution function (DCDF is found. The time behavior of the DCDF is recovered with successive estimations of scaled gamma distributions using the moments time data.

  12. Reactive molecular dynamics models from ab initio molecular dynamics data using relative entropy minimization

    Science.gov (United States)

    Arntsen, Christopher; Chen, Chen; Voth, Gregory A.

    2017-09-01

    We present two new multiscale molecular dynamics (MS-RMD) models for the hydrated excess proton in water developed directly from ab initio molecular dynamics (AIMD) simulation data of the same system. The potential of mean force along the proton transfer reaction coordinate and radial distribution functions for the MS-RMD models are shown to faithfully reproduce those of AIMD. The models are developed using an algorithm based on relative entropy minimization, thus demonstrating the ability of the method to rapidly generate accurate and highly efficient reactive MD force fields.

  13. Model-Based Requirements Analysis for Reactive Systems with UML Sequence Diagrams and Coloured Petri Nets

    DEFF Research Database (Denmark)

    Tjell, Simon; Lassen, Kristian Bisgaard

    2008-01-01

    In this paper, we describe a formal foundation for a specialized approach to automatically checking traces against real-time requirements. The traces are obtained from simulation of Coloured Petri Net (CPN) models of reactive systems. The real-time requirements are expressed in terms...... of a derivative of UML 2.0 high-level Sequence Diagrams. The automated requirement checking is part of a bigger tool framework in which VDM++ is applied to automatically generate initial CPN models based on Problem Diagrams. These models are manually enhanced to provide behavioral descriptions of the environment...

  14. Constraining predictions of tundra permafrost and vegetation through model-data feedbacks and data-assimilation

    Science.gov (United States)

    Davidson, C. D.; Dietze, M.

    2011-12-01

    Arctic climate is warming at a rate disproportionate to the rest of the world, and recent interest has emerged in using terrestrial biosphere models to understand and predict the response of tundra ecosystems to such warming. Of particular interest are the potential feedbacks between permafrost melting, plant community dynamics, and biogeochemical cycles. Here, we report on efforts to calibrate and validate version 2 of the Ecosystem Demography model (ED2) for the Alaskan tundra and on the use of model analyses to motivate targeted field measurements. ED2 is a terrestrial biosphere model unique in its ability to scale physiological and plant community dynamics to regional levels. We began by assessing the ability of ED2's land surface model to capture permafrost thermodynamics and hydrology. Simulations at Barrow and Toolik Lake, Alaska bore several incongruities with observed data, with soil temperatures significantly higher and soil moisture lower than observed. Modifications were made to increase the soil column depth and to simulate the effect of wind compaction on snow density, and in turn, the insulation of winter soils. In addition to these changes, a new soil class was created to represent unique characteristics within the organic horizon of tundra soils. Together these changes significantly improved permafrost dynamics without substantially altering dynamics in the temperate region. To capture tundra vegetation dynamics, tundra species were classified into three plant functional types (graminoid, deciduous shrub, evergreen shrub). ED2 was then iteratively calibrated for the tundra using the Predictive Ecosystem Analyzer (PEcAn), a scientific workflow and ecoinformatics toolbox developed to aid model parameterization and analysis. Initial parameter estimates were derived from a formal Bayesian meta-analysis of compiled plant trait data. Sensitivity analyses and variance decomposition demonstrated that model uncertainties were driven by the minimum

  15. Post Audit of a Field Scale Reactive Transport Model of Uranium at a Former Mill Site

    Science.gov (United States)

    Curtis, G. P.

    2015-12-01

    Reactive transport of hexavalent uranium (U(VI)) in a shallow alluvial aquifer at a former uranium mill tailings site near Naturita CO has been monitored for nearly 30 years by the US Department of Energy and the US Geological Survey. Groundwater at the site has high concentrations of chloride, alkalinity and U(VI) as a owing to ore processing at the site from 1941 to 1974. We previously calibrated a multicomponent reactive transport model to data collected at the site from 1986 to 2001. A two dimensional nonreactive transport model used a uniform hydraulic conductivity which was estimated from observed chloride concentrations and tritium helium age dates. A reactive transport model for the 2km long site was developed by including an equilibrium U(VI) surface complexation model calibrated to laboratory data and calcite equilibrium. The calibrated model reproduced both nonreactive tracers as well as the observed U(VI), pH and alkalinity. Forward simulations for the period 2002-2015 conducted with the calibrated model predict significantly faster natural attenuation of U(VI) concentrations than has been observed by the persistent high U(VI) concentrations at the site. Alternative modeling approaches are being evaluating evaluated using recent data to determine if the persistence can be explained by multirate mass transfer models developed from experimental observations at the column scale(~0.2m), the laboratory tank scale (~2m), the field tracer test scale (~1-4m) or geophysical observation scale (~1-5m). Results of this comparison should provide insight into the persistence of U(VI) plumes and improved management options.

  16. From reactive to proactive and selective control: developing a richer model for stopping inappropriate responses.

    Science.gov (United States)

    Aron, Adam R

    2011-06-15

    A better understanding of the neural systems underlying impulse control is important for psychiatry. Although most impulses are motivational or emotional rather than motoric per se, it is research into the neural architecture of motor response control that has made the greatest strides. This article reviews recent developments in the cognitive neuroscience of stopping responses. Most research of this kind has focused on reactive control-that is, how subjects stop a response outright when instructed by a signal. It is argued that reactive paradigms are limited as models of control relevant to psychiatry. Instead, a set of paradigms is advocated that begins to model proactive inhibitory control-that is, how a subject prepares to stop an upcoming response tendency. Proactive inhibitory control is generated according to the goals of the subject rather than by an external signal, and it can be selectively targeted at a particular response tendency. This may have wider validity than reactive control as an experimental model for stopping inappropriate responses.

  17. ParFlow.RT: Development and Verification of a New Reactive Transport Model

    Science.gov (United States)

    Beisman, J. J., III

    2015-12-01

    In natural subsurface systems, total elemental fluxes are often heavily influenced by areas of disproportionately high reaction rates. These pockets of high reaction rates tend to occur at interfaces, such as the hyporheic zone, where a hydrologic flowpath converges with either a chemically distinct hydrologic flowpath or a reactive substrate. Understanding the affects that these highly reactive zones have on the behavior of shallow subsurface systems is integral to the accurate quantification of nutrient fluxes and biogeochemical cycling. Numerical simulations of these systems may be able to offer some insight. To that end, we have developed a new reactive transport model, ParFlow.RT, by coupling the parallel flow and transport code ParFlow with the geochemical engines of both PFLOTRAN and CrunchFlow. The coupling was accomplished via the Alquimia biogeochemistry API, which provides a unified interface to several geochemical codes and allows a relatively simple implementation of advanced geochemical functionality in flow and transport codes. This model uses an operator-splitting approach, where the transport and reaction steps are solved separately. Here, we present the details of this new model, and the results of verification simulations and biogeochemical cycling simulations of the DOE's East River field site outside of Gothic, CO.

  18. Effectiveness of reactive case detection for malaria elimination in three archetypical transmission settings: a modelling study.

    Science.gov (United States)

    Gerardin, Jaline; Bever, Caitlin A; Bridenbecker, Daniel; Hamainza, Busiku; Silumbe, Kafula; Miller, John M; Eisele, Thomas P; Eckhoff, Philip A; Wenger, Edward A

    2017-06-12

    Reactive case detection could be a powerful tool in malaria elimination, as it selectively targets transmission pockets. However, field operations have yet to demonstrate under which conditions, if any, reactive case detection is best poised to push a region to elimination. This study uses mathematical modelling to assess how baseline transmission intensity and local interconnectedness affect the impact of reactive activities in the context of other possible intervention packages. Communities in Southern Province, Zambia, where elimination operations are currently underway, were used as representatives of three archetypes of malaria transmission: low-transmission, high household density; high-transmission, low household density; and high-transmission, high household density. Transmission at the spatially-connected household level was simulated with a dynamical model of malaria transmission, and local variation in vectorial capacity and intervention coverage were parameterized according to data collected from the area. Various potential intervention packages were imposed on each of the archetypical settings and the resulting likelihoods of elimination by the end of 2020 were compared. Simulations predict that success of elimination campaigns in both low- and high-transmission areas is strongly dependent on stemming the flow of imported infections, underscoring the need for regional-scale strategies capable of reducing transmission concurrently across many connected areas. In historically low-transmission areas, treatment of clinical malaria should form the cornerstone of elimination operations, as most malaria infections in these areas are symptomatic and onward transmission would be mitigated through health system strengthening; reactive case detection has minimal impact in these settings. In historically high-transmission areas, vector control and case management are crucial for limiting outbreak size, and the asymptomatic reservoir must be addressed through

  19. A neurodynamical model of visual attention: feedback enhancement of spatial resolution in a hierarchical system.

    Science.gov (United States)

    Deco, G; Zihl, J

    2001-01-01

    Human beings have the capacity to recognize objects in natural visual scenes with high efficiency despite the complexity of such scenes, which usually contain multiple objects. One possible mechanism for dealing with this problem is selective attention. Psychophysical evidence strongly suggests that selective attention can enhance the spatial resolution in the input region corresponding to the focus of attention. In this work we adopt a computational neuroscience perspective to analyze the attentional enhancement of spatial resolution in the area containing the objects of interest. We extend and apply the computational model of Deco and Schürmann (2000), which consists of several modules with feedforward and feedback interconnections describing the mutual links between different areas of the visual cortex. Each module analyses the visual input with different spatial resolution and can be thought of as a hierarchical predictor at a given level of resolution. Moreover, each hierarchical predictor has a submodule that consists of a group of neurons performing a biologically based 2D Gabor wavelet transformation at a given resolution level. The attention control decides in which local regions the spatial resolution should be enhanced in a serial fashion. In this sense, the scene is first analyzed at a coarse resolution level, and the focus of attention enhances iteratively the resolution at the location of an object until the object is identified. We propose and simulate new psychophysical experiments where the effect of the attentional enhancement of spatial resolution can be demonstrated by predicting different reaction time profiles in visual search experiments where the target and distractors are defined at different levels of resolution.

  20. A simple rule for quadrupedal gait generation determined by leg loading feedback: a modeling study

    Science.gov (United States)

    Fukuoka, Yasuhiro; Habu, Yasushi; Fukui, Takahiro

    2015-02-01

    We discovered a specific rule for generating typical quadrupedal gaits (the order of the movement of four legs) through a simulated quadrupedal locomotion, in which unprogrammed gaits (diagonal/lateral sequence walks, left/right-lead canters, and left/right-lead transverse gallops) spontaneously emerged because of leg loading feedbacks to the CPGs hard-wired to produce a default trot. Additionally, all gaits transitioned according to speed, as seen in animals. We have therefore hypothesized that various gaits derive from a trot because of posture control through leg loading feedback. The body tilt on the two support legs of each diagonal pair during trotting was classified into three types (level, tilted up, or tilted down) according to speed. The load difference between the two legs led to the phase difference between their CPGs via the loading feedbacks, resulting in nine gaits (32: three tilts to the power of two diagonal pairs) including the aforementioned.

  1. Direct coupling of a genome-scale microbial in silico model and a groundwater reactive transport model

    Science.gov (United States)

    Fang, Yilin; Scheibe, Timothy D.; Mahadevan, Radhakrishnan; Garg, Srinath; Long, Philip E.; Lovley, Derek R.

    2011-03-01

    The activity of microorganisms often plays an important role in dynamic natural attenuation or engineered bioremediation of subsurface contaminants, such as chlorinated solvents, metals, and radionuclides. To evaluate and/or design bioremediated systems, quantitative reactive transport models are needed. State-of-the-art reactive transport models often ignore the microbial effects or simulate the microbial effects with static growth yield and constant reaction rate parameters over simulated conditions, while in reality microorganisms can dynamically modify their functionality (such as utilization of alternative respiratory pathways) in response to spatial and temporal variations in environmental conditions. Constraint-based genome-scale microbial in silico models, using genomic data and multiple-pathway reaction networks, have been shown to be able to simulate transient metabolism of some well studied microorganisms and identify growth rate, substrate uptake rates, and byproduct rates under different growth conditions. These rates can be identified and used to replace specific microbially-mediated reaction rates in a reactive transport model using local geochemical conditions as constraints. We previously demonstrated the potential utility of integrating a constraint-based microbial metabolism model with a reactive transport simulator as applied to bioremediation of uranium in groundwater. However, that work relied on an indirect coupling approach that was effective for initial demonstration but may not be extensible to more complex problems that are of significant interest (e.g., communities of microbial species and multiple constraining variables). Here, we extend that work by presenting and demonstrating a method of directly integrating a reactive transport model (FORTRAN code) with constraint-based in silico models solved with IBM ILOG CPLEX linear optimizer base system (C library). The models were integrated with BABEL, a language interoperability tool. The

  2. Altered explorative strategies and reactive coping style in the FSL rat model of depression

    Directory of Open Access Journals (Sweden)

    Salvatore eMagara

    2015-04-01

    Full Text Available Modeling depression in animals is based on the observation of behaviors interpreted as analogue to human symptoms. Typical tests used in experimental depression research are designed to evoke an either-or outcome. It is known that explorative and coping strategies are relevant for depression, however these aspects are generally not considered in animal behavioral testing. Here we investigate the Flinders Sensitive Line (FSL, a rat model of depression, compared to the Sprague-Dawley (SD rat in three independent tests where the animals are allowed to express a more extensive behavioral repertoire. The multivariate concentric square field™ (MCSF and the novel cage tests evoke exploratory behaviors in a novel environment and the home cage change test evokes social behaviors in the re-establishment of a social hierarchy. In the MCSF test, FSL rats exhibited less exploratory drive and more risk-assessment behavior compared to SD rats. When re-exposed to the arena, FSL, but not SD rats, increased their exploratory behavior compared to the first trial and displayed risk-assessment behavior to the same extent as SD rats. Thus, the behavior of FSL rats was more similar to that of SDs when the rats were familiar with the arena. In the novel cage test FSL rats exhibited a reactive coping style, consistent with the reduced exploration observed in the MCSF. Reactive coping is associated with less aggressive behavior. Accordingly, FSL rats displayed less aggressive behavior in the home cage change test. Taken together, our data show that FSL rats express altered explorative behavior and reactive coping style. Reduced interest is a core symptom of depression, and individuals with a reactive coping style are more vulnerable to the disease. Our results support the use of FSL rats as an animal model of depression and increase our understanding of the FSL rat beyond the behavioral dimensions targeted by the traditional depression-related tests.

  3. Modelling the biogeochemical cycle of silicon in soils using the reactive transport code MIN3P

    Science.gov (United States)

    Gerard, F.; Mayer, K. U.; Hodson, M. J.; Meunier, J.

    2006-12-01

    We investigated the biogeochemical cycling of Si in an acidic brown soil covered by a coniferous forest (Douglas fir) based on a comprehensive data set and reactive transport modelling. Both published and original data enable us to make up a conceptual model on which the development of a numerical model is based. We modified the reactive transport code MIN3P, which solves thermodynamic and kinetic reactions coupled with vadose zone flow and solute transport. Simulations were performed for a one-dimensional heterogeneous soil profile and were constrained by observed data including daily soil temperature, plant transpiration, throughfall, and dissolved Si in solutions collected beneath the organic layer. Reactive transport modelling was first used to test the validity of the hypothesis that a dynamic balance between Si uptake by plants and release by weathering controls aqueous Si-concentrations. We were able to calibrate the model quite accurately by stepwise adjustment of the relevant parameters. The capability of the model to predict Si-concentrations was good. Mass balance calculations indicate that only 40% of the biogeochemical cycle of Si is controlled by weathering and that about 60% of Si-cycling is related to biological processes (i.e. Si uptake by plants and dissolution of biogenic Si). Such a large contribution of biological processes was not anticipated considering the temperate climate regime, but may be explained by the high biomass productivity of the planted coniferous species. The large contribution of passive Si-uptake by vegetation permits the conservation of seasonal concentration variations caused by temperature-induced weathering, although the modelling suggests that the latter process was of lesser importance relative to biological Si-cycling.

  4. Model-based rational feedback controller design for closed-loop deep brain stimulation of Parkinson's disease

    Science.gov (United States)

    Gorzelic, P.; Schiff, S. J.; Sinha, A.

    2013-04-01

    Objective. To explore the use of classical feedback control methods to achieve an improved deep brain stimulation (DBS) algorithm for application to Parkinson's disease (PD). Approach. A computational model of PD dynamics was employed to develop model-based rational feedback controller design. The restoration of thalamocortical relay capabilities to patients suffering from PD is formulated as a feedback control problem with the DBS waveform serving as the control input. Two high-level control strategies are tested: one that is driven by an online estimate of thalamic reliability, and another that acts to eliminate substantial decreases in the inhibition from the globus pallidus interna (GPi) to the thalamus. Control laws inspired by traditional proportional-integral-derivative (PID) methodology are prescribed for each strategy and simulated on this computational model of the basal ganglia network. Main Results. For control based upon thalamic reliability, a strategy of frequency proportional control with proportional bias delivered the optimal control achieved for a given energy expenditure. In comparison, control based upon synaptic inhibitory output from the GPi performed very well in comparison with those of reliability-based control, with considerable further reduction in energy expenditure relative to that of open-loop DBS. The best controller performance was amplitude proportional with derivative control and integral bias, which is full PID control. We demonstrated how optimizing the three components of PID control is feasible in this setting, although the complexity of these optimization functions argues for adaptive methods in implementation. Significance. Our findings point to the potential value of model-based rational design of feedback controllers for Parkinson's disease.

  5. Wetland eco-engineering: measuring and modeling feedbacks of oxidation processes between plants and clay-rich material

    Science.gov (United States)

    Saaltink, Rémon; Dekker, Stefan C.; Griffioen, Jasper; Wassen, Martin J.

    2016-09-01

    Interest is growing in using soft sediment as a foundation in eco-engineering projects. Wetland construction in the Dutch lake Markermeer is an example: here, dredging some of the clay-rich lake-bed sediment and using it to construct wetland will soon begin. Natural processes will be utilized during and after construction to accelerate ecosystem development. Knowing that plants can eco-engineer their environment via positive or negative biogeochemical plant-soil feedbacks, we conducted a 6-month greenhouse experiment to identify the key biogeochemical processes in the mud when Phragmites australis is used as an eco-engineering species. We applied inverse biogeochemical modeling to link observed changes in pore water composition to biogeochemical processes. Two months after transplantation we observed reduced plant growth and shriveling and yellowing of foliage. The N : P ratios of the plant tissue were low, and these were affected not by hampered uptake of N but by enhanced uptake of P. Subsequent analyses revealed high Fe concentrations in the leaves and roots. Sulfate concentrations rose drastically in our experiment due to pyrite oxidation; as reduction of sulfate will decouple Fe-P in reducing conditions, we argue that plant-induced iron toxicity hampered plant growth, forming a negative feedback loop, while simultaneously there was a positive feedback loop, as iron toxicity promotes P mobilization as a result of reduced conditions through root death, thereby stimulating plant growth and regeneration. Given these two feedback mechanisms, we propose the use of Fe-tolerant species rather than species that thrive in N-limited conditions. The results presented in this study demonstrate the importance of studying the biogeochemical properties of the situated sediment and the feedback mechanisms between plant and soil prior to finalizing the design of the eco-engineering project.

  6. Exploring the boundary-layer cloud-climate feedback through Single-Column Model in Radiative-Advective Equilibrium

    Science.gov (United States)

    Dal Gesso, Sara; Neggers, Roel

    2017-04-01

    Boundary-layer clouds remain the major contributor to the inter-model spread in future climate predictions. Although light has been shed on the low-level cloud feedback, much remains to be understood about the physical mechanisms at the basis of the response of these clouds to climate warming. In the present study, EC-EARTH Single Column Model (SCM) is used to explore the boundary-layer cloud-climate feedback by imposing a Radiative-Advective Equilibrium, namely a balance between the radiative cooling and the advection of warm air. 30-year simulations are performed with the SCM forced by high-frequency cfSites outputs of the CMIP5 simulations of the host General Circulation Model (GCM) for both the AMIP and AMIP4K experiments. As this study exclusively focuses on marine low-level cloud regimes, the simulations are performed at the Barbados Cloud Observatory in the so-called "dry period", when the large-scale forcing are representative of subtropical marine trade-wind conditions. A first step is to assess how representative long-term SCM simulations are of their host GCM. Subsequently, the SCM is forced by different GCMs within the same framework. In this way, the contribution of the physical parameterization to the boundary-layer cloud feedback is isolated from the dynamics, and systematically evaluated. Finally, a procedure to integrate Large-Eddy Simulations and observations into this framework is discussed.

  7. Can Ising model and/or QKPZ equation properly describe reactive-wetting interface dynamics?

    Science.gov (United States)

    Efraim, Yael; Taitelbaum, Haim

    2009-09-01

    The reactive-wetting process, e.g. spreading of a liquid droplet on a reactive substrate is known as a complex, non-linear process with high sensitivity to minor fluctuations. The dynamics and geometry of the interface (triple line) between the materials is supposed to shed light on the main mechanisms of the process. We recently studied a room temperature reactive-wetting system of a small (˜ 150 μm) Hg droplet that spreads on a thin (˜ 4000 Å) Ag substrate. We calculated the kinetic roughening exponents (growth and roughness), as well as the persistence exponent of points on the advancing interface. In this paper we address the question whether there exists a well-defined model to describe the interface dynamics of this system, by performing two sets of numerical simulations. The first one is a simulation of an interface propagating according to the QKPZ equation, and the second one is a landscape of an Ising chain with ferromagnetic interactions in zero temperature. We show that none of these models gives a full description of the dynamics of the experimental reactivewetting system, but each one of them has certain common growth properties with it. We conjecture that this results from a microscopic behavior different from the macroscopic one. The microscopic mechanism, reflected by the persistence exponent, resembles the Ising behavior, while in the macroscopic scale, exemplified by the growth exponent, the dynamics looks more like the QKPZ dynamics.

  8. In Situ Biostimulation at a Former Uranium Mill Tailings Site: Multicomponent Biogeochemical Reactive Transport Modeling

    Science.gov (United States)

    Yabusaki, S.; Fang, Y.; Long, P.

    2005-12-01

    In situ biostimulation at a Former Uranium Mill Tailings Site: Multicomponent Biogeochemical Reactive Transport Modeling Field experiments conducted at a former uranium mill tailings site in western Colorado are being used to investigate microbially mediated immobilization of uranium as a potential future remediation option for such sites. While the general principle of biostimulating microbial communities to reduce aqueous hexavalent uranium to immobile uraninite has been demonstrated in the laboratory and field, the ability to predictably engineer long lasting immobilization will require a more complete understanding of field-scale processes and properties. For this study, numerical simulation of the flow field, geochemical conditions, and micriobial communities is used to interpret field-scale biogeochemical reactive transport observed during experiments performed in 2002 to 2004. One key issue is identifying bioavailable Fe(III) oxide, which is the principal electron acceptor utilized by the acetate- oxidizing Geobacter sp. These organisms are responsible for uranium bioreduction that results in the removal of sufficient U(VI) to lower uranium groundwater concentrations to at or near applicable standards. The depletion of bioavailable Fe(III) leads to succession by sulfate reducers that are considerably less effective at uranium bioreduction. An important modeling consideration are the abiotic reactions (e.g., mineral precipitation and dissolution, aqueous and surface complexation) involving the Fe(II) and sulfide produced during biostimulation. These components, strongly associated with the solid phases, may play an important role in the evolving reactivity of the mineral surfaces that are likely to impact long-term uranium immobilization.

  9. Reactive Transport Modeling of Microbe-mediated Fe (II) Oxidation for Enhanced Oil Recovery

    Science.gov (United States)

    Surasani, V.; Li, L.

    2011-12-01

    Microbially Enhanced Oil Recovery (MEOR) aims to improve the recovery of entrapped heavy oil in depleted reservoirs using microbe-based technology. Reservoir ecosystems often contain diverse microbial communities those can interact with subsurface fluids and minerals through a network of nutrients and energy fluxes. Microbe-mediated reactions products include gases, biosurfactants, biopolymers those can alter the properties of oil and interfacial interactions between oil, brine, and rocks. In addition, the produced biomass and mineral precipitates can change the reservoir permeability profile and increase sweeping efficiency. Under subsurface conditions, the injection of nitrate and Fe (II) as the electron acceptor and donor allows bacteria to grow. The reaction products include minerals such as Fe(OH)3 and nitrogen containing gases. These reaction products can have large impact on oil and reservoir properties and can enhance the recovery of trapped oil. This work aims to understand the Fe(II) oxidation by nitrate under conditions relevant to MEOR. Reactive transport modeling is used to simulate the fluid flow, transport, and reactions involved in this process. Here we developed a complex reactive network for microbial mediated nitrate-dependent Fe (II) oxidation that involves both thermodynamic controlled aqueous reactions and kinetic controlled Fe (II) mineral reaction. Reactive transport modeling is used to understand and quantify the coupling between flow, transport, and reaction processes. Our results identify key parameter controls those are important for the alteration of permeability profile under field conditions.

  10. The sudden vector projection model for reactivity: mode specificity and bond selectivity made simple.

    Science.gov (United States)

    Guo, Hua; Jiang, Bin

    2014-12-16

    CONSPECTUS: Mode specificity is defined by the differences in reactivity due to excitations in various reactant modes, while bond selectivity refers to selective bond breaking in a reaction. These phenomena not only shed light on reaction dynamics but also open the door for laser control of reactions. The existence of mode specificity and bond selectivity in a reaction indicates that not all forms of energy are equivalent in promoting the reactivity, thus defying a statistical treatment. They also allow the enhancement of reactivity and control product branching ratio. As a result, they are of central importance in chemistry. This Account discusses recent advances in our understanding of these nonstatistical phenomena. In particular, the newly proposed sudden vector projection (SVP) model and its applications are reviewed. The SVP model is based on the premise that the collision in many direct reactions is much faster than intramolecular vibrational energy redistribution in the reactants. In such a sudden limit, the coupling of a reactant mode with the reaction coordinate at the transition state, which dictates its ability to promote the reaction, is approximately quantified by the projection of the former onto the latter. The SVP model can be considered as a generalization of the venerable Polanyi's rules, which are based on the location of the barrier. The SVP model is instead based on properties of the saddle point and as a result capable of treating the translational, rotational, and multiple vibrational modes in reactions involving polyatomic reactants. In case of surface reactions, the involvement of surface atoms can also be examined. Taking advantage of microscopic reversibility, the SVP model has also been used to predict product energy disposal in reactions. This simple yet powerful rule of thumb has been successfully demonstrated in many reactions including uni- and bimolecular reactions in the gas phase and gas-surface reactions. The success of the SVP

  11. Tuberculosis genes expressed during persistence and reactivation in the resistant rabbit model.

    Science.gov (United States)

    Kesavan, Anup K; Brooks, Megan; Tufariello, JoAnn; Chan, John; Manabe, Yukari C

    2009-01-01

    As previously published, after aerosol infection with Mycobacterium tuberculosis H37Rv, New Zealand white rabbits established infection with active bacillary replication, but later contained disease to a paucibacillary state through an effective adaptive response consistent with latency. Despite the heterogeneity among outbred rabbits, the resistant response was uniform. Immunosuppression resulted in reactivation with increased lung bacillary burden. Using this rabbit model, we isolated bacillary RNA from infected rabbit lungs and assessed transcriptional profiles of bacillary genes using RT-PCR to examine genes differentially regulated during active replication, persistence, steroid-induced reactivation, and post-steroid immune reconstitution. Genes involved in hypoxia response (fdxA), resuscitation promoting factors (rpfB), and DNA repair pathways (Rv2191) may be important in bacillary persistence. Further investigation into these gene pathways is warranted.

  12. Combined Active and Reactive Power Control of Wind Farms based on Model Predictive Control

    DEFF Research Database (Denmark)

    Zhao, Haoran; Wu, Qiuwei; Wang, Jianhui;

    2017-01-01

    This paper proposes a combined wind farm controller based on Model Predictive Control (MPC). Compared with the conventional decoupled active and reactive power control, the proposed control scheme considers the significant impact of active power on voltage variations due to the low X=R ratio...... of wind farm collector systems. The voltage control is improved. Besides, by coordination of active and reactive power, the Var capacity is optimized to prevent potential failures due to Var shortage, especially when the wind farm operates close to its full load. An analytical method is used to calculate...... the sensitivity coefficients to improve the computation efficiency and overcome the convergence problem. Two control modes are designed for both normal and emergency conditions. A wind farm with 20 wind turbines was used to verify the proposed combined control scheme....

  13. Using hybrid models to predict blood pressure reactivity to unsupported back based on anthropometric characteristics

    Institute of Scientific and Technical Information of China (English)

    Gurmanik KAUR‡; Ajat Shatru ARORA; Vijender Kumar JAIN

    2015-01-01

    Accurate blood pressure (BP) measurement is essential in epidemiological studies, screening programmes, and re-search studies as well as in clinical practice for the early detection and prevention of high BP-related risks such as coronary heart disease, stroke, and kidney failure. Posture of the participant plays a vital role in accurate measurement of BP. Guidelines on measurement of BP contain recommendations on the position of the back of the participants by advising that they should sit with supported back to avoid spuriously high readings. In this work, principal component analysis (PCA) is fused with forward stepwise regression (SWR), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and the least squares support vector machine (LS-SVM) model for the prediction of BP reactivity to an unsupported back in normotensive and hypertensive participants. PCA is used to remove multi-collinearity among anthropometric predictor variables and to select a subset of com-ponents, termed‘principal components’ (PCs), from the original dataset. The selected PCs are fed into the proposed models for modeling and testing. The evaluation of the performance of the constructed models, using appropriate statistical indices, shows clearly that a PCA-based LS-SVM (PCA-LS-SVM) model is a promising approach for the prediction of BP reactivity in com-parison to others. This assessment demonstrates the importance and advantages posed by hybrid models for the prediction of variables in biomedical research studies.

  14. Feedback Perceptions and Attribution by Secretarial Employees: Effects of Feedback-Content and Sender Characteristics

    Science.gov (United States)

    Raemdonck, Isabel; Strijbos, Jan-Willem

    2013-01-01

    Purpose: Theoretical explanations for the diverse reactive feedback from secretarial employees in different career phases are relatively unexplored. However, research examining age differences in the impact of feedback suggests that the effects of performance feedback may differ for employees in the early career phase and employees in the late…

  15. Reactive modelling of 1,2-DCA and DOC near the shoreline.

    Science.gov (United States)

    Colombani, N; Pantano, A; Mastrocicco, M; Petitta, M

    2014-11-15

    1,2-Dichloroethane (1,2-DCA) was found to be the most abundant compound among chlorinated hydrocarbons detected in a petrochemical plant in southern Italy. This site is located near the coastline, and it is set above an unconfined coastal aquifer, where seawater intrusion is present. The presence of organic and inorganic contaminants at this site has required the implementation of remediation strategies, consisting of pumping wells (hydraulic barrier) and a horizontal flow barrier. The purpose of this work was to assess the influence of salt water intrusion on the degradation rate of 1,2-DCA. This was done on a three-dimensional domain relative to a limited portion of a well characterized field site, accounting for density-dependent flow and reactive transport modelling of 1,2-DCA and Dissolved Organic Carbon (DOC). The modelling procedure was performed employing SEAWAT-4.0 and PHT3D, to reproduce the complex three-dimensional flow and transport domain. In order to determine the fate of 1,2-DCA, detailed field investigations provided intensive depth profile information. Different, kinetically controlled degradation rates were simulated to explain the observed, selective degradation of pollutants in groundwater. Calibration of the model was accomplished by comparison with the two different sets of measurements obtained from the MLS devices and from pumping wells. With the calibrated model, it was possible to distinguish between dispersive non-reactive processes and bacterially mediated reactions. In the non-reactive model, 1,2-DCA sorption was simulated using linear sorption coefficient determined with field data and 1,2-DCA degradation was simulated using a first order decay coefficient using literature data as initial guess. Finally, on the reactive transport model, where a two-step approach with partial equilibrium approach was implemented, the effects of neglecting the cation exchange capacity, omitting density-dependent flow, and refining the vertical

  16. Constitutive Relations for Reactive Transport Modeling: Effects of Chemical Reactions on Multi-Phase Flow Properties

    Science.gov (United States)

    Zhang, S.; Liu, H. H.; van Dijke, M. I.; Geiger, S.; Agar, S. M.

    2016-12-01

    The relationship between flow properties and chemical reactions is key to modeling subsurface reactive transport. This study develops closed-form equations to describe the effects of mineral precipitation and dissolution on multiphase flow properties (capillary pressure and relative permeabilities) of porous media. The model accounts for the fact that precipitation/dissolution only takes place in the water-filled part of pore space. The capillary tube concept was used to connect pore-scale changes to macroscopic hydraulic properties. Precipitation/dissolution induces changes in the pore radii of water-filled pores and consequently in the pore-size distribution. The updated pore-size distribution is converted back to a new capillary pressure-water saturation relation from which the new relative permeabilities are calculated. Pore network modeling is conducted on a Berea sandstone to validate the new continuum-scale relations. The pore network modeling results are satisfactorily predicted by the new closed-form equations. Currently the effects of chemical reactions on flow properties are represented as a relation between permeability and porosity in reactive transport modeling. Porosity is updated after chemical calculations from the change of mineral volumes, then permeability change is calculated from the porosity change using an empirical permeability-porosity relation, most commonly the Carman-Kozeny relation, or the Verma-Pruess relation. To the best of our knowledge, there are no closed-form relations available yet for the effects of chemical reactions on multi-phase flow properties, and thus currently these effects cannot be accounted for in reactive transport modeling. This work presents new constitutive relations to represent how chemical reactions affect multi-phase flow properties on the continuum scale based on the conceptual model of parallel capillary tubes. The parameters in our new relations are either pre-existing input in a multi-phase flow

  17. Astrocyte reactivity in related brain regions in a mouse model of MPTP-induced Parkinson's disease

    Institute of Scientific and Technical Information of China (English)

    Zhijun Zhang; Chunlin Xia; Yulin Dong; Guangming Lü; Juan Liu; Lin Ding; Hengjian Ni

    2009-01-01

    BACKGROUND: Severe injury to dopaminergic neuronal cell bodies and their axon terminals in the substantia nigra pars compacta (SNC) has been observed in both Parkinson's disease (PD) patients or in 1-methy-4-phenyl-1,2,3,6-tetrahydropyrindine(MPTP)-induced PD animal models, but only slight injury occurs in the adjacent ventral tegmental area (VTA). The mechanisms underlying this selective injury remain poorly understood.OBJECTIVE: To comparatively observe astrocyte reactivity in the SNC, caudate putamen (Cpu), VTA, and frontal association cortex (FrA).DESIGN, TIME AND SETTING: A cellular and molecular biology, randomized, controlled experiment was performed at the Institute of Neurobiology, Department of Human Anatomy, Medical School of Nantong University, between December 2006 and September 2008.MATERIALS: A total of 80 healthy adult male C57BL/6 mice were included in this study. MPTP was purchased from Sigma, USA.METHODS: Mice were randomly divided into a model group (n = 64) and a sham-operated group (n = 16). PD was induced in the mice from the model group by intraperitoneal injection of 20 mg/kg MPTP, once every three hours, for a total of 4 times.MAIN OUTCOME MEASURES: Tyrosine hydroxylase (TH)-immunoreactive neurons and glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were examined by dual immunofluorescence labeling. GFAP-immunoreactive astrocytes in the Cpu and FrA were determined by immunofluorescent staining. GFAP mRNA expression in the SNC, Cpu, VTA, and FrA was detected using real-time polymerase chain reaction. TH protein levels in the TH-immunoreactive axon terminals of the Cpu and FrA were detected by Western blotting.RESULTS: Numbers of TH-immunoreactive neurons in the SNC, and TH protein level in the Cpu, markedly decreased (by approximately 68%) 1 day after MPTP injection, and gradually increased at 3 days. Simultaneously, astrocyte reactivity was strengthened, in particular at 7 days. However, after MPTP injection, decreases in

  18. Moving from Batch to Field Using the RT3D Reactive Transport Modeling System

    Science.gov (United States)

    Clement, T. P.; Gautam, T. R.

    2002-12-01

    The public domain reactive transport code RT3D (Clement, 1997) is a general-purpose numerical code for solving coupled, multi-species reactive transport in saturated groundwater systems. The code uses MODFLOW to simulate flow and several modules of MT3DMS to simulate the advection and dispersion processes. RT3D employs the operator-split strategy which allows the code solve the coupled reactive transport problem in a modular fashion. The coupling between reaction and transport is defined through a separate module where the reaction equations are specified. The code supports a versatile user-defined reaction option that allows users to define their own reaction system through a Fortran-90 subroutine, known as the RT3D-reaction package. Further a utility code, known as BATCHRXN, allows the users to independently test and debug their reaction package. To analyze a new reaction system at a batch scale, users should first run BATCHRXN to test the ability of their reaction package to model the batch data. After testing, the reaction package can simply be ported to the RT3D environment to study the model response under 1-, 2-, or 3-dimensional transport conditions. This paper presents example problems that demonstrate the methods for moving from batch to field-scale simulations using BATCHRXN and RT3D codes. The first example describes a simple first-order reaction system for simulating the sequential degradation of Tetrachloroethene (PCE) and its daughter products. The second example uses a relatively complex reaction system for describing the multiple degradation pathways of Tetrachloroethane (PCA) and its daughter products. References 1) Clement, T.P, RT3D - A modular computer code for simulating reactive multi-species transport in 3-Dimensional groundwater aquifers, Battelle Pacific Northwest National Laboratory Research Report, PNNL-SA-28967, September, 1997. Available at: http://bioprocess.pnl.gov/rt3d.htm.

  19. Seagrass-sediment feedback : An exploration using a non-recursive structural equation model

    NARCIS (Netherlands)

    Folmer, Eelke O.; van der Geest, Matthijs; Jansen, Erik J.; Olff, Han; Anderson, T. Michael; Piersma, Theunis; van Gils, Jan A.

    2012-01-01

    The reciprocal effects between sediment texture and seagrass density are assumed to play an important role in the dynamics and stability of intertidal-coastal ecosystems. However, this feedback relationship has been difficult to study empirically on an ecosystem scale, so that knowledge is mainly ba

  20. Seagrass-Sediment Feedback: An Exploration Using a Non-recursive Structural Equation Model

    NARCIS (Netherlands)

    Folmer, E.O.; van der Geest, M.; Jansen, E.; Olff, H.; Anderson, T.M.; Piersma, T.; van Gils, J.A.

    2012-01-01

    The reciprocal effects between sediment texture and seagrass density are assumed to play an important role in the dynamics and stability of intertidal-coastal ecosystems. However, this feedback relationship has been difficult to study empirically on an ecosystem scale, so that knowledge is mainly ba

  1. Decreased reactivation of a herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) mutant using the in vivo mouse UV-B model of induced reactivation.

    Science.gov (United States)

    BenMohamed, Lbachir; Osorio, Nelson; Srivastava, Ruchi; Khan, Arif A; Simpson, Jennifer L; Wechsler, Steven L

    2015-10-01

    Blinding ocular herpetic disease in humans is due to herpes simplex virus type 1 (HSV-1) reactivations from latency, rather than to primary acute infection. The cellular and molecular immune mechanisms that control the HSV-1 latency-reactivation cycle remain to be fully elucidated. The aim of this study was to determine if reactivation of the HSV-1 latency-associated transcript (LAT) deletion mutant (dLAT2903) was impaired in this model, as it is in the rabbit model of induced and spontaneous reactivation and in the trigeminal ganglia (TG) explant-induced reactivation model in mice. The eyes of mice latently infected with wild-type HSV-1 strain McKrae (LAT((+)) virus) or dLAT2903 (LAT((-)) virus) were irradiated with UV-B, and reactivation was determined. We found that compared to LAT((-)) virus, LAT((+)) virus reactivated at a higher rate as determined by shedding of virus in tears on days 3 to 7 after UV-B treatment. Thus, the UV-B-induced reactivation mouse model of HSV-1 appears to be a useful small animal model for studying the mechanisms involved in how LAT enhances the HSV-1 reactivation phenotype. The utility of the model for investigating the immune evasion mechanisms regulating the HSV-1 latency/reactivation cycle and for testing the protective efficacy of candidate therapeutic vaccines and drugs is discussed.

  2. Models for evolution of reactive surface area during dissolution and precipitation

    Science.gov (United States)

    Pedersen, Janne; Jettestuen, Espen; Hildebrand-Habel, Tania; Vinningland, Jan Ludvig; Vadla Madland, Merete; Korsnes, Reidar Inge; Hiorth, Aksel

    2014-05-01

    During water flooding of a reservoir, minerals can dissolve and/or precipitate if the injected water is out of equilibrium with the formation. A net mass transfer between solid and fluid will result in a dynamically changing pore space, which in turn may change the permeability and/or the porosity of the reservoir. When secondary minerals precipitate from solution they will form on top of the primary minerals on the pore walls, and hence the reactive surface area of the individual minerals constituting the porous medium will change. This will in turn affect the dissolution/precipitation rates. In this work we study three different models for the evolution of reactive surface areas during flooding of a core with a brine that is in disequilibrium with the rock. The three models differ in the way secondary minerals are distributed on the solid surface: In model I the whole surface area of both primary and secondary minerals is reactive; hence there will be no screening effect when secondary minerals form. In model II secondary minerals form as a monolayer on the primary minerals that will screen primary minerals from the flow. Model I and II represent two extremes regarding the screening effect; namely no screening (model I) and full screening (model II). Model III is motivated from observations of unflooded and flooded chalk using scanning electron microscopy (SEM). In this model secondary minerals are assumed to form preferentially near crystal defects, being e.g. dislocations in crystallographic pattern or grain contacts. Also the rate of precipitation for forming minerals varies for precipitation onto primary (dissimilar) minerals and precipitation onto secondary (similar) minerals. The three models are implemented into a lattice Boltzmann (LB) based geochemical simulator, and simulation results are compared to results from a 3 years long core flooding experiment with outcrop chalk flooded with 0.219M MgCl2 at 130°C, as well as SEM studies. Before flooding 98wt

  3. The CGILS experimental design to investigate low cloud feedbacks in general circulation models by using single-column and large-eddy simulation models

    Science.gov (United States)

    Zhang, Minghua; Bretherton, Christopher S.; Blossey, Peter N.; Bony, Sandrine; Brient, Florent; Golaz, Jean-Christophe

    2012-04-01

    A surrogate climate change is designed to investigate low cloud feedbacks in the northeastern Pacific by using Single Column Models (SCMs), Cloud Resolving Models (CRMs), and Large Eddy Simulation models (LES), as part of the CGILS study (CFMIP-GASS Intercomparison of LES and SCM models). The constructed large-scale forcing fields, including subsidence and advective tendencies, and their perturbations in the warmer climate are shown to compare well with conditions in General Circulation Models (GCMs), but they are free from the impact of any GCM parameterizations. The forcing fields in the control climate are also shown to resemble the mean conditions in the ECMWF-Interim Reanalysis. Applications of the forcing fields in SCMs are presented. It is shown that the idealized design can offer considerable insight into the mechanisms of cloud feedbacks in the models. Caveats and advantages of the design are also discussed.

  4. Status Report on the Modeling of TRISO Energy Deposition, Time-Dependent Temperature Field and Doppler Feedback

    Energy Technology Data Exchange (ETDEWEB)

    Javier Ortensi; Abderrafi M Ougouag

    2009-07-01

    The Doppler feedback mechanism is a major contributor to the passive safety of gas-cooled, graphite-moderated high temperature reactors that use fuel based on Tristructural-Isotropic coated particles. It follows that the correct prediction of the magnitude and time-dependence of this feedback effect is essential to the conduct of safety analyses for these reactors. We present a fuel conduction model for obtaining better estimates of the temperature feedback during moderate and fast transients. The fuel model has been incorporated in the CYNOD-THERMIX-KONVEK suite of coupled codes as a single TRISO particle within each calculation cell. The heat generation rate is scaled down from the neutronic solution and a Dirichlet boundary condition is imposed as the bulk graphite temperature from the thermal-hydraulic solution. This simplified approach yields similar results to those obtained with more complex methods, requiring multi-TRISO calculations within one control volume, but with much less computational effort. We provide an analysis of the hypothetical total control ejection event in the PBMR-400 design that clearly depicts the improvement in the predictions of the fuel temperature.

  5. Comparison of numerical simulations of reactive transport and chemostat-like models

    Directory of Open Access Journals (Sweden)

    I. Haidar

    2011-12-01

    Full Text Available The objective of the paper is to evaluate the ability of reactive transport models and their numerical implementations (such as MIN3P to simulate simple microbial transformations in conditions of chemostat or gradostat models, that are popular in microbial ecology and waste treatment ecosystems. To make this comparison, we first consider an abstract ecosystem composed of a single limiting resource and a single microbial species that are carried by advection. In a second stage, we consider another microbial species in competition for the same limiting resource. Comparing the numerical solutions of the two models, we found that the numerical accuracy of simulations of advective transport models performed with MIN3P depends on the evolution of the concentrations of the microbial species: when the state of the system is close to a non-hyperbolic equilibrium, we observe a numerical inaccuracy that may be due to the discretization method used in numerical approximations of reactive transport equations. Therefore, one has to be cautious about the predictions given by the models.

  6. Small Signal Modeling Of Controller For Statcom Used In Distribution System For Reactive Power Management

    Directory of Open Access Journals (Sweden)

    Wahiddun Nisa

    2016-05-01

    Full Text Available In this paper non-linear model of the STATCOM is linearized and the following strategies have been adopted . Hence, a small signal model is adopted here. Here, the grid voltage lags the fundamental component of the STATCOM converter terminal voltage with a phase angle difference ' ' . Small signal modeling of the phase angle ' ' and modulation index ' m ' is also done. A single PI-controller for the reactive component current of the STATCOM has been designed. In this model, the DC-link capacitor voltage is held constant without using a separate controller. The STATCOM are designed using SVPWM technique. Through adjustment of the modulation index, fast modulation of the STATCOM reactive power output can be achieved due to high sensitivity of the same with respect to the output voltage of the STATCOM VSC. The model, with PI controllers has been simulated in MATLAB/SIMULINK environment with variation of the pre-charge voltage on the DClink capacitor with linear loads (inductive. Improvement of the power factor of the grid current is achieved for linear loads.

  7. On the multiplicity of solutions of the nonlinear reactive transport model

    Directory of Open Access Journals (Sweden)

    Elyas Shivanian

    2014-06-01

    Full Text Available The generalization of the nonlinear reaction–diffusion model in porous catalysts the so called one dimensional steady state reactive transport model is revisited. This model, which originates also in fluid and solute transport in soft tissues and microvessels, has been recently given analytical solution in terms of Taylor’s series for different families of reaction terms. This article considers the mentioned model without advective transport in the case of including Michaelis–Menten reaction term and shows that it is exactly solvable and furthermore, gives analytical exact solution in the implicit form for further physical interpretation. It is also revealed that the problem may admit unique or dual or even more triple solutions in some domains for the parameters of the model.

  8. Insights into the algebraic structure of Lorenz-like systems using feedback circuit analysis and piecewise affine models

    Science.gov (United States)

    Letellier, Christophe; Amaral, Gleison F. V.; Aguirre, Luis A.

    2007-06-01

    The characterization of chaotic attractors has been a widely addressed problem and there are now many different techniques to define their nature in a rather accurate way, at least in the case of a three-dimensional system. Nevertheless, the link between the structure of the ordinary differential equations and the topology of their solutions is still missing and only a few necessary conditions on the algebraic structure are known today. By using a feedback circuit analysis, it is shown that it is possible to identify the relevant terms of the equations, that is, the terms that really contribute to the structure of the phase portrait. Such analysis also provides some guidelines for constructing piecewise affine models. Moreover, equivalence classes can be defined on the basis of the active feedback circuits involved.

  9. Adolescents' Social Network Site Use, Peer Appearance-Related Feedback, and Body Dissatisfaction: Testing a Mediation Model.

    Science.gov (United States)

    de Vries, Dian A; Peter, Jochen; de Graaf, Hanneke; Nikken, Peter

    2016-01-01

    Previous correlational research indicates that adolescent girls who use social network sites more frequently are more dissatisfied with their bodies. However, we know little about the causal direction of this relationship, the mechanisms underlying this relationship, and whether this relationship also occurs among boys to the same extent. The present two-wave panel study (18 month time lag) among 604 Dutch adolescents (aged 11-18; 50.7% female; 97.7% native Dutch) aimed to fill these gaps in knowledge. Structural equation modeling showed that social network site use predicted increased body dissatisfaction and increased peer influence on body image in the form of receiving peer appearance-related feedback. Peer appearance-related feedback did not predict body dissatisfaction and thus did not mediate the effect of social network site use on body dissatisfaction. Gender did not moderate the findings. Hence, social network sites can play an adverse role in the body image of both adolescent boys and girls.

  10. Forcings and Feedbacks on Convection in the 2010 Pakistan Flood: Modeling Extreme Precipitation with Interactive Large-Scale Ascent

    CERN Document Server

    Nie, Ji; Sobel, Adam H

    2016-01-01

    Extratropical extreme precipitation events are usually associated with large-scale flow disturbances, strong ascent and large latent heat release. The causal relationships between these factors are often not obvious, however, and the roles of different physical processes in producing the extreme precipitation event can be difficult to disentangle. Here, we examine the large-scale forcings and convective heating feedback in the precipitation events which caused the 2010 Pakistan flood within the Column Quasi-Geostrophic framework. A cloud-revolving model (CRM) is forced with the large-scale forcings (other than large-scale vertical motion) computed from the quasi-geostrophic omega equation with input data from a reanalysis data set, and the large-scale vertical motion is diagnosed interactively with the simulated convection. Numerical results show that the positive feedback of convective heating to large-scale dynamics is essential in amplifying the precipitation intensity to the observed values. Orographic li...

  11. A prototype framework for models of socio-hydrology: identification of key feedback loops and parameterisation approach

    Science.gov (United States)

    Elshafei, Y.; Sivapalan, M.; Tonts, M.; Hipsey, M. R.

    2014-06-01

    It is increasingly acknowledged that, in order to sustainably manage global freshwater resources, it is critical that we better understand the nature of human-hydrology interactions at the broader catchment system scale. Yet to date, a generic conceptual framework for building models of catchment systems that include adequate representation of socioeconomic systems - and the dynamic feedbacks between human and natural systems - has remained elusive. In an attempt to work towards such a model, this paper outlines a generic framework for models of socio-hydrology applicable to agricultural catchments, made up of six key components that combine to form the coupled system dynamics: namely, catchment hydrology, population, economics, environment, socioeconomic sensitivity and collective response. The conceptual framework posits two novel constructs: (i) a composite socioeconomic driving variable, termed the Community Sensitivity state variable, which seeks to capture the perceived level of threat to a community's quality of life, and acts as a key link tying together one of the fundamental feedback loops of the coupled system, and (ii) a Behavioural Response variable as the observable feedback mechanism, which reflects land and water management decisions relevant to the hydrological context. The framework makes a further contribution through the introduction of three macro-scale parameters that enable it to normalise for differences in climate, socioeconomic and political gradients across study sites. In this way, the framework provides for both macro-scale contextual parameters, which allow for comparative studies to be undertaken, and catchment-specific conditions, by way of tailored "closure relationships", in order to ensure that site-specific and application-specific contexts of socio-hydrologic problems can be accommodated. To demonstrate how such a framework would be applied, two socio-hydrological case studies, taken from the Australian experience, are presented

  12. Variable reactivity of particulate organic matter in a global ocean biogeochemical model

    Science.gov (United States)

    Aumont, Olivier; van Hulten, Marco; Roy-Barman, Matthieu; Dutay, Jean-Claude; Éthé, Christian; Gehlen, Marion

    2017-05-01

    The marine biological carbon pump is dominated by the vertical transfer of particulate organic carbon (POC) from the surface ocean to its interior. The efficiency of this transfer plays an important role in controlling the amount of atmospheric carbon that is sequestered in the ocean. Furthermore, the abundance and composition of POC is critical for the removal of numerous trace elements by scavenging, a number of which, such as iron, are essential for the growth of marine organisms, including phytoplankton. Observations and laboratory experiments have shown that POC is composed of numerous organic compounds that can have very different reactivities. However, this variable reactivity of POC has never been extensively considered, especially in modelling studies. Here, we introduced in the global ocean biogeochemical model NEMO-PISCES a description of the variable composition of POC based on the theoretical reactivity continuum model proposed by Boudreau and Ruddick (1991). Our model experiments show that accounting for a variable lability of POC increases POC concentrations in the ocean's interior by 1 to 2 orders of magnitude. This increase is mainly the consequence of a better preservation of small particles that sink slowly from the surface. Comparison with observations is significantly improved both in abundance and in size distribution. Furthermore, the amount of carbon that reaches the sediments is increased by more than a factor of 2, which is in better agreement with global estimates of the sediment oxygen demand. The impact on the major macronutrients (nitrate and phosphate) remains modest. However, iron (Fe) distribution is strongly altered, especially in the upper mesopelagic zone as a result of more intense scavenging: vertical gradients in Fe are milder in the upper ocean, which appears to be closer to observations. Thus, our study shows that the variable lability of POC can play a critical role in the marine biogeochemical cycles which advocates for

  13. Imaging geochemical heterogeneities using inverse reactive transport modeling: An example relevant for characterizing arsenic mobilization and distribution

    DEFF Research Database (Denmark)

    Fakhreddine, Sarah; Lee, Jonghyun; Kitanidis, Peter K.

    2016-01-01

    -bearing reactive minerals as aquifer contaminants. We use synthetic applications to demonstrate the ability of inverse modeling techniques combined with mechanistic reactive transport models to image reactive mineral lenses in the subsurface and quantify estimation error using indirect, commonly measured...... such as managed aquifer recharge and recovery operations. The modeling investigation is carried out at various scales and considers different flow-through domains including (i) a ID lab-scale column (SO cm), (ii) a 2D lab-scale setup (60 cm x 30 cm) and (iii) a 2D field scale domain (20 nix 4 m). In these setups......, synthetic dissolved oxygen data and forward reactive transport simulations are used to image the spatial distribution of As-bearing pyrite using the Principal Component Geostatistical Approach (PCGA) for inverse modeling. (C) 2015 Elsevier Ltd. All rights reserved....

  14. Toward Optimized Bioclogging and Biocementation Through Combining Advanced Geophysical Monitoring and Reactive Transport Modeling Approaches

    Science.gov (United States)

    Hubbard, C. G.; Hubbard, S. S.; Wu, Y.; Surasani, V.; Ajo Franklin, J. B.; Commer, M.; Dou, S.; Kwon, T.; Li, L.; Fouke, B. W.; Coates, J. D.

    2012-12-01

    Bioclogging and biocementation offer exciting opportunities for solutions to diverse problems ranging from soil stabilization to microbially enhanced hydrocarbon recovery. The effectiveness of bioclogging and biocementation strategies is governed by processes and properties ranging from microbial metabolism at the submicron scale, to changes in pore geometry at the pore scale, to geological heterogeneities at the field scale. Optimization of these strategies requires advances in mechanistic reactive transport modeling and geophysical monitoring methodologies. Our research focuses on (i) performing laboratory experiments to refine understanding of reaction networks and to quantify changes in hydrological properties (e.g. permeability), the evolution of biominerals and geophysical responses (focusing on seismic and electrical techniques); (ii) developing and using a reactive transport simulator capable of predicting the induced metabolic processes to numerically explore how to optimize the desired effect; and (iii) using loosely coupled reactive transport and geophysical simulators to explore detectability and resolvability of induced bioclogging and biocementation processes at the field scale using time-lapse geophysical methods. Here we present examples of our research focused on three different microbially-mediated methods to enhance hydrocarbon recovery through selective clogging of reservior thief zones, including: (a) biopolymer clogging through dextran production; (b) biomineral clogging through iron oxide precipitation; and (c) biomineral clogging through carbonate precipitation. We will compare the utility of these approaches for enhancing hydrocarbon recovery and will describe the utility of geophysical methods to remotely monitor associated field treatments.

  15. Exploring Early Angiosperm Fire Feedbacks using Coupled Experiments and Modelling Approaches to Estimate Cretaceous Palaeofire Behaviour

    Science.gov (United States)

    Belcher, Claire; Hudpsith, Victoria

    2016-04-01

    Using the fossil record we are typically limited to exploring linkages between palaeoecological changes and palaeofire activity by assessing the abundance of charcoals preserved in sediments. However, it is the behaviour of fires that primarily governs their ecological effects. Therefore, the ability to estimate variations in aspects of palaeofire behaviour such as palaeofire intensity and rate of spread would be of key benefit toward understanding the coupled evolutionary history of ecosystems and fire. The Cretaceous Period saw major diversification in land plants. Previously, conifers (gymnosperms) and ferns (pteridophytes) dominated Earth's ecosystems until flowering plants (angiosperms) appear in the fossil record of the Early Cretaceous (~135Ma). We have created surface fire behaviour estimates for a variety of angiosperm invasion scenarios and explored the influence of Cretaceous superambient atmospheric oxygen levels on the fire behaviour occurring in these new Cretaceous ecosystems. These estimates are then used to explore the hypothesis that the early spread of the angiosperms was promoted by the novel fire regimes that they created. In order to achieve this we tested the flammability of Mesozoic analogue fuel types in controlled laboratory experiments using an iCone calorimeter, which measured the ignitability as well as the effective heat of combustion of the fuels. We then used the BehavePlus fire behaviour modelling system to scale up our laboratory results to the ecosystem scale. Our results suggest that fire-angiosperm feedbacks may have occurred in two phases: The first phase being a result of weedy angiosperms providing an additional easily ignitable fuel that enhanced both the seasonality and frequency of surface fires. In the second phase, the addition of shrubby understory fuels likely expanded the number of ecosystems experiencing more intense surface fires, resulting in enhanced mortality and suppressed post-fire recruitment of gymnosperms

  16. Elucidating reactivity regimes in cyclopentane oxidation: Jet stirred reactor experiments, computational chemistry, and kinetic modeling

    Energy Technology Data Exchange (ETDEWEB)

    Al Rashidi, Mariam J.; Thion, Sébastien; Togbé, Casimir; Dayma, Guillaume; Mehl, Marco; Dagaut, Philippe; Pitz, William J.; Zádor, Judit; Sarathy, S. Mani

    2017-01-01

    This study is concerned with the identification and quantification of species generated during the combustion of cyclopentane in a jet stirred reactor (JSR). Experiments were carried out for temperatures between 740 and 1250 K, equivalence ratios from 0.5 to 3.0, and at an operating pressure of 10 atm. The fuel concentration was kept at 0.1% and the residence time of the fuel/O2/N2 mixture was maintained at 0.7 s. The reactant, product, and intermediate species concentration profiles were measured using gas chromatography and Fourier transform infrared spectroscopy. The concentration profiles of cyclopentane indicate inhibition of reactivity between 850–1000 K for φ = 2.0 and φ = 3.0. This behavior is interesting, as it has not been observed previously for other fuel molecules, cyclic or non-cyclic. A kinetic model including both low- and high-temperature reaction pathways was developed and used to simulate the JSR experiments. The pressure-dependent rate coefficients of all relevant reactions lying on the PES of cyclopentyl + O2, as well as the C–C and C–H scission reactions of the cyclopentyl radical were calculated at the UCCSD(T)-F12b/cc-pVTZ-F12//M06-2X/6-311++G(d,p) level of theory. The simulations reproduced the unique reactivity trend of cyclopentane and the measured concentration profiles of intermediate and product species. Sensitivity and reaction path analyses indicate that this reactivity trend may be attributed to differences in the reactivity of allyl radical at different conditions, and it is highly sensitive to the C–C/C–H scission branching ratio of the cyclopentyl radical decomposition.

  17. Reactive transport modelling of biogeochemical processes and carbon isotope geochemistry inside a landfill leachate plume.

    Science.gov (United States)

    van Breukelen, Boris M; Griffioen, Jasper; Röling, Wilfred F M; van Verseveld, Henk W

    2004-06-01

    The biogeochemical processes governing leachate attenuation inside a landfill leachate plume (Banisveld, the Netherlands) were revealed and quantified using the 1D reactive transport model PHREEQC-2. Biodegradation of dissolved organic carbon (DOC) was simulated assuming first-order oxidation of two DOC fractions with different reactivity, and was coupled to reductive dissolution of iron oxide. The following secondary geochemical processes were required in the model to match observations: kinetic precipitation of calcite and siderite, cation exchange, proton buffering and degassing. Rate constants for DOC oxidation and carbonate mineral precipitation were determined, and other model parameters were optimized using the nonlinear optimization program PEST by means of matching hydrochemical observations closely (pH, DIC, DOC, Na, K, Ca, Mg, NH4, Fe(II), SO4, Cl, CH4, saturation index of calcite and siderite). The modelling demonstrated the relevance and impact of various secondary geochemical processes on leachate plume evolution. Concomitant precipitation of siderite masked the act of iron reduction. Cation exchange resulted in release of Fe(II) from the pristine anaerobic aquifer to the leachate. Degassing, triggered by elevated CO2 pressures caused by carbonate precipitation and proton buffering at the front of the plume, explained the observed downstream decrease in methane concentration. Simulation of the carbon isotope geochemistry independently supported the proposed reaction network.

  18. Case studies of mental models in home heat control: searching for feedback, valve, timer and switch theories.

    Science.gov (United States)

    Revell, Kirsten M A; Stanton, Neville A

    2014-05-01

    An intergroup case study was undertaken to determine if: 1) There exist distinct mental models of home heating function, that differ significantly from the actual functioning of UK heating systems; and 2) Mental models of thermostat function can be categorized according to Kempton's (1986) valve and feedback shared theories, and others from the literature. Distinct, inaccurate mental models of the heating system, as well as thermostat devices in isolation, were described. It was possible to categorise thermostat models by Kempton's (1986) feedback shared theory, but other theories proved ambiguous. Alternate control devices could be categorized by Timer (Norman, 2002) and Switch (Peffer et al., 2011) theories. The need to consider the mental models of the heating system in terms of an integrated set of control devices, and to consider user's goals and expectations of the system benefit, was highlighted. The value of discovering shared theories, and understanding user mental models, of home heating, are discussed with reference to their present day relevance for reducing energy consumption. Copyright © 2013 Elsevier Ltd and The Ergonomics Society. All rights reserved.

  19. Reactive Transport Models with Geomechanics to Mitigate Risks of CO2 Utilization and Storage

    Energy Technology Data Exchange (ETDEWEB)

    Deo, Milind [Univ. of Utah, Salt Lake City, UT (United States); Huang, Hai [Univ. of Utah, Salt Lake City, UT (United States); Kweon, Hyukmin [Univ. of Utah, Salt Lake City, UT (United States); Guo, Luanjing [Univ. of Utah, Salt Lake City, UT (United States)

    2016-03-28

    Reactivity of carbon dioxide (CO2), rocks and brine is important in a number of practical situations in carbon dioxide sequestration. Injectivity of CO2 will be affected by near wellbore dissolution or precipitation. Natural fractures or faults containing specific minerals may reactivate leading to induced seismicity. In this project, we first examined if the reactions between CO2, brine and rocks affect the nature of the porous medium and properties including petrophysical properties in the timeframe of the injection operations. This was done by carrying out experiments at sequestration conditions (2000 psi for corefloods and 2400 psi for batch experiments, and 600°C) with three different types of rocks – sandstone, limestone and dolomite. Experiments were performed in batch mode and corefloods were conducted over a two-week period. Batch experiments were performed with samples of differing surface area to understand the impact of surface area on overall reaction rates. Toughreact, a reactive transport model was used to interpret and understand the experimental results. The role of iron in dissolution and precipitation reactions was observed to be significant. Iron containing minerals – siderite and ankerite dissolved resulting in changes in porosity and permeability. Corefloods and batch experiments revealed similar patterns. With the right cationic balance, there is a possibility of precipitation of iron bearing carbonates. The results indicate that during injection operations mineralogical changes may lead to injectivity enhancements near the wellbore and petrophysical changes elsewhere in the system. Limestone and dolomite cores showed consistent dissolution at the entrance of the core. The dissolution led to formation of wormholes and interconnected dissolution zones. Results indicate that near wellbore dissolution in these rock-types may lead to rock failure. Micro-CT images of the cores before and after the experiments

  20. Identification and characterization of land use driven nitrogen fluxes using stable isotopes and reactive hydrologic modeling

    Science.gov (United States)

    Macko, S. A.; O'Connell, M. T.

    2015-12-01

    The Najinhe watershed is a topographically diverse, mixed agricultural and urban region in northeastern China that provides opportunities for identification of the impact of land use on nitrogen cycling. In addition to agricultural soil amendments, seasonal variation in atmospheric flow introduces dry and wet deposition from urban and desert sources. Both agricultural amendments and atmospheric sources are significant non-point inputs of reactive N, at estimated annual rates of 450 kg/ha and 30 kg/ha respectively in the nearby North China Plain.Both historic and current land use has influenced the biological processing of nitrogen in a particular area. Soil conditions, including moisture, texture, and organic content, control the capacity of a parcel for processing reactive nitrogen. Compounds derived from natural and anthropogenic sources exhibit characteristic stable isotopes of nitrogen and oxygen that serve as tracers of origin as well as integrators of biological processes. Analysis of bulk soils (including both organic and inorganic N contents) in the system shows δ15N ranging from 1.3 - 8.6 ‰ suggesting varying influence of anthropogenic inputs, fertilizers, soil organic nitrogen, and atmospheric sources based on land use.A distributed hydrologic model coupled with one focusing on reactive transport is able to help determine locations with the highest impact on the dissolved N in this system. Spatial statistical methods are employed to determine the biogeochemical influence of model locations whereas δ18O on soil NO3- and δ15N measurements on NO3- and NH4+ in surface water and soil extracts are used to calibrate and validate model predictions based on measured precipitation and streamflow values. Sources are integrated using a Bayesian mixing model to determine likely fate and transport parameters for various N inputs to the watershed. The application of the coupled hydrologic and transport models to a landscape scale catchment suggests integration and

  1. A Model of Critical Peer Feedback to Facilitate Business English Writing Using Qzone Weblogs among Chinese Undergraduates

    Science.gov (United States)

    Xianwei, Gao; Samuel, Moses; Asmawi, Adelina

    2016-01-01

    The purpose of this study was to explore critical thinking skills in peer feedback for Business English writing in order to facilitate the quality of peer feedback and quality of Business English writing. "Critical peer feedback" was conceptualized with the integration of "critical thinking" and "peer feedback" in…

  2. Model-based Optimization and Feedback Control of the Current Density Profile Evolution in NSTX-U

    Science.gov (United States)

    Ilhan, Zeki Okan

    Nuclear fusion research is a highly challenging, multidisciplinary field seeking contributions from both plasma physics and multiple engineering areas. As an application of plasma control engineering, this dissertation mainly explores methods to control the current density profile evolution within the National Spherical Torus eXperiment-Upgrade (NSTX-U), which is a substantial upgrade based on the NSTX device, which is located in Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ. Active control of the toroidal current density profile is among those plasma control milestones that the NSTX-U program must achieve to realize its next-step operational goals, which are characterized by high-performance, long-pulse, MHD-stable plasma operation with neutral beam heating. Therefore, the aim of this work is to develop model-based, feedforward and feedback controllers that can enable time regulation of the current density profile in NSTX-U by actuating the total plasma current, electron density, and the powers of the individual neutral beam injectors. Motivated by the coupled, nonlinear, multivariable, distributed-parameter plasma dynamics, the first step towards control design is the development of a physics-based, control-oriented model for the current profile evolution in NSTX-U in response to non-inductive current drives and heating systems. Numerical simulations of the proposed control-oriented model show qualitative agreement with the high-fidelity physics code TRANSP. The next step is to utilize the proposed control-oriented model to design an open-loop actuator trajectory optimizer. Given a desired operating state, the optimizer produces the actuator trajectories that can steer the plasma to such state. The objective of the feedforward control design is to provide a more systematic approach to advanced scenario planning in NSTX-U since the development of such scenarios is conventionally carried out experimentally by modifying the tokamak's actuator

  3. Atmosphere Clouds Model Algorithm for Solving Optimal Reactive Power Dispatch Problem

    Directory of Open Access Journals (Sweden)

    Lenin Kanagasabai

    2014-04-01

    Full Text Available In this paper, a new method, called Atmosphere Clouds Model (ACM algorithm, used for solving optimal reactive power dispatch problem. ACM stochastic optimization algorithm stimulated from the behavior of cloud in the natural earth. ACM replicate the generation behavior, shift behavior and extend behavior of cloud. The projected (ACM algorithm has been tested on standard IEEE 30 bus test system and simulation results shows clearly about the superior performance of the proposed algorithm in plummeting the real power loss. Normal 0 false false false EN-IN X-NONE X-NONE

  4. The Reactive-Causal Architecture: Introducing an Emotion Model along with Theories of Needs

    Science.gov (United States)

    Aydin, Ali Orhan; Orgun, Mehmet Ali

    In the entertainment application area, one of the major aims is to develop believable agents. To achieve this aim, agents should be highly autonomous, situated, flexible, and display affect. The Reactive-Causal Architecture (ReCau) is proposed to simulate these core attributes. In its current form, ReCau cannot explain the effects of emotions on intelligent behaviour. This study aims is to further improve the emotion model of ReCau to explain the effects of emotions on intelligent behaviour. This improvement allows ReCau to be emotional to support the development of believable agents.

  5. Integrated Modeling and Experimental Studies at the Meso Scale for Advanced Reactive Materials

    Science.gov (United States)

    2016-07-01

    problem (VRP) and vacuum tracking method for non-ideal EOS The vacuum Riemann problem (VRP) is by definition a Riemann problem with vacuum initial condition...T E C H N IC A L R E P O R T DTRA-TR-16-76 Integrated Modeling and Experimental Studies at the Meso- Scale for Advanced Reactive Materials...work in this grant was directed by Prof. D. Scott Stewart, (the Stewart-Group) and the experimental work and data collection was directed by Prof

  6. Reactive Flow Modeling of Liquid Explosives via ALE3D/Cheetah Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, I W; Bastea, S; Fried, L E

    2010-03-10

    We carried out reactive flow simulations of liquid explosives such as nitromethane using the hydrodynamic code ALE3D coupled with equations of state and reaction kinetics modeled by the thermochemical code Cheetah. The simulation set-up was chosen to mimic cylinder experiments. For pure unconfined nitromethane we find that the failure diameter and detonation velocity dependence on charge diameter are in agreement with available experimental results. Such simulations are likely to be useful for determining detonability and failure behavior for a wide range of experimental conditions and explosive compounds.

  7. Reactive transport modeling at uranium in situ recovery sites: uncertainties in uranium sorption on iron hydroxides

    Science.gov (United States)

    Johnson, Raymond H.; Tutu, Hlanganani; Brown, Adrian; Figueroa, Linda; Wolkersdorfer, Christian

    2013-01-01

    Geochemical changes that can occur down gradient from uranium in situ recovery (ISR) sites are important for various stakeholders to understand when evaluating potential effects on surrounding groundwater quality. If down gradient solid-phase material consists of sandstone with iron hydroxide coatings (no pyrite or organic carbon), sorption of uranium on iron hydroxides can control uranium mobility. Using one-dimensional reactive transport models with PHREEQC, two different geochemical databases, and various geochemical parameters, the uncertainties in uranium sorption on iron hydroxides are evaluated, because these oxidized zones create a greater risk for future uranium transport than fully reduced zones where uranium generally precipitates.

  8. Late Pliocene lakes and soils: a data - model comparison for the analysis of climate feedbacks in a warmer world

    Science.gov (United States)

    Pound, M. J.; Tindall, J.; Pickering, S. J.; Haywood, A. M.; Dowsett, H. J.; Salzmann, U.

    2013-06-01

    Based on a synthesis of geological data we have reconstructed the global distribution of Late Pliocene soils and lakes which are then used as boundary conditions in a series of model experiments using the Hadley Centre General Circulation Model (HadCM3) and the BIOME4 mechanistic vegetation model. By combining our novel soil and lake reconstructions with a fully coupled climate model we are able to explore the feedbacks of soils and lakes on the climate of the Late Pliocene. Our experiments reveal regionally confined changes of local climate and vegetation in response to the new boundary conditions. The addition of Late Pliocene soils has the largest influence on surface air temperatures, with notable increases in Australia, southern North Africa and Asia. The inclusion of Late Pliocene lakes generates a significant increase in precipitation in central Africa, as well as seasonal increases in the Northern Hemisphere. When combined, the feedbacks on climate from Late Pliocene lakes and soils improve the data to model fit in western North America and southern North Africa.

  9. Influence of dynamic vegetation on carbon-nitrogen cycle feedback in the Community Land Model (CLM4)

    Science.gov (United States)

    Sakaguchi, K.; Zeng, X.; Leung, LR; Shao, P.

    2016-12-01

    Land carbon sensitivity to atmospheric CO2 concentration (βL) and climate warming (γL) is a crucial part of carbon-climate feedbacks that affect the magnitude of future warming. Although these sensitivities can be estimated by earth system models, their dependence on model representation of land carbon dynamics and the inherent model assumptions has rarely been investigated. Using the widely used Community Land Model version 4 as an example, we examine how βL and γL vary with prescribed versus dynamic vegetation covers. Both sensitivities are found to be larger with dynamic compared to prescribed vegetation on decadal timescale in the late twentieth century, with a more robust difference in γL. The latter is a result of dynamic vegetation model deficiencies in representing the competitions between deciduous versus evergreen trees and tree versus grass over the tropics and subtropics. The biased vegetation cover changes the regional characteristics of carbon-nitrogen cycles such that plant productivity responds less strongly to the enhancement of nitrogen mineralization with warming, so more carbon is lost to the atmosphere with rising temperature. The result calls for systematic evaluations of land carbon sensitivities with varying assumptions for land cover representations to help prioritize development effort and constrain uncertainties in carbon-climate feedbacks.

  10. Late Pliocene lakes and soils: a data – model comparison for the analysis of climate feedbacks in a warmer world

    Directory of Open Access Journals (Sweden)

    M. J. Pound

    2013-06-01

    Full Text Available Based on a synthesis of geological data we have reconstructed the global distribution of Late Pliocene soils and lakes which are then used as boundary conditions in a series of model experiments using the Hadley Centre General Circulation Model (HadCM3 and the BIOME4 mechanistic vegetation model. By combining our novel soil and lake reconstructions with a fully coupled climate model we are able to explore the feedbacks of soils and lakes on the climate of the Late Pliocene. Our experiments reveal regionally confined changes of local climate and vegetation in response to the new boundary conditions. The addition of Late Pliocene soils has the largest influence on surface air temperatures, with notable increases in Australia, southern North Africa and Asia. The inclusion of Late Pliocene lakes generates a significant increase in precipitation in central Africa, as well as seasonal increases in the Northern Hemisphere. When combined, the feedbacks on climate from Late Pliocene lakes and soils improve the data to model fit in western North America and southern North Africa.

  11. Model for high rate gas flows in deformable and reactive porous beds

    Energy Technology Data Exchange (ETDEWEB)

    Weston, A M

    1985-01-08

    This report presents the development of a one dimensional planar Lagrange hydrodynamic computer model which describes the processes preceding detonation. The model treats gas flow, deflagration, and compaction in a porous bed of reactive material. The early part of deflagration to detonation experiment with porous HMX is simulated. Sensitivity of the simulation calculation to ignition and burn rate parameters is illustrated and discussed. The effects of changing the mean particle size of the porous material are investigated. There is widespread interest in runaway reaction hazards that may be associated with porosity in propellant and explosive materials. Experimentally, such reactions are initiated and observed in long, thick walled hollow tubes, filled with a granular porous bed of reactive material. We will present comparisons with an experiment on porous HMX to illustrate details of the model and to point out what we believe are important features of the observed phenomenon. A geometric finite element cell is devised that allows gas to flow through a compacting matrix. The experimental simulation considers the DDT process from initial squib burn through the onset of general matrix deflagration (convective burning), to the development of a fully dense compaction wave. While this simulation did not calculate turnover to detonation, it did illustrate that the transition occurred as soon as the compaction wave became fully dense. It is shown that deflagration and gas permeation lags compaction at the time of transition. This suggests that the actual transition involves an additional compaction dependent process. 18 references, 20 figures, 3 tables.

  12. Statistical model for combustion of high-metal magnesium-based hydro-reactive fuel

    Institute of Scientific and Technical Information of China (English)

    Hu Jian-Xin; Han Chao; Xia Zhi-Xun; Huang Li-Ya; Huang Xu

    2012-01-01

    We investigate experimentally and analytically the combustion behavior of a high-metal magnesium-based hydro-reactive fuel under high temperature gaseous atmosphere.The fuel studied in this paper contains 73% magnesium powders.An experimental system is designed and experimeuts are carried out in both argon and water vapor atmospheres.It is found that the burning surface temperature of the fuel is higher in water vapor than that in argon and both of them are higher than the melting point of magnesium,which indicates the molten state of magnesium particles in the burning surface of the fuel.Based on physical considerations and experimental results,a mathematical one-dimensional model is formulated to describe the combustion behavior of the high-metal magnesium-based hydro-reactive fuel.The model enables the evaluation of the burning surface temperature,the burning rate and the flame standoff distance each as a function of chamber pressure and water vapor concentration.The results predicted by the model show that the burning rate and the surface temperature increase when the chamber pressure and the water vapor concentration increase,which are in agreement with the observed experimental trends.

  13. Multiphase flow and multicomponent reactive transport model of the ventilation experiment in Opalinus clay

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, L.; Samper, J.; Montenegro, L.; Major, J.C.

    2008-10-15

    During the construction and operational phases of a high-level radioactive waste (HLW) repository constructed in a clay formation, ventilation of underground drifts will cause desaturation and oxidation of the rock. The Ventilation Experiment (VE) was performed in a 1.3 m diameter unlined horizontal microtunnel on Opalinus clay at Mont Terri underground research laboratory in Switzerland to evaluate the impact of desaturation on rock properties. A multiphase flow and reactive transport model of VE is presented here. The model accounts for liquid, vapor and air flow, evaporation/condensation and multicomponent reactive solute transport with kinetic dissolution of pyrite and siderite and local-equilibrium dissolution/precipitation of calcite, ferrihydrite, dolomite, gypsum and quartz. Model results reproduce measured vapor flow, liquid pressure and hydrochemical data and capture the trends of measured relative humidities, a